A-GQDs / RGO / TiO2 ternary composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses an A-GQDs / RGO / TiO2 ternary composite photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The ternary composite photocatalyst is composed of an A-GQDs / RGO composite substrate and titanium dioxide (TiO2) nano particles loaded on the surface of the A-GQDs / RGO composite substrate, the A-GQDs / RGO composite substrate is reduced graphene oxide (RGO) modified by aminated graphene quantum dots (A-GQDs), and the aminated graphene quantum dots are bonded with the reduced graphene oxide (RGO) through chemical bonds; through an interface mechanism and a synergistic effect among the titanium dioxide, the aminated graphene quantum dots and the reduced graphene oxide, the ternary composite catalyst not only realizes high dispersion of active sites of the titanium dioxide, but also effectively promotes generation and separation of photo-induced electron-hole pairs, and widens the absorption range and absorption efficiency of light; and the composite material has excellent conductivity and photocatalytic activity, and has a wide application prospect in the field of photocatalytic degradation of dye pollutants.

Description

Technical Field

[0001] The present invention specifically relates to an A-GQDs / RGO / TiO2 ternary composite photocatalyst and a preparation method and application thereof, belonging to the technical field of catalysts. Background Art

[0002] Currently, water safety issues caused by organic dye pollutants have attracted widespread attention, and the degradation or conversion of organic dye pollutants through photocatalysis has become a major topic. Titanium dioxide is a widely used photocatalytic semiconductor and has broad application prospects in water pollution prevention and control. However, traditional titanium dioxide has a wide energy band gap, and the photogenerated electrons and holes it produces are prone to recombination. The catalytic reaction can only occur under ultraviolet light. Under conditions where visible light cannot be fully utilized, its absorption is only a very small portion of the visible light range, which greatly hinders the application of titanium dioxide.

[0003] Graphene is an important two-dimensional carbon nanomaterial. Thanks to its excellent electrical conductivity and sufficiently large specific surface area, it is expected to act as a photogenerated electron acceptor, promote the effective separation of photogenerated electron-hole pairs in titanium dioxide, and hinder the recombination of photogenerated electrons and holes, showing good application prospects in the field of photocatalytic pollutant degradation.

[0004] Graphene quantum dots (GQDs) are an emerging zero-dimensional carbon nanomaterial consisting of single-layer or few-layer graphene sheets with a size of several nanometers to more than ten nanometers. They are nanoscale derivatives of graphene and have the sp 2 Hybrid carbon atomic structure. Compared with traditional graphene, graphene quantum dots not only have a higher specific surface area, more active edge sites, and tunable optical properties, but also exhibit significant quantum confinement and edge effects, which make them valuable for applications in many fields such as fluorescence imaging, electrochemical sensing, drug delivery, dye batteries, and photocatalysis.

[0005] In summary, combining the respective characteristics of graphene quantum dots, graphene and titanium dioxide materials, the development of a graphene quantum dot / graphene / titanium dioxide ternary composite material is of great significance for promoting the development of photocatalytic degradation of organic pollutants. Summary of the Invention

[0006] The purpose of the present invention is to provide an A-GQDs / RGO / TiO2 ternary composite photocatalyst and its preparation method and application; the ternary composite photocatalyst is composed of titanium dioxide (TiO2), amino-modified graphene quantum dots (A-GQDs) and reduced graphene oxide (RGO). Through the interface mechanism and synergistic effect among the three, the ternary composite catalyst not only achieves high dispersion of titanium dioxide active sites, but also effectively promotes the generation and separation of photogenerated electron-hole pairs, and broadens the absorption range and absorption efficiency of light. It has excellent conductivity and photocatalytic activity, and has broad application prospects in the field of photocatalytic degradation of dye pollutants.

[0007] The technical solutions of the present invention are as follows: The present invention provides an A-GQDs / RGO / TiO2 ternary composite photocatalyst, which is composed of an A-GQDs / RGO composite substrate and titanium dioxide nanoparticles loaded on the surface of the A-GQDs / RGO composite substrate; the A-GQDs / RGO composite substrate is reduced graphene oxide modified with amino graphene quantum dots, wherein the amino graphene quantum dots are bonded to the reduced graphene oxide through chemical bonds.

