High stability and reactivity of porous calcium tartrate supported nano zero-valent iron in aerobic environment and alkaline wastewater

Abstract

Nano zero-valent iron (nZVI) has remarkable reactivity, but its practical application is severely hindered by its easy aggregation and rapid oxidation after exposure in air. In this study, spherical porous calcium tartrate (CaTr) was synthesized with ultrasound technology and used to support nZVI. It was found that the as-obtained nZVI@CaTr was highly stable and reactive in oxygen-rich water under neutral/alkaline conditions. In the pH range of 4–9, the degradation efficiency of p-nitrophenol (PNP, 50 mg/L) by nZVI@CaTr7 exceeded 98.1 %. Importantly, nZVI@CaTr could be stored in air for a long time without inert gas protection. After 60 days and 120 days of air exposure, the removal efficiency of PNP still reached 83.3 % and 63.3 %, which was 2.8 and 9.7 times that of bare nZVI, respectively. Such an excellent performance could be attributed to two reasons: (i) spherical CaTr effectively inhibited the oxidation and aggregation of nZVI by favorable interactions with nZVI, and (ii) the abundant functional groups on the surface of CaTr acted as electronic mediators to significantly promote charge transfer between nZVI (electron donor) and PNP (electron acceptor). Therefore, cheap, air stable and highly effective nZVI@CaTr7 provided a potential application prospect for the degradation of environmental pollutants in aerobic environment and alkaline wastewater.