Construction of stable Ta3N5/g-C3N4 metal/non-metal nitride hybrids with enhanced visible-light photocatalysis

In this paper, a novel Ta3N5/g-C3N4 metal/non-metal nitride hybrid was successfully synthesized by a facile impregnation method. The photocatalytic activity of Ta3N5/g-C3N4 hybrid nitrides was evaluated by the degradation of organic dye rhodamine B (RhB) under visible light irradiation, and the result indicated that all Ta3N5/g-C3N4 samples exhibited distinctly enhanced photocatalytic activities for the degradation of RhB than pure g-C3N4. The optimal Ta3N5/g-C3N4 composite sample, with Ta3N5 mass ratio of 2%, demonstrated the highest photocatalytic activity, and its degradation rate constant was 2.71 times as high as that of pure g-C3N4. The enhanced photocatalytic activity of this Ta3N5/g-C3N4 metal/metal-free nitride was predominantly attributed to the synergistic effect which increased visible-light absorption and facilitated the efficient separation of photoinduced electrons and holes. The Ta3N5/g-C3N4 hybrid nitride exhibited excellent photostability and reusability. The possible mechanism for improved photocatalytic performance was proposed. Overall, this work may provide a facile way to synthesize the highly efficient metal/metal-free hybrid nitride photocatalysts with promising applications in environmental purification and energy conversion

Laser-driven growth of structurally defined transition metal oxide nanocrystals on carbon nitride photoelectrodes in milliseconds

Fabrication of hybrid photoelectrodes on a subsecond timescale with low energy consumption and possessing high photocurrent densities remains a centerpiece for successful implementation of photoelectrocatalytic synthesis of fuels and value-added chemicals. Here, we introduce a laser-driven technology to print sensitizers with desired morphologies and layer thickness onto different substrates, such as glass, carbon, or carbon nitride (CN). The specially designed process uses a thin polymer reactor impregnated with transition metal salts, confining the growth of transition metal oxide (TMO) nanostructures on the interface in milliseconds, while their morphology can be tuned by the laser. Multiple nano-p-n junctions at the interface increase the electron/hole lifetime by efficient charge trapping. A hybrid copper oxide/CN photoanode with optimal architecture reaches 10 times higher photocurrents than the pristine CN photoanode. This technology provides a modular approach to build a library of TMO-based composite films, enabling the creation of materials for diverse applications

Synthesis and Evaluation of Novel Photocatalysts for Photocatalytic Reactions

This study focuses on the design of low-dimensional (LD) photocatalysts for water oxidation in oxygen evolution reaction (OER). Through skillful approaches, such as morphological control, interface construction, defect or vacancy engineering, we developed a series of LD hybrids and examined their photo- and photoelectrochemical performances in OER. Attribute to the stable LD structure and synergistic effect of the components, the heterojunction or hierarchical materials showed enhanced charge separation, transportation, water oxidation kinetics and quantum efficiency

Synthesis and Applications of Nanomaterials for Photocatalysis and Electrocatalysis

This book supplies fundamental aspects regarding the use of different nanostructures as heterogeneous catalysts for energy and environmental applications. In recent decades, the attention of both scientific and industrial communities has become increasingly focused on the implementation of groundbreaking nanomaterials in all fields of human activity, especially toward improving energy efficiency and fulfilling environmental demands. Energy and environment represent a perfect blend: energy-saving environmental remediations and promising energetic devices meeting environmental concerns represent potential future challenges that humankind will face. In this context, the fine control of the nanosized species is the real tool to overcome the current issues and to improve the final performances. Herein, from an energetic point of view, oxygen evolution and reduction reactions (OER and ORR) are keys to deeply understanding the behaviour of water splitting devices and fuel cells as well as zinc/air batteries, respectively. Zinc tantalum oxynitride-based photoanodes and nitrogen-modified carbon doped with different metals will be presented and fully characterised. Concurrently, bismuth titanate nanosheets and noble metal core-shell nanoparticles can be adopted to enhance hydrogen evolution through photocatalytic water splitting, exploiting solar energy. Instead, for what concerns the environmental remediation, the use of pure (black, modified, and faceted TiO2, Ga2O3) and composite (graphene/titanate, Zn2\u2013SnO4/BiOBr, g-C3N4/Nb2O5, MnO2/TiO2 and CaIn2S4/ZnIn2S4) nanomaterials allow for air and water purification, especially under solar irradiation. Particularly, the complete photodegradation of noxious species (benzylic acid), organic dyes (rhodamine B, methylene blue and alizarin red), heavy metals (chromium), recalcitrant pharmaceutical active principles (cinnamic acid, ibuprofen and tetracycline), and VOCs (ethanol) will be thoroughly discussed. Finally, we would like to acknowledge all the authors who have contributed to this book with their scientific expertise, and we hope that the readers will find the arguments both useful and interesting

