Adsorbent For Adsorption Research Articles

ADSORBENT MATERIALS FOR EMERGING CONTAMINANT (TETRACYCLINE) REMOVAL

Water pollution is a serious environmental problem caused by activities. A group of pollutants that are not controlled in the environment but that cause harmful effects on the ecosystem are known as emerging pollutants. One of these groups of emerging pollutants detected in water bodies are pharmaceutical compounds. One of the main problems caused by pharmaceutical compounds as pollutant is bacterial resistance. are a family of antibiotics frequently used. Due to their poor absorption they are released into the environment through feces and urine as active ingredients. Wastewater treatment consists in three stages: primary, secondary, and tertiary treatment. Tertiary treatment employs methods such as reverse osmosis, oxidation-reduction, ultraviolet irradiation, and adsorption. Adsorption is used because it is a simple and effective. For the choice of an effective adsorbent material, surface area, porosity, adsorption capacity, mechanical stability, and factors such as profitability, regeneration, sustainability, and selectivity are considered. In the present review, the adsorbents commonly used in the treatment of water contaminated with were analyzed. The adsorbents used have been classified in a general way as metallic materials, polymers, ceramics, composites, and materials based on biomass.

Hydrophobic polymer tethered magnetic zirconium-based metal-organic framework as advance and recyclable adsorbent for microwave-assisted extraction of polycyclic aromatic hydrocarbons from environmental water samples

Hydrophobic poly (glycidyl methacrylate) tethered magnetic amino-functional zirconium metal-organic framework (UiO-66-NH2) was fabricated for the first time for rapid microwave-assisted magnetic solid-phase extraction of trace polycyclic aromatic hydrocarbons from environmental water samples. UiO-66-NH2 endowed the nanocomposite with remarkable specific surface area (175.2 m2/g) and short diffusion route, while poly (glycidyl methacrylate) provided hydrophobic interaction towards hydrophobic polycyclic aromatic hydrocarbons, both of which contributed to the satisfactory extraction performance. The successful preparation of the nanocomposite was confirmed by transmission electronic microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption experiment, powder X-ray diffraction patterns, contact angle measurement and vibrating sample magnetometry. In addition, an optimized protocol for microwave-assisted magnetic solid-phase extraction was carried out, including adsorbent amount (20–160 mg), adsorption time (30–150 s), desorption time (10–80 s) and desorption solvents (methanol, acetonitrile, acetone and ethyl acetate). Under the most favorable conditions, the microwave-assisted method afforded magnetic solid-phase extraction with short extraction time (1 min), a wide linear response (1.56–200 μg/L), good linearity (R2 ≥ 97.83%), low limits of detection (0.04–4.68 μg/L) and good precision (RSD ≤ 6.39%) for six polycyclic aromatic hydrocarbons. The proposed method was successfully applied in analysis of real water samples with mean recoveries in the range of 82.6–118.4% at three spiked levels and the relative standard deviations less than 10.7%. The results indicated that our developed method had great potential in enrichment and detection of trace polycyclic aromatic hydrocarbons in real aqueous samples.

Sequential experimental designs for discrimination among adsorption equilibrium models

Sequential experimental designs for model discrimination were used for the selection of the most appropriate adsorption isotherm for describing the adsorption of tartrazine onto magnesium oxide and of methyl orange onto activated carbon. Typical adsorption equilibrium models were considered. For the adsorption of tartrazine, it was observed that the sequential approach permitted the re-evaluation of the considered models, as new information was acquired, allowing the inclusion of models not considered initially. For the adsorption of methyl orange, it was observed that model discrimination was achieved only after five additional experiments. These results showed that the use of sequential experimental designs allowed the effective selection of experimental conditions for model discrimination, which might not be possible without the optimization of the design criterion. In both cases, the BET isotherm was the selected model, indicating that adsorption of both adsorbates onto different solids occurs with multilayer formation.

