Mesoporous H3PW12O40-silica composite: Efficient and reusable solid acid catalyst for the synthesis of diphenolic acid from levulinic acid

Mesoporous H₃PW₁₂O₄₀-silica composite catalysts with controllable H₃PW₁₂O₄₀ loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H₃PW₁₂O₄₀ loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0 m² g⁻¹), larger and well-distributed pore size (6.1–8.6 nm), larger pore volume (0.75–1.2 cm³ g⁻¹), and highly dispersed Keggin unit throughout the materials. Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites. As a novel kind of reusable solid acid catalyst, as-prepared H₃PW₁₂O₄₀-silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed.     

The performance of electric double layer capacitors using particulate porous carbons derived from PAN fiber and phenol-formaldehyde resin

Activated carbon fibers are known to contain pores with a small resistance for electrolyte migration while possessing a large electrical resistance between the fibers. A carbon powder derived from pulverization of PAN-based carbon fibers was examined as an electrode for electric double layer capacitors using H₂SO₄ as the electrolyte solution. The performance of conventional-type activated carbon powders derived from phenol-formaldehyde resin char was also measured for comparison. The fiber-derived carbon exhibited an electrical resistance comparable to that of the conventional carbons while showed a larger specific capacitance as well as a lesser extent of capacitance decrease at high currents due to a smaller pore resistance. An ultimate capacitance as high as 290 F g⁻¹ can be reached for this fiber-derived carbon powder (with a BET surface area of ≈1300 m² g⁻¹). This large capacitance value was suggested to be associated with the high activity feature of the pore wall.     

Synthesis and characterization of a polystyrenic resin functionalized by catechol: Application to retention of metal ions

Chelating solid phase extraction is a preconcentration method adapted for metal ions extraction in water and requires functionalization of a solid sorbent by an organic ligand. A new chelating resin has been prepared by grafting catechol on Amberlite^® XAD-4 with an imine bridge and reducing it to enhance stability of the modified resin. Synthesis was first carried out at molecular level to validate experimental conditions, optimize yields and facilitate characterization of solid sorbent (particularly by FTIR). Each synthesis step of grafting on Amberlite^® XAD-4 was characterized by FTIR, Py-GC–MS and TGA-DSC. BET measurements showed a decrease in specific area after grafting from 865 to 425 m² g⁻¹ and in total pore volume from 1.19 to 0.66 cm³ g⁻¹. The grafting rate of 33% was determined by back titration of –OH (0.31 ± 0.03 mmol g⁻¹ of resin) and –NH-functions (0.93 ± 0.02 mmol g⁻¹ of resin). The increase in the sorbent hydrophilicity was confirmed by evaluating the water regain. Finally the retention properties of Cd(II), Cu(II), Ni(II) and Pb(II) were determined by ICP-AES at a pH range from 2 to 9. Retention rates of 94% and 98% were found at pH 8 for Cu(II) and Pb(II), respectively. Sorption capacities of 25.8 ± 2.5 μmol g⁻¹ for Cd(II), 89.7 ± 8.4 μmol g⁻¹ for Cu(II), 49.0 ± 10.5 μmol g⁻¹ for Ni(II) and 31.5 ± 1.6 μmol g⁻¹ for Pb(II) were measured.     

Hydrothermally prepared nanocrystalline Mn–Zn ferrites: Synthesis and characterization

Nanocrystalline particles of Mn_xZn_1−xFe₂O₄ were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze–drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m² g⁻¹ and pore sizes in the mesopore region (i.e. 8–20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.     

Amorphous carbon nanofibres inducing high specific capacitance of deposited hydrous ruthenium oxide

Composites consisting of ruthenium oxide particles deposited on amorphous carbon nanofibres are prepared by a repetitive impregnation procedure. The choice of amorphous carbon nanofibres as support of amorphous ruthenium oxide leads to composites in which the deposited oxide consists of aggregates of extremely small primary particles (1–1.5 nm-size) and showing high porosity (specific surface area of 450 m² g⁻¹). This special deposition of the oxide seems to favour: (i) high oxide capacitance (1000 Fg⁻¹) at high oxide loadings (up to 20 wt%) and (ii) high capacitance retention (ca. 80% from the initial oxide capacitance) at high current densities (200 mA cm⁻²). Amorphous carbon nanofibres are suitable supports for amorphous ruthenium oxide and perhaps for other amorphous oxides acting as active electrode materials.     

