Weber-Morris Model Research Articles

Guidelines for general adsorption kinetics modeling

Adsorption processes are widely used in different technological areas and industry sectors, thus continuously attracting attention in the scientific research and publications. Design and scale-up of these processes are essentially based on the knowledge and understanding of the adsorption kinetics and mechanism. Adsorption kinetics is usually modeled by using several well-known models including the pseudo-first and pseudo-second order models, the Elovich equation, and the intra-particle diffusion based models. However, in the scientific literature there are a significant number of cases with the inappropriate use of these models, utilization of erroneous expressions, and incorrect interpretation of the obtained results. This paper is especially focused on applications of the pseudo-second order, intra-particle diffusion and the Weber-Morris models, which are illustrated with typical examples. Finally, general recommendations for selection of the appropriate kinetic model and model assumptions, data regression analysis, and evaluation and presentation of the obtained results are outlined.

In Ukrainian

Templated sol-gel synthesis of MCM-41‑type mesoporous silicas was realized in the presence of azo dyes (alizarin yellow and methyl red) as co-templates and silanes obtained on their basis as structure-forming components. It has been found from the results of low-temperature adsorption-desorption of nitrogen that using of azo dyes and dye-containing silanes in sol-gel synthesis leads to the substantial increase of surface area and total pore volume, and decrease of pore diameter of obtained mesoporous organosilicas. The X-ray diffraction analysis proved formation of hexagonally arranged structure of mesopores in synthesized organosilicas. It has been demonstrated due to visualization of mesoporous structure by transmission electron microscopy that all synthesized materials have hexagonally arranged structure of cylindrical pores, entrances to which are oriented outside of particles that provide accessibility of functional groups for sorbate molecules. Obtained organosilicas of MCM-41 type were used in study of dyes sorption from diluted phosphate buffer solutions as dependent on their equilibrium concentration, pH of medium, and duration of contact. It has been found that the most efficient sorption of alizarin yellow takes place at рН ~ 3 and methyl red at рН = 2.5-5.0. Analysis of kinetic curves carried out using Lagergren, Ho‑McKey, and Weber-Morris models has shown that process of azo dyes sorption by organosilicas is described by kinetic model of pseudo‑second order. The parameters of equilibrium sorption of alizarin yellow and methyl red on organosilicas of MCM‑41 type were calculated using Langmuir, Freundlich, Redlich‑Peterson, and Brunauer‑Emmett‑Teller models. Sorption of a number of acid dyes from their individual solutions was studied at pH 4.8. It has been found that chemical immobilization of methyl red on silica surface causes increase of acid dyes sorption. The contribution of cooperative interactions, which arise between the aromatic groups of azo dyes immobilized in surface layer of silica and dye molecules in a solution, in the process of their sorption was confirmed. Modification of silica surface with capable to self-aggregation dyes is a promising way in chemical design of sorption-active materials.

Brilliant red X-3B uptake by a novel polycyclodextrin-modified magnetic cationic hydrogel: Performance, kinetics and mechanism

A novel polycyclodextrin-modified magnetic cationic hydrogel (PCD-MCH) was developed and its performance, kinetics and mechanism for the removal of reactive brilliant red X-3B (X-3B) were studied. The results showed that the zeta-potential of PCD-MCH was 32.8 to 16.7mV at pH3.0–10.5. The maximum X-3B adsorption capacity of PCD-MCH was 2792.3mg/g. The adsorption kinetics could be well-described by the Weber–Morris model and the homogeneous surface diffusion model (HSDM). Diffusion stages corresponding to surface or film diffusion, intra-particle or wide mesopore diffusion, and narrow mesopore/micropore diffusion occurred at 0–120, 120–480 and 480–1200min, respectively. The latter two diffusion stages were rate-controlling for X-3B adsorption kinetics. At the initial X-3B concentration of 600mg/L, the diffusion coefficient (Ds) and external mass transfer coefficient in the liquid phase (kF) were 3×10−11cm2/min and 4.68×10−6cm/min, respectively. X-3B approaching the center of PCD-MCH particles could be observed at 360min. At the end of the third diffusion stage, the Cp at q/qe=0 was 45.20mg/L, which was close to the homogeneous Cp value of 46mg/L along the radius of PCD-MCH particles. At pH3.0–10.0, PCD-MCH showed stable X-3B adsorption capacities. After five regeneration-reuse cycles, the residual adsorption capacity of regenerated PCD-MCH was higher than 892.7mg/g. The corresponding adsorption mechanism was identified as involving electrostatic interactions, cyclodextrin cavities and hydrogen bonds, of which cyclodextrin cavities showed prominent capture performance towards dye molecules through the formation of inclusion complexes.

