Antimony(V) removal from water by hydrated ferric oxides supported by calcite sand and polymeric anion exchanger

We fabricated and characterized two hybrid adsorbents originated from hydrated ferric oxides （HFOs） using a polymeric anion exchanger D201 and calcite as host. The resultant adsorbents （denoted as HFO-201 and IOCCS） were employed for Sb（V） removal from water. Increasing solution pH from 3 to 9 apparently weakened Sb（V） removal by both composites, while increasing temperature from 293 to 313 K only improved Sb（V） uptake by IOCCS. HFO-201 exhibited much higher capacity for Sb（V） than for IOCCS in the absence of other anions in solution. Increasing ionic strength from 0.01 to 0.1 mol/L NaNO3 would result in a significant drop of the capacity of HFO-201 in the studied pH ranges; however, negligible effect was observed for 1OCCS under similar conditions. Similarly, the competing chloride and sulfate pose more negative effect on Sb（V） adsorption by HFO-201 than by IOCCS, and the presence of silicate greatly decreased their adsorption simultaneously, while calcium ions were found to promote the adsorption of both adsorbents. XPS analysis further demonstrated that preferable Sb（V） adsorption by both hybrids was attributed to the inner sphere complexation of Sb（V） and HFO, and Ca（II） induced adsorption enhancement possibly resulted from the formation of HFO-Ca-Sb complexes. Column adsorption runs proved that Sb（V） in the synthetic water could be effectively removed from 30 μg/L to below 5μg/L （the drinking water standard regulated by China）, and the effective treatable volume of IOCCS was around 6 times as that of HFO-201, implying that HFO coatings onto calcite might be a more effective approach than immobilization inside D201.

Surface chemistry of polymer-supported nano-hydrated ferric oxide for arsenic removal: effect of host pore structure

Immobilization of hydrous ferric oxide(HFO) particles inside solid hosts of porous structure is an important approach to improve their applicability in advanced water treatment such as arsenic and heavy metal removal. Here, we fabricated three polystyrene(PS)-based nano-HFOs and explored the effect of host pore structure on the surface chemistry of the immobilized HFOs. Potentiometric titration of the hybrids and surface complexation modeling of their adsorption towards arsenite and arsenate were performed to evaluate the surface chemistry variation of the loaded HFOs. Polymer hosts of higher surface area and narrower pore size would result in smaller particle size of HFOs and lower the value of the point of zero charge. Also, the site density(normalized by Fe mass) and the deprotonation constants of the loaded HFOs increased with the decreasing host pore size. Arsenite adsorption did not change the surface charge of the loaded HFOs, whereas arsenate adsorption accompanied more of the negative surface charges. Adsorption affinity of both arsenic species with three HFO hybrids were compared in terms of the intrinsic surface complexation constants optimized based on the adsorption edges. HFO loaded in polystyrene host of smaller pore size exhibits stronger affinity with arsenic species.

Improved performance and prolonged lifetime of titania-based materials: sequential use as adsorbent and photocatalyst

Lifetime is a key index in the evaluation of environmentally functional materials. Although it is well known that adsorption is the first step in photocatalysis, very little work has been done on the sequential use of materials as both adsorbents and photocatalysts. In this work, two titania-based materials, Ti O2 xerogel and Ti O2 photocatalyst nanoparticles, were fabricated and evaluated as adsorbent and photocatalyst for the remediation of contaminated water with an azo dye, Acid Orange 7(AO7), as the modeling pollutant. The Ti O2 xerogel showed a high adsorption capacity to AO7(769 mg/g) and could be regenerated easily with diluted Na OH solution(0.01 mol/L) for several cycles. The exhausted xerogel was calcined at 400 °C for 3 h and used as a photocatalyst for the degradation of AO7. Compared to the nanoparticles directly prepared from fresh Ti O2 xerogel, the Ti O2 nanoparticles from adsorption exhausted xerogel showed a much higher photocatalytic activity upon both UV and visible light irradiation. Thus the titania-based materials were endowed with improved performance as well as prolonged lifetime.

A millimeter-sized negatively charged polymer embedded with molybdenum disulfide nanosheets for efficient removal of Pb(Ⅱ)from aqueous solution

Molybdenum disulfide(MoS_(2))has excellent trapping ability for lead ions whereas its micro-/nanoscale size has greatly impeded its practical applications in the flow-through systems.Herein,a millimetersized nanocomposite MoS_(2)-001 was synthesized for Pb^(2+)removal by loading MoS_(2) nanosheets into a polystyrene cation exchanger D-001 by a facile hydrothermal method.The proposed structure and adsorption mechanism of MoS_(2)-001 was confirmed by the scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and X-ray photoelectron spectro scopy(XPS)analysis.The nanocomposite showed outstanding adsorption capacity and rapid adsorption kinetic for Pb^(2+)removal,and the adsorption behavior followed the Langmuir adsorption model and pseudo-firstmodel kinetic model.Pb^(2+)uptake by MoS_(2)-001 still maintains a high level even in the presence of extremely highly competitive ions(Ca(Ⅱ)and Mg(Ⅱ)),suggesting its high selectivity for Pb^(2+)adsorption.Besides,the fixed-bed column experiments further certified that MoS_(2)-001 is of great potential for Pb^(2+)removal from the wastewater in practical engineering applications.Even more gratifying is that the exhausted MoS_(2)-001 can be regenerated by NaCl-EDTANa_(2) solution without any significant adsorption capacity loss.Consequently,all the results indicated that MoS_(2)-001 is a promising candidate adsorbent for lead-containing wastewater treatment.