Shaowen Cao

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

g-C3N4-Based Photocatalysts for Hydrogen Generation.

Graphitic carbon nitride (g-C3N4)-based photocatalysts have attracted dramatically increasing interest in the area of visible-light-induced photocatalytic hydrogen generation due to the unique electronic band structure and high thermal and chemical stability of g-C3N4. This Perspective summarizes the recent significant advances on designing high-performance g-C3N4-based photocatalysts for hydrogen generation under visible-light irradiation. The rational strategies such as nanostructure design, band gap engineering, dye sensitization, and heterojunction construction are described. Finally, this Perspective highlights the ongoing challenges and opportunities for the future development of g-C3N4-based photocatalysts in the exciting research area.

Recent advances in visible light Bi-based photocatalysts

Abstract Photocatalysis is considered to be an effective solution for the current energy and environmental crises caused by industrial development. However, the practical application of conventional oxide photocatalysts is restricted by poor visible light adsorption because of their wide band gaps. The study of photocatalysts with a narrow band gap is thus a hot topic. Among oxide photocatalysts, Bi-based photocatalysts have attracted much interest because of their high visible light photocatalytic activity. This review summarizes recent advances into the type, preparation method, morphology control, composite construction, and properties of Bi-based photocatalysts. Finally, this review ends with a discussion on the future development of Bi-based photocatalysts in this exciting research area.

TiO2 nanosheets with exposed {001} facets for photocatalytic applications

TiO2 nanosheets with highly reactive {001} facets ({001}-TiO2) have attracted great attention in the fields of science and technology because of their unique properties. In recent years, many efforts have been made to synthesize {001}-TiO2 and to explore their applications in photocatalysis. In this review, we summarize the recent progress in preparing {001}-TiO2 using different techniques such as hydrothermal, solvothermal, alcohothermal, chemical vapor deposition (CVD), and sol gel-based techniques. Furthermore, the enhanced efficiency of {001}-TiO2 by modification of carbon materials, surface deposition of transition metals, and non-metal doping is reviewed. Then, the applications of {001}-TiO2-based photocatalysts in the degradation of organic dyes, hydrogen evolution, carbon dioxide (CO2) reduction, bacterial disinfection, and dye-sensitized solar cells are summarized. We believe this entire review on TiO2 nanosheets with {001} facets can further inspire researchers in associated fields.

Semiconductor-based photocatalytic CO2 conversion

Climate change and its impact on the Earth and Society has been recently reassessed by the International Panel on Climate Change. The panel estimates that the greenhouse gas emissions should be reduced by half by 2030 to mitigate climate change. Photocatalytic CO2 conversion is one of the promising technologies that can help with this modest goal. This review discusses the theoretical and practical aspects of CO2 conversion over semiconducting photocatalysts and overviews the recently reported CO2 conversion photocatalysts. A spectrum of photocatalysts reviewed in this work includes titania and its composites with metal oxides, metals, and advanced carbon allotropes; other solid photocatalysts, mostly based on germanium, gallium, tungsten, and niobium; graphitic carbon nitride; silver–silver halide plasmonic systems; photocatalytically active metal–organic frameworks; and graphene-based systems. Finally, a summary of the current state and an outlook for the future are provided.

Ultra-thin nanosheet assemblies of graphitic carbon nitride for enhanced photocatalytic CO2 reduction

A two-dimensional layered polymeric photocatalyst, graphitic carbon nitride (g-C3N4), is becoming the rising star in the field of solar-to-fuel conversion. However, the performance of commonly prepared g-C3N4 is usually very weak because of the high recombination rate of photogenerated charge carriers and a small amount of surface active sites. Here we demonstrate simultaneous texture modification and surface functionalization of g-C3N4via a stepwise NH3-mediated thermal exfoliation approach. The resulting g-C3N4 photocatalyst possesses a hierarchical structure obtained by the assembly of amine-functionalized ultrathin nanosheets and thus exhibits remarkably enhanced light harvesting, a high redox ability of charge carriers, increased CO2 adsorption and a larger amount of surface active sites, as well as improved charge carrier transfer and separation. Therefore the aforementioned hierarchical g-C3N4 consisting of amine-functionalized ultra-thin nanosheets shows much better performance for photocatalytic CO2 reduction than unmodified conventional g-C3N4 photocatalysts.

