3D nitrogen-doped graphene aerogel nanomeshes (N-GANMs) with hierarchical porous structures were facilely synthesized from graphene oxide and urea using iron nitrate as the etching agent. The resulting materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and N2 adsorption–desorption. The supercapacitor performance was characterized by cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy, respectively. Compared with the bare graphene aerogel (GA), N-GANMs showed higher specific surface area, more abundant meso-macroporous pores, and much better electrochemical properties. The specific capacitance of N-GANMs was as high as 345.8 F g−1, which was much higher than that of GA and most of the reported carbon-based materials, and the value remains at about 321.0 F g−1 over 2000 cycles at 1.0 A g−1 in 2.0 M KOH. In addition, the N-GANMs demonstrated a high energy density of 20.82 W h kg−1 at a power density of 449.97 W kg−1 and their cycle performance remained approximately 100% after 10 000 cycles at 5.0 A g−1 in 1.0 M Na2SO4. The excellent behaviors might have originated from their hierarchical porous structures and the incorporation of nitrogen.

•Hollow active carbon nanomesh (PCACM) is derived from biowaste-poplar catkins.•Hierarchical porous structure is constructed in PCACM architecture.•PCACM achieves excellent supercapacitive performances.The hollow activated carbon nanomesh (PCACM) with a hierarchical porous structure is derived from biowaste-poplar catkins by in-situ calcination etching with Ni(NO3)2·6H2O and KOH in N2 flow combined with an acid dissolution technique. This procedure not only inherits the natural tube morphology of poplar catkins, but also generates a fascinating nanomesh structure on the walls. PCACM possesses a large specific surface area (SBET = 1893.0 m2 g−1) and high total pore volume (Vp = 1.495 cm3 g−1), and displays an exciting meso-macoporous structure with a concentrated pore size distribution of 4.53 nm. The specific capacitance of PCACM is as high as 314.6 F g−1 at 1.0 A g−1 when used as the electrode materials for supercapacitor. Furthermore, the symmetric supercapacitor of PCACM with 1.0 M Na2SO4 solution as the electrolyte displays a high energy density of 20.86 Wh kg−1 at a power density of 180.13 W kg−1 within a wide voltage rage of 0–1.8 V, which is comparable or even obviously higher than those of other biomass derived carbon reported. It is noteworthy that PCACM also exhibits superior cycling stability and coulombic efficiency. The excellent electrochemical behaviors enable PCACM to be a promising electrode material for supercapacitors.Download high-res image (180KB)Download full-size image

•Magnetic chitosan (CS-Fe3O4) was synthesized and used to anchor Pd(0) nanoparticles.•Pd(0)/CS-Fe3O4 was used catalysts for NH3BH3 hydrolysis.•The catalysts exhibited excellent catalytic activity and reusability in the reaction.•The corresponding activation energy was as low as 35.94 kJ mol−1.Magnetic chitosan (CS-Fe3O4) was synthesized via a co-precipitation method and used as supports to anchor palladium nanoparticles (Pd(0)/CS-Fe3O4) by chemical reduction of PdCl2 with NaBH4. The results showed that the nanosized palladium particles were highly dispersed onto CS-Fe3O4 and the resulting Pd(0)/CS-Fe3O4 catalysts exhibited high catalytic activity and good recyclability for the hydrolysis of ammonia borane (NH3BH3, AB). The turnover frequency (TOF) of the catalysts was as high as 15.0molH2·molPd−1·min−1 at 30 °C and the catalytic activity had not obvious decrease even after eight recycle experiments. The results of kinetic experiments showed that the activation energy of the reaction (Ea) is 35.94 kJ mol−1. The orders of palladium and AB concentrations in the catalytic reaction were 0.70 and 0.62, respectively.Download high-res image (113KB)Download full-size image

•3D α-Fe2O3@GA composites are assembled via agas-liquid interfacial reaction method.•The composites possess a unique hierarchical structure and high contents of dispersed Fe2O3.•The composite electrodes exhibit high specific capacity and stable cycling performance.•The composite electrodes have excellent rate-capability.Three-dimensional (3D) a-Fe2O3@graphene aerogel (a-Fe2O3@GA) composites with an a-Fe2O3 content as high as 54 wt% were prepared via a gas-liquid interfacial assembly method. It was found that the a-Fe2O3 nanoparticles were well dispersed and embedded into the 3D porous structure of graphene aerogel (GA). Compared with that (SBET = 82 m2 g−1) of pristine a-Fe2O3, the resulting composites exhibited much higher specific surface area (SBET = 261 m2 g−1). The composites used as anode materials for lithium ion batteries maintained a high reversible capacity of 745 mAh g−1 at a current density of 100 mA g−1 or more than 240 mAh g−1 at a current density of 2000 mA g−1 after 100 cycles, and exhibited superior stable electrochemical cycling performance and excellent rate capability. The superior electrochemical performances were attributed to the synergistic effects of the unique 3D porous structure of the composites with high contents of well dispersed a-Fe2O3.Download high-res image (178KB)Download full-size image