[0008] The present invention also provides a method for preparing the above-mentioned A-GQDs / RGO / TiO2 ternary composite photocatalyst, comprising the following steps: S1. Deionized water, KOH solution, and amino-modified graphene quantum dots were added to a graphene oxide (GO) aqueous solution and fully dispersed. The resulting dispersion was hydrothermally reacted at 120-200 °C for 2-8 h to obtain a dispersion of A-GQDs / RGO composite substrate. S2. Add titanium dioxide nanoparticles to the dispersion of the A-GQDs / RGO composite substrate and fully disperse it, filter the obtained dispersion to obtain a solid product, and then dry and grind it to obtain the A-GQDs / RGO / TiO2 ternary composite photocatalyst.

[0009] The present invention first reduces graphene oxide to reduced graphene oxide by a hydrothermal reduction method, and composites it with amino graphene quantum dots to obtain an A-GQDs / RGO composite substrate composed of reduced graphene oxide modified with amino graphene quantum dots. The A-GQDs / RGO composite substrate is then dispersed in water, and titanium dioxide nanoparticles are uniformly loaded on the surface of the A-GQDs / RGO composite substrate by means of physical adsorption and physical blending, thereby constructing an A-GQDs / RGO / TiO2 ternary composite material.

[0010] Furthermore, the concentration of the graphene oxide aqueous solution in step S1 is 2 mg·mL -1 The concentration of KOH solution is 0.5 mol·L -1The KOH solution is added in a ratio of 1:3 by volume to the aqueous solution of graphene oxide.

[0011] Further, in step S1, the aminated graphene quantum dots are added in a ratio of (0.7-2.8):12 by mass of the aminated graphene quantum dots to the graphene oxide in the aqueous solution of graphene oxide.

[0012] Further, in step S2, the titanium dioxide nanoparticles have a particle size of 10-80 nm.

[0013] Further, in step S2, the titanium dioxide nanoparticles are added in a ratio of 1:(10-40) by mass of the graphene oxide in the aqueous solution of graphene oxide to the titanium dioxide nanoparticles.

[0014] The A-GQDs / RGO / TiO2 ternary composite photocatalyst provided by the application can be applied to photocatalytic degradation of dye pollutants.

[0015] Further, the dye pollutants can be Rhodamine B (RhB), methylene blue, methylene orange, and reactive black 5.

[0016] Compared with the prior art, the application has the following beneficial effects: 1. The application provides an A-GQDs / RGO / TiO2 ternary composite photocatalyst, which is composed of titanium dioxide, aminated graphene quantum dots, and reduced graphene oxide.

[0017] 2. The present invention first performs surface chemical modification on reduced graphene oxide with amino graphene quantum dots to construct an A-GQDs / RGO composite substrate, and then loads titanium dioxide on its surface by physical blending; the modification of amino graphene quantum dots can significantly increase the number of functional groups on the surface of reduced graphene oxide, further enhance its dispersibility and conductivity, thereby increasing the active centers of titanium dioxide, accelerating electron migration, reducing the recombination of photogenerated electron-hole pairs in the loaded titanium dioxide active centers, and extending the carrier lifetime. At the same time, the conductive amino graphene quantum dots and graphene sheets in the A-GQDs / RGO composite substrate also form a stable planar structure through chemical bonding, and the CN bond serves as an electron transfer bridge between the two, synergistically compounding. The active sites of pyridine N / amino N and the adsorption capacity of oxygen-rich groups in the material can further optimize the photogenerated carrier separation efficiency and the interfacial oxidation reaction kinetics of pollutants. Compared with nano-titanium dioxide particles or binary complexes composed of them with graphene quantum dots, reduced graphene oxide, etc., the ternary composite catalyst, by virtue of the above-mentioned interface mechanism and synergistic effect between components, improves the absorption range and absorption efficiency of the composite material, and significantly improves the electron transfer efficiency between the composite catalyst and the pollutant molecules. It has good conductivity and photocatalytic activity, and can generate more photogenerated electron-hole pairs under sunlight excitation, thereby showing good application prospects in the field of photocatalytic degradation of organic dye pollutants such as RhB, methylene blue, methylene orange, and reactive black 5.

[0018] 3. The preparation method provided by the present invention fully combines the respective properties and characteristics of reduced graphene oxide and amino graphene quantum dots. First, reduced graphene oxide and amino graphene quantum dots are compounded into an A-GQDs / RGO composite substrate by a hydrothermal method, and then dispersed in water to further blend with titanium dioxide nanoparticles in water. In this process, the amino graphene quantum dots are both the active component of the catalyst and, due to their own good hydrophilicity, become a dispersant for hydrophobic reduced graphene oxide in water, thereby significantly improving the water dispersibility of the prepared A-GQDs / RGO composite substrate, and achieving uniform loading of titanium dioxide nanoparticles in the dispersion on the surface of the A-GQDs / RGO composite substrate. No additional dispersant is required in the preparation process, ensuring the purity and efficiency of the preparation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Optical photographs of A-GQDs / RGO hydrogel immersed in different solutions.

