Simultaneous removal and oxidation of arsenic from water by δ-MnO2 modified activated carbon

The ubiquitous arsenic in groundwater poses a great risk to human health due to its environmental toxicity and carcinogenicity. In the present work, a new adsorbent, δ-MnO₂ modified activated carbon, was prepared, and its performance for the uptake of arsenate and arsenite species from aqueous solutions was investigated by batch experiments. Various techniques, including FESEM-EDX, p-XRD, XPS and BET surface area analysis, were employed to characterize the properties of the adsorbent and the arsenic adsorption mechanisms. The results showed that δ-MnO₂ covered on the surface and padded in the pores of the activated carbon. Adsorption kinetic studies revealed that approximately 90.1% and 76.8% of As(III) and As(V), respectively, were removed by the adsorbent in the first 9 hr, and adsorption achieved equilibrium within 48 hr. The maximum adsorption capacities of As(V) and As(III) at pH 4.0 calculated from Langmuir adsorption isotherms were 13.30 and 12.56 mg/g, respectively. The effect of pH on As(V) and As(III) removal was similar, and the removal efficiency significantly reduced with the increase of solution pH. Arsenite oxidation and adsorption kinetics showed that the As(V) concentration in solution due to As(III) oxidation and reductive dissolution of MnO₂ increased rapidly during the first 12 min, and then gradually decreased. Based on the XPS analysis, nearly 93.3% of As(III) had been oxidized to As(V) on the adsorbent surface and around 38.9% of Mn(IV) had been reduced to Mn(II) after As(III) adsorption. This approach provides a possible method for the purification of arsenic-contaminated groundwater.     

Pb（II） biosorption using chitosan and chitosan derivatives beads： Equilibrium, ion exchange and mechanism studies

The study examined the adsorption of Pb(II) ions from aqueous solution onto chitosan, chitosan-GLA and chitosan-alginate beads. Several important parameters influencing the adsorption of Pb(II) ions such as initial pH, adsorbent dosage and di erent initial concentration of Pb(II) ions were evaluated. The mechanism involved during the adsorption process was explored based on ion exchange study and using spectroscopic techniques. The adsorption capacities obtained based on non–linear Langmuir isotherm for chitosan, chitosan-GLA and chitosan-alginate beads in single metal system were 34.98, 14.24 and 60.27 mg/g, respectively. However, the adsorption capacity of Pb(II) ions were reduced in the binary metal system due to the competitive adsorption between Pb(II) and Cu(II) ions. Based on the ion exchange study, the release of Ca2+, Mg2+, K+ and Na+ ions played an important role in the adsorption of Pb(II) ions by all three adsorbents but only at lower concentrations of Pb(II) ions. Infrared spectra showed that the binding between Pb(II) ions and the adsorbents involved mostly the nitrogen and oxygen atoms. All three adsorbents showed satisfactory adsorption capacities and can be considered as an e cient adsorbent for the removal of Pb(II) ions from aqueous solutions.     

Shellac-coated iron oxide nanoparticles for removal of cadmium(II) ions from aqueous solution

This study describes a new effective adsorbent for cadmium removal from aqueous solution synthesized by coating a shellac layer, a natural biodegradable and renewable resin with abundant hydroxyl and carboxylic groups, on the surface of iron oxide magnetic nanoparticles. Transmission Electron Microscopy (TEM) imaging showed shellac-coated magnetic nanoparticle (SCMN) adsorbents had a core-shell structure with a core of 20 nm and shell of 5 nm. Fourier Transform Infrared Spectroscopic analysis suggested the occurrence of reaction between carboxyl groups on the SCMN adsorbent surface and cadmium ions in aqueous solution. Kinetic data were well described by pseudo second-order model and adsorption isotherms were fitted with both Langmuir and Freundlich models with maximum adsorption capacity of 18.80 mg/g. SCMN adsorbents provided a favorable adsorption capacity under high salinity conditions, and cadmium could easily be desorbed using mild organic acid solutions at low concentration.     

