Amidoxime Research Articles

Atom transfer radical polymerization with activators regenerated by electron transfer of acrylonitrile from silica nanoparticles, and adsorption properties of the resin for Hg2+ after amidoximation with hydroxylamine

AbstractPolyacrylonitrile (PAN) was grafted from surfaces of chloro‐modified silica‐gel with their surface chlorines as initiation sites, using an iron (III)‐mediated surface‐initiated atom transfer radical polymerization (ATRP) with activators regenerated by electron transfer (SI‐ARGET ATRP) method. The graft reaction exhibits first‐order kinetics with respect to the polymerization time in the low‐monomer‐conversion stage. The conversion of monomer (C%) and the percentage of grafting (PG%) increased with increasing of the polymerizing time and reached 23 and 730% after a polymerizing time of 24 hr, respectively. Hydroxylamine (NH2OH·HCl) was used to modify the cyano groups of SG‐g‐PAN to obtain amidoxime (AO) groups. The AO SG‐g‐PAN was used to remove Hg2+. The adsorption kinetics indicated that the pseudo‐second‐order model was more suitable to describe the adsorption kinetics of AO SG‐g‐PAN for Hg2+. The adsorption isotherms demonstrated that Langmuir model was much better than Freundlich model to describe the isothermal process. Copyright © 2010 John Wiley & Sons, Ltd.

Synthesis of polyacrylonitrile-grafted cross-linked N-chlorosulfonamidated polystyrene via surface-initiated ARGET ATRP, and use of the resin in mercury removal after modification

A novel method of surface modification was developed via iron (III)-mediated atom transfer radical polymerization, with activators regenerated by electron transfer (ARGET ATRP) on the surfaces of polystyrene resin-supported N-chlorosulfonamide groups. The well-defined polyacrylonitrile (PAN) was grafted onto the surfaces of the polystyrene (PS). The graft reaction exhibited first-order kinetics with respect to the polymerization time in the low-monomer-conversion stage. The cyano group of PAN-g-PS was modified by NH2OH·HCl to yield amidoxime (AO) groups. The AO groups had been demonstrated to be an efficient Hg-specific sorbent, which can remove Hg2+ from solutions. No interference arose from common metal ions, such as Pd2+, Ag+, and Cu2+. Three adsorption–desorption cycles demonstrated that this resin is suitable for reuse without any considerable change in adsorption capacity.

Synthesis of porous acrylonitrile/methyl acrylate copolymer beads by suspended emulsion polymerization and their adsorption properties after amidoximation

Porous acrylonitrile (AN)/methyl acrylate (MA) copolymer beads were prepared by suspended emulsion polymerization. The cyano groups in AN/MA copolymer beads were converted to amidoxime (AO) groups by reaction with hydroxylamine hydrochloride (NH(2)OH.HCl) to remove metal ions in aqueous solution. The untreated AN/MA and amidoximated AN/MA (AO AN/MA) copolymer beads were characterized by FTIR spectroscopy, SEM, and porous structural analysis. Both mesopores and macropores were presented in AN/MA and AO AN/MA copolymer beads. Qualitative experiments of adsorption were conducted to evaluate modified and unmodified resins on fixing Hg(2+), Ag(+), Cu(2+), Fe(3+) and Pb(2+) from aqueous solution using batch extractions. It was found that AO AN/MA copolymer beads have excellent adsorption capacities for Hg(2+), Ag(+) and Cu(2+), especially for Hg(2+), and it have good selectivity for Hg(2+). The equilibrium was established in 10h through adsorption kinetics study. The Langmuir model was much better than the Freundlich model to describe the isothermal process.

