Heteroatom-Doped Carbonaceous Photocatalysts for Solar Fuel Production and Environmental Remediation

Uracil-Doped Graphitic Carbon Nitride for Enhanced Photocatalytic Performance

g-C₃N₄ is a visible-light photocatalyst with a suitable band gap and good stability. Moreover, g-C₃N₄ is considered to be earth-abundant, which makes it an appealing photocatalyst. However, due to its small specific surface area, low utilization of visible light, and high photogenerated electron-hole pair recombination rate, the photocatalytic activity of g-C₃N₄ remains unsatisfactory. In this work, a highly efficient nonmetallic photocatalyst, i.e., g-C₃N₄ doped with uracil (denoted U-C₃N₄) was successfully developed. Based on the various characterizations and calculations, it is shown that the triazine group in g-C₃N₄ is replaced with the diazine group in uracil. This occurrence leads to the formation of a new electron-transfer pathway between triazine groups, which can promote the separation of photogenerated electrons and holes. Concurrently, due to the ultrathin structure of the as-prepared U-C₃N₄, the material possessed a larger specific surface area than pristine g-C₃N₄, which can provide more active sites. Furthermore, the transfer pathway between the electron and hole was also shortened, and the recombination of the electron and hole was inhibited. According to the results, an optimal hydrogen evolution rate of 31.7 mol h^-1 g^-1 was achieved by U-C₃N₄, which is 5.1 times higher as compared to that achieved by pristine g-C₃N₄ (6.26 mol h^-1 g^-1). For the photocatalytic degradation of rhodamine B, the reaction rate constant of U-C₃N₄ (11.3 × 10^-2 min^-1) is about 5.5 times that of g-C₃N₄ (2.07 × 10^-2 min^-1). Furthermore, the uracil-doped catalyst was also able to demonstrate good stability after five successive runs.

Oxygen vacancy-engineered surfaces of ZnO-decorated porous BiOI microspheres for strongly enhanced visible-light NO oxidation

Oxygen vacancy-engineered Surfaces of ZnO-decorated porous BiOI microspheres for strongly enhanced visible-light NO oxidation.

Post-annealed graphite carbon nitride nanoplates obtained by sugar-assisted exfoliation with improved visible-light photocatalytic performance

Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanoplates (CNNP) have become a hot research topic in photocatalysis due to their small thickness and large specific surface area that favors charge transport and catalytic surface reactions. However, the wide application of 2D g-C₃N₄ nanoplates prepared by ordinary methods suffers from increased band gaps with a poor solar harvesting capability caused by the strong quantum confinement effect and reduced conjugation distance. In this paper, a facile approach of exfoliation and the following fast thermal treatment of the bulk g-C₃N₄ is proposed to obtain a porous few-layered g-C₃N₄ with nitrogen defects. Due to the preferable crystal, textural, optical and electronic structures, the as-obtained porous CNNP demonstrated a significantly improved photocatalytic activity towards water splitting than the bulk g-C₃N₄ and even the 3 nm-thick CNNP obtained by sugar-assisted exfoliation of the bulk g-C₃N₄. The difference in the enhancement factors between the H₂O splitting and organic decomposition has revealed the effect of N defects. This study offers insightful outlooks on the scalable fabrication of a porous few-layered structure with a promoted photocatalytic performance.

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched active sites for promoted catalysis in styrene production

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched catalytic sites is fabricated by a facile two-step molten salt-oxidation strategy, generating an excellent catalyst for clean and energy-saving styrene production.

Single Atomic Cu-N2 Catalytic Sites for Highly Active and Selective Hydroxylation of Benzene to Phenol

Searching for an efficient single-atom catalyst for benzene hydroxylation to phenol is of critical importance, but it still remains a challenge. Herein, a single-atom catalyst with unique Cu-N₂ moieties (Cu₁-N₂/HCNS) was prepared and confirmed by HAADF-STEM and EXAFS. Turnover number (TON) over Cu₁-N₂/HCNS (6,935) is 3.4 times of Cu₁-N₃/HCNS (2,034) under the same reaction conditions, and both exhibit much higher phenol selectivity (close to 99%) and stability compared with Cu nanoparticles and nanoclusters. Experiments and DFT calculations reveal that atomically dispersed Cu species are active sites for benzene hydroxylation to phenol, and the Cu-N₂ is more active than Cu-N₃ owing to its much lower energy barrier concerning the activation of H₂O₂ led by its unique coordination state of local atomic structure. We envision that this work opens a new window for modulating coordination environments of single metallic atoms in catalysis design.

