The synthesis of orthorhombic nitrogen-doped niobium oxide (NbON) nanostructures was performed and a photocatalytic study carried out in their use in the conversion of toxic HS and water into hydrogen under UV-Visible light. Nanostructured orthorhombic NbON was synthesized by a simple solid-state combustion reaction (SSCR). The nanostructural features of NbON were examined by FESEM and HRTEM, which showed they had a porous chain-like structure, with chains interlocked with each other and with nanoparticles sized less than 10 nm. Diffuse reflectance spectra depicted their extended absorbance in the visible region with a band gap of 2.4 eV. The substitution of nitrogen in place of oxygen atoms as well as Nb-N bond formation were confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. A computational study (DFT) of NbON was also performed for investigation and conformation of the crystal and electronic structure. N-Substitution clearly showed a narrowing of the band gap due to N 2p bands cascading above the O 2p band. Considering the band gap in the visible region, NbON exhibited enhanced photocatalytic activity toward hydrogen evolution (3010 μmol h g) for water splitting and (9358 μmol h g) for HS splitting under visible light. The enhanced photocatalytic activity of NbON was attributed to its extended absorbance in the visible region due to its electronic structure being modified upon doping, which in turn generates more electron-hole pairs, which are responsible for higher H generation. More significantly, the mesoporous nanostructure accelerated the supression of electron and hole recombination, which also contributed to the enhancement of its activity.

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Herein, we report the in situ single-step hydrothermal synthesis of hierarchical 2D SnS@ZnIn 2 S 4 nanoheterostructures and the examination of their photocatalytic activity towards hydrogen generation from H 2 S and water under sunlight. The photoactive sulfides rationally integrate via strong electrostatic interactions between ZnIn 2 S 4 and SnS with two-dimensional ultrathin subunits, i.e. nanopetals. The morphological study of nano-heterostructures revealed that the hierarchical marigold flower-like structure is self-assembled via the nanopetals of ZnIn 2 S 4 with few layers of SnS nanopetals. Surprisingly, it also showed that the SnS nanopetals with a thickness of $25 nm couple in situ with the nanopetals of ZnIn 2 S 4 with a thickness of $25 nm to form a marigold flower-like assembly with intimate contact.Considering the unique band gap (2.0-2.4 eV) of this SnS@ZnIn 2 S 4 , photocatalytic hydrogen generation from water and H 2 S was performed under sunlight. SnS@ZnIn 2 S 4 exhibits enhanced hydrogen evolution, i.e. 650 mmol h À1 g À1 from water and 6429 mmol h À1 g À1 from H 2 S, which is much higher compared to that of pure ZnIn 2 S 4 and SnS. More significantly, the enhancement in hydrogen generation is 1.6-2 times more for H 2 S splitting and 6 times more for water splitting. SnS@ZnIn 2 S 4 forms type I band alignment, which accelerates charge separation during the surface reaction. Additionally, this has been provoked by the nanostructuring of the materials. Due to the nano-heterostructure with hierarchical morphology, the surface defects increased which ultimately suppresses the recombination of the electron-hole pair. The above-mentioned facts demonstrate a significant improvement in the interface electron transfer kinetics due to such a unique 2D nano-heterostructure semiconductor which is responsible for a higher photocatalytic activity.Scheme 2 Schematic of the photocatalytic mechanism of SnS@ZnIn 2 S 4 heterostructures.This journal is