Enhanced photocatalytic CO2-reduction activity of electrospun mesoporous TiO2 nanofibers by solvothermal treatment

Photocatalytic reduction of CO2 into renewable hydrocarbon fuels using semiconductor photocatalysts is considered as a potential solution to the energy deficiency and greenhouse effect. In this work, mesoporous TiO2 nanofibers with high specific surface areas and abundant surface hydroxyl groups are prepared using an electrospinning strategy combined with a subsequent calcination process, followed by a solvothermal treatment. The solvothermally treated mesoporous TiO2 nanofibers exhibit excellent photocatalytic performance on CO2 reduction into hydrocarbon fuels. The significantly improved photocatalytic activity can be attributed to the enhanced CO2 adsorption capacity and the improved charge separation after solvothermal treatment. The highest activity is achieved for the sample with a 2-h solvothermal treatment, showing 6- and 25-fold higher CH4 production rate than those of TiO2 nanofibers without solvothermal treatment and P25, respectively. This work may also provide a prototype for studying the effect of solvothermal treatment on the structure and photocatalytic activity of semiconductor photocatalysts.

Au/PtO nanoparticle-modified g-C3N4 for plasmon-enhanced photocatalytic hydrogen evolution under visible light.

Photocatalytic hydrogen evolution under visible light is of great potential for renewable energy development. In this work, unalloyed Au/PtO nanoparticle (NP) co-modified graphitic carbon nitride (g-C3N4) photocatalyst is fabricated through a simple photodeposition method. The obtained g-C3N4 composites with co-existed Au and PtO cocatalysts exhibit a considerable enhancement in the photocatalytic hydrogen evolution activity and possess good stability during cycling experiments. The optimal Au-PtO/g-C3N4 photocatalyst shows a H2 production rate of 16.9 μmol h(-1), which exceeds that of PtO/g-C3N4 and Au/g-C3N4 by a factor of 1.5 and 10.6, respectively. Further characterizations demonstrate that the synergetic action of electron-sink and catalytic effects of PtO along with surface plasmon resonance (SPR) effect of Au NPs, greatly improves the photocatalytic performance of g-C3N4 under visible light. Our study should bring in new insight into the design of effective g-C3N4-based photocatalysts for solar-to-fuel conversion.

Effects of the preparation method on the structure and the visible-light photocatalytic activity of Ag2CrO4

Summary Silver chromate (Ag2CrO4) photocatalysts are prepared by microemulsion, precipitation, and hydrothermal methods, in order to investigate the effect of preparation methods on the structure and the visible-light photocatalytic activity. It is found that the photocatalytic activity of the prepared Ag2CrO4was highly dependent on the preparation methods. The sample prepared by microemulsion method exhibits the highest photocatalytic efficiency on the degradation of methylene blue (MB) under visible-light irradiation. The enhanced photocatalytic activity could be ascribed to the smaller particle size, higher surface area, relatively stronger light absorption, and blue-shift absorption edge, which result in the adsorption of more MB molecules, a shorter diffusion process of more photogenerated excitons, and a stronger oxidation ability of the photogenerated holes. Considering the universalities of microemulsion, precipitation, and hydrothermal methods, this work may also provide a prototype for the comparative study of semiconductor based photocatalysis for water purification and environmental remediation.

Room-temperature synthesis of BiOI with tailorable (001) facets and enhanced photocatalytic activity.

The photocatalytic activity of bismuth oxyhalides largely depends on their morphologies and microstructures. In this work, hierarchically structured bismuth oxyiodide (BiOI) with tunable ratios of (110) and (001) facets are fabricated through a facile route combining solid-state reaction with subsequent hydrolysis at room temperature. The hierarchical structures endow BiOI with excellent visible-light photocatalytic performance for phenol degradation. Besides, the optimal ratio of (001) and (110) surfaces also plays an important role in enhancing the photocatalytic activity of BiOI. DFT calculation demonstrates that a surface heterojunction formed between (001) and (110) surfaces can improve the separation of electrons and holes on different surfaces and thus enhance the photocatalytic activity.