Surface Area Study of High Area Cobalt Aluminate Particles Prepared by the Sol-Gel Method

Cobalt aluminate particles were prepared by the sol-gel method, starting from aluminum sec-butoxide and cobalt salts with a Co:Al ratio of 1:3. Samples with the same composition were also prepared by the citrate-gel method from cobalt and aluminum nitrates and citric acid. The particles were calcined to temperatures between 400 and 1000°C, for the formation of the mixed oxide having spinel structure. The surface properties of the different samples (BET surface area and pore size distribution) were measured. The highest BET surface area obtained (about 339 m²/g) corresponds to a sample prepared by cobalt acetate and aluminum sec-butoxide, calcined at 400°C. The surface area of the sample is reduced progressively as the sample is calcined to higher temperatures (to about 65 m²/g at 1000°C). Narrow pore size distributions were observed with average pore radius ranging from 17–20 Å, for samples heated to 400°C, to about 55–65 Å, for samples heated to 1000°C. The different surface areas and porosities obtained for particles prepared by different methods, different precursors or calcination temperatures, are discussed.     

Surface characterization and heats of adsorption of chromatographic alumina gel

The porous nature of chromatographic alumina gel has been investigated by adsorption/condensation processes and electron microscopy. Having 63% porosity, the gel is very porous. Total pore volume as determined by the fluid-displacement method is 0.497 cm³ g^–1. Its specific surface area, as determined by water vapor adsorption, is 225 m² g^–1. Micropore volume, as determined by utilizing Gurwitsch's rule, turns out to be 0.262 cm³ g^–1. The greater portion of the surface area and pore volume occurs in small and transitional pores, with average pore radii (hydraulic) less than 2.1 nm.Organic vapors, such as methyl ethyl ketone, acetone, methyl acetate, and methyl alcohol, were adsorbed on the gel between 0 and 36°C under vacuum, and the data were recorded on a Cahn-1000 electrobalance device. Isosteric heats of adsorption were calculated by applying the Clausius Clapeyron equation to the adsorption isosters at different surface coverages. Two types of adsorption processes, one with low activation energy and other with high activation energy can be distinguished. The increase in values ofq _st indicates that increasing temperature changes physical adsorption into chemisorption.     

Effect of preparation pH on pore structure of silica gels

Surface characterization of silica gels prepared at different gelation pH from water glass and sulphuric acid were made by argon adsorption at 77 K using continuous volumetric method. While microporous silica gels prepared in the pH range of 1–3 had BET surface areas of 504–571 m² g^–1, total pore volumes of 0.26–0.31 cm³ g^–1 and micropore volumes of 0.16–0.23 cm³ g^–1, mesoporous silica gels prepared in the pH range of 3.36–0.65 had BET surface areas of 374–530 m² g^–1 and pore volumes of 0.61–0.79 cm³ g^–1.     

Ceria-Zirconia Nanostructured Materials for Catalytic Applications: Textural Characteristics and Redox Properties

Highly dispersed solid solutions of ceria-zirconia with nominal composition Ce_0.6Zr_0.4O₂ were prepared by sol-gel technique and the influence of the gel aging time (1 day–3 weeks) on the morphological and textural properties of the materials was investigated. The samples were calcined at 923 K for 8 h, then characterized by XRD, BET surface area and pore size measurements by gas adsorption and by mercury porosimetry. DTA, TEM and SEM analyses were also carried out. The aging of the gel seems to have a remarkable influence on the morphology of the materials, whose surface area and porosity increase by increasing aging time. The phase composition of the solid solutions of ceria-zirconia, as determined by XRD analysis, seems to be independent from the synthetic procedure; in any case a cubic phase (space group Fm-3m) was identified as the main component. XRD and TEM characterizations show the presence of highly dispersed crystallites, with diameters in the range 60–80 Å. The redox properties and hydrogen chemisorption capacity have been studied by TPR/TPD/TPO experiments. Oxygen storage capacity measurements were carried out by a pulse technique, to determine the overall reducibility of the solid, OSCC (Oxygen storage capacity complete). OBC (Oxygen buffering capacity) measurement were also performed to determine the ability of the ceria-zirconia oxides to attenuate fast oscillations (0.1 Hz) of oxygen partial pressure. The correlation between textural, structural and redox properties of the oxides is discussed.     

