Three-parameter Isotherm Research Articles

Enteromorpha compressa Macroalgal Biomass Nanoparticles as Eco-Friendly Biosorbents for the Efficient Removal of Harmful Metals from Aqueous Solutions

This study focuses on the biosorption of harmful metals from aqueous solutions using Enteromorpha compressa macroalgal biomass nanoparticles as the biosorbent. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were employed to characterize the biosorbent. The effects of pH, initial metal ion concentration, biosorbent dosage, and contact time on the biosorption process were investigated. The maximum biosorption capacity for metals was observed at a pH of 5.0. The experimental equilibrium data were analyzed using three-parameter isotherm models, namely Freundlich, Temkin, and Langmuir equations, which provided better fits for the equilibrium data. A contact time of approximately 120 min was required to achieve biosorption equilibrium for various initial metal concentrations. Cr(III), Co(II), Ni(II), Cu(II), and Cd(II) demonstrated distinct maximum biosorption capacities of 24.99375 mg/g, 25.06894 mg/g, 24.55796 mg/g, 24.97502 mg/g, and 25.3936 mg/g, respectively. Different kinetic models were applied to fit the kinetic data, including intraparticle diffusion, pseudo-second-order, and pseudo-first-order versions. The pseudo-second-order model showed good agreement with the experimental results, indicating its suitability for describing the kinetics of the biosorption process. Based on these findings, it can be stated that E. compressa nanoparticle demonstrates potential as an effective biosorbent for removing targeted metals from water.

Nonlinear Isotherm Adsorption Modelling for Copper Removal from Wastewater by Natural and Modified Clinoptilolite and Glauconite

The paper presents the results of the Cu2+ adsorption on natural and thermally/microwave-treated clinoptilolite and glauconite. XPS experiments were performed. The relationship between the adsorbed matter and the equilibrium concentration in wastewater is described by four two-parameter isotherm models and four three-parameter adsorption isotherm models.

Insights into isotherms, kinetics, and thermodynamics of adsorption of acid blue 113 from an aqueous solution of nutraceutical industrial fennel seed spent

Research studies have been carried out to accentuate Fennel Seed Spent, a by-product of the Nutraceutical Industry, as an inexpensive, recyclable and operational biosorbent for bioremediation of Acid Blue 113 (AB113) in simulated water-dye samples and textile industrial effluent (TIE). The physical process of adhesion of AB113 on the surface of the biosorbent depends on various parameters, such as the initial amount of the dye, amount and expanse of the biosorbent particles, pH of the solution and temperature of the medium. The data obtained was analyzed using three two-parameter and five three-parameter adsorption isotherm models to glean the adsorbent affinities and interaction mechanism of the adsorbate molecules and adsorbent surface. The adsorption feature study is conducted employing models of Weber-Morris, pseudo 1st and 2nd order, diffusion film model, Dumwald-Wagner and Avrami model. The study through 2nd order pseudo and Avrami models produced complementary results for the authentication of experimental data. The thermodynamic features, ΔG0, ΔH0, and ΔS0 of the adsorption process are acclaimed to be almost spontaneous, physical in nature and endothermic in their manifestation. Surface characterization was carried out using Scanner Electron Microscopy, and identification and determination of chemical species and molecular structure was performed using Infrared Spectroscopy (IR). Maximum adsorption evaluated using statistical optimization with different combinations of five independent variables to study the individual as well as combined effects by Fractional Factorial Experimental Design (FFED) was 236.18 mg g−1 under optimized conditions; pH of 2, adsorbent dosage of 0.500 g L−1, and an initial dye concentration of 209.47 mg L−1 for an adsorption time of 126.62 min with orbital shaking of 165 rpm at temperature 49.95 °C.

Low-cost magnetic carbons-based rubber seed husks materials for highly efficient removal for reactive black 5 and reactive blue 19 textile dyes from wastewater

