Exfoliated Molybdenum Disulfide-Wrapped CdS Nanoparticles as a Nano-Heterojunction for Photo-Electrochemical Water Splitting

Ternary nanostructure of CdS-rGO-Ag for enhanced photoelectrochemical application

In the present study, we have synthesized the ternary nanostructure of CdS-rGO-Ag by using the solvothermal method for the enhanced photocatalytic as well as electrocatalytic activity of the material. The optical properties of the prepared samples were characterized by using UV-visible spectroscopy and photoluminescence (PL) spectroscopy. A decline in the energy gap of CdS-rGO-Ag nanostructure to 1.90 ± 0.05 from 2.40 ± 0.08 eV (CdS) is observed and may be attributed due to the rGO-Ag-induced creation of trap states in between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of CdS. The observed significant PL quenching also confirms the inclusion of trap states in the prepared nanostructure CdS-rGO-Ag, suggesting efficient photoactivity. The enhanced photocatalytic activity of CdS-rGO-Ag for methylene blue (MB) dye degradation supports the photocatalytic activity of prepared nanostructures. Furthermore, the photoelectrochemical catalytic activity of the CdS-rGO-Ag catalyst investigated by using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) depicts the improved current density, lowering of overpotential. The decrement in charge transfer resistance and enhancement in photocurrent density under light illumination indicates the better photoelectrochemical performance of CdS-rGO-Ag.

Study of CdS/CdS Nanoparticles Thin Films Deposited by Soft Chemistry for Optoelectronic Applications

Chalcogenides semiconductors are currently being studied as active layers in the development of electronic devices in the field of applied technology. In the present paper, cadmium sulfide (CdS) thin films containing nanoparticles of the same material as the active layer were produced and analyzed for their application in fabricating optoelectronic devices. CdS thin films and CdS nanoparticles were obtained via soft chemistry at low temperatures. The CdS thin film was deposited via chemical bath deposition (CBD); the CdS nanoparticles were synthesized via the precipitation method. The construction of a homojunction was completed by incorporating CdS nanoparticles on CdS thin films deposited via CBD. CdS nanoparticles were deposited using the spin coating technique, and the effect of thermal annealing on the deposited films was investigated. In the modified thin films with nanoparticles, a transmittance of about 70% and a band gap between 2.12 eV and 2.35 eV were obtained. The two characteristic phonons of the CdS were observed via Raman spectroscopy, and the CdS thin films/CdS nanoparticles showed a hexagonal and cubic crystalline structure with average crystallite size of 21.3-28.4 nm, where hexagonal is the most stable for optoelectronic applications, with roughness less than 5 nm, indicating that CdS is relatively smooth, uniform and highly compact. In addition, the characteristic curves of current-voltage for as-deposited and annealed thin films showed that the metal-CdS with the CdS nanoparticle interface exhibits ohmic behavior.

Casein-Coated Molybdenum Disulfide Nanosheets Augment the Bioactivity of Alginate Microspheres for Orthopedic Applications

Defects and disorders of the bone due to disease, trauma, or abnormalities substantially affect a person's life quality. Research in bone tissue engineering is motivated to address these clinical needs. The present study demonstrates casein-mediated liquid exfoliation of molybdenum disulfide (MoS₂) and its coupling with alginate to create microspheres to engineer bone graft substitutes. Casein-exfoliated nano-MoS₂ was chemically characterized using different analytical techniques. The UV-visible spectrum of nano-MoS₂-2 displayed strong absorption peaks at 610 and 668 nm. In addition, the XPS spectra confirmed the presence of the molybdenum (Mo, 3d), sulfur (S, 2p), carbon (C, 1s), oxygen (O, 1s), and nitrogen (N, 1s) elements. The exfoliated MoS₂ nanosheets were biocompatible with the MG-63, MC3T3-E1, and C2C12 cells at 250 μg/mL concentration. Further, microspheres were created using alginate, and they were characterized physiochemically and biologically. Stereomicroscopic images showed that the microspheres were spherical with an average diameter of 1 ± 0.2 mm. The dispersion of MoS₂ in the alginate matrix was uniform. The alginate-MoS₂ microspheres promoted apatite formation in the SBF (simulated body fluid) solution. Moreover, the alginate-MoS₂ was biocompatible with MG-63 cells and promoted cell proliferation. Higher alkaline phosphatase activity and mineralization were observed on the alginate-MoS₂ with the MG-63 cells. Hence, the developed alginate-MoS₂ microsphere could be a potential candidate for a bone graft substitute.

