Method for manufacturing titanium dioxide composite and titanium dioxide composite manufactured thereby

Abstract

The present invention relates to a method for manufacturing a titanium dioxide composite and a titanium dioxide composite manufactured thereby. The method for manufacturing a titanium dioxide composite according to the present invention can be carried out through a simple solution method without heat treatment or light irradiation, and thus is advantageous for commercialization. In addition, the titanium dioxide composite according to the present invention is advantageous in that ethylene can be stably produced at a rate of 1.0 μmol / g·hr or more by electrochemically reducing carbon dioxide. In addition, the titanium dioxide composite according to the present invention can constantly maintain the production amount of ethylene even when repeatedly reused.

Description

Method for producing titanium dioxide complex and titanium dioxide complex produced thereby

[0001] The present invention relates to a method for producing a titanium dioxide composite and a titanium dioxide composite produced thereby.

[0002] Titanium dioxide exhibits relatively high reactivity and chemical stability under ultraviolet light, and its large surface area allows for rapid surface reaction, making it widely used as a photocatalyst for various solar-based clean energy and environmental technologies.

[0003] In particular, heterojunction titanium dioxide composed of anatase and rutile phases exhibited superior photocatalytic efficiency than titanium dioxide composed of only anatase or rutile phases.

[0004] However, since titanium dioxide has a wide band gap of 3.2 eV, it exhibits excellent photocatalytic efficiency in the ultraviolet range, but has a problem in that its photocatalytic efficiency is very low in the visible light range due to low light absorption.

[0005] To solve these problems, metals, inorganic components, or Ti are used to narrow the band gap of titanium dioxide. 3+ Research has been conducted to change the composition of titanium dioxide by doping with anatase and rutile phases, or to form an amorphous layer (disordered layer) on the surface of heterojunction titanium dioxide.

[0006] Meanwhile, Carbon Capture and Storage (CCS) technology, which captures and stores CO2, has been initially studied as a method to reduce greenhouse gases such as carbon dioxide (CO2). However, it has limitations in CO2 storage space and has the disadvantage of impacting the ecosystem. Therefore, active research is being conducted on Carbon Capture and Utilization (CCU) technology, which converts CO2 into useful substances. Among various CCU technologies, electrochemical CO2 conversion technology has the advantage of being directly linked to renewable energy and easy to scale up. Furthermore, it is attracting attention because it can produce high value-added products such as ethylene (C2H4) and ethanol (C2H5OH), as well as carbon monoxide (CO) and formic acid (HCOOH).

[0007] Most existing, proven electrochemical CO2 conversion technologies have targeted a mixture of syngas (CO) and hydrogen, or HCOOH. However, these technologies have limited market size and scalability, necessitating proven technologies that produce high-value-added products such as ethylene. Ethylene is a basic oil used in the petrochemical industry to produce various polymers, earning it the nickname "the rice of the petrochemical industry." However, existing ethylene production processes generate large amounts of CO2, necessitating a long-term alternative. Producing ethylene through electrochemical CO2 conversion technology not only reduces carbon dioxide emissions but also replaces existing, environmentally destructive processes.

[0008] C such as ethylene through electrochemical CO2 conversion 2+ In order to form the product, CO must first be formed and then their dimerization reaction must occur. Copper (Cu) can convert C through electrochemical CO2 conversion. 2+Copper is the only metal catalyst capable of producing a product. This is because copper possesses optimal binding energy for surface-adsorbed carbon monoxide (*CO), a key intermediate in the electrochemical CO2 conversion reaction. However, its low C2 selectivity during CO2 electrochemical reduction requires improvement.

[0009] To improve the above problems, research has been conducted to produce a heterogeneous composite catalyst by mixing titanium dioxide, which is widely used as a photocatalyst, with a platinum precursor or copper precursor and then performing photo-treatment and / or heat treatment. However, in this case, a problem has occurred in which electrons move from platinum or copper to titanium dioxide, causing oxidation of the surface of platinum or copper.

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] (Patent Document 001) KR 10-2257999 B1

[0013] The purpose of the present invention is to provide a method for producing a titanium dioxide composite capable of producing high value-added ethylene by reducing carbon dioxide, one of the representative thermal gases.

[0014] Another object of the present invention is to provide a titanium dioxide composite comprising reduced titanium dioxide; and amorphous non-oxide metal nanoparticles combined with the reduced titanium dioxide.

[0015] Another object of the present invention is to provide a catalyst or photocatalyst for carbon dioxide reduction comprising the titanium dioxide complex.

[0016] In order to achieve the above-mentioned object, the present invention provides a method for producing a titanium dioxide composite, comprising the steps of (1) mixing titanium dioxide with a reducing agent to obtain reduced titanium dioxide; and (2) stirring a mixed solution in which the reduced titanium dioxide and a non-oxide metal precursor are dispersed in a solvent to form a titanium dioxide composite; wherein the titanium dioxide composite comprises reduced titanium dioxide; and amorphous non-oxide metal nanoparticles combined with the reduced titanium dioxide.

[0017] In addition, the present invention provides a titanium dioxide composite comprising reduced titanium dioxide; and amorphous non-oxide metal nanoparticles combined with the reduced titanium dioxide.

[0018] In addition, the present invention provides a catalyst for carbon dioxide reduction reaction comprising the titanium dioxide complex.

[0019] In addition, the present invention provides a photocatalyst comprising the titanium dioxide complex.

[0020] The method for manufacturing a titanium dioxide composite of the present invention is advantageous for commercialization because it can be performed using a simple solution method without heat treatment or light irradiation.

[0021] Furthermore, the titanium dioxide composite according to the present invention has the advantage of being able to photocatalytically reduce carbon dioxide and stably produce ethylene at a rate of 1.0 μmol / g·hr or higher. Furthermore, the titanium dioxide composite according to the present invention can maintain a constant ethylene production rate even after repeated reuse.

[0022] Figures 1a-e show charge-mediated Cu / TiO according to an embodiment. 2-x The atomic structure and valence state of Cu are shown. The left side of Fig. 1a shows the photoreduction of Cu / TiO2 according to a comparative example, and the right side shows the photoreduction of Cu / TiO according to an example. 2-xSchematic diagram showing the charge-mediated nucleation of Cu / TiO2 according to a comparative example. Figures 1b and c are HR-TEM images (inset: Cu particle size distribution histogram) and enlarged images of Cu nanoparticles in the highlighted area (yellow box) according to a comparative example, and Figures 1d and e are HR-TEM images of Cu / TiO2 according to an embodiment. 2-x HR-TEM image and enlarged image of Cu nanoparticles in the highlighted area (yellow box). Figure 1f shows the TiO in bulk shown in the STEM image. 2-x EELS Ti-L of a selected area up to the surface 2,3 The edge is shown. Figure 1g shows the reference spectra of CuO, Cu2O and CuO along with Cu / TiO2 (green) and Cu / TiO 2-x EELS Cu-L at each selected point (blue) 2,3 Indicates an edge.

[0023] Figure 2a a is Cu / TiO according to the embodiment 2-x is a TEM image, and b is a HRTEM image and corresponding FFT image of Cu nanoparticles in the highlighted area (box) in a.

[0024] Figure 2b a is a TEM image of Cu / TiO2 according to a comparative example, and b is a HRTEM image of Cu nanoparticles in the highlighted area (box) in a and a corresponding FFT image.

[0025] Figures 3a and b show Cu / TiO prepared by stirring for 1 hour. 2-x c and d are STEM images before high-energy electron beam irradiation, and c and d are STEM images after high-energy electron beam irradiation.

