High efficiency photocatalysis for pollutant degradation with MoS2/C3N4 heterostructures

Design of a p-n heterojunction in 0D/3D MoS2/g-C3N4 composite for boosting the efficient separation of photogenerated carriers with enhanced visible-light-driven H2 evolution

Constructing a 0D/3D p-n heterojunction is a feasible strategy for accelerating photo-induced charge separation and promoting photocatalytic H₂ production. In this study, a 0D/3D MoS₂/g-C₃N₄ (0D/3D-MCN) photocatalyst with a p-n heterojunction was prepared via a facile light-assisted deposition procedure, and the 3D spongy-like g-C₃N₄ (3D-CN) was synthesized through simple thermolysis of NH₄Cl and melamine mixture. For comparison, 2D-MoS₂ nanosheets were also embedded in 3D-CN by a solution impregnation method to synthesize a 2D/3D-MCN photocatalyst. As a result, the as-prepared 0D/3D-MCN-3.5% composite containing 3.5 wt% 0D-MoS₂ QDs exhibited the highest photocatalytic H₂ evolution rate of 817.1 μmol h^-1 g^-1, which was 1.9 and 19.4 times higher than that of 2D/3D-MCN-5% (containing 5 wt% 2D-MoS₂ nanosheets) and 3D-CN, respectively. The results of XPS and electrochemical tests confirmed that a p-n heterojunction was formed in the 0D/3D-MCN-3.5% composite, which could accelerate the electron and hole movement in the opposite direction and retard their recombination; however, it was not found in 2D/3D-MCN-5%. This study revealed the relationship among the morphologies of MoS₂ using g-C₃N₄ as a substrate, the formation of a p-n heterojunction, and the H₂ evolution activity; and provided further insights into fabricating a 3D g-C₃N₄-based photocatalyst with a p-n heterojunction for photocatalytic H₂ evolution.

Hybridized 2D Nanomaterials Toward Highly Efficient Photocatalysis for Degrading Pollutants: Current Status and Future Perspectives

Organic pollutants including industrial dyes and chemicals and agricultural waste have become a major environmental issue in recent years. As an alternative to simple adsorption, photocatalytic decontamination is an efficient and energy-saving technology to eliminate these pollutants from water environment, utilizing the energy of external light, and unique function of photocatalysts. Having a large specific surface area, numerous active sites, and varied band structures, 2D nanosheets have exhibited promising applications as an efficient photocatalyst for degrading organic pollutants, particularly hybridization with other functional components. The novel hybridization of 2D nanomaterials with various functional species is summarized systematically with emphasis on their enhanced photocatalytic activities and outstanding performances in environmental remediation. First, the mechanism of photocatalytic degradation is given for discussing the advantages/shortcomings of regular 2D materials and identifying the importance of constructing hybrid 2D photocatalysts. An overview of several types of intensively investigated 2D nanomaterials (i.e., graphene, g-C₃ N₄ , MoS₂ , WO₃ , Bi₂ O₃ , and BiOX) is then given to indicate their hybridized methodologies, synergistic effect, and improved applications in decontamination of organic dyes and other pollutants. Finally, future research directions are rationally suggested based on the current challenges.

Surface Modification Strategy for Promoting the Performance of Non-noble Metal Single-Atom Catalysts in Low-Temperature CO Oxidation

As a bridge between homogeneous and heterogeneous catalyses, single-atom catalysts (SACs), especially the noble metal atoms, have received extensive attention from both the fundamental and applied perspectives recently. High cost and difficulty in synthesis are considerable factors, however, limiting the development and practical applications of SACs. Thus, seeking for non-noble SACs for substituting the noble ones is not only of vital importance but also a long-standing challenge. Herein, a surface modification strategy by introducing an oppositely charged dopant and inducing the charge transfer between the SAC and the substrate was proposed to improve the stability and catalytic performance of the non-noble Cu SAC. Using first-principles density functional theory (DFT) calculations, it was demonstrated that the introduction of C in the MoS₂ monolayer (C:MoS₂, experimentally available) can assist in stabilizing Cu and make it more positively charged, which will facilitate the adsorption of the reactants and further enhance the activity for CO oxidation. Strikingly, our results show that CO oxidation over Cu-C:MoS₂ is more favorable than over the Pt atom deposited on the pristine MoS₂ (Pt-MoS₂), exhibiting its potential in noble metal substitution and low-temperature CO oxidation. Additionally, Cu-C:MoS₂ was observed to have a response to visible light, which manifests that it may be a promising photocatalyst. The strategy proposed here provides an efficient route to regulate the electronic structures of SACs through charge transfer, which further promotes the reactivity of the non-noble metal SACs. We hope that this strategy can contribute to design more SACs with low cost and high efficiency, which will be beneficial for their practical applications.