Preparation of activated carbon from black wattle bark waste and its application for phenol adsorption

Black wattle bark waste is generated in large amounts by tannin extraction industries, which leads to an environmental problem. In literature there are few reports about reusing this waste, mainly in adsorption processes. An activated carbon from black wattle bark waste was produced, characterized and applied for phenol adsorption. Activated carbon was produced under different carbonization and activation conditions, being characterized and applied as an adsorbent for phenol removal from aqueous solution. The results showed that phenol adsorption capacity increased with the increase of carbonization temperature and of activating agent ratio and, decreased with the increase of carbonization time. Activated carbon presented a micro/mesoporous structure and the surface area was 414.97 m2 g−1. FTIR analysis showed that lactone and quinone groups compose the surface chemistry of the activated carbon. The adsorption kinetics followed the pseudo-second order model. The Weber-Morris model showed that the adsorption occurred by film and intra-particle diffusion, and the increase in stirring rate led to an increase in film diffusion. Temperature increase led to an increase in phenol adsorption capacity, and the highest value was around 98.57 mg g−1, obtained at 55 °C. The Freundlich isotherm model was the more suitable to represent the equilibrium data. Thermodynamic study indicated that phenol adsorption onto the developed activated carbon was a spontaneous, favorable, endothermic and entropy-controlled process. The activated carbon can be used in two cycles with a slight decrease in the equilibrium adsorption capacity and presented a good efficiency to remove phenolic compounds in a simulated industrial effluent.

Removal of Congo red and methylene blue using H2O2 modified activated carbon by microwave regeneration: isotherm and kinetic studies

Microwave-assisted heating technology was used for treating paracetamol decolorizing spent activated carbon (SAC). The regenerated activated carbon (RAC) was modified using hydrogen peroxide (H2O2) to obtain modified activated carbon (MRAC), which was used for removing Congo red (CR) and methylene blue (MB) in aqueous solution, achieving the goal of utilizing hazardous waste resources. The RAC BET surface area was 1254.46 m2 g−1, and the results showed that microwave treatment could effectively regenerate the spent carbon. To increase the adsorption capacity of activated carbon, the surface was modified with H2O2 to increase oxygen-containing functional groups. The adsorption behavior of CR and MB on MRAC was studied, and equilibrium data were simulated by using the Langmuir, Freundlich, Redlich–Peterson, and Temkin isotherm models. The isotherm experimental data were best fitted by the Redlich–Peterson model, and the maximum sorption capacities obtained were 254 and 318 mg g−1 for CR and MB on MRAC (7% H2O2), respectively. The adsorption kinetics were best described by the pseudo-second-order model, and the Weber–Morris model showed that the adsorption process includes three stages: boundary layer diffusion and two intra-particle diffusion stages. The kinetic and isotherm experimental evidence showed the high efficiency of MRAC (7% H2O2) adsorption for CR and MB and its potential for organic pollutant removal.