[0026] The left side of Fig. 4 shows Cu / TiO prepared by stirring for (a) 6 hours, (b) 24 hours, and (c) 72 hours. 2-x The TEM image is in the middle, the HRTEM image of Cu nanoparticles in the indicated area, and the right is Cu / TiO 2-xThis is a histogram of the size distribution of Cu nanoparticles.

[0027] Figure 5 is Cu / TiO according to an embodiment. 2-x This is a graph comparing the XRD patterns of TiO2.

[0028] Figure 6 is Cu / TiO 2-x and shows the surface oxidation state of Cu / TiO2 photocatalyst. Figure 6a shows Cu / TiO2 (solid line) and Cu / TiO 2-x (dotted line) is the FT-EXAFS spectrum of Cu / TiO2 (black) and Cu / TiO 2-x Soft XAS of Cu L-edge (red), and Fig. 6c, d are Cu / TiO2 and Cu / TiO under dark and light-irradiated operating conditions, respectively. 2-x This is the Cu 2p XPS spectrum.

[0029] Figure 7 is Cu / TiO 2-x And Cu / TiO2 photocatalytic activity was measured. Figure 7a shows Cu / TiO2 of different comparative examples and Cu / TiO of examples manufactured with different stirring times of 1 hour, 6 hours, and 24 hours. 2-x The photocatalytic CO2RR activity of Cu / TiO was compared. Figures 7b-d show Cu / TiO of the examples manufactured by varying the stirring time to 1 hour, 6 hours, and 24 hours. 2-x The production rates of CH4, CO, and C2H4 in CO2RR using Fig. 7e are Cu / TiO before and after heat treatment. 2-x It exhibits CO2RR activity.

[0030] Figure 8 is Cu / TiO for photocatalytic CO2RR. 2-x It shows the recyclability of .

[0031] Figure 9 shows a slab model of rutile TiO2.

[0032] Figures 10a and b are the adsorption models of Cu / TiO2. c, d are Cu / TiO 2-xrepresents the adsorption model.

[0033] Figure 11 is the result of DFT calculation. Figure 11a is Cu / TiO 2-x and the overall CO2RR path of Cu / TiO2, and Fig. 11b is a schematic diagram of the C1 and C2 adsorption paths of CO2RR, and Fig. 11c is a schematic diagram of Cu / TiO 2-x and the relative dimerization energy of Cu / TiO2.

[0034] The present invention relates to a method for producing a titanium dioxide composite and a titanium dioxide composite produced thereby.

[0035] The titanium dioxide composite according to the present invention exhibits the effect of: i) having high carbon dioxide reduction activity efficiency, and ii) photocatalytically reducing carbon dioxide to produce C2 or higher hydrocarbon compounds with high efficiency.

[0036] In order to exhibit all of these effects, the metal nanoparticles included in the titanium dioxide composite must have the following properties and structures: ① a high reduction state (low oxidation number), ② amorphous, and ③ small particle size. In addition, for this purpose, when manufacturing the titanium dioxide composite, ⓐ a non-oxide metal precursor must be used, ⓑ a specific range of mixing weight ratio, and ⓒ the process conditions of controlled stirring time must be met simultaneously.

[0037]

[0038] Hereinafter, the present invention will be described in detail.

[0039] The present invention relates to a method for producing a titanium dioxide composite, comprising the steps of (1) mixing titanium dioxide with a reducing agent to obtain reduced titanium dioxide; and (2) stirring a mixed solution in which the reduced titanium dioxide and a non-oxide metal precursor are dispersed in a solvent to form a titanium dioxide composite; wherein the titanium dioxide composite comprises reduced titanium dioxide; and amorphous non-oxide metal nanoparticles combined with the reduced titanium dioxide.

[0040] First, the above step (1) mixes titanium dioxide (TiO2) with a reducing agent to produce reduced titanium dioxide (TiO 2-x ) is the step of obtaining.

[0041] The above reduced titanium dioxide may include an amorphous rutile phase. The amorphous rutile phase may be formed by selective reduction of a crystalline rutile phase.

[0042] The above reduced amorphous rutile phase titanium dioxide may include, but is not limited to, amorphous having a disordered reduced rutile phase.

[0043] The amorphous rutile-phase titanium dioxide is one in which the intensities of the (110), (101), and (111) peaks among the peaks of the X-ray diffraction pattern of the crystalline rutile-phase titanium dioxide are reduced or do not exhibit the peaks. For example, the amorphous rutile-TiO2 is one in which the intensities of the (110), (101), and (111) peaks among the peaks of the X-ray diffraction pattern of the crystalline rutile-TiO2 are reduced by 80% or more, 85% or more, 90% or more, 95% or more, 97% or more, or 99% or more, or do not exhibit the peaks.

[0044] In one specific example, the step (1) may be to mix titanium dioxide including a crystalline rutile phase with a reducing agent to reduce the crystalline rutile phase to form an amorphous rutile phase.

[0045] The reducing agent may include an alkali metal and a basic organic solvent. For example, the alkali metal may include, but is not limited to, Li, Na, K, Rb, or Cs. For example, the basic organic solvent may be at least one selected from isopropylamine, bis(isopropyl)amine, diethylamine, dicyclohexylamine, and ethylenediamine, and more preferably, ethylenediamine, but is not limited thereto.

[0046] In one specific example, the reducing agent may include an alkali metal, such as Li / EDA (lithium in ethylenediamine), and a basic organic solvent containing an amine. In this case, the Li / EDA may include a metallic Li foil dissolved in ethylenediamine.

[0047] In one specific example, the reduction may be performed in a closed and anhydrous state, but may not be limited thereto.

[0048] The above reduced titanium dioxide particles can be combined with metal nanoparticles to form a titanium dioxide complex.

[0049] The reduced titanium dioxide may include a substituent selected from the group consisting of, but not limited to, -OH groups, -COOH groups, -SO3 groups, and combinations thereof.

[0050] The above reduced titanium dioxide may exhibit a blue color, but is not limited thereto.

[0051] Specifically, since the anatase phase exhibits a blue-black color when reduced and the rutile phase exhibits a white color when not reduced, the reduced titanium dioxide including the reduced anatase phase and the non-reduced rutile phase can exhibit a blue color. In addition, since the rutile phase exhibits a blue-black color when reduced and the anatase phase exhibits a white color when not reduced, the reduced titanium dioxide including the reduced rutile phase and the non-reduced anatase phase can exhibit a blue color.

[0052] In addition, the step (2) is a step of forming a titanium dioxide complex by stirring a mixed solution in which the reduced titanium dioxide and a non-oxide metal precursor are dispersed in a solvent. Unlike existing methods, the present invention can form a titanium dioxide complex by a simple solution method without heat treatment, light irradiation, or a reducing agent.

[0053] The present invention is such that electrons in the reduced titanium dioxide move toward metal ions through the stirring, thereby reducing the metal and causing it to grow in the form of nanoparticles on the surface of the reduced titanium dioxide. In other words, the metal ions are reduced through spontaneous electron exchange and grown on the surface of the titanium dioxide.

[0054] The non-oxide metal nanoparticles adsorbed and bound to the reduced titanium dioxide surface exist in a more reduced state than the non-oxide metal nanoparticles adsorbed and bound to the non-reduced titanium dioxide surface, and thus, when used as a catalyst for a carbon dioxide reduction reaction, C2 hydrocarbon compounds such as ethylene can be produced.

