Jianying Shi

Redox cycles promoting photocatalytic hydrogen evolution of CeO2 nanorods

Oriented hexagonal CeO2 NRs were directly grown on Ti substrates via a simple template-free electrochemical method. These CeO2 NRs with {110} planes as the main exposed surfaces show significant photocatalytic activity for hydrogen evolution with Na2S–Na2SO3 as sacrificial agents due to their special redox capacity.

The roles of defect states in photoelectric and photocatalytic processes for ZnxCd1−xS

This work aims to investigate the role that defect states play in photoelectric and photocatalytic processes. Ternary ZnxCd1−xS with wurtzite structure is firstly synthesized, and then the defect is characterized by photoluminescence (PL) spectroscopy. It is found that the photoelectrons trapped in surface defect states exhibit different behavior in the processes of photoelectric transfer and photocatalytic hydrogen evolution. During the photocatalytic process, the surface defect states in ZnxCd1−xS act as the electron pool to improve the photocatalytic activity of water-splitting reaction. In comparison, the surface defect states serve as the recombination center that decreases the efficiency of photoelectric transfer. This finding is of great significance for the design of effective photoelectric and photocatalytic material in the field of solar energy conversion.

Porous organic–inorganic hybrid aerogels based on Cr3+/Fe3+ and rigid bridging carboxylates

A general method to prepare organic–inorganic hybrid aerogels has been presented. A series of organic–inorganic hybrid aerogels were successfully produced from 3d trivalent transition metals (Cr3+, Fe3+) and bridging carboxylic acids. Gelation of the Cr(III) gels was achieved by heating the precursor solution to temperatures above 80 °C, which is in sharp contrast to usual supramolecular gels. Among a range of ligands used, highly porous aerogels could be prepared from rigid carboxylate, e.g.1,4-benzenedicarboxylate and 1,3,5-benzenetricarboxylate. The porous aerogels can be described as a coherent, rigid spongy network of continuous nanometre-sized particles, which is significantly different from the usual fibrous network of supramolecular gels. The aerogels have tunable porous structures with micro- and mesoporosity depending on their reactant concentrations. Their surface areas, pore volumes, and average pore sizes were analysed by using nitrogen sorption, and the accessibility of the pores to bulky molecules was also evaluated. It represents a strategy to prepare hybrid materials with large porosity utilising structurally simple building blocks as precursors.

Aqueous Cr(VI) reduction by electrodeposited zero-valent iron at neutral pH : Acceleration by organic matters

This work investigated the effect of co-existing organic matters on aqueous Cr(VI) reduction by electrodeposited zero-valent iron (ED Fe(0)) at neutral pH. The ED Fe(0) prepared in a solution containing mixture of saccharin, L-ascorbic acid and sodium dodecyl sulfate showed higher activity in reducing the aqueous Cr(VI) at neutral pH than that prepared without any organic presence. XRD and SEM indicated that the structure of ED Fe(0) was significantly improved to nano-scale by the presence of organic mixture in the preparation solution. Further, the ED Fe(0) activity in the Cr(VI) reduction at neutral pH was increased by the co-existence of citric acid or oxalic acid in the chromate solution. Electrochemical impedance spectroscopy (EIS) demonstrated that the corrosive current increased with the concentration of organic matter in the reaction solution. With the co-existing organic matters in the preparation solution, the ED Fe(0) corroded more rapidly due to its nano-size, thus the Cr(VI) reduction by the ferrous iron was accelerated. With the co-existing organic matters in the reaction solution, the Cr(VI) reduction was accelerated by a Fe(II) complex as the main electron donor, and a prevention of the passivation due to the Fe(III) and Cr(III) complexes also accelerated the Cr(VI) reduction.

A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium–palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h−1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

Controllable growth of La(OH)3 nanorod and nanotube arrays

Large-scale La(OH)3 nanorod/nanotube arrays have grown directly on Cu substrates via a template-free electrodeposition and selective etching process.

Function of Lattice Defects toward Photocatalytic Processes: View of Electronic Driven Force

Oxygen vacancies and Ti-related defects (OTDs) are the main lattice defects of , which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i) influence the energy structure of the pristine as the isolate acceptor/donor level or hybrid with the original orbital, (ii) provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii) act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites for , , and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.

