Facile synthesis of ZnO-clay minerals composites using an ultrasonic approach for photocatalytic performance

Abstract

Photocatalysts based on ZnO-clay minerals were prepared using palygorskite (Pal) and/or halloysite (Hal) as supports. The photocatalysts were obtained by the method of ultrasonic treatment, where the systems were sonicated for 3 h to achieve homogenization of the oxide nanoparticles in the clay mineral matrices. The materials were characterized by X-ray diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, EDS, Photoluminescence, Diffuse Reflectance Spectroscopies, and textural analysis. Their activity was evaluated via photocatalytic degradation of the antibiotic ciprofloxacin under visible light irradiation for 120 min in aqueous solution. The inhibition effect on oxidative species in the photocatalytic process was evaluated by sacrificial reagents including methyl alcohol, furfuryl alcohol, silver nitrate and EDTA for hydroxyl radicals, superoxide anion, electrons, and holes, respectively. Results indicated a homogeneous ZnO impregnation onto the surface of the clay minerals, maintaining the crystalline structure of inorganic matrices. Activity tests showed better photodegradation efficiency of ZnO-Pal/Hal (91% in 120 min) than of the ZnO-Pal and ZnO-Hal composites. Interactions caused by oxide incorporation promoted the separation of the generated charges, avoiding recombination through a load transfer mechanism and consequently improving the photochemical efficiency of the composite. The clay minerals behaved as suitable supports for the dispersion of the highly active ZnO, and presented good chemical stability through use/reuse operation cycles of the photocatalysts.