NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst, and preparation method and application thereof

Abstract

The application provides a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst and a preparation method and application thereof, the NaBiO3@Bi2O3 / g-C3N4 heterojunction contains oxygen vacancy and nitrogen vacancy defects, and shows 3D / 2D micro-morphology; Bi2O3 is wrapped on the surface of NaBiO3 to form a core-shell structure; the prepared heterojunction can absorb visible light in the range of 420-800 nm, and shows a double S-shaped charge transfer mechanism, photo-induced electron-hole pairs have high separation efficiency and strong oxidation-reduction capacity, and the heterojunction has good structural stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional materials, and particularly relates to a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst, a preparation method and application thereof. BACKGROUND

[0002] The rapid development of industries such as industry, agriculture, aquaculture, animal husbandry and medicine has led to serious environmental pollution, including air pollution and water pollution. Antibiotics are one of the typical water pollutants, which enter the aquatic ecosystem through animal manure, wastewater and other ways. Although the concentration of antibiotics in the water cycle system has been diluted to the level of ng·L -1 or μg·L -1 , but the presence of low-concentration antibiotics is still a key factor for enhancing bacterial resistance and inducing superbugs. NO in the air mainly comes from fossil fuel combustion and automobile exhaust emissions. After the treated exhaust gas is discharged into the air, the concentration of NO has been diluted to the level of ppb. But the presence of low-concentration NO is still one of the reasons for causing acid rain, haze, photochemical smog and ozone layer destruction.

[0003] In order to protect human health and maintain the sustainable development of society, it is imperative to control environmental pollution. Traditional environmental control methods, such as physical and chemical adsorption, microbial oxidation, biodegradation, membrane filtration, electrochemical regeneration, thermal catalytic oxidation, electrochemical catalytic oxidation and the like, can remove antibiotics and NO, but the removal effect of low-concentration pollutants is not satisfactory; in addition, the operation of the above methods is relatively complex, the energy consumption is large, and it may cause secondary pollution, which does not conform to the concept of green, environmental protection and sustainable development. In recent years, semiconductor-based photocatalyst technology has attracted widespread attention in the field of environmental pollution control, which has the characteristics of low energy consumption, mild reaction conditions, small secondary pollution, environmental friendliness and the like, and often shows relatively good effect for the removal of low-concentration pollutants.

[0004] The key to the practical application of semiconductor photocatalytic technology lies in the selection of photocatalytic materials. Bi-based semiconductor materials have been widely used as photocatalysts, such as BiOX (X = Cl, Bi, I), Bi2WO6, BiVO4, Bi2MoO6, Bi2O3, Bi2O2CO3, NaBiO3, BiOIO3, etc. Among the above materials, perovskite NaBiO3 is favored by researchers due to its intrinsic visible light absorption, high valence band potential and other characteristics. The photocatalytic activity of NaBiO3 is mainly limited by the high recombination rate of photo-generated carriers and the weak reduction ability of photo-generated electrons; in addition, the stability of NaBiO3 is relatively poor, which is easily reduced to Bi2O2CO3 during the reaction, resulting in a decrease in photocatalytic activity. Studies have shown that the photocatalytic performance of NaBiO3 can be improved by hetero-element doping, construction of heterojunction, deposition of metal, etc. However, there are few reports on improving the photocatalytic activity of NaBiO3 by constructing defect-regulated double-S-type heterojunction; in addition, there are no reports on improving the structural stability of NaBiO3. SUMMARY

[0005] The purpose of the present application is to provide a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst and its preparation method and application. The prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction contains oxygen vacancy and nitrogen vacancy defects, showing 3D / 2D micro-morphology, Bi2O3 is wrapped on the surface of NaBiO3 to form a core-shell structure; the prepared heterojunction can absorb visible light in the range of 420-800 nm, and shows a double-S-type charge transfer mechanism, the photo-generated electron-hole pairs have high separation efficiency and strong oxidation-reduction ability, and the heterojunction has good structural stability.

[0006] The present application is realized by the following technical solutions:

[0007] A NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst, which is a composite material of NaBiO3, Bi2O3 and graphite-like g-C3N4, Bi2O3 is wrapped on the surface of NaBiO3 to form a core-shell structure NaBiO3@Bi2O3, NaBiO3@Bi2O3 shows a nanoflower morphology formed by self-assembly of nanosheets; NaBiO3 and Bi2O3 crystal lattices both contain oxygen vacancy defects; g-C3N4 has a nanosheet structure and contains nitrogen vacancy defects in the crystal lattice.

[0008] The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst comprises the following steps:

[0009] Step 1: Dissolve NaBiO3 powder in water, and irradiate under ultraviolet light under stirring conditions to obtain a suspension A;

[0010] Step 2: HNO3 solution is added to the suspension A, and ultraviolet irradiation treatment is carried out under stirring to obtain a suspension B;

[0011] Step 3: g-C3N4 powder is added to the suspension B to obtain a suspension C; wherein the g-C3N4 powder is prepared by high-temperature thermal polymerization reaction in air using urea as raw material;

[0012] Step 4: the suspension C is subjected to ultraviolet irradiation treatment under stirring, and the obtained precipitate is washed and dried to obtain a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst.

[0013] Preferably, in step 1, the ultraviolet irradiation time is 0.5-3h, and in step 2, the ultraviolet irradiation time is 0.5-3h.

[0014] Preferably, in the suspension C obtained in step 3, the molar ratio of NaBiO3, HNO3 and g-C3N4 is (6-12):(12-21):(2-9).

[0015] Preferably, in the suspension C obtained in step 3, the concentrations of NaBiO3, HNO3 and g-C3N4 are 0.1-0.4mol·L -1 , 0.2-0.7mol·L -1 and 0.03-0.3mol·L -1 , respectively.

[0016] Preferably, in step 4, the ultraviolet irradiation time is 2-6h.

[0017] The application of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst in catalytic degradation of organic pollutants in water under visible light irradiation.

[0018] Preferably, the organic pollutants are ciprofloxacin, tetracycline hydrochloride, oxytetracycline, ofloxacin, norfloxacin or metronidazole.

[0019] The application of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst in catalytic degradation of gas pollutants under visible light irradiation.

[0020] Preferably, the gas pollutants are NO.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst contains oxygen vacancy defects in NaBiO3 and Bi2O3 and nitrogen vacancy defects in g-C3N4, and therefore can absorb visible light in the range of 420-800 nm. In the heterojunction, the work functions of g-C3N4, Bi2O3 and NaBiO3 are 4.73 eV, 6.65 eV and 8.77 eV, respectively. The work function of g-C3N4 is less than that of Bi2O3, and the work function of Bi2O3 is less than that of NaBiO3, indicating that the Fermi level and carrier concentration of g-C3N4 are higher than those of Bi2O3, and the Fermi level and carrier concentration of Bi2O3 are higher than those of NaBiO3. Therefore, after the coupling of g-C3N4, Bi2O3 and NaBiO3, the free electrons of g-C3N4 are transferred to Bi2O3, and the free electrons of Bi2O3 are transferred to NaBiO3, resulting in the upward bending of the energy band structure of g-C3N4 and the downward bending of the energy band structure of Bi2O3 at the g-C3N4 / Bi2O3 interface, and the upward bending of the energy band structure of Bi2O3 and the downward bending of the energy band structure of NaBiO3 at the Bi2O3 / NaBiO3 interface, while an internal built-in electric field is formed from g-C3N4 to Bi2O3 and from Bi2O3 to NaBiO3. Under the action of band bending and built-in electric field, the traditional double II-type heterojunction is converted into a double S-type heterojunction, and the photo-generated carriers have high separation efficiency and strong redox ability. In addition, the interface polarization charge transfer causes a large number of free electrons to accumulate on the NaBiO3 side, and positive oxygen vacancies are formed to balance the charge, resulting in further increase of the defect concentration in the NaBiO3@Bi2O3 / g-C3N4 heterojunction. The exciton dissociation effect of defects can further improve the separation efficiency of photo-generated electron-hole pairs. Therefore, the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst has good photocatalytic performance, and can mineralize antibiotics such as ciprofloxacin, tetracycline hydrochloride, metronidazole, ofloxacin, norfloxacin and oxytetracycline into H2O and CO2 under visible light irradiation, and can oxidize NO to NO2 / NO3 - / NO3 - In addition, the formation of the Bi2O3 coating layer on the surface of NaBiO3 improves the structural stability of NaBiO3, so that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst has good cycle stability.