ABSTRACT Suitable and cost-effective magnetic carbons (CA-HP-FeII/FeIII) were prepared from biobased rubber seed hull materials by chemical activation with phosphoric acid and ferric ions. Physical and chemical properties of the materials were investigated using XRD, FT-IR spectroscopy, SEM analysis, N2 adsorption/desorption, Raman analysis and EDX/EDX-mapping. Magnetic carbons were used to remove reactive black 5 and reactive blue 19 textile dyes in aqueous solution. The pH of the solution, the mass of magnetic carbons and the initial concentration of dyes were investigated. The activated carbon obtained has a surface area of 110 m2.g−1 with an amorphous structure. A maximum removal efficiency of 76.27% for reactive black dye 5 and 94.44% for reactive blue dye 19 was achieved, at optimum pH 2. Kinetic studies showed that non-linear Elovich’s model accurately describes the adsorption mechanism, which assumes an energetically heterogeneous magnetic carbon surface. The two-parameter non-linear models for the adsorption isotherms revealed that the adsorption of reactive black 5 and reactive blue 19 on CA-HP-FeII/FeIII satisfied the Temkin isotherm, demonstrating the exothermic nature of the adsorption process. The three-parameter adsorption isotherm reveals that the magnetic carbons have a heterogeneous surface with energetically diverse adsorption sites. Magnetic carbons were found to be attractive and suitable for the purification of these dyes.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Investigating the selective adsorption of CO2 by MIL-101(Cr)-NH2 and modeling the equilibrium data using a new three-parameter isotherm

Compared to MIL-101(Fe)-NH2, MIL-101(Cr)-NH2 has considerably higher adsorption of CO2. On the other hand, the adsorption of CH4 and N2 by MIL-101(Cr)-NH2 is lower than the adsorption of these gases by MIL-101(Fe)-NH2 leading to a higher selectivity of CO2 to CH4 and N2 for MIL-101(Cr)-NH2. The chemisorption mechanism is more influential in higher temperatures and pressure, which can be attributed to the performance of amines which can adsorb more CO2 at higher temperatures and pressure. The isosteric heat of CO2 adsorption on MIL-101(Cr)-NH2 was estimated equal to − 31 kJ mol-1.MIL-101(Cr)-NH2 was synthesized and characterized by the BET, XRD, FESEM, TGA, and DTA methods. The BET surface area of the synthesized MOF was achieved equal to 1768 m2 g-1. The adsorption capacity of pure CO2, CH4, and N2 was estimated using the volumetric method. A new three-parameter equation was presented to model the experimental adsorption data including both types I and II isotherm shapes. Using the Ideal Adsorbed Solution Theory (IAST), the selectivity of CO2 to CH4 at high pressure, and CO2 to N2 at lower pressures was estimated equal to 4.1 and 4.7, respectively. In addition to 25 °C, the adsorption tests were performed at 18 and 30 °C to estimate the adsorption heat of CO2 on MIL-101(Cr)-NH2 achieved equal to − 31 kJ mol-1. The adsorption isotherm of CO2 at 25 and 30 °C have been almost identical showing the role of the chemisorption mechanism of CO2 by the amine functional group, especially at higher temperatures and pressures. Furthermore, the resistance of synthesized MOF to water was investigated by putting it in contact with water for 24 h. The result showed that MIL-101(Cr)-NH2 can be classified as thermodynamically stable to water.

Investigation of adsorption of Basic Orange 2 dye on montmorillonite and error analysis

ABSTRACT. In this study, isotherm studies were investigated for the removal of basic orange 2 (BO2) dye on the montmorillonite surface. Two-parameter isotherm models such as Langmir, Freundlich, and Temkin isotherms and Three-parameter isotherm models such as Sips, Toth, and Khan isotherms were calculated by non-linear analysis method. The adsorption capacity at equilibrium was calculated by adding 0.035 g of adsorbent at 10-300 mg/L concentrations to 100 mL of synthetic dyestuff solution at room temperature. According to the results obtained, it was determined that the isotherm data matched the Langmuir isotherm with a regression coefficient of 0.995 from the Two-parameter models, and the Sips isotherm with a regression coefficient of 0.998 from the Three-parameter isotherm models. In addition, according to the results of error analysis, it was determined that the lowest error value fit the HYBRID model. SNE values support the HYBRID model.&#x0D; &#x0D; KEY WORDS: Adsorption, Basic orange 2, Isotherm models; Error analyses, Hybrid&#x0D; Bull. Chem. Soc. Ethiop. 2023, 37(1), 47-58. &#x0D; DOI: https://dx.doi.org/10.4314/bcse.v37i1.5

Comprehensive study of Acid Yellow 42 adsorption by green synthesized polypyrrole/tannicacid/iron nanocomposites

