CQDs / TiO2-x composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to a CQDs / TiO2-x composite material as well as a preparation method and application thereof. The surface of the introduced flax straw carbon quantum dots contains rich oxygen-containing functional groups, and the flax straw carbon quantum dots have the characteristics of high conductivity, large specific surface area, environmental friendliness and the like, and are relatively high in biocompatibility, excellent in electron transmission capability and good in light stability. By introducing the flax straw carbon quantum dots, on one hand, the photo-induced electron transfer efficiency can be remarkably improved, and the electron-hole pair recombination rate can be reduced; on the other hand, the specific surface area of the flax straw carbon quantum dots is high, a large number of adsorption sites are provided, the contact efficiency of pollutants and a photocatalyst is improved, the photocatalytic efficiency is further improved, and the photocatalytic performance is excellent; the flax straw carbon quantum dots are used as a carrier, so that the dispersity and stability of the material are improved.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis technology, and specifically relates to a CQDs / TiO 2-x Composite materials, preparation methods and applications thereof. Background Art

[0002] Photocatalytic technology is a green and environmentally friendly technology that uses light energy to drive redox reactions on the surface of materials. It does not require additional chemical reagents or heat energy. With its high efficiency, environmental protection and low cost, it has great development potential in many application fields.

[0003] Black titanium dioxide (TiO 2-x ), is a method of introducing oxygen vacancies and Ti on the surface of white TiO2 3+ Compared with white TiO2 photocatalytic materials, the light absorption and photocatalytic activity of the photocatalytic materials obtained by removing defects such as iodine and iodine have been improved.

[0004] However, TiO 2-x There is a problem of low electron-hole pair separation efficiency, which leads to low photocatalytic efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a CQDs / TiO 2-x Composite material and preparation method and application thereof, the CQDs / TiO 2-x The composite material has high photocatalytic efficiency.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a CQDs / TiO 2-x The composite material comprises flax straw carbon quantum dots and black titanium dioxide connected to the flax straw carbon quantum dots via Ti-OC chemical bonds.

[0008] Preferably, the mass ratio of the sesame straw carbon quantum dots to black titanium dioxide is 25-125:875-975.

[0009] Preferably, the CQDs / TiO 2-x The composite material has mesopores with a specific surface area of ​​139.95 to 171.11 m 2 / g, pore volume is 0.016090~0.016996cm 3 / g.

[0010] The present invention also provides the CQDs / TiO 2-x The preparation method of the composite material comprises the following steps:

[0011] The sesame straw is pre-carbonized to obtain a carbon precursor; the carbon precursor is mixed with H2O2 and water for hydrothermal reaction and then freeze-dried to obtain sesame straw carbon quantum dots; the sesame straw carbon quantum dots, water and TiO 2-x After mixing, heating under reflux to obtain the CQDs / TiO 2-x Composite materials.

[0012] Preferably, the pre-carbonization temperature is 200-300° C., and the holding time is 1-2 hours.

[0013] Preferably, the ratio of the mass of the carbon precursor to the volume of H2O2 is (1-2) g:(2-4) mL; and the volume ratio of H2O2 to water is 2-4:50-75.

[0014] Preferably, the temperature of the hydrothermal reaction is 160-200° C., and the insulation time is 5-7 hours.

[0015] Preferably, the vacuum degree of the freeze-drying is 0.1 to 0.5 mbar, the temperature is -60 to -80°C, and the insulation time is 12 to 24 hours.

[0016] Preferably, the heating reflux temperature is 80-120° C., and the insulation time is 4-6 hours.

[0017] The present invention also provides the CQDs / TiO 2-x Composite material or CQDs / TiO obtained by the preparation method described in the above scheme 2-x Application of composite materials in the field of photocatalysis.

