A comparative study of hexacyanoferrate-based Prussian blue analogue nanocrystals for catalytic reduction of 4-nitrophenol to 4-aminophenol

Catalytic reduction of 4-nitrophenol (4-NP) represents a useful method of converting 4-NP into a more environmentally friendly product, 4-aminophenol (4-AP). Prussian blue (PB) (Fe-3[Fe(CN)(6)](2)) and its Prussian blue Analogues (PBAs) (M-II[Fe(CN)(6)] PBAs (M-II = Mn, Co, Ni, and Zn) exhibit hierarchical porous structures, and electrochemical characteristics, making PBAs promising catalysts for 4-NP reduction. Nevertheless, very few literatures report the reduction of 4-NP to 4-AP employing PBAs, and no studies have been ever conducted to evaluate the effects of different M-II species of [Fe(CN)(6)]-based PBAs on the catalytic conversion of 4-NP to 4-AP. Herein, we examine the catalytic reductive performance of various (M-II[Fe(CN)(6)] PBAs (M-II = Mn, Co, Ni, and Zn), in the presence of sodium borohydride (NaBH4), on 4-NP reduction to 4-AP. The catalytic activity of PBAs for 4-NP reduction was in the order CoFeCN > NiFeCN > FeFeCN > MnFeCN > ZnFeCN. The corresponding activation energies are determined as 32, 43, 46, 47, and 54 kJ/mol for CoFeCN, NiFeCN, MnFeCN, FeFeCN and ZnFeCN, respectively. Especially, CoFeCN shows the highest catalytic activity with a rate constant of 0.457 min(-1) and a calculated turnover frequency of 6.3 x 10(-3)s(-1), which are higher than many reported noble metal catalysts because of its high surface area and catalytic activities towards hydrogen generation and hydrogenation. CoFeCN (and NiFeCN) also exhibit excellent reusabilities even after 6 consecutive reduction experiments. These findings demonstrate that PBAs, such as CoFeCN and NiFeCN, are highly advantageous catalysts for reduction of 4-NP and would be promising for reducing other nitro-aromatic compounds.