Titanium dioxide (TiO₂), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO₂, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO₂. Among all the defects identified in TiO₂, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO₂ with oxygen vacancies, and the defect related properties of TiO₂ including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO₂. In particular, photocatalytic applications with regard to defective TiO₂ are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.

Tremendous interest is devoted to fabricating numerous graphene (GR)–semiconductor composites toward improved conversion of solar energy, resulting from the observation that the photogenerated electrons from semiconductors (e.g., TiO₂, CdS) can be readily accepted or shuttled in the two-dimensional (2D) GR sheet. Yet although the hunt is on for GR–semiconductor composite based photoredox applications that aim to exploit the remarkable electronic conductivity of GR, the work necessary to find out how it could best be harnessed to improve the photocatalytic performance of semiconductors remains scanty. In this review, we highlight a few problems associated with improving the photocatalytic performance of semiconductors via methodological coupling with GR. In particular, we address strategies for harnessing the structure and electronic conductivity of GR via strengthening the interfacial contact, optimizing the electronic conductivity of GR, and spatially optimizing the interfacial charge carrier transfer efficiency. Additionally, we provide a brief overview of assembly methods for fabricating GR–semiconductor composites with controllable film infrastructure to meet the requirements of practical photocatalytic applications. Finally, we propose that, only with the principle of designing and understanding GR–semiconductor composites from a system-level consideration, we might get better at imparting the power of GR with unique and transformative properties into the composite system.

Coupling ZnO with carbon materials using a suitable integration method to form ZnO–carbon composites has been established as a promising strategy to ameliorate the photocatalytic performance of semiconductor ZnO. In this perspective article, we describe the recent advances and current status of enhancing the photocatalytic activity and anti-photocorrosion of semiconductor ZnO by coupling with versatile carbon materials, e.g., C₆₀, carbon nanotube, graphene and other carbon materials. The primary roles of carbon materials in boosting the photoactivity and photostability of ZnO have been outlined and illustrated with some selected typical examples. In particular, the three main kinds of mechanisms with regard to anti-photocorrosion of ZnO by coupling with carbon have been demonstrated. Finally, we give a concise perspective on this important research area and specifically propose further research opportunities in optimizing the photocatalytic performance of ZnO–carbon composites and widening the scope of their potential photocatalytic applications.

At present, the technological groundwork of atomically thin two-dimensional (2D) hetero-layered structures realized by successive thin film epitaxial growth is in principle constrained by lattice matching prerequisite as well as low yield and expensive production. Here, we artificially coordinate ultrathin 2D hetero-layered metal chalcogenides via a highly scalable self-surface charge exfoliation and electrostatic coupling approach. Specifically, bulk metal chalcogenides are spontaneously exfoliated into ultrathin layers in a surfactant/intercalator-free medium, followed by unconstrained electrostatic coupling with a dissimilar transition metal dichalcogenide, MoSe₂, into scalable hetero-layered hybrids. Accordingly, surface and interfacial-dominated photocatalysis reactivity is used as an ideal testbed to verify the reliability of diverse 2D ultrathin hetero-layered materials that reveal high visible-light photoreactivity, efficient charge transfer and intimate contact interface for stable cycling and storage purposes. Such a synthetic approach renders independent thickness and composition control anticipated to advance the development of ‘design-and-build’ 2D layered heterojunctions for large-scale exploration and applications.