Method for manufacturing photocatalyst for producing hydrogen

Abstract

The present disclosure relates to a method for manufacturing a photocatalyst for producing hydrogen, and a photocatalyst manufactured thereby. The photocatalyst manufacturing method according to the present disclosure has the advantage of improving hydrogen production efficiency by uniformly forming reduced graphene oxide as a shell on a core comprising titanium dioxide, thereby increasing UV radiation absorption and enabling photoexcited electrons from the titanium dioxide to be transferred to the reduced graphene oxide before recombining with holes, thus not only preventing a decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination, but also enhancing the photocatalytic reaction efficiency of titanium dioxide by expanding the photocatalytic reaction surface area.

Description

Method for manufacturing a photocatalyst for hydrogen production

[0001] The present invention relates to a method for manufacturing a photocatalyst for hydrogen production and a photocatalyst manufactured thereby.

[0002] The shortage of fossil fuels and environmental pollution have increased humanity's need for a transition to renewable energy and energy storage devices. In this context, hydrogen (H2) offers a cleaner, more economical, and non-polluting alternative. Currently, the primary sources of hydrogen production are non-renewable resources, such as methane (90%) and hydrocarbons (5%). Therefore, new and viable hydrogen production methods are urgently needed, and one of the most promising is photocatalytic water splitting, which can be performed under mild conditions. In particular, photocatalytic reforming using biomass-derived feedstocks offers a sustainable, renewable, and cost-effective method of hydrogen production.

[0003] However, titanium dioxide (TiO2), a commonly used photocatalyst, has the disadvantage of absorbing UV radiation, absorbing only 5% of sunlight, and rapid charge carrier recombination.

[0004] Accordingly, methods such as TiO2 composites and metal / non-metal doping are being developed to improve the efficiency of titanium dioxide (TiO2), but there is still a problem of low hydrogen production efficiency due to low photocatalytic efficiency.

[0005] According to one aspect of the present disclosure, a method for manufacturing a photocatalyst having high hydrogen production efficiency and a photocatalyst manufactured thereby can be provided.

[0006] According to one embodiment of the present disclosure for achieving the above-described technical problem, a method for producing a photocatalyst may be provided, including: a graphene oxide production step of producing a graphene oxide aqueous solution through a modified Hummer's method; a first mixed solution production step of adding titanium dioxide to the graphene oxide aqueous solution produced in the graphene oxide production step to produce a first mixed solution; a hydrothermal synthesis step of adding sodium hydroxide to the first mixed solution produced in the first mixed solution production step and performing hydrothermal synthesis to produce a hydrothermal synthesis solution; and a heat treatment step of drying and heat-treating the hydrothermal synthesis solution produced in the hydrothermal synthesis step.

[0007] According to one embodiment, in the first mixed solution preparation step, the graphene oxide in the graphene oxide aqueous solution may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of the solvent.

[0008] According to one embodiment, in the mixed solution preparation step, graphene oxide may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of titanium dioxide.

[0009] According to another embodiment for achieving the above-described technical problem, a method for producing a photocatalyst may be provided, including: a graphene production step of producing a graphene oxide aqueous solution through a modified Hummer's method; a reduced graphene production step of freeze-drying the graphene oxide aqueous solution produced in the graphene oxide production step and then thermally reducing it to produce reduced graphene oxide powder; a second mixed solution production step of adding the reduced graphene oxide powder produced in the reduced graphene oxide production step and titanium dioxide to the graphene oxide aqueous solution produced in the graphene oxide production step to produce a second mixed solution; a hydrothermal synthesis step of adding sodium hydroxide to the second mixed solution produced in the second mixed solution production step and hydrothermally synthesizing it to produce a hydrothermal synthesis solution; and a heat treatment step of drying and heat-treating the hydrothermal synthesis solution produced in the hydrothermal synthesis step.

[0010] According to one embodiment, in the second mixed solution preparation step, the graphene oxide and reduced graphene oxide powder may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of the graphene oxide aqueous solution solvent.

[0011] According to one embodiment, in the second mixed solution preparation step, the graphene oxide and reduced graphene oxide powder may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of titanium dioxide.

[0012] According to one embodiment, in the second mixed solution preparation step, the reduced graphene powder may be included in an amount of more than 0 parts by weight and less than or equal to 50 parts by weight based on 100 parts by weight of graphene oxide.

