BET Isotherm Research Articles

Prickly pear cactus cladodes powder of Opuntia ficus indica as a cost effective biosorbent for dyes removal from aqueous solutions.

The textiles manufacturing is one of the core industries that release a huge amount of dyes during the dyeing process. As a result, the growing demand of an efficient and low-cost treatment has given rise to alternative adsorbents. In the present study, prickly pear cactus cladodes powder (PPCP) of Opuntia ficus indica was investigated as an ecofriendly and low-cost biosorbent of Acid orange 51 (AO51) and Reactive Red 75 (RR75) dyes commonly used in dyeing. The FTIR spectroscopic characterization of PPCP showed the heterogeneity in surface structure and functional groups which confers to the biosorbent its capability to interact with acidic (AO51) and reactive (RR75) dyes molecules. Effects of pH, temperature, initial dye concentration and adsorbent dose on adsorption yield were investigated. The dyes uptake process was closely fitted to the pseudo-second order kinetic for both dyes. Experimental data were analyzed by applying the Langmuir, Freundlich, Dubinin-Raduskevich, Temkin, Redlich-Peterson, and BET isotherms equations. The models of BET and Langmuir were considered as the best isotherms models fitting experimental data, respectively, of RR75 and AO51. The maximum Langmuir monolayer biosorption capacities were of 198.9 and 45mg g-1, respectively for RR75 and AO51.

Synthesis, characterization, and kinetic study of activated carbon modified by polysulfide rubber coating for aqueous hexavalent chromium removal

Activated carbon (AC) is a widely used adsorbent with a limited selectivity for chromium species. In this study, polysulfide rubber (PSR) polymer was synthesized, characterized by FTIR, and coated on F400 granular AC to obtain AC-PSR. The material properties of this composite adsorbent were investigated using SEM, TEM, EDS, TGA, BET isotherm, and XPS. The effectiveness of AC-PSR for aqueous Cr(VI) removal was investigated, and compared against virgin AC. The results showed that despite a 23% decrease in the surface area of AC after PSR coating, AC-PSR had a higher capacity for Cr(VI) adsorption. Adsorption followed a pseudo-second-order biphasic diffusion model for both AC and AC-PSR. The reaction rate constants showed that despite faster initial kinetics between AC and Cr(VI) during the film diffusion step, AC-PSR exhibited faster kinetics during the intraparticle diffusion step. The Langmuir isotherm model was found to be the best model to describe the experimental data, which showed a higher adsorption capacity for AC-PSR (QM,AC=3.472mg/g vs. QM,AC-PSR=8.929mg/g) and a stronger binding between Cr(VI) and AC-PSR (bA,AC=0.391L/mg vs. bA,AC-PSR=0.696L/mg). Regenerated AC-PSR showed an 8% increase in Cr(VI) removal efficiency after the first cycle, and then maintained a ∼98% Cr(VI) removal for three additional successive cycles.

Islanding of EuVO4 on high-dispersed fluorine doped few layered graphene sheets for efficient photocatalytic mineralization of phenolic compounds and bacterial disinfection

Abstract In present work, EuVO4 (EV) nanoparticles were dispersed over fluorine doped graphene sheets (FG24) to synthesize EV/FG24 nanocomposite. Few layered fluorine doped graphene sheets were prepared by sonochemical exfoliation method using NaF as fluorine source. FG24 and EV/FG24 composites were successfully characterized by FESEM, TEM, RAMAN, XRD, TGA, XPS, BET isotherm, FTIR, photoluminescence and UV–visible spectral techniques. AFM and RAMAN analysis confirmed the formation of fluorine doped graphene sheets. The high dispersion of EV/FG24 in water was ascertained by zeta potential measurement and Tyndall scattering experiment. The photocatalytic activity of EV/FG24 was tested for the degradation of phenolic compounds and bacterial disinfection under visible light. As compared to conventional slurry photocatalytic system, no magnetic stirring was used during degradation experiments. The photodegradation rate was substantially influenced by adsorption of 2, 4-dinitrophenol (DNP) and phenol onto EV/FG24. The DNP and phenol were completely mineralized in 10 h. The selected bacteria were inactivated by EV/FG24 in 3 h. The effect of various radical scavengers revealed the pivotal role of hydroxyl radicals during disinfection mechanism. EV/FG24 exhibited significant recycle efficiency during photocatalytic process. EV/FG24 was used as a stable photocatalyst to depollute contaminated water.

