Ultrathin titanium dioxide nanowire-supported Co single-atom heterogeneous catalytic materials and their preparation and application

Abstract

This invention discloses an ultrathin TiO2 nanowire-supported Co single-atom heterogeneous catalytic material, its preparation, and application, belonging to the field of materials technology. The invention achieves a fine assembly of ultrathin TiO2 nanowires and Co single atoms through electrostatic adsorption, enhancing the catalyst's adsorption and activation of inert CO2, resulting in efficient photocatalytic CO2 reduction (CRR). The prepared Co-SAs@TiO2-NWs exhibit excellent cyclic and structural stability, providing a new strategy for regulating single-atom sites in ultrathin structures.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and in particular relates to an ultra-thin TiO2 nanowire-loaded Co single-atom heterogeneous catalytic material and its preparation and application. Background Art

[0002] The process by which semiconductor materials convert light energy into chemical energy under illumination is called photocatalysis. Specifically, when the energy of the photons in the incident light matches the band gap of the semiconductor material, the semiconductor absorbs the light energy under light excitation and mediates electron transitions to produce photogenerated carriers. Typically, photogenerated electrons jump from the valence band of the semiconductor to the conduction band, leaving holes at the corresponding position in the valence band. Electrons in the semiconductor conduction band (CB) have a reduction potential of +0.5 to -1.5 V (vs NHE) and often serve as the port for photocatalytic reduction reactions. Holes in the semiconductor valence band (VB) have an oxidation potential of +1.0 to +3.5 V (vs NHE) and often serve as the port for photocatalytic oxidation reactions.

[0003] Among the many transition metal oxide semiconductor materials, TiO2 has attracted researchers' attention due to its corrosion resistance, non-toxicity, durability, and low cost. As a classic material in photocatalysis research, TiO2 possesses semiconductor properties and exhibits exceptional redox activity upon photoexcitation. Over the past 20 years, TiO2 photocatalytic technology has rapidly developed, playing a crucial role in addressing various energy and environmental challenges, such as solar water splitting to produce H2, the decomposition of air pollutants and water at low concentrations, and photocatalytic CO2 reduction.

[0004] Single-atom catalysts (SACs) are a highly promising class of photocatalytic materials, often renowned for their high efficiency, boasting 100% atomic utilization. SACs have demonstrated strong potential in enhancing light harvesting, charge transfer kinetics, and surface reactions in photocatalytic systems. Currently, researchers are focusing on developing low-cost, non-precious metal SAC photocatalytic systems. Single-atom photocatalytic materials constructed from abundant transition metals are becoming a hot topic. Transition-metal SACs can modulate the material's band structure, enhance the light absorption capacity of the support, and act as electron pumps to facilitate the transport of photogenerated electrons, thereby enhancing surface charge separation and transfer. Furthermore, the unsaturated active sites in transition-metal SACs can tailor the catalyst's coordination configuration to optimize molecular adsorption and further activate molecules via photogenerated charge carriers, a process similar to homogeneous and enzyme catalysis. Due to these advantages, transition-metal SACs are widely used in photocatalytic applications such as small molecule activation, fine chemical production, and environmental remediation.

[0005] Currently, conventional single-atom synthesis methods suffer from high energy consumption, demanding conditions, cumbersome procedures, and uncontrollable problems, which seriously hinder the development of single-atom catalysts. Traditional bottom-up wet chemical methods are a convenient way to obtain single-atom catalytic materials. However, the single atoms obtained by this method are prone to aggregation and migration, resulting in uneven catalytic active centers and deactivation, and greatly reduced atom utilization and catalytic stability. Therefore, how to simply and efficiently prepare highly dispersed transition metal single-atom catalytic materials is a major current challenge. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides an ultrathin TiO2 nanowire-supported Co single atom (Co-SAs@TiO2-NWs) heterogeneous catalytic material and its preparation method and application. The purpose is to obtain an efficient photocatalytic CO2 reduction (CRR) catalyst by uniformly anchoring Co single atoms on the ultrathin TiO2 nanowire (TiO2-NWs) carrier.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] An ultrathin TiO2 nanowire-supported Co single atom (Co-SAs@TiO2-NWs) heterogeneous catalytic material, the preparation of which includes the following steps:

