Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g^-1 at pH 4.0 and 25 ℃. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl^-, SO₄^2- and PO₄^3- reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g^-1 after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

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.     

Adsorption Characteristics of Chromium(VI) Ions onto Fe(III)-Coordinated Amino-Functionalized Poly(glycidylmethacrylate)-Grafted TiO2-Densified Cellulose

An investigation was conducted with a newly developed adsorbent, iron(III)- coordinated amino-functionalized poly(glycidylmethacrylate)-grafted TiO₂-densified cellulose (Fe(III)-AM-PGDC) on the removal of chromium(VI) from aqueous solution. Batch experiments were performed under various conditions of time, pH, concentration, dose, ionic strength, and temperature. Adsorption of Cr(VI) on Fe(III)-AM-PGDC was dominated by ion exchange or outer-sphere complexation. The maximum adsorption capacity was found to be 109.76 mg g^?1. Thermodynamic study showed that adsorption of Cr(VI) onto Fe(III)-AM-PGDC is more favored. The complete removal of Cr(VI) from electroplating wastewater was achieved by the adsorbent. The adsorbent did not lose its adsorption capacity even after the fourth regeneration.     

Preparation of magnetic zeolite/chitosan composite using silane as modifier for adsorption of Cr(VI) from aqueous solutions

This study aimed to prepare an efficient, cost-effective, and separable magnetic zeolite/chitosan composite (MZFA/CS) adsorbent from solid waste to deal with the water pollution of Cr(VI). The MZFA/CS was characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Then, the effect of pH, temperature, initial concentration of Cr(VI) ions, and contact time was considered in the study. For a sorbent dose of 0.1 g in 50 mL of a Cr(VI) solution, at a contact time of 30 min, temperature of 30°C, and a pH of 3, an adsorption capacity (q_e) of 16.96 mg g⁻¹ was achieved. Adsorption kinetics and isotherm data obtained for all adsorption systems were well-fitted by pseudo-second-order and Langmuir models, respectively. The thermodynamic study suggested that the adsorption process is spontaneous and endothermic in nature. In summary, the adsorbent with better separability (Ms = 16.83 emu g⁻¹) and adsorbability was successfully fabricated.     

Single step modification of micrometer-sized polystyrene particles by electromagnetic polyaniline and sorption of chromium(VI) metal ions from water

This article describes a single-step reproducible approach for the surface modification of micrometer-sized polystyrene (PS) core particles to prepare electromagnetic PS/polyaniline–Fe₃O₄ (PS/PANi–Fe₃O₄) composite particles. The electromagnetic PANi–Fe₃O₄ shell was formed by simultaneous seeded chemical oxidative polymerization of aniline and precipitation of Fe₃O₄ nanoparticles. The weight ratio of PS to aniline was optimized to produce core–shell structure. PS/PANi–Fe₃O₄ composite particles were used as adsorbent for the removal of Cr(VI) via anion-exchange mechanism. The composite particles possessed enough magnetic property for magnetic separation. The adsorption was highly pH dependent. Adsorption efficiency reached 100% at pH 2 in 120 min when 0.05 g of composite particles was mixed with 30 mL 5 mg L⁻¹ Cr(VI) solution. The adsorption isotherm fitted best with Freundlich model and maximum adsorption capacity approached 20.289 mg g⁻¹ at 323 K. The prepared composite was found to be an useful adsorbent for the removal of soluble Cr(VI) ions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47524.     

Preparation of Cr(VI)-imprinted polypropylene nonwoven fibers using plasma polymerization-assisted grafting

Polypropylene (PP) fibers were grafted with glycidyl methacrylate (GMA) using plasma polymerization and then aminated, imprinted, and crosslinked to prepare Cr(VI)-imprinted fibers. The plasma polymerization conditions were optimized by single factor experiment and response surface methodology, and various properties and adsorption mechanism of the fibers were analyzed. The results showed that at pH 3, the imprinted fibers had a maximum Cr(VI) adsorption capacity of 173.36 mg/g, and the adsorption equilibrium could be reached within 40 min. In the presence of competing ions (SO₄²⁻, NO₃⁻ and PO₄³⁻) each at a concentration of 5 times of that of Cr(VI), the Cr(VI) adsorption rate of the fibers could be maintained at around 50%, which indicates that the imprinted fibers have high selectivity towards Cr(VI). The results also showed that the imprinted fibers had good reusability and enrichment ability, thus can be a good candidate for treating actual Cr(VI)-contaminated water.     

