Bi@Bi2(Ti2O7) / biochar-based composite material and preparation method and application thereof

Abstract

The present application relates to the field of photocatalyst, in particular to a kind of Bi@Bi2(Ti2O7) / biochar-based composite material and its preparation method and application.The present application prepares full-spectrum photocatalyst with plasmonic Bi in-situ deposited on Bi2(Ti2O7) / BC microspheres by one-pot hydrothermal method.The composite material prepared in the present application has adsorption and photocatalytic functions simultaneously, and has a high specific surface area, can quickly adsorb pollutants and carry out photocatalytic degradation, effectively improve the removal efficiency of pollutants.In the present application, Bi nanoparticles can produce narrow band gap effect, widen the light response range, can absorb visible light and near infrared light, enhance visible light catalytic capacity.In addition, the composite material of the present application has strong electronic conductivity, high interface charge separation efficiency and high photocurrent density, can efficiently utilize light energy in photocatalytic reaction, improve reaction efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalysts, in particular to a Bi@Bi2(Ti2O7) / biochar-based composite material and a preparation method and application thereof. BACKGROUND

[0002] The commonly used industrial technologies for treating trace pollutants such as Cr(VI) include adsorption, chemical oxidation-reduction, ion exchange and membrane separation, but their high cost, high energy consumption and large by-product pollution have become the limitations and challenges of the above technologies. Therefore, it is urgent to find efficient and environmentally friendly water treatment technologies to alleviate this problem.

[0003] Photocatalytic technology has attracted much attention in recent years due to its unique advantages in water pollution control. The photocatalyst used in photocatalytic technology usually includes a carrier with high specific surface area and a photocatalytically active material. The carrier is usually a carbon-based material such as biochar, and the photocatalytically active material can be selected from TiO2, g-C3N4, Bi-based semiconductor and other materials. Among them, bismuth-based semiconductors have excellent potential in photocatalytic degradation of pollutants due to their narrow band gap and good visible light response, but their stability and electron transport efficiency are not high, which limits their practical application.

[0004] CN110871101B discloses a preparation and application of a mesoporous carbon-bismuth titanate composite photocatalytic material. The scheme uses a hydrothermal method to prepare Bi 12 TiO 20 Mesoporous carbon-bismuth titanate composite photocatalytic material, by using Bi 12 TiO 20 as a matrix, combining the high specific surface area and conductivity of mesoporous carbon, improves the separation efficiency of photo-generated carriers, and exhibits good visible light catalytic performance. At the same time, the use of noble metals is avoided to reduce the material preparation cost, which is conducive to industrialization. However, it still has the problems of limited light absorption range, low quantum efficiency and low photocatalytic efficiency. SUMMARY

[0005] The present application relates to the field of photocatalysts, in particular to a Bi@Bi2(Ti2O7) / biochar-based composite material and a preparation method and application thereof.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] The application discloses a Bi@Bi2(Ti2O7) / biocarbon-based composite material, wherein the Bi2(Ti2O7) forms a microsphere structure with a porous structure with the biocarbon, and Bi elements are uniformly dispersed on the surface of the microsphere structure.

[0008] Preferably, in the Bi@Bi2(Ti2O7) / biocarbon-based composite material, the molar ratio of Ti elements to C elements is 1:3-1:4, and the molar ratio of Bi elements to Ti elements is 9:10-9:15.

[0009] The application further discloses a preparation method of the Bi@Bi2(Ti2O7) / biocarbon-based composite material.

[0010] S1. Bismuth nitrate pentahydrate, tetrabutyl titanate and urea are added into ethylene glycol (EG) in proportion, and stirred and uniformly mixed;

[0011] S2. After adding a biocarbon source, stirring is continued to form a mixed suspension;

[0012] S3. The mixed suspension obtained in the step S2 is subjected to a hydrothermal reaction in a high-pressure kettle at a temperature of 150-170 DEG C, after the reaction is completed, the Bi@Bi2(Ti2O7) / BC precursor is obtained by using ethanol for complete cleaning and then vacuum drying;

[0013] S4. The Bi@Bi2(Ti2O7) / BC precursor is calcined at a temperature of 280-320 DEG C under an inert gas atmosphere to form the Bi@Bi2(Ti2O7) / BC composite material.

[0014] Preferably, the molar ratio of the bismuth nitrate pentahydrate, tetrabutyl titanate and urea in the step S1 is 3:1:1.

[0015] Preferably, the biocarbon source in the step S2 is selected from one of straw, rice husk, sugarcane residue and wood chips; and the biocarbon source is first crushed and then sieved through a 100-mesh sieve before being added.

[0016] Preferably, the mass ratio of the addition amount of the biocarbon source to tetrabutyl titanate in the step S2 is 3:10-8:10.

[0017] Preferably, the method of vacuum drying in the step S3 is drying at 65 DEG C for 12h.

[0018] Preferably, in the step S4, the calcination is gradually heated to 280-320 DEG C in a gradually increasing temperature mode, and the temperature increasing speed is 10 DEG C / min.

