Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes
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摘要: 石墨烯协同TiO2光催化降解有机物是一种很有前景的解决水体污染问题的方法。本文以低成本煤炭作为石墨烯碳源，成功地制备了TiO2-石墨烯复合催化剂。利用扫描电子显微镜、原子力显微镜、X射线衍射仪和拉曼光谱仪等研究了TiO2-石墨烯复合催化剂的微观结构和形貌。煤基石墨烯的引入促进了TiO2光催化降解有机物的反应。特别是在水热还原法制备的TiO2-石墨烯催化剂中，TiO2堆积在石墨烯片层结构上形成层状结构。由于石墨烯的引入，复合催化剂表现出良好的导电性和光电响应特性，并展示出较高的光催化活性。Abstract: Graphene oxide (GO) obtained from coal-based graphite by the Hummers method was hydrothermally treated to obtain reduced GO (rGO). TiO2 was mixed with aqueous suspensions of GO and rGO and dried at 70 oC to obtain GO-TiO2 and rGO-TiO2 with 95% (mass fraction) TiO2. TiO2 was also combined with a GO suspension by hydrothermal treatment to obtain rGO-hTiO2 with 95% TiO2. The three hybrids were used as catalysts for the photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO). Of the three materials, rGO-hTiO2 had the highest catalytic activity for the degradation of Rh B and MO under visible light irradiation. The reasons for having the best catalytic activity are that the incorporation of rGO into TiO2 helps increase its adsorption capacities for Rh B and MO as evidenced by adsorption in dark, and a narrowing of the TiO2 band gap as revealed by diffuse UV reflectance spectroscopy. This reduces the rate of recombination of electron–hole pairs by there being intimate contact between the TiO2 particles and rGO, forming Ti-O-C bonds as confirmed by XPS, with the TiO2 particles being uniformly decorated on the rGO sheets.
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Key words:
- Coal-based graphene /
- Hydrothermal method /
- Photocatalytic degradation /
- Titanium dioxide
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Figure 1. (a) XRD patterns of TiO2, GO and composite catalysts. (b) Raman spectra of TiO2 and composite catalysts. (c) FT-IR spectra of TiO2, rGO and composite catalysts. (d) Ti2p, (e) O1s, and (f) C1s XPS spectra of rGO-hTiO2
Figure 2. SEM images of (a) rGO-hTiO2, (b) rGO-TiO2, (c) GO-TiO2 and (d) GO. AFM imagines of (e) and (f) AFM images of rGO-hTiO2
Figure 4. Adsorption-equilibrium and photocatalytic-degradation curves for (a) Rh B, (b) MO solutions over various catalysts. The first-order kinetics plots of (c) Rh B, (d) MO degradation over various catalysts. Cycle degradation experiments of (e) Rh B and (f) MO over the rGO-hTiO2 catalyst
Figure 5. (a) Diffuse reflectance absorption spectra, (b) band-gap energy plots, (c) transient photocurrent curves, and (d) EIS changes of TiO2 and the composites
Figure 6. Suggested mechanism of decomposition of Rh-B and MO through photodegradation by graphene/TiO2 composites
Table 1. Pore parameters of the catalysts
Samples SBET
(m2 g−1)Total pore volume
(mL g−1)Average pore diameter (nm) TiO2 29.61 0.52 69.70 rGO-hTiO2 35.89 0.51 34.18 GO-TiO2 35.52 0.61 35.00 rGO-TiO2 34.30 0.54 35.24 
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Table 2. The first-oeder reaction rate constants of the photocatalysts
Samples k (Rh B) k (MO) TiO2 0.00267 0.00320 rGO-hTiO2 0.01332 0.01481 GO-TiO2 0.00554 0.00571 rGO-TiO2 0.00998 0.01031
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