A defective g-C3N4/RGO/TiO2 composite from hydrogen treatment for enhanced visible-light photocatalytic H2 production

Developing self-floating N-defective graphitic carbon nitride photocatalyst for efficient photodegradation of Microcystin-LR under visible light

The frequent occurrence of algal blooms in water bodies leads to a significant accumulation of microcystin-LR (MC-LR). In this study, we developed a porous foam-like self-floating N-deficient g-C3N4 (SFGN) photocatalyst for efficient photocatalytic degradation of MC-LR. Both the characterization results and DFT calculations indicate that the surface defects and floating state of SFGN synergistically enhance light harvesting and photogenerated carrier migration rate. The photocatalytic process achieved a nearly 100 % removal rate of MC-LR within 90 min, while the self-floating state of SFGN maintained good mechanical strength. ESR and radical capture experiments revealed that the primary active species responsible for the photocatalytic process was OH. This finding confirmed that the fragmentation of MC-LR occurs as a result of OH attacking the MC-LR ring. LC-MS analysis indicated that majority of the MC-LR molecules were mineralized into small molecules, allowing us to infer possible degradation pathways. Furthermore, after four consecutive cycles, SFGN exhibited remarkable reusability and stability, highlighting the potential of floating photocatalysis as a promising technique for MC-LR degradation.

Composition-dependent activity of Mn-doping NiS2 nanosheets for boosting photocatalytic H2 evolution

Two-dimensional transition metal disulfides are excellent photocatalytic materials, which can be significantly improved by optimizing the composition and structure. Herein, Mn-doping NiS2 of (Ni1-xMnx)-S with various Ni/Mn molar ratios is proposed via a facile and low-cost solvothermal method. The optimal (Ni4/6Mn2/6)-S exhibits pinecone-like morphology composed of tiny nanosheets with enlarged active sites, which facilitates the separation of photoinduced electrons and holes, improves the electron transfer ability and conductivity, and enlarges the active sites compared with pure NiS2 and MnS. Also, the negative shift of the conduction band derived from Mott-Schottky plots and the empirical formula provides a high thermodynamic driving force for hydrogen catalytic reaction. (Ni4/6Mn2/6)-S performs an ultrahigh hydrogen evolution rate of 24.86 mmol g-1 h-1 under UV-visible light irradiation, which is 1.5 times higher than pure NiS2 (16.92 mmol g-1 h-1) and 2.3 times higher than pure MnS (10.69 mmol g-1 h-1). The outstanding repeatability of 86.7% retention and apparent quantum yield of 46.9% are also achieved. Therefore, this work offers a novel bimetallic sulfide of (Ni1-xMnx)-S to improve the conversion efficiency of solar energy to chemical energy for photocatalytic hydrogen production.

Reduced Graphene Oxide Supported Zinc Tungstate Nanoparticles as Proficient Electro-Catalysts for Hydrogen Evolution Reactions

The nanocomposites of reduced graphene oxide (rGO) supported zinc tungstate nanoparticles (ZnWO4-NPs) receive considerable attention in electro-catalytic hydrogen evolution reactions (HER) and reveal significantly higher electro-catalytic performances than pure ZnWO4-NPs in alkaline media (i.e., 0.5 M KOH electrolyte). The polarization studies show that the ZnWO4-NPs@rGO nanocomposites exhibit low energy loss and good electrode stability during electrochemical reactions for HER. Furthermore, the Tafel slope of ZnWO4-NPs@rGO nanocomposites is found to be approximately 149 mV/dec, which closely agrees with the reported Tafel values of the noble metal electrocatalyst. In contrast, the performance of the ZnWO4-NPs@rGO nanocomposite is found to be approximately 1.5 times higher than that of ZnWO4-NPs in hydrogen production efficiency. Our results emphasize the significance of the nanocomposites with enhanced electro-catalytic activities by lowering the energy loss during electro-catalysis in an alkaline medium.

Development and Mechanistic Studies of Ternary Nanocomposites for Hydrogen Production from Water Splitting to Yield Sustainable/Green Energy and Environmental Remediation

