Glutaraldehyde cross-linked epoxyaminated chitosan as an adsorbent for the removal and recovery of copper(II) from aqueous media

A novel glutaraldehyde cross-linked epoxyaminated chitosan (GA-C-ENCS) prepared through chemical modification was used as an adsorbent for the removal and recovery of Cu(II) from aqueous media. The adsorbent was characterized by FTIR, SEM-EDS, ESR, TG/DTG, BET-surface area and potentiometric titration. The Cu(II) adsorption process, which was pH dependent showed maximum removal at pH 6.0. Adsorption equilibrium was achieved within 3 h. The adsorption of Cu(II) followed a reversible-first-order kinetics. The equilibrium data were evaluated using the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The best interpretation for the equilibrium data was given by the Dubinin–Radushkevich isotherm. The adsorption capacity of the adsorbent increased from 3.11 to 3.71 mmol g⁻¹ when the temperature was increased from 20 to 50 °C. The complete removal of 20.7 mg L⁻¹ Cu(II) from electroplating industry wastewater was achieved by 0.4 g L⁻¹ GA-C-ENCS. Regeneration experiments were tried for four cycles and the results indicate a capacity loss of <7.0%.     

Efficiency of a novel nitrogen-doped Fe3O4 impregnated biochar (N/Fe3O4@BC) for arsenic (III and V) removal from aqueous solution: Insight into mechanistic understanding and reusability potential

Worldwide, arsenic contamination has become a matter of extreme importance owing to its potential toxic, carcinogenic and mutagenic impact on human health and the environment. The magnetite-loaded biochar has received increasing attention for the removal of arsenic (As) in contaminated water and soil. The present study reports a facile synthesis, characterization and adsorption characteristics of a novel magnetite impregnated nitrogen-doped hybrid biochar (N/Fe₃O₄@BC) for efficient arsenate, As(V) and arsenite, As(III) removal from aqueous environment. The as-synthesized material (N/Fe₃O₄@BC) characterization via XRD, BET, FTIR, SEM/EDS clearly revealed magnetite (Fe₃O₄) impregnation onto biochar matrix. Furthermore, the adsorbent (N/Fe₃O₄@BC) selectivity results showed that such a combination plays an important role in targeted molecule removal from aqueous environments and compensates for the reduced surface area. The maximum monolayer adsorption (Q_max) of developed adsorbent (N/Fe₃O₄@BC) (18.15 mg/g and 9.87 mg/g) was significantly higher than that of pristine biochar (BC) (9.89 & 8.12 mg/g) and magnetite nano-particles (MNPs) [7.38 & 8.56 mg/g] for both As(III) and As(V), respectively. Isotherm and kinetic data were well fitted by Langmuir (R² = 0.993) and Pseudo first order model (R² = 0.992) thereby indicating physico-chemical sorption as a rate-limiting step. The co-anions (PO₄^3-) effect was more significant for both As(III) and As (V) removal owing to similar outer electronic structure. Mechanistic insights (pH and FTIR spectra) further demonstrated the remarkable contribution of surface groups (OH^–, –NH₂ and –COOH), electrostatic attraction (via H- bonds), surface complexation and ion exchange followed by external mass transfer diffusion and As(III) oxidation into As(V) by (N/Fe₃O₄@BC) reactive oxygen species. Moreover, successful desorption was achieved at varying rates up to 7th regeneration cycle thereby showing (N/Fe₃O₄@BC) potential practical application. Thus, this work provides a novel insight for the fabrication of novel magnetic biochar for As removal from contaminated water in natural, engineering and environmental settings.     

Highly efficient,economic, and recyclable glutathione decorated magnetically separable nanocomposite for uranium(VI) adsorption from aqueous solution

A green and environment-friendly magnetically separable nanocomposite, glutathione@magnetite was fabricated sonochemically through the functionalization of Fe₃O₄ by glutathione which was well characterized using Fourier-transform infrared spectroscopy, ultravoilet-visible spectroscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometer, Brunauer-Emmett-Teller, and high-resolution transmission electron microscope. The parameters affecting adsorption including pH, temperature, contact time, initial adsorbate concentration, and adsorbent amount were optimized by batch experiments. The magnetic glutathione@magnetite was applied for the removal of uranium(VI) in water with maximum adsorption capacity found to be 333.33 mg/g in 120 min at a neutral pH at 25 °C showing high efficiency for U(VI) ions. Furthermore, adsorption results obtained from UV-vis spectroscopy were validated by inductively coupled plasma optical emission spectroscopy. The thermodynamic parameters, viz Gibbs free energy (ΔGº), standard enthalpy change (ΔHº), and standard entropy change (ΔSº) of the process were calculated using the Langmuir constants. The pseudo-second-order kinetics model is seen to be applicable for describing the uptake process using a kinetics test. Moreover, desorption studies reveals that glutathione@magnetite can be used repeatedly, and removal efficiency shows only a small decrease after six cycles. Thus, glutathione@magnetite acts as a potential adsorbent for the removal of U(VI) from the water with great adsorption performance.     