[0023] The application adopts an acid-assisted ultraviolet light irradiation method to prepare a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst, which is simple to operate and short in required time. The formation mechanism of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction is as follows: taking urea as a raw material, g-C3N4 powder is prepared by high-temperature thermal polymerization reaction in air. Due to incomplete condensation of urea molecules during the reaction, a large number of amino (-NH2) groups are adsorbed on the surface of the prepared g-C3N4 powder, and a certain concentration of nitrogen vacancies is contained in the crystal lattice, as shown in reaction formula (1). NaBiO3 powder is dispersed in deionized water, and the used NaBiO3 is composed of NaBiO3·2H2O and NaBiO3·xH2O. The presence of crystal water leads to the weakening of the Bi-O bond, the increase of the bond length and the decrease of the bond energy; under high-energy ultraviolet light irradiation, the Bi-O bond is broken and the lattice oxygen is overflowed, resulting in the formation of oxygen vacancies, as shown in reaction formula (2). Subsequently, under continuous ultraviolet light irradiation, HNO3 solution is slowly added to the suspension system of NaBiO3; under acidic conditions, NaBiO3 has strong oxidizing property, and HNO3 reacts with the surface material of NaBiO3, and the surface NaBiO3 is reduced to Bi2O3. After the formation of the Bi2O3 layer, the further reduction of NaBiO3 to Bi2O3 can be inhibited, and thus the NaBiO3@Bi2O3 with core-shell structure is obtained. The surface wrapping of Bi2O3 can improve the structural stability of NaBiO3; during the reaction, Bi 5+ ions are reduced to Bi 3+ ions, resulting in a large number of free electrons being bound in the Bi2O3 crystal lattice, positive oxygen vacancies being formed to balance the charge, and ultraviolet light irradiation can further promote the formation of oxygen vacancies, as shown in reaction formula (3). Then, g-C3N4 powder is added to the acidic dispersion system of NaBiO3@Bi2O3. Under acidic conditions, the -NH2 groups adsorbed on the surface of the g-C3N4 powder react with H + ions to generate NH4 +Ion dissociation into solution, as shown in reaction (4), leads to a large number of surface active C atom sites exposed. Under UV light irradiation, NaBiO3@Bi2O3 and g-C3N4 are both activated; there are a large number of local electrons at the oxygen vacancy sites on the surface of NaBiO3@Bi2O3, leading to the surface being negatively charged; the shedding of the -NH2 group on the surface of g-C3N4 leads to positively charged carbon atoms being exposed; under the action of electrostatic attraction, negatively charged NaBiO3@Bi2O3 is adsorbed on the surface of positively charged g-C3N4, forming a NaBiO3@Bi2O3 / g-C3N4 heterojunction, as shown in reaction (5). After NaBiO3, Bi2O3 and g-C3N4 are compounded, the polarization charge is transferred from g-C3N4 to Bi2O3 and from Bi2O3 to NaBiO3, a large number of free electrons accumulate on the side of NaBiO3, and positively charged oxygen vacancies are formed to maintain charge balance, leading to a further increase in the oxygen vacancy concentration in the NaBiO3@Bi2O3 / g-C3N4 heterojunction. Ultimately, a double-S-type NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst co-modified by oxygen vacancies and nitrogen vacancies is obtained, as shown in reaction (6).

[0024]

[0025]

[0026]

[0027] g-C3N4…(NH2) n +2mH + →g-C3N4…(NH2) n-m +mNH4 + (4)

[0028]

[0029] BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0031] Figure 2 is the amplified diffraction peak of the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application in the range of 35°-40°;

[0032] Figure 3 is the amplified diffraction peak of the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application in the range of 30°-35°;

[0033] Figure 4 is the FT-IR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0034] Figure 5 is the enlarged view of the FT-IR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application in the range of 780-840 cm -1

[0035] Figure 6 is the SEM image of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3;

[0036] Figure 7 is the element mapping image corresponding to the SEM image of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3;

[0037] Figure 8 is the N2 adsorption-desorption isotherm curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0038] Figure 9 is the pore size distribution curve corresponding to the desorption stage of the N2 adsorption-desorption isotherm curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0039] Figure 10 is the high-resolution N1s XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0040] Figure 11 is the high-resolution Bi 4f XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0041] Figure 12 is the high-resolution O1s XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0042] Figure 13 is the EPR spectrum of the photocatalyst prepared in Comparative Example 1;

[0043] Figure 14 is the EPR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application;

[0044] Figure 15 ​is the UV-visible diffuse reflectance spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0045] Figure 16 is the Kubelka-Munk conversion curve of g-C3N4, NaBiO3 and Bi2O3;

[0046] Figure 17 is the degradation curve of ciprofloxacin under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0047] Figure 18 is the kinetic fitting curve of ciprofloxacin catalytic degradation under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0048] Figure 19 is the TOC removal rate during the catalytic degradation of ciprofloxacin under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0049] Figure 20 is the degradation curve of tetracycline hydrochloride under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0050] Figure 21 is the kinetic fitting curve of tetracycline hydrochloride catalytic degradation under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0051] Figure 22 is the TOC removal rate during the catalytic degradation of tetracycline hydrochloride under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0052] Figure 23 is the degradation curve of metronidazole under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0053] Figure 24 is the kinetic fitting curve of metronidazole catalytic degradation under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0054] Figure 25 is the degradation curve of norfloxacin under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application;

[0055] Figure 26is a kinetic fitting curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application for visible light irradiation catalytic degradation of norfloxacin;

[0056] Figure 27 is a degradation curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application under visible light irradiation on ofloxacin;

[0057] Figure 28 is a kinetic fitting curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application for visible light irradiation catalytic degradation of ofloxacin;

[0058] Figure 29 is a degradation curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application under visible light irradiation on oxytetracycline;

[0059] Figure 30 is a kinetic fitting curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application for visible light irradiation catalytic degradation of oxytetracycline;

[0060] Figure 31 is a TOC removal rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in example 3 under visible light irradiation catalytic degradation of ofloxacin, norfloxacin, metronidazole and oxytetracycline;

[0061] Figure 32 is a cycle experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in example 3 under visible light irradiation catalytic degradation of ciprofloxacin;

[0062] Figure 33 is a cycle experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in example 3 under visible light irradiation catalytic degradation of tetracycline hydrochloride;

[0063] Figure 34 is an XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in example 3 before and after the cycle reaction of catalytic degradation of antibiotics under visible light irradiation;

[0064] Figure 35 is an active species capture experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in example 3 under visible light irradiation catalytic degradation of ciprofloxacin;

[0065] Figure 36is the removal curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation for photocatalytic oxidation of NO;

[0066] Figure 37 is the real-time NO and NO2 concentration during the visible light irradiation catalytic oxidation of NO reaction of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application;

[0067] Figure 38 is the cycle experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by example 3 under visible light irradiation for catalytic oxidation of NO;

[0068] Figure 39 is the real-time NO and NO2 concentration during the cycle experiment of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by example 3 under visible light irradiation for catalytic oxidation of NO;

[0069] Figure 40 is the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by example 3 before and after the cycle reaction under visible light irradiation for catalytic oxidation of NO;

[0070] Figure 41 is the active species capture experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation for oxidation of NO;

[0071] Figure 42 is the transient photocurrent response curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation;

[0072] Figure 43 is the electrochemical impedance spectrogram of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation;

[0073] Figure 44 is the cyclic voltammetry curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation;

[0074] Figure 45 is the time-resolved fluorescence decay curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application;

[0075] Figure 46 is the EPR spectrum of the DMPO-·O2 - produced by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the application under visible light irradiation;

[0076] Figure 47 is the EPR spectrum of DMPO-·OH generated by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application under visible light irradiation;

[0077] Figure 48 is the EPR spectrum of TEMPO-·O2 generated by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application under visible light irradiation; 1

[0078] Figure 49 is the work function of g-C3N4, Bi2O3 and NaBiO3;

[0079] Figure 50 is the XPS-VB spectrum of g-C3N4, Bi2O3 and NaBiO3;

[0080] Figure 51 is the photocatalytic mechanism of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the present application. DETAILED DESCRIPTION

[0081] In order to further understand the present application, the present application is described below in conjunction with examples, which are only further explanation of the features and advantages of the present application, and are not used to limit the claims of the present application.

[0082] The NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst described in the present application is a composite material of NaBiO3, Bi2O3 and graphite-like g-C3N4, wherein NaBiO3 is composed of NaBiO3·2H2O and NaBiO3·xH2O, both of which belong to hexagonal system, and the space groups are P3(123) and R-3(148) respectively, and the crystal lattice contains oxygen vacancy defects; Bi2O3 belongs to cubic system, and the space group is Pn-3m(224), and the crystal lattice contains oxygen vacancy defects; Bi2O3 is wrapped on the surface of NaBiO3 to form a core-shell structure NaBiO3@Bi2O3, and NaBiO3@Bi2O3 shows a nanoflower morphology formed by self-assembly of nanosheets; g-C3N4 is a nanosheet structure, and the crystal lattice contains nitrogen vacancy defects. The NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst contains oxygen vacancy and nitrogen vacancy defects, and the overall microstructure shows 3D / 2D morphology. The heterojunction can absorb visible light in the range of 420-800 nm, the photo-generated carriers show a double S-type charge transfer mechanism, the electron and hole pairs have high separation efficiency and strong oxidation and reduction ability, and have good structural stability. ​

[0083] The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst comprises the following steps:

[0084] Step 1: Put NaBiO3 powder into a quartz beaker, add water, and place it in an XPA-3 photochemical reaction instrument for magnetic stirring under ultraviolet light irradiation for a period of time to obtain a uniformly dispersed light brown suspension A;

[0085] Step 2: Slowly add HNO3 solution to the suspension A, continuously stir under the action of magnetic force, and irradiate under ultraviolet light for a period of time to obtain a uniformly dispersed brown-red suspension B;

[0086] Step 3: Add g-C3N4 powder to the suspension B to obtain a suspension C;

[0087] Step 4: Stir the suspension C under the action of high-speed magnetic stirring and ultraviolet light irradiation for a period of time, wash the obtained precipitate with deionized water and anhydrous ethanol respectively, and dry to obtain the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst.

