Photocatalytic device for a continuous process of co-converting CO2 + H2O to C1 oxygenated material in sunlight

Abstract

The present invention discloses a bifunctional photocatalytic device and process for the photocatalytic co-conversion of CO2 and H2O to value-added products in direct sunlight. More specifically, the present invention relates to an efficient and continuous process for the photocatalytic co-conversion of a mixture of CO2 and water to methanol and formaldehyde in the presence of a newly developed bifunctional photocatalytic device. The present invention provides a bifunctional photocatalytic device together with a co-catalyst and integrates them into a photocatalytic device using an artificial leaf approach, where the device is in the form of a thin film that operates under broad-spectrum solar radiation at ambient conditions. Additionally, the photocatalytic device size can be reduced to 1 cm. 2 10cm from 2 It is easy to scale to size and the process can be tuned to produce the desired product.

Description

[Technical Field]

[0001] The present invention relates to a dual-function photocatalytic device for a continuous process of photocatalytic co-conversion of CO2 and water into value-added products under direct sunlight. In particular, the present invention relates to a process for co-converting CO2 and water into value-added products such as methanol and formaldehyde by using a newly developed dual-function photocatalyst together with a co-catalyst and accumulating them in a photocatalytic device using an artificial leaf technique. [Background technology]

[0002] The pursuit of sustainable fuel / energy / chemical production to meet the demands of a constantly growing global population is one of the major challenges for humanity in this century. The continued use of fossil fuels for all energy / fuel needs in this century has led to an increase in disasters such as severe droughts and torrential rains, and global concerns about the climate change impact of greenhouse gas emissions, particularly CO2 emissions. Reducing our dependence on fossil fuel-based energy is urgently needed. The use of CO2 as a raw material for the chemical industry is an attractive and necessary strategy that improves carbon emissions while providing a sustainable, safe, and economical way to convert CO2 into value-added chemicals. Harnessing abundant sunlight in solving environmental problems is a promising approach and one of the ultimate goals for the sustainability of global development; therefore, photocatalytic conversion of CO2 using solar energy is the most intriguing pathway for generating value-added and renewable fuels / chemicals through CO2 conversion.

[0003] To date, scientists have achieved several results in accomplishing this conversion. A paper by Yimin A. Wu et al., titled "Facet-dependent active sites of as single Cu2O particle photocatalyst for CO2 reduction to methanol," published in the journal Nature Energy, Vol. 4, November 2019, pp. 957-968, reports the best CO2 reduction to methanol to date with a catalyst of 10% solar-fuel efficiency at a rate of 1.2 mol / hg. In this case, Cu2O nanoparticles were used in powder form suspended in water, and the reaction was evaluated with 0.01 g. A CO2 / H2O gas mixture was continuously flowed through the Cu2O dispersed in water until the solution was saturated with CO2. The CO2-saturated Cu2O-containing solution was illuminated with a 300 W Xe lamp for 0 and 60 minutes under continuous CO2 / H2O flow, and the product was periodically analyzed. This paper reports that the adsorption effect is dominant in the photocatalytic reduction of CO2 on the (110) plane of a single Cu2O particle to methanol, but the (100) plane of Cu2O is inactive. However, the results were demonstrated with a catalyst weight of 0.01 g (10 mg) of microparticles, producing 0.133 mmol / s of methanol, and it is claimed that 1.2 mol / hg of methanol is produced at higher scales, although this has not been demonstrated. In reality, 0.133 mmol / s and 1.2 mol / hg do not match due to extrapolation from s to h by a factor of 3600 (1 h = 3600 s). It should be noted that, unlike conventional catalysis, there are many difficulties / problems associated with extending photocatalytic activity experiments with larger quantities of photocatalyst, and in fact, lower activity has been reported at higher scales (e.g., 1 g level) of catalysts.

[0004] It is well known in the literature that the activity obtained with a small amount of photocatalytic particulate matter (typically 1-100 mg) does not increase linearly with increasing catalyst amount (approximately 1 g or more), but rather decreases.

[0005] There is also a need in the art to provide a process that can be extended to larger-sized photoanodes for collecting solar energy for the above chemical conversion at commercially viable levels.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The main object of the present invention is to provide a dual-functional photocatalyst device for a continuous process of photocatalytic co-converting CO2 and water into value-added products under direct sunlight.

[0008] Another object of the present invention is to provide an efficient and continuous process for the photocatalytic co-conversion of a mixture of CO2 and water in the presence of a newly developed dual-functional photocatalyst [photoanode] device.

[0009] Yet another object of the present invention is to provide a dual-functional photocatalyst device, which is in the form of a thin film that operates under broad-spectrum solar radiation at ambient conditions.

[0010] Yet another object of the present invention is to scale up the photocatalyst device from 1 cm 2 to 10 cm 2 in size and demonstrate the feasibility of its continuous process.

Means for Solving the Problems

[0011] Therefore, the present invention is a dual-function photocatalytic device, i. comprising a visible light absorbing semiconductor [VAS] coupled to the pores of a wide bandgap semiconductor, ii. In thin film form, it is integrated with a cocatalyst. The visible light absorbing semiconductor [VAS] is selected from a group consisting of 3d or 4d transition metals, metal oxides alone or in combination, which are abundant on Earth. The wide-bandgap semiconductor is selected from TiO2 or ZnO. The device provides a co-catalyst selected from a group consisting of 3d or 4d transition metals, metal oxides alone or in combination, which are abundant on Earth.

[0012] In one embodiment of the present invention, the visible light absorbing semiconductor [VAS] used is selected from the group consisting of BiVO4, CdS, and PbS.

[0013] In yet another embodiment of the present invention, the visible light absorbing semiconductor [VAS] is located in the mesopores of a wide-bandgap semiconductor in the form of quantum dots (QDs).

[0014] In another embodiment of the present invention, the cocatalyst is nanopalladium (Pd), platinum (Pt), gold (Au), silver (Ag), nickel (Ni), cobalt (Co), cuprous oxide (Cu2O), NiCu alloy, Ti, Si or Zn, nickel oxide, manganese oxide, iron oxide, NiFe, 0.5θ Pt @NiFe, 0.5θ Pt @NiCu, 0.5θ Pt Selected from the group consisting of Pd, NiFe alloy, or Pt-plated NiCu alloy.

[0015] In yet another embodiment of the present invention, the device exhibits stable activity for 50 hours while maintaining product yield and selectivity.

[0016] In yet another embodiment, the present invention provides a process for fabricating an optical anode device, which includes the step of bonding visible light-absorbing semiconductors from their ionic components and depositing them directly inside the pores of a wide-bandgap semiconductor.

