KR20110129519A - A cadmium sulfide quantum dots-tungsten oxide nanohybrid photo-catalyst and preparation method thereof - Google Patents

Abstract

PURPOSE: A cadmium sulfide quantum dots-tungsten oxide nanohybrid-based photo catalyst and a method for manufacturing the same are provided to improve the activity and the stability of the catalyst. CONSTITUTION: A method for manufacturing a cadmium sulfide quantum dots-tungsten oxide nanohybrid-based photo catalyst includes the following: A cadmium precursor and a sulfur precursor are reacted to synthesize cadmium sulfide quantum dots. The cadmium sulfide quantum dots are dispersed in a solvent using a dispersing agent. The dispersed cadmium sulfide quantum dots and a tungsten precursor are reacted in an acid solution in order to obtain CdS-WO_x nanohybrid. The CdS-WO_x nanohybrid is thermally treated. The dispersing agent is composed of an amine compounds. The thermal treating process is implemented in a range between 300 and 800 degrees Celsius.

Description

Cadmium sulfide quantum dot-tungsten oxide nanocomposite photocatalyst and its manufacturing method {A CADMIUM SULFIDE QUANTUM DOTS-TUNGSTEN OXIDE NANOHYBRID PHOTO-CATALYST AND PREPARATION METHOD THEREOF}

The present invention relates to a cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst and a method for manufacturing the same, and more specifically, to decompose water by photoreaction to generate oxygen and hydrogen, Cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite, comprising a nanocomposite of CdS QDs-WO _x (0 <x ≤ 3), a hybrid of tungsten oxide bonded to nanoscale It relates to a photocatalyst and a manufacturing method thereof.

Hydrogen energy is drawing attention as a next-generation renewable energy source that will replace existing fossil fuels with limited reserves. In particular, its importance has been continuously recognized through research results and market expansion on fuel cell commercialization accelerated from the mid-20th century. Polymer Electrolyte Membrane Fuel Cells (PEMFCs), which can operate at relatively low temperatures, have a very high power density, and can be miniaturized, are used in large-scale factories, transportation vehicles, and residential power generators. It has been actively researched for application to various aspects such as: RPG) and is currently entering the commercialization stage. However, in order to commercialize the polymer electrolyte fuel cell, it is necessary to develop a catalytic process for stably and efficiently producing high purity and high quality hydrogen gas as a raw material.

On the other hand, cadmium sulfide (Cadmium Sulfide, CdS) has a bandgap structure that is ideal for generating hydrogen by decomposition of water is attracting attention as a material of the photocatalyst for hydrogen generation. However, CdS has a disadvantage in that its light stability is poor and the structure collapses when subjected to light for a long time. In the past, various literatures have developed hybrid materials that are combinations of CdS quantum dots (QDs) and layered compounds. However, synthetic methods that are harmful to the human body due to the gaseous reaction of H ₂ S, which is very toxic in the conventional development method, have been widely known. In addition, most of the solution-phase reactions use the ion exchange method in the reaction between the layered compound and the quantum dot, which has a problem of diffusion of the quantum dot into the interlayer space and has a limitation in inserting a large amount of quantum dots between the layered layers of the layered compound. . In order to solve this problem, the present inventors react with a titanium oxide having a two-dimensional sheet structure having a surface negative charge and a CdS quantum dot having a positive charge to form a CdS quantum dot inserted between the titanium oxide, and the two-dimensional sheet form Titanium oxide of the structure is gathered to have a three-dimensional structure in the form of a layer structure or a card house, and the nano-hybrid, characterized in that the pores in the range of 0.1 to 1,000 nm is formed in the inner space of the layer or card house three-dimensional structure The patent has been filed for patents (see Korean Patent Application No. 2009-88682).

However, the size of the titanium oxide to which the CdS quantum dots bind is very large compared to that of the quantum dots in the case of the nano hybrids disclosed in the above literature, and to compensate for this, the nano hybrids obtained by hybridizing CdS and metal oxides in a nano-sized state Development is required.

Therefore, the technical problem to be achieved by the present invention is to produce a cadmium sulfide quantum dot catalyst and a tungsten oxide catalyst component, which is a photocatalyst suitable for generating hydrogen and oxygen, respectively, in the form of a nano hybrid in which nanoparticles are bonded in a nano-sized state. Cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst.