Preparation and characteristics of NiO-coated nano-fibriform silica

NiO-coated nano-fibriform silica (NFS) was prepared by an excessive soakage method and was characterized using transmission electron microscopy, X-ray diffraction, and physical N₂ adsorption techniques under different conditions. The results demonstrate that the coated NiO is of a cubic crystal form. The best preparation conditions are incubation in a water bath at 95 °C for 2 h and drying at 45 °C for 17 h, which lead to a higher NFS utilization ratio and thus lower cost, and a well-distributed NiO coating on the carrier NFS. Nitrogen adsorption isotherms for NiO-coated NFS are similar to a type IV curve, with a specific surface area of 292.7 m²/g, adsorptive capacity of 379.2 cm³/g, and pore volume of 0.59 cm³/g. The average pore diameter of NiO-coated NFS is 8.01 nm, but most pore diameters are in the range 2.1–3.9 nm. Comparison of NiO-coated NFS and NiO(Ni)-coated sol–gel silica as catalysts reveals that NiO-coated NFS may be an effective catalyst and that NFS may be a good catalyst carrier.     

Effect of pH on Competitive Adsorption of Cu(II), Ni(II), and Zn(II) from Water onto Chitosan Beads

The amounts of adsorption of Cu²⁺, Ni²⁺, and Zn²⁺ from single, binary, and tertiary nitrate solutions onto glutaraldehyde cross-linked chitosan beads were measured. The beads had an average particle size and pore volume of 2 mm and 0.06 cm³/g, respectively, and had a BET surface area of 60 m²/g. All experiments were performed at 298 K as a function of initial pH (2.0–5.0), total metal concentration (0.77–17.0 mol/m³), and molar concentration ratio (0.25–4) in the aqueous phase. It was shown that the amount of metal adsorption generally increased with increasing solution pH. Competitive adsorption was significant in binary and tertiary systems when Cu²⁺ was present. The selectivity factor reached maximum in an equilibrium pH range of 5.1–5.3 and 4.5–4.9 for the Cu-Ni and Cu-Zn binary systems, respectively. This adsorbent provided a possibility for selective separation of Cu²⁺ from such multi-component solutions.     

Nitrogen-Doped Porous Carbon Materials Derived from Graphene Oxide/Melamine Resin Composites for CO2 Adsorption

CO₂ adsorption in porous carbon materials has attracted great interests for alleviating emission of post-combustion CO₂. In this work, a novel nitrogen-doped porous carbon material was fabricated by carbonizing the precursor of melamine-resorcinol-formaldehyde resin/graphene oxide (MR/GO) composites with KOH as the activation agent. Detailed characterization results revealed that the fabricated MR(0.25)/GO-500 porous carbon (0.25 represented the amount of GO added in wt.% and 500 denoted activation temperature in °C) had well-defined pore size distribution, high specific surface area (1264 m²·g⁻¹) and high nitrogen content (6.92 wt.%), which was mainly composed of the pyridinic-N and pyrrolic-N species. Batch adsorption experiments demonstrated that the fabricated MR(0.25)/GO-500 porous carbon delivered excellent CO₂ adsorption ability of 5.21 mmol·g⁻¹ at 298.15 K and 500 kPa, and such porous carbon also exhibited fast adsorption kinetics, high selectivity of CO₂/N₂ and good recyclability. With the inherent microstructure features of high surface area and abundant N adsorption sites species, the MR/GO-derived porous carbon materials offer a potentially promising adsorbent for practical CO₂ capture.     

Physical Properties of Silica Aerogels Prepared with Polyethoxydisiloxanes

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, S_BET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m²/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m^–1 K^–1 at room temperature and 1 atm.     