The experimental test of the best abasorbents for controlling poly aromatic hydrocarbon on sea water around graving dock and hhip loading terminal

Bentonite and zeolite adsorbents have the ability to adsorb PAH content around the shipyard and ship loading and unloading areas. The factors that potentially affect the level are: a. The types of bentonite and zeolite adsorbents, b. Sampling time is 0, 2, 4, 6 and 8 hours. Adsorption of poly aromatic hydrocarbon by zeolite adsorbent as much as 150 gram done at certain place with volume of 3 liters of sea water taken from ship loading and unloading terminal area and at time variable 0, 7, 14, 28 and 42 days. Measurement of PAH on day 0 by way of direct examination of sea water concentration and PAH type. Determination of the best adsorbent, seen from the ability of the absorption of PAH both in the high concentration and the number of PAH types adsorbed, the results showed that zeolite adsorbents have better adsorption capacity because it has sufficient surface area and does not clot when exposed to water. The concentration of sea water PAH at ship loading and unloading terminal is very high, that is 65,45ppb, especially for PAH type of naphthalene and 2-Bromonaphthalene ie 28,3255 and 27, 2821ppb respectively. The ability of zeolite adsorbent and maximum adsorption of PAH at 28 days adsorption, ie 19, 75ppb is dominated by Benzo(a)pyrene type PAH with concentration of 19,2771ppb. Based on Linear Regression test to total PAh, it can be concluded that the value of R Square 0,190511343 which shows that the absorption time by zeolite absorbent and absorption power of poly aromatic hydrocarbons compound of the whole types has no significant effect. Therefore, polynomial testing is done through the equation y = -8,959x^3+62,858x^2-125,49x+72,379 yield value R^2= 1 which means absorption of 100% polyaromatic hydrocarbons compound in time.

MG@PD@TiO2 nanocomposite based magnetic solid phase extraction coupled with LC–MS/MS for determination of lysophosphatidylcholines biomarkers of plasma in psoriasis patients

Lysophosphatidylcholine (LPC) was commonly known as a class of significant differential metabolites of high relevance with many diseases including psoriasis, of which the accurate determination is of great importance to diagnosis or prediction to many diseases. However, it is challenging and complicated because of the enormous biological sample complexity and impurities interference. In this study, we synthesized a magnetic nanocomposite MG@PD@TiO2 and took advantage of the interactions of Lewis acid−base between the phosphate groups in LPCs and Ti ions on MG@PD@TiO2 nanomaterials for selective separation and enrichment of LPCs from complex biological matrix. The solid-phase extraction sample pretreatment process by means of MG@PD@TiO2 nanomaterials coupled with LC–MS/MS method was then applied to actual determination of six typical LPCs (LPC 10:0, 14:0, 16:0, 18:0, 18:1, 22:0) in human plasma. The extraction conditions were scientifically optimized by single-factor test (adsorbent amount, adsorption and desorption time, elution solvent type, eluant volume). Under the optimal conditions, the detection limits (LOD, S/N = 3) and quantification limits (LOQ, S/N = 10) were 1 and 5 ng/mL for LPC 10:0 and LPC 14:0, 0.02 and 0.1 ng/mL for LPC 16:0 and LPC 18:1, 0.05 and 0.2 ng/mL LPC 18:0 and LPC 22:0, respectively. The intra- and inter-day precisions were 3.82–12.60 % (n = 6) and 3.29–13.50 % (n = 6) respectively, the recoveries were in the range of 91.92–113.69 % and the stability of the analytes in the matrix performed well with RSDs≤15.51 %. Finally, the developed method was successfully applied to the accurate determination of six LPCs biomarkers of plasma in patients with psoriasis (n = 10) and control groups (n = 10).

Removal of methylene blue dye in water by using recoverable natural zeolite/Fe3O4 adsorbent

<p>In this paper, the low-cost and practical adsorption for removing methylene blue (MB) dye has been developed by using recoverable natural zeolite that was magnetized with Fe3O4. The magnetization was conducted by co-precipitation technique. The adsorbents obtained from the magnetization were characterized by XRD, FTIR, surface area analyzer and turbidity meter machines. The MB adsorption on the recoverable adsorbent was performed by batch experiment. The effect of Fe3O4 fraction on adsorbent characters, recoverability, and adsorption ability was evaluated. The adsorption kinetic and isotherm were also determined. The research results attributed that recoverable zeolite/Fe3O4 adsorbent has been successfully produced. It was found that the increase of Fe3O4 fraction in the adsorbent, has improved the recoverability, but in the same time, it caused the adsorption decreased. The fraction of Fe3O4 as much 33.30%w displayed compromisingly good capacity and recoverability. The maximum MB dye adsorption was reached by a condition of 0.25 g L-1 of the adsorbent dose, pH 8, and in 60 mins of the contact time The adsorption kinetic well fitted with pseudo second-order with the adsorption rate of 0.0238 mg g-1 min-1. The adsorption strongly agreed with the Langmuir isotherm with adsorption capacity of 32.258 mg g-1 .</p>