Reduced graphene oxide (rGO) was synthesized by chemical reduction of graphene oxide with hydrazine hydrate and used as supports to prepare a series of H3PW12O40 (HPW)-based porous solid acids for the first time. Esterification of levulinic acid with ethanol was used to investigate the catalytic properties of the resulting HPW/rGO catalysts. The results showed that the heterogeneous catalysts possessed a porous structure and that their textural characteristics and catalytic activities were influenced by the loading of HPW. Remarkably, they were efficient in the synthesis of ethyl levulinate, with the one with an HPW loading of 45 wt% exhibiting the best efficiency. The conversion of levulinic acid was as high as 96.9%. Meanwhile, the resulting HPW/rGO catalysts also have satisfactory durability. The conversion of levulinic acid still remains at about 53.1% after five cycles under the present conditions. Furthermore, the various catalytic reaction parameters, such as reaction time, ethanol-to-LA molar ratio, and the catalyst dosage, are optimized to maximize the conversion of levulinic acid over 45 wt% HPW/rGO catalysts.

•3D α-Fe2O3@GA composites were prepared from Fe(OH)3 colloids and GO via a hydrothermal process.•The composites exhibited high surface area, abundant meso- and macro-scale pores.•The electrode for LIBs exhibited excellent electrochemical properties.Three-dimensional (3D) α-Fe2O3 nanoparticle anchored graphene aerogel (Fe2O3@GA) composites were assembled by a hydrothermal method using Fe(OH)3 colloids and graphene oxides as starting materials. It was found that the Fe2O3 nanoparticles were uniformly embedded into the 3D networks of graphene aerogels and the resulting composites contained meso- and macro-scale pores. Remarkably, the composites possessed much higher surface area (SBET = 212.5 m2 g−1) and larger pore volume (Vp = 0.2073 cm3 g−1) than those of pure Fe2O3 (SBET = 19.8 m2 g−1, Vp = 0.1770 cm3 g−1). The Fe2O3@GA composites used as electrode materials for lithium ion batteries were demonstrated to exhibit high reversible capacity at large current densities and excellent cycling stabilities.

•3D Fe3O4@GA was assembled from Fe(OH)3 colloid and graphene oxide for the first time.•The electrochemical properties of Fe3O4@GA anode materials for LIBs were investigated.•The hybrid composite was approved to be a promising anode material for LIBs.A novel facile strategy was developed to prepare the Fe3O4@graphene aerogel (Fe3O4@GA) composites. Fe3O4 nanoparticles were uniformly dispersed into the 3D network of graphene aerogel and the resultant hybrid composites contained meso- and macro-scale pores with high specific surface area (276.9 m2 g−1) and large pore volume (0.3230 cm3 g–1). The electrochemical performance revealed that the Fe3O4@GA anode exhibited high reversible capacity (~941.5 mAh g−1 at a current density of 100 mA g−1), stable cycling performance, and excellent rate capability.

A series of composites consisting of anatase TiO2 nanocrystals and three-dimensional (3D) graphene aerogel (TiO2–GA) were self-assembled directly from tetrabutyl titanate and graphene oxides via a one-pot hydrothermal process. TiO2 was found to uniformly distribute inside the 3D network of GA in the resulting composites with large surface areas (SBET > 125 m2 g−1) and high pore volumes (Vp > 0.22 cm3 g−1). In comparison with GA and TiO2, the composites possessed much higher adsorption capacities and visible light photocatalytic activity in the degradation of rhodamine B (RhB). With an initial concentration of 20.0 mg L−1 of RhB, the adsorptive decolourization of RhB was as high as 95.1% and the total decolourization value reached up to 98.7% under visible light irradiation over 5.0 mg of the resulting composites. It was elucidated that the physical and chemical properties of the TiO2–GA composites could be ascribed to their unique 3D nanoporous structure with high surface areas and the synergetic activities of graphene nanosheets and TiO2 nanoparticles.

