Hybrid Sorbent Research Articles

Highly effective removal of heavy metals by polymer-based zirconium phosphate: A case study of lead ion

Zirconium phosphate (ZrP) has recently been demonstrated as an excellent sorbent for heavy metals due to its high selectivity, high thermal stability, and absolute insolubility in water. However, it cannot be readily adopted in fixed beds or any other flowthrough system due to the excessive pressure drop and poor mechanical strength resulting from its fine submicrometer particle sizes. In the present study a hybrid sorbent, i.e., polymer-supported ZrP, was prepared by dispersing ZrP within a strongly acidic cation exchanger D-001 and used for enhanced lead removal from contaminated waters. D-001 was selected as a host material for sorbent preparation mainly because of the Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid group on the exchanger surface, which would enhance permeation of the targeted metal ions. The hybrid sorbent (hereafter denoted ZrP-001) was characterized using a nitrogen adsorption technique, scanning electron microscope (SEM), and X-ray diffraction (XRD). Lead sorption onto ZrP-001 was found to be pH dependent due to the ion-exchange mechanism, and its sorption kinetics onto ZrP-001 followed the pseudo-first-order model. Compared to D-001, ZrP-001 exhibited more favorable lead sorption particularly in terms of high selectivity, as indicated by its substantially larger distribution coefficients when other competing cations Na +, Ca 2+, and Mg 2+ coexisted at a high level in solution. Fixed-bed column runs showed that lead sorption on ZrP-001 resulted in a conspicuous decrease of this toxic metal from 40 mg/L to below 0.05 mg/L. By comparison with D-001 and ZrP-CP (ZrP dispersion within a neutrally charged polymer CP), enhanced removal efficiency of ZrP-001 resulted from the Donnan membrane effect of the host material D-001. Moreover, its feasible regeneration by diluted acid solution and negligible ZrP loss during operation also helps ZrP-001 to be a potential candidate for lead removal from water. Thus, all the results suggested that ZrP-001 offers excellent potential for lead removal from contaminated water.

A Hybrid Sorbent Utilizing Nanoparticles of Hydrous Iron Oxide for Arsenic Removal from Drinking Water

Arsenic in drinking water, present primarily as inorganic As(III) (arsenite) or As(V) (arsenate), has been linked to a number of human ailments. This has prompted the United States Environmental Protection Agency (U.S. EPA) to lower the maximum contaminant level for arsenic in drinking water from 50 to 10 µg/L. ArsenXnp was developed to satisfy the need for an efficient, reliable, and reusable material to meet this new arsenic standard. ArsenXnp is a hybrid sorbent consisting of nanoparticles of hydrous iron oxide distributed throughout a porous polymeric bead. This combines the excellent handling, flow characteristics and attrition resistance of conventional ion exchange resins with the well-documented arsenic affinity of hydrous iron oxides. In field tests, the resin maintained an effluent arsenic concentration below 10 µg/L for 4 months of continuous operation with no mechanical problems and no pressure buildup across the resin bed. Arsenic is removed from solution due to the interaction with the nanoscale hydrous iron oxide surfaces rather than the anion exchange groups associated with the polymeric substrate, and the arsenic capacity is unaffected by common anions such as sulfate, chloride, or bicarbonate.

Hierarchically imprinted organic–inorganic hybrid sorbent for selective separation of mercury ion from aqueous solution

A new type of hierarchically organic–inorganic hybrid sorbent was prepared by a double-imprinting approach for the selective separation of Hg(II) from aqueous solution. In the imprinting process, both mercury ions and surfactant micelles (cetyltrimethylammonium bromide, CTAB) were used as templates, N-[3-(trimethoxy-silyl)propyl]ethylenediamine (TPED) as functional monomer, and tetraethoxysilane (TEOS) as cross-linking agent. The mercury ions and surfactant were removed from sorbent via acid leaching and ethanol extraction, respectively. The adsorption property and selective recognition ability of the sorbents were studied by equilibrium-adsorption method. Results showed that in the presence of Cu(II) or Cd(II) the biggest selectivity coefficient of the imprinted sorbents for Hg(II) was over 100, which is much higher than those of non-imprinted sorbents. The largest relative selectivity coefficient ( k′) of the ion-imprinted functionalized sorbent between Hg(II) and Cu(II) was over 300, and between Hg(II) and Cd(II) over 200. The uptake capacities and the selectivity coefficients of the hierarchically imprinted sorbent were much higher than those of the sorbent prepared without CTAB template. Furthermore, the new imprinted sorbent possessed a fast kinetics for the removal of Hg(II) from aqueous solution with the saturation time less than 5 min, and could be used repeatedly. This sorbent has been successfully applied to the separation and determination of the trace Hg(II) in real water samples and those spiked with standards. This new sorbent can be used as an effective solid-phase extraction material for the selective preconcentration and separation of Hg(II) in environmental samples.

