Removal of Copper(II) and Zinc(II) from Aqueous Solutions Using a Lignocellulosic-Based Polymeric Adsorbent Containing Amidoxime Chelating Functional Groups

In this study, the adsorption of Cu(II) and Zn(II) ions from aqueous solutions onto amidoximated polymerized banana stem (APBS) has been investigated. Infrared spectroscopy was used to confirm graft copolymer formation and amidoxime functionalization. The different variables affecting the sorption capacity such as pH of the solution, adsorption time, initial metal ion concentration, and temperature have been investigated. The optimum pH for maximum adsorption was 10.5 (99.99%) for Zn²⁺ and 6.0 (99.0%) for Cu²⁺ at an initial concentration of 10 mg L^?1. Equilibrium was achieved approximately within 3 h. The experimental kinetic data were analyzed using pseudo-first-order and pseudo-second-order kinetic models and are well fitted with pseudo- second-order kinetics. The thermodynamic activation parameters such as ΔG^o, ΔH^o, and ΔS^o were determined to predict the nature of adsorption. The temperature dependence indicates an exothermic process. The experimental isotherm data were well fitted to the Langmuir model with maximum adsorption capacities of 42.32 and 85.89 mg g^?1 for Cu(II) and Zn(II), respectively, at 20°C. The adsorption efficiency was tested using industrial effluents. Repeated adsorption/regeneration cycles show the feasibility of the APBS for the removal of Cu(II) and Zn(II) ions from water and industrial effluents.     

Utilization of waste plastic pet bottles to prepare copper-1,4-benzenedicarboxylate metal-organic framework for methylene blue removal

ABSTRACT

The study aims to use waste plastic PET bottles to recover terephthalic acid for preparing copper-1,4-benzenedicarboxylate, which was then utilized as an adsorbent for removal of methylene blue (MB) from aqueous solutions after carefully characterizing by XRD, FTIR, TGA, SEM, and EDX. The optimum conditions were established as pH = 6, 25°C, adsorbent dose of 1 g L^?1, contact time of 20 min, and agitation speed of 150 rpm. The adsorption process was spontaneous, exothermic, fitting well to Langmuir isotherm model with the maximum adsorption capacity of 41.01 mg g^?1 and more suitable to be described by the pseudo first-order kinetic model. It was indicated that the physical adsorption plays a leading role in the adsorption process. The recycling study was also conducted to confirm the long-term use of the synthesized adsorbent.     

Equilibrium Isotherms,Thermodynamics, and Kinetic Studies for the Adsorption of Food Azo Dyes onto Chitosan Films

The adsorption of FD&C red 2 and FD&C yellow 5 onto chitosan films (CFs) was evaluated by equilibrium isotherms, thermodynamics, and kinetic studies. The effects of temperature (298–328 K), initial dye concentration (50–300 mg L^?1), stirring rate (50–350 rpm), and contact time (0–120 min) were investigated at pH of 2.0 and 100 mg L^?1 of CFs. The dye concentration was determined by spectrophotometry. Freundlich and Langmuir models were used to represent the equilibrium data. The Langmuir model was the more adequate to represent the equilibrium data (R² > 0.99 and average relative error <2.50%) and the maximum adsorption capacities were 494.13 and 480.00 mg g^?1 for FD&C red 2 and FD&C yellow 5, respectively, obtained at 298 K. The R_L values ranged from 0.044 to 0.145. The adsorption was exothermic, spontaneous, and favorable. For the FD&C red 2, 90% of saturation was attained at 120 min and the Elovich model was the more appropriate. For the FD&C yellow 5, 95% of saturation was attained at 20 min and the pseudo first-order model was the more adequate to fit the kinetic data. CFs were easily separated from the liquid phase after the adsorption process, providing benefits for industrial applications, and its application range can be extended for azo dyes.     