Performance of Activated Natural Zeolite/Cu as a catalyst on Degradation of Glycerol into Ethanol Assisted by Ultrasonic

The purpose of this study was to convert glycerol into ethanol using the catalyst of activated natural zeolite/Cu assisted by ultrasonic. The catalyst was characterized using X-Ray Diffraction and BET isotherm adsorption. The degradation process carried out at the temperature of 60 °C and at various time of 1, 2, and 4 hours. The product of glycerol degradation was analyzed using Gas Chromatography. The results showed that the structure of natural zeolite was a mordenite. The BET analysis showed that the surface area of natural zeolite is 99.096 m2/g greater than that of natural zeolite impregnated Cu that is 6.597 m2/g. The total pores, however, a natural zeolite is 0.026 cm3 smaller than that of natural zeolite impregnated Cu that is 0.058 cm3. The highest yield of ethanol as the product of glycerol degradation was 3.704% produced when the sonication times is 2 hours using activated natural zeolite catalyst. The activated zeolite has a prospect to be used as a degradation reaction catalyst for molecules that goes through the Bronsted Lowry acid mechanism.

Kinetic Models of Batch Sorption in a Limited Volume

The batch sorption kinetics described by a nonlinear equation with a variable equilibrium parameter for the interface was considered. It was shown that a difference equation of this type can be reduced, with a certain approximation, to the pseudo first- and pseudo second-order kinetic equations with constant parameters that are convenient for processing the experimental data. The errors of this approximation are smaller than the characteristic experimental errors in constructing the kinetic curves. For the linear sorption isotherm and Langmuir isotherm, the sorption kinetics can be approximated by the pseudo first-order equation. In addition, for the Langmuir isotherm and BET isotherm of polymolecular sorption, the kinetics can be described by the sum of the pseudo first- and pseudo second-order equations, or only by the pseudo second-order equation. For all these cases, it was shown how the parameters of kinetic equations are related with the equilibrium characteristics of sorbents. Our analysis shows that the possibility of describing the experimental data obtained in batch kinetic experiments using pseudo first- or pseudo second-order models is related to the possibility of mathematical approximations and transformations and cannot be used to characterize the kinetic mechanisms.

Hydrothermal treatment for regeneration of activated carbon loaded with organic micropollutants

Hydrothermal treatment (HT) at 200 °C and 240 °C for 4 and 16 h was studied for the regeneration of granular activated carbon (AC) loaded with a range of organic micropollutants having a broad range of physico-chemical properties. Carbamazepine, diazinon, diclofenac, estrone, iohexol, metoprolol and sulfamethoxazole were fully converted. Limits were seen for the conversion of caffeine, ibuprofen and perfluorooctanesulfonate (PFOS). However, the degree of degradation was enhanced for the latter compounds in the adsorbed state as compared to experiments in aqueous solution. The methodology was tested in five loading and regeneration cycles for selected compounds with no change of the degradation potential and of the AC properties. In particular, the surface properties of the AC did not deteriorate upon HT as determined by the specific surface area (from BET isotherms), the point of zero charge, and the surface functional groups (from diffuse reflectance IR spectroscopy). As the total concentration of the loaded pollutants was minimized by HT, this method could be considered as a new low temperature regeneration technology for spent AC.

Green and facile synthesis of few-layer graphene via liquid exfoliation process for Lithium-ion batteries

A green and facile method using jet cavitation (JC) was utilized to prepare few layer graphene (FLG) derived from artificial graphite delamination without adding any strong acids and oxidants. The JC method not only provides high quality FLG with high yield but also demonstrate excellent electrochemical performance as anode materials for Li-ion batteries. Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) as well as BET isotherms and XPS are carried out in this study. The results of atomic force microscopy (AFM) further revealed that up to 85% of the prepared FLG were less than 10 layers. This exfoliation process happened mainly due to the cavitation-induced intensive tensile stress acting on the layered materials. Electrochemical measurements demonstrate that graphite anode delivered only 240 mAh/g while FLG anode achieved more than 322 mAh/g at 5C rate test. These results indicate that JC method not only paves the way for cheaper and safer production of graphene but also holds great potential applications in energy-related technology.

