Adsorption of acid dyes from aqueous solutions by the ethylenediamine-modified magnetic chitosan nanoparticles

The adsorption characteristics of Acid Orange 7(AO7) and Acid Orange 10 (AO10) from aqueous solutions onto the ethylenediamine-modified magnetic chitosan nanoparticles (EMCN) have been investigated. The EMCN were essentially monodispersed and had a main particle size distribution of 15-40 nm and saturated magnetization of 25.6 emu/g. The adsorption experiments indicated that the maximum adsorption capacity occurred at pH 4.0 for AO7 and pH 3.0 for AO10, respectively. Due to the small diameter and the high surface reactivity, the adsorption equilibrium of AO7 and AO10 onto the EMCN reached very quickly. Equilibrium experiments fitted well with the Langmuir isotherm model, and the maximum adsorption capacity of the EMCN at 298K was determined to be 3.47 mmol/g for AO7 and 2.25 mmol/g for AO10, respectively. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were estimated and the results indicated that the adsorption process was spontaneous and exothermic. Furthermore, the EMCN could be regenerated through the desorption of the dyes in NH(4)OH/NH(4)Cl solution (pH 10.0) and could be reused to adsorb the dyes again.     

Formicary-like carbon nanotube/copper hybrid nanostructures for carbon fiber-reinforced composites by electrophoretic deposition

An electrophoretic deposition process has been applied to produce unique carbon nanotube (CNT)/copper nanostructures on the carbon fiber surfaces. During the deposition process, ionized copper and positively charged CNTs are accelerated towards the carbon fiber under applied electric fields. An interconnected formicary-like network of nanotubes and nanoparticles is formed where copper nucleation and growth occurs predominantly at nanotube crossing and edge-contact locations. When embedded in a structural composite the CNT/copper structures create a highly conductive and strongly bonded network shown by significant enhancements in both electrical conductivity and interlaminar shear strength as compared to composites without the CNT/copper nanostructures.     

Application of oak powder/Fe3O4 magnetic composite in toxic metals removal from aqueous solutions

In this study, the capability of a magnetic composite of oak powder/Fe₃O₄ (OP/Fe₃O₄) for the adsorption of lead, cobalt, and nickel ions from aqueous solutions was examined. Characteristics and structure of oak powder (OP) and OP/Fe₃O₄ magnetic composite were explored by FTIR, SEM, TGA-DTG, VSM, and XRD analysis. The XRD results showed that OP/Fe₃O₄ magnetic composite and OP were in crystalline form. Kinetic behavior of adsorption process was studied using pseudo-first-order, pseudo-second-order, and Elovich models. Results indicated that the pseudo-second-order model (R²?>?0.999) can better describe the kinetic behavior of the metal adsorption process. Equilibrium behavior of the adsorption process was also tested using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Scatchard isotherm models. The results revealed that the adsorption equilibrium data for three metals match with the Freundlich isotherm model (R²?>?0.99). This indicates the effectiveness of heterogeneous surfaces in comparison with homogeneous ones in the adsorption process of metal ions. Moreover, the results showed that the adsorption process of metal ions with the OP/Fe₃O₄ magnetic composite is physical. Finally, negative values of enthalpy and entropy indicated that the process of the metal ion adsorption is spontaneous and exothermic.     

Magnetomicelles: composite nanostructures from magnetic nanoparticles and cross-linked amphiphilic block copolymers

We report the synthesis, characterization, and covalent surface chemistry of "magnetomicelles", cross-linked, amphiphilic block-copolymer micelles that encapsulate superparamagnetic iron oxide nanoparticles. Because these composite nanostructures assemble spontaneously from solution by simultaneous desolvation of nanoparticle and amphiphilic poly(styrene(250)-block-acrylic acid(13)) components, explicit surface functionalization of the particles is not required, and the encapsulation method was applied to different magnetic nanoparticle sizes and compositions. TEM images of the magnetomicelles illustrated that the number of encapsulated particles could be dictated rationally by synthetic conditions. The magnetic properties of the particles were characterized by SQUID magnetometry and followed the general Langevin magnetic model for superparamagnetic materials. The micellar shells of these particles were functionalized using covalent chemistry that would not ordinarily be possible on the magnetic particle surface. As a result, this noncovalent approach provides a new route to technological applications of hydrophobic magnetic nanomaterials that lack appropriate conjugate surface chemistry.     

