Background: Nickel stannate nanocomposites could be useful for removing organic and toxic water pollutants, such as methyl orange (MO). Aim: The synthesis of a nickel oxide–tin oxide nanocomposite (NiO-SnO₂ NC) via a facile and economically viable approach using a leaf extract from Ficus elastica for the photocatalytic degradation of MO. Methods: The phase composition, crystallinity, and purity were examined by X-ray diffraction (XRD). The particles’ morphology was studied using scanning electron microscopy (SEM). The elemental analysis and colored mapping were carried out via energy dispersive X-ray (EDX). The functional groups were identified by Fourier transform infrared spectroscopy (FTIR). UV–visible diffuse reflectance spectroscopy (UV–vis DRS) was used to study the optical properties such as the absorption edges and energy band gap, an important feature of semiconductors to determine photocatalytic applications. The photocatalytic activity of the NiO-SnO₂ NC was evaluated by monitoring the degradation of MO in aqueous solution under irradiation with full light spectrum. The effects of calcination temperature, pH, initial MO concentration, and catalyst dose were all assessed to understand and optimize the physicochemical and photocatalytic properties of NiO-SnO₂ NC. Results: NiO-SnO₂ NC was successfully synthesized via a biological route using F. elastica leaf extract. XRD showed rhombohedral NiO and tetragonal SnO₂ nanostructures and the amorphous nature of NiO-SnO₂ NC. Its degree of crystallinity, crystallite size, and stability increased with increased calcination temperature. SEM depicted significant morphological changes with elevating calcination temperatures, which are attributed to the phase conversion from amorphous to crystalline. The elemental analysis and colored mapping show the formation of highly pure NiO-SnO₂ NC. FTIR revealed a decrease in OH, and the ratio of oxygen vacancies at the surface of the NC can be explained by a loss of its hydrophilicity at increased temperatures. All the NC samples displayed significant absorption in the visible region, and a blue shift is seen and the energy band gap decreases when increasing the calcination temperatures due to the dehydration and formation of compacted large particles. NiO-SnO₂ NC degrades MO, and the photocatalytic performance decreased with increasing calcination temperature due to an increase in the crystallite size of the NC. The optimal conditions for the efficient NC-mediated photocatalysis of MO are 100 °C, 20 mg catalyst, 50 ppm MO, and pH 6. Conclusions: The auspicious performance of the NiO-SnO₂ NCs may open a new avenue for the development of semiconducting p–n heterojunction catalysts as promising structures for removing undesirable organic pollutants from the environment.

This paper comprises a comprehensive kinetic study for the adsorptive removal of As (V) from aqueous medium by mixed oxide (MO) of iron and silicon. The multi-linearity of the intraparticle diffusion model pointed towards the likelihood of both the pore and film diffusion. The Boyd model validated film diffusion to be the principal mechanism responsible for controlling the rate of the arsenate adsorption on MO. The negative entropy of activation (ΔS^#) suggested the adsorption mechanism to be associative in nature. The non-negative values of ΔG^# suggested the presence of an energy barrier to be surmounted for the reaction to occur.

Background: The photocatalytic degradation of toxic organic compounds has received great attention for the past several years. Dyes, such as methyl orange (MO), are one of the major pollutants which create environmental hazards in the hydrosphere, living organisms and human beings. During photocatalytic degradation, NPs are activated in the presence of UV–Vis radiation which in turn creates a redox environment in the system and behaves as a sensitizer for light-induced redox mechanisms. Tin oxide (SnO₂) is one of the prominent, but less investigated, nanomaterials compared to titanium oxide (TiO₂) and Zinc oxide (ZnO) nanoparticles (NPs). Methods: Herein, Buxus wallichiana (B. wallichiana) leaf extract was utilized as a reducing and capping agent for the biosynthesis of SnO₂ NPs. The effects of the calcination temperature on their photocatalytic, structure and surface properties were then examined. The degree of crystallinity and the crystallite size were determined through X-ray diffraction (XRD) analysis. The pore size and surface area were calculated by Burnett–Emmitt–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods based on nitrogen desorption data. Morphological changes were assessed by scanning electron microscopy (SEM). The optical behavior was analyzed through UV–Vis diffuse reflectance spectroscopy (DRS) data and the band gap subsequently calculated. The photocatalytic efficiency of SnO₂ NPs was evaluated by double beam UV–Vis spectrophotometry under the influence of initial MO concentration, catalyst dose and pH of MO solution. The surface functional moieties were identified using Fourier transform infrared (FTIR) spectroscopy. All the calcined SnO₂ NPs were used as photocatalysts for the mineralization of MO in aqueous media. Results: The degree of crystallinity and the crystallite size increased with the calcination temperature. The transmittance edge obtained for all the calcined SnO₂ NPs shows a maximum absorbance in the visible range (λ-max = 464 nm). Moving toward higher wavelengths, a sudden intense red shift (from 464 nm to 500 nm), attributed to the incorporation of a hydroxyl radical at the ortho-position in the benzene ring associated with the dimethylamine group of MO, was observed in the absorbance of the samples calcined up to 300 °C. The percentage degradation of MO was found to decrease with increasing calcination temperatures. The optimal photocatalytic activity toward MO (15 ppm) in a solution of pH = 6 was obtained with 15 mg SnO₂ NPs calcined at 100 °C. Conclusions: UV–Vis absorption spectroscopy demonstrates that the absorption spectra of MO are strongly modified by the calcination temperature. This work opens new avenues for the use of SnO₂ NPs as photocatalysts against the degradation of industrial effluents enriched with different dyes.

