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In this work, Al‐doped ZnO and Fe‐doped ZnO nanoparticles have been synthesized through the coprecipitation‐annealing method to create new and safer UV filters for sunscreen. The effects of metal doping on phase composition, crystal structure, surface morphology, specific surface area, and elemental composition were characterized by X‐ray diffraction, Raman spectroscopy, field emission electron scanning microscopy, nitrogen adsorption‐desorption experiments and energy‐dispersive X‐ray spectroscopy, respectively. The optical properties and photocatalytic activity of prepared powders were studied through UV‐visible diffuse reflectance spectroscopy and photocatalytic degradation of methylene blue under UV radiation. According to the experimental results, Al or Fe‐doped ZnO nanoparticles showed better UV absorption but significantly lower photocatalytic activity than the undoped ZnO sample, which enables the metal doped ZnO samples to become more effective and safer UV filter in sunscreen. The decline of photocatalytic activity can be attributed to the bulk defects caused by the insertion of Al3+or Fe3+ions in ZnO lattice. In particular, the sunscreen formulations using the metal doped ZnO nanoparticles display high SPF values and diverse colors changing from ivory to yellow‐brown, preventing leaving white cast on the skin, which is very suitable as sunscreen for people of color.

Mesoporous MFe2O4materials (M = Mn, Cu, and Co) as magnetic adsorbents for phosphate removal were synthesized by a simple coprecipitation method without annealing at high temperatures. Several techniques, including powder X‐ray diffraction, field emission electron scanning microscopy, nitrogen adsorption‐desorption and vibrating sample magnetometry were used to characterize the samples. The effects of M2+ions on their point of zero charge and their phosphate adsorption capacity were investigated. All three samples consist of nanosized particles with cubic spinel structure and ferromagnetic properties, which allows them to be easily separated from aqueous effluents using a magnet. According to the batch experiments, the adsorption isotherms and the adsorption kinetics for these mesoporous materials are well fitted with the nonlinear Langmuir model and the nonlinear pseudo‐second‐order model, respectively. Among them, CuFe2O4powder showed the best phosphate adsorption performance with the maximum P adsorption capacity of 27.49 mgP g‐1, which can be assigned to the highest surface area and the high pH value at its point of zero charge.

Abstract: The present paper reports the synthesis of magnetic photo-Fenton catalysts based on CuFe2O4via an environmentally friendly sol-gel method at different annealing temperatures (700, 800, and 900°C) using tamarind fruit extract as a chelating agent. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption, Fourier-transform infrared spectroscopy, and vibrating sample magnetometry. Their photo-Fenton catalytic performance was tested with oxalic acid for the degradation of Methylene Blue under UVA light and under visible light. According to the results, the annealing temperature was found to be the important factor, significantly affecting the oxalic acid-induced-photo-Fenton activity. When the annealing temperature increased from 700 to 800°C, the catalytic performance was strongly improved, which can be explained by the enhanced Fe3+content on the catalyst surface. At higher annealing temperature, due to the growth and agglomeration of particles, the specific surface area was decreased, consequently reducing the catalytic activity. The sample prepared at 800°C also displayed good ferromagnetic properties, making it the most promising recyclable material for wastewater treatment in this study.

Graphical Abstract:

In this work, the perspective of using a simple and environmentally friendly starch-assisted sol-gel method was explored to synthesized a series of light lilac-colored and heat reflective pigments based on Cr-doped Al2O3powders with varying Cr contents. Especially, KF was used as a fluxing agent to lower the annealing temperature and facilitate the integration of Cr3+ions into Al2O3lattice. The obtained pigments were characterized by powder X-ray diffraction, field emission electron microscopy, energy-dispersive X-ray spectroscopy, wavelength dispersive X-ray fluorescence spectroscopy, CIE L*a*b* color measurements, and NIR reflectance spectroscopy. According to the results, our Cr-doped pigments not only exhibited remarkable NIR reflectivity, with NIR solar reflectance values exceeding 40%, but also displayed vibrant magenta-purple hues. These colors and NIR reflectivity can be attributed to the incorporation of Cr3+ions into the single-phase α-Al2O3crystal network, coupled with the formation of microparticles bearing a flake-like morphology. Among different doping levels, the 5 mol% Cr-doped Al2O3sample closely matched the desired light lilac color and was chosen to formulate a water-based paint, which was subsequently proved to successfully provide heat-shielding ability for concrete bricks when exposed to an infrared lamp for 2 h.

An Erratum to this paper has been published: https://doi.org/10.3103/S1063455X24030123

Cu-modified ZnO photocatalysts were prepared using a thermal shock method with different copper-containing precursors (Cu(NO3)2, Cu(CH3COO)2, CuSO4) in order to study the impacts of the thermal shock method on the photocatalytic activity of ZnO under both UVA light and visible light irradiation. The influences of copper-containing precursors on the crystal structure, morphology, surface structure and surface composition were investigated by X-ray diffraction, transmission electron microscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. The UVA-light and visible-light-induced photocatalytic activities were evaluated through the degradation of methylene blue. According to the experimental results, ZnO catalysts modified with Cu(NO3)2and Cu(CH3COO)2exhibited higher performance than unmodified ZnO, which may be explained by the formation of oxygen vacancies and Cu(I) species on the surface of modified oxides. However, when ZnO was modified by CuSO4, the absence of oxygen vacancies and the presence of large sulphate ions on the ZnO surface were supposed to be the factors decreasing its photocatalytic activity.