Sorption and removal aqueous iron(III) ion by tris(2-aminoethyl)amine moiety functionalized silica gel

ABSTRACT The silica gel functionalized tris(2-aminoethyl)amine moiety (SG‐TAEA‐NH2) is utilized for the sorption of iron (III) ion from water by the batch sorption process. The kinetics and thermodynamics of sorption have been carried out by controlling different parameters such as initial concentration, dosage, temperature, and pH. The sorption equilibrium is achieved during the first 20 minutes. The maximum removal of Iron(III) ion is ca. 95% upon the study conditions of C i = 1 mg L−1, T = 35 ⁰C, 80 rpm, pH = 2, and dosage = 2 g L−1). Langmuir and Freundlich isotherm models are applied in order to describe the thermodynamic parameters and to understand the sorption behavior of Iron(III) ion onto SG‐TAEA‐NH2. The SG‐TAEA‐NH2-Fe(III) sorption follows Langmuir isotherm models (R2 > 0.997). The capacity (qmax ) and intensity (b) of Langmuir adsorption are calculated to be 2.553 mg.g−1 and 0.7691 L.mol−1, respectively. The reaction kinetic models of pseudo-first-order and pseudo-second-order, and the adsorption diffusion model of Weber-Morris intra-particle diffusion model have been used to describe the sorption rate and mechanism of the Iron(III) ion onto SG‐TAEA‐NH2 surface. The kinetic parameters, the rate constant, and sorption capacities have been calculated. The possible sorption mechanism of iron(III) ion onto the SG‐TAEA‐NH2 surface is proposed. The silica gel functionalized tris(2-aminoethyl)amine moiety may consider as an efficient filter to desalt low concentration of iron (III) ion.

Carbon-coated Mg–Al layered double oxide nanosheets with enhanced removal of hexavalent chromium

Carbon-coated Mg–Al layered double oxide (MgAl@C LDO) nanosheets were synthesized for the removal of hexavalent chromium (Cr(VI)) ions. Carbon coating could enhance the sorption capacity of Mg5Al1 LDO for the Cr(VI) removal. The sorption capacity of Mg5Al1@C LDO increased and then decreased with an increase in carbon-coated content, of which the Mg5Al1@C-2 with a carbon thickness of around 5.0nm exhibited the best sorption capacity. The sorption behaviors of Mg5Al1@C-2 was explained by Langmuir sorption model, pseudo-second-order model, Weber–Morris model, and Boyd kinetic model. Mg5Al1@C-2 for Cr(VI) removal was a spontaneous, endothermic, and chemisorption process.

CuO-modified activated carbon for the improvement of toluene removal in air

We used an impregnation method to prepare CuO/AC (activated carbon) composite materials of different CuO content and characterized them via scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), and Fourier transform infrared spectroscopy (FT-IR). The effect of CuO content on toluene adsorption/desorption was evaluated. We explored the reusability of AC and AC03 (CuO modified AC with CuO loading 0.3 wt.%) adsorbents via toluene adsorption/desorption cycle testing. We used quasi-first- and quasi-second-order models, the Bangham model, and the Weber–Morris model to fit the toluene adsorption data. The introduction of CuO species evidently improved the adsorption performance of activated carbon toward toluene. The CuO content markedly affected the specific surface area, CuO dispersal, the numbers of oxygen-containing functional groups on the surface, and adsorption performance of the prepared composite adsorbents. Low CuO content was not favorable for the formation of active adsorption sites, while high content greatly reduced the specific surface area, and even covered active adsorption sites. The toluene adsorption performance varied in the order AC03 > AC02 > AC05 > AC08 > AC01 (AC03, AC02, AC05, AC08 and AC01 are CuO modifying AC with CuO loading 0.3, 0.2, 0.5 0.8 and 0.1 wt.%, respectively). The breakthrough time and toluene adsorption capacity of the AC03 composite adsorbent were 94 min and 701.8 mg/g, respectively, and the recycling efficiency was 92.8% after thermal desorption at 200°C. The adsorption process was best described by the Bangham model and adsorption could be divided into three stages.