Removal of antibiotics from aqueous solution by using porous adsorbent templated from eco-friendly Pickering aqueous foams

The aqueous foam template without any solvent and only using the particles stabilizer has attracted much attention for preparation of the porous adsorbents. Herein, a novel porous adsorbent was fabricated via thermal-initiated polymerization of Pickering aqueous foams, which was stabilized by the natural sepiolite (Sep) and pine pollen, and utilized for the removal of antibiotic from aqueous solution. The stabilizing mechanism of Pickering aqueous foam of that the Sep was modified with the leaching substance from pine pollen and arranged orderly around the bubble to form a dense “shell” structure was revealed. The adsorbents possessed the hierarchical porous structure and excellent adsorption performance for antibiotic of chlorotetracycline hydrochloride (CTC) and tetracycline hydrochloride (TC). The equilibrium adsorption capacities of CTC and TC were achieved with 465.59 and 330.59 mg/g within 60 min at 25°C, respectively. The adsorption process obeyed Langmuir model and pseudo-second-order adsorption kinetic model. This work provided eco-friendly approach for fabricate porous adsorbents for wastewater treatment.     

Simultaneous adsorption of lead and cadmium on MnO2-loaded resin

MnO2-loaded D301 weak basic anion exchange resin has been used as adsorbent to simultaneously remove lead and cadmium ions from aqueous solution. The e ects of adsorbent dosage, solution pH and the coexistent ions on the adsorption were investigated. Experimental results showed that with the adsorbent dosage more than 0.6 g/L, both Pb2+ and Cd2+ were simultaneously removed at pH range 5–6. Except for HPO4 2??, the high concentration coexistent ions such as Na+, K+, Cl??, NO3??, SO4 2?? and HCO3??, showed no significant e ect on the removal e ciency of both Pb2+ and Cd2+ under the experimental conditions. The coexistence of Mg2+, Ca2+ caused the reduction of Cd2+ removal, but not for Pb2+. The adsorption equilibrium for Pb2+ and Cd2+ could be excellently described by the Langmuir isotherm model with R2 > 0.99. The maximum adsorption capacity was calculated as 80.64 mg/g for Pb2+ and 21.45 mg/g for Cd2+. The adsorption processes followed the pseudo first-order kinetics model. MnO2-loaded D301 resin has been shown to have a potential to be used as an e ective adsorbent for simultaneous removal of lead and cadmium ions from aqueous solution.     

Synthesis of malachite@clay nanocomposite for rapid scavenging of cationic and anionic dyes from synthetic wastewater

Synthesis of malachite@clay nanocomposite was successfully carried out for the removal of cationic (Methylene Blue, MB) and anionic dyes (Congo Red, CR) from synthetic wastewater. Nanocomposite was characterized by TEM, SEM, FT-IR, EDS analysis and zeta potential. TEM analysis indicated that the particle diameter of nanocomposite was in the range of 14 to 23 nm. Various important parameters viz. contact time, concentration of dyes, nanocomposite dosage, temperature and solution pH were optimized to achieve maximum adsorption capacity. In the case of MB, removal decreased from 99.82% to 93.67% while for CR, removal decreased from 88.55% to 75.69% on increasing dye concentration from 100 to 450 mg/L. pH study confirmed the higher removal of CR in acidic range while MB removal was higher in alkaline range. Kinetic study revealed the applicability of pseudo-second-order model for the adsorption of both dyes. Negative values of ΔG⁰ for both systems suggested the feasibility of dye removal and support for spontaneous adsorption of CR and MB on nanocomposite. Nanocomposite showed 277.77 and 238.09 mg/g Langmuir adsorption capacity for MB and CR respectively. Desorption of dyes from the dye loaded nanocomposite was easily carried out with acetone. The results indicate that the prepared malachite@clay nanocomposite is an efficient adsorbent with high adsorption capacity for the aforementioned dyes.     