Formation and electrochemical properties of composites of the C60–Pd polymer and multi-wall carbon nanotubes

Preparation and electrochemical properties of a novel type of the composite made of multi-wall carbon nanotubes (MWCNTs) and two-component polymer of palladium and C₆₀ (C₆₀–Pd) were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and piezoelectric microgravimetry. A composite film was prepared by electrochemical deposition of C₆₀–Pd on the layer of MWCNTs immobilized on the electrode surface. The polymer forms islands of shells on the carbon multi-wall core. This composite is electrochemically active in the negative potential range due to the electroreduction of the fullerene moiety. In this potential range, specific pseudo-capacitance of the film of the MWCNT/C₆₀–Pd composite is 425 F g⁻¹ in the acetonitrile solution of tetra(n-butyl)ammonium perchlorate. The presence of MWCNTs makes the composite conductive also at potentials less negative than potentials of the C₆₀ electroreduction. The double-layer specific capacitance of this film is close to 15 F g⁻¹.     

Influence of the type of sepiolite on the modification of the pore-size distribution in γ-Al2O3 supports

γ-Al₂O₃ modified supports with bimodal pore-size distributions were prepared by the addition of different types of natural sepiolites (α or β) into alumina. The supports were characterized by nitrogen physisorption, mercury porosimetry, X-ray diffraction, HRTEM and DTA techniques. A wide range of S_BET (94–238 m² g^− 1), pore volumes (0.3–0.82 cm³ g^− 1), and pore sizes were obtained in the supports depending on the type of sepiolite and its concentration added into alumina. The pore sizes were distributed as follows: mesopores around 1.8 nm in radius, mesopores in the radius range 3.0–25 nm and macropores between 25 and 300 nm in radius. The shape of the pore-size distributions depended on the type of sepiolite: the modal peak for pores larger than 3.0 nm was broad with β-type sepiolites and narrow with α-type sepiolites. The mesopore and macropore sizes can be controlled by the type of sepiolite as well as its concentration added to alumina.     

Graphitic mesoporous carbons synthesised through mesostructured silica templates

In this paper the fabrication and characterization of graphitizable and graphitized porous carbons with a well-developed mesoporosity is described. The synthetic route used to prepare the graphitizable carbons was: (a) the infiltration of the porosity of mesoporous silica with a solution containing the carbon precursor (i.e. poly-vinyl chloride, PVC), (b) the carbonisation of the silica–PVC composite and (c) the removal of the silica skeletal. Carbons obtained in this way have a certain graphitic order and a good electrical conductivity (0.3 S cm⁻¹), which is two orders larger than that of a non-graphitizable carbon. In addition, these materials have a high BET surface area (>900 m² g⁻¹), a large pore volume (>1 cm³ g⁻¹) and a bimodal porosity made up of mesopores. The pore structure of these carbons can be tailored as a function of the type of silica selected as template. Thus, whereas a graphitizable carbon with a well-ordered porosity is obtained from SBA-15 silica, a carbon with a wormhole pore structure results when MSU-1 silica is used as template. The heat treatment of a graphitizable carbon at a high temperature (2300 °C) allows it to be converted into a graphitized porous carbon with a relatively high BET surface area (260 m² g⁻¹) and a porosity made up of mesopores in the 2–15 nm range.     

Evolution of nanoporosity and electrochemical behavior in organosilicon polymer derived carbon hybrids

Nanoporous carbon hybrids with high specific surface area and pore volume have been prepared from inexpensive commercial precursors, such as nanocarbon and organosilicon polymers. The synthesized carbon hybrids were found to possess specific surface area from 916 to 1798 m² g^?1, pore volume in the range of 0.5–1.2 cc g^?1, and micropore volume up to 0.804 cc g^?1. Cyclic voltammetry in aqueous electrolyte indicated ideal supercapacitive behavior for certain samples. Specific capacitance in the range of 176–333 F g^?1for a moderate voltage scan rate of 20 mV s^?1 was observed for the carbon hybrids. The article explores a simple method for the fabrication of novel carbon hybrids with excellent porosity control and pore volume. The process can open new avenues for the fabrication of a series of novel carbon hybrids, where pore dimensions and specific surface area can be engineered with the careful selection of organosilicon polymers and process conditions.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

Ultra-high specific capacitance of self-doped 3D hierarchical porous turtle shell-derived activated carbon for high-performance supercapacitors

The turtle shell of biomass waste is used as raw material, and the natural inorganic salt contained in it is used as a salt template in combination with a chemical activation method to successfully prepare a high-performance activated carbon with hierarchical porous structure. The role of hydroxyapatite (HAP) and KOH in different stages of preparation was investigated. The prepared turtle shell-derived activated carbon (TSHC-5) has a well-developed honeycomb pore structure, which gives it a high specific surface area (SSA) of 2828 m² g^?1 with a pore volume of 1.91 cm³ g^?1. The excellent hierarchical porous structure and high heteroatom content (O 6.88%, N 5.64%) allow it to have an ultra-high specific capacitance of 727.9 F g^?1 at 0.5 A g^?1 with 92.27% of capacitance retention even after 10,000 cycles. Excitingly, the symmetric supercapacitor assembled from TSHC-5 activated carbon exhibits excellent energy density and cycling stability in a 1 M Na₂SO₄ aqueous solution. The energy density is 45.1 Wh·kg^?1 at a power density of 450 W kg^?1, with 92.05% capacitance retention after 10,000 cycles. Therefore, turtle shell-derived activated carbon is extremely competitive in sustainable new green supercapacitor electrode materials.     