Mesoporous MnO2 as enzyme immobilization host for amperometric glucose biosensor construction

Mesoporous MnO₂ (mesoMnO₂) is synthesized facilely through sol–gel process using nonionic surfactant polyxyethylene fatty alcohol (AEO₉) as template. Transmission electron microscopy (TEM) image and N₂ adsorption/desorption isotherm show that the obtained mesoMnO₂ material presents disordered porous structure and appropriate pore size suitable for the immobilization of glucose oxidase (GOx). An amperometric glucose biosensor based on GOx entrapped in mesoMnO₂ is fabricated, in which mesoMnO₂ also acts as a catalyst for the electrochemical oxidation of H₂O₂ produced by enzyme reaction. The biosensor shows fast and sensitive current response to glucose in the linear range of 0.0009–2.73 mM. The response time (t_95%) is less than 7 s. The sensitivity and detection limit are 24.2 μA cm⁻² mM⁻¹ and 1.8 × 10⁻⁷ M (S/N = 3), respectively. This indicates that mesoMnO₂ has promising application in enzyme immobilization and biosensor construction.     

Preparation of porous TiO2/silica composites without any surfactants

TiO₂-SiO₂ composites, with high specific surface area (up to 308 m²/g), large pore volume, and narrow distribution with average pore sizes of 3.2 nm, have been synthesized from wollastonite and titanium sulfate in the absence of any surfactants. Calcium sulfate, a microsolubility salt, plays an important role in the formation of pores in this porous TiO₂/silica composite. The microstructure and chemical composition of composite were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM) equipped with energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometer (XPS) and N₂ adsorption and desorption analysis. The as-prepared porous titanium dioxide-silicon dioxide composites with high specific surface area and well-crystallized anatase contents were used as an efficient photocatalyst.     

Synthesis and characterization of new silica–titania mixed oxide in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide by sol–gel technique

Silica–titania mixed oxide were prepared by sol–gel method from tetraethylorthosilicate and titanium (IV) isopropoxide as precursors in the presence of room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [C₄MIm][NTf₂]. The effects of [C₄MIm][NTf₂] on the structural and textural characteristics of silica–titania matrix are investigated in this paper. The materials obtained were well characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis X-ray powder diffraction (XRPD), field emission scanning electron microscope (FESEM) and N₂ adsorption–desorption analysis. It is believed that the [C₄MIm][NTf₂] plays an important role as a template and the high surface area of the samples is thought to mainly attribute to the formation of microporous in the reaction. The synthesized materials showed the presence of C–N groups in the FTIR spectrum which indicates the presence of RTIL in the silica–titania matrix. XRPD, FESEM and N₂ adsorption–desorption analysis results indicated that the composite materials possessed good microporous character. The subsequent material displayed average pore diameter of 1.70–2.12 nm, pore volume of 0.08–0.19 cm³/g and BET surface area of 191–386 m²/g. Increasing the content of RTIL resulted in an increase of the average pore diameter of the silica–titania gel.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.     

Adsorption Properties of Mesoporous Silica Gel with β-Cyclodextrin as a Pore-Forming Agent Relative to Moxifloxacin

A method for the synthesis of mesoporous silica gel using β-cyclodextrin as a pore-forming agent is developed. The physical properties and structure of the obtained adsorbent are studied by Fourier-transform IR spectroscopy and the low-temperature adsorption–desorption of nitrogen (BET) method. The material has an average specific surface area of 435 ± 5 m²/g and an average pore size of 5 ± 0.5 nm. This value of the pore size indicates the formation of complex structures from columnar associates of β-cyclodextrin in the synthesis of the material. The adsorption capacity of the obtained material is 0.2 ± 0.05 mg of 2-hydroxypropyl-β-cyclodextrin per milligram of the adsorbent. The dissociation constant of the complexes of moxifloxacin with β-cyclodextrin inside the pores of silica gel is of the order of 5 × 10^–3 M. The resulting system of SiO₂-β-CD is promising for application in the biomedical chemistry as a carrier of biologically active molecules, particularly as an antibacterial preparation of moxifloxacin.     

