Solar RRLVolume 4, Issue 8 2000354 EditorialFree Access Emerging Nanomaterials for Light-Driven Reactions: Past, Present, and Future Wee-Jun Ong, Corresponding Author Wee-Jun Ong weejun.ong@xmu.edu.my orcid.org/0000-0002-5124-1934 School of Energy and Chemical Engineering, Xiamen University Malaysia, Selangor Darul Ehsan, 43900 Malaysia College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005 ChinaSearch for more papers by this authorKazuhiko Maeda, Corresponding Author Kazuhiko Maeda maedak@chem.titech.ac.jp School of Science, Tokyo Institute of Technology, 2-12-1-NE-2 Ookayama, Meguroku Tokyo, 152-8550 JapanSearch for more papers by this author Wee-Jun Ong, Corresponding Author Wee-Jun Ong weejun.ong@xmu.edu.my orcid.org/0000-0002-5124-1934 School of Energy and Chemical Engineering, Xiamen University Malaysia, Selangor Darul Ehsan, 43900 Malaysia College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005 ChinaSearch for more papers by this authorKazuhiko Maeda, Corresponding Author Kazuhiko Maeda maedak@chem.titech.ac.jp School of Science, Tokyo Institute of Technology, 2-12-1-NE-2 Ookayama, Meguroku Tokyo, 152-8550 JapanSearch for more papers by this author First published: 11 August 2020 https://doi.org/10.1002/solr.202000354Citations: 1AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In 2020, the global energy consumption is anticipated to surpass 14 gigatons oil equivalent (5.8 × 1020 J).[1] To maintain the growth of high energy demand from the increasing global population and rapid industrial development, the consumption of energy is going to accelerate year by year. With the increasingly serious environmental contamination and global energy crisis, the development of clean and renewable energy has captivated interest among researchers and scientists to circumvent the worldwide challenges facing human beings at present. Among all forms of renewable energy, solar energy is an inexhaustible source of clean energy. The amount of solar energy reaching the earth is as high as 4 × 106 EJ per year, of which 5 × 104 EJ is deemed to be easily harvestable. Although people are gradually realizing the vast potential of solar energy, its current contribution to global energy is still below par. At present, how to efficiently harvest solar absorption as well as the development of flexible displays in solar technologies still markedly hinder practical industrialization and commercialization. As a result, novel fundamental understanding and practical techniques for solar technologies are of utmost significance to serve as a paradigm for solar technological readiness. This special issue of Solar RRL, “Nanomaterials for Light-Driven Reactions” encompasses 2 Progress Reports, 8 Reviews, 4 Communications, and 15 Full Papers by renowned research groups working at Nanyang Technological University, National Institute for Materials Science, Dalian Institute of Chemical Physics, Xiamen University Malaysia, Jawaharlal Nehru Centre for Advanced Scientific Research, Tianjin University, University of Bayreuth, Ulsan National Institute of Science and Technology, Université de Picardie Jules Verne, Ben Gurion University of the Negev, and so forth. The Special Issue highlights emerging works on the topics of various light-driven reactions using advanced nanomaterials (Figure 1). To date, substantial achievements have been devoted to the realm of light-driven reactions for attaining high-efficiency photocatalysis, photoelectrocatalysis, photovoltaics, solar cells, and bio-photoelectrochemical reactions, thus giving impetus to the breakthrough advancement in the field of solar technologies. In particular, a diverse range of advanced nanomaterials such as metal-free graphitic carbon nitride, metal, metal oxide, metal phosphide, metal dichalcogenide, metal nitride, perovskite, MXene, and metal-organic frameworks in a myriad of structures and morphologies such as nanosheets, nanowires, nanorods, nanocubes, and porous architectures have been discussed in these invited articles. Figure 1Open in figure viewerPowerPoint Summary of major research works presented in the special issue “Nanomaterials for Light-Driven Reactions” guest-edited by Prof. Wee-Jun Ong and Prof. Kazuhiko Maeda in Solar RRL. Shen et al. have provided a progress report on the synergy of low dimensionality and heterostructure design for graphitic carbon nitride (g-C3N4)-based heterostructures to modulate physicochemical properties (e.g. electronic band structure, increased visible light absorption, enhanced photoinduced charge carrier separation) and their application for water splitting, CO2 reduction, and pollutant degradation (1900435). Ong's group has recently reviewed the state-of-the-art development of 2D/2D heterostructured photocatalysts as an emerging platform for artificial photosynthesis by elucidating the interplay of 2D/2D heterojunction interfaces and the associated charge properties toward the photocatalytic enhancement in water splitting, CO2 reduction, and N2 fixation (2000132). Rao's group presented a variety of 2D catalysts, including transition metal dichalcogenides, carbon nitride, heterostructures, and covalently cross-linked 2D composites, for photocatalytic water splitting (2000050). Other than water splitting, Sun et al. systematically reviewed metal-free photocatalysts for CO2 reduction and discussed the theoretical calculations on possible reduction mechanisms and pathways as well as the in situ and operando techniques for mechanistic understanding (1900546). Zhang and co-workers provided an overview