Regression model,artificial intelligence,and cost estimation for phosphate adsorption using encapsulated nanoscale zero-valent iron

This study investigated the adsorption of PO₄^3? onto encapsulated nanoscale zero-valent iron (nZVI). At initial PO₄^3–: 10 mg · L^?1, the optimum condition was initial pH: 6.5, nZVI dosage: 20 g · L^?1, stirring-rate: 100 rpm, and time: 30 min, achieving PO₄^3? removal of 42%. The effect of pH and time on the PO₄^3? removal efficiency was quadratic-linear concave up, whereas the curve of nZVI dosage was quadratic-convex. Artificial neural network with a structure of 5?7?1 adequately predicted PO₄^3? removal (R²: 97.6%), and the sensitivity analysis demonstrated that pH was the most influential input. The cost of the adsorption unit was 3.15 $USD · m^?3.     

Removal of Orange II by Phosphonium-modified Algerian Bentonites

An Algerian montmorillonite was modified with two organic surfactants, methyltriphenyl phosphonium bromide and n-hexyltriphenyl phosphonium bromide. The solids obtained were used as adsorbents to remove Orange II, an anionic dye from aqueous solutions. Batch experiments were conducted to study the effects of temperature (20–60°C), initial concentration of adsorbate (50–150 mg L^?1) and pH of solution 6.5 on dye adsorption. Due to their organophilic nature, exchanged montmorillonites were able to adsorb Orange II at a very high level. Adsorption of Orange II for B-NHTPB and B-MTPB at different pH show that the adsorption capacity clearly decreases with an increase in pH of the initial solution from 2 to 8, this decrease being dramatic for pH > 8. This may be due to hydrophobic interactions of the organic dye with both phosphonium molecules and the remaining non-covered portion of siloxane surface. The kinetics of the adsorption was discussed on the basis of three kinetic models, i.e., the pseudo-first-order, the pseudo-second-order, and the intraparticle diffusion models. Equilibrium is reached after 30 min and 60 min for B-MTPB and B-NHTPB, respectively; the pseudo-second-order kinetic model described very well the adsorption of Orange II on modified bentonites. The non-linear Langmuir model provided the best correlation of experimental data, maximum adsorption of Orange II is 53.78 mg g^?1 for B-NHTPB and 33.79 mg g^?1 for B-MTPB. The thermodynamic parameters, such as free energy of adsorption (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were also determined and evaluated. From thermodynamic studies, it was deduced that the adsorption was spontaneous and exothermic.     

Activated carbon derived from macadamia nut shells: an effective adsorbent for phenol removal

In this study, activated carbon based on the waste macadamia nut shells (MAC) was investigated for potential use as an adsorbent for phenol removal. The pseudo second-order kinetic model best described the adsorption process. The extent of the phenol adsorption was affected by the pH solution and the adsorbent dosage. Equilibrium data fitted well to the Langmuir model with a maximum adsorption capacity of 341 mg g^?1. The calculated thermodynamic parameters suggested that the phenol adsorption onto MAC was physisorptive, spontaneous and exothermic in nature. Phenol desorption from loaded adsorbent was achieved by using 0.1 mol L^?1 NaOH, ethanol (100 %) and deionized water.     

Hydrothermal synthesis of mesoporous TiO<Subscript>2</Subscript> nanotubes and their adsorption affinity toward Basic Violet 2

Hydrothermal method was used to synthesize TiO₂ nanotubes (TNTs), which are considered as a novel adsorbent with high surface area and adsorption capacity. Different methods including X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) analysis were used to investigate and identify synthesized TNTs. The adsorption capacity of TNTs was investigated with regard to removing Basic Violet 2 (BV2) as a model organic pollutant from aqueous solution. The mean outer, inner diameter and thickness of the TNTs were found to be approximately 9, 4 and 2.5 nm, respectively. BET–BJH method was used for measuring specific surface area and pore volume of the TNTs which turned out to be 200.38 m² g^?1 and 0.44 cm³ g^?1, respectively. The results of the study indicated synthesized TNTs may be considered as efficient and effective adsorbent for removing BV2 (75.63%) from aqueous solution. The impact of the operational variables, i.e. initial BV2 concentration (2–20 mg L^?1), dosage of adsorbent (0.01–0.6 g), and pH (2–8) in relation to the adsorption capacity of BV2 onto TNTs were investigated. The experimental results of the study were meticulously taken into consideration for discussing and analyzing the adsorption isotherms and kinetics. It was found that the collected experimental data regarding the kinetic and isotherm examinations were compatible and well-matched with the pseudo-first order kinetic model and Langmuir isotherm model (R ²?=?0.9634).     

