Barrett , Joyner And Halenda Research Articles

Synthesis and Characterization of Phosphoric Silica Catalyst from Bamboo Leaves for Production of Triacetin

In this research, the bamboo leaf shows promise as an alternative raw material for silica production. This study investigated the performance of heterogeneous catalyst prepared from silica derived bamboo leaf ash after that impregnated with phosphoric acid at ratio various. The catalyst was characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Brunauer Emmet Teller (BET) and Barrett, Joyner and Halenda (BJH) method and triacetin product analyzed by GC-MS. The optimum condition phosphoric silica catalyst was obtained at phosphoric silica molar ratio of 1:2 and employed in the acetylation of glycerol, respectively. As result, 24 % selectivity for triacetin was obtained in the presence of catalytic amount 5%, molar ratio 1:9 at 100 °C for 4 hours. Bamboo leaf derived phosphoric silica calcined showed high potential to be used as an easy to prepare and high-performance solid catalyst for industrial scale.

Calcium-Assisted Regulation of the Structures of Porous Carbons at the Micro-Nano Scale

Here a facile and effective method was investigated to regulate the microstructures of porous carbons by adjusting the contents of calcium in precursors. The carbonization characteristics of precursors were characterized by thermogravimetric analysis (TGA) and differential thermogravimetric (DTG), and the results show that the weight loss rates of precursors decrease with the increases of calcium contents. The structures of carbonized samples and their derived porous carbons at the micrometer scale were characterized by Scanning electron microscopy (SEM), and the results show that the structures of carbonized samples change regularly with the increases of calcium contents in precursors, and porous carbons can inherit the structures from their corresponding carbonized samples. The pore characteristics of porous carbons at the nanometer scale were characterized by N2 adsorption and desorption, Barrett Joyner and Halenda (BJH) method and Horvath-Kawazoe (HK) method, and the results show that the existence of calcium in precursors can greatly increase the total pore volumes and specific surface areas of porous carbons derived from precursors, and interestingly it can be noticed that the micropore size distributions of porous carbons in the range of 0.58–10 nm are quite similar.

Iota-carrageenan based magnetic aerogels as an efficient adsorbent for heavy metals from aqueous solutions

Magnetic aerogels were prepared via physical cross-linking of Iota-carrageenan and polyamidoamine (PAMAM) dendrimer using different amounts of magnetic nanoparticles (1, 3 and 5%). A blank sample of chemically cross-linked Iota-carrageenan was prepared for comparison. The prepared magnetic nanoparticles and aerogels were fully characterized using particle size analyzer, X-ray diffraction (XRD), vibrating Sample Magnetometer (VSM), FT-IR, SEM and energy-dispersive X-ray (EDX). The surface area and porosity were calculated using Brunauer, Emmett, and Teller (BET), Barrett, Joyner and Halenda (BJH) equations. The nitrogen contents of the aerogels were determined using the Kjeldal method. These aerogels are environmentally safe, eco-friendly and cheap. The adsorption behavior of the aerogels was evaluated for Cr (VI), Co2+, Cu2+, Cd2+, Mn7+, and Alphanol fast blue dye. The synergetic effect for the presence of the chelating groups with different natures (i.e. sulfate and amine) was revealed via the high ability of the aerogels to remove the cations and oxyanions in a similar manner. The prepared aerogels had high removal efficiency with selectivity order Co2+ > Cu2+ > Mn7+ > Cd2+ > Cr (VI). The maximum adsorption efficiency of Co2+ was 99% achieved by using CAR M3.