2D/2D Heterojunction of R-scheme Ti3C2 MXene/MoS2 Nanosheets for Enhanced Photocatalytic Performance

Combination of two-dimensional (2D) materials and semiconductors is considered to be an effective way for fabricating photocatalysts for solving the environmental pollution and energy crisis. In this work, novel 2D/2D heterojunction of R-scheme Ti₃C₂ MXene/MoS₂ nanosheets is successfully synthesized by hydrothermal reaction. The photocatalytic activity of the Ti₃C₂ MXene/MoS₂ composites is evaluated by photocatalytic degradation and hydrogen evolution reaction. Especially, 0.5 wt% Ti₃C₂ MXene/MoS₂ sample exhibits optimum methyl orange (MO) degradation and H₂ evolution rate of 97.4% and H₂ evolution rate of 380.2 μmol h^-1 g^-1, respectively, which is attributed to the enhanced optical absorption ability and increased specific surface area. Additionally, Ti₃C₂ MXene coupled with MoS₂ nanosheets is favorable for improving the photocurrent response and reducing the electrochemical impedance, leading to the enhanced electron transfer of excited semiconductor and inhibition of charge recombination. This work demonstrates that Ti₃C₂ MXene could be a promising carrier to construct 2D/2D heterojunction in photocatalytic degradation and hydrogen evolution reaction.

Effects of defects in g-C3N4 on excited-state charge distribution and transfer: Potential for improved photocatalysis

Graphite phase carbon nitride (g-C₃N₄) with triazine ring structures is a polymeric metal-free semiconductor with a medium bandgap and two-dimensional layered structure. g-C₃N₄ has attracted attention because of its photocatalytic applications, such as the photodegradation of pollution and hydrogen production via water splitting. Defective elements and sites are two essential factors in rationally designing highly-efficient photocatalysts based on g-C₃N₄ at the nanoscale. When the molecule absorbs energy and enters an excited state, electrons migrate and the charge distribution changes accordingly. The properties of the excited states of g-C₃N₄ are related to its defect elements and sites. Therefore, it is necessary to understand the effects of defects on excited states in the design of g-C₃N₄ catalysts. In this paper, the excited-state characteristics of intrinsic g-C₃N₄ and g-C₃N₄ with C- and N-atom defects are analyzed by density functional theory. We apply quantum chemistry and wave function analysis to determine the hole-electron distributions and charge transfer directions. To measure and discuss the characteristics of electron excitation using quantitative numerical methods, the D, Sr, H, and t indices are calculated. Our results promote a deeper understanding of the roles of defective elements and sites in photocatalysis by g-C₃N₄.

Size-controlled MoS2 nanosheet through ball milling exfoliation: parameter optimization, structural characterization and electrocatalytic application

Unique properties and potential applications of 2D materials draw much attention for mass production of thin-layer 2D materials. Ball milling exfoliation of 2D materials has been rarely used, in spite of a promising dry phase production method, because of the superficial information in the mechanism and the effect of the operating parameters on the yield, size and thickness. Here, we investigate systematically the ball milling operating parameters in the exfoliation of bulk MoS₂ in the presence of sodium cholate (SC) as an exfoliant. The yield and dimensions of the exfoliated MoS₂ nanosheet were monitored by changing the parameters such as the weight ratio of bulk MoS₂ and SC (SC/MoS₂), the filling ratio in the volume of milling ball and container (φ), milling ball size (d _B), milling revolution speed (n _R ), and initial mass of bulk MoS₂ ([Formula: see text]). The yield of exfoliation is found to be 95% at the optimum ball milling conditions (SC/MoS₂ = 0.75, φ = 50%, [Formula: see text] = 0.20 g). In addition, yield and size of the exfoliated MoS₂ were controlled by the conditions of the ball milling. As for the evaluation of the exfoliated MoS₂, we developed a novel method by use of the XRD profile to determine the size and thickness of the ball-milled MoS₂ powder with less than 30% difference from those determined by the well-known absorption method. Finally, the size and thickness of the MoS₂ nanosheets prepared by ball milling exfoliation were correlated with their electrocatalytic and photoelectrocatalytic activities.

