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

A Stable Perovskite Sensitized Photonic Crystal P-N Junction with Enhanced Photoelectrochemical Hydrogen Production

The slow photon effect in inverse opal photonic crystals represents a promising approach to manipulate the interactions between light and matter through the design of material structures. This study introduces a novel ordered inverse opal photonic crystal (IOPC) sensitized with perovskite quantum dots (PQDs), demonstrating its efficacy for efficient visible-light-driven H2 generation via water splitting. The rational structural design contributes to enhanced light harvesting. The sensitization of the IOPC with PQDs improves optical response performance and enhances photocatalytic H2 generation under visible light irradiation compared to the IOPC alone. The designed photoanode exhibits a photocurrent density of 3.42 mA cm-2 at 1.23 V vs RHE. This work advances the rational design of visible light-responsive photocatalytic heterostructure materials based on wide band gap metal oxides for photoelectrochemical applications.

Optimizing the performance of Auy/Nix/TiO2NTs photoanodes for photoelectrochemical water splitting

Water splitting using photoelectrochemical (PEC) techniques is thought to be a potential method for creating green hydrogen as a sustainable energy source. How to create extremely effective electrode materials is a pressing concern in this area. In this work, a series of Nix/TiO2 anodized nanotubes (NTs) and Auy/Nix/TiO2NTs photoanodes were prepared by electrodeposition via cyclic voltammetry and UV-photoreduction, respectively. The photoanodes were characterized by several structural, morphological, and optical techniques and their performance in PEC water-splitting for oxygen evolution reaction (OER) under simulated solar light was investigated. The obtained results revealed the nanotubular structure of TiO2NTs was preserved after deposition of NiO and Au nanoparticles while the band gap energy was reduced allowing for effective utilization of solar light with lower charge recombination rate. The PEC performance was monitored and it was found that the photocurrent densities of Ni20/TiO2NTs and Au30/Ni20/TiO2NTs were 1.75-fold and 3.25-fold that of pristine TiO2NTs, respectively. It was confirmed that the performance of the photoanodes depends on the number of electrodeposition cycles and duration of photoreduction of gold salt solution. The observed enhanced OER activity of Au30/Ni20/TiO2NTs could be attributed to the synergism between the local surface plasmon resonance (LSPR) effect of nanometric gold which increased solar light harvesting and the p-n heterojunction formed at the NiO/TiO2 interface which led to better charge separation and transportation suggesting its potential application as an efficient and stable photoanode in PEC water splitting for H2 production.

Gold-Promoted Electrodeposition of Metal Sulfides on Silicon Nanowire Photocathodes To Enhance Solar-Driven Hydrogen Evolution

Constructing composite structures is the key to breaking the dilemma of slow reaction kinetics and easy oxidation on the surface of lightly doped p-type silicon nanowire (SiNW) array photocathodes. Electrodeposition is a convenient and fast technique to prepare composite photocathodes. However, the low conductivity of SiNWs limits the application of the electrodeposition technique in constructing composite structures. Herein, SiNWs were loaded with Au nanoparticles by chemical deposition to decrease the interfacial charge transfer resistance and increase active sites for the electrodeposition. Subsequently, co-catalysts CoS, MoS₂, and Ni₃S₂ with excellent hydrogen evolution activity were successfully composited by electrodeposition on the surface of SiNWs/Au. The obtained core-shell structures exhibited excellent photoelectrochemical hydrogen evolution activity, which was contributed by the plasma property of Au and the abundant hydrogen evolution active sites of the co-catalysts. This work provided a simple and efficient solution for the preparation of lightly doped SiNW-based composite structures by electrodeposition.

Quantum Dots, Passivation Layer and Cocatalysts for Enhanced Photoelectrochemical Hydrogen Production

Solar-driven photoelectrochemical (PEC) hydrogen production is one potential pathway to establish a carbon-neutral society. Nowadays, quantum dots (QDs)-sensitized semiconductors have emerged as promising materials for PEC hydrogen production due to their tunable bandgap by size or morphology control, displaying excellent optical and electrical properties. Nevertheless, they still suffer from anodic corrosion during long-term cycling, offering poor stability. This Review discussed advancements to improve long-term stability of QDs particularly in terms of cocatalysts and passivation layers. The working principle of PEC cells was reviewed, along with all important configurations adopted over recent years. The equations to assess PEC performance were also described. A greater emphasized was placed on QDs and incorporation of cocatalysts or passivation layers that could enhance the PEC performance by influencing the charge transfer and surface recombination processes.

