Bismuth sulfide micro flowers decorated nickel foam as a promising electrochemical sensor for quantitative analysis of melamine in bottled milk samples

Here, we demonstrate hydrothermally grown bismuth sulfide (Bi2S3) micro flowers decorated nickel foam (NF) for electrochemical detection of melamine in bottled milk samples. The orthorhombic phase of hydrothermally grown Bi2S3is confirmed by the detailed characterization of x-ray diffraction and its high surface area micro flowers-like morphology is investigated via field emission scanning electron microscope. Furthermore, the surface chemical oxidation state and binding energy of Bi2S3/NF micro flowers is analyzed by x-ray photoelectron spectroscopy studies. The sensor exhibits a wide linear range of detection from 10 ng l-1to 1 mg l-1and a superior sensitivity of 3.4 mA cm-2to melamine using differential pulse voltammetry technique, with a lower limit of detection (7.1 ng l-1). The as-fabricated sensor is highly selective against interfering species of p-phenylenediamine (PPDA), cyanuric acid (CA), aniline, ascorbic acid, glucose (Glu), and calcium ion (Ca2+). Real-time analysis done in milk by the standard addition method shows an excellent recovery percentage of ̴ 98%. The sensor's electrochemical mechanism studies reveal that the high surface area bismuth sulfide micro flowers surface interacts strongly with melamine molecules through hydrogen bonding and van der Waals forces, resulting in a significant change in the sensor's electrical properties while 3D skeletal Nickel foam as a substrate provides stability, enhances its catalytic activity by providing a more number /of active sites and facilitates rapid electron transfer. The work presented here confirms Bi2S3/NF as a high-performance electrode that can be used for the detection of other biomolecules used in clinical diagnosis and biomedical research.

A comparative study of photocatalytic activity of Na+-Ag+ ion-exchanged glass-ceramics with metallic Ag, semiconductor AgBr, and hybrid Ag-AgBr nanoparticles

Photocatalytic glass-ceramics doped with metallic Ag, semiconductor AgBr, and hybrid metal-semiconductor Ag-AgBr nanostructures were synthesized via low-temperature Na+-Ag+ ion exchange. The spectral features of the nanostructures in the silicate glass matrix as well as their photocatalytic performance were studied in detail. Glass-ceramics containing hybrid metal-semiconductor nanostructures were shown to possess one order of magnitude higher photocatalytic activity compared to their counterparts with metallic and semiconductor nanostructures. Hybrid metal-semiconductor nanostructures allow enhancement of the net density of photogenerated hot electrons.

Engineering of Solar Energy Harvesting Tb3+-Ion-Doped CdS Quantum Dot Glasses for Photodissociation of Hydrogen Sulfide

The photocatalytic properties of CdS quantum dots (Q-dots) and Tb3+-doped CdS Q-dots dispersed in a borosilicate glass matrix were investigated for the photodissociation of hydrogen sulfide (H2S) into hydrogen (H2) gas and elemental sulfur (S). The Q-dot-containing glass samples were fabricated using the conventional melt-quench method and isothermal annealing between 550 and 600 °C for 6 h for controlling the growth of CdS and Tb3+-ion-doped CdS Q-dots. The structure, electronic band gap, and spectroscopic properties of the Q-dots formed in the glass matrix after annealing were analyzed using Raman and UV-visible spectroscopies, X-ray powder diffraction, and transmission electron microscopy. With increasing annealing temperature, the average size range of the Q-dots increased, corresponding to the decrease of electronic band gap from 3.32 to 2.24 eV. For developing the model for photocatalytic energy exchange, the excited state lifetime and photoluminescence emission were investigated by exciting the CdS and Tb3+-doped CdS quantum states with a 450 nm source. The results from the photoluminescence and lifetime demonstrated that the Tb3+-CdS photodissociation energy exchange is more efficient from the excited Q-dot states compared to the CdS Q-dot glasses. Under natural sunlight, the hydrogen production experiment was conducted, and an increase of 26.2% in hydrogen evolution rate was observed from 0.02 wt % Tb3+-doped CdS (3867 μmol/h/0.5 g) heat-treated at 550 °C when compared to CdS Q-dot glass with a similar heat treatment temperature (3064 μmol/h/0.5 g). Furthermore, the photodegradation stability of 0.02 wt % Tb3+-CdS was analyzed by reusing the catalyst glass powders four times with little evidence of degradation.