[0088] In step 1, the ultraviolet light source used is a 300W mercury lamp, which is horizontally placed in a quartz cold finger tube, and the quartz beaker is located 8-12cm below the mercury lamp.

[0089] In the suspension C obtained in step 3, the molar ratio of NaBiO3, HNO3 and g-C3N4 is (6-12):(12-21):(2-9).

[0090] In the suspension C obtained in step 3, the concentrations of NaBiO3, HNO3 and g-C3N4 are 0.1-0.4mol·L -1 , 0.2-0.7mol·L -1 , and 0.03-0.3mol·L -1 , respectively.

[0091] In step 1, the ultraviolet light irradiation time is 0.5-3h, and in step 1, the ultraviolet light irradiation time is 0.5-3h.

[0092] In step 4, the ultraviolet light irradiation time is 2-6h, the drying temperature is 60-90℃, and the drying time is 12-24h.

[0093] The NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the preparation method can decompose organic pollutants and remove gaseous pollutants under visible light irradiation; the organic pollutants are ciprofloxacin, tetracycline hydrochloride, metronidazole, norfloxacin, ofloxacin and oxytetracycline; and the gaseous pollutant is NO.

[0094] Comparative Example 1

[0095] Step 1: weigh 10 g of urea and place it in a corundum crucible with a lid;

[0096] Step 2: place the above crucible in the center of a muffle furnace;

[0097] Step 3: increase the temperature from room temperature to 550℃ at a rate of 15℃·min -1 , keep the temperature for 4 h, and then cool the furnace to 50℃, to obtain g-C3N4 photocatalyst powder;

[0098] Comparative Example 2

[0099] Step 1: weigh 2.240 g of NaBiO3 powder and place it in a 100 mL quartz beaker, add 40 mL of deionized water;

[0100] Step 2: place the above beaker in an XPA-3 photochemical reaction instrument, and under the action of continuous high-speed magnetic stirring, irradiate with ultraviolet light for 5 h;

[0101] Step 3: wash the obtained precipitate with deionized water and anhydrous ethanol for 3 times respectively, and dry at 70℃ for 16 h to obtain NaBiO3 photocatalyst powder.

[0102] Comparative Example 3

[0103] Step 1: weigh 2.240 g of NaBiO3 powder and place it in a 100 mL quartz beaker, add 40 mL of deionized water, and place it in an XPA-3 photochemical reaction instrument, and under the action of ultraviolet light and magnetic stirring for 30 min, obtain a uniformly dispersed light brown suspension A;

[0104] Step 2: slowly add 12 mL of 1 mol·L -1 HNO3 solution to the above suspension A, and under the action of continuous magnetic stirring, irradiate with ultraviolet light for 30 min to obtain a uniformly dispersed brown-red suspension B;

[0105] Step 3: continue to irradiate the above brown-red suspension B with ultraviolet light under the action of high-speed magnetic stirring for 4 h, wash the obtained precipitate with deionized water and anhydrous ethanol for 3 times respectively, and dry at 70℃ for 16 h to obtain NaBiO3@Bi2O3 photocatalyst powder.

[0106] Example 1

[0107] Step 1: weigh 1.800 g of NaBiO3 powder and place it in a 100 mL quartz beaker, add 40 mL of deionized water, and place it in an XPA-3 photochemical reaction instrument, and under the action of ultraviolet light and magnetic stirring for 30 min, obtain a uniformly dispersed light brown suspension A;

[0108] Step 2: 8 mL of 1 mol·L -1 HNO3 solution was slowly added into the above suspension A, under the continuous magnetic stirring, UV light irradiation for 30 min, a uniformly dispersed brown-red suspension B was obtained;

[0109] Step 3: 0.360 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0110] Step 4: The above suspension C was irradiated by UV light for 2 h under the high-speed magnetic stirring, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 60°C for 20 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0111] Example 2

[0112] Step 1: 3.360 g of NaBiO3 powder was placed in a 100 mL quartz beaker, 60 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and was magnetically stirred under UV light irradiation for 30 min to obtain a uniformly dispersed light brown suspension A;

[0113] Step 2: 16 mL of 1 mol·L -1 HNO3 solution was slowly added into the above suspension A, under the continuous magnetic stirring, UV light irradiation for 30 min, a uniformly dispersed brown-red suspension B was obtained;

[0114] Step 3: 0.210 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0115] Step 4: The above suspension C was irradiated by UV light for 4 h under the high-speed magnetic stirring, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 90°C for 12 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0116] Example 3:

[0117] Step 1: 2.240 g of NaBiO3 powder was placed in a 100 mL quartz beaker, 40 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and was magnetically stirred under UV light irradiation for 30 min to obtain a uniformly dispersed light brown suspension A;

[0118] Step 2: 12 mL of 1 mol·L -1 HNO3 solution was slowly added into the above suspension A, under the continuous magnetic stirring, UV light irradiation for 30 min, a uniformly dispersed brown-red suspension B was obtained;

[0119] Step 3: 0.390 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0120] Step 4: The above suspension C was irradiated by ultraviolet light for 4 h under the action of high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 70℃ for 12 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0121] Example 4

[0122] Step 1: 2.800 g of NaBiO3 powder was placed in a 100 mL quartz beaker, 30 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and was magnetically stirred for 30 min under ultraviolet light irradiation to obtain a uniformly dispersed light brown suspension A;

[0123] Step 2: 16 mL of 1 mol·L -1 of HNO3 solution was slowly added into the above suspension A, and was irradiated by ultraviolet light for 30 min under the action of continuous magnetic stirring to obtain a uniformly dispersed brown-red suspension B;

[0124] Step 3: 0.420 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0125] Step 4: The above suspension C was irradiated by ultraviolet light for 3 h under the action of high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 80℃ for 24 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0126] Example 5

[0127] Step 1: 2.100 g of NaBiO3 powder was placed in a 100 mL quartz beaker, 50 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and was magnetically stirred for 30 min under ultraviolet light irradiation to obtain a uniformly dispersed light brown suspension A;

[0128] Step 2: 4 mL of 1 mol·L -1 of HNO3 solution was slowly added into the above suspension A, and was irradiated by ultraviolet light for 30 min under the action of continuous magnetic stirring to obtain a uniformly dispersed brown-red suspension B;

[0129] Step 3: 0.560 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0130] Step 4: The above suspension C was irradiated with ultraviolet light for 5h under high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 90℃ for 12h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0131] Example 6

[0132] Step 1: 3.200g of NaBiO3 powder was weighed and placed in a 100mL quartz beaker, 60mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and magnetically stirred for 30min under ultraviolet light irradiation to obtain a uniformly dispersed light brown suspension A;

[0133] Step 2: 15mL of 1mol·L -1 of HNO3 solution was slowly added to the above suspension A, and ultraviolet light irradiation was carried out for 30min under continuous magnetic stirring to obtain a uniformly dispersed brown-red suspension B;

[0134] Step 3: 0.720g of g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0135] Step 4: The above suspension C was irradiated with ultraviolet light for 6h under high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 70℃ for 15h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0136] Example 7

[0137] Step 1: 1.800g of NaBiO3 powder was weighed and placed in a 100mL quartz beaker, 40mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and magnetically stirred for 30min under ultraviolet light irradiation to obtain a uniformly dispersed light brown suspension A;

[0138] Step 2: 10mL of 1mol·L -1 of HNO3 solution was slowly added to the above suspension A, and ultraviolet light irradiation was carried out for 30min under continuous magnetic stirring to obtain a uniformly dispersed brown-red suspension B;

[0139] Step 3: 0.820g of g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0140] Step 4: The above suspension C was irradiated with ultraviolet light for 6h under high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 80℃ for 18h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0141] Example 8

[0142] Step 1: 2.400g NaBiO3 powder was weighed and placed in a 100mL quartz beaker, 50mL deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument under ultraviolet light irradiation and magnetic stirring for 30min to obtain a uniformly dispersed light brown suspension A;

[0143] Step 2: 6mL of 1mol·L -1 HNO3 solution was slowly added to the above suspension A, and under the action of continuous magnetic stirring, ultraviolet light irradiation was carried out for 30min to obtain a uniformly dispersed brown-red suspension B;

[0144] Step 3: 0.450g g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0145] Step 4: The above suspension C was irradiated with ultraviolet light under the action of high-speed magnetic stirring for 2h, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 70℃ for 21h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0146] Example 9

