Authors: Mohammad Rafe Hatshan | Mujeeb Khan | Mohamed E. Assal | Mohammed Rafi Shaik | Mufsir Kuniyil | Abdulrahman Al–Warthan | Mohammed Rafiq H. Siddiqui | Syed Farooq Adil
Source: ACS Omega (article, 2024-01-04)
Field: Chemistry — Organic Chemistry

Green, Solvent-Free Mechanochemical Synthesis of Nano Ag<sub>2</sub>O/MnO<sub>2</sub>/N-Doped Graphene Nanocomposites: An Efficient Catalyst for Additive-Base-Free Aerial Oxidation of Various Kinds of Alcohols Herein, we report a solvent-less, straightforward, and facile mechanochemical technique to synthesize nanocomposites of Ag<sub>2</sub>O nanoparticles-doped MnO<sub>2</sub>, which is further codoped with nitrogen-doped graphene (N-DG) [i.e., (X %)N-DG/MnO<sub>2</sub>-(1% Ag<sub>2</sub>O)] using physical milling of separately prepared N-DG and Ag<sub>2</sub>O NPs-MnO<sub>2</sub> 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 eco-friendly oxidizing agent (O<sub>2</sub> 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<sub>2</sub>-(1% Ag<sub>2</sub>O) [i.e., undoped catalyst] and MnO<sub>2</sub>-(1% Ag<sub>2</sub>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<sub>2</sub>-(1% Ag<sub>2</sub>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<sub>2</sub>-(1% Ag<sub>2</sub>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<sub>2</sub>-(1% Ag<sub>2</sub>O). Interestingly, it is also found that the N-DG/MnO<sub>2</sub>-(1% Ag<sub>2</sub>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. Nanocomposite ; Catalysis ; Graphene ; Doping ; Nano- ; Base (topology) ; Materials science ; Free base ; Chemical engineering ; Nanotechnology ; Chemistry ; Organic chemistry ; Composite material ; Optoelectronics Oxidative Organic Chemistry Reactions ; Vanadium and Halogenation Chemistry ; Porphyrin and Phthalocyanine Chemistry