Fabrication of Novel Magnetic Nanoparticles of Multifunctionality for Water Decontamination

Efficient and powerful water purifiers are in increasing need because we are facing a more and more serious problem of water pollution. Here, we demonstrate the design of versatile magnetic nanoadsorbents (M-QAC) that exhibit excellent disinfection and adsorption performances at the same time. The M-QAC is constructed by a Fe₃O₄ core surrounded by a polyethylenimine-derived corona. When dispersed in water, the M-QAC particles are able to interact simultaneously with multiple contaminants, including pathogens and heavy metallic cations and anions, in minutes. Subsequently, the M-QACs along with those contaminants can be easily removed and recollected by using a magnet. Meanwhile, the mechanisms of disinfection are investigated by using TEM and SEM, and the adsorption mechanisms are analyzed by XPS. In a practical application, M-QACs are applied to polluted river water 8000-fold greater in mass, producing clean water with the concentrations of all major pollutants below the drinking water standard of China. The adsorption ability of M-QAC could be regenerated for continuous use in a facile manner. With more virtues, such as low-cost fabrication and easy scaling up, the M-QAC have been shown to be a very promising multifunctional water purifier with rational design and to have great potential for real water purification applications

Interaction between Organic Compounds and Catalyst Steers the Oxidation Pathway and Mechanism in the Iron Oxide-Based Heterogeneous Fenton System

In the past decades, extensive efforts have been devoted to the mechanistic understanding of various heterogeneous Fenton reactions. Nevertheless, controversy still remains on the oxidation mechanism/pathway toward different organic compounds in the classical iron oxide-based Fenton reaction, largely because the role of the interaction between the organic compounds and the catalyst has been scarcely considered. Here, we revisited the classic heterogeneous ferrihydrite (Fhy)/H2O2 system toward different organic compounds on the basis of a series of degradation experiments, alcohol quenching experiments, theoretical modeling, and intermediate analysis. The Fhy/H2O2 system exhibited highly selective oxidation toward the group of compounds that bear carboxyl groups, which tend to complex with the surface Fe(III) sites of the Fhy catalyst. Such interaction results in a nonradical inner sphere electron transfer process, which seizes one electron from the target compound and features negligible inhibition by the radical quencher. In contrast, for the oxidation of organic compounds that could not complex with the catalyst, the traditional HO· process makes the main contribution, which proceeds via hydroxyl addition reaction and could be readily suppressed by the radical quencher. This study implies that the interaction between the organic compounds and the catalyst plays a decisive role in the oxidation pathway and mechanism of the target compounds and provides a holistic understanding on the iron oxide-based heterogeneous Fenton system

Enhanced Phosphate Removal by Nanosized Hydrated La(III) Oxide Confined in Cross-linked Polystyrene Networks

A new nanocomposite adsorbent La-201 of extremely high capacity and specific affinity toward phosphate was fabricated and well characterized, where hydrated La­(III) oxide (HLO) nanoclusters were immobilized inside the networking pores of the polystyrene anion exchanger D-201. La-201 exhibited enhanced phosphate adsorption in the presence of competing anions (chloride, sulfate, nitrate, bicarbonate, and silicate) at greater levels (up to molar ratio of 20), with working capacity 2–4 times higher than a commercial Fe­(III) oxide-based nanocomposite HFO-201 in batch runs. Column adsorption runs by using La-201 could effectively treat ∼6500 bed volumes (BV) of a synthetic feeding solution before breakthrough occurred (from 2.5 mg P/L in influent to <0.5 mg P/L in effluent), approximately 11 times higher magnitude than that of HFO-201. The exhausted La-201 could be regenerated with NaOH–NaCl binary solution at 60 °C for repeated use without any significant capacity loss. The underlying mechanism for the specific sorption of phosphate by La-201 was revealed with the aid of STEM-EDS, XPS, XRD, and SSNMR analysis, and the formation of LaPO₄·<i>x</i>H₂O is verified to be the dominant pathway for selective phosphate adsorption by the immobilized nano-HLO. The results indicated that La-201 was very promising in highly efficient removal of phosphate from contaminated waters

Structure Evolution of Iron (Hydr)oxides under Nanoconfinement and Its Implication for Water Treatment

In the development of nanoenabled technologies for large-scale water treatment, immobilizing nanosized functional materials into the confined space of suitable substrates is one of the most effective strategies. However, the intrinsic effects of nanoconfinement on the decontamination performance of nanomaterials, particularly in terms of structural modulation, are rarely unveiled. Herein, we investigate the structure evolution and decontamination performance of iron (hydr)­oxide nanoparticles, a widely used material for water treatment, when confined in track-etched (TE) membranes with channel sizes varying from 200 to 20 nm. Nanoconfinement drives phase transformation from ferrihydrite to goethite, rather than to hematite occurring in bulk systems, and the increase in the nanoconfinement degree from 200 to 20 nm leads to a significant drop in the fraction of the goethite phase within the aged products (from 41% to 0%). The nanoconfinement configuration is believed to greatly slow down the phase transformation kinetics, thereby preserving the specific adsorption of ferrihydrite toward As­(V) even after 20-day aging at 343 K. This study unravels the structure evolution of confined iron hydroxide nanoparticles and provides new insights into the temporospatial effects of nanoconfinement on improving the water decontamination performance

Enhanced Removal of Fluoride by Polystyrene Anion Exchanger Supported Hydrous Zirconium Oxide Nanoparticles

