Mesoporous High Surface Area Research Articles

Very High Surface Area Mesoporous Thin Films of SrTiO3 Grown by Pulsed Laser Deposition and Application to Efficient Photoelectrochemical Water Splitting.

Very high surface area, self-assembled, highly crystalline mesoporous SrTiO3 (STO) thin films were developed for photoelectrochemical water splitting. Much improved performance of these mesoporous films compared to planar STO thin films and any other form of STO such as single crystal samples and nanostructures was demonstrated. The high performance resulted from very large surface area films and optimization of carrier concentration.

Nanostructured cobalt-modified molybdenum carbides electrocatalysts for hydrogen evolution reaction

A series of nanostructured catalysts based on cobalt-modified molybdenum carbides, intended as alternative replacement for platinum has been developed for the hydrogen evolution reaction (HER) from brine. The catalysts were synthesized by simple impregnation of the metal salts on carbon support and followed by pyrolysis in CH4 atmosphere. The obtained catalysts show impressive HER activities in both brine and alkaline media. At current density of −7.0 mA cm−2, the overpotential for Co modified Mo/C catalysts was greater than that obtained with a commercial Pt/C catalyst by 63–89 mV and 15–148 mV for brine and alkaline solution, respectively. Our findings for HER in both media are consistent with electrochemical desorption of hydrogen gas following the Volmer-Heyrovsky mechanism as the rate-determining step. The HER activities of the catalysts were correlated to their high mesopore surface areas with active pores, nanocrystallites, and low charge transfer resistances as confirmed by electrochemical impedance spectroscopy.

Adsorption of divalent heavy metal ion by mesoporous-high surface area chitosan/poly (ethylene oxide) nanofibrous membrane

In this study, chitosan/poly (ethylene oxide) nanofibres were fabricated at different chitosan:PEO weight ratio by electrospinning process. The effects of chitosan/PEO composition onto adsorption capability for Cu(II), Zn(II) and Pb(II) ions were studied. Formation of beadless fibres were achieved at 60:40 chitosan:PEO ratio. Average fiber diameter, maximum tensile strength and the specific surface area of the beadless fibres were found to be 115±31nm, 1.58MPa and 218m2/g, respectively. Chitosan/PEO composition that produced beadless fibres tend to possess higher hydrophilicity and maximum specific surface area. These characteristics lead the beadless fibres to the maximum adsorption capability. Adsorption equilibrium data were analysed by Langmuir and Freundlich isotherm. Freundlich isotherm showed the better fit with the experimental data and proved the existence of the monolayer adsorption conditions. The maximum adsorption capacity of the beadless fibres for Cu(II), Zn(II) and Pb(II) ions were found to be 120, 117 and 108mgg−1, respectively.

Fe incorporated mesocellular foam as an effective and stable catalyst: Effect of Fe concentration on the characteristics and activity in Fenton-like oxidation of acid red B

Fe incorporated mesocellular foam catalysts (FeMCFs) developed by direct synthesis method were characterized and catalytic degradation of acid red B dye (ARB) via Fenton-like reaction was demonstrated. The shape and particle sizes of FeMCF changed significantly with an increase in the Fe concentration (4–12wt.%) accompanied with the formation of Fe particles agglomerated on the external surface of the catalysts. Interestingly, the sponge-like foam structure coupled with large pores of MCF could be maintained for all concentrations of Fe added. FT-IR and UV–vis DRS analyses revealed that Fe was successfully incorporated mostly within the mesostructure of MCF rather than being distributed on the external surface at Fe loadings of 4–10wt.%. However, formation of minor amount of iron oxides distributed on the external surface of FeMCF12 was detected by the appearance of broad bands in the range of 300–400nm. An increase in the Fe content (4–12wt.%) gave a slight decrease in the surface area (708–606m2/g) and pore properties of the FeMCF. The increase in the Fe concentration from 4 to 12wt.% progressively increased the degradation from 63 to 100%. The high decolourisation and degradation efficiencies of FeMCF10 could be explained in terms of combined factors such as high mesopore surface area (552m2/g), large cell size (8nm) and the presence of isolated Fe species leading to high accessibility of active sites without mass transfer limitations. FeMCF10 exhibited long term stability and good structural stability after it was used for five consecutive degradation cycles.