[0055] In the present invention, when a titanium dioxide composite manufactured by applying non-reduced titanium dioxide instead of reduced titanium dioxide is used as a catalyst for a carbon dioxide reduction reaction, only C1 hydrocarbon compounds such as carbon monoxide and methane are generated, and C2 hydrocarbon compounds such as ethylene are not generated.

[0056] The above non-oxide metal precursor may be a non-oxide metal precursor of at least one metal selected from among W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li, preferably a non-oxide metal precursor of Cu or Pt, more preferably a non-oxide metal precursor of Cu, and even more preferably Cu(NO3)2·2.5H2O.

[0057] In the present invention, when a titanium dioxide composite manufactured by applying an oxide-based metal precursor instead of a non-oxide-based metal precursor is used as a catalyst for a carbon dioxide reduction reaction, only C1 hydrocarbon compounds such as carbon monoxide and methane are generated, and C2 hydrocarbon compounds such as ethylene are not generated.

[0058] The solvent may be a lower alcohol having 1 to 4 carbon atoms, preferably 5 to 20% by volume of methanol, ethanol, propanol or butanol, more preferably 5 to 15% by volume of methanol, ethanol, propanol or butanol, and more preferably 5 to 15% by volume of ethanol.

[0059] The above mixed solution may contain reduced titanium dioxide and a metal precursor in a weight ratio of 100:10 to 30, preferably in a weight ratio of 100:15 to 25, and more preferably in a weight ratio of 100:17 to 20.

[0060] If the reduced metal precursor included in the above mixed solution is less than 10 parts by weight based on 100 parts by weight of the reduced titanium dioxide, a problem may arise in which metal nanoparticles are not observed on the surface of the reduced titanium dioxide or the size of the metal nanoparticles produced becomes excessively small, and if it exceeds 30 parts by weight, a problem may arise in which the size of the metal nanoparticles bonded to the surface of the reduced titanium dioxide becomes excessively large under specific conditions.

[0061] In addition, the mixed solution may contain 100 to 150 parts by weight, preferably 110 to 130 parts by weight, of the mixture of the reduced titanium dioxide and the metal precursor per 100 parts by volume of the solvent.

[0062] When the amount of the mixture of the reduced titanium dioxide and the metal precursor included in the above mixed solution is less than 100 parts by weight per 100 parts by volume of the solvent, the spontaneous electron exchange decreases, thereby reducing the amount of metal nanoparticles adsorbed on the surface of the reduced titanium dioxide. When the amount exceeds 150 parts by weight, a problem may arise in which the size of the formed metal nanoparticles is not uniform.

[0063] Additionally, the pH of the mixed solution may be adjusted to 8 to 11, preferably 9 to 10, before stirring.

[0064] If the pH of the above mixed solution is less than pH 8, the amount of metal nanoparticles formed on the surface of titanium dioxide may decrease, and if the pH exceeds 11, the size of the metal nanoparticles formed on the surface of titanium dioxide may increase, which may cause a problem.

[0065] In the present invention, the stirring may be performed at room temperature for 2 to 10 hours, preferably 4 to 8 hours, and more preferably 5.5 to 6.5 hours. In the present invention, if the stirring time is less than 2 hours, metal nanoparticles are not observed on the surface of the reduced titanium dioxide, and if the stirring time exceeds 10 hours, a problem may arise in which the metal nanoparticles exhibit a crystal structure under specific process conditions.

[0066] The method for manufacturing a titanium dioxide composite of the present invention is advantageous for commercialization because it can be performed using a simple solution method without heat treatment or light irradiation.

[0067] In addition, since the titanium dioxide complex manufactured according to the method of the present invention exists in a more reduced state than metal nanoparticles manufactured according to a conventional method, a C2 compound such as ethylene can be generated during a carbon dioxide reduction reaction using the titanium dioxide complex.

[0068] In one specific example, the titanium dioxide composite manufactured according to the above method may have amorphous non-oxide metal nanoparticles bonded to the surface of reduced titanium dioxide.

[0069] The average diameter of the metal nanoparticles bound to the surface of the above reduced titanium dioxide may be 0.5 to 2 nm, preferably 0.8 to 1.6 nm, and more preferably 1.0 to 1.4 nm.

[0070] In addition, the metal nanoparticles may satisfy the following equation 1.

[0071] [Formula 1]

[0072] 1 ≤ M + / M 2+ ≤ 3

[0073] In the above equation 1,

[0074] M is one or more metals selected from W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li,

[0075] M + is M + is the ratio of the valence state of

[0076] M 2+ is M 2+ is the ratio of the valence states of an element.

[0077] Specifically, the metal nanoparticles (M) are monovalent metal cations (M + ) and divalent metal cations (M 2+ ) and the valence ratio of the monovalent metal cation to the divalent metal cation (M + / M 2+ ) may be 1 to 3, preferably 1.5 to 2.5, and more preferably 1.8 to 2.2.

[0078] The valence ratio of monovalent metal cations to divalent metal cations contained in the above metal nanoparticles (M + / M 2+ ) is less than 1, C2 hydrocarbon compounds such as ethylene cannot be produced when used in a carbon dioxide reduction reaction, and when it exceeds 3, the efficiency of the carbon dioxide reduction reaction decreases, and the ethylene production rate may decrease to less than 1.0 μmol / g·hr.

[0079] In one specific example, the metal nanoparticles are Cu nanoparticles, and more specifically, Cu + / Cu 2+ It may be included as 1 to 3, preferably 1.5 to 2.5, more preferably 1.8 to 2.2.

[0080] In particular, although not explicitly described in the following examples or comparative examples, etc., in the method for producing a titanium dioxide composite according to the present invention, the catalytic performance of the titanium dioxide composite was confirmed while changing i) the composition of reduced titanium dioxide, ii) the type of metal precursor, iii) the type of solvent, iv) the weight ratio of the reduced titanium dioxide and the metal precursor included in the mixed solution, v) the mixing ratio of the mixture of the reduced titanium dioxide and the metal precursor included in the mixed solution, and the solvent, vi) the pH of the mixed solution, and vii) the stirring time.

[0081] As a result, unlike under other conditions and in other numerical ranges, only when all of the conditions below are satisfied, no loss of metal nanoparticles within the titanium dioxide composite was observed even after more than 300 carbon dioxide reduction reactions, and the initial carbon dioxide reduction reaction efficiency was the same as that of the carbon dioxide reduction reaction over 300 times within the error range of the measuring device, confirming excellent durability.

[0082] i) The reduced titanium dioxide includes an amorphous rutile phase, ii) The metal precursor is Cu(NO3)2·2.5H2O, iii) The solvent is 5 to 20 volume% of ethanol, iv) The mixed solution includes the reduced titanium dioxide and the metal precursor in a weight ratio of 100:15 to 20, v) The mixed solution includes 110 to 130 parts by weight of the mixture of the reduced titanium dioxide and the metal precursor with respect to 100 parts by volume of the solvent, vi) The pH of the mixed solution is adjusted to 9 to 10 before the stirring, vii) The stirring is performed at room temperature for 5.5 to 6.5 hours.

[0083] Meanwhile, if any one of the above conditions i) to vii) is not satisfied, it is not desirable in that the loss of metal nanoparticles in the titanium dioxide complex is observed after 300 carbon dioxide reduction reactions, which may lower the carbon dioxide reduction reaction efficiency.

[0084]

[0085] In addition, the present invention relates to a titanium dioxide composite comprising reduced titanium dioxide; and amorphous non-oxide metal nanoparticles combined with the reduced titanium dioxide.

[0086] The above titanium dioxide complex may be manufactured by the above-described method.