Synthesis of onion-like mesoporous silica from sodium silicate in the presence of α,ω-diamine surfactant

Mesoporous silicas with vesicular and onion-like morphologies were assembled through hydrogen-bonding pathway from sodium silicate as silica source and electrically neutral α,ω-diamine, Jeffamine D2000 surfactant (H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂) as template in aqueous media at different synthesis temperatures (25, 60 and 100 °C). Assembling the material at 100 °C afforded onion-like core shell mesoporous silica, while at relatively lower temperature, e.g. 25 and 60 °C, multilamellar vesicles were obtained. Mesoporous silica with onion-like morphology was also obtained by a two-step synthesis involving an aging period of 20 h at room temperature followed by a hydrothermal stage (1–12 h) at 100 °C. The heavily cross-linked (Q⁴/Q³ ratio of 4.43) onion-like mesophase silica exhibited high hydrothermal stability. The BET surface area, pore volume and KJS (Kruk-Jaroniec-Sayari) pore diameter of the onion-like mesoporous silica were found to be 464 m² g⁻¹, 1.16 m³ g⁻¹ and 7.2 nm, respectively.     

Hydrothermal preparation of octadecahedron Fe3O4 thin film for use in an electrochemical supercapacitor

A Fe₃O₄ film with regularly edge-affected cubic (octadecahedron) morphology was successfully prepared on stainless steel foil by a simple and benign hydrothermal process. The potential for the use of the film in a supercapacitor was tested by investigating the electrochemical behavior of the Fe₃O₄ film using cyclic voltammetry (CV) and galvanostatic charge/discharge tests. The Fe₃O₄ film showed a CV indicative of a typical pseudocapactive behavior in 1 mol L⁻¹ Na₂SO₃ solution. Furthermore, this film exhibited a specific capacitance of 118.2 F g⁻¹ at the current of 6 mA between −1 and 0.1 V with a capacity retention of 88.75% after 500 cycles.     

Preparation of controlled porosity carbon aerogels for energy storage in rechargeable lithium oxygen batteries

Porous carbon aerogels are prepared by polycondensation of resorcinol and formaldehyde catalyzed by sodium carbonate followed by carbonization of the resultant aerogels in an inert atmosphere. Pore structure of carbon aerogels is adjusted by changing the molar ratio of resorcinol to catalyst during gel preparation and also pyrolysis under Ar and activation under CO₂ atmosphere at different temperatures. The prepared carbons are used as active materials in fabrication of composite carbon electrodes. The electrochemical performance of the electrodes has been tested in a Li/O₂ cell. Through the galvanostatic charge/discharge measurements, it is found that the cell performance (i.e. discharge capacity and discharge voltage) depends on the morphology of carbon and a combined effect of pore volume, pore size and surface area of carbon affects the storage capacity. A Li/O₂ cell using the carbon with the largest pore volume (2.195 cm³/g) and a wide pore size (14.23 nm) showed a specific capacity of 1290 mA h g⁻¹.     

Textural and Structural Properties of Mesoporous Silica Synthesized Under Refluxing Conditions

Mesoporous silica with pore sizes of 3–6 nm has been synthesized under refluxing and autogenous pressure conditions of hydrothermal synthesis from precursor gels having different alkaline pH. The mesoporous silica prepared is characterized by powder X-ray diffraction, nitrogen adsorption-desorption measurement and scanning electron microscopy. Thermal stability has been tested by XRD analysis of mesoporous silica after thermal treatment at 823 K, 6 h; 1023 K, 1 h and 1223 K, 1 h. The results indicate that the mesoporous silica prepared under refluxing condition from precursor gel of pH 11 has large surface area (ca.1103 m² g^{− 1}) and pore volume (ca. 0.868 cm³ g^{− 1}) and is thermally stable at 1223 K. The surface area, pore volumes and pore wall thickness increase as the pH of the precursor gel is increased for refluxing condition of synthesis. The comparison of textural properties revealed that the refluxing condition is advantageous over autogenous pressure condition for obtaining mesoporous silica with higher surface area (852 m² g^{− 1}), pore volume (0.894 cm³ g^{− 1}) and pore diameter > 4 nm with wall thickness of 1.59 nm, when synthesized from precursor gel of pH 9.2. The ²⁹Si NMR spectra showed that a great part of the Si atoms exists as silanol groups. The mesoporous silica made at the lower pH (9.2) under refluxing conditions have more condensed framework. In calcined mesoporous silica, the proportion of partly condensed silica (Q³) is higher than fully condensed silica (Q⁴).     

