Nano-TiO2 modified with 2-mercaptobenzimidazole as an efficient adsorbent for removal of Ag(I) from aqueous solutions

Nano-TiO₂ was modified with 2-mercaptobenzimidazole via surfactant activation and used as an adsorbent for the removal of Ag(I) under optimum conditions. The adsorbent was characterized using powder X-ray diffraction and FT-IR spectroscopy. The equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models. Langmuir isotherm describes the adsorption data better than Freundlich isotherm and Temkin. Kinetic studies showed that the pseudo second order kinetic model fits the adsorption kinetic processes well. Maximum adsorption capacity for Ag(I) was 128.2 mg g⁻¹ of nano-TiO₂. The method was successfully applied to the removal of silver from radiology film processing wastewater samples.     

Continuous Adsorption of a Cationic Dye on Surface Modified Rice Husk: Statistical Optimization and Dynamic Models

The continuous adsorption of a cationic dye (Methylene Blue, MB) on surface-modified rice husk was investigated. First, rice husk was submitted to ultrasound-assisted, supercritical CO₂ and NaOH treatments. The adsorbents were characterized. Then, the continuous adsorption was optimized by response surface methodology (RSM), using raw rice husk as the adsorbent. Finally, under the optimal conditions, breakthrough curves were obtained using all adsorbents and the models were used to interpret these curves. The optimal bed performance was reached at a flow rate of 5?mL?min^?1 and an initial MB concentration of 10?mg?L^?1. Under these conditions, the breakthrough time was 109?min, the length of the mass transfer zone was 20.1?cm, and the maximum capacity of the column was 1.55?mg?g^?1. All surface modifications were able to improve the rice husk characteristics in relation to the MB adsorption. Consequently, the bed performance was significantly improved when the surface-modified adsorbents were used. The breakthrough times were 109, 240, 155, and 385?min, respectively, when raw rice husk, UA–rice husk, SCO₂–rice husk, and NaOH–rice husk were used. The length of the mass transfer zone was 20.1, 7.9, 15.9, and 9.3?cm for raw rice husk, UA–rice husk, SCO₂–rice husk, and NaOH–rice husk, respectively. The dynamic models were able to fit the adsorption data and provided physically consistent parameters.     

MODIFIED PLANTAIN PEEL AS CELLULOSE-BASED LOW-COST ADSORBENT FOR THE REMOVAL OF 2,6-DICHLOROPHENOL FROM AQUEOUS SOLUTION: ADSORPTION ISOTHERMS,KINETIC MODELING,AND THERMODYNAMIC STUDIES

In this study, the feasibility of using modified plantain peel to remove 2,6-dichlorophenol from iaqueous solutions was investigated under batch mode. The effects of physical factors such as initial 2,6-dichlorophenol concentration, contact time, biosorbent particle size, biosorbent dosage and temperature on the removal process were evaluated. The results showed that biosorption of 2,6-dichlorophenol was dependent on these factors. The equilibrium biosorption data were analyzed by the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) adsorption isotherm models. The four tested isotherm models provided good fits to the experimental data obtained at 30°C; however, the Freundlich isotherm model provided the best correlation (R² = 0.9874) of the experimental data. The maximum monolayer biosorption capacity (Q _max ) was found to be 14.25 mg/g. The biosorption kinetics data of 2,6-dichlorophenol were analyzed by pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, and liquid film diffusion models. The five kinetic models fitted well to the biosorption kinetic data; however, the pseudo-second-order kinetic model gave the best fit when the biosorption mechanism was controlled by film diffusion. Thermodynamic quantities such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), standard entropy change of biosorption (ΔS°), and activation energy (E_a) were evaluated, and it was found that the biosorption process was spontaneous, feasible, endothermic in nature and of dual nature, physisorption and chemisorption; however, the physisorption process was dominant. Therefore, modified plantain peel has potential for application as an effective bioadsorbent for removal of 2,6-dichlorophenol from aqueous solution.     

