Oxalate modification enabled advanced phosphate removal of nZVI: In Situ formed surface ternary complex and altered multi-stage adsorption process

Phosphorylated zerovalent Iron boosts active hydrogen species generation from water dissociation for superior Hg(II) Reduction

Mercury (Hg) is a toxic metal of great concern, and its reduction from Hg(II) to Hg(0) is crucial to prevent its mobilization and transformation to even more hazardous methylmercury. Fe° could reduce Hg(II), but the role of active hydrogen species (*H) remains unexplored. Herein, we prepared the phosphate-modified zero-valent iron by ball milling (P-ZVIbm) and investigated its Hg(II) reduction and immobilization capacity compared with the ZVIbm counterpart. P-ZVIbm rapidly adsorbed and reduced Hg(II) from water at a rate 22 times faster than ZVIbm, with *H accounting for 36 % of Hg(II) reduction. A greatly higher proportion of negative surface electrostatic potential on P-ZVIbm (50.38 %) than ZVIbm (37.61 %) facilitated the adsorption of Hg(II) cation. H2O adsorption on P-ZVIbm was more favorable, as demonstrated by the in situ ATR-FTIR spectra, H2O TPD-mass spectra, and the substantially lower adsorption energy (-0.78 eV) than ZVIbm (-0.17 eV). The energy span of H2O dissociation to *H also decreased from 2.80 eV on ZVIbm to 1.99 eV on P-ZVIbm. Moreover, *H adsorption energy on P-ZVIbm (1.70 eV) was lower than on ZVIbm (-1.20 eV), thereby inhibiting consumption of *H by H2 evolution. P-ZVIbm demonstrated remarkable efficacy in removing Hg(II), Cu(II), Ni(II), Cd(II), and Pb(II) from electroplating and mining wastewater. These results highlight P-ZVIbm as a promising material for Hg(II) and other heavy metal remediation and underscore the essential role of *H in the enhanced Hg(II) reduction.

Highly efficient phosphate extraction from water using bio-composites of nano zero valent iron supported on orange peel powder (nZVI@OPP): performance evaluation and mechanistic insights

In recent times, nZVI composites have been developed as environmentally friendly adsorbents to tackle the issue of eutrophication in freshwater bodies. Herein, we synthesized nano zero valent iron loaded orange peel powder (nZVI@OPP) in different proportions (1:1, 1:3, 1:5, and 1:10) and investigated its PO43- elimination potential from water. Among them, nZVI@OPP (1:5) composite presented excellent PO43- removal performance (93.3%) comparable to that of 1:1 (100.0%) and 1:3 (98.9%), and therefore was selected for further analysis. The physicochemical properties of nZVI@OPP (1:5) also showed porous and irregular surface with more available sorption sites and reactive functional groups than planar and crystal surface of raw OPP, as revealed by SEM-EDX, XRD, FT-IR, and elemental mapping. The optimum conditions (nZVI@OPP (1:5) dosage: 2 g/L, contact time: 60 min, pH: 7, initial PO43- concentration: 10 mg/L, and temperature: 298 K) indicated 93.3% PO43- removal from simulated water samples. Based on higher R2 values, PSO kinetic and Langmuir isotherm models showed better fitting with PO43- sorption data. Moreover, various coexisting anions posed a negative impact on PO43- removal in the given order: NO3- < SO42 < Cl- < mixed anions, while no significant impact of thermal variations on PO43- removal was observed. The spent nZVI@OPP (1:5) also showed reasonable reusability potential when removing PO43- from aqueous solution. The dominant PO43- removal mechanisms including physisorption, chemisorption, ligand exchange, and complexation reactions were identified. In general, the current study provides new insights into the importance of selecting appropriate mixing proportion of nZVI and OPP, with the potential of extracting maximum PO43- content from water considering economic and waste management perspective.

Azo-Enhanced Raman Scattering Probing Proton Transfer between Water and Nanoscale Zero-valent Iron

The interaction between a solid and water at their interface, especially proton transfer, impacts molecular-scale catalysis, macroscopic environmental science, and geoscience. Although being highly desired, directly probing proton transfer between a solid and water is a great challenge, given the subnanometer to nanometer scale of the interface. The fundamental challenge lies in the lack of a measurement tool to sensitively observe local proton concentration without introducing an exogenous electrode or nanoparticle with a minimum size of tens of nanometers. Here, we demonstrate an azo-enhanced Raman scattering strategy to design a 2 nm long small-molecule pH probe with a chelating group anchoring to the solid surface. Empowered by the intramolecular Raman enhancing sensitivity, the probe directly observes proton transfer between water and nanoscale zero-valent iron (nZVI), a famous environmental material for pollution control. This molecular-scale interfacial probing methodology offers a powerful tool to pave the way for advanced environmental and geochemical discernment and management.

Construction of immobilized laccase hydrogels via sodium alginate-dopamine/polyethylene glycol and its efficient degradation of dyeing wastewater

Laccases with highly catalytic properties have been widely used in developing green applications for water remediation. However, the poor stability and low reutilization rate of free laccase make it difficult to be applied practically. Hence, in this study, an immobilized laccase was prepared using dopamine (DA) functionalized sodium alginate (SA)/polyethylene glycol (PEG) composite hydrogels to realize the recyclability of the laccase. The SA/PEG composite hydrogels, as the protective carrier for laccase, exhibited excellent catalytic stability in various interfering environments. After 30 days, Lac@SA-PDA/PEG beads could remain 70.23 % of the initial activity, as the residual activity of free laccase was only 12.35 %. When free laccase and Lac@SA-PDA/PEG beads were used for decolorization of Reactive Blue 19 (RB-19,100 mg/L), the degradation rate of Lac@SA-PDA/PEG is 6.88 times higher than free laccase. More importantly, the SA-PDA/PEG composite hydrogel exhibited a high reutilization rate, which after six cycles, Lac@SA-PDA/PEG beads retained 90.23 % of its initial activity. Besides, the degradation effect of Lac@SA-PDA/PEG on different dyes was analyzed. In addition, the conjectured degradation pathways of RB-19 by laccase were analyzed. The work showed that immobilized laccase has tremendous potential for the treatment of dyestuff wastewater.