Activated carbon/iron oxide composites for the removal of atrazine from aqueous medium

The adsorption features of activated carbon and the oxidation properties of iron oxides were combined in a composite to produce new materials for atrazine removal from aqueous medium. Activated carbon/iron oxide composites were prepared at 1/1 and 5/1 mass ratios and characterized with powder X-ray diffractometry (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and nitrogen adsorption measurements. The adsorption and oxidation processes were evaluated in batch experiments, in order to monitor the atrazine removal capacity of these composites. The main iron oxide actually present in the composites was goethite (alpha-FeOOH). Impregnation with iron oxide reduced the surface area by its deposition in the activated carbon pores. However, a higher iron concentration promoted a higher oxidation rate, indicating that the efficiency of the oxidation reaction is related with the iron content and not with the pre-concentration of the contaminant on the carbon surface through adsorption process.     

A method for preparing ferric activated carbon composites adsorbents to remove arsenic from drinking water

Iron oxide/activated carbon (FeO/AC) composite adsorbent material, which was used to modify the coal-based activated carbon (AC) 12 x 40, was prepared by the special ferric oxide microcrystal in this study. This composite can be used as the adsorbent to remove arsenic from drinking water, and Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Then, the arsenic desorption can subsequently be separated from the medium by using a 1% aqueous NaOH solution. The apparent characters and physical chemistry performances of FeO/AC composite were investigated by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Batch and column adsorption experiments were carried out to investigate and compare the arsenic removal capability of the prepared FeO/AC composite material and virgin activated carbon. It can be concluded that: (1) the main phase present in this composite are magnetite (Fe(3)O(4)), maghemite (gamma-Fe(2)O(3)), hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeO(OH)); (2) the presence of iron oxides did not significantly affect the surface area or the pore structure of the activated carbon; (3) the comparisons between the adsorption isotherms of arsenic from aqueous solution onto the composite and virgin activated carbon showed that the FeO/AC composite behave an excellent capacity of adsorption arsenic than the virgin activated carbon; (4) column adsorption experiments with FeO/AC composite adsorbent showed that the arsenic could be removed to below 0.01 mg/L within 1250 mL empty bed volume when influent concentration was 0.5mg/L.     

A review on carbon/magnetic metal composites for microwave absorption

At present,developing high-efficiency microwave absorption materials with properties including light-weight,thin thickness,strong absorbing intensity and broad bandwidth is an urgent demand to solve the electromagnetic pollution issues.An ideal microwave absorber should have excellent dielectric and magnetic loss capabilities,thereby inducing attenuation and absorption of incident electromagnetic radiation.Recently,various carbon/magnetic metal composites have been developed and expected to become promising candidates for high-performance microwave absorbers.In this review,we introduce the mechanisms of microwave absorption and summarize the recent advances in carbon/magnetic metal composites.Preparation methods and microwave absorption properties of carbon/magnetic metal com-posites with different components,morphologies and microstructures are discussed in detail.Finally,the challenges and future prospects of carbon/magnetic metal absorbing materials are also proposed,which will be useful to develop high-performance microwave absorption materials.     

Magnetic chitosan nanoparticles for removal of Cr(VI) from aqueous solution

A simple method was introduced to prepare magnetic chitosan nanoparticles by co-precipitation via epichlorohydrin cross-linking reaction. The average size of magnetic chitosan nanoparticles is estimated at ca. 30 nm. It was found that the adsorption of Cr(VI) was highly pH-dependent and its kinetics follows the pseudo-second-order model. Maximum adsorption capacity (at pH 3, room temperature) was calculated as 55.80 mg·g^? 1, according to Langmuir isotherm model. The nanoparticles were thoroughly characterized before and after Cr(VI) adsorption. From this result, it can be suggested that magnetic chitosan nanoparticles could serve as a promising adsorbent for Cr(VI) in wastewater treatment technology.     

New solutions for designing promising devices based on low-voltage field emission from carbon nanostructures

New approaches to the problems of criticality of field emission with respect to the construction and technological factors are analyzed, and examples of their practical application are considered. These approaches provide practical applications of carbon nanotubes and carbonaceous planar-edge field-emission structures in extreme electronics areas.     

