To face the acute problem of water contamination, intensive scientific activity focuses on advanced photocatalytic treatment based on titanium dioxide nanomaterials. Herein, we investigate the development of innovative photocatalysts consisting of copper-modified core-shell titania nanocomposites (m–TiO2/Cu), synthesized using a smoldering combustion sol–gel route. The structural and chemical analysis (XRD, Raman, UV/vis, EDS, TEM, porosimetry, FTIR, EPR and XPS) confirmed that the mixed m–TiO2/Cu nanostructures are formed by a TiO2 core, crystalized in the anatase phase, an external nitrogen rich carbonic shell, which acted as a sensitizer and well dispersed species consisting of copper oxide and possibly plasmonic nanoparticles depending on the Cu loading. The synthesized materials were successfully employed for the photocatalytic degradation of caffeine – CA, salicylic acid – SA and hexavalent chromium – Cr(VI) emerging contaminants frequently detected in wastewaters, under UVA and solar illumination. Copper addition contributes to the photooxidation process enhancing the final degradation efficiencies of CA and SA, while preserving the performance of the reference material for the Cr(VI) photoreduction. An optimum copper loading was determined for both illumination conditions and the results are compatible with a photocatalytic mechanism implying enhanced light absorption and more effective separation of the photogenerated charge carriers. © 2018 Elsevier B.V.

Photonic crystal-assisted semiconductor photocatalysis has been attracting significant attention as an advanced photon management approach that combines light harvesting with the macro/mesoporous structured materials properties permitting enhanced mass transport and high adsorption. In this work, surface functionalization of well-ordered photonic band gap engineered TiO2 inverse opal films fabricated by the convective evaporation-induced co-assembly method was performed by graphene oxide nanocolloids (nanoGO). The loading of GO nanosheets was determined by the films’ macropore size, with minimal effects on their long range periodicity and photonic properties. While nanoGO deposition reduced mesoporosity of the nanocrystalline titania walls, their surface functionality was greatly improved by the abundant oxygen groups of the GO nanosheets leading to increased pollutant adsorption. Slow photon amplification in the aqueous phase methylene blue photodegradation was identified for the unmodified TiO2 photonic films under both UV–vis and Vis illumination upon spectral overlap of the low energy edge of the inverse opal stop band (in water) with the dye electronic absorption, due to (red) slow photons localized in the titania skeleton that distinctly accelerated dye photodegradation kinetics. The photocatalytic efficiency was further improved for the nanoGO functionalized TiO2 inverse opal films via the synergetic action of interfacial electron transfer from TiO2 to the GO nanosheets. Under UV–vis light, the functionalized photonic films outperformed benchmark mesoporous Aeroxide® P25 TiO2 films where nanoGO modification, despite the enhanced dye adsorption, resulted in adverse effects in photocatalytic degradation due to pore clogging. Combination of the exceptional structural and photonic properties of TiO2 inverse opals with the high adsorption capacity and charge separation afforded by GO nanocolloids is proposed as a promising modification route for the development of efficient photocatalytic films. © 2018 Elsevier B.V.

The development of nanostructured semiconductors with tailored morphology and electronic properties for surface-enhanced Raman scattering (SERS) has been attracting significant attention as a promising alternative to conventional coinage metal SERS substrates. In this work, functionalized TiO2 photonic crystals by graphene oxide nanocolloids (nanoGO) are demonstrated as highly sensitive, recyclable, plasmon-free SERS substrates that combine slow-photon amplification effects with the high adsorption capacity and surface reactivity of GO nanosheets. Comparative evaluation of photonic band gap engineered nanoGO-TiO2 inverse opal films was performed on methylene blue SERS detection under different laser excitations in combination with rigorous theoretical simulations of the photonic band structure. A very low detection limit of 6 × 10-7 M and an enhancement factor of 5 × 104 along with excellent self-cleaning performance and reusability could be achieved by the interplay of slow-photon effects assisted by interfacial charge transfer between the analyte and the nanoGO-TiO2 semiconducting substrate. Slow-photon management in combination with judicious engineering of chemical enhancement in photonic nanostructures is accordingly proposed as an advanced approach for the design of efficient dielectric SERS substrates. © 2019 The Royal Society of Chemistry.

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. © 2019 by the authors.