MoS2/CdS Heterostructure for Enhanced Photoelectrochemical Performance under Visible Light

Effect of CdS loading on the properties and photocatalytic activity of MoS2 nanosheets

Molybdenum sulfide (MoS2) and modified MoS2 with different percentages of CdS (10%, 30%, and 50% CdS@MoS2) were successfully synthesized and characterized. The photocatalytic performance of the MoS2 and CdS@MoS2 was evaluated by degrading brilliant green (BG), methylene blue (MB), and rhodamine B (RhB) dyes under visible light irradiation. Amongst the synthesized photocatalysts, 50% CdS@MoS2 exhibited the highest photocatalytic activity, degrading 97.6%, 90.3%, and 75.5% of BG, MB, and RhB dyes, respectively within 5 h. The active species involved in the degradation processes were investigated. All trapping agents inhibited BG and MB degradation to a similar extent, indicating that all of the probed active species play an important role in the degradation of BG and MB. In contrast, h+ and O2•- were found to be the main reactive species in the photocatalytic RhB degradation. A potential mechanism for the photocatalytic degradation of dyes using CdS@MoS2 has been proposed. This work highlights the potential of CdS@MoS2 as a photocatalyst for more efficient water remediation applications.

MXene-based novel nanocomposites doped SnO2 for boosting the performance of perovskite solar cells

Since being first published in 2018, the use of two-dimensional MXene in solar cells has attracted significant interest. This study presents, for the first time, the synthesis of an efficient hybrid electrocatalyst in the form of a nanocomposite (MXene/CoS)-SnO2 designed to function as a high-performance electron transfer layer (ETL). The study can be divided into three distinct parts. The first part involves the synthesis of single-layer Ti3C2Tx MXene nanosheets, followed by the preparation of a CoS solution. Subsequently, in the second part, the fabrication of MXene/CoS heterostructure nanocomposites is carried out, and a comprehensive characterization is conducted to evaluate the physical, structural, and optical properties. In the third part, the attention is on the crucial characterizations of the novel nanocomposite-electron transport layer (ETL) solution, significantly contributing to the evolution of perovskite solar cells. Upon optimising the composition, an exceptional power conversion efficiency of more than 17.69% is attained from 13.81% of the control devices with fill factor (FF), short-circuit current density (Jsc), and open-circuit voltage (Voc) were 66.51%, 20.74 mA/cm2, and 1.282 V. Therefore, this PCE is 21.93% higher than the control device. The groundbreaking MXene/CoS (2 mg mL-1) strategy reported in this research represents a promising and innovative avenue for the realization of highly efficient perovskite solar cells.

Development of MoS2-ZnO heterostructures: an efficient bifunctional catalyst for the detection of glucose and degradation of toxic organic dyes

The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform for the remediation of environmental as well as health issues.

Spontaneous Hetero-attachment of Single-Component Colloidal Precursors for the Synthesis of Asymmetric Au-Ag2X (X = S, Se) Heterodimers

Finding simple, easily controlled, and flexible synthetic routes for the preparation of ternary and hybrid nanostructured semiconductors is always highly desirable, especially to fulfill the requirements for mass production to enable application to many fields such as optoelectronics, thermoelectricity, and catalysis. Moreover, understanding the underlying reaction mechanisms is equally important, offering a starting point for its extrapolation from one system to another. In this work, we developed a new and more straightforward colloidal synthetic way to form hybrid Au-Ag₂X (X = S, Se) nanoparticles under mild conditions through the reaction of Au and Ag₂X nanostructured precursors in solution. At the solid-solid interface between metallic domains and the binary chalcogenide domains, a small fraction of a ternary AuAg₃X₂ phase was observed to have grown as a consequence of a solid-state electrochemical reaction, as confirmed by computational studies. Thus, the formation of stable ternary phases drives the selective hetero-attachment of Au and Ag₂X nanoparticles in solution, consolidates the interface between their domains, and stabilizes the whole hybrid Au-Ag₂X systems.