Development of Environmentally Friendly Modified Fe-PAN Fibrous Catalyst and Its Application in Degradation of Dye

Modified Fe-PAN fibrous catalyst (Fe-AO-PAN) was formulated at the room temperature by the reaction of amidoxime (AO) modified polyacrylonitrile (PAN) fiber (AO-PAN) with FeCl3, which was in turn used as an environmentally friendly heterogeneous photocatalyst in the oxidative degradation reaction of the standard target dye Rhodamine B in the presence of hydrogen peroxide. This paper investigated the influences of the iron ion concentration in solution (CFe) and reaction temperature to the iron ion content in Fe-AO-PAN catalyst (CFe-AO?PAN); studied the effects of CFe-AO?PAN, pH, intensity of light irradiation and etc. on the decoloration rate of the dye; and analyzed the oxidative degradation procedure of the dye by ultraviolet-visible light spectrum analysis. The results indicate that CFe-AO?PAN increases with the rise of CFe or reaction temperature; the decoloration rate of Rhodamine B increases with the rise of CFe-AO?PAN or radiation intensity, as well as the decrease of initial concentration of the dye; and Fe-AO-PAN shows higher catalytic activity in the solution of pH less than or equal to 6.0, however lower catalytic activity in a strongly basic medium. In addition, ultraviolet-visible light spectrum analysis proves that Fe-AO-PAN can effectively catalyze the break of azo bond and aromatic ring in the dye molecular, but can not be reutilized efficiently.

Exchanges of Uranium(VI) Species in Amidoxime-Functionalized Sorbents

Amidoxime (AO)-functionalized polymer sorbents used in this study were prepared by two different routes involving UV grafting and electron-beam grafting of acrylonitrile (AN) into poly(propylene) fibrous and microporous sheets, and subsequent conversion of AN to AO groups by reacting the precursor sorbent with hydroxylamine. The values of self-diffusion coefficient (D(s)) of UO(2)(2+) in fibrous and sheet AO sorbents were found to be 1.1 x 10(-6) and 2.3 x 10(-10) cm(2) s(-1), respectively. The higher diffusion mobility of UO(2)(2+) in the fibrous AO sorbent was attributed to its higher free volume as observed in scanning electron microscopic studies. The water content was also found to be maximum in AO-fibrous sorbent (165-200 wt %) and minimum in AO-sheet sorbent (70 wt %). In fibrous AO sorbent, the values of D(s) for Na(+) and Sr(2+) were found to be comparable to their self-diffusion coefficients in the aqueous medium. This indicated that the retardation in diffusion mobility of the ions was a minimum in the fibrous AO sorbent. However, D(s) of UO(2)(2+) in the fibrous membrane was found to be significantly lower than that of Sr(2+), which has a self-diffusion coefficient comparable to that of UO(2)(2+) in aqueous medium. This could be attributed to stronger binding of UO(2)(2+) with AO groups as compared to Sr(2+). To understand the parameters affecting the U(VI) sorption from seawater, the U(VI) exchange rates between fibrous AO sorbent (S) and seawater (aq) involving (H(+)/Na(+))(S) right harpoon over left harpoon ([UO(2)(CO(3))(3)](4-))(aq) and (UO(2)(2+))(S) right harpoon over left harpoon ([UO(2)(CO(3))(3)](4-))(aq) systems were experimentally measured. The exchange profiles thus obtained were found to be non-Fickian and much slower than (H(+))(S) right harpoon over left harpoon (UO(2)(2+))(aq) and (UO(2)(2+))(S) right harpoon over left harpoon (UO(2)(2+))(aq) exchanges. This seems to suggest that the reaction kinetics involved in decomplexation of [UO(2)(CO(3))(3)](4-) into UO(2)(2+), which forms a complex with AO groups, is the rate-determining step in sorption of U(VI) from seawater. The kinetics of U(VI) sorption in AO-gel and AO-fibrous sorbents followed the pseudo-second-order rate equation. The density of AO groups in the sorbents and their conditioning were found to influence the U(VI) sorption from seawater.

Electron Beam Grafted Polymer Adsorbent for Removal of Heavy Metal Ion from Aqueous Solution

An electron beam grafted adsorbent was synthesized by post irradiation grafting of acrylonitrile (AN) on to a non‐woven thermally bonded polypropylene (PP) sheet using 2 MeV electron beam accelerator. The grafted poly(acrylonitrile) chains were chemically modified to convert a nitrile group to an amidoxime (AMO) group, a chelating group responsible for metal ion uptake from an aqueous solution. The effect of various experimental variables viz. dose, dose rate, temperature, and solvent composition on the grafting extent was investigated. PP grafted with the amidoxime group (AMO‐g‐PP) was tested for its suitability as an adsorbent for removal of heavy metal ions such as Co2+, Ni2+, Mn2+, and Cd2+ from aqueous solution. Langmuir and Freundlich adsorption models were used to investigate the type of adsorption of these ions. The adsorption capacities of the adsorbent for the metal ions were found to follow the order Cd2+>Co2+>Ni2+>Mn2+. The kinetics of adsorption of these ions indicated that the rate of adsorption of Cd2+ was faster than that of other ions studied.

