Adsorbent For Removal Of Metal Ions Research Articles

Cadmium biosorption: Lake waters in Bengaluru-mitigation of cadmium-induced oxidative stress by Selaginella bryopteris

ABSTRACT Heavy metals cause alarming levels of environmental and health problems and among them Cadmium has become a threat to organisms and natural resources like soil and water alike. It accumulates in living systems thereby causing oxidative stress. Efforts are made for bioremediation of heavy metals by employing biosorption, which is a well-known economic method for removal and in the current study Selaginella bryopteris was used as biosorbent. The biosorption capacity was optimized by its physicochemical parameters such as pH, dosage, contact time, and temperature. Cadmium-induced Reactive Oxygen Species levels and the antioxidant potential of S. bryopteris in ameliorating them were studied in Drosophila melanogaster. Water-quality analysis was performed using Chemical Oxygen Demand(COD) and Biological Oxygen Demand (BOD) and effect of S.bryopteris on these parameters were also analyzed. Further the concentration of Cadmium via colorimetric assay and Atomic Absorption Spectroscopy(AAS) was employed to quantify the Cadmium in lake water samples before and after treatment with biosorbent. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) were performed to characterize the surface properties for adsorptive removal of metal ions, and antioxidant studies were conducted to assess the role of S. bryopteris in suppressing oxidative stress.

Pattern identification in data about unmodified waste eggshell application as an adsorbent for metal ion removal from aqueous media

Abstract In recent years, a significant increase in the amount of research published about the application of eggshells for the removal of metal ions from aqueous solutions has been observed. The paper presents different aspects of metal adsorption from aqueous solutions on untreated eggshells. Pretreatment procedures and tested parameters for the adsorption differ significantly across all the reviewed data, providing a source of variance for the results. For untreated eggshells, the range of the reported BET surface area is from 0.07 m2/g to 8.941 m2/g. Correlation between particle size and BET surface area has been highlighted. Reported removal efficiencies for the untreated eggshell have been compared. Reported results show that eggshell is most employed for the removal of Pb(II), Cd(II), and Cu(II) from aqueous solutions. Eggshell capacity to remove metal ions from the main group elements has also been demonstrated. While results look promising, not enough data are present to make reliable conclusions about its efficiency with other (mainly transition) metal ions – which makes it a possible research direction. Based on the reported data, multiple removal pathways are involved. Several eggshell modification methods and possibilities of creating new adsorbents using eggshells only as a part of the raw material have been assessed. Finally reported eggshell modification methods have been assessed and it is clear that to compare different material’s effectiveness as an adsorbent, comparing only materials adsorption capacities is insufficient. Certain environmental water pollution removal studies using adsorption demand further study, such as metal ion specification in aqueous solution, in different processing water, and even in wastewater.

Effective removal of Cr(VI) and Pb(II) ions from mining wastewater using eco-friendly synthesized magnesium oxide nanoparticles incorporated rice husk ash

This study explored the effective adsorptive performance of magnesium oxide (MgO) nanoparticles incorporated rice husk ash (RHA) to address the removal of Chromium (VI) and Lead (II) from mining wastewater from aqueous environment. MgO nanoparticles were synthesized using a magnesium salt precursor and moringa oleifera leaf extract and then impregnated onto RHA to create MgO-RHA nano composite. Different analytical techniques were employed to characterize the RHA and MgO-RHA nanocomposites. The prepared adsorbents were used in batch adsorptive studies and the concentrations of the metal ions were measured before and after treatment using atomic absorption spectrophotometry. Morphological analysis confirmed that the adsorbents developed exhibited a dispersed and porous nature. BET analysis revealed that RHA, MgO, and MgO-RHA had surface areas of 93.04, 32.02, and 102.71 m2/g, respectively. MgO-RHA outperforms RHA in removing metal ions due to its increased surface area and functionality. MgO-RHA demonstrated higher removal percentages of up to 79.20 % and 96.02 % for Cr(VI) and Pb(II), respectively. The Pseudo-second order kinetics and Langmuir isotherm demonstrated the highest degree of conformity to the experimental data, considering the coefficient of determination (R2), smallest value of SSE and chi-square (ᵪ2). Thermodynamic results indicated that the adsorption process was characterized by endothermicity, spontaneity and chemisorption controlled. In summary, the performance of the MgO-RHA nanocomposite surpassed that of RHA alone, which serves as a better adsorbent for metal ion removal.