[0009] 1) Dissolve polyvinylpyrrolidone (PVP) and potassium ferrocyanide (K4Fe(CN)6·3H2O) in HCl solution, then add titanium sulfate (Ti(SO4)2) and stir thoroughly to prepare a reaction precursor solution;

[0010] 2) pouring the reaction precursor solution obtained in step 1) into a hydrothermal reactor for heating reaction, centrifuging, washing, and drying until the water is completely evaporated to obtain a self-assembled composite material of TiO2 and Prussian blue (PB) (OA-PB / TiO2);

[0011] 3) dispersing the self-assembled composite material of TiO2 and Prussian blue (OA-PB / TiO2) obtained in step 2) in a hydrochloric acid solution, centrifuging, washing, and drying to obtain ultrathin TiO2 nanowires (TiO2-NWs);

[0012] 4) Dissolving cobalt acetate (C4H6CoO4·4H2O) in deionized water to form a solution, followed by adding the ultrathin TiO2 nanowires (TiO2-NWs) obtained in step 3), stirring and mixing, centrifuging, washing, drying, calcining, and naturally cooling to obtain Co-SAs@TiO2-NWs.

[0013] Furthermore, in the reaction precursor solution obtained in step 1), the content of polyvinyl pyrrolidone was 3.8 g / 50 mL, the content of potassium ferrocyanide was 0.12 g / 50 mL, the content of Ti(SO4)2 was 0.0682 g / 50 mL, and the concentration of the HCl solution used was 0.1 mol·L -1 .

[0014] Furthermore, the dissolution in step 1) is performed by magnetic stirring at a stirring speed of 500 rpm and a stirring time of 30 min.

[0015] Furthermore, the stirring in step 1) is performed by magnetic stirring, and the stirring time is 30 min.

[0016] Furthermore, in step 2), a hydrothermal reactor with a polytetrafluoroethylene liner is used to carry out the reaction.

[0017] Furthermore, the heating in step 2) is performed in a programmed temperature control box, the heating reaction temperature is 80° C., and the time is 24 h.

[0018] Furthermore, in step 3), the amount of the self-assembled composite material of TiO2 and Prussian blue is 100 mg per 50 mL of hydrochloric acid solution; the concentration of the hydrochloric acid solution is 0.1 mol·L -1 .

[0019] Furthermore, the dispersion in step 3) is carried out by magnetic stirring with a stirring speed of 500 rpm and a stirring time of 20 min.

[0020] Furthermore, the washing in steps 2)-3) is specifically washing with deionized water 3 times, and then washing with ethanol 3 times.

[0021] Furthermore, the content of cobalt acetate in the solution in step 4) is 10 mg / 15 mL.

[0022] Furthermore, the mass ratio of the ultrathin TiO2 nanowires to cobalt acetate used in step 4) is 3:2.

[0023] Furthermore, the stirring in step 4) is performed by magnetic stirring, with a stirring speed of 500 rpm and a stirring time of 6 h.

[0024] Furthermore, the washing in step 4) is specifically washing with ethanol twice and then washing with deionized water twice.

[0025] Furthermore, the centrifugation speed in steps 2) to 4) is 8000 rpm and the time is 3-5 min.

[0026] Furthermore, the drying in steps 2) to 4) is carried out in an oven at 60° C. for 10 h.

[0027] Furthermore, the calcination in step 4) is carried out in a muffle furnace at a temperature of 350° C. for 2 h.

[0028] The Co-SAs@TiO2-NWs obtained above can be used for photocatalytic CO2 reduction.

