Kang-Qiang Lu

Recent progress in carbon quantum dots: synthesis, properties and applications in photocatalysis

Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials, by virtue of their unique physicochemical, optical and electronic properties, have displayed tremendous momentum in numerous fields such as biosensing, bioimaging, drug delivery, optoelectronics, photovoltaics and photocatalysis. In particular, the rich optical and electronic properties of CQDs including efficient light harvesting, tunable photoluminescence (PL), extraordinary up-converted photoluminescence (UCPL) and outstanding photoinduced electron transfer have attracted considerable interest in different photocatalytic applications for the sake of full utilization of the solar spectrum. This review aims to demonstrate the recent progress in the synthesis, properties and photocatalytic applications of CQDs, particularly highlighting the fundamental multifaceted roles of CQDs in photoredox processes. Furthermore, we discuss the challenges and future direction of CQD-based materials in this booming research field, with a perspective toward the ultimate achievement of highly efficient and long-term stable CQD-based photocatalysts.

Insight into the Role of Size Modulation on Tuning the Band Gap and Photocatalytic Performance of Semiconducting Nitrogen-Doped Graphene

Considerable attention has been focused on transforming graphene (GR) into semiconducting GR by diverse strategies, which can perform as one type of promising photocatalyst toward various photoredox reactions. Herein, we report a facile alkali-assisted hydrothermal method for simultaneous tailoring of the lateral size of GR and nitrogen (N) doping into the GR matrix, by which small-sized N-doped GR (S-NGR) can be obtained. For comparison, large-sized N-doped GR (L-NGR) has also been achieved through the same hydrothermal treatment except for the addition of alkali. The photocatalytic activity test shows that S-NGR exhibits much higher activity than L-NGR toward the degradation of organic pollutants under visible-light irradiation. Structure-photoactivity correlation analysis and characterization suggest that the underlying origin for the significantly enhanced visible-light photoactivity of S-NGR in comparison with L-NGR can be assigned to the lateral size decrease in the NGR sheet, which is able to tune the band gap of semiconducting NGR, to facilitate the separation and transfer of photogenerated charge carriers, and to improve the adsorption capacity of NGR toward the reactant. It is expected that this work will cast new light on the judicious utilization of semiconducting GR with controlled size modulation and heteroatom doping to tune its physicochemical properties, thereby advancing further developments in the rational design of more efficient semiconducting GR materials for diverse applications in photocatalysis.

Photoredox catalysis over graphene aerogel-supported composites

Three-dimensional (3D) graphene aerogels, by virtue of their unique physicochemical properties, which result from the intrinsic properties of graphene and 3D porous structure characteristics, have attracted ever-increasing research interest in the field of photocatalysis for the sake of efficient utilization of solar energy. Herein, we intend to afford a concise review on the recent progress regarding the synthetic method of graphene aerogels and the promising applications of graphene aerogel-based photocatalysts in pollutant elimination, water splitting, CO2 reduction, organic synthesis and atmospheric ammonia synthesis. In particular, the superiorities of 3D graphene aerogel-based photocatalysts for various solar-driven photoredox applications have been demonstrated. Furthermore, in addition to discussing opportunities offered by graphene aerogel-supported photocatalysts, we will also describe the existing challenges and the future direction of graphene aerogel-based photocatalysts in this burgeoning research area. It is hoped that this review could spur multidisciplinary research interest for advancing the rational utilization of 3D graphene aerogels to synthesize more efficient photocatalysts for practical applications.

Stabilizing ultrasmall Au clusters for enhanced photoredox catalysis

Recently, loading ligand-protected gold (Au) clusters as visible light photosensitizers onto various supports for photoredox catalysis has attracted considerable attention. However, the efficient control of long-term photostability of Au clusters on the metal-support interface remains challenging. Herein, we report a simple and efficient method for enhancing the photostability of glutathione-protected Au clusters (Au GSH clusters) loaded on the surface of SiO2 sphere by utilizing multifunctional branched poly-ethylenimine (BPEI) as a surface charge modifying, reducing and stabilizing agent. The sequential coating of thickness controlled TiO2 shells can further significantly improve the photocatalytic efficiency, while such structurally designed core-shell SiO2-Au GSH clusters-BPEI@TiO2 composites maintain high photostability during longtime light illumination conditions. This joint strategy via interfacial modification and composition engineering provides a facile guideline for stabilizing ultrasmall Au clusters and rational design of Au clusters-based composites with improved activity toward targeting applications in photoredox catalysis.The improvement of photostability of Au clusters on metal-support interface remains challenging. Here, the authors report a joint strategy via interfacial modification and composition manipulation to enhance the photostability and activity of glutathione-protected Au clusters.

Constructing film composites of silicon nanowires@CdS quantum dot arrays with ameliorated photocatalytic performance

Silicon nanostructure-based composites have recently aroused intensive interest because of their promising potential to convert solar energy into chemical fuels. Here, we report a facile approach to construct the film composites of n-type CdS quantum dot (QD) decorated p-type vertically aligned one-dimensional (1D) silicon nanowire (SiNWs@CdS) arrays with enhanced activity and recyclable operability for photocatalytic hydrogen evolution in comparison with the single component counterpart. The photoelectrochemical results confirm the formation of a p–n heterojunction in the interface of SiNWs and CdS QDs, which can create an internal electric field to facilitate the separation and transport of photoinduced charge carriers, thereby leading to the concomitant improvement of both the photoactivity and photostability of the SiNWs@CdS array composite. This work is expected to provide an instructive recipe for fabricating p–n heterojunction 1D-based composite arrays with a film structure to boost charge carrier separation and transfer, and to achieve efficient artificial solar energy conversion.