Engineering Mn-Doped CdS Thin Films Through Chemical Bath Deposition for High-Performance Photoelectrochemical Water Splitting

Doping conventional materials with a second element is an exciting strategy for enhancing catalytic performance via electronic structure modifications. Herein, Mn-doped CdS thin films were successfully synthesized with the aid of the chemical bath deposition (CBD) by varying the pH value (8, 10, and 12) and the surfactant amount (20, 40, 60 mg). Different morphologies like nano-cubes, nanoflakes, nano-worms, and nanosheets were obtained under different deposition conditions. The optimized Mn-doped CdS synthesized at pH=8 exhibited better photoelectrochemical (PEC) performance for oxygen evolution reaction (OER) than pure CdS films, with a maximum photocurrent density of 300 μA/cm2 at an external potential of 0.5 V, under sunlight illumination. The observed performance is attributed to the successful Mn doping, porosity, high surface area, and nanosphere morphology.

Surface Engineering of Cu2O Photocathodes via Facile Graphene Oxide Decoration for Improved Photoelectrochemical Water Splitting

Copper oxide (Cu2O) has attracted significant interest as an efficient photocathode for photoelectrochemical (PEC) water splitting owing to its abundance, suitable band gap, and band-edge potential. Nevertheless, a high charge recombination rate restricts its practical photoconversion efficiency and reduces the PEC water-splitting performance. To address this challenge, we present the facile electrodeposition of graphene oxide (GO) on the Cu2O photocathode surface. To determine the effect of varying GO weight percentages on PEC performance, varying amounts of GO were deposited on the Cu2O photocathode surface. The optimally deposited GO-Cu2O photocathode exhibited a photocurrent density of -0.39 to -1.20 mA/cm2, which was three times that of a photocathode composed of pristine Cu2O. The surface decoration of Cu2O with GO reduced charge recombination and improved the PEC water-splitting performance. These composites can be utilized in strategies designed to address the challenges associated with low-efficiency Cu2O photocathodes. The physicochemical properties of the prepared samples were comprehensively characterized by field-emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Raman spectroscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy. We believe that this research will pave the way for developing efficient Cu2O-based photocathodes for PEC water splitting.

Thermal Effect on Photoelectrochemical Water Splitting Toward Highly Solar to Hydrogen Efficiency

Photoelectrochemical (PEC) hydrogen production is an emerging technology that uses renewable solar light aimed to establish a sustainable carbon-neutral society. The barriers to commercialization are low efficiency and high cost. To date, researchers have focused on materials and systems. However, recent studies have been conducted to utilize thermal effects in PEC hydrogen production. This Review provides a fresh perspective to utilize the thermal effects for PEC performance enhancement while delineating the underlying principles and equations associated with efficiency. The fundamentals of the thermal effect on the PEC system are summarized from various perspectives: kinetics, thermodynamics, and empirical equations. Based on this, materials are classified as plasmonic metals, quantum dot-based semiconductors, and photothermal organic materials, which have an inherent response to photothermal irradiation. Finally, the economic viability and challenges of these strategies for PEC are explained, which can pave the way for the future progress in the field.

Insights into the Fe3+ Doping Effects on the Structure and Electron Distribution of Cr2O3 Nanoparticles

Herein, we carefully investigated the Fe3+ doping effects on the structure and electron distribution of Cr2O3 nanoparticles using X-ray diffraction analysis (XRD), maximum entropy method (MEM), and density functional theory (DFT) calculations. We showed that increasing the Fe doping induces an enlargement in the axial ratio of c/a, which is associated with an anisotropic expansion of the unit cell. We found that as Fe3+ replaces Cr in the Cr2O3 lattice, it caused a higher interaction between the metal 3d states and the oxygen 2p states, which led to a slight increase in the Cr/Fe-O1 bond length followed by an opposite effect for the Cr/Fe-O2 bonds. Our results also suggest that the excitations characterize a well-localized bandgap region from occupied Cr d to unoccupied Fe d states. The Cr2O3 and Fe-doped Cr2O3 nanoparticles behave as Mott-Hubbard insulators due to their band gap being in the d-d gap, and Cr 3d orbitals dominate the conduction band. These findings suggest that the magnitude and the character of the electronic density near the O atom bonds in Cr2O3 nanoparticles are modulated by the Cr-Cr distances until its stabilization at the induced quasi-equilibrium of the Cr2O3 lattice when the Fe3+ doping values reaches the saturation level range.

Novel Nanoarchitectured Cu2Te as a Photocathodes for Photoelectrochemical Water Splitting Applications

Designing photocathodes with nanostructures has been considered a promising way to improve the photoelectrochemical (PEC) water splitting activity. Cu₂Te is one of the promising semiconducting materials for photoelectrochemical water splitting, the performance of Cu₂Te photocathodes remains poor. In this work, we report the preparation of Cu₂Te nanorods (NRs) and vertical nanosheets (NSs) assembled film on Cu foil through a vapor phase epitaxy (VPE) technique. The obtained nano architectures as photocathodes toward photoelectrochemical (PEC) performance was tested afterwards for the first time. Optimized Cu₂Te NRs and NSs photocathodes showed significant photocurrent density up to 0.53 mA cm^-2 and excellent stability under illumination. Electrochemical impedance spectroscopy and Mott-Schottky analysis were used to analyze in more detail the performance of Cu₂Te NRs and NSs photocathodes. From these analyses, we propose that Cu₂Te NRs and NSs photocathodes are potential candidate materials for use in solar water splitting.