Low-cost adsorbents for heavy metals uptake from contaminated water: a review

In this article, the technical feasibility of various low-cost adsorbents for heavy metal removal from contaminated water has been reviewed. Instead of using commercial activated carbon, researchers have worked on inexpensive materials, such as chitosan, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The results of their removal performance are compared to that of activated carbon and are presented in this study. It is evident from our literature survey of about 100 papers that low-cost adsorbents have demonstrated outstanding removal capabilities for certain metal ions as compared to activated carbon. Adsorbents that stand out for high adsorption capacities are chitosan (815, 273, 250 mg/g of Hg(2+), Cr(6+), and Cd(2+), respectively), zeolites (175 and 137 mg/g of Pb(2+) and Cd(2+), respectively), waste slurry (1030, 560, 540 mg/g of Pb(2+), Hg(2+), and Cr(6+), respectively), and lignin (1865 mg/g of Pb(2+)). These adsorbents are suitable for inorganic effluent treatment containing the metal ions mentioned previously. It is important to note that the adsorption capacities of the adsorbents presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentration of adsorbate.     

Use of Ponkan mandarin peels as biosorbent for toxic metals uptake from aqueous solutions

Waste Ponkan mandarin (Citrus reticulata) peel was used as biosorbent to extract Ni(II), Co(II) and Cu(II) from aqueous solutions at room temperature. To achieve the best adsorption conditions the influence of pH and contact time were investigated. The isotherms of adsorption were fitted to the Langmuir equation. Based on the capacity of adsorption of the natural biosorbent to interact with the metallic ions, the following results were obtained 1.92, 1.37 and 1.31 mmol g(-1) for Ni(II), Co(II) and Cu(II), respectively, reflecting a maximum adsorption order of Ni(II)>Co(II)>Cu(II). The quick adsorption process reached the equilibrium before 5, 10 and 15 min for Ni(II), Co(II) and Cu(II), respectively, with maximum adsorptions at pH 4.8. In order to evaluate the Ponkan mandarin peel a biosorbent in dynamic system, a glass column was fulfilled with 1.00 g of this natural adsorbent, and it was fed with 5.00 x 10(-4)mol l(-1) of Ni(II) or Co(II) or Cu(II) at pH 4.8 and 3.5 ml min(-1). The lower breakpoints (BP(1)) were attained at concentrations of effluent of the column attained the maximum limit allowed of these elements in waters (>0.1 mg l(-1)) which were: 110, 100 and 130 bed volumes (V(effluent)/V(adsorbent)), for Ni(II), Co(II) and Cu(II), respectively. The higher breakpoints (BP(2)) were attained when the complete saturation of the natural adsorbent occurred, and the values obtained were: 740, 540 and 520 bed volumes for Ni(II), Co(II) and Cu(II), respectively.     

Untreated coffee husks as biosorbents for the removal of heavy metals from aqueous solutions

The objective of this work was to propose an alternative use for coffee husks (CH), a coffee processing residue, as untreated sorbents for the removal of heavy metal ions from aqueous solutions. Biosorption studies were conducted in a batch system as a function of contact time, initial metal ion concentration, biosorbent concentration and pH of the solution. A contact time of 72 h assured attainment of equilibrium for Cu(II), Cd(II) and Zn(II). The sorption efficiency after equilibrium was higher for Cu(II) (89-98% adsorption), followed by Cd(II) (65-85%) and Zn(II) (48-79%). Even though equilibrium was not attained in the case of Cr(VI) ions, sorption efficiency ranged from 79 to 86%. Sorption performance improved as metal ions concentrations were lowered. The experimental sorption equilibrium data were fitted by both Langmuir and Freundlich sorption models, with Langmuir providing the best fit (R2>0.95). The biosorption kinetics was determined by fitting first and second-order kinetic models to the experimental data, being better described by the pseudo-second-order model (R2>0.99). The amount of metal ions sorbed increased with the biosorbent concentration in the case of Cu(II) and Cr(VI) and did not present significant variations for the other metal ions. The effect of the initial pH in the biosorption efficiency was verified in the pH range of 4-7, and the results showed that the highest adsorption capacity occurred at distinct pH values for each metal ion. A comparison of the maximum sorption capacity of several untreated biomaterial-based residues showed that coffee husks are suitable candidates for use as biosorbents in the removal of heavy metals from aqueous solutions.     

