A visible light-electric field synergistic method capable of regulating glutamic acid oxidation

Abstract

The application provides a visible light-electric field synergistic method capable of regulating glutamic acid oxidation, and belongs to the technical field of photoelectrochemistry. The method uses photoelectrochemistry technology and takes glutamic acid as a single raw material to realize the method for the directional synthesis of multiple high-value-added amino acids. The method takes industrial-grade glutamic acid aqueous solution as a raw material, adopts a controllable photoelectrochemical reaction system, adjusts the electrode potential, illumination conditions, temperature and catalyst composition, realizes the selective synthesis of aspartic acid, gamma-aminobutyric acid and beta-alanine products from the same precursor, and the reaction process is completely driven by sunlight or external renewable power, without the addition of enzyme preparations, expensive coenzymes or chemical reducing agents, so that the problems of high cost, poor stability of traditional enzyme methods and serious pollution, high energy consumption of chemical synthesis are solved from the source.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrochemical technology, specifically relating to a visible light-electric field synergistic method for regulating glutamate oxidation. Background Technology

[0002] Amino acids, as essential basic biochemicals, have wide applications in the food, pharmaceutical, feed, and chemical industries, with a huge global annual demand. Glutamic acid, in particular, is not only a key flavor enhancer and food additive but also an important precursor for the synthesis of various high-value-added amino acids and organic acids. Many amino acids derived from or related to glutamic acid possess extremely high market value and application potential. Aspartic acid is a key intermediate in the tricarboxylic acid cycle and urea cycle in organisms; γ-aminobutyric acid (GABA), as the most important inhibitory neurotransmitter in the mammalian central nervous system, has attracted much attention in the health food and pharmaceutical fields, and is widely used in functional products to improve sleep, relieve anxiety, and help lower blood pressure; β-alanine is a precursor to carnosine synthesis and is experiencing rapid market demand growth in the sports nutrition field as a dietary supplement to enhance muscle endurance and alleviate muscle soreness.

[0003] Currently, most amino acid production methods can only achieve the synthesis of a single target product, making it difficult to simultaneously convert a single raw material into multiple high-value-added products. From a biological and enzymatic perspective, the enzymatic or chemical conversion pathways of glutamic acid are relatively well-developed. However, enzyme preparations are expensive, and the stability and reusability of enzymes limit their industrial application, raising concerns about sustainability. Therefore, developing a new photoelectrocatalytic method that is driven by renewable energy, requires no enzymes, and can convert glutamic acid into multiple high-value-added amino acids and organic acids in one step has significant practical implications and broad market prospects for improving the atom economy of the amino acid industry, reducing energy consumption and costs, and promoting the upgrading of green biomanufacturing.

[0004] The main cause of pollution in traditional enzymatic processes is high-concentration organic wastewater, but the primary source of pollution lies in the fermentation waste liquid. After fermentation, a large amount of high chemical oxygen demand (COD) fermentation waste liquid (containing residual culture medium, bacterial metabolites, and miscellaneous proteins) is generated. If not properly treated, this can severely eutrophicate water bodies. Traditional free enzymes retain only 48.7% of their activity after incubation at 60°C for 4 hours, and the conversion rate decreases by more than 20% after 10 consecutive batches. The poor stability stems from the fact that enzymes, as proteins, are susceptible to inactivation due to environmental factors (temperature, pH, shear forces from mechanical stirring), and coenzymes are easily lost during the reaction, leading to the collapse of the catalytic system.

