Ag quantum dot modified TiO2 photocatalyst and preparation method thereof

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to an Ag quantum dot modified TiO2 photocatalyst and a preparation method thereof. The preparation method comprises the following steps: firstly, dissolving TiO2 in ethanol, ultrasonically stirring, then adding silver nitrate, completely dissolving, putting into a plasma reactor, applying voltage, discharging for a period of time, and centrifugally drying to obtain the Ag quantum dot modified TiO2 photocatalyst. The photocatalyst synthesized under the condition of 75% ethanol can completely degrade BPA.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically an Ag quantum dot modified TiO2 photocatalyst and its preparation method. Background Technology

[0002] Titanium dioxide (TiO2), as a classic wide-bandgap semiconductor photocatalytic material, has shown great application potential in environmental purification, energy conversion, and antibacterial applications. Its core advantages lie in its strong oxidation capacity, excellent physicochemical stability, non-toxic properties, and relatively low cost. However, its widespread commercial application has always been constrained by two inherent scientific bottlenecks: First, due to its relatively wide bandgap of approximately 3.2 eV, TiO2 can only absorb and utilize less than 5% of the ultraviolet light in the solar spectrum, while it is almost unresponsive to the visible light that dominates solar energy, resulting in extremely low light energy utilization. Second, the electron-hole pairs generated after photoexcitation readily recombine rapidly in bulk or on the surface, rather than migrating to the surface to participate in the expected redox reaction, causing its quantum efficiency and photocatalytic activity to remain at a low level.

[0003] To overcome these limitations, the scientific community has conducted long-term and extensive research. Among these efforts, modifying composite photocatalysts with noble metal nanoparticles has proven to be an effective technical approach. Silver (Ag) nanoparticles, in particular, when combined with TiO2, can form a Schottky barrier at the interface, acting as an efficient "electron trap" to preferentially capture photogenerated electrons, thereby achieving effective spatial separation of electrons and holes and significantly suppressing their recombination probability. More importantly, the unique surface plasmon resonance effect of silver nanoparticles allows them to efficiently capture visible light energy like an antenna, transferring energy to TiO2 or directly injecting "hot electrons" through a specific mechanism. This cleverly extends the material's photoresponse range from the ultraviolet region to the visible light region, fundamentally improving the utilization efficiency of solar energy.

[0004] Despite the promising prospects of Ag / TiO2 composites, traditional preparation methods have certain limitations. Current mainstream synthesis strategies, such as photoreduction, heavily rely on high-intensity ultraviolet light sources and are slow, often resulting in unevenly distributed and out-of-size deposited silver particles. While the widely used chemical reduction method is simple to operate, it inevitably introduces additional chemical reducing agents (such as sodium borohydride) and stabilizers. The residue of these impurity molecules not only contaminates the catalyst surface but may also mask its active sites, leading to catalytic performance degradation and deviating from the principles of green chemistry. Furthermore, the industrially common impregnation-calcination method, although enabling mass production, involves calcination at hundreds of degrees Celsius, resulting in significant energy consumption and severe sintering and coarsening of silver particles, as well as irreversible damage to the microstructure of the TiO2 support. Ultimately, the prepared composite material falls far short of the ideal microstructure and performance.

[0005] Based on the current state of technology, liquid-phase plasma technology has emerged as a promising green synthesis platform. It generates a transiently highly active region rich in high-energy electrons, active free radicals, ultraviolet photons, and accompanied by localized extreme physical conditions by breaking down the liquid medium under high voltage. This technology shows great potential in the field of nanomaterial synthesis due to its unique advantages of speed, efficiency, and the absence of additives. However, existing technologies mostly focus on using liquid-phase plasma to achieve single functions, such as simply reducing metal nanoparticles or degrading organic pollutants. No research has yet creatively applied it to the complex synergistic reaction of simultaneously coordinating the in-situ deposition of semiconductor substrates and noble metal modifiers. Summary of the Invention

[0006] To overcome the above problems, this invention provides an Ag quantum dot-modified TiO2 photocatalyst and its preparation method. It uses liquid-phase plasma as a powerful "microreactor" that integrates reduction, excitation, synthesis and modification functions, and prepares Ag quantum dot-modified TiO2 nanomaterials with high photocatalytic performance in one step, thus providing a feasible technical solution to solve the historical problems of traditional methods.

