PHOTOCATALYST COMPOSITE, METHOD OF PREPARING THE SAME AND METHOD OF PRODUCING HYDROGEN

Abstract

The present invention provides a photocatalyst composite, a method of preparing the same, and a method of producing hydrogen. The method of preparing the photocatalyst composite includes a step of preparing g-C.sub.3N.sub.4, a step of preparing CuFeO.sub.2 and a step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2. Preparing g-C.sub.3N.sub.4 includes heating a predetermined weight of melamine at a predetermined heating rate for a predetermined time to obtain g-C.sub.3N.sub.4 powder. Preparing CuFeO.sub.2 includes hydrothermal synthesis followed by drying to obtain CuFeO.sub.2 powder. Synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2 includes mixing the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps with a predetermined ratio to obtain a photocatalyst composite of g-C.sub.3N.sub.4/CuFeO.sub.2 in which the photocatalyst composite has a heterogeneous structure. The method of producing hydrogen includes adding plastic to an alkaline solution to form a pretreatment solution and performing hydrogen production through a photoreforming reaction in the plastic pretreatment solution using the aforementioned photocatalyst composite.

Claims

1. A photocatalyst composite, which is g-C.sub.3N.sub.4/CuFeO.sub.2 and has a heterogeneous structure.

2. The photocatalyst composite of claim 1, wherein g-C.sub.3N.sub.4 and CuFeO.sub.2 used to form the photocatalyst composite are powders, and a weight ratio for constituting the composite is 1:1 to 7:1.

3. A method of preparing a photocatalyst composite, comprising: a step of preparing g-C.sub.3N.sub.4, heating a predetermined weight of melamine at a predetermined heating rate for a predetermined time to obtain g-C.sub.3N.sub.4 powder; a step of preparing CuFeO.sub.2, performing a hydrothermal synthesis followed by drying to obtain CuFeO.sub.2 powder; and a step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, mixing the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps with a predetermined ratio to obtain a photocatalyst composite of g-C.sub.3N.sub.4/CuFeO.sub.2, wherein the photocatalyst composite has a heterogeneous structure.

4. The method of preparing the photocatalyst composite of claim 3, wherein in the step of preparing g-C.sub.3N.sub.4, 2 g of melamine is placed in an Al.sub.2O.sub.3 crucible, followed by being covered with a crucible lid and then heated at a rate of 2 C./min to 550 C. and maintained for 4 hours.

5. The method of preparing the photocatalyst composite of claim 3, wherein in the step of preparing CuFeO.sub.2, a predetermined amount of CuSO.sub.4.Math.5H.sub.2O, a predetermined amount of FeSO.sub.4.Math.7H.sub.2O and a predetermined amount of NaOH are dissolved in a predetermined amount of H.sub.2O to prepare a precursor solution, and a predetermined amount of the precursor solution is then placed into an autoclave and kept at a predetermined temperature for a predetermined time, and a black powder is obtained by centrifugation, followed by repeated washing with a mixed solution of ethanol and water, and the black powder is then dispersed in water and dried at a predetermined temperature to obtain the CuFeO.sub.2 powder.

6. The method of preparing the photocatalyst composite of claim 3, wherein in the step of preparing CuFeO.sub.2, 7.5 mmol of CuSO.sub.4.Math.5H.sub.2O, 7.5 mmol of FeSO.sub.4.Math.7H.sub.2O and 110 mmol of NaOH are dissolved in 35 ml of H.sub.2O to prepare a precursor solution, and 16 ml of the precursor solution is then placed into an autoclave and kept at 160 C. for 6 hours, and the black powder is obtained by centrifugation and followed by repeated washing with a mixed solution of ethanol and water, followed by dispersing the black powder in water and drying at 60 C. to obtain the CuFeO.sub.2 powder.

7. The method of preparing the photocatalyst composite of claim 3, wherein in the step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps are mixed in a weight ratio of 1:1 to 7:1 to obtain the photocatalyst composite.

