Developing an efficient TiO2-coated biofilm carrier for intimate coupling of photocatalysis and biodegradation

Intimate coupling of photocatalysis and biodegradation (ICPB) shows promise to remove recalcitrant organic compounds from water, because photocatalysis breaks the compounds into biodegradable intermediates that are immediately mineralized by microorganisms inside a macroporous carrier, where they are protected from UV light and free radicals. Key to successful ICPB is a carrier capable of accumulating biofilm in its interior and strongly adhering photocatalyst on its exterior. We employed a low-temperature sintering method, the O method, to adhere TiO2 to sponge-type macroporous carriers. The O method achieved a 7-fold increase of TiO2 density, compared to the previously used sol–gel method, and it conserved the macropores for biofilm accumulation. Although the O-method carrier met the basic requirements of ICPB when degrading 2,4,5 trichlorophenol, it had low photocatalytic activity for breaking down more complex aromatics, like reactive dyes. Therefore, we improved the sintering method in two steps called the D and DN methods: reducing the TiO2 concentration and then removing trimesic acid in the coating solution. The photocatalytic efficiency towards reactive black 5 increased 5 fold for the D method and 10 fold for DN method, and the DN carrier had superior TiO2 adherence during long-term operation.

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► A carrier was developed for intimately coupled photocatalysis and biodegradation.
► Photocatalytic efficiency was strongly enhanced by modifying the TiO2 coating procedure.
► Catalyst deterioration was minimized with a thinner and more uniform coating pattern.
► Recalcitrant organic contaminants were efficiently eliminated using this carrier.