Surface Area and Porosity Development on Granular Activated Carbon by Zirconium: Adsorption Isotherm Studies

In this study, a new series of coconut shell based granular activated carbons (GAC) are prepared by impregnating with zirconium ions as zirconyl chloride and activated under superheated steam. These carbons are designated with activation temperature/ conditions as GAC 383 (activated at 383K), GACO 383 (HNO3 oxidised), GACZR 1273 (ZrOCl2 activated at 1273K) and GACOZR 1273 (HNO3 oxidised, ZrOCl2 activated at 1273K). Surface characteristics of these carbons are evaluated using Boehm titration methods, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction techniques (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The pore volume and the respective specific surface area of each carbon are determined by BET, I plot, Langmuir, Freundlich, and Dubinin-Radushkevich isotherms using N2 adsorption data at 77K. Analysis shows that zirconium ion enhances the surface area and porosity of granular activated carbon. The adsorption characteristics of newly prepared GAC are tested by solid-liquid equilibria using phenol as adsorbate. Equilibrium phenol adsorption data fitted to standard isotherm models of Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) equations. Adsorption constants and parameters indicate that zirconium impregnated granular activated carbons are relatively more efficient for the removal of phenol than the native carbon used.

Catalytic cracking of isopropylbenzene over hybrid HZSM-12/M41S (M41S = MCM-41 or MCM-48) micro-mesoporous materials

ABSTRACTThe catalytic cracking of isopropylbenzene was investigaded over hybrid ZSM-12/MCM-41 and HZSM-12/MCM-48 micro-mesoporous materials, in order to verify the effect of the acid site of the accessibility of mesoporous channels combined with the acid sites into the zeolite. The hybrid materials were synthesized by the hydrothermal method using the template mechanism. The obtained materials were characterized by X-ray diffraction and BET isotherms using nitrogen adsorption-desorption at 77 K. The X-ray diffraction patterns presented characteristic peaks of the microporous and mesoporous phases. These analysis revealed the formation of ordered hexagonal MCM-41 or cubic MCM-48 mesoporous phases, associated with the ZSM-12 structure. In order to generate acid sites, the materials were ion exchanged with ammonium chloride solution. The calcined hybrid materials were tested as catalyst for cracking of isopropyl-benzene, using a fixed bed reactor at 450 oC and nitrogen gas. The catalytic tests showed that the HZSM-12/AlMCM-41 and HZSM-12/MCM-48 hybrid materials have potential for use in cracking reactions, bening more active than the zeolite or the M41S alone. The catalytic activities of the hybrid materials can be associated with a synergistic effect between the acid sites present on the zeolitic phase and the mesoporous phase. In order to verify how the structure of the hybrid materials may affect and control their catalytic performances, the results were compared with HZSM-12 physically mixed with MCM-41 and MCM-48.

The prediction of moisture adsorption isotherm for sucrose powder in Côte d’Ivoire

Moisture sorption isotherms play an essential role in preservation and storage of dehydrated food. To study the behavior of sucrose, it’s moisture adsorption isotherm was investigated using the static gravimetrique method at laboratory temperature (29 ±1°C) in a water activity range (aw) of 0.07-0.97. The results showed that the equilibrium moisture content of sucrose increase substantially above aw = 0.6. The moisture adsorption isotherm was sigmoid in shap, showing a type III BET isotherm. The data obtained were fitted to several models including two-parameter (BET, Hasley, Kuhn and Oswin), three parameter (GAB). A non-linear least square regression analysis was used to evaluate the models constants. The GAB model best fitted the experimental data in the wide range of water activity. The best fitted equation provide a sound basis for futur work on the drying and storage of sucrose. The accurate moisture content and the stability profile of sucrose were determined. The results of determination show that sucrose powder was stable below 7.7% RH at 29°C. The content of water adsorbed in the monomolecular layer was calculated (GAB Xm=0.950 g H2O/100 g solids; BET Xm= 1.072 g H2O/100 g solids).