Water is a precious natural resource. Unfortunately, bodies of water become polluted by waste, such as untreated wastewater and detritus, along with oil spills, with minimum or no consideration for their limited capacity to renew themselves. Among these pollutants, dyes are harmful as they are persistent and not biodegradable in nature. The present study demonstrates the removal of crystal violet (CV), a toxic cationic dye, by using three systems: Peroxymonosulfate (PMS), UV-254 nm radiation and UV/P5MS. The effects of various parameters, such as the effects of the initial dose of crystal violet, initial concentration of PMS, pH, typical inorganic ions, etc., were also investigated. The effect of pH was investigated in the range of 1.92–12.07. Similarly, the effect of various anions such as NO₂^•−, HCO₃^•−, CO₃^•2−, SO₄^•2− and CH₃COO^•− was investigated for the degradation of target pollutants. The order of degradation of crystal violet was UV/PMS > PMS > UV with removal efficiencies of 97%, 76% and 42%, respectively, at reaction times of 60 min. The degradation of crystal violet was enhanced significantly at a pH range of 10.52–12.07. Electrical energy per order (EE/O) values for UV/PMS, PMS and UV were calculated to be 1.68, 3.62 and 48.96 KWh/m³/order, respectively. The addition of inorganic ions inhibited the removal of CV in the order of SO₄^•2− > NO₂^•− > HCO₃^•− > CO₃^•2− > CH₃COO^•−. Moreover, the kinetic studies on the degradation of CV by the UV-254 nm, PMS, and UV/PMS systems, were also carried out and found to follow pseudo-first-order kinetics. The study revealed that oxidation processes are most efficacious for the removal of organic dyes from wastewater.

(1) Background: In this investigation, a composite of MgO nanoparticles with Itsit biochar (MgO-IBC) has been used to remove arsenate from contaminated water. The reduced adsorption capacity of biochar (IBC), due to loss of functionalities under pyrolysis, is compensated for with the composite MgO-IBC. (2) Methods: Batch scale adsorption experiments were conducted by using MgO-IBC as an adsorbent for the decontamination of arsenate from water. Functional groups, elemental composition, surface morphology, and crystallinity of the adsorbent were investigated by using FTIR, EDX, SEM and XRD techniques. The effect of pH on arsenate adsorption by MgO-IBC was evaluated in the pH range of 2 to 8, whereas the temperature effect was investigated in the range of 303 K to 323 K. (3) Results: Both pH and temperature were found to significantly influence the overall adsorption efficiency of MgO-IBC for arsenate adsorption with lower pH and higher temperature being suitable for higher arsenate adsorption. A kinetics study of arsenate adsorption confirmed an equilibrium time of 240 min and a pseudo-second-order model well-explained the kinetic adsorption data, whereas the Langmuir model best fitted with the equilibrium arsenate adsorption data. The spontaneity and the chemisorptive nature of arsenate adsorption was confirmed by enthalpy, entropy, and activation energy. Comparison of adsorbents in the literature with the current study indicates that MgO-IBC composite has better adsorption capacity for arsenate adsorption than several previously explored adsorbents. (4) Conclusions: The higher adsorption capacity of MgO-IBC confirms its suitability and efficient utilization for the removal of arsenate from water.

Bergenia ciliata (B. ciliate) leaf extract was used as a capping and stabilizing agent to synthesize copper oxide nanoparticles (CuO NPs). The selection of B. ciliate is purely based on its rich phytochemical composition and less utilization in green chemistry. The X-ray diffraction (XRD) analysis showed that the CuO NPs were found to be highly crystalline, while the irregular morphology and other structural properties were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the average particle size was found to be 50.05 nm. Energy dispersive X-ray (EDX) spectroscopy was used to determine the percentage composition and purity, whereas Fourier transform infrared (FTIR) spectroscopy was utilized to examine the surface functional groups. CuO NPs were tested for their antibacterial properties against Gram-positive and Gram-negative bacteria, and the activity was found to increase with an increasing concentration of CuO NPs in the wells. The dose-dependent antioxidant potential is slightly higher than ascorbic acid.