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?

The use of solar energy to produce molecular hydrogen and oxygen (H2 and O2) from overall water splitting is a promising means of renewable energy storage. In the past 40 years, various inorganic and organic systems have been developed as photocatalysts for water splitting driven by visible light. These photocatalysts, however, still suffer from low quantum efficiency and/or poor stability. We report the design and fabrication of a metal-free carbon nanodot-carbon nitride (C3N4) nanocomposite and demonstrate its impressive performance for photocatalytic solar water splitting. We measured quantum efficiencies of 16% for wavelength λ = 420 ± 20 nanometers, 6.29% for λ = 580 ± 15 nanometers, and 4.42% for λ = 600 ± 10 nanometers, and determined an overall solar energy conversion efficiency of 2.0%. The catalyst comprises low-cost, Earth-abundant, environmentally friendly materials and shows excellent stability.

http://science.sciencemag.org/content/sci/347/6225/970.full.pdf

Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway

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

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

Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70 : 30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.

Graphitic carbon nitride (g-C3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation

A series of ZnIn2S4 floriated microspheres consisting of flakes were synthesized by a facile template-free hydrothermal method. The obtained ZnIn2S4 products were characterized by X-ray diffraction...

Template-Free Hydrothermal Synthesis of ZnIn2S4 Floriated Microsphere as an Efficient Photocatalyst for H2 Production under Visible-Light Irradiation

AgIn5S8/TiO2 nanocomposite is prepared through a one-pot hydrothermal method, which is used for photocatalytic H2 production under visible-light irradiation. The effects of AgIn5S8/TiO2 molar ratio in the nanocomposites on the crystal phase, microstructure, optical absorption properties, and photocatalytic H2 evolution activity are investigated comparatively. The pristine AgIn5S8 shows a sharp absorption edge at ∼705 nm, corresponding to a bandgap of ∼1.76 eV, and its visible-light-driven photoactivity for H2 production can be remarkably enhanced by coupling with TiO2. The AgIn5S8/TiO2 nanocomposite with molar ratio of 1:10 has the maximum photoactivity for H2 production, improved by 7.7 times as compared with the pristine AgIn5S8. The enhanced photoactivity can be ascribed to some AgIn5S8 nanoparticles closely contacting the TiO2 nanoparticles to form heterojunction structure. This configuration of the composite photocatalyst results in an efficient charge separation at the interface, followed by fast di...

Preparation of AgIn5S8/TiO2 Heterojunction Nanocomposite and Its Enhanced Photocatalytic H2 Production Property under Visible Light

Multiwalled carbon nanotubes (MWCNTs) and ZnIn2S4 composites were prepared by a facile hydrothermal method, which was used for hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained MWCNTs/ZnIn2S4 composites were characterized by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry analyses (TG-DSC), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), Fourier transform IR spectroscopy (FTIR) and Photoluminescence spectra (PL). It was found that the MWCNTs were embedded into the interior of floriated ZnIn2S4 microspheres. The effects of the composite ratio in the MWCNTs/ZnIn2S4 on the photocatalytic activity for hydrogen production were investigated. The results show that the 3 wt% MWCNTs/ZnIn2S4 composite reaches its maximum photocatalytic hydrogen production efficiency with an apparent quantum efficiency as high as 23.3% under 420 nm light irradiation. The significantly enhanced photoactivity for the present composite originates from the synergetic effect of its component intrinsic properties. A possible mechanism of the MWCNTs/ZnIn2S4 composite as a photocatalyst for H2 evolution was proposed.

Preparation of a MWCNTs/ZnIn2S4 composite and its enhanced photocatalytic hydrogen production under visible-light irradiation

The In2S3/(Pt-TiO2) nanocomposite photocatalyst consisting of floriated In2S3 decorated with TiO2 nanoparticles was synthesized by a multi-step method, which was used for the hydrogen production under visible-light (λ ≥ 420 nm) irradiation. The obtained In2S3/(Pt-TiO2) nanocomposite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectra (DRS), and photoluminescence spectra (PL). It is found that the Pt-TiO2nanoparticles embedded in the interstices of the floriated In2S3 formed intimate contacts between the In2S3 and Pt-TiO2, which is a benefit to significantly enhance the charge separation and then the photocatalytic activity. The effects of the mass ratio in the In2S3/(Pt-TiO2) nanocomposites and Pt-loaded amount on the photoactivity for the hydrogen production were investigated comparatively. The results show that the In2S3/(Pt-TiO2) nanocomposite with a mass ratio of 3 : 2 has the maximum photocatalytic hydrogen production rate of 135 μmol h−1 under visible-light irradiation, and the possible mechanism of the obtained In2S3/(Pt-TiO2) nanocomposite as a photocatalyst for hydrogen production was proposed.

Bo Chai

Papers

Graphitic carbon nitride (g-C3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation

Template-Free Hydrothermal Synthesis of ZnIn2S4 Floriated Microsphere as an Efficient Photocatalyst for H2 Production under Visible-Light Irradiation

Preparation of AgIn5S8/TiO2 Heterojunction Nanocomposite and Its Enhanced Photocatalytic H2 Production Property under Visible Light

Preparation of a MWCNTs/ZnIn2S4 composite and its enhanced photocatalytic hydrogen production under visible-light irradiation

Synthesis of floriated In2S3 decorated with TiO2 nanoparticles for efficient photocatalytic hydrogen production under visible light