Wenji Zheng

Multishelled NiO Hollow Microspheres for High-performance Supercapacitors with Ultrahigh Energy Density and Robust Cycle Life.

Multishelled NiO hollow microspheres for high-performance supercapacitors have been prepared and the formation mechanism has been investigated. By using resin microspheres to absorb Ni2+ and subsequent proper calcinations, the shell numbers, shell spacing and exterior shell structure were facilely controlled via varying synthetic parameters. Particularly, the exterior shell structure that accurately associated with the ion transfer is finely controlled by forming a single shell or closed exterior double-shells. Among multishelled NiO hollow microspheres, the triple-shelled NiO with an outer single-shelled microspheres show a remarkable capacity of 1280 F g−1 at 1 A g−1, and still keep a high value of 704 F g−1 even at 20 A g−1. The outstanding performances are attributed to its fast ion/electron transfer, high specific surface area and large shell space. The specific capacitance gradually increases to 108% of its initial value after 2500 cycles, demonstrating its high stability. Importantly, the 3S-NiO-HMS//RGO@Fe3O4 asymmetric supercapacitor shows an ultrahigh energy density of 51.0 Wh kg−1 at a power density of 800 W kg−1, and 78.8% capacitance retention after 10,000 cycles. Furthermore, multishelled NiO can be transferred into multishelled Ni microspheres with high-efficient H2 generation rate of 598.5 mL H2 min−1 g−1Ni for catalytic hydrolysis of NH3BH3 (AB).

Bis-ammonium immobilized polystyrenes with co-catalyzing functional end groups as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate from CO2 and epoxides

A series of novel bis-ammonium ionic liquid immobilized polystyrene (BisAm-i-PS) heterogeneous catalysts with co-catalyzing functional end groups of –CH2COOH, –CH2CH2OH, and –CH2CH2NH2 were synthesized for the cycloaddition reaction of CO2 and epoxides without any additional co-catalyst and organic solvent. All the ammonium immobilized catalysts showed high selectivity. Bis-ammonium immobilized catalysts were more efficient than single-ammonium ones. The yield was further increased by introducing the functional end groups. Both –CH2COOH and –CH2CH2OH terminated BisAm-i-PS catalysts achieved high activities (yield: >99%), while the –NH2 terminated one had a slightly lower activity (yield: 97.3%) under the same reaction conditions. The effects of different parameters, such as the halide anions of the catalysts, reaction temperature, initial pressure and reaction time were also investigated with –CH2CH2OH terminated BisAm-i-PS (BisAm-OH-i-PS) as the catalyst. Under optimal reaction conditions (1.2 MPa, 130 °C and 2.5 h), BisAm-OH-i-PSs with 2Br− and 2I− showed very high efficiencies. For each of them, propylene carbonate selectivity and yield were more than 99% and 99%, respectively. In addition, the catalyst possessed good stability, and both catalytic activity and selectivity were always more than 99% for 5 times of recycle tests.

A highly responsive UV photodetector based on hierarchical TiO2 nanorod/nanoparticle composite

Hierarchical TiO2 nanorod/nanoparticle composites were successfully prepared by TiCl4 modification of vertically aligned TiO2 nanorod (NR) arrays. After the hydrolysis of TiCl4 at room temperature, TiO2 nanoparticles (NPs) were deposited on the surface of TiO2 NRs. Morphology and structure analysis demonstrated that the TiO2 NPs were distributed around the entire surface of TiO2 NRs due to the easy permeation of TiCl4 solution between the NR space. Moreover, the high concentration of TiCl4 and long reaction time are favorable for the generation of more TiO2 NPs, which correspondingly increases the surface area of the composite to a large extent. Compared with most reported TiO2-based UV photodetectors (PDs), the present TiO2 NR/NP composite-based PDs simultaneously exhibit an extremely high response and a relatively fast response speed. The maxima of responsivity and response speed, which are 1973 A W−1 and 0.47 s (rise time) and 1.02 s (decay time), respectively, are obtained from the sample of TiO2 NR/NP-0.4 M-72 h. The fast and high photoresponses are ascribed to the large surface area provided by TiO2 NPs, the well-defined electron transport pathway offered from TiO2 NRs and the homojunction formed at the interface between them. Moreover, together with the high responsivity and the relatively fast response speed, significant UV light selectivity and a very good linear relationship between a photoresponse and the UV light intensity suggest that the present UV PDs are very competitive and highly applicable in UV light detection.

Interpenetrated Networks between Graphitic Carbon Infilling and Ultrafine TiO2 Nanocrystals with Patterned Macroporous Structure for High-Performance Lithium Ion Batteries

Interpenetrated networks between graphitic carbon infilling and ultrafine TiO2 nanocrystals with patterned macropores (100-200 nm) were successfully synthesized. Polypyrrole layer was conformably coated on the primary TiO2 nanoparticles (∼8 nm) by a photosensitive reaction and was then transformed into carbon infilling in the interparticle mesopores of the TiO2 nanoparticles. Compared to the carbon/graphene supported TiO2 nanoparticles or carbon coated TiO2 nanostructures, the carbon infilling would provide a conductive medium and buffer layer for volume expansion of the encapsulated TiO2 nanoparticles, thus enhancing conductivity and cycle stability of the C-TiO2 anode materials for lithium ion batteries (LIBs). In addition, the macropores with diameters of 100-200 nm in the C-TiO2 anode and the mesopores in carbon infilling could improve electrolyte transportation in the electrodes and shorten the lithium ion diffusion length. The C-TiO2 electrode can provide a large capacity of 192.8 mA h g-1 after 100 cycles at 200 mA g-1, which is higher than those of the pure macroporous TiO2 electrode (144.8 mA h g-1), C-TiO2 composite electrode without macroporous structure (128 mA h g-1), and most of the TiO2 based electrodes in the literature. Importantly, the C-TiO2 electrode exhibits a high rate performance and still delivers a high capacity of ∼140 mA h g-1 after 1000 cycles at 1000 mA g-1 (∼5.88 C), suggesting good lithium storage properties of the macroporous C-TiO2 composites with high capacity, cycle stability, and rate capability. This work would be instructive for designing hierarchical porous TiO2 based anodes for high-performance LIBs.

Fabrication of a visible light detector based on a coaxial polypyrrole/TiO2 nanorod heterojunction

A visible light detector can be fabricated using a coaxial polypyrrole/TiO2 nanorod composite. Based on the composite, the detector exhibits high responsivity up to 0.45 A W−1, impressive stability and excellent linear dependence of the photoresponse on visible light intensity. All of these properties make the polypyrrole/TiO2 nanorod composite very competitive and highly applicable in visible light detection.

Quaternary-ammonium-immobilized polystyrenes as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate: Effects of linking chains and pendent hydroxyl group

Abstract Spherical polystyrene-supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2 and epoxides. The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations. It was found that, compared with a short linking chain, a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants, thus enhancing the reaction kinetics. The hydroxyl group can stretch the C–O bonds of the epoxides, promoting the reaction thermodynamics. As a result, for the cycloaddition of propylene oxide, the yield of propylene carbonate is much higher for the catalyst with a long linking chain (yield: 91.4%) compared with the yield for that with a short chain (yield: 70.9%), and is further increased in the presence of pendent hydroxyl groups (yield: 98.5%). The catalyst also shows a high catalytic activity even at mild temperature and good reusability (yield: ≥ 96% for 10 cycles), and the selectivity is always above 99%.