[0005] Traditional high-temperature and high-pressure chemical synthesis methods (taking maleic acid ammoniation as an example) consume over 200 kWh of energy per kilogram of target product, according to comprehensive energy consumption data. The severe pollution and high energy consumption are due to the reliance on strong acids, strong bases, and heavy metal catalysts, the harsh reaction conditions (>100℃, 1-10 MPa), and the extensive use of organic solvents for extraction and separation, resulting in high-salt organic wastewater and large emissions of VOCs. In contrast, the embodiments of this invention can drive the reaction under room temperature and light conditions, the catalyst activity decreases by less than 2% after 10 batches of reuse, and the comprehensive energy consumption is reduced by more than 90%. The entire process involves no organic solvents, significantly improving the stability, economy, and environmental friendliness of the process. Summary of the Invention

[0006] The purpose of this invention is to provide a method for efficiently preparing various high-value-added amino acids and organic acids using glutamic acid as a precursor and photoelectrochemical technology. The method uses glutamic acid as a single raw material, with sunlight or external clean electricity as the energy input, and operates under ambient temperature and pressure conditions, without enzymes or microorganisms. Through a photoelectrochemical system with dual redox active sites, eight high-value-added products—aspartic acid, γ-aminobutyric acid, β-alanine, glycolic acid, succinic acid, α-ketoglutarate, formic acid, and acetic acid—are simultaneously obtained.

[0007] To achieve the above objectives, the present invention provides a visible light-electric field synergistic method for regulating glutamate oxidation, comprising the following steps: Argon gas is introduced into an electrolyte containing glutamic acid, and then a photoelectrochemical reaction is carried out under an applied voltage to obtain a mixed solution containing amino acids. The mixed solution includes aspartic acid, γ-aminobutyric acid, and β-alanine.

[0008] Preferably, the concentration of glutamic acid in the glutamic acid-containing electrolyte is 2 mM to 2000 mM.

[0009] Preferably, the electrolyte in the glutamic acid-containing electrolyte is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution, and potassium hydroxide solution.

[0010] Preferably, the temperature range of the photoelectrochemical reaction is 25°C to 150°C, and the pressure is atmospheric pressure.

[0011] Preferably, the photoelectrochemical reaction takes 12 to 1000 hours.

[0012] Preferably, the light intensity of the light source used in the photoelectrochemical reaction is 40~550 mW / cm². 2 .

[0013] Preferably, the argon gas flow rate is 10~50 mL / min, the argon gas is introduced for ≥1 h before the reaction, and is continuously introduced during the reaction.

[0014] Preferably, the photoelectrochemical reaction system is as follows: using Ag / AgCl as a reference electrode, using an iron sheet as a counter electrode placed in the counter electrode compartment, and using a photoanode as a working electrode placed in the working electrode compartment, wherein the working electrode compartment and the counter electrode compartment are separated by a Nafion membrane; an electrolyte containing glutamic acid is added to the working electrode compartment and the counter electrode compartment respectively.

[0015] Preferably, the applied voltage for the photoelectrochemical reaction is 0V~1.5V.

[0016] More preferably, the photoanode is prepared from an FTO substrate covered by a main catalyst; the main catalyst is at least one of metal oxide, metal sulfide, g-C3N4, silicon, and multi-component composite semiconductor. The metal oxide is at least one of TiO2, Fe2O3, ZnO, WO3, and BiVO4; the metal sulfide is at least one of ZnS, CdS, and Cu2S; and the multi-element composite semiconductor is at least one of Si / TiO2 and CdS / TiO2.

[0017] The beneficial effects of invention: This invention provides a visible light-electric field synergistic method for controlling glutamate oxidation, utilizing photoelectrochemical technology to achieve the targeted synthesis of various high-value-added amino acids and organic acids using glutamate as a single raw material. This method uses industrial-grade glutamate aqueous solution as raw material and employs a controllable photoelectrochemical reaction system. By adjusting electrode potential, illumination conditions, temperature, and catalyst composition, it achieves the selective synthesis of aspartic acid, γ-aminobutyric acid, and β-alanine products starting from the same precursor. The reaction process is entirely driven by sunlight or externally supplied renewable electricity, eliminating the need for enzyme preparations, expensive coenzymes, or chemical reducing agents. This fundamentally solves the problems of high cost, poor stability, severe pollution, and high energy consumption associated with traditional enzymatic methods and chemical synthesis. Attached Figure Description