3D flower like δ-MnO2/MXene Nano-hybrids for the removal of hexavalent Cr from wastewater

Herein, 3D flower-like δ-MnO₂, MXene and δ-MnO₂/MXene in-situ hybrid (IH) composites were prepared (via hydrothermal and solution treatment methods) for the effective removal of Cr (VI) from the contaminated water. The effect of various experimental parameters including contact time, pH levels and initial Cr (VI) ions concentration was determined and compared under static conditions. The kinetics of Cr (VI) adsorption onto δ-MnO₂, MXene, and IH confirmed the existence of a pseudo-second-order model. The obtained results reveal that the removal of Cr (VI) largely depends on the pH of the solution. The adsorption isotherm data fits best for Freundlich model, illustrating a multi-site adsorption mechanism of Cr (VI) ion on these adsorbents. The maximum Cr (VI) adsorption capacities onto δ-MnO₂, MXene and IH are 235.65 mg g⁻¹, 273.1 mg g⁻¹ and 353.87 mg g⁻¹, respectively. The study reveals that hetero-engineered approach of synthesizing transition metal oxides with MXenes provides abundant opportunities to remove contaminants from water with better efficiency due to reduction and electrostatic interaction.     

Facile synthesis of imprinted submicroparticles blend polyvinylidene fluoride membranes at ambient temperature for selective adsorption of methyl <Emphasis Type="Italic">p</Emphasis>-hydroxybenzoate

We developed a simple phase inversion technique to prepare molecularly imprinted membrane (MIM) at room temperature for membrane selective adsorption and separation of methyl p-hydroxybenzoate (M4HB). The prepared SMIP-MIM was characterized by SEM, FT-IR, TGA. Compared with non-imprinted membrane (NIM_1-5) adsorbent, SMIP-MIM_1-5 adsorbent with high specific surface area and showed higher binding capacity, faster kinetic and better selectively adsorption capacity for M4HB. The maximum isotherm adsorption capacity for M4HB of SMIP-MIM₄ was 3.519mg·g^?1, and the experimental data was well fitted to the slips model by multiple analysis. The maximum kinetic adsorption capacity and equilibrium adsorption time for SMIP-MIM₄ were 1.335mg·g^?1 and 160 min, respectively. The mechanism for dynamic adsorption of M4HB onto SMIP-MIM₄ was found to follow pseudo-first-order model and pseudo-second-order model. Additionally, the permeability separation factor of SMIP-MIM₄ for M4HB compared to a structural analogues methyl 2-hydroxybenzoate (M2HB) could reach 2.847. The adsorption capacity of SMIP-MIM₄ for M4HB and M2HB was 0.549mg·cm^?2 and 1.563mg·cm^?2, respectively. The adsorption behavior of M4HB through SMIP-MIM₄ followed the retarded permeation mechanism.     

Removal of Cr(VI) from aqueous solution using amino‐modified Fe3O4–SiO2–chitosan magnetic microspheres with high acid resistance and adsorption capacity

A novel, bioadsorbent material of polyethylenimine‐modified magnetic chitosan microspheres enwrapping magnetic silica nanoparticles (Fe₃O₄–SiO₂–CTS‐PEI) was prepared under relatively mild conditions. The characterization results indicated that the adsorbent exhibited high acid resistance and magnetic responsiveness. The Fe₃O₄ loss of the adsorbent was measured as 0.09% after immersion in pH 2.0 water for 24 h, and the saturated magnetization was 11.7 emu/g. The introduction of PEI obviously improved the adsorption capacity of Cr(VI) onto the adsorbent by approximately 2.5 times. The adsorption isotherms and kinetics preferably fit the Langmuir model and the pseudo‐second‐order model. The maximum adsorption capacity was determined as 236.4 mg/g at 25°C, which was much improved compared to other magnetic chitosan materials, and the equilibrium was reached within 60 to 120 min. The obtained thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. Furthermore, the Cr(VI)‐adsorbed adsorbent could be effectively regenerated using a 0.1 mol/L NaOH solution, and the adsorbent showed a good reusability. Due to the properties of good acid resistance, strong magnetic responsiveness, high adsorption capacity, and relatively rapid adsorption rate, the Fe₃O₄–SiO₂–CTS‐PEI microspheres have a potential use in Cr(VI) removal from acidic wastewater. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43078.     

Removal of Chromium(VI) and Chromium(III) from Aqueous Solution by Grainless Stalk of Corn

Abstract

Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of k _ads of 0.037 and 0.018 min^?1 were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g^?1 at pH 0.84 for Cr(VI), and as 7.3 mg g^?1 at pH 4.6 for Cr(III), at 20°C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH ≈ 1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.     

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.     