Novel BiVO4-nanosheet-supported MoS2-nanoflake-heterostructure with synergistic enhanced photocatalytic removal of tetracycline under visible light irradiation

This paper describes a simple in-situ hydrothermal technique for the production of BiVO₄/MoS₂ binary nanocomposites as visible-light-driven catalysts. The as-prepared samples were analyzed by structural, morphological, compositional, optical, surface area, and photocurrent analyses. The lattice fringe spaces at 0.304 nm and 0.612 nm were indexed to the (112) and (002) crystal planes of BiVO₄ and MoS₂, respectively. Antibacterial photocatalytic capabilities were assessed using tetracycline (TC). Consequently, it was observed that the BiVO₄/MoS₂ nanocomposite demonstrated improved antibacterial removal ability compared with the pristine samples. The BiVO₄/MoS₂ nanocomposite exhibited 97.46% removal of TC compared with the pure BiVO₄ (43.76%) and MoS₂ (35.28%) samples within 90 min. Thus, the photocatalytic performance was observed to follow the given order: BiVO₄/MoS₂ nanocomposite > BiVO₄ > MoS₂. The removal of TC after 90 min of irradiation was approximately 97.46%, 96.62%, 95.59%, and 94.45% after the 1st, 2nd, 3rd, and 4th cycles, respectively. Thus, the recycling tests revealed the stability of the photocatalyst, which exhibited a TC removal efficiency of 94.45% without distinct decay, even after the 4th cycle. According to the trapping results, hydroxyl radicals and holes were the key species and demonstrated a greater influence on the photocatalytic performance than superoxide radicals. The increased activity of the BiVO₄/MoS₂ nanocomposite may be attributed to its large surface area and tunable bandgap, which accelerate the charge-transport characteristics of the photocatalytic system. This insight and synergetic effects can provide a new approach for the development of novel heterostructure photocatalysts.

Probing into crystallography and morphology properties of MoS2 nanoflowers synthesized via temperature dependent hydrothermal method

This paper reports the formation of flower-like hierarchical molybdenum disulfide (MoS2) nanoparticles following a simple one-step hydrothermal process with varying temperatures (200 °C and 220 °C). The as-synthesized particles were examined crystallographically by X-ray diffraction (XRD) method which revealed the formation of hexagonal MoS2 (2H-MoS2) and that the crystallite size of the particles increased with increasing hydrothermal temperature. Surface morphological characteristics of the particles were investigated by a field emission scanning electron microscope (FESEM) and interesting details were revealed such as the rounded 3D flower-like microstructure of the MoS2 particles and the petals of the flowers were composed of platelets built up by stacked-up MoS2 nanosheets. With the increase in hydrothermal temperature, the interlayer spacing of stacked layers of intense (002) plane is slightly decreased although the crystallinity of the material is improved. Both diameter and thickness of the nanoflowers and the nanoplatelets increased twice with increasing the temperatures. A visual crystallographic perspective was presented through simulation of 3D wireframe unit cell associated with the individual lattice planes as observed in the XRD pattern of the samples. In addition, a plausible growth mechanism is proposed for the formation of the obtained MoS2 nanoflowers on the basis of experimental observations and analysis.

Exfoliation of 2D materials by saponin in water: Aerogel adsorption / photodegradation organic dye

The biggest challenge for the paint industry is to clean the contaminated waste dye solution before it released into the water or to reuse it to create new paint and to protect the water from environmental pollution. Here in this work, exfoliating layered transition metal dichalcogenide materials prepare to the exfoliated 2D materials thin sheets in water with the assistance of natural saponin. Then, the three-dimensional (3D) MoS₂-aerogel composite was synthesized by using greenway exfoliated two-dimensional (2D) MoS₂ thin sheets to form MoS₂-aerogel composite. The prepared 3D MoS₂-aerogel composite demonstrates excellent 94% methylene blue (MB) dye adsorption ability over 5 min. Moreover, the adsorbed MB of the MoS₂-aerogel shows ∼80% dye degradation activity in the presence of visible light. Therefore, these synthesized 3D MoS₂-aerogel composite could be an excellent candidate for photocatalytic applications in the future.