[0018] Figure 1 The X-ray diffraction results are those of the photoelectric anode prepared in this invention; Figure 2 These are LSV curves of the glutamate decomposition process in Examples 1 and 2; Figure 3 The yields of different amino acids in Examples 3-6 at different potentials; Figure 4 The yields of the three amino acids under different applied fixed voltages in Examples 5-9; Figure 5 The yields of the three amino acids in Examples 4 and 10-11; Figure 6 The yields of the three amino acids in Examples 4 and 12-13; Figure 7 The yield of amino acids in Example 12; Figure 8 The yield of amino acids in Example 13. Detailed Implementation

[0019] This invention provides a visible light-electric field synergistic method for regulating glutamate oxidation, the steps of which are as follows: Argon gas is introduced into an electrolyte containing glutamic acid, and then a photoelectrochemical reaction is carried out to obtain a mixed solution containing amino acids; the mixed solution includes aspartic acid, γ-aminobutyric acid, and β-alanine.

[0020] Preferably, the concentration of glutamic acid in the glutamic acid-containing electrolyte is 2 mM to 2000 mM. More preferably, the concentration of glutamic acid in the glutamic acid-containing electrolyte is 2 to 20 mM, and even more preferably, the concentration is 20 mM.

[0021] Preferably, the electrolyte in the glutamic acid-containing electrolyte is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution, and potassium hydroxide solution.

[0022] In a specific embodiment of the present invention, the electrolyte is a phosphate buffer solution with a pH value of 7.

[0023] Preferably, the temperature range of the photoelectrochemical reaction is 25℃~150℃, more preferably 25℃~80℃; the pressure is atmospheric pressure.

[0024] Preferably, the photoelectrochemical reaction takes 12 to 1000 hours.

[0025] Preferably, the light intensity of the light source used in the photoelectrochemical reaction is 40~550 mW / cm². 2 .

[0026] Preferably, the argon gas flow rate is 10~50 mL / min, the argon gas is introduced for ≥1 h before the reaction, and is continuously introduced during the reaction.

[0027] Preferably, the photoelectrochemical reaction system is as follows: using Ag / AgCl as a reference electrode, using an iron sheet as a counter electrode placed in the counter electrode compartment, and using a photoanode as a working electrode placed in the working electrode compartment, wherein the working electrode compartment and the counter electrode compartment are separated by a Nafion membrane; an electrolyte containing glutamic acid is added to the working electrode compartment and the counter electrode compartment respectively.

[0028] Preferably, the applied voltage for the photoelectrochemical reaction is 0V~1.5V.

[0029] More preferably, the photoanode is prepared from an FTO substrate covered by a main catalyst; the main catalyst is at least one of metal oxides (TiO2, Fe2O3, ZnO, WO3, BiVO4), metal sulfides (ZnS, CdS, Cu2S), g-C3N4, silicon, and multi-component composite semiconductors (Si / TiO2, CdS / TiO2).

[0030] In a specific embodiment of the present invention, the photoanode is anatase TiO2 / FTO photoanode or hematite Fe2O3 / FTO photoanode.

[0031] The preparation method of the anatase TiO2 / FTO photoanode includes the following steps: (1) Substrate treatment: Select a substrate with a size of 1×2 cm. 2 Using FTO conductive glass as a substrate, one end is shielded with a mask to precisely define the effective working area of ​​the electrode (approximately 1 cm²). 2 and electrical contact area; (2) Cavity preparation and cleaning: Place the treated substrate into the magnetron sputtering deposition chamber and evacuate the chamber to a high vacuum (base vacuum ≤ 2.0 × 10⁻⁶). -4 The working pressure was adjusted to 8.6 Pa, followed by the introduction of high-purity argon gas (Ar, purity >99.999%). Under these conditions, the plasma was turned on to bombard and clean the FTO substrate surface for 10 minutes to thoroughly remove organic contaminants. (3) Thin film deposition: A high-purity titanium target with a diameter of 50.8 mm (purity > 99.99 wt%) was used. The working gas pressure was adjusted to 2.0 Pa. Sputtering deposition was carried out continuously for 5 hours under the optimized parameters of DC sputtering power of 460 W. During the process, titanium atoms were sputtered out and reacted with the residual oxygen in the cavity to directly form a well-crystallized anatase TiO2 thin film on the FTO substrate, thus obtaining a TiO2 / FTO photoelectric anode.