Synthesis and characterization of zinc stannate nanostructures for the adsorption of chromium (VI) ions and photo-degradation of rhodamine 6G

The zinc stannate nanostructure was synthesized via sol-gel route and its physicochemical, adsorption and photocatalytic properties were studied. The specific surface area (S) was calculated by Brunauer–Emmett–Teller (BET) and Barrett, Joyner and Halenda (BJH) methods using N2 adsorption-desorption. The SBET and SBJH were found to be 105 and 138 m2 g−1 respectively with the average pore size of 2.5 nm. Based on diffraction data, cubic geometry was assigned to the crystallites with average size of 31.74 nm. The morphology of the particles was studied though transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and the average particles size as calculated from TEM was 21.6 nm. The band gap calculated from the diffuse reflectance spectrum was 3.36 eV. The percentage composition and purity were determined by energy dispersive X-ray (EDX), whereas surface functional moieties were detected by Fourier transform infrared (FTIR) spectroscopy. The batch method was used to study the adsorption of Cr(VI) ions by varying, initial electrolyte concentration, pH, and temperature of solution. The parameters extracted from Langmuir and Freundlich models shows that the adsorption process was more feasible at higher temperature and lower pH. The maximum sorption capacity of the adsorbent was found to be 32.81 mg g−1. The 1:1 exchange mechanism was proposed between Cr(VI) and surface protons while the thermodynamic study reveals the endodermic nature of the adsorption process. The photocatalytic performance of the zinc stannate was examined against Rhodamine 6G where 98.17% degradation was achieved in 390 min.

Mesoporous Multi-Metal Citrates as Scavengers for Organic Dyes

In this work we have established excellent adsorption properties of Multi-metal citrate complexes for the capture of Organic dyes. These complexes exhibit mesoporous character with pore diameter ≈ 40A and narrow pore size distribution in their structure as demonstrated by fitting experimental adsorption data into Barrett, Joyner and Halenda (BJH) and Density Functional Theory (DFT) models. Thus these materials have the potential of being used as scavengers for dye stuff removal from industrial waste discharge in the water stream and may replace the high cost carbon adsorbents to capture dye molecules and curb water pollution with resultant toxic, carcinogenic and mutagenic effects of dye stuff on living beings. The mesoporous Zinc, Nickel, Iron, Copper multi-metal citrate complexes with different combinations of these metal ions and citric acid linker have been synthesized under mild hydrothermal conditions through green synthetic pathways. Because of their biocompatibility and non toxicity, these low cost mesoporous materials may prove boon for transport of dyes used as contrast agents during diagnostics applications due to their increased image contrast and chemical stability.

Catalytic Activity of Sulfated and Phosphated Catalysts towards the Synthesis of Substituted Coumarin

New modified acidic catalysts were prepared from the treatment of silica, titania and silica prepared from hydrolyzed tetraethyl orthosilicate (TEOS) with sulfuric and phosphoric acid. The sulfated and phosphated silica synthesized from TEOS were calcined at 450 and 650 °C. These catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The surface areas, total pore volume, and mean pore radius of the acidic catalysts were investigated, while the pore size distribution was determined by the Barrett, Joyner and Halenda (BJH) method. The catalytic activity of the sulfated and phosphated silica and/or titania were examined with the Pechmann condensation reaction, in which different phenols reacted with ethyl acetoacetate as a neat reaction to obtain the corresponding coumarin derivatives. The results indicated that the treatment of the catalysts with sulfuric or phosphoric acid led to a decrease in the phases’ crystallinity to a certain degree. The morphology and the structure of the acidified catalysts were examined and their particle size was calculated. Furthermore, the amount of the used catalysts played a vital role in controlling the formation of the products as well as their performance was manipulated by the number and nature of the active acidic sites on their surfaces. The obtained results suggested that the highest catalytic conversion of the reaction was attained at 20 wt % of the catalyst and no further increase in the product yield was detected when the amount of catalyst exceeded this value. Meanwhile the phenol molecules were a key feature in obtaining the final product.

Study of Porosity and Surface Groups of Activated Carbons Produced from Alternative and Renewable Biomass: Buriti Petiole

This study reports the production of activated carbon (AC) from chemical activation with sodium hydroxide in pyrolysis temperature of 500 to 600 °C using alternative and renewable material, Buriti petiole. The characterization of the material was performed by simultaneous thermogravimetry-differential thermal analysis (TG–DTA), scanning electron microscopy (SEM), nitrogen adsorption–desorption isotherms at -196 °C by the BET (Brunauer, Emmett and Teller) and BJH (Barrett, Joyner and Halenda) methods for mesoporous materials. Infrared spectroscopy (FT–IR) and TG/DT–FTIR coupled system were used to study the surface groups. Adsorption tests for the activated carbons samples (ACs) were carried out using the methylene blue (MB) cationic and anionic orange G (OG) dyes, the most satisfactory results were methylene blue dye. These results indicated the formation of mesoporous adsorbent materials with BET surface areas obtained between 340 m 2 g -1 and 1715 m 2 g -1 . The chemical activation of the carbons with sodium hydroxide produced highly mesoporous material suitable for adsorption of cationic and anionic dyes in aqueous solution. DOI: http://dx.doi.org/10.17807/orbital.v9i1.878