Kinetics, thermodynamics and mechanisms of phosphate sorption onto bottle gourd biomass modified by (3-chloro-2-hydroxypropyl) trimethylammonium chloride

The sorption kinetics and thermodynamic parameters of phosphate removal from aqueous solution using quaternary ammonium–modified bottle gourd biomass as a sorbent were studied in a batch reactor. The cationic sorbent, containing trimethylammonium and hydroxypropyl groups, was obtained through the chemical reactions of the lignocellulosic Lagenaria vulgaris shell with (3-chloro-2-hydroxypropyl)trimethylammonium chloride. Experimental data of phosphate sorption from aqueous solutions of different initial concentrations (5–140 mg P L−1) have been analysed by reaction kinetics and diffusion models. The characteristic rate constants calculated by linear and non-linear regression analyses of the experimental results are presented. The phosphate sorption reaches equilibrium in 20–30 min, depending on the initial phosphate concentration. The maximum sorption capacity of quaternary ammonium–modified bottle gourd (QABG) sorbent was 18 mg P g−1at 20 oC. The sorption system is best described by a non-linear equation of the pseudo first-order model ( R2 > 0.996). The Weber–Morris model indicated that the sorption process took place in three steps, whereby the intra-particle diffusion is not the only rate-controlling step. In addition, the effect of temperature (20 oC–50 oC) on sorption kinetics was also investigated. The various thermodynamic parameters suggest that phosphate sorption is favoured and is an exothermic process. The activation energy and the sticking probability confirmed that anion exchange is the dominant mechanism. These results provide valuable information for the potential use of agricultural residues in the treatment of wastewaters.

Arsenic removal by copper-impregnated natural mineral tufa part II: a kinetics and column adsorption study.

This batch and column kinetics study of arsenic removal utilized copper-impregnated natural mineral tufa (T-Cu(A-C)) under three ranges of particle size. Non-competitive kinetic data fitted by the Weber-Morris model and the single resistance mass transfer model, i.e., mass transfer coefficient kfa and diffusion coefficient (Deff) determination, defined intra-particle diffusion as the dominating rate controlling step. Kinetic activation parameters, derived from pseudo-second-order rate constants, showed low dependence on adsorbent geometry/morphology and porosity, while the diffusivity of the pores was significant to removal efficacy. The results of competitive arsenic adsorption in a multi-component system of phosphate, chromate, or silicate showed effective arsenic removal using T-Cu adsorbents. The high adsorption rate-pseudo-second-order constants in the range 0.509-0.789gmg-1min-1 for As(V) and 0.304-0.532gmg1min1 for As(III)-justified further application T-Cu(A-C) in a flow system. The fixed-bed column adsorption data was fitted using empirical Bohart-Adams, Yoon-Nelson, Thomas, and dose-response models to indicate capacities and breakthrough time dependence on arsenic influent concentration and the flow rate. Pore surface diffusion modeling (PSDM), following bed-column testing, further determined adsorbent capacities and mass transport under applied hydraulic loading rates.

Preparation of polydopamine-modified zeolitic imidazolate framework-8 functionalized electrospun fibers for efficient removal of tetracycline

This work shows a simple and environmental friendly methodology to obtain a kind of polydopamine coating assisted preparation of zeolitic imidazolate framework-8 (ZIF-8) functionalized composite electrospun fiber (ZIF-8/PDA/PAN fibers) adsorbent. Characterization of the composite electrospun fiber was carried out and the tetracycline (TC) adsorption properties from water were also studied in detail. At the same time, principle adsorption mechanisms were thoroughly studied. The results show that the pseudo-second-order model can simulate sorption kinetics well, while sorption isotherms are able to significantly conform to the Freundlich model, and the adsorption capacity of the fibers can reach 478.18 mg/g at 298 K. In addition, the Weber–Morris model indicates that the processes of adsorption of ZIF-8/PDA/PAN fibers for TC involve surface adsorption as well as intraparticle diffusion, and the limit rate step is not only the intraparticle diffusion but also the binding of the sorbate to the sorbent. Moreover, the adsorption efficiency toward TC by ZIF-8/PDA/PAN fibers still reached over 85% of its initial adsorption capacity after five adsorption/desorption cycles, which signified that the adsorbents is stable and recyclable. This work indicates that the obtained ZIF-8/PDA/PAN fibers have practical application prospects in the field of antibiotic adsorption.

Magnetic nanoparticles coated with aminated polymer brush as a novel material for effective removal of Pb(II) ions from aqueous environments.