[0017] In yet another embodiment, the present invention is a process for photocatalytically co-converting a mixture of CO2 and water into a value-added product in a batch mode, i. The steps include injecting CO2 into water to the maximum saturation level and placing a photocatalytic device in a quartz reactor under a light source at a temperature in the range of 1 to 60°C, The process is provided in which the light source used is selected from UV+visible light, visible light, and direct sunlight.

[0018] In yet another embodiment, the present invention is a process for photocatalytically co-converting a mixture of CO2 and water into a value-added product in a continuous mode, i. The step includes placing a photocatalytic device in a quartz reactor under a light source at a temperature in the range of 1 to 60°C and continuously flowing CO2 through water, The process is provided in which the light source used is selected from UV+visible light, visible light, and direct sunlight.

[0019] In yet another embodiment of the present invention, the value-added product is selected from methanol and formaldehyde.

[0020] In yet another embodiment of the present invention, the conversion efficiency of the above-mentioned CO2 to value-added products is in the range of 35 to 55%.

[0021] In yet another embodiment of the present invention, the above process can be adjusted to produce a desired value-added product selected from methanol and formaldehyde. [Brief explanation of the drawing]

[0022] [Figure 1]This figure shows TEM images of photoanode materials exhibiting bismuth vanadate [BiVO4] QDs in the mesopores of titania and heterojunctions formed between BiVO4 and TiO2. BiVO4 QDs are observed to be in the size range of 3–5.5 nm, characterized by dark contrast. Larger titania particles can be seen with light / gray contrast. The scale bars are 20 and 5 nm in panels (a) and (b), respectively. [Figure 2] This figure shows a photocatalytic device made from a Pd-BiVO4 / TiO2 film and the HPLC results obtained for product analysis of water and CO2 co-conversion after 5 hours of irradiation in the presence of direct sunlight. [Figure 3] This figure shows the NMR spectra recorded for products obtained after co-conversion of water and CO2 in the presence of a photocatalytic device made from a Pd-BiVO4 / TiO2 film. Note the similarity between the products obtained by NMR and HPLC analysis in Figure 2. [Figure 4] This figure shows the product yield obtained as a function of irradiation time for the coconversion of water and CO2 in the presence of a photocatalytic device made from Pd-BiVO4 / TiO2. [Figure 5] This figure shows the conversion of CO2 and the selectivity of the products obtained as a function of irradiation time for the coconversion of water and CO2 in the presence of a photocatalytic device made from Pd-BiVO4 / TiO2. [Figure 6] This figure illustrates a stability study for the co-conversion of water and CO2 in the presence of a photocatalytic device made from Pd-BiVO4 / TiO2 under direct sunlight. The experiment was conducted daily for 7 hours (between 9 AM and 5 PM) from March to April 2021. [Figure 7] This figure shows a digital photograph of a device fabricated from a 1-9 cm² optical anode BiVO4 / TiO2. [Figure 8] This diagram illustrates a continuous process experiment setup for a large-scale device. This device can accommodate device sizes up to 100 cm². [Modes for carrying out the invention]

[0023] The present invention provides a dual-function photocatalytic device, the photocatalyst being composed of semiconductors by creating heterojunctions between two or more semiconductors, more specifically, it being composed of quantum dots (QDs) of suitable semiconductors in the pores of a wide-bandgap semiconductor such as TiO2 or ZnO.

[0024] The present invention i. Visible light absorbing semiconductors (VAS) in wide-bandgap semiconductors, ii. comprising a thin film cocatalyst, The wide-bandgap semiconductor is selected from TiO2 or ZnO. VAS provides a dual-function optical anode device selected from a group consisting of abundant 3d or 4d transition metals, metal oxides alone or in combination with other metal oxides found on Earth.

[0025] The VAS used is selected from the group consisting of BiVO4, CdS, and PbS.

[0026] The VAS used is preferably BiVO4 in the pores of TiO2 as quantum dots with a size of 3 to 5.5 nm.

[0027] The co-catalyst is selected from a group consisting of 3d or 4d transition metals, metal oxides alone or in combination, which are abundant on Earth.

[0028] Furthermore, the co-catalysts include palladium (Pd), platinum (Pt), gold (Au), silver (Ag), nickel (Ni), cobalt (Co), cuprous oxide (Cu2O), NiCu alloy, Ti, S or Zn, nickel oxide, manganese oxide and iron oxide, NiFe, 0.5θ Pt @NiFe, 0.5θ Pt @NiCu, 0.5θ Pt Selected from the group consisting of @Pd.

[0029] Preferably, Pd nanocubes and NiCu alloys are used as co-catalysts.

[0030] VAS exist in the form of quantum dots (QDs) in the mesopores of wide-bandgap semiconductors [TiO2].

[0031] The co-catalyst is selected from the group consisting of nanopalladium, NiCu alloy, NiFe alloy, and Pt-plated NiCu alloy.

[0032] The photocatalyst is composed of BiVO4 / TiO2 and Pd as a co-catalyst. BiVO4QD and TiO2 act as active visible and UV light absorbing photocatalytic components, respectively.

[0033] The present invention provides a process for photocatalytically co-converting a mixture of CO2 and water into a value-added product in the presence of a newly developed dual-function photocatalyst and co-catalyst in device form, under direct sunlight or simulated sunlight.

[0034] Therefore, the present invention provides a photocatalytic production process for liquid and / or gaseous chemicals and / or fuels, such as methanol, formic acid, formaldehyde, and two-carbon-containing products (such as ethanol), by irradiating a mixture of CO2 and water in the presence of a photocatalyst in the form of a thin-film device, wherein the device operates under broad-spectrum sunlight. Optionally, it also operates in UV, visible, and / or UV+visible light sources.

[0035] The photocatalytic coconversion process of a CO2 and water mixture consists of injecting carbon dioxide (CO2) into water and a photocatalytic device placed in a quartz reactor under sunlight or a suitable light source at a temperature in the range of 1 to 60°C. The CO2 was dissolved in the water to the maximum saturation level.

[0036] Lower temperatures increase the solubility of CO2, improving the reaction rate towards higher yields in a single batch. The CO2-saturated aqueous solution is illuminated with sunlight in the presence of a photocatalytic device to produce value-added products, which are periodically analyzed by HPLC analysis. Optionally, product analysis can also be performed by NMR method. In many cases, HPLC and NMR methods were used in parallel for quantitative measurements.