Chemically modified olive stone: a low-cost sorbent for heavy metals and basic dyes removal from aqueous solutions

In the present work, we have investigated the sorption efficiency of treated olive stones (TOS) towards cadmium and safranine removal from their respective aqueous solutions. TOS material was prepared by treatment of olive stones with concentrated sulfuric acid at room temperature followed up by a subsequent neutralization with 0.1 M NaOH aqueous solution. The resulting material has been thoroughly characterized by SEM, energy-dispersive X-ray (EDX), MAS (13)C NMR, FTIR and physicochemical parameters were calculated. The sorption study of TOS at the solid-liquid interface was investigated using kinetics, sorption isotherms, pH effect and thermodynamic parameters. The preliminary results indicate that TOS exhibit a better efficiency in terms of sorption capacities toward the two pollutants (128.2 and 526.3 mg/g for cadmium and safranine, respectively) than those reported so far in the literature. Moreover, the sorption process is ascertained to occur fast enough so that the equilibrium is reached in less than 15 min of contact time. The results found in the course of this study suggest that ion exchange mechanism is the most appropriate mechanism involved in cadmium and safranine removal. Finally, the sorption efficiency of TOS is compared to those of other low-cost sorbents materials yet described in the literature.     

Easy synthesis of surface-tunable carbon-encapsulated magnetic nanoparticles: adsorbents for selective isolation and preconcentration of organic pollutants

We have prepared core/shell structured carbon-encapsulated magnetic nanoparticles (CMNPs) with a simple method by using inorganic iron salt and glucose solution as precursor substance. The synthetic procedure does not require the use of organic solvents. We have utilized X-ray photoelectron spectroscopy, infrared spectroscopy, X-ray diffraction, and Raman analysis to examine the surface properties of CMNPs prepared at different temperature. The specific surface areas, magnetization and contents of graphitized carbon on carbon shell of CMNPs increase with heat treatment temperature. The obtained CMNPs are used to adsorb or preconcentrate bisphenol A (BPA), 4-n-nonylphenol (4-NP), 4-tert-octylphenol (4-OP), diethyl phthalate (DEP), dipropyl phthalate (DPP), dibutyl phthalate (DBP) dicyclohexyl phthalate (DCHP), dioctyl phthalate (DOP), sulfonamide, tetracyclines, and quinolones antibiotics organic compounds from water samples. The adsorption of analytes is mainly based on π-π stacking interaction, hydrophobic interaction and hydrogen bonds between analytes and graphitic carbon. As a result, the adsorption or extraction behaviors of CMNPs to analytes are controlled by the content of oxygen-containing species and graphitized carbon on carbon shell of CMNPs. CMNPs prepared at 200 °C have ample oxygen-containing species (80%) on surface and favor the adsorption and extraction of quinolones antibiotics. CMNPs heated at 300-500 °C with the graphitization efficiency of carbon shell lower than 50% exhibit great preconcentration performance to BPA, 4-NP, 4-OP, DBP, DCHP, DOP, tetracyclines, and quinolones antibiotics. CMNPs prepared at 850 °C are highly graphitized (80%) and have strong adsorption affinity to all model analytes; however, they can quantitatively extract only highly polar sulfonamide antibiotics and moderately polar DEP, DPP because of hard desorption of other model analytes. We suggest that the appropriate adsorbent to certain organic contaminants can be obtained with this technique just by tuning the heat temperature without any post-treatment.     

Sorption of some rare earth elements from aqueous solutions using copolymer/activated carbon composite: Multivariate optimization approach

The present study investigated the sorption of Ce³⁺, Nd³⁺ and Gd³⁺ cations from aqueous solutions via the use of a synthesized poly (acrylamide-acrylic acid)/activated carbon ((P-AM-AA)/AC) prepared by ? Radiation-Induced Template polymerization technique. The effect of absorbed ? radiation dose rate (kGy/hr) and cross linker concentration on the sorption efficacy of the synthesized composite toward the concerned lanthanides was studied. The structure of the synthesized composite was confirmed by different characterization techniques. Batch sorption studies for Ce³⁺, Nd³⁺ and Gd³⁺ onto (P-AM-AA)/AC were investigated as a function of contact time, pH and cations concentration. The response surface methodology (RSM) was employed to optimize and simulate the sorption of the concerned cations from the solution onto the synthesized material. The studied factors include initial cation concentration, solution pH, contact time and temperature. From the desirability analysis it is found that, the optimal sorption efficacy of the cations onto the synthesized sorbent was determined as 50 mg/l, 3.9 pH, 7 min and 333 K for acquiring percentage sorption more than 98% with optimal desirability of 0.99.     