[0087] The above titanium dioxide complex is a composite in which amorphous non-oxide metal nanoparticles are bonded or adsorbed to the surface of reduced titanium dioxide.

[0088] The average diameter of the above metal nanoparticles may be 0.5 to 2 nm, preferably 0.8 to 1.6 nm, and more preferably 1.0 to 1.4 nm.

[0089] If the average diameter of the metal nanoparticles is less than 0.5 nm, they may exist in the form of single atoms or copper clusters rather than nanoparticles, and if it exceeds 2 nm, the surface area of ​​the metal nanoparticles may decrease, which may cause a problem in that the efficiency of the carbon dioxide reduction reaction decreases.

[0090] In addition, the metal nanoparticles may satisfy the following equation 1.

[0091] [Formula 1]

[0092] 1 ≤ M + / M 2+ ≤ 3

[0093] In the above equation 1,

[0094] M is one or more metals selected from W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li,

[0095] M + is M + is the ratio of the valence state of

[0096] M 2+ is M 2+ is the ratio of the valence states of an element.

[0097] Specifically, the metal nanoparticles (M) are monovalent metal cations (M + ) and divalent metal cations (M 2+ ) and the valence ratio of the monovalent metal cation to the divalent metal cation (M + / M 2+ ) may be 1 to 3, preferably 1.5 to 2.5, and more preferably 1.8 to 2.2.

[0098] The valence ratio of monovalent metal cations to divalent metal cations contained in the above metal nanoparticles (M + / M 2+ ) is less than 1, C2 hydrocarbon compounds such as ethylene cannot be produced when used in a carbon dioxide reduction reaction, and when it exceeds 3, the efficiency of the carbon dioxide reduction reaction decreases, and the ethylene production rate may decrease to less than 1.0 μmol / g·hr.

[0099] In one specific example, the metal nanoparticles are Cu nanoparticles, and more specifically, Cu + / Cu 2+ It may be included as 1 to 3, preferably 1.5 to 2.5, more preferably 1.8 to 2.2.

[0100] The above titanium dioxide complex may include reduced titanium dioxide and metal nanoparticles in a weight ratio of 1:0.02 to 0.2, preferably 1:0.02 to 0.1, more preferably 1:0.02 to 0.08, more preferably 1:0.03 to 0.07, and more preferably 1:0.04 to 0.06.

[0101] When the metal nanoparticles included in the titanium dioxide complex are less than 0.02 parts by weight based on 1 part by weight of reduced titanium dioxide, the ratio of the metal nanoparticles on the titanium dioxide complex may be insufficient, so that ethylene may not be produced or the ethylene production rate may decrease to less than 1.0 μmol / g·hr. When the ratio exceeds 0.2 parts by weight, the ratio of the metal nanoparticles on the titanium dioxide complex may be excessive, so that the light absorption efficiency may be lowered, resulting in a problem of a decrease in the ethylene production rate.

[0102] The above titanium dioxide complex can be used as a catalyst for carbon dioxide reduction.

[0103] The products of the carbon dioxide reduction reaction using the above titanium dioxide complex include CH4, CO and C2H4.

[0104] Specifically, the titanium dioxide composite according to the present invention can photocatalytically reduce carbon dioxide to produce CH4, CO and C2H4, and in particular, can produce high value-added C2H4 at a rate of 1.0 μmol / g·hr or more, specifically 1.0 to 2.5 μmol / g·hr, more specifically 1.5 to 2.5 μmol / g·hr, more specifically 1.5 to 2.0 μmol / g·hr, and even more specifically 1.8 to 2.0 μmol / g·hr, can produce CO at a rate of 1.0 μmol / g·hr or more, specifically 1.0 to 10 μmol / g·hr, more specifically 3 to 7 μmol / g·hr, more specifically 4 to 6 μmol / g·hr, and even more specifically 4.5 to 5.5 μmol / g·hr, and can produce CH4 at a rate of 1.0 μmol / g·hr or more, specifically 1.0 It can be produced at a rate of ~ 5 μmol / g·hr, more specifically 1.5 to 3 μmol / g·hr, and even more specifically 1.8 to 2.5 μmol / g·hr.

[0105] In addition, the titanium dioxide composite according to the present invention can be reused while maintaining a constant amount of ethylene production.

[0106] In particular, although not explicitly described in the following examples or comparative examples, the catalytic performance was confirmed by changing ① the type of metal, ② the average diameter of metal nanoparticles, ③ the ratio of monovalent metal cations / divalent metal cations of the metal nanoparticles, ④ the weight ratio of reduced titanium dioxide and metal nanoparticles included in the titanium dioxide complex, ⑤ the crystal structure, etc. of the titanium dioxide complex according to the present invention.

[0107] As a result, unlike under other conditions and in other numerical ranges, only when all of the conditions below are satisfied, no loss of metal nanoparticles within the titanium dioxide composite was observed even after more than 300 carbon dioxide reduction reactions, and the initial carbon dioxide reduction reaction efficiency was the same as that of the carbon dioxide reduction reaction over 300 times within the error range of the measuring device, confirming excellent durability.

[0108] ① The metal nanoparticles are Cu nanoparticles, ② the average diameter of the metal nanoparticles is 1.0 to 1.4 nm, ③ the ratio of monovalent metal cations / divalent metal cations contained in the metal nanoparticles is 1.8 to 2.2, ④ the titanium dioxide complex is a weight ratio of reduced titanium dioxide and metal nanoparticles of 1:0.04 to 0.06, ⑤ TEM analysis results show that it has an amorphous structure.

[0109] Meanwhile, if any one of the above conditions ① to ⑤ is not satisfied, it is not desirable in that the loss of metal nanoparticles in the titanium dioxide complex may be observed after 300 or more carbon dioxide reduction reactions, which may lower the carbon dioxide reduction reaction efficiency.

[0110]

[0111] In addition, the present invention relates to a photocatalyst comprising the above titanium dioxide complex.

[0112] In one specific example, the photocatalyst may be a catalyst for reducing carbon dioxide, and specifically, may reduce carbon dioxide to produce CH4, CO and C2H4, and in particular, may produce high value-added C2H4 at a rate of 1.0 μmol / g·hr or more, specifically 1.0 to 2.5 μmol / g·hr, more specifically 1.5 to 2.5 μmol / g·hr, more specifically 1.5 to 2.0 μmol / g·hr, and even more specifically 1.8 to 2.0 μmol / g·hr, may produce CO at a rate of 1.0 μmol / g·hr or more, specifically 1.0 to 10 μmol / g·hr, more specifically 3 to 7 μmol / g·hr, more specifically 4 to 6 μmol / g·hr, and even more specifically 4.5 to 5.5 μmol / g·hr, and may produce CH4 at a rate of 1.0 μmol / g·hr or more, Specifically, it can be produced at a rate of 1.0 to 5 μmol / g·hr, more specifically, 1.5 to 3 μmol / g·hr, and even more specifically, 1.8 to 2.5 μmol / g·hr.

[0113] Conventional photocatalysts for carbon dioxide reduction required noble metal catalysts and electrolyte additives in an overcurrent state for the carbon dioxide reduction reaction, but the photocatalyst including the titanium dioxide composite of the present invention can reduce carbon dioxide to produce high value-added ethylene and the like without using the noble metal catalyst.

[0114]

[0115] Hereinafter, the present invention will be described in detail by examples, but the present invention is not limited to the following examples.

