Nitrogen doping has been an effective way to tailor the properties of graphene and render its potential use for various applications. Three common bonding configurations are normally obtained when doping nitrogen into the graphene: pyridinic N, pyrrolic N, and graphitic N. This paper reviews nitrogen-doped graphene, including various synthesis methods to introduce N doping and various characterization techniques for the examination of various N bonding configurations. Potential applications of N-graphene are also reviewed on the basis of experimental and theoretical studies.

https://s3-eu-west-1.amazonaws.com/pfigshare-u-files/1431849/NitrogenReviewonRecentProgressinNitrogenDopedGrapheneSynthesisCharacterizationandItsPotentialApplications.pdf

Review on Recent Progress in Nitrogen-Doped Graphene: Synthesis, Characterization, and Its Potential Applications

Graphene, a single layer of graphite, possesses a unique two-dimensional structure, high conductivity, superior electron mobility and extremely high specific surface area, and can be produced on a large scale at low cost. Thus, it has been regarded as an important component for making various functional composite materials. Especially, graphene-based semiconductor photocatalysts have attracted extensive attention because of their usefulness in environmental and energy applications. This critical review summarizes the recent progress in the design and fabrication of graphene-based semiconductor photocatalysts via various strategies including in situ growth, solution mixing, hydrothermal and/or solvothermal methods. Furthermore, the photocatalytic properties of the resulting graphene-based composite systems are also discussed in relation to the environmental and energy applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation and photocatalytic disinfection. This critical review ends with a summary and some perspectives on the challenges and new directions in this emerging area of research (158 references).

Graphene-based semiconductor photocatalysts

Photocatalytic water splitting represents a promising strategy for clean, low-cost, and environmental-friendly production of H2 by utilizing solar energy. There are three crucial steps for the photocatalytic water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic H2 and O2 evolution reactions. While significant achievement has been made in optimizing the first two steps in the photocatalytic process, much less efforts have been put into improving the efficiency of the third step, which demands the utilization of cocatalysts. To date, cocatalysts based on rare and expensive noble metals are still required for achieving reasonable activity in most semiconductor-based photocatalytic systems, which seriously restricts their large-scale application. Therefore, seeking cheap, earth-abundant and high-performance cocatalysts is indispensable to achieve cost-effective and highly efficient photocatalytic water splitting. This review for the first time summarizes all the developed earth-abundant cocatalysts for photocatalytic H2- and O2-production half reactions as well as overall water splitting. The roles and functional mechanism of the cocatalysts are discussed in detail. Finally, this review is concluded with a summary, and remarks on some challenges and perspectives in this emerging area of research.

Earth-abundant cocatalysts for semiconductor-based photocatalytic water splitting

Solar driven catalysis on semiconductors to produce clean chemical fuels, such as hydrogen, is widely considered as a promising route to mitigate environmental issues caused by the combustion of fossil fuels and to meet increasing worldwide demands for energy. The major limiting factors affecting the efficiency of solar fuel synthesis include; (i) light absorption, (ii) charge separation and transport and (iii) surface chemical reaction; therefore substantial efforts have been put into solving these problems. In particular, the loading of co-catalysts or secondary semiconductors that can act as either electron or hole acceptors for improved charge separation is a promising strategy, leading to the adaptation of a junction architecture. Research related to semiconductor junction photocatalysts has developed very rapidly and there are a few comprehensive reviews in which the strategy is discussed (A. Kudo and Y. Miseki, Chemical Society Reviews, 2009, 38, 253–278, K. Li, D. Martin, and J. Tang, Chinese Journal of Catalysis, 2011, 32, 879–890, R. Marschall, Advanced Functional Materials, 2014, 24, 2421–2440). This critical review seeks to give an overview of the concept of heterojunction construction and more importantly, the current state-of-the art for the efficient, visible-light driven junction water splitting photo(electro)catalysts reported over the past ten years. For water splitting, these include BiVO4, Fe2O3, Cu2O and C3N4, which have attracted increasing attention. Experimental observations of the proposed charge transfer mechanism across the semiconductor/semiconductor/metal junctions and the resultant activity enhancement are discussed. In parallel, recent successes in the theoretical modelling of semiconductor electronic structures at interfaces and how these explain the functionality of the junction structures is highlighted.

/pdf/visible-light-driven-heterojunction-photocatalysts-for-water-33q4busijg.pdf

Visible-light driven heterojunction photocatalysts for water splitting – a critical review

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Engineering heterogeneous semiconductors for solar water splitting

A series of N-doped graphene (N-graphene)/CdS nanocomposites were synthesized by calcination and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, N2 adsorption analysis, ultraviolet–visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of as-prepared N-graphene/CdS for hydrogen production from water under visible light irradiation at λ ≥ 420 nm was investigated. The results show that N-graphene/CdS nanocomposites have a higher photocatalytic activity than pure CdS. Transient photocurrents measured with a photoelectrochemical test device show that the photocurrent of the N-graphene/CdS sample is much increased as compared to the sole CdS. This enhanced photoresponse indicates that the photoinduced electrons in the CdS prefer separately transferring to the N-doped graphene. As a consequence, the radiative recombination of the electron–hole pairs is hampered and the...

http://www.dstuns.iitm.ac.in/grouppresentations/2011/Highly%20Durable.pdf

Highly Durable N-Doped Graphene/CdS Nanocomposites with Enhanced Photocatalytic Hydrogen Evolution from Water under Visible Light Irradiation

Photocatalytic degradation of persistent organic pollutants by Co-Cl bond reinforced CoAl-LDH/Bi12O17Cl2 photocatalyst: mechanism and application prospect evaluation.

Hydrogen is widely believed to be a promising fuel to solve the global energy crisis and environmental issues. The catalytic system represented by metal‐supported catalysts is an important process of upgrading the hydrogen source in industry. Single‐atom catalysts (SACs), which inherit the advantages of homogeneous and heterogeneous catalysts, provide a broad prospect for low‐cost H2 production technology. This review focuses on the potential mechanisms in the rational design of SACs, including active sites, coordination configuration, mass loading, heteroatom‐doping, and metal−support interaction. The design strategies of single metal atoms on different supports are reviewed to give a proposal on how to immobilize the atomic active sites and modulate the geometric/electronic structures of SACs. Subsequently, the synergistic effect in SACs and the dynamic evolution of the atomically dispersed heterometal catalysts are introduced, aiming to provide further guidelines for H2 evolution SACs. H2 generation from the water−gas shift reaction and electro‐/photocatalytic water splitting are the main research directions at present. The latest progress of SACs employed in these applications is thoroughly reviewed. At the end of this review, personal perspectives on the prospects and challenges of H2 evolution SACs are put forward, hoping to promote the rapid development of SACs toward superior H2 evolution performance.

Han-Qin Yu

Papers

Highly Durable N-Doped Graphene/CdS Nanocomposites with Enhanced Photocatalytic Hydrogen Evolution from Water under Visible Light Irradiation

Photocatalytic degradation of persistent organic pollutants by Co-Cl bond reinforced CoAl-LDH/Bi12O17Cl2 photocatalyst: mechanism and application prospect evaluation.

Single‐Atom Catalysts for Hydrogen Generation: Rational Design, Recent Advances, and Perspectives

Highly efficient removal of oxytetracycline using activated magnetic MIL-101(Fe)/γ-Fe2O3 heterojunction catalyst.

Construction of PDIsa/BiOBr type-I scheme heterojunction for efficient ciprofloxacin photocatalytic degradation