[0013] According to one embodiment, the graphene oxide production step may include an oxidation step of mixing expanded graphite, potassium permanganate, water, and sulfuric acid, stirring them, maintaining them at a constant temperature, and reacting them for a constant period of time to produce a graphene oxide slurry; a filtration step of mixing 50 to 200 parts by weight of water with respect to 100 parts by weight of the graphite oxide slurry produced in the oxidation step, centrifuging the mixture to discharge the filtrate, and separating the graphene oxide slurry; and a graphene oxide production step of mixing 5,000 to 20,000 parts by weight of water with respect to 100 parts by weight of the graphite oxide slurry separated in the filtration step, purifying impurities in an ion resin exchange tower, and then filtering the mixture to produce a graphene oxide aqueous solution.

[0014] According to one embodiment, the sodium hydroxide may be included in an amount of 100 parts by weight or more and 300 parts by weight or less based on 100 parts by weight of graphene oxide.

[0015] According to another embodiment for achieving the above-described technical task, a photocatalyst may be provided, comprising: a core including titanium dioxide; and a shell positioned on the titanium dioxide and including reduced graphene oxide.

[0016] According to one embodiment of the present disclosure, photocatalytic efficiency can be improved, thereby improving hydrogen production efficiency.

[0017] Figure 1 is an SEM image of a photocatalyst manufactured according to one embodiment.

[0018] FIG. 2 and FIG. 3 are a line graph (FIG. 2) and a bar graph (FIG. 3) showing the hydrogen production efficiency results of Examples 1 to 3 and Comparative Examples 1 to 4, respectively, according to one embodiment.

[0019] Figure 4 is a graph showing the PL spectra of the photocatalysts of Example 1 and Comparative Example 2.

[0020] A photocatalyst manufacturing method according to one embodiment may include a graphene oxide manufacturing step of manufacturing a graphene oxide aqueous solution through a modified Hummer's method; a first mixed solution manufacturing step of manufacturing a first mixed solution by adding titanium dioxide to the graphene oxide aqueous solution manufactured in the graphene oxide manufacturing step; a hydrothermal synthesis step of manufacturing a hydrothermal synthesis solution by adding sodium hydroxide to the first mixed solution manufactured in the first mixed solution manufacturing step and performing hydrothermal synthesis; and a heat treatment step of drying and heat-treating the hydrothermal synthesis solution manufactured in the hydrothermal synthesis step.

[0021] According to another embodiment, a photocatalyst manufacturing method may include a graphene oxide manufacturing step of manufacturing a graphene oxide aqueous solution through a modified Hummer's method; a reduced graphene oxide manufacturing step of freeze-drying the graphene oxide aqueous solution manufactured in the graphene oxide manufacturing step and then thermally reducing it to manufacture reduced graphene oxide powder; a second mixed solution manufacturing step of adding the reduced graphene oxide powder manufactured in the reduced graphene oxide manufacturing step and titanium dioxide to the graphene oxide aqueous solution manufactured in the graphene oxide manufacturing step to manufacture a second mixed solution; a hydrothermal synthesis step of adding sodium hydroxide to the second mixed solution manufactured in the second mixed solution manufacturing step and hydrothermally synthesizing it to manufacture a hydrothermal synthesis solution; and a heat treatment step of drying and heat-treating the hydrothermal synthesis solution manufactured in the hydrothermal synthesis step.

[0022] A photocatalyst according to another embodiment may include a core comprising titanium dioxide; and a shell positioned on the titanium dioxide and comprising reduced graphene oxide.

[0023] The above objectives, other objectives, features, and advantages will be readily understood through the following preferred embodiments, illustrated in the accompanying drawings. However, the embodiments described herein are not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to sufficiently convey the technical concepts to those skilled in the art.

[0024] In describing each drawing, similar reference numerals are used to designate similar components. In the attached drawings, the dimensions of structures are shown exaggerated for clarity of the present invention. Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component, without departing from the scope of the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0025] In this specification, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0026] Furthermore, when we say that a layer, membrane, region, board, or other part is "on" another part, this includes not only cases where it is "directly above" the other part, but also cases where there are other parts in between. Conversely, when we say that a layer, membrane, region, board, or other part is "under" another part, this includes not only cases where it is "directly below" the other part, but also cases where there are other parts in between.

[0027] Unless otherwise specified, all numbers, values, and / or expressions expressing quantities of ingredients, reaction conditions, polymer compositions, and blends used herein are approximations that inherently reflect, among other things, the various uncertainties of measurement that arise in obtaining such values, and therefore should be understood as being modified in all instances by the term "about." Furthermore, whenever a numerical range is disclosed herein, such range is continuous and includes every value from the minimum value to the maximum value inclusive, unless otherwise indicated. Furthermore, whenever such a range refers to an integer, every integer from the minimum value to the maximum value inclusive, unless otherwise indicated, is included.