[0037] The photocatalytic co-conversion process of a CO2 and water mixture may be carried out in a batch process or in a continuous process. To convert the batch process to a continuous process as described above, the co-conversion of CO2 and water is carried out under continuous flow of CO2 in direct sunlight in a three-neck quartz reactor for CO2 circulation and for recovering the products. The products formed in the gas phase are condensed and recovered in a cold trap outside the reactor and analyzed for their content by GC and HPLC. The products remaining in the solution are also analyzed by HPLC and / or NMR methods. The product concentrations measured from the cold trap and from the solution are summed to obtain the total amount and selectivity of the products.

[0038] The fabrication process of the sunlight-responsive photocatalytic device consists of binding the light-absorbing quantum dots from their ionic components and depositing them directly inside and outside the pores of a TiO2 or ZnO thin film.

[0039] A uniform-thickness titania film in the range of 8 - 12 microns thick was prepared by the standard doctor blade method. Therefore, the prepared TiO2 or ZnO thin film had quantum dots accumulated in its pores by the successive ionic layer adsorption and reaction (SILAR) method. To insert BiVO4 into the pores of the titania thin film prepared by the doctor blade method, the titania thin film was treated with Bi 3+The samples were then treated with the SILAR method using vanadyl species-containing solutions in a specific order. SILAR promotes the uniform binding of 3-5.5 nm BiVO4QDs in the mesopores of TiO2 or ZnO and their distribution throughout the film thickness. This facilitates the creation of heterostructures between BiVO4 and TiO2 by utilizing the SILAR method for BiVO4 binding in TiO2. The heterostructure of BiVO4 and TiO2 throughout the film promotes electron dispersion toward cocrystallization, and therefore toward better activity of the photocatalyst, in addition to the effective separation of electron-hole pairs.

[0040] The support for the thin film is selected from the group consisting of any conductive or semiconducting surface, including glass plates, glass tubes / glass containers, indium tin oxide (ITO) glass plates, fluorine-doped tin oxide (FTO) glass plates, silicon wafers, stainless steel, and preferably FTO, ITO, silicon wafers, and stainless steel plates.

[0041] The conversion efficiency of carbon dioxide into value-added chemicals is in the range of 35-55%, and the solar-fuel efficiency (STF) is calculated to be approximately 11.2% by using the equation STF = energy of methanol produced / solar energy irradiated onto the device.

[0042] Within this disclosure, direct sunlight was used without any filters. However, standard light sources and simulated sunlight with filters, UV+visible, visible, and UV light sources may also be used at will.

[0043] In this disclosure, “wide bandgap semiconductor” means any semiconductor material having a bandgap of 2 to 4 eV and having a conduction band energy that is negative than the reduction potential of CO2 to any conceivable reduction product, including but not limited to HCHO, CH3OH, CO, HCOOH, CH4, etc. Wide bandgap semiconductors include, but are not limited to, TiO2 or ZnO.

[0044] The present invention provides a photocatalytic coconversion process for water and CO2, the process comprising placing a photocatalytic device in a reactor in the presence of direct sunlight and carrying out a flow of CO2 to produce a product.

[0045] The present invention provides a photocatalytic production process for liquid and / or gaseous chemicals and / or fuels, such as methanol, formic acid, formaldehyde, and two-carbon products (such as ethanol), by irradiating a mixture of CO2 and water in the presence of a photocatalyst in the form of a thin-film device, wherein the device operates under broad-spectrum sunlight. Optionally, it also operates under UV+visible light sources.

[0046] The present invention a) The steps include injecting gaseous carbon dioxide CO2 into water and placing a photocatalytic device in a quartz reactor under sunlight or a suitable light source at a temperature in the range of 1 to 60°C, b) A step of dissolving carbon dioxide (CO2) in water to the maximum saturation level, c) A step of producing value-added products by illuminating a CO2-saturated aqueous solution with sunlight in the presence of a photocatalytic device, The present invention provides a process for photocatalytically co-converting a mixture of CO2 and water into a value-added product in direct sunlight, comprising the step of analyzing the value-added product by HPLC analysis and / or NMR analysis.

[0047] The value-added product is selected from methanol or formaldehyde.

[0048] Lower temperatures increase CO2 solubility, improving the reaction rate for higher yields in single batches.

[0049] The photocatalytic coconversion process of a CO2 and water mixture may be carried out in a batch process or a continuous process.

[0050] To convert the batch process into a continuous process, as described above, the coconversion of CO2 and water is carried out in a three-neck quartz reactor under a continuous flow of CO2 in direct sunlight for CO2 circulation and product recovery. The product formed in the gas phase is condensed and recovered in a cold trap outside the reactor and its contents are analyzed by GC and HPLC. The product remaining in solution is also analyzed by HPLC and / or NMR. The product concentrations measured from the cold trap and from the solution are summed to obtain the total amount and selectivity of the product.

[0051] The process provides CO2 reduction, and a modified TiO2 device, i.e., a mesoporous titania thin film prepared by the doctor blade method, in which quantum dots are bonded to the pores of titania and assembled with a cocatalyst, is irradiated with direct sunlight in the presence of CO2 and H2O to form methanol and formaldehyde.

[0052] The advantage of this method is the direct conversion of solar energy into value-added chemicals using wireless photochemical devices.

[0053] A titania thin film with BiVO4 quantum dots bonded to its pores has a visible light band gap of approximately 2.4 eV, thus consuming nearly 47% of the solar spectrum that falls to Earth. The method is simple to apply without any sophisticated devices, simply by using CO2 and water.

[0054] In yet another embodiment, the device size can be expanded to a larger size to maximize solar absorption and subsequent production of large quantities of value-added chemicals such as methanol and formaldehyde.

[0055] The conversion efficiency of carbon dioxide into value-added chemicals through this process ranges from 35% to 55% relative to the amount of carbon dioxide, and the solar-fuel efficiency is approximately 11.2%.

[0056] Another embodiment of the present invention provides a dual-function photocatalytic device, the photocatalyst being composed of semiconductors by creating heterojunctions between two or more semiconductors, more specifically, it being composed of quantum dots (QDs) of suitable semiconductors in the pores of a wide-bandgap semiconductor such as TiO2 or ZnO. In a particularly useful embodiment, the photocatalyst is composed of BiVO4 / TiO2 and Pd as a co-catalyst, with BiVO4QD and TiO2 being the active visible and UV light absorbing photocatalytic components, respectively.

[0057] The fabrication process for photocatalytic devices that respond to sunlight consists of bonding light-absorbing quantum dots from their ionic components and directly depositing them inside the pores of a TiO2 or ZnO thin film.