[0020] Figure 2 Comparison chart of FT-IR characterization of A-GQDs, RGO, and A-GQDs / RGO.

[0021] Figure 3XPS spectra of RGO and A-GQDs / RGO.

[0022] Figure 4 (a) and (b) are TEM images of RGO / TiO2 of Comparative Example 2; (c) is a TEM image of the sample of Example 1; and (d) is a high-resolution TEM image of the sample of Example 1.

[0023] Figure 5 The UV-Vis DRS spectra of the samples of Example 1 and Comparative Examples 1 and 2 are shown.

[0024] Figure 6 Raman comparison chart of RGO, RGO / TiO2 and A-GQDs / RGO / TiO2.

[0025] Figure 7 (a) Photocatalytic degradation of RhB by TiO2, RGO / TiO2 and A-GQDs / RGO / TiO2 composite materials; (b) First-order kinetic simulation diagram of RhB degradation.

[0026] Figure 8 (a) Photocatalytic degradation of RhB by A-GQDs / RGO / TiO2 composite materials at different hydrothermal times; (b) First-order kinetic simulation diagram of RhB degradation.

[0027] Figure 9 (a) Photocatalytic degradation of RhB by A-GQDs / RGO / TiO2 composite materials at different A-GQDs contents; (b) First-order kinetic simulation diagram of RhB degradation.

[0028] Figure 10 (a) Photocatalytic degradation of RhB by A-GQDs / RGO / TiO2 composites at different GO / TiO2 mass ratios; (b) First-order kinetic simulation diagram of RhB degradation. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments. The given embodiments are only for illustrating the present invention, rather than for limiting the scope of the present invention.

[0030] Unless otherwise specified, the materials, reagents, etc. used in the following examples can be obtained from commercial sources; the methods in the following examples are conventional methods unless otherwise specified.

[0031] Example 1 Example 1 provides an A-GQDs / RGO / TiO2 ternary composite photocatalyst, and the preparation method of the ternary composite photocatalyst comprises the following steps: S1. First, add 6 mL of 2 mg mL -1A 0.5 M graphene oxide (GO) aqueous solution was placed in a small beaker, followed by the addition of 24 mL of deionized water, 2 mL of 0.5 M KOH solution, and 1.4 mg of amino-modified graphene quantum dots (A-GQDs). The mixture was then ultrasonically dispersed for 60 minutes. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined hydrothermal reactor and placed in an electrically heated constant-temperature forced-air drying oven at 180 °C for 4 hours to produce a black A-GQDs / RGO mixed dispersion.

[0032] S2. 240 mg of TiO2 nanoparticles with a particle size between 10 and 80 nm were then added to the A-GQDs / RGO mixed dispersion. The mixture was ultrasonically dispersed for 30 minutes. The resulting dispersion was then filtered using a 0.22 μm polyvinylidene fluoride filter membrane. The resulting solid sample was dried in an oven at 80°C. Finally, the dried sample was ground to obtain the A-GQDs / RGO / TiO2 ternary composite photocatalyst, which was then sealed and stored in a small centrifuge tube.

[0033] The A-GQDs / RGO / TiO2 ternary composite photocatalyst prepared by the above preparation method is composed of an A-GQDs / RGO composite substrate and titanium dioxide nanoparticles loaded on the surface of the A-GQDs / RGO composite substrate; wherein the A-GQDs / RGO composite substrate is reduced graphene oxide modified with amino graphene quantum dots, and the amino graphene quantum dots are bonded to the reduced graphene oxide through chemical bonds.

[0034] The A-GQDs / RGO / TiO2 ternary composite photocatalysts provided in Examples 2 to 9 are also composed of an A-GQDs / RGO composite substrate and titanium dioxide nanoparticles loaded on the surface of the A-GQDs / RGO composite substrate. The preparation method differs from that in Example 1 in that: the amount of amination-modified graphene quantum dots added in step S1 is different, the hydrothermal reaction temperature or duration of the mixed liquid in the electric constant temperature blower drying oven is different, or the amount of TiO2 nanoparticles added in step S2 is different. The amount of amination-modified graphene quantum dots added, the hydrothermal reaction temperature and duration of the mixed liquid, and the amount of TiO2 nanoparticles added in the above embodiments are shown in Table 1.

