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

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminant. These compounds can have both chronic and acute harmful effects on natural flora and fauna. The presence of pharmaceutical contaminants in ground waters, surface waters (lakes, rivers, and streams), sea water, wastewater treatment plants (influents and effluents), soils, and sludges has been well doccumented. A range of methods including oxidation, photolysis, UV-degradation, nanofiltration, reverse osmosis, and adsorption has been used for their remediation from aqueous systems. Many methods have been commercially limited by toxic sludge generation, incomplete removal, high capital and operating costs, and the need for skilled operating and maintenance personnel. Adsorption technologies are a low-cost alternative, easily used in developing countries where there is a dearth of advanced technologies, skilled personnel, and available capital, and adsorption appears to be the most broadly feasible pharmaceutical removal method. Adsorption remediation methods are easily integrated with wastewater treatment plants (WWTPs). Herein, we have reviewed the literature (1990-2018) illustrating the rising environmental pharmaceutical contamination concerns as well as remediation efforts emphasizing adsorption.

Pharmaceuticals of Emerging Concern in Aquatic Systems: Chemistry, Occurrence, Effects, and Removal Methods.

Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves

Novel visible-light-driven carbon quantum dots (CQDs)/Bi2WO6 hybrid materials were synthesized via a facile hydrothermal method. Multiple techniques were applied to investigate the structures, morphologies, optical and electronic properties and photocatalytic performance of as-prepared samples. The nanostructured hybrid material was formed with CQDs attached on the surface of Bi2WO6 sphere-like structure. The photocatalytic activity of the CQDs/Bi2WO6 hybrid materials was evaluated sufficiently by using rhodamine B (RhB), colorless antibiotic agent ciprofloxacin (CIP), tetracycline hydrochloride (TC), and endocrine disrupting chemical bisphenol A (BPA), as target organic pollutants. The as-prepared CQDs/Bi2WO6 hybrid materials exhibited much higher photocatalytic activities than pure Bi2WO6, which showed a broad spectrum of photocatalytic degradation activity. The enhanced activities were attributed to the interfacial transfer of photogenerated electrons from Bi2WO6 to CQDs, leading to effective charge separation of Bi2WO6. The modification by using CQDs (electron acceptor) was an effective way to improve photocatalytic efficiency, which can be extended to a general strategy for other semiconductors. The ESR analysis and free radicals trapping experiments indicated that the O2 − and h+ were the main active species for the photocatalytic degradation. A possible mechanism of CQDs for the enhancement of visible light performance was proposed.

Novel visible-light-driven CQDs/Bi2WO6 hybrid materials with enhanced photocatalytic activity toward organic pollutants degradation and mechanism insight

The novel two-dimensional (2D) porous ultrathin oxygen-doped g-C3N4 nanosheets (PUOCNs) were prepared. The comprehensive characterization methods were used to study morphology, microstructure, crystal structure, chemical states and photocatalytic performance of PUOCNs. 2D porous ultrathin structure and the introduction of oxygen are beneficial to the enhancement of the photocatalytic activity of PUOCNs. The average H2 evolution rate of PUOCNs is ∼189.3 μmol h−1, which is ∼5.2 times higher than that of the bulk g-C3N4 and the degradation efficiency of organic dye methyl orange (MO) is almost 71 times higher than that of the bulk g-C3N4. The enhanced photocatalytic activity is due to the more adsorption sites and more active sites, the enhanced redox ability and improved electron transport ability, which leads to less recombination and a more efficient separation of photogenerated electron and hole pairs. Through XPS VB and ESR analysis, the photocatalytic mechanism was also researched in detail.

Template-free synthesis of 2D porous ultrathin nonmetal-doped g-C3N4 nanosheets with highly efficient photocatalytic H2 evolution from water under visible light

Hydroxyl-graphene quantum dots (GQDs) modified mesoporous graphitic carbon nitride (mpg-C 3 N 4 ) composites were fabricated through electrostatic interactions. A variety of techniques were applied to discuss systematic effect on the morphology, optical, electronic properties and structure of GQDs/mpg-C 3 N 4 composites. Remarkably, the 0.5 wt% GQDs/mpg-C 3 N 4 composites exhibited higher photocatalytic activity than that of the pure mpg-C 3 N 4 by using rhodamine B (RhB) and colorless tetracycline hydrochloride (TC) as pollutants under visible light irradiation. The results indicated that uniform dispersion of GQDs on the surface of mpg-C 3 N 4 and intimate contact between the two materials contributed to the enhanced activity. Radical trapping experiments and electron spin resonance tests both certified that the GQDs/mpg-C 3 N 4 composites can generate more O 2 − species and a small fraction of holes for photocatalytic degradation.

Haiyan Ji

Papers

Novel visible-light-driven CQDs/Bi2WO6 hybrid materials with enhanced photocatalytic activity toward organic pollutants degradation and mechanism insight

Template-free synthesis of 2D porous ultrathin nonmetal-doped g-C3N4 nanosheets with highly efficient photocatalytic H2 evolution from water under visible light

Graphene quantum dots modified mesoporous graphite carbon nitride with significant enhancement of photocatalytic activity

Application of graphene-like layered molybdenum disulfide and its excellent adsorption behavior for doxycycline antibiotic

Synthesis of g-C3N4/Ag3VO4 composites with enhanced photocatalytic activity under visible light irradiation