Radiation synthesis and chemical modifications of p(AAm-co-AAc) hydrogel for improving their adsorptive removal of metal ions from polluted water

The research focuses on utilizing gamma irradiation to synthesize polyacrylic acid-co-polyacrylamide p(AAm-co-AAc) hydrogels. The effect of synthetic parameters on physicochemical features of p(AAm-co-AAc) hydrogls were examined, including acrylic acid (AAc): acrylamide (AAm) weight ratios, monomer concentration, and gamma irradiation dosage (kGy). At the optimum synthetic conditions (30 kGy and 75% AAc), different chemical modifications are explored to incorporate sulfonate, hydroxyl, carboxyl, cysteine, thiol, and amine functional groups within the bare hydrogel (Cpd 0) structure. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses confirmed the success development of functionalized hydrogels (namely Cpd 1 to 6) with three-dimensional porous structures. These modified hydrogels include Cpd 1, a sulfonated hydrogel through a sulfonation reaction; Cpd 2, modified via NaOH hydrolysis; Cpd 3, modified using thionyl chloride; Cpd 4, incorporating cysteine modification through reaction with cysteine; Cpd 5, with 4-(Dimethylamino) benzaldehyde; and Cpd 6, modified with 3,4-Dimethylbenzoic acid.The effect of hydrogel composition and surface functionalities on the swelling capacity and interactions with scale-forming/heavy metal ions (e.g., Ba2+, Sr2+, and Cu2+) was investigated in saline water solution (NaCl = 1000 mg/L). Batch adsorption studies reveal that all modified hydrogels exhibited higher removal efficiency for the three metal ions than unmodified p(AAm-co-AAc) hydrogel, validating the key role of surface functionalities in tailoring hydrogel affinity for metal ions adsorption. Amongst these, NaOH-treated hydrogel (Cpd 2) outperformed all other modified ones in the removal of Cu2+, Ba2+, and Sr2+ ions, with maximum capacities of 13.67, 36.4, and 27.31 mg/g, respectively. Based on adsorption isotherm and kinetic modeling, the adsorption process of the three metal ions onto all modified hydrogels better obeyed Freundlich isotherm and pseudo-first-order kinetic models. Thermodynamic studies also indicated that the adsorption behavior of Sr2+ ions can exhibit both exothermic and endothermic characteristics, depending on the nature of hydrogel surface chemistry. Conversely, the adsorption process of Cu2+ and Ba2+ ions onto all modified hydrogels is endothermic, suggesting favorable chemical adsorption mechanisms. These findings reveal that the specific adsorption performance of hydrogel is dependent on the type of modification and the targeted heavy metal ions. Based on the nature of hydrogel surface functionality, surface modifications can change the charge density, hydrophilicity, and overall chemical environment of the hydrogel, offering a versatile approach to optimize the adsorption affinity/selectivity of hydrogel's in removing scale-forming/heavy metals from water solutions.

Sorption of Pb2+, Zn2+, Cu2+ and Ni2+ Ions on Na-enriched Natural Zeolite for Wastewater Treatment Process: A Kinetic Approach