In order to achieve the above technical problem, the present invention generates oxygen and hydrogen by decomposing water by a photoreaction, CdS QDs-WO _x (0 <x It provides a cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nano hybrid photocatalyst comprising a nano hybrid of ≤ 3).

In addition, the present invention comprises the steps of synthesizing cadmium sulfide (CdS) quantum dots by reacting a cadmium precursor and a sulfur precursor; Ii) dispersing the CdS quantum dots in a solvent using a dispersant; Iii) reacting the dispersed CdS quantum dots with a tungsten precursor in an acid solution to produce CdS-WO _x (0 <x ≤ 3) nano hybrids; Iii) cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst manufacturing method comprising the step of heat-treating the CdS-WO _x nano hybrids.

The present invention also provides a method for preparing a cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst, wherein the dispersant is an amine compound.

In addition, the present invention provides a method for producing a cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst, characterized in that the heat treatment is performed in the range of 300 to 800 ℃.

The cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst of the present invention is a nano hybrid in which a cadmium sulfide quantum dot catalyst and a tungsten oxide catalyst component, which is a photocatalyst suitable for hydrogen and oxygen generation by photolysis of water, are combined in a nano-sized state. It can be produced in the form of a sieve, but also has excellent catalytic activity and stability.

1 is a UV-vis spectrum of NH ₄ ⁺ -CdS quantum dots (QDs)
2 is a TEM image and ED pattern of NH ₄ ⁺ -CdS quantum dots
3 is a zeta potantial measurement result of NH ₄ ⁺ -CdS quantum dots
4 is an XRD pattern of CdS quantum dots and CdS-WO _x nano hybrids and heat treatment materials.
FIG. 5 is an SEM image of CdS QDs and CdS-WO _x nanohybrids and heat treatment materials
FIG. 6 shows TEM, FTT image and ED pattern of CdS QDs and CdS-WO _x nanohybrid 600 ° C. heat treated materials
7 is electron mapping image of CdS-WO _x nanohybrids (nanohybrid)
8 is a thermal gravity analysis of CdS-WO _x nanohybrids (nanohybrid)
9 shows solid UV-vis spectra (○ NH ₄ ⁺ -CdS QDs) (-CdS-WO _x ) (---- CdS of CdS QDs and CdS-WO _x nanohybrids, heat-treated materials and reference materials -WO _x -330) (□ Bulk CdS)) (◇ Ammonium metatungstate) (△ WO ₃ )
10 is a photograph showing photochromism of CdS-WO _x nanohybrids (nanohybrid)
11 shows a band structure of CdS-WO _x nanohybrids: type II band-edge alignment
FIG. 12 shows the results of comparing photostability of CdS QDs and CdS-WO _x nanohybrids (nanohybrid)

Hereinafter, the present invention will be described in detail.

The cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst of the present invention decomposes water by photoreaction to generate oxygen and hydrogen, and a hybrid form of cadmium sulfide quantum dot and tungsten oxide combined with a nano-sized It is characterized by including a nano hybrid of the chain CdS QDs-WO _x . As used herein, the term 'CdS QD' or 'CdS QDs' refers to cadmium sulfide quantum dots, and the term CdS QDs-WO _x refers to a state in which cadmium sulfide quantum dots and tungsten oxide are bonded to each other. The term 'nano size' means a size in the range of 1 to 10 nm for CdS QDs and 10 to 100 nm for CdS QDs-WO _x nanocomposites. In addition, the term 'nano hybrid' is a nano-sized material formed by combining nano-sized cadmium sulfide quantum dots and tungsten oxide, and has a new band gap energy different from the band gap energy of each precursor material before bonding. Means sieve.

Among various metal oxides, tungsten oxide (WO _x ) has a bandgap structure that is ideal for generating oxygen by decomposing water. If tungsten oxide and CdS are hybridized, CdS-tungsten oxide (CdS-WO _x ) nano hybrids (nanohybrid) were synthesized because they can be used as photocatalysts that generate both hydrogen and oxygen in one material.