[0028] In this specification, when a range is described for a variable, the variable will be understood to include all values ​​within the described range including the described endpoints of the range. For example, the range "5 to 10" will be understood to include the values ​​5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and any value between integers that fall within the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. Also, for example, a range of "10% to 30%" would be understood to include all integers up to and including 30%, as well as any subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and any value between reasonable integers within the stated range, such as 10.5%, 15.5%, 25.5%, etc.

[0029] Conventional photocatalysts have the disadvantage of being able to absorb only 5% of sunlight and of charge carriers rapidly recombining. To improve photocatalytic efficiency, methods such as TiO2 composites and metal / non-metal doping have been developed, but the photocatalytic efficiency is still low, resulting in low hydrogen production efficiency.

[0030] Accordingly, the inventors of the present invention conducted extensive research to solve this problem and discovered that when a photocatalyst is manufactured by mixing graphene oxide and titanium dioxide manufactured by the modified Hummus method in appropriate amounts and then hydrothermally synthesizing it with sodium hydroxide added in a specific amount, the photocatalytic efficiency is high and the hydrogen production efficiency is excellent, and this has been completed.

[0031] The photocatalyst manufacturing method of the present disclosure may include a graphene oxide manufacturing step of manufacturing a graphene oxide aqueous solution through a modified Hummer's method; a first mixed solution manufacturing step of manufacturing a first mixed solution by adding titanium dioxide to the graphene oxide aqueous solution manufactured in the graphene oxide manufacturing step; a hydrothermal synthesis step of manufacturing a hydrothermal synthesis solution by adding sodium hydroxide to the first mixed solution manufactured in the first mixed solution manufacturing step and performing hydrothermal synthesis; and a heat treatment step of drying and heat-treating the hydrothermal synthesis solution manufactured in the hydrothermal synthesis step.

[0032] The photocatalyst manufactured according to the present disclosure has the advantage of efficiently and uniformly forming reduced graphene oxide in a shell shape on a core including titanium dioxide, thereby increasing UV radiation absorption, preventing a decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing electrons photoexcited in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes, and increasing the photocatalytic reaction surface area to increase the photocatalytic reaction efficiency of titanium dioxide, thereby improving hydrogen production efficiency.

[0033] The graphene oxide production step of the present disclosure can produce a graphene oxide aqueous solution through a modified Hummus method.

[0034] In a graphene oxide production step according to one embodiment of the present disclosure, a graphene oxide solution can be produced through a modified Hummer's method, which comprises an oxidation step of mixing expanded graphite, potassium permanganate, water, and sulfuric acid, stirring, maintaining the mixture at a constant temperature, and reacting for a constant period of time to produce a graphite oxide slurry, a filtration step of mixing 50 to 200 parts by weight of water with respect to 100 parts by weight of the graphite oxide slurry produced in the oxidation step, centrifuging the mixture to discharge the filtrate, and separating the graphite oxide slurry, and a graphene oxide production step of mixing 5,000 to 20,000 parts by weight of water with respect to 100 parts by weight of the graphite slurry separated in the filtration step, purifying impurities in an ion resin exchange tower, and then filtering the mixture to produce a graphene oxide solution.

[0035] In general, graphite oxide is easily dispersed in water and exists as a negatively charged thin film plate in polar solvents, so an exfoliation process is required to form graphene oxide.

[0036] Accordingly, the graphene oxide manufacturing step according to one embodiment of the present disclosure utilizes a chemical exfoliation method called the modified Hummers method. Generally, when graphite itself is peeled off layer by layer, graphene composed only of sp2 carbon is electrically and thermodynamically unstable and clumps together on its own. However, according to the graphene oxide manufacturing step according to one embodiment, by mixing and stirring expanded graphite, potassium permanganate, water, and sulfuric acid to exfoliate the graphite through a strong oxidation reaction, there is an advantage in that graphene oxide can be stably and easily manufactured.

[0037] Therefore, in the graphene oxide production step according to one embodiment of the present disclosure, it is most preferable to produce a graphene oxide solution through a modified Hummer's method, which comprises an oxidation step of mixing expanded graphite, potassium permanganate, water, and sulfuric acid, stirring, maintaining the mixture at a constant temperature, and reacting for a constant period of time to produce a graphite oxide slurry, a filtration step of mixing 50 to 200 parts by weight of water with respect to 100 parts by weight of the graphite oxide slurry produced in the oxidation step, centrifuging the mixture to discharge the filtrate, and separating the graphite oxide slurry, and a filtration step of mixing 5,000 to 20,000 parts by weight of water with respect to 100 parts by weight of the graphite oxide slurry separated in the filtration step, purifying impurities in an ion resin exchange tower, and then filtering the mixture to produce a graphene oxide solution.