ABSTRACT In this study, a green synthesis of polypyrrole/tannic acid/iron (PTI) nanocomposites was performed, using adsorption for the removal of Acid Yellow 42 (AY42) dye. The characteristics of PTI nanocomposites were defined applying scanning electron microscope (SEM), X-ray diffraction (XRD), zeta potential and Fourier transform infrared spectrometer (FTIR). The effects of different parameters such as pH, initial concentration of dye, temperature, adsorbent dose, and adsorption time were investigated. The process optimization was performed through L18 orthogonal array using the Taguchi design method. The initial concentration 30 ppm, temperature 55°C, adsorbent dose 0.06 g, adsorption time 30 min, and pH 2 were found as the optimal conditions for the removal of AY42 in batch mode. Kinetic studies illustrated that the AY42 dye adsorption process onto PTI nanocomposites followed the General order model. The obtained value of q e using the general order model (24.39 mg/g) is identical to the experimental value of q e (24.89 mg/g). The Langmuir adsorption isotherm and three-parameter isotherms (Hill, Sip, Redlich–Peterson, Khan, Toth, and Koble-Corrigan) show the best fit to AY42 dye adsorption data on PTI nano-adsorbent as compared to the two-parameter isotherm (Freundlich, and Temkin) models. The isothermal analysis showed that the maximum adsorption capacity of the Langmuir model would be as 116.5, 119.1, and 140.1 mg/g at 40, 50, and 60°C, respectively. Adsorption-desorption tests showed stable adsorption efficiency. The adsorption efficiency at the first stage is 98.19%, which reaches 95% at the seventh step.

Mathematical modelling of moisture sorption isotherms of some fruits

The moisture sorption isotherms of some fruits namely pear and quince were determined at 15, 30, 45 and 60oC over a range of water activity from 0.110 to 0.920 using the standard, static-gravimetric method. The experimental sorption data were fitted with generated three-parameter sorption isotherm models on Mitrevski et al., and the referent Anderson model known in the scientific and engineering literature as Guggenheim-Anderson-de Boer (GAB) model. In order to find which models give the best results, large number of numerical experiments was performed. After that, several statistical criteria for estimation and selection of the best sorption isotherm model was used. The performed statistical analysis shows that the generated three-parameter model from Mitrevski et al. gave the best fit to the sorption data of pear and quince than the referent three-parameter Anderson model. Keywords: Sorption isotherms Pear Quince Statistical criteria

Nonlinear Analysis of The Kinetics and Equilibrium for Adsorptive Removal of Paranitrophenol by Powdered Activated Carbon

Paranitrophenol (PNP) is one of the toxic chemicals, non-degradable, and bioaccumulative. In the present work, the nonlinear analysis method was used to assess the kinetics and equilibrium for PNP adsorption on commercially available Powdered Activated Carbon (PAC) from an aqueous solution. The adsorption kinetic data were analyzed using the Pseudo First Order (PFO), Pseudo Second Order (PSO), and Elovich models. The experimental data were fitted using two-parameter isotherms model (Langmuir, Freundlich and Temkin) and three parameters isotherms model (Sips, Redlich – Peterson and Toth). For the kinetic study, the adsorption process fitted the PSO model. Among two-parameter models, the Freundlich is better described for PNP adsorption on PAC. From three-parameter isotherms, the Sips model was found to be the best representative for PNP adsorption on the PAC. The results of the present study showed the efficiency of using PAC as an adsorbent for the removal of PNP from an aqueous solution.

Evaluation of Cephalexin and Amoxicillin removal from aqueous media using activated carbon produced from Aloe vera leaf waste

The present work illustrates the applicability of carbon nanoparticles produced from aloe vera leaf waste as a cost-effective agricultural adsorbent for the removal of Amoxicillin and Cephalexin from aqueous media. The presence of these pharmaceutical compounds as antibiotics in medicine remedies leads to entering in water bodies, which raised concerns for the poisoning of aquatic organisms. The adsorptive removal evaluation of Amoxicillin and Cephalexin as pollutants from aqueous solutions was investigated by the atomic adsorption Spectrometry. In the experimental framework, the influence of several factors including, initial concentrations, pH, contact time, temperature, and adsorbent dosage were evaluated. The activity of carbon was examined by aqueous samples of H2SO4 (Av-S-Ac) and HNO3 (Av-N-Ac). Chemical modifications led to an increase in sorption ability. The empirical data were fitted first-order quasi-linear, second-order quasi-linear kinetic models, and Langmuir, Freundlich, Temkin, Redlich-Patterson three-parameter, and Duinin-Radushkevich isotherms models. The maximum adsorption capacity was achieved at pH = 3, adsorbent dose: 100 mg and initial concentration of 50 mg/L at 25 °C. The study showed that experimental data were well-fitted by the pseudo-second-order kinetic model (R2 > 0.99) and Langmuir isotherm model (R2 > 0.99) and the maximum uptake capacities for Cephalexin were 25.56 and 26.34 mg/g and for Amoxicillin 28.86 and 29.11 mg/g in (Av-S-Ac) and (Av-N-Ac) adsorbents, respectively.