Tungsten oxide is white at +6 and blue at +5, which leads to oxidation-reduction photochromism. The ammonium metatungstate used as a precursor of tungsten oxide in the CdS-WO _x nanocomposite is W ^+6, so it is white.The tungsten part is white because the nanocomposite is yellow like CdS quantum dots before heat treatment. Able to know. That is, tungsten is in a state of W ^{+ 6 in} the yellow CdS-WO _x nanomixture. However, when light is received, photochromism occurs within a few seconds, which is changed from yellow to green, which is reduced to tungsten +6 valence to +5 valence, becoming blue, mixed with yellow of CdS quantum dots, and the final color of the nanocomposite becomes green. Through this process, it can be seen that tungsten in the CdS-WO _x nanocomposite can be in the range of +5 to +6 valence, and therefore _x in the chemical formula of tungsten oxide (WO _x ) is 0. It is preferable that it is more than 3 or less range, More preferably, x is in the range of 2.5-3.

In addition, since CdS-WO _x is used as a catalyst, it is expected that the smaller the particle size, the wider the specific surface area and the better the catalytic activity. Therefore, CdS was synthesized in the form of quantum dot.

The cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst of the present invention comprises the steps of synthesizing a cadmium sulfide (CdS) quantum dot by reacting a cadmium precursor with a sulfur precursor; Ii) dispersing the CdS quantum dots in a solvent using a dispersant; Iii) reacting the dispersed CdS quantum dots with a tungsten precursor in an acid solution to produce a CdS-WO _x nano hybrid; Iii) it may be prepared by a method comprising the step of heat-treating the CdS-WO _x nanocomposite.

In order to synthesize cadmium sulfide quantum dots (CdS QD) by reacting a cadmium precursor with a sulfur precursor, conventionally, a high temperature of 250 ° C. or higher, a vacuum or inert gas atmosphere, the use of a toxic solvent, the necessity of various synthesis steps in the synthesis, a low yield, etc. There were disadvantages. In order to secure these shortcomings, in the present invention, the low temperature of 40 ~ 60 ℃, the atmosphere, using non-toxic water as a solvent, QD synthesis and surface modification step performed all at once to shorten the synthesis step, higher yields have.

In addition, in order to hybridize cadmium sulfide quantum dots and tungsten oxide, synthesis of surface-modified CdS QD is required. Therefore, in the present invention, it is preferable to disperse the CdS quantum dots in a nano size state using a dispersant and to modify the surface cationicly. In order to hybridize the two materials, each must first be well dispersed, using water that is safe and readily available. Water is slightly lower than 7 due to the influence of carbon dioxide dissolved in air in the air at room temperature, and if the surface of the quantum dot is modified with an amine compound (dispersant), the amine compound with a pH higher than 7 attracts hydrogen ions in the water toward the quantum dot. Finally, the quantum dot surface is NH ₄ ⁺ to give a cation. That is, when the amine compound is used as a dispersant, it is preferable to modify the surface of the quantum dot with the amine compound because the quantum dot can be dispersed and the cationic modification can be simultaneously performed. The amine compound is not particularly limited, and it is preferable that the substituents connected to nitrogen have a short chain length of C6 or less, because the carbon chain (organic chain) connecting the amine dot surface and the amine group is compared with other materials. This is because it is the shortest so that the quantum dots are not submerged by the organic material and the activity can be maximized. In a preferred embodiment of the present invention, 2-mercaptoethylamine hydrochloride was used as the amine compound.

In the present invention, the dispersed CdS quantum dots and tungsten precursors are reacted to give CdS-WO _x In the step of preparing the nano hybrids, it is preferable to react in an acid solution since the species of tungsten polyanion is present as the single species (W ₁₂ O ₃₉ ^-6 ) near pH 3-4. to be. In addition, the single species (W ₁₂ O ₃₉ ^-6 ) have a negative charge stronger than that of other species of tungsten polyanion, WO ₄ ^2- or W ₆ O ₂₀ (OH) ^5- , and thus have a positively charged CdS quantum dot and an electrostatic charge. It is more advantageous to combine by attraction.

Preferably, the heat treatment is performed in the range of 300 to 800 ° C., when the heat treatment temperature is lower than 300 ° C., the bond between the CdS quantum dots and tungsten oxide is weakened, whereas when the heat treatment temperature is higher than 800 ° C., the separation of the nanocomposite is performed. Because it can happen.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only intended to illustrate the invention and should not be construed as limiting the scope of the invention by these examples.