Low-cost and easily available natural zeolite is a promising adsorbent for metal ions removal in wastewater treatment. The possibility of using zeolitic tuff from Serbia in the form of Na-enriched natural zeolite (Na-Z) for the adsorption of Pb2+, Zn2+, Cu2+, and Ni2+ ions from wastewater was investigated in the presented paper. The research included Na-Z characterization and determination of adsorption kinetics in individual ion adsorption tests using non-linear pseudo-first-order (PFO), pseudo-second-order (PSO) and mixed-order (MO) kinetic models. The results indicate that the adsorption processes of metal ions on Na-Z are complex processes dominated by multiple rate-limiting mechanisms and best defined by the MO model. The mechanisms of ion diffusion and adsorption to active sites are equally represented in the Pb2+ ions adsorption process. The mechanism of ion diffusion is more pronounced in the Zn2+ ions adsorption process, while in the case of the adsorption of Cu2+ and Ni2+ ions adsorption on the active sites is the main kinetic mechanism. Within the MO model, the PFO rate (external/internal diffusion) and the PSO rate (adsorption on the active sites) were calculated and results were applied to a multicomponent wastewater sample in order to determine and explain the adsorption efficiency in wastewater treatment. The results show that the rate of adsorption of individual metal ions and the efficiency of ion removal from a multicomponent wastewater sample are influenced by several factors including the radius of the hydrated ion and the free energy of hydration. The achieved removal of metal ions by Na-Z is Pb2+ (89%) > Cu2+ (72%) > Zn2+ (61%) > Ni2+ (58%) and defines Na-enriched natural zeolite as an effective adsorbent in wastewater treatment.

Self-cross-linking of metal-organic framework (MOF-801) in nanocellulose aerogel for efficient adsorption of Cr (VI) in water

Chromium (Cr) poses significant hazards to both human health and the natural environment. Therefore, in this study, metal-organic framework (MOF-801) was compounded with nanocellulose aerogel for the first time. And a nanocellulose/metal-organic framework composite aerogel was developed for efficient chromium ion adsorption. The resulting aerogel has an ultra-low density (0.017 g/cm3) and high porosity (98.87%). The removal efficiency of this aerogel for Cr (VI) (93.86%) was measured to be higher than that of cellulose nanofiber aerogel (TCNF: 50.08%) and MOF-801 powder (59.86%). It was also higher than the cellulose nanocellulose aerogel prepared without MOF-801 (TMPA: 70.58%). This is because MOF-801 cross-linked with nanocellulose increased its porosity and provided a large number of adsorption sites. The maximum adsorption of Cr (VI) by this aerogel was 350.64 mg/g (5.96 mg/cm3). The adsorption mechanism was investigated by adsorption isotherms, adsorption kinetics, XPS, and FT-IR analysis. The aerogel has good reusability, with no significant loss of adsorption performance over 6 cycles. It is worth mentioning that 0.69 g (V: 7.363 cm3) of aerogel could effectively remediate 3710 mL of chromium-containing wastewater in a fixed-bed column adsorption experiment. In addition, the aerogel can effectively remove many metal ions from wastewater. As a result, the aerogel made in this study has the ability to be an effective adsorbent for metal ion removal.

Adsorptive Removal of Potentially Toxic Elements From Wastewater Using Peanut Shells Biochar

This study aimed to investigate the efficiency of the peanut shell biochar that prepared by physical activation using pyrolysis process at 550°C as a low cost adsorbent for metal ions removal from wastewater. The biochar surface morphology, chemical functional groups and the porous structure were investigated by SEM, FTIR and BET method respectively. Different parameters that affect the metal ions adsorption were taken in consideration during adsorption experiments. These parameters included pH value (3 – 8), initial metal concentration (5 – 100mg/l), biochar dose (0.5 – 4g), contact time (5 – 240 min) and temperature (25 – 60°C). The results showed that the optimum metal ions adsorption conditions were pH 6, metal concentration 20mg/l, biochar dose 2.5g, 60min of contact time and 60°C of solution temperature. The adsorbent removal efficiency for the studied metal ions exceeded 80% from the total metal concentration. The obtained results confirmed the efficiency of the biochar from peanut shell as an active adsorbent for metal ions removal from aqueous solutions.

Kinetic and equilibrium study of pyrolyzed sugarcane bagesse as adsorbents for Pb2+ and Cd2+ in an aqueous medium

ABSTRACT Sugarcane bagesse was utilised as a low-cost adsorbent for the removal of metal ions. The study was done at a temperature of 35°C, and the maximum adsorption capacities for Pb(II) and Cd(II) ions were 3.02 and 2.90 mg/g, respectively, for sugarcane bagasse. These results were determined using the following optimum conditions: initial metal ion concentration of 100 mg/dm3, adsorbent weight of 0.5 g, time of 30 min and pH of 6. The adsorption of the metal ions by the adsorbents decreased with an increase in the initial concentration of the metal ions in an aqueous solution. The rate of adsorption also increased with temperature. The adsorption showed a good fit to the Langmuir model compared to the Freundlich adsorption model. The Langmuir dimensionless constant (RL) for the adsorption of Pb(II) ion and Cd(II) ion ranged from 0.081 to 0.123 and 0.115 to 0.172, respectively, which confirms favourable adsorption. The adsorption process showed that the pseudo-second-order kinetics was a better fit than the pseudo-first-order kinetics. The result of this work showed a low-cost and efficient potential of sugarcane bagasse to be employed as a good adsorbent for metal ion removal.

