Sulfur-doped g-C3N4 with enhanced photocatalytic CO2-reduction performance

Enhanced visible light photocatalytic hydrogen evolution of sulfur-doped polymeric g-C3N4 photocatalysts

In this study, to overcome the low charge transportation efficiency and poor visible light absorption ability, and achieve highly efficient photocatalytic applications, carbon nitride nanosheets with oxygen and carbon co-doping were successfully designed and fabricated. The resultant carbon nitride nanosheets exhibited efficient photocatalytic H2 evolution and CO2 reduction performance, highlighting the efficacy of such a strategy. The highest H2 evolution rate could reach 698.43 μmol g-1 h-1, higher than that for graphitic carbon nitride (GCN). For CO2 reduction, the photocatalytic system shows a high CO selectivity, and MG3.0 achieves the largest CO generation amount of 55.2 μmol g-1. This enhanced photocatalytic reduction performance could be attributed to oxygen and carbon co-doping, which achieves fast electron extraction and transfer, and improved visible light absorption ability. It should be noted that the excessive addition of glucose in the synthesis process could enhance conductivity and promote visible light absorption of carbon nitride, but suppress the H2 evolution and CO2 reduction ability. Simultaneously, the photocatalytic reduction mechanism is discussed. This work confirms that a carbon nitride semiconductor with oxygen and carbon co-doping could be easily prepared by this strategy, achieving efficient photocatalytic applications.

Photocatalytic reduction of CO2 into renewable hydrocarbon fuels is an alternative way to develop reproducible energy, which is also a promising way to solve the problem of the greenhouse effect. In this work, graphitic carbon nitride (g-C3N4) was synthesized by directly heating thiourea at 550 °C and then a certain amount of Pt was deposited on it to form g-C3N4-Pt nanocomposites used as catalysts for photocatalytic reduction of CO2 under simulated solar irradiation. The main products of photocatalysis were CH4, CH3OH and HCHO. The deposited Pt acted as an effective cocatalyst, which not only influenced the selectivity of the product generation, but also affected the activity of the reaction. The yield of CH4 first increased upon increasing the amount of Pt deposited on the g-C3N4 from 0 to 1 wt%, then decreased at 2 wt% Pt loading. The production rates of CH3OH and HCHO also increased with the content of Pt increasing from 0 to 0.75 wt% and the maximum yield was observed at 0.75 wt%. The Pt nanoparticles (NPs) could facilitate the transfer and enrichment of photogenerated electrons from g-C3N4 to its surface for photocatalytic reduction of CO2. At the same time, Pt was also used a catalyst to promote the oxidation of products. The transient photocurrent response further confirmed the proposed photocatalytic reduction mechanism of CO2. This work indicates that the deposition of Pt is a good strategy to improve the photoactivity and selectivity of g-C3N4 for CO2 reduction.

