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-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.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

A review on g-C3N4-based photocatalysts

Photocatalysis is considered as one of the promising routes to solve the energy and environmental crises by utilizing solar energy. Graphitic carbon nitride (g-C3N4) has attracted worldwide attention due to its visible-light activity, facile synthesis from low-cost materials, chemical stability, and unique layered structure. However, the pure g-C3N4 photocatalyst still suffers from its low separation efficiency of photogenerated charge carriers, which results in unsatisfactory photocatalytic activity. Recently, g-C3N4-based heterostructures have become research hotspots for their greatly enhanced charge carrier separation efficiency and photocatalytic performance. According to the different transfer mechanisms of photogenerated charge carriers between g-C3N4 and the coupled components, the g-C3N4-based heterostructured photocatalysts can be divided into the following categories: g-C3N4-based conventional type II heterojunction, g-C3N4-based Z-scheme heterojunction, g-C3N4-based p–n heterojunction, g-C3N4/metal heterostructure, and g-C3N4/carbon heterostructure. This review summarizes the recent significant progress on the design of g-C3N4-based heterostructured photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers. Moreover, their applications in environmental and energy fields, e.g., water splitting, carbon dioxide reduction, and degradation of pollutants, are also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced g-C3N4-based heterostructured photocatalysts are presented.

g-C3N4-Based Heterostructured Photocatalysts

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

In this work, n-type porous graphite-like C3N4 (denoted as p-g-C3N4) was fabricated and modified with p-type nanostructured BiOI to form a novel BiOI/p-g-C3N4 p–n heterojunction photocatalyst for the efficient photocatalytic degradation of methylene blue (MB). The results show that the BiOI/p-g-C3N4 heterojunction photocatalyst exhibits superior photocatalytic activity compared to pure BiOI and p-g-C3N4. The visible-light photocatalytic activity enhancement of BiOI/p-g-C3N4 heterostructures could be attributed to its strong absorption in the visible region and low recombination rate of the electron–hole pairs because of the heterojunction formed between BiOI and p-g-C3N4. It was also found that the photodegradation of MB molecules is mainly attributed to the oxidation action of the generated O2˙− radicals and partly to the action of hvb+via direct hole oxidation process.

Novel p–n heterojunction photocatalyst constructed by porous graphite-like C3N4 and nanostructured BiOI: facile synthesis and enhanced photocatalytic activity

Enhanced Photocatalytic Activity over Flower-like Sphere Ag/Ag2CO3/BiVO4 Plasmonic Heterojunction Photocatalyst for Tetracycline Degradation

Graphitic carbon nitride (g-C3N4) was hybridized by hierarchical yolk–shell TiO2 spheres via a solvothermal method by mixing the as-prepared g-C3N4 with the precursor of the TiO2 yolk–shell spheres in dimethylformamide (DMF). The introduction of DMF made the TiO2 yolk–shell spheres to be dispersed well on the surface of g-C3N4, thus improving the specific surface area of the materials. The g-C3N4 has a unique two-dimensional layered structure, which is favorable for hybridizing with TiO2. The sufficient contact interface between TiO2 and g-C3N4 could be beneficial to the separation of photogenerated charges. Multiple reflections of light within the interior cavities of titania microspheres with a yolk–shell structure can increase their light absorption. The photocatalytic experimental results indicated that the as-prepared composite TiO2/g-C3N4 (TCN) showed enhanced photocatalytic activities compared with pure TiO2 and g-C3N4. A suitable combination of g-C3N4 with TiO2 produced the highest photocatalytic activity. Moreover, the photocatalytic activity of TCN with a yolk–shell structure is higher than that of TiO2/g-C3N4 without a yolk–shell structure. Based on our experimental results, a possible photocatalytic mechanism with holes and superoxide radical species as the main active species in photocatalysis was proposed. The TCN photocatalysts prepared in this case, with high photocatalytic activity and high stability, were a promising candidate for possible practical application in industrial production.

Constructing graphite-like carbon nitride modified hierarchical yolk–shell TiO2 spheres for water pollution treatment and hydrogen production

Without Pt as cocatalyst, the photocatalytic hydrogen evolution activity of graphitic carbon nitride (g-C3N4) or even its composite is normally rather low (<1 μmol h−1). Exploring Pt-free cocatalysts to substitute precious Pt is of great importance in the photocatalytic field. In the present work, Ag2S-modified g-C3N4 (Ag2S/g-C3N4) composite photocatalysts were prepared via a simple precipitation method. The results demonstrated that the photocatalytic H2-production activity of g-C3N4 can be remarkably increased by the combination of Ag2S. The optimal Ag2S loading was found to be 5 wt%, giving a H2 production of 10 μmol h−1, around 100 times that of pure g-C3N4. The enhanced photocatalytic activity can be mainly attributed to the effective charge transfer between g-C3N4 and Ag/Ag2S, of which the latter is formed by simultaneous photodeposition in the photocatalytic H2 evolution reaction and acts as an efficient co-catalyst for the g-C3N4. This work showed the possibility for utilization of Ag2S or Ag/Ag2S as a substitute for Pt in the photocatalytic production of H2 using g-C3N4.

Ag2S/g-C3N4 composite photocatalysts for efficient Pt-free hydrogen production. The co-catalyst function of Ag/Ag2S formed by simultaneous photodeposition

Novel TiO2–In2O3@g–C3N4 hybrid system was synthesized by a facile solvothermal method. The photocatalytic activity of the TiO2–In2O3@g–C3N4 hybrid material was evaluated via degradation of RhB and hydrogen-production. It could be found that TiO2–In2O3@g–C3N4 ternary composites exhibit the highest RhB degradation rate, which was 6.6 times than that of pure g–C3N4. As expected, the H2-generation rate of the as-prepared ternary materials was found to increase by 48 times than that of pure g–C3N4. The enhanced activities were mainly attributed to the interfacial transfer of photogenerated electrons and holes among TiO2, In2O3 and g–C3N4, leading to the effective charge separation on these semiconductors, which were evidenced by photoluminescence spectroscopy, electrochemical impedance spectroscopy and photocurrent analysis. The photocatalytic mechanism and photostability of the ternary hybrid materials were also proposed. This work may provide a stepping stone towards the design and practical application of multifunctional hybrids photocatalysts in the photocatalytic degradation of pollutions and hydrogen generation.

A new visible light active multifunctional ternary composite based on TiO2–In2O3 nanocrystals heterojunction decorated porous graphitic carbon nitride for photocatalytic treatment of hazardous pollutant and H2 evolution

Jimin Xie

Papers

Novel p–n heterojunction photocatalyst constructed by porous graphite-like C3N4 and nanostructured BiOI: facile synthesis and enhanced photocatalytic activity

Enhanced Photocatalytic Activity over Flower-like Sphere Ag/Ag2CO3/BiVO4 Plasmonic Heterojunction Photocatalyst for Tetracycline Degradation

Constructing graphite-like carbon nitride modified hierarchical yolk–shell TiO2 spheres for water pollution treatment and hydrogen production

Ag2S/g-C3N4 composite photocatalysts for efficient Pt-free hydrogen production. The co-catalyst function of Ag/Ag2S formed by simultaneous photodeposition

A new visible light active multifunctional ternary composite based on TiO2–In2O3 nanocrystals heterojunction decorated porous graphitic carbon nitride for photocatalytic treatment of hazardous pollutant and H2 evolution