Synthesis and electrochemical performance of mesoporous nickel oxide using mixed surfactant template

Nickel oxide is an environment-friendly transition metal oxide with relatively low cost and a kind of excellent electrode materials for supercapacitor. High surface area with favourable porosity can facilitate the electrochemical performance of NiO. Mesoporous nickel oxide was synthesised by a hydrothermal homogeneous precipitation method in this research, using mixed anionic/non-ionic surfactant as template. The influence of mixing ratio of the two constituents in the mixed surfactant was investigated. The prepared NiO samples were characterised by N2 adsorption–desorption, X-ray diffraction, scanning electron microscope and high-resolution transmission electron microscope measurements. Also, the electrochemical performances of the NiO electrode were determined by cyclic voltammetry at different scan rate and chronopotentiometry at different current density. The results showed that the prepared NiO had mesoporous structure and high specific surface area while the electrochemical performances exhibited high redox capacity, good cycle stability and great rate capability.

Production of high surface area mesoporous activated carbons from waste biomass using hydrogen peroxide-mediated hydrothermal treatment for adsorption applications

High-surface area mesoporous activated carbons were prepared from biomass by incorporating H2O2 as an oxidizing agent during hydrothermal pre-treatment of the raw material (coconut shell). Use of H2O2 led to enhanced formation of OFGs in the hydrochar precursor and resulted in activated carbons possessing high mesopore and BET surface areas. A strong interdependence is observed between the extent of formation of oxygenated functional groups (OFGs) in the hydrochars obtained from the hydrothermal pre-treatment and mesopore area in corresponding carbons. The mesoporous carbons showed high adsorption capacity for Rhodamine B up to 714mg/g.

Nickel Oxide Nanoparticle-Assembled Microspheres with a High Rate Capability for Lithium Storage

This paper presents the massive preparation of nickel oxide nanoparticle-assembled mesoporous microspheres using acid-treated carbon microspheres as sacrificial templates. The microstructure and morphology of the hollow NiO microspheres are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption methods. Scanning electron microscopy and transmission electron microscopy images reveal that these hollow spheres are assembled by NiO particles with sizes of ~20 nm. The nickel oxide nanoparticle-assembled mesoporous microspheres feature high surface area and good electronic conductivity, leading to high capacity and excellent cycling performance as anode materials for lithium-ion batteries.

Hydrothermal Synthesis and Photocatalytic Activity of Mesoporouse TiO<sub>2</sub> with High Surface Area and Different Pore Size

Mesoporous TiO2with high surface area (SBET) and different pore size was successfully fabricated via hydrothermal method using cetyltrimethylammonium bromide and PEO-PPO-PEO as the structure-directing agents, and tetrabutyl titanate (TBT) as titanium source.SBETand pore size of the materials were adjusted by using different amount of TBT.SBETwas increased as TBT changing from 0.5 g to 1.0 g, and then dropped as 2.0 g TBT added. Among as-prepared samples (PC), PC-1.0 showed the highestSBETof 92.72 m2g1. With the increase amount of TBT, pore size increased from 10.36 nm to 12.72 nm. The phtocatalysis study showed that PC-1.0 had the highest percent degradation of 99.6 %. We believed that the design and synthesis of mesoporous TiO2with changing mesopores andSBETare important for both fundamental and technological viewpoints.