[0007] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0008] A method for preparing Ag quantum dot-modified TiO2 photocatalyst includes the following steps:

[0009] S1. Disperse TiO2 powder in an aqueous ethanol solution or anhydrous ethanol to form a dispersion;

[0010] S2. Add the silver-containing precursor to the dispersion and stir until dissolved to obtain the reaction precursor solution;

[0011] S3. The reaction precursor solution is subjected to liquid-phase plasma discharge treatment to make the silver-containing precursor...

[0012] The bulk material is reduced in situ and deposited on the TiO2 surface to form Ag quantum dots;

[0013] S4. The product after plasma discharge treatment is subjected to solid-liquid separation and dried to obtain...

[0014] Ag quantum dot modified TiO2 photocatalyst.

[0015] In step S1, the volume percentage of ethanol in the ethanol-water solution is 75%.

[0016] In step S2, the silver-containing precursor is silver nitrate.

[0017] The concentration of the silver-containing precursor in the reaction precursor solution is 1-20 mmol / L.

[0018] In step S3, the reaction precursor liquid is subjected to liquid-phase plasma discharge treatment by applying a voltage of 10kV.

[0019] An Ag quantum dot-modified TiO2 photocatalyst is prepared by the above-mentioned method for preparing Ag quantum dot-modified TiO2 photocatalyst.

[0020] The silver element in the Ag quantum dots is simultaneously in the zero-valence state of silver Ag. 0 Silver Ag in positive monovalent state + It exists, in which zero-valent silver (Ag) exists. 0 It consists of nanoparticles with a diameter of 4-6 nm, loaded onto the TiO2 surface.

[0021] Application of the Ag quantum dot-modified TiO2 photocatalyst in the degradation of organic pollutants.

[0022] A method for degrading organic pollutants using Ag quantum dot-modified TiO2 photocatalyst involves adding the Ag quantum dot-modified TiO2 photocatalyst and persulfate to an aqueous system containing organic pollutants, and then reacting under visible light irradiation to achieve the degradation of BPA in the aqueous system containing organic pollutants.

[0023] The beneficial effects of this invention are:

[0024] The Ag quantum dot-modified TiO2 photocatalyst prepared by the method of this invention can completely degrade BPA within 10 min. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the method of the present invention;

[0026] Figure 2The X-ray diffraction patterns of the products obtained in Example 1 and Comparative Example 1 of this invention are shown below.

[0027] Figure 3 The image shows an electron micrograph of the Ag quantum dot-modified TiO2 photocatalyst prepared in Example 1 of this invention, with the left side being a scanning electron microscope image and the right side being a transmission electron microscope image.

[0028] Figure 4 This is a region scan elemental energy spectrum distribution of the Ag quantum dot modified TiO2 photocatalyst prepared in Example 1 of this invention;

[0029] Figure 5 (a) is the X-ray absorption near-edge structure spectrum of the AgK edge obtained by spectroscopic analysis of Ag foil, Ag2O and Ag / TiO2 catalyst obtained in Example 1;

[0030] Figure 5 (b) is the Fourier transform extended X-ray absorption fine structure spectrum obtained by spectroscopic analysis of Ag foil, Ag2O and the Ag / TiO2 catalyst obtained in Example 1;

[0031] Figure 5 (c) is a wavelet transform contour plot of the extended X-ray absorption fine structure spectrum signal of the Ag foil at the AgK edge;

[0032] Figure 5 (d) is the wavelet transform contour plot of the extended X-ray absorption fine structure spectrum signal of Ag2O at the AgK edge;

[0033] Figure 5 (e) is a wavelet transform contour plot of the extended X-ray absorption fine structure spectrum signal of Ag / TiO2 prepared in Example 1 of the present invention at the AgK edge;

[0034] Figure 6 The graphs show the effects of different ethanol ratios on BPA degradation in Examples 1-5.

[0035] Figure 7 The graph shows the effect of different AgNO3 dosages on BPA degradation during step S2 of Example 1.

[0036] Figure 8 Graphs showing the degradation effects of different catalysts on BPA;

[0037] Figure 9 This is a diagram illustrating the effect of reusing the Ag / TiO2 catalyst of this invention. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1:

[0040] First, 0.5 g of TiO2 was dispersed in 200 mL of 75% (v / v) ethanol aqueous solution and ultrasonically stirred for 10 min to obtain a dispersion. Then, silver nitrate was added to the dispersion and completely dissolved to obtain a reaction precursor solution with a concentration of 10 mmol / L. The reaction precursor solution was placed in a quartz cylindrical plasma reactor, and a 10 kV AC voltage was applied to the reaction precursor solution to discharge the liquid-phase plasma in the reaction precursor solution for 2 min, so that the silver-containing precursor was reduced in situ and deposited on the TiO2 surface to form Ag quantum dots. The product after plasma discharge treatment was centrifuged and dried to obtain the Ag quantum dot modified TiO2 photocatalyst, denoted as Ag / TiO2.

