Surapol Padungthon

Nexus between polymer support and metal oxide nanoparticles in hybrid nanosorbent materials (HNMs) for sorption/desorption of target ligands

Metal oxide nanoparticles like hydrated ferric oxide (HFO) or hydrated zirconium oxide (HZrO) are excellent sorbents for environmentally significant ligands like phosphate, arsenic, or fluoride, present at trace concentrations. Since the sorption capacity is surface dependent for HFO and HZrO, nanoscale sizes offer significant enhancement in performance. However, due to their miniscule sizes, low attrition resistance, and poor durability they are unable to be used in typical plug-flow column setups. Meanwhile ion exchange resins, which have no specific affinity toward anionic ligands, are durable and chemically stable. By impregnating metal oxide nanoparticles inside a polymer support, with or without functional groups, a hybrid nanosorbent material (HNM) can be prepared. A HNM is durable, mechanically strong, and chemically stable. The functional groups of the polymeric support will affect the overall removal efficiency of the ligands exerted by the Donnan Membrane Effect. For example, the removal of arsenic by HFO or the removal of fluoride by HZrO is enhanced by using anion exchange resins. The HNM can be precisely tuned to remove one type of contaminant over another type. Also, the physical morphology of the support material, spherical bead versus ion exchange fiber, has a significant effect on kinetics of sorption and desorption. HNMs also possess dual sorption sites and are capable of removing multiple contaminants, namely, arsenate and perchlorate, concurrently.

Comment on "Polymerization of silicate on hematite surfaces and its influence on arsenic sorption".

Its Influence on Arsenic Sorption” A of the paper, “Polymerization of Silicate on Hematite Surfaces and Its Influence on Arsenic Sorption” 1 present a long-term investigation pertaining to polymerization of silicate (or hydrated silica) onto hematite surface and its influence on arsenic sorption. Authors emphasize how naturally present iron oxide or hematite will be affected in the presence of dissolved silica in attenuating arsenic(V) and arsenic(III) species even in the absence of human interventions. Experimental conditions and the observations of the study relate to the natural environment. This correspondence aims to expand and correlate some of the findings of the study to engineered systems for arsenic removal. We also want to raise a fundamental question: Will the sorption of other environmentally significant ligands, be it fluoride or phosphate, onto other metal oxide surfaces, be it aluminum or zirconium oxide or even amorphous iron oxide, encounter similar effects in the presence of hydrated silica that inevitably exists in every surface or groundwater? The authors observed “higher competitiveness of silica in suspension pre-equilibrated with silica for 48 h, compared to suspension to which arsenic and silica were simultaneously added.” Also, such competing effect is significantly greater at pH of 8 than at pH less than 7. Frequently, packedor fixed-bed sorption processes are employed to remove trace concentrations of arsenic in water using hydrated Fe(III) oxide particles as the selective sorbent. In such engineered processes, in accordance with the principles of chromatographic separation, arsenic is sorbed at the top of the column in preference to silica and other competing anions. The bulk of the silica, which is present at nearly 2 orders of magnitude greater than arsenic in contaminated groundwater, binds to iron oxide surfaces near the bottom of the column as illustrated in Figure 1A. This situation is exactly similar to the batch system investigated in the paper where iron oxide is presaturated with silica in the absence of arsenic. Such an environment promotes sorption of hydrated silicate anion in close proximity to each other followed by slow polymerization reaction. Once polymerized, desorption of dior trimers of silicate species is more difficult than nonpolymerized single silicate species. Furthermore, the zero point of charge (pHzpc) of this silica layer is significantly lower than that of iron oxide, that is, they are negatively charged even at neutral pH. Access of anionic arsenate onto iron oxide surface is thus impaired due to the Donnan exclusion effect, thereby diminishing arsenic sorption. Following exhaustion with arsenic, Iron oxidebased sorbents in the packed bed are routinely regenerated using 1−3% NaOH solution. However, once polymerized, silicates are not amenable to complete regeneration under the regenerating conditions, thus lowering arsenic removal capacity in the subsequent sorption cycles. Figure 1B shows arsenic and silica recovery during regeneration of an anion exchanger supported iron oxide nanoparticles. Note that while arsenic desorption is 95% complete, the same for silica is significantly lower and only 45%, confirming progressive silica accumulation or fouling on iron oxide surfaces.