[0032] The hematite α The preparation method of Fe2O3 / FTO photoanode is as follows: First, take a 1×2 cm piece2 The FTO conductive glass sheets were ultrasonically cleaned (150W) for 30 minutes each in deionized water, ethanol and acetone to ensure that the surface was hydrophilic.

[0033] Then, a solution containing 0.15 M ferric chloride hexahydrate (FeCl3·6H2O) and 1 M sodium nitrate (NaNO3) was prepared. 10 mL of this solution was pipetted into a 50 mL polytetrafluoroethylene (PTFE) liner. An FTO conductive glass slide was inserted obliquely at the bottom, conductive side down, and transferred to a high-pressure vessel. The slide was then placed in a 120 °C oven and heated for 4 hours, after which it was allowed to cool to room temperature. The FTO conductive glass slide was removed, rinsed thoroughly with anhydrous ethanol and deionized water, and the crystals on the non-conductive side were wiped away with paper. The sample was then dried in a 60 °C vacuum drying oven for 12 hours, resulting in the growth of a FeOOH layer on the FTO conductive surface. The sample was then placed in a muffle furnace and annealed at 600 °C for 1 hour, with a heating rate of 2 °C / min. After cooling to room temperature, the sample was removed, yielding a brick-red sample. α -Fe2O3.

[0034] Phase analysis of the prepared photoanode thin film was performed using grazing-angle X-ray diffraction (XRD), such as... Figure 1 As shown, where, Figure 1 (a) XRD pattern of TiO2 / FTO photoanode. Figure 1 (b) is the XRD pattern of the α-Fe₂O₃ / FTO photoanode, from... Figure 1 Observations revealed that the prepared TiO2 was anatase phase and the prepared Fe2O3 was hematite phase.

[0035] Example 1 A visible light-electric field synergistic method for regulating glutamate oxidation, comprising the following steps: Argon gas was introduced into an electrolyte containing glutamic acid (the concentration of glutamic acid was 20 mM, and the electrolyte was a phosphate buffer solution with a pH of 7) at a flow rate of 30 mL / min. Argon gas was introduced for 1 hour before the reaction and then continuously introduced during the reaction. The photoelectrochemical reaction was carried out at 25 °C and atmospheric pressure for 3 days to obtain the oxidative decomposition products of glutamic acid. The photoelectrochemical reaction system is as follows: Ag / AgCl is used as the reference electrode, an iron sheet is used as the counter electrode and placed in the counter electrode compartment, and the anatase TiO2 / FTO photoanode is used as the working electrode and placed in the working electrode compartment. The working electrode compartment and the counter electrode compartment are separated by a Nafion membrane. 30 mL of glutamic acid-containing electrolyte is added to each of the working electrode compartment and the counter electrode compartment, and argon gas is continuously introduced. The power supply is turned on, and the applied voltage is adjusted to 0-1.4 V, using a light intensity of 100 mW / cm².2 The working electrode is illuminated by a light source, which drives the glutamic acid in the electrolyte to undergo a photoelectrochemical oxidation decomposition reaction.

[0036] Example 2 A visible light-electric field synergistic method for regulating glutamate oxidation is described. The steps are the same as in Example 1, except that the photoanode used in Example 2 is a hematite Fe2O3 / FTO photoanode.

[0037] Electrochemical detection was performed using a Chenhua electrochemical workstation, and the LSV (linear sweep voltammetry) curves for the glutamic acid decomposition process in Examples 1 and 2 are shown below. Figure 2 As shown, where, Figure 2 (a) is the LSV curve obtained by changing the current density as a function of potential under chopping conditions for TiO2 / FTO in Example 1. Figure 2 (b) is the LSV curve obtained by the change of current density with potential under the Fe2O3 / FTO chopping condition in Example 2. Figure 2 It can be seen that both photoanodes in Example 1 and Example 2 have photoresponse under illumination.