An ion-imprinted silica-supported organic–inorganic hybrid sorbent prepared by a surface imprinting technique combined with a polysaccharide incorporated sol–gel process for selective separation of cadmium(II) from aqueous solution

Ion-imprinting concept and polysaccharide incorporated sol–gel process were applied to the preparation of a new silica-supported organic–inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared shell/core composite sorbent, covalently surface coating on the supporting silica gel was achieved by using a Cd(II)-imprinting sol–gel process starting from an inorganic precursor, γ-glycidoxypropyltrimethoxysiloxane (GPTMS), and a functional biopolymer, chitosan (CS). The sorbent was prepared through self-hydrolysis of GPTMS, self-condensation and co-condensation of silanol groups (Si-OH) from siloxane and silica gel surface, in combination with in situ covalent cross-linking of CS with partial amine shielded by Cd(II) complexation. Extraction of the imprinting molecules left a predetermined arrangement of ligands and tailored binding pockets for Cd(II). The prepared sorbent was characterized by using X-ray energy dispersion spectroscopy (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Batch experiments were conducted to study the sorption performance by removal of Cd(II) when present singly or in binary system, an aqueous Cd(II) and Zn(II) mixture. The ion-imprinted composite sorbent offered a fast kinetics for the sorption of Cd(II) and the maximum capacity was 1.14 mmol g −1. The uptake capacity of the imprinted sorbent and the selectivity coefficient were much higher than that of the non-imprinted sorbent. The imprinted sorbent exhibited high reusability. The prepared functional sorbent was shown to be promising for the preconcentration of cadmium in environmental and biological samples.

Arsenic Removal Using Polymer-Supported Hydrated Iron(III) Oxide Nanoparticles: Role of Donnan Membrane Effect

The conditions leading to the Donnan membrane equilibrium arise from the inability of ions to diffuse out from one phase in a heterogeneous system. In a polymeric cation exchanger, negatively charged sulfonic acid groups are covalently attached to the polymer chains, and thus, they cannot permeate out of the polymer phase. Conversely, a polymeric anion exchanger contains a high concentration of non-diffusible positively charged quaternary ammonium functional groups. It is well-established that submicron or nanoscale hydrated iron(III) oxide (HFO) particles exhibit high sorption affinity toward both arsenates and arsenites. In this study, commercially available cation and anion exchangers were used as host materials for dispersing HFO nanoparticles within the polymer phase using a technique previously developed. The resulting polymeric/inorganic hybrid sorbent particles were subsequently used for arsenic removal in the laboratory. The most significant finding of the study is that the anion exchanger as a substrate containing dispersed HFO offered substantially higher arsenate removal capacity as compared to the cation exchanger, all other conditions remaining identical. In fact, HFO nanoparticles dispersed within the gel-type cation exchanger were unable to remove arsenic. The Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid groups in the cation exchanger did not allow permeation of arsenate into the polymer phase (i.e., arsenate was excluded from the spherical beads dispersed with HFO nanoparticles). On the contrary, anion-exchanger-supported HFO particles or HAIX offered very high arsenic removal capacity; less than 10% of influent arsenic broke through after 10 000 bed vol. HAIX was also amenable to efficient regeneration with 2% NaOH and 3% NaCl and capable of simultaneously removing both perchlorate and arsenic selectively. According to the information in the open literature, HAIX is the first hybrid sorbent that utilizes the Donnan membrane effect of the host material for sorption enhancement. From a generic viewpoint, other metal oxide/metal nanoparticles may also be judiciously embedded in appropriate support materials that would reject or enhance permeation of targeted ionic solutes.

Preparation and Characterization of Magnetically Active Dual-Zone Sorbent

The present study reports the preparation and performance evaluation of a new class of hybrid sorbent that is, (i) magnetically active, (ii) selective toward a wide array of target inorganic and organic environmental contaminants, and (iii) amenable to efficient regeneration and reuse. The preparation of this material is operationally simple and involves partial sulfonation of a widely available polymeric material, followed by dispersion of iron oxide nanoparticles within the polymer phase using a simple chemical−thermal technique developed earlier. Experimental results show that the new sorbent material, referred to as dual-zone sorbent (DZS), can remove arsenites or As(III); arsenates or As(V); copper(II); and dichlorophenol, a synthetic organic compound, simultaneously in addition to being magnetically active. These new hybrid particles exhibit complementary attributes that are not present in currently available commercial polymeric or inorganic ion exchangers. The newly developed polymeric−inorganic m...

Hybrid sorbent with thioetheric sites

Hybrid sorbent with thioetheric sites

An imprinted organic--inorganic hybrid sorbent for selective separation of cadmium from aqueous solution.