Preparation of a g-C3N4/Co3O4/Ag2O ternary heterojunction nanocomposite and its photocatalytic activity and mechanism

A g-C₃N₄/Co₃O₄/Ag₂O nanocomposite shows good photocatalytic activities towards the degradation of RhB and H₂O₂ production via the two-electron reduction of oxygen.

Dynamic charge transfer through Fermi level equilibration in the p-CuFe2O4/n-NiAl LDH interface towards photocatalytic application

The Ni Al LDH–CuFe₂O₄ p–n heterojunction, through vacuum energy level bending, inhibits electron hole recombination and enhances photocatalytic activity.

Functionalized Hybridization of 2D Nanomaterials

The discovery of graphene and subsequent verification of its unique properties have aroused great research interest to exploit diversified graphene-analogous 2D nanomaterials with fascinating physicochemical properties. Through either physical or chemical doping, linkage, adsorption, and hybridization with other functional species into or onto them, more novel/improved properties are readily created to extend/expand their functionalities and further achieve great performance. Here, various functionalized hybridizations by using different types of 2D nanomaterials are overviewed systematically with emphasis on their interaction formats (e.g., in-plane or inter plane), synergistic properties, and enhanced applications. As the most intensely investigated 2D materials in the post-graphene era, transition metal dichalcogenide nanosheets are comprehensively investigated through their element doping, physical/chemical functionalization, and nanohybridization. Meanwhile, representative hybrids with more types of nanosheets are also presented to understand their unique surface structures and address the special requirements for better applications. More excitingly, the van der Waals heterostructures of diverse 2D materials are specifically summarized to add more functionality or flexibility into 2D material systems. Finally, the current research status and faced challenges are discussed properly and several perspectives are elaborately given to accelerate the rational fabrication of varied and talented 2D hybrids.

Synthesis of Flower-Like g-C3N4/BiOBr and Enhancement of the Activity for the Degradation of Bisphenol A Under Visible Light Irradiation

The high recombination rates of photogenerated electron-holes greatly inhibit the catalytic activity of semiconductor photocatalysts. Herein, the heterojunctions of the flower-like g-C₃N₄/BiOBr composites were synthesized as photocatalysts by a simple hydrothermal process. The X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectrometer were utilized to characterize the sample's structure and light absorption properties. The results demonstrated that BiOBr-g-C₃N₄-4:1 showed excellent photocatalytic properties and 96.6% of bisphenol (BPA) was removed in 120 min with illumination of visible light due to its narrower band gap than that of pure BiOBr. BiOBr offer little electrons during the photocatalytic reaction. Moreover, the heterostructure between BiOBr and g-C₃N₄ facilitates the separation of photogenerated carriers. Excellent stability was exhibited after five cyclic degradation of methyl orange (MO) with the illumination of visible light. The active species trapping experiment indicated that superoxide radical anions (O2•-) and hole (h⁺) have a great effect on the reaction. A possible mechanism was proposed to explain the whole process of photocatalytic reaction.

Ultrafast Carrier Dynamics of the Exciton and Trion in MoS2 Monolayers Followed by Dissociation Dynamics in Au@MoS2 2D Heterointerfaces

Many-body states like excitons, biexcitons, and trions play an important role in optoelectronic and photovoltaic applications in 2D materials. Herein, we studied carrier dynamics of excitons and trions in monolayer MoS₂ deposited on a SiO₂/Si substrate, before and after Au NP deposition, using femtosecond transient absorption spectroscopy. Luminescence measurements confirm the presence of both an exciton and trion in MoS₂, which are drastically quenched after deposition of Au NPs, indicating electron transfer from photoexcited MoS₂ to Au. Ultrafast study reveals that photogenerated free carriers form excitons with a time scale of ∼500 fs and eventually turn into trions within ∼1.2 ps. Dissociation of excitons and trions has been observed in the presence of Au, with time scales of ∼600 fs and ∼3.7 ps, respectively. Understanding the formation and dissociation dynamics of the exciton and trion in monolayer MoS₂ is going to help immensely to design and develop many new 2D devices.