Chitosan and cyanoguanidine-crosslinked chitosan coated glass beads and its application in fixed bed adsorption

Abstract

The aim of this work was to coat glass beads with chitosan and cyanoguanidine-crosslinked chitosan and, afterward, to verify the potential of the coated beads as adsorbent for the FD&C Red 40 dye in fixed bed column. The coating was realized in eight experimental conditions, varying the technique (dip coating or casting) and the coating solution composition (different proportions of chitosan, cyanoguanidine, glycerol, sorbitol, sodium alginate, NaOH and CaCl₂). The beads coated in the eight experimental conditions were then applied to adsorb FD&C Red 40 in a fixed bed column, from aqueous solutions at pH 3.0 and 6.0. The breakthrough curves were fitted according to Thomas and Yoon-Nelson dynamic models. The coating was dependent of the solution composition. The casting technique presented coating percentage values of 92%, while the dip coating technique presented only 43%. The breakthrough curves revealed that the use of glass beads coated with cyanoguanidine-crosslinked chitosan had good performance, attaining adsorption capacity values higher than 80?mg g^?1. Thomas and Yoon-Nelson models were able to predict the breakthrough curves in all conditions.     

A novel method of unburned hydrocarbons and NOx gases capture from vehicular exhaust using natural biosorbent

Automobile emissions are composed of NO_x and unburned hydrocarbon that contribute significantly to major environmental and health issues. In this study, encapsulated Moringa oleifera beads (EMBs) were synthesized using Moringa oleifera pod powder that was cross-linked with calcium alginate and used as a biosorbent for reducing the emission gas concentrations from the single-cylinder diesel engine. The breakthrough curve was attained from single and double stage of fixed bed column by the influence of temperature ranging from (80°C–120°C) ± 5°C with a feed flow rate varying from 8 to 10 kg hr^–1 and bed height varying from 15 to 30 cm. Based on the experimental results, the maximum biosorption capacity (q_o) was found to be 14.45 and 123.51 mg g^–1 for HC and NO_x, respectively, and was obtained at 80°C–90°C with double stage of BH–30cm under flow rate of 8 kg hr^–1. Further, breakthrough curves were investigated, and the experimental data were fitted using well-established models like Thomas, Yoon–Nelson, and Wang models. In addition, mass transfer models like Weber–Morris and Boyd were investigated to identify the rate-limiting step of the overall biosorption process.     

Removal of Carbon Dioxide from Light Gas Mixtures using a Porous Strontium(II) Silicoaluminophosphate Fixed Bed: Closed Volume and Portable Applications

A Sr²⁺ -SAPO-34 bed was assembled to study CO₂ dynamic adsorption under conditions that emulate those found in closed volume and portable applications. Although the surface area was reduced by 7% during pelletization, adsorption capacities estimated from breakthrough curves compared well with static volumetric adsorption data. Modeling of the breakthrough adsorption was achieved using a Linear Driving Force mass transfer rate model, showing good agreement with the experimental data and confirming fast kinetics and efficient use of the bed. Fast kinetics were also evidenced by the length of the unused section of the bed as calculated from a Mass Transfer Zone model. Adsorption capacity degradation was not observed after multiple regeneration cycles. Apparent and equilibrium adsorption isotherm data estimated from the bed and static volumetric experiments at 25° C were compared to that of 5A Zeolite. These showed that Sr²⁺ -SAPO-34 is a superior adsorbent for CO₂ removal in the low partial pressure range (<1500 ppm). CO₂ and H₂ O multicomponent adsorption breakthrough curves were also gathered for a CO₂ inlet concentration of 1000 ppm and dew points of ?5 and 8° C. The addition of moisture resulted in a decrease in total processed gas volume by 31 and 47%, respectively.     