Experimental Realization and Computational Investigations of B2S2 as a New 2D Material with Potential Applications

A new two-dimensional material B₂S₂ has been successfully synthesized for the first time and validated using first-principles calculations, with fundamental properties analyzed in detail. B₂S₂ has a similar structure as transition-metal dichalcogenides (TMDs) such as MoS₂, and the experimentally prepared free-standing B₂S₂ nanosheets show a uniform height profile lower than 1 nm. A thickness-modulated and unique oxidation-level dependent band gap of B₂S₂ is revealed by theoretical calculations, and vibration signatures are determined to offer a practical scheme for the characterization of B₂S₂. It is shown that the functionalized B₂S₂ is able to provide favorable sites for lithium adsorption with low diffusion barriers, and the prepared B₂S₂ shows a wide band photoluminescence response. These findings offer a feasible new and lighter member for the TMD-like 2D material family with potential for various aspects of applications, such as an anode material for Li-ion batteries and electronic and optoelectronic devices.

Strategies to improve electrocatalytic performance of MoS2-based catalysts for hydrogen evolution reactions

Electrocatalytic hydrogen evolution reactions (HERs) are a key process for hydrogen production for clean energy applications. HERs have unique advantages in terms of energy efficiency and product separation compared to other methods. Molybdenum disulfide (MoS₂) has attracted extensive attention as a potential HER catalyst because of its high electrocatalytic activity. However, the HER performance of MoS₂ needs to be improved to make it competitive with conventional Pt-based catalysts. Herein, we summarize three typical strategies for promoting the HER performance, i.e., defect engineering, heterostructure formation, and heteroatom doping. We also summarize the computational density functional theory (DFT) methods used to obtain insight that can guide the construction of MoS₂-based materials. Additionally, the challenges and prospects of MoS₂-based catalysts for the HER have also been discussed.

In this review, we summarize three general classes of effective strategies to enhance the HER activity of MoS₂ and DFT calculation methods, i.e. defect engineering, heterostructure formation, and heteroatom doping.

Activating a TiO2/BiVO4 Film for Photoelectrochemical Water Splitting by Constructing a Heterojunction Interface with a Uniform Crystal Plane Orientation

The construction of a heterojunction has been considered one of the most effective strategies to improve the photoelectrochemical (PEC) performance of photoanodes; however, most researchers only focus on the design and preparation of a novel and efficient heterojunction photoelectrode, and the investigation on the effect of the heterojunction interface structure on PEC performance is ignored. In this work, a TiO₂/BiVO₄ photoanode with a uniform crystal plane orientation in the heterojunction interface (TiO₂-110/BiVO₄-202) was prepared by an in situ transformation method. We found that the PEC activity of the TiO₂/BiVO₄ photoanode can be activated by constructing such a heterojunction interface. Compared with a TiO₂/BiVO₄ photoanode with a random crystal plane orientation prepared by a simple soaking-calcining method (S-TiO₂/BiVO₄, 0.04 mA/cm² at 1.23 V_RHE), the TiO₂/BiVO₄ photoanode prepared by the in situ transformation method (I-TiO₂/BiVO₄) exhibits a significantly better PEC performance, and the photocurrent density of I-TiO₂/BiVO₄ is about 2.2 mA/cm² at 1.23 V_RHE under visible light irradiation without a cocatalyst. This is mainly attributed to the fact that I-TiO₂/BiVO₄ has a faster electron transfer rate in the heterojunction interface according to the results of PEC analysis. Furthermore, density functional theory (DFT) calculations show that the BiVO₄-202 surface has a higher Fermi energy level, thereby expediting the photogenerated carrier transport in the heterojunction interface. This work corroborates and strengthens the view that the heterojunction interface structure has a significant effect on the PEC performance.