Adsorption of copper, and zinc onto novel Ca-alginate-biochar composite prepared by biochars produced from pyrolysis of groundnut husk

Alginate-based composites have been studied for adsorption technology as adsorbents due to their biocompatible, non-toxic, and cost-effective properties. In this work, groundnut husk biochar (GHB), calcium alginate (CA), and groundnut husk biochar/calcium alginate novel composites (%10) (CA-GHB1) and (% 20) (CA-GHB2) are synthesized and characterized using BET, SEM, EDX, FTIR, TGA. Adsorption performance is compared among GHB, CA, CA-GHB1, and CA-GHB2 composites to remove Cu(II), Zn (II) from aqueous solutions. Factors affecting adsorption, as well as kinetics, equilibrium, and thermal properties of adsorption, were studied using conventional equations. Adsorption isotherm models were used for two and three-parameter isotherm models to understand the interaction between the adsorbent and the adsorbate. 24.3, 44.6, 45.6, and 40.73 mg g−1 for removal of Cu(II) on GHB, CA, CA-GHB1, and CA-GHB2 and 32.16, 25.07, 36.09, and 40.55 mg g−1 for removal of Zn(II) on GHB, CA, CA-GHB1, and CA-GHB2 found maximum adsorption capacity (Qm) calculated from Langmuir isotherm. According to D-R isotherm data, the adsorption process is classified as physical adsorption. Thermodynamically, the adsorption process is non-spontaneous and endothermic.

The Preparation of Eco-Friendly Magnetic Adsorbent from Wild Water Hyacinth (Eichhornia crassipes): The Application for Removing Lead Ions from Industrial Wastewater

Water hyacinth ( Eichhornia crassipes) is a wild floating plant that can be found widely in pond or river areas. The plant grows fiercely and causes many harmful issues to the ecosystem around its covered area. This work provides a utilization method that converts wild water hyacinth to reliable magnetic biochar which can be used as a very effective adsorbent for the removal of lead ion Pb(II) in industrial wastewater. The mentioned magnetic biochar can be prepared via a modified pyrolysis process at 550°C with the support of cobalt sulfates as magnetite precursors and limited oxygen from the sweeping gas (the gas mixture ratio is 4 : 1 nitrogen/oxygen). The produced samples were hydrophobic biochar with high oxygen-containing functional groups that are suitable for the removal of inorganic contaminants. The impregnation of cobalt (II, III) oxides provided high magnetic separation performance and additional adsorption sites on the produced magnetic biochar. As indicated by the obtained result, the WHB-Co2M sample possesses a highly porous structure (0.126 cc/g), higher thermal stability (thermal durability reaches 900°C), relatively stable magnetic properties (14.74 emu/g), and a larger surface area (192 m2/g). These beneficial properties led to its suitability to serve as an adsorbent in removing lead ions in the contaminated effluent, recording 95% of removal efficiency and adsorption capacity of 67.815 mg/g. As indicated in the result, all prepared magnetic biochar samples were fitted to two-parameter (Langmuir models) and three-parameter (Sips model) isotherm models. Therefore, the adsorption process in this work could be carried out on both homogeneous and heterogeneous adsorbent surfaces. The adsorption kinetics of the removal process also was described by the pseudo-first-order, pseudo-second-order, and Elovich models to reveal the adsorption and desorption rate of the as-prepared magnetic biochar. This work indicates a successful waste refinery route of converting lignocellulosic biomass such as water hyacinth into value-added material for use as promising heavy metal adsorbents.