Synthesis, Characterization and Performance Validation of Hybrid Cation Exchanger Containing Hydrated Ferric Oxide Nanoparticles (HCIX-Fe) for Lead Removal from Battery Manufacturing Wastewater

This study is aimed to synthesize, characterize and validate the performance of a novel hybrid nanoadsorbent for selective removal of lead from a battery manufacturing wastewater. The hybrid nanosorbent, named as HCIX-Fe, was prepared by impregnating hydrated Fe (III) oxide (HFO) nanoparticles inside polymeric cation exchange resin containing negatively charged sulfonic acid (-SO3-) fixed functional groups. HCIX-Fe was characterized by SEM-EDX and XRD to confirm the distribution and determination of phase of HFO dispersed inside the hybrid nanosorbent. Fixed-bed column runs with HCIX-Fe beads were carried out using wastewater from a battery manufacturing plant. The wastewater had a pH of 1.8 and contained of 3.5 mg/L of Pb2+ coexisted with 250 mg/L Ca2+ ions. The results have shown that HCIX-Fe column could treat lead-contaminated water up to 6,500 bed volumes (BVs) before the occurrence of breakthrough concentration of 0.2 mg/L Pb2+ resulting in a removal capacity of 6.85 mg Pb2+/ml of the HCIX-Fe bed. Under similar condition, adsorbent columns with cation exchange resin (C100), granulated activated carbon (GAC) and granulated activated carbon impregnated with HFO (GAC-Fe), could treat the same wastewater only until 400, 900 and 1,500 BVs, respectively. When compared with the parent adsorbents, impregnation by HFO greatly enhanced the Pb2+ removal capacity of C100 and GAC by 1,625% and 167%, respectively. Both HFO and high density of sulfonic acid (-SO3-) in the host cation exchanger are individually capable of selective removal of Pb2+ ions; however the hybrid material demonstrated a synergistic effect for Pb2+ removal through the Donnan Membrane effect. Due to amphoteric behavior of HFO, the HCIX-Fe could be regenerated and reused with 10 BVs of 2% HNO3 and 1% FeCl3·6H2O solution.

Binary Fe and Mn Oxide Nanoparticle Supported Polymeric Anion Exchanger for Arsenic Adsorption: Role of Oxides, Supported Materials,and Preparation Solvent

In this work, binary Fe/Mn oxide nanoparticles were incorporated onto the matrix of anion exchange resin, resulting in hybrid polymeric/inorganic nanoadsorbent named as A502P-Fe/Mn. During synthesis process, effects of various types of metal oxides, preparation solvent, supporting materials, and loading cycles were also investigated. To reduce the charge repulsion force between cationic Fe3+ and Mn4+ ions and fixed-positively charged quaternary amine (R4N+) functional groups of the anion exchange support, mixed solution containing DI/ethanol was introduced to dissolve metal salts during the preparation process. The data obtained by equilibrium batch test indicated that the A502P-Fe/Mn prepared from mixed 50:50 of DI and ethanol exhibited the highest As (V) sorption capacity. The synthesized material was further characterized by using scanning electron microscope (SEM) equipped with energy dispersive X ray spectroscopy (EDX) to verify the existence and distribution of elemental Fe, Mn, and As inside the polymeric beads. Equilibrium As (V) sorption isotherm, effect of solution pH, and point of zero charge of material were also evaluated. This A502P-Fe/Mn can have a promising potential for arsenic removal applications.

Trace Lead Removal in Drinking Water Using High Capacity Polymeric Supported Hydrated Iron Oxide Nanoparticles

Ferric oxide nanoparticles are environmentally benign and can be selective toward lead, especially in neutral to mildly alkaline pH of groundwater. However, due to very fine particles and low mechanical strength, it prevents these materials to apply in point of use filter or large scale fixed-bed adsorption. In this study, polymeric gel cation exchanger, Purolite C100, supported ferric oxide nanoparticles, C100-Fe, was synthesized, characterized, and tested with challenging water according to NSF standards 53. From SEM-EDX studies, it can imply that high concentration of iron can be doped and distributed within the gel phase structure of the C100 approximately 22% by mass. The TEM micrographs confirm the size of hydrated ferric oxide fall into the nanometer range about 10-60 mm. The fixed-bed adsorption experiments demonstrated that C100-Fe can remove lead below the stringent standard of 0.05 mg/L up to 15,000 BVs, whereas the GAC, GAC-Fe, and C100 can treat the same test water only 1200, 1700, and 3500 BVs, respectively. The results confirm that C100-Fe can be efficiently substituted to the traditional GAC for lead removal in drinking water.