Breaking the Limitation of Elevated Coulomb Interaction in Crystalline Carbon Nitride for Visible and Near-Infrared Light Photoactivity

Most near-infrared (NIR) light-responsive photocatalysts inevitably suffer from low charge separation due to the elevated Coulomb interaction between electrons and holes. Here, an n-type doping strategy of alkaline earth metal ions is proposed in crystalline K⁺ implanted polymeric carbon nitride (KCN) for visible and NIR photoactivity. The n-type doping significantly increases the electron densities and activates the n→π* electron transitions, producing NIR light absorption. In addition, the more localized valence band (VB) and the regulation of carrier effective mass and band decomposed charge density, as well as the improved conductivity by 1-2 orders of magnitude facilitate the charge transfer and separation. The proposed n-type doping strategy improves the carrier mobility and conductivity, activates the n→π* electron transitions for NIR light absorption, and breaks the limitation of poor charge separation caused by the elevated Coulomb interaction.

TiO2nanotubes-MoS2/PDA-LL-37 exhibits efficient anti-bacterial activity and facilitates new bone formation under near-infrared laser irradiation

Titanium dioxide (TiO₂), as one of the titanium (Ti)-based implants, holds a promise for a variety of anti-bacterial application in medical research. In the current study, a functional molybdenum disulfide (MoS₂)/polydopamine (PDA)-LL-37 coating on titanium dioxide (TiO₂) implant was prepared. Anodic oxidation and hydrothermal treatment was given to prepare TiO₂nanotubes-MoS₂/PDA-LL-37 (T-M/P-L). Thein vitroosteogenic effect of T-M/P-L was evaluated by measuring mesenchymal stem cell (MSC) adhesion, proliferation, alkaline phosphatase (ALP) activity, extracellular matrix (ECM) mineralization, collagen secretion and osteoblast-specific messenger RNAs (mRNAs) expression. The determination on the anti-bacterial ability of T-M/P-L was followed. Furthermore, the ability of T-M/P-L to promote bone formationin vivowas evaluated. Near-infrared (NIR) laser irradiation exposure enabled the T-M/P-L coating-endowed Ti substrates to hold effective anti-bacterial ability. T-M/P-L promoted the adhesion and proliferation of MSCs. In addition, an increase was witnessed regarding the ALP activity, collagen secretion and ECM mineralization, along with the expression of runt-related transcription factor 2, ALP and osteocalcin in the presence of T-M/P-L. Additionally, T-M/P-L could stimulate endothelial cells to secrete vascular endothelial growth factor (VEGF) and promote capillary-like tubule formation. Upon NIR laser irradiation exposure, T-M/P-L not only exhibited efficientin vivoanti-bacterial activity but also facilitated new bone formation. Collectively, T-M/P-L had enhanced anti-bacterial and osteogenic activity under NIR laser irradiation.

The role of sodium dodecyl sulfate mediated hydrothermal synthesis of MoS2 nanosheets for photocatalytic dye degradation and dye-sensitized solar cell application

The novel properties and exciting behavior of two-dimensional nanosheet-based materials have piqued the interest of research all over the world. In this study, bulk molybdenum disulfide (bulk MoS₂) and sodium dodecyl sulfate-mediated molybdenum disulfide nanosheets (MoS₂-SDS NS) were synthesized via a facile sonication and hydrothermal process. The findings from the characterization revealed that the addition of sodium dodecyl sulfate (SDS) surfactant reduces the crystal phase and changes the structural morphology of bulk MoS₂. Furthermore, the photocatalytic and photovoltaic performance of bulk MoS₂ and MoS₂-SDS NS were also investigated. The results show that by using methylene blue dye, the photocatalytic efficiency increased from 56.30% to 91.84% at 150 min under UV-Visible light irradiation, and the photo-conversion efficiency (PEC (%)) of the dye-sensitized solar cell increased from 1.47% to 3.81% for bulk MoS₂ and MoS₂-SDS NS, respectively. Finally, we discussed in-depth the effect of SDS surfactants on MoS₂, which can improve their photovoltaic and photocatalytic performance.

