Activity of sol-gel derived nanocrystalline WO₃ films in photoelectrochemical generation of reactive chlorine species

Conventional chlor-alkali method used for production of chlorine gas and chlorine-based disinfectants is among the most energy-intensive processes in chemical industry, therefore, more sustainable alternatives with lower carbon footprint are sought. Photoelectrochemical (PEC) generation of reactive chlorine species (Cl₂, HClO, ClO⁻) is a promising technology in the area of water disinfection and purification, as it combines the advantages of (i) using the renewable solar energy; (ii) possibility to produce disinfectants on-site and on-demand and (iii) eliminates the need for sophisticated infrastructure for storage and handling of chlorine species. In the present study nanocrystalline tungsten (VI) oxide layers were formed on conducting glass substrate using simple sol-gel synthesis technique and polytethylene glycol as a structure-directing agent. It is shown that addition of PEG in moderate amounts favours formation of the structure of interconnected nanocrystalline particles, which ensures effective separation and transport of photogenerated charge carriers and, therefore, is crucial for the photoelectrochemical activity of the films. This is corroborated by the analysis of SEM and XRD data, revealing the influence of polytethylene glycol from the initial stages of WO₃ phase crystallization. Faradaic efficiency of photoelectrochemical hypochlorite formation is shown to be about 30%, and antimicrobial effect of PEC chlorination with WO₃ photoanodes is demonstrated on Gram-positive Bacillus sp. and Gram-negative E.coli C41(DE3) bacteria.