Intraparticle Diffusion Kinetic Models Research Articles

Synthesis of magnetic 3D graphene decorated with CaCO3 for anionic azo dye removal from aqueous solution: Kinetic and RSM modeling approach

In this work, a new magnetic 3D graphene aerogel/CaCO3 nanocomposite was synthesized successfully using a one-step in situ self-assembly of graphene oxide in the presence of CaCO3 and Fe3O4 nanoparticles. The product was characterized using various techniques such as Field Emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM) and X-ray diffraction (XRD). The prepared nanocomposite was used as a novel absorbent to remove Acid Red 88 (AR88) dye from aqueous solutions as an anionic azo dye model. The effects of operational parameters such as absorbent dosage, dye concentration, pH and contact time on AR88 removal were investigated by using response surface methodology (RSM). From RSM results, the optimized values in the range of quantities used in this work for 100% removal of AR88 dye were found to be 87mg nanocomposite, 14mg/L dye (AR88) concentration, pH 6 and contact time 18min. Absorption of AR88 obeyed intra-particle diffusion kinetic model. These results suggest that the magnetic 3D graphene aerogel/CaCO3 nanocomposite is a good candidate for the rapid removal of AR88 from aqueous solutions.

Recovery of phosphate and dissolved organic matter from aqueous solution using a novel CaO-MgO hybrid carbon composite and its feasibility in phosphorus recycling

Metal oxide-Carbon composites have been developed tailoring towards specific functionalities for removing pollutants from contaminated environmental systems. In this study, we synthesized a novel CaO-MgO hybrid carbon composite for removal of phosphate and humate by co-pyrolysis of dolomite and sawdust at various temperatures. Increasing of pyrolysis temperature to 900 °C generated a composite rich in carbon, CaO and MgO particles. Phosphate and humate can be removed efficiently by the synthesized composite with the initial solution in the range of pH 3.0–11.0. The phosphate adsorption was best fitted by pseudo-second-order kinetic model, while the humate adsorption followed the pseudo-second-order and the intra-particle diffusion kinetic models. The maximum adsorption capabilities quantified by the Langmuir isotherm model were up to 207 mg phosphorus (or 621 mg phosphate) and 469 mg humate per one-gram composite used, respectively. Characterization of composites after adsorption revealed the contributions of phosphate crystal deposition and electrostatic attraction on the phosphate uptake and involvement of π − π interaction in the humate adsorption. The prepared composite has great potential for recovering phosphorus from wastewater, and the phosphate sorbed composite can be employed as a promising phosphorus slow-releasing fertilizer for improving plant growth.

Removal of cationic and anionic dyes using purified and surfactant-modified Tunisian clays: Kinetic, isotherm, thermodynamic and adsorption-mechanism studies

ABSTRACTPurified and surfactant-modified Tunisian clays were investigated for their capacity to remove cationic and anionic dyes (crystal violet, CV and methyl orange, MO) from aqueous solution. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and potentiometric acid-base titration. Batch-sorption experiments were carried out to evaluate the influence of pH, contact time, initial dye concentration and temperature on the adsorption of dyes. Pseudo-first order, pseudo-second order, intra-particle diffusion and Elovich kinetic models were considered to evaluate the kinetic parameters. To understand the interaction of the dye with the adsorbent, Langmuir, Freundlich, Temkin and Dubinin-Radushkevish isotherms were applied. Thermodynamics studies were conducted to calculate the changes in free energy (Δ°G), enthalpy (Δ°H) and entropy (Δ°S). A difference in the maximum adsorption capacity was observed, suggesting that the retention of dyes was influenced by structure, functional groups of dyes and surface properties of the adsorbents. Moreover, different mechanisms may control the removal of dyes. The purified Tunisian clays are excellent adsorbents for removal of the cationic dye CV and its modified form is suitable for removal of the anionic dye, MO, from aqueous solution.

