Porous g-C3N4/WO3 photocatalyst prepared by simple calcination for efficient hydrogen generation under visible light

W-N heteroatom-interface in melon carbon nitride/N-doped tungsten oxide Z-Scheme photocatalyst toward improved photocatalytic hydrogen generation activity

The construction of heterointerface in photocatalyst is an efficient approach to boost the separation and utilization efficiency of charge carriers, which is challenging and crucial in photocatalysis. Here, the construction of melon-structured carbon nitride/N-doped WO3 (MCN/NWx) heterojunction photocatalyst was achieved by a method of prealcoholysis combined with thermal polymerization, where N-doping of WO3 was achieved in-situ in the formation of heterojunction. The promoted charge separation efficiency was realized through the charge transfer from the conduction band of N-doped WO3 to the valence band of the MCN. Density functional theory calculation results showed that the formation of the W-N heteroatom-interface led to the increase of density of states at the heterointerface and decrease of the band gap. The MCN/NWx nanocomposite featured a metallic band structure of the nanocomposite photocatalysts, resulting in the enhanced photocatalytic activity. The photocatalytic hydrogen evolution activity of the MCN/NW2 was enhanced about 2.5 times than that of MCN. This research provides a novel insight into the construction of a novel heteroatom-junction that boosts the separation efficiency of charge carriers, and thereby improves the photocatalytic activity.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

A novel construction strategy of photoelectrochemical immunosensor for detecting neuron-specific enolase: Sensing mode integrating photoanode and photocathode

In the realm of photoelectrochemical (PEC) analysis, it is customary to employ a lone photoanode or photocathode system for analyte detection. Nonetheless, such a single detection scheme inherently carries some deficiencies. While photoanode-based PEC immunoassay methods do exhibit conspicuous photocurrent responses and heightened sensitivity, they do suffer from inadequate resistance to interference when detecting in real sample detection. Photocathode-based analysis methods are capable of effectively surmounting the limitations of photoanode-based analysis methods, but their stability is poor. Based on the above reasons, this paper reports a novel immunosensing system combining ITO/WO₃/Bi₂S₃ photoanode and ITO/CuInS₂ photocathode. The system that incorporates both photoanode and photocathode exhibits a steady and discernible photocurrent, possesses robust resistance to external interference, and has effectively accomplished the quantification of NSE in the linear range from 5 pg/mL to 30 ng/mL. Remarkably, the detection limit has been determined to be 1.59 pg/mL. Besides the notable advantages of satisfactory stability, exceptional specificity, and outstanding reproducibility, the sensing system also introduces an innovative approach to fabricate PEC immunosensors.

Ternary nanocomposites of CdS/WO3/g-C3N4 for hydrogen production

The sustainable rise in global warming and the consumption of fossil fuels considerably contribute to energy and environmental issues. To address these issues, semiconductor heterostructures can be used to generate clean energy sources as alternative energy sources and to reduce environmental impacts. Herein, we report the synthesis of a ternary semiconductor of the CdS/WO₃/g-C₃N₄ (i.e. C-CNW) nanostructured composite for hydrogen production and dye degradation under visible-light irradiation. The structural properties of the prepared materials were studied using a series of investigational analyses. The 3C-CNW nanostructure photocatalyst exhibited faster malachite green (MG) dye photodegradation within 105 min and the highest hydrogen production rate is 868.23 μmol g^-1 h^-1 under visible light illumination. Moreover, the photocatalytic hydrogen production of the 3C-CNW nanostructure photocatalyst with various scavengers was analyzed. Its higher photocatalytic activity is ascribed to the Z-scheme mechanism, which induces rapid diffusion of photoinduced charges within the ternary photocatalyst with its optical bandgap. This proposed strategy is useful to improve photocatalysts that play a role in mitigating energy and environmental issues.