[0058] Uniform thickness titania films ranging from 8 to 12 microns were prepared using a standard doctor blade method. Quantum dots were then accumulated within the pores of the prepared TiO2 or ZnO thin films by continuous ion layer adsorption and reaction (SILAR) method.

[0059] To insert BiVO4 into the pores of a titania thin film prepared by the doctor blade method, the titania thin film is prepared by Bi 3+ The samples were then treated using the SILAR method with vanadyl or metavanadic acid species-containing solutions in a specific order.

[0060] Ionic precursors bound to mesopores lead to BiVO4 formation within the pores upon calcination at 450°C. Importantly, SILAR facilitates the binding of BiVO4 precursors to TiO2 mesopores, supporting the formation of uniformly distributed BiVO4QDs with a particle size of 3–5.5 nm throughout the film thickness. This facilitates the creation of heterostructures between BiVO4 and TiO2 by utilizing the SILAR method for BiVO4 binding in TiO2. The BiVO4 and TiO2 heterostructures throughout the film promote electron dispersion toward cocatalysis, and thus toward better activity of the photocatalyst, in addition to effective separation of electron-hole pairs. Importantly, this is the first demonstration of the binding of an oxide material from its precursor (or ionic component) to another oxide material. The distinct pore size or pore size range associated with titania does not allow BiVO4 particles to grow larger than the pore diameter, thus enabling precise particle size control. The TEM image shown in Figure 1 completely supports the presence of BiVO4 exclusively within the pores of titania and shows the conjugation observed between BiVO4 and titania.

[0061] SILAR facilitates the uniform binding and distribution of BiVO4QDs with a particle size of 3–5.5 nm in the mesopores of TiO2, as well as their distribution throughout the film thickness. High-resolution images show that the BiVO4QDs have a spherical shape with a particle size in the range of 3–5.5 nm (Figure 1). Clear heterostructure formation between BiVO4 and TiO2 was observed using the SILAR method for QD binding in mesoporous TiO2 (Figure 1b). Mesoporous TiO2 films fabricated by the doctor blade method are Bi 3+ and VO3 - It allows for the diffusion of ionic components, and as a result, BiVO4QDs are formed in the pores of TiO2 in response to firing. The BiVO4 and TiO2 heterostructure observed throughout the film promotes electron dispersion toward cocrystal, in addition to better electron-hole separation.

[0062] The support for the thin film is selected from the group consisting of any conductive or semiconducting surface, including glass plates, glass tubes / glass containers, indium tin oxide (ITO) glass plates, fluorine-doped tin oxide (FTO) glass plates, silicon wafers, and stainless steel. In certain useful embodiments, the substrates chosen for the thin film are FTO, ITO, silicon wafers, and stainless steel plates.

[0063] The integration of wide-bandgap semiconductors with photo-absorbing semiconductors in the form of quantum dots is one promising method, as quantum dots exhibit high surface area, possess tunable band gaps and band edge positions for quantum confinement, and have shorter charge transfer pathways, thus providing more potential energy for photochemical reactions. Quantum dots of BiVO4, CdS, and PbS can be used to integrate wide-bandgap semiconductors. Semiconductors with mesoporous structures are recognized as efficient for improving photocatalytic activity toward CO2 reduction due to their high surface area and improved adsorption of CO2.

[0064] VAS-QD is selected from the group consisting of BiVO4, CdS, and PbS. In particularly useful embodiments, the VAS used is BiVO4 in the pores of TiO2.

[0065] The total film thickness was maintained in the range of approximately 8–15 μm, as confirmed by thickness measurements using a lateral spectroscopy and SEM analysis. It is worth noting that no separate layers of deposited components were observed, but rather only a single, uniform, and smooth layer of thin film was seen on the FTO. Therefore, it is believed that the porous structure of TiO2 is Bi 3+ and VO3 - This allows for diffusion, which may lead to the formation of BiVO4 in the pores of TiO2 in response to calcination. The selectivity of the product can be adjusted not only by the reaction time but also by using different co-catalysts.

[0066] Under experimental conditions, 1 mg of BiVO4 / TiO2 (97.5 ± 0.5 wt% of which is titania and 2.0-2.5 wt% of which is BiVO4QD) was poured into a 1 cm³ solution.2 The Pd cocatalyst is coated as a thin film over an area and assembled with the Pd cocatalyst as a device. This device is kept in 30 ml of deionized water (pH=7) in a 50 ml quartz reactor at room temperature (28±3°C). The reaction mixture is first completely degassed using 99.9% CO2 gas at 25-30°C for 10 minutes to remove any dissolved oxygen. Subsequently, the reaction mixture is kept in an ice bath (1-3°C) and continuously purged with CO2 for a further 30 minutes to obtain a saturated aqueous solution of CO2. The total amount of CO2 dissolved in water is measured to be 1.48 mmol, which is determined by a simple titration with NaOH solution (0.01 M). The possible reaction sequences that can occur under experimental conditions are given below: 2CO2 + 2H2O → 2HCHO + 2O2 2HCHO + 2H2O → 2CH3OH + O2 The total is 2CO2 + 4H2O → 2CH3OH + 3O2

[0067] Therefore, simply extending the reaction time leads to a higher selectivity for methanol, while formaldehyde is selectively produced in a shorter time. Methanol yield is 30-50 μmol / h.mg.cm 2 (1cm 2 Within the area of ​​a 1 mg catalyst (BiVO4 + TiO2) applied over a wide area, the formaldehyde yield is 100-130 μmol / h.mg.cm². 2The maximum conversion efficiency of carbon dioxide to value-added chemicals is observed to be in the range of 35–55%. The selectivity for methanol and formaldehyde is approximately 30% and 70%, respectively. The low and high yield ranges shown above for both products are due to standard laboratory conditions (1 solar) and direct sunlight, respectively. When the experiment is conducted in direct sunlight, a range of up to 35% higher CO2 conversion and higher product yields is observed. This is due to the amount of light from sunlight, and also depends on the time of day it is irradiated. In addition, exposure to direct sunlight raises the temperature between 45–60°C, depending on the time and solar flux conditions. The available significant high temperatures, under the above conditions, increase the reaction rate, which is an additional advantage when conducting the reaction in direct sunlight. Generally, higher activity is observed between 11 AM and 3 PM, and activity decreases before and after the above time window.

[0068] Table 1: Pd cocatalyst and integrated BiVO4 / TiO21cm³ in batch processes under 1 solar conditions 2 CO2 conversion as a function of irradiation time with respect to size of the optical anode, as well as product selectivity and yield.