[0035] Table 1 Dosages of GO, A-GQDs and TiO2 and hydrothermal reaction time of Examples 1 to 7

[0036] Comparative Example 1 This comparative example provides a photocatalyst, which is TiO2 nanoparticles with a particle size between 10 and 80 nm, and has the same properties as the TiO2 nanoparticles used in the A-GQDs / RGO / TiO2 ternary composite photocatalyst preparation method described in Example 1.

[0037] Comparative Example 2 This comparative example provides an RGO / TiO2 composite photocatalyst. The difference from Example 1 is that the composite photocatalyst does not contain amination-modified graphene quantum dots. The binary composite photocatalyst is prepared according to the following steps: S1, add 6 mL of 2 mg mL -1 A 0.5 M graphene oxide (GO) aqueous solution was placed in a small beaker, followed by the addition of 24 mL of deionized water and 2 mL of a 0.5 M KOH solution. The mixture was then ultrasonically dispersed for 60 minutes. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted in an electrically heated constant-temperature forced-air drying oven at 180 °C for 4 hours to obtain a black RGO dispersion.

[0038] S2. Add 240 mg of TiO2 nanoparticles to the RGO dispersion and ultrasonically disperse for 30 minutes. Filter the resulting dispersion through a 0.22 μm polyvinylidene fluoride filter membrane, and dry the resulting solid sample in an oven at 80°C. Finally, grind the dried sample to obtain the RGO / TiO2 composite photocatalyst, which is then sealed and stored in a small centrifuge tube.

[0039] Performance Testing To reveal the interfacial mechanism and synergistic effect between the components of the A-GQDs / RGO / TiO2 ternary composite photocatalyst of the present invention, the present invention characterized the interaction between A-GQDs and RGO in the A-GQDs / RGO composite matrix and the overall structural characteristics of the resulting composite material. The composite material was then applied to the photocatalytic degradation of organic dye pollutants to evaluate the photocatalytic performance of the composite material. The experimental results are as follows: (1) Study on the interaction between A-GQDs and RGO in A-GQDs / RGO composite substrate Referring to the preparation conditions of the A-GQDs / RGO composite substrate in Example 1, an A-GQDs / RGO composite hydrogel was prepared, and the specific steps were as follows: 14 mL of 2 mg mL -1A 0.5 M graphene oxide (GO) aqueous solution was placed in a small beaker, followed by the addition of 1 mL of 0.5 M KOH solution and 5.6 mg of A-GQDs, followed by ultrasonic dispersion for 60 minutes. Finally, the mixed solution was transferred to a 25 mL polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 180 °C in an electrically heated constant-temperature forced-air drying oven for 4 hours to obtain the A-GQDs / RGO hydrogel. The prepared A-GQDs / RGO composite hydrogel was then purified by soaking it in a blue-capped bottle containing 250 mL of deionized water for 4 days, changing the water daily. The purified A-GQDs / RGO composite hydrogel could be further soaked in distilled water for storage to maintain its original pore structure.

[0040] For structural characterization, the A-GQDs / RGO hydrogel was freeze-dried in liquid nitrogen for 24 h to obtain a porous solid sample.

[0041] The assembly mechanism of A-GQDs / RGO hydrogel was explored through chemical stability experiments. The purified A-GQDs / RGO hydrogel was immersed in 0.5 M KOH, HCl and CO(NH2)2 solutions, respectively, and the dissolution behavior of A-GQDs was dynamically monitored. Figure 1 The results show that after immersing A-GQDs / RGO hydrogel in 0.5 M KOH for 1 day, only a slight discoloration of the solution occurs, indicating that the amount of A-GQDs released is extremely low and can be ignored. Figure 1 As can be seen in (b) and (c), the A-GQDs / RGO hydrogel remains colorless after being immersed in 0.5 M HCl or CO(NH2)2 for the same length of time, indicating that no A-GQDs are released. Comparative analysis shows that strong acid / base environments fail to destroy the composite structure, demonstrating that there are no pH-dependent non-covalent interactions (such as π-π stacking or hydrogen bonding) between A-GQDs and RGO.