Removal of Orange II from Aqueous Solutions Using N-Vinyl Imidazole-based Hydrogels as Adsorbents

Poly(N-vinyl imidazole) hydrogel (p-VIm) and its partially quaternized analogue (p-VIm-Ar) were prepared and used for the removal of Orange II (OII). A fourier transform infrared spectrophotometer, scanning electron microscope with an energy dispersive X-ray spectrometer attached, thermogravimetric analyzer, zeta potential analyzer, and a drop shape analyzer were used for the characterization of the hydrogels. The influence of some experimental parameters, such as pH of the OII solution, contact time, and initial OII concentration on the adsorption process, was examined, and the obtained data were used to calculate the isotherm and kinetic parameters. Adsorption processes of OII onto adsorbents were coherent with the Langmuir isotherm and pseudo-second-order kinetic models. The quaternized analogue exhibited remarkable adsorption performance in the pH range of 2–12, while the effective adsorption with p-VIm occurred only at pH 2.0. The maximum adsorption capacity values of adsorbents were determined as 2331 (for p-VIm) and 1327 mg g^?1 (for p-VIm-Ar) at pH 2.0 and 132 (for p-VIm) and 1357 mg g^?1 (for p-VIm-Ar) at pH 6.0.     

Removal of Rhodamine B Dye Using Activated Carbon Prepared from Palm Kernel Shell and Coated with Iron Oxide Nanoparticles

The efficacy of activated carbon prepared from Palm Kernel Shell (PKSAC) from agriculture biomass and coated with magnetic nanoparticle (Fe₃O₄) in the removal of Rhodamine B dye was investigated. Adsorption experiments were carried out at various initial pH, adsorbent dosage, initial dye concentration, particle size, and temperature. Kinetic analyses were conducted using pseudo first order, pseudo second order and intra particle diffusion models. However, the regression results showed that the adsorption kinetics was represented more accurately by the pseudo second order model. The pseudo second order kinetic constant obtained was 1.7 × 10^?4 min^?1 at 323 K when 200 mg L^?1 dye concentration was used. The equilibrium data were well described by both Langmuir and Freundlich isotherm models. The Langmuir adsorption capacity was 625 mgg^?1. The rate of adsorption improved with increasing temperature and the process was endothermic with ΔH value assessed at 80 kJmol^?1. Results obtained reveal that activated carbon prepared from Palm Kernel Shell coated with magnetic nanoparticle from agriculture biomass can be an attractive option for dye removal from industrial effluent.     

Application of mesoporous magnetic nanosorbent developed from macadamia nut shell residues for the removal of recalcitrant melanoidin and its fractions

ABSTRACT

A novel mesoporous magnetic nanosorbent developed from macadamia nut shell residues was applied as an adsorbent for the removal of dissolved organic carbon (DOC) associated with melanoidin and its fractions in a batch system. The most favored molecular fraction of the melanoidin for adsorption onto the nanosorbent was 1–5 kDa with adsorption capacity of 10.26 mg DOC g^?1 achieving 68.4% removal efficiency. The sorption behaviors were all well fitted to a pseudo-second-order kinetic model and Langmuir isotherm. Optimum operating conditions needed for the maximum uptake of 14.7 mg DOC g^?1 were found to be pH of 6.3, temperature of 41.7°C at the dosage of the magnetic nanosorbent of 877.7 ppm.     

