Highly efficient reduction of p-Nitrophenol by sodium borohydride over binary ZIF-67/g-C₃N₄ heterojunction catalyst

Abstract

In this study, a facile coprecipitation based synthesis scheme was used to prepare a non-noble metal doped graphitic carbon nitride-based catalyst ZIF-67/g-C₃N₄ (abbreviated as ZIF-CN) for the reduction of nitrophenols (NPs) in presence of sodium borohydride (NBH). The binary nanocomposite involves Co-nanoparticles (diameter: 5–10 nm), embedded in the conductive g-C₃N₄ (gCN) layer. The synthesized catalyst exhibits excellent reduction activities towards various nitrophenols (NPs) including 4-nitrophenol (PNP), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). The rate constant of PNP reduction in ZIF-CN(5)/NBH system was 3.8 times and 7.3 times that of pristine ZIF-67 and gCN, respectively, in presence of 0.15 g/l catalyst and 10.0 mM NBH, at pH 7. The presence of anions (at 0.1 mM), i.e.,H₂PO₄^-,HCO₃^-,SO^2/4-and decreases the rate of PNP reduction, whereas, Cl^- marginally influences the process. The continuous, conductive gCN sheets introduce large number of active sites for adsorption BH₄^-and NP and subsequent electron transfer from the π-complex to the Co-nodes, forming active hydrogen species, accelerating the reduction. Moreover, the synthesized ZIF-CN catalyst can be reused for at least 10 consecutive cycles, without considerable loss of catalytic activity. Therefore, the synthesized ZIF-CN catalyst has enormous potential towards NP reduction, at ambient conditions.