(Manufacture) Example 1

Stage 1. Synthesis of CdS Quantum Dots (QDs) with Surface Modified by Amine (NH ₄ ⁺ -Synthesis of CdS QDs)

Cadmium acetate dehydrate 5 (mmol) as a Cd precursor, thioacetamide 6.25 (mmol) as a sulfur precursor, and 2-mercaptoethylamine hydrocholide 12.5 (mmol) to amine the surface of the quantum dots with a positive charge Was added to 250 ml of distilled water. The solution was refluxed at 40 ° C. for 5 hours and further refluxed at 60 ° C. for 5 hours, and then cooled at room temperature. The cooled solution was filtered under reduced pressure to filter out impurities, and the filtered solution was concentrated to about 10 ml. 20 ml of 2-propanol was added and the solution turned cloudy. Only the solid was filtered through a centrifuge, and the solid was dispersed in 5 ml of distilled water, and 10 ml of 2-propanol was added to precipitate. After this procedure was repeated two more times, the solid obtained was dried overnight under vacuum at 45 ° C. 1 is a NH ₄ ⁺ -CdS UV-vis spectrum of QDs, Figure 2 is a TEM image and the ED pattern of NH ₄ ⁺ -CdS QDs. The results of FIG. 1 and the CdS QDs formula (see Chem. Mater 2003, 15, 2854) showed that the size of NH ₄ ⁺ -CdS QDs synthesized in step 1 was about 2.5 nm. This is consistent with the TEM image results in FIG. In addition, Figure 3 is a result of the zeta potential measurement of NH ₄ ⁺ -CdS QDs, because the surface charge is about 52.3 mV it can be seen that the surface of the QDs modified well with amine.

Step 2. Synthesis of CdS QDs with Tungsten Oxide Nanoohybrid (CdS-WO) _x Synthesis)

0.2424 g of NH ₄ ⁺ -CdS QDs synthesized in step 1 and 0.087 g of ammonium metatungstate were dispersed in 30 ml of distilled water, respectively. After adding HCl to both solutions to pH 4, ammonium metatungstate solution was added dropwise to the NH ₄ ⁺ -CdS QDs solution. After the ammonium metatungstate solution entered the NH ₄ ⁺ -CdS QDs solution, stirring was continued at room temperature for about 2 hours. Precipitating by centrifugation gave only solids, the obtained solid was dispersed in distilled water and precipitated again three more times, and then the final product was dried under vacuum at 45 ° C. overnight. CdS-WO _x made using these CdS QDs was heat-treated at temperatures of 330, 600 and 800 ° C. in an N ₂ atmosphere, respectively.

4 is an XRD result of CdS QDs and heat treatment materials of CdS-WO _x and CdS-WO _x . XRD peaks are very wide up to 330 ° C heat-treated material, but for 600 ° C and 800 ° C heat-treated materials, the resulting peaks coincide with CdS hexagonal and WO ₃ hexagonal peaks, so the crystal structure of CdS-WO _x is hexagonal. It can be seen that. 5, it can be seen from the CdS-WO _x synthesized at room temperature that the larger the temperature of the heat treatment, the larger the particle size, the less smooth the surface of the particle. Particularly, in case of 800 ℃ heat-treated sample, large particles and nano-needle parts are separated. According to the EDS analysis, large particles are cadmium and sulfur ratio, and nano needles are made of tungsten. The proportion was overwhelmingly dominant. Thus, it can be seen that separation between CdS and tungsten oxide occurred in the 800 ° C. heat-treated sample. According to the TEM and FFT images of FIG. 6, CdS-WO _x before heat treatment exists in a state in which CdS having crystallinity and tungsten polyanion having amorphous properties are combined. However, when CdS-WO _x is heat-treated, both crystallinities of CdS and tungsten oxide exist, and tungsten oxide and CdS adhere well. This is in good agreement with the result of electron mapping in which homogeneously Cd, S, and W are present (FIG. 7). As a result of ICP analysis, the ratio of cadmium and tungsten was 4.53: 1, and the result of EDS analysis was sulfur: cadmium ratio of 1.14: 1. Since CdS QDs assume that cadmium and sulfur are present at 1: 1, the remaining 0.14 sulfur is the 2-mercaptoethylamine hydrocholide (SCN) used to modify the surface of CdS QDs to amines. The amount attached to. In addition, the result of thermal analysis (TG) (Fig. 8) shows that the mass loss of water is about 10%, so that the chemical formula of CdS-WO _x is 4.53 (CdS) (SCN) _0.14 (WO _x ) .zH ₂ O (z = mass reduction of about 10 Inferred%).

