Boosting visible light harvesting and charge separation in surface modified TiO2 photonic crystal catalysts with CoOx nanoclusters

Photonic crystal structuring has emerged as a promising approach to improve the utilization of solar energy by metal oxide semiconductor photocatalysts based on the combination of slow-light, pore interconnectivity and high surface accessibility of macroporous periodic structures with judicious compositional modifications of the materials' properties. In this work, surface modification of photonic band gap engineered TiO2 inverse opals fabricated by the convective evaporation-induced co-assembly technique was performed with nanoscale Co oxides using the chemisorption-calcination-cycle method in order to explore the interplay of metal oxide heterostructuring and photonic amplification for the development of visible light-activated photonic catalysts. Fine tuning of the films' photonic and electronic properties by controlling the inverse opal macropore size and Co oxides' loading and composition resulted in significant enhancement of the photocatalytic activity for organics decomposition under visible light, exceeding that of benchmark mesoporous TiO2 films subjected to the same treatment. The underlying mechanism was related to the slow-photon-assisted light harvesting by low amounts of Co oxide nanoclusters that exert minimal effects on the inverse opal periodicity and texture, while enabling visible light electronic absorption and promoting charge separation via strong interfacial coupling on the nanocrystalline titania skeleton of the photonic crystals.