Photoactive nano-confined Pt in titania nanotubes (Pt-TiNT) via microwave-assisted flow synthesis

Pt-TiNT with PtO nanoparticles dispersed within the lumen and interlayer spaces of titania nanotubes (TiNT) were prepared by a new process involving titanate nanosheets (TiNS) synthesis in an optimized microwave-assisted flow reactor, followed by ion-exchange with a Pt precursor, before triggering the titanate layer rolling to trap the Pt precursor clusters inside the titania nanotubes, followed by a thermal treatment. TEM, XRD, and Raman analyses confirm the total conversion of TiO2 into TiNS in 15 min at 120 °C and 4 bar, and the TiNS transformation into 181 nm-long TiNT with 10 and 6 nm outer and inner diameter, respectively. The 2% Pt-TiNT comprises 0.7 nm PtO clusters (according to XPS), causing slight distortions of the interlayer spaces, while a few larger 2–3 nm Pt clusters reside within the lumen. As a result, Pt-TiNT is 14-fold more active than TiNT for visible light (400–780 nm) photocatalytic oxidation of diclofenac under 2136 μW·cm−2 irradiation, and>1000-fold better than the uncatalyzed photoconversion reaction under 100 mW·cm−2 artificial solar lighting. In addition, nano-confinement of PtO clusters narrowed the bandgap of the TiNT, which, combined with its excellent absorptivity to harvest light, allowed a broader spectral range of photon energies to activate the photocatalyst.