PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst as well as preparation and application thereof

Abstract

The invention discloses a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst and preparation and application thereof.The composite catalyst comprises carbon nitride nanosheets and PbBiO2Br nanosheets, the carbon nitride nanosheets are carboxyl functionalized carbon nitride, the PbBiO2Br nanosheets are highly dispersed on the surfaces of the carbon nitride nanosheets, and the PbBiO2Br nanosheets are uniformly distributed on the surfaces of the carbon nitride nanosheets. The PbBiO2Br nanosheet is tightly anchored on the surface of the carbon nitride nanosheet through electrostatic self-assembly coupling high-temperature calcination, so as to form the composite photocatalyst with a 2D / 2D interface contact structure. CCN plane charge transfer is improved through carboxyl functionalization, the 2D / 2D structure of the composite photocatalyst has the advantages of large interface contact area, multiple active reaction sites, short mass transfer path, stable structure and the like, and the composite photocatalyst is high in visible light absorption capacity, high in photo-induced electron plane / interface transmission rate, high in electron hole separation efficiency and high in reactive oxygen substance yield; the good degradation performance is realized on bisphenol A in a water body.

Description

Technical Field

[0001] The present invention relates to the technical field of visible light catalysis, and in particular to a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst and a preparation method and application thereof. Background Art

[0002] Bisphenol A (BPA) is a typical organic chemical synthetic product, widely used in the manufacture of daily necessities such as beverage containers and baby bottles. However, during the production and disposal of products, BPA will inevitably be discharged into the water environment. Even at lower exposure concentrations, BPA's unique physiological toxicity can interfere with the nervous and endocrine systems, posing a huge threat to human health. What's more serious is that due to BPA's strong π-conjugated structure and biological toxicity, traditional water treatment processes cannot effectively remove BPA. In order to remove BPA from water bodies, a variety of technologies have been used, including adsorption, Fenton reaction, and electrochemical oxidation. Among them, semiconductor photocatalytic technology can efficiently mineralize organic pollutants by forming high-energy reactive oxygen species (ROS), and has attracted much attention in the field of environmental remediation.

[0003] PbBiO2Br is an n-type semiconductor with a moderate band gap (~2.47 eV). Due to its excellent reactivity under visible light, it has become a research hotspot in the fields of photosynthesis and photodegradation. However, the further photocatalytic application of PbBiO2Br is still hindered by slow carrier migration and rapid electron-hole recombination. In order to overcome these defects and improve the photocatalytic efficiency of PbBiO2Br, various strategies have been developed, such as shortening the carrier transport path through morphology regulation or enhancing the spatial separation of electrons and holes through heterojunction engineering. Among them, PbBiO2Br-based heterojunctions have been proven to be an effective method, because the staggered band structure and different work functions of the photocatalyst can form an electric field at the heterojunction interface, accelerating the interfacial transfer of electrons.

[0004] Graphitic carbon nitride (g-C3N4) has become a hot research topic in the field of photocatalysis due to its superior light absorption ability, environmental friendliness and physical and chemical stability. In addition, g-C3N4 has a good band structure and can be highly compatible with PbBiO2Br to form an effective interface heterojunction. However, current technology makes it difficult to effectively establish a good interface contact when constructing a heterojunction, and the two phases are more mechanically stacked. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst and its preparation and application, by carboxyl functionalizing carbon nitride nanosheets, and enhancing its solution dispersibility during the functionalization process, and then coupling with PbBiO2Br nanosheets to construct an efficient heterojunction, forming a 2D / 2D carboxyl functionalized carbon nitride / PbBiO2Br (CCN / PBOB) heterojunction catalyst with strong interface contact. This new heterojunction has excellent surface / surface contact and extremely strong charge transfer ability, can quickly activate molecular oxygen to produce a large number of active oxygen species, and then effectively degrade BPA in water.

[0006] In order to achieve the above-mentioned object, the present invention first provides a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst, comprising carbon nitride nanosheets and PbBiO2Br nanosheets, wherein the carbon nitride nanosheets are carboxyl functionalized carbon nitride, the PbBiO2Br nanosheets are highly dispersed on the surface of the carbon nitride nanosheets, and the PbBiO2Br nanosheets are tightly anchored on the surface of the carbon nitride nanosheets through electrostatic self-assembly coupling and high-temperature calcination to form a 2D / 2D interface contact structure.

[0007] Based on a general inventive concept, the present invention also provides a method for preparing a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst, comprising the following steps:

[0008] S1, placing urea in a muffle furnace for high-temperature calcination to obtain initial carbon nitride, adding the initial carbon nitride to a nitric acid solution to form an initial carbon nitride suspension, fully stirring the initial carbon nitride suspension, and then heating and refluxing the suspension, washing it with a large amount of deionized water, and drying it to obtain carboxyl-functionalized carbon nitride nanosheets;

[0009] S2, adding hexadecyltrimethylammonium bromide, bismuth nitrate pentahydrate, and lead nitrate into deionized water to form a mixed solution, adjusting the pH of the mixed solution to alkaline using sodium hydroxide, and placing the mixed solution in a reactor for hydrothermal reaction to obtain PbBiO2Br nanosheets;

[0010] S3. Add the carboxyl-functionalized carbon nitride nanosheets obtained in step S1 and the PbBiO2Br nanosheets obtained in step S2 into deionized water for ultrasonic dispersion to obtain a suspension, slowly add the PbBiO2Br nanosheet suspension into the carboxyl-functionalized carbon nitride nanosheet suspension, stir at room temperature and then centrifuge, freeze-dry to obtain a mixture, place the obtained mixture in a muffle furnace, and calcine at high temperature to obtain a PbBiO2Br-anchored carboxyl-functionalized carbon nitride composite catalyst.