Preparation and characterization of wheat straw biochar loaded with aluminium/lanthanum hydroxides: a novel adsorbent for removing fluoride from drinking water

ABSTRACT In this work, a novel adsorbent of aluminium/lanthanum loaded wheat straw biochar (Al-La-WSB), was prepared by using a facile approach and used for fluoride removal. The Al-La-WSB and its pristine wheat straw biochar (WSB) were characterized by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray powder diffraction (XRD) methods. Batch adsorption experiments were carried out to investigate adsorbent performance, the highest removal rate was observed at pH 9, contact time of 7 h and Al-La-WSB dose of 1 g L−1. Lagergren pseudo-second-order kinetics and Langmuir isotherm model fitted the experimental data well. The maximum fluoride adsorption capacity of Al-La-WSB at different experiment temperature of 298, 308 and 318 K, was 51.28 mg g–1, 46.73 mg g–1 and 50.25 mg g–1, respectively, which was better than most reported adsorbents. The Al-La-WSB performed well over a considerable wide pH range of 3–10 and carried positive charge at pH < 4.8. The presence co-existing ions of SO4 2−, HCO3 −, Cl− and NO3 − had a minor impact on fluoride adsorption besides PO4 3−. Regeneration experiment results showed that the Al-La-WSB had an excellent reusability. According to the adsorbent characterization and batch adsorption experiment, the adsorption of fluoride on the Al-La-WSB was primarily a chemisorption, involving electrostatic interactions and ion exchange, which nitrate ion and hydroxyl played a major role. The results suggested that the Al-La-WSB could be a great adsorbent for removing fluoride from drinking water.

Correlating the Adsorption Preference and Mass Transfer of Xenon in RHO-Type Molecular Sieves

The adsorption and diffusion of adsorbates or reactants are the most essential steps in zeolite-based processes for gas separation and catalysis. An explicit description of the relationship between...

Current approaches and methodologies to explore the perceptive adsorption mechanism of dyes on low-cost agricultural waste: A review

Discharging of dyes containing effluents into water bodies has severely affected various forms of life because of their carcinogenic nature. Many conventional methods have been failed to treat the dyes contaminated water due to their less effectivity or economically not feasible. Among different techniques, adsorption is gaining importance in pollutant management due to its low operating cost, universal nature, and ease of operation. This review article highlights the feasibility of agricultural waste material in its natural and modified form as a low-cost adsorbent for the treatment of dyes and the preparation of the activated carbon (AC) and their dye adsorption characteristics. This review paper also illustrates the effectiveness of operational parameters, kinetics, and isotherm models to understand the adsorbent behavior and adsorption mechanism. The importance of response surface methodology (RSM) programmed in optimizing the adsorption process to remove dyes was also discussed. Moreover, the discussion on challenges and prospects about adsorption technology for future research such as exploitation of agricultural wastes on a commercial scale, building economy incentive standards, designing the methodologies, and eco-friendly ways to recycle the wastes were proposed. • Exploration of agricultural waste as an efficient adsorbent for the removal of dye. • Extensive discussion of Response surface modeling associated with adsorption process. • Summarized the adsorption mechanism, isotherm and kinetic models. • Influence of the operational parameters on adsorption process was investigated. • Future prospects were also discussed.

Determination of organochlorine pesticides in water using GC combined with dispersive solid-phase extraction with single-walled carbon nanotubes

SummaryIn this study, single-walled carbon nanotubes (SWNTs) were used to determine organochlorine pesticides (chlorothalonil and pentachloronitrobenzene) in water using dispersive solid-phase extraction (DSPE), followed by gas chromatography (GC). The optimal adsorption conditions were determined by analyzing the effect of adsorbent dosage, adsorption time, eluent type and volume, and elution time. Under the optimal conditions, a good linearity was obtained at concentrations from 10 to 400 μg L−1 with correlation coefficients ranging from 0.9991 to 0.9986. The limits of detection (LOD) for the two organochlorine pesticides were 0.025 and 0.049 μg L−1, and the limits of quantification (LOQ) were 0.080 and 0.156 μg L−1, respectively. The accuracy of the proposed method was evaluated by measuring the recovery of the spiked samples, which ranged from 82.5% to 110.5% at spiking levels of 0.5–10 μg L−1 with relative standard deviations lower than 5.6% (n = 6). This method was successfully applied to determine the target analytes in canal water, drinking water, and water taken from the inlets and outlets of a wastewater treatment plant. The results demonstrate that the developed method has great potential for determining the two organochlorine pesticides in water samples.