Rapid growth in economy and society currently relies on fossil fuels heavily, leading to serious concern on energy sustainability and environmental pollution. This has aroused increasing interest in solar energy, which is the most abundant and green energy source. However, it remains a significant challenge in storing and harnessing solar energy due to its diurnal and seasonal fluctuation along with uneven distribution. Moreover, its energy density is relatively low; and the energy supply from traditional solar cells is time-varying. Consequently, it is difficult to synchronize the generation and usage of electricity from solar cells. In contrast, photocatalytic water splitting can convert solar energy to chemical energy, which can be stored in the form of hydrogen, an ideal energy carrier that is characteristic of cleanness and operational convenience. Also, photocatalytic CO2 reduction can transform greenhouse gas to valuable fuels. Furthermore, photocatalytic degradation of organic pollutants can decontaminate air, water, and soil. Additionally, photocatalytic disinfection and sterilization can reduce human exposure to pathogens and toxins. Therefore, photocatalysis has received extensive attention globally, becoming the hotspot and frontier across several fields, including chemistry, materials science, energy and environment engineering. In this special issue (Part 1), 2 progress reports, 12 review articles and 15 research articles have been published. Classified based on applications, 8 papers concern with hydrogen evolution, 7 papers involve CO2 reduction, 2 articles deal with pollutant decomposition, and 11 papers are related to nitrate reduction, nitrogen fixation, organic synthesis, syngas synthesis, NADH (nicotinamide adenine dinucleotide) regeneration and so on. From the materials perspective, 8 papers discuss C3N4, 4 articles involve CdS, 3 paper concern with conjugated polymers, other papers cover TiO2, CdSe, CoMn alloy, PbI2/CuI, silicon, metal-organic frameworks (MOFs), perovskite oxides, Bi2MoO6 and so on. Photocatalytic H2 production is of great interest from both theoretical and practical viewpoints because of its potential application in converting solar energy into storable chemical energy. Herein, Zhen and Xue (solr.202000440) have reviewed surface functionalization of polymeric carbon nitride at atomic and molecular levels for photocatalytic H2 production and CO2 reduction applications. Then, Yu et al. have (solr.202000372) reported enhanced photocatalytic H2 production activity of g-C3N4, which are prepared by one-step crystallization and cyano-group modification. Yang and co-workers (solr.202000414) have presented the fabrication of 2D/2D CdS/MXene Schottky heterojunctions by electrostatic self-assembly and solvothermal method and their application in high-efficiency photocatalytic hydrogen production. Tang and colleagues (solr.202000281) have reported the molecular cobalt catalysts grafted on a conjugated microporous polymer for high-efficiency H2 production. Zhao et al. (solr.202000415) have prepared a CdS/MoS2 nanooctahedron heterostructure with a tight interface for enhanced photocatalytic H2 evolution and biomass upgrading. Wu's group (solr.202000474) have reported a per-6-thiol-cyclodextrin engineered [FeFe]-H2ase mimic/CdSe quantum dot assembly for effective photocatalytic H2 evolution. Xu et al. (solr.202000486) have synthesized a lignin-modified g-C3N4 nanoarchitecture with an ultrathin layered topography for efficient photocatalytic H2 production. Finally, Kwon et al. (solr.202000411) have reported a self-assembly between the CdS quantum dots and the RuO2/reduced graphene oxide nanosheets, showing enhanced photocatalytic H2 production activity. Nowadays, there is increasing interest in solutions to the increasing CO2 level in the atmosphere. Photocatalytic reduction of CO2 into storable solar fuels is an appealing strategy to simultaneously overcome both environmental problems and energy crisis. In this special issue, Wang's group (solr.202000443) has firstly discussed the active sites of catalysts for CO2 activation and conversion. Then, Liang et al. (solr.202000478) have summarized recent research progress in g-C3N4 and its composite photocatalysts for CO2 reduction. Huang's group (solr.202000430) has reviewed junction engineering for photocatalytic and photoelectrocatalytic CO2 reduction. Zhang et al. (solr.202000387) have demonstrated an all-earth-abundant photothermal silicon platform for CO2 catalysis with nearly 100% sunlight absorption ability. Jia's group (solr.202000313) has reported anchoring single-atom Ru on CdS, showing enhanced CO2 capture and charge accumulation for highly selective photothermocatalytic CO2 reduction to solar fuels. Xiang et al. (solr.202000351) have prepared an ultrathin S-scheme heterojunction based on few-layer g-C3N4 and monolayer Ti3C2Tx MXene for photocatalytic CO2 reduction. Finally, Zhang's group (solr.202000326) has reported an ultraviolet-visible-near-infrared responsive Cu2-xS/g-C3N4 composite photocatalyst and its photocatalytic CO2 reduction performance. It worth noting that significant efforts have been made to prepare high-performance photocatalysts for environment remediation including air purification, hazardous waste removal, water purification, and etc. Herein Xu et al. (solr.202000416) have fabricated a g-C3N4/NH2-UIO-66 composite photocatalyst with enhanced photocatalytic removal efficiency for hexavalent chromium. Zhu's group (solr.202000453) has reported the enhanced photocatalytic phenol degradation activity in the presence of g-C3N4/PDI (perylenetetracarboxylic diimide). Janáky and co-workers (solr.202000418) have reported the preparation of PbI2/CuI nanocomposite electrode and its solar photoelectroreduction of nitrate ions. Peng's group (solr.202000487) has summarized updated research progresses in photocatalytic nitrogen-fixation reaction over semiconductors. Su and colleagues (solr.202000444) have surveyed recent advance in the rational harnessing of photoexcited hole-electron pairs in semiconductor photocatalysts, and the application in oxidative and reductive synthetic transformations for chemical and pharmaceutical production. Ouyang's group (solr.202000488) has reported the fabrication of CoMn alloy using a metal-segregation method and its enhanced photothermal conversion of syngas to light olefins. Qian and Zhang (solr.202000489) have commented the recent advance in the conjugated microporous polymers in visible light promoted chemical transformations such as water splitting, CO2 reduction, organic photoredox reactions, and etc. Chen and colleague (solr.202000442) have reviewed the current research status of Bi2MoO6-based photocatalysts and their surface/interface modification strategies and applications. Dong and co-workers (solr.202000419) have reviewed the synthesis strategy, interfacial effect and photocatalytic application of perovskite nanocrystals-based heterostructure photocatalysts. Hao and Li (solr.202000454) have reviewed visible-light initiated synergistic/cascade reactions over metal-organic frameworks. Ma's group (solr.202000397) has highlighted the 2D/2D Z-Scheme heterojunctions for photocatalytic application. Wang et al. (solr.202000392) have reviewed two-dimensional silicon (2D Si) for catalysis and photocatalysis applications. Liu's group (solr.202000339) has summarized the key developments of conjugated photocatalytic systems for NADH (nicotinamide adenine dinucleotide) regeneration. As the guest editors, we thank all the authors for their prompt response to the paper call and their valuable contribution to this special issue. All the manuscripts were refereed through rigorous peer-review processes. We greatly appreciate the timely and conscientious evaluation of manuscripts by the reviewers. Last but not least, we are grateful to Dr. Lulu Ma, Editor of Solar RRL, for her tremendous support and dedication. Jiaguo Yu received his B.S. and M.S. in chemistry from Central China Normal University and Xi'an Jiaotong University, respectively; his Ph.D. in Materials Science from Wuhan University of Technology (WUT). In 2000, he became a Professor at WUT. His research interests include photocatalysis, adsorption, supercapacitor, electrocatalysis, formaldehyde removal and so on. He is Foreign Member of Academia Europaea (The Academy of Europe) (2020), Foreign Fellow of the European Academy of Sciences (2020) and Fellow of the Royal Society of Chemistry (2015). Tierui Zhang is currently Professor at the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. He obtained his Ph.D. degree in Chemistry from Jilin University, China in 2003. He worked as a postdoctoral fellow in the labs of Prof. Markus Antonietti, Prof. Charl F.J. Faul, Prof. Hicham Fenniri, Prof. Z. RyanTian, Prof. Yadong Yin, and Prof. Yushan Yan. His current scientific interests focus on catalyst nanomaterials for energy conversion. Nianqiang Wu is currently Armstrong-Siadat Endowed Professor in Materials Science at University of Massachusetts Amherst, USA. He has received his Ph.D. degree in Materials Science and Engineering from Zhejiang University, China. Dr. Wu is Fellow of the Electrochemical Society (FECS) and Royal Society of Chemistry (FRSC). His research interest lies in: 1) photocatalysts and photoelectrochemical cells, 2) electrochemical energy storage, and 3) biosensing, microfluidics and photodynamic therapy.