Extended π-conjugative n-p type homostructural graphitic carbon nitride for photodegradation and charge-storage applications

An n-p type homostructural metal-free graphitic carbon nitride (g-C₃N₄) semiconductor is designed and developed for pollutant abatement and energy storage application. The successful grafting of vibrio-like morphology-based g-C₃N₄ by 2, 5-Thiophenedicarboxylic acid (TDA) molecule and the development of amide-type linkage substantiated the prosperous uniting of g-C₃N₄ with organic TDA moiety is demonstrated. An extended π-conjugative TDA grafted g-C₃N₄ exhibited band gap tunability with broadband optical absorbance in the visible region. Mott-Schottky analysis exhibited the formation of n-p type homostructural property. As a result, obtained TDA grafted g-C₃N₄ has extended π-conjugation, high surface area and adequate separation of charge carriers. The change in the photocatalytic performance of grafted g-C₃N₄ is inspected for degradation of acid violet 7 (AV 7) dye under visible light irradiation. The charge storage capacity of grafted g-C₃N₄ was additionally assessed for supercapacitive behaviour. The charge capacitive studies of grafted g-C₃N₄ exhibited the areal capacitance of 163.17 mF cm⁻² and robust cyclic stability of 1000 cycles with capacity retention of 83%.

Wide spectral degradation of Norfloxacin by Ag@BiPO4/BiOBr/BiFeO3 nano-assembly: Elucidating the photocatalytic mechanism under different light sources

Metallic Ag deposited BiPO₄/BiOBr/BiFeO₃ ternary nano-hetero-structures were rationally designed and synthesized by a simple precipitation-wet impregnation-photo deposition method. The plasmonic junction possesses an excellent wide spectrum photo-response and makes best use of BiPO₄ which is otherwise a poor photocatalyst. Ag@BiPO₄/BiOBr/BiFeO₃ showed superior photocatalytic activity for degradation of norfloxacin (NFN) under visible, ultra-violet, near-infra-red and natural solar light. Especially catalyst APBF-3 (0.3 wt% Ag@BiPO₄/BiOBr/BiFeO₃) shows 98.1% degradation of NFN (20 mg/L) in 90 min under visible light and 99.1% in less than 45 min under UV exposure. Free radical scavenging experiments and electron spin resonance (ESR) results has been used for explanation of charge transfer, photocatalytic mechanism and role of radicals for binary, ternary and Ag deposited ternary junctions for UV and visible exposure. Metallic Ag in addition to its surface plasmon resonance helps in protection of high conduction band and valence band in the three semiconductors. A dual Z-scheme mechanism has been predicted by comparing with possibilities of double charge and vectorial charge transfer.

Bimetallic PtAu Alloy Nanoparticles-Integrated g-C3N4 Hybrid as an Efficient Photocatalyst for Water-to-Hydrogen Conversion

Herein, we report the synthesis of metal (Pt and Au) and metal alloy (PtAu) nanoparticles (NPs)-integrated graphitic carbon nitride (g-C₃N₄) hybrids using a facile solvothermal route for water-splitting application. The metal and metal alloy NPs with varying percentages of Pt and Au are found to be in the size range of 3-5 nm and uniformly distributed on the g-C₃N₄ sheets. The metal and metal alloy NPs act as cocatalyst for g-C₃N₄ to enhance the photocatalytic activity for hydrogen (H₂) generation through higher light absorption and efficient charge separation. The alloy composition plays an important role to maximize the photoactivity, with an optimized PtAu/g-C₃N₄ sample delivered 1009 μmol g^-1 h^-1 of H₂. The visible light assisted photocatalytic H₂ evolution is further investigated with the optimized PtAu alloy NPs-integrated g-C₃N₄. This study presents a robust, stable, and easily synthesizable PtAu/g-C₃N₄ hybrid material as a promising photocatalyst for H₂ generation through water splitting.