[0019] The composite material disclosed by the application can remove one or more of hexavalent chromium, ciprofloxacin, methyl orange, methylene blue and rhodamine B under the action of photocatalysis; and can also be used for preparing a catalyst for removing one or more of hexavalent chromium, ciprofloxacin, methyl orange, methylene blue and rhodamine B.

[0020] The application has the advantages that:

[0021] 1. The main material of the application is a porous microsphere structure formed by Bi2(Ti2O7) and biochar, and Bi elements are uniformly dispersed on the surface of the microspheres. The composite material prepared by the application has both adsorption and photocatalytic functions, and has a high specific surface area, so that the pollutants can be quickly adsorbed and photocatalytically degraded, and the removal efficiency of the pollutants is effectively improved. At the same time, the material has good chemical stability in the photocatalytic process, and the activity does not change significantly after 10 cycles of experiments.

[0022] 2. The Bi nanoparticles in the application can produce a narrow band gap effect, widen the light response range, absorb visible light and near-infrared light, and enhance the visible light catalytic ability. In terms of electrochemical performance, the material has strong electronic conductivity, high interface charge separation efficiency and high photocurrent density, so that the light energy can be efficiently utilized in the photocatalytic reaction, and the reaction efficiency is improved.

[0023] 3. The application has a wide application range, and can efficiently photocatalytically remove various pollutants such as hexavalent chromium, ciprofloxacin, methyl orange, methylene blue and rhodamine B. When a sacrificial agent is added, the removal efficiency of some pollutants can reach more than 90%, or even complete degradation, and the generation of intermediate products can be avoided. In addition, the application uses straw, rice husk and other cheap biomass as the source of biochar, so that the preparation cost is low, and the deposition of noble metals is not needed, thereby avoiding the high cost of noble metals, and the application is more conducive to large-scale popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The flow chart of the preparation method of the application is shown.

[0025] Figure 2 The test result images of the samples of each embodiment of the application are shown; wherein (a) is the XRD pattern of each embodiment; (b) is the SEM image of the sample of example 4 with a magnification of 5 mu m; (c) is the SEM image of the sample of example 4 with a magnification of 500 nm; (d) is the TEM image of the sample of example 4; (e) is the HRTEM image of the sample of example 4; (f) is the overall element distribution map of the sample of example 4; (g) is the Bi element distribution map of the sample of example 4; (h) is the Ti element distribution map of the sample of example 4; (i) is the C element distribution map of the sample of example 4; (j) is the O element distribution map of the sample of example 4; and (k) is the EDX pattern of the sample of example 4.

[0026] Figure 3 XPS spectra of the sample of Example 4 of the present application, wherein (a) is the panoramic spectrum of the sample of Example 4; (b) is the high resolution XPS spectrum of C 1s of the sample of Example 4; (c) is the high resolution XPS spectrum of Bi 4f of the sample of Example 4; (d) is the high resolution XPS spectrum of Ti 2p of the sample of Example 4; (e) is the high resolution XPS spectrum of O 1s of the sample of Example 4.

[0027] Figure 4 UV-Vis absorption spectra (a) and corresponding band gap energies (b) of the samples of each example of the present application.

[0028] Figure 5 Nitrogen adsorption-desorption isotherms (a) and corresponding pore size distribution curves (b) of the samples of Example 4, Control Group 1 and Control Group 2.

[0029] Figure 6 EIS Nyquist plots (a) and photocurrent transients (b) under 300 W Xe lamp irradiation (λ > 420 nm) of the samples of each example in 1 M Na2S04solution.

[0030] Figure 7 Absorption-photocatalytic reduction of Cr(VI); wherein (a) is the absorption-photocatalytic reduction of Cr(VI) without catalyst; (b) is the absorption-photocatalytic reduction of Cr(VI) using only Bi@BT / BC-4 as catalyst; (c) is the absorption-photocatalytic reduction of Cr(VI) using TA and Example 4; (d) is the absorption-photocatalytic reduction of Cr(VI) using the samples of each example; (e) is the absorption-photocatalytic reduction of Example 4 composite in the presence and absence of sacrificial agents TA, BQ, EDTA, K2S2O8; (f) is the absorption-photocatalytic reduction of Cr(VI) using the composite of Example 4.

[0031] Figure 8 Absorption-photocatalytic degradation of MO; wherein (a) is the absorption-photocatalytic degradation of MO without catalyst; (b) is the absorption-photocatalytic degradation of MO using only Bi@BT / BC-4 as catalyst; (c) is the absorption-photocatalytic degradation of MO using K2S2O8and Example 4; (d) is the absorption-photocatalytic degradation of MO using the samples of each example.

[0032] Figure 9The figure is the absorption-photocatalytic degradation of MB; wherein, (a) absorption-photocatalytic degradation of MB without catalyst; (b) absorption-photocatalytic degradation of MB when only Bi@BT / BC-4 is used as catalyst; (c) absorption-photocatalytic degradation of MB when K2S2O8 and the sample of example 4 are used; (d) absorption-photocatalytic degradation of MB when each sample of example is used.

