Evaluation of Nano Zero-Valent Iron (nZVI) Activity in Solution and Immobilized in Hydrophilic PVDF Membrane for Drimaren Red X-6BN and Bisphenol-a Removal in Water

Abstract

Fenton reactions that involve nano zero-valent iron (nZVI) have shown high promise in the removal of organic pollutants. In this work, nZVI stabilized with carboxymethyl cellulose (CMC) was evaluated for drimaren red X-6BN (DRX-6BN, 10 mg/L) and bisphenol-a (BPA, 800 mg/L) removal. Oxidation reactions were conducted for removal of both compounds by varying nZVI/CMC concentration (0.01–5 g/L), hydrogen peroxide (H2O2, 0.01–0.1 g/L), and pH (3–9). DRX-6BN degradation rate was the highest (kinetic constant (kobs) = 4.622 h−1) when working at pH 3 and 3 g/L of nZVI/CMC. Increasing H2O2 concentration could not improve the reaction. For BPA, all the conditions tested showed removals of more than 96% with 0.02 g/L of H2O2. This result was compared with the activity of nZVI loaded in hydrophilic PVDF (Polyvinylidene fluoride) membranes by polyacrylic acid (PAA) to entrap nanoparticles to the membrane surface. As expected, the attachment of nZVI onto the membranes diminished nanoparticles’ activity; however, it is important to highlight the need for preparing a stable catalytic membrane, which could enhance pollutant removal of microfiltration membranes’ systems. This was confirmed by the percentage of iron leaching from functionalized membranes, where a higher concentration of iron in the bulk solution leads to enhancement on BPA removal. Issues with BPA diffusion resistance inside the pores were overcome by conducting the nZVI/PAA/PVDF membranes in the cross-flow system, reaching 40% of BPA removal after 3 h of permeation.