[0011] Preferably, the stirring time of the initial carbon nitride suspension in step S1 is 24 to 48 hours, and the concentration of the nitric acid solution is 2 to 8 mmol / L.

[0012] Preferably, in step S1, the high temperature calcination time is 2 to 6 hours, the high temperature calcination temperature is 500 to 550° C., the heating reflux temperature is 125° C., and the heating reflux time is 18 to 30 hours.

[0013] Preferably, in step S2, the molar ratio of hexadecyltrimethylammonium bromide, bismuth nitrate pentahydrate and lead nitrate is 1:1:1, the pH of the mixed solution is adjusted to 12-14 using sodium hydroxide, the hydrothermal reaction temperature is 120-160° C., and the hydrothermal reaction time is 6-18 h.

[0014] Preferably, the concentrations of hexaalkyltrimethylammonium bromide, bismuth nitrate pentahydrate and lead nitrate in the mixed solution of step S2 are 12 to 30 mmol / L.

[0015] Preferably, in step S3, the mass ratio of carboxyl-functionalized carbon nitride nanosheets to PbBiO2Br nanosheets is 10:1-3, the ultrasonic time is 0.5-1.5 h, and the stirring time is 2-6 h.

[0016] Preferably, in step S3, the calcination temperature is 120-200° C., the calcination time is 1-3 hours, and the calcination atmosphere is a nitrogen atmosphere.

[0017] Preferably, the speed of centrifugal separation in step S3 is 4000-8000 r / min.

[0018] Based on a general inventive concept, the present invention also provides an application of a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst in removing bisphenol A from water. The application method of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst in removing bisphenol A from water is as follows: adding the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst to wastewater containing bisphenol A, stirring under dark conditions, and then turning on a xenon lamp light source for illumination reaction.

[0019] Preferably, the content of bisphenol A in the wastewater is 0-30 mg / L, and the usage of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst is 0.2-1 mg / ml.

[0020] Preferably, the stirring time is 30 to 60 minutes; the xenon lamp light source power is 300W; and the illumination reaction time is 60 to 150 minutes.

[0021] The main principle of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst provided by the present invention to efficiently remove the pollutant bisphenol A (BPA) in water is:

[0022] Under illumination, semiconductor photocatalysts carbon nitride (CN) and PbBiO2Br (PBOB) will generate electrons and holes. Electrons are reducing and holes are oxidizing, but electrons and holes in the monomers are very easy to recombine and annihilate. The electrons of carbon nitride (CN) are mainly located near the N atom, while holes exist in the remaining area. When CN is functionalized with carboxyl groups to form carboxyl-functionalized carbon nitride (CCN), the electrons of CCN are redistributed and mainly accumulate on the introduced carboxyl groups, indicating that the overlap of the negative charge center and the positive charge center is destroyed. The dipole moments (μ) of CN and CCN are calculated to be 0 and 3.18 Debye, respectively, and the direction of the dipole moment is parallel to the carboxyl to heptazine unit. It can be inferred that a strong polarization electric field is formed between the carboxyl and heptazine units, which serves as the intrinsic driving force for the directional transfer of electrons in the CCN skeleton. When CCN and PBOB construct a 2D / 2D heterojunction, the carboxyl groups can transfer electrons in the CCN body in a directional manner by introducing a polarization electric field, and the interfacial electric field formed between CCN and PBOB can quickly transfer holes in CCN and combine with electrons in PBOB, achieving spatial separation of electrons and holes in CCN and PBOB through a unique planar / interfacial electron transfer method. The spatially separated electrons can react with molecular oxygen in water to generate reactive oxygen species (ROS) such as superoxide radicals (·O2-), hydrogen peroxide (H2O2) and hydroxyl radicals (·OH). These ROS have strong oxidizing properties and can degrade BPA in water together with holes.

[0023] The CCN ultrathin nanosheet structure with high dispersion performance prepared by the method of the present invention significantly enhances the surface / surface contact with PBOB, and can significantly shorten the migration distance of photogenerated electrons and holes, and facilitate the mass transfer process of pollutants, thereby improving the photocatalytic activity of the catalyst.

[0024] The above scheme of the present invention has the following beneficial effects:

[0025] (1) The CCN / PBOB composite catalyst provided by the present invention is synthesized by a high-temperature calcination method coupled with electrostatic self-assembly of CCN and PBOB, wherein carboxyl functionalization improves CCN planar charge transfer, and PBOB nanosheets are tightly anchored on the surface of CCN to form a 2D / 2D interface contact structure, which accelerates electron interface transfer; wherein both CCN and PBOB are nanosheet structures, especially CCN has an ultrathin nanosheet structure, and finally the 2D / 2D structure of the CCN / PBOB composite photocatalyst formed after high-temperature calcination has the advantages of large interface contact area, multiple active reaction sites, short mass transfer path and stable structure;

[0026] (2) CCN / PBOB is a novel visible light photocatalyst with the advantages of strong visible light absorption, fast plane / interface transport rate of photogenerated electrons, high electron-hole separation efficiency, and high yield of active oxygen species;

[0027] (3) CCN / PBOB has high performance in photocatalytic degradation of BPA, no secondary pollution of degradation products, strong anti-interference ability, and can effectively adapt to interferences such as different environmental water samples, solution pH, and high concentration of inorganic salt ions;