Synthesis and Photoluminescence Properties of MoS2/Graphene Heterostructure by Liquid-Phase Exfoliation

Here, we report the synthesis of MoS2/graphene heterostructure in single-stage, liquid-phase exfoliation using a 7:3 isopropyl alcohol/water mixture. Further, the synthesized heterostructure was characterized using UV-visible and micro-Raman spectroscopies, transmission electron microscopy (TEM), and dynamic light scattering (DLS) analysis. UV-visible and micro-Raman analyses confirmed that the synthesized heterostructure had mostly few-layered (two-to-four sheets) MoS2. The photophysical properties of the heterostructure were analyzed using steady-state and time-resolved luminescence techniques. Enhanced photoluminescence was observed in the case of the heterostructure probably due to an increase in the defect sites or reduction in the rate of nonradiative decay upon formation of the sandwiched heterostructure. Applications of this heterostructure for fluorescence live-cell imaging were carried out, and the heterostructure demonstrated a better luminescence contrast compared to its individual counterpart MoS2 in phosphate-buffered saline (PBS).

Nanodots Derived from Layered Materials: Synthesis and Applications

Layered 2D materials, such as graphene, transition metal dichalcogenides, transition metal oxides, black phosphorus, graphitic carbon nitride, hexagonal boron nitride, and MXenes, have attracted intensive attention over the past decades owing to their unique properties and wide applications in electronics, catalysis, energy storage, biomedicine, etc. Further reducing the lateral size of layered 2D materials down to less than 10 nm allows for preparing a new class of nanostructures, namely, nanodots derived from layered materials. Nanodots derived from layered materials not only can exhibit the intriguing properties of nanodots due to the size confinement originating from the ultrasmall size, but also can inherit some unique properties of ultrathin layered 2D materials, making them promising candidates in a wide range of applications, especially in biomedicine and catalysis. Here, a comprehensive summary on the materials categories, advantages, synthesis methods, and potential applications of these nanodots derived from layered materials is provided. Finally, personal insights about the challenges and future directions in this promising research field are also given.

SnS2/TiO2 Nanocomposites for Hydrogen Production and Photodegradation under Extended Solar Irradiation

Earth–abundant transition metal chalcogenide materials are of great research interest for energy production and environmental remediation, as they exhibit better photocatalytic activity due to their suitable electronic and optical properties. This study focuses on the photocatalytic activity of flower-like SnS2 nanoparticles (composed of nanosheet subunits) embedded in TiO2 synthesized by a facile hydrothermal method. The materials were characterized using different techniques, and their photocatalytic activity was assessed for hydrogen evolution reaction and the degradation of methylene blue. Among the catalysts studied, 10 wt. % of SnS2 loaded TiO2 nanocomposite shows an optimum hydrogen evolution rate of 195.55 µmolg−1, whereas 15 wt. % loading of SnS2 on TiO2 exhibits better performance against the degradation of methylene blue (MB) with the rate constant of 4.415 × 10−4 s−1 under solar simulated irradiation. The improved performance of these materials can be attributed to the effective photo-induced charge transfer and reduced recombination, which make these nanocomposite materials promising candidates for the development of high-performance next-generation photocatalyst materials. Further, scavenging experiments were carried out to confirm the reactive oxygen species (ROS) involved in the photocatalytic degradation. It can be observed that there was a 78% reduction in the rate of degradation when IPA was used as the scavenger, whereas around 95% reduction was attained while N2 was used as the scavenger. Notably, very low degradation (<5%) was attained when the dye alone was directly under solar irradiation. These results further validate that the •OH radical and the superoxide radicals can be acknowledged for the degradation mechanism of MB, and the enhancement of degradation efficiency may be due to the combined effect of in situ dye sensitization during the catalysis and the impregnation of low bandgap materials on TiO2.

