BET Isotherm Research Articles

Removal of Cr(VI) from aqueous solution using chitosan-g-poly(butyl acrylate)/silica gel nanocomposite

The present work deals with the preparation of the novel sorbent, glutaraldehye crosslinked silica gel/chitosan-g-poly(butyl acrylate) (Cs-g-PBA/SG) nanocomposite by sol–gel method for removal of toxic chromium ion. Prepared nanosorbent was then characterized by FTIR, XRD, DLS, SEM, BET isotherm for its formation and suitability. Its sorption capacity and sorption isotherms were brought under batch mode to suit the optimal parameters viz., contact time, pH, adsorbent dose and initial metal ion concentration which influence the sorption. The theoretical modeling such as Langmuir and Freundlich isotherm adsorption were applied to describe isotherm constants. Equilibrium data agreed well with the Langmuir isotherm model (R2=0.9763) with maximum adsorption capacity of 55.71 (mg/g). The kinetic studies showed that the adsorption follows the pseudo-second-order kinetics (R2=0.9999). From the results, it was concluded that Cs-g-PBA/SG nanocomposite is an excellent biosorbent for Cr removal from wastewater.

Trimetallic catalyst synthesized multi-walled carbon nanotubes and their application for hydrogen storage

Multi-walled carbon nanotubes (MWCNTs) were synthesized by rapid thermal decomposition method using trimetallic catalyst supported MgO. MWCNTs prepared via trimetallic catalyst shows much higher BET specific surface area compared to current monometallic and bimetallic catalyst. As-grown and pristine MWCNTs were found to adsorb nitrogen reversibly and their adsorption uptake exhibits type-II BET isotherm. Existence of small impurities, such as metal and metal oxides present in the MWCNTs, was confirmed by thermogravimetric analysis as well as via energy-dispersive X-ray spectroscopy. An over 10 wt% enhancement of hydrogen storage capacity of as-grown MWCNTs compared to pristine was found to be due to the presence of impurities. Fast kinetics and complete reversibility gives indication that the process responsible for hydrogen adsorption uptake in MWCNTs is physisorption. A linear relation between hydrogen uptake (~0.22 and 0.20 wt%) and equilibrium hydrogen pressure was obtained for both as-grown and pristine MWCNTs.

Moisture Adsorption Characteristics of Sandesh Powder

Sorption studies were carried out for sandesh powder at 10, 20 and 40 o C to determine its moisture adsorption characteristics. The adsorption curves obtained were observed to follow a sigmoid shape and corresponds to type II, with a definite inversion due to the temperature effect above 0.79 water activity. The GAB, BET and Caurie isotherm models were attempted to describe the experimental data and were found to give the best fit between experimental and predicted values as indicated by R 2 values. Monolayer moisture content was calculated using the BET and GAB model. Caurie model was used to compute the properties of sorbed water viz., monolayer water, number of adsorbed monolayer, density, and surface area of adsorption in sandesh powder. The net isosteric heat of sorption of water in sandesh powder estimated using Clausius-Clapeyron equation at different moisture contents indicated its strong dependence on moisture content.

Sustainable approach for recycling seafood wastes for the removal of priority hazardous substances (Hg and Cd) from water

Mercury and cadmium are considered by the water framework directive priority hazardous substances. In this work, the capacity of crab carapace and clam shell wastes to remove mercury and cadmium from water was evaluated under batch conditions, for realistic contamination scenarios in monometallic and binary solutions. The results evidenced that in monometallic solutions and under studied operational conditions, both biosorbents can achieve Hg2+ removal efficiencies higher than 80% and the kinetic process is well described by two of the most widely used equations, the pseudo-second order and the Elovich model. In terms of biosorption equilibrium, crab carapace and clam shell wastes displayed very distinct behaviours. While clam shells achieve the complete monolayer coverage and the isotherm is well described by the Langmuir model, crab carapace powder display a more unusual behaviour, that is well described by the BET isotherm, and is characterized by an almost convex shape to the concentration axis, with an infinite slope for an Hg2+ concentration in solution around 25μg/L. In binary solutions, both wastes are able to uptake simultaneously Hg2+ and Cd2+, however the uptake of Hg2+ was inhibited in some extent, attributed to the high kinetic and equilibrium selectivities of the bio-wastes for cadmium.

