Two-dimensional TiO2-based nanosheets co-modified by surface-enriched carbon dots and Gd2O3 nanoparticles for efficient visible-light-driven photocatalysis

Abstract

Two-dimensional TiO2-based nanosheets (TNSs) co-modified by surface-enriched carbon dots (CDs) and Gd2O3 nanoparticles: (Gd-C-TNSs), capable of exhibiting visible-light-driven photo catalysis were synthesized using a two-pot hydrothermal route. The samples had a sheet-like structure, thickness of approximately 3.6nm, large specific surface area of 240–350cm2/g. The CDs (2–3nm) and Gd2O3 nanoparticles (1–2nm) were highly dispersed over the surface of the nanosheets. The co-modification by Gd2O3 nanoparticles and CDs influenced the crystallinity, crystal structure, and surface area of the TNSs, and improved the visible-light absorption. Surface photocurrent and fluorescence spectral studies revealed that the photo-generated charge carrier separation efficiency could be improved by an appropriate amount of modification. A very high efficiency was obtained using 0.5 at% Gd/Ti and 3.0g/L of CDs. The visible-light-induced photocatalytic activity is enhanced under the isolated Cr(VI) system, isolated Rhodamin B (RhB) system, and the synergism between RhB degradation and Cr(VI) reduction for the Gd-C-TNSs photocatalysts. Initially, the photocatalytic activity gradually increased with an increase in the amount of CDs, and then decreased after attaining a maximum, in the case where 0.5 at% Gd/Ti and 3.0g/L of CDs were used. The enhancement in the photocatalytic activity was attributed to the synergetic effect of the Gd2O3 nanoparticles, TNSs, and CDs in the Gd-C-TNSs composites. The effect led to a fast separation and slow recombination of photo-induced electron–hole pairs. An alternate mechanism for enhanced visible-light photocatalytic activity was also considered.