[0033] Figure 10 The figure is the absorption-photocatalytic degradation of RhB; wherein, (a) absorption-photocatalytic degradation of RhB without catalyst; (b) absorption-photocatalytic degradation of RhB when only Bi@BT / BC-4 is used as catalyst; (c) absorption-photocatalytic degradation of RhB when K2S2O8 and the sample of example 4 are used; (d) absorption-photocatalytic degradation of RhB when each sample of example is used.

[0034] Figure 11 The figure is the absorption-photocatalytic degradation of CIP; wherein, (a) absorption-photocatalytic degradation of CIP without catalyst; (b) absorption-photocatalytic degradation of CIP when only Bi@BT / BC-4 is used as catalyst; (c) absorption-photocatalytic degradation of CIP when K2S2O8 and the sample of example 4 are used; (d) absorption-photocatalytic degradation of CIP when each sample of example is used. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0036] The present application discloses a Bi@Bi2(Ti2O7) / biocarbon-based composite material, wherein Bi2(Ti2O7) and biocarbon (BC) form a microsphere structure with a porous structure, and Bi elements are uniformly dispersed on the surface of the microsphere structure. The molar ratio of Ti to C is 1:3-1:4; and the molar ratio of Bi to Ti is 9:10-9:15.

[0037] The present application discloses a preparation method of a Bi@Bi2(Ti2O7) / BC composite material, comprising the following steps:

[0038] S1. Add bismuth nitrate pentahydrate, tetrabutyl titanate and urea in a molar ratio of 3:1:1 into 60 mL of ethylene glycol (EG) and stir for 2 h at room temperature, wherein the addition amount of each raw material is: bismuth nitrate pentahydrate 24.256 g (0.050 mol), tetrabutyl titanate 5.672 g (0.017 mol), and urea 1.001 g (0.017 mol);

[0039] S2. Continue stirring for 2 h after adding the biochar source to form a mixed suspension; the biochar source is crushed and sieved through a 100-mesh sieve before being added;

[0040] S3. Transfer the mixed suspension obtained in step S2 into a 100-mL Teflon-coated autoclave and hydrothermally react at a temperature of 160℃ for 6 h; after the reaction is complete, clean thoroughly with ethanol and then vacuum dry at 65℃ for 12 h to obtain a Bi@Bi2(Ti2O7) / BC precursor;

[0041] S4. Calcine the Bi@Bi2(Ti2O7) / BC precursor at a temperature of 300℃ under a N2 gas atmosphere to form a Bi@Bi2(Ti2O7) / BC composite material; the calcination is performed using a gradual heating method, the heating rate is 10℃ / min, and the calcination time is 5 h.

[0042] The biochar in the application can be one of straw, rice husk, sugarcane residue, and wood chips; the appropriate biochar raw material can be selected according to the production place and actual demand.

[0043] In step S2, different amounts of straw powder are added to adjust the ratio of Bi2(Ti2O7) to biochar in the final product. In order to simplify the description, Bi2(Ti2O7) is abbreviated as BT; Bi@Bi2(Ti2O7) / BC is abbreviated as Bi@BT / BC.

[0044] Table 1: Each example and the corresponding amount of added straw powder

[0045]

[0046] Each of the above examples only varies in the amount of added straw powder, and the rest of the preparation conditions remain the same.

[0047] The prepared composite material is detected by the following methods respectively:

[0048] 1. X-ray diffraction (Shimadzu, Cu Kα λ=1.54060Å) test of the crystal phase composition and crystal structure of the material by applying a voltage (45 kV), a current (100 mA), and a scattering angle (2θ / 20°-80°).

[0049] 2. The structure was analyzed by X-ray photoelectron spectroscopy (XPS-Al K - 1486.6 eV) with applied voltage (12 kV), current (23 mA).

[0050] 3. Optical properties were measured by UV / Vis diffuse reflectance spectroscopy (Shimadzu UV-3600).

[0051] 4. High-resolution transmission electron microscopy (HRTEM-JEM-2100F) with an accelerating voltage (200 kV), scanning electron microscopy (SEM, Hitachi, SU-8100) with an applied voltage (5.0 KV), and energy dispersive spectroscopy (EDS, Oxford, X-MaxN 80T) were used to analyze the elemental content and distribution.

[0052] 5. Specific surface area and pore size were determined by nitrogen adsorption-desorption isotherm analysis at 77 K by the Brunauer-Emmett-Teller (BET) method (Micromeritics ASAP 2460).

[0053] 6. Photocurrent response and electrochemical impedance spectroscopy (EIS) were measured and recorded on an electrochemical workstation (CHI-660E, Chenhua Instruments Co., Shanghai, China) using a three-electrode system (Ag / AgCl reference electrode, carbon rod, and the prepared sample-covered nickel foam as the working electrode). The method was as follows:

[0054] The working electrode sample was prepared by dispersing 10 mg of the photocatalyst in 0.5 mL of ethanol and 0.5 mL of ultrapure water, and then ultrasonically treating for 2 h. Then, 0.1 mL of the slurry was repeatedly dropped onto a nickel foam substrate (1 x 2 cm), and the drying and dropping were repeated until the sample solution was completely added. Transient current and EIS measurements were performed in a 1 M Na2SO4 electrolyte solution at room temperature (25 ± 0.2 °C). The measurement was performed at 1 V, with a frequency range of 0.01 Hz to 100 kHz and an alternating current amplitude of 5 mV.

