Introduction of several preparation methods for semiconductor / graphene composite photocatalysts

The preparation method has a direct influence on the morphology, structure, size of composite photocatalysts, and the binding method of graphene to semiconductors. This paper mainly describes several methods for preparing semiconductor / graphene composite photocatalysts, including water-heat / solvent heat method, solution mixing method and in-situ growth method.

Preparation of semiconductor / graphene composite photocatalyst by hydrothermal / solvent thermal method

Hydrothermal / solvent thermal method is a traditional method of crystal growth of semiconductor materials. It is now also an effective method for synthesizing semiconducte/graphene composites. The preparation process is generally to load semiconductors or semiconductor precursors to graphene oxides.(GO) or graphene, Graphene oxide is reduced to graphene under hot water and solvent conditions.

The hydrotherm/solvent heat method synthesizes the semiconductor / graphene composite photocatalyst. Chemical bonding can often be produced between the semiconductor and graphene. The resulting composite photocatalyst can fully exert the synergistic effects of graphene and semiconductor. It is conducive to improving its photocatalytic energy. Zhang et al. synthesized chemically bonded TiO2(P25) / GR Nano complexes by a one-step hydrothermal method. As the hydrothermal reaction progresses, the reduction of GO and the load of P25 are completed simultaneously. The prepared P25 / GR photocatalyst has excellent dyestuff adsorption ability and effective charge separation.

Synthesis of semiconductor / graphene composite photocatalyst by hydrothermic / solvent thermal method, Semiconductor particles tend to form a relatively uniform distribution on graphene. For example, Neppolian et al. obtained a evenly distributed Pt/TiO2 / GO composite photocatalyst by hydrothermal method. Li et al. obtained a uniform distribution of CdS by solvent thermal method. Semiconductor / graphene composite photocatalyst. Wu et al.. / GR nanoparticles, ZnO nanoparticles densely and evenly deposited on graphene tablets. Wang et al.[ 26] TiO2 / RGO(reduced graphene oxide) nanoparticles with good particle dispersion were prepared by hydrothermal method.

Some special forms of semiconductor/graphene composite photocatalysts can also be obtained by hydrothermal / solvent heat method. Ding et al. obtained ultra-thin TiO2 nanoparticles on graphene exposed to high-energy(001) crystal surfaces by solvent heat method. Shen et al. synthesized leaves using an improved one-step hydrothermal method. TiO2 / RGO composites. Zou et al. used a simple and common direct hydrothermal method of nanocrystalline nuclei to synthesize TiO2, ZnO, MnO2, CuO, and ZrO2 nanometer rod arrays on both sides of flexible graphene to form sandwich composite structures. MO/G/MO, Not only is the morphology uniform, but the semiconductor and graphene are chemically bonded.

2, solution mixing method preparation of semiconductor / graphene composite photocatalyst

A composite photocatalyst is prepared by mixing a graphene(or graphene oxide) suspension with a solution containing a semiconductor powder(or semiconductor precursor Ion), and then prepared by simple treatment such as drying, calcination, etc.. This method is called solution mixing method. Compared with Yushui heat / solvent heat method, The reaction condition is mild, the method is simple and the preparation cost is low.

There are many reports on the preparation of semiconductor / graphene composite photocatalysts by solution mixing method. Among them, TiCl4 suspension is directly mixed with graphene oxide suspension, and graphene oxide is reduced to graphene by hydrated Hydrazine., TiO2 / GR composite photocatalyst. Liu et al. mixed GO with TiO2 nanometer rods(or nanoparticles) in the form of a solution to produce TiO2 nanometer rods / GO and TiO2 nanometer particles / GO as shown in Figure 4. Two composite photocatalyst. Except TiO2, Combinations of other semiconductors and graphene can also be prepared by solution mixing method, such as ZnO / GR complex, SnO2 / GR and Sr2 Ta2 O 7-xNx / GR complex.

The solution mixing method is simple to operate and the reaction conditions are mild. A variety of semiconductor / graphene composite photocatalysts can be produced at the same time. Iwase, etc., will contain three solutions of GO, Bi VO4, Ru/SrTiO3: Rh, respectively. Mixed, prepared Bi VO 4/RGO, Ru / SrTiO 3: Rh / RGO composite photocatalyst. Ng and others mixed graphene oxide solution with three photocatalytic materials(WO3, Bi VO 4, TiO2). Three semiconductor / graphene composite photocatalyst were prepared.

3, in situ growth method preparation of semiconductor / graphene composite photocatalyst

In-situ growth method is also one of the most effective methods for preparing semiconductor / graphene composite photocatalysts. This method often uses semiconductor precursors combined with graphene oxides(or graphene) to control the hydrolysis of semiconductor precursors. Semiconductors grow crystalline nuclei on graphene. Graphene oxide is reduced to give semiconductor / Graphene composite photocatalyst.

Zhang Qiong et al. used graphite and titanium sulfate as initial reactants at low temperatures(<; 100oC) Preparation of titanium oxide-graphene intercalated composite material, hydrolyzed by Ti(SO4) 2[ TiO] The 2 + group diffuses into the graphene oxide layer through electrostatic attraction and grows in situ at low temperatures to form TiO2-GO intercalated composites. Jiang et al. use vacuum and surfactant to assist in the expansion graphite sandwich. In situ growth of TiO2 nanoparticles, The vacuum environment can promote the invasion of TiO2 precursor solution Ti(OBu) 4 and surfactants into the layer of expanded graphite, and then with the help of surfactants, countless TiO2 nanoparticles grow evenly in situ in the layer. Gradually formed TiO2 / GR complexes. Zhang et al. added SnCl2 and TiCl3 Ionic solutions to GO dispersions, SnCl2 and TiCl3 reduced GO, The corresponding SnO2 and TiO2 nanocrystals are hydrolyzed to form. ZnO/GR composite photocatalysts can also be synthesized by in-situ growth method. When the ZnO precursor Zn2 + aqueous solution is added to the graphene oxide suspension, Zn2 + is adsorbed on graphene oxide flakes, and graphene oxides are reduced with NaOH and NaBH4 to obtain a ZnO/GR composite photocatalyst. Du et al.. P123, TTIP, TiCl4, GO consists of an ethanol or tetrahydrofuran colloidal suspension, which is then soaked in a suspension by a glass substrate coated with a polystyrene protein membrane, repeatedly impregnated several times, and finally reduced and calcined graphene oxides with Hydrazine steam, A stratified ordered macroporous-mesoporous TiO2 / GR composite film with polystyrene rubber spheres as the template can be obtained, as shown in Figure 6. Lambert et al. reported that in the presence of GO water dispersion, By hydrolyzing TiF4 in situ to synthesize flower-shaped TiO2 / GO composites, Li and others directly in situ to synthesize uniform mesoporous TiO2 nanowires on graphene tablets.

4, other methods to prepare semiconductor / graphene composite photocatalyst

In addition to the above three methods, there are also some methods that can achieve the preparation of semiconductor / graphene composite photocatalysts, such as electrochemical deposition method, atomic layer deposition method, etc., but subject to the conditions of preparation technology and cost, These methods are less used in actual synthesis. Such as Du and others[ 48] Electrochemical deposition of ZrO2 / GR on a glassy carbon electrode; Meng et al.[ 49] TiO2 / GR composites were prepared by atomic layer deposition(ALD). TiO2 deposited 75 times on graphene and formed after vacuum calcination at 250 °C.

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