[0028] (4) The CCN / PBOB photocatalyst has excellent recycling performance. After multiple cycles, the degradation performance of BPA has not decreased significantly. The product of the present invention provides an effective way to remove BPA in actual water bodies and has great commercial application prospects;

[0029] (5) The novel composite photocatalyst CCN / PBOB preparation method provided by the present invention is highly operable, safe and reliable, low-cost, and the raw materials are readily available. The reaction conditions during the synthesis process are mild and the energy consumption is low. The preparation method of the present invention is easy to realize large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 The X-ray diffraction spectrum and UV-visible absorption spectrum of the photocatalyst in Experimental Example 1 of the present invention are shown in FIG. Figure 1 (a) is the X-ray diffraction pattern, Figure 1 (b) is the UV-visible absorption spectrum;

[0032] Figure 2 The XPS total spectra of CN, CCN and CCN / PBOB-2 in Experimental Example 1 of the present invention are ( Figure 2 a) and O1s spectrum ( Figure 2 b);

[0033] Figure 3 This is the water drop angle test diagram of UCCN and CCN in Experimental Example 1 of the present invention, where Figure 3 (a) is the water drop angle test image of UCCN. Figure 3 (b) is the water drop contact angle test diagram of CCN;

[0034] Figure 4 This is an electron microscope image of the material in Experimental Example 1 of the present invention, wherein Figure 4 (a)~ Figure 4 (e) Scanning electron micrographs of carboxyl-functionalized bulk carbon nitride (CBCN), carboxyl-functionalized carbon nitride nanosheets (CCN), PbBiO2Br nanosheets (PBOB), UCCN / PBOB-2, and PbBiO2Br-modified carboxyl-functionalized carbon nitride (CCN / PBOB-2), respectively; Figure 4 (f) Transmission electron microscopy image of CCN / PBOB-2;

[0035] Figure 5 is the electrostatic potential distribution and dipole moment of CN and CCN in Experimental Example 1 of the present invention; wherein Figure 5 (a) is the electrostatic potential distribution and dipole moment of CN, Figure 5 (b) is the electrostatic potential distribution and dipole moment of CCN;

[0036] Figure 6 is the unit cell structure and work function of CCN, CN and PBOB in Experimental Example 1 of the present invention, wherein Figure 6 (a)~ Figure 6 (c) Unit cell structures of CCN, CN and PBOB respectively; Figure 6 (d)~ Figure 6 (f) Work function diagrams of CCN, CN, and PBOB, respectively;

[0037] Figure 7 is the unit cell structure and work function of CN / PBOB-2 and CCN / PBOB-2 in Experimental Example 1 of the present invention; wherein Figure 7 (a)~ Figure 7 (b) The unit cell structures of CN / PBOB-2 and CCN / PBOB-2, Figure 7 (c)~ Figure 7 d are the work functions of CN / PBOB-2 and CCN / PBOB-2, respectively;

[0038] Figure 8 The photoluminescence (PL) spectra and photocurrent curves of the composite photocatalysts (CCN / PBOB-1, CCN / PBOB-2, CCN / PBOB-3) and the photocatalyst CN / PBOB-2 in Experimental Example 1 of the present invention are shown in FIG. Figure 8 (a) is the photoluminescence (PL) spectrum. Figure 8 (b) is the photocurrent curve;

[0039] Fig. 9 is the degradation performance curve of BPA by different photocatalysts in Example 4 of the present invention, wherein Fig. 9 (a) is the degradation performance curve of BPA by different PbBiO2Br modified carboxyl functionalized carbon nitrides (CCN / PBOB-1, CCN / PBOB-2, CCN / PBOB-3). Fig. 9(b) Comparison of the degradation performance curves of photocatalysts CCN / PBOB-M, CN / PBOB-2 and UCCN / PBOB-2 for BPA;

[0040] Fig.10 This is the degradation performance curve of BPA under different pH and inorganic ion interference in Experimental Example 2 of the present invention, wherein: Fig.10 (a) is the degradation performance curve of BPA by CCN / PBOB-2 under different pH interferences. Fig.10 (b) is the degradation performance curve of BPA by CCN / PBOB-2 under different inorganic ion interferences;

[0041] Fig.11 This is the degradation performance curve of BPA in different concentrations of HA and different water samples in Experimental Example 2 of the present invention, where: Fig.11 (a) is the degradation performance curve of BPA by CCN / PBOB-2 under the interference of different concentrations of HA. Fig.11 (b) is the degradation performance curve of BPA in different water samples;

[0042] Fig.12 The stability test result of the composite photocatalyst in Experimental Example 3 of the present invention is shown in FIG. Fig.12 (a) is the cyclic degradation performance curve of CCN / PBOB-2 for BPA. Fig.12 (b) is the X-ray diffraction pattern of CCN / PBOB-2 before and after the reaction. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0044] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0045] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0046] Example 1

[0047] Preparation of PbBiO2Br Anchored Carboxyl Functionalized Carbon Nitride Composite Catalyst (CCN / PBOB-2)

[0048] (1) 20 g of urea was placed in a muffle furnace, heated to 550 °C, and maintained for 4 h to obtain CN nanosheets. 1 g of CN powder was placed in a flask containing 50 mL of nitric acid solution (5 mmol / L), and the suspension was stirred at room temperature for 24 h, and then refluxed at 125 °C for 24 h. After the reaction was completed, it was washed with a large amount of deionized water and freeze-dried to obtain CCN nanosheets.