Synthesis of High Surface Area Mesoporous Silica Powder Using Anionic Surfactant

Over the past several years, synthesized mesoporous nanosilica (SiO2) powders have been developed by many different methods. The methods include precipitation and microemulsion, the Stöber method, chemistry, and technology. In this study, mesoporous silica powders are synthesized by the sol-gel method. The sol-gel method obtains a high purity silica powder; however, the process yields a low percentage. Past syntheses of SiO2 powder precursors are expensive, but this study needs to find a replacement precursor for low cost alternatives. A high surface area was used to form an anion surfactant sodium dodecyl sulfate, which regulates the molar concentration. The particles size variability was changed by the precursor molar ratio of the sodium silicate solution with hydrochloric acid.

Fabrication and Excellent Catalytic Performance of Three-dimensional Ordered Mesoporous Molybdenum Oxides

Three-dimensional (3D) ordered and wormhole-like MoO3 mesoporous structures were synthesized based on ultrasound-assisted vacuum impregnation method. Carbon template was used in the synthesis process, which was prepared by using mesoporous molecular sieve KIT-6. Hexaammonium molybdate acted as molybdenum source. The as-prepared MoO3 samples were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), thermogravimetric analysis/differenctial scanning calorimetry (TG/DSC), and N2 adsorption-desorption measurement. The catalytic performance of MoO3 mesoporous structure was evaluated by hydrogen temperature-programmed reduc- tion (H2-TPR), and complete oxidation of toluene and carbon monoxide (CO). It was found that the initiation tem- peratures of toluene were 203℃, 215℃ and 225℃, respectively, and the initiation temperatures of CO were 114℃, 158℃ and 180℃, respectively, with their conversion rates of 50%, 90% and 100%, respectively. The well catalytic performance was attributed to 3D ordered mesoporous structure and high surface area of as-obtained MoO3 materials.

On the Interaction of Phosphines with High Surface Area Mesoporous Silica

To increase the efficiency and selectivity of homogeneous catalysts, particularly useful in the synthesis of fine chemicals and drugs, fine-tuning of the steric and electronic properties of the complexes can be achieved by modification of the ligands in the coordination sphere of the metal center. Considerable efforts have been devoted in order to immobilize such well-defined catalysts on solid substrates, e.g., silica, to facilitate catalysts’ recovery and to reduce contamination of desired products by metallic impurities. However, the presence of the silica surface can play a very important role in tuning the electronic properties of the metal, its steric environment, or in participating in the reactivity of the complex. In this context, several moieties have been used to anchor metallic catalysts on surfaces, but one of the most interesting is phosphine. Herein, we report on the addition of PPh2Cl to mesoporous silica, which leads to the grafting and the oxidation of the phosphine species, even in the ...

ChemInform Abstract: Mesoporous Silica Nanoparticles: Synthesis, Biocompatibility and Drug Delivery

AbstractReview: 267 refs.

Preparation of High Surface Area Mesoporous Activated Carbon: Kinetics and Equilibrium Isotherm

Activated carbon prepared from palm shell by phosphoric acid impregnation, at significantly favorable experimental conditions is characterized for the porous nature and adsorption of methylene blue dye molecules. The activation is carried out using a 2-stage activation process with the activation in a self-generated atmosphere. An activation temperature of 500°C, with an activation time of 75 minutes using a phosphoric acid impregnation ratio of 3 has yielded an activated carbon having unique characteristics. An activated carbon with a yield of 48%, total pore volume of 1.9 cm3/g, surface area of 1956 m2/g, an average pore diameter of 3.8 nm, with the ratio of the mesopore to the total surface area in excess of 75% has been prepared. The activated carbon exhibits a high methylene blue equilibrium adsorption capacity of 438 mg/g with the adsorption isotherm increasing with an increase in the adsorption temperature. Among the various adsorption isotherm models, the Langmuir model is able to explain the adsorption process well, evidenced by the proximity of the model with the experimental data. Among the different kinetic models tested with the experimental kinetic data, a pseudo-second-order model is found to fit the experimental data with close proximity.

Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells Using High Surface Area Mesoporous Carbon Counter Electrode

Development of new counter electrode materials is vital for commercialization of efficient dye-sensitized solar cells (DSCs) process. Research on DSCs has been focused mainly on using platinum as counter electrode, which makes them expensive. In this paper, we report DSCs fabricated with high surface area mesoporous carbon thin film with uniform spherical particles as counter electrode. An overall light-to-electricity efficiency as high as 7.6% has been achieved under illumination of air mass (AM) 1.5 sunlight (100 mW/cm2). In comparison with activated carbon, high surface area mesoporous carbon shows superior performance. Our results show that mesoporous carbon with high specific surface area and uniform pore size distribution proved to be better efficient electrode material for DSCs.

Hierarchical Zeolite Beta via Nanoparticle Assembly with a Cationic Polymer

Nanozeolite aggregates with secondary pores of tunable sizes were prepared by the flocculating action of a cationic polymer. Specifically, highly concentrated zeolite beta precursor gels were hydrothermally converted in the presence of the cationic polymer polydiallyldimethylammonium chloride (PDDA). Without polymer, highly crystalline zeolite beta in the form of nanosized particles was obtained from colloidal solutions at high yield. Upon addition of polymer, these nanoparticles were flocculated into self-sustaining, easily retrievable mesoporous aggregates in a one-step procedure at nearly 100% yield, showing interparticle pores with very high mesopore volumes and surface areas. The influence of the amount of polymer, its molecular weight as well as the nature of the silica precursor on pore characteristics, crystallinity, and morphology were studied with nitrogen sorption, mercury intrusion porosimetry and electron microscopy, respectively. Changing the polymer concentration is a powerful parameter to ...

Hydrothermal Synthesis of Porous α-Fe<sub>2</sub>O<sub>3</sub> Nanorods

Porous α-Fe2O3 nanorods were successfully prepared by the hydrothermal method. The structure and morphology of the as-prepared α-Fe2O3 nanorods were characterized by powder X-ray diffracton (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and N2-sorption analysis. XRD studies ind icated that the as-prepared product was well-crystallized hematite phase of α-Fe2O3. The SEM and TEM images showed that the obtained α-Fe2O3 sample consisted of porous nanorods with the length of about 200 nm and diameter of about 50 nm. N2-sorption analysis indicated that the as-prepared sample possess mesoporous structure and high surface area (255.2 m2•g-1).

Desilication Mechanism Revisited: Highly Mesoporous All‐Silica Zeolites Enabled Through Pore‐Directing Agents

The role of pore-directing agents (PDAs) in the introduction of hierarchical porosity in silicalite-1 in alkaline medium was investigated. By incorporation of various PDAs in aqueous NaOH, homogenously distributed mesopores were introduced in 2.5 μm silicalite-1 crystals. It was proven for the first time that framework aluminum is not a prerequisite for the introduction of intracrystalline mesoporosity by desilication. The pore-directing role is not directly exerted by framework trivalent cations metals, but by species on the external surface of the zeolite. The inclusion of metal complexes (Al(OH)(4)(-), Ga(OH)(4)(-)) and tetraalkyl ammonium cations (tetramethyl ammonium (TMA(+)), tetrapropyl ammonium (TPA(+))) in the alkaline solution led to distinct mesopore surface areas (up to 286 m(2) g(-1)) and pore sizes centered in the range of 5-20 nm. In the case alkaline treatment was performed in the presence of Al(OH)(4)(-), all aluminum partially integrated in the zeolite giving rise to both Lewis and Brønsted acidity. Apart from the concentration and location, the affinity of the PDA to the zeolite surface plays a crucial role in the pore formation process. If the PDA is attracted too strongly (e.g., TMA(+)), the dissolution is reduced dramatically. When the pore-directing agent is not attracted to the zeolite's external surface, excessive dissolution occurs (standard alkaline treatment). TPA(+) proved to be the most effective PDA as its presence led to high mesopore surface areas (>200 m(2) g(-1)) over a broad range of PDA concentrations (0.003-0.1 M). Importantly, our results enable to extend the suitability of desilication for controlled mesopore formation to all-silica zeolites.