Hydrothermally treated aluminosilicate clay (HTAC) for remediation of fluoride and pathogens from water: Adsorbent characterization and adsorption modelling

Presence of fluoride and pathogen in drinking water is an issue of concern due to their health effects and as such much effort is being directed towards finding sustainable material for use in water treatment. Adsorption based water treatment techniques are often considered as the most effective and easy to use in rural set up. However, most of the adsorbents are not multifunction and are only effective towards fluoride. In this study aluminosilicate activated clay was hydrothermally treated and applied for fluoride and pathogen removal from water. Fourier transform infrared (FTIR), Brunauer-Emmett-Teller method (BET), X-ray diffraction spectroscopy (XRD) and Scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS) techniques were employed to characterize hydrothermally treated aluminosilicate clay (HTAC). Batch defluoridation experiments were used to evaluate the fluoride removal efficiency while well diffusion assay method was used to evaluate the antimicrobial efficiency. The BET results showed increase in surface area from 17.19 m2/g to 33.56 m2/g after treatment. Batch defluoridation showed maximum adsorption capacity of 1.75 mg/g with 53% fluoride removal from initial fluoride concentration of 6 mg/L using 0.8 g/40 mL dosage at initial pH 5.8 and contact time of 5 min at room temperature. The adsorption kinetics data showed a better fit to pseudo-second order model while the adsorption isotherm data showed correlation coefficient and chi-square values of 0.98 and 0.01, respectively indicating a better fit to both Langmuir and Freundlich adsorption isotherms. The regeneration studies showed that the material can be reused for up to six times using 0.1 M KCl as regenerant. Antimicrobial studies showed that HTAC has potency against Escherichia coli (E. coli) strains. The study showed that synthesized HTAC has strong potential for application in fluoride and pathogen removal.

Possibility of Removing Phosphates from Activated Charbon Made from Date Kernels

Phosphates in natural waters and whatever their origin, promote the formation of algae, reduce dissolved oxygen and reduce biodiversity in aquatic ecosystems. At high doses, phosphate salts can cause health problems. The objective of our study was to develop a simple, efficient and environmentally friendly sorption depollution technique on available and inexpensive media. We have studied the adsorption of phosphate on activated carbons prepared from date kernels. Batch tests were carried out in order to study different operating parameters such as the effect of contact time, pH, initial phosphate concentration and adsorbent dosage and adsorption kinetic. The sorption equilibrium was analyzed by Langmuir, Freundlich isotherms model. Results show that the phosphate adsorption was reversible and the quantity adsorbed reached its maximum value (14.49 mg/g) after 40 minutes. It was also found that phosphate uptake was affected by variation of pH, initial concentration of phosphate and activated carbon dosage. The adsorption improved with an acidic pH (pH = 6), initial concentration and adsorbent dosage. The results of kinetic studies revealed that adsorption phosphate on activated carbon based on date kernels (Biocar) and the intra-particle diffusion involved in the adsorption mechanism. Also, isotherm study showed that Langmuir isotherm best fit the data and the adsorption was a physical type.

Adsorption of CO2 on palm shell based activated carbon modified by deep eutectic solvent: Breakthrough adsorption study

Adsorption process technology using solid adsorbents in capturing CO2 is an alternative approach to solve the global greenhouse issue. As such, cost-effective, environmentally friendly and high-performance adsorbents have been developed to this end. This paper describes the preparation of adsorbents derived from palm shell waste with high carbon content, which is then functionalized with deep eutectic solvent (DES) a mixture of choline hydroxide:urea and choline hydroxide:glycerol to enhance the CO2 adsorption capacity. Adsorbents are characterized by their structural, morphological, and chemical properties using XRD, FTIR, SEM, EDX, and BET surface area. The relationship between adsorbent surface characteristics and CO2 adsorption performance was studied. CO2 breakthrough experiments were carried out in a fixed-bed adsorption column at different adsorption temperatures (25–55 °C), feed flow rates (200–600 mL/min), and the initial CO2 concentrations (10–20%). It was found that the amount of CO2 uptake decreased with an increase in adsorption temperature, and feed flow rate. It was observed that DES-based activated carbon with a mixture of choline hydroxide:urea (ACDES 9) exhibited the highest CO2 adsorption capacity (37.2 mg/g) at an adsorption temperature of 25 °C, feed flow rate of 200 mL/min, and CO2 concentrations of 10%. Furthermore, the modified adsorbent still showed good performance even after 11 adsorption-desorption cycles.