[0049] (2) 1.5 mmol of CTAB, bismuth nitrate pentahydrate and lead nitrate were added to 60 mL of deionized water, and the pH of the suspension was adjusted to 14 using a 2 mol / L NaOH solution. After stirring for 30 min, the suspension was transferred to a 100 mL reactor and subjected to a hydrothermal reaction at 140 °C for 12 h. The product was then washed with ethanol and deionized water and dried to obtain PBOB nanosheets.

[0050] (3) 40 mg of the PBOB nanosheets obtained in step (2) were added to 10 mL of deionized water and ultrasonically dispersed for 30 min to obtain suspension A. 200 mg of the CCN nanosheets obtained in step (1) were added to 30 mL of deionized water and ultrasonically dispersed for 30 min to obtain suspension B. Subsequently, suspension A was added dropwise to suspension B, and after stirring at room temperature for 4 h, the product was washed with deionized water and freeze-dried to obtain a CCN / PBOB mechanical mixture (CCN / PBOB-M). The above mechanical mixture CCN / PBOB-M was placed in a muffle furnace and calcined at 150° C. in a N2 atmosphere for 1 h to obtain a PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst, numbered CCN / PBOB-2.

[0051] Example 2

[0052] Preparation of PbBiO2Br Anchored Carboxyl Functionalized Carbon Nitride Composite Catalyst (CCN / PBOB-1)

[0053] In this embodiment, the preparation method of the PbBiO2Br nanosheet-modified carboxyl-functionalized carbon nitride nanosheet is basically the same as that in Example 1, except that the amount of PbBiO2Br nanosheet used in this embodiment is 20 mg. The PbBiO2Br / carboxyl-functionalized carbon nitride composite photocatalyst prepared in this embodiment is numbered CCN / PBOB-1.

[0054] Example 3

[0055] Preparation of PbBiO2Br Anchored Carboxyl Functionalized Carbon Nitride Composite Catalyst (CCN / PBOB-3)

[0056] In this embodiment, the preparation method of the PbBiO2Br nanosheet-modified carboxyl-functionalized carbon nitride nanosheet is basically the same as that in Example 1, except that the amount of PbBiO2Br nanosheet used in this embodiment is 60 mg. The PbBiO2Br / carboxyl-functionalized carbon nitride composite photocatalyst prepared in this embodiment is numbered CCN / PBOB-3.

[0057] Comparative Example 1

[0058] Preparation of bulk carboxyl-functionalized carbon nitride (CBCN)

[0059] 10g of melamine was placed in a muffle furnace, heated to 550°C, and maintained for 4 hours. After the reaction, the product was ground and passed through a 200-mesh sieve to obtain block BCN. 1g of BCN powder was placed in a flask containing 50mL of nitric acid solution (5mmol / L), and the above suspension was refluxed at 125°C for 24 hours. After the reaction, it was washed with a large amount of deionized water and freeze-dried to obtain carboxyl functionalized block carbon nitride (CBCN).

[0060] Comparative Example 2

[0061] Preparation of CN / PBOB-2 composite photocatalyst

[0062] (1) Place 20 g of urea in a muffle furnace, heat to 550 °C, and maintain for 4 h to obtain CN nanosheets

[0063] (2) 1.5 mmol of CTAB, bismuth nitrate pentahydrate and lead nitrate were added to 60 mL of deionized water, and the pH of the suspension was adjusted to 14 using a 2 mol / L NaOH solution. After stirring for 30 min, the suspension was transferred to a 100 mL reactor and subjected to a hydrothermal reaction at 140 °C for 12 h. The product was then washed with ethanol and deionized water and dried to obtain PBOB nanosheets.

[0064] (3) 40 mg of the PBOB nanosheets obtained in step S2 were added to 10 mL of deionized water and ultrasonically dispersed for 30 min to obtain suspension A. 200 mg of the CN nanosheets obtained in step S1 were added to 30 mL of deionized water and ultrasonically dispersed for 30 min to obtain suspension B. Subsequently, suspension A was added dropwise to suspension B, stirred at room temperature for 4 h, and the product was washed with deionized water and dried to obtain a CN / PBOB mechanical mixture. The above CN / PBOB mechanical mixture was placed in a muffle furnace and calcined at 150 ° C for 1 h in a N2 atmosphere to obtain a CN / PBOB composite photocatalyst, numbered CN / PBOB-2.

[0065] Comparative Example 3

[0066] Preparation of UCCN / PBOB-2 composite photocatalyst

[0067] In this example, the preparation method of the PbBiO2Br nanosheet-modified carboxyl-functionalized carbon nitride nanosheet is basically the same as that in Example 1, except that: in the preparation of the carboxyl-functionalized carbon nitride in step (1) in this comparative example, the 24h sufficient stirring step is not performed, and the obtained carbon nitride product is recorded as UCCN nanosheet. The PbBiO2Br / carboxyl-functionalized carbon nitride composite photocatalyst prepared in this comparative example is numbered UCCN / PBOB-2.

[0068] Experimental Example 1

[0069] Photocatalyst performance characterization

[0070] The PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalysts (CCN / PBOB-1, CCN / PBOB-2, CCN / PBOB-3) prepared in Examples 1 to 3 of the present invention and the catalysts prepared in Comparative Examples 1 to 3 (CBCN, CN / PBOB-2, UCCN / PBOB-2) were analyzed by X-ray diffraction, UV-visible light absorption, contact angle test and the like, and the following results were obtained: Figure 1 The spectrum shown, where Figure 1 (a) is the X-ray diffraction pattern, Figure 1 (b) is the UV-visible absorption spectrum.

