Surface Chemistry of Nanosized Hydrated Ferric Oxide Encapsulated Inside Porous Polymer: Modeling and Experimental Studies

Elucidating the effect of porous host on the intrinsic physicochemical properties and reactivity of the encapsulated nanosized hydrous ferric oxides (HFOs) is believed important to better understand how HFOs interact with ionic pollutants inside the pore region. Here we prepared a hybrid adsorbent (HFO–CMPS) by dispersing nanosized HFOs onto an inactive porous polymeric support (i.e., chloromethylated polystyrene, CMPS). A surface complexation model (SCM) was employed to quantitatively evaluate the acid–base reactions and adsorption behaviors of HFO–CMPS as compared to the bare HFOs. Results demonstrated that the intrinsic equilibrium constants for acid–base reactions of surface sites of HFOs distinctly changed upon loading, that is, the log K(+) values decreased, while its log K(−) values increased, resulting in its pHpzc value shifting from ∼8.2 to ∼6.3. Meanwhile, the titration curves of HFO–CMPS showed a markedly weaker dependence upon ionic strength. The results of model fittings of Cu­(II) and As­(V) adsorption indicate that the change of Coulombic terms, reflecting the effect of the electrical potential on the adsorption activities, played an important role in the difference in pH-dependent adsorption of Cu­(II) and As­(V) between HFO–CMPS and bare HFOs. Additionally, the greater tendency of the encapsulated HFOs to dissolve in acidic solution was observed and may be due to its weaker pH buffering capacity, which possibly results from size-dependency of surface charges. All the results indicated that porous hosts play a significant role in the properties of the attached metal oxides for their application in water treatment

New Strategy To Enhance Phosphate Removal from Water by Hydrous Manganese Oxide

Hydrous manganese oxide (HMO) is generally <i>negatively</i> charged at circumneutral pH and cannot effectively remove anionic pollutants such as phosphate. Here we proposed a new strategy to enhance HMO-mediated phosphate removal by immobilizing nano-HMO within a polystyrene anion exchanger (NS). The resultant nanocomposite HMO@NS exhibited substantially enhanced phosphate removal in the presence of sulfate, chloride, and nitrate at greater levels. This is mainly attributed to the pH_pzc shift from 6.2 for the bulky HMO to 10.5 for the capsulated HMO nanoparticles, where HMO nanoparticles are <i>positively</i> charged at neutral pH. The ammonium groups of NS also favor phosphate adsorption through the Donnan effect. Cyclic column adsorption experiment indicated that the fresh HMO@NS could treat 460 bed volumes (BV) of a synthetic influent (from the initial concentration of 2 mg P­[PO₄^3–]/L to 0.5 mg P­[PO₄^3–]/L), while only 80 BV for NS. After the first time of regeneration by NaOH-NaCl solution, the capacity of HMO@NS was lowered to ∼300 BV and then kept constant for the subsequent 5 runs, implying the presence of both the reversible and irreversible adsorption sites of nano-HMO. Additional column adsorption feeding with a real bioeffluent further validated great potential of HMO@NS in advanced wastewater treatment. This study may provide an alternative approach to expand the usability of other metal oxides in water treatment

MgO-Based Granular Sorbent Pelletized by Using Ordered Mesoporous Silica as Binder for Low-Temperature CO₂ Capture

Cyclic CO2 adsorption by using MgO as a sorbent at low temperatures is considered a promising route for postcombustion CO2 capture. However, most MgO-based sorbents are in the form of fine powder and cannot be used in a fluidized bed reactor, and at the same time, suffer from a rapid loss in CO2 uptake capacity due to the decrease of surface area aroused by pore shrinking and grain sintering. In this study, mesoporous silicas with highly ordered pore structures have been used as binders, for the first time, to fabricate MgO-based sorbent pellets via a simple and scalable extrusion–spheronization approach. The obtained MgO-based pellets exhibit high porosity attributed to the nature of the mesoporous binder, leading to a significantly increased stability and CO2 uptake capacity. Especially for the low-concentration CO2 that is comparable to the flue gas from a coal-fired power plant, the results show that the ordered mesoporous silica binder provides a remarkable promotion effect and excellent stability in the capture performance. The CO2 uptake capacity of the best-performing sorbent, 20-KIT-6–100, displays a small decline of 6.86% (from 1.02 mmol of CO2/g in the first cycle to 0.95 mmol of CO2/g in the 10th cycle). It is envisaged that mesoporous materials hold great potential to be used as binders in reinforcing the metal oxide-based sorbents for flue-gas CO2 capture in practical applications