[0038] Examples 3-4 A visible light-electric field synergistic method for regulating glutamate oxidation is described. The steps are the same as in Example 1, except that the applied voltages in Examples 3 and 4 are fixed at 1.1V and 1.4V, respectively, and the amino acids in the product are a mixture of aspartic acid, γ-aminobutyric acid, and β-alanine.

[0039] Examples 5-6 A visible light-electric field synergistic method for regulating glutamate oxidation is described. The steps are the same as in Example 2, except that the applied voltages in Examples 5 and 6 are fixed at 1.1V and 1.4V, respectively, and the amino acid in the product is aspartic acid.

[0040] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products. The yields of the three amino acids (aspartic acid, γ-aminobutyric acid, and β-alanine) obtained using TiO2 / FTO as a catalyst in Examples 3-4 are shown in the following graphs at different potentials. Figure 3 As shown in (a), the yield graphs of amino acids (aspartic acid) obtained by Fe2O3 / FTO as catalyst in Examples 5-6 at different potentials are as follows. Figure 3 As shown in (b). The amino acid yields in Examples 3-6 are shown in Table 1.

[0041] Table 1

[0042] Depend on Figure 3It can be seen that TiO2 / FTO has a higher yield as a catalyst than Fe2O3 / FTO, which is attributed to the higher current density of TiO2 / FTO compared to Fe2O3 / FTO.

[0043] To further investigate the effects of different parameters on the experiment, the following example was set up.

[0044] Examples 7-9 A visible light-electric field synergistic method for regulating glutamate oxidation is provided according to the method in Example 1, with the light intensity limited to 100 mW / cm². 2 The temperature was 25°C, and the applied fixed voltages in Examples 5-9 were defined as 0.2V, 0.5V, 0.8V, 1.1V, and 1.4V, respectively. The amino acids in the products were all a mixture of aspartic acid, γ-aminobutyric acid, and β-alanine.

[0045] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products. The yields of the three amino acids (aspartic acid, γ-aminobutyric acid, and β-alanine) under different applied fixed voltages in Examples 5-9 were determined as follows: Figure 4 As shown in Table 2, by Figure 4 As shown in Table 2, the product yield is relatively high at a voltage of 1.1V.

[0046] Table 2

[0047] Examples 10-11 A set of visible light-electric field synergistic method experiments for regulating glutamate oxidation is provided according to the method in Example 1, with the applied fixed voltage limited to 1.1V and the light intensity to 100mW / cm². 2 Examples 10 and 11 were respectively limited to temperatures of 50°C and 80°C. The amino acid in the product of Example 10 was a mixture of aspartic acid, γ-aminobutyric acid, and β-alanine; the amino acid in the product of Example 11 was a mixture of aspartic acid and γ-aminobutyric acid.

[0048] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products. The yields of the three amino acids (aspartic acid, γ-aminobutyric acid, and β-alanine) in Examples 3 and 10-11 at a potential of 1.1V were as follows: Figure 5 As shown in Table 3, the yields of Examples 10-11 are as follows: Figure 5 As shown in Table 1-3, the product yield is highest at a temperature of 25℃.

[0049] Table 3

[0050] Examples 12-13 Following the method in Example 1, a set of visible light-electric field synergistic method experiments were provided to regulate glutamate oxidation, with the applied fixed voltage limited to 1.1V, the temperature to 25℃, and the light intensity limited to 40mW / cm². 2 70mW / cm 2 The amino acids in the product are a mixture of aspartic acid and γ-aminobutyric acid.

[0051] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products. The yields of the three amino acids (aspartic acid, γ-aminobutyric acid, and β-alanine) in Examples 3 and 12-13 at a potential of 1.1V were as follows: Figure 6 As shown in Table 4, the yields of Examples 12-13 are as follows: Figure 6 It can be seen that when the light intensity is 100mW / cm 2 The product yield is the highest.