MoS2-Based Nanocomposites for Photocatalytic Hydrogen Evolution and Carbon Dioxide Reduction

Photocatalysis is a facile and sustainable approach for energy conversion and environmental remediation by generating solar fuels from water splitting. Due to their two-dimensional (2D) layered structure and excellent physicochemical properties, molybdenum disulfide (MoS₂) has been effectively utilized in photocatalytic H₂ evolution reaction (HER) and CO₂ reduction. The photocatalytic efficiency of MoS₂ greatly depends on the active edge sites present in their layered structure. Modifications like reducing the layer numbers, creating defective structures, and adopting different morphologies produce more unsaturated S atoms as active edge sites. Hence, MoS₂ acts as a cocatalyst in nanocomposites/heterojunctions to facilitate the photogenerated electron transfer. This review highlights the role of MoS₂ as a cocatalyst for nanocomposites in H₂ evolution reaction and CO₂ reduction. The H₂ evolution activity has been described comprehensively as binary (with metal oxide, carbonaceous materials, metal sulfides, and metal-organic frameworks) and ternary composites of MoS₂. Photocatalytic CO₂ reduction is a more complex and challenging process that demands an efficient light-responsive semiconductor catalyst to tackle the thermodynamic and kinetic factors. Photocatalytic reduction of CO₂ using MoS₂ is an emerging topic and would be a cost-effective substitute for noble catalysts. Herein, we also exclusively envisioned the possibility of layered MoS₂ and its composites in this area. This review is expected to furnish an understanding of the diverse roles of MoS₂ in solar fuel generation, thus endorsing an interest in utilizing this unique layered structure to create nanostructures for future energy applications.

Defect-assisted photocatalytic activity of glass-embedded gallium oxide nanocrystals

The use of glassceramics in photocatalysis is an attractive option for the realization of smart optical fibers and self-cleaning windows. Here we present the photocatalytic activity of germanosilicate glasses embedding Ga₂O₃ nanocrystals prepared by batch melting and glass heat treatment. The powdered material is used for UV-assisted degradation of rhodamine in water. The kinetics show changes after repeated experiments. In the first cycle, the apparent rate is governed by a second-order reaction with a Gaussian-like shape, whereas the second cycle follows a first-order reaction. The modification appears to be correlated with perturbations in the defect population. Photoluminescence has been used to monitor the evolution of such defects. Kinetic data on photoreactions and defect formation have been modelled in a combined frame in which the defect concentration determines the photocatalytic activity. The results prove the photocatalytic ability of the studied glassceramics. Moreover, the general validity of the kinetic model can be of interest for other systems in which the photocatalytic response depends on photoreactive species concentration.

Fabrication of Durable Ordered Ta2O5 Nanotube Arrays Decorated with Bi2S3 Quantum Dots

One of the most important challenges in the fabrication of ordered tantalum pentaoxide (Ta₂O₅) nanotube arrays (NTs) via the electrochemical method is the formation of nanotubes that adhere well to the Ta substrate. In this paper, we propose a new protocol that allows tight-fitting Ta₂O₅ nanotubes to be obtained through the anodic oxidation of tantalum foil. Moreover, to enhance their activity in the photocatalytic reaction, in this study, they have been decorated by nontoxic bismuth sulfide (Bi₂S₃) quantum dots (QDs) via a simple successive ionic layer adsorption and reaction (SILAR) method. Transmission electron microscopy (TEM) analysis revealed that quantum dots with a size in the range of 6-11 nm were located both inside and on the external surfaces of the Ta₂O₅ NTs. The effect of the anodization time and annealing conditions, as well as the effect of cycle numbers in the SILAR method, on the surface properties and photoactivity of Ta₂O₅ nanotubes and Bi₂S₃/Ta₂O₅ composites have been investigated. The Ta₂O₅ nanotubes decorated with Bi₂S₃ QDs exhibit high photocatalytic activity in the toluene degradation reaction, i.e., 99% of toluene (C₀ = 200 ppm) was degraded after 5 min of UV-Vis irradiation. Therefore, the proposed anodic oxidation of tantalum (Ta) foil followed by SILAR decorating allows a photocatalytic surface, ready to use for pollutant degradation in the gas phase, to be obtained.

Sacrificial-template-free synthesis of core-shell C@Bi2S3 heterostructures for efficient supercapacitor and H2 production applications

Core-shell heterostructures have attracted considerable attention owing to their unique properties and broad range of applications in lithium ion batteries, supercapacitors, and catalysis. Conversely, the effective synthesis of Bi₂S₃ nanorod core@ amorphous carbon shell heterostructure remains an important challenge. In this study, C@Bi₂S₃ core-shell heterostructures with enhanced supercapacitor performance were synthesized via sacrificial- template-free one-pot-synthesis method. The highest specific capacities of the C@Bi₂S₃ core shell was 333.43 F g^-1 at a current density of 1 A g^-1. Core-shell-structured C@Bi₂S₃ exhibits 1.86 times higher photocatalytic H₂ production than the pristine Bi₂S₃ under simulated solar light irradiation. This core-shell feature of C@Bi₂S₃ provides efficient charge separation and transfer owing to the formed heterojunction and a short radial transfer path, thus efficiently diminishing the charge recombination; it also facilitates plenty of active sites for the hydrogen evolution reaction owing to its mesoporous nature. These outcomes will open opportunities for developing low-cost and noble-metal-free efficient electrode materials for water splitting and supercapacitor applications.

Hierarchical CdMoO4 nanowire–graphene composite for photocatalytic hydrogen generation under natural sunlight

Herein, a facile in situ solvothermal technique for the synthesis of a CdMoO₄/graphene composite photocatalyst for hydrogen generation under natural solar light.