Thermodynamic and column studies of Au(I) adsorption on weak alkaline anion exchange fibre from cyanide leaching solution

A novel method of adsorption of Au(I) from cyanide leaching solution with weak alkaline anion exchange fibre (WAAEF) was studied here. The thermodynamics of Au(I) from cyanide leaching solution by the WAAEF from 288 K to 308K have been investigated. Langmuir, Freundlich and Temkin models were adopted and the results confirmed that the Freundlich model fitted best with the equilibrium data. Thermodynamic calculation indicated that the absorption of Au(I) from cyanide leaching solution by WAAEF was an endothermic process with increased entropy. In the dynamic adsorption process, the optimal operational conditions, i.e. flow rate 670.0 BV?h^?1, loading density 0.211 g?cm^?3 and pH value 8.89 of the original solution, were obtained. Dynamic analytical analysis depicted that the elution yield could exceed up to 97% using a mixture of 3% H₂SO₄ and 8% (NH₂)₂CS solution at a flow rate of 100.5 BV?h^?1.     

Oxidative coupling of 2,6‐dimethylphenol catalyzed by copper(II) complexes in aqueous solution

The oxidative coupling reaction of 2,6‐dimethylphenol (DMP) with H₂O₂ catalyzed by four copper(II) complexes was investigated in Tris‐HNO₃ buffer solution at 25°C. The kinetics of formation of diphenoquinone (DPQ, 4‐(3,5‐dimethyl‐4‐oxo‐2,5‐cyclohexadienylidene)‐2,6‐dimethyl‐2,5‐cyclohexadienone) from DMP was studied in detail. The kinetic parameters k₂ and K_m were obtained in the pH range of 6.0–9.0. The copper(II) complexes exhibited the optimal catalytic activity at around pH 7.0. The pH effect was reasonably explicated by the catalytic kinetic model suggested in this work. The catalytic mechanism was discussed. The deprotonized associated radical LCu^I(OH^?)‐^?OOH was suggested as the possible predominant species to oxidize DMP. The C? C and C? O coupling products were analyzed and the ratio of poly (2,6‐dimethyl‐1,4‐phenylene ether) (PPE) to DPQ was also evaluated. Both in weak acidic (pH < 6.5) and in alkaline aqueous solution (pH > 8) were suitable to the C? O coupling reaction in our catalytic systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparison of the adsorption dynamics of air on zeolite 5A and carbon molecular sieve beds

Adsorption and desorption in zeolite 5A and CMS beds were compared by using a ternary mixture (N₂/ O₂/Ar; 78 : 21 : 1 vol%). Because the breakthrough curves for both beds show a tail by temperature variance, a non-isothermal mathematical model was applied to the simulation of adsorption dynamics. The LDF model with a constant rate parameter was enough to predict the experimental breakthrough and temperature curves of an equilibrium separation bed, while the modified LDF model with a concentration-dependent parameter should be applied to a kinetic separation bed. In the CMS bed initially saturated with He, Ar was the first breakthrough component with N₂ following after a short interval. Then, after a long interval, the breakthrough of O₂ occurred with a broad roll-up due to its fast diffusion rate and the relatively slow diffusion rate of N₂. In the CMS bed initially saturated with O₂, the breakthrough curves of O₂ and N₂ showed a very broad shape because of the slow diffusion of N₂ into CMS. In the zeolite 5A bed, the breakthrough time sequence was Ar, O₂, and N₂ at very close time intervals. After the sharp roll-ups of O2 and Ar, the variation of the breakthrough curves was negligible. The inflection of the temperature profile in the zeolite 5A bed was caused by the crossover of the O₂ and N₂MTZs, while in the CMS bed it was caused by the difference in the diffusion rates of O₂ and N₂.     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

Kinetics and Equilibrium Studies for the Removal of Cobalt,Manganese, and Silver in Ethanol using Dowex 50W-x8 Cation Exchange Resin