[0042] FT-IR of A-GQDs / RGO composite hydrogel Figure 2 As shown in Figure 2, compared with pure A-GQDs and RGO, the C=C absorption peak in the A-GQDs / RGO composite shifts to a lower wavenumber of 1574 cm -1 At 1211 cm -1 A new absorption peak attributed to CN stretching vibration appears at , which directly confirms that A-GQDs and RGO form a stable interface through chemical bonding. This bonding structure not only integrates the conductive skeleton of RGO with the quantum confinement effect of A-GQDs, but its interfacial chemical bonds can also serve as electron transport channels for carrier transmission, which is of great significance for the carrier separation efficiency during photocatalytic degradation in the A-GQDs / RGO / TiO2 ternary composite catalytic system.

[0043] X-ray photoelectron spectroscopy (XPS) of A-GQDs / RGO is shown in Figure 2. Figure 3 As shown, the full spectrum of RGO and A-GQDs / RGO ( Figure 3 (a) Two obvious peaks are shown at both positions of 284.80 eV and 532.42 eV, which are typical C 1s and O 1s peaks, respectively. With the loading of A-GQDs, the relative intensity of the C 1s peak of A-GQDs / RGO weakens, while the relative intensity of the O 1s peak increases. In addition, A-GQDs / RGO also shows a N 1s peak at 400.13 eV, confirming that A-GQDs are successfully loaded on the RGO surface. As shown in Table 2, the calculated C / O atomic number ratios in RGO and A-GQDs / RGO are 6.21 and 5.13, respectively, further verifying that the introduction of A-GQDs increases the oxygen content.

[0044] Table 2 Element percentages of RGO and A-GQDs / RGO composites

[0045] The C 1s spectrum of A-GQDs / RGO is as follows Figure 3 (b) corresponds to CC / C=C bond (284.80 eV), CN bond (285.77 eV), CO bond (286.48 eV) and C=O bond (288.07 eV), respectively. The appearance of CN bond directly proves that A-GQDs and RGO are chemically bonded. The high-resolution N1s fine spectrum of A-GQDs / RGO is shown in Figure 2. Figure 3 As shown in (c), the three peaks are pyridinic N (398.58 eV), amino N (400.09 eV) and graphitic N (401.28 eV), indicating that nitrogen species participate in the construction of the interface in multiple forms. A-GQDs / RGO O 1S fine spectrum ( Figure 3 (d) shows that two peaks appeared in A-GQDs / RGO, namely C=O bond (531.02 eV) and CO bond (532.86 eV).

[0046] In summary, A-GQDs and RGO are bonded through C-N bonds to form a three-dimensional A-GQDs / RGO structure. In this structure, the C-N bond can serve as an electron transfer bridge and cooperate with the active sites of pyridine N / amino N and the adsorption capacity of oxygen-rich groups, becoming an important structural basis for optimizing the photogenerated carrier separation efficiency and the interfacial oxidation reaction kinetics of pollutants.

[0047] (2) Structural characterization of A-GQDs / RGO / TiO2 ternary composite photocatalyst Figure 4 HRTEM images of the catalysts of Example 1 and Comparative Example 2, respectively. Figure 4 (a) and (b) show that in the TEM images of RGO / TiO2 of Comparative Example 2, a large number of elliptical TiO2 nanoparticles are densely anchored on the surface of graphene sheets through interfacial bonding, confirming that the RGO and TiO2 components can be effectively compounded by simple mixing. Further analysis Figure 4 The TEM images of Example 1 in (c) found that although the typical graphene sheet layer folding structure was not observed, the presence of RGO in the substrate could still be confirmed based on the comparative analysis of the RGO / TiO2 system. In addition, A-GQDs were also not observed, which can be due to their ultra-low loading amount and atomic-level dispersion characteristics on the surface of RGO. Figure 4 (d) is the HRTEM image of Example 1, showing that there is a characteristic lattice spacing of 0.21 nm in the composite, which is highly matched with the (100) crystal plane of graphite carbon. Combined with the characteristics of the hydrothermal synthesis process, this structural evidence fully indicates that A-GQDs have been successfully loaded in the composite through in-situ growth.

[0048] Figure 5 UV-Vis DRS of A-GQDs / RGO / TiO2, TiO2 and RGO / TiO2 of Example 1 and Comparative Examples 1-2. The experiments showed that pure TiO2 nanoparticles only have absorption characteristics in the ultraviolet region, while after doping with RGO, the absorption range is significantly expanded to the solar region. When the A-GQDs / RGO composite doping system is further introduced, the absorption intensity is further enhanced. It is worth noting that the spectral red shift phenomenon caused by doping can be attributed to the synergistic effect of the π-π transition of RGO and the n-π transition of A-GQDs; this result shows that the introduction of RGO and A-GQDs can effectively improve the light absorption range and light absorption efficiency of the composite material, which can make the A-GQDs / RGO / TiO2 composite catalyst produce more photoelectron-hole pairs under solar excitation, which is of great significance to the improvement of the photocatalytic efficiency of the catalyst.

