Synthesis of nanoiron by microemulsion with Span/Tween as mixed surfactants for reduction of nitrate in water

Denitrification of nitrate in groundwater using iron nanoparticles has received increasing interest in recent years. In order to fabricate iron nanoparticles with homogeneously spherical shape and narrow size distribution, a simple and “green” method was developed to synthesize iron nanoparticles. The conventional microemulsion methods were modified by applying Span 80 and Tween 60 as mixed surfactants. The maximum content of water in the Water-in-oil (W/O) microemulsion and its appropriate forming conditions were found, and then the microemulsion system consisting of saturated Fe²⁺ solution was used to synthesize α-Fe ultrafine particles by redox reaction. The nanoparticles were characterized by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the average diameter of the particle is about 80–90 nm. The chemical activity of the obtained iron nanoparticles was studied by the denitrification experiment of nitrate. The results show that under the experimental conditions, iron removed most of the 80 mg/L nitrate within 30 min. The mass balance of nitrate reduction with nanoscale Fe indicates that endproducts are mainly ammonia. Two possible reaction pathways for nitrate reduction by nanoscale iron particles have been proposed in this work.