[0116]

[0117] <Example>

[0118] Example: Titanium dioxide composite (Cu / TiO 2-x )

[0119] (1) Reduced titanium dioxide (TiO 2-x ) manufacturing

[0120] Li metal (0.56 mg) was dissolved in 80 mL of ethylenediamine (EDA 99%, Junsei) to prepare a 1 mmol / mL Li / EDA solution. TiO2 nanoparticles including anatase and rutile phases (anatase, size: ~21 nm, rutile, size: ~140 nm, P-25, size: 20~40 nm) were added to the Li / EDA solution and stirred for 6 days. The reaction was performed under sealed and anhydrous conditions. After sufficient reaction, 0.1 M HCl solution was slowly added dropwise to the mixture to quench the excess electrons and form a Li salt. Thereafter, the obtained product was washed several times with deionized water and dried at room temperature under vacuum conditions to obtain reduced titanium dioxide (Blue TiO). 2-x ) was obtained.

[0121] In this specification, “TiO 2-x " means oxygen-deficient titanium dioxide, i.e. reduced titanium dioxide.

[0122] (2) Cu / TiO 2-x Manufacturing of

[0123] (1) Reduced titanium dioxide (Blue TiO) manufactured in step 2-x ) 100 mg and Cu(NO3)2·2.5H2O (98%, Sigma Aldrich) 18.3 mg were dispersed in 100 ml of 10% (v / v) ethanol to prepare a mixed solution, and the pH of the mixed solution was adjusted to pH 9.5 using NaOH. Thereafter, the mixed solution was stirred at room temperature for 6 hours. The reactant was centrifuged, washed several times with deionized water, and dried to obtain a titanium dioxide complex (Cu / TiO 2-x ) was obtained. The titanium dioxide complex (Cu / TiO 2-x ) is TiO 2-x and Cu nanoparticles at a weight ratio of 1:0.05.

[0124]

[0125] Comparative example

[0126] A mixed solution was prepared by dispersing 100 mg of TiO2 nanoparticles (nanopowder, 21 nm primary particle size (TEM), ≥ 99.5% trace metal basis, Sigma Aldrich) and 18.3 mg of Cu(NO3)2·2.5H2O (98%, Sigma Aldrich) in 100 ml of 10% (v / v) ethanol, and the pH of the mixed solution was adjusted to pH 9.5 using NaOH. Thereafter, the mixed solution was irradiated with light for 6 hours using a 150 W Xe lamp solar simulator (PEC-L01, PECCELL) to obtain a titanium dioxide composite (Cu / TiO2).

[0127]

[0128] <Experimental Method>

[0129] TEM analysis

[0130] (S)TEM analyses were performed using a dual Cs-corrected (CETCOR and ASCOR, CEOS) field-emission TEM instrument (JEM-ARM 200F, JEOL) operating at 80 kV. HR-TEM images were captured using a 4096 × 4096 pixel COMS camera (Gatan OneView Camera, USA). Low-loss EELS was performed to analyze the qualitative differences in the electronic structure. Low-loss EELS between the zero-loss peak and the core-loss edge was expressed by measuring the plasmon excitation energy. Spectra were acquired at 80 kV using an EEL spectrometer (Gatan GIF Quantum ER 965, USA) in a STEM instrument (JEM-ARM 200F, JEOL) equipped with a spherical aberration corrector (ASCOR, CEOS) with an energy resolution of 0.6 eV. The probe convergence and collection angles were 23 mrad and 36 mrad, respectively.

[0131]

[0132] Characterization method

[0133] X-ray absorption fine structure (XAFS) measurements were performed at the 8C nanoprobe XAFS beamline (BL8C) of the Pohang Light Source (PLS-II). The energy of the storage ring electron beam was 3.0 GeV with a ring current of ~360 mA. The X-ray beam was monochromated with a Si(111) double crystal, where the beam intensity was reduced by 30% to eliminate higher-order harmonics. The X-ray beam was delivered to a secondary source aperture with a beam size adjusted to 0.5 mm (v) × 1 mm (h). XAFS spectra were collected in fluorescence mode using a Xi drift detector. The obtained XAFS spectra were processed using Demeter software. The EXAFS spectra were Fourier transformed using a Hanning window ranging from 1.0 Å to 3.1 Å. The amplitude attenuation factor (So2) was set to 0.8. XPS spectra were obtained using an X-ray photoelectron spectrometer (Nexsa, Therma Scientific). XRD patterns were analyzed using an X-ray diffractometer (Ultima IV, Rigaku). XPS measurements were performed using a K-alpha instrument (Thermo Scientific Inc.) equipped with an aluminum anode (Al Kα = 1486.6 eV). The X-ray power for the measurements was 12 kV at 3 mA.

[0134]

[0135] Photocatalytic activity measurement

[0136] Photocatalytic CO2RR was performed at 100 mW / cm by a 500 W high pressure Hg lamp (OPM2-502HQ, USHIO). 2 The experiment was performed using a quartz reactor (160 mL) that investigated the illumination of Cu / TiO2 and Cu / TiO 2-xThe photocatalyst (20 mg) was dispersed in 70 ml of deionized water, and the suspension was purged with CO2 gas for 30 min. The suspension was continuously stirred to ensure uniform photoirradiation during the CO2RR. The generated gaseous product was analyzed by gas chromatography (7890B GC system, Agilent) every 30 min, and the liquid product was analyzed by 400 MHz FT-NMR spectroscopy (AVANCE III HD 400, Bruker Biospin). The same reactor was purged again after each reaction cycle for reusability testing.

[0137]

[0138] DFT calculation

[0139] DFT calculations were performed using VASP (Vienna ab initio simulation package). Exchange-correlation effects were accounted for using the Perdew-Burke-Ernzerhof functional, and the projector-augmented wave pseudopotential was used. A kinetic energy cutoff of 400 eV was used to account for plane-wave expansion. The spin-polarized DFT + U method using Dudarev's approach was used to account for the localization of Coulomb interactions and unrealistic self-interactions in the DFT calculations. In this model, the effective value (Ueff) for Ti was 4.2 eV, and for Cu, 7 eV. The Brillouin zone was sampled using a 2 × 2 × 1 Monkhorst-Pack k-point grid for the TiO2 slab model calculations. The most stable (110) plane of the rutile TiO2 surface was used in the slab model. The top layer and adsorbates were fully relaxed, while the bottom two layers were fixed. The convergence criterion for energy for self-consistent field (SCF) iterations is 1 x 10 -5 eV. The force on each atom was 0.03 eV·Å -1All calculations were relaxed until they became smaller. Using the equation below, the DFT energy was corrected by zero-point energy (ZPE) and entropy (S) to obtain the Gibbs free energy.

[0140] △G=△E+△ZPE-T△S

[0141] In the above equation, E represents the DFT energy, ZPE represents the zero-point energy, T represents the temperature, and S represents the entropy. The vibrational frequencies for ZPE correction and entropy calculation were determined using density functional perturbation theory.

[0142]

[0143] <Experimental Results>

[0144] Test Example 1: Reduced TiO 2-x Charge-mediated nucleation of Cu nanoparticles in the surface layer

[0145] Cu / TiO according to an embodiment of the present invention 2-x Silver reduced TiO 2-x The Cu nanoparticles are charge-mediated coupled in the surface layer, which is different from the photoreduction of Cu / TiO2 according to the comparative example (Fig. 1a).