Synthesis of high surface area nanometer magnesia by solid-state chemical reaction

Nanometer MgO samples with high surface area, small crystal size and mesoporous texture were synthesized by thermal decomposition of MgC₂O₄ · 2H₂O prepared from solid-state chemical reaction between H₂C₂O₄ · 2H₂O and Mg (CH₃COO)₂ · 4H₂O. Steam produced during the decomposition process accelerated the sintering of MgO, and MgO with surface area as high as 412 m² · g⁻¹ was obtained through calcining its precursor in flowing dry nitrogen at 520°C for 4 h. The samples were characterized by X-ray diffraction, N₂ adsorption, transmission electron microscopy, thermogravimetry, and differential thermal analysis. The as-prepared MgO was composed of nanocrystals with a size of about 4–5 nm and formed a wormhole-like porous structure. The MgO also had good thermal stability, and its surface areas remained at 357 and 153 m²·g⁻¹ after calcination at 600 and 800°C for 2 h, respectively. Compared with the MgO sample prepared by the precipitation method, MgO prepared by solid-state chemical reaction has uniform pore size distribution, surface area, and crystal size. The solid-state chemical method has the advantages of low cost, low pollution, and high yield, therefore it appears to be a promising method in the industrial manufacture of nanometer MgO. Translated from Chinese Journal of Catalysis, 2006, 27(9): 793–798 (in Chinese)     

Fabrication and characterization of γ-Al2O3–clay composite ultrafiltration membrane for the separation of electrolytes from its aqueous solution

In this paper, we have reported the preparation of low cost γ-Al₂O₃ membrane on a macroporous clay support by dip-coating method. For the synthesis of γ-Al₂O₃ top layer on the support, a stable boehmite sol is prepared using aluminium chloride salt as a starting material by sol–gel route. The structural properties of the composite membrane as well as γ-Al₂O₃ powder is carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm data, Fourier transform infrared analysis (FTIR) and dynamic light scattering (DLS) analysis. The mean particle size of the boehmite sol used for coating is found to be 30.9 nm. The pore size distribution of the γ-Al₂O₃–clay composite membrane is found to be in the range of 5.4–13.6 nm. Separation performance of the membrane in terms of flux and rejection of single salts solution such as MgCl₂ and AlCl₃ as a function of pH, salt concentration and applied pressure is also studied. The rejection and flux behavior are found to be strongly dependent on electrostatic interaction between the charged molecules and γ-Al₂O₃–clay composite membrane. The intrinsic rejection has been determined by calculating the concentration at membrane surface (C_m) using Speigler–Kedem model. It is found that the observed rejection shows anomalous trend with increase in applied pressure and the intrinsic rejection increases with increase in applied pressure, a trend typical of the separation of electrolyte through charged membranes. At acidic pH, both the salt solution shows higher rejection. With increase in the salt concentration, observed rejection of salt decreases due to the enhanced concentration polarization. The maximum rejection of MgCl₂ and AlCl₃ is found to be 72% and 88%, respectively for salt concentration of 3000 ppm.     

Photocatalytic hydrogen evolution over mesoporous TiO2/metal nanocomposites

Na⁺ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m²/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO₂ samples prepared were found to have photocatalytic activity in Cu^II, Ni^II and Ag^I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO₂ Degussa P25.The effects of the thermal treatment of mesoporous TiO₂ upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO₂/Ag⁰ to TiO₂/Ni⁰ to TiO₂/Cu⁰ was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites.     