Shellfish waste-derived mesoporous chitosan for impressive removal of arsenic(V) from aqueous solutions: A combined experimental and computational approach

Novel shellfish waste-derived chitosan (CS) has been developed to adsorb As(V) from simulated wastewater under evaluating adsorption process parameters. The coexistence of some competing ions, like SiO₃^2-, Cl^-, NO₃^– and PO₄^3- as well as the regeneration capacity of the spent adsorbent, was explored. The experimental data were modeled using several kinetics and isotherm models to understand the mechanism related to the uptake process. As(V) uptake was relatively rapid and highly dependent on pH. The Avrami-fractional-order expression supported data best, while the Liu equation described well isotherm data at pH 5.0. The maximum uptake capability (Liu) was 12.32 mg/g, and the highest removal performance (99 %) was obtained at optimum pH 5.0. Molecular dynamics simulations were performed to more clearly illuminate the atomic-level interactions between arsenic species and CS surface in both acidic and basic mediums. After four adsorption–desorption cycles, CS exhibited more than 90 % As(V) removal efficiency. The results of this study indicates that low cost shellfish derived chitosan is promising for efficient removal of As(V) from water body and can be used to remove other pollutants from watewater.     

Chitosan–magnetite nanocomposites (CMNs) as magnetic carrier particles for removal of Fe(III) from aqueous solutions

This research focuses on removal of Fe(III) from aqueous solution using chitosan–magnetite nanocomposites as potential sorbent. The presence of nanosized magnetic particles within the nanocomposites was confirmed by TEM and SAED analysis. The particles with diameter 508 μm and 84 μm, follow Frendlich sorption isotherm at 30 °C, and the Frendlich constants (K_F, 1/n) have been found to be 5.974 mg g⁻¹, 2.66 and 35.98 mg g⁻¹, 1.385, respectively. Out of various kinetic models, the experimental data for dynamic uptake of Fe(III) is best fitted on ‘pseudo-second order’ kinetic model. The linear nature of plots between log (% sorption) and log (time) is indicative of intra-particle diffusion. For the particles with diameters 508 μm and 84 μm, the value of k_id was found to be 1.78 mg l⁻¹ min^−0.5 and 2.13 mg l⁻¹ min^−0.5. The sorption mean free energy from the Dubinin–Radushkevic isotherm was found to be 7.04 kJ mol⁻¹ indicating chemical nature of sorption. The increase in chitosan content in sorbent particles is found to enhance the Fe(III) uptake. The various thermodynamic parameters have also been evaluated. Finally, the presence of Cu²⁺ ions in the sorbate is found to decrease the uptake of Fe(III).     

Quartzite an efficient adsorbent for the removal of anionic and cationic dyes from aqueous solutions

Quartzite obtained from local source was investigated for the removal of anionic dye congo red (CR) and cationic dye malachite green (MG) as an adsorbent from aqueous solution in batch experiment. The adsorption process was studied as a function of dye concentration, contact time, pH and temperature. Adsorption process was described well by Langmuir and Freundlich isotherms. The adsorption capacity remained 666.7 mg/g for CR dye and 348.125 mg/g for MG dye. Data was analyzed thermodynamically, ΔH⁰ and ΔG⁰ values proved that adsorption of CR and MG is an endothermic and spontaneous process. Adsorption data fitted best in the pseudo-first order kinetic model. The adsorption data proved that quartzite exhibits the best adsorption capacity and can be utilized for the removal of anionic and cationic dyes.     

Poly（vinylpyridine） adsorbent for the removal of SIPA from its aqueous solution

Poly(vinylpyridine) WH-225 resin was prepared and characterized.Compared with the commercial hypercrosslinked adsorbent NDA-100 and macroporous adsorbent XAD-4 resins,the newly synthesized poly(vinylpyridine) WH-225 resin exhibited the highest adsorption capacity toward SIPA from aqueous solution.     