Fabrication of copper coated polymer foam and their application for hexavalent chromium removal

The polymer foam coated with zero-valent copper (Cu⁰) was designed and prepared for the removal of hexavalent chromium (Cr(VI)) in water. Firstly, porous poly(tert-butyl acrylate) was fabricated by concentrated emulsion polymerization and then acrylic acid groups were generated on the surface of foam by hydrolysis reaction. Secondly, with the help of the large amount reactive carboxylic acid groups, polyethyleneimine (PEI) were chemically grafted onto the surface by the reaction between amine group and acrylic acid group. Finally, zero-valent copper was reduced by sodium borohydride (NaBH₄) and coated on the surface of polymer foam. Thus the copper functionalized porous adsorbent (Cu⁰–PEI–PAA) was constructed, and then applied for removing Cr(VI) from aqueous solution. The removal mechanism of Cr(VI) involved redox reaction by zero-valent copper and adsorption by amine groups, simultaneously. As a result, 99.5% of Cr(VI) could be removed within 2 h, and the maximum removal capacity for Cr(VI) of Cu⁰–PEI(1800)–PAA was 9.16 mg/g. Furthermore, the effect of initial concentration of Cr(VI), pH value, and temperature on the Cr(VI) removal was investigated. Therefore, the as-prepared zero-valent copper-loaded polymer foam could be an efficient and promising remediation material to remove Cr(VI) from wastewater.     

Adsorption of urea,creatinine, and uric acid from three solution types using spherical activated carbon and its recyclability

In this paper, we propose that the urinary toxins from the wastewater be adsorbed on an adsorbent such as spherical activated carbon and the latter be regenerated by subjecting it to high temperatures to recycle activated carbon and also to recycle the water used in dialysis. We studied the adsorption of artificial waste dialysate, which is a mixed solution of urea, creatinine, and uric acid, and the separate solutions for each of these and found that their extents of adsorption onto the spherical activated carbon material were nearly identical. The amount of adsorption was approximately 1.4 mg·g⁻¹ for urea, 18 mg·g⁻¹ for creatinine, and 20 mg·g⁻¹ for uric acid. The urea, creatinine, and uric acid adsorbed onto the spherical activated carbon decomposed on heat treatment at 500 °C, and the adsorption capacity of the spherical activated carbon was regenerated. Our study successfully demonstrated that the spherical activated carbon can be recycled in the waste dialysate treatment process.     

Equilibrium kinetic and thermodynamic studies of Cr(VI) adsorption onto a novel adsorbent of <Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> waste: Batch and column reactors

Cr(VI) adsorption onto Eucalyptus camaldulensis sawdust (ECS) waste was investigated in batch and column reactors. Various parameters, including the adsorbent dose, pH, initial concentration, particle size, contact time and temperature were optimized. The maximum adsorption capacity (35.58mg g^-1, 71.16%) was achieved at pH 2.0. Data fitted well to Freundlich and Halsey’s models (R²=0.992), indicating the multilayer adsorption of Cr(VI). It obeys the pseudo-second order kinetics. Endothermic and non-spontaneous nature of Cr(VI) adsorption was observed with positive values of changes in enthalpy (9.83 kJ mol^-1), and Gibbs-free energy (1.52, 1.38, 1.24, 1.10 and 0.97 kJ mol^-1), respectively. In this column study, the breakthrough curve time increased from 670 to 1,270min by increasing the bed height from 5 to 15 cm, respectively. Column data was found well fitted to bed depth service time model. Adsorption capacity at 60% breakthrough was 2,443.636mg L^-1. The study indicates that ECS waste can be a promising adsorbent for Cr(VI) remediation from industrial effluents.     

CO2 adsorption performance of polyethyleneimine-modified ion-exchange resin

A series of solid amine adsorbents were prepared by the template method with ion-exchange resin (D001) as the carrier and polyethyleneimine (PEI) as the modifier. The absorbents were characterized by energy disperse spectroscopy (EDS), scanning electron microscope (SEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) techniques. The effects of PEI loading, adsorption temperature and influent velocities on CO₂ adsorption capacity in a fixed-bed reactor were investigated. The results show that the solid amine adsorbent prepared by the template method had a better PEI dispersion, stability and CO₂ adsorption capacity. The maximum CO₂ adsorption capacity was 3.98 mmol·g^?1 when PEI loading was 30%, the adsorption temperature was 65°C and the influent velocity was 40 mL·min^?1. The CO₂ adsorption capacity decreased only by 9.50% after 10 cycles of adsorption–desorption tests. The study of kinetics indicates that both chemical adsorption and physical adsorption occurred in the CO₂ adsorption process. The CO₂ adsorption process included fast breakthrough adsorption and gradually approaching equilibrium stage. The particle internal diffusion process was the control step for CO₂ adsorption.     