Soluble Graphene Nanosheets for the Sunlight-Induced Photodegradation of the Mixture of Dyes and its Environmental Assessment

Currently, the air and water pollutions are presenting the most serious global concerns. Despite the well known tremendous efforts, it could be a promising sustainability if the black carbon (BC) soot can be utilized for the practical and sustainable applications. For this, the almost complete aqueous phase photodegradation of the three well-known organic pollutant dyes as crystal violet (CV); rhodamine B (RhB); methylene blue (MB) and their mixture (CV + RhB + MB), by using water-soluble graphene nanosheets (wsGNS) isolated from the BC soot under the influence of natural sunlight is described. The plausible mechanism behind the photocatalytic degradation of dyes and their mixture has been critically analyzed via the trapping of active species and structural analysis of photodegraded products. The impact of diverse interfering ions like Ca2+, Fe3+, SO42-, HPO42-, NO3-, and Cl- on the photodegradation efficiency of wsGNS was also investigated. Importantly, the environmental assessment of the whole process has been evaluated towards the growth of wheat plants using the treated wastewater. The initial studies for the fifteen days confirmed that growth of wheat plants was almost the same in the photodegraded wastewater as being noticed in the control sample, while in case of dyes contaminated water it showed the retarded growth. Using the natural sunlight, the overall sustainability of the presented work holds the potential for the utilization of pollutant soot in real-practical applications related to the wastewater remediation and further the practical uses of treated water.

Combining iodic acid and nitric acid to fabricate carbon nitride tubes for enhanced hydrogen evolution under visible light

This work presents a facile mixed-acid approach to prepare defect-enriched porous g-C₃N₄ tubes with outstanding photocatalytic performance for hydrogen evolution.

Preassembly Strategy To Fabricate Porous Hollow Carbonitride Spheres Inlaid with Single Cu-N3 Sites for Selective Oxidation of Benzene to Phenol

Developing single-atom catalysts with porous micro-/nanostructures for high active-site accessibility is of great significance but still remains a challenge. Herein, we for the first time report a novel template-free preassembly strategy to fabricate porous hollow graphitic carbonitride spheres with single Cu atoms mounted via thermal polymerization of supramolecular preassemblies composed of a melamine-Cu complex and cyanuric acid. Atomically dispersed Cu-N₃ moieties were unambiguously confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure spectroscopy. More importantly, this material exhibits outstanding catalytic performance for selective oxidation of benzene to phenol at room temperature, especially showing phenol selectivity (90.6 vs 64.2%) and stability much higher than those of the supported Cu nanoparticles alone, originating from the isolated unique Cu-N₃ sites in the porous hollow structure. An 86% conversion of benzene, with an unexpectedly high phenol selectivity of 96.7% at 60 °C for 12 h, has been achieved, suggesting a great potential for practical applications. This work paves a new way to fabricate a variety of single-atom catalysts with diverse graphitic carbonitride architectures.

Reconstructing Supramolecular Aggregates to Nitrogen-Deficient g-C3N4 Bunchy Tubes with Enhanced Photocatalysis for H2 Production

Developing a facile method to overcome the intrinsic shortcomings of g-C₃N₄ photocatalyst concerning its insufficient visible light absorption and dissatisfactory separation efficiency of charge carriers is of great significance but remains a challenge. In this work, we report, for the first time, a sapiential strategy for preparing highly efficient nitrogen-deficient g-C₃N₄ featuring bunchy microtubes [R-tubular carbon nitride (TCN)] via a KOH-assisted hydrothermal treatment of rodlike melamine-cyanuric acid (RMCA) supramolecular aggregates followed by heating the reconstructed RMCA, in which KOH serves as an all-rounder for breaking hydrogen bonds, accelerating hydrolysis of melamine and nitrogen defects forming. This approach endows R-TCN with unique bunchy microtube morphology, enriched nitrogen defects, textural properties, and electronic structure, which result in narrower band gap, higher electric conductivity, more active sites, more negative conductive band, significantly increased visible light harvesting capability, and improved separation efficiency of charge carriers. As a consequence, R-TCN shows 2.44 and 39 times higher hydrogen evolution rate (8.19 μmol h^-1) than that of the pristine TCN from RMCA and bulk g-C₃N₄ from melamine. This new discovery may open a new avenue to fabricate highly efficient g-C₃N₄ catalysts.

Enhanced visible light photocatalytic non-oxygen coupling of amines to imines integrated with hydrogen production over Ni/CdS nanoparticles

Non-oxygen coupling of amines to imines, initiated by hydrogen evolution over Ni/CdS nanoparticles with visible light, smoothly happens. Outstanding catalytic performance was achieved, originating from integrating effect of coupling reaction and solar-driven reduction of aqueous protons.

Enhanced photocarriers separation of novel CdS/pt/Mo2C heterostructure for visible-light-driven hydrogen evolution

The production of H₂ from water using photocatalysts is a promising way of generating clean, renewable and alternative energy. The key issue is to develop active and stable photocatalysts. Here, we report a novel CdS/Pt/Mo₂C heterostructure photocatalyst, where Pt nanoparticles are closely supported on CdS/Mo₂C. The UV-vis spectrum and EIS Nyquist plots show that Mo₂C can boost the absorption in the UV-vis region and improve the separation of the photogenerated electron–hole pairs from CdS. The Pt nanoparticles act as the active co-catalyst that promotes the transient photocurrent response. As a result, the CdS/Pt/Mo₂C photocatalyst exhibits an excellent H₂ evolution activity up to 1828.82 μmol h⁻¹ g⁻¹ under visible-light irradiation, 8.5 and 16.2 times higher than that of pristine CdS and CdS/Mo₂C, respectively. Moreover, a high apparent quantum yield (AQY) of 9.39% is obtained at 400 nm for the CdS/Pt/Mo₂C heterostructure photocatalyst.

The production of H₂ from water using photocatalysts is a promising way of generating clean, renewable and alternative energy.