•HPW–MCM-41 mesoporous materials were facilely prepared for the first time.•Their catalytic activity for the green synthesis of benzoic acid was investigated.•10 wt% HPW–MCM-41 was approved to be the optimal catalyst under the reaction condition.HPW–MCM-41 mesoporous materials were firstly prepared via introducing 12-tungstophosphoric acid (HPW) into MCM-41 with an open synthesis process. The characterization results indicated that the materials retained the mesoporous structure of MCM-41 and bulk HPW was highly dispersed into MCM-41. Catalytic tests showed that HPW–MCM-41 exhibited good catalytic properties for the oxidation of benzaldehyde to benzoic acid with aqueous hydrogen peroxide solution, in the absence of any organic solvent and co-catalysts. The sample containing 10 wt% HPW with larger surface area and pore volume was found to be more active than the others under the same reaction conditions.

•5–45 wt.% HPWA-SBA-15 mesoporous acid catalysts were prepared and characterized.•The catalytic properties for benzaldehyde oxidation with H2O2 were firstly studied.•HPWA-SBA-15 was approved to be a very efficient and environmentally benign catalyst.HPWA-SBA-15 mesoporous catalysts were prepared via directly introducing 12-tungstophosphoric acid (HPWA) into SBA-15 by a hydrothermal method. The samples were characterized by XRD, XRF, FT-IR, DR UV–vis, SEM, TEM, NH3-TPD, and nitrogen adsorption–desorption. The influence of different HPWA amounts on the structure and catalytic properties for benzaldehyde oxidation with 30 wt.% H2O2 was comparatively studied. The results indicated that the HPWA-SBA-15 materials retained the mesopore structure of SBA-15 and the XRD patterns of bulk HPWA would not appear until the HPWA loading increased to 40 wt.%. Catalytic performance tests revealed that HPWA-SBA-15 was an efficient catalyst for the oxidation of benzaldehyde to benzoic acid, and the sample with 35 wt.% HPWA loading was found to be more active than the others under the same reaction conditions.

•5–45 wt.% HPW/MCM-41 mesoporous materials were prepared and characterized.•Their catalytic activities for benzaldehyde oxidation with H2O2 were studied.•HPW/MCM-41 was approved to be an efficient catalyst.•30 wt.% HPW/MCM-41 was the optimized catalyst under the conditions.Mesoporous molecular sieves MCM-41 and bulk 12-tungstophosphoric acid (HPW) were synthesized and employed to prepare 5–45 wt.% HPW/MCM-41 mesoporous materials. Characterization results suggested the good dispersion of HPW within MCM-41 when the loading of HPW was less than 35 wt.% and HPW/MCM-41 retained the typical mesopore structure of the supports. The results of the catalytic oxidation of benzaldehyde to benzoic acid with 30% H2O2, in the absence of any organic solvent and co-catalysts, indicated that HPW/MCM-41 was an efficient catalyst and 30 wt.% HPW/MCM-41 sample exhibited the highest catalytic activity among these materials.

Mesoporous, tungsten-containing molecular sieve (W-SBA-15) composites were successfully synthesized via one-step hydrothermal processing using tetraethyl orthosilicate (TEOS) as the silica precursor, sodium tungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO20PO70EO20, Mav = 5800) as a structure-directing reagent. The influence of various synthesis factors, such as TEOS/sodium tungstate (Si/W) molar ratios, stirring solution temperatures, TEOS pre-hydrolysis time, and crystallization temperatures, on the structure of the W-SBA-15 composite were investigated. The prepared materials were characterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), diffuse reflectance ultraviolet–visible spectroscopy (DR UV–vis), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The results showed that all the W-SBA-15 composite materials retained the mesopore structure of SBA-15 and the tungsten oxide species successfully substituted silica in the framework.

Ceria were prepared by various processes. The prepared samples and commercial ceria were used as supports to prepare the CuO/CeO2 catalysts via an impregnation method. The samples were characterized by using TEM, XRD, H2-TPR, and their catalytic activities in low-temperature CO oxidation were also investigated.

AbstractIn this work, we have reported the influence of the addition of base (KOH) on the physic-ochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XR.D), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by Eb (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.

W-MCM-41 mesoporous materials were directly synthesized via an alkali-hydrothermal method and characterized by using various techniques. The effect of different Si/W molar ratios in the gels on the structure and catalytic performance in cyclohexene oxidation was comparatively investigated in details. The results showed that the as-prepared materials retained good mesoporous structure and the one prepared with Si/W = 40 displayed the best catalytic properties.Graphical abstractHighlights► W-MCM-41 mesoporous materials were directly prepared and characterized. ► The catalytic performance for cyclohexene oxidation was studied. ► W-MCM-41 material was approved to be a very efficient catalyst.