[0069] [Table 1]

[0070] The experimental results shown in Table 2 are for 10 cm 2 The study was conducted under similar conditions, except for the use of a larger device (4cm × 2.5cm). The results obtained are shown in Table 2, which are in close agreement with Table 1, suggesting a linear increase in activity with increasing device size.

[0071] Table 2: Pd cocatalyst and integrated BiVO4 / TiO2 10cm³ in batch processes under solar conditions 2 CO2 conversion, product selectivity, and yield as a function of irradiation time with the photoanode.

[0072] [Table 2]

[0073] A 1cm sheet coated solely with titania, without any BiVO4QDs, to measure the activity contribution from titania. 2 Photocatalytic activity experiments were also conducted using a photoanode device. The same experimental conditions as those shown in Table 1 were maintained. Even after 5 hours of continuous irradiation under 1 solar conditions, no significant conversion of CO2 or formation of any products was observed. This highlights the excellent role of BiVO4QD in converting sunlight into value-added chemicals. 10cm 2 The device (Table 2) showed a 10-fold higher product yield value (1cm 2 The results shown in Table 1 (compared to the device) are due to the 10-fold increase in the amount of BiVO4QD, highlighting the linear increase in activity with device size and QD content. In light of this direct correlation, the photocatalytic activity of device sizes containing 1 mg of BiVO4QD is shown in Table 3.

[0074] Table 3: Product yield from 1 mg of BiVO4QD coupled to a large-area BiVO4 / TiO2 photoanode device.

[0075] [Table 3]

[0076] A simple linear multiplication of the values ​​given in Table 3 yields production rates of 2.42 and 3.34 mol / gh for MeOH and HCHO per gram of BiVO4QD. This is again based on the average rate obtained at the end of the 5-hour reaction time. Since both are single-carbon products (like CO2), the total product concentration is considered to be 5.76 mol / gh, assuming that both products are equal. In fact, an equivalent amount of CO2 (5.76 moles of CO2 corresponds to 253.4 g) is converted into value-added products in a 5-hour reaction time. For this reason, the solar-fuel conversion efficiency for methanol was calculated using the above photocatalytic system and a solar simulator with 1 solar condition. The incident light power density was 100 mW / cm². 2 The irradiation area is 100 cm². 2 The possible chemical reactions are: CO2 + 2H2O → CH3OH + 3 / 2O2. The Gibbs free energy of this reaction is 702.2 kJ / mol.

[0077] The solar-fuel efficiency is 11.2%, and is calculated as follows: ={(CH3OH yield * ΔG) / (P total *area)} {(1.6mmol / s×702kJ / mol) / (100mW / cm 2 ×100cm 2 )} = 11.2%

[0078] To maximize the conversion efficiency for the photocatalytic coconversion of CO2 and water into value-added products, a continuous process was employed, with CO2 gas continuously blown into the solution through the reaction. In addition to solar conditions, a continuous flow of CO2 was carried out in the presence of direct sunlight in a specially designed reactor (illustrated in Figure 8) containing a Pd-BiVO4 / TiO2 photocatalytic device. Product vapors that escaped into the gas phase were also collected and analyzed in a trap kept in a condenser or ice bath outside the reactor. Liquid products were also analyzed by HPLC, as in the batch process. Both values ​​were summed to obtain the total product formation. The results are given in Table 4 and compared with those obtained from the batch process.

[0079] Table 4: 1 cm under continuous and batch processes in addition to solar conditions. 2 CO2 conversion, as well as product selectivity and yield, were observed as a function of irradiation time with a size light anode.

[0080] [Table 4]

[0081] Table 4 clearly shows that the continuous process improves the CO2 conversion rate compared to the batch process, regardless of whether it is under 1-sun or direct sunlight conditions, and it should also be noted that direct sunlight improves the rate compared to the batch process. The amount of light from sunlight plays a significant role in improving the reaction rate. Another important observation is that the selectivity trend of the product remains the same regardless of whether it is a batch or continuous process. The rate of CO2 conversion (and product formation) initially (1h) increases 2.5 times in the continuous process in sunlight (337μmol) compared to the batch process under 1-sun conditions (134μmol), while after 5 hours of reaction, this trend shows a 1.4-fold increase in yield from batch to continuous mode. Simply running the reaction in direct sunlight for a longer period, preferably 7 hours between 9am and 5pm, will improve the yield. 2 The device yielded 547 μmol (59% selectivity) for methanol and 370 μmol (41% selectivity) for formaldehyde. Furthermore, the device's stability was evaluated in the presence of direct sunlight for 50 hours, the results of which are shown in Figure 6. The device's consistent product yield, even after 50 hours of reaction, suggests its stability for sustainable photocatalytic coconversion of CO2 and water into value-added products. 4 cm 2 (2cm x 2cm) and 9cm 2 Further studies were conducted on the (3cm × 3cm) optical anode device (Figure 7) using a continuous process under direct sunlight, and the observed product yields are shown in Table 5.

[0082] Table 5: Pd cocatalyst and integrated 4cm 2 and 9cm 2 CO2 conversion, as well as product selectivity and yield, were observed as a function of irradiation time with the photoanode.

[0083] [Table 5]

[0084] 1cm in direct sunlight 2 Compared to the device, 4cm 2 While the optical anode device showed a product yield value approximately three times higher, 9cm 2 The size device exhibits approximately six times higher product yield values. Interestingly, both devices show the same selectivity trend for the product, which is worth highlighting.

[0085] High-performance liquid chromatography (HPLC, Agilent Technologies, modal 1250 infinity) was used to analyze liquid samples for the identification of reduction products such as methanol and formaldehyde. Product formation was confirmed by comparing experimental data with those of standard samples. Calibration curves were obtained to correlate the concentrations of methanol and formaldehyde with the HPLC peak areas. The HPLC was equipped with an RI detector (40°C) and a guard column in series. + The system is equipped with an Aminex column (305 mm × 7.8 mm). The mobile phase used was 0.6 mL min while maintaining the column temperature at 60°C. -1 The gas product was analyzed using gas chromatography with a flow rate of 0.03 M H2SO4, a TCD detector, and a Carbosieve S II column, with helium as the carrier gas and a column temperature of 100°C. However, in the current experiment, no gas reduction products were formed from reactions such as CH4 or CO. Only oxidation products, i.e., oxygen, were analyzed using gas chromatography.

[0086] A series of control experiments were conducted to confirm the origin of the photoactivity of the BiVO4 / TiO2 photoanode. A Pd-BiVO4 / TiO2 photocatalytic film was left overnight in the dark in a reactor packed with CO2 and H2O, but no reaction products were detected. When only the BiVO4 film was placed under irradiation with CO2 and H2O, no activity was observed. Finally, when Pd / TiO2 was irradiated, no conversion products were detected, indicating that water splitting was the dominant reaction compared to the CO2 reduction reaction.