[0041] This device is a common laboratory setup, commercially available, and was purchased from Nanjing Suman Plasma Technology Co., Ltd. Specifically, it is an apparatus for preparing Ag quantum dot-modified TiO2 photocatalysts, comprising: a high-voltage terminal, a high-voltage electrode, a plasma reactor, a magnetic stirrer, and a low-voltage terminal. The high-voltage terminal is electrically connected to the plasma reactor and its internal liquid via the high-voltage electrode. A magnetic stirrer is located below the plasma reactor, and a rotor is placed inside. The magnetic stirrer drives the rotor to rotate. The plasma reactor and its internal liquid are also electrically connected to the low-voltage terminal, forming a DC circuit from the high-voltage terminal to the high-voltage electrode to the plasma reactor and then to the low-voltage terminal. In use, the precursor solution is placed in the plasma reactor, and power is applied.

[0042] The morphology of the Ag / TiO2 obtained in Example 1 was characterized, such as... Figure 2 It can be seen that the TiO2 used belongs to the anatase (standard diffraction card number .21-1272) structure, and the diffraction peaks at 25.3°, 37.8°, 48.0°, and 53.8° are attributed to the diffraction of the (101), (004), (200), and (105) crystal planes of TiO2, respectively. Compared with TiO2, the diffraction peak positions and peak widths of p-TiO2 and Ag / TiO2 did not change, indicating that plasma treatment does not change the crystal phase of TiO2. No characteristic peaks of Ag were observed in the XRD pattern of Ag / TiO2, possibly due to the low Ag loading.

[0043] The preparation method of p-TiO2 is the same as in Example 1, except that silver nitrate is not added to the dispersion; instead, the dispersion is directly subjected to liquid-phase plasma discharge treatment, which is a dielectric barrier discharge. The final catalyst sample is denoted as p-TiO2.

[0044] The morphology and size of Ag particles prepared by liquid-phase plasma in this invention were tested using scanning electron microscopy and transmission electron microscopy, such as... Figure 3 As shown, TiO2 consists of 20-40 nm particles, and zero-valent silver (Ag) was synthesized. 0 The particle size was 4-6 nm, indicating the formation of Ag quantum dots. Transmission electron microscopy clearly showed the lattice fringes of the sample, with corresponding interplanar spacings of 0.349 nm and 0.239 nm, corresponding to the (101) crystal plane of TiO2 and the (111) crystal plane of Ag, respectively. Elemental distribution energy dispersive spectroscopy characterization results showed that Ag, Ti, and O were uniformly distributed. Figure 4 .

[0045] The coordination structure of the Ag atoms surrounding the Ag in the Ag / TiO2 catalyst was analyzed by X-ray absorption near-edge structure (XANES) spectroscopy, and the results are as follows: Figure 5 As shown in Figure 5a, the X-ray absorption near-edge structure spectrum of the Ag potassium edge indicates that its absorption edge energy position is intermediate between that of the metallic Ag foil (Ag... 0 ) and silver oxide Ag2O (Ag + This key characteristic clearly indicates that the Ag in the sample is in a mixed valence state, meaning that reduced metallic Ag is also present. 0 And oxidized ionic Ag + Fourier transform of the K-space data yields the R-space plot (5b). It can be seen that the oscillation peak at 1.68 Å corresponds to the Ag-O shell, the oscillation peak at 2.71 Å corresponds to the Ag-Ag / Ti shell, and the oscillation peak at 3.28 Å corresponds to the Ag-O-Ag / Ti shell. Combined with the two-dimensional plot obtained from wavelet transform (…),… Figure 5 c- Figure 5 e) This indicates that Ag is dispersed in ultrasmall quantum dots and at the atomic level. + Species coexist and there are significant interfacial interactions between them and the TiO2 carrier.

[0046] Example 2:

[0047] Same as Example 1, except that:

[0048] 0.5 g of TiO2 was dispersed in 200 mL of 75% ethanol solution. Silver nitrate was added to the dispersion to make the concentration of silver nitrate in the resulting reaction precursor solution 20 mmol / L.