Photocatalysts lead vitally to water purifications and decarbonise environment each by wastewater treatment and hydrogen (H2) production as a renewable energy source from water-photolysis. This work deals with the photocatalytic degradation of ciprofloxacin (CIP) and H2 production by novel silver-nanoparticle (AgNPs) based ternary-nanocomposites of thiolated reduce-graphene oxide graphitic carbon nitride (AgNPs-S-rGO2%@g-C3N4) material. Herein, the optimised balanced ratio of thiolated reduce-graphene oxide in prepared ternary-nanocomposites played matchlessly to enhance activity by increasing the charge carriers’ movements via slowing down charge-recombination ratios. Reduced graphene oxide (rGO), >2 wt.% or <2 wt.%, rendered H2 production by light-shielding effect. As a result, CIP degradation was enhanced to 95.90% by AgNPs-S-rGO2%@g-C3N4 under the optimised pH(6) and catalyst dosage(25 mg/L) irradiating beneath visible-light (450 nm, 150 watts) for 70 min. The chemical and morphological analysis of AgNPs-S-rGO2%@g-C3N4 surface also supported the possible role of thiolation for this enhancement, assisted by surface plasmon resonance of AgNPs having size < 10 nm. Therefore, AgNPs-S-rGO2%@g-C3N4 has 3772.5 μmolg−1 h−1 H2 production, which is 6.43-fold higher than g-C3N4 having cyclic stability of 96% even after four consecutive cycles. The proposed mechanism for AgNPs-S-rGO2%@g-C3N4 revealed that the photo-excited electrons in the conduction-band of g-C3N4 react with the adhered water moieties to generate H2.

Modular Assembly of Electron Transfer Pathway in Bimetallic MOF for Photocatalytic Ammonia Synthesis

It is a long-term pursuit to implement the green and sustainable photocatalytic production of ammonia via the conversion of water and nitrogen under mild conditions. Due to the rapid recombination...

Advancing Photoelectrochemical Energy Conversion through Atomic Design of Catalysts

Powered by inexhaustible solar energy, photoelectrochemical (PEC) hydrogen/ammonia production and reduction of carbon dioxide to high added-value chemicals in eco-friendly and mild conditions provide a highly attractive solution to carbon neutrality. Recently, substantial advances have been achieved in PEC systems by improving light absorption and charge separation/transfer in PEC devices. However, less attention is given to the atomic design of photoelectrocatalysts to facilitate the final catalytic reactions occurring at photoelectrode surface, which largely limits the overall photo-to-energy conversion of PEC system. Fundamental catalytic mechanisms and recent progress in atomic design of PEC materials are comprehensively reviewed by engineering of defect, dopant, facet, strain, and single atom to enhance the activity and selectivity. Finally, the emerging challenges and research directions in design of PEC systems for future photo-to-energy conversions are proposed.

Two-dimensional graphitic carbon nitride/N-doped carbon with a direct Z-scheme heterojunction for photocatalytic generation of hydrogen

Photocatalysts with a direct Z-scheme heterojunction are promising by virtue of the effectively enhanced separation of charge carriers, high retention of redox ability and the absence of backward photocatalytic reactions. Their activity depends on band alignment and interfacial configurations between two semiconductors for charge carrier kinetics and the effective active sites for photochemical reactions. Herein, a two-dimensional (2D) graphitic carbon nitride/N-doped carbon (C₃N₄/NC) photocatalyst is synthesized by a gas template (NH₄Cl)-assisted thermal condensation method. C₃N₄/NC has the synthetic merits of a direct Z-scheme heterojunction, 2D-2D interfacial contact, and enhanced specific surface area to improve charge separation kinetics and provide abundant active sites for photochemical reaction. It exhibits an over 46-fold increase of the photocatalytic hydrogen production rate compared to bulk C₃N₄ under visible light illumination. This work demonstrates the great potential of 2D Z-scheme heterojunctions for photocatalysis and will inspire more related work in the future.

Enhanced Photocatalytic Activity of Hybrid rGO@TiO2/CN Nanocomposite for Organic Pollutant Degradation under Solar Light Irradiation

The three-component hybrid (rGO/TiO2/CN) nanocomposite was prepared in order to enhance the photocatalytic properties of anatase TiO2 nanoparticles (NPs) under solar-like irradiation. The rGO/TiO2/CN was prepared in a mixture of the reduced graphene oxide (rGO, 8 wt%), anatase TiO2 nanoparticles (NPs), and graphitic carbon nitride (g-C3N4, 16 wt%). It was self-assembled through the one-step hydrothermal method, followed by an annealing process. The photocatalyst was thoroughly characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the TiO2, TiO2/rGO, TiO2/CN and hybrid rGO/TiO2/CN nanocomposite was studied through the degradation of a rhodamine B (RhB) aqueous solution under solar-like irradiation. The results showed that the highest photocatalytic activity was achieved by the rGO/TiO2/CN mixture, which can be attributed to the synergistic effect of the incorporation of both rGO and g-C3N4 with TiO2. Further, the influence of the pH value of the RhB dye aqueous solution and different water matrix (Milli-Q, tap, and alkaline water) on the photocatalytic efficiency of the rGO/TiO2/CN nanocomposite was examined. In addition, a recycle test was performed for hybrid rGO@TiO2/CN to investigate the effectiveness of the photodegradation of RhB dye in three successive cycles. The conducted results indicate that the pH value of RhB dye aqueous solution and water matrices play an important role in the photocatalytic degradation rate.