Fabrication of visible-light responsive TiO2@C photocatalyst with an ultra-thin carbon layer to efficiently degrade organic pollutants

Titanium dioxide (TiO2) is considered a promising photocatalyst due to its remarkable properties, such as photostability, low energy consumption and non-toxicity. However, some intrinsic drawbacks of TiO2 including high band gap energy and easy recombination of electron-hole pairs seriously hinder its practical application in photocatalysis. In this study, a 1-nm-thick carbon coating layer was introduced onto the surface of TiO2 (TiO2@C) by carbonizing kraft lignin to improve the photocatalytic performance. Compared with TiO2, TiO2@C shows absorption in both visible-light and UV-light regions, a decrease in band gap energy from 3.31 to 3.27 eV and excellent electronic conductivity, which favour the generation and separation of photo-generated carriers. In addition, the ultra-thin carbon coating can guarantee the penetration of sunlight, and TiO2@C, which remains afloat on the water, can contact with wastewater and absorb sufficient sunlight due to the hydrophobicity and loose structure. The investigation of photocatalytic degradation towards methylene blue (MB) and tetracycline (TC) under artificial visible-light irradiation demonstrates that the prepared TiO2@C has relatively superior photocatalytic activity. The absorbed MB and TC are almost completely degraded by TiO2@C within 10 min and 35 min, respectively. Given the simple modification and excellent photocatalysis, the prepared TiO2@C exhibits great potential applications in contaminated water treatment. This study provides a feasible carbon-coating strategy to improve the photocatalytic performance of TiO2, which can be extended to the rational design of other photocatalysts.