[0018] The present invention provides a CQDs / TiO 2-x Composite material. The surface of sesame straw carbon quantum dots (CQDs) introduced in the present invention contains rich oxygen-containing functional groups, has the characteristics of high conductivity, large specific surface area and environmental friendliness, high biocompatibility, excellent electron transport ability and good light stability. 2-x Composited with sesame straw carbon quantum dots with adsorption function, CQDs / TiO with synergistic adsorption and photocatalytic effects was obtained. 2-x Composite materials. The present invention introduces sesame straw carbon quantum dots, which can significantly improve the TiO 2-x The photogenerated electron transfer efficiency is improved, the recombination rate of electron-hole pairs is reduced, and the band gap is reduced from 3.02 to 2.34eV; on the other hand, the sesame straw carbon quantum dots have a high specific surface area, which provides a large number of adsorption sites, which helps to improve the contact efficiency between pollutants and photocatalysts, thereby improving the photocatalytic efficiency and excellent photocatalytic performance; in addition, sesame straw carbon quantum dots as a carrier can effectively alleviate the 2-x agglomeration problem, thereby improving the CQDs / TiO2-x Dispersion and stability of composite materials.

[0019] The present invention also provides the CQDs / TiO 2-x Preparation method of composite material. The present invention uses sesame straw, a specialty of Lanzhou, as an organic carbon source, cuts the macromolecular carbon material into nanoparticles, obtains sesame straw carbon quantum dots with adsorption properties, and then heats and refluxes (TiO 2-x The surface is rich in hydroxyl groups (-OH), while CQDs usually carry oxygen-containing functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH). Under heating conditions, the two undergo dehydration condensation to form Ti-OC chemical bonds. CQDs and TiO 2-x Composite, the obtained CQDs / TiO 2-x The composite material is in an amorphous state. The preparation method provided by the present invention has simple steps, convenient operation, low cost and is suitable for industrial production.

[0020] The present invention also provides the CQDs / TiO 2-x Composite material or CQDs / TiO obtained by the preparation method described in the above scheme 2-x Application of composite materials in the field of photocatalysis. The CQDs / TiO 2-x The composite material can be used as a photocatalyst to photocatalytically degrade organic pollutants such as methylene blue (MB) with a high removal rate and a short removal cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. 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 any creative work.

[0022] Figure 1 TiO 2-x With CQDs / TiO 2-x FT-IR images of the composite materials;

[0023] Figure 2 TiO 2-x With CQDs / TiO 2-x SEM images of the composite material;

[0024] Figure 3 CQDs / TiO 2-x N2 adsorption-desorption isotherms and pore size distribution of the composite material (inset);

[0025] Figure 4 CQDs / TiO2-x XRD patterns of the composite materials;

[0026] Figure 5 CQDs / TiO 2-x XPS graph of the composite material;

[0027] Figure 6 CQDs / TiO 2-x UV-Vis DRS diagram of the composite material;

[0028] Figure 7 CQDs / TiO with different composite ratios 2-x Photocatalytic effect of composite materials on MB;

[0029] Figure 8 CQDs / TiO 2-x UV-visible absorption curve of MB by the composite material;

[0030] Figure 9 CQDs / TiO in the presence of different anions 2-x Photocatalytic degradation diagram of MB by composite materials;

[0031] Figure 10 CQDs / TiO at different pH values 2-x Photocatalytic degradation diagram of MB by composite materials;

[0032] Figure 11 CQDs / TiO 2-x Graph of cyclic testing of composite materials. DETAILED DESCRIPTION

[0033] The present invention provides a CQDs / TiO 2-x The composite material comprises flax straw carbon quantum dots and black titanium dioxide connected to the flax straw carbon quantum dots via Ti-OC chemical bonds.

[0034] In the present invention, the mass ratio of the sesame straw carbon quantum dots to black titanium dioxide can be 25-125:875-975, specifically 125:875, 115:885, 105:895, 95:905, 85:915, 75:925, 65:935, 55:945, 45:955, 35:965 or 25:975.

[0035] In the present invention, the CQDs / TiO 2-x The composite material has mesopores and the specific surface area can be 139.95~171.11m 2 / g, and the pore volume can be 0.016090~0.016996cm 3 / g.

[0036] The present invention also provides the CQDs / TiO 2-x The preparation method of the composite material comprises the following steps:

[0037] The sesame straw is pre-carbonized to obtain a carbon precursor;

[0038] The carbon precursor is mixed with H2O2 and water for hydrothermal reaction and then freeze-dried to obtain sesame straw carbon quantum dots;

[0039] The sesame straw carbon quantum dots, water and TiO 2-x After mixing, heating under reflux to obtain the CQDs / TiO 2-x Composite materials.