[0029] The TiO2-NWs prepared in this invention are uniformly sized hedgehog-like structures formed by the orderly assembly of nanowires from the inside out. Their ultrathin nanowire structure facilitates charge transport and the anchoring and exposure of catalytic sites. The abundant pores between the nanowires not only provide pathways for the transport of reactants and products but also create a spatial confinement effect, encapsulating individual transition metal atoms within a limited space. Therefore, TiO2-NWs serve as an excellent carrier for anchoring Co sites, inhibiting the aggregation and migration of single atoms and promoting their dispersion. Furthermore, the ultrathin TiO2-NWs possess numerous advantages in constructing efficient photocatalytic CO2 reduction (CRR) systems, including high specific surface area, high charge transport efficiency, and high chemical stability.

[0030] At the same time, the transition metal Co, which is abundant in surface reserves and often serves as a catalytic site for CRR, has a high affinity for CO2 molecules. This study uses ultrathin TiO2 nanowires as a carrier and cobalt acetate as a single-atom source of cobalt to prepare the Co-SAs@TiO2-NWs heterogeneous catalytic material via a simple synthetic route. This provides a new strategy for the simple and efficient preparation of highly dispersed transition metal single-atom catalytic materials and for constructing efficient CRR systems using ultrathin TiO2.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention uses electrostatic action to drive the anchoring of single-atom Co on ultrathin TiO2 nanowires. The ultrathin TiO2 nanowires have a large specific surface area and abundant mesoporous channels between the nanowires. In addition, the surface of the TiO2 nanowires is negatively charged. These unique structural characteristics enhance its affinity to the Co site precursor Co. 2+ After heat treatment, the Co sites are highly dispersed on the TiO2 support in the form of single atoms, with a strong metal-support interaction between the two.

[0033] (2) The Co sites on the ultrathin TiO2 nanowires prepared by the present invention have strong photocatalytic CO2 reduction activity and stability. CO =28.40 mmol·g -1 ·h -1, TOF up to 4.99 min -1 , is one of the most efficient CRR catalytic materials reported in the literature; and has good cycle and structural stability.

[0034] (3) The present invention utilizes the Co single-atom sites constructed by ultrathin structures to accelerate charge transfer, enhance CO2 adsorption and activation, and provide a new strategy for the regulation of single-atom sites in ultrathin structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Zeta potential (a) of TiO2-NWs prepared in the example and its XRD pattern (b), N2 adsorption-desorption curve (c) and pore size distribution (d) of Co-SAs@TiO2-NWs and Co-SAs@TiO2-NPs prepared in the comparative example.

[0036] Figure 2 SEM images (a), TEM images (bd) of TiO2-NWs and SEM images (e), TEM images (fh) of Co-SAs@TiO2-NWs prepared in the examples.

[0037] Figure 3 HADDF-STEM image (a), STEM image (b), AC-TEM image (c), HADDF-STEM image (d), element distribution map (eg), AC-TEM image (h) and sub-spacing map (i) of Co-SAs@TiO2-NWs prepared in the example.

[0038] Figure 4 EDS (a) and XPS (bd) graphs of Co-SAs@TiO2-NWs prepared in Example.

[0039] Figure 5 The SEM image (a), TEM image (b), and element distribution diagram (cf) of Co-SAs@TiO2-NPs prepared in comparative example.

[0040] Figure 6 The CRR performance diagram of TiO2-NWs, Co-SAs@TiO2-NWs prepared in the example and Co-SAs@TiO2-NPs prepared in the comparative example.

[0041] Figure 7 The cyclic stability test diagram (a) and XRD patterns (b) and SEM images (cd) of the Co-SAs@TiO2-NWs prepared in the example before and after photocatalytic reaction. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings, i.e., embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined as long as they do not conflict with each other. Example

[0043] The preparation steps of Co single atom@ultrathin TiO2 nanowire (Co-SAs@TiO2-NWs) heterogeneous catalytic material are as follows:

[0044] (1) 3.8 g of polyvinylpyrrolidone (PVP) and 0.12 g of potassium ferrocyanide (K4Fe(CN)6·3H2O) were added sequentially into a 50 mL HCl solution (0.1 mol·L -1 ) in a beaker and stirred with a magnetic stirrer at 500 rpm for 30 min to form a light green solution, then 0.0682 g of titanium sulfate (Ti(SO4)2) was added, and the beaker containing the mixed solution was transferred to an ultrasonic stirrer and ultrasonically stirred for 30 min;

