As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor–semiconductor heterojunction, the semiconductor–metal heterojunction, the semiconductor–carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degradation of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.

Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances

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.

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

Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

Solar-driven water splitting provides a leading approach to store the abundant yet intermittent solar energy and produce hydrogen as a clean and sustainable energy carrier. A straightforward route to light-driven water splitting is to apply self-supported particulate photocatalysts, which is expected to allow solar hydrogen to be competitive with fossil-fuel-derived hydrogen on a levelized cost basis. More importantly, the powder-based systems can lend themselves to making functional panels on a large scale while retaining the intrinsic activity of the photocatalyst. However, all attempts to generate hydrogen via powder-based solar water-splitting systems to date have unfortunately fallen short of the efficiency values required for practical applications. Photocatalysis on photocatalyst particles involves three sequential steps: (i) absorption of photons with higher energies than the bandgap of the photocatalysts, leading to the excitation of electron-hole pairs in the particles, (ii) charge separation and migration of these photoexcited carriers, and (iii) surface chemical reactions based on these carriers. In this review, we focus on the challenges of each step and summarize material design strategies to overcome the obstacles and limitations. This review illustrates that it is possible to employ the fundamental principles underlying photosynthesis and the tools of chemical and materials science to design and prepare photocatalysts for overall water splitting.

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Rationally designed Ta3N5/BiOCl S-scheme heterojunction with oxygen vacancies for elimination of tetracycline antibiotic and Cr(VI): Performance, toxicity evaluation and mechanism insight

Developing efficient and easily recyclable photocatalysts has drawn much attention. Herein, we report the design and synthesis of Ta3N5/Bi2MoO6 core–shell fiber-shaped heterojunctions as a kind of efficient and easily recyclable photocatalyst. Ta3N5 nanofibers have been prepared by an electrospinning–calcination–nitridation method, and then in situ growth of Bi2MoO6 on their surfaces is realized by a solvothermal method. The resulting Ta3N5/Bi2MoO6 heterojunctions are composed of porous Ta3N5 nanofibers (diameter: ∼200 nm) whose surfaces are decorated with Bi2MoO6 nanosheets (length: 100–200 nm; thickness: ∼15 nm). They exhibit remarkably enhanced photocatalytic activities for the degradation of rhodamine B (RhB) and para-chlorophenol (4-CP) under visible light, compared with pure Bi2MoO6 or Ta3N5. In particular, the heterojunction with a Ta3N5/Bi2MoO6 molar ratio of 1/1 achieves the highest photodegradation efficiency of RhB (99.5%), which is about 1.85 times that (53.7%) of Bi2MoO6 and 1.66 times that (60.1%) of the mechanical mixture (49.8 wt% Bi2MoO6 + 50.2 wt% Ta3N5). The superior photocatalytic properties can be attributed to the efficient separation of photo-induced electron–hole pairs and the high BET surface area. The dominant active species are determined to be superoxide and the photogenerated holes. More importantly, the Ta3N5/Bi2MoO6 heterojunction can be easily recycled by simple sedimentation while maintaining good stability. This work offers more valuable insights into the design of efficient and easily recyclable photocatalysts for environmental remediation.

Synthesis of Ta3N5/Bi2MoO6 core–shell fiber-shaped heterojunctions as efficient and easily recyclable photocatalysts

Constructing novel semiconductor heterojunctions is one of the most significant approaches to improving the photocatalytic performance of a photocatalyst. Herein, the Ag3VO4/Bi2WO6 heterojunction was prepared through in-situ anchoring Ag3VO4 nanoparticles (size: ∼21 nm) on the surface of Bi2WO6 microflowers (diameter: 2.5–4.5 μm) by a facile deposition route. The photocatalytic activity of these heterojunctions were studied by decomposing cationic dye rhodamine B (RhB), anionic dye methyl orange (MO) and neutral para-chlorophenol (4-CP) under visible light irradiation (λ > 400 nm). Among all the tested catalysts, the heterojunction with a Ag3VO4/Bi2WO6 molar ratio of 0.15/1 displays the maximum activity with the RhB degradation rate constant of up to 0.0392 min−1, a 6.7 or 1.7 times more enhancement compared with the pure Bi2WO6 or Ag3VO4. It is found that the introduction of Ag3VO4 is in favor of suppressing the electron-hole pair recombination of Bi2WO6, leading to an enhanced photocatalytic activity with good stability. The photogenerated holes (h+) and superoxide radicals ( O 2 - ) play critical roles during the photocatalytic process. Ag3VO4/Bi2WO6 will have great potential in applications for environmental remediation due to the facile preparation method and superior photocatalytic activity.

Facile synthesis of flower-like Ag3VO4/Bi2WO6 heterojunction with enhanced visible-light photocatalytic activity

Designing oxygen vacancy mediated bismuth molybdate (Bi2MoO6)/N-rich carbon nitride (C3N5) S-scheme heterojunctions for boosted photocatalytic removal of tetracycline antibiotic and Cr(VI): Intermediate toxicity and mechanism insight.

Shijie Li

Papers

Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances

Rationally designed Ta3N5/BiOCl S-scheme heterojunction with oxygen vacancies for elimination of tetracycline antibiotic and Cr(VI): Performance, toxicity evaluation and mechanism insight

Synthesis of Ta3N5/Bi2MoO6 core–shell fiber-shaped heterojunctions as efficient and easily recyclable photocatalysts

Facile synthesis of flower-like Ag3VO4/Bi2WO6 heterojunction with enhanced visible-light photocatalytic activity

Designing oxygen vacancy mediated bismuth molybdate (Bi2MoO6)/N-rich carbon nitride (C3N5) S-scheme heterojunctions for boosted photocatalytic removal of tetracycline antibiotic and Cr(VI): Intermediate toxicity and mechanism insight.