Superlative photoelectrochemical properties of 3D MgCr-LDH nanoparticles influencing towards photoinduced water splitting reactions

In the present work, we report the synthesis of single system three-dimensional (3D) open porous structure of MgCr-LDH nanoparticles in a substrate-free path by using one-step formamide assisted hydrothermal reaction followed by visible light irradiation for significant photoelectrochemical (PEC) properties that manifest towards photocatalytic H₂ and O₂ production. The as-prepared nanostructured materials were characterized by various physico-chemical characterization techniques. Moreover, this unique synthetic approach produces 3D open porous network structure of MgCr-LDH nanoparticles, which were formed by stacking of numerous 2D nanosheets, for effective light harvestation, easy electronic channelization and unveil superlative PEC properties, including high current density (6.9 mA/cm²), small Tafel slope of 82 mV/decade, smallest arc of the Nyquist plot (59.1 Ω cm⁻²) and photostability of 6000 s for boosting water splitting activity. In addition, such perfectly self-stacked 2D nanosheets in 3D MgCr-LDH possess more surface active defect sites as enriched 50% oxygen vacancy resulting a good contact surface within the structure for effective light absorption along with easy electron and hole separation, which facilitates the adsorption of protons and intermediate for water oxidation. Additionally, the Cr³⁺ as dopant pull up the electrons from water oxidation intermediates, thereby displaying superior photocatalytic H₂ and O₂ production activity of 1315 μmol/h and 579 μmol/h, respectively. Therefore, the open 3D morphological aspects of MgCr-LDH nanoparticles with porous network structure and high surface area possess more surface defect sites for electron channelization and identified as distinct novel features of this kind of materials for triggering significant PEC properties, along with robustly enhance the photocatalytic water splitting performances.

Uplifting the charge carrier separation and migration in Co-doped CuBi2O4/TiO2 p-n heterojunction photocathode for enhanced photoelectrocatalytic water splitting

Here, cobalt-doped copper bismuth oxide (Co-CuBi₂O₄) was synthesized via a facile hydrothermal method for photoelectrocatalytic (PEC) hydrogen production. The results disclosed that the 5% Co-doped CuBi₂O₄ has better PEC activity which is ∼3 fold higher than pristine CuBi₂O₄. The doping of cobalt in CuBi₂O₄ improves the interfacial charge transfer at an electrode/electrolyte interface and reduces the recombination rate of photogenerated electron-hole pairs. This higher performed 5% Co-doped CuBi₂O₄ photocathode further modified with TiO₂-P25 to form a Co-CuBi₂O₄/TiO₂ p-n heterojunction. This Co-CuBi₂O₄/TiO₂ photocathode displayed a photocurrent density of 330 μA cm^-2 at +0.5 V vs. RHE which was ∼2 fold higher than Co-CuBi₂O₄. Because this p-n junction affords inner electric field in the space charge region that helps for further minimization of electron-hole recombination, which facilitate efficient charge separation and transport thereby enhance the PEC water reduction.

Phyto-fabricated Cr2O3 nanoparticle for multifunctional biomedical applications

Aim: The biosynthesis of chromium oxide nanoparticles (Cr₂O₃ NPs), using Hyphaene thebaica as a bioreductant, for assessment of their potential nanomedicinal applications. Materials & methods: Biosynthesized Cr₂O₃ NPs were characterized by x-ray diffraction, Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy, scanning and transmission electron microscopy, selected area electron diffraction, UV-Vis spectroscopy and ζ-potential measurement. In vitro assays were used to assess the biological properties of Cr₂O₃ NPs. Results: Nanoparticles with size approximately 25-38 nm were obtained with a characteristic Cr-O vibration at 417 cm^-1. A broad spectrum antimicrobial potential and antioxidant nature is reported. Slight inhibition of polio virus and biocompatibility at low doses was observed. Conclusion: We conclude a multifunctional nature of biogenic Cr₂O₃ NPs.

Bio-redox potential of Hyphaene thebaica in bio-fabrication of ultrafine maghemite phase iron oxide nanoparticles (Fe2O3 NPs) for therapeutic applications

Maghemite (Fe₂O₃-NPs) nanoparticles were synthesized by a convenient, green and cost effective method using aqueous fruit extracts of Hyphaene thebaica. Different techniques like FTIR, XRD, UV-Vis, Raman, HR-TEM, EDS. SAED, Zeta potential were used to establish the nature of Fe₂O₃-NPs, while the therapeutic properties were studied using different biological assays including antiviral, antibacterial, antifungal, antioxidant and enzyme inhibition assays. XRD pattern revealed sharp peaks and a crystalline nature of Fe₂O₃-NPs. HR-TEM revealed quasi-spherical and cuboidal morphologies, while the particle size in ~10 nm. FTIR indicated a sharp peak centered at ~444 cm^-1 which is the characteristic FeO band vibration. SAED pattern indicated the crystalline nature while EDS also confirmed the synthesis of Fe₂O₃ NPs. Zeta potential was obtained in different solvents and physiological buffers indicating highest value in water (-26.5 mV) and lowest in DMSO (-15.8 mV). Tested bacterial strains, Bacillus subtilis was found to be inhibited significantly. Aspergillus flavus appeared to be susceptible to all of the tested concentration of Fe₂O₃ NPs. Maximum 40.78% FRSA was obtained at 400 μg/mL. Cell culture based studies on RD cells and L20B cells indicated reduction in viability of cells with increase concentration of Fe₂O₃ NPs. Moderate inhibition of polio virus-1 and polio virus-2 was observed, after culturing the virus in the L20B cells. Excellent Protein Kinase (PK) inhibition was revealed. Hemolytic potential and cytotoxic potential was indicated to be dose dependent. In conclusion, the present report for the first time reports the synthesis of Fe₂O₃ NPs from H. thebaica fruits and reveals their biomedical potential including antiviral potential.