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

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 and use expensive reagents and catalysts involving Au, Ag and Re. In this work, a one-step greener approach has been realized to mechanochemically prepare a cost-effective molybdenum disulfide (MoS2) and oxalic acid dihydrate composite for the catalytic reduction of nitrophenols into their corresponding amine in aqueous medium. The catalyst is bulk sized and works in-situ by virtue of the electroactivation of the morphologically rough MoS2 surface with nascent active sites. Such active sites are different from the conventional defect based active sites since these are composed of paramagnetic Mo5+ centers. These paramagnetic centers are generated during the mechanical grinding process and get exposed to the reactant at the outset of the reduction providing alternative reduction pathways. The epitactically 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 obeys first-order kinetics with a remarkable rate constant. These findings are based on thorough analysis using UV-visible spec-troscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman and electron paramagnetic resonance spectrosco-pies, high-resolution mass spectrometry along with first-principles quantum mechanical solid-state calculations.