BET adsorption reaction model based on the pseudo steady-state hypothesis for describing the kinetics of adsorption in liquid phase

A multilayer adsorption reaction model in liquid phase based on BET isotherm fundamentals has been developed from the pseudo steady-state hypothesis of adsorption on the accumulating adsorbate layers. The model accurately reproduces the adsorption isotherms and kinetic profiles of different adsorption systems reported in the literature, and especially those of mesoporous carbon materials used to adsorb organic compounds in aqueous solutions. The kinetic rate constant evaluated for each of the adsorption systems permitted them to be sorted according to the adsorption rate, regardless of the operation parameters employed in the experiments. The model also allowed the effect of the equilibrium parameters and operation variables on the adsorption rate to be analyzed. The analysis yielded similar trends to those reported in literature.

Experimental and Kinetic Studies on Penicillin G Adsorption by Lemna minor

This study examined the ability of dried duckweed (Lemna minor) to remove soluble Penicillin G from aqueous solution. Batch experiments were conducted to investigate the effects of pH, contact time, initial Penicillin G concentration, biomass dose and temperature on penicillin G adsorption. Maximum adsorption capacity of the duckweed was 36.18 mg g-1 when 94.6% of the Penicillin G was removed. The adsorption equilibriums were analyzed by Langmuir, Freundlich, Temkin and BET isotherm models. It was found that he data fitted to Langmuir better than isotherm other models. Batch kinetic experiments showed that the adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.99. The adsorption capacity of penicillin G increased from 31.11 to 41.82 mg/g with increasing the temperature from 20 to 50, indicating that the process is endothermic. According to achieved results, it was defined that Lemna minor not only was an inexpensive absorbent, but also a quite effective factor in removal of Penicillin G from water and wastewater.

Arsenic(III) adsorption from aqueous solutions on novel carbon cryogel/ceria nanocomposite

Carbon cryogel/ceria composite, with 10 wt.% of ceria, was synthesized by mixing of ceria and carbon cryogel (CC). The sample was characterized by field emission scanning electron microscopy, nitrogen adsorption and X-ray diffraction. The adsorption of arsenic(III) ions from aqueous solutions on carbon cryogel/ceria nanocomposite was studied as a function of time, solution pH and As(III) ion concentration. The results are correlated with previous investigations of adsorption mechanism of arsenic(III) on carbon cryogel. Adsorption dose experiments showed that the mass of the adsorbent was reduced for 20 times, in comparison with pure CC, for the same amount of adsorbed arsenic(III) ions. BET isotherm was used to interpret the experimental data for modelling liquid phase adsorption.

Geometry Optimization as Molecular Modeling on Activating Carbon with Polypirrole

ABSTRACTActivation of carbon using polypyrrole as activating agent is searched through Molecular Modeling. The Geometry Optimizations carried out helped to observe carbon effect when is attacked by a polymer in order to give an estimation of the pore size diameter of carbon. In this first approximation pore size diameters is about 30 % with respect to BET (Brunauer, P. Emmett y E. Teller) isotherms experimental data.

