Copper hexacyanoferrate nanocrystal as a highly efficient non-noble metal catalyst for reduction of 4-nitrophenol in water

As Prussian Blue analogues (PBAs) represent one of the most classical families of coordination compounds and exhibit versatile catalytic activities, PBAs have been considered as useful heterogeneous catalysts for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, especially, due to their ability to attain pronounced conversions of reactants under mild conditions, environmental friendliness and great stability. Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, Cu-based PBA has never been developed and thoroughly investigated for 4-NP reduction. Thus, in this study, copper hexacyanoferrate, Cu^II₃[Fe(CN)₆]₂ (CuFeCN) is particularly synthesized and proposed for the first time as a catalyst for reduction of 4-NP in the presence of NaBH₄. CuFeCN exhibits a very high catalytic activity towards reduction of 4-NP to 4-AP with 100% conversion within 4 min. The activity factor (AF) at room temperature, 8057.14 s^-1 g^-1, is between 1 and 2 orders higher than all other MFeCN Prussian blue analogues (M = Co, Fe, Ni, Zn, and Mn). In addition, CuFeCN shows excellent reusability to achieve 100% conversion of 4-NP to 4-AP with highly stable rate constants over successive 7 cycles. The activation energy (E_a) and turn over frequency (TOF) for the reduction of 4-NP to 4-AP catalyzed by CuFeCN system are determined as 24.6 kJ mol^-1 and 36.93 min^-1, respectively, which are both significantly more superior than most of reported catalysts in literatures. These advantageous properties make CuFeCN ideal to be developed into a promising catalyst for elimination of nitroaromatic contaminants in water.