[0147] Step 1: 3.200g NaBiO3 powder was weighed and placed in a 100mL quartz beaker, 40mL deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument under ultraviolet light irradiation and magnetic stirring for 30min to obtain a uniformly dispersed light brown suspension A;

[0148] Step 2: 8mL of 1mol·L -1 HNO3 solution was slowly added to the above suspension A, and under the action of continuous magnetic stirring, ultraviolet light irradiation was carried out for 30min to obtain a uniformly dispersed brown-red suspension B;

[0149] Step 3: 0.360g g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0150] Step 4: The above suspension C was irradiated with ultraviolet light under the action of high-speed magnetic stirring for 5h, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 90℃ for 15h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0151] Example 10

[0152] Step 1: 2.700 g of NaBiO3 powder was weighed and placed in a 100 mL quartz beaker, 30 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and under the action of magnetic stirring and ultraviolet light irradiation for 30 min, a uniformly dispersed light brown suspension A was obtained;

[0153] Step 2: 12 mL of 1 mol·L -1 of HNO3 solution was slowly added to the above suspension A, and under the action of continuous magnetic stirring and ultraviolet light irradiation for 30 min, a uniformly dispersed brown-red suspension B was obtained;

[0154] Step 3: 0.540 g of g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0155] Step 4: The above suspension C was irradiated under ultraviolet light for 4 h under the action of high-speed magnetic stirring, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 60℃ for 18 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0156] Example 11

[0157] Step 1: 3.000 g of NaBiO3 powder was weighed and placed in a 100 mL quartz beaker, 60 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and under the action of magnetic stirring and ultraviolet light irradiation for 30 min, a uniformly dispersed light brown suspension A was obtained;

[0158] Step 2: 16 mL of 1 mol·L -1 of HNO3 solution was slowly added to the above suspension A, and under the action of continuous magnetic stirring and ultraviolet light irradiation for 30 min, a uniformly dispersed brown-red suspension B was obtained;

[0159] Step 3: 0.600 g of g-C3N4 powder was added to the above suspension B to obtain suspension C;

[0160] Step 4: The above suspension C was irradiated under ultraviolet light for 6 h under the action of high-speed magnetic stirring, the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and dried at 90℃ for 18 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0161] Example 12

[0162] Step 1: 1.800 g of NaBiO3 powder was weighed and placed in a 100 mL quartz beaker, 50 mL of deionized water was added, and it was placed in an XPA-3 photochemical reaction instrument, and under the action of magnetic stirring and ultraviolet light irradiation for 30 min, a uniformly dispersed light brown suspension A was obtained;

[0163] Step 2: 10 mL of 1 mol·L -1 HNO3 solution was slowly added into the above suspension A, and under the continuous magnetic stirring, the suspension was irradiated by UV light for 30 min to obtain a uniformly dispersed brown-red suspension B;

[0164] Step 3: 0.240 g of g-C3N4 powder was added into the above suspension B to obtain suspension C;

[0165] Step 4: The above suspension C was irradiated by UV light for 3 h under the high-speed magnetic stirring, and the obtained precipitate was washed with deionized water and anhydrous ethanol for 3 times respectively, and then dried at 70℃ for 15 h to obtain NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder.

[0166] Figure 1 is the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application. The curves a-c, d-g are the XRD patterns of the photocatalyst powders prepared in Comparative Examples 1-3 and Examples 1-4, respectively, and the target used for testing is a cobalt target. In the XRD pattern of g-C3N4, the diffraction peaks at about 14.9° and 32.4° correspond to the (100) and (002) crystal planes of the graphite-like phase carbon nitride, respectively. In the XRD pattern of NaBiO3, the characteristic diffraction peaks of NaBiO3·2H2O (No. 30-1161) and NaBiO3·xH2O (No. 30-1160) can be observed simultaneously, indicating that the two phases coexist in the sample. After introducing HNO3 into the reaction system, the XRD diffraction peaks of NaBiO3 are significantly weakened, and the characteristic diffraction peaks of Bi2O3 (No. 27-0052) appear, indicating that part of NaBiO3 is reduced to Bi2O3. In the XRD pattern of NaBiO3@Bi2O3 / g-C3N4, the characteristic diffraction peaks of NaBiO3·2H2O, NaBiO3·xH2O and Bi2O3 can be observed simultaneously. Since the main diffraction peaks of g-C3N4 overlap with those of Bi2O3, the diffraction peaks of g-C3N4 are not observed in the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction.

[0167] Figure 2is the diffraction peak of the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application in the range of 35°-40°. In the figure, curves a-c, d-g are the diffraction peaks of the XRD pattern of the photocatalyst powder prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4 in the range of 35°-40°. Compared with NaBiO3, the main diffraction peak of NaBiO3·xH2O in the XRD pattern of NaBiO3@Bi2O3 shifts to the low angle direction; compared with NaBiO3@Bi2O3, the main diffraction peak of NaBiO3·xH2O in the XRD pattern of NaBiO3@Bi2O3 / g-C3N4 heterojunction shifts to the high angle direction.

[0168] Figure 3 is the diffraction peak of the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application in the range of 30°-35°. In the figure, curves a-c, d-g are the diffraction peaks of the XRD pattern of the photocatalyst powder prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4 in the range of 30°-35°. Compared with NaBiO3@Bi2O3, the main diffraction peak of Bi2O3 in the XRD pattern of NaBiO3@Bi2O3 / g-C3N4 heterojunction shifts to the low angle direction. Figure 2 and Figure 3 , there is a strong interaction between NaBiO3, Bi2O3 and g-C3N4, rather than a simple physical mixing.

[0169] Figure 4 is the FT-IR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application. In the figure, curves a-c, d-g are the FT-IR spectra of the photocatalyst powder prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4. In the FT-IR spectrum of g-C3N4, the characteristic absorption peaks in the range of 3400-3000 cm -1 , 1600-1000 cm -1 and 809 cm -1 correspond to the stretching vibration mode of -OH / -NH2 group, the stretching vibration mode of CN heterocycle and the bending vibration mode of triazine ring, respectively. In the FT-IR spectrum of NaBiO3@Bi2O3 / g-C3N4, the characteristic absorption peaks of g-C3N4 can be observed, and it can be known from the XRD pattern that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is successfully prepared.

[0170] Figure 5is the amplification diagram of the FT-IR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application in the range of 780-840 cm -1 -1, 2 and 3, respectively. It can be seen from the figure that, after being compounded with NaBiO3@Bi2O3, the characteristic absorption peak of g-C3N4 at about 809 cm -1 -1, 2 and 3, respectively. It can be seen from the figure that, after being compounded with NaBiO3@Bi2O3, the characteristic absorption peak of g-C3N4 at about 809 cm -1 -1, 2 and 3, respectively. It can be seen from the figure that, after being compounded with NaBiO3@Bi2O3, the characteristic absorption peak of g-C3N4 at about 809 cm

[0171] Figure 6 is the SEM image of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3. In the figure, irregular nanosheet morphology and nanoflower morphology formed by self-assembly of nanosheets can be observed, which correspond to g-C3N4 and NaBiO3@Bi2O3, respectively, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction prepared in the present application exhibits 3D / 2D micro-morphology, and the thickness of the g-C3N4 nanosheet is about 27 nm, and the diameter of the NaBiO3@Bi2O3 microsphere is about 3.4 μm.

[0172] Figure 7 is the element mapping image corresponding to the SEM image of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3. In the element mapping image, the existence of C, N, Na, Bi and O elements can be detected, further indicating that g-C3N4, Bi2O3 and NaBiO3 coexist in the composite material prepared in the present application.

[0173] Figure 8 is the N2 adsorption-desorption isotherm curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the present application. In the figure, curves a-d are the N2 adsorption-desorption isotherm curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3, respectively. All the samples exhibit type IV N2 adsorption-desorption isotherm curves accompanied by obvious hysteresis loops, confirming the mesoporous characteristics. The BET specific surface areas of g-C3N4, NaBiO3, NaBiO3@Bi2O3 and NaBiO3@Bi2O3 / g-C3N4 are 82.531 m 2 ·g -1 , 26.787 m 2 ·g -1 , 29.929 m 2 ·g -1and 44.148 m 2 ·g -1 The BET specific surface area of g-C3N4 is the largest, the BET specific surface area of NaBiO3@Bi2O3 / g-C3N4 is lower than that of g-C3N4 but higher than that of NaBiO3@Bi2O3, and the relatively high specific surface area is beneficial to the adsorption of pollutant molecules; meanwhile, the specific surface area of NaBiO3@Bi2O3 / g-C3N4 is between that of g-C3N4 and that of NaBiO3@Bi2O3, which further confirms the formation of the heterojunction.