Equilibrium modeling,kinetic and thermodynamic studies on the adsorption of Cr(VI) using activated carbon derived from matured tea leaves

A new porous carbon with high surface area of 1,313.41 m² g^?1 with pore volume 1.359 cm³ g^?1 has been synthesized from matured tea leaves by chemical activation method using phosphoric acid. The carbon was found to be highly efficient for removal of Cr(VI) from aqueous solution. The effects of various parameters such as contact time, initial metal ion concentration, pH, temperature and amount of adsorbent on the extent of adsorption were studied. Langmuir, Freundlich and Temkin adsorption models were used to interpret the experimental data. The adsorption data were best fitted with Langmuir isotherm model. The adsorption capacity of Cr(VI) onto the activated carbon calculated from Langmuir isotherm was found to be 30.8 mg g^?1 at pH 4.8 and temperature 303 K. The adsorption capacity increases from 25.36 to 32.04 mg g^?1 with an increase in temperature from 303 to 323 K at initial Cr(VI) concentration of 60 mg L^?1. The adsorption process followed a pseudo second order kinetic model. Thermodynamic parameters ΔH⁰ (28.6 KJ mol^?1), ΔG⁰ at three different temperatures [(?0.145, ?1.09, ?2.04) KJ mol^?1] and ΔS⁰ (94.87 J mol^?1 K^?1) were calculated. These values confirm the adsorption process to be endothermic and spontaneous in nature.     

Physicochemical Aspects on Fluoride Adsorption for Removal from Water by Synthetic Hydrous Iron(III) – Chromium(III) Mixed Oxide

Fluoride removal with varying different parameters at 303 ± 1.6 K and pH 6.5 ± 0.2 was investigated by hydrous iron(III)-chromium(III) bimetal oxide. The kinetic and equilibrium data fitted with the pseudo-second order and Langmuir isotherm equations very well (R² = 0.99?1.00), respectively. The Langmuir capacity (θ) and free energy (E_DR) of adsorption evaluated were 16.34 (±0.50) mg·g^?1 and 15.81 kJ·mol^?1, respectively. The estimated thermodynamic parameters viz. ΔH⁰, ΔG⁰, and ΔS⁰ indicated that the reaction was endothermic but spontaneous for entropy increase. The small-scale column filtration of high fluoride (C₀ = 7.37 mg·L^?1) water gave encouraging results.     

Nanocomposite Bead (NCB) Based on Bio-polymer Alginate Caged Magnetic Graphene Oxide Synthesized for Adsorption and Preconcentration of Lead(II) and Copper(II) Ions from Urine,Saliva and Water Samples

The present study describes the successful fabrication of bio-polymeric nanocomposite bead (NCB) of alginate caged magnetic graphene oxide (Alg-MGO). NCB was obtained by crosslinking of sodium alginate and calcium ions in the presence of MGO. Analytical techniques Fourier transform infra-red (FT-IR), field emission scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the Alg-MGO. Analytical application is conducted with magnetic solid phase extraction (MSPE) method for determination of Cu(II) and Pb(II) in urine, saliva and river water sample. The linear concentration range obtained were 0.33–25.00 µg L^??1 with appropriate coefficient of determination (R²?=?0.99) and low limit of detection (LOD?=?0.21–0.71 µg L^??1, n?=?3). The newly developed MSPE-NCB was successfully validated with standard reference material (SRM 2670a, NIST). Metal ions removal process was studied at high concentration level (1–200 mg L^??1) and isotherm models were applied. Langmuir isotherm is well fitted to experiments due to high value of coefficient of determination (R²) and proper adsorption capacity 96.13 and 103.09 mg g^??1 obtained for Cu(II) and Pb(II), respectively. Thermodynamic model is suggested spontaneous process, endothermic nature and physical sorption mechanism for uptake of selected metal ions from aqueous solution.     