8. The method of preparing the photocatalyst composite of claim 3, wherein in the step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps are mixed in a weight ratio of 1:1 to 7:1 and dispersed in an ethanol-water mixed solution followed by sonicating and then stirring until the solvent completely evaporates and then heated at no more than 300 C. for 2 hours in a tube furnace under N.sub.2 atmosphere to obtain the photocatalyst composite or the powders are mixed and then physically ground to obtain the photocatalyst composite.

9. A method of producing hydrogen, comprising: adding plastic to an alkaline solution to form a pretreatment solution and performing a hydrogen production reaction by photoreforming the pretreatment solution using the photocatalyst composite of claim 1.

10. The method of producing hydrogen of claim 9, wherein in the step of forming the pretreatment solution, the plastic is added to a KOH solution with a predetermined volume molar concentration to form the pretreatment solution containing the treated plastic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the above and other objects, features, advantages and embodiments of the present invention easier to understand, the accompanying drawings are described as follows:

[0018] FIG. 1 shows a schematic diagram of the process of preparing a photocatalyst composite according to the embodiments of the present invention.

[0019] FIG. 2 shows X-ray diffraction (XRD) patterns of photocatalysts and a photocatalyst composite according to an embodiment of the present invention.

[0020] FIG. 3 shows a transmission electron microscope (TEM) image of a photocatalyst composite according to an embodiment of the present invention.

[0021] FIG. 4 shows a high-resolution TEM (HR-TEM) image of a photocatalyst composite according to an embodiment of the present invention.

[0022] FIG. 5 shows Fourier-transform infrared spectroscopy (FTIR) spectra of photocatalysts and a photocatalyst composite according to an embodiment of the present invention.

[0023] FIG. 6 shows X-ray photoelectron spectroscopy (XPS) spectra of photocatalysts and a photocatalyst composite according to an embodiment of the present invention.

[0024] FIG. 7 shows the photoluminescence (PL) spectra of a photocatalyst and a photocatalyst composite according to an embodiment of the present invention.

[0025] FIG. 8 illustrates the hydrogen production performance of photoreforming plastics of photocatalysts and a photocatalyst composite according to an embodiment of the present invention.

[0026] FIG. 9 illustrates hydrogen production conditions of photoreforming plastic of a photocatalyst composite according to an embodiment of the present invention.

[0027] FIG. 10 illustrates the hydrogen production effects of a photocatalyst composite in seawater according to an embodiment of the present invention.

[0028] According to usual working methods, various features and components in the figures are not drawn to the actual scale. The drawing method is to present specific features and components related to the present invention in the best way. In addition, the same or similar reference symbols are used in different drawings to refer to similar elements and components.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following disclosure provides different embodiments or examples to achieve different features of the provided subject matters. The specific examples of components and arrangements described below are for simplifying the present disclosure and are not intended to be limiting; the size and shape of the components are not limited by the disclosed range or numerical values but may depend on the process conditions of the components or the required characteristics. For example, cross-sectional views are used to describe the technical features of the present invention, and these cross-sectional views are schematic diagrams of idealized embodiments. Therefore, variations in the shapes shown in the figures due to manufacturing processes and/or tolerances are to be expected and should not be limited thereby.

[0030] Furthermore, spatially relative terms, such as below, beneath, lower, over and higher, etc., are used to easily describe the relationship between elements or features depicted in the diagrams; in addition, spatially relative terms include not only orientations depicted in diagrams but also different orientations in which the components are used or operated.