[0040] The present invention pre-carbonizes flax straw to obtain a carbon precursor. In the present invention, the particle size of the flax straw can be 74 to 256 μm, specifically 192 μm, 128 μm or 96 μm. The present invention adopts the above raw materials to achieve high-value utilization of biomass resources, with low raw material cost and renewable nature, in line with the concepts of green chemistry and circular economy. Due to the high lignin content of flax straw and the synergistic effect of multiple components (such as lignin-derived aromatic structures) and the optimization of surface functional groups, the yield of carbon quantum dots can be 10% to 30%, which is higher than that of ordinary carbon quantum dots (yield of 5% to 20%); compared with other straws (such as wheat and corn straw), flax straw has low ash content, sufficient carbonization, low pollution and high utilization rate; CQDs derived from flax straw biomass have low toxicity, which makes the composite material of the present invention have good biocompatibility and may be expanded to the fields of bioimaging or medicine.

[0041] In the present invention, the pre-carbonization temperature can be 200-300°C, specifically 250°C, and the holding time can be 1-2 hours, specifically 1.5 hours. The pre-carbonization can be performed in an air atmosphere and the pre-carbonization equipment can be a muffle furnace. The pre-carbonization method helps decompose cellulose, hemicellulose, and lignin in the biomass to generate a carbon precursor, making subsequent H2O2 more easily permeable and reactive.

[0042] After obtaining the carbon precursor, the present invention mixes the carbon precursor with H2O2 and water (referred to as the first mixing) for a hydrothermal reaction, followed by freeze-drying to obtain sesame straw carbon quantum dots. In the present invention, the ratio of the mass of the carbon precursor to the volume of H2O2 can be (1-2) g:(2-4) mL, specifically 1 g:3 mL.

[0043] In the present invention, the water may be distilled water; the volume ratio of H2O2 to water may be 2-4:50-75, specifically 3:55, 3:60, 3:65, or 3:70. The present invention uses sesame straw as a carbon source and H2O2 as an oxidant, eliminating the need for acid. H2O2, as a mild oxidant, avoids the introduction of harmful byproducts and reduces corrosion to equipment, resulting in a safe and pollution-free process.

[0044] In the present invention, the first mixing may be stirring mixing; the first mixing time may be 30 to 60 minutes, specifically 45 minutes.

[0045] In the present invention, the equipment for the hydrothermal reaction may include a PTFE-lined stainless steel autoclave and a forced air drying oven; the temperature of the hydrothermal reaction may be 160 to 200°C, specifically 180°C, and the holding time may be 5 to 7 hours, specifically 6 hours. The present invention utilizes the oxidative effect of H2O2 through the hydrothermal reaction to further accelerate the dehydration, condensation, and aromatization processes of the carbon precursor, decompose the natural components of the biomass (lignin, cellulose), introduce a large number of hydroxyl (-OH) and carboxyl (-COOH) groups, and enhance the water solubility and surface reactivity of the carbon quantum dots.

[0046] In the present invention, after the hydrothermal reaction, the obtained system may be cooled, solid-liquid separated and impurities removed in sequence; the final temperature of the cooling may be room temperature; the solid-liquid separation may include centrifugation and filtration in sequence; the centrifugal speed may be 800-1500 rpm, specifically 1000 rpm, and the centrifugal time may be 15-30 min, specifically 22 min; the filtration may use a 0.22 μm microporous membrane; the impurity removal may be dialysis; the specification of the dialysis bag for dialysis may be 1-10 kDa, specifically 5 kDa.

[0047] In the present invention, the vacuum degree of the freeze-drying can be 0.1 to 0.5 mbar, specifically 0.3 mbar, the temperature can be -60 to -80°C, specifically -70°C, and the holding time can be 12 to 24 hours, specifically 18 hours. The present invention prevents CQD nanoparticles from agglomerating through freeze-drying, retains surface functional groups and fluorescent properties, and improves the dispersibility and storage stability of CQDs.