Near-Infrared-Responsive Photocatalysts

Broadening the absorption of light to the near-infrared (NIR) region is important in photocatalysis to achieve efficient solar-to-fuel conversion. NIR-responsive photocatalysts that can utilize diffusive solar energy are attractive for alleviating the energy crisis and environmental pollution. Over the past few years, considerable progress on the component and structural design of NIR-responsive photocatalysts have been reported. This study aims to systematically summarize recent progress toward the material design and mechanism optimization of NIR-responsive photocatalysts in this area. Depending on the main strategies for harvesting NIR photons, NIR-responsive photocatalysts can be categorized as direct NIR-light photocatalysts, indirect NIR-light photocatalysts, and photothermal photocatalysts. Furthermore, the construction and application of different NIR-responsive photocatalytic systems are summarized. Conclusions and perspectives are presented to further explore the potential of NIR-responsive photocatalysts in this field.

Interfacial Charge Transport in 1D TiO2 Based Photoelectrodes for Photoelectrochemical Water Splitting

1D nanostructured photoelectrodes are promising for application as photoelectrochemical (PEC) devices for solar energy conversion into hydrogen (H₂ ) owing to the optical, structural, and electronic advantages. Titanium dioxide (TiO₂ ) is the most investigated candidate as a photoelectrode due to its good photostability, low production cost, and eco-friendliness. The obstacle for TiO₂ 's practical application is the inherent wide bandgap (UV-lights response), poor conductivity, and limited hole diffusion length. Here, a comprehensive review of the current research efforts toward the development of 1D TiO₂ based photoelectrodes for heterogeneous PEC water splitting is provided along with a discussion of nanoarchitectures and energy band engineering influences on interfacial charge transfer and separation of 1D TiO₂ composited with different dimensional photoactive materials. The key focus of this review is to understand the charge transfer processes at interfaces and the relationship between photogenerated charge separation and photoelectrochemical performance. It is anticipated that this review will afford enriched information on the rational designs of nanoarchitectures, doping, and heterojunction interfaces for 1D TiO₂ based photoelectrodes to achieve highly efficient solar energy conversion.

Facile synthesis and defect optimization of 2D-layered MoS2 on TiO2 heterostructure for industrial effluent, wastewater treatments

Current research is paying much attention to heterojunction nanostructures. Owing to its versatile characteristics such as stimulating morphology, affluent surface-oxygen-vacancies and chemical compositions for enhanced generation of reactive oxygen species. Herein, we report the hydrothermally synthesized TiO₂@MoS₂ heterojunction nanostructure for the effective production of photoinduced charge carriers to enhance the photocatalytic capability. XRD analysis illustrated the crystalline size of CTAB capped TiO₂, MoS₂@TiO₂ and L-Cysteine capped MoS₂@TiO₂ as 12.6, 11.7 and 10.2 nm, respectively. The bandgap of the samples analyzed by UV–Visible spectroscopy are 3.57, 3.66 and 3.94 eV. PL spectra of anatase phase titania shows the peaks present at and above 400 nm are ascribed to the defects in the crystalline structure in the form of oxygen vacancies. HRTEM reveals the existence of hexagonal layered MoS₂ formation on the spherical shaped TiO₂ nanoparticles at the interface. X-ray photoelectron spectroscopy recommends the chemical interactions between MoS₂ and TiO_2, specifically, oxygen vacancies. In addition, the electrochemical impedance spectroscopy studies observed that L-MT sample performed low charge transfer resistance (336.7 Ω cm²) that promotes the migration of electrons and interfacial charge separation. The photocatalytic performance is evaluated by quantifying the rate of Congo red dye degradation under visible light irradiation, and the decomposition efficiency was found to be 97%. The electron trapping recombination and plausible photocatalytic mechanism are also explored, and the reported work could be an excellent complement for industrial wastewater treatment.

