Facile preparation of high-performance hydrochar/TiO2 heterojunction visible light photocatalyst for treating Cr(VI)-polluted water

In order to remedy the shortcomings of narrow absorption wavelength range and low photogenerated carrier separation efficiency of TiO2 photocatalyst, hydrochar (HC) was chosen to modify TiO2 by constructing HC/TiO2 heterojunction composite. HC/TiO2 composites were synthesized from glucose, tetrabutyl titanate and deionized water by a simple one-pot hydrothermal way, and their photocatalytic Cr(VI) reduction properties were studied. The results indicated that HC/TiO2 composites had tremendously improved photocatalytic Cr(VI) reduction activity, in comparison with TiO2, HC and a number of newly reported TiO2-based visible light photocatalysts. When the mass percentage of glucose to tetrabutyl titanate was 14, the obtained HC/TiO2-2 possessed the maximal photocatalytic activity, which was 19 times that of TiO2 and 14.3 times that of HC under visible light (wavelength > 420 nm) irradiation, and 3.2 times that of TiO2 under ultraviolet-visible light (Xenon lamp) irradiation. Furthermore, the photocatalytic stability of HC/TiO2-2 was also excellent. Additionally, proper choice of the photocatalysis experiment parameters could further raise the photocatalytic Cr(VI) reduction efficiency of HC/TiO2-2. The exceptionally elevated photocatalytic activity of HC/TiO2-2 was found to be due to its type-II heterojunction structure, which drastically heightened the separation and transfer efficiencies of photogenerated electrons and holes. Besides, HC/TiO2-2 also showed great potential for practical application in photocatalytic treatment of the Cr(VI) effluents discharged from freezing brine and black chromium plating industries.