[0055] 7. Photocatalytic activity test

[0056] The photocatalytic activity of the synthesized composite in the visible and near-infrared light range for removing Cr(VI) and antibiotics (CIP) and organic dyes (MB, MO, and RhB) was evaluated.

[0057] A pls-ssx 300 xenon lamp (Perfect Light) was used as the light source to provide a stable light intensity (50 W / m2) in the wavelength range of λ > 420 nm. 2). The reaction system was maintained at room temperature using a thermostatic cooling tank. For the photocatalytic test, 100 mg of photocatalyst was mixed with 100 ml of Cr(VI) and MB, MO and RhB (10 ppm), and stirred in the dark for 30 min to determine the maximum adsorption of pollutants on the surface of the photocatalyst, and then irradiated. The distance between the xenon lamp and the reaction liquid surface was controlled at about 10 cm, and the liquid was irradiated for a certain time. Every certain time, 2 ml of aqueous solution was extracted and filtered using a 0.22 um filter. The concentrations of Cr(VI), CIP and MB, MO and RhB were determined by ultraviolet-visible spectrophotometry, and the total chromium concentration was measured by Optima7000DV inductively coupled plasma spectrometer (ICP). The photocatalytic activity was represented by the (Ct / Co) and irradiation time (t) curve, where (Ct) was the concentration at a certain time, and (Co) was the initial concentration.

[0058] In addition, control groups were set up: control group 1 was straw biochar (BC), and control group 2 was titanium dioxide TiO2.

[0059] The test results are as follows:

[0060] 1. Structure and morphology of crystals

[0061] Bi elemental substance can be obtained by reducing Bi 3+ , and part of the Bi elemental substance can exist stably in a reduced state provided by ethylene glycol (EG). The XRD pattern of the prepared sample is shown in Figure 2 (a). From the standard card corresponding to the XRD pattern, it can be seen that cubic Bi2(Ti2O7) (JCPDS #96-153-3741) is generated, which is composed of Bi-O and Ti-O.

[0062] It is known from the crystallographic open database (COD #1533740) that the bond length of Bi-O in Bi2Ti2O7 is longer than that of Ti-O, indicating that the Bi-O bond is more easily broken, thereby forming Bi elemental substance. The diffraction peaks of Bi@BT / BC can be assigned to two components, namely elemental bismuth (JCPDS #01-085-1330) in a hexagonal system and Bi2Ti2O7. The results show that Bi-deposited BT / BC is successfully prepared by a hydrothermal-calcination reaction.

[0063] The morphology of the sample Bi@BT / BC-4 prepared in Example 4 was observed by SEM, as shown in Figure 2(b) and (c). Sample Bi@BT / BC-4 presents a uniform spherical structure, with Bi elemental uniformly embedded on the surface of BT / BC, indicating that ethylene glycol (EG) can be used as an organic complexing agent to make the material have a microspherical morphology. The Bi surface can be easily oxidized by oxygen in the air to form a thin layer of bismuth oxide, which can be seen from Figure 2 (d). In addition, the present application measured the BET specific surface area and pore volume of the prepared samples to evaluate their potential as photocatalysts. As shown in Table 2, Bi@BT / BC-4 has the largest specific surface area compared to other control groups, which can provide more reaction sites and enhance the light absorption capacity during the photocatalytic reaction.

[0064] Table 2 XPS composition and S of Example 4, Control Group 1 and Control Group 2 materials BET Analysis results

[0065]

[0066] The microstructure of Bi@BT / BC-4 was characterized by TEM and HRTEM. As shown in Figure 2 (d) and (e), there are two lattice spacings of 0.297 nm and 0.326 nm, corresponding to the (222) crystal plane of Bi2Ti2O7 and the (012) crystal plane of Bi elemental, respectively. TEM further proves that Bi is successfully deposited on BT / BC. In addition, Bi is highly dispersed on the surface of BT / BC, with a particle size mainly in the range of 1-3 nm, and the Bi formed has a small particle size, which means that Bi@BT / BC-4 has a larger metal-semiconductor interface area, which can improve the charge transfer efficiency.

[0067] As shown in Figure 2 (f)-(j), the EDS element mapping results show that Bi@BT / BC-4 is composed of Bi, Ti, C and O, and all elements are uniformly distributed on the surface. This is consistent with the atomic percentage data in Table 2. As shown in Figure 2 (k), the EDX chart shows that the Bi@BT / BC material contains a high content of Bi and Ti elements, and high metal element loading can effectively improve the photocatalytic activity of the material.

[0068] 2. X-ray photoelectron spectroscopy

[0069] The present application uses X-ray photoelectron spectroscopy (XPS) to detect the chemical state and surface chemical composition of Bi@BT / BC-4. As shown in Figure 3 (a) and Table 2, the full spectrum confirms that Bi@BT / BC-4 is mainly composed of Bi, Ti, O and C elements. The high-resolution XPS spectra of C 1s, Bi 4f, Ti 2p and O 1s of the prepared composite sample are shown in Figure 3In (b)-(e).