Sunlight-Operated TiO2-Based Photocatalysts

Photo-catalysis is a research field with broad applications in terms of potential technological applications related to energy production and managing, environmental protection, and chemical synthesis fields. A global goal, common to all of these fields, is to generate photo-catalytic materials able to use a renewable energy source such as the sun. As most active photocatalysts such as titanium oxides are essentially UV absorbers, they need to be upgraded in order to achieve the fruitful use of the whole solar spectrum, from UV to infrared wavelengths. A lot of different strategies have been pursued to reach this goal. Here, we selected representative examples of the most successful ones. We mainly highlighted doping and composite systems as those with higher potential in this quest. For each of these two approaches, we highlight the different possibilities explored in the literature. For doping of the main photocatalysts, we consider the use of metal and non-metals oriented to modify the band gap energy as well as to create specific localized electronic states. We also described selected cases of using up-conversion doping cations. For composite systems, we described the use of binary and ternary systems. In addition to a main photo-catalyst, these systems contain low band gap, up-conversion or plasmonic semiconductors, plasmonic and non-plasmonic metals and polymers.

The fabrication of an MoS2 QD-AuNP modified screen-printed electrode for the improved electrochemical detection of cefixime

Herein, we report a voltammetric method for the nanomolar detection of cefixime, a third-generation antibiotic. The determination of cefixime is validated on a glassy carbon electrode (GCE) as well as on a screen-printed carbon electrode (SPCE). In the present study, we have reported a facile "one step simple hydrothermal synthesis" of MoS2 quantum dots and with the oxidation of aurochloric acid for the further formation of an MoS2 QD-AuNP composite. The as-synthesized nanocomposite was characterized via UV-Vis spectroscopy, FTIR spectroscopy, XRD, TEM and EDX techniques, and further applied in the modification of working electrodes, showing excellent electroactivity. The sensing of cefixime was done via cyclic and differential pulse voltammetry techniques. The presence of the only anodic peak in the voltammogram reveals the irreversible oxidation of cefixime in the potential range of about 1.3 ± 0.1 V vs. Ag/AgCl. The study was also performed at different scan rates, which indicate a diffusion-controlled mechanism. The proposed cefixime sensor showed a linear response in the concentration range of 0.33-90.82 μM (at S/N = 3) with a limit of detection (LOD) of 3.9-4.5 nm. The electrochemical sensitivity is calculated as 8.63 μA μM-1 cm-2 and 7.07 μA μM-1 cm-2 in buffer and pharmaceutical formulation (commercially available cefixime tablet), respectively. The effects of several interferents were also investigated. The proposed sensor is effectively used for estimating cefixime in phosphate buffer and the commercially available cefixime tablets with no cross-reactivity or matrix effects and shows a promising prospect for real applications.

Defect Control in the Synthesis of 2 D MoS2 Nanosheets: Polysulfide Trapping in Composite Sulfur Cathodes for Li-S Batteries

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS₂ materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS₂ nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS₂ additive, the relationship between synthetically induced defects in 2 D MoS₂ materials and resultant electrochemistry was elucidated and described.

Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting

Clean water and the increased use of renewable energy are considered to be two of the main goals in the effort to achieve a sustainable living environment. The fulfillment of these goals may include the use of solar-driven photocatalytic processes that are found to be quite effective in water purification, as well as hydrogen generation. H2 production by water splitting and photocatalytic degradation of organic pollutants in water both rely on the formation of electron/hole (e-/h+) pairs at a semiconducting material upon its excitation by light with sufficient photon energy. Most of the photocatalytic studies involve the use of TiO2 and well-suited model compounds, either as sacrificial agents or pollutants. However, the wider application of this technology requires the harvesting of a broader spectrum of solar irradiation and the suppression of the recombination of photogenerated charge carriers. These limitations can be overcome by the use of different strategies, among which the focus is put on the creation of heterojunctions with another narrow bandgap semiconductor, which can provide high response in the visible light region. In this review paper, we report the most recent advances in the application of TiO2 based heterojunction (semiconductor-semiconductor) composites for photocatalytic water treatment and water splitting. This review article is subdivided into two major parts, namely Photocatalytic water treatment and Photocatalytic water splitting, to give a thorough examination of all achieved progress. The first part provides an overview on photocatalytic degradation mechanism principles, followed by the most recent applications for photocatalytic degradation and mineralization of contaminants of emerging concern (CEC), such as pharmaceuticals and pesticides with a critical insight into removal mechanism, while the second part focuses on fabrication of TiO2-based heterojunctions with carbon-based materials, transition metal oxides, transition metal chalcogenides, and multiple composites that were made of three or more semiconductor materials for photocatalytic water splitting.