Organic solvents such as ethanol, find a wide range of applications in fuel, pharmaceutical industries, food industries, and paint formulations, among others. The removal of Ag(I), Co(II), and Mn(II) ions in ethanol by cation exchange resin, Dowex 50W-x8, was investigated. The adsorption characteristics of metal ions onto Dowex 50W-x8 resin were described by Langmuir isotherms. The maximum sorption exchange capacities at 298 K were obtained as 47.4 mg g^?1, 52.6 mg g^?1, and 58.5 mg g^?1 for Ag(I), Co(II), and Mn(II), respectively. The data was also fitted to Temkin and Dubinin-Radushkevich adsorption isotherm models to evaluate other adsorption properties. The ion exchange of silver, cobalt, and manganese on cation exchange resin followed pseudo-second-order kinetics, and the intraparticle diffusion was rate-determining step. The thermodynamic parameters indicated that the sorption of metal ions onto Dowex 50W-x8 resin was spontaneous (negative ΔG°) and endothermic in nature (positive ΔH°) implying that the adsorption capacity increased with increasing temperature. The resin can be regenerated by eluting metal ions with 3.0 mol L^?1 HNO₃ followed by washing it with 10 mL of Millipore water and 10 mL of 2.0 M NaOH, respectively. The proposed method was applied for metal ion removal in real ethanol samples.     

Preparation of Microfibrous Entrapped Activated Carbon Composites and its Application for Benzene Adsorption

Microfibrous composites consisting of 150-200 μm activated carbon particles entrapped in 6.5 μm stainless steel fibers were prepared by wet layup papermaking and sintering process. The effects of a variety of operation parameters on the properties of microfibrous composites were investigated. The composite bed with microfibrous entrapped activated carbon was developed to purify air contaminated with benzene. The experimental results showed that the microfibrous composite with a ratio of 13:6 (W/W, carbon/ fibers) was of a relatively higher carbon entrapment ratio under the conditions of adding 2 L water, stirring at 50 Hz for 10 min, and then sintering at 1050^°C for 20 min. The breakthrough time of 5.0 cm composite bed increased by 28 min compared with that of a 5.0 cm individual GACs bed, and bed utilization increased 18.4% at 1% breakthrough concentration. The Bohart-Adams and Yoon-Nelson models were applied to analyze the experimental data of composite bed. The Bohart-Adams model fitted well with the experimental data for the C/C₀ region up to 0.5 but showed large discrepancies above this value. The Yoon-Nelson model predicted values were in very good agreement with the experimental results in the C/C₀ region above 0.05.     

Reuse of Aluminum‐based Water Treatment Sludge to Immobilize a Wide Range of Phosphorus Contamination: Equilibrium Study with Different Isotherm Models

Abstract

The adsorption equilibrium of a wide range of phosphorus species by an aluminum‐based water treatment sludge (Al‐WTS) was examined in this study. Four kinds of adsorption‐isotherm models, namely Langmuir, Freundlich, Temkin, and Dubinin‐Radushkevich, were used to fit the adsorption equilibrium data. In order to optimize the adsorption‐isotherm model, correlation coefficient (R²) and four error functions were employed to facilitate the evaluation of fitting accuracy. Experiments have demonstrated that the Al‐WTS may be an excellent raw material to adsorb P in a polluted aqueous environment with adsorption ability in the order of KH₂PO₄ (ortho‐P)>Na(PO₃)₆ (poly‐P)>C₁₀H₁₄N₅O₇P · H₂O (organic‐P). More importantly, this study provides an entire comparison of the four isotherms in describing the P adsorption behavior. By considering both the standard least‐square based R² and the results of four error functions analysis, this study reveals that the Freundlich isotherm appears to be the best model to fit the experimental equilibrium data. Langmuir and Temkin isotherms are also good models in current experimental conditions while the Dubinin‐Radushkevich isotherm poorly described the adsorption behavior. The error analysis in this study provides vital evidence to reflect its role in facilitating the optimization in the adsorption isotherm study. Obviously, R² seems inadequate in optimizing multi‐isotherm models due to its inherent bias resulting from the least‐squares linearization.     