[0087] A very good rate of methanol formation was observed under saturated CO2 conditions in pure water without the use of any sacrificial substances, with a selectivity of 48 ± 5 μmol / h / mg. Another value-added product, HCHO, was observed along with methanol, with a formation rate of 67 ± 5 μmol / h / mg in saturated CO2 solution. Overall, the device with Pd-BiVO4QD in TiO2 can reduce 115 ± 5 μmol / h / mg of CO2 to value-added products.

[0088] The different catalytic structures of a single photocatalyst are another major reason for obtaining quantum dot BiVO4 compared to different, and therefore layered, BiVO4, playing a crucial role in improving CO2 reduction activity by creating heterojunctions in the pores of TiO2 throughout the film, leading to effective separation of electron-hole pairs and sufficient dispersion of electrons toward cocrystals, ultimately resulting in the greater yield and higher formation rate observed in layered BiVO4.

[0089] (Examples) The following embodiments are given as examples and should not be construed as limiting the scope of the present invention.

[0090] (Example 1) Photocatalytic thin film preparation The substrate selected for this method was an FTO board. First, the FTO board was properly cleaned with isopropyl alcohol, and then the conductive side of the FTO was treated with TiCl3. 1 cm of the board 2TiO2 paste was applied to the surface using the doctor blade method, dried at 60°C for 2 hours, and then baked at 450°C for 30 minutes. The detailed procedure for the TiO2 paste was as follows: 1 g of TiO2 powder (Degussa P25) was stirred with 33 ml of ethanol and 0.33 ml of glacial acetic acid for 10 minutes, and then sonicated for 10 minutes. 0.5 g of ethyl cellulose was added to the above mixture and stirred for 10 minutes, followed by sonication for 10 minutes. Finally, 3 ml of terpineol was added to the mixture, and stirring and sonication were continued for 30 minutes. After this, the solvent was evaporated using a rotary vaporizer to obtain a paste of uniform thickness. This titania paste was uniformly applied to an FTO plate, and the thickness of such a film ranged from 8 to 14 μm.

[0091] In this specification, to enable photocatalytic devices to operate efficiently in the widest range of solar radiation, heterojunctions are created by bonding quantum dots to the pores of TiO2, more specifically, the semiconductor used to create these heterojunctions is BiVO4, and the process is carried out by the SILAR method. Further details are as follows:

[0092] A Bi ion-containing solution was prepared by mixing 25 mM Bi(NO3)3 with a mixture of acetic acid and water at 25°C in a ratio of 1:19. Similarly, a 25 mM NH4VO3 solution was prepared by dissolving the required amount of NH4VO3 in water at 75°C. Both solutions were used in the SILAR method to deposit BiVO3QDs into the porous structure of a titania membrane. A pre-coated TiO2 membrane on FTO was immersed in a Bi bath for 20 seconds, followed by an IV bath for another 20 seconds. This constituted one SILAR cycle. As the number of SILAR cycles performed increased, the amount / content of QDs in the titania membrane gradually increased, and in particular, 10 SILAR cycles were applied to the TiO2 membrane for maximum device activity. After each cycle, the membrane was rinsed with deionized water and dried in air. After 10 SILAR cycles, the membrane was annealed in air at 450°C for 2 hours to form uniform BiVO4QDs in the pores of the TiO2. Therefore, part of the device became a BiVO4 / TiO2 optical anode.

[0093] (Example 2) Photocatalytic thin film preparation CdS / TiO2 As explained in Example 1, 1 cm 2 A TiO2 film is coated over the size using the doctor blade method. To activate the device in sunlight, CdS is used as a quantum dot by the SILAR method. The details are as follows: The pre-coated TiO2 film is first immersed in an aqueous solution of cadmium precursor (i.e., 0.1 M Cd(NO3)2) at 25°C for 1 minute, then washed with deionized water, and subsequently immersed in a sulfide precursor of 0.1 M Na2S solution at 25°C for 1 minute. This is known as the 1 SILAR cycle of CdS. Five such CdS SILAR cycles were performed on the TiO2 film. To avoid photocorrosion, two SILAR cycles of ZnS were performed using 0.1 M Zn(CH3CHOO)2 and 0.1 M Na2S solutions, respectively, for 1 minute each. ZnS is used as a passivation layer. Finally, the film is dried in an oven at 60°C. This is another example of a fabricated optical anode device, referred to as a CdS / TiO2 optical anode.

[0094] (Example 3) Co-catalyst synthesis: Pd nanoparticles (100) Pd nanocube (Pd NC The synthesis of ) was carried out as follows: 105 mg of PVP (polyvinylpyrrolidone), 60 mg of ascorbic acid, and 300 mg of KCl were added to 8 mL of water in a 25 mL three-neck round-bottom flask (RBF), and the mixture was kept at 90°C with constant stirring. After 5 minutes, 3 mL of water containing 57 mg of K2PdCl4 was added to the solution, and the mixture was kept at the same temperature (90°C) for 3 hours with constant stirring. After 3 hours, the resulting brown-black nanoparticle solution was cooled to 25°C and collected in a centrifuge bottle. The nanoparticles were washed by centrifugation at 10,000 rpm for 10 minutes once with an excess of acetone and three times with an ethanol / hexane mixture (1:5 ratio). The final precipitate was dispersed in water for further washing.

[0095] (Example 4) Co-catalyst synthesis - NiCu alloy nanoparticles NiCu nanoparticles were synthesized by solvothermal technique with the help of oleylamine as a reducing agent, in addition to capping. The detailed synthesis procedure for NiCu nanoparticles is as follows: 25 ml of oleylamine was measured into a 100 ml three-neck round-bottom flask and kept at 120°C for 10 minutes to remove any trace amounts of water from the oleylamine. To this preheated oleylamine, nickel(II) nitrate hexahydrate and copper(II) acetate monohydrate, nickel and copper precursors in a 2:1 molar ratio, were added. The reaction mixture was gradually increased to 220°C and magnetically stirred for 1 hour. After 1 hour, the color of the solution changed from green to black, indicating the formation of NiCu alloy nanoparticles. The resulting black solution was cooled to 25°C, and the formed nanoparticles were separated by centrifugation. Subsequently, they were washed with ethanol and centrifuged, and this procedure was repeated three times, and finally the nanoparticles were recovered in ethanol solvent.

