Solar-assisted stainless-steel TiO2-based coatings for water disinfection and decontamination

In this study, a photocatalytic inorganic coating based on pre-formed TiO2 nanoparticles at two loads of catalyst (100 and 200 g/L) and suitable silica precursors which act as a binder of a sol-gel origin, has been deposited on stainless-steel substrates (referred to as TEOS/TiO2_100g/L and TEOS/TiO2_200g/L, respectively), and assessed for water disinfection and decontamination. A preliminary set of tests was carried out under artificial radiation. A methylene blue removal of > 90% under UVA radiation/> 65% under visible radiation in 120 min of treatments was obtained for both immobilized substrates. Then, the photocatalytic activity of the immobilized TiO2 was tested under natural sunlight for the simultaneous removal of a mix of contaminants of emerging concern (CECs) (sulfamethoxazole (antibiotic) and imidacloprid (insecticide)) (> 80%) and the inactivation of Escherichia coli in isotonic water. The best performance was obtained with the stainless-steel coated with TEOS/TiO2_200g/L. Very good results were obtained in both water matrices, reaching > 80% removal of CECs and > 5 Log Reduction Values (LRV) of E. coli in less than 125 and 250 kJ/m2 of solar UVA dose (or 60 and 120 min of treatment time), respectively. The durability and reusability of the stainless-steel coated with TEOS/TiO2_200g/L were also evaluated by performing 10 consecutive cycles of use under natural sunlight. The characterization of the substrate after the reusing showed a slight change in the topography of the coating, nevertheless, the photocatalytic activity for water disinfection and decontamination during the testing remained intact, demonstrating their suitability for up-scaling and implementation in large photocatalytic reactors. Besides, no ecotoxicity on treated samples using Aliivibrio fischeri was observed.