Towards Green, Enhanced Photocatalysts for Hydrogen Evolution

This book gathers selected research on the preparation, characterization and application of new organic/inorganic composites endowed with photo(electro)catalytic properties for the photocatalytic production of H2. In these pilot studies, the photoactive materials were tested under either UV-visible or, even more conveniently, under visible light for H2 evolution in “sacrificial water splitting” or “photoreforming” systems. In addition, a review article on the use of 2D materials and composites as potential photocatalysts for water splitting is included

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams

Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe2O4, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion

Silver-montmorillonite modified titanium dioxide assisted carbon nitride nanocomposites for photocatalytic hydrogen production through water splitting

Photocatalytic hydrogen (H2 ) generation is one o f the most promising solutions to convert solar power into clean energy to replace non-renewable fossil fuel. The objective of this study is to investigate montmorillonite (MMT) dispersed and silver (Ag)-bridged protonated carbon nitride/titanium dioxide (pCN/TiO2) Zscheme heterojunction composite for stimulating photocatalytic H2 evolution under UV and visible light in different photocatalytic reactor systems. The newly designed MMT-Ag/pCN-TiO2 composite photocatalysts were fabricated through a sol-gel assisted hydrothermal method and were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray mapping, transmission electron microscopy, Brunauer-Emmett-Teller, ultraviolet-visible (UV-vis) spectroscopy and photoluminescence spectroscopy. The photocatalytic activity was tested using slurry, fixed bed and monolith photo-reactor systems for continuous H2 production. Using slurry system, MMT-Ag/pCN-TiO2 photo-catalyst produced 667 |imol h-1 of H2 which is 8.41 and 9.66 times higher than pCN/TiO2 and TiO2 samples, respectively. The efficiency was improved due to formation of heterojunction with faster charges separation, whereas, Ag provides hot photo-generated electrons by surface plasmon resonance and MMT traps electrons for H2 production. Optimization reveals that the highest production of H2 was obtained at pH 7, glycerol concentration of 5 wt. % and 0.15 g of catalyst loading using slurry reactor. Furthermore, by applying an engineering approach MMT-Ag/pCN-TiO2 showed H2 production rate was increased to 8230 prnol h- 1 using a monolith reactor, which are 9.01 and 12.34 times higher than fixed-bed and slurry photo-reactors. The monolith honeycomb reactor exhibited a higher apparent quantum yield and space yield of 39.85 % and 54.86 |imol h-1cm"3 compared to slurry (22.36 %, 5.13 |imol h-1cm"3) and fixed-bed reactors (4.42 %, 6.09 |imol h-1cm"3). The superior performance of a monolith reactor was due to higher photon flux utilization, large illuminated surface area and processing volume. The schematic of type II heterojunction and Z-scheme mechanism of MMTAg/ pCN-TiO2 were developed and the photocatalytic performance was compared in all types o f systems. In conclusion, excellent performance o f composite catalyst using a monolith reactor compared to a slurry and fixed-bed reactor for H2 production would offer a new opportunity in engineering approach for renewable fuels applications

Pore confinement effects and stabilization of carbon nitride oligomers in macroporous silica for photocatalytic hydrogen production

An ordered macroporous host (mac-SiO2) has been used to prevent aggregation of layered photocatalysts based on carbon nitride. Using typical carbon nitride synthesis conditions, cyanamide was condensed at 550 °C in the presence and absence of mac-SiO2. Condensation in the absence of mac-SiO2 results in materials with structural characteristics consistent with the carbon nitride, melon, accompanied by ca. 2 wt% carbonization. For mac-SiO2 supported materials, condensation occurs with greater carbonization (ca. 6 wt%). On addition of 3 wt% Pt cocatalyst photocatalytic hydrogen production under visible light is found to be up to 10 times greater for the supported composites. Time-resolved photoluminescence spectroscopy shows that excited state relaxation is more rapid for the mac-SiO2 supported materials suggesting faster electron-hole recombination and that supported carbon nitride does not exhibit improved charge separation. CO2 temperature programmed desorption indicates that enhanced photoactivity of supported carbon nitride is attributable to an increased surface area compared to bulk carbon nitride and an increase in the concentration of weakly basic catalytic sites, consistent with carbon nitride oligomers