[0096] (Example 5) Co-catalyst synthesis: NiCu alloy coated with a half-layer of Pt (0.5θ Pt @NiCu) NiCu alloy coated with a semilayer of Pt was synthesized by a special method. As described in Example 4, NiCu alloy nanoparticles were first prepared. The NiCu alloy was treated with NaBH4 in a 1:4 ratio with ethanol in a round-bottom flask (RBF) with stirring for 30 minutes. Subsequently, the solution was refluxed at 80°C for 1 hour. Then, it was centrifuged and washed with ethanol, and since the surface of the NiCu alloy was coated with hydride ions, NiCu@H - I named it that. NiCu@H - The sample was treated in RBF with ethanol and K2PtCl4 in an 8:1 ratio, subjected to sonication for 30 minutes, and then refluxed at 74°C for 12 hours. Finally, it was centrifuged and washed with ethanol at 0.5θ. Pt I got @NiCu.

[0097] (Example 6) Co-catalyst synthesis - NiFe nanoparticles NiFe nanoparticles were synthesized using hydrothermal technology. The detailed synthesis procedure for NiFe nanoparticles is as follows: To prepare 1:3 NiFe nanoparticles, 0.025 M nickel nitrate and 0.075 M iron nitrate precursor were weighed and dissolved in 10 ml of distilled water. 10 ml of 1 M NaOH solution was added and stirred for 10 minutes to form an alkaline solution. 5 ml of hydrazine solution was added to the solution to reduce the metal ions, and 0.01 M sodium dodecyl sulfate was added as a surfactant. Stirring was continued at 30°C for 2 hours. The solution was transferred to a Teflon®-coated autoclave and kept in an oven heated to 140°C for 6 hours. After cooling to room temperature, the solution was washed with deionized water and ethanol and dried in an oven at 60°C for 2 hours. This co-catalyst was named NiFe.

[0098] (Example 7) NiFe(0.5θ) coated with a half-layer of Pt Pt @NiFe) Cocatalyst synthesis: First, NiFe was synthesized by the solvent heat method as described in Example 6. The NiFe alloy was treated with NaBH4 in a 1:4 ratio with ethanol while stirring in RBF for 30 minutes, and then refluxed at 80°C for 1 hour. Next, it was centrifuged and washed with ethanol, and since the surface of the NiFe alloy was coated with hydride ions, it was removed as NiFe@H - I named it that. NiFe@H - The sample was treated in RBF with ethanol in an 8:1 ratio of K2PtCl4. This solution was subjected to sonication for 30 minutes, then refluxed at 74°C for 12 hours. It was then centrifuged, washed with ethanol, and dried. This is 0.5θ Pt Known as @NiFe

[0099] (Example 8) Pd nanoparticles coated with a half-layer of Pt (0.5θ Pt @Pd) Synthesis: As explained in Example 3, first Pd nanoparticles (Pd NC ) was prepared. Pd NCThe NP was treated with NaBH4 in a 1:4 ratio with ethanol while stirring in RBF for 30 minutes, followed by reflux at 80°C for 1 hour. Then it was centrifuged and washed with ethanol, and Pd@H - It was named as such. In 25 mL RBF, Pd@H - To a 10 mL solution of nanoparticles, the desired amount of K2PtCl4 (due to the semi-monolayer of Pt on Pd) dissolved in 5 mL of water was added, and sonic treatment was continued for 30 minutes. The mixture was then kept at 70°C for 12 hours with constant stirring. The final solution was washed with 30°C water. The final precipitate was collected and dried at 60°C for 12 hours for application. This catalyst was then subjected to 0.5θ. Pt Show as @Pd

[0100] (Example 9) Photocatalytic CO2 reduction (batch process) 1cm 2 A thin-film photocatalytic device was prepared with 1 mg of Pd-BiVO4 / TiO2 and assembled with a Pd co-catalyst. This photochemical device was kept in 30 ml of deionized water at pH=7, with the water acting as an in-situ hydrogen source in a 50 ml quartz reactor and sealed using a diaphragm. The reaction mixture was completely saturated with CO2 using 99.9% CO2 gas for approximately 40 minutes. The pH of the solution was measured to 6.2, indicating the acidic nature of the solution due to CO2 dissolution. To dissolve the maximum amount of CO2 in the water, the reaction flask was placed in an ice bath at saturation. The reaction flask was illuminated under static solar conditions for at least 5 hours. To analyze the product, gas phase samples were extracted at regular time intervals using a sealed syringe in addition to the aqueous phase. No gas phase product was observed, while the liquid product was analyzed by HPLC.

[0101] (Example 10) Photocatalytic CO2 reduction (batch process): NiCu-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4 / TiO2 thin-film photocatalytic device was prepared by the SILAR method following a doctor blade. Instead of Pd, a NiCu alloy cocatalyst was assembled. This device was used for the co-conversion of CO2 with water, as described in Example 9. It was observed that this device was selective for the reduction of CO2 and showed slightly lower activity compared to its Pd counterpart.

[0102] (Example 11) Photocatalytic CO2 reduction (batch process): Pd-CdS / TiO2 thin film As described in Example 2, a Cds QD-decorated TiO2 film was prepared as a photoanode and integrated with Pd as a cocatalyst. This Pd-CdS / TiO2 device was evaluated for CO2 reduction activity as described in Example 9. This device was found to be significantly effective for water splitting as well.

[0103] (Example 12) Photocatalytic CO2 reduction (continuous process) Under direct sunlight, a Pd-BiVO4 / TiO2 photocatalyst device was placed in a specially designed reactor (Figure 8) and a continuous flow of CO2 was carried out. The product formed in the gas phase was collected and analyzed in a condenser or trap kept in an ice bath outside the reactor. The liquid product was also analyzed by HPLC as in Example 9. The product present in aqueous solution was analyzed and, in addition to the value obtained from the condensed product, the total product formation was obtained. Other reaction conditions were the same as described in the first method. The selectivity remained the same as shown in Table 1, but the yield of product formation was observed to have increased 2.5 to 3 times. This indicates a high reaction rate in direct sunlight.

[0104] (Example 13) Photocatalytic CO2 reduction (continuous process): NiCu-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4QD-decorated TiO2 film was prepared as a photoanode and integrated with NiCu as a cocatalyst (as described in Example 4). This NiCu-BiVO4 / TiO2 device was evaluated for CO2 reduction activity as described in Example 12. It was observed that this device is selective for CO2 reduction and exhibits slightly lower activity compared to its Pd counterpart.