[0038] The first mixed solution preparation step of the present disclosure can prepare the first mixed solution by adding titanium dioxide to the graphene oxide aqueous solution prepared in the graphene oxide preparation step.

[0039] According to one embodiment of the present disclosure, in the first mixed solution preparation step, the graphene oxide in the graphene oxide aqueous solution may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight, specifically, more than or equal to 2 parts by weight and less than or equal to 10 parts by weight, and more specifically, more than or equal to 2 parts by weight and less than or equal to 5 parts by weight, based on 100 parts by weight of the solvent. If the content of graphene oxide is too low outside the content range, the effect of preventing a decrease in the photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing photoexcited electrons in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes is reduced, and if the content of graphene oxide is too high, the high content of reduced graphene oxide may interfere with the interaction between light and the titanium dioxide surface, thereby reducing the photocatalytic efficiency.

[0040] According to one embodiment of the present disclosure, in the first mixed solution preparation step, the graphene oxide in the graphene oxide aqueous solution may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight, specifically, more than or equal to 2 parts by weight and less than or equal to 10 parts by weight, and more specifically, more than or equal to 2 parts by weight and less than or equal to 5 parts by weight, based on 100 parts by weight of titanium dioxide. If the content of graphene oxide is too low outside the content range, the effect of preventing a decrease in the photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing photoexcited electrons in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes is reduced, and if the content of graphene oxide is too high, the high content of reduced graphene oxide may interfere with the interaction between light and the titanium dioxide surface, thereby reducing the photocatalytic efficiency.

[0041] Therefore, by including appropriate amounts of graphene oxide and titanium dioxide in the first mixed solution manufactured in the first mixed solution manufacturing step according to the embodiment of the present disclosure, the reduced graphene oxide produced by reducing graphene oxide on a core including titanium dioxide in the final photocatalyst is uniformly formed as a shell, thereby increasing UV radiation absorption, and preventing a decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing electrons photoexcited in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes, and thereby increasing the photocatalytic reaction surface area to increase the photocatalytic reaction efficiency of titanium dioxide, thereby improving hydrogen production efficiency.

[0042] In addition, the present disclosure can perform a second mixed solution preparation step of preparing a second mixed solution by adding reduced graphene oxide powder as well as titanium dioxide to the graphene oxide aqueous solution.

[0043] The reduced oxide graphene production step for producing the reduced oxide graphene powder of the present disclosure can produce reduced oxide graphene powder by freeze-drying and then thermally reducing the graphene oxide aqueous solution produced in the reduced oxide graphene production step.

[0044] According to one embodiment of the present disclosure, freeze-drying can be performed under conditions of a temperature of -50°C to -20°C and a pressure of 8 mTorr to 12 mTorr for producing reduced oxide graphene, and thermal reduction can be performed under conditions of a temperature of 800°C to 1200°C in a nitrogen atmosphere.

[0045] In the second mixed solution preparation step according to one embodiment of the present disclosure, the graphene oxide and the reduced graphene oxide powder may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight, more specifically, more than or equal to 2 parts by weight and less than or equal to 5 parts by weight, based on 100 parts by weight of the graphene oxide aqueous solution solvent, and further, the graphene oxide and the reduced graphene oxide powder may be included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight, more specifically, more than or equal to 2 parts by weight and less than or equal to 5 parts by weight, based on 100 parts by weight of titanium dioxide. If the content of graphene oxide and reduced graphene oxide powder is too low outside the content range, the effect of preventing the decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing photoexcited electrons in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes is reduced, and if the content of graphene oxide and reduced graphene oxide powder is too high, the high content of reduced graphene oxide may interfere with the interaction between light and the titanium dioxide surface, thereby reducing the photocatalytic efficiency.

[0046] In the second mixed solution preparation step according to one embodiment of the present disclosure, the reduced graphene oxide powder may be included in an amount of more than 0 parts by weight and less than or equal to 50 parts by weight, specifically, more than or equal to 10 parts by weight and less than or equal to 50 parts by weight, and more specifically, more than or equal to 25 parts by weight and less than or equal to 50 parts by weight, based on 100 parts by weight of graphene oxide. If the amount of the reduced graphene oxide powder is too low, the conductivity of the photocatalyst is lowered, so that electrons are not smoothly transported within the photocatalyst, which results in a disadvantage of lowering the photocatalytic efficiency. In addition, if the amount of the reduced graphene oxide powder is too high, the graphene oxide and titanium dioxide are unevenly distributed due to the characteristics of the irregular shape of the reduced graphene, which results in a disadvantage of lowering the photocatalytic efficiency.