In the present study, a poly (vinylbenzyl chloride) grafted Fe3O4 nanoparticle (Fe3O4@PVBC) was prepared by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and subsequently coated with tris (aminoethyl) amine (TAEA). Then, Fe3O4@PVBC-TAEA nanoparticles were utilized as a novel adsorbent for removal of Pb(II) from aqueous media and optimal adsorption conditions were determined with response surface methodology (RSM). The used adsorbent was characterized by using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). RSM with central composite design (CCD) was carried out to evaluate the effect of initial pH, initial Pb(II) concentration (C0, mg/L), adsorbent dosage (mg), and contact time (min). The optimum initial pH, C0, adsorbent dosage, and contact time were found to be 5.88, 46.51mg/L, 17.41mg, and 108.21min, respectively. The maximum removal efficiency and adsorption capacity were 97.07% and 129.65mg/g under these conditions, respectively. The kinetic data revealed that the adsorption mechanism could be best explained by the pseudo-second-order and Weber-Morris models. The isotherm studies found that both the Langmuir and Freundlich isotherm models fitted the experimental data well. The thermodynamic analysis indicated that the adsorption nature is exothermic, applicable, and spontaneous.

Nonlinear regression approach for acid dye remediation using activated adsorbent: Kinetic, isotherm, thermodynamic and reusability studies

In the present article, a new adsorbent synthesized from Salvadora persica (miswak) powder with chemical activation has been applied to remove Acid Violet 17 dye from aqueous solution. Characterization of the synthesized adsorbent was carried out using the techniques of FTIR, SEM, BET, zeta potential and DLS. The effect of pH, adsorbent dose, contact time, initial dye concentration and temperature were assessed in batch operation. Maximum removal was favored at pH of 2, adsorbent dose of 2 g/L and temperature as 333 K. Chemical activation has increased surface area of raw adsorbent from 58.38 to 124.99 m2/g. Nonlinear regression has been applied for the model fitting of the experimental data. Kinetic data was well described by pseudo-second-order model. Weber-Morris model established involvement of multiple steps in governing the adsorption mechanism. Isotherm data was well described by Freundlich model. Root mean square error analysis was also applied to check the best model fitting. Maximum adsorption capacity values were obtained as 74.28 and 141.30 mg/g for raw adsorbent and activated adsorbent, respectively. Thermodynamic calculations established endothermic and feasible nature of the adsorption. The obtained removal of 97.24 ± 0.69% for simulated solution reduced to 91.17 ± 0.86% in case of real effluent containing 100 mg/L of dye solution as attributed to other compounds present in the actual industrial effluent which can compete on adsorption sites along with the targeted dye. Reusability study performed using ethanol as an eluent confirmed suitability of synthesized adsorbent for dye removal from wastewater. The obtained maximum adsorption capacity along with good reusability results depicted that activated Salvadora persica could be used as an efficient adsorbent for sequestration of Acid Violet 17 from the aqueous phase.

Enhanced SO2 fluidized adsorption dynamic by hierarchically porous activated coke

Porous materials such as activated cokes have been widely utilized in the adsorption removal of atmospheric SO2 emission. Pore configuration of coke is a key factor affecting its SO2 rapid adsorption dynamics, which is critically important for fluidization adsorption craft. Herein, activated coke adsorbents with typically microporous structure and hierarchically porous structure were prepared by a catalytic physical activation method from Chinese large-reserve Zhundong coal, which were used as model adsorbents to investigate the effect of pore configuration on SO2 fluidized adsorption dynamics. SO2 fluidized-state adsorption experiments indicate that hierarchically porous coke has a more rapid initial adsorption dynamic than microporous type coke, and coke with 44.2% meso-/macropores volume shows the highest initial adsorption rate of 7.37 mg g−1·min−1. Additionally, the fitting of Weber-Morris model provides the dominate factors for SO2 adsorption kinetics in each sub-process: SO2 adsorption capacity of microporous-dominated adsorption stages account for 70%–80% of total, and when it comes close to adsorption saturation, the main dominant factor of kinetic becomes the ratio of meso-/macropores volume. This work is of significance for the application of SO2 adsorption craft in fluidized bed and also provides insight into the role of hierarchically porous configuration in gas molecule rapid adsorption.