Mesoporous high surface area Ce0.9Gd0.1O1.95 synthesized by spray drying

Mesoporous gadolinium doped cerium dioxide with high surface area was produced by spray drying using Pluronic 123 as surfactant. The powder, when calcined at 400°C, had a BET surface area of 136m2g−1 and was polycrystalline as confirmed by XRD and TEM. XEDS confirmed Ce, Gd and O, as the only elements present in the powders. Nitrogen adsorption measurements showed that the material was mesoporous with pore diameters of approximately 10nm, which was later confirmed by TEM studies. TEM–EELS were used to confirm that Ce was in the +4 oxidation state. SEM studies showed particles of 10nm diameter, corresponding to the crystallite size calculated from XRD data. The similar size range of the mesopores and the observed crystallite size indicates that the porosity is partly formed from intergranular mesoporosity. Using the spray drying method of a surfactant assisted liquid precursor solution it can be possible to manufacture mesoporous gadolinium doped ceria in large quantities in a continuous production.

Mesoporous zeolites as enzyme carriers: Synthesis, characterization, and application in biocatalysis

We study the application of hierarchical ZSM-5 zeolites, combining micropores and intracrystalline mesopores, as carriers for lipase enzymes compared with purely microporous ZSM-5 and mesoporous MCM-41. Strategies to improve enzyme immobilization by modification of the support porosity and surface properties ( e.g. by reaction with organosilane, or by treatment with the enzyme cross-linking agent glutaraldehyde) are also reported. Spectroscopic screening of catalyst activity and recyclability for the aqueous phase hydrolysis of p-nitrophenyl esters, permits evaluation of the influence of support properties and immobilization conditions on the performance of the resulting biocatalysts. An excellent correlation is observed between the mesopore surface area, the enzyme uptake, and the corresponding biocatalyst activity, demonstrating the functional character of mesopores in hierarchical zeolites. Modification of the mesopore walls prior to enzyme immobilization is essential to attain an active and recyclable biocatalyst. Enzymes immobilized on purely inorganic supports exhibit rapid loss of activity attributed to enzyme leaching. Despite the high mesopore surface area of surface-functionalized MCM-41, the mono-dimensionality of the mesopores results in restricted accessibility and a reduced enzyme uptake. In comparison, the interconnected mesopores of the hierarchical zeolites remain accessible after surface functionalization showing good adsorption properties. Lipase immobilized on thiol-functionalized mesoporous ZSM-5 was found to be the most efficient biocatalyst.

Activation of carbon-supported platinum nanoparticles by zeolite-type cesium salts of polyoxometallates of molybdenum and tungsten towards more efficient electrocatalytic oxidation of methanol and ethanol

The activity of Vulcan-supported Pt nanoparticles (Pt40%/Vulcan XC-72) towards oxidation of methanol and ethanol is increased by admixing them with zeolite-type cesium salts of heteropolymolybdic and heteropolytungstic acids: Cs 2.5H 0.5PMo 12O 40, Cs 2.5H 1.5SiMo 12O 40, Cs 2.5H 0.5PW 12O 40, and Cs 2.5H 1.5SiW 12O 40. It is apparent from IR measurements that these salts remain the Keggin-type structure. They are electroactive and undergo reversible redox transitions, as well as they are hydrated and contain mobile protons. As evidenced from cyclic voltammetric, stair-case voltammetric and chronoamperometric diagnostic experiments, the electrocatalytic enhancement effect has been most pronounced upon application of phosphododecamolybdate and phosphododecatungstate salts. The overall activation effect may also reflect the micro and mesoporous (zeolite-type) high surface area morphology of polyoxometallate cesium salts. The presence of well-defined polyoxometallate clusters in the vicinity of Pt is expected increase population of reactive oxo groups at the electrocatalytic interface.