Synthesis of carbon doped WO₃·0.33H₂O hierarchical photocatalyst with improved photocatalytic activity

Graphical abstract: Interstitial carbon in WO₃·0.33H₂O matrix enhanced the photocatalytic activity under visible light. - Highlights: • Carbon-doped tungsten trioxide has been synthesized via a mild liquid phase method. • The existence and position of carbon are discussed by some detailed characterization. • Carbon doping improved the photocatalytic activity. • Carbon doping induces defects and reduces the recombination of photo-generated carriers. - Abstract: A carbon doping method is developed to overcome the drawback of conventional carbon doping method. The carbon dopant is synthesized by treating carbon with dilute nitric acid through hydrothermal process. Carbon-doped WO₃·0.33H₂O (C−WO₃·0.33H₂O) is obtained by adding the carbon dopant solution, and then through an additional hydrothermal process. Based on XRD, Raman and XPS, carbon have been incorporated into the interstitial position of WO₃·0.33H₂O unit cell rather than substitution of oxygen in lattice of WO₃·0.33H₂O, which induces distortion of WO₆ octahedron and lattice defect. In addition, carbon doping also induces the emergence of new level above the valence band. The new level increases the migration pathway of photo-generated carriers, which reduces the recombination rate of photo-generated carriers. The changes of band structure, distortion of WO₆ octahedron and lattice defect are beneficial to improve the photocatalytic performance of WO₃·0.33H₂O. Compared with pristine WO₃·0.33H₂O, C−WO₃·0.33H₂O display better photocatalytic performance on degradation of rhodamine B (RhB), which include the faster de-ethylation process and cycloreversion process. Moreover, the experiments of radical quenchers confirmed that the h⁺ display the main influence on degradation of RhB. This study implies that carbon can be doped into some metal oxide hydrates through a mild preparation process, which provides a possible way for the synthesis of carbon doped thermal unstable materials.