Review on adsorptive removal of metal ions and dyes from wastewater using tamarind-based bio-composites

Review on adsorptive removal of metal ions and dyes from wastewater using tamarind-based bio-composites

Eco-friendly activated carbon developed from rice hulls for chromium and iron ion removal

Rice hulls, a harmful biowaste, were used to produce nanosized activated carbon (RHAC) by combustion and phosphoric acid treatment. The developed RHAC was characterised using various structural and morphological techniques (scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen (N2) adsorption). The prepared RHAC was used to remove heavy metal ions (iron (III) (Fe3+) and chromium (VI) (Cr6+)) by using the adsorption mechanism. Adsorption parameters, such as contact time, dose and initial concentration of the heavy metal ions, were investigated. Five adsorption models (two and three parameters) were studied. Also, the adsorption kinetics through the intraparticle diffusion model was applied. RHAC showed adsorption capacities of 47.00 and 45.00 mg/g for iron (III) and chromium (VI), respectively. The findings recommend using RHAC as a low-cost and eco-friendly adsorbent for metal ion removal and water-treatment applications.

Synthesis of oxidized Dioscorea dumentorum starch nanoparticles for the adsorption of lead(II) and cadmium(II) ions from wastewater

The search for efficient adsorbents for the treatment of wastewater has led to the exploration of derivatized starches. Here, Dioscorea dumentorum starch was isolated, oxidized and acid-hydrolyzed in a dual-modification approach. The native starch (NTS) and the resulting oxidized starch nanoparticles (Oxy-SNPs) were characterized by FTIR, SEM, XRD and TGA, and then applied in removing Pb2+ and Cd2+ ions from simulated wastewater. Investigation of the functional properties of the starches as well as their characterization confirmed the success of the modification and the suitability of the Oxy-SNPs as adsorbent for metal-ions removal. Adsorption of Pb2+ and Cd2+ ions increased with augmentation of initial metal-ions concentration. Metal removal peaked and flattened after 90 min. Freundlich isotherm gave a superior fitting of experimental data above the Langmuir and Dubinin-Radushkevich (D-R) isotherms, indicating energetically heterogeneous Oxy-SNPs surface. Kinetic data followed the pseudo-second-order model with R2 values of 0.9934 and 0.9989 for Pb2+ and Cd2+ ions, respectively, signifying that the valency forces caused sharing or exchange of electrons during the interactions. Thermodynamic parameter showed that the processes were feasible, exothermic and occurred with decrease disorderliness. Energy values calculated from D-R model (35.36 kJ/mol for Pb2+; 28.87 kJ/mol for Cd2+), the good fitting of Elovich model and the magnitude of ΔHº being <29 kJ/mol all suggest chemical adsorption.

Facile synthesis of economical feasible fly ash–based zeolite–supported nano zerovalent iron and nickel bimetallic composite for the potential removal of heavy metals from industrial effluents

