Reactivity characterization of SiO2-coated nano zero-valent iron for iodoacetamide degradation: The effects of SiO2 thickness, and the roles of dehalogenation, hydrolysis and adsorption

Synthesis, magnetic properties, biotoxicity and potential mechanism of modified nano zero-valent iron for decolorization of dye wastewater

SiO2-coated nano zero-valent iron (nZVI) has emerged as a fine material for the treatment of dye wastewater due to its large specific surface area, high surface activity, and strong reducibility. However, the magnetic properties based on which SiO2-coated nZVI (SiO2-nZVI) could effectively separate and recover from treated wastewater, and the biotoxicity analysis of degradation products of the dye wastewater treated by SiO2-nZVI remain unclear. In this study, SiO2-nZVI was synthesized using a modified one-step synthesis method. The SiO2-nZVI nanoparticles were characterized using Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Fully automatic specific surface and porosity analyzer, Vibrating sample magnetometer, and Zeta potential analyzer. The removal rate of methyl orange (MO) by SiO2-nZVI composite reached 98.35% when the degradation performance of SiO2-nZVI treating MO was optimized. Since SiO2-nZVI analysed by magnetic hysteresis loops had large saturation magnetization and strong magnetic properties, SiO2-nZVI exhibited excellent ferromagnetic behaviour. The analysis of the degradation products showed that the MO treated by SiO2-nZVI was converted into a series of intermediates, resulting in reducing the toxicity of MO. The potential mechanism of MO degradated by SiO2-nZVI was speculated through degradation process and degradation kinetics analysis. Overall, the SiO2-nZVI composite may be regarded as a promising catalyst for decolorization of dye wastewater.

The superior performance of silica gel supported nano zero-valent iron for simultaneous removal of Cr (VI)

Pure nano zero-valent iron (NZVI) was fabricated under optimum conditions based on material production yield and its efficiency toward acid blue dye-25 decolorization. The optimum prepared bare NZVI was immobilized with two different supports of silica and starch to fabricate their composites nanomaterials. The three different prepared zero-valent iron-based nanomaterials were evaluated for removal of hexavalent chromium (Cr(VI)). The silica-modified NZVI recorded the most outstanding removal efficiency for Cr(VI) compared to pristine NZVI and starch-modified NZVI. The removal efficiency of Cr(VI) was improved under acidic conditions and decreased with raising the initial concentration of Cr(VI). The co-existence of cations, anions, and humic acid reduced Cr(VI) removal efficiency. The removal efficiency was ameliorated from 96.8% to 100% after adding 0.75 mM of H2O2. The reusability of silica-modified NZVI for six cycles of Cr(VI) removal was investigated and the removal mechanism was suggested as the physicochemical process. Based on Langmuir isotherm, the maximal Cr(VI) removal capacity attained 149.25 mg/g. Kinetic and equilibrium data were efficiently fitted using the pseudo-second-order and Langmuir models, respectively confirming the proposed mechanism. Diffusion models affirmed that the adsorption rate was governed by intraparticle diffusion. Adsorption thermodynamic study suggested the spontaneity and exothermic nature of the adsorption process. This study sheds light on the technology that has potential for magnetic separation and long-term use for effective removal of emerging water pollutants.

Zero-valent bimetallic catalyst/absorbent for simultaneous facilitation of MgSO3 oxidation and arsenic uptake

Cobalt (Co)-based catalysts can efficiently reduce the heat waste from sulfate concentration by enhancing sulfite oxidation during wet flue gas desulfurization system. However, arsenic (As) can poison such catalysts and migrate into the sulfate by-products, resulting in severe secondary pollution. In this study, a zero-valent Co/iron (Fe)-based nanoparticle (NZV-Co₂Fe₁) was fabricated and applied as a bifunctional catalyst/adsorbent. The catalytic stability of the Co-based catalyst was enhanced by the introduction of Fe because the poisonous effect of As was substantially suppressed because of the high adsorption capacity of Fe for As. Compared with the noncatalytic benchmark, the presence of 0.5 g/L NZV-Co₂Fe₁ can increase the rate of MgSO₃ oxidation by approximately 12-fold even at a high concentration of As (2.5 mg/L). The Langmuir model was fitted to the As adsorption isotherms, indicating that As uptake is a single-layer adsorption process. The pseudo-second-order kinetic model indicated that As was removed through chemisorption. The oxidation pathway of As(III) involves reactive radicals (mainly OH, SO₄^- and SO₅^-) and ligand-to-metal charge transfer between SO₃^2- and Co²⁺. The availability of MgSO₃ improved the removal efficiency at high concentrations of As(III) (1 mg/L). These results indicate that using NZV-Co₂Fe₁ as a catalyst to purify the by-products of flue gas desulfurization can effectively prevent secondary pollution.