Semiconductor photocatalysts have received much attention in recent years due to their great potentials for the development of renewable energy technologies, as well as for environmental protection and remediation. The effective harvesting of solar energy and suppression of charge carrier recombination are two key aspects in photocatalysis. The formation of heterostructured photocatalysts is a promising strategy to improve photocatalytic activity, which is superior to that of their single component photocatalysts. This Feature Article concisely summarizes and highlights the state-of-the-art progress of semiconductor/semiconductor heterostructured photocatalysts with diverse models, including type-I and type-II heterojunctions, Z-scheme system, p–n heterojunctions, and homojunction band alignments, which were explored for effective improvement of photocatalytic activity through increase of the visible-light absorption, promotion of separation, and transportation of the photoinduced charge carries, and enhancement of the photocatalytic stability.

Photocatalytic reduction of CO₂ into hydrocarbon fuels, an artificial photosynthesis, is based on the simulation of natural photosynthesis in green plants, whereby O₂ and carbohydrates are produced from H₂O and CO₂ using sunlight as an energy source. It couples the reductive half-reaction of CO₂ fixation with a matched oxidative half-reaction such as water oxidation, to achieve a carbon neutral cycle, which is like killing two birds with one stone in terms of saving the environment and supplying future energy. The present review provides an overview and highlights recent state-of-the-art accomplishments of overcoming the drawback of low photoconversion efficiency and selectivity through the design of highly active photocatalysts from the point of adsorption of reactants, charge separation and transport, light harvesting, and CO₂ activation. It specifically includes: i) band-structure engineering, ii) nanostructuralization, iii) surface oxygen vacancy engineering, iv) macro-/meso-/microporous structuralization, v) exposed facet engineering, vi) co-catalysts, vii) the development of a Z-scheme system. The challenges and prospects for future development of this field are also present.

To realize practical applications of the photocatalysis technique, it is necessary to synthesize semiconductor photocatalysts with specific facets that induce high reactive activities and high reactive selectivity. However, a challenge lies in the synthesis of metal oxides containing more than one type of metal with specific facets. Usually, surfactants are used to control the crystal morphology, which induces surface contamination for the final products. Here, using the GaOOH nanoplate as precursor, ZnGa₂O₄ nanocubes with exposed {100} facets are synthesized by an hydrothermal ion-exchange route without requiring the introduction of morphology controlling agents. These ZnGa₂O₄ nanocubes exhibit improved performance in the photoreduction of CO₂ into CH₄ or water splitting into hydrogen. Theoretical calculations indicates that the light-hole effective mass on the {100} facets of ZnGa₂O₄ corresponds to the high hole mobility, which contributes to the efficient water oxidation to offer the protons for promoting CO₂ photoreduction into hydrocarbon fuels.

As global energy demand continues to grow, the need to find a carbon-neutral and sustainable energy source for future generations has become imperative. An especially attractive solution is to store solar energy in the form of chemical fuel via artificial photosynthesis to convert carbon dioxide into hydrocarbons. An artificial photosynthesis system is introduced based on a zinc gallogermanate solid solution photocatalyst that can convert the carbon dioxide and water into methane. The solid solution of cubic spinel ZnGa₂O₄ and pseudocubic inverse spinel Zn₂GeO₄ is successfully synthesized by hydrothermal ion exchange reaction. Introducing Zn₂GeO₄ into ZnGa₂O₄ can effectively narrow band gap by the upshift of valence band edge from the enhanced p-d (O2p-Zn3d) repulsion effect by incorporating s and p orbitals of Ge, and the downshift of conduction band edge by introducing the low-energy s orbital of Ge. The zinc gallogermanate solid solution has a light-hole effective mass, which is beneficial to improving hole mobility, and thus enhancing the ability of photocatalyst in water oxidation to provide protons for CO₂ photoreduction. As a result of band gap narrowing and high hole mobility, the zinc gallogermanate solid solution exhibits high activity in converting CO₂ and H₂O into CH₄ and O₂.