[0071] from Figure 1 As can be seen in (a), CCN has a strong peak at 27.2° (002) and a weak peak at 13.1° (100), which correspond to the interlayer stacking and in-plane stacking of heptazine units, respectively, and are both typical characteristic peaks of graphitic carbon nitride. For PBOB, all detected peaks can be attributed to the tetragonal phase PbBiO2Br (JCPDS: 38-1008). In the CCN / PBOB composite material, it can be observed that all characteristic peaks belonging to CCN and PBOB are monitored. It is worth noting that with the increase of PBOB content, the (002) peak of CCN gradually decreases, further indicating the successful combination of the two phases. In addition, the spectra of CCN / PBOB-2 and CN / PBOB-2 show similar shapes, indicating that the carboxyl functionalization of graphitic carbon nitride does not significantly affect the crystal structure of the composite material. From Figure 1 As can be seen in b, CCN exhibits obvious absorption in the range of 300nm to 460nm, while PBOB has an absorption band edge around 500nm. By combining CCN and PBOB, the resulting CCN / PBOB composite material exhibits an enhanced absorption band with a gradually red-shifted edge around 460-500nm. In addition, compared with CN, only a small blue shift was observed in the absorption of CCN, indicating that carboxyl functionalization does not significantly affect the photoresponse ability of graphite phase carbon nitride.

[0072] Figure 2 The XPS spectra of CN, CCN and CCN / PBOB-2 prepared in Example 1 of the present invention are as follows ( Figure 2 a) and O1s spectrum ( Figure 2 b) From Figure 2 (a) It can be seen that both CN and CCN show basic C, N, and O element peaks, but the O content in CCN is much higher. In addition to the C, N, and O element peaks, Pb, Bi, and Br peaks were also detected in CCN / PBOB-2. Figure 2 (b) It can be seen that a clear peak (532.4 eV) belonging to adsorbed H2O can be observed in the O1s spectrum of CN, while the peak at 531.1 eV deconvoluted from CCN belongs to OC=O (carboxyl group). In addition, a peak at 529.4 eV is detected in CCN / PBOB-2, which belongs to the lattice oxygen peak in PBOB.

[0073] Figure 3 These are the water drop angle test images of UCCN and CCN, where Figure 3 (a) is the water drop angle test diagram of UCCN prepared in comparative example 3, Figure 3 (b) is a test diagram of the water drop contact angle of CCN in Example 1. Figure 3 It can be seen that the contact angle of UCCN prepared without sufficient stirring is 42.3°, while the contact angle of CCN prepared after sufficient stirring is 31.5°, which indicates that CCN has higher dispersibility in water, which is conducive to the subsequent surface / surface contact with PBOB.

[0074] Figure 4 is the electron microscope image of the material, Figure 4 (a)~ Figure 4 (e) are scanning electron micrographs of carboxyl-functionalized bulk carbon nitride (CBCN) in Comparative Example 1, carboxyl-functionalized carbon nitride nanosheets (CCN) in Example 1, PbBiO2Br nanosheets (PBOB) in Example 1, UCCN / PBOB-2 in Comparative Example 3, and PbBiO2Br-modified carboxyl-functionalized carbon nitride (CCN / PBOB-2) in Example 1, respectively; Figure 4 (f) is a transmission electron micrograph of CCN / PBOB-2 in Example 1. Figure 4 It can be seen that CBCN is a typical block structure ( Figure 4 a), while CCN exhibits an ultrathin nanosheet structure ( Figure 4 b). Compared with the bulk structure, the ultrathin nanosheet structure can significantly shorten the migration distance of photogenerated electrons and holes and facilitate the mass transfer process of pollutants, thereby improving the photocatalytic activity of the catalyst. In addition, PBOB is a small nanosheet ( Figure 4c). For the UCCN / PBOB-2 composite photocatalyst, a large number of PBOBs can be seen stacked on the CCN in a disorderly and upright manner. The interface contact area between the two is small, and no effective surface / surface contact is formed ( Figure 4 d). For the CCN / PBOB-2 composite material, it can be seen that PBOB is highly dispersed on the CCN surface, indicating that the early sufficient stirring process helps to strengthen the anchoring of PBOB on the CCN surface and form a good surface / surface (2D / 2D) contact ( Figure 4 e). This is because sufficient stirring in the early stage helps disperse CCN in the aqueous solution and promotes subsequent contact with PBOB molecules. Transmission electron microscopy results show that PBOB and CCN are in close contact, and there is a clear interface between the two phases ( Figure 4 f), which indicates that an effective CCN / PBOB heterojunction structure has been formed.

[0075] Figure 5 is CN( Figure 5 (a)) and CCN( Figure 5 (b)) Electrostatic potential distribution and dipole moment. Figure 5 (a) It can be seen that the electrostatic potential distribution of CN shows a uniform color distribution, which originates from the symmetrical structure of the heptazine unit. Among them, the electrons are mainly located near the N atom, while the holes exist in the rest of the area. For CCN ( Figure 5 b), the electrons are redistributed and mainly accumulated on the introduced carboxyl groups, indicating that the overlap of the negative and positive charge centers is destroyed. At the same time, the dipole moments (μ) of CN and CCN are calculated to be 0 and 3.18 Debye, respectively, and the direction of the dipole moment is parallel to the carboxyl to heptazine unit. It can be inferred that a strong polarization electric field is formed between the carboxyl and heptazine units, which serves as the intrinsic driving force for the in-plane directional transfer of electrons in the CCN skeleton.