[0049] Figure 6 Raman spectra of A-GQDs / RGO / TiO2 and RGO / TiO2 of Example 1 and Comparative Example 2, the results show that the Raman spectrum of the A-GQDs / RGO / TiO2 composite material presents both the D peak and G peak of graphite carbon, and the characteristic vibration peaks of anatase TiO2, which are E g , B g , A 1g +B 1g and E gThe coexistence of these multi-component peaks directly confirms the successful composite of A-GQDs / RGO and TiO2 nanoparticles. Compared to the pure RGO system, the D / G peak intensity ratio of the composite material is significantly reduced, indicating that the A-GQDs repair the structural defects of the RGO sheets through chemical bonding, effectively improving the order of the carbon-based network.

[0050] (3) Application of A-GQDs / RGO / TiO2 ternary composite photocatalyst in photocatalytic degradation of organic dye pollutants In order to illustrate the photocatalytic degradation effect of the A-GQDs / RGO / TiO2 ternary composite photocatalyst on organic dye pollutants, the present invention takes the organic dye pollutant RhB as an example, selects samples with different preparation conditions in Examples 1 to 7, and selects the samples with the catalyst dosage of 25 mg and the RhB concentration of 28.7 mg·L -1 , the solution volume was 100 mL, and the catalytic degradation of RhB dye was carried out by simulating sunlight with a xenon lamp.

[0051] like Figure 7 As shown in (a), compared with TiO2 and RGO / TiO2 in Comparative Examples 1-2, the A-GQDs / RGO / TiO2 in Example 1 exhibited significantly improved photocatalytic activity, achieving complete degradation of RhB within only 80 min. In order to compare the photocatalytic activities of different photocatalysts, the relationship curve obtained by fitting the first-order kinetic equation (Formula 1) is shown in FIG. Figure 7 (b) The rate constants k are shown in Table 3. The reaction rate constants k of TiO2, RGO / TiO2 and A-GQDs / RGO / TiO2 composite materials are 0.01558 min -1 , 0.02619 min -1 、0.04873 min -1 The kinetic constant of A-GQDs / RGO / TiO2 is increased to 3.13 times that of pure TiO2, which fully verifies the significant promoting effect of heterogeneous structure on the photocatalytic process.

[0052] Formula (1) Table 3 Reaction kinetics of RhB degradation by TiO2, RGO / TiO2, and A-GQDs / RGO / TiO2 composites sample Pseudo-first-order reaction kinetic equation [CAT] k (min -1 )]]> <![CDATA[R 2 ]]> <![CDATA[TiO2]]> y = 0.01558x+0.01481 0.01558 0.99647 [RGO / TiO2] y = 0.02619x-0.03346 0.02619 0.99061 <![CDATA[A-GQDs / RGO / TiO2]]> y = 0.04873x+0.18125 0.04873 0.98126 Figure 8The catalytic RhB degradation performance of the A-GQDs / RGO / TiO2 catalysts prepared with different hydrothermal times in Examples 1 and 6-7 are named A-GQDs / RGO / TiO2-2h, A-GQDs / RGO / TiO2-4h, and A-GQDs / RGO / TiO2-8h according to the hydrothermal time. The results show that the A-GQDs / RGO / TiO2 catalysts prepared with different hydrothermal times all exhibit excellent catalytic RhB degradation performance. The rate relationship curves obtained by fitting the first-order kinetic equation and the calculated rate constant k value are shown in FIG. Figure 8 (b) and Table 4 show that the performance of A-GQDs / RGO / TiO2-4h is relatively the best, which may be related to the dual regulatory effect of hydrothermal time on the material structure. Moderate hydrothermal time can enhance the interfacial bonding strength between A-GQDs / RGO and TiO2 and optimize the carrier transport path, but excessive extension will lead to excessive reduction of RGO, induce densification of the carbon-based skeleton, hinder the uniform dispersion of TiO2 nanoparticles, and weaken the photocatalytic activity.