Robust Silica Aerogel Microspheres from Rice Husk Ash to Enhance the Dissolution Rate of Poorly Water-Soluble Drugs

The present paper demonstrates the capability of specially prepared robust silica aerogel microspheres (RSAMs) to enhance the dissolution rate of poorly water-soluble drugs. A sol-gel/mineral oil emulsion method has been developed for RSAMs from rice husk ash (RHA), a biogenic source. The particles were characterized for their Brunauer–Emmett–Teller (BET) specific surface area, Barrett, Joyner and Halenda (BJH) pore volume and pore diameter, and morphology by optical microscopy and scanning electron microscopy (SEM). The dissolution rate of ibuprofen, a poorly water-soluble drug, was investigated by adsorbing it onto RSAMs upon dissolving it in supercritical carbon dioxide (scCO2) at 150 bar and 40°C. This resulted in a loading of ∼0.13 g ibuprofen/g loaded RSAMs in 24 h. X-ray diffraction analysis was used to characterize the nature of the adsorbed ibuprofen onto RSAMs. It was observed that the loaded drug on the aerogels is in amorphous form. An in vitro drug-release kinetic studies confirmed a significant enhancement in the dissolution rate, namely ∼100% of the loaded ibuprofen released as compared to that of ∼11% of crystalline ibuprofen in 15 min.

Fabrication and nano structural study on La2O3-Co3O4-ZrO2 composite

We report on the synthesis, morphology, chemically and structurally of La2O3-Co3O4-ZrO2 nanostructure. The La2O3-Co3O4-ZrO2 nanostructure was synthesized by a method based on the co-precipitation. Composite powders have been characterized by XRD (X-ray diffraction), SEM (scanning electron microscopy) and BET (Brunauer-EmmettTeller). X-ray diffraction showed the formation of nano crystalline, La2Zr2O7, ZrO2, La(OH)3 and Co3O4 phases. Scanning electron microscopy revealed that nanostructure formed by increasing the calcinations temperatures. With BET and BJH (Barrett, Joyner and Halenda) method the pore size distribution was determined. The effects of chemical compositions and calcinations temperature on the surface topography and the crystallization of phases were studied. The lattice strain of nanocrystallite during thermal treatment was calculated.

Adsorptive characterization of porous solids: Error analysis guides the way

Adsorptive characterization using nitrogen at 77K is one of the most widely used techniques to assess textural properties of porous solids, such as pore volume, specific surface area and pore size distributions. Based on a thorough error analysis the influence of experimental uncertainties on the accuracy of volumetric nitrogen adsorption isotherms and derived properties using the most popular methods is analyzed in detail, comprising the pore volume and specific surface area determined using the method posed by Brunauer, Emmet and Teller (BET) and the pore size distribution according to the method developed by Barrett, Joyner and Halenda (BJH). Based on series of isotherms measurements with different sorbents (MOFs, zeolite, activated carbon and alumina) and on examples from literature (MIL-101), the extensive error analysis shows that these methods may yield highly inaccurate or even statistically irrelevant (BJH) results. To improve the meaningfulness of derived properties and to minimize statistical uncertainties, practical recommendations and guidelines are proposed for experimental operation variables and data analysis.