Starch/rice husk ash based superabsorbent composite: high methylene blue removal efficiency

Superabsorbent hydrogels composites based on the biopolymer starch (ST) and rice husk ash (RHA) were successfully developed and tested towards the removal of methylene blue (MB), a cationic dye. RHA content hit the morphology, mechanical and water uptake properties of the composite. Batch adsorption experiments, carried out under pH 5 at 33 °C and with 2000 mg L^?1 as the initial concentration of MB, showed that at 5 wt% RHA the composite exhibited a remarkable adsorption capacity reaching up to 1906.3 mg g^?1 within 60 min. The adsorption kinetics followed the pseudo-second-order model and intraparticle diffusion was involved in this process. The Langmuir adsorption isotherm suggested a monolayer formation and spontaneous process. Thermodynamic parameters confirmed the spontaneity of the adsorption and suggested electrostatic interaction among the cationic dye molecules and the anionic adsorption sites on the adsorbent surface. FTIR analysis confirmed the adsorption process occurs via electrostatic mechanism associated with hydrophobic interactions. The adsorbents showed reusability with slight loss of adsorption capacity in five consecutive adsorption/desorption cycles. These results demonstrate ST/RHA superabsorbent composite as a low-cost, eco-friendly, robust and powerful adsorbent material for wastewater remediation.     

Dynamics and Thermodynamics Studies on the Lead and Cadmium Removal from Aqueous Solutions by Padina sp. Algae: Studies in Single and Binary Metal Systems

Raw and modified biomasses prepared from Padina sp. algae have been used as sorbent for the removal of lead and cadmium from single and binary aqueous solutions. The effects of chemical pretreatment, exposure time, initial solution pH, initial metal concentration, and temperature on the metal uptake by the algae were investigated. It was observed that initial solution pH considerably influenced Pb and Cd uptake. The maximum removal occurred at initial pH of 5.0 for lead and 6.0 for cadmium. Also, alkali modified biomass has been shown to have a high uptake capacity for both lead and cadmium. The kinetic and equilibrium experimental data fitting tested with various models. The pseudo-first-order kinetic model and Langmuir isotherm provided the best correlation of the kinetic and equilibrium experimental data, respectively. The maximum uptake estimated from the Langmuir isotherm was 264 mg g^?1 for lead and 164 mg g^?1 for cadmium ions. Experimental biosorption data in binary system were well described by the extended Langmuir model. Various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS° were calculated.     

Fe2+-modified Vermiculite for the Removal of Chromium (VI) from Aqueous Solution

A novel adsorbent: Fe²⁺-modified vermiculite was prepared in a two-step reaction. Adsorption experiments were carried out as a function of pH, contact time, and concentration of Cr(VI). It was found that Fe²⁺-modified vermiculite was particularly effective for the removal of Cr(VI) at pH 1.0. The adsorption of Cr(VI) reached equilibrium within 60 min, and the pseudo-second-order kinetic model best described the adsorption kinetics. The adsorption data follow the Langmuir model more than the Freundlich model. At pH 1.0, the maximum Cr(VI) sorption capacity (Q _max ) was 87.72 mg · g^?1. Desorption of Cr(VI) from Fe²⁺-modified vermiculite using NaOH treatment exhibited a higher desorption efficiency by more than 80%. The sorption mechanisms including electrostatic interaction and reduction were involved in the Cr (VI) removal. The results showed that Fe²⁺-modified vermiculite can be used as a new adsorbent for Cr(VI) removal which has a higher adsorption capacity and a faster adsorption rate.     

Competitive Separation of Lead,Cadmium, and Nickel from Aqueous Solutions Using Activated Carbon: Response Surface Modeling,Equilibrium, and Thermodynamic Studies

