Enhancing the characteristics and reactivity of nZVI: Polymers effect and mechanisms

Nanoscale zero-valent iron (nZVI) is regarded as one of the most effective materials for environmental remediation. However, nZVI particles tend to aggregate rapidly due to their magnetic properties which leads to decrease their effectiveness in water treatment. To overcome the aggregation problem of nZVI particles and increase their reactivity, four different polymers were used during the synthesis of nZVI including polyacrylamide (PAA), carboxymethyl cellulose (CMC), Polyethylene sorbitan monolaurate (PSM) and polyvinylpyrrolidone (PVP). These polymers were used with different mass ratios varied between 0.04 and 0.40 %, in order to acquire the optimal mass ratio with nZVI and achieve the highest removal of nitrate and phosphorus. The mechanism of polymers adsorption onto the surface of nZVI was explored by conducting SEM-EDX, XRD, and FTIR analysis. TEM was used to examine the suface morphology of nZVI before and after being stabilized with 4 polymers. Results showed that, the sizes were found to be 9.53, 65.4, 106.4, 106.6 and 108.8 nm, using TEM and ImageJ, corresponding to CMC-nZVI, bare-nZVI, PAA-nZVI, PSM-nZVI and PVP-nZVI, respectively. The efficiency of bare and stabilized nZVI on nitrate reduction was found to be in the following the order: PVP-nZVI 99.5% > PAA-nZV 99% > PSM-nZV 97% > CMC-nZVI 70% > bare-nZVI 55.6%. Whereas, for phosphorus adsorption, PAA-nZV 97% was the most effective type, followed by bare-nZVI 76.3%, PSM-nZVI 75%, PVP-nZVI 73% and CMC-nZVI 71%. Therefore, PAA-nZVI exhibited an excellent performance over the rest for both nitrate and phosphorus removal at a wide range of pH. For this reason, four kinetic models were investigated to describe the reaction rate of nitrate and phosphorus removal by PAA-nZVI.