Highly Efficient Adsorption of Aqueous Pb(II) with Mesoporous Metal-Organic Framework-5: An Equilibrium and Kinetic Study

Mesoporous metal-organic framework-5 (MOF-5), with the composition Zn4O(BDC)3, showed a high capacity for the adsorptive removal of Pb(II) from 100% aqueous media. After the adsorption process, changes in both morphology and composition were detected using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) system, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. The experimental evidence showed that Zn(II) liberation from MOF-5 structure was provoked by the water effect demonstrating that Pb(II) removal is not due to ionic exchange with Zn. A kinetic study showed that Pb(II) removal was carried out in 30 min with a behavior of pseudo-second-order kinetic model. The experimental data on Pb(II) adsorption were adequately fit by both the Langmuir and BET isotherm models with maximum adsorption capacities of 658.5 and 412.7 mg/g, respectively, at pH 5 and 45°C. The results of this work demonstrate that the use of MOF-5 has great potential for applications in environmental protection, especially regarding the removal of the lead present in industrial wastewaters and tap waters.

Chitosan-/PVA-coated magnetic nanoparticles for Cu(II) ions adsorption

The magnetic chitosan/PVA/iron oxide nanoparticles have been synthesized for the usage of Cu(II) ions removal from aqueous solution. The structure and morphology of the adsorbent was investigated by X-Ray diffraction, scanning electron microscope, and Fourier transform infrared analyses. Adsorption performances of the adsorbents were tested as a function of Cu(II) ion concentration, pH value, time, and temperature. The adsorption kinetics and isotherms were analyzed by Lagergren first-order, pseudo-second-order, Elovich equation, intra-particle diffusion models, and Langmuir, Freundlich, DR and BET isotherms, respectively. The kinetics results pointed out pseudo-second-order. Maximum sorption capacity of the adsorbent was estimated to be 500 mg/g at pH 5.0. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were also determined and indicated that the sorption process was endothermic in nature. The magnetic results showed that the adsorbent can be manipulated by an external magnet with sufficient separation. The process is clean, safe, and easy enough for the removal of Cu(II) ions.

Kinetics and Equilibrium Studies of the Removal of Blue Basic 41 and Methylene Blue from Aqueous Solution Using Rice Stems

Synthetic dyes are among the most common contaminants of the environment. Therefore, the aim of this study was investigation the removal of Basic Blue 41 (BB41) and Methylene Blue (MB) from industrial effluents by useing raw and modified rice stems. In this study raw and modified rice stems treated chemically with Citric Acid (CA) and were used to explore the potentiality of rice stems for removal of BB41 and MB dyes. Effect of various parameters including pH, contact time, adsorbent dose and initial dye concentration on the adsorption were studied. To characterize the adsorbents, Scanning Electron Microscope (SEM) was used. The adsorbent surface functional groups identified with Fourier Transform InfraRed (FT-IR) spectroscopy.The applicability of the adsorption data was explained by Langmuir, Freundlich, Temkin and BET isotherms. The results showed that increasing of contact time and adsorbent dose, dye removal increases for both raw and modified adsorbents. Dye adsorption on to adsorbent increased with increasing of pH. Also the results indicated that dye removal efficiency was increased by decreasing initial dye concentration. Among studied isotherms, data were fitted well by Langmuir model (R2>0.98) for both raw and modified adsorbents. Also, adsorption kinetics were more fitted by pseudo second order model (R2>0.99).The results of the present work showed that rice stem was a good, low cost and effective adsorbent for removal of BB14 and MB from industrial effluents.

-CHYMOTRYPSIN IMMOBILIZED ENZYME: PHYSICAL, ACTIVITY & STABILITY PROPERTIES

In this study, α-chymotrypsin enzyme was used as a substrate while micropore Y-zeolite, which is HY, USY and NaY as a support. The purpose of this study was to compare the physical properties of zeolite and immobilization of enzyme with zeolite. The characteristics such as BET surface area, isotherm adsorption, BJH adsorption, pore size, t-plot and pore volume have been studied. Furthermore, a comparison has been conducted between immobilized and mobile enzyme for their ability to adsorb hydrolysate at λ=410 nm. The stability of the immobilized enzyme was also determined by varying the parameters of phosphate and tris-chloride buffer and loading of sample solution. Based on the result obtained, HY zeolite has the best physical properties compared to USY and NaY zeolite. Besides that, immobilized enzyme gave higher hydrolysate adsorption activity than the free enzyme. Stability results showed that pH of phosphate and tris-chloride buffer and amount of sample solution play an important role in obtaining the stable immobilized enzyme.

