Forward Solute Transport in Forward Osmosis Using a Freestanding Graphene Oxide Membrane

Identifying the Stripping of Oxide Debris from Graphene Oxide: Evidence from Experimental Analysis and Molecular Simulation

In this study, characteristics of oxidation debris (OD) and its stripping mechanism from graphene oxide (GO) were explored. The results demonstrated that OD contains three components, namely, protein-, fulvic acid-, and humic acid-like substances; among these, protein-like substances with lower molecular weight and higher hydrophilicity were most liable to be stripped from GO and were the primary components stripped from GO at pH < 10, whereas humic acid- and fulvic acid-like substances were stripped from GO at pH > 10. During the stripping of OD, hydrogen bonds from carboxyl and carbonyl were the first to break, followed by hydrogen bonds from epoxy. Subsequently, π-π interactions were broken, and hydrogen bond interactions induced by hydroxyl groups were the hardest to break. After the stripping of OD, the recombination of OD on GO was observed, and regions containing relatively fewer oxygen-containing functional groups were favorable binding sites for the readsorbed OD. The stripping and recombination of OD on GO resulted in an uneven GO surface, which should be considered during the development of GO-based environmental materials and the evaluation of their environmental behavior.

Simultaneous Nitrite Resourcing and Mercury Ion Removal Using MXene-Anchored Goethite Heterogeneous Fenton Composite

The integrated system of gas-phase advanced oxidation process combined with sulfite-based wet absorption process is a desirable method for simultaneous removal of SO₂, NO, and Hg⁰, but due to the enrichment of nitrite and Hg²⁺, resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional β-FeOOH@MXene heterogeneous Fenton material, of which the crystalline phase, morphology, structure, and composition were revealed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, and transmission electron microscopy. It exhibits excellent performance on nitrite oxidation (99.5%) and Hg²⁺ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg²⁺ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and β-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe₂O₃ into β-FeOOH in the hydrothermal method and greatly reduced its monomer size; (ii) the introduced ≡Ti(III)/≡Ti(II) accelerated the regeneration of ≡Fe(II) via rapid electron transfer, thereby improving the heterogeneous Fenton reaction; and (iii) MXene strongly immobilized β-FeOOH to greatly inhibit Fe-leaching. HO^•, ^•O₂^--, and ¹O₂ were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO₂^- oxidation in the descending order HO^• > ¹O₂ > ^•O₂^-. Quantum chemical calculations revealed that ^•OH-induced oxidation of NO₂^- or HNO₂ was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg²⁺ removal mechanism, with Hg₂Cl₂, HgCl₂, and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg²⁺.