Template-free synthesis of salmon pink tube-shaped structure carbon nitride with enhanced visible light photocatalytic activity

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion. Herein, an effective strategy, hydrothermal-calcination, for synthesizing extremely active carbon nitride (salmon pink) from a low-cost precursor melamine, is reported. The salmon pink carbon nitride with tube-shaped structure significantly enhanced response to visible light, improved efficiency of charge separation and remarkably enhanced efficiency of methyl orange (MO) degradation than bulk g-C₃N₄ (light orange). The M-10-200-24-600 composite possessed the most wonderful ability towards MO degradation irradiated by visible light, which could achieve a highest degradation efficiency of 84% within 120 min. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar-energy conversion.

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion.

Fabrication of 2D heterojunction photocatalyst Co-g-C3N4/MoS2 with enhanced solar-light-driven photocatalytic activity

Co-Doping and formation of a 2D heterojunction with MoS₂ can significantly boost the photocatalytic activity of g-C₃N₄.

Nanoporous 2D semiconductors encapsulated by quantum-sized graphitic carbon nitride: tuning directional photoinduced charge transfer via nano-architecture modulation

A reversed charge transfer pathway in photoredox catalysis has been achieved by rational structure engineering through electrostatically integrating g-C₃N₄ quantum dots with nanoporous CdS nanosheets.

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles

A novel heterostructured nanocomposite UCNPs@SiO2@Ag/g-C3N4 was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C3N4. Its photocatalytic properties and photocatalytic mechanism were investigated. The as-synthesized photocatalyst with excellent improvement in the solar absorption and separation efficiency of photoinduced electron-hole pairs exhibited optimum solar-induced photocatalytic activity in dye degradation and hydrogen production. The experimental results showed that the rates of degradation of Rhodamine B (RhB) and hydrogen evolution were about 10 and 12 times higher than that of pristine g-C3N4, respectively. The excellent photocatalytic activity was attributed to the synergetic effect of upconversion nanoparticles (UCNPs) and Ag nanoparticles (NPs) on the modification of the photocatalytic properties of g-C3N4, resulting in a broad light response range for g-C3N4 as well as the fast separation and slow recombination of photoinduced electron-hole pairs. This study provides new insight into the fabrication of g-C3N4-based nanocomposite photocatalysts with high catalytic efficiency through the artful assembly of UCNPs, Ag NPs and g-C3N4 into a hetero-composite nanostructure. The prominent improvement in photocatalytic activity enables the potential application of g-C3N4 in the photocatalytic degradation of organic pollutants and hydrogen production utilizing solar energy.

High-Performance Photocatalytic Hydrogen Production and Degradation of Levofloxacin by Wide Spectrum-Responsive Ag/Fe3O4 Bridged SrTiO3/g-C3N4 Plasmonic Nanojunctions: Joint Effect of Ag and Fe3O4

Highly photoresponsive semiconductor photocatalysis for energy and environmental applications require judicious choice and optimization of semiconductor interfaces for wide spectral capabilities. This work aims at rational designing of highly active SrTiO₃/g-C₃N₄ junctions bridged with Ag/Fe₃O₄ nanoparticles for utilizing Z-scheme transfer and surface plasmon resonance effect of Ag augmented by iron oxide. The SrTiO₃/(Ag/Fe₃O₄)/g-C₃N₄ (SFC) catalyst was employed for photocatalytic hydrogen production and photodegradation of levofloxacin (LFC; 20 mg/L) under UV, visible, near infra-red, and natural solar light exhibiting high performance. Under visible light (<780 nm), SFC-3 sample (30 wt % g-C₃N₄ and 3% Ag/Fe₃O₄) shows a H₂ evolution of 2008 μmol g^-1 h^-1 which is ∼14 times that of bare g-C₃N₄. In addition, 99.3% removal of LFC was degraded in 90 min under visible light with retention of activity under sun. The inherent topological properties, complete, higher charge separation, and reduced recombination allowed this catalyst for a high photocatalytic response which was proved by UV-diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, and photocurrent response measurements. Scavenging experiments and electron spin resonance analysis reveal that the mechanism shifts from a dual charge transfer in case of binary junction to essential Z-scheme with incorporation of Ag/Fe₃O₄. Both ^•O₂^- and ^•OH are main active radicals in visible light, whereas ^•O₂^- majorly participate under UV. The synergistic effect of SrTiO₃, g-C₃N₄, and plasmon resonance of Ag/Fe₃O₄ not only improves light response and reduce recombination but also enhances the redox-ability of charge carriers. A H₂ production mechanism and LFC degradation pathway (degradation, defluorination, and hydrolysis) has been predicted. This work paves a way for development of photocatalysts working in practical conditions for pollution and energy issues.