Fabrication of silica aerogel and carbon–silica composite for dynamic adsorption of benzene from dry and wet gas streams

ABSTRACT In the present study, the white kaolin-derived silica (SA) and silica-carbon aerogel composite (CSA) were successfully synthesised as useful adsorbents for the effective removal of benzene from dry and wet gas streams. The physicochemical features of the adsorbents were characterised using SEM, BET, XPS, and TGA, and the adsorption properties of benzene were investigated through breakthrough time curves and equilibrium study. The specific surface areas of SA and CSA were 628 and 783 m2 g−1, respectively, demonstrating the high porosity of the synthesised adsorbents. The dynamic adsorption and isotherm performances of SA and CSA confirmed that both adsorbents have superior adsorption properties and Khan isotherm for both developed adsorbents were the fittest model among the two- and three-parameter isotherm models studied and provided a maximum adsorption capacity of 366.2 and 224.4 for SA and CSA mg g−1, respectively. Furthermore, the reusability tests revealed that the SA and CSA could be efficiently recovered at 180°C. Our experimental outcomes indicated that the prepared SA and CSA can be applied as efficient and inexpensive adsorbents for the removal of benzene from gaseous streams.

Enhanced sequestration of chromium (VI) onto spent self-indicating silica gels coated with Harpephyllum caffrum stem bark extract

ABSTRACT This study investigates the capacity of spent self-indicating silica gels modified with Harpephyllumcaffrum(wild plum) stem bark extract to remove hexavalent chromium from wastewater. The physicochemical properties of the adsorbents were assessed using FESEM, FTIR, PXRD, TGA and BET surface analyser. The batch adsorption technique was used to examine the capacity of spent self-indicating silica gel (SIPP) and modified spent self-indicating silica gel (SIP) to eliminate Cr(VI) from the aqueous solution. The uptake capacity of the sorbents was noticed to increase with increasing adsorbent dose, contact time and initial concentration of Cr(VI). On the contrary, the potential of SIPP and SIP were observed to decline with increasing solution pH, similarly as found for most Cr(VI) absorbents. However, the uptake capacity of the SIPP and SIP were noticed to be optimum at 0.05 g adsorbent dosage and 180 min contact time. Meanwhile, the kinetic behaviour of SIPP and SIP in the removal of Cr(VI) was best described by the Elovich kinetic model. Furthermore, the uptake of Cr(VI) onto SIP and SIPP was sufficiently described by the three-parameter isotherm Sips and Freundlich isotherms respectively. The Cr(VI) adsorption was endothermic, entropy-driven, and feasible. The application of Harpephyllum caffrumstem bark extract on SIPP as Cr(VI) adsorbent was significant and the reusability of the adsorbent portrayed the capacity of SIP to adapt to a full-scale wastewater treatment practice.

Nanofibrous membrane of polyacrylonitrile with efficient adsorption capacity for cadmium ions from aqueous solution: Isotherm and kinetic studies

The nanofibrous membrane of polyacrylonitrile (NMP) was successfully synthesized after NaOH and NaHCO3 treatment aiming its functionalization using electrospinning for cadmium ion (Cd2+) adsorption. Field emission scanning electron microscopy (FE-SEM) revealed that small particles attached to the surface of functionalized PAN nanofibers. Equilibrium was attained after 60 min following a rapid uptake of Cd2+ with maximum adsorption capacity and percentage removal at an optimum solution pH of 7.0. The adsorbent dose of 0.3 g and 90 mg L−1 of initial Cd2+ concentration yielded the maximum adsorption capacity. The pseudo-second-order kinetic model was the best fitted to the adsorption data, indicating that the chemisorption is the controlling mechanism of adsorption. The physisorption was proposed based on the calculated values of the mean free energy of adsorption from the D–R isotherm (E < 8 kJ mol−1). Furthermore, three-parameter isotherm models indicated the homogeneous and heterogeneous Cd2+ adsorption onto NMP adsorbent.

Analysis of the AlN phase transition on a sapphire surface within a universal 2D lattice gas model in MBE

The AlN phase transition on the (0001) Al2O3 surface was investigated. It was experimentally estimated that the AlN formation rate as a function of temperature has a different character in two temperature regions. In the region of relatively low temperatures (T < 1210 K), the AlN formation rate is limited by chemical reactions. At higher temperatures (T > 1210 K), the formation of an ordered AlN phase is determined by a continuous two-dimensional phase transition within the filled AlN-lattice-gas cells formed on the sapphire surface. A three-parameter isotherm is proposed to describe the process. The observed phase transition in the AlN lattice gas is a continuous phase transition or a second-order transition.