[0049] Example 3:

[0050] Same as Example 1, except that 0.5 g of TiO2 was dispersed in 200 mL of ultrapure water, and the concentration of silver nitrate in the resulting reaction precursor solution was 1 mmol / L.

[0051] Example 4:

[0052] Same as Example 1, except that: 0.5 g of TiO2 was dispersed in 200 mL of 25% (v / v) ethanol aqueous solution, and the concentration of silver nitrate in the resulting reaction precursor solution was 10 mmol / L.

[0053] Example 5:

[0054] Same as Example 1, except that: 0.5 g of TiO2 was dispersed in 200 mL of 50% ethanol aqueous solution, and the concentration of silver nitrate in the resulting reaction precursor solution was 10 mmol / L.

[0055] Example 6:

[0056] Same as in Example 1, except that the concentration of silver nitrate in the precursor solution is 1 mmol / L;

[0057] Example 7:

[0058] Same as in Example 1, except that the concentration of silver nitrate in the precursor solution is 2 mmol / L;

[0059] Example 8:

[0060] Same as in Example 1, except that the concentration of silver nitrate in the precursor solution is 5 mmol / L;

[0061] Example 9:

[0062] Same as in Example 1, except that the concentration of silver nitrate in the precursor solution was 20 mmol / L.

[0063] To evaluate the degree of photocatalytic activation of persulfate prepared in this invention, the following experiments were conducted using bisphenol A (BPA) as the target pollutant. The specific steps are as follows: 25 mg of the Ag quantum dot-modified TiO2 photocatalyst prepared in Examples 1-5 were weighed and the following operations were performed:

[0064] The Ag quantum dot-modified TiO2 photocatalyst was placed in a 100 mL glass beaker, and 50 mL of a 20 mg L⁻¹ photocatalyst was added to the beaker. -1A BPA solution was prepared. The catalyst was sonicated for 10 min to ensure uniform dispersion in the solution. The solution was then magnetically stirred for 20 min in the dark until adsorption-desorption equilibrium was reached. Subsequently, 25 mg of potassium persulfate (PS) was rapidly added, followed by irradiation under a xenon lamp. During irradiation, a 1.5 mL sample was taken every 5 min and filtered through a 0.45 μm pore size membrane. The BPA concentration of the filtered liquid was determined by high-performance liquid chromatography (HPLC).

[0065] First, the effect of different ethanol contents on BPA degradation during the liquid-phase plasma synthesis of Ag quantum dots was investigated. Figure 6 As shown, the results indicate that the ethanol ratio has a significant impact on the performance of the final photocatalyst: in a pure water environment, due to Ag... + The reduction efficiency was low; Ag / TiO2 exhibited the weakest degradation ability, with a BPA degradation efficiency of only 55% after 30 minutes. After adding a 25% (v / v) ethanol aqueous solution, ethanol acted as a sacrificial agent to promote Ag degradation. + Rapid reduction enabled a BPA degradation efficiency of 80%. The photocatalysts prepared with ethanol volume fractions of 50–100% exhibited optimal photocatalytic performance, with those prepared at 75% and 100% ethanol volume fractions achieving almost complete BPA degradation within approximately 10 minutes. The high-ethanol environment enhanced the plasma reduction process, leading to the deposition of numerous well-dispersed Ag quantum dots on the TiO2 surface, effectively promoting photogenerated electron migration and separation, and significantly improving photocatalytic efficiency.

[0066] Next, the photocatalytic degradation performance of Ag / TiO2 materials prepared in the liquid-phase plasma discharge process using different concentrations (1–20 mM) of AgNO3 in the precursor solution, as described in Examples 1 and 6-9 (75% ethanol aqueous solution), on BPA was investigated. The results showed that the AgNO3 concentration significantly affected the photocatalytic activity. The sample with 1 mM AgNO3 in the precursor solution exhibited a relatively weak degradation rate, but complete removal of BPA was still achieved within 30 min. When the AgNO3 concentration in the precursor solution was increased to 2 mM, the catalytic activity of the resulting photocatalyst improved, but the initial degradation kinetics remained relatively slow. When the AgNO3 concentration in the precursor solution was further increased to 5 mM and 10 mM, the degradation rate of the resulting photocatalyst significantly accelerated, achieving 100% removal of BPA within 10–20 min. Notably, the material prepared with 20 mM AgNO3 in the precursor solution exhibited the best performance, with its BPA dropping to 0 within 5 minutes, demonstrating the fastest and most complete degradation behavior. Overall, increasing the AgNO3 concentration can enhance plasma-induced Ag... +The reduction process allows more and more dispersed Ag quantum dots to be loaded onto the TiO2 surface, thereby effectively promoting the separation of photogenerated carriers and the transfer of interfacial electrons, and significantly improving the photocatalytic degradation efficiency of BPA.

