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Photocatalysts comprising nanosized TiO2particles on activated carbon (AC) were prepared by a sol-gel method. The TiO2/AC composites were characterized by X-ray diffraction (XRD), thermogravimetric (TG) analysis, nitrogen adsorption, scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive X-ray (EDX). Their photocatalytic activities were studied through the degradation of Rhodamine B (RhB) in photocatalytic reactor at room temperature under ultraviolet (UV) light irradiation and the effect of loading cycles of TiO2on the structural properties and photocatalytic activity of TiO2/AC composites was also investigated. The results indicate that the anatase TiO2particles with a crystal size of 10–20 nm can be deposited homogeneously on the AC surface under calcination at 500°C. The loading cycle plays an important role in controlling the loading amount of TiO2and morphological structure and photocatalytic activity of TiO2/AC composites. The porosity parameters of these composite photocatalysts such as specific surface area and total pore volume decrease whereas the loading amount of TiO2increases. The TiO2/AC composite synthesized at 2 loading cycles exhibits a high photocatalytic activity in terms of the loading amount of TiO2and as high as 93.2% removal rate for RhB from the 400 mL solution at initial concentration of 2 × 10−5 mol/L under UV light irradiation.

Coal tar pitch (CTP), a by-product of coking industry, has a unique molecule structure comprising an aromatic nucleus and several side chains bonding on this graphene-like nucleus, which is very similar to the structure of graphene quantum dots (GQDs). Based on this perception, we develop a facile approach to convert CTP to GQDs only by oxidation with hydrogen peroxide under mild conditions. One to three graphene layers, monodisperse GQDs with a narrow size distribution of 1.7 ± 0.4 nm, are obtained at high yield (more than 80 wt. %) from CTP. The as-produced GQDs are highly soluble and strongly fluorescent in aqueous solution. This simple strategy provides a feasible route towards the commercial synthesis of GQDs for its cheap material source, green reagent, mild condition, and high yield.

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