Cadmium sorption by sodium and thiourea-modified zeolite-rich tuffs

In the present investigation, two zeolite-rich tuffs from Guaymas and El Cajon(State of Sonora), which were conditioned with a sodium chloride solution and subsequently modified with a thiourea solution, were chosen to evaluate the removal of Cd from aqueous systems. The zeolitic materials were characterized by scanning electron microscopy and X-ray diffraction. The surface area was also determined. The experiments were performed in a batch system, and the influences of p H, contact time between phases, and the concentration of Cd in the solution on the adsorption by sodium or thiourea-modified zeolite-rich tuff were investigated. It was found that the efficiency of Cd ion removal from aqueous solutions is influenced by the p H of the aqueous systems. The Cd adsorption kinetic data were well fitted to a pseudo-second-order model in all cases. The Langmuir and Langmuir–Freundlich isotherms adequately described the Cd sorption behavior by the zeolite from El Cajon pretreated with Na Cl and the zeolite from Guaymas modified with thiourea, respectively.     

Sequestration of toxic Pb（II） ions by chemically treated rubber （Hevea brasiliensis ） leaf powder

Rubber leaf powder (an agricultural waste) was treated with potassium permanganate followed by sodium carbonate and its performance in the removal of Pb(II) ions from aqueous solution was evaluated. The interactions between Pb(II) ions and functional groups on the adsorbent surface were confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX). The effects of several important parameters which can affect adsorption capacity such as pH, adsorbent dosage, initial lead concentration and contact time were studied. The optimum pH range for lead adsorption was 4–5. Even at very low adsorbent dosage of 0.02 g, almost 100% of Pb(II) ions (23 mg/L) could be removed. The adsorption capacity was also dependent on lead concentration and contact time, and relatively a short period of time (60–90 min) was required to reach equilibrium. The equilibrium data were analyzed with Langmuir, Freundlich and Dubinin-Radushkevich isotherms. Based on Langmuir model, the maximum adsorption capacity of lead was 95.3 mg/g. Three kinetic models including pseudo first-order, pseudo second-order and Boyd were used to analyze the lead adsorption process, and the results showed that the pseudo second-order fitted well with correlation coefficients greater than 0.99.     

Synthesis of linear low-density polyethylene-g-poly(acrylic acid)-co-starch/organo-montmorillonite hydrogel composite as an adsorbent for removal of Pb(Ⅱ) from aqueous solutions

The purpose of this work is to remove Pb(II) from the aqueous solution using a type of hydrogel composite. A hydrogel composite consisting of waste linear low density polyethylene, acrylic acid, starch, and organo-montmorillonite was prepared through emulsion polymerization method. Fourier transform infrared spectroscopy(FTIR), Solid carbon nuclear magnetic resonance spectroscopy(CNMR)), silicon-29 nuclear magnetic resonance spectroscopy(Si NMR)), and X-ray diffraction spectroscope((XRD) were applied to characterize the hydrogel composite. The hydrogel composite was then employed as an adsorbent for the removal of Pb(II) from the aqueous solution. The Pb(II)-loaded hydrogel composite was characterized using Fourier transform infrared spectroscopy(FTIR)),scanning electron microscopy(SEM)), and X-ray photoelectron spectroscopy((XPS)). From XPS results, it was found that the carboxyl and hydroxyl groups of the hydrogel composite participated in the removal of Pb(II). Kinetic studies indicated that the adsorption of Pb(II)followed the pseudo-second-order equation. It was also found that the Langmuir model described the adsorption isotherm better than the Freundlich isotherm. The maximum removal capacity of the hydrogel composite for Pb(II) ions was 430 mg/g. Thus, the waste linear low-density polyethylene-g-poly(acrylic acid)-co-starch/organo-montmorillonite hydrogel composite could be a promising Pb(II) adsorbent.     

Pb(Ⅱ) biosorption using chitosan and chitosan derivatives beads: Equilibrium,ion exchange and mechanism studies

The study examined the adsorption of Pb(II) ions from aqueous solution onto chitosan, chitosan-GLA and chitosan-alginate beads. Several important parameters influencing the adsorption of Pb(II) ions such as initial pH, adsorbent dosage and different initial concentration of Pb(II) ions were evaluated. The mechanism involved during the adsorption process was explored based on ion exchange study and using spectroscopic techniques. The adsorption capacities obtained based on non-linear Langmuir isotherm for ch...     