[0076] Figure 6 is the unit cell structure and work function of CCN, CN and PBOB in Example 1 of the present invention, wherein Figure 6 (a)~ Figure 6 (c) Unit cell structures of CCN, CN and PBOB respectively; Figure 6 (d)~ Figure 6 (f) Work function diagrams of CCN, CN and PBOB, respectively. Figure 6 It can be seen that the work functions (Φ) of CCN, CN, and PBOB are 4.75, 4.51, and 5.19, respectively. Among them, the work function of PBOB is higher than that of CCN and CN, so when they are combined to form a heterojunction, electrons will migrate from CCN and CN to PBOB.

[0077] Figure 7 is the unit cell structure and work function of CN / PBOB-2 and CCN / PBOB-2 of the present invention; wherein Figure 7 (a)~ Figure 7 (b) are the unit cell structures of CN / PBOB-2 prepared in Comparative Example 2 and CCN / PBOB-2 prepared in Example 1, Figure 7 (c)~ Figure 7 d are the work functions of CN / PBOB-2 and CCN / PBOB-2, respectively. Figure 7 It can be seen that the work functions (Φ) of CCN / PBOB-2 and CN / PBOB-2 are 5.02 and 4.91 eV, respectively, indicating that electron interface transfer has occurred between CCN and CN after contact with PBOB.

[0078] Figure 8 The photoluminescence (PL) spectra and photocurrent curves of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalysts (CCN / PBOB-1, CCN / PBOB-2, CCN / PBOB-3) prepared in Examples 1 to 3 of the present invention and the photocatalyst CN / PBOB-2 prepared in Comparative Example 2 are shown in FIG. Figure 8 (a) is the photoluminescence (PL) spectrum. Figure 8 (b) is the photocurrent curve. Figure 8 (a) It can be seen that both CCN and CN show obvious PL emission peaks at around 460nm, which originates from the recombination of photogenerated electrons and holes in graphite phase carbon nitride. Compared with CCN, CCN / PBOB composites show obvious PL quenching effect, especially CCN / PBOB-2, whose PL signal is the weakest, much lower than CN / PBOB-2. The quenched PL signal of CCN / PBOB-2 indicates that the intrinsic recombination of photogenerated charge carriers is significantly restricted by carboxyl functionalization and interface engineering. Figure 8 (b) It can be seen that CCN / PBOB-2 (1.03 μA) presents the highest current intensity compared with the relatively low current signals of CN (0.45 μA), CCN (0.64 μA) and CN / PBOB-2 (0.85 μA), which confirms that it has the strongest planar / interfacial charge separation efficiency.

[0079] Example 4

[0080] Application of PbBiO2Br nanosheets modified carboxyl functionalized carbon nitride nanosheets composite photocatalyst in degradation of BPA in water

[0081] (1) Weigh 30 mg each of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalysts (CCN / PBOB-1, CCN / PBOB-2, CCN / PBOB-3) prepared in Examples 1 to 3 and the photocatalysts (CBCN, CN / PBOB-2) prepared in Comparative Examples 1 to 2, and the control group is CN, CCN, and PBOB prepared in Example 1. The above products are placed in 50 mL of a 20 mg / L BPA solution, respectively. After the mixed solution is stirred for 30 min to reach adsorption equilibrium, a 300 W xenon lamp light source is turned on, and the photocatalyst is irradiated under a 420 nm filter for 100 min to perform a photocatalytic degradation reaction on BPA.

[0082] (2) During the reaction, 2 mL of the reaction solution was extracted every 20 minutes. After the reaction solution was filtered through a 0.22 μm filter membrane, the BPA concentration in the filtrate was detected using high performance liquid chromatography. The detection conditions of high performance liquid chromatography were: the mobile phase consisted of ethanol and water in a volume ratio of 70 / 30, the flow rate was 1 mL / min, and the detection wavelength was 270 nm. The detection results were as follows: Fig. 9 shown.

[0083] from Fig. 9 (a) It can be seen that in the absence of a photocatalyst, the self-decomposition of BPA is negligible. For PBOB, only 34.4% of BPA was degraded after 100 min of reaction. The degradation rate of CN was about 49.7%, and after carboxyl functionalization, the degradation efficiency of CCN for BPA was improved to 60.6%. In addition, the degradation rate of CBCN for BPA was only 53.8%, which shows that compared with the bulk structure, the nanosheet structure of CCN can effectively improve its photocatalytic performance, mainly because the ultra-thin sheet structure can significantly shorten the mass transfer distance of pollutants and reduce the transmission distance of photogenerated electrons. When CCN was in contact with PBOB, the photocatalytic performance of the obtained CCN / PBOB composite material was significantly enhanced, among which the CCN / PBOB-2 sample achieved the highest BPA removal efficiency of up to 88.7%. It is worth noting that further increasing the loading amount of PBOB will lead to a decrease in the performance of CCN / PBOB-3, which may be due to the excessive deposition of PBOB covering the surface reaction sites of CCN and hindering the separation of carriers. In addition, from Fig. 9 As can be seen from (b), the reactivity of CCN / PBOB-M, CN / PBOB-2, and UCCN / PBOB-2 is much lower than that of CCN / PBOB-2, indicating that the calcination process, carboxyl functionalization of carbon nitride, and face / face (2D / 2D) contact between CCN and PBOB are beneficial to the enhancement of the performance of CCN / PBOB composites.