[0146] Looking at Figure 1a, the photoreduction of the comparative example (left side of Figure 1a) is the high-energy photoelectrons generated from TiO2 are reduced to Cu O (reduced Cu O ) and the photoelectrons combine with adsorbed oxygen molecules to form oxygen anions. Then, the oxygen anions oxidize the surface of Cu nanoparticles to form Cu 2+ forms a dominant CuO and minimizes the surface energy through particle maturation. In contrast, charge-mediated nucleation under dark conditions according to an embodiment of the present invention (right side of Fig. 1a) is TiO 2-x Ti on the surface 3+Itinerant electrons within the 3d orbitals of Cu undergo site-specific redox interactions. + It forms the dominant Cu2O.

[0147]

[0148] The Cu nanoparticles on the titanium dioxide composite according to the above examples and comparative examples were comparatively analyzed using high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS), respectively.

[0149] As a result, it was confirmed that the average size of the photoreduced Cu nanoparticles on the titanium dioxide composite according to the comparative example was about 2.1 nm (Figs. 1b and 1c), while the average size of the Cu nanoparticles on the titanium dioxide composite according to the embodiment of the present invention was about 1.2 nm (Figs. 1d and 1e).

[0150] Also, Cu / TiO according to the embodiment 2-x It was confirmed that the Cu nanoparticles formed on the surface exhibited a somewhat disordered or amorphous atomic structure (Fig. 2a), whereas the Cu nanoparticles formed on the Cu / TiO2 surface according to the comparative example exhibited a well-crystallized face-centered cubic (fcc) structure (Fig. 2b).

[0151]

[0152] Meanwhile, Cu / TiO of the present invention 2-x To monitor the nucleation and growth of Cu nanoparticles formed on the surface, the same procedure as in the example was performed but the stirring time was varied to 1 hour, 6 hours, 24 hours, and 72 hours, and Cu / TiO 2-x was manufactured.

[0153] Looking at Figure 3, Cu / TiO with a stirring time of 1 hour 2-x When manufacturing TiO 2-xIt can be confirmed that Cu nanoparticles are not observed at all on the surface and exist in the form of a seed layer.

[0154] Also, looking at Figure 4, Cu / TiO manufactured by stirring for 6 hours, 24 hours, and 72 hours 2-x is TiO 2-x Cu nanoparticles are observed on the surface, and it can be confirmed that the Cu nanoparticles grow as the stirring time increases. In particular, Cu / TiO manufactured by stirring for 6 hours 2-x In , the Cu nanoparticles had the smallest average size (1.2 nm), were uniformly dispersed, and exhibited an amorphous atomic arrangement structure that was ideal for controlling surface catalytic reactions in an aqueous environment. This amorphous structure indicates that the formation of Cu nanoparticles occurred through a two-step crystallization mechanism, i.e., nucleation in an amorphous phase and subsequent crystallization. Meanwhile, Cu / TiO prepared by stirring for 24 and 72 hours 2-x In this case, the Cu nanoparticles exhibited a distinct crystal structure.

[0155] Oxygen-deficient, reduced TiO 2-x Ti on the surface 3+ To confirm the site-specific binding of Cu nanoparticles to TiO, electron energy loss spectroscopy (EELS) was used. 2-x The atomic states of Cu and Ti at the interface were confirmed.

[0156] Bulk TiO2 to TiO 2-x The surface of, Four sampling areas among Cu were shown in HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) images (Fig. 1f).

[0157] Looking at Fig. 1f, the EELS Ti-L2,3 edge corresponding to the bulk region (region 1, green) is e for the Ti L2 and L3 edges, respectively. g and t 2g The peak was clearly visible, indicating that Ti of crystalline TiO2 4+ is a characteristic. In addition, the EELS Ti-L2,3 edge corresponding to region 2 (orange) near the surface is partially merged e g and t 2g The EELS Ti-L2,3 edge of region 2 is generally consistent with the low-energy loss region 3 (red), which is a result of reduced TiO 2-x Ti of 3+ is a characteristic of Cu / TiO. For reference, Cu / TiO 2-x Since the XRD pattern shows that the crystalline rutile peak (R) almost completely disappears compared to TiO2 (Fig. 5), the TiO 2-x It can be seen that it has an amorphous (disordered) atomic structure.

[0158] In addition, Cu nanoparticles (area 4, blue) did not produce a Ti-L2,3EEL signal, indicating that SMSI (strong metal-support interaction)-induced oxide encapsulation did not occur. Considering that there were no photogenerated electrons involved in the reduction process, the Cu-Ti 3+ The combination of the above amorphous TiO 2-x It can be seen that this is due to charge mediation through local electrons on the surface.

[0159]

[0160] Figure 1g shows the Cu / TiO2 and Cu / TiO 2-x Cu-L2,3EEL spectrum corresponding to the center of each Cu nanoparticle. In Fig. 1g, the spectrum of the Cu / TiO2 (green) is the CuO (Cu 2+) showed a main peak at ~934 eV, which is the same as that of Cu / TO. 2-x The spectrum of (blue) is Cu2O(Cu + ) showed a main peak at 935.5 eV, which is the same as that of Cu / TiO. In addition, the Cu / TiO 2-x The EEL spectrum of showed unique and broad peaks at 939 eV, 943 eV, and 947 eV.

[0161]

[0162] Cu / TiO of the present invention 2-x In the above TiO 2-x The Cu nanoparticles on the surface have a lower valence state and an irregular atomic coordination, which can be usefully utilized in photocatalytic CO2RR. The Cu nanoparticles are TiO 2-x It is stabilized at the nucleation stage on the surface.

[0163]

[0164] Test Example 2: Cu / TiO 2-x Analysis of my Cu nanoparticles

[0165] Cu / TiO2 of the example -x And the atomic structure of each Cu nanoparticle of Cu / TiO2 in the comparative example was analyzed by XAS (X-ray absorption spectroscopy) and EXAFS (Extended X-ray absorption fine structure) (Fig. 6 and Table 1). In Table 1 below, N is the coordination number, R is the interatomic distance, and δ 2 is the Debye-Waller factor (binding disorder), and R-factor is the quality criterion of the EXAFS fit.

[0166] Distinction PathNR(Å)δ 2(Å)R-factor(%)ExampleCu-O41.96±0.010.005±0.0010.2Cu-Ti23.06±0.010.015±0.002Cu-O-Ti123.48±0.010.010±0.001Comparative ExampleCu-O41.95±0.010.005±0.0010.6Cu-Ti23.03±0.010.011±0.002Cu-O-Ti83.46±0.010.008±0.001

[0167] In Fig. 6a and Table 1, Cu-L 2,3 The Fourier transform extended X-ray absorption fine structure (FT-EXAFS) spectrum of the edge shows three features at radial distances of 1.5 Å, 2.5 Å, and 2.7 Å, which correspond to Cu-O, Cu-Ti, and Cu-O-Ti bonds, respectively. The oxygen deficiency (Vo) on the TiO2 surface is attributed to Cu 2+ Ti interacts strongly with metal precursors 3+ -Vo-Cu + moiety, which induces reversible charge transfer between Ti and Cu, resulting in Cu + stabilizes. Therefore, the Cu / TiO of the embodiment 2-x Compared to Cu / TiO2 of the comparative example, it has a lower Cu-Ti magnitude and a higher Cu-O-Ti FT magnitude, and the Cu-O-Ti coordination number increases. In addition, Cu / TiO of the example 2-x Since both Cu / TiO2 of the comparative example have Cu-O coordination, which is the main characteristic of Cu / TiO2, the above change in local coordination structure indicates that there is a connection between Cu and oxygen deficiency that can induce local charge transfer.