[0031] First, the content of the embodiments of the present invention relates to a photocatalyst composite and a method of preparing the same, a method of photocatalytic hydrogen production, and a method of photoreforming plastics for hydrogen production. For example, using hydrolyzed plastic (e.g., plastic waste) as a raw material with the help of a suitable photocatalyst, hydrogen is produced under sunlight irradiation, and the hydrolyzed plastic is degraded into economically valuable chemicals. In addition, the photocatalyst composite of the embodiments of the present invention is composed of non-toxic and earth-abundant elements, such as a heterostructure photocatalyst g-C.sub.3N.sub.4/CuFeO.sub.2, which can be prepared by a simple and low-cost method. In short, an embodiment of the present invention is to synthesize the heterostructure photocatalyst g-C.sub.3N.sub.4/CuFeO.sub.2 (i.e., the photocatalyst composite) from the separately prepared g-C.sub.3N.sub.4 and CuFeO.sub.2, and hydrogen is efficiently produced by photoreforming plastic waste. Furthermore, in an embodiment of the present invention, plastic waste (e.g., polyester plastics) is first formed into a hydrolyzed plastic solution in an alkaline solution, and then the heterostructure photocatalyst g-C.sub.3N.sub.4/CuFeO.sub.2 (i.e., the photocatalyst composite) is used as the photocatalyst for photocatalytic hydrogen production and photoreforming plastics for hydrogen production.

[0032] Below, the technical content of the embodiments of the present invention will be further described in detail with reference to the relevant drawings.

[0033] First, please refer to FIG. 1, which is a schematic diagram of the process of preparing a photocatalyst composite according to the embodiments of the present invention. As shown in FIG. 1, a procedure of preparing the photocatalyst includes (1) a step (10) of preparing g-C.sub.3N.sub.4, (2) a step (20) of preparing CuFeO.sub.2, and (3) a step (30) of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2.

[0034] In the step (10) of preparing g-C.sub.3N.sub.4, 2 g of melamine is placed in an Al.sub.2O.sub.3 crucible, followed by being covered with a crucible lid and then heated at a rate of 2 C./min to 550 C. and maintained for 4 hours.

[0035] In the step (20) of preparing CuFeO.sub.2, CuFeO.sub.2 is synthesized by a hydrothermal method. Specifically, 7.5 mmol of CuSO.sub.4.Math.5H.sub.2O, 7.5 mmol of FeSO.sub.4.Math.7H.sub.2O and 110 mmol of NaOH are dissolved in 35 ml of H.sub.2O to prepare a precursor solution, where the precursor solution is brown. Afterwards, 16 ml of the brown precursor solution is moved to a 23 ml autoclave and kept at 160 C. for 6 hours. Next, a resulting black powder is collected by centrifugation and washed repeatedly with a mixed solution of ethanol and water. Finally, the black powder is dispersed in water and dried at 60 C. to obtain CuFeO.sub.2.

[0036] In the step (30) of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, in order to prepare the heterostructure, g-C.sub.3N.sub.4 and CuFeO.sub.2 are dispersed in an ethanol-water mixed solution with a volume ratio of 1:1 followed by sonicating for 30 minutes. The mixed solution is then continuously stirred at 80 C. until the solvent completely evaporates, and a mixed powder is obtained. Afterwards, the mixed powder is ground or heated at 300 C. for 2 hours in a tube furnace under N.sub.2 atmosphere. Next, the mixed powder is washed with water and then collected by centrifugation, followed by drying in a vacuum oven at 60 C. to obtain a photocatalyst composite composed of g-C.sub.3N.sub.4/CuFeO.sub.2. In an embodiment of the present invention, a weight ratio of g-C.sub.3N.sub.4 and CuFeO.sub.2 used to synthesize g-C.sub.3N.sub.4/CuFeO.sub.2 is 5:1.

[0037] In addition, in other embodiments of the present invention, a method of preparing a photocatalyst composite also includes (1) a step (10) of preparing g-C.sub.3N.sub.4, (2) a step (20) of preparing CuFeO.sub.2, and (3) a step (30) of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2. However, in the step of preparing g-C.sub.3N.sub.4 in other embodiments of the present invention, another weight of melamine is placed in an Al.sub.2O.sub.3 crucible, followed by being covered with a crucible lid and then heated at another heating rate for another length of time to obtain g-C.sub.3N.sub.4 powder. In the step of preparing CuFeO.sub.2 in other embodiments of the present invention, CuFeO.sub.2 powder is obtained by synthesizing through a hydrothermal method or another method followed by drying. In the step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2 in other embodiments of the present invention, the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps are mixed in another ratio to obtain a photocatalyst composite of g-C.sub.3N.sub.4/CuFeO.sub.2, in which the photocatalyst composite has a heterogeneous structure.