Comparison of Cr(VI) Adsorption Using Synthetic Schwertmannite Obtained by Fe3+ Hydrolysis and Fe2+ Oxidation: Kinetics,Isotherms and Adsorption Mechanism

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe³⁺ hydrolysis (SCH_A) and Fe²⁺ oxidation (SCH_B). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g⁻¹ for SCH_A and SCH_B. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO₄²⁻ groups.     

Removal of toxic metal Cr(VI) from aqueous solutions using sawdust as adsorbent: Equilibrium, kinetics and regeneration studies

In the present study, a low-cost adsorbent is developed from the naturally and abundantly available sawdust which is biodegradable. The removal capacity of Cr(VI) from aqueous solutions and from the synthetically prepared industrial effluent of electroplating and tannery industries is obtained. The batch experiments are carried out to investigate the effect of the significant process parameters such as initial pH, change in pH during adsorption, contact time, adsorbent amount, and the initial Cr(VI) concentration. The maximum adsorption of Cr(VI) on sawdust is obtained at an initial pH value of 1. The value of pH increases with increase in contact time and initial Cr(VI) concentration. The equilibrium data for the adsorption of Cr(VI) on sawdust is tested with various adsorption isotherm models such as Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Tempkin, Dubinin–Radushkevich and Generalized equation. The Langmuir isotherm model is found to be the most suitable one for the Cr(VI) adsorption using sawdust and the maximum adsorption capacity obtained is 41.5 mg g⁻¹ at a pH value of 1. The adsorption process follows the second-order kinetics and the corresponding rate constants are obtained. Desorption of Cr(VI) from sawdust using acid and base treatment exhibited a higher desorption efficiency by more than 95%. A feasible solution is proposed, for the disposal of the contaminant (acid and base solutions) containing high concentration of Cr(VI) obtained during the desorption process. The interference of other ions which are generally present in the electroplating and tannery industrial effluent streams on the Cr(VI) removal is investigated.     

Use of polyethylene films photografted with 2‐(dimethylamino)ethyl methacrylate as a potential adsorbent for removal of chromium (VI) from aqueous medium

A new polymeric adsorbent material based on polyethylene (PE) was prepared by photografting of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) as a positively chargeable monomer to a PE film. The effects of the experimental parameters, such as the pH value, temperature, and grafted amount on adsorption of chromium(VI) (Cr(VI)) ions were investigated for the DMAEMA‐grafted PE (PE‐g‐PDAMEMA) films. The maximum adsorption capacity was obtained at the initial pH value of 3.0 for a PE‐g‐PDMAEMA film with 1.8 mmol/g and the maximum adsorption capacity obtained was higher than or compatible to those of many of the other polymeric adsorbents prepared for Cr(VI) ions. The adsorption kinetics obeyed the mechanism of the pseudo‐second order kinetic model and adsorption of Cr(VI) ions on PE‐g‐PDMAEMA films was well expressed by the Langmuir isotherm model. A high Langmuir adsorption constant suggests that the adsorption of Cr(VI) ions occurs between protonated dimethylamino groups and ions mainly through the electrostatic interaction. Cr(VI) ions adsorbed were successfully desorbed from a PE‐g‐PDMAEMA film in solutions of NaCl, NH₄Cl, NH₄Cl containing NaOH, and NaOH and a PE‐g‐PDMAEMA film was regenerated and repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43360.     

High adsorption of Cd (II) by modification of synthetic zeolites Y,A and mordenite with thiourea

Zeolites Y, A and mordenite (ZY, ZA and ZM) were obtained from diatomite in a template-free system, and the products were modified by thiourea (TU). Characterization studies results indicated that the TU molecules were loaded onto the exterior surfaces of the synthetic zeolites as well as the channels. Elemental analysis and energy-dispersive X-ray spectrometer proved that the TU molecules loaded on to ZA were more than ZY and ZM. Removal of Cd(II) was investigated, and it was found that the modified zeolites have higher removal capacity, modified ZA is especially noticeable. In the adsorption experiments, the effects of various parameters such as sorbent content, contact time, concentration of cadmium solution, pH, selectivity and regeneration were discussed. At the best removal efficiency by modified zeolites, the maximum adsorption capacity is 94.3 mg·g⁻¹, 103.2 mg·g⁻¹ and 89.7 mg·g⁻¹ at 25 °C, respectively. The sorbents show good efficiency for the removal of Cd(II) in the presence of different multivalent cations and have good regeneration effect. For the modified samples, removal experiments take place via ion exchange and complexation processes.