Efficient photocatalytic hydrogen evolution on N-deficient g-C3N4 achieved by a molten salt post-treatment approach
TL;DR: In this article, a molten salt post-treatment approach has been developed to reconstruct pristine graphitic carbon nitride (g-C3N4), in which molten salts serve as a generalist for accelerating the polycondensation and deamination reaction.
Abstract: Graphitic carbon nitride (g-C3N4) is a fascinating metal-free photocatalyst for active solar hydrogen production. However, the photocatalytic activity of pristine g-C3N4 is dramatically restricted by the inherent shortcomings of fast charge recombination because of incomplete polymerization. Thus, increasing the extent of polymerization can be one of an efficient way to enhance its photocatalytic activity. Herein, a molten salt post-treatment approach has been developed to reconstruct pristine g-C3N4, in which molten salts serve as a generalist for accelerating the polycondensation and deamination reaction. This approach endows g-C3Nx with enriched nitrogen defects, and unique electronic structure, which results in narrower bandgap and higher electrical conductivity, significantly improve visible light harvesting capability and separation efficiency of charge carriers. As a consequence, the g-C3Nx shows 2.2 times higher the H2 evolution rate than bulk g-C3N4. This discovery may open a novel avenue to fabricate highly efficient g-C3N4 catalysts.
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TL;DR: In this paper, a comprehensive study on vacancy defect engineered graphite-like carbon nitride (g-C3N4; abbreviated as GCN) photocatalysts is presented.
Abstract: As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C3N4; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured from its fascinating physicochemical and photoelectronic structural features. However, certain inherent drawbacks, involving rapid reassembly of photocarriers, low specific surface area and insufficient optical absorption, limit the wide-range applicability of GCN. Generation of 0D point defects mainly by introducing vacancies (C and/or N) into the framework of GCN has spurred extensive consideration owing to their distinctive qualities to manoeuvre substantially, the optical absorption, radiative carrier isolation, and surface photoreactions. The present review endeavours to summarise a comprehensive study on vacancy defect engineered GCN. Starting from the basic introduction of defects and C/N vacancy modulated GCN, numerous advanced strategies for the controlled designing of vacancy rich GCN have been explored and discussed. Afterwards, light was thrown on the various substantial technologies which are useful for characterising and identifying the introduction of defects in GCN. The salient significance of defect engineering in GCN has been reviewed concerning its impact on optical absorption, charge isolation and surface photoreaction ability. Typically, the achievement of defect engineered GCN has been scrutinised toward various applications like photocatalytic water splitting, CO2 conversion, N2 fixation, pollutant degradation, and H2O2 production. Finally, the review ends with conclusions and vouchsafing future challenges and opportunities on the intriguing and emerging area of vacancy defect engineered GCN photocatalysts.
294 citations
TL;DR: In this paper, the degradation of tetracycline (TC) under visible-light irradiation in the presence of persulfate (PS) activation was investigated by a simple one-step thermal polymerization of urea and oxamide.
236 citations
TL;DR: The graphitic carbon nitride (g-C3N4) has an attractive band structure, good chemical stability, earth-abundant and significantly easily fabricated which makes an application for the generation of hydrogen by water splitting as discussed by the authors.
Abstract: The future energy crisis and environmental degradation can only mitigate by harvesting solar energy into renewable, safe, economical and clean technology like water splitting. The graphitic carbon nitride has an attractive band structure, good chemical stability, earth-abundant and significantly easily fabricated which makes an application for the generation of hydrogen by water splitting. In this paper, we try to critically focus on the current progress and future development of the different strategies of water splitting using graphitic carbon nitride (g-C3N4) for hydrogen generation. In this context, we discuss recent strategies like metal and non-metal doping (electronic structure), morphology tuning (geometric structuring), use of mediators (Z-scheme technology), defects engineering, plasmonic materials, dye-sensitization, perovskite oxides, carbon nitrides, carbon dots, metal organic framework, and a bimetallic cocatalyst. Finally, we summarize the recent advances and future developments of g-C3N4 bases photocatalysis.
217 citations
TL;DR: In this article, graphitic carbon nitride (g-C3 N4 ) with an atomically thin sheet-like structure is applied for prominent piezocatalytic and photo-enhanced piezoelectric H2 production.