Parametric and Adsorption Kinetic Studies of Reactive Black 5 Removal from Textile Simulated Wastewater Using Oil Palm (Elais guineensis) Empty Fruit Bunch

The potential of empty fruit bunch as a low-cost biosorbent for the removal of Reactive Black 5 from aqueous solution was investigated in this study. The influences of pH, contact time, initial concentration and biosorbent dosage were studied in batch experiments at room temperature. The empty fruit bunch used in this study was characterized by mR spectroscopy and it was found that O-H, N-H, and C=O stretching were present. Maximum adsorption uptake of Reactive Black 5 dye was found to be at pH 2. At pH 2, the adsorption was rapid at the first 5 minutes of contact, with uptake of more than 50%, and equilibrium was achieved in 30 minutes of agitation. It was also found that higher biosorbent dosage increases dye uptake, of up to 90%. Kinetic studies showed good correlation coefficient for a pseudo-second-order kinetic model. Langmuir, Freundlich, and BET isotherm models were applied to describe the biosorption of Reactive Black 5 dyes onto empty fruit bunch. Langmuir model fitted the equilibrium data better, giving correlation coefficient of 0.9999 and a maximum adsorption capacity of 7.3421 mg/g. Both pseudo-second-order kinetic model and Langmuir model indicates monolayer coverage on adsorbent. The results showed that empty fruit bunch have the potential to be applied as alternative low-cost biosorbent in the remediation of dye contamination in waste water.

Tailored Carbon Nanotubes for High-Performance Lithium-Sulfur Batteries

Significant effort has been invested into addressing critical problems of lithium-sulfur batteries since they are considered as the next generation energy storage material due to their high specific energy density and low cost.1 Critical problems still remain including poor cycle life and rate capability originated from the insulating nature of sulfur and polysulfide intermediate dissolution into the electrolyte.2 Despite the considerable success in alleviating the problems such as drastic capacity fading and poor rate capability, commercial application still has a long way to go, especially at high current rate conditions. Here, we report a noble carbon matrix for lithium-sulfur batteries based on a partially unzipped multi-walled carbon nanotube(MWCNT) with favorable properties for the improved lithium-sulfur batteries. Partially unzipped MWCNT has additional benefit in that it was prepared by facile and scalable way without use of toxic or expensive materials. In contrast to MWCNT and fully unzipped nanoribbon, partially unzipped MWCNT clearly exhibited a unique structure of coexistence of carbon nanotube and nanoribbon in one tube as illustrated in Figure 1. The experimental optimization results were fully discussed with TEM, SAED patterns, EDS mapping, RAMAN, XPS, BET isotherms and EIS characterizations. Partially unzipped MWCNT showed increased surface area and pore volume with preserved electron conductive pathway owing to opened inner pores of MWCNT. Newly developed the pores of partially unzipped MWCNT were decorated with oxygen containing functional groups and acted as a stable polysulfide reservoir as illustrated in Figure 2. The synergistic effect of unique pore structure and oxygen containing functional groups led to the improved electrochemical performance at a high current rate of 8375 mA g-1 (5 C). Partially unzipped MWCNT-sulfur composite delivered 688.5 mAh g-1 at the initial discharge and retained 544.2 mAh g-1 after 100 cycles at the high current rate of 5 C as given in Figure 3. Furthermore, to understand the mechanism of the improved electrochemical performance of partially unzipped MWCNT, Partially unzipped MWCNT-sulfur was studied utilizing the Monte Carlo (MC) simulations. This modelling explains why the polysulfide dissolution into the bulk electrolyte was alleviated thus led to the improved electrochemical performance. We believe that our work can provide insight to many researchers in that partially unzipped MWCNT opens up a new concept of exploiting MWCNT inner pores. Reference 1. Chung, W. J.; Griebel, J. J.; Kim, E. T.; Yoon, H.; Simmonds, A. G.; Ji, H. J.; Dirlam, P. T.; Glass, R. S.; Wie, J. J.; Nguyen, N. A. et al. The use of elemental sulfur as an alternative feedstock for polymeric materials. Nat. Chem. 2013, 5, 518-524. 2. Manthiram, A.; Fu, Y.;Su, Y.-S. Challenges and Prospects of Lithium-Sulfur Batteries. Acc. Chem. Res. 2012, 46, 1125-1134. Figure 1