Plasma synthesis of carbon powder with embedded Fe3C nanoparticles for magnetic separation of biomolecules

In this article we report the synthesis of a carbon powder with embedded magnetic nanoparticles. Precursors, ferrocene and ethylene glycol, were loaded in a quartz combustion tube and pyrolysed by microwave plasma under vacuum conditions. The synthesized powder was similar to graphite in texture, but strongly attracted by magnetic fields. Several analytical techniques were carried out, including X-ray Photoelectron Spectroscopy, Transmission and Scanning Electron microscopies, X-ray Diffraction and BET isotherm. The resulting material is a ramified framework of carbon, similar to activated carbon, with embedded Fe3C/C core-shell nanoparticles. BET analysis gives a type IV isotherm, common for mesoporous adsorbents. A protocol was developed for the purification of nucleic acids by magnetic separation. The material gives satisfactory results for DNA extraction. It is concluded that due to the non-toxicity nature of the C shells and the outstanding magnetic property of the Fe3C nanoparticles this absorptive carbonaceous material can be applied in fields of biomedicine or biotechnology.

Activity Reduction of 232Th and 40K from Simulated Underground Water Using a Clay-Based Membrane

In this research, the activities of 232Th and 40K in simulated underground water were reduced using inexpensive clay-based membrane. Starch (10 and 15 wt%) was added to the clay, compacted and fired up to 1300°C to produce the porous membranes. The characterization of the raw clay and the produced membranes was conducted using XRF, XRD, TGA/DTA, BET and FESEM. The activities of 232Th and 40K in the waste and permeated water were counted using gamma spectroscopy. The produced membranes were having pore sizes in the range 39.68-46.10nm; from the BET isotherm, it shows the membranes produced are mesoporous. Also, the steady flux of the filtered water was found to be in the range 3.83×10-7-1.77×s10-6 m3m-2s-1. Activities of thorium and potassium in the permeated water were found to be 4.57-5.61 Bq/l and 15.49-25.19 Bq/l respectively. This shows that inexpensive clay can be used to reduce the activities of thorium and potassium in underground water from mining, fracking and produced water from oil and gas.

Application of cane bagasse adsorption on nitrate removal from groundwater sources: adsorption isotherm and reaction kinetics

Removal or reduction of nitrogen compounds in natural waters resulted from discharge of industrial and agricultural activities, which has environmental and human health problems, is necessary. In this study, the effect of initial nitrate concentration (15.5, 50, 80, 120 and 200 mg/L), pH (1-7) and contact time (4.5-36 h) on the adsorption efficiency of cane bagasse modified by ZnCl2 was investigated to remove nitrate from groundwater sources in Izeh city, Khuzestan province of Iran. Adsorption performance was evaluated using Freundlich, Langmuir and Bet isotherms and the first-order and pseudo-second order feed removal models. Results showed that for modified bagasse, the system reached equilibrium after 32 h and the maximum adsorption occurred at pH = 4. Also, the removal efficiency increased by decreasing the concentration of nitrate. The adsorption process followed the Langmuir isotherm. The results of the study showed that the modified bagasse fiber absorbent has a great potential for nitrate removal. Because of the inexpensiveness of bagasse fiber and especially bagasse abundance in Khuzestan province, it is suggested to remove nitrate from groundwater of Izeh city via cane sugar (bagasse) modified by zinc chloride.

Slurry-Phase Ethylene Polymerization Using Pentafluorophenyl- and Pentafluorophenoxy-Modified Solid Polymethylaluminoxanes

Postsynthesis modification of solid polymethylaluminoxane (sMAO) with tris(pentafluorophenyl)borane or pentafluorophenol produces highly active metallocene supports “sMMAOs” for use in slurry-phase ethylene polymerization. Characterization of the sMMAOs using elemental analysis, BET isotherm, SEM-EDX, diffuse FT-IR, and solid-state NMR spectroscopy reveals that the surface methyl groups are exchanged for C6F5 and C6F5O moieties respectively, giving a material with reduced aluminum content and a lower specific surface area than sMAO. rac-Ethylenebis(1-indenyl) zirconium dichloride, {(EBI)ZrCl2} immobilized on B(C6F5)3- and C6F5OH-modified sMAO displayed activity increases of 66% and 71% respectively for ethylene polymerization compared to the same zirconocene catalyst precursor on unmodified sMAO. In the case of B(C6F5)3-modified sMAO, this enhanced polymerization activity is accompanied by excellent control of polymer particle size and morphology, and a small decrease in polymer molecular weight and polyd...