Few‐layered graphitic carbon nitride (g‐C3N4) has been considered a popular base for constructing composite materials in photocatalytic CO2 reduction and H2 generation applications, particularly for constructing g‐C3N4 based composites based on the idea of nanoarchitectonics. The photocatalytic activity of these constructed g‐C3N4 composites relies on the composition, morphology, microstructure of the material. This review aims to focus on the summary of latest progress in the development of few‐layered g‐C3N4 nanosheets based noble metal clusters/nanoparticles and other semiconductor nanomaterials modified composite materials constructed using the technology of nanoarchitectonics for photocatalytic H2 generation and CO2 reduction. This review covers a brief introduction of the enhanced photogenerated carrier separation and transfer as well as extended light absorption of superior thin g‐C3N4 nanosheets based photocatalysts; discussions on the mechanism of g‐C3N4 based photocatalyst involved photocatalytic H2O splitting and CO2 reduction system; the latest progress in the study of nanoarchitectonics of a variety of g‐C3N4 based heterostructures including type II, Z‐scheme, S‐scheme, and Schottky junction. Major challenges on nanoarchitectonics of superior thin g‐C3N4 based heterostructures, as well as the recommendations for future studies of these materials to attain higher efficiency in photocatalytic H2 generation and CO2 reduction, are also concluded.

Photocatalytic CO2 reduction into value-added chemical fuels using sunlight as the energy input has been a thorny, challenging and long-term project in the environment/energy fields because of to its low efficiency. Herein, a series of CdS/Co-BDC composite photocatalysts were constructed by incorporating CdS nanoparticles into Co-BDC using a dual-solvent in situ growth strategy for improving photocatalytic CO2 reduction efficiency. The composites were characterized through XRD, SEM, TEM, XPS, DRS and EPR techniques in detail. 18% CdS/Co-BDC composites showed superior performance for the photocatalytic CO2 reduction to CO, which was 8.9 and 19.6 times higher than that showed by the pure CdS and Co-BDC, respectively. The mechanism of enhanced photocatalytic CO2 reduction performance was analyzed. The CdS/Co-BDC composites showed better adsorption for CO2. Detailed analysis of XPS, transient photocurrent responses, and electrochemical impedance spectroscopy (EIS) shows the existence of strong charge interaction between CdS and Co-BDC and the photo-electrons of CdS can be transferred to Co-BDC. Additionally, Co-oxo of Co-BDC plays the role of a redox-active site and promotes the reduction performance via the method of valence transition of Co(ii)/Co(iii) redox.

Carbon-based two-dimensional layered materials for photocatalytic CO2 reduction to solar fuels

Efficient visible-light-driven photocatalytic hydrogen evolution and CO2 reduction over silver-modified tubular carbon nitride with enriched nitrogen vacancies.

Spontaneous reduction of copper on Ti3C2Tx as fast electron transport channels and active sites for enhanced photocatalytic CO2 reduction

In-plane benzene incorporated g-C3N4 microtubes: Enhanced visible light harvesting and carrier transportation for photocatalytic CO2 reduction

Rational one-step synthesis of cobalt clusters embedded-graphitic carbon nitrides for the efficient photocatalytic CO2 reduction under ambient conditions

Synthesis of 2D/2D structural Ti3C2 MXene/g-C3N4 via the Schottky junction with metal oxides: Photocatalytic CO2 reduction with a cationic scavenger

3D Flower-like Zinc doping Engineered Bismuth Vanadium Oxide Architecture for Boosted Photocatalytic CO2 Reduction to CH3OH

A P-doped BiOBr nanosheet for enhanced photocatalytic CO2 reduction efficiency

Contemporary advances in photocatalytic CO2 reduction using single-atom catalysts supported on carbon-based materials