Sorption of Cd(II)-MGDA Complexes on Polyacrylate Anion Exchangers

The possibility of polyacrylic anion exchangers application in the removal of Cd(II) complexes with MGDA (methylglycinediacetic acid) from aqueous solutions was presented. Batch sorption experiments were performed using Amberlite IRA 458 and Amberlite IRA 958. The initial solution pH, the initial concentration of sorbed complexes in the molar ratio M(II)-MGDA = 1:1, the temperature, as well as the contact time were varied. The kinetics of Cd(II) sorption in the presence of MGDA was analyzed. The Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models were also applied to describe the adsorption isotherm. The values of the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated that in the majority of cases the sorption process was spontaneous and endothermic. From the determined breakthrough curves, the distribution coefficients and the ion exchange capacities were calculated.     

Ion Exchange Adsorption Studies of Miglitol in a Fixed Bed

The adsorption of miglitol on the D001 resin in a fixed bed was studied at different flow rates, temperatures, and height‐to‐diameter ratios (H/D). The exhaustion time decreased and the height of the mass transfer zone (H_MTZ) increased with increasing flow rate. The surface area of the adsorbent increased with decreasing solution flow rate. Breakthrough curves at different flows were described by the Thomas, Yoon–Nelson, and Adams‐Bohart models. The rate constants for the kinetic models increased with increasing flow rate. The theoretical and experimental times required for 50 % adsorbate breakthrough slightly differed at varying flow rates. The change trend in the values of the maximum volumetric adsorption capacity was the same as that of the values at the maximum adsorption capacity of the D001 resin. The temperature did not obviously affect the breakthrough curves. The slope of the breakthrough curve decreased and the H_MTZ increased with increasing H/D ratio. The adsorption capacities of the fixed bed for H/D = 7.6 and 0.7 were greater than that for H/D = 1.5.     

Recovery of 1,4‐Dimethyl Piperazine from Aqueous Solutions Using Polymeric Adsorbent and Ion‐Exchange Resins

Abstract

Strong and weakly acidic ion exchange resins and polymeric adsorbents are used for recovery of 1,4‐dimethyl piperazine (DMP) from aqueous solutions. Sorption of the amine in undissociated form is the primary mechanism of uptake of DMP on the ion‐exchange resins. Equilibrium adsorption data for DMP on the resins, at various temperatures, are fitted in Langmuir adsorption isotherm. Kinetic studies show that intraparticle diffusional resistance controls the sorption of DMP into the resin matrix. A mathematical model based on intraparticle diffusion and external mass transfer is used for simulating breakthrough profiles and compared with the experimental results for a fixed bed of weakly acidic Indion‐652 resin. The DMP loaded bed of the resin was effectively regenerated with methanol.     

Physico-chemical study of dew melon peel biochar for chromium attenuation from simulated and actual wastewaters

This work introduces a biochar as novel adsorbent prepared from the dew melon peel by pyrolysis method, and demonstrates its potential for eliminating Cr(VI) from simulated and actual wastewaters. The dew melon peel biochar (DPB) was characterized by several techniques and methodologies such as, BET, SEM, FTIR, Boehm titration, ultimate analysis, and pHzpc. DPB is a microporous material with the BET specific surface area of 196 m²/g. The effects of different parameters including pH, amount of adsorbent, Cr(VI) concentration, and mixing time on the removal of Cr(VI) from wastewater were studied. Maximum adsorption (98.6%) was observed at pH 6 and 100 mg/L metal concentration. The equilibrium adsorption was analyzed by Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms. Kinetic data were evaluated by pseudo-first order, pseudo-second order, intraparticle diffusion, film diffusion (Boyd), Elovich, and Avrami models. The kinetic data were best fitted to the pseudo-second order model. The Langmuir isotherm model gives the better correlation to predict the adsorption equilibrium, with a maximum adsorption capacity of 198.7 mg/g. The thermodynamic parameters showed that the adsorption of Cr(VI) was endothermic and spontaneous. Competition between the co-existing ions of Cl^?, NO ₃ ^? , SO ₄ ^2? , PO ₄ ^3? , and HCO ₃ ^? on the adsorption process was studied. The efficacy of DPB was successfully examined by analyzing the removal of Cr(VI) from two industrial wastewaters. The results indicate that DPB is promising as an effective and economical adsorbent for Cr(VI) ions removal and could be repeatedly used with no significant loss of adsorption efficiency.     

