Acid-induced molecule self-assembly synthesis of Z-scheme WO3/g-C3N4 heterojunctions for robust photocatalysis against phenolic pollutants

Searching for effective strategies of boosting charge carrier separation and improving photooxidation ability are highly desirable to design graphitic carbon nitride-based photocatalysts for efficient organic pollutant degradation. Here we demonstrate an in situ acid-induced self-assembly of melamine and sodium tungstate method combined with hydrothermal treatment, by forming WO3/melamine-cyanuric acid supramolecular complex, to fabricate porous sheet-like WO3/g-C3N4 heterojunctions with oxygen doping; meanwhile, the morphology of WO3/g-C3N4 nanosheets can be further regulated by selecting different short-chain carboxylic acids. The heterojunctions exhibit enhanced visible-light photocatalytic activity than bulk g-C3N4 and supramolecule-based g-C3N4 in degradation of phenolic pollutants, acetaminophen and methylparaben. The tests including active species trapping, photoelectrochemistry and photoluminescence firmly evidence that the extraordinary Z-scheme charge transfer manner plays dominated role to this excellent activity, which can accelerate charge carrier separation and retain powerful redox ability of electrons on conduction band of g-C3N4 and holes on valence band of WO3 simultaneously; additionally, porous sheet-like nanostructures and oxygen doping also positively influence the activity via improving light harvesting, providing plentiful active sites, shortening charge carrier migration distance and further facilitating charge carrier separation. LC–MS analysis and TOC monitoring find the target pollutants are completely degraded under oxidation of holes, superoxide and hydroxyl radicals.