One of the key features of a nano catalyst for photocatalysis is the band gap, because, through its analysis, the potential of the catalyst can be determined. In this investigation, the impact on the band gap of different catalysts made by the sol–gel method, compared with TiO2 P25 Sigma-Aldrich, showing the effect of using gold or ruthenium as a metal supported on TiO2, with two different dosage percentages of 1 and 3 percent, was analysed. Additionally, two oxidation states of the catalyst, the reduced form and the oxidized form of the metal, were used to see the effect on the band gap. The experiments show that the gold addition has a higher beneficial effect on the band gap for the UV region (ultra violet region), and the ruthenium addition has a higher beneficial effect for the UV/visible region. The preferred oxidation state for the band gap was the oxidized state. The characterisation of the catalyst provided an insight into the relation between the band gap and the catalyst itself.
Zinc nitrate (ZnON) and zinc acetate (ZnOA) were used as precursors for the synthesis of zinc oxide (ZnO) nanoparticles by the sol–gel method. The ZnO powder was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy, X-ray diffraction (UV–Vis DRS), Fourier transform infrared spectroscopy (FTIR), physisorption of nitrogen, and X-ray photoelectron spectroscopy (XPS). On the other hand, the photocatalytic activity of the samples was tested in the degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4-Dichlorophenol (2,4-DCP) under UV-light irradiation. The ZnON and ZnOA showed polycrystalline irregular structures and rod-like morphology with mean sizes of 40 and 99 nm, respectively. The precursor type influenced the bandgap, crystallite size, surface area, total pore volume, and pore diameter. The XPS results showed high contents of C and N in the ZnO samples, and as a consequence, the solids present remarkable differences in the C/N, O/C, and O/Zn atomic ratios, which significantly influenced the physicochemical characteristics. The ZnON and ZnOA exhibit photocatalytic properties against 2,4-D (74.7 and 90.9%, respectively) and 2,4-DCP (78.4 and 86.7%, respectively) and better performance of ZnOA. These results are promising and indicate the potential to use this material as a photocatalyst to degrade organic pesticides.
The objective of this research was to perform characterization of Mexican diatomite through different techniques and to analyze its efficiency in the adsorption of ciprofloxacin present in synthetic water. Mexico has large deposits of diatomite land that have not been well characterized; characterization is important in order to increase the use of this biomaterial in more specialized applications, such as the adsorption of emerging pollutants. Some of the emerging contaminants found in wastewater and surface water are antibiotics, such as ciprofloxacin. With the characterization, it was confirmed that diatomite is a nanostructured material composed of silicon oxide. Different forms of diatoms were found as well, corresponding to the species Discostella, Amphipleura and Cymbopleura, which showed a porous structure on the order of 50–380 nm with a surface area of 27·51 m2/g. The variables that were used to corroborate the adsorption efficiency of ciprofloxacin onto diatomite were the concentration of ciprofloxacin and initial pH for a period of time of 12 h. In this research, the data suggest a good affinity between ciprofloxacin and the diatomite. The adsorption efficiency at pH 9 was between 18 and 34%, and in the case of pH 6, it was between 64 and 75%.
Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method were studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model.
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