[0084] Experimental Example 2

[0085] Investigation of the degradation performance of PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst in complex water environment

[0086] (1) Effects of different pH values ​​and (b) inorganic ion interference on the catalytic performance of CCN / PBOB-2

[0087] 30 mg of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst (CCN / PBOB-2) in Example 1 was weighed and placed in 50 mL of a 20 mg / L BPA solution. Subsequently, the pH of the reaction solution was adjusted to 3.0, 5.0, 6.2 (initial pH), 8.0 and 10.0 by 0.1 mol / L NaOH solution or 0.1 mol / L H2SO4 solution, and the mixed solution was stirred for 30 min to reach adsorption equilibrium, and then a 300 W xenon lamp light source was turned on and irradiated under a 420 nm filter for 100 min to perform a photocatalytic degradation reaction on BPA.

[0088] 30 mg of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst (CCN / PBOB-2) in Example 1 was weighed and placed in 50 mL of a 20 mg / L BPA solution. Subsequently, NaCl, NaNO3, Na2SO4 and NaH2PO4 solids were added to make the inorganic salt ion concentration in the reaction solution reach 2 mmol / L. After the mixed solution was stirred for 30 min to reach adsorption equilibrium, a 300 W xenon lamp light source was turned on and irradiated under a 420 nm filter for 100 min to perform a photocatalytic degradation reaction on BPA.

[0089] (2) Effects of different HA concentrations and different water samples on the catalytic performance of CCN / PBOB-2

[0090] 30 mg of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst (CCN / PBOB-2) in Example 1 was weighed and placed in 50 mL of a 20 mg / L BPA solution. Subsequently, HA solid was added to make the HA concentration in the reaction solution reach 1 mg / L, 5 mg / L, 10 mg / L, and 15 mg / L, respectively. After the mixed solution was stirred for 30 min to reach adsorption equilibrium, a 300 W xenon lamp light source was turned on and irradiated under a 420 nm filter for 100 min to perform a photocatalytic degradation reaction on BPA.

[0091] 30 mg of the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst (CCN / PBOB-2) in Example 1 was weighed and placed in 50 mL of a 20 mg / L BPA solution. The BPA solution was prepared with filtered Taozi Lake water, Xiangjiang River water and municipal water. After the mixed solution was stirred for 30 min to reach adsorption equilibrium, a 300 W xenon lamp light source was turned on and irradiated under a 420 nm filter for 100 min to perform a photocatalytic degradation reaction on BPA.

[0092] (3) During the photocatalytic degradation reaction of the above experiments (1) and (2), 2 mL of the reaction solution was extracted every 20 minutes. After the reaction solution was filtered through a 0.22 μm filter membrane, the BPA concentration in the filtrate was detected using high performance liquid chromatography. The detection conditions of high performance liquid chromatography were: the mobile phase consisted of ethanol and water in a volume ratio of 70 / 30, the flow rate was 1 mL / min, and the detection wavelength was 270 nm. The results are shown in Figure 2. Fig.10 , 11 shown.

[0093] Fig.10 The degradation performance curve of BPA by CCN / PBOB-2 under different pH and inorganic ion interference. Fig.10 (a) It can be seen that the photocatalytic behavior of CCN / PBOB-2 changes significantly with the change of solution pH, and the highest BPA removal rate is achieved at pH 6.2 (initial BPA solution pH). When the pH is adjusted to 5.0 and 3.0, a slight decrease in BPA removal performance is observed. However, in an alkaline environment, the photocatalytic activity of CCN / PBOB-2 is significantly limited, and about 76.5% and 65.9% of BPA are removed at pH 8.0 and 10.0. The significant decrease in performance under alkaline conditions may be due to the presence of a large amount of OH-, which can consume part of the photogenerated holes (h + ), and the photogenerated holes (h + ) is an important reactive species in the degradation of BPA. Fig.10 (b) It can be seen that NO3 - and SO4 2- The addition of Cl had no significant effect on the degradation of BPA. - When H2PO4 was added, it had a significant inhibitory effect on the degradation of BPA, which can be attributed to the scavenging effect of Cl-, which can react with ROS to generate Cl· with weaker redox ability. - , in addition to forming less reactive phosphate radicals, the strong affinity makes it easy to attach to the CCN / PBOB-2 surface, thereby blocking the reaction sites and hindering the mass transfer between the catalyst and BPA.

[0094] Fig.11The degradation performance curve of CCN / PBOB-2 on BPA in different HA concentrations and different water samples. Fig.11 a It can be seen that under visible light irradiation, relatively low HA concentrations (1 and 5 mg / L) had no obvious effect on the degradation of BPA. When the HA concentration increased to 10 and 15 mg / L, the photocatalytic activity of CCN / PBOB-2 was significantly degraded, and the BPA removal efficiency decreased to 79.5% and 72.5%, respectively. The reduced reactivity can be attributed to the following two aspects. On the one hand, the light-shielding properties of HA may hinder the light absorption of CCN / PBOB-2, thereby limiting the generation of carriers. On the other hand, HA molecules can act as scavengers to interact with ROS and h + Binds to the skin, reducing their exposure to BPA molecules. Fig.11 b It can be seen that the degradation of BPA in urban water did not show significant changes compared with deionized water. In contrast, in river water (Xiangjiang River in Changsha) and lake water (Taozi Lake in Changsha), the reaction performance decreased to a certain extent. After 100 min of reaction, BPA was degraded by 83.1% and 79.4%, respectively. The performance degradation may be due to the presence of some inorganic ions and organic substances in lake water and river water, which may consume some active species.