[0105] (Example 14) Photocatalytic CO2 reduction (continuous process): 0.5θ Pt @NiCu-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4QD decorated TiO2 film was prepared as a photoanode, and 0.5θ was used as a cocatalyst. Pt It was integrated with @NiCu. This device was evaluated for CO2 reduction activity as described in Example 12. Here, along with the clear appearance of bubbles from the device, a noteworthy amount of CH4 was also observed as a reduction product.

[0106] (Example 15) Photocatalytic CO2 reduction (continuous process): NiFe-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4QD-decorated TiO2 film was prepared as a photoanode and integrated with NiFe as a cocatalyst. This NiFe-BiVO4 / TiO2 device was evaluated for CO2 reduction activity as described in Example 12. The NiFe-BiVO4 / TiO2 device was found to be exclusively selective for methanol as a CO2 reduction product.

[0107] (Example 16) Photocatalytic CO2 reduction (continuous process): 0.5θ Pt @NiFe-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4QD decorated TiO2 film was prepared as a photoanode, and 0.5θ was used as a cocatalyst. Pt Integrated with @NiFe. This device has a 0.5θ Pt @NiFe-BiVO4 / TiO2 was evaluated for CO2 reduction activity as described in Example 12. 0.5θPt @NiFe-BiVO4 / TiO2 shows more methanol formation compared to Example 15.

[0108] (Example 17) Photocatalytic CO2 reduction (continuous process): 0.5θ Pt @Pd-BiVO4 / TiO2 thin film As described in Example 1, a BiVO4QD decorated TiO2 film was prepared as a photoanode, and 0.5θ was used as a cocatalyst. Pt This device was integrated with Pd. The CO2 reduction activity of this device was evaluated as described in Example 12. Both formaldehyde and methanol were observed as CO2 reduction products for this device, similar to those of the Pd-based device. However, more methanol was observed for this device than for the Pd-based device alone.

[0109] Advantages of the invention A simple and efficient method for photocatalytic coconversion of a mixture of carbon dioxide and water into value-added chemicals in direct sunlight using an economically feasible photocatalytic device.

[0110] A dual-function photocatalyst (reducing CO2 in addition to water) is provided by binding a precursor of a light-absorbing photocatalytic quantum dot to the mesopores of a wide-bandgap semiconductor.

[0111] The co-conversion of carbon dioxide and water into value-added chemicals in direct sunlight is demonstrated to be a continuous process.

[0112] Significant increases in process and catalyst temperatures due to sunlight improve reaction rates without incurring additional costs.

[0113] Thin-film photocatalytic device size is 9 cm without loss of activity. 2 It can be extended to this extent and can be easily extended further, and therefore there are no problems associated with powder catalysts.

[0114] The entire photocatalytic coconversion process can be carried out using various light sources, such as direct sunlight, standard laboratory light sources, UV light, and UV+visible light sources.

[0115] Product selectivity and conversion efficiency can be adjusted by using various co-catalysts.

[0116] This study directly demonstrated the reduction of CO2 to formaldehyde and methanol.

[0117] In the proposed thin-film device, improved contact facilitates higher efficiency by enabling light absorption across the entire thickness of the device and allowing charge diffusion and charge utilization across a large scale of the device.

[0118] Stable activity is demonstrated for at least 50 hours while maintaining product yield and selectivity.

[0119] Neither BiVO4 nor TiO2 alone can perform CO2 reduction, such as water splitting to formaldehyde and methanol. In fact, it is BiVO4 in the pores of titania. This unique combination of QDs leads to effective light absorption by BiVO4 followed by charge separation, resulting in not only superior sustainable activity but also scalability.

[0120] Sustainable CO2 conversion activity to value-added products was demonstrated in batch and continuous mode reactions under direct sunlight without pH adjustment.

[0121] The significantly higher activity observed in this BiVO4QD, which is bound to titania pores and involves the sequential reduction of CO2 to formaldehyde and then to methanol, is highly unique.

Claims

1. A dual-function photocatalytic device for a process of photocatalytically co-converting a mixture of CO2 and water into methanol and formaldehyde, i. A visible light absorbing semiconductor [VAS] coupled to a pore in a wide-bandgap semiconductor called an optical anode, and ii. It is integrated with the cocatalyst in thin film form, The visible light absorbing semiconductor [VAS] is selected from the group consisting of 3d or 4d transition metals, metal oxides alone or in combination thereof. Wide-bandgap semiconductors, TiO ２ Or selected from ZnO, A device in which the co-catalyst is selected from the group consisting of 3d or 4d transition metals, metal oxides alone, or combinations thereof.

2. The visible light absorbing semiconductor [VAS] used is BiVO ４ The device according to claim 1, selected from the group consisting of CdS and PbS.

3. The device according to claim 1, wherein the visible light absorbing semiconductor [VAS] is in the form of quantum dots (QDs) in the mesopores of the wide bandgap semiconductor.

4. The aforementioned co-catalysts include nanopalladium (Pd), platinum (Pt), gold (Au), silver (Ag), nickel (Ni), cobalt (Co), and cuprous oxide (Cu). ２ O), NiCu alloy, Ti, Si or Zn, nickel oxide, manganese oxide, iron oxide, NiFe, 0.5θ Ｐｔ @NiFe, 0.5θ Ｐｔ @NiCu, 0.5θ Ｐｔ The device according to claim 1, selected from the group consisting of Pd, NiFe alloy, or Pt-plated NiCu alloy.

5. The device according to claim 1, wherein the device exhibits stable activity for 50 hours while maintaining product yield and selectivity.

6. A process for fabricating an optical anode device according to claim 1, comprising the step of bonding visible light-absorbing semiconductors from their ionic components and depositing them directly inside the pores of a wide-bandgap semiconductor.

7. CO in batch mode ２ A process for photocatalytically co-converting a mixture of water and other substances into a value-added product, i. CO2 in water ２ The steps include injecting the solution to the maximum saturation level and placing the photocatalytic device described in claim 1 into a quartz reactor under a light source at a temperature in the range of 1 to 60°C, The light source used is selected from UV + visible light, visible light, and direct sunlight. The value-added product is selected from methanol and formaldehyde. process.

8. Photocatalytic co-conversion of a mixture of CO ２ and water into value-added products, the process comprising: i. Place the photocatalytic device described in claim 1 in a quartz reactor under a light source at a temperature in the range of 1 to 60°C and add CO2 to water. ２ This includes a step of continuously playing the following: The light source used is selected from UV + visible light, visible light, and direct sunlight. The value-added product is selected from methanol and formaldehyde. process.

9. The aforementioned CO ２ The process according to claim 7 or 8, wherein the conversion efficiency to value-added products is in the range of 35 to 55%.

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