Thermodynamics studies on the adsorption of phenol from aqueous solution by coffee husk activated carbon

Activated carbons (ACs) obtained from coffee husk by KOH activation at 650 (ACK-650) and 750oC (ACK-750), were used as an adsorbent for the adsorption of phenol from aqueous solution. The ACs was characterized by SEM, EDX, BET, and Boehm titration techniques. The experimental equilibrium data of phenol adsorption was analyzed by eight isotherm models, which are four two-parameter equations (Langmuir, Freundlich, Elovich, and Temkin) and four three-parameter equations (Redlich-Peterson, Sips, Radke-Prausnitz, and Toth). The results reveal that in general, three-parameter isotherms can provide better prediction than two-parameter isotherms. The best fit for ACK-650 sample is Sips isotherm, while for ACK-750 sample is Redlich–Peterson isotherm. Isosteric heat and thermodynamic parameters ΔGo, ΔHo, and ΔSo of the adsorption were determined, and the results showed that the adsorption of phenol was exothermic and physical in nature. A scale-up of a batch system is designed for 2 to 10 L phenol with an initial concentration of 100 mg L-1.

Highly Efficient Adsorption of Cd(II) onto Carboxylated Camelthorn Biomass: Applicability of Three-Parameter Isotherm Models, Kinetics, and Mechanism

A series of malonic acid treated camelthorn (MATC) sorbents were produced via the reaction of camelthorn biomass with malonic acid, and factors affecting the extent of modification were investigated, including malonic acid concentration, dehydration time and temperature. The optimum sorbent, by carboxylic acid content, was subsequently characterised for surface charge behaviour (pHPZC), surface chemical functionalities (FTIR), morphological structure (SEM), and available surface area. The sorbent was subsequently utilised for adsorption of Cd(II) ions from aqueous media, and parameters influencing adsorption at 30 °C, such as sorbent dose, initial solution pH, exposure time, metal concentration, were investigated. Isothermal analyses were performed using eight models, including two and three parameter equations, with appropriateness of fit assessed via non-linear regression analysis. The adsorption data indicated that the Langmuir model gives the most appropriate fit to experimental curves, with the models ordered as Langmuir > Hill > Toth > Sips > Jossens > Khan > Redlich-Peterson > Freundlich. The highest uptake (qmax) of 582.6 mg g−1 was determined at pH 6. The Freundlich constants, KF and n, at 30 °C were found to be 24.94 mg g−1 and 2.33, respectively. The value of n (2.33), being in the range 0–10, indicates that adsorption of Cd(II) ions onto malonic acid treated camelthorn biomass is favourable. Evaluation of a series of kinetic models, allowed elucidation of the adsorption mechanism, as a pseudo-second order model gave the most appropriate fit, indicating that chemisorption processes are involved. Cd(II) ions adsorption onto MATC is enhanced by a higher level of active surface sites but was show to be independent of surface area. The work presented here indicates that this sorbent offers effective adsorption potential for Cd(II) ions from water, with potential in wastewater processing.

Chitosan-based hydrogels for the sorption of metals and dyes in water: isothermal, kinetic, and thermodynamic evaluations

The aim of the present study was to evaluate a chitosan-based hydrogel and chitosan/magnetite-based composite hydrogel as potential matrices for water treatment through sorption experiments involving metals and dyes. Cadmium and methylene blue were used as model pollutants. The best isotherm fits were found using three-parameter isotherms, indicating both the formation of a monolayer and multi-site interactions in the hydrogel networks due to the diffusion of the solutes and macromolecular relaxation of the polymer chains. Maximum methylene blue sorption capacities of the chitosan-based hydrogel and chitosan/magnetite-based composite hydrogel were 23.389 and 23.478 mg g−1, respectively. These values were respectively 90.038 and 80.383 mg g−1 for cadmium sorption. The best kinetic fit for the interaction of methylene blue and cadmium to the chitosan-based hydrogel was the nonlinear pseudo-second-order kinetic model, indicating that a chemical reaction controls the adsorption rate between the hydrogel and pollutant. The opposite was found for interaction with the chitosan/magnetite-based composite hydrogel, suggesting that the active-site occupation rate is proportional to the number of non-occupied active sites. The thermodynamic results revealed that the sorption processes were favorable and endothermic, with the possible occurrence of physical interactions. However, hydrogel swelling can alter the sorption isotherm, kinetics, and thermodynamics. The interaction of methylene blue and cadmium with both hydrogels was confirmed by Fourier-transform infrared spectroscopy and thermogravimetric analyses.