Enhanced solar water disinfection using ZnO supported photocatalysts

Nano-structured ZnO photocatalysts on cellulose and polyester supports were developed for enhancing solar water disinfection (SODIS). The photocatalysts were fabricated by a two-step hydrothermal method, in which ZnO nanoparticles were synthesized and deposited on a cellulose or polyester support as a seed layer, followed by the growth of one-dimensional ZnO nanorods on the seed layer in a liquid bath containing zinc nitrate and hexamethylenetetramine as sources of precursors. The morphologies and phase compositions of the synthesized ZnO nanorods from different growth conditions were investigated with field emission scanning electron microscope and X-ray diffraction (XRD), respectively. The crystallinity size of the ZnO nanorods was in the range of 17-30 nm and increased with the precursor concentration. The XRD patterns also revealed that higher growth solution concentrations led to higher intensity of XRD peaks, indicating higher crystallinity. Additionally, to test for SODIS enhancement, experiments using 200-mL transparent polyethylene bags as SODIS reactors, with ZnO photocatalysts inside, and water samples containing 10⁶ CFU of Escherichia Coli were conducted in a laboratory UVA setup. The photocatalyst with a polyester support resulted in a 15% higher disinfection efficiency than that of the one with a cellulose support. Moreover, a field test of enhanced SODIS was conducted in actual sunlight, using specially designed SODIS reactors containing ZnO photocatalysts with a polyester support. Nearly total disinfection (97-98% efficiency) was achieved within the first 15 min of every test. The treated water was also tested for zinc contents, which could be released from the photocatalysts, by ICP-OES. The results were lower than 2 mg/L.