Abstract: Utilizing mechanical energy to produce hydrogen is emerging as a promising way to generate renewable energy, but is challenged by low efficiency and scanty cognition. In this work, graphitic carbon nitride (g-C3 N4 ) with an atomically thin sheet-like structure is applied for prominent piezocatalytic and photo-enhanced piezocatalytic H2 production. It is revealed that the anomalous piezoelectricity in g-C3 N4 originates from the strong in-plane polarization along the a-axis, contributed by the superimposed polar tri-s-triazine units and flexoelectric effect derived from the structured triangular cavities, which provides powerful electrochemical driving force for the water reduction reaction. Furthermore, the photo-enhanced charge transfer enables g-C3 N4 nanosheets to reserve more energized polarization charges to fully participate in the reaction at the surface reactive sites enriched by strain-induced carbon vacancies. Without any cocatalysts, an exceptional photo-piezocatalytic H2 evolution rate of 12.16 mmol g-1 h-1 is delivered by the g-C3 N4 nanosheets, far exceeding that of previously reported piezocatalysts and g-C3 N4 photocatalysts. Further, high pure-water-splitting performance with production of the value-added oxidation product H2 O2 via photo-piezocatalysis is also disclosed. This work not only exposes the potential of g-C3 N4 as a piezo-semiconductor for catalytic H2 evolution, but also breaks a new ground for the conversion of solar and mechanical energy by photomediated piezocatalytic reaction.
213 citations
TL;DR: In this article, the recent progress of photocatalysis in antibiotic wastewater was summarized, including antibiotics degradation and hydrogen energy conversion, and the photocatalysts commonly used were also discussed.
198 citations
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TL;DR: Graphitic carbon nitride nanosheets are extracted via simple liquid-phase exfoliation of a layered bulk material, g-C3N4, to exhibit excellent photocatalytic activity for hydrogen evolution under visible light.
Abstract: Graphitic carbon nitride nanosheets are extracted, produced via simple liquid-phase exfoliation of a layered bulk material, g-C3N4. The resulting nanosheets, having ≈2 nm thickness and N/C atomic ratio of 1.31, show an optical bandgap of 2.65 eV. The carbon nitride nanosheets are demonstrated to exhibit excellent photocatalytic activity for hydrogen evolution under visible light.
2,137 citations
TL;DR: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea, with superior visible-light photocatalytic performance compared to pristine g-C2 N4.
Abstract: A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .
1,535 citations
TL;DR: An effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported, and it was found that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.
Abstract: The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported. The g-C3N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.
978 citations
TL;DR: This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.
Abstract: Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO2 is considered as a potential route for solving ever-increasing energy crisis and greenhouse effect. Herein, hierarchical porous O-doped graphitic carbon nitride (g-C3 N4 ) nanotubes (OCN-Tube) are prepared via successive thermal oxidation exfoliation and curling-condensation of bulk g-C3 N4 . The as-prepared OCN-Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20-30 nm. The hierarchical OCN-Tube shows excellent photocatalytic CO2 reduction performance under visible light, with methanol evolution rate of 0.88 µmol g-1 h-1 , which is five times higher than bulk g-C3 N4 (0.17 µmol g-1 h-1 ). The enhanced photocatalytic activity of OCN-Tube is ascribed to the hierarchical nanotube structure and O-doping effect. The hierarchical nanotube structure endows OCN-Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O-doping optimizes the band structure of g-C3 N4 , resulting in narrower bandgap, greater CO2 affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.
972 citations
TL;DR: Owing to the interfacial interaction between BP and CN, efficient charge transfer occurred, thereby enhancing the photocatalytic performance, and the present results show that BP/CN is a metal-free photocatalyst for artificial photosynthesis and renewable energy conversion.
Abstract: In the drive toward green and sustainable chemistry, exploring efficient and stable metal-free photocatalysts with broadband solar absorption from the UV to near-infrared region for the photoreduction of water to H2 remains a big challenge. To this end, a binary nanohybrid (BP/CN) of two-dimensional (2D) black phosphorus (BP) and graphitic carbon nitride (CN) was designed and used as a metal-free photocatalyst for the first time. During irradiation of BP/CN in water with >420 and >780 nm light, solid H2 gas was generated, respectively. Owing to the interfacial interaction between BP and CN, efficient charge transfer occurred, thereby enhancing the photocatalytic performance. The efficient charge-trapping and transfer processes were thoroughly investigated with time-resolved diffuse reflectance spectroscopic measurement. The present results show that BP/CN is a metal-free photocatalyst for artificial photosynthesis and renewable energy conversion.
857 citations