[0070] like Figure 3 As shown in (b), the C 1s spectrum can be decomposed into three peaks with binding energies of 284.80, 286.34, and 288.45 eV. The peak at 284.80 eV represents the C=C peak of sp2 hybridized carbon atoms in the carbonaceous material. The peaks at 286.34 eV and 288.45 eV represent CO and O=CO, respectively. Furthermore, no C-Ti bond peak was detected near 281.5 eV, indicating that C-Ti bonds are absent in the composite material between the BC and TiO2 samples.

[0071] like Figure 3 As shown in (c), the 164.40 and 159.10 eV peaks of Bi@BT / BC-4 are attributed to metallic Bi. 0 The Bi 4f 7 / 2 and Bi 4f 5 / 2 peaks. Furthermore, Figure 3 In (c), two weak peaks at 156.91 and 162.16 eV can also be observed, which are attributed to the semi-metallic Bi. This evidence demonstrates that Example 4 successfully generated elemental bismuth in its zero-valence state, existing as nanoparticles. Furthermore, the characteristic peaks of "semi-metallic Bi" (156.91 and 162.16 eV) indicate that the generated bismuth nanoparticles have a high proportion of exposed surface atoms, exhibiting higher chemical reactivity and catalytic activity; thus demonstrating the excellent performance of the Bi@BT / BC-4 composite material in catalytic applications.

[0072] In addition, the surface of Bi elemental particles is oxidized by air to form a thin layer of bismuth oxide, which can prevent the metallic bismuth from being further oxidized, thereby improving the stability of Bi@BT / BC-4 in the photocatalytic process.

[0073] Figure 3 (d) is a high-resolution XPS scan of the Ti 2p peak. As shown in the figure, the two XPS peaks at 458.18 and 464.14 eV are attributed to Ti. 4+ 2p3 / 2 and Ti 4+ 2p1 / 2. Furthermore, the peak at 466.07 eV indicates the presence of Ti. 3+ Explanation of Ti 4+ Due to the reducing power of ethylene glycol (EG), a reduction reaction occurs during the treatment, thereby generating Ti. 3+ Due to the presence of Ti 3+ The narrowing band gap of Bi@BT / BC-4 allows it to absorb light with longer wavelengths and lower energy, thereby improving its ability to catalyze under visible light.

[0074] exist Figure 3In (e), the O 1s peak was resolved into two peaks at 529.74 and 531.20 eV. They can be assigned to lattice oxygen and surface adsorbed oxygen. BC in Bi@BT / BC-4 can act as a trapping center for photo-generated electrons, thus reducing the probability of their recombination with holes.

[0075] 3. UV-Vis absorption spectra

[0076] The UV-Vis absorption spectra of the prepared samples were investigated in the spectral range of 200-800 nm. As shown in Figure 4 (a), the Bi@BT / BC-4 sample exhibited an absorption edge at about 518 nm, indicating that the prepared Bi@BT / BC-4 sample had excellent visible light response characteristics. In addition, the light absorption of samples 1-7 in the entire visible and near-infrared light regions was significantly enhanced.

[0077] As shown in Figure 4 (b), the band gap energy values of Bi@BT / BC-1, Bi@BT / BC-2, Bi@BT / BC-3, and Bi@BT / BC-4 were 2.81 eV, 2.72 eV, 2.70 eV, and 2.63 eV, respectively, while Bi@BT / BC-5, Bi@BT / BC-6, and Bi@BT / BC-7 did not exhibit an absorption edge. This indicates that the doping amount of BC has a great influence on the band gap width of the material. A doping amount of 0.1-1 g can enhance the absorption effect of the material in the visible light range; while excessive doping of BC will lead to a decrease in the absorption performance of the material. The reason may be that excessive carbon will gather to hinder the effective penetration of light.

[0078] The band gap energy of Bi@BT / BC-4 was determined by XPS valence band spectroscopy, as shown in Figure 4 (b), the valence band (VB) potential of Bi@BT / BC-4 (V = +2.63 eV) is lower than the water oxidation level (V = +1.99 eV). Based on the band gap obtained from the UV-vis-NIR diffuse reflectance spectrum, the conduction band (CB) edge of Bi@BT / BC-4 is estimated to be -0.42 eV. This indicates that the conduction band position of Bi@BT / BC-4 is sufficient to drive the oxygen reduction reaction, and has good potential for photocatalytic oxygen production.

[0079] 4. Nitrogen adsorption-desorption isotherm analysis

[0080] To further analyze the structural properties of the samples, the isotherms and pore size distributions were measured by N2 adsorption-desorption experiments, as shown in Figure 5 (a) and Figure 5(b), the specific surface area, pore volume and average pore size results are shown in Table 2. The hysteresis loop of adsorption / desorption was observed on the isotherm of control group 1 (BC), control group 2 (TiO2) and Bi@BT / BC-4 composite photocatalyst. According to the classification of IUPAC, the three belong to H1, H1 and H3 type respectively, which indicates that the above-mentioned materials are relatively mesoporous, and the pore size range is within 2-50 nm.