[0038] In other embodiments of the present invention, in the step of preparing CuFeO.sub.2, another amount of CuSO.sub.4.Math.5H.sub.2O, another amount of FeSO.sub.4.Math.7H.sub.2O and another amount of NaOH are dissolved in another amount of H.sub.2O to prepare a precursor solution, and another amount of the precursor solution is placed into an autoclave and kept at a different temperature for a different length of time, and a black powder is obtained through centrifugation. After repeated washing with a mixed solution of ethanol and water, the black powder is dispersed in water and dried at another temperature to obtain CuFeO.sub.2 powder.

[0039] In other embodiments of the present invention, in the step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the aforementioned steps may be mixed in another weight ratio to obtain a photocatalyst composite.

[0040] In other embodiments of the present invention, in the step of synthesizing g-C.sub.3N.sub.4/CuFeO.sub.2, in addition to mixing the g-C.sub.3N.sub.4 powder and the CuFeO.sub.2 powder obtained in the previous steps in another weight ratio, it can also be ultrasonic treated for another length of time and then heated at another temperature not exceeding 300 C. for another length of time in a tube furnace under N.sub.2 atmosphere to obtain a photocatalyst composite.

[0041] From the above, it can be seen that the process of preparing the photocatalyst of the embodiments of the present invention is relatively simple compared with the prior art and does not require expensive equipment.

[0042] In addition, it should be noted that through the process of preparing the photocatalyst of the embodiment of the present invention, the photocatalyst composite can be obtained, and a material of the photocatalyst composite is g-C.sub.3N.sub.4/CuFeO.sub.2, which has a heterogeneous structure and does not exist additional crystalline impurities. Furthermore, in the embodiment of the present invention, g-C.sub.3N.sub.4 and CuFeO.sub.2 used to form the photocatalyst composite are both powders, and a weight ratio thereof is 5:1; in other embodiments, the photocatalyst composite with a weight ratio of g-C.sub.3N.sub.4 and CuFeO.sub.2 of 1:1, 3:1 or 7:1 is also better than pure g-C.sub.3N.sub.4 and CuFeO.sub.2. It should be noted here that the photocatalyst composite of the embodiments of the present invention is a photocatalyst that contains neither precious metals nor toxic metals, has good hydrogen production activity in photoreforming plastics to generate hydrogen, and can oxidize the hydrolyzed plastics into other valuable chemicals through the photogenerated holes.

[0043] A process of photoreforming plastics to generate hydrogen according to the embodiment of the present invention is explained below.

[0044] A method of producing hydrogen in an embodiment of the present invention includes adding plastic to an alkaline solution to form a pretreatment solution and generating hydrogen by performing a photoreforming reaction in the pretreatment solution using the aforementioned photocatalyst composite.

[0045] In an embodiment of the present invention, in the step of forming the pretreatment solution, the plastic is added to a KOH solution with a molar concentration of 10M. After stirring at 80 C. for a predetermined time, the KOH solution is filtered to remove impurities. A predetermined amount of water is then added to the filtered plastic solution for dilution to form the pretreatment solution containing the treated plastic. In other embodiments, the pretreatment solution can be formed by directly placing the plastic into 5M of KOH solution at room temperature, and the solution is directly used as a solution for the photoreforming reaction for hydrogen production.

[0046] In other embodiments of the present invention, in the step of forming the pretreatment solution, the plastic is added to the KOH solution with a molar concentration of 10M or another alkaline aqueous solution, and a water source may be water, tap water or seawater. After stirring at 80 C. or another temperature for another length of time, the solution is filtered to remove impurities, and another amount of water, tap water or seawater is added to the filtered plastic solution for dilution to form a pretreatment solution containing the treated plastic.

[0047] As can be seen from the above, the photocatalyst composite of the embodiments of the present invention is, for example, a photocatalyst composite composed of g-C.sub.3N.sub.4 (photocatalyst I)/CuFeO.sub.2 (photocatalyst II). The photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) exhibits good hydrogen production activity in an alkaline aqueous solution containing a variety of polyester plastics and monomers, which is much higher than the activity of using g-C.sub.3N.sub.4 (photocatalyst I) or CuFeO.sub.2 (photocatalyst II) alone as a catalyst.

