Reduction of nitrate by bimetallic Fe/Ni nanoparticles

Bimetallic Fe/Ni nanoparticles were synthesized and their nitrate reduction capacity was studied. Nitrate (354 mg L(-1), equal to 5.71 mmol L(-1)) reduction was performed using Fe/Ni nanoparticles with various Ni contents (1.0, 5.0, 10 and 20%) in an unbuffered condition. Optimum nitrate reduction rate (1.03 +/- 0.087 x 10(-4) mol x min(-1) x greduc(-1)) was obtained with 5.0% nano-scale Fe/Ni, while only 25% nitrate (1.05 +/- 0.091 x 10(-5) mol x min(-1) x greduc(-1)) was transformed by nano-scale Fe(0) within the same reaction time, which means that these bimetallic nanoparticles are obviously more reactive than monometallic nano-scale Fe(0). For this bimetallic system a near-neutral initial pH (6.5) is more favourable than an acidic condition (2.0 and 4.0). Relatively air-stable nano-scale Fe/Ni particles were developed by slowly aging them for 22 h and exhibited similar reactivity to freshly synthesized nano-scale Fe(0). Although undesirable transformation of nitrate (91.0 +/- 0.37%) to ammonium was observed in this study, Fe/Ni particles showed a much higher nitrate reduction rate and an optimum reduction rate at near-neutral pH, which may have important implications for nitrate-contaminated site remediation.