Carbon Self-Doped Carbon Nitride Nanosheets with Enhanced Visible-Light Photocatalytic Hydrogen Production

In this study, we prepared carbon self-doped carbon nitride nanosheets through a glucose synergic co-condensation method. In the carbon self-doped structure, the N atoms in the triazine rings were substituted by C atoms, resulting in enhanced visible-light photocatalytic hydrogen production, which is three-times higher than that of bulk carbon nitride. The enhanced photocatalytic hydrogen production was attributed to the higher charge-carrier transfer rate and widened light absorption range of the carbon nitride nanosheets after carbon self-doping. Thus, this work highlights the importance of carbon self-doping for improving the photocatalytic performance. Meanwhile, it provides a feasible method for the preparation of carbon self-doped carbon nitride without destroying the 2D conjugated backbone structures.

Size-Tunable Natural Mineral-Molybdenite for Lithium-Ion Batteries Toward: Enhanced Storage Capacity and Quicken Ions Transferring

Restricted by the dissatisfied capacity of traditional materials, lithium-ion batteries (LIBs) still suffer from the low energy-density. The pursuing of natural electrode resources with high lithium-storage capability has triggered a plenty of activities. Through the hydro-refining process of raw molybdenite ore, containing crushing-grinding, flotation, exfoliation, and gradient centrifugation, 2D molybdenum disulfide (MoS2) with high purity is massively obtained. The effective tailoring process further induce various sizes (5, 2, 1 and 90 nm) of sheets, accompanying with the increasing of active sites and defects. Utilized as LIB anodes, size-tuning could serve crucial roles on the electrochemical properties. Among them, MoS2-1 μm delivers an initial charge capacity of 904 mAh g-1, reaching up to 1,337 mAh g-1 over 125 loops at 0.1 A g-1. Even at 5.0 A g-1, a considerable capacity of 682 mAh g-1 is remained. Detailedly analyzing kinetic origins reveals that size-controlling would bring about lowered charge transfer resistance and quicken ions diffusion. The work is anticipated to shed light on the effect of different MoS2 sheet sizes on Li-capacity ability and provides a promising strategy for the commercial-scale production of natural mineral as high-capacity anodes.

MnO2 Nanosheet-based Fluorescence Sensing Platform for Sensitive Detection of Endonuclease

A novel fluorescence sensing platform for ultrasensitive detection of S1 nuclease activity has been constructed based on MnO₂ nanosheets and FAM labeled single-stranded DNA (FAM-ssDNA). In this system, MnO₂ nanosheets were found to have different adsorbent ability toward ssDNA and mono- or oligonucleotide fragments. FAM-ssDNA could adsorb on MnO₂ nanosheets and resulted in significant fluorescence quenching through fluorescence resonance energy transfer (FRET), while mono- or oligonucleotide fragments could not adsorb on MnO₂ nanosheets and still retained strong fluorescence emission. With the addition of S1 nuclease, FAM-ssDNA was cleaved into mono- or oligonucleotide fragments, which were not able to adsorb on MnO₂ nanosheets and the fluorescence signal was never quenched. The different fluorescence intensity allowed for examination of S1 nuclease activity. The developed method can detect S1 nuclease activity in the range of 0 - 20 U mL^-1 with a detection limit of 0.05 U mL^-1. Benefits of the system include less time-consuming processes and more simple design compared to other endonuclease assays. Satisfactory performance for S1 nuclease in complex samples has been successfully demonstrated with the system. The developed assay could potentially provide a new platform in bioimaging and clinical diagnosis.

