A Novel Shift in the Absorbance Maxima of Methyl Orange with Calcination Temperature of Green Tin Dioxide Nanoparticle-Induced Photocatalytic Activity

Abstract

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.

Green Synthesis of NiO-SnO2 Nanocomposite and Effect of Calcination Temperature on Its Physicochemical Properties: Impact on the Photocatalytic Degradation of Methyl Orange

“…The photocatalytic reaction mechanism depends on the band gap energy of the catalyst and light energy or wavelength. Semiconductors are mostly used as catalysts as they sensitize the irradiations of redox process (light simulated) due to their electronic structure, which is characterized by a vacant conduction band and a filled valence band [ 15 ]. When a photon of equal or greater energy than the band gap energy of the semiconductor hits its surface, the valence band electrons are perturbed and are shifted towards the conduction band [ 13 , 14 , 15 ].…”

“…Semiconductors are mostly used as catalysts as they sensitize the irradiations of redox process (light simulated) due to their electronic structure, which is characterized by a vacant conduction band and a filled valence band [ 15 ]. When a photon of equal or greater energy than the band gap energy of the semiconductor hits its surface, the valence band electrons are perturbed and are shifted towards the conduction band [ 13 , 14 , 15 ]. The donor molecules are oxidized by the holes left in the valence band, which then react with the water molecules to generate hydroxyl radicals.…”

“…The reaction mixture was stirred and heated to 60 °C for 30 min, and sodium hydroxide solution was added to adjust the pH to 10. The prepared Ni(OH) 2 gel was aged for 6 h. In the second step, following an adjusted protocol previously published [ 15 , 19 ], 0.98 g of tin (II) chloride dehydrates were dissolved in 50 mL of distilled water, and 20 mL of the plant extract was added. The sodium hydroxide solution was added to adjust the pH to 10.…”

“…SEM is a high-resolution surface imaging method in which the incident electron beam scans across the sample surface and interacts with the sample to generate backscattered and secondary electrons that are used to create an image of the sample surface microarchitecture [ 13 , 14 , 15 , 16 ]. The morphology of the prepared SnO 2 NPs was analyzed via SEM model JSM 5910 (JEOL, Tokyo, Japan).…”

“…Different types of metal and metal oxide nanoparticles have been synthesized for various applications, such as catalysis, energy storage devices, dye-based solar cells, and biomedicines [ 2 , 7 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”