[0081] The hysteresis loop isotherm of BC has no obvious saturated adsorption platform, indicating that the pore structure is very irregular, while the hysteresis loop adsorption isotherm of Bi@BT / BC-4 has a saturated adsorption platform, reflecting that the pore size distribution is relatively uniform. In Figure 5 As can be seen in (a), Bi@BT / BC-4 has a larger adsorption capacity than BC and TiO2. The same conclusion can be drawn from the S BET It can be concluded that the specific surface area of Bi@BT / BC-4 is increased by 71.3% compared with TiO2 and by 45.0% compared with BC, which can effectively improve the adsorption capacity.

[0082] In addition, compared with control group 1 using pure biochar, the specific surface area and pore volume of the composite material are significantly higher, and the pore size of the composite material is smaller, indicating that the increase of specific surface area corresponds to the mesoporous structure, and the successful doping of Bi2Ti2O7 and biochar. The increase of specific surface area and the appearance of mesoporous structure increase the adsorption site, and also more conducive to the progress of photocatalytic reaction.

[0083] 5. Electrochemical analysis

[0084] Electrochemical impedance spectroscopy (EIS) measurement was used to study the electrochemical properties of the composite material. The semicircular Nyquist curve refers to the total impedance or charge transfer impedance at the contact interface between the working electrode coated with the sample and the electrolyte solution. The electronic conductivity of the sample is determined by the radius of the circular arc on the EIS diagram, and the smaller the radius of the circular arc, the stronger the electronic conductivity of the synthetic material.

[0085] As shown in Figure 6 (a), the radius of the circular arc of each example sample decreases and then increases with the addition of BC. Among them, the radius of the circular arc of the Bi@BT / BC-4 sample is the smallest, indicating that the conductivity of the Bi@BT / BC-4 sample is the largest, that is, the interface separation efficiency of the Bi@BT / BC-4 sample is the fastest, and the photocatalytic activity is the highest.

[0086] As shown in Figure 6 (b), under light, the photoelectric current density of Bi@BT / BC-4 is the highest, indicating that the addition amount of BC in Example 4 is the optimal choice.

[0087] 6. Synergistic adsorption-photocatalytic reduction of Cr(VI)

[0088] In order to explore the adsorption-photocatalytic performance of the prepared Bi@BT / BC-x composite materials, the experiments of the synergistic adsorption-photocatalytic reduction of Cr(VI) under the irradiation of the wavelength range of λ>420 nm were carried out.

[0089] As shown in Figure 7 (a), under the irradiation, when no catalyst and sacrificial agent were used, Cr(VI) could not be reduced. As shown in Figure 7 (b), when only Bi@BT / BC-4 was used as the catalyst, Cr(VI) was only adsorbed, and the adsorption-photocatalytic reduction rate was 60.81%.

[0090] Figure 7 As shown in (c), in the presence of the Bi@BT / BC-4 catalyst and tartaric acid (TA), the adsorption-photocatalytic reduction efficiency of Cr(VI) was 98.05% at 80 min. In the presence of TA, it was shown that the Bi@BT / BC-4 catalyst had excellent catalytic activity for Cr(VI).

[0091] As shown in Figure 7 (d), in the presence of TA, the catalysts prepared in each example, Bi@BT / BC-1, Bi@BT / BC-2, Bi@BT / BC-3, Bi@BT / BC-5, Bi@BT / BC-6 and Bi@BT / BC-7 had the efficiencies of 37.61%, 43.93%, 70.21%, 83.65%, 59.14% and 76.07% respectively at 80 min.

[0092] From the comparative examples 1-4, it can be concluded that BC has adsorption properties and can act as an “electron acceptor”, which can effectively accelerate the migration of electrons from Bi to Bi2(Ti2O7), and effectively improve the adsorption-photocatalytic efficiency of Cr(VI) under visible light irradiation. However, when the content of BC is further increased, the photocatalytic activity will decrease due to the hindering of the penetration of visible light.

[0093] In order to study the reaction mechanism, a series of sacrificial agents were used to carry out the experiments of the adsorption-photocatalytic reduction of Cr(VI) by the composite materials. Potassium persulfate (K2S2O8), tartaric acid (TA), ethylenediaminetetraacetic acid (EDTA) and benzoquinone (BQ) were used as the sacrificial agents of e - , h + , •OH and •O2 - . As shown in Figure 7 (e):

[0094] When K2S2O8 was added to the reaction system, the synergistic adsorption-photocatalytic efficiency of Cr(VI) was reduced to 24.61% after 80 min of sunlight irradiation, indicating that the e -) play a major role in the photocatalytic process.

[0095] However, when the sacrificial agent is TA, EDTA and BQ, the adsorption-photocatalytic efficiency reaches 98.05%, 76.01% and 71.45% respectively after 80 min of sunlight irradiation, indicating that h + , ·OH, and ·O2 - are not the important active ions in the photocatalytic reaction.