MoS2 Quantum Dots@TiO2 Nanotube Arrays: An Extended-Spectrum-Driven Photocatalyst for Solar Hydrogen Evolution

TiO₂ nanotube arrays (TiO₂ NTAs) decorated with molybdenum disulfide quantum dots (MoS₂ QDs) were synthesized by a facile electrodeposition method and used as a composite photocatalyst. MoS₂ QDs/TiO₂ NTAs showed enhanced photocatalytic activity compared with pristine TiO₂ NTAs for solar light-promoted H₂ evolution without adding any sacrificial agents or cocatalysts. The photocatalytic activity was influenced by the amount of MoS₂ QDs coated on TiO₂ NTAs. The optimal composition showed excellent photocatalytic activity, achieving H₂ evolution rates of 31.36, 5.29, and 1.67 μmol cm^-2  h^-1 corresponding to ultraviolet (UV, λ<420 nm), visible (Vis, λ≥420 nm), and near-infrared (NIR, λ>760) illumination, respectively. The improved photocatalytic activity was attributed to the decreased bandgap and the surface plasmonic properties of MoS₂ QDs/TiO₂ NTAs, which promoted electron-hole pair separation and the absorption capacity for Vis and NIR light. This study presents a facile approach for fabricating MoS₂ QDs/TiO₂ NTA heterostructures for efficient photocatalytic H₂ evolution, which will facilitate the development of designing new photocatalysts for environment and energy applications.

Synthesis and photocatalytic activity of mesoporous g-C3N4/MoS2 hybrid catalysts

The key to solving environmental and energy issues through photocatalytic technology requires highly efficient, stable and eco-friendly photocatalysts. Graphitic carbon nitride (g-C₃N₄) is one of the most promising candidates except for its limited photoactivity. In this work, a facile and scalable one-step method is developed to fabricate an efficient heterostructural g-C₃N₄ photocatalyst in situ coupled with MoS₂. The strong coupling effect between the MoS₂ nanosheets and g-C₃N₄ scaffold, numerous mesopores and enlarged specific surface area helped form an effective heterojunction. As such, the photocatalytic activity of the g-C₃N₄/MoS₂ is more than three times higher than that of the pure g-C₃N₄ in the degradation of RhB under visible light irradiation. Improvement of g-C₃N₄/MoS₂ photocatalytic performance is mainly ascribed to the effective suppression of the recombination of charge carriers.

Perovskite-structured CaTiO3 coupled with g-C3N4 as a heterojunction photocatalyst for organic pollutant degradation

A novel graphitic carbon nitride (g-C₃N₄)-CaTiO₃ (CTCN) organic-inorganic heterojunction photocatalyst was synthesized by a facile mixing method, resulting in the deposition of CaTiO₃ (CT) nanoflakes onto the surface of g-C₃N₄ nanosheets. The photocatalytic activity of the as-synthesized heterojunction (along with the controls) was evaluated by studying the degradation of an aqueous solution of rhodamine B (RhB) under UV, visible and natural sunlight irradiation. The CTCN heterojunction with 1:1 ratio of g-C₃N₄/CT showed the highest photocatalytic activity under sunlight irradiation and was also demonstrated to be effective for the degradation of a colorless, non-photosensitizing pollutant, bisphenol A (BPA). The superior photocatalytic performance of the CTCN heterojunction could be attributed to the appropriate band positions, close interfacial contact between the constituents and extended light absorption (both UV and visible region), all of which greatly facilitate the transfer of photogenerated charges across the heterojunction and inhibit their fast recombination. In addition, the two-dimensional (2D) morphology of g-C₃N₄nanosheets and CT nanoflakes provides enough reaction sites due to their larger surface area and enhances the overall photocatalytic activity. Furthermore, the active species trapping experiments validate the major role played by superoxide radicals (O₂^-•) in the degradation of pollutants. Based on scavenger studies and theoretically calculated band positions, a plausible mechanism for the photocatalytic degradation of pollutants has been proposed and discussed.

ZnO/MoX2 (X = S, Se) composites used for visible light photocatalysis

Hybrid density functional has been adopted to investigate the structural, electronic, and optical properties of ZnO/MoS₂ and ZnO/MoSe₂ composites as compared with the results of ZnO, MoS₂, and MoSe₂ monolayers. The results indicate that MoS₂ and MoSe₂ monolayers could contact with monolayer ZnO to form ZnO/MoS₂ and ZnO/MoSe₂ heterostructures through van der Waals (vdW) interactions. The calculated bandgap of ZnO/MoS₂ (ZnO/MoSe₂) is narrower than that of ZnO or MoS₂ (MoSe₂) monolayers, facilitating the shift of light absorption edges of the composites towards visible light in comparison with bare ZnO and MoX₂ monolayers. Through the application of strain, the ZnO/MoS₂ and ZnO/MoSe₂ composites which own suitable bandgaps, band edge positions, efficient charge separation, and good visible light absorption will be promising for visible light photocatalytic water splitting. These results provide a route for design and development of efficient ZnO/MoS₂ and ZnO/MoSe₂ photocatalysts for water splitting.