Introducing a self-consistent test and the corresponding modification in the Barrett, Joyner and Halenda method for pore-size determination

A standard method to obtain the mesopore size distribution of adsorbents is the Barrett, Joyner and Halenda (BJH) analysis of the N2 adsorption–desorption isotherm at 77K. The availability, over the last two decades, of well-defined model adsorbents in the mesopore range, together with other forms of isotherm analysis with the help of the Density Functional Theory (DFT) has shown that the BJH method tended to underestimate the pore-width when they are smaller than 10nm. Regarding this fact, we have reported an improved BJH method, where we have remarked that the reconstruction of the adsorption–desorption isotherm from the BJH results leads to some inconsistency. We therefore proposed a simple means to cancel the mentioned discrepancy and inconsistency. This correction can be made by simply adding a corrective term to the standard BJH equation, which value is selected to meet a self-consistent criterion, i.e. the reconstructed isotherm should fit the original one. In the first article, the method was applied for some ordered mesoporous materials (OMM) synthesized in our laboratory, showing only the results without major details. In this work, we validate the test for other samples, in other pore size ranges, introducing some remarks in theoretical aspects and in the importance of obtaining and taking into account the micropore volume. Finally, a detailed procedure to apply the proposal method using only the experimental data of the analysis is presented.

Improved calculations of pore size distribution for relatively large, irregular slit-shaped mesopore structure

Present methods for determining pore volume (PV), pore size distribution (PSD), and average pore width (APW) of irregular mesoporous materials from N2 adsorption, including the widely used model developed by Barrett, Joyner and Halenda (BJH), are likely to produce inaccurate results due to simplistic assumptions and approximations. For example, in assuming a simple cylindrical pore geometry and due to various empirical approximations, the BJH method typically underestimates APW for aluminas by 10–30% using the desorption branch of the N2 adsorption isotherm. Here we report improved calculations of PSD based on the Kelvin equation and a proposed Slit Pore Geometry (SPG) model for slit-shaped mesopores of relatively large pore size (>10nm). Two structural factors, α and β, are introduced to correct for non-ideal pore geometries. The volume density function for a log normal distribution is used to calculate the geometric mean pore diameter and standard deviation of the PSD. The Comparative Adsorption (αs) Method (CAM) is also employed to independently assess mesopore surface area and volume. Values of APW calculated by the SPG method are typically 6–20% greater than values predicted by BJH model using the desorption branch of N2 adsorption isotherm. Pore areas and pore volumes calculated from the SPG model are also in excellent agreement with those determined independently by CAM. The SPG method is demonstrated to be especially applicable to determination of PV, PSD, and APW for aluminas and other medium to large pore diameter mesoporous solids consisting of slab-like nano-crystals.

On the Cation Dependence of Interlamellar and Interparticular Water and Swelling in Smectite Clays

The osmotic character of long-range interlamellar swelling in smectite clays is widely accepted and has been evidenced in the interlayer space by X-ray diffraction. Such a behavior in mesopores was not experimentally confirmed until the determination of the mesopore size distribution in Na-montmorillonite prepared from MX80 bentonite using thermoporometry experiments. This is confirmed here for other montmorillonite samples where the interlayer cations are alkaline and Ca(2+) cations. The nature of the interlayer cation is found as strongly influencing the behavior of the size and the swelling of mesopores. These results are supported by the BJH (Barrett, Joyner and Halenda) pore radius values issued from the nitrogen adsorption-desorption isotherms at the dry state. Thermoporometry results as a function of relative humidity ranging from 11% to 97% have shown an evolution of the mesopore sizes for a purified Na-montmorillonite. New thermoporometry data are presented in this article and confirm that the interparticle spaces in K-, Cs-, or Ca-montmorillonites are not strongly modified for all the range of relative humidity: the swelling is not observed or is strongly limited. It appears in contrast that only Li- and Na-montmorillonites undergo a mesopore swelling, distinct from the interlayer swelling. More generally, our results confirm the possibility to use thermoporometry or differential scanning calorimetry to study the structure and the evolution of swelling materials in wetting conditions such as natural clays or biological cells. In this paper, we describe the different key steps of the hydration of swelling clays such as montmorillonites saturated with alkaline cations. Using thermoporometry results combined with X-ray diffraction data, we distinguish the evolution of the porosity at the two different scales and propose a sequence of hydration dependent on the interlayer cation. From this study, it is shown that the interlayer spaces are not completely filled when the mesopores start to fill up. This implies that the swelling observed in the mesopores for Li and Na samples is due to an osmotic swelling. For the other samples, it is difficult to conclude definitively. Furthermore, we determine the different proportion of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry, and (3) recent adsorption isotherm results. It is found that the interlayer space is never completely filled by water at the studied relative humidity values for all samples except for the Cs sample.