[0168] Figure 6b is Cu / TiO of the embodiment 2-xAnd the surface state of each Cu nanoparticle of Cu / TiO2 in the comparative example was analyzed using Cu L-edge soft-XAS. Cu / TiO at photoelectron energies of 939 eV and 956 eV within the Cu L3 and L2 edges. 2-x The Auger electron yield (AEY) of Cu + is increasing and Cu 2+ indicates that it remains relatively constant. Cu / TiO of the example 2-x And Cu nanoparticles of Cu / TiO2 in the comparative example all have a unique mixed valence state (Cu + Wow Cu 2+ ) but the Cu / TiO of the present invention 2-x Cu-Ti in 3+ Charge-mediated coupling involving Cu + The atomic ratio of the .

[0169]

[0170] Figure 6c and Table 2 below show Cu / TiO of the example 2-x And the surface oxidation state of each Cu / TiO2 in the comparative example was analyzed by X-ray photoelectron spectroscopy (XPS), Cu + / Cu 2+ ratio (Cu 2+ Cu for + The atomic ratio of Cu / TiO is directly compared. Table 2 below shows the Cu / TiO of the examples. 2-x And the area of ​​the deconvoluted peak region in the Cu 2P XPS spectrum of each of Cu / TiO2 (a) as-synthesized and (b) after CO2RR is expressed as a percentage.

[0171] (a) Synthetic state (b) After CO2RR Area%Cu + / Cu 2+ ratioArea%Cu + / Cu 2+ ratio example Cu + 58.581.94Cu +70.163.41Cu 2+ 30.26Cu 2+ 20.57 Comparison Example Cu + 27.390.49Cu + 29.520.52Cu 2+ 57.27Cu 2+ 56.05

[0172] Looking at Table 2 and Figure 6c above, Cu in the Cu 2P XPS spectrum + (green) and Cu 2+ Cu in Cu / TiO2 according to the comparative example from the deconvoluted peak corresponding to (blue) + / Cu 2+ The ratio of (Cu 2+ Cu for + The atomic ratio of Cu) is 0.49 and the strong and broad Cu at ~942 eV 2+ It can be confirmed that the satellite peaks based on the Cu / TiO 2-x Cu of + / Cu 2+ ratio (Cu 2+ Cu for + The atomic ratio of Cu is 1.94. + Ga Cu 2+ It can be confirmed that it is about twice as much as Cu / TiO according to the example. 2-x Cu nanoparticles are relatively Cu 2+ Unlike the comparative examples that are rich in Ti 3+ Cu by local charge mediation through + As it increases further, it is more advantageous for CO2RR.

[0173] Also, Cu / TiO of the example under actual CO2RR experimental conditions using lighting 2-x The ex situ Cu 2P XPS spectra of Cu / TiO2 and comparative examples were analyzed (Table 2 and Fig. 6d).

[0174] As a result, as shown in Table 2 and Fig. 6d, Cu / TiO2 of the comparative example in the photocatalytic CO2RR has Cu+ / Cu 2+ While the ratio was maintained at 0.52, Cu / TiO of the example 2-x Cu is further reduced to Cu + / Cu 2+ The ratio increased from 1.94 to 3.41.

[0175]

[0176] Test Example 3: Cu / TiO 2-x Photocatalytic CO2RR activity of

[0177] Cu / TiO2 of the comparative example, and Cu / TiO of the example manufactured by varying the stirring time to 1 hour, 6 hours, and 24 hours 2-x The photocatalytic CO2RR activity was measured (Fig. 7a).

[0178] Figure 7a shows Cu / TiO2 of a comparative example and Cu / TiO of an example manufactured while varying the stirring time to 1 hour, 6 hours, and 24 hours. 2-x It shows the accumulated products in CO2RR using. Looking at Fig. 7a, the charge-mediated coupling sample Cu / TiO according to the embodiment 2-x It can be confirmed that Cu / TiO2 according to the comparative example produces only general C1 products (CH4 and CO), while producing C2H4. In particular, Cu / TiO of the example manufactured with a stirring time of 6 hours 2-x In the case of the Cu / TiO of the example manufactured by varying the stirring time to 1 hour, 6 hours, and 24 hours, the production of CH4 and C2H4 was greatly increased, but the CO2RR activity was decreased overall. Figures 7b-d show the Cu / TiO of the example manufactured by varying the stirring time to 1 hour, 6 hours, and 24 hours. 2-x It shows the production rates of CH4, CO and C2H4 in CO2RR using. In particular, Cu / TiO of the example manufactured with a stirring time of 6 hours 2-xIn this case, the CH4 production rate is 2.09 μmol / g·hr, the CO production rate is 5.04 μmol / g·hr, and the C2H4 production rate is 1.85 μmol / g·hr, which are significantly higher rates than the comparative example Cu / TiO2 (CH4 production rate 0.38 μmol / g·hr, CO production rate 3.74 μmol / g·hr).

[0179]

[0180] Cu (Cu) in metallic form 0 ) can act as an active site of the photocatalytic CO2RR. In order to confirm this, Cu / TiO was prepared by stirring for 6 hours. 2-x was heat-treated at 350°C for 2 hours under inert conditions (Ar). According to the heat treatment, the Cu / TiO of the present invention 2-x The Cu is reoxidized to TiO2, thereby forming Cu 0 can be reduced to

[0181] The above Cu / TiO 2-x and heat-treated Cu / TiO 2-x (Cu / TiO 2-x The FT-EXAFS spectra of AT) are compared and shown in Table 3 below.

[0182] Distinction PathNR(Å)δ 2 (Å)R-factor(%)Cu / TiO 2-x Cu-O41.96±0.010.005±0.0010.2Cu-Ti23.06±0.010.015±0.002Cu-O-Ti123.48±0.010.010±0.001Cu / TiO 2-x ATCu-O31.93±0.020.007±0.0010.5Cu-Cu32.55±0.020.008±0.001Cu-Ti23.04±0.050.015±0.007Cu-O-Ti83.42±0.030.011±0.003

[0183] Looking at Table 3 above, heat-treated Cu / TiO 2-x (Cu / TiO 2-xAT) indicates a metallic Cu-Cu bond, and it can be confirmed that the Cu-O-Ti coordination is reduced again to the level of Cu / TiO2 of the comparative example.

[0184] Looking at Figure 7e, the Cu 0 Combined heat-treated Cu / TiO 2-x (Cu / TiO 2-x AT) can be confirmed that the production of CH4 and C2H4 is dramatically reduced. This is because the Cu 0 This means that CO2RR plays a detrimental role.

[0185] Also, Cu / TiO of the embodiment 2-x The production amount of C2H4 accumulated through photocatalytic CO2RR using Cu / TiO was measured. 2-x The cycle of washing and reusing (CO2RR per cycle for 3 hours) was performed three times (Fig. 8). Looking at Fig. 8, the Cu / TiO of the example 2-x It can be confirmed that the production of C2H4 accumulated through CO2RR remains constant even after washing and reuse.

[0186]

[0187] Experimental Example 4: Dimerization Pathway of C2H4

[0188] To understand the CO2RR adsorption behavior for C2H4 production of Cu / TiO2, density functional theory (DFT) calculations were performed.

[0189] For reference, as shown in Fig. 9, a rutile TiO2(110) crystal slab with bridging oxygen (red) for Cu adsorption was modeled. Also, as shown in Fig. 10, Cu + (yellow) is stably cross-linked and adsorbed to oxygen (red) (c, d in Fig. 10), whereas Cu 2+(Yellow) was directly adsorbed on oxygen (red) (Fig. 10a, b), which was stabilized by interaction with adjacent Ti atoms (gray).