[0174] Figure 9 The pore size distribution curve corresponding to the desorption stage of the N2 adsorption-desorption isotherm of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application. In the figure, curves a-d are the pore size distribution curves corresponding to the desorption stage of the N2 adsorption-desorption isotherm of the photocatalyst powder prepared in Comparative Examples 1-3 and Example 3. The total pore volume of g-C3N4, NaBiO3, NaBiO3@Bi2O3 and NaBiO3@Bi2O3 / g-C3N4 is 0.4191 cm 3 ·g -1 , 0.1296 cm 3 ·g -1 , 0.1744 cm 3 ·g -1 and 0.2474 cm 3 ·g -1 , and the total pore volume of NaBiO3@Bi2O3 / g-C3N4 is between that of g-C3N4 and that of NaBiO3@Bi2O3; the corresponding average pore diameters are 19.385 nm, 19.518 nm, 15.395 nm and 25.033 nm, respectively, and the average pore diameter of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction is the largest, which is beneficial to the adsorption of pollutants and the migration of products.

[0175] Figure 10This is the high-resolution N1s XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in this invention. In the figure, curves a and b are the high-resolution N1s XPS spectra of the photocatalyst powders prepared in Comparative Example 1 and Example 3, respectively. The high-resolution N1s XPS spectrum of the prepared photocatalyst can be fitted to four characteristic peaks. In the N1s spectrum of g-C3N4, the characteristic peaks at 398.61 eV, 399.88 eV, 400.81 eV, and 403.78 eV are attributed to CN=C bond, N-(C)3 group, C-NH2 group, and π excitation, respectively. After being combined with NaBiO3@Bi2O3, the binding energies of the above-mentioned N species increased to 399.19 eV, 401.26 eV, 403.42 eV and 406.38 eV, respectively, indicating that after g-C3N4 is combined with NaBiO3@Bi2O3, its electron cloud density decreases and polarization charge is transferred from g-C3N4 to NaBiO3@Bi2O3.

[0176] Figure 11 This is the high-resolution Bi 4f XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in this invention. In the figure, curves ac represent the high-resolution Bi 4f XPS spectra of the photocatalyst powders prepared in Comparative Example 2, Comparative Example 3, and Example 3, respectively. In the Bi 4f spectrum of NaBiO3, the characteristic peaks at 158.51 eV and 163.83 eV correspond to Bi 4f peaks, respectively. 5+ Bi4f ions 7 / 2 and Bi 4f 5 / 2 The characteristic peaks at 157.58 eV and 162.88 eV correspond to Bi orbitals, respectively. 3+ Bi 4f ions 7 / 2 and Bi4f 5 / 2 Orbit, Bi 3+ The formation of ions is attributed to the presence of oxygen vacancies. Due to the formation of Bi₂O₃, in NaBiO₃@Bi₂O₃, Bi... 3+ The ion concentration increased from 7.56% to 35.03%. In NaBiO3@Bi2O3, Bi... 5+ 4f 7 / 2 and Bi 5+ 4f 5 / 2 The binding energies decreased to 158.43 eV and 163.77 eV, respectively, indicating an increase in electron cloud density and a transfer of polarization charge from Bi₂O₃ to NaBiO₃. During the reaction, Bi... 5+ The ions are reduced to Bi 3+ The presence of ions results in a large number of free electrons being bound in the crystal lattice, while positively charged oxygen vacancies are formed to balance the charge. Therefore, in NaBiO3@Bi2O3, Bi... 3+The charge density of the ion is greater than that of NaBiO3, corresponding to its relatively small binding energy. In the NaBiO3@Bi2O3 / g-C3N4 heterojunction, Bi 3+ The ion and Bi 5+ The binding energy of the ion is lower than that of NaBiO3@Bi2O3, and Bi 3+ The ion concentration increases from 35.03% to 36.65%, indicating that the polarization charge is continuously transferred from g-C3N4 to NaBiO3@Bi2O3.

[0177] Figure 12 is the high-resolution O1s XPS spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application. In the figure, curves a-c are the high-resolution O1s XPS spectra of the photocatalyst powders prepared in Comparative Example 2, Comparative Example 3, and Example 3, respectively. The binding energy of the lattice oxygen of NaBiO3 is 529.98 eV, and the binding energy of the lattice oxygen of NaBiO3@Bi2O3 decreases to 529.74 eV, indicating that the electron cloud density of its lattice oxygen is higher than that of NaBiO3. This phenomenon is also related to the increase in the oxygen vacancy concentration. The interface polarization charge is transferred from g-C3N4 to NaBiO3@Bi2O3, resulting in the accumulation of a large number of free electrons on the NaBiO3@Bi2O3 side, which further increases the electron cloud density of its lattice oxygen, and the binding energy decreases to 529.64 eV.

[0178] Figure 13 is the EPR spectrum of the photocatalyst powder prepared in Comparative Example 1. A weak signal can be observed in the EPR spectrum of the g-C3N4 photocatalyst powder prepared in Comparative Example 1, corresponding to the single electron capture signal of the nitrogen vacancy site. Due to the super-thin two-dimensional structure of g-C3N4, the single electron density is reduced; and the nitrogen vacancy has a significant exciton capture effect, therefore, the EPR signal of g-C3N4 is relatively weak.

[0179] Figure 14 is the EPR spectrum of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application. In the figure, curves a-c are the EPR spectra of the photocatalyst powders prepared in Comparative Example 2, Comparative Example 3, and Example 3, respectively. The EPR spectra of NaBiO3, NaBiO3@Bi2O3, and NaBiO3@Bi2O3 / g-C3N4 heterojunction can all observe obvious EPR signals at g = 2.001, corresponding to the single electron capture signal of the oxygen vacancy site. Corresponding to NaBiO3, the formation of oxygen vacancies in its lattice is due to the overflow of lattice oxygen atoms caused by ultraviolet light radiation. In an acidic environment, NaBiO3 is partially reduced to Bi2O3, Bi 5+ The ion-captured electrons are reduced to Bi 3+The free electrons are bound in the Bi2O3 lattice, and oxygen vacancies are formed to maintain charge balance. In addition, part of the free electrons in the Bi2O3 lattice are transferred to NaBiO3, further promoting the formation of positively charged oxygen vacancies, resulting in an increase in the oxygen vacancy concentration in NaBiO3@Bi2O3, corresponding to its relatively strong EPR signal. After g-C3N4 is compounded with NaBiO3 and Bi2O3, driven by the difference in carrier concentration, the free electrons of g-C3N4 are transferred to Bi2O3, and the free electrons of Bi2O3 are transferred to NaBiO3, and a large number of free electrons accumulate on the side of NaBiO3, resulting in the formation of a higher concentration of oxygen vacancies to balance the charge. Therefore, the EPR signal intensity of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is higher than that of NaBiO3@Bi2O3. The presence of high-concentration defects can provide more active sites for the adsorption and activation of pollutants.

[0180] Figure 15 Figure 1 is the UV-Vis diffuse reflectance spectrum of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder. In the figure, curves a-d are the UV-Vis diffuse reflectance spectra of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3 and Example 3, respectively. g-C3N4 can absorb part of the visible light, and its light absorption edge is about 460 nm; the appearance of the Urbach absorption tail near the light absorption edge is due to the presence of nitrogen vacancies. The light response range of NaBiO3 is relatively wide, and its light absorption edge is located at about 558 nm, and the formation of the absorption shoulder near the light absorption edge is due to the presence of oxygen vacancies. The oxygen vacancy concentration in NaBiO3@Bi2O3 is higher than that in NaBiO3, and its light absorption edge is significantly red-shifted, and it can utilize visible light in the range of 420-800 nm. The light absorption edge of the NaBiO3@Bi2O3 / g-C3N4 heterojunction is between g-C3N4 and NaBiO3, and it can also absorb visible light in the range of 420-800 nm.

[0181] Figure 16 Figure 2 is the Kubelka-Munk conversion curve of g-C3N4, NaBiO3 and Bi2O3. According to the intercept of the linear part of the curve with the X-axis, the band gap of g-C3N4, NaBiO3 and Bi2O3 is calculated to be 2.57 eV, 2.19 eV and 2.34 eV, respectively.

[0182] Figure 17 Figure 3 is the degradation curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder under visible light irradiation on ciprofloxacin. In the figure, curves a-c, d-g are the degradation curves of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3 and Example 1-Example 4 under visible light irradiation on ciprofloxacin. The initial concentration of ciprofloxacin is 20 mg·L-1 The amount of catalyst used during the reaction was 20 mg, the amount of pollutant was 50 mL, and the light source used was a 500 W xenon lamp with a 420 nm cut-off filter. As can be seen from the figure, the degradation activity of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application to ciprofloxacin under visible light irradiation was obviously higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 24 min of visible light irradiation, the degradation efficiency of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 to ciprofloxacin was 36.53%, 28.97% and 57.73% respectively, and the degradation efficiency of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Examples 1-4 to ciprofloxacin was increased to 70.81%, 85.92%, 94.41% and 77.24% respectively, and the degradation activity of the heterojunction photocatalyst prepared in Example 3 to ciprofloxacin was the highest.