[0096] The composite material prepared by the present application is composed of adsorption material and photocatalyst. Among them, biochar is used as the main adsorption material, and Bi@BT constitutes the main catalytic system. The present application makes full use of the characteristics of biochar as an "electron acceptor" and an adsorbent, which can accelerate the transfer of electrons from Bi to Bi2(Ti2O7). The narrow band gap effect formed by the deposition of Bi nanoparticles in carbonaceous material further enhances the response range of the photocatalyst to light.

[0097] In the process of extensive practical application, the repeatability and chemical stability of the photocatalyst are key influencing factors. Therefore, the adsorption-photocatalytic reduction of Cr(VI) on Bi@BT / BC-4 photocatalyst was studied. The total experimental test lasted for 800 min, and after each 80 min reaction, the used Bi@BT / BC-4 sample was washed with deionized water for several times, dried at 60°C for 12 hours, and then re-dispersed into a new Cr(VI) reaction solution. The experimental results show that, as shown in Figure 7 (f), after 10 repeated cycles under adsorption and sunlight irradiation, the activity of Bi@BT / BC-4 does not change significantly, indicating that Bi@BT / BC-4 has excellent chemical stability under visible light irradiation.

[0098] 7. Synergistic adsorption-photocatalytic degradation of organic pollutants

[0099] In actual wastewater, there are a variety of trace environmental pollutants. Therefore, synergistic adsorption-photocatalytic degradation tests were conducted on other possible pollutants in wastewater, such as ciprofloxacin (CIP), methyl orange (MO), methylene blue (MB) and rhodamine B (RhB).

[0100] The absorption peak of methyl orange (MO) is about 464 nm. Under light irradiation, without adding catalyst, as shown in Figure 8 (a), MO cannot be adsorbed-photocatalytically degraded. As shown in Figure 8 (b), when only catalyst is added, the degradation rate of MO under light irradiation for 25 min is 62.15%. As shown in Figure 8 (c), when Bi@BT / BC-4 and K2S2O8 exist at the same time under natural light, MO can be completely degraded in about 10 min.

[0101] As Figure 8 As shown in FIG. 10 (d), the degradation performance of MO by Bi@BT / BC-1, Bi@BT / BC-2, Bi@BT / BC-3, Bi@BT / BC-5, Bi@BT / BC-6 and Bi@BT / BC-7 was 40.77%, 45.69%, 87.39%, 99.89%, 69.02%, 64.88% and 74.15% respectively at 10 min.

[0102] The absorption peak of methylene blue (MB) can be at 664 nm. The absorption peak of rhodamine B (RhB) is at 553 nm. As shown in FIG. 8 (a) and FIG. 9 (a), similar to the adsorption-photocatalytic degradation of MO, under light irradiation, MB and RhB cannot be degraded substantially without the addition of catalysts. Figure 9 As shown in FIG. 8 (b) and FIG. 9 (b), Figure 10 As shown in FIG. 8 (a) and FIG. 9 (a), similar to the adsorption-photocatalytic degradation of MO, under light irradiation, MB and RhB cannot be degraded substantially without the addition of catalysts.

[0103] As shown in FIG. 8 (b) and FIG. 9 (b), Figure 9 As shown in FIG. 8 (b) and FIG. 9 (b), Figure 10 As shown in FIG. 8 (b) and FIG. 9 (b), the degradation rates of MB and RhB under light irradiation for 25 min were 55.64% and 59.43% respectively when only catalysts were added.

[0104] As shown in FIG. 8 (c) and FIG. 9 (c), Figure 9 As shown in FIG. 8 (c) and FIG. 9 (c), Figure 10 As shown in FIG. 8 (c) and FIG. 9 (c), after using Bi@BT / BC-4 catalyst and K2S2O8, MB and RhB only needed 10 and 4 min respectively to achieve complete decolorization.

[0105] As shown in FIG. 8 (d) and FIG. 9 (d), Figure 9 As shown in FIG. 8 (d) and FIG. 9 (d), Figure 10 As shown in FIG. 8 (d) and FIG. 9 (d), in the presence of light irradiation and K2S2O8, the degradation efficiencies of MB by Bi@BT / BC-1, Bi@BT / BC-2, Bi@BT / BC-3, Bi@BT / BC-4, Bi@BT / BC-5, Bi@BT / BC-6 and Bi@BT / BC-7 were 38.97%, 37.98%, 78.69%, 99.79%, 73.08%, 49.05% and 57.17% respectively at 10 min, and the degradation efficiencies of RhB were 42.16%, 47.87%, 79.11%, 99.81%, 61.89%, 57.17% and 67.25% respectively at 4 min. Bi@BT / BC-4 catalyst showed the best degradation performance.

[0106] Ciprofloxacin (CIP) is widely used in agriculture, social production and medical applications due to its antibacterial effect. When CIP is released into water, it not only endangers the survival of freshwater organisms, but also continues to accumulate, destroys the microbial environment of humans, and increases the drug resistance of bacteria. Figure 11(c) shows that the degradation rate of CIP is up to 91.51% using Bi@BT / BC-4 photocatalyst and K2S2O8. Without adding catalyst, CIP cannot complete self-degradation, as shown in Figure 11 (a).

