Abstract

In this study, we demonstrated that the choice of precursor has a strong effect on the reduction of nitrate (NO3) using zero-valent copper (Cu0) synthesized by sodium borohydride (NaBH4). Different precursors: CuSO4, CuO, Cu2O, Cu powder, and Cu mesh were used to reduce NO3 at 677 mg-N/L under the reducing conditions of NaBH4. Compared with the prehydrolyzed samples, those prepared without prehydrolysis exhibited lower reduction rates, longer times and higher concentrations of nitrite (NO2) intermediate. It was found that one-time addition of NaBH4 resulted in higher reduction rate and less NO2 intermediate than two-step addition. Results showed that Cu0 from CuSO4 possessed the smallest particle size (890.9 nm), highest surface area (26.0 m2/g), and highest reaction rate (0.166 min−1). Values of pseudo-first-order constant (kobs) were in the order: CuSO4 > CuO > Cu2O > Cu powder >Cu mesh. However, values of surface area-normalized reaction rate (kSA) were approximately equal. It was proposed that NO3 was reduced to NO2 on Cu0, and then converted to NH4+ and N2, respectively; H2 generated from both NaBH4 hydration and Cu (II) reduction contributed to NO3 reduction as well.

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