Oxalate-promoted dissolution of hydrous ferric oxide immobilized within nanoporous polymers: Effect of ionic strength and visible light irradiation

•Dissolution of bulky/hybrid HFO was compared in the presence of oxalate at pH = 4.•Dissolution of hybrid HFO turns slower than bulky HFO.•Increasing ionic strength only promotes dissolution of hybrid HFO.•Photochemical reduction occurs only for bulky HFO and promotes the dissolution.•Polymeric surface chemistry affected dissolution of the immobilized HFO.

Oxalate is supposed to affect the applicability of hydrated ferric oxide (HFO)-based composites for environmental remediation because it would enhance HFO dissolution. Here, we examined the effect of ionic strength and visible light irradiation on the oxalate-induced dissolution of HFO, which is supported by two porous polystyrene beads binding chloromethyl groups (P–C) and sulfonate groups (P–S) respectively. As compared to the bare HFO, the dissolution of the immobilized HFO was considerably slower as a result of the slower oxalate adsorption. Compared to P–C, P–S could favor HFO dispersion greatly and achieve HFO nanoparticles of smaller size and higher surface area, resulting in more oxalate uptake with HFO–P–S than with HFO–P–C and a faster dissolution of the former composite. Increasing ionic strength from 0.01 to 0.1 M did not expose any significant effect on the dissolution kinetics of the bare HFO, but apparently promoted HFO dissolution for both composites. In the presence of visible light irradiation, an obvious photochemical reduction of Fe(III) into Fe(II) was observed for the bare HFO, which greatly promoted the iron leaching from solid to solution. However, it did not occur for both composites because the solid polymers keep the inside HFO nanoparticles from light irradiation.

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