[0048] After obtaining flax straw carbon quantum dots, the present invention combines the flax straw carbon quantum dots, water and TiO 2-x After mixing (recorded as the second mixing), heating under reflux to obtain the CQDs / TiO 2-x Composite material. In the present invention, the sesame straw carbon quantum dots and TiO 2-xThe mass ratio of the total mass of the cellulose acetate gel to the mass ratio of water can be 1:20-30, specifically 1:22, 1:24, 1:26 or 1:28.

[0049] In the present invention, the flax straw carbon quantum dots and TiO 2-x The mass ratio of can be 25-125:875-975, specifically can be 125:875, 115:885, 105:895, 95:905, 85:915, 75:925, 65:935, 55:945, 45:955, 35:965 or 25:975.

[0050] In the present invention, the second mixing may include stirring mixing and ultrasonic mixing in sequence; the ultrasonic mixing time may be 10 to 20 minutes, specifically 15 minutes.

[0051] In the present invention, the heating reflux temperature can be 80-120° C., specifically 100° C., and the insulation time can be 4-6 hours, specifically 5 hours.

[0052] In the present invention, after the heating and reflux, the obtained system may also be subjected to solid-liquid separation, solid washing and drying in sequence; the solid-liquid separation may be centrifugation; the solid washing may be water washing; the water used for the water washing may be distilled water; the number of water washings may be 2 to 3 times; the drying temperature may be 50 to 75°C, specifically 60°C, the vacuum degree may be -0.08 to -0.1 MPa, specifically -0.09 MPa, and the insulation time may be 12 to 24 hours, specifically 18 hours.

[0053] The present invention also provides the CQDs / TiO 2-x Composite material or CQDs / TiO obtained by the preparation method described in the above scheme 2-x Application of composite materials in the field of photocatalysis.

[0054] The CQDs / TiO provided by the present invention 2-x The composite material can be used as a photocatalyst to photocatalytically degrade organic pollutants such as methylene blue (MB) with a high removal rate and a short removal cycle.

[0055] In the specific test of the present invention, CQDs / TiO 2-x The test method for the removal rate of methylene blue dye by photocatalytic degradation of the composite material can be:

[0056] Weigh CQDs / TiO 2-x20 mg of the composite material was added to 50 mL of a 100 mg / L methylene blue solution. The reaction was allowed to proceed in the dark at room temperature for 30 min, and the initial concentration of methylene blue in the methylene blue solution was determined. A photocatalytic decolorization test was performed under visible light. The solution was collected every 20 min, centrifuged, and the supernatant was diluted 20 times. The absorbance was measured at the maximum absorption wavelength of methylene blue (664 nm) using a UV-visible spectrophotometer, and the removal rate of methylene blue was calculated. The removal rate calculation formula is as follows:

[0057]

[0058] In the formula: η is the removal rate, the unit is %; C0 is the initial concentration of methylene blue in the methylene blue solution, the unit is mg / L; C t is the concentration of methylene blue in the methylene blue solution at time t, in mg / L.

[0059] In order to further illustrate the present invention, the scheme of the present invention is described in detail below with reference to the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] (1) Preparation of sesame straw carbon quantum dots

[0062] In this example, sesame straw was used as the carbon source and H2O2 was used as the oxidant to hydrothermally prepare sesame straw carbon quantum dots. The specific steps are as follows:

[0063] Flax straw with a particle size of 149 μm (100 mesh) was heated in a muffle furnace at 250°C for 2 hours. 2.0 g of the heated flax straw was placed in a beaker, and 2 mL of H2O2 and 60 mL of distilled water were added and stirred for 30 minutes to obtain a mixed solution. The mixed solution was poured into a 100 mL PTFE-lined stainless steel autoclave, tightened, and placed in a forced air drying oven. The temperature was set to 180°C and the heating time was 6 hours. After cooling to room temperature, the solution was centrifuged at 1000 rpm for 15 minutes in a centrifuge, filtered using a 0.22 μm microporous membrane filter, and then placed in a dialysis bag (specification 5 kDa) for dialysis to remove impurity ions and obtain a pure solution. The pure solution was then placed in a culture dish and placed in a freeze dryer, reduced to 0.3 mbar, and freeze-dried at -70°C for 18 hours to obtain flax straw carbon quantum dots, recorded as CQDs.

