The evergrowing energy crisis and environmental degradation have instigated scientists to explore sophisticated, versatile energy conversion systems. Photoconversion, which conveys solar power to chemical energy, has emerged as an eminent energy conversion approach to accomplish the demands. Recent years have seen the rocketing rise of semiconductor heterostructures as an ideal material paradigm for the realization of miscellaneous photoconversion applications ranging from water splitting, CO 2 reduction and environmental purification to photosynthesis. With tailored functionalities from synergetic effects, semiconductor heterostructures come into prominence as the forefront of photocatalyst development. This topical review summarizes the photoconversion applications developed so far by employing semiconductor heterostructures, with a focus on the heterostructure design principle, interfacial charge dynamics and key factors dictating the overall performance. Future research outlooks and perspectives on the progress of photoconversion technology are also presented.

SrTiO3 cubes with tunable sizes of 160–290 nm have been synthesized by mixing TiCl4, SrCl2, and LiOH in pure ethanol or a water/ethanol mixed solution at just 70 °C for 3 h. Replacing water/ethanol with water/hexanol and water/ethylene glycol, and fine tuning the amounts of other reagents, resulted in the formation of edge-truncated cubes and {100}-truncated rhombic dodecahedra, respectively. X-ray diffraction and transmission electron microscopy characterization, supported by Rietveld refinement analysis, have revealed shape-dependent tuning in lattice parameters. The cubes display slight size-related optical band shifts, and they show clearly more blue-shifted light absorption than the other particles exposing significant {110} faces. The {100}-truncated rhombic dodecahedra are far more efficient than cubes at photodegradation of methylene blue and photocatalyzed hydrogen evolution from water in the presence of methanol. The photocatalytic activity variation should arise from different degrees of surface band bending for the {100} and {110} faces of SrTiO3, suggesting surface facet control as a strategy for enhancing photocatalyzed hydrogen production.

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An Au-mediated Cu2O-based Z-scheme heterostructure system is demonstrated for use as efficient photocathodes in photoelectrochemical (PEC) reduction. The samples are prepared by electrodepositing a Cu2O layer on the surface of Au particle-coated TiO2 nanorods. For TiO2-Au-Cu2O, the embedded Au particles function as a charge transfer mediator to enhance the electron transportation from the conduction band of TiO2 to the valence band of Cu2O. Such a vectorial charge transfer leads to the concentration of electrons at the conduction band of Cu2O and the collection of holes at the valence band of TiO2, providing TiO2-Au-Cu2O with substantially high redox abilities for reduction applications. Time-resolved photoluminescence spectra and electrochemical impedance spectroscopy analysis suggest that interfacial charge transfer is significantly improved because of the Au-mediated Z-scheme charge transfer mechanism. By virtue of the high redox ability and improved interfacial charge transfer, TiO2-Au-Cu2O performs much better as a photocathode in H2 production and CO2 reduction than pure Cu2O and binary TiO2-supported Cu2O do. Remarkably, the photocurrent density of TiO2-Au-Cu2O toward PEC CO2 reduction can reach as high as −1.82 mA/cm2 at +0.11 V vs RHE. The incident photon-to-current conversion efficiency data manifest that TiO2-Au-Cu2O surpasses both pure Cu2O and binary TiO2-supported Cu2O in PEC reduction across the whole photoactive region. The current study paves a valuable approach of devising Z-scheme photocathode for the construction of sophisticated artificial photosynthesis systems capable of solar-to-fuel conversion.

We synthesized nitrogen (N)-doped graphene quantum dots (N-GQDs) using a top-down hydrothermal cutting approach. The concentration of N dopants was readily controlled by adjusting the concentration of the N source of urea. When N dopants were incorporated into GQDs, visible absorption was induced by C–N bonds, which created another pathway for generating photoluminescence (PL). Time-resolved PL data revealed that the carrier lifetime of GQDs was increased upon doping with the optimized N concentration. The photoelectrochemical properties of N-GQDs toward water splitting were studied, and the results showed that 2N-GQDs prepared with 2 g of urea produced the highest photocurrent. The photocatalytic activity of 2N-GQDs powder photocatalyst for hydrogen production was also examined under AM 1.5G illumination, showing substantial enhancement over that of pristine GQDs. Electrochemical impedance spectroscopy data further revealed a significant improvement in charge dynamics and reaction kinetics and an increased carrier concentration as a result of N doping.

Enrichment cultures obtained from soil exposed to benzene, toluene, and xylene (BTX) mineralized benzene and toluene but cometabolized only xylene isomers, forming polymeric residues. This observation prompted us to investigate the metabolism of 14C-labeled BTX hydrocarbons in soil, either individually or as mixtures. BTX-supplemented soil was incubated aerobically for up to 4 weeks in a sealed system that automatically replenished any O2consumed. The decrease in solvent vapors and the production of14CO2 were monitored. At the conclusion of each experiment, 14C distribution in solvent-extractable polymers, biomass, and humic material was determined, obtaining14C mass balances of 85 to 98%. BTX compounds were extensively mineralized in soil, regardless of whether they were presented singly or in combinations. No evidence was obtained for the formation of solvent-extractable polymers from xylenes in soil, but14C distribution in biomass (5 to 10%) and humus (12 to 32%) was unusual for all BTX compounds and especially for toluene and the xylenes. The results suggest that catechol intermediates of BTX degradation are preferentially polymerized into the soil humus and that the methyl substituents of the catechols derived from toluene and especially from xylenes enhance this incorporation. In contrast to inhibitory residues formed from xylene cometabolism in culture, the humus-incorporated xylene residues showed no significant toxicity in the Microtox assay.

A CIGS-based photocathode combined with an earth abundant Co–S catalyst has demonstrated remarkable photoelectrochemical hydrogen generation in neutral electrolyte.

Design of metal-semiconductor interfaces and heterostructures is of strong interest for various catalytic applications including photocatalysis. In this work, a series of hollow Au nanosphere (HGN)-Cu 2 O core-shell nanostructures with varying core surface rugosity are synthesized and investigated for possible photocatalytic applications. HGN surface rugosity is tuned by pH modification during galvanic exchange and carboxyl groups are utilized as coordination sites to deposit uniform Cu 2 O shells onto the gold surfaces. Final core-shell structures are verified by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). Information regarding chemical state and electronic band structure is acquired by Xray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Ultrafast transient absorption (TA) reveals that charge separation in bHGN-Cu 2 O may effectively provide longer-lived photoexcited carriers, offering great potential for utilization in advanced photocatalytic processes.