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In this work, we aimed to prepare chromium substituted cobalt ferrite Co(CrxFe1–x)2O4 powders by a simple coprecipitationannealing method with different Cr contents to create novel magnetic adsorbents for the removal of phosphate ions from water. The effects of Cr substitution on the crystal structure, phase composition, morphology, surface atomic composition, surface area and magnetic properties of our adsorbents were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption-desorption and vibrating sample magnetometry. According to the results, all our Co(CrxFe1–x)2O4 samples exhibited higher phosphate adsorption than CoFe2O4 powder but their magnetic properties were reduced for increasing Cr substitution. Among them, the Co(Cr0.25Fe0.75)2O4 sample was found to be the most promising material since its magnetic properties are still high to allow it to be easily separated from the solution and its maximum P adsorption capacity (according to the Langmuir model) was estimated to be 4.84 times higher than CoFe2O4, which can be attributed to the presence of Cr3+ ions on the surface and the enhanced surface specific area of this substituted sample. Moreover, the adsorption data of Co(Cr0.25Fe0.75)2O4 sample also fitted well to the pseudo second order kinetic model, revealing the adsorption rate constant of 0.87 mgP–1s–1, two times superior to CoFe2O4.

In this work, we proposed to synthesize CuFe2O4/Fe2O3 core-shell materials with different Fe2O3 contents in order to create new and efficient photo-Fenton-like catalysts for the degradation of methylene blue with oxalic acid as a radical-producing source. The catalysts were prepared through two stages: first, CuFe2O4 was prepared by a hydroxide coprecipitation – annealing method and then, Fe2O3 was immobilized on CuFe2O4 surface by a simple impregnation – annealing procedure. According to the experimental results, our CuFe2O4/Fe2O3 core-shell materials exhibit high photo-Fenton-like catalytic activity for the degradation of methylene blue under both UVA light and visible light, as well as good ferromagnetic properties, which allows them to be easily separated from the solution by a magnet. Among them, the catalyst prepared with the molar CuFe2O4/Fe2O3 ratio of 1:2 showed the best catalytic performance with the rate constant of 2.103 h–1 under UVA light and 0.542 h–1 under visible light, which were 2 times higher than CuFe2O4 sample. The enhanced catalytic activities of our core-shell materials can be attributed to the high content of surface Fe3+ species, high specific surface area and the presence of rod-like Fe2O3 particles on their surface.

Ag-modified ZnO, F-modified ZnO and (Ag, F)-modified ZnO nanoparticles were prepared by thermal shock method in order to study the effects of doping agents on their crystal structure, morphology, optical properties, surface structure and photocatalytic activity. The catalysts were characterized by XRD, FE-SEM, TEM, FTIR, UV–Visible diffuse reflectance and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA and visible light irradiation. According to the results, the thermal shock process with AgNO3 did not modify the morphology but successfully created silver species on the surface of ZnO, which induces the visible light absorption and then increases the photocatalytic activity. The enhanced phototcatalytic performance was also observed in F-modified ZnO sample owing to the increase of surface hydroxyl groups and the formation of zinc vacancies. Among three modified ZnO samples, (Ag, F)-modified ZnO was found to be the best sample with the photocatalytic activity enhanced by the factor of 3 under both UVA and visible light, which may be attributed to the synergic effects of AgNO3 and KF used in thermal shock process. Keywords: ZnO nanoparticles, Ag-doping, F-doping, Thermal shock method, Photocatalytic activity

ZnO nanoparticles were modified with KF using thermal shock method at various temperatures in order to improve the photocatalytic activity of ZnO under both UVA and visible light irradiation. The influences of KF-modification on the crystal structure, morphology, UV–visible absorption, specific surface area as well as surface structure of ZnO were respectively characterized by XRD, FE-SEM, UV–Visible diffuse reflectance, N2 adsorption and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA irradiation. According to the results, the thermal shock process with KF did not modify the structure, the particle size and the optical properties of ZnO nanoparticles but successfully increase their UVA and visible light induced photocatalytic activity. This enhancement of activity may be attributed to the increase of surface hydroxyl groups and zinc vacancies of modified ZnO samples. Keywords: ZnO nanoparticles, Thermal shock, KF, Methylene blue, Photocatalytic activity