Biosynthesis and Characterization of Iron Nanoparticles for Effective Adsorption of Cr(VI)

In this study, iron nanoparticles (FeNPs) were synthesized via a green method using loquat (Eriobotrya japonica) leaves aqueous extract as a renewable reducing agent. The synthesized FeNPs were characterized by DLS, XRD, FT-IR, SEM/EDX, and TEM analysis, and then, they were used as an adsorbent for Cr(VI) removal from aqueous solutions. Batch adsorption experiments were carried out to investigate the optimum adsorption parameters such as the initial pH of the solution, temperature, initial Cr(VI) concentration, and adsorbent concentration. The optimum adsorption conditions were determined as initial pH 3.0, temperature 45°C, and adsorbent concentration 1 g/L. Also, a linear increase was observed in adsorbed Cr(VI) amounts with the increasing initial Cr(VI) concentrations. The biosynthesized FeNPs showed the high removal levels higher than 90% for Cr(VI) adsorption at a wide range of initial Cr(VI) concentrations (50–500 mg/L). The experimental equilibrium data were modelled with Langmuir and Freundlich isotherm models, and it was found that experimental equilibrium data could be well described by the Langmuir isotherm model. The maximum monolayer coverage capacity of FeNPs for Cr(VI) adsorption was found to be 312.5 mg/g. The pseudo-first-order and the pseudo-second-order kinetic models were applied to the experimental adsorption data, and it was concluded that the data were defined as the best agreement with the pseudo-second-order kinetic model. Weber–Morris model was used to investigate the effect of mass transfer on the adsorption of Cr(VI) onto FeNPs; it was observed that both the film (boundary layer) and intraparticle diffusion affected the studied adsorption process. The thermodynamic studies suggested that Cr(VI) adsorption onto FeNPs was endothermic and nonspontaneous, and the positive ΔS value indicated increased disorder at the solid-solution interface during the adsorption.

Batch and Continuous Systems for Zn, Cu, and Pb Metal Ions Adsorption on Spent Mushroom Compost Biochar

Spent mushroom compost biochar (SMCB) was prepared by carbonization and tested for the removal of heavy metals (Zn(II), Cu(II), and Pb(II)) by adsorption. The sorption of heavy metals was evaluated by studying several factors, such as the initial solution pH, contact time, temperature, and individual and competitive adsorption. Kinetic and equilibrium studies were carried out to determine the mechanism involved during adsorption. The Weber–Morris model demonstrated the significance of intraparticle diffusion on the adsorption process. In addition, thermodynamic studies showed that the process is endothermic and favorable, with good affinity of metals to the biochar. At last, SMCB was used as the adsorbent in a continuous fixed-bed column. The breakthrough curve was obtained for each heavy metal, and Thomas and Clark models were fitted. When all three metals coexisted in solution, competitive adsorption took place in both batch and continuous systems, showing that Pb has higher affinity to SMCB than Cu and Zn.

Sorption Kinetics of 2,4-D and Diuron Herbicides in a Urea-Fertilized Andisol

Sorption kinetics studies of herbicides, using different models, are an important tool for determining the mechanisms and kinetic parameters that explain the bioavailability and environmental behavior of these compounds. However, little is known about the combined effects of fertilizers and herbicides and how it could modify these processes on the soil. The aim of this study was to evaluate the sorption kinetics of diuron and 2,4-D in an Andisol treated with urea using various kinetic models. The experiments were carried out in batch, independently for each herbicide, with urea application in an equivalent dose of 200 kg N ha−1 and artificial pH modifications. The results showed no differences in sorption kinetics due to urea for diuron; however 2,4-D showed differences with urea and changes in pH conditions. The data fitted well with the pseudo-second-order model (R2 > 0.996), showing a maximum soil adsorption capacity of 11.9, 10.8, and 9.61 mg kg−1 for diuron, 2,4-D, and 2,4-D-urea, respectively. The initial adsorption rate was similar for both herbicides, but a significant increase in the rate constant was observed for 2,4-D at acid pH. We conclude from the Elovich and Weber-Morris models that both herbicides were adsorbed mainly during the first stage, followed by lower adsorption in the slower second stage. According to these models, mass transfer across the boundary layer, and to a lesser degree intraparticle diffusion mechanisms, controlled sorption kinetics for both herbicides. The results suggest that urea application could influence sorption process of acid herbicides for pH changes in soils.