[0052] Table 4

[0053] Example 14 Following the method in Example 2, a set of visible light-electric field synergistic method experiments are provided to regulate glutamate oxidation, with the applied fixed voltage limited to 1.1V and the light intensity to 100mW / cm². 2 In Example 14, the temperature was limited to 80°C. The amino acid in the product was aspartic acid.

[0054] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products. The yields of aspartic acid in Examples 5 and 14 at a potential of 1.1V were as follows: Figure 7 As shown in Table 5, the yield of Example 14 is obtained from... Figure 7 As shown in Tables 1 and 5, the product yield is highest at a temperature of 25℃.

[0055] Table 5

[0056] Example 15 Following the method in Example 2, a set of visible light-electric field synergistic method experiments were provided to regulate glutamate oxidation, with the applied fixed voltage limited to 1.1V, the temperature to 25℃, and the light intensity limited to 70mW / cm². 2 The amino acid in the product is aspartic acid.

[0057] High-performance liquid chromatography (HPLC) was used for quantitative detection of the products, and the yields of aspartic acid in Examples 4 and 15 at a potential of 1.1V were obtained as follows: Figure 8 As shown in Table 6, the yield of Example 17 is obtained from... Figure 8 It can be seen that when the light intensity is 100mW / cm2 The product yield is the highest.

[0058] Table 6

[0059] In summary, the photoelectrochemical method provided by this invention, using a TiO2 / FTO electrode, can efficiently and selectively convert glutamic acid into aspartic acid, γ-aminobutyric acid, and β-alanine under optimized conditions of an applied voltage of 1.1V, a reaction temperature of 25℃, and a light intensity of 100 mW / cm². This system exhibits significant response under light irradiation, good reaction stability, and high product yield and synthesis efficiency, providing a practical new route for the green and controllable synthesis of amino acids.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A visible light-electric field synergistic method for regulating glutamate oxidation, characterized in that, Includes the following steps: Argon gas is introduced into an electrolyte containing glutamic acid, and then a photoelectrochemical reaction is carried out under an applied voltage to obtain a mixed solution containing amino acids. The mixed solution includes aspartic acid, γ-aminobutyric acid, and β-alanine.

2. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The concentration of glutamic acid in the electrolyte containing glutamic acid is 2 mM to 2000 mM.

3. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The glutamic acid-containing electrolyte is at least one of phosphate buffer, potassium bicarbonate solution, potassium carbonate solution, sodium bicarbonate solution, potassium carbonate solution, hydrochloric acid solution, sulfuric acid solution, sodium hydroxide solution, and potassium hydroxide solution.

4. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The temperature range of the photoelectrochemical reaction is 25°C to 150°C, and the pressure is atmospheric pressure.

5. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The photoelectrochemical reaction takes 12 to 1000 hours.

6. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The light intensity of the light source used in the photoelectrochemical reaction is 40~550mW / cm². 2 .

7. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The argon gas flow rate is 10~50 mL / min, the argon gas is introduced for ≥1 h before the reaction, and is continuously introduced during the reaction.

8. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 1, characterized in that, The photoelectrochemical reaction system is as follows: using Ag / AgCl as the reference electrode, using an iron sheet as the counter electrode and placing it in the counter electrode compartment, and using a photoanode as the working electrode and placing it in the working electrode compartment. The working electrode compartment and the counter electrode compartment are separated by a Nafion membrane. An electrolyte containing glutamic acid is added to the working electrode compartment and the counter electrode compartment, respectively.

9. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 8, characterized in that, The applied voltage for the photoelectrochemical reaction is 0V~1.5V.

10. The visible light-electric field synergistic method for regulating glutamate oxidation according to claim 8, characterized in that, The photoanode is prepared from an FTO substrate covered with a main catalyst; the main catalyst is at least one of metal oxide, metal sulfide, g-C3N4, silicon, and multi-component composite semiconductor. The metal oxide is at least one of TiO2, Fe2O3, ZnO, WO3, and BiVO4; the metal sulfide is at least one of ZnS, CdS, and Cu2S; and the multi-element composite semiconductor is at least one of Si / TiO2 and CdS / TiO2.

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