Tin(IV) oxide nanoparticles (SnO 2 NPs) have attracted great attention in various fields such as environmental remediation, sensing, catalysis, and lithium ion batteries. This led to an intense development of different synthetic pathways for production of SnO 2 NPs. At present, production of SnO 2 NPs depends largely on methods that involve toxic chemicals and harsh reaction conditions, which have been identified as a major drawback and potential threats to human health and the environment. Alternatively, green synthesis has gained popularity, as it is eco-friendly and cost-effective and generates minimal waste. This paper focuses on green biosynthesis of SnO 2 NPs using various plants and their different plant parts, including an evaluation of their potential applications. This work also emphasizes the effects of plant extracts and solvents on the size, morphology, and other properties of the synthesized SnO 2 NPs.
Cerium oxide (CeO2) can exhibit good photocatalytic and photoantibacterial activities. However, its light-harvesting property is rather limited due to its large band gap. In order to boost these properties, doping with metal ions can improve light absorption and charge mobility. In this report, CeO2 and palladium−doped CeO2 (Pd−CeO2) NPs were synthesized via the microwave-assisted synthesis method. The structural, optical, and morphological studies of CeO2 and Pd−CeO2 NPs were carried out using various techniques. Mixed phases of CeO2/Ce2O3 were observed in pure CeO2 (S−CeO2) and Pd−CeO2. However, the Ce2O3 phase gradually disappeared upon doping with a higher percentage of Pd. Almost spherical particles were observed with average sizes between 6 and 13 nm. It was found that the incorporation of Pd reduced the particle size. Moreover, band gap energies of S−CeO2 and Pd−CeO2 NPs were reduced from 2.56 to 2.27 eV, and the PL intensities were also quenched with more Pd doping. The shifts in the conduction band and valence band were found to cause the reduction in the band gap energies of S−CeO2 and Pd−CeO2 NPs. In the case of photocatalytic degradation of methylene blue, photoelectrochemical, and photoantibacterial activities, Pd−CeO2 NPs showed enhanced activities under visible light irradiation. Therefore, Pd−CeO2 NPs have been shown to be a visible-light active material.
As one of the most significant rare earth oxides, the redox ability of cerium oxide (CeO 2 ) has become the primary factor that has attracted considerable interest over the past decades. In the present study, irregular pentagonal CeO 2 (S-CeO 2 ) and different amounts of (1, 4, 8, and 12% Co) cobalt-doped CeO 2 nanoparticles (Co-CeO 2 NPs) with particle sizes between 4 and 13 nm were synthesized via the microwave-assisted synthesis method. The structural, optical, and morphological studies of S-CeO 2 and Co-CeO 2 were carried out using various techniques. The shifts in the conduction band and valence band were found to cause the reduction of the band gap energies of S-CeO 2 and Co-CeO 2 NPs. Moreover, the quenching of photoluminescence intensity with more Co doping showed the enhanced separation of charge carriers. The photocatalytic activities of S-CeO 2 and Co-CeO 2 NPs for methylene blue dye degradation, 4-nitrophenol reduction, and their photoantibacterial properties under visible-light irradiation were investigated. Findings showed that, due to the lower band gap energy (2.28 eV), more than 40% of both photocatalytic activities were observed for 12% Co-CeO 2 NPs. On the other hand, higher antibacterial impact in the presence of light shows that the Co doping has a considerable influence on the photoantibacterial response of Co-CeO 2 . Therefore, microwave-assisted synthesized CeO 2 and Co-CeO 2 NPs have shown potential in photocatalytic dye degradation, chemical reduction, and photoantibacterial activities.
The influence of cobalt doping in SnO 2 crystal lattice tailored the optical, structural, and surface properties of SnO 2 . Co 2+ was successfully doped in SnO 2 (Co-SnO 2 ) via green synthesis using Tradescantia spathacea aqueous leaf extract. Powder X-ray diffraction patterns of the synthesized nanoparticles showed a rutile structure with no impurities. As Co-doping was increased, the average crystallite size increased from 13.25 nm to 32.32 nm and BET results showed reduced surface area. The presence of organic compounds of the aqueous leaf extract was confirmed by Fourier-transform infrared spectroscopy. UV-visible diffuse reflectance spectroscopy showed a red shift suggesting a band gap reduction with Co-doping. The photoluminescence study showed a peak quenching with the increase in Co-doping. Spherical and smaller particles were observed by scanning electron microscopy. The density of states was proposed using X-ray photoelectron spectroscopy and UV-visible diffuse reflectance spectroscopy data. A novel antioxidant study of SnO 2 and Co-SnO 2 nanoparticles was done under visible light irradiation using 2,2-diphenyl-1-picrylhydrazyl free radicals and was compared to conventional antioxidant method in the dark. Photocatalytic 4nitrophenol conversion was also conducted in the dark and under visible light irradiation. The enhancement in the photoantioxidant activities and photocatalytic conversion of 4-nitrophenol to 4-nitrophenolate using SnO 2 and Co-SnO 2 was observed under visible light irradiation.Keywords SnO 2 . Tin(IV) oxide . Co-doped SnO 2 . Aqueous leaf extract . Tradescantia spathacea . Radical scavenging activity . 4-Nitrophenol
The ideal methods for the preparation of semiconductors should be reproducible and possess the ability to control the morphology of the particles with monodispersity yields. Apart from that, it is also crucial to synthesize a large quantity of desired materials with good control of size, shape, morphology, crystallinity, composition, and surface chemistry at a reasonably low production cost. Metal oxides and chalcogenides with various morphologies and crystal structures have been obtained using different anion metal precursors (and/or different sulfur sources for chalcogenides in particular) through typical synthesis methods. Generally, spherical particles are obtained as it is thermodynamically favorable. However, by changing the anion precursor salts, the morphology of a semiconductor is influenced. Therefore, precursors having different anions show some effects on the final forms of a semiconductor. This review compiled and discussed the effects of anions (NO3−, Cl−, SO42-, CH3COO−, CH(CH3)O−, etc.) and different sources of S2- on the morphology and crystal structure of selected metal oxides and chalcogenides respectively.
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