[0048] Next, please refer to FIG. 2. FIG. 2 is XRD patterns of photocatalysts and a photocatalyst composite according to an embodiment of the present invention. The XRD results of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention show that all diffraction peaks are composed of the two sets of diffraction peaks of g-C.sub.3N.sub.4 and CuFeO.sub.2, and there are no additional crystalline impurities.

[0049] In addition, as shown in FIGS. 3 and 4, FIG. 3 is a TEM image of a photocatalyst composite according to an embodiment of the present invention. FIG. 4 is an HR-TEM image of a photocatalyst composite according to an embodiment of the present invention. FIGS. 3 and 4 show the microstructure and morphology of g-C.sub.3N.sub.4/CuFeO.sub.2, and g-C.sub.3N.sub.4 presents a stacked wrinkled layered structure. The two materials are intertwined to form a heterostructure, which provides more photocatalytic reaction sites to enhance photocatalytic performance.

[0050] In addition, as shown in FIGS. 5 and 6, FIG. 5 shows FTIR spectra of the photocatalysts and the photocatalyst composite according to an embodiment of the present invention. FIG. 6 is the XPS spectra of the photocatalysts and the photocatalyst composite according to an embodiment of the present invention. The FTIR and XPS results in FIGS. 5 and 6 show that the surface composition and chemical state prove that the g-C.sub.3N.sub.4/CuFeO.sub.2 composite material (i.e., the photocatalyst composite) has been successfully prepared in the embodiment of the present invention.

[0051] In addition, as shown in FIG. 7, FIG. 7 illustrates the PL spectra of photocatalyst I and the photocatalyst composite according to an embodiment of the present invention. The PL results in FIG. 7 show that the g-C.sub.3N.sub.4/CuFeO.sub.2 heterojunction successfully suppressed the recombination of photogenerated electron-hole pairs.

[0052] In addition, as shown in FIG. 8, FIG. 8 illustrates the hydrogen production performance of photocatalyst I, photocatalyst II and the photocatalyst composite according to an embodiment of the present invention. The results in FIG. 8 show that g-C.sub.3N.sub.4/CuFeO.sub.2 has excellent photocatalytic hydrogen production activity for photoreforming different types of plastics than that of g-C.sub.3N.sub.4 and CuFeO.sub.2 alone. For photoreforming polyester fibers, the photocatalytic hydrogen production activity of g-C.sub.3N.sub.4/CuFeO.sub.2 is increased by more than 60 times and 100 times than g-C.sub.3N.sub.4 and CuFeO.sub.2, respectively. In addition, although not shown in the figures, for common plastic monomers such as ethylene glycol (EG), lactic acid (LA) or 1,4-butanediol (BTO), the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention also has hydrogen production activities much higher than that of g-C.sub.3N.sub.4 and CuFeO.sub.2 alone. In addition, although not shown in the figures, proton nuclear magnetic resonance results show that an oxidation product of the photocatalyst composite of an embodiment of the present invention exhibits a formate signal.

[0053] In addition, although not shown in the figures, when discussing simplifying the process of preparing the catalyst, after preparing respective g-C.sub.3N.sub.4 and CuFeO.sub.2, an artificial physical grinding method is used to prepare the photocatalyst composite. The results show that even though the activity of the product after grinding is lower than that of g-C.sub.3N.sub.4/CuFeO.sub.2 prepared by the standard process, the photocatalyst composite of an embodiment of the present invention is still much higher than the respective activity of g-C.sub.3N.sub.4 and CuFeO.sub.2.

