New insight into the bioinspired sub-10 nm Sn(HPO4)2 confinement for efficient heavy metal remediation in wastewater

Efficient Removal and Recovery of Ag from Wastewater Using Charged Polystyrene-Polydopamine Nanocoatings and Their Sustainable Catalytic Application in 4-Nitrophenol Reduction

This study addresses the long-standing challenges of removing and recovering trace silver (Ag) ions from wastewater while promoting their sustainable catalysis utilization. We innovatively developed a composite material by combining charged sulfonated polystyrene (PS) with a PDA coating. This composite serves a dual purpose: effectively removing and recovering trace Ag+ from wastewater and enabling reused Ag for sustainable applications, particularly in the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The PS-PDA demonstrated exceptional selectivity to trace Ag+ recycling, which is equal to 14 times greater than the commercial ion exchanger. We emphasize the distinct roles of different charged functional groups in Ag+ removal and catalytic reduction performance. The negatively charged SO3H groups exhibited the remarkable ability to rapidly enrich trace Ag ions from wastewater, with a capacity 2-3 times higher than that of positively-N+(CH3)3Cl and netural-CH2Cl-modified composites; this resulted in an impressive 96% conversion of 4-NP to 4-AP within just 25 min. The fixed-bed application further confirmed the effective treatment capacity of approximately 4400 L of water per kilogram of adsorbent, while maintaining an extremely low effluent Ag+ concentration of less than 0.1 mg/L. XPS investigations provided valuable insights into the conversion of Ag+ ions into metallic Ag through the enticement of negatively charged SO3H groups and the in situ reduction facilitated by PDA. This breakthrough not only facilitates the efficient extraction of Ag from wastewater but also paves the way for its environmentally responsible utilization in catalytic reactions.

High performance forward osmosis membrane with ultrathin hydrophobic nanofibrous interlayer

The novel thin film composite (TFC) forward osmosis (FO) membrane with electrospinning nanofibers as support layer can alleviate internal concentration polarization (ICP). While the macropores of the nanofiber support layer cause defects in the polyamide (PA) layer. Therefore, hydrophobic polyvinylidene fluoride (PVDF) fine nanofibers were used as an interlayer to modulate the process of interfacial polymerization (IP) in this study. The results showed that the introduction of the interlayer improved the hydrophobicity of the support layer for achieving uniform, thin and defect-free selective polyamide (PA) layer. The water flux of TFC-PVDF was 58.26 LMH in the FO mode of 2 M NaCl, which was two times higher than that of the unmodified FO membrane. Lower reverse salt flux (4.91 gMH) and structural parameter (179.43 μm) alleviated the ICP. In addition, TFC-PVDF membrane showed good anti-fouling performance for SA (flux recovery ratio of 93.97%) due to high hydrophilicity, low zeta potential and low roughness. This study provides an easy and promising method to prepare defect-free PA selective layer on the macropores nanofiber support layer. The novel FO membrane shows high desalination performance and anti-fouling properties.

Improved fractionation method using amphipathic NDAM for the efficient separation of disinfection by-product precursors in natural organic matter

The hydrophilic substances in natural organic matter (NOM) are the main precursor of disinfection by-products (DBPs) formed during disinfection processes. The fractionation of the components in NOM based on hydrophilicity contributes to elaborating the behavior of NOM during disinfection. However, the traditional NOM fractionation method using two hydrophobic resins of DAX-8 and XAD-4 lays emphasis on the separation of hydrophobic substances, limiting the thorough study of the hydrophilic components in NOM. In this work, the amphiphilic resin NDAM was employed as a replacement of XAD-4 to realize more thorough separation of the hydrophilic substances. Compared with the divinylbenzene (DVB) structure of XAD-4, the NDAM possesses a more hydrophilic skeleton of N-vinylpyrrolidone (NVP) and DVB which favors the adsorption of hydrophilic components in NOM. The two fractionation methods of DAX-8 + XAD-4 and DAX-8 + NDAM were applied to fractionate NOM, and the obtained fractions were characterized via fluorescence spectra, UV spectra, acid-base titration, the partition coefficients of aqueous two-phase systems(ATPs), and 1H nuclear magnetic resonance (1H-NMR). The results showed that the transphilic fractions separated by XAD-4 accounted for 11.09% of NOM, while the proportion increased to 20.33% with the method of NDAM fractionation. Besides, the hydrophilic components enriched by NDAM not only have more π-conjugated systems and more aromatic structure but also contain more oxygen-containing and nitrogen-containing functional groups. In addition, the hydrophilic fractions separated by NDAM contained more DBP precursors. The NDAM separates more NOM which can produce bromine-containing DBPs into HPIA, and the DBP productivity of HPIN is significantly higher than that of XAD-4. In general, the NOM fractionation method proposed in this study utilizing NDAM resin could fractionate the hydrophilic fractions in NOM more thoroughly, showing application potential in the analysis and control of DBPs formed from NOM.