Characterizing the capacity of hyporheic sediments to attenuate groundwater nitrate loads by adsorption

Nitrate has been recognized as a global threat to environmental health. In this regard, the hyporheic zone (saturated media beneath and adjacent to the stream bed) plays a crucial role in attenuating groundwater nitrate, prior to discharge into surface water. While different nitrate removal pathways have been investigated over recent decades, the adsorption capacity of hyporheic sediments under natural conditions has not yet been identified. In this study, the natural attenuation capacity of the hyporheic-sediments of the Ghezel-Ozan River, located in the north-west of Iran, was determined. The sampled sediments (from 1 m below the stream bed) were characterized via XRD, FT-IR, BET, SEM, BJH, and Zeta potential. Nitrate adsorption was evaluated using a batch experiment with hyporheic pore-water from each study site. The study was performed in the hyporheic sediments of two morphologically different zones, including Z1 located in the parafluvial zone having the clay sediment texture (57.8% clay) with smectite/Illite mixed layer clay type and Z2 located in the river confluence area containing silty clay sediment texture (47.6% clay) with smectite/kaolinite mixed layer clay type. Data obtained from the batch experiment were subjected to pseudo-first order, pseudo-second order, intra-particle diffusion, and Elovich mass transfer kinetic models to characterize the nitrate adsorption mechanism. Furthermore, to replicate nitrate removal efficiencies of the hyporheic sediments under natural conditions, the sampled hyporheic pore-waters were applied as initial solutions to run the batch experiment. The results of the artificial nitrate solution correlated well with pseudo-second order (R2>95%; in both Z1 and Z2) and maximum removal efficiencies of 85.3% and 71.2% (adsorbent dosage 90 g/L, pH = 5.5, initial adsorbate concentration of 90 mg/L) were achieved in Z1 and Z2, respectively. The results of the nitrate adsorption analysis revealed that the nitrate removal efficiencies varied from 17.24 ± 1.86% in Z1 during the wet season to 28.13 ± 0.89% in Z2 during the dry season. The results obtained by this study yielded strong evidence of the potential of hyporheic sediments to remove nitrate from an aqueous environment with great efficiency.

Adsorption of UV-quenching substances (UVQS) from landfill leachate with activated carbon

Co-treatment of landfill leachate with sewage at publicly owned treatment works (POTWs) is a common leachate management practice. However, the UV absorbing property of UV-quenching substances (UVQS) present in municipal landfill leachate may significantly reduce the efficiency of disinfection at POTWs that adopt ultraviolet irradiation for disinfection. The UVQS represents an emerging concern in the solid waste and wastewater treatment industries. This study aimed to evaluate the performance of activated carbon (AC) for removal of UVQS from landfill leachate in order to address the leachate UV-quenching issue. Results showed that the abatement of leachate UV254 absorbance with AC followed a pseudo-2nd-order reaction or intra-particle diffusion kinetics model. The adsorption isotherm patterns for leachate UV254 absorbance, dissolved organic carbon (DOC), and chemical oxygen demand (COD) well fit the Freundlich models. AC was capable of effectively adsorbing UV-quenching organic matter, regardless of humic acid (HA), fulvic acid (FA), and hydrophilic (HPI) isolates, via both chemisorption and physical adsorption mechanisms. Of note, after the AC adsorption, the residual UV254 absorbance was linearly correlated with COD remaining in leachate and exponentially correlated with residual DOC in leachate, separately. Furthermore, fluorescence excitation-emission matrix (EEM) analyses could indicate the removal of hydrophobic UVQS during AC adsorption, but could not reflect the presence or variation of hydrophilic UVQS. Findings of this study demonstrate that AC adsorption provides an effective treatment option for mitigation of the leachate-induced UV transmittance impacts on POTWs.

Cadmium removal from aqueous solution by low-cost native and surface modified Sorghum x drummondii (Sudangrass)

In an attempt to find inexpensive and effective biosorbents and modification methods, cadmium sorption ability of native Sorghum x drummondii, commonly called sudangrass, and its modified biomass was studied for the first time. From several modified biosorbents, 0.05 M NaOH-modified sudangrass performed the best and hence was used for further experiments. Both sorbents were characterized and various parameters were investigated on their sorption performance. Equilibrium time was reduced from 90 to 20 min after modification. Intra-particle diffusion and pseudo-second order kinetic models were found as best-fitting models for sudangrass and NaOH-modified sudangrass, respectively. Langmuir isotherm model described equilibrium data with the highest accuracy. Maximum monolayer adsorption capacity of cadmium onto sudangrass and NaOH-modified sudangrass was obtained as 1.52 and 7.76 mg g−1, respectively, showing a five-fold improvement for cadmium sorption. Sorption mechanism and thermodynamic investigations suggested that cadmium removal by modified sudangrass is a chemisorption and endothermic process, while cadmium removal by sudangrass is predominantly physisorption and exothermic. This study indicated that both native and modified sudangrass sorbents are capable of removing cadmium ions from aqueous solution with modified biosorbent having a much higher potential for this application.