[0067] Finally, the effects of different catalysts on BPA degradation were investigated, and the results are as follows: Figure 8 As shown, in photocatalysis (vis) and persulfate (PDS) alone, the removal rate of BPA was only 20% within 30 min. After adding TiO2, the removal rate of BPA increased by 10%, indicating that the addition of catalyst can improve the coupling efficiency of photocatalysis and persulfate to a certain extent. However, in the Ag / TiO2+vis+PDS system, the removal rate of BPA reached 100% within only 10 min, indicating that the supported Ag quantum dots can significantly improve the separation of photogenerated carriers of TiO2 and improve the efficiency of photocatalytic activation of PDS.

[0068] In addition, the effectiveness of catalyst reuse was evaluated, such as... Figure 9 As shown, after 5 cycles, the BPA removal rate was >95%, indicating that Ag / TiO2 has good recycling efficiency.

[0069] Example 10:

[0070] In Example 1, TiO2 powder was replaced with g-C3N4 powder to prepare Ag quantum dot-supported graphitic carbon nitride (g-C3N4) photocatalyst. The specific procedure was as follows: 0.5 g of g-C3N4, 0.34 g of silver nitrate, and a 75% (v / v) ethanol aqueous solution were mixed. The resulting mixture was discharged at 10 kV for 2 min, and the discharged product was then centrifuged and dried to obtain the Ag / g-C3N4 catalyst. The catalyst was used in the above experiments targeting bisphenol A (BPA) for BPA removal. For g-C3N4, the BPA removal rate was only 50% after 30 min of reaction; however, the Ag / g-C3N4 catalyst completely removed BPA within 15 min, representing an 80% improvement in degradation efficiency compared to the unmodified g-C3N4 at 15 min.

[0071] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A method for preparing an Ag quantum dot modified TiO2 photocatalyst, characterized in that, Includes the following steps: S1. Disperse TiO2 powder in an aqueous ethanol solution or anhydrous ethanol to form a dispersion; S2. Add the silver-containing precursor to the dispersion and stir until dissolved to obtain the reaction precursor solution; S3. The reaction precursor solution is subjected to liquid-phase plasma discharge treatment to make the silver-containing precursor... The bulk material is reduced in situ and deposited on the TiO2 surface to form Ag quantum dots; S4. The product after plasma discharge treatment is subjected to solid-liquid separation and dried to obtain... Ag quantum dot modified TiO2 photocatalyst.

2. The method for preparing Ag quantum dot-modified TiO2 photocatalyst according to claim 1, characterized in that, In step S1, the volume percentage of ethanol in the ethanol-water solution is 75%.

3. The method for preparing Ag quantum dot-modified TiO2 photocatalyst according to claim 1, characterized in that, In step S2, the silver-containing precursor is silver nitrate.

4. The method for preparing Ag quantum dot-modified TiO2 photocatalyst according to claim 3, characterized in that, The concentration of the silver-containing precursor in the reaction precursor solution is 1-20 mmol / L.

5. The method for preparing Ag quantum dot-modified TiO2 photocatalyst according to claim 1, characterized in that, In step S3, the reaction precursor liquid is subjected to liquid-phase plasma discharge treatment by applying a voltage of 10kV.

6. An Ag quantum dot modified TiO2 photocatalyst, characterized in that, It is prepared by the method described in any one of claims 1 to 5 for preparing the Ag quantum dot modified TiO2 photocatalyst. 7.The Ag quantum dot modified TiO2 photocatalyst according to claim 6, characterized in that, The silver element in the Ag quantum dots is in zero-valence state silver Ag 0 and positive monovalence state silver Ag + exists, wherein the zero-valence state silver Ag 0 is a nanoparticle with a diameter of 4-6 nm and is loaded on the surface of TiO2.

8. The application of an Ag quantum dot-modified TiO2 photocatalyst as described in claim 6 or 7 in the degradation of organic pollutants.

9. A method for degrading organic pollutants by using the TiO2 photocatalyst modified by the Ag quantum dots according to claim 6 or 7, characterized in that, In an aqueous system containing organic pollutants, the Ag quantum dot-modified TiO2 photocatalyst and persulfate are added, and the reaction is carried out under visible light irradiation to achieve the degradation of BPA in the aqueous system containing organic pollutants.

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