Heavy metals contamination of water is one of the environmental issue globally. Thus prepared fly ash–based zeolite (FZA)–supported nano zerovalent iron and nickel (nZVI/Ni@FZA) bimetallic composite from low-cost fly ash waste for the potential treatment of anion (Cr(VI) and cation Cu(II)) heavy metals from industrial effluents at pH 3 and 5, respectively in this study. The systematic interaction between FZA and nZVI/Ni and the adsorptive removal mechanism was studied. The mean surface area of the nZVI/Ni@FZA (154.11 m2/g) was much greater than that of the FZA (46.6 m2/g) and nZVI (4.76 m2/g) independently, as determined by BET-N2 measurements. The effect of influence factors on the removal of Cr(VI) and Cu(II) by nZVI/Ni@FZA, such as pH effect, initial concentration effect, time effect, temperature effect, coexisting metals, and ionic strength, and cumulative loading ability, were discussed. The maximum adsorption capacity of nZVI/Ni@FZA was 48.31 mg/g and 147.06 mg/g towards Cr(VI) and Cu(II), respectively. These were higher than those of nZVI@FZA and FZA. It demonstrated that Ni could play an important role in enhancing the reduction ability of nZVI. Furthermore, isothermal and kinetic results revealed that both heavy metal adsorption processes were rate limiting monolayer Langmuir adsorption on homogeneous surfaces. Thermodynamic results suggested that the adsorptive removal of metal ions was endothermic with spontaneity. The applicability of nZVI/Ni@FZA on real industrial wastewater treatment results demonstrate that the concentration of heavy metals were removed under the acceptable standard levels. Further the adsorption capacity of nZVI/Ni@FZA was higher than the nZVI@FZA and FZA. The overall results demonstrated that nZVI/Ni@FZA was a promising, efficient, and economically feasible sorbent for potential wastewater treatment. Moreover this is first report on the preparation nZVI/Ni@FZA bimetallic composite.

Sorption of U(VI), Mn (II), Cu(II), Zn(II), and Cd(II) from multi-component phosphoric acid solutions using MARATHON C resin.

Crude phosphoric acid is a vital component used in making phosphate fertilizers. Depending on the processes used in producing the crude phosphoric acid, it usually contains organic and inorganic contaminants. To make environmentally friendly phosphate fertilizers, these contaminants must be removed from the crude phosphoric acid stock used in making fertilizers. In this paper, commercially available strong cation exchange resin, Marathon C, was used to study the adsorptive removal of U(IV), Mn(II), Cd(II), Zn(II), and Cu(II) from synthetic multi-component phosphoric acid solutions and commercial crude phosphoric acid. Important parameters on the adsorption process such as the effects of contact time, initial metal ion concentration, sorbent dose, and concentration of phosphoric acid were investigated. The results suggested that the adsorption process reached equilibrium within 240min for the five metal ions studied and the resin had adsorptive affinity for the metal ions in the order of U(IV) > Zn(II) > Cu(II) > Mn(II) > Cd(II). The results from the kinetics and isotherm models from the studies are very consistent with pseudo-second-order kinetic and Langmuir isotherm models. Simultaneous adsorptive removal of metal ions from the crude phosphoric acid strongly suggests that the Marathon C resin could be used in removing toxic metal ions from crude phosphoric acids used in making phosphate fertilizer.

Insights into interactions of Cr(III) and organic matters during adsorption onto titanate nanotubes: Differential absorbance and DFT study

Organic Matter (OM) with different molecular weight and functional groups can impact the adsorptive removal of metal ions, and the influence trend can be facilitated, inhibited or unchanged. However, the association capabilities of different ligands were superficially expounded. Based on the sorption behavior of Cr(III) onto titanate nanotubes (TNTs) with coexisting citric acid (CA), humic acid (HA) and fulvic acid (FA), this study highlighted differential absorbance and DFT simulations to quantitatively detect the mutual effect. As results, adsorption capacities of Cr(III) obviously enhanced from ca. 60 mg/g to 85 mg/g with CA or FA; while HA can slightly promote Cr(III) adsorption. UV spectra scanning proved that FA and HA led to the remarkable red shift of peak A1 (232 nm), A2 (262 nm), A3 (295 nm), A4 (431 nm) of Cr(III), and the area ratio of A2/A3 followed the order Cr-HA > Cr-FA > Cr-CA ≈ Cr. DFT calculations further confirmed that the simultaneous formation of ligand-metal-adsorbents complex and electrostatic effect promoted Cr(III) adsorption, with binding energies of −202.9 ~ −420.8 kJ/mol and − 3958 kJ/mol, respectively. Meanwhile, the bridge connection of OM mainly appeared in the outer sphere of TNTs, as the larger molecular scale prevented their insertion into the inner spacing of TNTs, especially for HA and FA. Therefore, the adsorption mechanism was the combined actions of electrostatic attraction, bridge connection of OM and steric effect. This study can give insights into OM effects on metal adsorption, and quantificationally describe the junction state of ternary complex.