Benefit of Hydrophilicity for Adsorption of Methyl Orange and Electro-Fenton Regeneration of Activated Carbon-Polytetrafluoroethylene Electrodes.

Activated carbon (AC)-polytetrafluoroethylene (PTFE) electrodes were prepared and applied for methyl orange (MO) adsorption and electro-Fenton regeneration. The addition of PTFE to AC significantly decreased the hydrophilicity, which in turn, decreased both the amount of MO adsorbed and the regeneration efficiency. With the minimum amount of binder (a 7:1 mass ratio of AC to binder), the MO adsorption was 176 mg g-1. The amount adsorbed decreased to 23 mg g-1 for the electrode with a 1:1 mass ratio of AC to binder. For these ratios, the regeneration efficiencies were 81% and 49%, respectively. The adsorption kinetics were well fit by a Weber-Morris model. The diffusion rate constants obtained from this model were linearly related to the hydrophilicity of the electrode, i.e., the higher the hydrophilicity the higher the adsorption rate. Based on the results, an adsorption capacity >50 mg g-1 in 8 h with a regeneration efficiency of >70% at cathodic potential of -0.8 V (vs Ag/AgCl) can be obtained if the contact angle of water on the electrodes is lower than 90°.

A Novel Cu(II) Ion-Imprinted Alginate–Chitosan Complex Adsorbent for Selective Separation of Cu(II) from Aqueous Solution

A novel Cu(II) ion-imprinted complex adsorbent [Cu(II)-IIP] from alginate and chitosan was prepared by a three-step process of beading–combining–crosslinking with Cu2+ as the template ion. The Cu(II)-IIP showed higher capacity and selectivity for Cu(II) than the non-imprinted polymer. The theoretical maximum adsorption capacity of Cu(II)-IIP reached 83.33 mg/g, and the separation factor (α) for Cu(II) versus Zn(II) was 2.28. The adsorption of Cu2+ onto the Cu(II)-IIP was perfectly described by the Langmuir isotherm model. The adsorption kinetics agreed with the pseudo-first-order model in the first 8 h and more fitted pseudo-second-order model after then. Weber–Morris model confirmed that the adsorption rate would be controlled dominantly by the intraparticle diffusion and the inner surface binding. Moreover, the Cu(II)-IIP complex adsorbent exhibited good regeneration, and the adsorption capacity was stable within the first three adsorption–desorption cycles without significant reduction.

Efficient multistep arsenate removal onto magnetite modified fly ash

The modification of the fly ash (FA) by magnetite (M) was performed to obtain FAM adsorbent with improved adsorption efficiency for arsenate removal from water. The novel low cost adsorbents are characterized by liquid nitrogen porosimetry (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MB) and Fourier transform infrared (FTIR) spectroscopy. The optimal conditions and key factors influencing the adsorbent synthesis are assessed using the response surface method (RSM). The adsorption experiment was carried out in a batch system by varying the contact time, temperature, pH, and mass of the adsorbent. The adsorption capacity of the FAM adsorbent for As(V), calculated by Langmuir model, was 19.14 mg g−1. The thermodynamic parameters showed spontaneity of adsorption with low endothermic character. The kinetic data followed the pseudo-second-order kinetic model (PSO), and Weber-Morris model indicated intra-particle diffusion as rate limiting step. Alternative to low desorption capability of the FAM was found by five consecutive adsorption/magnetite precipitation processes which gave exhausted layered adsorbent with 65.78 mg g−1 capacity. This research also has shed light on the mechanism of As(V)-ion adsorption, presenting a promising solution for the valorization of a widely abundant industrial waste.