[0183] Figure 18 is the kinetic curve of the photocatalytic degradation of ciprofloxacin under visible light irradiation of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application. In the figure, curves a-c, d-g are the kinetic curves of the photocatalytic degradation of ciprofloxacin under visible light irradiation of the photocatalyst powders prepared in Comparative Examples 1-3 and Examples 1-4 respectively. As shown in the figure, under visible light irradiation, the degradation rates of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 to ciprofloxacin were 0.0168 min -1 , 0.0135 min -1 , 0.0311 min -1 , and the degradation rates of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalysts prepared in Examples 1-4 to ciprofloxacin were increased to 0.0466 min -1 , 0.0795 min -1 , 0.1131 min -1 and 0.0586 min -1 , and the degradation rate of the heterojunction photocatalyst prepared in Example 3 to ciprofloxacin was the highest, which was 6.73, 8.38 and 3.64 times of that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 respectively.

[0184] Figure 19is the TOC (total organic carbon) removal rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application during photocatalytic degradation of ciprofloxacin under visible light irradiation. In the figure, curves a-d are the TOC removal rates of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 during photocatalytic degradation of ciprofloxacin under visible light irradiation. As can be seen from the figure, the TOC removal rate gradually increases with the extension of the light irradiation time, indicating that ciprofloxacin is gradually mineralized into H2O and CO2. After 24 min of visible light irradiation, the TOC removal rates of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 in photocatalytic degradation of ciprofloxacin are 20.18%, 30.91% and 51.23% respectively; under the same reaction conditions, the TOC removal rate of the heterojunction photocatalyst prepared in Example 3 in photocatalytic degradation of ciprofloxacin is significantly increased to 86.49%, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application has a high mineralization ability for ciprofloxacin under visible light irradiation.

[0185] Figure 20 is the degradation curve of tetracycline hydrochloride by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application under visible light irradiation. In the figure, curves a-c, d-g are the degradation curves of tetracycline hydrochloride by the photocatalyst powders prepared in Comparative Examples 1-3 and Examples 1-4 under visible light irradiation. The initial concentration of tetracycline hydrochloride is 40 mg·L -1 , the catalyst dosage is 20 mg, the pollutant dosage is 50 mL, and the light source used is a 500 W xenon lamp with a 420 nm cutoff filter. As can be seen from the figure, the degradation activity of tetracycline hydrochloride by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application under visible light irradiation is also higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 12 min of visible light irradiation, the degradation efficiencies of tetracycline hydrochloride by g-C3N4, NaBiO3 and NaBiO3@Bi2O3 are 19.24%, 37.44% and 50.76% respectively, and the degradation efficiencies of tetracycline hydrochloride by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalysts prepared in Examples 1-4 are increased to 59.69%, 74.47%, 95.10% and 86.34% respectively. The heterojunction photocatalyst prepared in Example 3 has the highest degradation activity for tetracycline hydrochloride.

[0186] Figure 21is the kinetic curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application for photocatalytic degradation of tetracycline hydrochloride under visible light irradiation. In the figure, curves a-c, d-g are the kinetic curves of the photocatalyst powders prepared by Comparative Example 1-Comparative Example 3, Example 1-Example 4 for photocatalytic degradation of tetracycline hydrochloride under visible light irradiation. As can be seen from the figure, under visible light irradiation, the degradation rates of tetracycline hydrochloride by g-C3N4, NaBiO3, NaBiO3@Bi2O3 are 0.0157 min -1 , 0.0390 min -1 , 0.0582 min -1 , and the degradation rates of tetracycline hydrochloride by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalysts prepared by Example 1-Example 4 are increased to 0.0735 min -1 , 0.1081 min -1 , 0.2514 min -1 and 0.1541 min -1 , respectively. The degradation rate of tetracycline hydrochloride by the heterojunction photocatalyst prepared by Example 3 is the highest, which is 16.01, 6.45 and 4.32 times of g-C3N4, NaBiO3 and NaBiO3@Bi2O3, respectively.

[0187] Figure 22 is the TOC removal rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application during photocatalytic degradation of tetracycline hydrochloride under visible light irradiation. Columnar graphs a-d are the TOC removal rates of the photocatalyst powders prepared by Comparative Example 1-Comparative Example 3, Example 3 during photocatalytic degradation of tetracycline hydrochloride under visible light irradiation. After visible light irradiation for 12 min, the TOC removal rate of tetracycline hydrochloride by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst can reach 89.72%, which is 6.99, 2.85 and 2.41 times of g-C3N4 (12.84%), NaBiO3 (31.46%) and NaBiO3@Bi2O3 (37.21%), respectively, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared by the present application also has high mineralization capacity for tetracycline hydrochloride under visible light irradiation.

[0188] Figure 23 is the degradation curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application for metronidazole under visible light irradiation. In the figure, curves a-d are the degradation curves of the photocatalyst powders prepared by Comparative Example 1-Comparative Example 3, Example 3 for metronidazole under visible light irradiation. The initial concentration of metronidazole is 20 mg·L -1mg, the amount of catalyst used during the reaction is 20 mg, the amount of pollutants used is 50 mL, and the light source used is a 500W xenon lamp with a 420nm cut-off filter. As can be seen from the figure, the degradation activity of the prepared heterojunction photocatalyst on metronidazole under visible light irradiation is obviously higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 60 min of visible light irradiation, the degradation efficiency of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst on metronidazole is significantly increased from 27.59% (g-C3N4), 37.68% (NaBiO3), 40.51% (NaBiO3@Bi2O3) to 82.78%.

[0189] Figure 24 is the kinetics curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder of the application on the photocatalytic degradation of metronidazole under visible light irradiation. In the figure, curves a-d are the kinetics curves of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3 and Example 3 on the photocatalytic degradation of metronidazole under visible light irradiation. The degradation rate of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst of Example 3 on metronidazole under visible light irradiation is 0.0305 min -1 , which is 6.78, 4.12 and 3.76 times of g-C3N4 (0.0045 min -1 ), NaBiO3 (0.0074 min -1 ) and NaBiO3@Bi2O3 (0.0081 min -1 ) respectively.

[0190] Figure 25 is the degradation curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder of the application on norfloxacin under visible light irradiation. In the figure, curves a-d are the degradation curves of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3 and Example 3 on norfloxacin under visible light irradiation. The initial concentration of norfloxacin is 20 mg·L -1, the catalyst dosage is 20 mg, the pollutant dosage is 50 mL, and the light source used is a 500W xenon lamp with a 420nm cut-off filter. As can be seen from the figure, the degradation activity of the prepared heterojunction photocatalyst on norfloxacin under visible light irradiation is obviously higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 60 min of visible light irradiation, the degradation efficiency of norfloxacin on g-C3N4, NaBiO3 and NaBiO3@Bi2O3 is 39.45%, 41.52% and 60.76% respectively, and under the same reaction conditions, the degradation efficiency of norfloxacin on the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 can reach 94.31%.

[0191] Figure 26 is the kinetic curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder under visible light irradiation. In the figure, curves a-d are the kinetic curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 under visible light irradiation. Under visible light irradiation, the degradation rate of norfloxacin on the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is 0.0496min -1 , which is 5.98, 5.77 and 3.31 times the degradation rate of norfloxacin on g-C3N4 (0.0083min -1 ), NaBiO3 (0.0086min -1 ) and NaBiO3@Bi2O3 (0.0150min -1 ) respectively.

[0192] Figure 27 is the degradation curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder on ofloxacin under visible light irradiation. In the figure, curves a-d are the degradation curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 on ofloxacin under visible light irradiation. The initial concentration of ofloxacin is 20mg·L -1, the catalyst dosage is 20 mg, the pollutant dosage is 50 mL, and the light source used is a 500W xenon lamp with a 420nm cut-off filter. As can be seen from the figure, the degradation activity of the prepared heterojunction photocatalyst on ofloxacin under visible light irradiation is obviously higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 40 min of visible light irradiation, the degradation efficiency of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 on ofloxacin is 44.41%, 51.28% and 73.59% respectively, and under the same reaction conditions, the degradation efficiency of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 on ofloxacin is increased to 93.50%

[0193] Figure 28 is the kinetic curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application under visible light irradiation for photocatalytic degradation of ofloxacin. In the figure, curves a-d are the kinetic curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 under visible light irradiation for photocatalytic degradation of ofloxacin. Under visible light irradiation, the degradation rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 on ofloxacin can reach 0.0666min -1 , which is 5.01, 3.80 and 2.02 times the degradation rate of g-C3N4 (0.0133min -1 ), NaBiO3 (0.0175min -1 ) and NaBiO3@Bi2O3 (0.0329min -1 ) on ofloxacin, respectively.

[0194] Figure 29 is the degradation curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared by the present application under visible light irradiation on oxytetracycline. In the figure, curves a-d are the degradation curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 under visible light irradiation on oxytetracycline. The initial concentration of oxytetracycline is 20mg·L -1, the amount of catalyst used during the reaction is 20 mg, the amount of pollutants used is 50 mL, and the light source used is a 500 W xenon lamp with a 420 nm cut-off filter. As can be seen from the figure, the prepared heterojunction photocatalyst has a degradation activity of oxytetracycline under visible light irradiation, which is also higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 40 min of visible light irradiation, the degradation efficiency of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 on oxytetracycline is 47.61%, 49.06% and 71.44% respectively, and under the same reaction conditions, the degradation efficiency of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 on oxytetracycline is increased to 92.64%.

