Fe-doped HTaWO6 (H1−3xFexTaWO6, x = 0.23) nanotubes as highly active solid acid catalysts were prepared via an exfoliation–scrolling–exchange process. The specific surface area and pore volume of undoped nanotubes (20.8 m2 g−1, 0.057 cm3 g−1) were remarkably enhanced through Fe3+ ion-exchange (>100 m2 g−1, 0.547 cm3 g−1). Doping Fe ions into the nanotubes endowed them with improved thermal stability due to the stronger interaction between the intercalated Fe3+ ions and the host layers. This interaction also facilitated the preservation of effective Brønsted acid sites and the generation of new acid sites. The integration of these functional roles resulted in Fe-doped nanotubes with high acidic catalytic activities in the Friedel–Crafts alkylation of anisole and the esterification of acetic acid. Facile accessibility to active sites, generation of effective Brønsted acid sites, high stability of the tubular structure and strong acid sites were found to synergistically contribute to the excellent acidic catalytic efficiency. Additionally, the activity of cycled nanocatalysts can be easily recovered through annealing treatment.

•High specific capacitive TiO2(B)@C/rGO nanoarchitetures were successfully synthesized.•Complete utilization of Faradic and non-Faradic capacitance of nanohybrids was realized by using formulated electrolyte.•4 V operating potential was actualized with the presence of ionogel polymer separator.Novel TiO2(B)@C/rGO nanoarchitectures are fabricated by combining hydrothermal treatment, ions exchange, and topological phase transformation as well as carbon modification. Asymmetric hybrid Li-ion nanohybrids supercapacitors with high energy and power densities are constructed by combining hybridized anode, which can supply both pseudo capacitance from TiO2(B) and electrochemical double layer capacitance (EDLC) from nanocarbons (graphene nanosheets and amorphous carbon layer), and activated carbon (AC) as EDLC type cathode. The high power density is realized readily via both the modification of nanocarbons, which not only improve the electric conductivity but introduce extra Faradic capacitance, and the employment of high-voltage formulated ionic liquids electrolyte as well as ionogel polymer separator. Such a balanceable and complementary design between electrode and electrolyte allow rapid ion and electron transport in ionic liquid-based electrolyte and hybridized electrodes. The maximum energy and power density of 59.4 W h/kg and 17.3 kW/kg can be readily realized at 40 °C on account of the special characteristic of ionic liquids. These results clearly demonstrate that high performance nanohybrid supercapacitors can be actualized through the subtle combination of nanohybridized electrodes and high voltage formulated ionic-liquid/lithium-salt electrolytes, which make them promising power-type energy storage devices for hybrid electric vehicles.Download high-res image (279KB)Download full-size image

Layered inorganic–organic TiO2–ILs hybrids with tunable basal spacing were fabricated through electrostatic interaction between 2D inorganic nanosheets and organic imidazolium-based ILs. Imidazolium cations with various sizes were intercalated into lamellar titanate nanosheets, forming layered structures with slabs turbostratic restacking. The effects of cation sizes on the interfacial properties of hybrids were comprehensively investigated by XRD, SEM, TEM, AFM, FT-IR, Raman and TG techniques. The results confirmed that the ratio of interlayer imidazolium cations declined with increasing carbon chain length. A CO2 absorption experiment was conducted and TiO2–ILs compounds displayed enhanced CO2 absorption capacity with the increase of alkyl chain length, which could be attributed to the synergistic interfacial effects induced by diverse interactions between ILs and inorganic nanosheets. An absorption mechanism was proposed on account of ion-exchangeable characteristic of these layered hybrids and the intercalated H2O molecules were found to play a crucial role in CO2 uptake.

Colloidal mesoporous magnetite nanoparticles with tunable porosity were realized by a simple and scalable solvothermal route with the aid of AOT as ligands. AOT was used to induce the anisotropic crystal growth of smaller nanocrystals and restrain their tight aggregation so as to form more mesoscale pores. Morphologies and microstructures investigation by SEM and TEM revealed that the bigger nanoparticles were composed of smaller nanocrystals with an average size of 18 nm. A possible formation mechanism was proposed for the mesoporous nanoparticles. Study of nitrogen adsorption–desorption isotherm revealed that the Brunauer–Emmett–Teller (BET) specific surface area of mesoporous nanoparticles is up to 209 m2/g, resulting from the slit-shaped pores created by the aggregation of polyhedral nanocrystals. Magnetic properties study indicated that the as-prepared nanoparticles are superparamagnetic at room temperature. Optimized mesoporous magnetite nanoparticles exhibit a maximum Cr(VI) ion sorption capacity of 12.9 mmol/g, and its absorption behavior followed a Freundlich model. Microwave absorption study indicated that porous nanoparticles own higher permeability values than that of solid nanoparticles, leading to a higher dielectric loss in the frequency range of 2–18 GHz.

Layered HNb3O8/graphene hybrids with numerous heterogeneous interfaces and hierarchical pores were fabricated via the reorganization of exfoliated HNb3O8 nanosheets with graphene nanosheets (GNs). Numerous interfaces and pores were created by the alternative stacking of HNb3O8 nanosheets with limited size and GNs with a buckling and folding feature. The photocatalytic conversation of CO2 into renewable fuels by optimized HNb3O8/G hybrids yields 8.0-fold improvements in CO evolution amounts than that of commercial P25 and 8.6-fold improvements than that of HNb3O8 bulk powders. The investigation on the relationships between microstructures and improved photocatalytic performance demonstrates that the improved photocatalytic performance is attributed to the exotic synergistic effects via the combination of enhanced specific BET surface area, increased strong acid sites and strong acid amounts, narrowed band gap energy, depressed electron–hole recombination rate, and heterogeneous interfaces.

A new type of magnetically recyclable solid acid catalyst was designed and retro-synthesized via a two-step template method. Magnetic Fe3O4 cores were synthesized by a solvothermal approach, and then coated with a silica layer by a sol–gel process in order to improve their stability in acid environments. HNbMoO6 nanosheets used as outer shell precursors were obtained by exfoliating a layered tri-rutile transition metal oxide (LiNbMoO6) via proton exchange and intercalation of tetrabutylammonium cations. Negatively charged nanosheets were assembled upon the Fe3O4@SiO2 particles using poly(diallyldimethylammonium chloride) as an opposite polyelectrolyte via a layer-by-layer sequential adsorption process. Protonation of the outer layer was realized by acid exchange treatment. The protonated core–shell nanocomposites showed effective catalytic properties for Friedel–Crafts alkylation reaction and high magnetic recyclability. These results highlight that the rational design and controllable synthesis of multifunctional catalysts is a promising strategy in “green chemistry” and “green technologies”.

A new type of magnetically recyclable solid acid catalyst was designed and retro-synthesized via a two-step template method. Magnetic Fe3O4 cores were synthesized by a solvothermal approach, and then coated with a silica layer by a sol–gel process in order to improve their stability in acid environments. HNbMoO6 nanosheets used as outer shell precursors were obtained by exfoliating a layered tri-rutile transition metal oxide (LiNbMoO6) via proton exchange and intercalation of tetrabutylammonium cations. Negatively charged nanosheets were assembled upon the Fe3O4@SiO2 particles using poly(diallyldimethylammonium chloride) as an opposite polyelectrolyte via a layer-by-layer sequential adsorption process. Protonation of the outer layer was realized by acid exchange treatment. The protonated core–shell nanocomposites showed effective catalytic properties for Friedel–Crafts alkylation reaction and high magnetic recyclability. These results highlight that the rational design and controllable synthesis of multifunctional catalysts is a promising strategy in “green chemistry” and “green technologies”.