[0064] (2) Preparation of CQDs / TiO 2-x Composite materials

[0065] Weigh 0.025 g of CQDs, add 20 mL of distilled water, stir evenly, and then add 0.975 g of TiO 2-xThe mixture was refluxed at 80 °C for 4 h, centrifuged, washed with distilled water for 3 times, and then dried in a vacuum environment at 60 °C for 18 h to obtain CQDs / TiO 2-x Composite material, denoted as 2.5% CQDs / TiO 2-x .

[0066] Example 2

[0067] The preparation method of this embodiment is the same as that of Example 1, except that the mass of CQDs is 0.050 g, and the TiO 2-x The mass of CQDs / TiO is 0.950 g. 2-x Composite material, denoted as 5.0% CQDs / TiO 2-x .

[0068] Example 3

[0069] The preparation method of this embodiment is the same as that of Example 1, except that the mass of CQDs is 0.075 g, and the TiO 2-x The mass of CQDs / TiO is 0.925 g. 2-x Composite material, denoted as 7.5% CQDs / TiO 2-x .

[0070] Example 4

[0071] The preparation method of this embodiment is the same as that of Example 1, except that the mass of CQDs is 0.100 g, and the TiO 2-x The mass of CQDs / TiO is 0.900 g. 2-x Composite material, denoted as 10% CQDs / TiO 2-x .

[0072] Example 5

[0073] The preparation method of this embodiment is the same as that of Example 1, except that the mass of CQDs is 0.125 g, and the TiO 2-x The mass of CQDs / TiO is 0.875 g. 2-x Composite material, denoted as 12.5% ​​CQDs / TiO 2-x .

[0074] Test Example 1

[0075] CQDs, TiO 2-x and CQDs / TiO prepared in Example 3 2-x The composite material was analyzed by infrared spectroscopy (FTIR). Figure 1 shown.

[0076] according to Figure 1 It can be seen that all spectra are at 3378cm -1 There is a peak at 1630 cm, attributed to OH stretching vibration -1 The OH bending vibration is nearby, so CQDs, TiO 2-x and CQDs / TiO 2-x There are a lot of hydroxyl groups on the surface of the composite materials; the introduction of CQDs increases the 2-x Surface disorder leads to the broadening of the Ti-O vibration peak, and CQDs cover the TiO 2-x The surface further weakens the Ti-O vibration signal; CQDs / TiO 2-x Composite materials at 1000cm -1 The following absorption band shifted, indicating that CQDs / TiO 2-x Ti-OC bonds were formed in the composite materials.

[0077] Test Example 2

[0078] TiO 2-x and CQDs / TiO prepared in Example 3 2-x The composite materials were tested by scanning electron microscope (SEM), and the results were as follows Figure 2 As shown, (a) is TiO 2-x SEM images of (b) CQDs / TiO 2-x SEM image of the composite material.

[0079] according to Figure 2 By comparison, it was found that TiO 2-x When CQDs are not loaded, the aggregates show an uneven morphology, while the CQDs / TiO 2-x The surface roughness of the composite material is reduced, which is due to the uniform dispersion of CQDs on the TiO 2-x surface, forming a continuous or discrete nanoscale covering layer.

[0080] Test Example 3

[0081] The CQDs / TiO prepared in Example 3 2-x The composite material was subjected to nitrogen adsorption and desorption test and BET analysis, and the results were as follows: Figure 3 As shown, the inset is CQDs / TiO 2-x Pore ​​size distribution of the composite material.

[0082] according to Figure 3 It can be seen that CQDs / TiO 2-x The isotherm curve of the composite material is a Langmuir IV isotherm with an H3 type hysteresis loop (steep desorption curve and flat adsorption curve).2-x The pores of the composite material are mainly mesopores; the measured data show that CQDs / TiO 2-x The specific surface area of ​​the composite material is 139.95m 2 / g, than TiO 2-x (171.11m 2 / g) decreased by 18%; the specific surface area of ​​CQDs / TiO 2-x The pore volume of the composite material is 0.016090 cm 3 / g, and TiO 2-x (0.016996cm 3 This is because the sesame straw carbon quantum dots themselves have a very small size and can easily enter the TiO 2-x In the pores, the effective surface area decreases instead, which verifies that the CQDs filled TiO 2-x The phenomenon of pores.