[0045] (2) Pour the brown mixture obtained in step (1) into a hydrothermal kettle with a polytetrafluoroethylene liner, and place the hydrothermal kettle in a program constant temperature control box at a temperature of 80 °C and heat for 24 h;

[0046] (3) After the reaction, the product was collected by centrifugation at 8000 rpm for 5 min, washed three times with deionized water, and then washed three times with ethanol, and then dried in an oven at 60 °C for 10 h until the water was completely evaporated to obtain dark green OA-TiO2 / PB;

[0047] (4) Disperse 100 mg of OA-PB / TiO2 in 50 mL of hydrochloric acid solution (0.1 mol·L -1 ) and stirred at 500 rpm for 20 min. When the dispersion changed from dark green to light yellow, the sample was centrifuged at 8000 rpm for 5 min and the product was collected. It was washed with deionized water three times and then with ethanol three times, and then dried in an oven at 60 °C for 10 h to obtain light yellow TiO2-NWs.

[0048] (5) Weigh 10 mg of cobalt acetate (C4H6CoO4·4H2O) and add it to 15 mL of deionized water. Stir the mixture at 500 rpm for 3 min at room temperature to completely dissolve the C4H6CoO4·4H2O. Then add 15 mg of TiO2-NWs and stir the mixture at 500 rpm for 6 h at room temperature. The obtained sample was centrifuged at 8000 rpm for 5 min, washed twice with ethanol and deionized water, respectively, and then dried in an oven at 60 °C for 10 h.

[0049] (6) The dried sample from step (5) was placed in a muffle furnace and calcined at 350 °C for 2 h. After natural cooling, pale yellow Co-SAs@TiO2-NWs were obtained.

[0050] Comparative Example Preparation of Co single atoms (Co-SAs@TiO2-NPs) using commercial TiO2 as a carrier

[0051] 10 mg of cobalt acetate (C4H6CoO4·4H2O) was weighed and added to 15 mL of deionized water. The mixture was stirred at room temperature at 500 rpm for 3 min to completely dissolve the C4H6CoO4·4H2O. Then 15 mg of commercial TiO2 was added and stirred at room temperature at 500 rpm for 6 h. The obtained sample was centrifuged at 8000 rpm for 5 min, washed twice with ethanol and deionized water respectively, and then dried in an oven at 60 ℃ for 10 h. After natural cooling, Co-SAs@TiO2-NPs were obtained.

[0052] Figure 1 Zeta potential (a) of TiO2-NWs prepared in Example and XRD pattern (b), N2 adsorption-desorption curve (c) and pore size distribution (d) of Co-SAs@TiO2-NWs and Co-SAs@TiO2-NPs prepared in Comparative Example. As can be seen from the figure, the surface potential of TiO2-NWs is -2.85 mV (a). By utilizing its negatively charged property, the positively charged Co 2+ Adsorbed onto the surface of TiO2-NWs, and then stabilized on the surface of TiO2-NWs support as CRR active center by heat treatment. At the same time, TiO2-NWs and Co-SAs@TiO2-NWs are both typical rutile TiO2 (b, JCPDS: No.21-1276). The specific surface area of ​​Co-SAs@TiO2-NWs is 140.6 m 2·g, which is very close to the original support and much larger than the specific surface area of ​​Co-SAs@TiO2-NPs; in addition, both TiO2-NWs and Co-SAs@TiO2-NWs present type IV isotherms, indicating that they both have rich mesoporous structures (c), and the pore size of both is 3.6 nm, which may represent the width of the gaps between nanowires (d).

[0053] Figure 2 SEM images (a) and TEM images (bd) of TiO2-NWs and SEM images (e) and TEM images (fh) of Co-SAs@TiO2-NWs prepared in Example 1. As shown, the TiO2-NWs are a uniformly sized hedgehog-like structure composed of nanowires assembled from the inside out (ad). These ultrathin nanowires facilitate charge transport and the anchoring and exposure of catalytic sites. Furthermore, the abundant pores between the nanowires provide pathways for the transport of reactants and products. Therefore, TiO2-NWs serve as an ideal carrier for anchoring Co sites. After anchoring the Co sites, the resulting Co-SAs@TiO2-NWs exhibit no significant morphology change (eh), maintaining the hedgehog-like structure of nanowires.

