Green, Solvent-Free Mechanochemical Synthesis of Nano Ag₂O/MnO₂/N-Doped Graphene Nanocomposites: An Efficient Catalyst for Additive-Base-Free Aerial Oxidation of Various Kinds of Alcohols

Abstract

Herein, we report a solvent-less, straightforward, and facile mechanochemical technique to synthesize nanocomposites of Ag 2 O nanoparticles-doped MnO 2 , which is further codoped with nitrogen-doped graphene (N-DG) [i.e., (X %)N-DG/MnO 2 −(1% Ag 2 O)] using physical milling of separately prepared N-DG and Ag 2 O NPs−MnO 2 annealed at 400 °C over an eco-friendly ball-mill process. To assess the efficiency in terms of catalytic performance of the nanocomposites, selective oxidation of benzyl alcohol (BlOH) to benzaldehyde (BlCHO) is selected as a substrate model with an ecofriendly oxidizing agent (O 2 molecule) and without any requirements for the addition of any harmful additives or bases. Various nanocomposites were prepared by varying the amount of N-DG in the composite, and the results obtained highlighted the function of N-DG in the catalyst system when they are compared with the catalyst MnO 2 −(1% Ag 2 O) [i.e., undoped catalyst] and MnO 2 −(1% Ag 2 O) codoped with different graphene dopants such as GRO and H-RG for alcohol oxidation transformation. The effects of various catalytic factors are systematically evaluated to optimize reaction conditions. The N-DG/MnO 2 −(1% Ag 2 O) catalyst exhibits premium specific activity (16.0 mmol/h/g) with 100% BlOH conversion and <99.9% BlCHO selectivity within a very short interval. The mechanochemically prepared N-DG-based nanocomposite displayed higher catalytic efficacy than that of the MnO 2 −(1% Ag 2 O) catalyst without the graphene dopant, which is N-DG in this study. A wide array of aromatic, heterocyclic, allylic, primary, secondary, and aliphatic alcohols have been selectively converted to respective ketones and aldehydes with full convertibility without further oxidation to acids over N-DG/MnO 2 −(1% Ag 2 O). Interestingly, it is also found that the N-DG/MnO 2 −(1% Ag 2 O) can be efficiently reused up to six times without a noteworthy decline in its effectiveness. The prepared nanocomposites were characterized using various analytical, microscopic, and spectroscopic techniques such as X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman, field emission scanning electron microscopy, and Brunauer−Emmett−Teller.

Ceria Nanoparticles on Modified MXene for Aerobic Oxidation of 4-Methoxybenzyl Alcohol

“…A notable innovation in this green approach involves using molecular oxygen (O 2 ) as the oxidant. − This method is particularly commendable not only because oxygen is plentiful and inexpensive but also because it mainly produces water as a byproduct, thus reducing the hazardous waste associated with conventional oxidation processes. The pursuit of sustainable methods has led to the development of numerous new techniques for converting benzyl alcohols to benzaldehydes, frequently using catalysts that contain precious metals such as Rh, Pd, Pt, Ru, and Au. − However, the scarcity and high cost of these metals are barriers to their widespread commercial use. In recent years, there has been significant research into catalysts made from more available and affordable non-noble metals such as Cu, Ni, V, Mo, Fe, and Zr, − aimed at promoting the aerobic oxidation of alcohols while ensuring economic and environmental sustainability.…”