Methylene Blue removal from aqueous solution by a biocomposite synthesized from sodium alginate and wastes of oil extraction from almond peanut

In this study, the removal of Methylene Blue dye was investigated by biocomposite beads synthesized from sodium alginate and wastes of oil extraction from almond peanut. Prepared biocomposite was characterized using X-ray diffraction, Infrared spectroscopy, scanning electron microscopy, Energy Dispersive X-Ray analysis. The adsorption capacities of Methylene Blue were investigated with respect to the effect of the adsorbent amount, pH value, and initial dye concentration. The kinetic adsorption data were analyzed by the pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion kinetic models. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. The pseudo-second-order kinetic and Freundlich isotherm equations were found to describe the adsorption mechanism. The thermodynamic studies showed that the adsorption process is a spontaneous and exothermic process with increased entropy. The removal percentage and maximum adsorption capacity of Methylene Blue by biocomposite were equal to 90% and 22.8mg/g, respectively. The high registered capacities of Methylene Blue removal suggest the potential use of the biocomposite in the treatment of contaminated wastewaters.

Adsorptive removal of cationic dye from aqueous solutions by ZnO/ZnMn2O4 nanocomposite

ABSTRACTThe ZnO/ZnMn2O4 nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g−1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated.

Effects of Fulvic Acid on TNT Adsorption in Soil

abstractIn order to study the effect of fulvic acids (FA) on the migration of TNT in soil, batch experiments in which 2%, 5%, and 10% (w/w) of FA were added to soils were conducted. Adsorption kinetics and adsorption-desorption isotherms of TNT in soils were investigated, with results of the kinetics tests showing that the adsorption process could be divided into a fast and a slow stage and that FA could extend the adsorption time. Kinetic data were fit to pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion kinetic models. The fitting results showed that a pseudo second-order kinetic model best described the adsorption process, while Elovich and intra-particle diffusion kinetic models could accurately predict the adsorption at higher FA content. The adsorption-desorption isotherms were predicted using Linear, Freundlich, and Langmuir isotherm models. Results showed that the Freundlich model best described the adsorption-desorption process, and that FA increased adsorption capacity and enhanced the adsorption affinity. The hysteresis index suggested that FA could reduce the desorption of TNT in soil.

Adsorption of heavy metals (Cu 2+ and Zn 2+ ) on novel bifunctional ordered mesoporous silica: Optimization by response surface methodology

Abstract In order to develop new technologies in adsorption-based water treatment systems, the main objective of this research is the removal of copper and zinc heavy metals from aqueous solution using modified biocompatible silica magnetic nanoadsorbents. In this regard, the magnetic SBA-15 based Chitosan composite modified with amine groups (Fe2O3@SBA-15 − CS − APTMS), with different weight percentages, were synthesized and further characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and nitrogen adsorption/desorption analysis. The adsorption performance of Fe2O3@SBA-15 − CS − APTMS (3 mL) for copper and zinc removal from aqueous solution was studied in a batch system using response surface methodology (RSM) design of experiment. All the prepared adsorbents were tested under the obtained optimum operational parameters and their adsorptive behavior was compared. In order to investigate the adsorption rate and maximum adsorption capacity, the experimental data were fitted to Langmuir, Freundlich, Temkin, Redlich–Peterson and Sips isotherms and pseudo first-order, pseudo second-order and intraparticle diffusion kinetic models. In addition, analysis of adsorption efficiency at different temperatures revealed the thermodynamic aspects of adsorption such as the variations in Gibbs free energy (ΔG0), standard enthalpy (ΔH0) and standard entropy (ΔS0). The obtained maximum adsorption capacities of Fe2O3@SBA-15 − CS − APTMS (6 mL) at 313 K for copper and zinc were 107.30 mg/g and 100.47 mg/g, respectively.

Molecularly imprinted particle embedded composite cryogel for selective tetracycline adsorption