Co-Synthesis and Drug Delivery Properties of Mesoporous Hydroxyapatite-Silica Composites

In this work, mesoporous hydroxyapatite-silica (HA-silica) composite materials with four different Si:Ca:P ratios were sol-gel derived through self-assembly using triblock copolymer Pluronics P123 as template. The composition and mesoporous structure formed were characterized by X-ray diffraction and electron microscopy. The XRD patterns indicated that the intensity of the HA phase becomes stronger as the Ca/Si ratio of the composite increases. From nitrogen gas analysis at 77 K, type IV isotherm plots for typical mesoporous materials were observed for all of the samples. However, the mesoporous structure of HA-silica tends to becomes less ordered as the Ca/Si ratio increases. Promising consistency between the pore sizes from the Barrett, Joyner and Halenda (BJH) method, Transmission Electron Microscopy (TEM) and Small Angle X-ray diffraction (SAXRD) was also observed. The formation mechanism of mesoporous HA-silica composites was proposed, where the interaction between the crystallization of HA and the surfactant liquid crystal determines the regularity of the meso-structure. In vitro drug loading and release studies showed that drug loading capacity is dependent on the pore volume of the sample, and the mesoporosity of the samples were responsible for the sustained release of drugs. In vitro cell culture of the samples showed promising biocompatibility where osteosarcoma cells were observed to grow favourably on the synthesized composites.

Influence of the presence of Al<SUB align=right>2O<SUB align=right>3 on Ni-Mo-W trimetallic catalysts for HDS

This work presents Ni-Mo-W tri-metallic catalysts of the type 'NEBULA', (Soled et al., 2001) bulk and supported, named NEBDMDS, NEB1 (5% Al2O3), NEB2 (25% Al2O3) and NEB3 (50% Al2O3). The materials were prepared from water-soluble ammonium salts by direct precipitation with nickel nitrate. Supported catalysts were synthesised obtaining a gel, which was aged, dried and calcinated. The precursors were sulphiding in a tubular furnace with a flow of DMDS (Dimethyl-disulphide)/N2. The generated catalysts were evaluated in the reaction of hydrodesulphurisation (HDS) of the dibenzothiophene (DBT). They were characterised by the adsorption of nitrogen using the Brunauer, Emmett and Teller (BET) method and Barrett Joyner and Halenda (BJH) method, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electronic Microscopy (TEM). The increase of the content of Al2O3 in the catalysts influenced on the decrease of the catalytic activity. The NEBDMDS catalyst presented the catalytic activity higher of 13.1 mol/s g.

The comparative characterization of structural heterogeneity of mesoporous activated carbon fibers (ACFs)

The comparative analysis of the most widely used methods of mesoporosity characterization of two activated carbon fibers is presented. Not only the older methods are used, i.e. Barrett, Joyner and Halenda ( BJH), Dubinin (the so-called first variant— D 1ST and the so-called second variant— D 2ND ), Dollimore and Heal ( DH), and Pierce ( P) but the recently developed ones, i.e. the method of Nguyen and Do ( ND) and that developed by Do ( Do) are also applied. Additionally, the method of the characterization of fractality is put to use (fractal analog of FHH isotherm). The results are compared and discussed.

Improved Pore-Size Analysis of Carbonaceous Adsorbents

An improvement was proposed for the pore-size analysis of active carbons based on low-temperature (77 K) nitrogen adsorption isotherms measured over a wide range of relative pressures (5 × 10−7–0.995). It was shown that the applicability of the Barrett, Joyner and Halenda (BJH) computational method based on the Kelvin equation could be extended significantly towards small mesopores and large micropores when a proper t-curve was used to represent the film thickness of nitrogen adsorbed on the carbon surface. It was proposed that the aforementioned t-curve be obtained from the nitrogen adsorption isotherm at 77 K on a macroporous carbon black by fitting its multilayer part to the calibrated t-curve for nitrogen adsorbed at 77 K on a macroporous silica. To date, the Harkins–Jura or Halsey t-curves have been used to describe the pressure-dependence of the film thickness. This appears to be inaccurate, especially in the range of low relative pressures. It was shown that this inaccuracy makes the pore-size analysis questionable. However, the t-curve proposed in this work gave the pore-size distribution functions for the carbons studied thereby reproducing the total pore volume and showing realistic behaviour in the range at the borderline between micropores and mesopores.