Influence of Bi chemical state on the photocatalytic performance of Bi-doped NaTaO3

Abstract NaBiO3 and Bi(NO3)3 were used to synthesize Bi-doped NaTaO3. The influence of the Bi chemical state on the photocatalytic activity was investigated using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and diffused reflectance spectroscopy to study the structure, chemical state and light absorption characteristics, respectively. The photocatalytic activity was evaluated by the H2 evolution water splitting reaction. The monoclinic phase of NaTaO3 remained intact for the two Bi-doped samples, but the Ta–O–Ta bond was distorted from 180° after Bi doping. XPS results indicated that Bi3+ was doped into NaTaO3 with the Bi(NO3)3 precursor, while Bi5+ and Bi3+ were doped into NaTaO3 with the NaBiO3 precursor. The two samples showed identical light absorption, where doping with Bi extended the light absorption to long wavelength light as expected. However, Bi3+ doping did not promote the photocatalytic activity of NaTaO3, while Bi5+ and Bi3+ doping did. The distorted Ta–O–Ta bond from 180° due to doping with Bi was detrimental for charge carrier transfer in the photocatalytic process. In contrast, the vacancies or defects in the NaTaO3 lattice induced by Bi doping for charge balance were beneficial for charge carrier separation. The opposing action of these two factors resulted in the activity of the Bi3+-doped sample being comparable with pristine NaTaO3. For Bi5+- and Bi3+-doped NaTaO3, a high concentration of defects was induced by the high valence Bi5+ ion and this led to its higher photocatalytic activity. Our results indicated that charge carrier transfer is a priority factor in the photocatalytic process and the doping of a high valence ion in the ABO3 structure is a way to promote the separation of charge carriers.

Enhancement of the photocatalytic activity of a TiO2/carbon aerogel based on a hydrophilic secondary pore structure

Improving the separation and utilization of electrons and holes in a photocatalytic process is a guarantee for high photocatalytic efficiency. We report a strategy to enhance the photocatalytic performance based on fabrication of a hydrophilic secondary pore structure by incorporating TiO2 into a porous carbon aerogel (CA) with a 9.3 nm pore diameter, where TiO2 resides on both the inner and outer surfaces of CA as evidenced by N2 sorption isotherms and transmission electron microscopy. In such a structure, the spatial separation efficiency of photoelectrons and photoholes is supposed to get enhanced with interface electrons transferring into the inner surface of the pores via conductive CA. As a result, HO˙ formation can be promoted in the confined inter surface of the hydrophilic secondary channel through O2 reduction with the participation of photoelectrons and H2O. And the remaining photoholes on the outer surface can oxidize water to generate HO˙ as well. In contrast, TiO2 is mainly dispersed on the outer surface of CA as small pore diameters of 3.4 and 4.3 nm; as a result, only uncombined photoholes on the outer surface contribute to HO˙ generation via the water oxidation route. In line with this understanding, TiO2/CA (9.3 nm) shows the largest amount of HO˙ and thereby the highest efficiency of dimethyl phthalate degradation, as respectively evidenced by the electron paramagnetic resonance spectroscopy and the photocatalytic degradation test. These findings unveil the contribution of the surface/interface synergy effect on the separation and utilization of electrons and holes in photocatalytic process, and provide a potential strategy to enhance the photocatalytic performance.

A TiN0.3/CeO2 photo-anode and its photo-electrocatalytic performance

Abstract A TiN0.3/CeO2 photo-anode was synthesized by the electro-deposition of CeO2 on TiN0.3 supported on a Ti substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study its structure and morphology. The crystalline nature of TiN0.3 and CeO2 was confirmed by XRD, and SEM images showed that CeO2 spheres uniformly distributed on the TiN0.3 surface. In addition to visible light absorption by TiN0.3, UV light was also harvested by the outer CeO2 component on the TiN0.3/CeO2 combined photo-anode. In the photo-electrochemical measurement, TiN0.3/CeO2 showed four times higher photo-current density than TiN0.3 or CeO2, and the photo-current stabilization was also significantly improved compared to TiN0.3 or CeO2. The specific double-layer structure of TiN0.3/CeO2 contributed to its improved photo-electrocatalytic performance. Electron transfer from CeO2 to TiN0.3 driven by the hetero-junction and hole consumption by Ce3+ at the TiN0.3/CeO2 interface promoted the separation of electron and hole in the CeO2 layer, which improved the photo-current generation. Ce3+ that existed in CeO2 acted as the adsorption and activation site for H2O and accelerated the oxidation of H2O on the CeO2 surface, which further led to the high and stable photo-current density generated in TiN0.3/CeO2. This finding is useful for the design and synthesis of an effective photo-electrocatalysis material for solar energy conversion.