Construction of Built-In Electric Field in TiO2@Ti2O3 Core-Shell Heterojunctions toward Optimized Photocatalytic Performance.

A series of Ti2O3@TiO2 core-shell heterojunction composite photocatalysts with different internal electric fields were synthesized using simple heat treatment methods. The synthesized Ti2O3@TiO2 core-shell heterojunction composites were characterized by means of SEM, XRD, PL, UV-Vis, BET, SPV, TEM and other related analytical techniques. Tetracycline (TC) was used as the degradation target to evaluate the photocatalytic performance of the synthesized Ti2O3@TiO2 core-shell heterojunction composites. The relevant test results show that the photocatalytic performance of the optimized materials has been significantly enhanced compared to Ti2O3, while the photocatalytic degradation rate has increased from 28% to 70.1%. After verification via several different testing and characterization techniques, the excellent catalytic performance is attributed to the efficient separation efficiency of the photogenerated charge carriers derived from the built-in electric field formed between Ti2O3 and TiO2. When the recombination of electrons and holes is occupied, more charges are generated to reach the surface of the photocatalyst, thereby improving the photocatalytic degradation efficiency. Thus, this work provides a universal strategy to enhance the photocatalytic performance of Ti2O3 by coupling it with TiO2 to build an internal electric field.

Efficient Charge Transfer Channels in Reduced Graphene Oxide/Mesoporous TiO2 Nanotube Heterojunction Assemblies toward Optimized Photocatalytic Hydrogen Evolution.

Interface engineering is usually considered to be an efficient strategy to promote the separation and migration of photoexcited electron-hole pairs and improve photocatalytic performance. Herein, reduced graphene oxide/mesoporous titanium dioxide nanotube heterojunction assemblies (rGO/TiO2) are fabricated via a facile hydrothermal method. The rGO is anchored on the surface of TiO2 nanosheet assembled nanotubes in a tightly manner due to the laminated effect, in which the formed heterojunction interface becomes efficient charge transfer channels to boost the photocatalytic performance. The resultant rGO/TiO2 heterojunction assemblies extend the photoresponse to the visible light region and exhibit an excellent photocatalytic hydrogen production rate of 932.9 µmol h-1 g-1 under simulated sunlight (AM 1.5G), which is much higher than that of pristine TiO2 nanotubes (768.4 µmol h-1 g-1). The enhancement can be ascribed to the formation of a heterojunction assembly, establishing effective charge transfer channels and favoring spatial charge separation, the introduced rGO acting as an electron acceptor and the two-dimensional mesoporous nanosheets structure supplying a large surface area and adequate surface active sites. This heterojunction assembly will have potential applications in energy fields.

Engineering oxygen vacancies in CoO@Co3O4/C nanocomposites for enhanced electrochemical performances.

Efficient electrocatalyst materials for several applications, including energy storage and conversion, have become vital for achieving technological progress. In this work, a CoO@Co3O4/C composite with abundant oxygen vacancies was successfully synthesized. The concentration of the oxygen vacancies was well controlled by changing the degree of vacuum during the heat treatment and was characterized by XPS and EPR. The existence of the porous structure arising from the cobalt oxide particles embedded in the carbon matrix provided an efficient charge and gas transmission path, significantly improving the performance of electrocatalytic oxygen evolution. Sufficient reactive sites were provided from both the oxygen vacancies and the heterogeneous interface. The mechanism of enhanced OER originating from the built-in electric field derived from oxygen vacancies was investigated. Consequently, the CoO@Co3O4/C composites offered an OER overpotential of 287 mV at a current density of 10 mA cm-2 with good stability in 1 mol L-1 KOH. In addition, combined with surface photovoltage (SPV), transient photovoltage (TPV), DFT, and in situ Raman spectroscopy, the effect of oxygen defects on the electron migration ability and transformation of the intermediate products were investigated to further understand the nature of catalytic activity in OER.

In Situ Implanting of Single Tungsten Sites into Defective UiO-66(Zr) by Solvent-Free Route for Efficient Oxidative Desulfurization at Room Temperature.

Design of single-site catalysts with catalytic sites at atomic-scale and high atom utilization, provides new opportunities to gain superior catalytic performance for targeted reactions. In this contribution, we report a one-pot green approach for in situ implanting of single tungsten sites (up to 12.7 wt.%) onto the nodes of defective UiO-66(Zr) structure via forming Zr-O-W bonds under solvent-free condition. The catalysts displayed extraordinary activity for the oxidative removal of sulfur compounds (1000 ppm S) at room temperature within 30 min. The turnover frequency (TOF) value can reach 44.0 h-1 at 30 °C, which is 109.0, 12.3 and 1.2 times higher than that of pristine UiO-66(Zr), WO3 , and WCl6 (homogeneous catalyst). Theoretical and experimental studies show that the anchored W sites can react with oxidant readily and generate WVI -peroxo intermediates that determine the reaction activity. Our work not only manifests the application of SSCs in the field of desulfurization of fuel oil but also opens a new solvent-free avenue for fabricating MOFs based SSCs.

A long-term stable aqueous aluminum battery electrode based on one-dimensional molybdenum-tantalum oxide nanotube arrays.

Aluminum ion aqueous batteries (AIBs) are among the most promising candidates for high energy density devices due to the multivalent redox processes associated with Al3+ ion intercalation. However, only a few stable AIB electrode materials have been reported so far. MoO3 is a very promising electrode material due to its octahedral layered crystal structure which can accommodate multivalent cation by intercalation. However, the poor electrochemical stability of MoO3 and the sluggish intercalation kinetics of Al3+ ion in Mo oxides electrodes limit its practical application. In this work, we propose a strategy to overcome such shortcomings of MoO3 by fabricating electrodes composed of self-ordered one-dimensional (1D) MoTaOx nanotubes synthesized via electrochemical anodization of Mo-Ta alloy substrates. We show that this approach allows for direct incorporation of Ta in the Mo oxide nanotubes. The resulting MoTaOx nanotubes, composed of octahedral MoO3 and rhombohedral Mo2Ta2O11 phases, exhibit remarkable electrochemical stability and Al-ion storage properties in aqueous electrolytes that are superior to that of pristine Mo oxide or other most efficient electrode materials reported to date. Such MoTaOx nanotube-based electrodes can achieve a specific capacity of 1180 mA h cm-3 (337 mA h g-1, 141 µA h cm-2) at 1.25 A cm-3 (∼0.35 A g-1, 0.15 mA cm-2). More importantly, the capacity retention of such nanotube array electrodes remains above 83% of the initial capacity after 3000 cycles.