Water dissolvable MoS2 quantum dots/PVA film as an active material for destructible memristors

This report demonstrates the fabrication of a flexible, water-soluble MoS₂ QDs/PVA (polyvinyl alcohol) film sandwiched between Cu electrodes as a resistive memory.

CoS2/TiO2 Nanocomposites for Hydrogen Production under UV Irradiation

Transition metal chalcogenides have intensively focused on photocatalytic hydrogen production for a decade due to their stronger edge and the quantum confinement effect. This work mainly focuses on synthesis and hydrogen production efficiencies of cobalt disulfide (CoS2)-embedded TiO2 nanocomposites. Materials are synthesized by using a hydrothermal approach and the hydrogen production efficiencies of pristine CoS2, TiO2 nanoparticles and CoS2/TiO2 nanocomposites are compared under UV irradiation. A higher amount of hydrogen production (2.55 mmol g-1) is obtained with 10 wt.% CoS2/TiO2 nanocomposite than pristineTiO2 nanoparticles, whereas no hydrogen production was observed with pristine CoS2 nanoparticles. This result unveils that the metal dichalcogenide-CoS2 acts as an effective co-catalyst and nanocrystalline TiO2 serves as an active site by effectively separating the photogenerated electron-hole pair. This study lays down a new approach for developing transition metal dichalcogenide materials with significant bandgaps that can effectively harness solar energy for hydrogen production.

MoS2 quantum dots chemically modified with porphyrin for solid-state broadband optical limiters

MoS₂ quantum dots (MQDs) with unique electronic and optical properties are promising broadband nonlinear optical (NLO) materials for ultrafast optical applications. It would be very interesting and challenging to functionalize MQDs with another hotspot optoelectronically active molecule "porphyrin". Herein, by treating MQDs with tetraphenylporphyrin (TPP) diazonium salts, we synthesized a novel nanohybrid material, MQD-TPP, in which TPP was covalently functionalized to the surface of MQDs via a C-S linkage. To explore its solid-state broadband NLO application, the MQD-TPP nanohybrid was encapsulated into a poly(methyl methacrylate) (PMMA) matrix for the open-aperture Z-scan measurements at 532 and 1064 nm. In contrast to MQDs/PMMA and TPP/PMMA, the MQD-TPP/PMMA film exhibited superior nonlinear optical and optical limiting responses with the largest nonlinear coefficients (β_eff) and the lowest optical limiting (OL) thresholds of about 1059.17 cm GW^-1 and 1.62 J cm^-2 at 532 nm and 831.13 cm GW^-1 and 1.97 J cm^-2 at 1064 nm, respectively.

MoS2 nanotubes loaded with TiO2 nanoparticles for enhanced electrocatalytic hydrogen evolution

Efficient and stable non-precious metal catalysts composed of earth-abundant elements are crucial to the hydrogen evolution reaction (HER) in high-energy conversion efficiency. Herein, TiO₂/MoS₂-NTs catalyst, in which the MoS₂ nanotubes were loaded with TiO₂ nanoparticles, have been synthesized via a facile solvothermal and hydrothermal method. The as-prepared TiO₂/MoS₂-NTs electrocatalyst demonstrated enhanced electrocatalytic hydrogen evolution performance compared with MoS₂-NTs. Electrochemical measurements reveal the overpotential and Tafel slope of as-prepared TiO₂/MoS₂-NTs are −0.21 V and 42 mV dec⁻¹. The HER improvement is proposed to be attributed to the increased edge sites results from the interfaces and synergic effect between TiO₂ nanoparticles and MoS₂ nanotubes.

Polarization curves of TiO₂, MoS₂-NTs and TiO₂/MoS₂-NTs in 0.5 M H₂SO₄ solution.