The ZnO/MoS₂ (ZnO/MoSe₂) heterostructures with the strain of –2% (+2%) have suitable bandgap and band edge position for hydrogen production via visible light photocatalytic water splitting.

Green synthesis of MoS2 nanoflowers for efficient degradation of methylene blue and crystal violet dyes under natural sun light conditions

Hydrothermally synthesized MoS₂ NFs have been employed as an efficient photocatalyst for the degradation of MB and CV dyes under sunlight.

In situ ion exchange synthesis of MoS2/g-C3N4 heterojunctions for highly efficient hydrogen production

Tight nanojunctions between g-C₃N₄ and MoS₂ were constructed, which facilitate the separation of photogenerated charge carriers.

Controllable synthesis of graphitic carbon nitride nanomaterials for solar energy conversion and environmental remediation: the road travelled and the way forward

This review discusses advances in the synthesis and design of g-C₃N₄-based nanomaterials and their various photocatalytic and photoredox applications.

Construction of 2D/2D layered g-C3N4/Bi12O17Cl2 hybrid material with matched energy band structure and its improved photocatalytic performance

A series of visible-light-induced 2D/2D layered g-C₃N₄/Bi₁₂O₁₇Cl₂ composite photocatalysts were successfully synthesized by a one step chemical precipitation method with g-C₃N₄, BiCl₃ and NaOH as the precursors at room temperature and characterized through XRD, FTIR, XPS, TEM, BET and UV-vis DRS measurements. The results of XRD, FTIR and XPS indicated that g-C₃N₄ has been introduced in the Bi₁₂O₁₇Cl₂ system. The TEM image demonstrated that there was strong surface-to-surface contact between 2D g-C₃N₄ layers and Bi₁₂O₁₇Cl₂ nanosheets, which contributed to a fast transfer of the interfacial electrons, leading to a high separation rate of photoinduced charge carriers in the g-C₃N₄/Bi₁₂O₁₇Cl₂ system. Rhodamine B was considered as the model pollutant to investigate the photocatalytic activity of the resultant samples. The g-C₃N₄/Bi₁₂O₁₇Cl₂ composite showed a clearly improved photocatalytic degradation capacity compared to bare g-C₃N₄ and Bi₁₂O₁₇Cl₂, which was ascribed to the interfacial contact between the 2D g-C₃N₄ layers and Bi₁₂O₁₇Cl₂ sheet with a matched energy band structure, promoting the photoinduced charges' efficient separation. Finally, combined with the results of the trapping experiment, ESR measurements and the band energy analysis, a reasonable photocatalytic mechanism over the 2D/2D layered g-C₃N₄/Bi₁₂O₁₇Cl₂ composite was proposed.

Surface-to-surface contact g-C₃N₄/Bi₁₂O₁₇Cl₂ hybrid material with a matched energy band structure could efficiently transfer photoinduced charges, improving the photocatalytic activity.

NGQD active sites as effective collectors of charge carriers for improving the photocatalytic performance of Z-scheme g-C3N4/Bi2WO6 heterojunctions

NGQDs as effective active sites and collectors of charge carriers in Z-scheme g-C₃N₄/Bi₂WO₆ heterojunctions.

Two-Dimensional Transition Metal Oxide and Chalcogenide-Based Photocatalysts

Two-dimensional (2D) transition metal oxide and chalcogenide (TMO&C)-based photocatalysts have recently attracted significant attention for addressing the current worldwide challenges of energy shortage and environmental pollution. The ultrahigh surface area and unconventional physiochemical, electronic and optical properties of 2D TMO&Cs have been demonstrated to facilitate photocatalytic applications. This review provides a concise overview of properties, synthesis methods and applications of 2D TMO&C-based photocatalysts. Particular attention is paid on the emerging strategies to improve the abilities of light harvesting and photoinduced charge separation for enhancing photocatalytic performances, which include elemental doping, surface functionalization as well as heterojunctions with semiconducting and conductive materials. The future opportunities regarding the research pathways of 2D TMO&C-based photocatalysts are also presented.