Abstract The aim of this study was to prepare a composite cryogel for selective tetracycline (TC) adsorption. The composite cryogel was prepared by embedding TC-imprinted poly (hydroxyethyl methacrylate-N-methacryloyl- l -glutamic acid methyl ester [poly(HEMA-MAGA)] particles into poly(hydroxyethyl methacrylate) [PHEMA] cryogel. Molecular imprinting was used to prepare poly(HEMA-MAGA) particles with selective recognition sites for TC molecule. The TC-imprinted poly(HEMA-MAGA) particles were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and zeta size analysis. The morphology of the composite cryogel was investigated by using scanning electron microscope (SEM). Swelling degree, specific surface area, pore volume and pore diameter of TC-imprinted composite cryogel were also determined. TC solutions in different concentrations (5–85 mg/L, pH 5.0) were used to determine TC adsorption capacity of the TC-imprinted composite cryogel for three different temperatures (4 °C, 13 °C and 25 °C). TC adsorption capacity of the TC-imprinted composite cryogel was determined as 680 mg TC/ g at 25 °C (pH 5.0). TC adsorption data were fitted with Freundlich adsorption isotherm model for three different temperatures (4 °C, 13 °C and 25 °C). Both pseudo-second-order and intraparticle diffusion kinetic models explained the adsorption process. The prepared TC-imprinted composite cryogel can be repeatedly used for TC adsorption. The composite cryogel has high adsorption capacity and selectivity, demonstrating the applicability for selective TC adsorption.

Studies on adsorption of oxytetracycline from aqueous solutions onto hydroxyapatite

The presence of antibiotics in the water and wastewater has raised problems due to potential impacts on the environment and consequently their removal is of great importance. For this reason, this article aims to perform a study on the possibility of oxytetracycline (OTC) adsorption from aqueous medium by using the hydroxyapatite (HA) nanopowders as adsorbent materials. The hydroxyapatite nanopowders were synthesized by wet precipitation method by using orthophosphoric acid and calcium hydroxide as raw materials and investigated by XRD, SEM-EDX, FTIR and BET methods. The uncalcined and calcined hydroxyapatite samples have hexagonal crystal structure with crystal sizes smaller than 100nm and a specific surface area of 316m2/g and 139m2/g, respectively. The adsorption behavior of oxytetracycline, a zwitterionic antibiotic, on nanohydroxyapatite was investigated as a function of pH, contact time, adsorbent dosage and drug concentration by means of batch adsorption experiments. High oxytetracycline removal rates of about 97.58% and 89.95% for the uncalcined and calcined nanohydroxyapatites, respectively, were obtained at pH8 and ambient temperature. The adsorption process of oxytetracycline onto nanohydroxyapatite samples was found to follow a pseudo-second order and intraparticle diffusion kinetic models. The maximum adsorption capacities of 291.32mg/g and 278.27mg/g for uncalcined and calcined nanohydroxyapatite samples, respectively, have been found. The adsorption mechanism of OTC on the hydroxyapatite surface at pH8 can be established via surface complexation. The obtained results are indicative of good hydroxyapatite adsorption ability towards oxytetracycline drug.

C-dots/Fe3O4 magnetic nanocomposite as nanoadsorbent for removal of heavy metal cations

In this work, C-dots/Fe3O4 magnetic nanocomposite as nanoadsorbent was implemented for adsorption of Cu(II), Cr(III) and Pb(II) cations from aqueous solutions. The effect of various parameters on adsorption process of all three mentioned cations such as nanoadsorbent dosage, initial cation concentration, contact time and pH were explored to find the mechanism of adsorption. Different kinetic models including pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion kinetic models were used to fit experimental data. In this way, pseudo-second-order model described the kinetic data of all three cations well. Also, equilibrium isotherm studies were examined by application of different conventional isotherms such as Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich models to explain the experimental data. The Freundlich isotherm fitted equilibrium data of all three cations, whereas other models were not fitted well. Results indicate that the adsorption of all three cations is followed by chemisorption mechanism via electrostatic attraction at heterogeneous surface of nanoadsorbent.

Investigation the adsorption properties of graphene oxide and polyaniline nano/micro structures for efficient removal of toxic Cr(VI) contaminants from aqueous solutions; kinetic and equilibrium studies

Graphene oxide (GO) and polyaniline (PANI) were synthesized and characterized by different techniques to be used as efficient adsorbents for hexavalent chromium Cr(VI) from aqueous solutions. The adsorption behavior of both GO and PANI is controlled mainly by the solution pH achieving the best uptake capacity at the acidic conditions. The uptake equilibrium was attained after 120 and 180 min for the adsorption of Cr(VI) by GO and PANI, respectively. Pseudo-second order, Intra-particle diffusion, and Elovich kinetic models were evaluated to understand the adsorption mechanism. The obtained results represented mainly by pseudo-second-order kinetic model rather than by the other models. The adsorption equilibrium studies well described using three traditional isotherm models (Langmuir, Freundlich and Temkin models). The theoretical estimation of the maximum uptake capacity of Cr(VI) ions (qmax) using Go and PANI are 49 and 59 mg/g, respectively. Monolayer model with one energy site was used as advanced isotherm model for more interpretation of the adsorption behavior of the studied adsorbents. The calculated parameters of studied model give more information about the number of receptor adsorption sites, the number of adsorbed Cr(VI) ions per site, average occupation sites and monolayer adsorption quantity and total saturation adsorption quantity.