A hierarchical double-imprinting concept was applied to the preparation of a new organic-inorganic hybrid sorbent for selective separation of Cd(II) from aqueous solution. In the prepared hierarchically imprinted sorbent, both Cd(II) and surfactant micelles (cetyltrimethylammonium bromide) were used as templates. The sorbent was prepared through self-hydrolysis, self-condensation, and co-condensation of the cross-linking agent (tetraethoxysilicate) and the functional precursor (3-(2-aminoethylamino)-propyltrimethoxysilane) in an alkaline media followed by gelation. The selectivity of the sorbent was investigated by a batch competitive ion-binding experiment using an aqueous Cd(II) and Zn(II) mixture. The largest selectivity coefficient for Cd(II) in the presence of Zn(II) was found to be over 100; the largest relative selectivity coefficient between Cd(II) and Zn(II), over 200. The uptake capacity of the prepared hierarchically imprinted sol-gel sorbent and the selectivity coefficient are much higher than those of the sorbent prepared in the absence of CTAB-template. The sorbent possesses a fast kinetics for the removal of Cd(II) from aqueous solution.

Arsenic removal using a polymeric/inorganic hybrid sorbent

A fixed-bed sorption process can be very effective in removing trace concentrations of arsenic from contaminated groundwater provided: the sorbent is very selective toward both As(III) and As(V) species; the influent and treated water do not warrant any additional pre- or post- treatment; pH and composition of the raw water with respect to other electrolytes remain unchanged besides arsenic removal, and the sorbent is durable with excellent attrition resistance properties. In addition, the sorbent should be amenable to efficient regeneration for multiple reuse. This study reports the results of an extensive investigation pertaining to arsenic removal properties of a polymeric/inorganic hybrid sorbent. Each hybrid sorbent particle is essentially a spherical macroporous cation exchanger bead within which agglomerates of nanoscale hydrated Fe oxide (HFO) particles have been uniformly and irreversibly dispersed using a simple chemical–thermal treatment. The new sorbent, referred to as hybrid ion exchanger or HIX, combines excellent mechanical and hydraulic properties of spherical polymeric beads with selective As(III) and As(V) sorption properties of HFO nanoparticles at circum-neutral pH. Comparison of the results of fixed-bed column runs between the new sorbent and the polymeric anion exchanger confirmed that both As(V) and As(III) were removed very selectively with HIX. Equally important, no pH adjustment, pre- or post-treatment was warranted. Besides the absence of arsenic, the treated water composition was identical to that of influent water. HIX was amenable to efficient in situ regeneration with caustic soda and could subsequently be brought into service following a short rinse with carbon dioxide sparged water. During fixed-bed column runs, intraparticle diffusion was identified as the primary rate-limiting step for both As(III) and As(V) sorption. Repeated use of the same HIX particles during various laboratory investigations provided strong evidence that the new sorbent possesses excellent attrition resistance properties and retains its arsenic removal capacity over cycles.

Hierarchically Imprinted Sorbents for the Separation of Metal Ions

Molecular imprinting involves arranging monomers of polymerization synthesis around a template molecule so that complexes between the monomer and template molecules are formed. Subsequent polymerization of the monomer molecules results in trapping template molecules in a highly cross-linked amorphous polymer matrix. Extraction of the imprint molecules leaves a predetermined arrangement of ligands and a tailored binding pocket. Such imprinted polymers have been used to mimic antibody functions to resolve racemates, and to separate mixtures of metal cations. Thus far, the organization of precursor monomers has been achieved mainly in inhomogeneous organic polymer matrices, with little control over structural parameters, such as pore sizes and surface areas. The authors report the first synthesis of imprinted hybrid sorbent materials with precise control of not only adsorption sites but also pore structures. The concepts behind multilevel imprinting are as follows. Surfactant micelles and metal ions both act as templates in these hierarchically imprinted sorbents. The metal ion and the surfactant are removed from the silica matrix via acid leaching and ethanol extraction, respectively. This results in the formation of different-sized imprints within the silica matrix, each with a specific function.

A new hybrid inorganic sorbent for heavy metals removal

Iron oxyhydroxides, commonly known as ferrihydrites, are unable to remove dissolved heavy metals at acidic pH, especially below 5.0, due to fierce competition from hydrogen ions. A new hybrid iron-rich inorganic sorbent has been identified and extensively studied in relation to heavy metals removals in fixed-bed processes for influent pH as low as 3.5. Every single particle of this new hybrid sorbent essentially contains ferrihydrite along with a crystalline silicate phase, akermanite, in close proximity (in the order of 100Å) to one another. Akermanite has a unique ability to produce hydroxyl ions through incongruent hydrolysis reactions without being washed out from the fixed bed. The simultaneous presence of akermanite and ferrihydrite in a single particle has a synergistic effect on the sorption process: while akermanite helps neutralize aqueous-phase hydrogen ions (thus enhancing sorption capacity of ferrihydrites), neighboring sorption sites in ferrihydrites quickly remove dissolved heavy metals, thus avoiding precipitation. Equally important, the hybrid sorbent can be regenerated with any amine/ammoniacal solution and reused for multiple number of cycles. Some precipitations may occur within the column at relatively high influent concentrations of heavy metals (around 50 mg/l) or due to chromatographic effect. Such precipitates are, however, amenable to removals by conventional backwashing