Effects of high relative humidity on the dynamic adsorption of dimethyl methylphosphonate (DMMP) on activated carbon

The effects of high relative humidity (RH) on the breakthrough of the nerve agent simulant dimethyl methylphosphonate (DMMP) vapor in beds of ASC-impregnated, activated carbon were investigated. Maximum concentrations of DMMP at room temperature and RH > 60% were found to be lower by more than an order of magnitude than in dry air. The breakthrough time (t_B) of 1.2 × 10⁻⁴ g l⁻¹ DMMP in pre-humidified beds and humid air of RH = 90% was shortened by a factor of 1.6 relative to adsorption in dry beds and dry air. Analysis of the breakthrough curves according to the Wheeler–Jonas model indicated that the high RH lowered the dynamic adsorption capacity (W_E) but had nearly no effect on the critical bed weight (W_C). The reduction of W_E by humidity correlates with the observed displacement of adsorbed water by DMMP. The use of DMMP for testing filter performance is limited to low and intermediate relative humidities. On the other hand, DMMP in dry air can be used to advantage for testing the capacity of new or used respirator filters and for the detection of filter channeling.     

Kinetic and thermodynamic studies of adsorption of Cu2+ and Pb2+ onto amidoximated bacterial cellulose

Removal of Cu²⁺ and Pb²⁺ from aqueous solutions by adsorption onto amidoximated bacterial cellulose (Am-BC) was investigated. The effects of pH, initial concentration, contact time and temperature were studied in batch experiments. The pseudo-first and pseudo-second orders and intraparticle diffusion equation were used to evaluate the kinetic data and the constants were determined. The experimental data fits well to the pseudo-second order kinetic model, which indicates that the chemical adsorption is the rate-determining step, instead of mass transfer. The equilibrium adsorption data were described by the Langmuir, Freundlich, and Temkin isotherms. The Am-BC showed a better fit to the Langmuir isotherm. The separation factor (R _L ) revealed the favorable nature of the isotherm. The thermodynamic parameters (ΔH _ads⁰, ΔS _ads⁰, ΔG _ads⁰) for Cu²⁺ and Pb²⁺ adsorption onto Am-BC were also determined from the temperature dependence. The values of enthalpy and entropy indicated that this process was spontaneous and exothermic. The experimental studies indicate that Am-BC would be a potential effective adsorbent to remove the metal ions from wastewater.     

Removal of Submicron Silica Particles from tert-Amyl Alcohol by Dielectric/Electric Packed Bed Filtration

Abstract

A packed bed with an applied electric field is used to remove submicron and nanometer particles from a nonconducting or slightly conducting solution. Several studies have shown that the application of an electric field to a packed bed significantly increases the performance of the filtration. To enhance the electric-field filtration efficiency, it is desired that the packing materials have a higher dielectric constant than the solution so that the electric-field lines will be diverted into the packing materials.

In the present studies, a dc voltage of 0 to 8 kV/cm is applied to a packed bed (2.5-cm diameter and 3.0-cm length) filled with 1-mm-diameter glass beads. The filtration medium contains submicrometer or nanometer SiO₂ particles dispersed in tert-amyl alcohol. Two particle sizes are investigated: the average particle sizes are about 300 nm and 50 nm, respectively.

Visible light spectrophotometry is used to estimate the amount of SiO₂ particles in the effluent. The experimental results are presented as a series of breakthrough curves. The effect of the applied electric field on the breakthrough curve on two different particle sizes is presented. Depending on the applied electric field and the conductivity of the system, heating of the packed bed may occur. The operating current and temperature of the packed bed are also presented.