Here we fabricated a novel nanocomposite HZO-201, an encapsulated nanosized hydrous zirconium oxide (HZO) within a commercial porous polystyrene anion exchanger D201, for highly efficient defluoridation of water. HZO-201 exhibited much higher preference than activated alumina and D201 toward fluoride removal when competing anions (chloride, sulfate, nitrate, and bicarbonate) coexisted at relatively high levels. Fixed column adsorption indicated that the effective treatable volume of water with HZO-201 was about 7–14 times as much as with D201 irrespective of whether synthetic solution or groundwater was the feeding solution. In addition, HZO-201 could treat >3000 BV of the acidic effluent (around 3.5 mg F^–/L) per run at pH 3.5, compared to only ∼4 BV with D201. The exhausted HZO-201 could be regenerated by NaOH solution for repeated use without any significant capacity loss. Such attractive performance of HZO-201 resulted from its specific hybrid structure, that is, the host anion exchanger D201 favors the preconcentration of fluoride ions inside the polymer based on the Donnan principle, and the encapsulated nanosized HZO exhibits preferable sequestration of fluoride through specific interaction, as further demonstrated by XPS spectra. The influence of solution pH, competitive anions, and contact time was also examined. The results suggested that HZO-201 has a great potential in efficient defluoridation of groundwater and acidic mine drainage

Visible Light Photocatalytic Degradation of RhB by Polymer-CdS Nanocomposites: Role of the Host Functional Groups

Surface groups of the host polystyrene beads play an important role in the properties of the polymer-based nano-CdS composites in terms of the distribution, dispersion, crystal structure, pH-dependent stability of nano-CdS, and thereafter affect their photocatalytic activity. Surface modification of the host materials can be taken as an effective and general approach to mediate the structure and properties of the nanocomposite materials

Highly Efficient Water Decontamination by Using Sub-10 nm FeOOH Confined within Millimeter-Sized Mesoporous Polystyrene Beads

Millimeter-sized polymer-based FeOOH nanoparticles (NPs) provide a promising option to overcome the bottlenecks of direct use of NPs in scaled-up water purification, and decreasing the NP size below 10 nm is expected to improve the decontamination efficiency of the polymeric nanocomposites due to the size and surface effect. However, it is still challenging to control the dwelled FeOOH NP sizes to sub-10 nm, mainly due to the wide pore size distribution of the currently available polymeric hosts. Herein, we synthesized mesoporous polystyrene beads (MesoPS) via flash freezing to assemble FeOOH NPs. The embedded NPs feature with α-crystal form, tunable size ranging from 7.3 to 2.0 nm and narrow size distribution. Adsorption of As­(III/V) by the resultant nanocomposites was greatly enhanced over the α-FeOOH NPs of 18 × 60 nm, with the iron mass normalized capacity of As­(V) increasing to 10.3 to 14.8 fold over the bulky NPs. Higher density of the surface hydroxyl groups of the embedded NPs as well as their stronger affinity toward As­(V) was proved to contribute to such favorable effect. Additionally, the as-obtained nanocomposites could be efficiently regenerated for cyclic runs. We believe this study will shed new light on how to fabricate highly efficient nanocomposites for water decontamination

Using Defect Control To Break the Stability–Activity Trade-Off in Enzyme Immobilization via Competitive Coordination

Immobilization of enzymes within metal–organic frameworks is a powerful strategy to enhance the long-term usability of labile enzymes. However, the thus-confined enzymes suffer from the trade-off between enhanced stability and reduced activity because of the contradiction between the high crystallinity and the low accessibility. Here, by taking laccase and zeolitic imidazolate framework-8 (ZIF-8) as prototypes, we disclosed an observation that the stability–activity trade-off could be solved by controlling the defects via competitive coordination. Owing to the presence of competitive coordination between laccase and the ligand precursor of ZIF-8, there existed a three-stage process in the de novo encapsulation: nucleation–crystallization–recrystallization. Our results show that the biocomposites collected before the occurrence of recrystallization possessed both increased activity and enhanced stability. The findings here shed new light on the control of defects through the subtle use of competitive coordination, which is of great significance for the engineering application of biomacromolecules

Fabrication of a New Hydrous Zr(IV) Oxide-Based Nanocomposite for Enhanced Pb(II) and Cd(II) Removal from Waters

To overcome the technical bottleneck of fine hydrated Zr­(IV) oxide particles in environmental remediation, we irreversibly impregnated nanosized hydrated Zr­(IV) oxide inside a commercial cation exchange resin D-001 and obtained a new nanocomposite NZP. NZP exhibited efficient removal of lead and cadmium ions in a pH range of 2–6, where no Zr­(IV) leaching was detected from NZP. As compared to D-001, NZP showed more preferable adsorption toward both toxic metals from the background Ca­(II) solution at greater levels. The synthetic Pb­(II) or Cd­(II) solution containing other ubiquitous metal ions was employed as the feeding influent for column adsorption, and the results indicated that the treatable volume of NZP is around 3–4 times that of D-001 before reaching the breakthrough point set according to the effluent discharge standard of China. With respect to Pb­(II) removal from an acidic mining effluent, the treatable volume of NZP was 13 times higher than that of D-001. The exhausted NZP could be effectively regenerated by HNO₃–Ca­(NO₃)₂ binary solution for repeated use without any significant capacity loss. The superior performance of NZP was attributed to the Donnan membrane effect exerted by the host D-001 as well as the impregnated HZO nanoparticles of specific interaction toward toxic metals, as confirmed by the comparative isothermal adsorption and X-ray photoelectron spectroscopic study

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