Editorial: Special Issue on Photocatalytic Nanocomposite Materials (PNMs)

This Special Issue titled “Photocatalytic Nanocomposite Materials” (PNMs) is devoted to the research into new-generation PNMs, particularly for the processes of solar radiation energy conversion with its focus lying on the physicochemical principles of creating new materials with purposeful properties for their specific applications [...]

Photoactive Heterostructures: How They Are Made and Explored

In our review we consider the results on the development and exploration of heterostructured photoactive materials with major attention focused on what are the better ways to form this type of materials and how to explore them correctly. Regardless of what type of heterostructure, metal–semiconductor or semiconductor–semiconductor, is formed, its functionality strongly depends on the quality of heterojunction. In turn, it depends on the selection of the heterostructure components (their chemical and physical properties) and on the proper choice of the synthesis method. Several examples of the different approaches such as in situ and ex situ, bottom-up and top-down, are reviewed. At the same time, even if the synthesis of heterostructured photoactive materials seems to be successful, strong experimental physical evidence demonstrating true heterojunction formation are required. A possibility for obtaining such evidence using different physical techniques is discussed. Particularly, it is demonstrated that the ability of optical spectroscopy to study heterostructured materials is in fact very limited. At the same time, such experimental techniques as high-resolution transmission electron microscopy (HRTEM) and electrophysical methods (work function measurements and impedance spectroscopy) present a true signature of heterojunction formation. Therefore, whatever the purpose of heterostructure formation and studies is, the application of HRTEM and electrophysical methods is necessary to confirm that formation of the heterojunction was successful.

CuS nanoparticles decorated MoS2 sheets as an efficient nanozyme for selective detection and photocatalytic degradation of hydroquinone in water

Cost effective and efficient CuS–MoS₂ nanocomposite with enhanced peroxidase enzyme mimetics and photocatalytic activity was synthesized by simple hydrothermal method and successfully utilized for sensing and detection of toxic hydroquinone molecules in aqueous medium.

Visible Light-Driven Photoelectrocatalytic Water Splitting Using Z-Scheme Ag-Decorated MoS2/RGO/NiWO4 Heterostructure

Herein, we have successfully constructed a solid-state Z-scheme photosystem with enhanced light absorption capacity by combining the optoelectrical properties of AgNPs with those of the MoS2/RGO/NiWO4 (Ag-MRGON) heterostructure. The Ag-MRGON Z-scheme system demonstrates improved photo-electrochemical (PEC) water-splitting performance in terms of applied bias photon-to-current conversion efficiency (ABPE), which is 0.52%, and 17.3- and 4.3-times better than those of pristine MoS2 and MoS2/NiWO4 photoanodes, respectively. The application of AgNPs as an optical property enhancer and RGO as an electron mediator improved the photocurrent density of Ag-MRGON to 3.5 mA/cm2 and suppressed the charge recombination to attain the photostability of ∼2 h. Moreover, the photocurrent onset potential of the Ag-MRGON heterojunction (i.e., 0.61 VRHE) is cathodically shifted compared to those of NiWO4 (0.83 VRHE), MoS2 (0.80 VRHE), and MoS2/NiWO4 heterojunction (0.73 VRHE). The improved PEC water-splitting performance in terms of ABPE, photocurrent density, and onset potential is attributed to the facilitated charge transfer through the RGO mediator, the plasmonic effect of AgNPs, and the proper energy band alignments with the thermodynamic potentials of hydrogen and oxygen evolution.