Preparation of hydrophilic amidoxime fibers by cografting acrylonitrile and methacrylic acid from an optimized monomer composition

To improve the adsorption rate of uranium from seawater, hydrophilic amidoxime (AO) fibers were prepared by cografting of methacrylic acid (MAA) with acrylonitrile (AN) onto polypropylene fibers and subsequent conversion of the produced cyano group to an amidoxime group by reaction with hydroxylamine. An optimum amidoximation time of 0.75 h was selected at a weight ratio of AN to MAA ( x/y) of 80/20. By varying x/y in the monomer mixture, cografted polymers were prepared. The value of x/y governed the AO group density and water content of the resultant fibrous adsorbents. As x/y increased, the AO group density of the fiber increased and its water content decreased. The AO/MAA adsorbent, based on the PP fibers prepared by cografting at an x/y of 60/40 and subsequent amidoximation, exhibited the highest uranium adsorption rate in the flow-through mode.

Comparison of Amidoxime Adsorbents Prepared by Cografting Methacrylic Acid and 2-Hydroxyethyl Methacrylate with Acrylonitrile onto Polyethylene

Methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) were cografted with acrylonitrile (AN) onto polyethylene fiber by radiation-induced graft polymerization. The cyano groups produced were converted to amidoxime groups (−C(NOH)NH2) by reaction with hydroxylamine (NH2OH) to recover uranium in seawater. Various weight ratios of AN/MAA or AN/HEMA in the monomer mixture for cografting generated MAA- and HEMA-cografted amidoxime (AO) fibers with various hydrophilicities. The amidoxime group density and water content were balanced to enhance the uranium adsorption from seawater. MAA-cografted AO fibers exhibited a higher adsorption rate than HEMA-cografted AO fibers. The optimum value of the weight ratio of AN/MAA = 60/40 in the monomer mixture was observed both in a submerged mode at an ocean site and in a flow-through mode in the laboratory. The amount of uranium adsorbed was 0.90 g/kg of the MAA-cografted AO fiber at 293−298 K after 20 days of contact at the ocean site.

Uranium uptake during permeation of seawater through amidoxime-group-immobilized micropores

The polymer chains containing an amidoxime (AO) group capable of specifically collecting uranium in seawater were grafted onto a microporous hollow-fiber membrane. Crosslinking of the grafted polymer branches by bivalent ions such as Mg and Ca ions in seawater permitted permeation of seawater through the AO-group-immobilized micropores. The logarithm of the ratio of uranium concentration at the outlet to that at the inlet linearly decreased with an increasing residence time of seawater across the AO hollow-fiber membrane, which indicates that the chelate formation of the AO group immobilized on the microporous membrane with uranyl species governed the overall uranium uptake rate.

Metal collection using chelating hollow fiber membrane

Three kinds of functional groups, iminodiacetate (IDA), amidoxime (AO), and phosphoric acid (PA), were introduced into a micro filtration hollow fiber membrane by radiation-induced grafting and subsequent chemical modification. The chelating hollow fibers containing AO or IDA groups exhibited a 1.1 m 3/(m 2-hr) pure water flux at 100% grafting of each precursor monomer, while the hollow fiber containing the PA group had a negligible flux. Breakthrough curves were obtained by permeating a metal-ion-containing feed solution radially from inside to outside of the chelating hollow fiber. The IDA chelating hollow fiber was superior to the AO chelating hollow fiber with regard to the collection of cobalt ion. The IDA hollow fiber, whose degree of glycidyl methacrylate grafting ranged from 20 to 260%, had a saturation capacity of cobalt ion of 0.13-1.3 mole Co per kg of base polymer.