Valorization of waste micro-algal biomass - collected from coke oven effluent treatment plant and evaluation of sorption potential for fluoride removal.

Fluoride contamination in groundwater is now becoming a global concern. In the present study, removal of fluoride using dry biomass (DBM) of a micro-algal consortium of Chlorococcum infusionum and Leptolyngbya foveolaurum, collected from a coke-oven effluent treatment plant, Durgapur, India, has been investigated. The large volume of algal bloom in the industrial effluent has created serious disposal issues and caused severe environmental concerns. A biosorption technique has been carried out to valorize the waste algae biomass into a potential adsorbent. Response Surface Methodology (RSM) is used to model and optimize fluoride removal. Maximum fluoride removal (72%) is obtained at pH 4, 5 mg/L initial fluoride concentration, 0.5 g/L adsorbent dose (AD), and 25 °C temperature during one-factor-at-a-time (OFAT) analysis. The optimum condition of removal as specified by RSM is - initial concentration of fluoride: 30 mg/L, pH: 4.5, AD: 3.5 g/L and temperature: 30 °C. FESEM-EDX, FTIR and BET isotherm studies are done to characterize raw and fluoride treated biomass. Lagergren first order kinetic model and Freundlich isotherm model, are found to analyze best kinetic and equilibrium data, respectively. Adsorption capacity of DBM has been found to be 34.36 mg/g. The kinetics of fluoride removal have been well described by COMSOL Multiphysics.

Sorption of vanillin on highly basic anion exchanger under static conditions

The kinetics of the sorption of vanillin by a granulated anion exchanger is studied under static conditions. A comparison of the kinetic curves of the uptake of hydroxybenzaldehyde by gel and macroporous anion exchanger shows that macroporous sorbent has better kinetic characteristics. The effect temperature has on the capacity of an anion exchanger and the time needed to establish sorption equilibrium is found, and the activation energy of vanillin uptake is determined. Studying the effect experimental factors have on the rate of sorption and using the formal kinetics approach, it is established that in the investigated range of concentrations, the limiting stage of the uptake of vanillin by an anion exchanger with the functional groups of a quaternary ammonium base is that of external diffusion. Vanillin sorption by a highly basic anion exchanger in hydroxyl form is characterized by polymolecular uptake best described by a BET isotherm; at the same time, the uptake of sorbate by a chloride form is of a monomolecular character and can be described by a Freindlich isotherm. Structural changes in the anion exchanger sorbed hydroxybenzaldehyde are identified via FTIR spectroscopy.

Study of physisorption isotherm of water on technical nickel surface with a wide pressure range

During the pumping process of unbaked all-metal vacuum systems after air exposure, water dominates in a time of ∼105 s (>10−6 Pa). The pumping rates of vacuum systems are difficult to be calculated because of the term of the re-adsorption rates. Under the assumption of quasi-equilibrium state between the adsorption and the gas phases, theoretically, the isotherms of water can be used to solve the pumping equation without the re-adsorption term. Thus, it is important to measure the isotherms of water on technical metal surfaces. In this work, the physisorption isotherm of water on the nickel surface with a wide pressure range (from 1.59 Pa to saturated vapor pressure Ps) is measured using an all-metal apparatus. The results show that the experimental data agree quite well with the empirical isotherm of Redhead within 0.16 ≤ ψ ≤ 0.95 (ψ = P/Ps, P is the pressure; 1.0 ≤ θ ≤ 4.4, and θ is the surface coverage), and the BET isotherm within 0.04 ≤ ψ ≤ 0.40 (0.7 ≤ θ ≤ 1.5). When 1.59 ≤ P ≤ 250 Pa (θ ≤ 0.85), there is a linear relationship between θ and ln(P). This follows the Temkin isotherm, and it confirms the common experimental phenomenon that parts of the outgassing curves of vacuum systems are approximately P = constant × t−1. The results also indicate that some water is weakly trapped in the pores and the grain boundaries of technical metals, and it diffuses and desorbs very slowly.