[0047] That is, not only is the second mixed solution manufactured in the second mixed solution manufacturing step according to the embodiment of the present disclosure provided with appropriate amounts of graphene oxide and titanium dioxide, but also reduced graphene oxide powder is introduced at an appropriate ratio to graphene oxide, thereby improving the reduction efficiency and defect healing of graphene oxide, thereby further improving the conductivity of the final product, the photocatalyst. Consequently, compared to when only graphene oxide is introduced, the photocatalytic reaction efficiency is superior, and thus there is an advantage of superior hydrogen production efficiency.

[0048] The hydrothermal synthesis step of the present disclosure can produce a hydrothermal synthesis solution by adding sodium hydroxide to the first mixed solution produced in the first mixed solution production step or the second mixed solution produced in the second mixed solution production step and performing hydrothermal synthesis.

[0049] According to one embodiment of the present disclosure, sodium hydroxide may be added in an amount of 100 parts by weight to 300 parts by weight based on 100 parts by weight of graphene oxide. Beyond the content ratio, if the sodium hydroxide is too little, dispersibility may be reduced, and if the sodium hydroxide is too much, it may act as an impurity, lowering the pH and reducing dispersibility.

[0050] Through hydrothermal synthesis according to one embodiment of the present disclosure, not only can the crystal structure of titanium dioxide be changed, but graphene oxide can be reduced to form reduced graphene oxide, and the titanium dioxide and the formed reduced graphene oxide can react to ultimately form a photocatalyst having a core including titanium dioxide and a shell including reduced graphene oxide on the core.

[0051] The hydrothermal synthesis step according to one embodiment of the present disclosure may be performed at a temperature of 120°C to 130°C for 20 to 24 hours. Beyond this range, if the temperature is too low, graphene oxide may not be reduced, and if the temperature is too high, the pressure may increase, deforming the autoclave reactor.

[0052] The heat treatment step of the present disclosure is a step of drying and heat treating the hydrothermal synthesis solution prepared in the hydrothermal synthesis step to finally obtain a photocatalyst.

[0053] According to one embodiment of the present disclosure, drying may be performed at a temperature of 70°C to 80°C, followed by heat treatment at a temperature of 290°C to 300°C for 3 to 4 hours. Beyond the conditions, if the temperature is too low or the time is too short, there is a disadvantage that the calcination reaction does not occur, and if the temperature is too high or the time is too long, there is a disadvantage that the reactants are oxidized and the final product is lost.

[0054] The method for manufacturing a photocatalyst according to the present disclosure includes graphene oxide and titanium dioxide in appropriate amounts, so that reduced graphene oxide is uniformly formed as a shell on a core containing titanium dioxide in the final photocatalyst, thereby increasing UV radiation absorption, and preventing a decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination by allowing photoexcited electrons in titanium dioxide to be transferred to reduced graphene oxide before recombination with holes, thereby increasing the photocatalytic reaction surface area and increasing the photocatalytic reaction efficiency of titanium dioxide, thereby improving hydrogen production efficiency. In addition, by introducing reduced graphene oxide powder in an appropriate ratio to graphene oxide, the reduction efficiency and defect healing of graphene oxide are improved, thereby further improving the conductivity of the photocatalyst as a final product, so that the photocatalytic reaction efficiency is superior and the hydrogen production efficiency is superior compared to when only graphene oxide is introduced.

[0055] Accordingly, the photocatalyst according to the present disclosure has the advantage of increasing UV radiation absorption rate, allowing electrons photoexcited in titanium dioxide to be transferred to reduced graphene oxide before they recombine with holes, thereby preventing a decrease in photocatalytic reaction efficiency due to rapid charge carrier recombination, and increasing the photocatalytic reaction surface area to increase the photocatalytic reaction efficiency of titanium dioxide, thereby improving hydrogen production efficiency.

[0056]

[0057] The present invention will be described in more detail below through examples. However, these examples are intended to exemplify the present invention and the scope of the present invention is not limited to these examples.

[0058]

[0059] Example 1: Preparation of photocatalyst from graphene oxide (5rGO-TiO2)

[0060] - Graphene oxide manufacturing

[0061] 1) Oxidation step: 450 parts by weight of potassium permanganate, 20,000 parts by weight of water, and 20,000 parts by weight of sulfuric acid are mixed with 100 parts by weight of expanded graphite, stirred, and maintained at 60°C for 3 hours to produce an oxide graphite slurry.

[0062] 2) Filtration step: Mix 100 parts by weight of water with 100 parts by weight of the manufactured graphite oxide slurry, centrifuge the mixture to drain the filtrate, and separate the graphite oxide slurry.

[0063] 3) Graphene oxide manufacturing step: 100 parts by weight of graphite oxide slurry is mixed with 10,000 parts by weight of water, and impurities are purified in an ion resin exchange tower, then filtered to produce a graphene oxide aqueous solution.