Interpreting interfacial semiconductor-liquid capacitive characteristics impacted by surface states: a theoretical and experimental study of CuGaS2

Semiconductor-liquid interfaces are essential to the operation of many energy devices. Crucially, the operational characteristics of such devices are dependent upon both the flat band potential and doping concentration present in their solid-state semiconducting region. Traditionally, capacitive "linear" Mott-Schottky plots have often been utilized to extract these two parameters. However, significant concentrations of surface states within semiconductor-liquid junctions can give rise to strong non-linearities that prevent an effective linearity-based analysis. In this work, we detail a theoretical approach for estimating both the doping concentration and flat band potential from the capacitive characteristics of semiconductor-liquid junctions heavily impacted upon by surface states. Our theoretical approach is applied to CuGaS2 immersed in an aqueous electrolyte, for which excellent convergent values of the doping concentration and flat band potential are obtained across a wide range of impedance measurement frequencies. The results suggest a marked improvement over a linearity-based approach that could assist the analysis of many types of semiconductor-liquid junctions subject to high concentrations of surface states.

Carrier Dynamics and Transfer across the CdS/MoS2 Interface upon Optical Excitation

Carrier dynamics across the interface of heterostructures have important technological, photovoltaic, and catalytic implications. Using first-principles time-dependent density functional theory, we have systematically investigated the charge transfer of excited carriers from CdS to MoS₂ and found that two interdependent mechanisms are responsible for the transfer, one slow and one fast. While the slower process may be attributed to typical electron-phonon coupling, the interfacial dipole resulting from this transfer enables a fast secondary process involving a level crossing of the excited carrier state in CdS with receiving states in MoS₂. An analysis based on the interfacial binding energy reveals that the Cd-terminated (001) interface is by far the most energetically favorable, which in addition to its calculated fast resonant electron transfer suggests it is a good candidate to explain the experimentally observed charge transfer between CdS and MoS₂.

Core-Shell Nanostructures of Graphene-Wrapped CdS Nanoparticles and TiO2 (CdS@G@TiO2): The Role of Graphene in Enhanced Photocatalytic H2 Generation

Aiming to achieve enhanced photocatalytic activity and stability toward the generation of H2 from water, we have synthesized noble metal-free core-shell nanoparticles of graphene (G)-wrapped CdS and TiO2 (CdS@G@TiO2) by a facile hydrothermal method. The interlayer thickness of G between the CdS core and TiO2 shell is optimized by varying the amount of graphene quantum dots (GQD) during the synthesis procedure. The most optimized sample, i.e., CdS@50G@TiO2 generated 1510 µmole g−1 h−1 of H2 (apparent quantum efficiency (AQE) = 5.78%) from water under simulated solar light with air mass 1.5 global (AM 1.5G) condition which is ~2.7 times and ~2.2 time superior to pure TiO2 and pure CdS respectively, along with a stable generation of H2 during 40 h of continuous operation. The increased photocatalytic activity and stability of the CdS@50G@TiO2 sample are attributed to the enhanced visible light absorption and efficient charge separation and transfer between the CdS and TiO2 due to incorporation of graphene between the CdS core and TiO2 shell, which was also confirmed by UV-vis, photoelectrochemical and valence band XPS measurements.

NiSe2/CdS composite nanoflakes photocatalyst with enhanced activity under visible light

Degrading organic pollutants using a photocatalyst under visible light is one of the effective ways to solve the increasingly serious environmental pollution problem. In this work, we have loaded a small amount of NiSe₂ nanoflakes on the surface of CdS using a simple and low-cost solvothermal synthesis method. The samples were characterized with detailed X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), photocurrent, photoluminescence spectrometer (PL), photocatalytic properties, etc. The results show that a 2 mol% load of NiSe₂ increases the rate of degradation of Rhodamine B (RhB) to more than twice the original rate (0.01000 min⁻¹versus 0.00478 min⁻¹). Meanwhile, the sample has excellent stability. The improved photocatalytic properties can be attributed to the face-to-face contact between the nanoflakes, accelerated separation and transfer of photon-generated carriers. This work provides a suitable co-catalyst that can be used to optimize the performance of other photocatalytic materials.

The obtained NiSe₂/CdS composite nanoflakes exhibit greatly enhanced photocatalytic properties due to the accelerated separation of photon-generated carriers.