Removal of heavy metal ions by dithiocarbamate-anchored polymer/organosmectite composites

In this study, the dithiocarbamate-anchored polymer/organosmectite composites were prepared for the removal of heavy metal ions (lead, cadmium and chromium) from aqueous media containing different amounts of these ions (50–750 ppm) and at different pH values (2.0–8.0). Initially, the modification of the natural smectite minerals was performed by treatment with quartamin styrene and chloromethylstyrene. Then, modified smectite nanocomposites were reacted with carbondisulfide, in order to incorporate dithiocarbamate functional groups into the nanolayer of organoclay. The dithiocarbamate-anchored nano-composites have been characterized by FTIR and used in the adsorption–desorption process. The maximum adsorptions of heavy metal ions onto the dithiocarbamate-anchored polymer/organosmectite composites from their solution was 170.7 mg g^− 1 for Pb(II); 82.2 mg g^− 1 for Cd(II) and 71.1 mg g^− 1 for Cr(III). Competition between heavy metal ions (in the case of adsorption from mixture) yielded adsorption capacities of 70.4 mg g^− 1 for Pb(II); 31.8 mg g^− 1 for Cd(II) and 20.3 mg g^− 1 for Cr(III). Desorption of the heavy metal ions from composite was studied in 0.5 M NaCl and very high desorption rates, greater than 93%, were achieved in all cases. Adsorption–desorption cycles showed the feasibility of repeated uses of this nanocomposite.     

Synthesis and dye separation performance of ferromagnetic hierarchical porous carbon

Ferromagnetic hierarchical porous carbon (FHPC) with nickel particles embedded in the hierarchical porous carbon skeleton was synthesized. The hierarchical macro–mesoporous skeleton was formed by dissolving a salt template of Na₂CO₃ and the ferromagnetic nickel particles were produced by in situ carbothermal reduction of nickel oxide. The saturation magnetization, remnant magnetization and coercive force of FHPC are 11.3 emu g⁻¹, 2.3 emu g⁻¹ and 55.7 Oe. The ferromagnetic property enables the magnetic separation of the FHPC from water. The surface chemical environments of the FHPC consist of different oxygen functional groups, like –OH, >COO and >CO groups, as well as a trace amount of aliphatic species of –CH₃ or -CH_2^- structures. Dye separation performance of the FHPC was investigated using methylene orange, and the adsorption capacity was 0.16 mg m⁻² with the adsorption kinetics constant of 2.2 m² mg⁻¹ min⁻¹, which is superior to that of magnetic carbon spheres.     

Preparation and electrochemical performance of micro-nanostructured nickel

Micro-nanostructured nickel has been prepared as anode materials for Li ion batteries, via a rheological phase reaction method. Ni₂C₂O₄·xH₂O (x = 2 or 2.5) as precursors are obtained from the solid–liquid rheological mixture of (NH4)₂C₂O₄·H₂O and Ni(NO₃)₂. The nickel powders are prepared by thermal decomposition of the precursors. The structural, morphological and electrochemical performance are investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and typical electrochemical tests. The micro-nanostructured nickel displays an initial discharge capacity of 457 mAh g⁻¹. It also has a remarkable cycling stability with an average capacity fade of 0.17% per cycle from 13th to 50th cycle in 0.01–3.00 V versus Li at a constant current density of 100 mA g⁻¹.     

Sawdust: A green and economical sorbent for thallium removal

Removal/preconcentration of thallium(I) ions from aqueous solution by sawdust; a waste material derived from the commercial processing of Cedrus Deodar wood for furniture production was investigated. A simple and low-cost modification results in increasing the sorption capacity of raw sawdust from 2.71 to 13.18 mg g⁻¹. Sorption was found to be rapid (98% within 8 min). The binding of metal ions was found to be pH dependent, optimal sorption accruing at around pH 6–9. Potentiometeric titrations of sawdust revealed two distinct pK_a values, the first having the value similar to carboxylic groups (3.3–4.8) and second comparable with that of amines (8.53–10.2) with the surface site densities of 1.99 × 10⁻⁴ and 7.94 × 10⁻⁵ mol g⁻¹, respectively. Retained Tl(I) ions were eluted with 5 ml 0.1 mol l⁻¹ HCl. Detection limit of 0.0125 μg ml⁻¹ was achieved with an enrichment factor of 160. Recovery was quantitative using sample volume of 800 ml. The Langmuir, Freundlich and D–R isotherm equations were used to describe partitioning behavior for the system at different temperatures. Kinetic and thermodynamic behavior of sawdust for Tl(I) ions removal was also studied.     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.