Artificial neural network modelling for biodecolorization of Basic Violet 03 from aqueous solution by biochar derived from agro-bio waste of groundnut hull: Kinetics and thermodynamics

In this study, Levenberg Marquardt back propagation algorithm was used to train the Artificial Neural Network (ANN) and to predict the adsorptive removal of cationic dye Basic Violet 03 (BV03) by biochar derived from biowaste of groundnut hull. The experimental conditions such as solution pH, biochar dose, initial dye concentration, contact time and temperature were used as input variables and BV03 percentage removal as target. The hidden and the output layer of the network was trained by tangent sigmoid and liner transfer functions. The feasibility of the adsorption process is evaluated by the kinetic studies and it exhibited that pseudo-second order kinetic models fit well with experimental data. The adsorbent stability and adsorption mechanism has been discoursed by the thermodynamic characteristics and sorption free energy. The predicted target values were compared with the experiment resulted in a better correlation coefficient of 0.9920. Thus, the results attained from this ANN model was found to be effective in predicting the percentage removal of BV03 dye at any given operating condition.

Adsorption application of activated carbon from ripe black locust seed pods for wastewater taken from Ergene River, Turkey

ABSTRACT Ergene River contains many chemical substances and therefore, it has negative effects on the surrounding ecosystem and local people. To find a solution to these chemical substances and also to determine the adsorption performance of the activated carbon obtained from ripe black locust seed pods, the adsorption of various elements was studied on this activated carbon in Ergene River water sample. In Ergene River water sample, the adsorption performances of Mn, Cr, Ni, Co, Cd, V, Ti, Na, Mg, K, Ca, S, P, B, Pb, Cu, Zn, Sn, and Al on the activated carbon were studied under various operating conditions.For this aim, operating condition effects, such as adsorbent dosage, adsorption temperature, and contact time on these element adsorptions were investigated. 0.4 g activated carbon was found to be adequate for the above 90% removals of most elements from 50 mL Ergene River sample, and it was noticed that adsorption temperature differently affected adsorption performances of each element in the experiments at 25, 35, and 45°C. Also, the adsorption equilibriums of most elements in activated carbon/Ergene River solution were rapidly reached in first 5 min, but reaching adsorption equilibriums of Co, Sn, Mg, K, and Ca took more times (until 1500 min). Moreover, the desorption study of these elements from the activated carbon adsorbed with chemical substances in Ergene River sample was achieved by using HCl solutions with various concentrations of 0.1, 0.5, 1, 2, 3, 4, 5, and 6 M. As a result, the activated carbon obtained from ripe black locust seed pods displayed promising performance for the most elements, bad odour, and colour removals in Ergene River sample.

Effective removal of methylated phenol and chlorinated phenol from aqueous solutions using a new activated carbon derived from Halodule uninervis waste

Due to the toxicity of methylated and chlorinated phenols, it is necessary to remove them from aqueous solutions. Therefore, a highly efficient adsorbent was developed from the dead leaves of Halodule uninervis seagrass (SG) through a chemical and thermal activation process. The prepared activated carbon (SGAC) was characterized and investigated for removal of 2,4-Dimethylphenol (DMP) and 2,4-Dichlorophenol (DCP) from aqueous solutions. The batch adsorption mode was used and the effects of adsorption conditions were studied. SGAC adsorbent showed high adsorption capacities which were 364 mg DMP/g and 333 mg DCP/g. The adsorption experimental results fitted Freundlich and Langmuir models and followed pseudo-second-order kinetics. The adsorption of both adsorbates was spontaneous. The prepared adsorbent was able to remove 90% of DMP and 97% of DCP from the synthetic wastewater. This study indicated that SGAC adsorbent is efficient and reusable in the synthetic wastewater for at least four times.

