One-Step Mechanochemical Synthesis of Bulk Sized Electroactive MoS2/Oxalic Acid Dihydrate Composite for Catalytic Nitrophenol Reductions.

Abstract

Nitrophenols are used in fabricating explosives and reported to be carcinogenic in nature, dictating a necessity for its efficient and eco-friendly reduction. Majority of such reductions involve multistep protocols that use expensive reagents. In this work, a one-step greener approach has been developed to mechanochemically prepare a cost-effective molybdenum disulfide (MoS2) and oxalic acid dihydrate based composite to catalytically reduce nitrophenols into their corresponding amine in aqueous medium. The catalyst works in-situ by virtue of the electroactivation of the morphologically rough MoS2 surface which generates nascent active sites. The active sites are composed of paramagnetic Mo5+ centers generated during the mechanical grinding process. The peritectoidically transformed oxalic acid dihydrate which is physisorbed on the MoS2 surface during the catalyst's preparation process, gets released in aqueous medium lowering the pH and accelerating the hydrolysis of BH4- . The BH4- quickly interacts with the nascent active sites propagating the reduction at a faster rate. We establish an Eley-Rideal mechanism that is responsible for remarkably high-rate constant. These findings are based on thorough analysis using UV-visible spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman and electron paramagnetic resonance spectroscopies, high-resolution mass spectrometry along with first-principles quantum mechanical solid-state calculations.