A Critical Review on Enhancement of Photocatalytic Hydrogen Production by Molybdenum Disulfide: From Growth to Interfacial Activities

Ultrathin 2D molybdenum disulfide (MoS₂ ), which is the flagship of 2D transition-metal dichalcogenide nanomaterials, has drawn much attention in the last few years. 2D MoS₂ has been banked as an alternative to platinum for highly active hydrogen evolution reaction because of its low cost, high surface-to-volume ratio, and abundant active sites. However, when MoS₂ is used directly as a photocatalyst, contrary to public expectation, it still performs poorly due to lateral size, high recombination ratio of excitons, and low optical cross section. Besides, simply compositing MoS₂ as a cocatalyst with other semiconductors cannot satisfy the practical application, which stimulates the pursual of a comprehensive insight into recent advances in synthesis, properties, and enhanced hydrogen production of MoS₂ . Therefore, in this Review, emphasis is given to synthetic methods, phase transitions, tunable optical properties, and interfacial engineering of 2D MoS₂ . Abundant ways of band edge tuning, structural modification, and phase transition are addressed, which can generate the neoteric photocatalytic systems. Finally, the main challenges and opportunities with respect to MoS₂ being a cocatalyst and coherent light-matter interaction of MoS₂ in photocatalytic systems are proposed.

Tailoring the Porosity in Iron Phosphosulfide Nanosheets to Improve the Performance of Photocatalytic Hydrogen Evolution

Metal sulfide photocatalysts are typically required during water splitting to produce hydrogen. However, the rapid recombination of photogenerated electron-hole pairs in these highly unstable photocatalysts has restricted hydrogen production to small-scale batch reactions. In this work, porous transition-metal thiophosphites were used to enable continuous long-term hydrogen production through photocatalysis. A wide bandgap (2.04 eV) was essential for generating hydrogen at a rate of 305.6 μmol h^-1  g^-1 , 180 % faster than nonporous FePS₃ nanosheets. More importantly, the high in-plane stiffness of these approximately 7 nm thick porous FePS₃ nanosheets ensured structural stability during 56 h of continuous photocatalysis reactions. The reaction results with D₂ O instead of H₂ O indicated that hydrogen mainly came from H₂ O. Furthermore, a sacrificial reagent (triethylamine) was photodegraded into diethylamine and acetaldehyde through a monoelectronic oxidation process, as indicated by HPLC and LC-MS. This synthesis strategy reported for FePS₃ porous nanosheets paves a new pathway for designing other dianion-based inorganic nanocrystals for hydrogen energy applications.

Electrocatalytic Performance of Titania Nanotube Arrays Coated with MoS2 by ALD toward the Hydrogen Evolution Reaction

The electrochemical splitting of water provides an elegant way to store renewable energy, but it is limited by the cost of the noble metals used as catalysts. Among the catalysts used for the reduction of water to hydrogen, MoS₂ has been identified as one of the most promising materials as it can be engineered to provide not only a large surface area but also an abundance of unsaturated and reactive coordination sites. Using Mo[NMe₂]₄ and H₂S as precursors, a desired thickness of amorphous MoS₂ can be deposited on TiO₂ nanotubes by atomic layer deposition. The identity and structure of the MoS₂ film are confirmed by spectroscopic ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The electrocatalytic performance of MoS₂ is quantified as it depends on the tube length and the MoS₂ layer thickness through voltammetry, steady-state chronoamperometry, and electrochemical impedance spectroscopy. The best sample reaches 10 mA/cm² current density at 189 mV overpotential in 0.5 M H₂SO₄. All of the various geometries of our nanostructured electrodes reach an electrocatalytic proficiency comparable with the state-of-the-art MoS₂ electrodes, and the dependence of performance parameters on geometry suggests that the system can even be improved further.

Two dimensional MoS2 meets porphyrins via intercalation to enhance the electrocatalytic activity toward hydrogen evolution

Two-dimensional MoS₂ meets porphyrin molecules to form unique 1T' phase intercalated complexes via a one-step procedure of hydrothermal reactions. The resultant Mn-porphyrin-MoS₂ exhibits excellent electrocatalytic activity toward the hydrogen evolution reaction, with a Tafel slope of 35 mV dec^-1 and 10 mA cm^-2 at an overpotential of 0.125 V. Spin-polarized density functional theory calculations confirmed that the intercalation of Mn-porphyrin into 1T'-MoS₂ is quite favourable due to strong charge transfer from Mn metals. Their outstanding catalytic performance could be ascribed to the high electron concentration as well as the low activation barrier of the Heyrovsky reaction.