Tetraethylenepentamine modified magnetic cellulose nanocrystal composites for removal of Congo red with high adsorption capacity

A tetraethylenepentamine modified magnetic cellulose nanocrystal composites (Fe3O4@CNC-TEPA) was prepared by the coprecipitation method and Schiff base reaction, which could adsorb Congo red (CR) efficiently. The morphology and structure of the nanoparticles were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), zeta potential (ZETA), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET). Subsequently, the Fe3O4@CNC-TEPA adsorbed CR was investigated by comparative experiments, selective adsorption experiments, effect of pH, effect of adsorbent dosage, adsorption isotherms, thermodynamics parameters, adsorption kinetics, leaching experiments, desorption and reusability experiments. Results revealed the fact that the nanoparticles showed excellent adsorption capacity of CR (1049 mg g−1) due to the abundant hydroxyl and amino groups on the surface of the Fe3O4@CNC-TEPA. The adsorption process was best described by the the Langmuir equation and pseudo-second-order kinetic model. Moreover, the Fe3O4@CNC-TEPA loaded with CR can be recycled with NaOH solution easily, which can be used repeatedly for CR adsorption. After six cycles, the adsorption capacity was still about 81.5% of the original particles’. The environmentally friendly nanoparticles have great application prospects as adsorbents for removing CR.

Anharmonic Correction to Adsorption Free Energy from DFT-Based MD Using Thermodynamic Integration.

Adsorption processes are often governed by weak interactions for which the estimation of entropy contributions by means of the harmonic approximation is prone to be inaccurate. Thermodynamic integration (TI) from the harmonic to the fully interacting system (λ-path integration) can be used to compute anharmonic corrections. Here, we combine TI with (curvilinear) internal coordinates in periodic systems to make the formalism available in computational studies. Our implementation of ab initio molecular dynamics in VASP is independent of the reaction path and can be thus applied to study adsorption processes relative to the gas phase and does hence provide a useful tool for computational catalysis. We discuss the application of the approach on three model systems for which exact semianalytical solutions exist and illustrate and quantify the importance of anharmonic vibrations, hindered rotations, and hindered translations (dissociation). Eventually, we apply the method to study the adsorption of small adsorbates in a zeolite (H-SSZ-13).

ANN Modelling of the Adsorption of Herbicides and Pesticides Based on Sorbate-Sorbent Interphase

Herbicides and pesticides (H & P) are commonly used in agricultural practice and is a serious environmental pollutant in contemporary times. Studies have shown that it can be efficiently mitigated from the environment by adsorption. The aim of this study was to utilise Artificial Neural Networks (ANN) to model the adsorption of H & P from aqueous media based on the sorbate-sorbent interphase. The sorbate-sorbent interphase was characterised by the relative molecular mass (g/mol), specific surface area (m2/g), effective surface area (mol/m2), solubility (mol/l), and preferential adsorption (sorbate mol on sorbent/sorbate mol in solution). The coefficient of determination (R2) at training, validation and testing were 0.9825, 0.9428 and 0.9793 respectively. The accuracy of the model was substantiated by direct comparison and parity plots. The paired samples correlation showed a strong positive correlation (0.980) and statistical significance (p < 0.05) between the model predictions and experimental results. This study reveals that information on the adsorbent specific surface area, adsorbent effective surface area, adsorbate preferential adsorption, adsorbate solubility and adsorbate relative molecular mass can be used to accurately predict the mass adsorption capacity for any H & P from aqueous media.

Adsorption of Pb (II) ions from aqueous solutions using carbon nanotubes: A systematic review

The presence of Pb (II) ions, as a major pollutant source, in the water resources causes global health concerns. The adsorption method has been conventionally used for the determination and removal of Pb (II) ions. In this systematic review, all the adsorption-based studies during 1991–2020, which have used carbon nanotubes (CNTs) as the adsorbent of Pb (II), were reviewed and those qualifying the related requirements were selected for more evaluation. The experimental conditions including pH, temperature, initial concentration, adsorbent dosage, ionic strength, and contact time as well as adsorbent regeneration and adsorption capacity/recovery were extracted. Almost all of the included papers carried out adsorption experiments at room temperature and showed that the higher temperature leads to a higher adsorption rate. More than 47.0% of included studies assigned the optimum pH at 6–7, and reported that a higher pH leads to the metal precipitation. Moreover, the increase of initial concentration improved the adsorption capacity whereas it leads to the decrease of metal ion recovery. Most of the articles (42.2%) have fitted the Langmuir isotherm model, which reveals that the Pb (II) uptake on the CNT surface is a homogenous and monolayer process. Using isotherm behavior, the thermodynamic parameters (i.e. ΔG°, ΔH°, and ΔS°) were calculated in 19.8% of included studies and the results denoted the spontaneous process for Pb (II) adsorption. Furthermore, about 42.6% of included studies have described the adsorption kinetic by the pseudo-second-order model and suggested the chemisorption as the rate-limiting step. Consequently, the review results revealed that CNT composites are promising adsorbents for Pb (II) uptake from aqueous solutions.