[0054] In addition, as shown in FIG. 9, FIG. 9 illustrates hydrogen production conditions of photoreforming plastics using the photocatalyst composite according to an embodiment of the present invention. FIG. 9 shows the performance of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) in an embodiment of the present invention in different concentrations of KOH aqueous solutions. The results show that g-C.sub.3N.sub.4/CuFeO.sub.2 has good hydrogen production activity in KOH aqueous solutions from 3M to 10M, and it has the best hydrogen production activity when the concentration of KOH is 5M. In addition, although not shown in the figures, the activity of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) with different ratios is much higher than the respective performances of g-C.sub.3N.sub.4 and CuFeO.sub.2, confirming that the heterostructure of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention inhibits light-induced charge recombination, thereby promoting hydrogen production. In addition, although not shown in the figures, after observing a relationship between activity of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) in an embodiment of the present invention and the concentrations of a hydrolyzed plastic, it is found that when the concentration of the polyester microfiber is lower than 30 mg mL.sup.1, the activity increases rapidly with the increment of hydrolyzed plastic concentration; however, when the concentration is higher than 40 mg mL.sup.1, the activity of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention reaches saturation.

[0055] In addition, as shown in FIG. 10, FIG. 10 illustrates the hydrogen production effects of a photocatalyst composite in seawater according to an embodiment of the present invention. The results in FIG. 10 show that when the seawater content exceeded 50%, hydrogen production activity of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention decreases because of high salinity and various impurities in seawater, which might cause side reactions and low stability. It might be that too much Na and Cl-occupied the surface of the photocatalyst, and thus, hydrogen evolution was hindered, or other competing side reactions were induced. However, in 100% of alkaline natural seawater, the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention still has hydrogen production activity of 1508.2 mol h.sup.1g.sub.cat.sup.1. In addition, although not shown in the figures, the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2), according to an embodiment of the present invention, could exceed an amount of 3,000 mol g.sub.cat.sup.1 after 48 hours of illumination.

[0056] It should be noted again that the present application proposes a low-cost method to prepare the heterostructure photocatalyst g-C.sub.3N.sub.4/CuFeO.sub.2 that does not contain precious metals and toxic elements. For photocatalytic reforming of plastic waste, it exhibits good hydrogen production activity.

[0057] In addition, the PL spectra show that the heterojunction of the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention successfully suppress the recombination of the photogenerated electron and hole pairs, so it can effectively utilize electrons and holes excited by light for the photocatalytic hydrogen production in reforming plastics.

[0058] In addition, for various types of polyester plastics and their monomers, such as polyethylene terephthalate (PET), polylactic acid (PLA), polybutylene succinate (PBS) or polyester microfiber, the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention all shows good hydrogen production activity, showing advantages of the photocatalyst in the versatility of plastic reforming.

[0059] In addition, in a seawater environment, the photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) in an embodiment of the present invention still shows good activity in photoreforming plastics for hydrogen production, showing that the technical strategy of the present application can also solve problems of producing green hydrogen and high-priced organic acids in areas lacking freshwater resources. The photocatalyst composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention also has good hydrogen production activity in photoreforming plastics in other common water sources, such as tap water and ditch water, which shows advantages of the photocatalytic composite (g-C.sub.3N.sub.4/CuFeO.sub.2) of an embodiment of the present invention in versatility in various water sources.

[0060] To sum up, the photocatalyst composite (photocatalyst I/photocatalyst II) provided by the embodiments of the present invention contains neither precious metals nor toxic metals, and still has promising activity in hydrogen production by photoreforming plastics reaction, and can oxidize the hydrolyzed plastics into other valuable chemicals through the photogenerated holes. In addition, photocatalyst I/photocatalyst II provided by the embodiments of the present invention exhibits good hydrogen production activity in alkaline solutions for a variety of polyester plastics and monomers, which is much higher than the activities of using photocatalyst I or photocatalyst II alone as a catalyst. Furthermore, the method of preparing the photocatalyst provided by the embodiments of the present invention is simple and does not require expensive equipment. It should also be noted here that the plastic pretreatment provided by the embodiments of the present invention can reduce the impact of impurities on the light absorption of the photocatalyst.

[0061] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will understand that the technical solution of the present invention can be modified or equivalent substitutions may be made without departing from the spirit and scope of the technical solution of the present invention.