Bifunctional g-C3N4/carbon nanotubes/WO3 ternary nanohybrids for photocatalytic energy and environmental applications

Ternary nanohybrids based on mesoporous graphitic carbon nitride (g-C3N4) were synthesized and presented for developing stable and efficient Hydrogen (H2) production system. Based on photocatalytic activity, optimization was performed in three different stages to develop carbon nanotubes (CNTs) and WO3 loaded g-C3N4 (CWG-3). Initially, the effect of exfoliation was investigated, and a maximum specific surface area of 100.77 m2/g was achieved. 2D-2D interface between WO3 and g-C3N4 was targeted and achieved, to construct a highly efficient direct Z-scheme heterojunction. Optimized binary composite holds the enhanced activity of about 2.6 folds of H2 generation rates than the thermally exfoliated g-C3N4. Further, CNT loading towards binary composite in an optimized weight ratio enhances the activity by 6.86 folds than the pristine g-C3N4. Notably, optimized ternary nanohybrid generates 15,918 μmol h-1. g-1cat of molecular H2, under natural solar light irradiation with 5 vol% TEOA as a sacrificial agent. Constructive enhancements deliver remarkable H2 production and dye degradation activities. Results evident that, the same system can be useful for pilot-scale energy generation and other photocatalytic applications as well.

An Insight into Carbon Nanomaterial-Based Photocatalytic Water Splitting for Green Hydrogen Production

At present, the energy shortage and environmental pollution are the burning global issues. For centuries, fossil fuels have been used to meet worldwide energy demand. However, thousands of tons of greenhouse gases are released into the atmosphere when fossil fuels are burned, contributing to global warming. Therefore, green energy must replace fossil fuels, and hydrogen is a prime choice. Photocatalytic water splitting (PWS) under solar irradiation could address energy and environmental problems. In the past decade, solar photocatalysts have been used to manufacture sustainable fuels. Scientists are working to synthesize a reliable, affordable, and light-efficient photocatalyst. Developing efficient photocatalysts for water redox reactions in suspension is a key to solar energy conversion. Semiconductor nanoparticles can be used as photocatalysts to accelerate redox reactions to generate chemical fuel or electricity. Carbon materials are substantial photocatalysts for total WS under solar irradiation due to their high activity, high stability, low cost, easy production, and structural diversity. Carbon-based materials such as graphene, graphene oxide, graphitic carbon nitride, fullerenes, carbon nanotubes, and carbon quantum dots can be used as semiconductors, photosensitizers, cocatalysts, and support materials. This review comprehensively explains how carbon-based composite materials function as photocatalytic semiconductors for hydrogen production, the water-splitting mechanism, and the chemistry of redox reactions. Also, how heteroatom doping, defects and surface functionalities, etc., can influence the efficiency of carbon photocatalysts in H2 production. The challenges faced in the PWS process and future prospects are briefly discussed.

Fabrication and Characterization of Highly Efficient As-Synthesized WO3/Graphitic-C3N4 Nanocomposite for Photocatalytic Degradation of Organic Compounds

The incorporation of tungsten trioxide (WO₃) by various concentrations of graphitic carbon nitride (g-C₃N₄) was successfully studied. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and Diffused Reflectance UV-Vis techniques were applied to investigate morphological and microstructure analysis, diffused reflectance optical properties, and photocatalysis measurements of WO₃/g-C₃N₄ photocatalyst composite organic compounds. The photocatalytic activity of incorporating WO3 into g-C₃N₄ composite organic compounds was evaluated by the photodegradation of both Methylene Blue (MB) dye and phenol under visible-light irradiation. Due to the high purity of the studied heterojunction composite series, no observed diffraction peaks appeared when incorporating WO₃ into g-C₃N₄ composite organic compounds. The particle size of the prepared composite organic compound photocatalysts revealed no evident influence through the increase in WO₃ atoms from the SEM characteristic. The direct and indirect bandgap were recorded for different mole ratios of WO₃/g-C₃N_4, and indicated no apparent impact on bandgap energy with increasing WO₃ content in the composite photocatalyst. The composite photocatalysts’ properties better understand their photocatalytic activity degradations. The pseudo-first-order reaction constants (K) can be calculated by examining the kinetic photocatalytic activity.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