[0083] Test Example 4

[0084] The CQDs / TiO prepared in Example 3 2-x The composite material was subjected to X-ray diffraction (XRD) analysis, and the results were as follows: Figure 4 shown.

[0085] according to Figure 4 It can be seen that there is no obvious characteristic peak in the figure, which is consistent with TiO 2-x Similarly, this means that CQDs do not change the TiO 2-x Therefore, CQDs / TiO 2-x The composite material is still in an amorphous state, and the introduction of CQDs does not change the TiO 2-x crystal structure.

[0086] Test Example 5

[0087] The CQDs / TiO prepared in Example 3 2-x The composite materials were analyzed by X-ray photoelectron spectroscopy (XPS) to explore the CQDs and TiO 2-x The interaction between Figure 5 As shown, where CQDs / TiO 2-x Full spectrum of composite materials, O element energy spectrum segment, Ti element energy spectrum segment and C element energy spectrum segment.

[0088] according to Figure 5 The full spectrum shows that CQDs / TiO 2-x The elemental composition of the composite material is complex, CQDs / TiO 2-xIn addition to C, Ti and O elements, the composite material also has a variety of impurity peaks of elements such as Si and N. The impurity peaks may be related to elements such as Si and N. Figure 5 It can be seen that there are three energy spectrum peaks at the binding energy positions of 529.7eV, 531.4eV and 535.5eV, corresponding to Ti-O, Ov / CO and OH, respectively, which indicates that CQDs and TiO 2-x There is a Ti-OC chemical bond between them; according to Figure 5 It can be seen that there are two energy spectrum peak shifts at the binding energy of 463.9eV and 458.29eV, which are related to the TiO 2-x There is a slight shift compared to the previous figure, which may be related to the formation of Ti-OC chemical bonds; according to Figure 5 It can be seen that there are two energy spectrum peaks at the binding energy of 287.8eV and 284.8eV. The energy spectrum peak at 284.8eV corresponds to the CQDs / TiO 2-x The CQDs in the composite material have two chemical bonds, CC and C=C, and the energy spectrum peak at 287.8eV corresponds to C=O and CO bonds, which all indicate that CQDs / TiO 2-x CQDs exist in the composite material.

[0089] Test Example 6

[0090] TiO 2-x and CQDs / TiO prepared in Example 3 2-x The composite materials were subjected to UV-Vis diffuse reflectance (UV-VisDRS) analysis to analyze the CQDs / TiO 2-x The optical properties of the composite materials are shown in Figure 2. Figure 6 As shown, the first material is TiO 2-x The second material is CQDs / TiO 2-x Composite materials.

[0091] according to Figure 6 As can be seen from the middle left picture, after CQDs composite, CQDs / TiO 2-x The absorption spectrum of the composite material has undergone a certain red shift, increasing from 438nm to 570nm, which significantly enhances the absorption capacity of visible light. 2-x The composite material has a higher 2-x A wider range of light absorption improves the utilization rate of solar energy; hv and (αhv) 2 Draw the horizontal and vertical axes respectively, and the results are as follows Figure 6 In the middle right figure, the horizontal tangent line can be obtained as TiO 2-x and CQDs / TiO 2-xThe Eg of the composite materials are 3.02 and 2.34 eV, respectively, and the band gap width is reduced from 3.02 eV to 2.34 eV. The reduction in the band gap width reduces the energy required for electron transition, promotes the generation of photogenerated carriers, and helps to improve photocatalytic activity.