[0054] Figure 3 The HADDF-STEM image (a), STEM image (b), AC-TEM image (c), HADDF-STEM image (d), element distribution map (eg), AC-TEM image (h) and sub-spacing map (i) of the Co-SAs@TiO2-NWs prepared in the example. As shown in the figure, the lattice fringes on the long-range ordered nanowires have the same growth orientation over a large range, that is, they all grow towards the

[001] direction. The spacing of the lattice fringes is about 3.31Å, corresponding to the (110) crystal plane of rutile TiO2. No other Co species phase is found (a, b). Its diameter is about ~4 nm, indicating that the nanowires of Co-SAs@TiO2-NWs have an ultra-thin structure (c). Co, Ti and O elements are evenly distributed in Co-SAs@TiO2-NWs, indicating that there is no obvious aggregation of Co element (dg). At the same time, brighter spots can be clearly observed on the TiO2-NWs support. This is because Co atoms are heavier than Ti atoms, so Co atoms appear brighter in the Z-direction contrast image. Therefore, these spots represent Co single atoms, further confirming the existence of Co single atoms (h, i).

[0055] Figure 4The EDS (a) and XPS (bd) images of Co-SAs@TiO2-NWs prepared in the example. As shown in the figure, Co-SAs@TiO2-NWs are composed of three elements: Co, Ti, and O (a, b). 3 / 2 The signal peak at can be fitted into a combination of three peaks, and the dominant peak at the binding energy of 781.3 eV represents Co 2+ The peak at the binding energy of 784.6 eV represents Co 3+ , while the peak at the binding energy of 788.3 eV represents the satellite peak of Co (c). After the formation of Co single atoms, the position of Ti2p obviously shifts to a lower binding energy by about 0.1 eV (d), indicating that there is a strong electronic interaction between Co single atoms and TiO2-NWs supports.

[0056] Figure 5 The SEM images (a), TEM images (b), and elemental distribution maps (cf) of the Co-SAs@TiO2-NPs prepared as a comparative example are shown in the figure. As shown in the figure, the Co-SAs@TiO2-NPs prepared using commercial TiO2 exhibit an irregular bulk morphology. Compared with TiO2-NWs, defects such as lower specific surface area, porosity, and charge transfer efficiency limit their application in photocatalytic CO2 reduction.

[0057] Application Examples

[0058] The Co-SAs@TiO2-NWs heterogeneous catalytic material obtained in the example was used for photocatalytic CO2 reduction, and the specific steps were as follows:

[0059] (1) Weigh 8 mg of ruthenium pyridine and a certain amount of photocatalytic material and add them to the reactor. Then use a pipette to measure 3 mL of acetonitrile (C2H3N), 2 mL of deionized water (H2O), and 1 mL of triethanolamine (TEOA) and add them to the reactor respectively;

[0060] (2) Completely seal the reactor with vacuum grease and vacuum airtight glue, repeatedly extract the air in the reactor through a water circulation vacuum pump, and inject CO2 gas;

[0061] (3) Repeat the pumping-venting cycle three times, and finally stir for another 30 minutes while introducing CO2 gas;

[0062] (4) The temperature in the quartz beaker was controlled at about 30 °C by the condensation reflux system, and then the reactor treated in the above steps was placed in the beaker, and the xenon lamp light source (300 W) facing the reactor was turned on;

[0063] (5) Every hour, 0.5 mL of the gas after the reaction was extracted using a vacuum needle, and the gas phase products (such as CO, H2 and CH4) contained in the gas after the reaction were detected by gas chromatography.