9 is a solid-state UV-vis spectroscopy results of the CdS-WO _x, 10 is a photo showing a picture chromism (photochromism) developing the CdS-WO _x nano hybrid material (nanohybrid), 11 is a CdS-WO _x nano Band structure of the hybrid (nanohybrid): type II band-edge alignment. The bandgap energy obtained by Kubelka-Munk equation is shown in Table 1. It can be seen from each bandgap energy difference that there is re-engeneering of the bandgap energy at CdS-WO _x . This can also be seen through the photochromism phenomenon (Fig. 10). The phenomenon of FIG. 10 occurs when light having a wavelength of more than 420 nm (using 450 W Xe lamp) is irradiated to ammonium metatungstate used as a tungsten precursor and CdS-WO _x . CdS-WO _x changes color as soon as light is irradiated, while ammonium metatungstate does not change color after 1 hour of light irradiation. Through solid UV-vis spectroscopy and photochromism, the band structure of CdS-WO _x is a type II band-edge where the conduction and valance bands of CdS are higher than those of tungsten oxide. Inferred by alignment (Figure 11). When the light stability of the surface-modified CdS QDs and CdS-WO _x was evaluated (FIG. 12), the light stability of the latter was significantly increased.

Table 1 below shows the bandgap energy of CdS QDs and CdS-WO _x nano hybrids (nanohybrid), heat treatment materials, and reference materials.

Sample Name Bandgap Energy (eV) NH ₄ ⁺ -CdS QDs 2.83 CdS-WO _x 2.73 CdS-WO _x -330 1.9 Ammonium metatungstate (ref.) 3 WO ₃ (ref.) 2.6 Bulk CdS 2.3

Example 2 Hydrogen Generation Experiments of CdS QDs-Tungsten Oxide Nanohybrids

After finely grinding the final step of two steps, 0.05g of nano hybrids (nanohybrid) per 100ml of 0.1M Na ₂ S and 0.02M Na ₂ SO ₃ solution was added well dispersed. After argon gas was flowed into the photocatalyst vessel for 30 minutes to make it in an inert atmosphere, light was emitted at a wavelength of 420 nm or more from a 450 W light source, and gas was collected every hour to analyze the components by gas chromatography. CdS-WO _x was used as a photocatalyst to generate hydrogen by decomposing water in the visible region. The generation rate of hydrogen was 13.24 (micromol / h), and 23.14 (micromol / h) when Pt-loaded with platinum as co-catalyst. In both cases, even after 30 hours of irradiation with visible light, hydrogen continued to be generated at a similar rate, indicating that the catalytic activity was continued without photolysis of CdS-WO _x .

The embodiments of the present invention described above should not be construed as limiting the technical idea of the present invention. The scope of protection of the present invention is limited only by the matters described in the claims, and those skilled in the art will be able to modify the technical idea of the present invention in various forms. Therefore, such improvements and modifications will fall within the protection scope of the present invention, as will be apparent to those skilled in the art.

Claims (4)

It decomposes water by photoreaction to generate oxygen and hydrogen,
Cadmium sulfide quantum dot-tungsten oxide characterized in that it comprises a nano hybrid of cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x , 0 <x ≤ 3), a hybrid of cadmium sulfide quantum dots and tungsten oxide (CdS QDs-WO _x ) Nanohybrid Photocatalysts. Iii) reacting the cadmium precursor with the sulfur precursor to synthesize cadmium sulfide (CdS) quantum dots;
Ii) dispersing the CdS quantum dots in a solvent using a dispersant;
Iii) reacting the dispersed CdS quantum dots with a tungsten precursor in an acid solution to produce a CdS-WO _x nano hybrid;
Iii) Cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nanocomposite photocatalyst manufacturing method comprising the step of heat-treating the CdS-WO _x nanocomposite (0 <x ≤ 3). The method of claim 2,
Cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nano hybrid photocatalyst manufacturing method, characterized in that the dispersing agent is an amine compound. The method of claim 2,
Cadmium sulfide quantum dot-tungsten oxide (CdS QDs-WO _x ) nano hybrid photocatalyst manufacturing method, characterized in that the heat treatment is performed in the range of 300 to 800 ℃.

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