Solventless Mechanochemical Fabrication of ZnO–MnCO3/N-Doped Graphene Nanocomposite: Efficacious and Recoverable Catalyst for Selective Aerobic Dehydrogenation of Alcohols under Alkali-Free Conditions

Abstract

Catalytic efficacy of metal-based catalysts can be significantly enhanced by doping graphene or its derivatives in the catalytic protocol. In continuation of previous work regarding the catalytic properties of highly-reduced graphene oxide (HRG), graphene-oxide (GO) doped mixed metal oxide-based nanocomposites, herein we report a simple, straightforward and solventless mechanochemical preparation of N-doped graphene (NDG)/mixed metal oxide-based nanocomposites of ZnO–MnCO3 (i.e., ZnO–MnCO3/(X%-NDG)), wherein N-doped graphene (NDG) is employed as a dopant. The nanocomposites were prepared by physical milling of separately fabricated NDG and ZnO–MnCO3 calcined at 300 °C through eco-friendly ball mill procedure. The as-obtained samples were characterized via X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), Raman, Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and surface area analysis techniques. To explore the effectiveness of the obtained materials, liquid-phase dehydrogenation of benzyl alcohol (BOH) to benzaldehyde (BH) was chosen as a benchmark reaction using eco-friendly oxidant (O2) without adding any harmful surfactants or additives. During the systematic investigation of reaction, it was revealed that the ZnO–MnCO3/NDG catalyst exhibited very distinct specific-activity (80 mmol/h.g) with a 100% BOH conversion and <99% selectivity towards BH in a very short time. The mechanochemically synthesized NDG-based nanocomposite showed remarkable enhancement in the catalytic performance and increased surface area compared with the catalyst without graphene (i.e., ZnO–MnCO3). Under the optimum catalytic conditions, the catalyst successfully transformed various aromatic, heterocyclic, allylic, primary, secondary and aliphatic alcohols to their respective ketones and aldehydes with high selectively and convertibility without over-oxidation to acids. In addition, the ZnO–MnCO3/NDG was also recycled up to six times with no apparent loss in its efficacy.

Biologically-induced synthetic manganese carbonate precipitate (BISMCP) for potential applications in heavy metal removal

“…This software demonstrated a typical FT-IR spectrum of biologically-induced mineralization of MnCO 3 , as shown in Fig. 2 The spectral peaks in MCP-4 to MCP-9 centered at 1420.90 cm −1 , 865.67 cm −1 , and 717.91 cm −1 are related to C O binding and are known to be the typical peaks of rhodochrosite material or MnCO 3 [ 29 , 41 , 50 , 80 , 86 ]. The broader peak at 3452.24 cm −1 correlated to O–H binding and N–H binding, which were related to the characteristics of the hydroxyl and amino groups and could be attributed to sugars, carboxylic acids, nucleic acids, or amino acids [ 26 ].…”

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

“…Our research group has developed several metal NP-based catalysts and their graphene nanocomposites and investigated their catalytic properties toward the oxidation of alcohols. ,, In our previously reported investigation, we reported that Ag 2 O NPs are highly effective dopants for MnO 2 , and the catalyst (1% Ag 2 O)–MnO 2 calcined at 400 °C afforded outstanding effectiveness for aerobic oxidation of a wide array of alcohols with the eco-friendly oxidant O 2 , which was later studied by doping the same with GRO and HRG, and their catalytic aptitude was also explored , Herein, we prepared novel Ag 2 O–MnO 2 /(X %)­N-DG nanocomposites via a facile and eco-friendly two-steps method with the coprecipitation procedure followed by the mechanochemical ball-milling procedure, as described in Scheme , and explored their efficacy with selective aerial oxidation of BlOH as a substrate model. The mechanochemical ball milling technique assists in the inhibition of agglomeration.…”