Haiquan Xie

Photocatalytic CO₂ reduction is considered to be an appealing way of alleviating environmental pollution and energy shortages simultaneously under mild condition. However, the activity is greatly limited by the poor separation of the photogenerated carriers. Ion doping is a feasible strategy to facilitate the charge transfer. In this work, Ni-doped Bi₄O₅I₂ photocatalyst is successfully fabricated using a one-pot hydrothermal method. A few doping levels appear in the energy band of Bi₄O₅I₂ after Ni doping, which are used as springboards for electrons transition, thus promoting photoexcited electrons and holes separation. As a consequence, a remarkably enhanced yield of CO and CH₄ (6.2 and 1.9 μmol g⁻¹ h⁻¹) is obtained over the optimized Bi₄O₅I₂-Ni15, which is approximately 2.1 and 3.8 times superior to pure Bi₄O₅I₂, respectively. This work may serve as a model for the subsequent research of Bi-based photocatalysts to implement high-performance CO₂ photoreduction.

Hydrogen evolution by photocatalytic technology has been one of the most promising and attractive solutions, and can harvest and convert the abundant solar energy into green, renewable hydrogen energy. As a new kind of photocatalytic material, graphitic carbon nitride (g-C₃N₄) has drawn much attention in photocataluytic H₂ production due to its visible light response, ease of preparation and good stability. For a higher photocatalyic performance, N defects were introduced in to the traditional g-C₃N₄ in this work. The existence of N defects was proved by adequate material characterization. Significantly, a new absorption region at around 500 nm of N-deficient g-C₃N₄ appeared, revealing the exciting n-π* transition of lone pair electrons. The photocatalytic H₂ production performance of N-deficient g-C₃N₄ was increased by 5.8 times. The enhanced photocatalytic performance of N-deficient g-C₃N₄ was attributed to the enhanced visible light absorption, as well as the promoted separation of photo-generated carries and increased specific surface area.

Graphitic carbon nitride (g-C₃N₄) is gaining more and more attentions as a promising metal-free photocatalyst for H₂ production. Nevertheless, from the perspective of practical applications, the photocatalytic performance over g-C₃N₄ in visible-light region needs a further improvement. In this work, C doping and C quantum dots (QDs) are co-integrated in g-C₃N₄ by a one-step thermal polymerization method to obtain an advanced C QDs/C doped g-C₃N₄ photocatalyst. The synergistic effects of C doping and C QDs modification promote the photocatalytic activity of g-C₃N₄ significantly. The optimal C QDs/C doped g-C₃N₄ exhibits a significant improvement on visible-light-driven photocatalytic hydrogen production (205 μmol g⁻¹ h⁻¹) with an apparent quantum yield (AQE) at 420 nm reaching 1.24%, which is approximately nine-fold enhancement than that of pristine g-C₃N₄. The increased photocatalytic activity mainly benefits from the enhanced visible light absorption and carrier separation efficiency. This study may open a new perspective for the design and fabrication of C-modified g-C₃N₄ for photocatalytic hydrogen production.

Photocatalytic water splitting and carbon dioxide photoreduction are considered effective strategies for alleviating the energy crisis and environmental pollution. Polynuclear metal-oxo clusters possess excellent electron storage/release ability and unique catalytic properties via intermetallic synergy, which enables them with great potential in environmentally friendly photosynthesis. Importantly, metal-oxo clusters with precise structure can not only act as high-efficiency catalysts but also provide well-defined structural models for exploring structure–activity relationships. In this review, we systematically summarize recent progress in the catalytic application of polynuclear metal-oxo clusters, including polyoxometalate clusters, low-cost transition metal clusters, and metal-oxo-cluster-based metal–organic frameworks for water splitting and CO₂reduction. Furthermore, we discuss the challenges and solutions to the problems of polynuclear metal-oxo clusters in photocatalysis.

Transition metal-substituted polyoxometalates (POMs) were filled into a metal–organic framework (MOF) to construct a series of POM@MOF composites (PMo₁₂O₄₀@MIL-101, PMo₁₁VO₄₀@MIL-101, PMo₁₀V₂O₄₀@MIL-101). The composite materials possess ultra-high adsorption ability, especially for PMo₁₀V₂O₄₀@MIL-101, with an adsorption capacity of 912.5 mg·g⁻¹ for cationic antibiotic tetracycline in wastewater, much higher than that of isolated MIL-101(Fe) and the commonly used adsorption materials, such as activated carbon and graphene oxide. In particular, they can be used as efficient photocatalysts for the photodegradation of antibiotics under visible light irradiation. The complete photodegradation of the adsorbed species can induce the facile reusability of these composites for multiple cycles. This work opens an avenue to introduce POMs into an MOF matrix for the simultaneous adsorption and photodegradation of antibiotics.

Seawater desalination provides a convenient method for the sustainable production of fresh water. However, the preparation of low-cost, high-efficiency solar absorbers remains a huge challenge. To this end, our research group designed and produced a cheap absorber—a membrane made of natural polymer chitin with black FeS and Fe₃O₄, respectively. Due to the hierarchical pore structure, excellent photothermal performance and good hydrophilicity of the film, their water evaporation rates reached 1.47 kg/m²/h and 1.55 kg/m²/h under one sunlight, respectively. Under about 10 suns, the highest desalination efficiency of FeS/chitin and Fe₃O₄/chitin are 90% and 74%, respectively, and their salinities are also in line with the World Health Organization drinking water standards. These results indicate the potential of chitin-based nanomaterials as high-efficiency solar absorbers to produce fresh water.