Carbon quantum dot/mixed crystal TiO2 composites via a hydrogenation process: an efficient photocatalyst for the hydrogen evolution reaction

Abstract

The creation of stable and efficient photocatalysts that produce hydrogen from water under solar light is a burgeoning area of research. As a prospective candidate, TiO₂ has been widely studied. Herein, we further designed and synthesized composites of mixed crystal TiO₂ with high-performance carbon quantum dots (CQDs) via a facile approach. The CQDs were made by electrolyzing graphite rods and the mixed crystal TiO₂ from titanium oxysulfate under a hydrothermal reaction, and then the resulting materials were heated to a high temperature under H₂. All the characterization proved that the CQDs had been successfully modified onto TiO₂ with both anatase and brookite phases. The newly synthesized samples showed an excellent performance for hydrogen evolution using AM 1.5 light sources. The large hydrogen evolution yield was 280 μmol h⁻¹, which was higher than that produced by pure TiO₂. It indicates that CQDs as electron storage could improve the separation of charges and inhibit the recombination of electron–hole pairs. Concurrently, the formation of heterostructures between the two phases of TiO₂ would help electron–hole separation, which is another reason for the good performance of the photocatalyst.