Preparation of unsaturated polyester Ce(IV) phosphate by plastic waste bottles and its application for removal of Malachite green dye from water samples

In this paper, recycling of polyethyleneterephthalate (PET), a non-biodegradable plastic, was carried out by preparing unsaturated polyester Ce(IV) phosphate (USPECe(IV)P) composite cation exchanger. Various samples of USPECe(IV)P was prepared by mixing different volume ratios of unsaturated polyester in an inorganic Ce(IV) phosphate gel and characterized by TGA/DTA, XRD, SEM, Fourier transform infra-red spectroscopy (FTIR) instrumental methods. The composite has been employed as adsorbents for the removal of Malachite green dye from waste water. The nature of possible adsorbent and dye interaction was examined by the FTIR technique. The adsorption of MG was found to be maximum (98%) at pH 8. The extent of removal of MG was found to be dependent on adsorbent dose, temperature and time. The equilibrium data for adsorption was best represented by the Friendlich isotherm. Thermodynamic parameters (ΔH⁰ and ΔG⁰) suggest an endothermic and spontaneous process. Kinetic studies show better applicability of an intraparticle diffusion kinetic model.     

A comparative study of microwave and chemically treated Acacia nilotica leaf as an eco friendly adsorbent for the removal of rhodamine B dye from aqueous solution

The use of cheap and eco friendly adsorbents prepared from freely and abundantly available Acacia nilotica leaves have been investigated by batch methods. Microwave treated A. nilotica leaves (MVM) are more effective than chemically treated A. nilotica leaves (CVM) for the removal of rhodamine B (RH B) from aqueous solution. The effect of initial pH, contact time and initial dye concentration of RH B onto CVM and MVM has been investigated. The applicability of the linear form of Langmuir model to CVM and MVM was proved by the high correlation coefficients R² = 0.9413 and 0.9681 for RH B adsorption. The R² values were greater than 0.994 for all RH B concentrations, which indicates the applicability of the pseudo-second-order kinetic model. The recycling ability of MVM is greater than CVM. The preparation of MVM does not require an additional chemical treatment step and it attains rapid equilibrium. Hence it is agreeing with the principles of green chemistry and less time is required to possess high adsorption of RH B. Therefore, the eco friendly adsorbent MVM is expected to be environmentally and economically feasible for the removal of RH B from aqueous solutions.     

Preparation and characterization of magnetic chitosan nanocomposites for removal of Cu2+ from aqueous solution

In this article, highly efficient magnetic chitosan nanoparticles were prepared by the glutaraldehyde cross-linking method and then chemically-modified with amino groups through reaction between triethylenetramine and glycidyl methacrylate. The adsorption kinetics and isotherms of these novel adsorbents fit the pseudo-second-order model and the Langmuir model. The maximum adsorption capacities were 293?mg/g at pH?=?4.3 and t?=?1.4 hours. The rate-limiting step was the chemical adsorption. Further recycling experiments showed that the adsorbent provided the potential regeneration and reuse after adsorbing Cu²⁺. All the experimental results demonstrated that the adsorbent had a potential application in Cu²⁺ removal from wastewater.     

An evaluation of coal fly ash as an adsorbent for the removal of methylene blue from aqueous solutions: kinetic and thermodynamic studies

Abstract

In this study the effect of the dose and particle size of the adsorbent, initial dye concentration, initial pH, contact time and temperature were investigated for the removal of by means of fly ash (FA) methylene blue (MB) from an aqueous solution. The FA dose was found to be 2.0?g and the under 270 mesh sized particles were found to be effective particles for adsorption. The adsorption process reached its maximum value at 0.5?mg/L dye concentration and attained equilibrium within 10?minutes. The adsorption isotherm was found to follow the Langmuir model. The estimated adsorption free energy (ΔG^o), enthalpy change (ΔH^o), and entropy change (ΔS^o) for the adsorption process were ?37.77?kJ mol^?1, ?13.44?kJ mol^?1 and 122 J mol^?1 K^?1 respectively at 298 K. The maximum adsorption capacity is 0,12?mg g^?1 at 298 K and 0,07?mg g^?1 at 398 K. The adsorption process was exothermic, feasible and spontaneous. The positive value of ΔS^o shows the affinity of FA for MB while the low value of ΔG^o suggests a physical adsorption process.     