Assessment of the banana pseudostem as a low-cost biosorbent for the removal of reactive blue 5G dye

In this work, the removal of reactive blue 5G (RB5G) dye using the drying biomass of banana pseudostem (BPS) was investigated. The characterization of BPS particles was performed. Improvement in the RB5G dye removal performance at the following sorption conditions was evidenced: pH 1, 30°C sorption temperature and 40 rpm shaking, regardless of the particle size range. Kinetic RB5G dye sorption data obtained at better conditions fit well in an Elovich model. A combined Langmuir–BET isotherm model provides a good representation of the RB5G dye equilibrium sorption data, which shows the evidence of a physical sorption process on the BPS surface. Based on the results, the removal of RB5G dye molecules by BPS is based on a physical sorption process.

Adsorption of wood extractives and model compounds onto bentonite

The adsorption of wood extractives and representative model compounds into two different forms of bentonite was studied. The colloidal dispersion showed limited solubility which affected the shape of the adsorption isotherm. Modelling of the adsorption isotherms showed excellent fits with Freundlich and BET isotherm models indicating that multilayer adsorption with cooperative binding was occurring. The wood extractives were found to have greater affinity with the bentonite surface than the model compounds. Bentonite B was found to be a better adsorbent than bentonite A due to the differences in exchangeable cations present and its greater swelling capacity and surface area. The addition of ethanol during the preparation of the colloidal dispersions, as done by previous researchers when studying adsorption of the oleic acid, triolein and abietic acid, appears to reduce the affinity and capacity of the adsorption onto bentonite.

Gelatin-assisted sol–gel derived TiO2 microspheres for hydrogen storage

TiO2 is an important photocatalyst candidate for solar energy or hydrogen energy harvesting. Creation of porous structures or high surface area within TiO2 microspheres may potentially address the challenge to improve their efficiency. In present work, we report the sol–gel fabrication of mesoporous TiO2 microspheres that assembled from nanoparticles with the assistance of gelatin template. The phase structure, morphology, and mesoporous characteristics were analyzed by X-ray diffraction, transmission electron microscopy, and BET measurements. Particularly, the gelatin-assisted fabricated TiO2 nanoparticles (∼10–20 nm) were achieved to assemble TiO2 microspheres with diameters of 0.2–0.5 μm, which yielded a typical type-IV BET isotherm curve (N2 hysteresis loop) with a large surface area of 98.3 m2/g and a small pore size of 11.9 nm. A simplified model was proposed to investigate the effect mechanism of gelatin on the formation of TiO2 mesoporous microspheres. The room temperature pressure-dependent hydrogen evolution of the gelatin-assisted fabricated TiO2 nanostructures has also been investigated, suggesting that gelatin favors high surface area and improves the hydrogen storage performance, and the achieved TiO2 microspheres could be potential candidates to be utilized as the photocatalyst for hydrogen evolution.