Biosorption of Hexavalent Chromium by Pseudomonas aeruginosa Strain ANSC: Equilibria Isothermic, Kinetic and Thermodynamic Studies

Pseudomonas aeruginosa strain ANSC, a non-genetically modified bacterial strain isolated from soil was used to study and evaluate biosorption potentials for hexavalent chromium (Cr[VI]) from aqueous solution. Living, heat-killed, and permeabilised cells were all used and found to be capable of reducing and sorbing Cr(VI). The influences of initial Cr(VI) ion concentration (50-150 mg/L), contact time (2 h, 10 min intervals), pH (2-8), temperature (30-60℃) and biosorbent mass (1.0-5.0 g/l) were reported. Adsorption of Cr(VI) is highly pH- and temperature-dependent, and the results indicate that the optimum pH and temperature for removal were found to be 2 and 60℃ respectively. The hexavalent chromium biosorption equilibrium could be better described by Langmuir isotherm than it could by Freundlich isotherm. A comparison of kinetic models applied to the adsorption of Cr(VI) ions onto the biosorbents was evaluated for the pseudo first-order, pseudo second-order, and intra-particle diffusion kinetic models. Results show that the pseudo second-order kinetic model was evidenced to correlate better the experimental data. The rate of hexavalent chromium adsorption increased following permeabilisation of the outer and/or cytoplasmic membrane by surfactants such as Triton X100, Tween 80, toluene, sodium deoxycholate and sodium dodecyl sulphate. The adsorption process has been found endothermic, and thermodynamic parameters of Gibb's free energy (ΔG°), change in enthalpy (ΔH°) and change in entropy (ΔS°) were calculated. Pseudomonas aeruginosa strain ANSC evidenced an effective biosorbent for the removal of hexavalent chromium in aqueous form.

Application of ZnO nanorods as an adsorbent material for the removal of As(III) from aqueous solution: kinetics, isotherms and thermodynamic studies

Removal of metals from wastewaters causes a big concern from the environmental point of view due to their extreme toxicity towards aquatic life and humans. Application of As(III) from aqueous solution by ZnO nanorods as adsorbent has been investigated in the present study. The synthesized nanorods were characterized by XRD, FT-IR spectroscopy, SEM, and thermogravimetric analysis. Optimum biosorption conditions were determined with respect to pH, adsorbent dose, contact time, and temperature. The experimental data were examined using the Lagergren’s first-order, pseudo-second-order and intraparticle diffusion kinetic models. The results revealed that the pseudo-second-order kinetic model provided the best description of the data. Langmuir and Freundlich isotherm models were applied to the equilibrium data. The maximum As(III) sorption capacity of ZnO nanorods was found to be 52.63 mg/g at pH 7, adsorbent dose 0.4 g, contact time 105 min, and temperature 323 K. The calculated thermodynamic parameters, ΔGo (between − 5.741, − 5.342 and − 4.538 kJ/mol at 303–323 K), ∆Ho (13.75 kJ/mol) and ∆So (0.0616 J/mol K) showed that the sorption of As(III) onto ZnO nanorods was feasible, spontaneous and exothermic, respectively.

Preparation of CeO2 nanofibers derived from Ce-BTC metal-organic frameworks and its application on pesticide adsorption

In this study, CeO2 nanofibers derived from Ce(1,3,5-BTC)(H2O)6 (Ce-BTC) metal organic frameworks were prepared, and then the affinity of CeO2 towards 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated. After the Ce-BTC nanoparticles were synthesized by hydrothermal method, the Ce-BTC was calcinated, and CeO2 nanofibers were obtained. The Ce-BTC and CeO2 were characterized by SEM, XRD, FTIR and AFM methods, respectively. The adsorption studies of 2,4-D from water with CeO2 were carried out as batch type. The Langmuir, Freundlich and Sips isotherms were applied to the experimental data. And pseudo second order, intra-particle diffusion and Bangham kinetic models were used for determination of the kinetic mechanism of the adsorption. The maximum adsorption capacity for 2,4-D was found to be 86.16, 95.78 and 84.29 mg/g for each temperature (298, 308 and 318 K), respectively.