[0190]

[0191] Currently, the overall CO2RR mechanism for C2H4 production is known to occur via OCCO dimerization. However, photocatalytic CO2RR for C2H4 production under aqueous conditions involves more complex multistep reactions.

[0192] The DFT calculation results in Fig. 11a show that CO2 is Cu + (-1.68 eV) and Cu 2+ (-2.31 eV) can be easily reduced to adsorbed CO(*CO) via the *COOH intermediate, but Cu 2+ indicates that Cu is more preferred. Nevertheless, Cu 2+ The direct bond dimerization of *CO to *OCCO (-1.41 eV) involves a high energy barrier that is difficult to overcome considering the spontaneity of the photocatalytic reaction. Instead, a series of hydrogenation pathways toward *CHO (-3.43 eV) leading to *CHOH (-4.87 eV) are favored, and the spontaneous dimerization pathway of *COCHO (-1.42 eV) is energetically forbidden. On the other hand, C + The subsequent reaction of *CO(-1.68 eV) is strongly favored by the C2 pathway initiated by the close-bond adsorption of *CO(*CO + *CO, -3.9 eV). Here, the direct C-C coupling of *OCCO(-4.16 eV) and *HOCCOH(-8.87 eV), induced by the coupling of the hydrogenated *COH half, respectively, as intermediates for C2H4 production, was calculated to release very large energies.

[0193] Figure 11b is Cu + and Cu 2+ represent the adsorption pathways that produce C2 and C1 products, respectively.

[0194] Also, Cu 2+ / TiO2 and Cu + / TiO 2-x The relative dimerization energies between (*+CO ~ *+2CO) were investigated respectively. Figure 11c shows Cu 2+ / TiO2 is energetically unstable after dimerization, whereas Cu + / TiO 2-x It is very stable and is advantageous for the production of C2 hydrocarbon compounds.

[0195] Therefore, Cu + / Cu 2+ The Cu / TiO of the present invention, which is oxygen-stabilized, has a working valence state ratio of 3.0 or more, preferably 3.0 to 4.0, more preferably 3.2 to 3.6. 2-x is Cu + -It is an ideal photocatalyst that can spontaneously produce C2H4 through dimerization.

[0196]

[0197] The method for producing a titanium dioxide composite according to the present invention comprises the steps of: driving unassisted photocatalytic CO2RR through a simple dark condition deposition method; and producing C2H4 under simple dispersed aqueous conditions using Cu + / TiO 2-x cast TiO of the present invention was synthesized. 2-x The strategically designed charge-mediated coupling under oxygen-free and site-specific environmental conditions provided by enables spontaneous stabilization of low-valence Cu without the assistance of photogenerated electrons. The present method for controlling the electronic state of Cu, which is prone to autooxidation, suggests that it can be extended to the synthesis of metal-supported heterocatalysts. The DFT results of the present invention show that Cu + It indicates that C2H4 can be stably produced at a rate of 1.85 μmol / g·hr by favoring the CC bonding pathway of both *OCCO and *HOCCOH.

[0198]

[0199] Although the present invention has been described with reference to the preferred embodiments mentioned above, various modifications and variations are possible without departing from the spirit and scope of the invention. Furthermore, the appended claims encompass such modifications and variations as fall within the spirit of the present invention.

Claims

1. (1) A step of obtaining reduced titanium dioxide by mixing titanium dioxide with a reducing agent; and (2) A method for producing a titanium dioxide composite, comprising: a step of forming a titanium dioxide composite by stirring a mixed solution in which the reduced titanium dioxide and a non-oxide metal precursor are dispersed in a solvent; A method for producing a titanium dioxide composite, characterized in that the titanium dioxide composite comprises reduced titanium dioxide; and amorphous non-oxide-based metal nanoparticles combined with the reduced titanium dioxide.

2. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the above-mentioned reduced titanium dioxide includes an amorphous rutile phase.

3. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the metal is at least one selected from among W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li.

4. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the metal precursor is Cu(NO3)2·2.5H2O.

5. In paragraph 1, A method for producing a titanium dioxide complex, characterized in that the solvent is a lower alcohol having 1 to 4 carbon atoms.

6. In paragraph 1, A method for producing a titanium dioxide complex, characterized in that the solvent is 5 to 20 volume% of methanol, ethanol, propanol or butanol.

7. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the above mixed solution contains reduced titanium dioxide and a metal precursor in a weight ratio of 100:10 to 30.

8. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the above mixed solution contains 100 to 150 parts by weight of the mixture of the reduced titanium dioxide and the metal precursor relative to 100 parts by volume of the solvent.

9. In paragraph 1, A method for producing a titanium dioxide complex, characterized in that the pH of the above mixed solution is adjusted to 8 to 11 before the stirring.

10. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the above stirring is performed at room temperature for 2 to 10 hours.

11. In paragraph 1, The above reduced titanium dioxide contains an amorphous rutile phase, The above metal precursor is Cu(NO3)2·2.5H2O, The solvent is 5 to 20% by volume of ethanol, The above mixed solution contains reduced titanium dioxide and a metal precursor in a weight ratio of 100:15 to 20, The above mixed solution contains 110 to 130 parts by weight of the mixture of the reduced titanium dioxide and the metal precursor per 100 parts by volume of the solvent, The above mixed solution has its pH adjusted to 9 to 10 before stirring. A method for producing a titanium dioxide composite, characterized in that the above stirring is performed at room temperature for 5.5 to 6.5 hours.

12. In paragraph 1, A method for producing a titanium dioxide composite, characterized in that the average diameter of the metal nanoparticles is 0.5 to 2 nm.

13. In paragraph 1, A method for producing a titanium dioxide composite, wherein the metal nanoparticles satisfy the following formula 1: [Formula 1] 1 ≤ M + / M 2+ ≤ 3 In the above equation 1, M is one or more metals selected from W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li, M + is M + is the ratio of the valence state of M 2+ is M 2+ is the ratio of the valence states of an element.

14. Reduced titanium dioxide; and A titanium dioxide composite comprising amorphous non-oxide metal nanoparticles combined with the above reduced titanium dioxide.

15. In paragraph 14, A titanium dioxide composite characterized in that the average diameter of the metal nanoparticles is 0.5 to 2 nm.

16. In paragraph 14, The above metal nanoparticles are titanium dioxide composites characterized by satisfying the following formula 1: [Formula 1] 1 ≤ M + / M 2+ ≤ 3 In the above equation 1, M is one or more metals selected from W, Mo, Cr, Re, Ir, Ta, Hf, Fe, Ni, Cu, Zn, Mn, Y, Zr, Sn, V, Bi, Sr, Ti, Ca, Nb, K, Na and Li, M + is M + is the ratio of the valence state of M 2+ is M 2+ is the ratio of the valence states of an element.

17. In paragraph 14, The above titanium dioxide complex is characterized in that it contains reduced titanium dioxide and metal nanoparticles in a weight ratio of 1:0.02 to 0.

2.

18. In paragraph 14, The above titanium dioxide complex is a non-crystalline non-oxide metal nanoparticle bonded to the surface of reduced titanium dioxide, The above metal nanoparticles are Cu nanoparticles, The average diameter of the above metal nanoparticles is 1.0 to 1.4 nm, A titanium dioxide composite characterized in that the metal nanoparticles include monovalent metal cations and divalent metal cations, and the atomic ratio of monovalent metal cations to divalent metal cations is 1.8 to 2.

2.

19. A catalyst for reducing carbon dioxide, comprising a titanium dioxide complex selected from any one of claims 14 to 18.

20. A photocatalyst comprising a titanium dioxide complex selected from any one of claims 14 to 18.

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