Effective removal of Cu(II) from aqueous solution over graphene oxide encapsulated carboxymethylcellulose-alginate hydrogel microspheres: towards real wastewater treatment plants.

In the current study, the graphene oxide (GO) encapsulated carboxymethyl cellulose-Alginate (CMC-Alg) hydrogel microspheres were prepared via ionotropic gelation method and characterized using FTIR, TGA, SEM-EDS and surface charge by determining pHpzc. The adsorption of Cu2+ ions from aqueous solution on the graphene oxide embedded CMC-Alg was studied under different experimental conditions, and the results showed that embedded beads had high adsorption capacity compared with pure CMC-Alg beads due to synergetic effect between functional groups GO and CMC-Alg matrix. Adsorption capacities at equilibrium were calculated experimentally as 22.10, 39.96, 41.72 and 64mg/g for pure CMC-Alg, CMC-Alg/GO 1%, CMC-Alg/GO 3% and CMC-Alg/GO 5%, respectively. The adsorption kinetics were found to follow the pseudo-second-order, and the equilibrium data fitted well with the Langmuir adsorption isotherm. Moreover, the intraparticle diffusion model has been inspected pointing that the adsorption process was found to be sequence of surface adsorption and intraparticle diffusion (IPD). The results suggest that graphene oxide embedded CMC-Alg bead matrix can be efficiently used as an adsorbent for metal ions removal from wastewater.

Hydrophilic triazine-based dendron for copper and lead adsorption in aqueous systems: Performance and mechanism

In this study, a triazine-based dendron produced by the reaction of cyanuric chloride and diamine was synthesized successfully and applied in the adsorption of copper and lead ions in aqueous systems. The effects of pH, contact time, adsorbent dosage, solution temperature, initial concentration, coexisting substances and desorption were systematically performed in the case of adsorption operations. The adsorption of the both heavy metal ions followed the pseudo-second-order kinetic model best, with the equilibrium adsorption time at 120 min. The adsorption isotherms were well-described by the Langmuir model and the calculated maximum adsorption capacity of Cu2+ and Pb2+ was 103.68 and 133.47 mg g−1 at 25 °C, respectively. Based on the Dubinin-Radushkevich (D-R) isotherm model and calculation of adsorption free energy, the sorption processes for Cu2+ and Pb2+ were both chemisorption. Desorption and reuse experiments demonstrated that without significant loss in its original performance that could be reused in five cycles. The high density of terminal hydroxyl groups on the dendron was believed to participate in the chemical sorption process of Cu2+ and Pb2+ due to electrostatic attraction and surface complexation in the binding process. These results suggested the triazine-based dendron can be used as an efficient adsorbent for metal ions removal from wastewater.

Adsorption performance and mechanistic study of heavy metals by facile synthesized magnetic layered double oxide/carbon composite from spent adsorbent

To reuse the spent magnetic MgAl-layered double hydroxide after humic acid adsorption, this work provided a simple calcination method to prepare the magnetic layered double oxide/carbon (Mag-LDO/C) nanocomposite. The characterization results indicated the Mag-LDO/C was a carbonaceous composite with a large number of functional groups and superparamagnetic property. Then the adsorption performance of Mag-LDO/C for heavy metals was studied by batch experiments. The Mag-LDO/C exhibited excellent removal efficiencies for Cd(II), Pb(II), and Cu(II) with maximum adsorption capacities of 386.1, 359.7, and 192.7 mg/g, respectively. The batch sorption data were studied by the pseudo-second-order kinetic equation and the Langmuir isothermal model, and they matched well. According to the zeta potentials, X-ray diffraction patterns, and X-ray photoelectron spectra of Mag-LDO/C after heavy metals adsorption, the interaction mechanisms were ascribed to the precipitation, surface complexation, and electrostatic attraction. After reaction, the solid-liquid separation of Mag-LDO/C could quickly achieve using a magnet. Additionally, the Mag-LDH/C exhibited excellent adsorption capacities in various simulated wastewater and well sorption recyclability, proving the valuable applications of Mag-LDO/C synthesized from spent adsorbent for metal ions removal in actual water environment.