[0092] Test Example 7

[0093] Methylene blue (MB) is a cationic phenothiazine dye. Due to its unique structure and properties, it is used as a textile dye, biological stain and disinfectant. It has strong absorption in the visible light region (λ = 664nm). Its degradation process is easy to track by UV-visible spectroscopy, and the degradation products (such as colorless methylene blue) are low in toxicity. It has become a common pollutant for evaluating the performance of photocatalysts. 2-x ) is excited to generate electron-hole pairs under light, and the mineralization of MB molecules into CO2, H2O and inorganic ions through redox reactions is a green, efficient and sustainable feasible solution.

[0094] TiO 2-x and CQDs / TiO prepared in Examples 1 to 5 2-x The photocatalytic performance of the composite materials was tested to explore the effect of sesame straw carbon quantum dots content on CQDs / TiO 2-x Effect of CQDs on the photocatalytic properties of CQDs / TiO composites 2-x The mass percentage in the composite material was used as an indicator, and the photocatalytic test was carried out on 100 mg / L MB solution. The results are as follows Figure 7 shown.

[0095] according to Figure 7 It can be seen that when the CQDs content is 0%, the photocatalytic performance is the worst, only 44.88%; when the CQDs content gradually increases from 0% to 7.5%, the photocatalytic performance gradually improves; when the CQDs content is 7.5%, the photocatalytic performance is the best, at 61.11%; and when the CQDs content exceeds 7.5%, the photocatalytic performance decreases with the increase of CQDs content. This is because low-content CQDs can act as excellent electron acceptors and quickly capture TiO 2-x The photogenerated electrons in the conduction band significantly inhibit the recombination of electron-hole pairs, thereby improving the charge separation efficiency and enhancing the photocatalytic activity. However, excessive CQDs will form recombination centers at the composite interface, which will become bridges for the recombination of electron-hole pairs, resulting in a decrease in charge separation efficiency and photocatalytic activity.

[0096] Test Example 8

[0097] The CQDs / TiO prepared in Example 3 2-xThe composite material photocatalytic degradation of MB was analyzed by UV-visible absorption. The results are as follows Figure 8 shown.

[0098] according to Figure 8 According to the Lambert-Beer law, the absorbance is proportional to the concentration of MB in the solution. The curve shows that the absorbance decreases with time, so the concentration of MB decreases with time, indicating that MB is absorbed by CQDs / TiO 2-x The composite material undergoes photocatalytic oxidation and reduction to small molecules. The decrease in absorbance at 664 nm in the UV-visible absorption curve indicates that MB is converted to small molecules by CQDs / TiO 2-x Photocatalytic redox reactions produce small molecules.

[0099] Test Example 9

[0100] The CQDs / TiO prepared in Example 3 2-x The photocatalytic performance of the composite materials was tested to explore the effect of inorganic anions in simulated wastewater on the CQDs / TiO 2-x The effect of the photocatalytic performance of the composite material was tested by adding 10 mmol / L of Cl - 、NO3 - 、SO4 2- 、HCO3 - and H2PO4 - , then add CQDs / TiO 2-x The composite material photocatalytically degraded MB. Figure 9 shown.

[0101] according to Figure 9 It can be seen that the addition of Cl - 、NO3 - 、SO4 2- 、HCO3 - or H2PO4 - Afterwards, CQDs / TiO 2-x The removal efficiency of MB by the composite material decreased from 61.11% to 42.95%, 56.61%, 44.95%, 51.92% and 40.59%, respectively. - CQDs / TiO 2-x The composite material has the strongest inhibitory effect on removing MB. The results of the inhibitory effect test show that the common inorganic anions in wastewater do not significantly interfere with the photocatalytic performance of the composite material of the present invention. - 、H2PO 4- The influence of ions is slightly stronger, so they can be shielded or destroyed before photocatalysis to eliminate their interference and improve the photocatalytic performance.

[0102] Test Example 10

[0103] The CQDs / TiO prepared in Example 3 2-x The photocatalytic performance of the composite materials was tested to explore the effect of simulated wastewater pH on the CQDs / TiO 2-x The effect of the photocatalytic performance of the composite material was tested by the following method: in an MB solution with an initial mass concentration of 100 mg / L, CQDs / TiO 2-x The dosage of the composite material was 20 mg, and the initial pH value of the MB solution was adjusted to 3, 5, 7, 9 or 11, respectively. The results of photocatalytic removal of MB were as follows: Figure 10 shown.