[0064] - Preparation of the first mixed solution

[0065] A graphene oxide dispersion in which graphene oxide is uniformly distributed is prepared by sonicating a graphene oxide solution having a content of 5 parts by weight of graphene oxide based on 100 parts by weight of solvent in 80 mL of DI water for 1 hour. Then, TiO2 (P25) powder is slowly added to the graphene oxide dispersion while stirring. The TiO2 and graphene oxide dispersion are further stirred for 1 hour to ensure complete mixing, thereby preparing a first mixed solution having a content of 5 parts by weight of graphene oxide based on 100 parts by weight of titanium dioxide.

[0066] - Sequential synthesis

[0067] After adding 32 g of sodium hydroxide (NaOH) to the first mixed solution, it is placed in a Teflon-lined autoclave and heated at 130°C for 24 hours in an air atmosphere. Then, the heated resultant is washed with DI water, dispersed in a 0.1 M HCl solution, and maintained with stirring at room temperature overnight. Then, the maintained resultant is washed several times with DI water, centrifuged, dried at 80°C, and heat-treated at 300°C for 4 hours to finally manufacture a photocatalyst powder as shown in Fig. 1.

[0068] Example 2: Preparation of photocatalysts from graphene oxide with different contents (2rGO-TiO2)

[0069] Compared to Example 1,

[0070] Except that when preparing the first mixed solution, a graphene oxide aqueous solution having a content of 2 parts by weight of graphene oxide per 100 parts by weight of solvent was used,

[0071] A photocatalyst powder is prepared in the same manner as in Example 1.

[0072] Example 3: Preparation of photocatalyst from graphene oxide with different contents (10rGO-TiO2)

[0073] Compared to Example 1,

[0074] Except that when preparing the first mixed solution, a graphene oxide aqueous solution having a content of 10 parts by weight of graphene oxide per 100 parts by weight of solvent was used,

[0075] A photocatalyst powder is prepared in the same manner as in Example 1.

[0076] Example 4: Preparation of photocatalyst from graphene oxide and reduced graphene oxide.

[0077] Compared to Example 1,

[0078] The following reduction oxide graphene manufacturing steps are additionally performed,

[0079] Except for preparing a second mixed solution by adding reduced graphene powder so that the content of reduced graphene and reduced graphene powder is 5 parts by weight based on 100 parts by weight of the graphene oxide solution solvent (the reduced graphene powder is 10 parts by weight based on 100 parts by weight of graphene oxide),

[0080] A photocatalyst is manufactured in the same manner as in Example 1.

[0081] - Manufacturing of reduced oxide graphene

[0082] The graphene oxide aqueous solution prepared in Example 1 is freeze-dried at a temperature of -40°C for 1 hour and then thermally reduced at a temperature of 1100°C in a nitrogen atmosphere to prepare reduced graphene oxide powder.

[0083] Example 5: Preparation of photocatalysts from graphene oxide and reduced graphene oxide with different content ratios.

[0084] Compared to Example 4,

[0085] When preparing the second mixed solution

[0086] Except for adding reduced graphene powder at a content ratio of 25 parts by weight based on 100 parts by weight of graphene oxide,

[0087] A photocatalyst is manufactured in the same manner as in Example 1.

[0088] Example 6: Preparation of photocatalyst from graphene oxide and reduced graphene oxide with different content ratios.

[0089] Compared to Example 4,

[0090] When preparing the second mixed solution

[0091] Except for adding reduced graphene powder at a content ratio of 50 parts by weight based on 100 parts by weight of graphene oxide,

[0092] A photocatalyst is manufactured in the same manner as in Example 1.

[0093] Comparative Example 1: Commercial Photocatalyst

[0094] Prepare P25 TiO2 (Merck) photocatalyst.

[0095]

[0096] Comparative Example 2: Pure TiO2 photocatalyst

[0097] Prepare a bare TiO2 (Daejunghwagum) photocatalyst.

[0098] Comparative Example 3: Production of photocatalysts from graphene oxide with different contents.

[0099] Compared to Example 1,

[0100] Except that when preparing the first mixed solution, a graphene oxide aqueous solution having a content of 0.5 parts by weight of graphene oxide per 100 parts by weight of solvent was used,

[0101] A photocatalyst powder is prepared in the same manner as in Example 1.

[0102] Comparative Example 4: Production of photocatalysts from graphene oxide with different contents.

[0103] Compared to Example 1,

[0104] Except that when preparing the first mixed solution, a graphene oxide aqueous solution having a content of 1 part by weight of graphene oxide per 100 parts by weight of solvent was used,

[0105] A photocatalyst powder is prepared in the same manner as in Example 1.