Removal of Cd2+ from water by Friedel’s salt (FS: 3CaO.Al2O3·CaCl2·10H2O): Sorption characteristics and mechanisms

The development of low-cost and efficient new mineral adsorbents has been a hot topic in recent years. In this study, Friedel’s salt (FS:3CaO·A12O3 ·CaCl2 ·10H2O), a hexagonal layered inorganic absorbent, was synthesized to remove Cd2+ from water. The adsorption process was simulated by Langmuir and Freundlich models. The adsorption mechanism was further analyzed with TEM, XRD, FT-IR analysis and monitoring of metal cations released and solution pH variation. The results indicated the adsorbent FS had an outstanding ability for Cd(Ⅱ) adsorption. The maximum adsorption capacity of the FS for Cd(Ⅱ) removal can reach up to 671.14 mg/g. The nearly equal numbers of Cd2+ adsorbed and Ca2+ released demonstrated that ion-exchange (both surface and inner) of the FS for Cd(Ⅱ) played an important role during the adsorption process. Furthermore, the surface of the FS after adsorption was microscopically disintegrated while the inner lamellar structure was almost unchanged. The behavior of Cd(Ⅱ) adsorption by FS was significantly affected by surface reactions. The mechanisms of Cd2+ adsorption by the FS mainly included surface complexation and surface precipitation. In the present study, the adsorption process was fitted better by the Langmuir isotherm model (R2 = 0.9999) than the Freundlich isotherm model (R2 = 0.8122). Finally, due to the high capacity for ion-exchange on the FS surface, FS is a promising layered inorganic adsorbent for the removal of Cd(Ⅱ) from water.     

Influence of moderate pre-oxidation treatment on the physical, chemical and phosphate adsorption properties of iron-containing activated carbon

A novel adsorbent based on iron oxide dispersed over activated carbon(AC) were prepared, and used for phosphate removal from aqueous solutions. The influence of pre-oxidation treatment on the physical, chemical and phosphate adsorption properties of iron-containing AC were determined. Two series of ACs, non-oxidized and oxidized carbon modified by iron(denoted as AC-Fe and AC/OFe), resulted in a maximum impregnated iron of 4.03% and 7.56%, respectively. AC/O-Fe showed 34.0%–46.6% higher phosphate removal efficiency than the AC-Fe did. This was first attributed to the moderate pre-oxidation of raw AC by nitric acid, achieved by dosing Fe(II) after a pre-oxidation, to obtain higher iron loading, which is favorable for phosphate adsorption. Additionally, the in-situ formed active site on the surface of carbon, which was derived from the oxidation of Fe(II) by nitric acid dominated the remarkably high efficiency with respect to the removal of phosphate. The activation energy for adsorption was calculated to be 10.53 and 18.88 kJ/mol for AC-Fe and AC/OFe, respectively. The results showed that the surface mass transfer and intra-particle diffusion were simultaneously occurring during the process and contribute to the adsorption mechanism.     

Kinetics and thermodynamic studies of Methyl Orange removal by polyvinylidene fluoride-PEDOT mats

We report the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT)-modified polyvinylidene fluoride electrospun fibers and their use as a novel adsorbent material for the removal of the anionic dye Methyl Orange (MO) from aqueous media. This novel adsorbent material can be used to selectively remove MO on a wide pH range (3.0–10.0), with a maximum capacity of 143.8 mg/g at pH 3.0. When used in a recirculating filtration system, the maximum absorption capacity was reached in a shorter time (20 min) than that observed for batch mode experiments (360 min). Based on the analyses of the kinetics and adsorption isotherm data, one can conclude that the predominant mechanism of interaction between the membrane and the dissolved dye molecules is electrostatic. Besides, considering the estimated values for the Gibbs energy, and entropy and enthalpy changes, it was established that the adsorption process is spontaneous and occurs in an endothermic manner. The good mechanical and environmental stability of these membranes allowed their use in at least 20 consecutive adsorption/desorption cycles, without significant loss of their characteristics. We suggest that the physical-chemical characteristics of PEDOT make these hybrid mats a promising adsorbent material for use in water remediation protocols and effluent treatment systems.     