Removal of methylene blue from aqueous solutions using Poly(AA-co-DVB)

Functional cross-linked polymers (Poly(AA-co-DVB)) were synthesized using a one-step method. The properties of Poly(AA-co-DVB) were measured by SEM, FTIR, and TGA. The adsorption capacity of the Poly(AA-co-DVB) was investigated using methylene blue as an adsorbate. The effect of the mole compositions of acrylic acid and divinylbenzene monomers on the adsorption capacity was investigated in detail. The initial pH of solutions and contact time were also studied. The kinetics and isotherms of the adsorption process were also investigated. The result showed that the maximum equilibrium adsorption capacity was 1698.9?mg/g at room temperature and the adsorption kinetic was well fitted by a pseudo-second-order model and the adsorption isotherm agreed well with the Langmuir model.     

Removal of As(III) and As(V) by natural and synthetic metal oxides

The removal properties of As(III) and As(V) by the several metal oxides having different mineral type and content of metals were investigated in batch and column reactors. The used metal oxides were Fe-oxide loaded sand (ILS), Mn-oxide loaded sand (MLS), activated alumina (AA), sericite (SC) and iron sand (IS). From the pH-edge adsorption experiments with AA and ILS, maximum As(III) adsorption was observed around neutral pH while As(V) adsorption was followed an anionic-type behavior. Among five metal oxides, AA showed the greatest removal capacity for both As(III) and As(V) through adsoption process but it has little oxidation capacity for As(III). Eventhough IS had much greater content of Fe-oxides than ILS, it showed a relatively lower removal capacity for both As(III) and As(V). This result suggests that adsorption of arsenic onto metal oxides is controlled by not only the contents of Fe-oxides but also mineral type of Fe-oxides. Column tests were performed at different combinations of metal oxides in a column reactor to find the best column system, which effectively treat both As(III) and As(V) at the same time. Among several combinations, the column reactors packed with MLS-AA and MLS-ILS showed a near complete oxidation of As(III) by MLS for a long time and the greatest adsorption of total arsenic compared to the column reactor packed with MLS-IS.     

Optimization of polyacrylonitrile-cysteine resin synthesis and its selective removal of Cu(Ⅱ) in aqueous solutions

Polyacrylonitrile beads(PAN) cysteine(CS) was synthesized from polyacrylonitrile beads(PAN) and cysteine(CS).The content of the functional group and the percentage conversion of the functional group of PAN-CS prepared under the optimum condition using response surface methodology(RSM) for the first attempt were 3.22 mmol/g and 35.78%.The structure was characterized by ET-IR and elemental analysis.The adsorption properties of the resin for Cu(Ⅱ) were investigated by batch and column experiments.Batch adsorption results suggested that PAN-CS had higher adsorption capability for Cu(Ⅱ)than other metal ions and maximum saturated adsorption capacity was 184.7 mg/g.The resin and its metal complexes were studied by FT-IR.Furthermore,the resin can be eluted easily using 1 mol/L HC1.PAN-CS can provide a potential application for selective removal of copper from waste solution.     

Efficacy of Polyaniline (PANI) nanofibres for capturing Diclofenac (DC) drug from its aqueous solutions

Pharmaceutical drug contamination in water nowadays is deteriorating the ecological components. A remedial approach is therefore a necessity. This study focuses on the synthesis of PANI nanofibres employing the oxidative polymerization method using ammonium persulphate (APS) as oxidant. The synthesized nanofibres were characterized using HR-TEM, FT-IR and XRD. The HRTEM image exhibited the nano-range structure of PANI with a rough surface. The FT-IR spectra inferred about the role of surface capping groups involved in the uptake mechanism. The crystallinity of PANI was well assessed by the X-Ray Diffraction analysis. The interaction between the studied drug diclofenac (DC) and polyaniline (PANI) showed a rapid equilibrium time 120 min favored at pH 5.0 achieving maximum adsorptive capacity (q_e) of 471.08 mg g ^?1. The uptake process followed the pseudo-second order kinetic model (R² = 1) with intra-particle diffusivity model (R² = 0.9810) as the governing step and best fitting values into Langmuir isotherm model (R² = 0.9822) inferred about the favourable adsorption of DC forming monolayer over PANI having q_m to be 943.83 mg g^?1. The drug DC was easily desorbed up to 85.31% by using 0.1 M aq ethanol and was exhausted after five cycles of reusability. The whole adsorptive mechanism involved electrostatic interactions along with hydrogen bonding.     