Schiff base complex sol–gel method for LaCoO3 perovskite preparation with high-adsorbed oxygen

A novel Schiff base complex sol–gel method has been used to prepare LaCoO₃ producing high ratios of adsorbed (or surface) oxygen (α) to lattice oxygen (β). The as-prepared gels, characterized by Fourier transform infrared spectroscopy (FTIR), showed that both lanthanum and cobalt ions were complexed before calcinations. IR spectra revealed that CO₃²⁻ and NO₃⁻ presented on the sample surfaces during heat treatment. High-resolution transmission electron microscopic (HRTEM) images of all samples showed resolved lattice fringes with the inter-planar spacing 0.37–0.39 nm of the (0 1 2) plane in hexagonal perovskite. BET surface areas of LaCoO₃ nano-crystals were 11.7–18.6 m²/g. Ratios of adsorbed (or surface) oxygen (α) to lattice oxygen (β) quantified by X-ray photoemission spectroscopy showed that LaCoO₃ prepared by the Schiff base complex method produced higher ratios when bases had higher nitrogen content in molecules. Carbonate and nitrate which were resulting from the oxidation of functional groups in the Schiff base complex, can produce gaseous compounds and leave vacant sites for oxygen in the gas phase to adsorb.     

Sol–gel synthesis of macroporous TiO2 from ionic precursors via phase separation route

Monolithic macroporous titanium dioxide (TiO₂) derived from ionic precursors has been successfully prepared via the sol–gel route accompanied by phase separation in the presence of formamide (FA) and poly(vinylpyrrolidone) (PVP). The addition of FA promotes the gelation, whereas PVP enhances the polymerization-induced phase separation. Appropriate choice of the starting compositions allows the production of cocontinuous macroporous TiO₂ monoliths in large dimensions, and controls the size of macropores. The resultant dried gel is amorphous, whereas anatase and rutile phases are precipitated at 500 and 900 °C respectively, without spoiling the macroporous morphology. Nitrogen adsorption–desorption measurements revealed that the dried gels exhibits mesostructure with a median pore size of about 3 nm and BET surface area of 228 m²/g, whereas 15 nm and 73 m²/g for the gels calcined at 600 °C.     

Development and tailoring of amino-functionalized activated carbon based Cucumerupsi manni Naudin seed shells for the removal of nitrate ions from aqueous solution

The removal of nitrate ions with ethylenediamine (EDA)-functionalized activated carbon (AC-NH₂) was studied in this work. Activated carbon prepared from Cucumerupsi manni Naudin seed shells using ZnCl₂ (ACZ) was functionalized with EDA via a nitric acid oxidation followed by acyl chlorination and amidation process. The effect of pH, contact time, initial concentration and co-existing ions on the adsorption of nitrate ions have been investigated. The FTIR and elemental analysis revealed that amino groups were successfully grafted onto the ACZ after functionalization. The surface area and average pore of ACZ were found to be 1008.99 m²/g and 2.02 nm respectively. However, it was noticed that, after functionalization (AC-NH₂), its surface area decreases to 113.43 m²/g meanwhile, its pore diameter increases to 2.48 nm. The experimental results of adsorption showed that AC-NH₂ exhibit excellent nitrate ions uptake performance compared to ACZ which is attributed to the presence of the grafted amino groups on the ACZ. Nitrate adsorption follows pseudo-first-order kinetic model while the equilibrium adsorption data was best fitted the Freundlich isotherm suggesting that the adsorption process was predominated by physisorption. This study demonstrates that the prepared AC-NH₂ is a promising adsorbent for nitrate ions removal from aqueous media.     

Sol-Gel Derived Nanocomposites and Nanoporous Oxide Powders and Related Coatings for the Reversible Chemisorption of Hydrogen Sulfide

Two types of nanocomposites and nanoporous powders and related coatings were prepared by the sol-gel route. These silica-based materials contain dispersed reactive oxides, ZnO and ZnCr₂O₄, respectively. Experiments evidenced their ability of reversible chemisorption of H₂S as ZnS. Their attractive porous characteristics (small pore size 2–2.5 nm, high specific surface area 900–1100 m²· g^–1, high porosity 50–60%) are not significantly modified during the successive treatments of H₂S chemisorption and oxide regeneration. These preliminary results encourage to pursue this study which aims at the preparation of nanofilters for the desulfurization of gas mixtures.