Adsorption isotherm, kinetic and thermodynamic studies for the removal of Pb(II), Cd(II), Zn(II) and Cu(II) ions from aqueous solutions using Albizia lebbeck pods

Powdered adsorbent prepared from Albizia lebbeck pods as agricultural waste has been used for the adsorption of Pb(II), Cd(II), Zn(II) and Cu(II) ions from aqueous solutions. The powdered adsorbent was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Brunauer–Emmett–Teller. Effects of various parameters like contact time, solution pH, initial concentration dosage and temperature were investigated on a batch adsorption system. Equilibrium and kinetic experiments were carried out at the optimum pH of 6, 8 and 10 at 29 °C using particle size of 250 μm for Cd(II), Pb(II), Zn(II) and Cu(II) ions. Changes in free energy, enthalpy and entropy were also evaluated. The adsorption data fitted well with the Langmuir isotherm model with correlation coefficient (R^{2} > 0.94), whereas the adsorption kinetics followed the pseudo-second-order kinetics. The thermodynamic parameters proved that adsorption of metal ions is endothermic and non-spontaneous at low temperatures, while spontaneity occurred at higher temperatures. This study shows that powdered Albizia lebbeck pods prove to be a promising inexpensive adsorbent for metal ion removal from aqueous solutions.

A kinetic and mechanistic study of adsorptive removal of metal ions by imidazole-functionalized polymer graft banana fiber

Chemically modified fibrous bio-adsorbent extracted from banana trunk was synthesized for potential application in adsorption of heavy metal from wastewater. Glycidyl methacrylate (GMA) polymer graft was first introduced onto the fiber through electron beam irradiation technique. GMA-grafted fiber was subsequently functionalized with imidazole (IMI) group through epoxide ring-opening reaction where amine density of 2.00 mmol/g was achieved. The adsorbent was characterized with Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (ATR-FTIR), and Thermogravimetric Analyzer (TGA). An extensive kinetic and mechanistic study on the adsorptive removal of metal ions (Cu2+, Pb2+ and Zn2+) by IMI-functionalized GMA-grafted banana fiber is presented. The effects of pH and initial concentration on adsorption capacity were investigated. The adsorption data were correlated with pseudo-first and second order model and the isotherms were analyzed with Langmuir and Freundlich model in order to explain the kinetics and adsorption mechanisms of different metal ions. The thermodynamic studies revealed that the adsorption process for metal ions was exothermic. We also demonstrated that the IMI-GMA-grafted fiber can be regenerated using dilute HNO3 solution, and can be recycled up to 10 times while maintaining satisfactory adsorption performance. Lastly, the chemically modified bio-sorbent was used to treat a local domestic sewage water.

Polyethylenimine modified graphene oxide hydrogel composite as an efficient adsorbent for heavy metal ions

Graphene oxide embedded calcium alginate (GOCA) beads were synthesized and further functionalized/reduced with polyethylenimine to increase their adsorption capacity towards heavy metal ions. The adsorption of metal ions such as Pb (II), Hg (II) and Cd (II) from aqueous solutions on the functionalized GOCA was studied under different experimental conditions and the results showed that the functionalized beads had high adsorption capacity compared to the non-functionalized beads. The maximum uptake of heavy metal ions was 602, 374, 181 mg/g for Pb (II), Hg (II) and Cd (II) ions respectively. The kinetics were found to follow the pseudo-second-order and the equilibrium data fitted well with the Langmuir adsorption isotherm. Thermodynamic parameters such as standard Gibbs Energy (ΔG0), standard enthalpy (ΔH0) and standard entropy (ΔS0) changes were calculated. Adsorption-desorption studies were carried out successfully up to five cycles using a mixture of HCl (pH 5) and 200 ppm CaCl2 solution as eluent. The newly synthesized beads showed superior metal ion removal capacity compared to alginate beads and polyethylenimine functionalized GO combined capability due to synergetic effect. The results suggest that the functionalized graphene oxide in calcium alginate bead matrix can be efficiently used as an adsorbent for metal ions removal from wastewater.