[0064] Figure 6 The CRR performance diagram of TiO2-NWs, Co-SAs@TiO2-NWs and Co-SAs@TiO2-NPs prepared in the example. As shown in the figure, pure TiO2-NW has no Co sites and no CO is produced after 3 h of reaction, which indicates that the TiO2-NWs support has almost no CRR activity. Compared with TiO2-NWs without Co loading, the CO yield (V CO ) is 28.4mmol·g -1 ·h -1 , the yield of H2 (V H2 ) is 13.9 mmol·g -1 ·h -1 , indicating that the transition metal Co site acts as the catalytic center for CRR; in contrast, the CO yield (V CO ) is 3.21 mmol·g -1 ·h -1 , the yield of H2 (V H2 ) is 1.52 mmol·g -1 ·h -1 It can be seen that the photocatalytic CO2 reduction performance of Co-SAs@TiO2-NWs prepared in the example is much better than that of Co-SAs@TiO2-NPs.

[0065] Figure 7 The cyclic stability test diagram (a) of the Co-SAs@TiO2-NWs prepared in the example and the XRD pattern (b) and SEM images (cd) before and after photocatalytic reaction. As shown in the figure, Co-SAs@TiO2-NWs can still maintain the same V after 4 uses as when it was first used. CO and V H2 , and the ratio of CO to H2 remains close to 2:1 (a). Furthermore, the physical phase, main exposed surface, and morphology of the Co-SAs@TiO2-NWs after the reaction remain unchanged, remaining a hedgehog-shaped rutile TiO2 structure assembled from nanowires (bd), indicating that Co-SAs@TiO2-NWs possesses excellent cycling and structural stability.

[0066] It will be easily understood by those skilled in the art that the above description is merely a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an ultrathin TiO2 nanowire-supported Co single-atom heterogeneous catalytic material, characterized by: The following steps are involved: 1) Dissolve polyvinyl pyrrolidone and potassium ferrocyanide in HCl solution, then add titanium sulfate and stir thoroughly to prepare a reaction precursor solution; 2) pouring the reaction precursor solution obtained in step 1) into a hydrothermal reactor for heating reaction, and then centrifuging, washing, and drying to obtain a self-assembled composite material of TiO2 and Prussian blue; 3) dispersing the self-assembled composite material of TiO2 and Prussian blue obtained in step 2) in a hydrochloric acid solution, centrifuging, washing, and drying to obtain ultrathin TiO2 nanowires; 4) Dissolving cobalt acetate in deionized water to form a solution, then adding the ultrathin TiO2 nanowires obtained in step 3) to the solution, stirring and mixing, centrifuging, washing, drying, and calcining to obtain an ultrathin TiO2 nanowire-supported Co single-atom heterogeneous catalytic material.

2. The preparation method according to claim 1, wherein: Step 1) The content of polyvinyl pyrrolidone in the reaction precursor solution is 3.8 g / 50 mL, the content of potassium ferrocyanide is 0.12 g / 50 mL, the content of Ti(SO4)2 is 0.0682 g / 50 mL, and the concentration of the HCl solution used is 0.1 mol·L -1 .

3. The preparation method according to claim 1, wherein: The heating reaction temperature in step 2) is 80° C. and the time is 24 h.

4. The preparation method according to claim 1, wherein: In step 3), the amount of the self-assembled composite material of TiO2 and Prussian blue is 100 mg per 50 mL of hydrochloric acid solution; the concentration of the hydrochloric acid solution is 0.1 mol·L -1 .

5. The preparation method according to claim 1, wherein: Step 4) The content of cobalt acetate in the solution is 10 mg / 15 mL.

6. The preparation method according to claim 1, wherein: The mass ratio of the ultrathin TiO2 nanowires to cobalt acetate used in step 4) is 3:

2.

7. The preparation method according to claim 1, wherein: The calcination temperature in step 4) is 350° C. and the calcination time is 2 h.

8. The preparation method according to claim 1, wherein: The drying temperature in steps 2) to 4) is 60° C. and the drying time is 10 h.

9. An ultrathin TiO2 nanowire-supported Co single-atom heterogeneous catalytic material prepared by the method according to any one of claims 1 to 8.

10. Use of the ultrathin TiO2 nanowire-supported Co single-atom heterogeneous catalytic material according to claim 9 in photocatalytic CO2 reduction.

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