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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. Full article

The preparation of nickel oxide nanoparticles (NiO NPs) was carried out using an environmentally friendly and novel green synthetic strategy that included the use of Buxus wallichiana leaf extract as a reducing agent. Energy-dispersive X-ray (EDX), Fourier-transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA) techniques were used to characterize the resulting NiO NPs. At various concentrations, NiO NPs were tested for their percentage scavenging activity against the ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) free radical, with an IC50 value of 234.84 g/L. Furthermore, the bactericidal activity of NiO NPs was studied by the agar well diffusion method against two Gram-positive bacterial strains (B. licheniformis and B. subtilis) and two Gram-negative bacterial strains (E. coli and K. pneumoniae). Full article