[0095] Experimental Example 3

[0096] Study on the cyclic stability of PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst

[0097] Weigh the PbBiO2Br modified carboxyl functionalized carbon nitride composite photocatalyst CCN / PBOB-2 prepared in Example 1, place it in 50mL of a BPA solution with a concentration of 20mg / L, stir the mixed solution for 30min to reach adsorption equilibrium, turn on a 300W xenon lamp light source, illuminate under a 420nm filter for 100min, and perform photocatalytic degradation of BPA. During the reaction, 2mL of the reaction solution was extracted every 20min, and after the reaction solution was filtered through a 0.22μm filter membrane, the BPA concentration in the filtrate was detected by high performance liquid chromatography. The detection conditions of high performance liquid chromatography are as follows: the mobile phase is composed of ethanol and water in a volume ratio of 70 / 30, the flow rate is 1mL / min, and the detection wavelength is 270nm. After each catalytic reaction, the composite photocatalyst CCN / PBOB-2 is separated by a centrifuge at 8000rpm, and the separated composite photocatalyst CCN / PBOB-2 is used to repeat the test according to the above steps, and the cycle is repeated five times. The test results are as follows. Fig.12 shown.

[0098] from Fig.12 As can be seen in (a), after five cycles of testing, no obvious performance deactivation was detected for CCN / PBOB-2, and the BPA removal rate still reached 82.8%. Fig.12 As can be seen in (b), the XRD patterns of CCN / PBOB-2 before and after use are almost the same, indicating that the phase structure is not significantly affected, further revealing the good stability of CCN / PBOB-2.

[0099] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst, characterized in that: The invention comprises carbon nitride nanosheets and PbBiO2Br nanosheets. The carbon nitride nanosheets are carboxyl functionalized carbon nitride. The PbBiO2Br nanosheets are highly dispersed on the surface of the carbon nitride nanosheets. The PbBiO2Br nanosheets are tightly anchored on the surface of the carbon nitride nanosheets through electrostatic self-assembly coupling and high-temperature calcination to form a 2D / 2D interface contact structure.

2. A method for preparing the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst as claimed in claim 1, characterized in that: The following steps are involved: S1, placing urea in a muffle furnace for high-temperature calcination to obtain initial carbon nitride, adding the initial carbon nitride to a nitric acid solution to form an initial carbon nitride suspension, fully stirring the initial carbon nitride suspension, and then heating and refluxing the suspension, washing it with a large amount of deionized water, and drying it to obtain carboxyl-functionalized carbon nitride nanosheets; S2, adding hexadecyltrimethylammonium bromide, bismuth nitrate pentahydrate, and lead nitrate into deionized water to form a mixed solution, adjusting the pH of the mixed solution to alkaline using sodium hydroxide, and placing the mixed solution in a reactor for hydrothermal reaction to obtain PbBiO2Br nanosheets; S3. Add the carboxyl-functionalized carbon nitride nanosheets obtained in step S1 and the PbBiO2Br nanosheets obtained in step S2 into deionized water for ultrasonic dispersion to obtain a suspension, slowly add the PbBiO2Br nanosheet suspension into the carboxyl-functionalized carbon nitride nanosheet suspension, stir at room temperature and then centrifuge, freeze-dry to obtain a mixture, place the obtained mixture in a muffle furnace, and calcine at high temperature to obtain a PbBiO2Br-anchored carboxyl-functionalized carbon nitride composite catalyst.

3. The preparation method according to claim 2, characterized in that: The stirring time of the initial carbon nitride suspension in step S1 is 24 to 48 hours, and the concentration of the nitric acid solution is 2 to 8 mmol / L.

4. The preparation method according to claim 2, characterized in that: In the step S1, the high temperature calcination time is 2 to 6 hours, the high temperature calcination temperature is 500 to 550° C., the heating reflux temperature is 125° C., and the heating reflux time is 18 to 30 hours.

5. The preparation method according to claim 2, characterized in that: In the step S2, the molar ratio of hexadecyltrimethylammonium bromide, bismuth nitrate pentahydrate and lead nitrate is 1:1:1, the pH of the mixed solution is adjusted to 12-14 using sodium hydroxide, the hydrothermal reaction temperature is 120-160° C., and the hydrothermal reaction time is 6-18 hours.

6. The preparation method according to claim 2, characterized in that: In the step S3, the mass ratio of the carboxyl functionalized carbon nitride nanosheets to the PbBiO2Br nanosheets is 10:1-3, the ultrasonic time is 0.5-1.5 hours, and the stirring time is 2-6 hours.

7. The preparation method according to claim 2, characterized in that: In the step S3, the calcination temperature is 120-200° C., the calcination time is 1-3 hours, and the calcination atmosphere is a nitrogen atmosphere.

8. Use of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst as claimed in claim 1 or the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst prepared by the preparation method according to any one of claims 2 to 7 in removing bisphenol A from water, characterized in that: The application method of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst in removing bisphenol A from water is as follows: adding the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst to wastewater containing bisphenol A, stirring under dark conditions, and then turning on a xenon lamp light source for illumination reaction.

9. The use according to claim 8, characterized in that: The content of bisphenol A in the wastewater is 0-30 mg / L, and the usage amount of the PbBiO2Br anchored carboxyl functionalized carbon nitride composite catalyst is 0.2-1 mg / ml.

10. The use according to claim 8, characterized in that: The stirring time is 30 to 60 minutes; the xenon lamp light source power is 300W; and the illumination reaction time is 60 to 150 minutes.

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