WO3 Fibers/g-C3N4 Z-Scheme Heterostructure Photocatalysts for Simultaneous Oxidation/Reduction of Phenol/Cr (VI) in Aquatic Media

A sequence of WO3/g-C3N4 composites was synthesized at various % weight ratios (1, 5, 6.5, 8, 10, and 15%) of WO3 into g-C3N4 via electrospinning and wet-mixing method. The prepared photocatalytic materials were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV–vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), N2 porosimetry and dynamic light scattering (DLS). Electrospun fibers of WO3 with diameter 250–300 nm was prepared using polyvinylpyrrolidone (PVP) polymer and used for the synthesis of composite WO3/g-C3N4 heterojunction structures. Results showed mesoporous materials with triclinic WO3 crystal phase, surface areas up to 67.7 m2g−1 and band gaps lower than 2.5 eV confirming the absorption to visible light region. The photocatalytic performance of the prepared photocatalysts were assessed towards the oxidation of phenol and reduction of Cr (VI), in single and binary systems using simulated solar light illumination, that followed first-order kinetics. The WO3/g-C3N4 composites were found to exhibit improved photocatalytic performances compared to the pure WO3 and g-C3N4 with 6.5 wt% WO3/g-C3N4 and 5 wt% WO3/g-C3N4 composites being the most efficient catalysts for the oxidation of phenolics and reduction of Cr (VI), respectively. The improved performance was explained by a Z-scheme photocatalytic mechanism which was proposed based on scavenging experiments and the determination of the corresponding energy levels of valence and conduction bands. The study demonstrated that such composites present interesting photocatalytic properties that can be further expanded to other environmental depollution applications as well as in energy applications.

g-C3N4 Sensitized by an Indoline Dye for Photocatalytic H2 Evolution

Protonated g-C3N4 (pCN) formed by treating bulk g-C3N4 with an aqueous HCl solution was modified with D149 dye, i.e., 5-[[4[4-(2,2-diphenylethenyl) phenyl]-1,2,3,3a,4,8b-hexahydrocyclopent[b]indol-7-yl] methylene]-2-(3-ethyl-4-oxo-2-thioxo-5-thiazolidinylidene)-4-oxo-thiazolidin-2-ylidenerhodanine, for photocatalytic water splitting (using Pt as a co-catalyst). The D149/pCN-Pt composite showed a much higher rate (2138.2 µmol·h−1·g−1) of H2 production than pCN-Pt (657.0 µmol·h−1·g−1). Through relevant characterization, the significantly high activity of D149/pCN-Pt was linked to improved absorption of visible light, accelerated electron transfer, and more efficient separation of charge carriers. The presence of both D149 and Pt was found to be important for these factors. A mechanism was proposed.

Oxide-based composites: applications in thermo-photocatalysis

Recent progress on oxide-based thermo-photocatalytic composite systems. Role of plasmonic, defect-related, and thermal effects on the catalytic performance.

Facile one-pot synthesis of defect-engineered step-scheme WO3/g-C3N4 heterojunctions for efficient photocatalytic hydrogen production

Defect-engineered step-scheme WO₃/g-C₃N₄ heterojunctions synthesized by a facile one-pot method greatly improve the photocatalytic activity for hydrogen evolution.

g-C3N4 Modified by meso-Tetrahydroxyphenylchlorin for Photocatalytic Hydrogen Evolution Under Visible/Near-Infrared Light

A new photocatalyst denoted as mTHPC/pCN was prepared by modifying protonated graphitic carbon nitride (pCN) by meso-tetrahydroxyphenylchlorin (mTHPC). Relevant samples were characterized via various methods including zeta potential measurements, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N₂ adsorption–desorption, transmission electron microscopy, ultraviolet-visible–near-infrared spectroscopy, electrochemical impedance spectroscopy, photocurrent response measurements, electron spin resonance spectroscopy, and phosphorescence spectroscopy. Compared with pCN, mTHPC/pCN shows enhanced absorption in the visible and near-infrared regions and thus higher photocatalytic activity in hydrogen evolution. A possible mechanism for mTHPC/pCN is proposed.