of oxygen vacancies in semiconductive metal oxides, including their emerging roles, fabrication techniques, characterizations, and photocatalytic applications (2000037). Additionally, Xu et al. focused on the effects of surface/interface engineering of carbon-based materials in versatile systems for enhanced applications in emerging solar energy conversion and storage (1900577). Moreover, Ye et al. reviewed the recent progress of high-stability metal–organic frameworks (MOFs) for photocatalytic solar fuel production (1900547). In another review, Zhang et al. summarized the recent advances of photoelectrodes based on pure organic materials, such as polythiophenes, graphitic carbon nitrides, conjugated acetylenic polymers, and N-containing fused-ring small molecules, for water splitting (1900395). Apart from pristine organic materials, Wang's group presented a review on metal oxide photoanodes for photoelectrochemical (PEC) water oxidation by describing effective enhancement strategies such as the construction of nanostructures, introduction of dopants, control of crystal facets, design of heterojunctions, modification of interfaces, and the integration of multiple strategies (1900509). The last review article of this special issue came from Wang's group at Soochow University, China, who highlighted the current endeavor to achieve low-temperature flexible perovskite solar cells (FPSCs). Particularly, the methods for ameliorating the stability and flexibility of FPSCs were presented by taking into account of the electrode materials, device encapsulation, and structural effects (1900556). Over the past few years, there have been a plethora of research works focusing on g-C3N4 for water splitting. Wang et al. have successfully doped phosphorus (P) into polymeric g-C3N4 (PCN) films through in situ polymerization process, which enhanced the ability of water oxidation owing to increased valence potential of P-doped PCN as compared to the undoped one (2000168). Other than water oxidation, Tang's group employed a series of visible-light-responsive Ce-UiOs developed through metal substitution and ligand modification for the application in aerobic oxidation of benzyl alcohol (1900449). In another similar application on the organic transformation, Sauvage et al. loaded gold nanoparticles on large bandgap semiconductor CeO2 under simulated sunlight irradiation for aerobic oxidation of free sugars. The enhancement stemmed from a thermal activation process induced by near-infra-red (NIR) light rather than the plasmonic contribution of Au nanoparticles (2000084). Feng et al. reported a high-performance PEC bioassay system based on the PEC and oxidase-catalytic coupled reactions at an air–liquid–solid triphase joint interface, which could be generalized to construct high-performance PEC bioassay systems for accurate analyte determination (1900185). As is widely known, water splitting for hydrogen (H2) and oxygen (O2) evolution has been extensively studied for the past decade. In particular, H2 is appealing to serve as a clean energy since it represents a chemical fuel with the highest energy density (140 MJ kg−1) on a gravimetric basis. Shalom's group utilized sulfur-based supramolecular assemblies composed of bismuthiol and melamine to synthesize ordered carbon nitride for excellent photocatalytic H2 evolution apart from the degradation of rhodamine B dye (2000017). Motivated by large interfacial contact area in ultrathin 2D/2D heterojunction interfaces, Xu et al. integrated 2D Ni(OH)2 as an operational cocatalyst with 2D g-C3N4 for photocatalytic H2 evolution without using Pt cocatalysts (1900538). In another similar work, Li et al. fabricated cocatalyst-free 2D/2D CdS/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts via in situ hydrothermal route, which manifested excellent H2 production with an apparent efficiency of 6.9% at 420 nm (1900423). Other than the development of binary photocatalysts, Li et al. have successfully constructed ternary nanostructure photocatalysts via a self-sacrificial strategy by forming a hierarchical architecture of In(OH)3 nanocubes decorated NiS-ZnIn2S4 (ZIS) hybrid nanosheets (ZIS/In(OH)3-NiS). Interestingly, the H2 generation rate was by far one of the highest among ZnIn2S4-based photocatalysts reported to date, which will provide a valuable reference to comprehend the structure-determining properties of nanohybrid architecture (2000027). Furthermore, Chen's group has electrodeposited Ni–M (M = Co, Fe, Mo) as a surface catalyst onto p-type silicon micropillar arrays for solar-driven hydrogen evolution. More importantly, the incorporation of high-valence Mo species as a key promoter for the in situ formation of active Ni2+ species on the surface of alloys was successfully evidenced, which was crucial to demystify the dynamic electronic and atomic structures of highly active surface catalysts (2000028). By means of first-principles density functional theory (DFT) simulations, Chen et al. have surveyed the solar catalytic activity toward hydrogen evolution reaction for all low-index surfaces of dissimilar nickel phosphides (Ni3P, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, and NiP3) (1900360). Very recently, there has been a driving force to investigate the O2 evolution from another half-reaction of water splitting. For example, Xu et al. demonstrated that 2D MXene (Ti3C2) with high electron conductivity functioned as a robust electron transfer and transport medium after being hybridized with Ag3PO4 for effective photocatalytic O2 generation (1900434). In another work, Zhang et al. adopted foreign Sc atoms with identical ionic radius to Ta atoms to modulate the structure and photocatalytic activity of Ta3N5. The synergy of Sc doping and CoOx cocatalysts on the promotion of charge separation and surface catalysis, respectively, facilitated the O2 generation in Ta3N5 (1900445). Besides that, Lee's group incorporated Ti4+ and Sn4+ into Fe3+ sites of ZnFe2O4 photoanodes as electron donors, in which the intentional external doping accelerated charge migration with boosted charge carrier density to enhance the bulk charge separation efficiency for photoelectrochemical water splitting (1900328). On top of that, Marschall's group has successfully developed phase-pure and highly crystalline CaFe2O4 with a sponge-like macroporous structure for improved H2 generation as well as overall water splitting upon the deposition of Rh/CrOx (1900570). Recently, g-C3N4 has been employed as robust photocatalysts for CO2 reduction. For instance, Yu's group presented a facile engineering of nanocage g-C3N4 using supramolecular complexes of melamine and cyanuric acid with strengthened hydrogen bonding, which were treated under freeze-drying, for boosted CO2 adsorption and reduction. This interesting work serves as a protocol for modulating the microstructure of g-C3N4 through tuning the weak intermolecular interaction (1900469). Not only that, Maeda's group has synthesized copolymerized carbon nitride nanosheets by heating a mixture of urea and 2-aminobenzonitrile for the visible-light CO2 reduction to formate with the aid of a ruthenium (II) complex catalyst (1900461). In another work, Liu et al. dispersed metallic molybdenum dioxide (MoO2) cocatalysts on g-C3N4 nanosheets to construct a Schottky junction photocatalyst, hence ameliorating the charge transfer and separation for the production of CO from the CO2 reduction (1900416). By mimicking the natural photosynthesis, Wong's group constructed ternary g-C3N4/ZnNCN@ZIF-8 hybrid photocatalysts with robust interfacial interactions via Zn-N bonding to enhance CO2 conversion efficiency, which stemmed from the synergistic contributions of g-C3N4/ZnNCN interfacial Z-scheme heterostructuring and surface-passivated ZIF-8 grafting (1900440). In addition to photocatalytic energy conversion in water splitting and CO2 reduction, Ho et al. exploited a g-C3N4/TiO2 composite hydrosol, in which the TiO2 hydrosol acted as a source of photocatalyst and dispersant for g-C3N4, for air-purifying pavement, thus offering a viable catalyst for environmental remediation (2000170). In short, the collection of invited papers highlights the latest advances in engineering nanomaterials for light-drive reactions based on numerous technological and scientific aspects. We are confident that the mesmerizing breadth of nanomaterials for light-driven reactions published in this Special Issue will inspire immense enthusiasm among researchers in solar energy across the globe. We anticipate that they will draw considerable attention to the field of solar technologies, hence populating concerted efforts toward high-efficiency, robust stability, cost-effective, and environmentally friendly solar technologies in years to come. Lastly, we sincerely thank the Editor-in-Chief of Solar RRL, Dr. Stefan Hildebrandt and the entire editorial team for providing us the opportunity to lead and publish this Special Issue to cast a new epoch for the exploration of solar technologies as an alternative to the conventional fossil fuels. We are grateful to all invited authors and reviewers for their contributions. This would not have been successful without the untiring support and dedication from everyone. Acknowledgements W.-J.O. acknowledges financial assistance and start-up grants from Xiamen University Malaysia. This work was supported by Xiamen University Malaysia Research Fund (XMUMRF/2019-C3/IENG/0013). Biographies Wee-Jun Ong received his B.Eng. and Ph.D. in chemical engineering from Monash University. He is an Associate Professor in School of Energy and Chemical Engineering at Xiamen University Malaysia. Previously, he was a staff scientist at Agency for Science, Technology and Research (A*STAR), Singapore. In 2019, he was a visiting scientist in Professor Xinliang Feng's group at Technische Universität Dresden, Germany. In 2019, he was a visiting professor at Lawrence Berkeley National Laboratory, USA. His research interests include the design of nanomaterials for photocatalytic, photoelectrocatalytic, and electrochemical H2O splitting, CO2 reduction, and N2 fixation. For more details, refer to https://sites.google.com/site/wjongresearch/. Kazuhiko Maeda received his Ph.D. degree from The University of Tokyo (2007) under the supervision of Professor Kazunari Domen. During 2008–2009, he was a postdoctoral researcher at Pennsylvania State University, where he worked with Professor Thomas E. Mallouk. In 2009, he joined The University of Tokyo as an Assistant Professor. Moving to the Tokyo Institute of Technology in 2012, he was promoted to an Associate Professor. His research interests include water splitting and CO2 reduction using photocatalysts and photoelectrodes. For more details, refer to http://www.chemistry.titech.ac.jp/~ishitani/member/kmaeda/Home.html. References 1 Statistical Review of World Energy, https://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy.html (accessed: July, 2020). Citing Literature Volume4, Issue8Special Issue: Nanomaterials for Light-Driven ReactionsAugust 20202000354 FiguresReferencesRelatedInformation