[0053] Table 4 Reaction kinetics of RhB degradation by A-GQDs / RGO / TiO2 composites at different hydrothermal times sample Pseudo-first-order reaction kinetic equation <![CDATA[k (min -1 )]]> <![CDATA[R 2 ]]> <![CDATA[A-GQDs / RGO / TiO2-2h]]> y = 0.04522x-0.0333 0.04522 0.98126 <![CDATA[A-GQDs / RGO / TiO2-4h]]> y = 0.04873x+0.18125 0.04873 0.9802 <![CDATA[A-GQDs / RGO / TiO2-8h]]> y = 0.04329x+0.0678 0.04329 0.97442 Figure 9 The catalytic RhB degradation performance of the A-GQDs / RGO / TiO2 catalysts with different A-GQDs loading amounts in Examples 1 to 3 is shown. According to the mass ratios of A-GQDs to RGO in the A-GQDs / RGO / TiO2 catalysts of 0.7:12, 1.4:12 and 2.8:12, they are named A-GQDs / RGO / TiO2, respectively. 0.5 / RGO / TiO2, A-GQDs1 / RGO / TiO2, A-GQDs2 / RGO / TiO2, such as Figure 9 As shown in (a), the A-GQDs / RGO / TiO2 catalysts with different A-GQDs loadings all showed a photocatalytic RhB degradation performance close to 100%. The rate relationship curves fitted by the first-order kinetic equation and the calculated rate constant k values ​​are shown in Figure 2. Figure 9 (b) and Table 5, A-GQDs 0.5 The rate constants k of A-GQDs1 / RGO / TiO2, A-GQDs2 / RGO / TiO2 were 0.04623 min -1 、0.04873 min -1 , 0.04362 min -1The overall difference is very small, among which A-GQDs1 / RGO / TiO2 has a relatively better performance, which may be related to the dual action mechanism of A-GQDs. When added in appropriate amounts, its amino-functionalized surface effectively repairs the structural defects of RGO through chemical bonding. At the same time, the intercalation effect of A-GQDs forms a hierarchical porous structure, which increases the exposure of active sites. Excessive loading will cause A-GQDs to agglomerate, block the mesoporous channels and hinder the interfacial contact between TiO2 and pollutants.

[0054] Table 5 Reaction kinetics of RhB degradation by A-GQDs / RGO / TiO2 composites at different A-GQDs contents sample Pseudo-first-order reaction kinetic equation <![CDATA[k (min -1 )]]> <![CDATA[R 2 ]]> A-GQDs 0.5 / RGO / TiO2 y = 0.04623x+0.07393 0.04623 0.98299 <![CDATA[A-GQDs1 / RGO / TiO2]]> y = 0.04873x+0.18125 0.04873 0.98126 <![CDATA[A-GQDs2 / RGO / TiO2]]> y = 0.04362x+0.05854 0.04362 0.98842 Figure 10 The catalytic RhB degradation performance of A-GQDs / RGO / TiO2 catalysts prepared with different GO to TiO2 mass ratios in Examples 1 and 4-5 is shown. According to the mass ratio of TiO2 to GO, the prepared catalysts are named RGO / A-GQDs / TiO2(10), RGO / A-GQDs / TiO2(20) and RGO / A-GQDs / TiO2(40) in descending order. The reaction rate constants k of the catalysts are shown in Table 6. The results show that different RGO / A-GQDs / TiO2 have good catalytic performance, among which RGO / A-GQDs / TiO2(20) with a GO / TiO2 mass ratio of 1:20 shows the best performance. As the mass ratio is optimized from 1:10 to 1:20, the RhB degradation efficiency is significantly increased from 97.5% to 100% within 80 min. However, when the GO ratio is further reduced to 1:40, the degradation efficiency drops sharply to 91.7%. This threshold effect stems from the dual effects of TiO2 loading. That is, when the mass ratio is 1:20, the RGO / A-GQDs substrate achieves monodisperse anchoring of TiO2 nanoparticles through physical mixing, constructing an efficient electron transmission channel, while excessive TiO2 will cause particle agglomeration due to exceeding the substrate's carrying capacity, resulting in a decrease in active site density and intensified carrier recombination.

