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

Nitrophenols are used in fabricating explosives and reported to be carcinogenic in nature, dictating a necessity for their efficient and eco-friendly reduction. The majority of such reductions involve multistep protocols that use expensive reagents. Herein, 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 a remarkably high rate constant. These findings are based on a 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.