[0106] Comparative Example 5: Production of photocatalysts from graphene oxide with different contents.

[0107] Compared to Example 1,

[0108] Except that when preparing the first mixed solution, a graphene oxide aqueous solution having a content of 20 parts by weight of graphene oxide per 100 parts by weight of solvent was used,

[0109] A photocatalyst powder is prepared in the same manner as in Example 1.

[0110] Comparative Example 6: Production of photocatalyst from graphene oxide and reduced graphene oxide with different content ratios.

[0111] Compared to Example 4,

[0112] When preparing the second mixed solution

[0113] Except for adding reduced graphene powder in a content ratio of 100 parts by weight based on 100 parts by weight of graphene oxide,

[0114] A photocatalyst is manufactured in the same manner as in Example 1.

[0115] Experimental Example 1: Examining the efficiency of photocatalysts by measuring their hydrogen production efficiency.

[0116] Hydrogen was produced by irradiating sunlight using the photocatalysts of Examples / Comparative Examples 1 to 6. Specifically, the reaction for hydrogen production was carried out in a 150 mL tubular quartz reactor with a round bottom, and 5 mg of the catalyst was added to 50 mL of a 5% glycerol aqueous solution in the quartz reactor, which was then sealed with a gas-tight rubber septum. Then, the reactor was evacuated for 30 minutes, and the 5% glycerol solution was purged with N2 gas for 30 minutes. The hydrogen production reaction was performed under natural sunlight (10:00 AM to 3:00 PM) while measuring the light intensity using an LT Lutron LX-101A digital light meter (130,000 Lux), and the amount of H2 gas generated during the reaction was monitored at hourly intervals by collecting gas samples in a sealed syringe. Sample analysis was performed using a gas chromatograph (Shimadzu GC-2014) equipped with a TCD detector and a molecular sieve 5A column using N2 as a carrier gas. The results are shown in Figs. 2, 3, Table 1, and Table 2.

[0117] Example 1 Comparative Example 5 Comparative Example 2 Comparative Example 1 Hydrogen production efficiency (mol / g / h) 24,880 10,610 6,640 1,920

[0118]

[0119]

[0120] By examining FIG. 2, FIG. 3, and Table 1, it can be confirmed that the photocatalysts of Examples 1 to 3 have superior hydrogen production performance due to superior photocatalytic activity compared to the photocatalysts of Comparative Examples 1 and 2.

[0121] In particular, it was confirmed that the photocatalyst according to Example 1 produced 24,880 μmol / g / h of hydrogen, which is approximately 3.7 times and 12.9 times higher than the photocatalysts of Comparative Examples 1 and 2, respectively.

[0122] In addition, the photocatalysts according to Examples 1 to 3 have higher hydrogen production efficiency than the photocatalysts according to Comparative Examples 3 to 5, and it was confirmed that when the first mixed solution was prepared using an aqueous graphene oxide solution having a content of 2 to 10 parts by weight of graphene oxide based on 100 parts by weight of solvent according to Examples 1 to 3, and particularly when the aqueous graphene oxide solution having a content of about 5 parts by weight was used, a photocatalyst having the best hydrogen production performance could be prepared.

[0123] Example 1 (Pure GO) Example 4 (Rgo 10%) Example 5 (Rgo 25%) Example 6 (Rgo 50%) Comparative Example 6 (Rgo 100%) Hydrogen production efficiency (umol / g / h) 24,880 25,000 30,000 28,000 20,000

[0124]

[0125] In addition, referring to Table 2, it was confirmed that the photocatalysts of Examples 4 to 6 manufactured with reduced graphene oxide and graphene oxide had better hydrogen production efficiency than Example 1 manufactured only with graphene oxide. However, in the case of the photocatalyst of Comparative Example 6 having a high reduced graphene content, it was confirmed that the hydrogen production efficiency was lower than that of the photocatalyst of Example 1. Therefore, it was confirmed that the photocatalysts manufactured with a content of 10 to 50 parts by weight of reduced graphene based on 100 parts by weight of graphene oxide, and especially with a content of about 25 parts by weight, when manufacturing the second mixed solution according to Examples 4 to 6 had better hydrogen production efficiency.

[0126] Experimental Example 2: Photoluminescence (PL) spectrum analysis of a photocatalyst

[0127] The PL spectra of the photocatalysts of Example 1 and Comparative Example 2 were analyzed at room temperature using a 384 nm argon laser and a Hamamatsu R928 Si PMT device as a detector, and the results are shown in Fig. 4.