Selective adsorption of silver ions from aqueous solution using polystyrene-supported trimercaptotriazine resin

Trimercaptotriazine-functionalized polystyrene chelating resin was prepared and employed for the adsorption of Ag(I) from aqueous solution. The adsorbent was characterized according to the following techniques: Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy and the Brunauer-Emmet-Teller method. The effects of initial Ag(I) concentration, contact time, solution pH and coexisting ions on the adsorption capacity of Ag(I) were systematically investigated. The maximum adsorption capacity of Ag(I) was up to 187.1 mg/g resin at pH 0.0 and room temperature. The kinetic experiments indicated that the adsorption rate of Ag(I) onto the chelating resin was quite fast in the first 60 min and reached adsorption equilibrium after 360 min. The adsorption process can be well described by the pseudo second-order kinetic model and the equilibrium adsorption isotherm was closely fitted by the Langmuir model. Moreover, the chelating resin could selectively adsorb more Ag(I) ions than other heavy metal ions including: Cu(II), Zn(II), Ni(II), Pb(II) and Cr(III) during competitive adsorption in the binary metal species systems, which indicated that it was a highly selective adsorbent of Ag(I) from aqueous solution.     

Removal of phosphate by Fe-coordinated amino-functionalized 3D mesoporous silicates hybrid materials

Phosphate removal from aqueous waste streams is an important approach to control the eutrophication downstream bodies of water. A Fe(III) coordinated amino-functionalized silicate adsorbent for phosphate adsorption was synthesized by a post-grafting and metal cation incorporation process. The surface structure of the adsorbent was characterized by X-ray di raction, N2 adsoropion/desoprotion technique, and Fourier transform infrared spectroscopy. The experimental results showed that the adsorption equilibrium data were well fitted to the Langmuir equation. The maximum adsorption capacity of the modified silicate material was 51.8 mg/g. The kinetic data from the adsorption of phosphate were fitted to pseudo second-order model. The phosphate adsorption was highly pH dependent and the relatively high removal of phosphate fell within the pH range 3.0–6.0. The coexistence of other anions in solutions has an adverse e ect on phosphate adsorption; a decrease in adsorption capacity followed the order of exogenous anions: F?? > SO2?? 4 > NO??3 > Cl??. In addition, the adsorbed phosphate could be desorbed by NaOH solutions. This silicate adsorbent with a large adsorption capacity and relatively high selectivity could be utilized for the removal of phosphate from aqueous waste streams or in aquatic environment.     

Removal of cadmium using MnO2 loaded D301 resin

MnO2 loaded weak basic anion exchange resin D301 （Anion exchange resin, macroreticular weak basic styrene） as adsorbent has been prepared and applied to the removal of cadmium. The adsorption characteristics have been investigated with respect to effect of pH, equilibrium isotherms, removal kinetic data, and interference of the coexisting ions. The results indicated that the Cd^2＋ could be efficiently removed using MnO2 loaded D301 resin in the pH range of 3-8 from aqueous solutions with the co-existence of high concentration of alkali and alkaline-earth metals ions. The saturate adsorption capacity of the Cd^2＋ was 77.88 mg/g. The adsorption process followed the pseudo first-order kinetics. The equilibrium data obtained in this study accorded excellently with the Langmuir adsorption isotherm.     

Ciprofloxacin adsorption from aqueous solution onto chemically prepared carbon from date palm leaflets

A chemically prepared carbon was synthesized from date palm leaflets via sulphuric acid carbonization at 160℃. Adsorption of ciprofloxacin (CIP) from aqueous solution was investigated in terms of time, pH, concentration, temperature and adsorbent status (wet and dry). The equilibrium time was found to be 48 hr. The adsorption rate was enhanced by raising the temperature for both adsorbents, with adsorption data fitting a pseudo second-order model well. The activation energy, E_a, was found to be 17 kJ/mol, indicating a diffusion-controlled, physical adsorption process. The maximum adsorption was found at initial pH 6. The wet adsorbent showed faster removal with higher uptake than the dry adsorbent, with increased performance as temperature increased (25-45℃). The equilibrium data were found to fit the Langmuir model better than the Freundlich model. The thermodynamic parameters showed that the adsorption process is spontaneous and endothermic. The adsorption mechanism is mainly related to cation exchange and hydrogen bonding.     