[0104] according to Figure 10 It can be seen that when the pH value is 5, CQDs / TiO 2-x The composite material has the best removal effect on MB, which is 65.72%. This is because the removal of ·OH and ·O2 - Coexistence and synergistic degradation of MB resulted in the highest photocatalytic efficiency. When the pH value was 3, CQDs / TiO 2-x The removal efficiency of the composite material for MB was only 47.73%. This is because MB is a cationic dye and excessive H + It occupies a large number of photogenerated holes and reduces the generation of OH. When the pH value is 11, CQDs / TiO 2-x The removal efficiency of the composite material for MB was 52%, which was because the strong alkalinity reduced the O2 - The formation of CQDs may lead to poor dispersion due to deprotonation, resulting in a decrease in photocatalytic effect.

[0105] Test Example 11

[0106] The CQDs / TiO prepared in Example 3 2-x The stability of the composite material was analyzed by the following test method: the CQDs / TiO 2-x After washing with water and alcohol, the composite material was dried in a forced air drying oven at 60°C for 3 h, weighed, and added to the MB solution again. The photocatalytic reduction efficiency changed with the number of cycles. Figure 11 shown.

[0107] according to Figure 11 It can be seen that with the increase of recycling times, the MB removal rate decreased from 61.11% to 54.34%, which indicates that the CQDs / TiO 2-x The composite material has good stability against MB degradation and improves the 2-x The problem of poor cycle stability is more in line with the actual application of dye wastewater treatment.

[0108] From the above examples, it can be seen that the CQDs / TiO 2-x The composite material has a synergistic effect of adsorption and photocatalysis, high efficiency of photogenerated electron transfer, low recombination rate of electron-hole pairs, and a band gap width reduced from 3.02 to 2.34 eV. It has high photocatalytic efficiency, excellent photocatalytic performance, and good dispersibility and stability.

[0109] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A CQDs / TiO 2-x A composite material, characterized in that The invention comprises flax straw carbon quantum dots and black titanium dioxide connected to the flax straw carbon quantum dots via Ti-OC chemical bonds.

2. CQDs / TiO according to claim 1 2-x A composite material, characterized in that The mass ratio of the sesame straw carbon quantum dots to black titanium dioxide is 25-125:875-975.

3. CQDs / TiO according to claim 1 or 2 2-x A composite material, characterized in that The CQDs / TiO 2-x The composite material has mesopores with a specific surface area of ​​139.95 to 171.11 m 2 / g, pore volume is 0.016090~0.016996cm 3 / g.

4. The CQDs / TiO according to any one of claims 1 to 3 2-x The method for preparing a composite material is characterized in that: The following steps are involved: The sesame straw is pre-carbonized to obtain a carbon precursor; The carbon precursor is mixed with H2O2 and water for hydrothermal reaction and then freeze-dried to obtain sesame straw carbon quantum dots; The sesame straw carbon quantum dots, water and TiO 2-x After mixing, heating under reflux to obtain the CQDs / TiO 2-x Composite materials.

5. The preparation method according to claim 4, characterized in that The pre-carbonization temperature is 200-300° C., and the heat preservation time is 1-2 hours.

6. The preparation method according to claim 4, characterized in that The ratio of the mass of the carbon precursor to the volume of H2O2 is (1-2) g: (2-4) mL; The volume ratio of H2O2 to water is 2-4:50-75.

7. The preparation method according to claim 4 or 6, characterized in that: The temperature of the hydrothermal reaction is 160-200° C., and the insulation time is 5-7 hours.

8. The preparation method according to claim 4, characterized in that The vacuum degree of the freeze drying is 0.1 to 0.5 mbar, the temperature is -60 to -80°C, and the insulation time is 12 to 24 hours.

9. The preparation method according to claim 4, characterized in that The heating reflux temperature is 80-120° C., and the heat preservation time is 4-6 hours.

10. The CQDs / TiO according to any one of claims 1 to 3 2-x Composite material or CQDs / TiO obtained by the preparation method according to any one of claims 4 to 9 2-x Application of composite materials in the field of photocatalysis.

Images