Laterite clay-based geopolymer as a potential adsorbent for the heavy metals removal from aqueous solutions

This study is focused on the investigation of low iron lateritic clay-based geopolymer as a potential adsorbent for the higher uptake of Ni(II) and Co(II) ions from aqueous solutions. BET analysis revealed that the sieved geopolymer sample (SGS) was characterized by 17.441 m²/g of surface area, 0.005 cm³/g of pore volume, and 13.549 Å of pore diameter. SEM investigation confirmed the presence of pores and cavities onto the surface of SGS. XRD analysis showed that the geopolymer is semi-crystalline in nature. It was found that the adsorption ability of SGS remained 520 mg/g for Ni(II) ions and 500 mg/g for Co(II) ions when 0.5 M solutions were stirred with SGS for 60 min. The temperature and pH of the solution were maintained at 60 °C and 7.0, respectively. The adsorption data of both heavy metal (HM) ions fitted best in the pseudo-second-order kinetic model. The low activation energy value i.e. 2.507 kJ/mol for Ni(II) ions and 2.286 kJ/mol for Co(II) ions confirmed adsorption is physisorption. Adsorption data were tested with Langmuir and Freundlich models, the data showed comparatively better fitting in the Freundlich model. The greater value of monolayer adsorption capacity (Xm) for Ni(II) ions was found 1.77 × 10⁻² mol/g while for Co(II) ions it remained 1.69 × 10⁻² mol/g confirming the better interaction of metal ions with the adsorbent surface. Negative values of ΔG° confirmed the spontaneity of the process while the positive value of ΔS° showed the randomness of adsorbate particles. The positive value of ΔH° showed that the adsorption process remained endothermic for both HM ions. The experimental results confirmed the ability of laterite clay-based geopolymer for better removal of HM ions and hence can be employed for the wastewater treatment processes at low-cost adsorbent.     

Removal of As(III) and Cr(VI) from aqueous solutions by Bixa orellana leaf biosorbent and As(III) removal using bacterial isolates from heavy metal contaminated site

Arsenic and chromium have affected wider area in the world including Gangetic plains of India due to its toxicity and carcinogenic characteristics. Entry of As(III) into food chain has also escalated problem. A novel approach has been adopted to develop remediation technique using bacteria and herbs. The bioremediation study showed Bixa orellana as an accumulator of As(III) of Cr(VI) which was validated by SEM-EDX, FTIR and other kinetic analyses. Maximum percentage removal of Cr(VI) with fixed bio mass of B. orellana is 82.8% for an initial concentration of 3 ppm Cr(VI) concentration whereas maximum percentage removal of As(III) is 40.42 for an initial concentration of 6 ppm As(III).The R² values and graphs showed that Freundlich as well as Elovich model best fitted to the experimental data. Three bacteria isolated from the coal mines of Rajmahal hills showed As(III) resistance and bioremediation potentials (up to 150 ppm). The 16S rRNA genotyping of these isolates was done (GenBank accession no: MK231250, MK231251 and MK231252) which showed similarity with Stenotrophomonas maltophilia, Uncultured gamma proteobacteria clone and Bacterium E1. Further, the presence of genes involved in arsenic biotransformation like aox, acr and ars was also confirmed in these bacterial isolates. Maximum percentage removal od As(III) in 50 ppm concentration by ASBBRJM16, ASBBRJM85 and ASBBRJM87 bacteria are 60.66%, 28.36% and 10.30% respectively for an initial concentration of 50 ppm As(III). Our results suggest that bacterial isolates may be adopted as an effective tool to remove As(III) from aqueous medium in spite of different cell structures and composition.     

Magnetite nanoparticles for removal of heavy metals from aqueous solutions: synthesis and characterization

Fe₃O₄ magnetic nanoparticles were synthesized by co-precipitation method. The structural characterization showed an average nanoparticle size of 8 nm. The synthesized Fe₃O₄ nanoparticles were tested for the treatment of synthetic aqueous solutions contaminated by metal ions, i.e. Pb(II), Cu(II), Zn(II) and Mn(II). Experimental results show that the adsorption capacity of Fe₃O₄ nanoparticles is maximum for Pb(II) and minimum for Mn(II), likely due to a different electrostatic attraction between heavy metal cations and negatively charged adsorption sites, mainly related to the hydrated ionic radii of the investigated heavy metals. Various factors influencing the adsorption of metal ions, e.g., pH, temperature, and contacting time were investigated to optimize the operating condition for the use of Fe₃O₄ nanoparticles as adsorbent. The experimental results indicated that the adsorption is strongly influenced by pH and temperature, the effect depending on the different metal ion considered.