Adsorption Performance and Mechanisms of Methylene Blue Removal by Non-magnetic and Magnetic Particles Derived from the Vallisneria natans Waste

Vallisneria natans (V. natans) is a submerged aquatic plant, and its dried biomass waste was used to prepare magnetic particle biomass adsorbent by chemical co-precipitation via FeSO4·7H2O and FeCl3·6H2O as iron precursors. Brunauer–Emmett–Teller specific surface area, total pore volume, and average pore width were 7.434 m2 g−1, 0.013 cm3 g−1, and 6.992 nm for magnetic V. natans, correspondingly, and 3.575 m2 g−1, 0.004 cm3 g−1, and 4.476 nm for non-magnetic V. natans, respectively. The adsorption kinetics of methylene blue (MB) is a more appropriate fit for pseudo-second-order kinetic model than pseudo-first-order and intraparticle diffusion kinetic models. Isotherm results showed that the adsorption of MB onto the non-magnetic and magnetic adsorbents agrees well with Dubinin–Radushkevich isotherm model. Moreover, the thermodynamics study implied that the adsorption of MB onto both adsorbents is a spontaneous and exothermic process. The maximum adsorption capacities of MB on non-magnetic and magnetic V. natans were 657.90 and 473.93 mg g−1 at 303 K, correspondingly.

Functionalization of powdered walnut shell with orthophosphoric acid for Congo red dye removal

ABSTRACTThis study investigates the adsorption of Congo red dye on walnut shell powder based activated carbon in batch process (WNAA). Walnut shell powder was carbonized by treating with phosphoric acid (H3PO4), and the adsorbent was characterized using Fourier Transform-Infrared spectrophotometer (FT-IR), Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX), and pH point of zero charge (pHpzc), respectively. Operational parameters such as contact time, initial dye concentration, and pH were investigated using batch-adsorption techniques. The adsorption uptake was found to increase with increase in initial dye concentration and contact time. The optimum CR dye uptake was observed at pH 3.12 corresponding to 94.53% removal. Pseudo-first-order, pseudo-second-order, Elovich, and Intraparticle diffusion kinetic models were used to test the adsorption data. The pseudo-second order exhibited the best fit out of the four kinetic models used. Equilibrium data were fitted to the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. Langmuir model fitted the adsorption data most with maximum monolayer coverage of 40 mg/g. Thermodynamic parameters such as Gibbs free energy, enthalpy, entropy, and the activation energy were determined. It was found that Congo red dye adsorption was spontaneous and endothermic. 0.02M Hydrochloric acid was used to regenerate the adsorbent prepared, and the regenerated adsorbent was used for dye adsorption. Congo red dye adsorption capacity ranged from 90% to 93% at three consecutive times. This study has shown that walnut shell is a good adsorbent in the treatment of Congo red dye from aqueous solutions.

Utilization of salt activated Raphia hookeri seeds as biosorbent for Erythrosine B dye removal: Kinetics and thermodynamics studies

The use of a non-conventional precursor, Raphia hookeri seeds, (RHS) for the production of activated carbon through thermal and salt activation for the adsorption of Erythrosine B (EB) dye in an aqueous solution was investigated. The physicochemical properties of the prepared activated carbon were studied using standard methods. Scanning electron microscopy (SEM) displayed the surface morphology micrograph and Fourier Transform Infrared was used to identify the functional groups of the activated carbon. Adsorptive performance tests at various temperatures were evaluated at optimum results of 75 µm adsorbent particle size, 1 g adsorbent dosage, 100 mg/L adsorbate concentration and pH 4. An equilibration time of 90 minutes is sufficient at 30 °C for 87.78% adsorption of EB on SARHS. Experimental data were fitted into non-linearized pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models. PSO better fitted the experimental data based on SSE (%), RMS and R2 results. Computations from intra-particle diffusion kinetic model reveal that intra-particle diffusion is not the only rate-limiting step governing the adsorptive process. Results from Analysis of Variance (ANOVA) confirmed that there were statistical significant differences between the adsorption efficiencies of salt activated raphia hookeri seeds (SARHS) at different time intervals (P-Value < 0.05). Tukey’s Honest Significant Difference (HSD) post hoc method was employed for the identification of the location of these differences. The values calculated for ΔG°, ΔS° and ΔH° thermodynamic parameters were −29.60 KJ mol−1, 0.089 KJ mol−1 and −0.705 KJ mol−1 respectively confirming that the adsorptive process is feasible, spontaneous and exothermic in nature.