We report the photocatalytic activities of ZnO, Ag-doped ZnO, and Mn-doped ZnO nanoparticles (NPs). Ag-doped and Mn-doped ZnO samples were synthesized using a coprecipitation method and calcined at 600°C. XRD, SEM, EDX, and UV-vis spectroscopy techniques were employed for characterization of the synthesized samples. The photocatalytic activities of the samples were evaluated by measuring the photocatalytic decolorization of methyl violet with sunlight being the source of energy. XRD patterns of the samples confirmed the wurtzite structure without change which was indicative of the absence of Mn- and Ag-related secondary phases for the doped ZnO. The UV-vis spectra indicated the band gap energy of ZnO, Ag-doped ZnO, and Mn-doped ZnO to be 2.98, 2.80, and 2.64 eV, respectively. Photocatalytic decolorization of methyl violet for the synthesized samples was found to be favorable at a pH of 9.0, catalyst dose of 1 g/L, and initial dye concentration of 4.5 × 10−4 g/L. Mn-doped ZnO and Ag-doped ZnO photocatalytic decolorization efficiency was significantly higher than undoped ZnO. Incorporation of Mn and Ag enhanced the visible-light photocatalytic activity of ZnO; this could be due to the ability of these metals to increase the surface defects of ZnO which in turn shift their optical absorption towards the visible region.

In this study, a N-doped Cu2O/ZnO nanocomposite was prepared by a co-precipitation and thermal decomposition technique from CuCl2, 2H2O, ZnSO4, 7H2O and CO(NH2)2 as precursors. The as-synthesized nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared analysis (FT–IR) and an ultraviolet–visible (UV–Vis) reflectance spectrometer. From the XRD diffractogram of N-doped Cu2O/ZnO nanocomposite, cubic and hexagonal wurtzite crystal structures of Cu2O, and ZnO, respectively were identified. The UV-vis reflectance spectra illustrated that the absorption edge of N-doped Cu2O/ZnO nanocomposite is more extended to the longer wavelength than ZnO, Cu2O and Cu2O/ZnO nanomaterials. FT–IR bands confirmed the presence of ZnO, Cu2O, and nitrogen in the N-doped Cu2O/ZnO nanocomposite. Photocatalytic activity of the as-synthesized nanocomposite was tested for methyl red degradation using sunlight as an energy source by optimizing the concentration of the dye and amount of the catalyst loaded. The degradation efficiency was greater in N-doped Cu2O/ZnO nanocomposite as compared to ZnO, Cu2O and Cu2O/ZnO nanomaterials. This is due to the coupling of the semiconductors which increases the absorption and exploitation capability of solar light and increases the charge separation as well. Besides that, nitrogen doping can extend absorption of light to the visible region by decreasing the energy gap. Therefore, N-doped Cu2O/ZnO nanocomposite is a solar light-active photocatalyst which can be used in the degradation of organic pollutants.

This study was aimed to investigate the efficiency of locally available low-cost and eco-friendly activated agricultural biosorbents produced from corncob and sorghum husk for the removal of fluoride from aqueous solution using batch adsorption. The activated biosorbents were characterized using SEM, XRD and FTIR spectroscopy. Effects of particle size (0.063–1.0 mm), contact time (15–120 min), pH (2–12), dose (2–10 g), and initial concentration (0.5–5.0 mg/L) were investigated. The morphology analysis revealed that biosorbents showed the presence of a high binding capacity for fluoride adsorption. The maximum adsorption was attained; size of the adsorbent 0.063 mm, pH 7, contact time 60 min, and 6 g dose of the biosorbents. Moreover, the adsorption kinetics followed the pseudo-second-order model and the adsorption isotherms fitted well to the Langmuir model. Furthermore, a field study was conducted using real water sample collected from Semema, Tigray, Ethiopia, and maximum fluoride removal was observed to be 79.44% and 77.05% for the activated carbons of Corncob and Sorghum husk at optimum conditions. Therefore, this experimental finding indicated that activated carbon of Corncob and Sorghum husk can be used as efficient, cheap, and eco-friendly biosorbents for the removal of fluoride from drinking water at community level.