Carbon dioxide capture and conversion by an environmentally friendly chitosan based meso-tetrakis(4-sulfonatophenyl) porphyrin

We have demonstrated the facile, environmentally friendly and sustainable preparation of chitosan based meso-tetrakis(4-sulfonatophenyl)porphyrin (CS-TPPS) for adsorption and catalytic conversion of carbon-dioxide (CO2). The ionic complexation between chitosan (CS) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) is confirmed by ultraviolet-visible (UV–vis) and Fourier transform infrared spectroscopy (FTIR). Physical properties, such as crystallinity, thermal stability, surface morphology and porosity were analyzed by X-ray diffraction, thermal analysis, scanning electron microscopy and BET isotherm analysis. CS-TPPS shows adsorption capacity of 0.9mmol CO2/g compared to the adsorption capacity of 0.05mmol CO2/g of pure chitosan and an adsorption capacity of 0.2mmol CO2/g of pure TPPS. It also exhibits higher conversion of CO2 and propylene oxide into cyclic carbonate (66%), compared to pure chitosan (31%). The results are encouraging, and may open new perspectives for the use of biopolymers involving porphyrin based material in environmental and industrial applications.

Gas adsorption on commercial magnesium stearate: Effects of degassing conditions on nitrogen BET surface area and isotherm characteristics

Commercial grades of magnesium stearate have been analysed by nitrogen adsorption having been pre-treated at temperatures between 30°C and 110°C and in the as-received state. Characteristics of nitrogen adsorption/desorption isotherms are assessed through the linearity of low relative pressure isotherm data and the BET transform plot together with the extent of isotherm hysteresis. Comparison is made between thermal gravimetric analysis and mass loss on drying. Features of gas adsorption isotherms considered atypical are identified and possible causes presented. It is shown that atypical isotherm features and issues of applying BET theory to the calculation of SBET are linked to the presence of hydrated water and that these depend on the hydration state: being more pronounced for the di-hydrate than the mono-hydrate. Dehydration reduces the extent of atypical features. SBET of a mono-hydrate sample is 5.6m2g−1 and 3.2m2g−1 at 40°C and 100°C degassing respectively but 23.9m2g1 and 5.9m2g−1 for di-hydrate containing samples under comparable degassing. Di-hydrated samples also show SBET >15m2g1, BET C-values <7 and BET correlation coefficients <0.98 before dehydration. Possible mechanisms for atypical isotherms are critically discussed together with the suitability of applying BET theory to nitrogen adsorption data.

Development of lignin based multifunctional hybrid materials for Cu(II) and Cd(II) removal from the aqueous system

In the paper the synthesis and comprehensive physicochemical characterization of a new group of adsorbents containing inorganic oxides and functional biopolymers from the lignocellulose group o such as TiO2/lignin, TiO2-SiO2/lignin and MgO-SiO2/lignin are presented. The obtained materials were evaluated taking into account their physicochemical properties and utility as sorbents towards Cu(II) and Cd(II) ions. Among others, surface activity, porous structure, particle size distribution, SEM images, adsorptive properties (BET isotherms) and electrokinetic properties (zeta potential and electrophoretic mobility) as well as effectiveness of the surface functionalization by the FT-IR method were determined. In addition, the optimum conditions for the adsorption process, its theoretical description and determination of interactions at the adsorbent-adsorbate interface were also included. The kinetic, adsorption and thermodynamic parameters were calculated using the common models. The adsorption and the kinetic data were well described using the Langmuir and pseudo-second order models. The results showed the affinity is greater in the case of Cd(II) and next Cu(II). The metal ion adsorption is a heterogeneous, endothermic and spontaneous reaction on the hybrid material surface.