Use of waste materials--Bottom Ash and De-Oiled Soya, as potential adsorbents for the removal of Amaranth from aqueous solutions

Bottom Ash, a power plan t waste material and De-Oiled Soya, an agriculture waste product were successfully utilized in removing trisodium 2-hydroxy-1-(4-sulphonato-1-naphthylazo)naphthalene-3,6-disulphonate--a water-soluble hazardous azo dye (Amaranth). The paper incorporates thermodynamic and kinetic studies for the adsorption of the dye on these two waste materials as adsorbents. Characterization of each adsorbent was carried out by I.R. and D.T.A. curves. Batch adsorption studies were made by measuring effects of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, temperature etc. Specific rate constants for the processes were calculated by kinetic measurements and a first order adsorption kinetics was observed in each case. Langmuir and Freundlich adsorption isotherms were applied to calculate thermodynamic parameters. The adsorption on Bottom Ash takes place via film diffusion process at lower concentrations and via particle diffusion process at higher concentrations, while in the case of De-Oiled Soya process only particle diffusion takes place in the entire concentration range.     

Impregnated activated carbon for the adsorption of Gd(III) radionuclides from aqueous solutions

Activated carbons (ACs) impregnated by FeCl₃, SnCl₄ and ZnCl₂ are used as adsorbents for the removal of Gd(III) radionuclides from aqueous solutions. Adsorption of Gd(III) is investigated as a function of pH, concentration of adsorbate, contact time, ionic strength and temperature. Gadolinium is efficiently removed (R%?>?95%) at pH values ≥4.8 (for FeAC and SnAC) and 2.9 (for ZnAC). The pseudo-first-order, the pseudo-second-order and Elovich kinetic models are used to analyze the kinetic data of Gd(III), at the studied concentrations (30, 100 and 200?mg/L) onto the employed materials. Of these models, Elovich is the only one that well-fitted the experimental kinetics onto the applied materials at all of the studied Gd(III) concentrations. Equilibrium data of Gd(III) are analyzed by the Freundlich, Temkin, Dubnin–Radushkevich (D-R) and Redlich–Petrson isotherm models. The adsorption efficiency of Gd(III) onto FeAC and SnAC is deleteriously affected by increasing the ionic strength, while adsorption onto ZnAC is unaffected. The thermodynamic parameters are calculated and it is revealed that the adsorption of Gd(III) onto the employed materials is an endothermic process. Desorption studies of Gd(III)-loaded ACs are performed using different desorbing agents (HCl, ZnCl₂, FeCl₃ and SnCl₄) at various concentrations (0.0005, 0.0025, 0.01 and 0.025?M).     

Comparison of the efficiency of palladium and silver nanoparticles loaded on activated carbon and zinc oxide nanorods loaded on activated carbon as new adsorbents for removal of Congo red from aqueous solution: Kinetic and isotherm study

The adsorption of Congo red (CR) into three new adsorbents including Palladium and silver nanoparticles loaded on activated carbon (Pd NPs-AC, Ag NPs-AC) and zinc oxide nanorods loaded on activated carbon (ZnO-NRs-AC) in a batch method has been studied following the optimization of effective variables including pH, amount of adsorbents and time. The experimental data was fitted to conventional kinetic models including the pseudo first-order and second-order Elovich and intraparticle diffusion model and based on calculated respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients. It was found that for all adsorbents the removal process follows the pseudo second other kinetic model with involvement of interparticle diffusion model. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Tempkin and Dubinin and Radushkevich equations and it was found for all adsorbents that the removal process followed the Langmuir isotherm.     

Preparation and application of attapulgite/iron oxide magnetic composites for the removal of U(VI) from aqueous solution

Recently, magnetic sorbents have received considerable attention because of their excellent segregative features and sorption capacities. Herein, attapulgite/iron oxide magnetic (ATP/IOM) composites were prepared and characterized. The sorption results indicated that ATP/IOM composites were superior to ATP and iron oxides individually for the removal of U(VI) from aqueous solution. Based on X-ray photoelectron spectroscopy (XPS) analysis and surface complexation model, the main sorption species of U(VI) on ATP were==X(2)UO(2)(0) below pH 4.0 and==S(s)OUO(2)(+), ==S(w)OUO(2)CO(3)(-), and==S(w)OUO(2)(CO(3))(2)(3-) above pH 5.0. However the prevalent species on ATP/IOM composites were==S(s)OUO(2)(+) and==S(w)OUO(2)(CO(3))(2)(3-) over the observed pH range. ATP/IOM composites are a promising candidate for pre-concentration and immobilization of radionuclides from large volumes of aqueous solutions, as required for remediation purposes.