[0055] Table 6 Reaction kinetics of RhB degradation by A-GQDs / RGO / TiO2 composites at different GO / TiO2 mass ratios sample Pseudo-first-order reaction kinetic equation [CD AT] k (min -1 )]]> <![CDATA[R 2 ]]> [A-GQDs / RGO / TiO2(10)] y = 0.04211x + 0.19587 0.04211 0.97794 <![CDATA[A-GQDs / RGO / TiO2(20)]]> y =0.04873x+0.18125 0.04873 0.98126 [A-GQDs / RGO / TiO2(40)] y = 0.03152x+0.05969 0.03152 0.99314 To sum up, the application forms a two-dimensional structure A-GQDs / RGO by bonding A-GQDs and RGO through C-N bond as a composite substrate, and uniformly loads TiO2 active centers on the surface thereof through physical adsorption, physical blending and other means, thereby constructing an A-GQDs / RGO / TiO2 composite catalytic system; the above characterization and RhB degradation experiment show that the introduction of A-GQDs / RGO effectively inhibits the agglomeration of TiO2 nanoparticles, and the loading of A-GQDs significantly increases the functional group content of the composite material and improves the electrical conductivity of the material; this interface mechanism and the synergistic effect between components significantly inhibit the recombination of the photo-generated electron-hole pairs of the TiO2 active center, endow the composite material with good photocatalytic activity, and enhance the electron transfer efficiency between the composite material and RhB molecules.

[0056] In addition, the above experiment also shows that by changing the hydrothermal time in the preparation process, the loading amount of A-GQDs and the mass ratio of GO / TiO2, the reduction degree of RGO and the loading amount of A-GQDs and TiO2 in the A-GQDs / RGO / TiO2 composite catalytic system can be controlled, so that the accurate control of the distribution of TiO2 and A-GQDs active sites can be realized, which lays an important structural foundation for the good photocatalytic degradation activity of the catalyst for organic dye pollutants; in addition to the RhB dye pollutant degradation given in the examples, the adjustability of the catalyst structure also endows the A-GQDs / RGO / TiO2 composite catalyst with good catalytic degradation performance for methylene blue, methylene orange, reactive black 5 and other organic dye pollutants.

[0057] The above examples of the application are only examples for clearly illustrating the application, and are not intended to limit the embodiments of the application; for ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and it is impossible to enumerate all the embodiments here, and what is obvious is included in the technical solution of the application.

Claims

1. An A-GQDs / RGO / TiO2 ternary composite photocatalyst, characterized in that: The ternary composite photocatalyst consists of an A-GQDs / RGO composite substrate and titanium dioxide nanoparticles loaded on the surface of the A-GQDs / RGO composite substrate; the A-GQDs / RGO composite substrate is reduced graphene oxide modified with amino graphene quantum dots, wherein the amino graphene quantum dots are bonded to the reduced graphene oxide through chemical bonds.

2. A method for preparing the A-GQDs / RGO / TiO2 ternary composite photocatalyst as claimed in claim 1, characterized in that: The steps include: S1. Deionized water, KOH solution, and amino-modified graphene quantum dots were added to the graphene oxide aqueous solution and fully dispersed. The resulting dispersion was hydrothermally reacted at 120-200 °C for 2-8 h to obtain a dispersion of A-GQDs / RGO composite substrate. S2. Add titanium dioxide nanoparticles to the dispersion of the A-GQDs / RGO composite substrate and fully disperse it, filter the obtained dispersion to obtain a solid product, and then dry and grind it to obtain the A-GQDs / RGO / TiO2 ternary composite photocatalyst.

3. The method for preparing the A-GQDs / RGO / TiO2 ternary composite photocatalyst according to claim 2, characterized in that: The concentration of the graphene oxide aqueous solution in step S1 is 2 mg mL -1 The concentration of KOH solution is 0.5 mol·L -1 The KOH solution is added in a ratio of 1:3 by volume to the graphene oxide aqueous solution.

4. The method for preparing the A-GQDs / RGO / TiO2 ternary composite photocatalyst according to claim 2, characterized in that: In step S1, the amination-treated graphene quantum dots are added at a mass ratio of (0.7-2.8) to the mass ratio of graphene oxide in the graphene oxide aqueous solution:

12.

5. The method for preparing the A-GQDs / RGO / TiO2 ternary composite photocatalyst according to claim 2, characterized in that: The particle size of the titanium dioxide nanoparticles in step S2 is between 10 and 80 nm.

6. The method for preparing the A-GQDs / RGO / TiO2 ternary composite photocatalyst according to claim 2, characterized in that: In step S2, titanium dioxide nanoparticles are added in a ratio of 1:(10-40) of the mass ratio of graphene oxide to titanium dioxide nanoparticles in the graphene oxide aqueous solution.

7. Applying the A-GQDs / RGO / TiO2 ternary composite photocatalyst as claimed in claim 1 to the photocatalytic degradation of organic dye pollutants.

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