[0195] Figure 30 is the kinetic curve of the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder photocatalytic degradation of oxytetracycline under visible light irradiation. In the figure, curves a-d are the kinetic curves of the photocatalyst powders prepared in Comparative Examples 1-3 and Example 3 photocatalytic degradation of oxytetracycline under visible light irradiation. As shown in the figure, the degradation rates of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 on oxytetracycline are 0.0149 min -1 , 0.0180 min -1 and 0.0276 min -1 , respectively, and the degradation rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 on oxytetracycline is increased to 0.0620 min -1 , which is 4.16, 3.44 and 2.25 times that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3, respectively.

[0196] Figure 31 is the TOC removal rate of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 during photocatalytic degradation of metronidazole, norfloxacin, ofloxacin and oxytetracycline under visible light irradiation. After 60 min, 60 min, 40 min and 40 min of visible light irradiation, the TOC removal rates of the prepared heterojunction during photocatalytic degradation of metronidazole, norfloxacin, ofloxacin and oxytetracycline under visible light irradiation are 70.30%, 89.34%, 84.80% and 81.55%, respectively, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application also has a high mineralization capacity for other antibiotics under visible light irradiation.

[0197] Figure 32is the recycling experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 for photocatalytic degradation of ciprofloxacin under visible light irradiation. During the 1st to 6th recycling reaction, the degradation efficiency of the heterojunction photocatalyst prepared in Example 3 on ciprofloxacin was 94.41%, 94.61%, 91.61%, 91.15%, 90.32%, and 89.68% respectively after 24 min of visible light irradiation. After 6 recycling reactions, the degradation efficiency of the heterojunction on ciprofloxacin only decreased by about 4.73%.

[0198] Figure 33 is the recycling experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 for photocatalytic degradation of tetracycline hydrochloride under visible light irradiation. During the 1st to 6th recycling reaction, the degradation efficiency of the heterojunction photocatalyst prepared in Example 3 on tetracycline hydrochloride was 95.10%, 96.01%, 94.46%, 94.22%, 92.22%, and 91.31% respectively after 24 min of visible light irradiation. After 6 recycling reactions, the degradation efficiency of the heterojunction on tetracycline hydrochloride only decreased by about 3.79%.

[0199] During the recycling reaction, the degradation efficiency of the heterojunction photocatalyst prepared in Example 3 on ciprofloxacin and tetracycline hydrochloride remained basically stable, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application has good recycling stability.

[0200] Figure 34 is the XRD pattern of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 before and after the degradation recycling reaction. As can be seen from the figure, after 6 recycling reactions, the XRD pattern of the heterojunction did not change significantly, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application has good structural stability during the solid-liquid reaction.

[0201] Figure 35is the active species capture experiment result of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 during photocatalytic degradation of ciprofloxacin under visible light irradiation. During the reaction, disodium ethylenediaminetetraacetate, tert-butyl alcohol, p-benzoquinone and β-carotene were used as hole, hydroxyl radical, superoxide radical and singlet oxygen capture agents, respectively. As can be seen from the figure, after introducing disodium ethylenediaminetetraacetate, tert-butyl alcohol, p-benzoquinone and β-carotene into the reaction system, the degradation efficiency of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst on ciprofloxacin is reduced from 94.41% to 29.85%, 42.44%, 58.62% and 84.02%, respectively, indicating that the role of each active species during photocatalytic degradation of antibiotics is in the order of hole > hydroxyl radical > superoxide radical > singlet oxygen.

[0202] Figure 36 is the degradation curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application during photocatalytic oxidation of NO under visible light irradiation. In the figure, curves a-c, d-g are the degradation curves of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4 during photocatalytic oxidation of NO under visible light irradiation. The initial concentration of NO is about 750 ppb, the catalyst dosage during the reaction is 20 mg, and the light source used is a 300 W xenon lamp with a 420 nm cutoff filter. As can be seen from the figure, the oxidation activity of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application on NO under visible light irradiation is significantly higher than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3. After 13 min of visible light irradiation, the removal rate of NO by g-C3N4, NaBiO3 and NaBiO3@Bi2O3 is about 44.72%, 41.23% and 52.68%, respectively, and the removal efficiency of NO by the heterojunction photocatalysts prepared in Example 1-Example 4 under the same reaction conditions is increased to 63.99%, 76.12%, 85.97% and 70.24%, respectively. The heterojunction photocatalyst prepared in Example 3 has the highest removal activity on NO.

[0203] Figure 37are the real-time NO and NO2 concentrations during the photocatalytic oxidation of NO by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application under visible light irradiation. In the figure, curves a-c, d-g are the real-time NO and NO2 concentrations during the photocatalytic oxidation of NO by the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3 and Example 1-Example 4 under visible light irradiation. For g-C3N4, NaBiO3 and NaBiO3@Bi2O3, the NO2 concentration in the reaction system increases from 89 ppb, 80 ppb and 33 ppb to 204 ppb, 208 ppb and 130 ppb, respectively, during the photocatalytic oxidation of NO. For the heterojunction photocatalysts prepared in Example 1-Example 4, the maximum NO2 concentration in the reaction system is about 100 ppb, 89 ppb, 92 ppb and 68 ppb, respectively, during the photocatalytic oxidation of NO. Compared with g-C3N4, NaBiO3 and NaBiO3@Bi2O3, the amount of toxic NO2 produced by the heterojunction photocatalyst prepared in the application under visible light irradiation is significantly reduced, indicating that the heterojunction can oxidize NO to NO2 under visible light irradiation - / NO3 - , i.e. achieving deep photocatalytic oxidation of NO.

[0204] Figure 38 are the results of the cyclic experiments of the photocatalytic oxidation of NO by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application under visible light irradiation. During the 1st to 6th cyclic reactions, the removal efficiency of the photocatalytic oxidation of NO by the prepared heterojunction under visible light irradiation is 85.97%, 84.18%, 82.68%, 82.41%, 81.63% and 79.76%, respectively, after 13 min of visible light irradiation. After 6 cyclic reactions, the removal efficiency of NO by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 3 only decreases by about 6.21%, indicating that the heterojunction photocatalyst prepared in the application also has good cyclic stability under gas-solid reaction conditions.

[0205] Figure 39 are the real-time NO and NO2 concentrations during the photocatalytic oxidation of NO by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 under visible light irradiation during the cyclic reaction. As can be seen from the figure, the maximum NO2 concentration in the reaction system during the 1st to 6th cyclic reactions is 92 ppb, 106 ppb, 91 ppb, 82 ppb, 96 ppb and 96 ppb, respectively, i.e. the oxidation ability of the heterojunction photocatalyst prepared in the application for NO does not weaken with the prolongation of the reaction time.

[0206] Figure 40are XRD patterns of NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 before and after the photocatalytic oxidation of NO under visible light irradiation. After 6 cycles of reaction, the XRD pattern of the prepared heterojunction photocatalyst does not change significantly, indicating that the prepared NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst also has good structural stability under gas-solid reaction conditions.

[0207] Figure 41 are the results of active species capture experiments of NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 for the photocatalytic oxidation of NO under visible light irradiation. p-benzoquinone, potassium iodide, tert-butyl alcohol and β-carotene are used as superoxide radical, hole, hydroxyl radical and singlet oxygen capture agents, respectively. As can be seen from the figure, after introducing p-benzoquinone, potassium iodide, tert-butyl alcohol and β-carotene into the reaction system, the NO removal efficiency is reduced from 85.97% to 21.95%, 38.29%, 59.89% and 45.19%, respectively, indicating that the order of the role of each active species during the photocatalytic oxidation of NO is as follows: superoxide radical > hole > singlet oxygen > hydroxyl radical.

[0208] Figure 42 are the transient photocurrent response curves of NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application under visible light irradiation. In the figure, curves a-c, d-g are the transient photocurrent response curves of photocatalyst powder prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4 under visible light irradiation. During the test, the catalyst dosage is 20 mg, a 300W xenon lamp with a 420 nm cut-off filter is used as a visible light source, and a 0.1 mol·L-1 Na2SO4 solution is used as an electrolyte. As can be seen from the figure, all samples show fast and stable photocurrent response. -1 -2 -2 -2 -2 -2 -2 -2 ​​​​​​​The photocurrent density of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is obviously greater than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3, indicating that the construction of the heterojunction improves the separation efficiency of the photo-generated electron-hole pairs.

