Carbon black supported on a Mn-MIL-100 framework as high-efficiency electrocatalysts for nitrophenol reduction

Abstract

• The effects of metal ions in MIL-100 on PNP degradation were firstly studied. • Higher PNP electro-reduction efficiency was achieved by using Mn-MOF/C@CP. • The carbon black layer facilitated the charge-transfer process in a wide range of pH. • Possible electron transfer mechanism involving in PNP reduction was proposed. In order to achieve a high electroreduction efficiency of p -nitrophenol (PNP), fabrication of X-MIL-100 (X-MOF, X = Al, Fe, Mn)/carbon black (C) catalysts onto carbon paper (CP) cathode was investigated in this study. The successful synthesis of X-MOF was verified by X-ray diffraction, while the effects of metal ions in MIL-100 series on PNP degradation efficiency were preliminarily studied through cyclic voltammetry (CV) test. According to the CV and X-ray photoelectron spectroscopy results, Mn-MOF/C@CP showed the highest electrocatalytic activity due to the unique existence of the mixed valence metal cluster Mn 2+ /Mn 3+ in Mn-MIL-100. Compared with Mn-MOF@CP and CP electrode, the improved electrocatalytic activity of Mn-MOF/C@CP was confirmed by CV. Besides, it was found that the electrochemical activity and stability of Mn-MOF/C modified CP electrode were significantly improved in wide range of pH. The removal efficiency of Mn-MOF/C@CP for PNP reduction were as high as 96% in 12 h, while it was only 66% in 16 h for the blank CP. The excellent electrocatalytic activity of Mn-MOF/C@CP for PNP reduction could be attributed to the synergistic effect of carbon black and the versatile valence of Mn. In addition, the possible electron transfer mechanism involving in the electroreduction of PNP by Mn-MOF/C@CP was proposed. The improved electrocatalytic activity and increased PNP reduction efficiency demonstrated that Mn-MOF/C catalyst could have a promising future in electroreduction of recalcitrant PNP.