Facile green preparation of single- and two-component modified activated carbon fibers for efficient trace heavy metals removal from drinking water

Trace heavy metals exist in drinking water, having great adverse effects on human health and making it a huge challenge to remove. Herein, novel materials have been prepared by a simple and green method using single- (polydopamine (PDA) or 2,3-dimercaptopropanesulfonic sodium (DMPS)) (PDA-OACF or DMPS-OACF) and two-component (PDA and DMPS) (DMPS-PDA-OACF) functionalized activated carbon fibers pretreated by hydrogen peroxide for the removal of trace heavy metals. The as-prepared DMPS-OACF (7.5,20) under DMPS addition of 7.5 mg and sonication time of 20 min retained large specific surface area, micro-mesoporous structure and rich functional groups and showed better adsorption performance for trace lead and mercury. It also exhibited wide applicable ranges of pH (3.50-10.50) and concentration (50-1136 μg L^-1), rapid adsorption kinetics, and excellently selective removal performance for trace lead. The maximum lead adsorption capacity reached 16.03 mg g^-1 when the effluent lead concentration met World Health Organization (WHO) standard and the adsorbent can be regenerated by EDTA solution. The fitting results of adsorption kinetics and isotherm models revealed that the lead adsorption process was multi-site adsorption on heterogeneous surfaces and chemical adsorption. The excellent adsorption properties for trace heavy metals were attributed that the sulfur/oxygen/nitrogen-containing functional groups boosted diffusion and adsorption by electrostatic attraction and coordination, suggesting that DMPS-OACF (7.5,20) has great application potential in the removal of trace heavy metals.

Fabrication of silk sericin-anthocyanin nanocoating for chelating and saturation-visualization detection of metal ions

Silk sericin (SS) is a natural water-soluble protein with the potential to chelate metal ions via its polar groups. However, the difficulty of identifying the saturation of SS limits its application as filter films. One solution is to construct SS filter films with an indicator to reflect the degree of saturation of silk sericin. Hence, the nanocoating consisting of co-assembled SS protein and anthocyanin (C3G) nanoparticles is designed, constructed, and characterized to chelate metal ions with a saturation-visualization detection behavior. Here, metal ions Zn²⁺ and Al³⁺ are chosen as models to explore the chelating ability of SS and indicator behaviors of C3G, which could indicate the saturation degree of SS. Interestingly, after the saturation of SS in the solution and filter film situations, the visible color progressively shifts from pink to blue (Zn²⁺) or violet (Al³⁺), with the corresponding redshift of UV-Vis absorbance of C3G. Remarkable removal effectiveness of Zn²⁺ and Al³⁺, namely 93.16% and 53.97%, as well as an evident saturation-visualization detection, were identified by filter paper films with the nanocoating. Our research provides a fresh viewpoint for designing SS filter films that could effectively remove metal ions while enabling real-time viewing.

Converting Chrysotile Nanotubes into Magnesium Oxide and Hydroxide Using Lanthanum Oxycarbonate Hybridization and Alkaline Treatment for Efficient Phosphate Adsorption

Magnesium oxide and hydroxide nanomaterials comprise a class of promising advanced functional metal nanomaterials whose use in environmental and material applications is increasing. Several strategies to synthesize these nanomaterials have been described but are unsustainable and uneconomic. This work reports on a processing strategy that turns natural magnesium-rich chrysotile into magnesium oxide and hydroxide nanoparticles via nanoparticle hybridization and an alkaline process while enabling La-based nanoparticles to coat the chrysotile nanotube surfaces. The adsorbent's resulting hybrid nanostructure had an outstanding capacity for phosphate uptake (135.2 mg P g^-1) and enhanced regeneration performance. Furthermore, the adsorbent featured wide applicability with respect to the coexistence of competitive anions and a broad range of pH conditions, and its high-performance phosphate removal from sewage effluent was also demonstrated. Spectroscopic and microscopic analyses revealed the scavenging ability of phosphate by the La-based and Mg-based nanoparticles and the multiple capture mechanisms involved, including surface complexation and ion exchange. This proposed approach expands chrysotile's potential use as a magnesium-rich nanomaterial and harbors great promise for the removal of pollutants in a variety of real-world settings.

Recyclable structured toxic industrial nickel-containing sludge for efficient anionic contaminant adsorption

Safe, efficient, and simultaneous treatment of toxic industrial sludge and anionic contaminant crisis in one route still remains a persistent global challenge. Herein, we proposed a facile waste-control-waste conceptual design strategy to develop low-cost and high-performance sludge-based adsorbent for not only recycling of toxic waste nickel-containing sludge (NCS) but for the efficient removal of anionic contaminants in wastewater. The as-designed Ni-Al layered double oxides/calcined NCS (Ni-Al LDOs/CNCS) (216.96 m²/g, 0.44 cm³/g) with hierarchical porous structure possessed a larger specific surface area and well-developed porosity compared with raw NCS (60.52 m²/g, 0.26 cm³/g). It was proved that a higher hydrothermal temperature (180 °C) and a longer hydrothermal time (24 h) both promote the in situ assembly of LDHs nanosheets on CNCS surface. Significantly, the sludge-based adsorbent displayed high adsorption capacity towards five representative anions including F^- (~ 31.1 mg/g), SO₄^2- (~ 37.7 mg/g), NO₃^- (~ 21.8 mg/g), Cl^- (~ 28.0 mg/g), and H₂PO₄^- (~ 35.8 mg/g). Furthermore, the adsorbent maintained desirable adsorption capacity even after 6 adsorption/desorption cycles. Therefore, this study could be potentially extended toward design of other industrial waste sludge-derived high value-added advanced materials and for wastewater treatment applications.