Critical appraisal of classical methods for determination of mesopore size distributions of MCM-41 materials

Abstract Classical methods for evaluation of the pore size distributions (PSD) from low temperature (77 K) nitrogen adsorption isotherms were compared by using a series of hexagonally ordered mesoporous silicas (MCM-41) of different pore sizes. This comparison involved the methods proposed by Barrett, Joyner and Halenda (BJH), Dollimore and Heal (DH) as well as Broekhoff and de Boer (BdB) simplified recently by Lukens et al. These methods were examined by using the statistical film thickness (t-curve) reported by Halsey (H), and Kruk, Jaroniec and Sayari (KJS). A detailed comparison of aforementioned methods shows that the BJH method with Kelvin-type equation and t-curve determined on the basis of MCM-41 materials as suggested by KJS provides the most reliable PSD. In contrast to other methods, the BJH–KJS method gives an accurate estimate of the pore width and reproduces the pore volume.

Derivation of the Expanded Form of the BJH Equation and its Application to the Pore Structure Analysis of Mesoporous Adsorbents

The BJH equation, [Formula: see text], used for pore structure analyses via its application to the N2desorption isotherms at 78 K of porous materials, has been modified by substituting the value of ciand expanding the last term. The quantity vnis the volume of the pores involved in the nth desorption step and is given in terms of the volume of N2, (ΔV)n, exuded from the porous material, the constants Rnand ciwhich depend on the average pore size and average thickness of the physically adsorbed multilayer, Δtnbeing the decrease in thickness of the multilayer as a result of the nth desorption step and Aithe surface area of the set of pores involved in the ith desorption step. A derivation of the modified equation is presented. It has been applied to the N2desorption data of bone char used by Barrett, Joyner and Halenda (BJH). The effect of the multilayer thickness (t) values given by Pierce and de Boer on the pore size distribution of bone char has been studied. The pore size distribution data are compared with those obtained by the original BJH and Pierce methods. The pore system conforms very well with the idealised open-ended cylindrical pore model.The expanded BJH equation has also been applied to the desorption isotherms of fresh and sintered silica-alumina cracking catalysts over the entire range of silica/alumina ratios. The multilayer thickness (t) values given by de Boer have been used in the calculations. The pore systems of the catalysts, vacuum-dried at 400°C, are observed to conform to the cylindrical pore model as revealed by the excellent agreement between the cumulative surface areas obtained in P.S.D. calculations and the BET surface areas. The pore systems of the catalysts, sintered at different temperatures in a dry oxygen stream, deviate considerably from the cylindrical pore model. Enlargement of the pores and their nonconformity with the ideal pore model are attributed to modifications of the pore structures brought about by the phenomenon known as ‘self-steaming’ with the water vapour released from the catalysts.

Knudsen diffusion of various gases through a barium sulphate packed bed

The diffusion coefficients, D k, of helium, krypton, carbon dioxide and air through a packed bed of barium sulphate calculated from the Knudsen diffusion flow equation were found to be a cumulative parameter obtained from the contribution of the diffusion coefficient through the voids of the packed bed, D v , and the diffusion coefficient through the pores, D p , within barium sulphate. The surface area of compacted and uncompacted material obtained from low temperature gas adsorption and the Brunauer, Emmett and Teller equation (BET), together with the void sizes and pore sizes in compacted material obtained by Barrett, Joyner and Halenda (B.J.H.) isotherm analysis, when compared with the surface area values obtained by Knudsen diffusion and permeametry, indicated that the coefficients D v and D p evaluate the void and pore areas in compacted barium sulphate, respectively.