ADSORPTION BEHAVIOUR OF HAZARDOUS ORGANIC SOLUTIONS ONTO NEW POLYMERIC SORBENT

The fate of herbicides in soil, and surface and groundwaters is determined by several factors including retention, transformation, and transport processes. Environmental pollutants removed from waters of these chemicals is important for all biologic life. In this study, adsorption of textile dyestuffs or adsorption of pesticides such as bisphenol A, 4-amino nitrophenol, phenoxyacetic acid were examined on PVBCIm. This polymer was obtained by modifying polyvinyl benzyl chloride (PVBC) resin with imidazole. This method, has been extended to chloro methyl group to preparepoly (N-vinyl imidazole) (PVIm) graft chains on crosslinked polyvinyl benzyl chloride (PVBC) polymer. In the aqueous solution the adsorption of organic waste was determined by UV-vis spectrophotometer. For different concentrations of hazardous organic wastes in aqueous solution, Freundlich, Langmuir, and BET isotherms were applied at 25 oC.

Ni/Ti layered double hydroxide: synthesis, characterization and application as a photocatalyst for visible light degradation of aqueous methylene blue.

Visible light responsive 2 : 1 Ni/Ti layered double hydroxide (LDH) was synthesized by a single step hydrothermal route using commercially available Ni(NO3)2·6H2O, TiCl4 and urea. The material exhibited significant absorption in the visible range with a very narrow band gap (2.68 eV). This could be attributed to structural defects as confirmed by diffuse reflectance spectroscopy (DRS), photoluminescence (PL), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. FT-IR, TGA, DTA, DSC, HR-TEM and SEM-EDX measurements yielded information about structural aspects, thermal stability and surface morphology. Surface and pore characteristics of the material were obtained from the BET isotherm for N2 adsorption at 77 K. Zeta potential measurements were used to characterize the electrical properties of the surface while XPS revealed changes in surface states and oxygen deficiencies. The material was found to be an excellent photocatalyst for the degradation of aqueous methylene blue in visible light. The photocatalytic properties of the material were explained on the basis of the narrow band gap, the high surface area and the presence of surface defects. The photocatalytic activity improved in alkaline media [pH 11.0, catalyst load 15 mg in 200 ml dye solution, dye concentration 1 × 10(-6) M (= 0.3198 mg L(-1))] due to the electrostatic attractions between the dye cations and the negative charges on the Ni/Ti LDH surface. The catalytic activity was found to be higher than the common commercial catalysts like ZnO, ZnS, NiO, TiO2 and Degussa P25. The catalytic activity was retained even after five methylene blue degradation cycles, demonstrating that the LDH could be an important addition to the field of wastewater treatment.

Modeling and Simulation of Natural Gas Production from Unconventional Shale Reservoirs

Modeling and simulation of unconventional reservoirs are much more complicated than the conventional reservoir modeling, because of their complex flow characteristics. Mechanisms, which control the flow in the reservoir, are still under the investigation of researchers. However, it is important to investigate applications of mechanisms which are present to our knowledge. This paper presents the theory and applications of flow mechanisms in unconventional reservoir modeling. It is a well-known fact that most of the reservoir flow problems are non-linear due to pressure dependency of particular parameters. It is also widely accepted that fully numerical solutions are costly both computational and time wise. Therefore, the presented model in this paper follows semi-analytical solution methods. Gas adsorption in unconventional reservoirs is the major pressure dependent mechanism; in addition existence of natural fractures is also taken considerable attention. This paper aims to investigate combined effect of existence of natural fractures gas adsorption, and gas slippage effect while keeping the computational effort in acceptable range. Unlike the existing literature (Langmuir is widely used), BET multi-layer isotherm employed in this paper for gas adsorption modeling. A modified dual porosity modeling is used for natural fracture and gas slippage effect modeling. For model verification purposes a history matched is performed with real field data from Marcellus shale. The proposed model in this paper shows a good agreement with the field data. It is observed that BET isotherm models early time production performance more accurately than Langmuir isotherm. It is also concluded that gas adsorption significantly improves the production performances of unconventional reservoirs, with natural fractures. In addition, gas slippage has a slight effect in long term production.