A novel, in situ simultaneous reduction-hydrolysis technique (SRH) is developed for fabrication of TiO₂--graphene hybrid nanosheets in a binary ethylenediamine (En)/H₂O solvent. The SRH technique is based on the mechanism of the simultaneous reduction of graphene oxide (GO) into graphene by En and the formation of TiO₂ nanoparticles through hydrolysis of titanium (IV) (ammonium lactato) dihydroxybis, subsequently in situ loading onto graphene through chemical bonds (Ti–O–C bond) to form 2D sandwich-like nanostructure. The dispersion of TiO₂ hinders the collapse and restacking of exfoliated sheets of graphene during reduction process. In contrast with prevenient G-TiO₂ nanocomposites, abundant Ti³⁺ is detected on the surface of TiO₂ of the present hybrid, caused by reducing agent En. The Ti³⁺ sites on the surface can serve as sites for trapping photogenerated electrons to prevent recombination of electron–hole pairs. The high photocatalytic activity of G-TiO₂ hybrid is confirmed by photocatalytic conversion of CO₂ to valuable hydrocarbons (CH₄ and C₂H₆) in the presence of water vapor. The synergistic effect of the surface-Ti³⁺ sites and graphene favors the generation of C₂H₆, and the yield of the C₂H₆ increases with the content of incorporated graphene. The work may open a new doorway for new significant application of graphene for selectively catalytic C–C coupling reaction

Graphene-semiconductor nanocomposites, considered as a kind of most promising photocatalysts, have shown remarkable performance and drawn significant attention in the field of photo-driven chemical conversion using solar energy, due to the unique physicochemical properties of graphene. The photocatalytic enhancement of graphene-based nanocomposites is caused by the reduction of the recombination of electron-hole pairs, the extension of the light absorption range, increase of absorption of light intensity, enhancement of surface active sites, and improvement of chemical stability of photocatalysts. Recent progress in the photocatalysis development of graphene-based nanocomposites is highlighted and evaluated, focusing on the mechanism of graphene-enhanced photocatalytic activity, the understanding of electron transport, and the applications of graphene-based photocatalysts on water splitting, degradation or oxidization of organic contaminants, photoreduction of CO₂ into renewable fuels, toxic elimination of heavy metal ions, and antibacterial applications.

One-dimensional Fe₂V₄O₁₃ nanoribbons 10–20 μm long and 20–30 nm thick growing directly on a stainless-steel mesh (SSM) have been successfully obtained by a simple and facile hydrothermal reaction without any templates or surfactants. The SSM served as not only the Fe source but also the substrate for the deposition of vanadium and oxide elements. The Fe₂V₄O₁₃ nanoribbon as an easily reused photocatalyst shows great potential for the efficient photoreduction of CO₂ into renewable hydrocarbon fuel (CH₄) and for the removal of organics from air under visible-light illumination.

Robust hollow spheres consisting of molecular-scale alternating titania (Ti_0.91O₂) nanosheets and graphene (G) nanosheets are successfully fabricated by a layer-by-layer assembly technique with polymer beads as sacrificial templates using a microwave irradiation technique to simultaneously remove the template and reduce graphene oxide into graphene. The molecular scale, 2D contact of Ti_0.91O₂ nanosheets and G nanosheets in the hollow spheres is distinctly different from the prevenient G-based TiO₂ nanocomposites prepared by simple integration of TiO₂ and G nanosheets. The nine times increase of the photocatalytic activity of G-Ti_0.91O₂ hollow spheres relative to commercial P25 TiO₂ is confirmed with photoreduction of CO₂ into renewable fuels (CO and CH₄). The large enhancement in the photocatalytic activity benefits from: 1) the ultrathin nature of Ti_0.91O₂ nanosheets allowing charge carriers to move rapidly onto the surface to participate in the photoreduction reaction; 2) the sufficiently compact stacking of ultrathin Ti_0.91O₂ nanosheets with G nanosheets allowing the photogenerated electron to transfer fast from the Ti_0.91O₂ nanosheets to G to enhance lifetime of the charge carriers; and 3) the hollow structure potentially acting as a photon trap-well to allow the multiscattering of incident light for the enhancement of light absorption.

Graphene-based nanostructures are considered as promising alternatives to silicon-based mesostructures in future electronic nanodevices. The lithographical patterning of graphene, which are essential steps in any form of microelectronic processing, present interesting challenges because of the atomic layer thickness of graphene. Mesoscopic devices based on graphene require high spatial resolution patterning that will induce as little damage as possible. This research news highlights and evaluates recent developments in the nanostructuring and patterning of graphene.