Superior efficiency of BN/Ce2O3/TiO2 nanofibers for photocatalytic hydrogen generation reactions

Abstract

One-dimensional BN/Ce2O3/TiO2 heteroarchitectures with high visible-light photocatalytic activity have been successfully obtained by an electrospinning technique. The properties of the prepared nanofibers were controlled using different ratios of cerium. The results of XPS characterization revealed that the Ce element is present in the valence state + III on the surface of the TiO2 nanofibers. Rietveld refinement of XRD data reveals that introducing small concentrations of Ce3+ (<3.0 at%) into the electrospinning solution leads to the formation of small amounts of rutile and brookite phases, a decrease in the crystallite size of the main anatase phase and a slight decrease in the c parameter and unit cell volume of the anatase phase. In contrast, only the anatase phase, which has a similar crystallite size and lattice parameters to that formed in the undoped sample, is observed when 3 at.% Ce is used. These results suggest that Ce3+ ions did not substitute Ti4+ ions in the lattice of both anatase and rutile phases, which can be explained by the large difference in the ionic radius of Ti4+ and Ce3+ ((r (Ti4+) = 60.5 pm, r (Ce3+) = 101.7 pm). Scanning electron microscopy demonstrates that the diameter of the obtained nanofibers decreases from 240 nm for pristine TiO2 to 101 nm, 70 nm, 40 nm for 2% Ce/TiO2 (CET2), BN/TiO2 (BT) and BN/2% Ce/TiO2 (BCET2), respectively. The d-spacing decreased by 0.3 nm after Ce incorporation as demonstrated by high-resolution transmission electron microscopy. XPS proved the presence of BN nanosheets along with Ce2O3 and TiO2 into the nanofibers. Compared with the pure TiO2 nanofibers (NF), the obtained Ce/Ti ratio of 2% (molar ratio) showed an enhancement of the visible-light photocatalytic activity to water splitting, which is 46 times higher than that of bare TiO2 NF. The Ce2O3 might improve the separation of photogenerated electrons and holes derived from the coupling effect of TiO2 and cerium oxide. This work also examines the modification of TiO2 (anatase) properties with hexagonal boron nitride (h-BN) and the impact this coupling has on photocatalytic activity. XPS proved the presence of BN nanosheets along with Ce2O3 and TiO2 into the nanofibers. The electron transfer rate was improved by BN exfoliation. The photocatalytic results indicated that the BN/Ce2O3/TiO2 nanofibers improve hydrogen production up to 5100 μmol/g for 6 h under visible light, which could be due to the presence of BN sheets that enhanced the separation of the photo-induced electron–hole pairs in TiO2 and increased the specific surface area compared to pure TiO2 and Ce2O3/TiO2 nanofibers. Moreover, the BN/Ce2O3/TiO2 could be easily recycled without decrease in the photocatalytic activity because of its one-dimensional nanostructure nature. Moreover, the present work focuses on the ternary composite of BN/Ce2O3/TiO2 for optimization of electronic and phonon transport properties using the state-of-the-art density functional theory (DFT). The calculated electronic density of states (DOS) modulus shows an excellent agreement compared with available theoretical and experimental data for hydrogen production.