In this study, the competitive separation of lead, cadmium, and nickel ions from aqueous solutions using a commercial activated carbon (AC) has been investigated and optimized using response surface methodology (RSM). The optimal conditions to reach the highest adsorption capacity for these metals were found as follows: initial pH = 6.3, temperature = 56.8°C, and shaking speed = 308 rpm. Under these conditions, the sequence of adsorption capacity toward the metal ions was as follows: Pb (II): 9.44 mg g^?1 > Cd (II): 9.37 mg g^?1 > Ni (II): 4.52 mg g^?1. The effect of shaking speed on the adsorption capacity of AC was higher than the effects of the initial pH and temperature, indicating the more important role of physisorption than chemisorption in the adsorption of these metal ions. This was confirmed by the results of thermodynamic studies. The equilibrium adsorption data were fitted to the Freundlich, Langmuir adsorption isotherm models and the Dubinin–Radushkevich model parameters were evaluated. All the models were tested and all were shown to represent the experimental data satisfactorily. The thermodynamic parameters such as ΔH, ΔS, and ΔG were computed from the experimental data. These values show that the adsorption is endothermic and spontaneous. The positive value of ΔS° indicates increasing of randomness at the solid/liquid interface during the adsorption of metal ions on AC.     

Synthesis and application of amine functionalized silica mesoporous magnetite nanoparticles for removal of chromium(VI) from aqueous solutions

In this research, novel nanoparticles of Kit-6 mesoporous silica magnetite were synthesized with 9.6 nm pore diameter and 241.68 m² g^?1 surface area. The synthesized mesoporous magnetite nanoparticles (MMNPs) were functionalized with amine groups. Scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption method confirmed the morphology and structure of the synthesized nanoparticles. The amine functionalized MMNPs were used for sorption of toxic chromate ions from aqueous samples. The effect of various experimental parameters (four factors at three levels) on the sorption efficiency of Cr(VI) was studied and optimized via Taguchi L₉ (3⁴) orthogonal array experimental design. At optimum conditions, the sorption of the Cr(VI) was best described by a pseudo second-order kinetic model with R² = 0.9999 and q_eq = 129.8 mg g^?1, suggesting chemisorption mechanism. Adsorption data were fitted well to the Langmuir isotherm and the synthesized sorbent showed complete ion removal with 185.2 mg g^?1sorption capacity.     

Synthesis and swelling behavior of metal-chelating superabsorbent hydrogels based on sodium alginate-<Emphasis Type="Italic">g</Emphasis>-poly(AMPS-<Emphasis Type="Italic">co</Emphasis>-AA-<Emphasis Type="Italic">co</Emphasis>-AM) obtained under microwave irradiation

A metal-chelating superabsorbent hydrogel based on poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) grafted onto sodium alginate backbone, NaAlg-g-poly(AMPS-co-AA-co-AM) is prepared under microwave irradiation. The Taguchi method is used for the optimization of synthetic parameters of the hydrogel based on water absorbency. The Taguchi L₉ (3⁴) orthogonal array is chosen for experimental design. Mass concentrations of crosslinker MBA \(C_{\text{MBA}}\) initiator KPS \(C_{\text{KPS}}\), sodium alginate \(C_{\text{NaAlg}}\) and mass ratio of monomers \(C_{\text{AM/AA/AMPS}}\) are chosen as four factors. The analysis of variance of the test results indicates the following optimal conditions: 0.8 g L^?1 of MBA, 0.9 g L^?1 of KPS, 8 g L^?1 of NaAlg and \(R_{\text{AM/AA/AMPS}}\) equals to 1:1.1:1.1. The maximum water absorbency of the optimized final hydrogel is found to be 822 g g^?1. The relative thermal stability of the optimized hydrogel in comparison with sodium alginate is demonstrated via thermogravimetric analysis. The prepared hydrogel is characterized by FTIR spectroscopy and scanning electron microscopy. The influence of the environmental parameters on water absorbency such as the pH and the ionic force is also investigated. The optimized hydrogel is used as adsorbent for hazardous heavy metal ions Pb(II), Cd(II), Ni(II) and Cu(II) and their competitive adsorption is also discussed. Isotherm of adsorption and effect of pH, adsorption dosage and recyclability are investigated. The results show that the maximum adsorption capacities of lead and cadmium ions on the hydrogel are 628.93 and 456.62 mg g^?1, respectively. The adsorption is well described by Langmuir isotherm model. The hydrogel is also utilized for the loading of potassium nitrate as an active agrochemical agent and the release of this active agent has also been investigated.