Preparation and characterization of a lipoid adsorption material and its atrazine removal performance

A novel adsorbent named lipoid adsorption material (LAM), with a hydrophobic nucleolus (triolein) and a hydrophilic membrane structure (polyamide), was synthesized to remove hydrophobic organic chemicals (HOCs) from solution. Triolein, a type of lipoid, was entrapped by the polyamide membrane through an interfacial polymerization reaction. The method of preparation and the structure of the LAM were investigated and subsequent experiments were conducted to determine the characteristics of atrazine (a type of HOC) removal from wastewater using LAM as the adsorbent. The results showed that LAM had a regular structure compared with the prepolymer, where compact particles were linked with each other and openings were present in the structure of the LAM in which the fat drops formed from triolein were entrapped. In contrast to the atrazine adsorption behavior of powdered activated carbon (PAC), LAM showed a persistent adsorption capacity for atrazine when initial concentrations of 0.57, 1.12, 8.31 and 19.01 mg/L were present, and the equilibrium time was 12 hr. Using an 8 mg/L initial concentration of atrazine as an indicator of HOCs in aqueous solution, experiments on the adsorption capacity of the LAM showed 69.3% removal within 6–12 hr contact time, which was close to the 75.5% removal of atrazine by PAC. Results indicated that LAM has two atrazine removal mechanisms, namely the bioaccumulation of atrazine by the nucleous material and physical adsorption to the LAM membrane. Bioaccumulation was the main removal mechanism.     

Pb(II) removal from water using Fe-coated bamboo charcoal with the assistance of microwaves

Bamboo charcoal(BC) was used as starting material to prepare iron-modified bamboo charcoal(Fe-MBC) by its impregnation in FeCl 3 and HNO 3 solutions simultaneously,followed by microwave heating.The material can be used as an adsorbent for Pb(Ⅱ) contaminants removal in water.The composites were prepared with Fe molar concentration of 0.5,1.0 and 2.0 mol/L and characterized by means of N 2 adsorption-desorption isotherms,X-ray diffraction spectroscopy(XRD),scanning electron microscopy coupled with energy dispersive X-ray spectrometry(SEM-EDS),Fourier transform infrared(FT-IR) and point of zero charge(pH pzc) measurements.Nitrogen adsorption analyses showed that the BET specific surface area and total pore volume increased with iron impregnation.The adsorbent with Fe molar concentration of 2 mol/L(2Fe-MBC) exhibited the highest surface area and produced the best pore structure.The Pb(Ⅱ) adsorption process of 2Fe-MBC and BC were evaluated in batch experiments and 2Fe-MBC showed an excellent adsorption capability for removal Pb(Ⅱ).The adsorption of Pb(Ⅱ) strongly depended on solution pH,with maximum values at pH 5.0.The ionic strength had a significant effect on the adsorption at pH < 6.0.The adsorption isotherms followed the Langmuir isotherm model well,and the maximum adsorption capacity for Pb(Ⅱ) was 200.38 mg/g for 2Fe-MBC.The adsorption processes were well fitted by a pseudo second-order kinetic model.Thermodynamic parameters showed that the adsorption of Pb(Ⅱ) onto Fe-MBC was feasible,spontaneous,and exothermic under the studied conditions,and the ion exchange mechanism played an significant role.These results have important implications for the design of low-cost and effective adsorbents in the removal of Pb(Ⅱ) from wastewater.     

Removal of heavy metals from aqueous solution by sawdust adsorption

The adsorption of lead, cadmium and nicel from aqueous solution by sawdust of walnut was investigated. The effect of contact time, initial metal ion concentration and temperature on metal ions removal has been studied. The equilibrium time was found to be of the order of 60 min. Kinetics fit pseudo first-order, second-order and intraparticle diffusion models, hence adsorption rate constants were calculated. The adsorption data of metal ions at temperatures of 25, 45 and 60~C have been described by the Freundlich and Langmuir isotherm models. The thermodynamic parameters such as energy, entropy and enthalpy changes for the adsorption of heavy metal ions have also been computed and discussed. Ion exchange is probably one of the major adsorption mechanisms for binding divalent metal ions to the walnut sawdust. The selectivity order of the adsorbent is Pb（I1）~Cd（II）〉Ni（I1）. From these results, it can be concluded that the sawdust of walnut could be a good adsorbent for the metal ions from aqueous solutions.