Structural Insight on Defect-Rich Tin Oxide for Smart Band Alignment Engineering and Tunable Visible-Light-Driven Hydrogen Evolution

Abstract

Herein, a series of defect-rich tin oxides, Sn x O y , were synthesized with tunable Sn2+/Sn4+ composition ratio and defect chemistry, aiming to explore the impact of local structural modulation, non-stoichiometric chemistry, and defective center on the modulation of band gap values, band edge potential positions, and photocatalytic hydrogen evolution performance. The phase structure, morphology, surface component, and photoelectric properties were analyzed by multiple testing methods. The modulation of the Sn2+/Sn4+ molar ratio was analyzed by X-ray photoelectron spectroscopy and the spectra of Mossbauer and electron spin resonance, which indicated the existence of interstitial tin and oxygen vacancy, predicting a highly disordered local structure. In addition, the photocatalytic activity was evaluated by water splitting for hydrogen production under visible light. The optimal photocatalytic activity toward H2 production rate reached 58.6 μmol·g–1·h–1 under visible light illumination. However, the photocatalytic activity gradually decreased with an increase of synthetic temperature. Much higher Sn2+/Sn4+ molar ratio in the present defective tin oxide gave rise to more negative band edge potentials for hydrogen production. Meanwhile, the driving force was decreased with the diminished Sn2+. Large amounts of hydroxyl groups, Sn2+, and relatively negative potential of conduction band in non-stoichiometric Sn x O y play critical roles in visible light harvesting and photocatalytic water splitting. Furthermore, the relationships among crystal structure, electronic properties, and photocatalytic activities were clarified by theoretical calculation. This work provides a novel strategy for the development of highly efficient photocatalytst by regulating the internal electronic structure and surface defects.

High Visible Light Photocatalytic Activity of SnO2‐x Nanocrystals with Rich Oxygen Vacancy

“…The existence of these two peaks can be assigned to the angular vibration of the O−Sn−O bond and the stretching vibration of the Sn−O bond, respectively, which is a typical SnO 2 characteristic peak [21] . With the increase of Sn 2+ , the above two peaks obviously merge into a single peak located at 630 cm −1 , which confirms that the Sn−O bond (503 cm −1 ) is converted from terminal bond to bridging bond (630 cm −1 ) [20] . The broad and weak infrared absorption bands appear around the 800–1250 cm −1 and are enhanced with the increase of Sn 2+ concentration.…”

“…The broad and weak infrared absorption bands appear around the 800–1250 cm −1 and are enhanced with the increase of Sn 2+ concentration. These absorption bands are considered as electronic transitions from the intrinsic donor level to the tin dioxide sample conduction band, indicating that the doped sample has very abundant oxygen vacancies [20,22] . The absorbance peak near 3577 cm −1 in the spectra is attributed to the O−H stretching vibration of adsorbed water molecules and a peak around 1619 cm −1 is the H−O−H bending deformation vibration of free water molecules [23] .…”

“…As shown in Figure 4c, the O 1s XPS spectra of SnO 2‐x (the S1 : 9 sample) and SnO 2 nanocrystals (the S10 : 0 sample) show dramatic difference. The O 1s XPS spectra can be resolved into three peaks located at 530.95 eV, 531.9 eV and 532.75 eV, attributing to lattice oxygen (O L ), oxygen vacancies (O V ) and hydroxyl oxygen (O H ) respectively [20,31] . Based on the fitting curve, the relative contents of oxygen vacancies were calculated to 16.5 % and 33.2 % for SnO 2 and SnO 2‐x nanocrystals (the S1 : 9 sample), respectively.…”

“…By theoretical calculation, Song et al. revealed the crystal structure, electronic properties of non‐stoichiometric Sn x O y , which could play critical roles in visible light harvesting and photocatalytic water splitting [20] . Although these studies have proposed the applications of SnO 2‐x nanocrystals with oxygen vacancy, the precise control of oxygen vacancy is still not clear enough.…”

Topological synthesis of crystalline Ag/T‐Nb2O5 nanobelts with enhanced solar photoelectrochemical properties for splitting water

“…), surface/interface chemistry, electronic structure, and morphological structure of semiconductor, and it has been found that these inherent properties have a great influence on the photocatalytic activity of semiconductor. [6] This is very important to design and develop high efficient semiconductor photocatalytic materials.…”