The influence of the textural properties of ZnO nanoparticles on adsorption and photocatalytic remediation of water from pharmaceuticals

• ZnO nanoparticle photocatalysts of different size have been prepared.
• The degradation performance of drugs was tested down to low ppm or ppb range.
• Tests were performed with reliable catalytic conditions at low cat-to-drug ratio = 1.
• Smaller crystals are more active, due to increased BET area and higher adsorption.
• Adsorption is markedly enhanced at very low catalyst and drug concentrations.

The pollution of surface, ground and drinking water by pharmaceuticals in low concentration is a new emerging problem. Zinc oxide nanoparticles of different sizes have been characterized by XRD, TEM, UV–Vis/DRS and N2 adsorption–desorption measurements. The photocatalytic degradation of low concentrated pharmaceuticals tetracycline and ibuprofen at low photocatalyst amount and at low photocatalyst to substrate mass ratio (cat-to-sub ratio) have been investigated in details. The influence of pH value, ZnO and drug concentrations as well as the contribution of adsorption has been deeply studied. The formation of intermediates has been investigated by electrospray ionization-time of flight-mass spectroscopy. Zinc oxide is known to promote the formation of reactive OH radicals and therefore is of special interest for the photocatalytic remediation of water from pharmaceuticals. Smaller particles are more active than larger ones due to increased specific surface area and adsorption. Interestingly, adsorption of the drug on ZnO is markedly improved at low concentration (<5 ppm), leading to the different degradation behaviors, compared to ppm concentrated solution.

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