[0209] Figure 43 is the electrochemical impedance spectrogram of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application under visible light irradiation. In the figure, curves a-c, d-g are the electrochemical impedance spectrograms of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3, Example 1-Example 4 under visible light irradiation. During the test, the catalyst dosage is 20 mg, a 300W xenon lamp plus a 420 nm cut-off filter is used as the visible light source, and a 0.1 mol·L -1 of Na2SO4 solution is used as the electrolyte. The obtained Nyquist point diagram is fitted using ZSimpWin software, and the selected equivalent circuit model is R s (R ct (CQ)), wherein R s , R ct , C and Q are the solution resistance, charge transfer resistance, space charge capacitance and electrochemical double layer capacitance, respectively. From the fitting results, the charge transfer resistance of g-C3N4, NaBiO3 and NaBiO3@Bi2O3 is 4.197 kΩ, 3.445 kΩ and 3.128 kΩ, respectively, and the charge transfer resistance of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in Example 1-Example 4 is reduced to 2.712 kΩ, 2.185 kΩ, 1.778 kΩ and 1.927 kΩ, respectively. The charge transfer resistance of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is obviously smaller than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3, indicating that the construction of the heterojunction can promote the interface charge separation and transfer.

[0210] Figure 44 is the cyclic voltammogram of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application under visible light irradiation. In the figure, curves a-d are the cyclic voltammograms of the photocatalyst powders prepared in Comparative Example 1-Comparative Example 3, Example 3. During the test, the catalyst dosage is 20 mg, a 300W xenon lamp plus a 420 nm cut-off filter is used as the visible light source, and a 0.1 mol·L -1Na2SO4 solution was used as electrolyte. As can be seen from the figure, the redox peak produced by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst under visible light irradiation is obviously stronger than that of g-C3N4, NaBiO3 and NaBiO3@Bi2O3, indicating that the photo-generated electrons and holes of the heterojunction photocatalyst prepared in the application have stronger redox capacity.

[0211] Figure 45 is the time-resolved fluorescence decay curve of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in the application. In the figure, curves a and b are the time-resolved fluorescence decay curves of the photocatalyst powders prepared in Comparative Example 1 and Example 3, respectively. The wavelength used for testing is 340 nm. The obtained curve is fitted by a three-index function, wherein the longer lifetime (τ3) corresponds to the band-to-band recombination of photo-generated electron-hole pairs, and the shorter lifetime (τ1 and τ2) corresponds to the relaxation of photo-generated electrons in the defect state. The lifetime (τ1 = 2.7067 ns, τ2 = 7.7217 ns, τ3 = 30.1312 ns) of the photo-generated carriers of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst is obviously longer than that of g-C3N4 (τ1 = 1.6215 ns, τ2 = 4.4966 ns, τ3 = 18.2999 ns), indicating that the construction of the heterojunction can prolong the lifetime of the photo-generated carriers, and thus improve the utilization rate of photo-generated electrons and holes.

[0212] Figure 46 is the EPR spectrum of DMPO-·O2 - substance produced by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 under visible light irradiation. In the figure, curves a-c are the EPR spectra of DMPO-·O2 - substance produced by the photocatalyst powders prepared in Comparative Example 1, Comparative Example 3 and Example 3 under visible light irradiation. In the figure, the four characteristic peaks with an intensity ratio of about 1:1:1:1 correspond to the EPR signal of superoxide free radicals, indicating that g-C3N4, NaBiO3@Bi2O3 and NaBiO3@Bi2O3 / g-C3N4 can all produce superoxide free radicals under visible light irradiation. The EPR signal of the heterojunction photocatalyst prepared in Example 3 is stronger than that of g-C3N4 and NaBiO3@Bi2O3, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in the application can produce a higher concentration of superoxide free radicals to participate in the photocatalytic reaction under visible light irradiation.

[0213] Figure 47This figure shows the EPR spectrum of the DMPO-·OH substance generated by the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 under visible light irradiation. In the figure, curves ac represent the EPR spectra of the DMPO-·OH substance generated by the photocatalyst powders prepared in Comparative Example 1, Comparative Example 3, and Example 3 under visible light irradiation. In the figure, the four characteristic peaks with an intensity ratio of approximately 1:2:2:1 correspond to the EPR signal of hydroxyl radicals. g-C3N4, NaBiO3@Bi2O3, and NaBiO3@Bi2O3 / g-C3N4 can all generate hydroxyl radicals under visible light irradiation. The EPR signal of the heterojunction photocatalyst prepared in Example 3 is significantly stronger than that of g-C3N4 and NaBiO3@Bi2O3, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in this invention can generate a higher concentration of hydroxyl radicals to participate in the photocatalytic reaction under visible light irradiation.

[0214] Figure 48 The TEMP- of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst powder prepared in Example 3 under visible light irradiation. 1 The EPR spectrum of O2. In the figure, curves ac represent the TEMP- spectroscopy of the photocatalyst powders prepared in Comparative Example 1, Comparative Example 3, and Example 3 under visible light irradiation. 1 The EPR spectrum of O2 is shown. In the figure, the three characteristic peaks with an intensity ratio of approximately 1:1:1 correspond to the EPR signal of singlet oxygen. g-C3N4, NaBiO3@Bi2O3, and NaBiO3@Bi2O3 / g-C3N4 can all generate singlet oxygen under visible light irradiation. The EPR signal generated by the heterojunction photocatalyst prepared in Example 3 is significantly stronger than that of g-C3N4 and NaBiO3@Bi2O3, indicating that the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst prepared in this invention can generate a higher concentration of singlet oxygen to participate in the photocatalytic reaction under visible light irradiation.

[0215] Figure 49 These are the work functions of g-C3N4, Bi2O3, and NaBiO3. Based on density functional theory using first-principles calculations, the work functions of g-C3N4, Bi2O3, and NaBiO3 are calculated to be 4.73 eV, 6.65 eV, and 8.77 eV, respectively.

[0216] Figure 50 These are the XPS-VB spectra of g-C3N4, Bi2O3, and NaBiO3. The valence band potentials of g-C3N4, Bi2O3, and NaBiO3 are +1.54 eV, +2.18 eV, and +2.45 eV, respectively. According to E... CB =E VB -E gThe conduction band potential of g-C3N4, Bi2O3 and NaBiO3 is calculated to be -1.03 eV, -0.16 eV and +0.26 eV, respectively.

[0217] Figure 51 is the photocatalytic mechanism of the NaBiO3@Bi2O3 / g-C3N heterojunction photocatalyst prepared in the application.

Claims

1. A NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst, characterized in that, This catalyst is a composite material of NaBiO3, Bi2O3, and the graphite-like phase g-C3N4. Bi2O3 is coated on the surface of NaBiO3 to form a core-shell structure NaBiO3@Bi2O3, which exhibits a nanoflower morphology formed by the self-assembly of nanosheets. Both NaBiO3 and Bi2O3 contain oxygen vacancy defects in their crystal lattices; g-C3N4 is a nanosheet structure with nitrogen vacancy defects in its crystal lattice. The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst includes the following steps: Step 1: Dissolve NaBiO3 powder in water and irradiate it with ultraviolet light under stirring to obtain suspension A; Step 2: Add HNO3 solution to suspension A and irradiate with ultraviolet light under stirring to obtain suspension B; Step 3: Add g-C3N4 powder to suspension B to obtain suspension C; wherein, g-C3N4 powder is prepared by high-temperature thermal polymerization reaction in air using urea as raw material; Step 4: The suspension C was subjected to ultraviolet light irradiation under stirring conditions. The resulting precipitate was washed and dried to obtain the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst.

2. The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, Includes the following steps: Step 1: Dissolve NaBiO3 powder in water and irradiate it with ultraviolet light under stirring to obtain suspension A; Step 2: Add HNO3 solution to suspension A and irradiate with ultraviolet light under stirring to obtain suspension B; Step 3: Add g-C3N4 powder to suspension B to obtain suspension C; wherein, g-C3N4 powder is prepared by high-temperature thermal polymerization reaction in air using urea as raw material; Step 4: The suspension C was subjected to ultraviolet light irradiation under stirring conditions. The resulting precipitate was washed and dried to obtain the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst.

3. The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that, In step 1, the ultraviolet light irradiation time is 0.5-3 h, and in step 2, the ultraviolet light irradiation time is 0.5-3 h.

4. The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that, The molar ratio of NaBiO3, HNO3 and g-C3N4 in the suspension C obtained in step 3 is (6-12):(12-21):(2-9).

5. The preparation method of a NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that, The concentrations of NaBiO3, HNO3, and g-C3N4 in the suspension C obtained in step 3 were 0.1-0.4 mol·L⁻¹. -1 0.2-0.7 mol·L -1 and 0.03-0.3 mol·L -1 .

6. The preparation method of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 2, characterized in that, In step 4, the ultraviolet light irradiation time is 2-6 hours.

7. The application of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1 in the catalytic degradation of organic pollutants in water under visible light irradiation.

8. The application according to claim 7, characterized in that, The organic pollutants are ciprofloxacin, tetracycline hydrochloride, oxytetracycline, ofloxacin, norfloxacin, or metronidazole.

9. The application of the NaBiO3@Bi2O3 / g-C3N4 heterojunction photocatalyst according to claim 1 in the catalytic degradation of gaseous pollutants under visible light irradiation.

10. The application according to claim 9, characterized in that, The gaseous pollutant is NO.

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