[0107] As shown in Figure 11 (b), the degradation rate of CIP is 67.34% under light irradiation for 40 min when only catalyst is added. Notably, Figure 11 In (b), the original peak position of CIP in the UV-Vis absorption spectrum is 272 nm, and after CIP is degraded for 10 min, the peak value is shifted. It shows that intermediate products are generated during the degradation of CIP, thereby reducing the enrichment of CIP and causing the change of peak position.

[0108] However, Figure 11 No peak shift occurs in the reaction process of (c), which shows that the sacrificial agent has a high synergistic adsorption-photocatalysis effect with Bi@BT / BC-4, which can quickly absorb and degrade CIP and avoid the generation of intermediate products.

[0109] Figure 11 (d) shows the performance of Bi@BT / BC-1, Bi@BT / BC-2, Bi@BT / BC-3, Bi@BT / BC-4, Bi@BT / BC-5, Bi@BT / BC-6 and Bi@BT / BC-7 in degrading MO for 40 min, and the efficiencies are 48.49%, 67.88%, 81.08%, 91.51%, 65.14%, 16.62% and 20.79%, respectively. The Bi@BT / BC-4 catalyst shows the best adsorption-photocatalytic degradation performance.

[0110] In summary, the full-spectrum photocatalyst (Bi@Bi2(Ti2O7) / BC) with plasmonic Bi deposited in Bi2(Ti2O7) / BC microspheres in situ is prepared by one-pot hydrothermal method in the application. Bi elemental particles are generated by reducing Bi 3+ After the generation of Bi elemental particles, they are deposited in Bi2(Ti2O7) / BC microspheres in situ. The preparation process of the application also optimizes the addition amount of biochar. After adding the sacrificial agent, the optimized composite photocatalyst can efficiently photocatalyze Cr(VI), CIP and MB, MO and RhB under visible light and near-infrared light irradiation.

[0111] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can make equivalent replacement or change according to the technical solution and inventive concept of the application within the technical range disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. A Bi@Bi2(Ti2O7) / biochar-based composite material, characterized in that, The Bi2(Ti2O7) forms a microsphere structure with a porous structure with the biochar, and Bi elements are uniformly dispersed on the surface of the microsphere structure. The preparation method of the Bi@Bi2(Ti2O7) / biochar-based composite material comprises the following steps: S1. Bismuth nitrate pentahydrate, tetrabutyl titanate and urea are added into ethylene glycol in a certain proportion, and stirred and mixed uniformly; S2. After adding the biochar source, continue to stir to form a mixed suspension; S3. The mixed suspension obtained in step S2 is subjected to hydrothermal reaction in an autoclave at a temperature of 150-170°C, and after the reaction is completed, it is washed thoroughly with ethanol and then vacuum dried to obtain a Bi@Bi2(Ti2O7) / BC precursor; S4. The Bi@Bi2(Ti2O7) / BC precursor is calcined at a temperature of 280-320°C in an inert gas atmosphere to form a Bi@Bi2(Ti2O7) / BC composite material.

2. The Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 1, characterized in that, The molar ratio of Ti to C elements is 1:3-1:4, and the molar ratio of Bi to Ti is 9:10-9:

15.

3. A method for preparing the Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 1, characterized in that, Comprises the following steps: S1. Bismuth nitrate pentahydrate, tetrabutyl titanate and urea are added into ethylene glycol in a certain proportion, and stirred and mixed uniformly; S2. After adding the biochar source, continue to stir to form a mixed suspension; S3. The mixed suspension obtained in step S2 is subjected to hydrothermal reaction in an autoclave at a temperature of 150-170°C, and after the reaction is completed, it is washed thoroughly with ethanol and then vacuum dried to obtain a Bi@Bi2(Ti2O7) / BC precursor; S4. The Bi@Bi2(Ti2O7) / BC precursor is calcined at a temperature of 280-320°C in an inert gas atmosphere to form a Bi@Bi2(Ti2O7) / BC composite material.

4. The preparation method of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 3, characterized in that, The molar ratio of bismuth nitrate pentahydrate, tetrabutyl titanate and urea in step S1 is 3:1:

1.

5. The preparation method of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 3, characterized in that, The biochar source in step S2 is selected from one of straw, rice husk, sugarcane residue and wood chips; The biochar source is first crushed before being added, and then sieved through a 100-mesh sieve.

6. The preparation method of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 5, characterized in that, The mass ratio of the added amount of the biochar source to tetrabutyl titanate in step S2 is 3:10-8:

10.

7. The preparation method of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 3, characterized in that, The method of vacuum drying in step S3 is to dry at 65°C for 12h.

8. The preparation method of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 3, characterized in that, In step S4, the calcination is gradually heated to 280-320°C for calcination; the heating rate is 10°C / min.

9. Use of the Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 1, characterized in that, The material is used to remove one or more of hexavalent chromium, ciprofloxacin, methyl orange, methylene blue and rhodamine B under the action of photocatalysis.

10. Use of Bi@Bi2(Ti2O7) / biochar-based composite material according to claim 9, characterized in that, The material is used to prepare a catalyst for removing one or more of hexavalent chromium, ciprofloxacin, methyl orange, methylene blue and rhodamine B.

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