Titanium dioxide sol–gel-coated expanded clay granules for use in photocatalytic fluidized-bed reactor

• Titania-coated expanded clays for operation in fluidized-bed photocatalytic reactor.
• Improvement of coating properties adapting sol–gel composition.
• Antibiotic removal by combination of photocatalysis and adsorption on bed material.

An experimental research into the titania coatings on granulated expanded clay to be used in fluidized-bed photocatalytic reactor was undertaken. The preparation procedures were performed via sol–gel method using dip coating techniques. Two sol–gel compositions based on tetrabutyl orthotitanate and titanium tetraisopropoxide as well as two commercial TiO2 sols were examined. The impacts of titania precursor concentration, modification of sol–gel by industrially available TiO2 nanoparticles, the substrate withdrawal speed and thermal treatment conditions on the coatings’ properties were studied. The photocatalytic activity of expanded clay-supported titania was evaluated by the degradation of an emerging micropollutant, tetracycline family antibiotic doxycycline. Mechanically stable and active coatings with properties dependent on sol–gel processing parameters were obtained. The application of porous titania sol–gel-coated expanded clays could combine pollutants’ adsorption and their photocatalytic degradation. The compromise between coatings’ improved photocatalytic performance, on the one hand, and their adhesion and attrition properties, significant for fluidized-bed operation, on the other hand, lead to the determination of appropriate processing parameters.

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