Abstract
Surface functionalization of TiO2 inverse opals by graphene oxide nanocolloids (nanoGO) presents a promising modification for the development of advanced photocatalysts that combine slow photon-assisted light harvesting, surface area, and mass transport of macroporous photonic structures with the enhanced adsorption capability, surface reactivity, and charge separation of GO nanosheets. In this work, post-thermal reduction of nanoGO–TiO2 inverse opals was investigated in order to explore the role of interfacial electron transfer vs. pollutant adsorption and improve their photocatalytic activity. Photonic band gap-engineered TiO2 inverse opals were fabricated by the coassembly technique and were functionalized by GO nanosheets and reduced under He at 200 and 500 °C. Comparative performance evaluation of the nanoGO–TiO2 films on methylene blue photodegradation under UV-VIS and visible light showed that thermal reduction at 200 °C, in synergy with slow photon effects, improved the photocatalytic reaction rate despite the loss of nanoGO and oxygen functional groups, pointing to enhanced charge separation. This was further supported by photoluminescence spectroscopy and salicylic acid UV-VIS photodegradation, where, in the absence of photonic effects, the photocatalytic activity increased, confirming that fine-tuning of interfacial coupling between TiO2 and reduced nanoGO is a key factor for the development of highly efficient photocatalytic films.
Highlights
Over the last decades, TiO2 has been widely studied as a low cost, nontoxic, and highly stable photocatalyst, which can degrade a great number of gaseous and aqueous pollutants for environmental remediation [1]
TiO2 inverse opals, fabricated via the coassembly of polystyrene colloidal spheres with the water soluble Titanium(IV) bis(ammonium lactato)dihydroxide (TiBALDH) precursor, were surface-functionalized with graphene oxide (GO) nanosheets and, subsequently, thermally reduced at 200 and 500 ◦ C
Aqueous phase photodegradation of the methylene blue (MB) dye under UV-VIS and visible light showed that thermal reduction of the GO–TiO2 photonic films at 200 ◦ C, in synergy with slow photon amplification, improved the MB
Summary
TiO2 has been widely studied as a low cost, nontoxic, and highly stable photocatalyst, which can degrade a great number of gaseous and aqueous pollutants for environmental remediation [1]. The photocatalytic efficiency of TiO2 is, limited by the recombination of photogenerated charge carriers [2] and its wide energy band gap (3.0–3.2 eV), which requires ultraviolet light for electron excitation [3]. Particular interest has been recently placed on TiO2 photonic crystals, a promising titania modification featuring a periodic and mesoporous structure that can manipulate light propagation at specific wavelengths [4]. Because of their periodicity, photonic crystals—the most common being the inverse opal structure fabricated by the self-assembly of colloidal opal templates [5,6]—exhibit photonic band gaps (PBGs), which constitute frequency regions within the crystal where electromagnetic irradiation cannot propagate. At wavelengths near the PBG edges, Materials 2019, 12, 2518; doi:10.3390/ma12162518 www.mdpi.com/journal/materials
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