[0128] The PL spectrum originates from the radiative emission resulting from the relaxation of the photoexcited state to the ground state, which signifies the recombination of electrons in the conduction band with holes in the valence band. The electron / hole recombination process can be confirmed by comparing the spectra of the photocatalysts of Example 1 (5rGO-TiO2) and Comparative Example 2 (bare TiO2) through Fig. 3. The strong signal around 520-650 nm indicates radiation arising from electron excitation in the TiO2 band. In addition, the small peak observed at a higher wavelength at 700 nm originates from the relaxation of the excited state by defects or vacancies on the TiO2 surface. The abrupt decrease in the PL intensity of the photocatalyst of Example 1 (5rGO-TiO2) confirmed that the photoexcited electrons were efficiently transferred from the TiO2 to the rGO surface. Therefore, it was confirmed that the rGO of the photocatalyst of Example 1 (5rGO-TiO2) efficiently accepts electrons and prevents electron / hole recombination, thereby enhancing the activity compared to the photocatalyst of Comparative Example 2. In addition, it was confirmed that the activity was enhanced by the strong interaction between the conductive rGO layer (shell) formed by hydrothermal conditions and the TiO2 nanotube (core).

[0129] Simple modifications or changes of the present invention can be easily implemented by a person having ordinary skill in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims

1. Graphene oxide production step of producing a graphene oxide aqueous solution using the modified Hummus method; A first mixed solution manufacturing step of manufacturing a first mixed solution by adding titanium dioxide to the graphene oxide aqueous solution manufactured in the graphene oxide manufacturing step; A hydrothermal synthesis step of adding sodium hydroxide to the first mixed solution prepared in the first mixed solution preparation step and performing hydrothermal synthesis to prepare a hydrothermal synthesis solution; and A method for manufacturing a photocatalyst, comprising a heat treatment step of drying and heat treating a hydrothermal synthesis solution manufactured in a hydrothermal synthesis step.

2. In paragraph 1, In the above first mixed solution preparation step, A method for manufacturing a photocatalyst, wherein graphene oxide in a graphene oxide solution is included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of solvent.

3. In paragraph 1, In the above mixed solution manufacturing step, A method for manufacturing a photocatalyst, wherein graphene oxide is included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of titanium dioxide.

4. Graphene oxide production step of producing a graphene oxide aqueous solution using the modified Hummus method; A reduced graphene production step for producing reduced graphene powder by freeze-drying and then thermally reducing the graphene oxide solution produced in the graphene oxide production step; A second mixed solution preparation step of preparing a second mixed solution by adding reduced oxide graphene powder and titanium dioxide prepared in the reduced oxide graphene preparation step to the graphene oxide aqueous solution prepared in the graphene oxide preparation step; A hydrothermal synthesis step of preparing a hydrothermal synthesis solution by adding sodium hydroxide to the second mixed solution prepared in the second mixed solution preparation step and performing hydrothermal synthesis; and A method for manufacturing a photocatalyst, comprising a heat treatment step of drying and heat treating a hydrothermal synthesis solution manufactured in a hydrothermal synthesis step.

5. In paragraph 4, In the second mixed solution manufacturing step, A method for manufacturing a photocatalyst, wherein the oxide graphene and reduced oxide graphene powder are included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of the graphene oxide aqueous solution solvent.

6. In paragraph 4, In the second mixed solution manufacturing step, A method for manufacturing a photocatalyst, wherein graphene oxide and reduced graphene oxide powder are included in an amount of more than 0 parts by weight and less than or equal to 10 parts by weight based on 100 parts by weight of titanium dioxide.

7. In paragraph 1 or paragraph 4, The above graphene oxide manufacturing step is An oxidation step of mixing and stirring expanded graphite, potassium permanganate, water, and sulfuric acid, maintaining the mixture at a constant temperature, and reacting for a certain period of time to produce graphite oxide slurry; A filtration step of mixing 50 to 200 parts by weight of water with 100 parts by weight of the graphite oxide slurry manufactured in the oxidation step, then centrifuging to discharge the filtrate and separating the graphite oxide slurry; and A photocatalyst manufacturing method, comprising a step of manufacturing a graphene oxide solution by mixing 5,000 to 20,000 parts by weight of water with 100 parts by weight of the graphite oxide slurry separated in the above filtration step, purifying impurities in an ion resin exchange tower, and then filtering the mixture.

8. In paragraph 1 or paragraph 4, A method for manufacturing a photocatalyst, wherein the sodium hydroxide is included in an amount of 100 parts by weight or more and 300 parts by weight or less based on 100 parts by weight of graphene oxide.

9. A core containing titanium dioxide; and A photocatalyst comprising a shell positioned on the titanium dioxide and containing reduced oxide graphene.

Images