Eco-Friendly Mechanochemical Preparation of Ag2O–MnO2/Graphene Oxide Nanocomposite: An Efficient and Reusable Catalyst for the Base-Free, Aerial Oxidation of Alcohols

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

Herein, we report a solvent-less, straightforward, and facile mechanochemical technique to synthesize nanocomposites of Ag2O nanoparticles-doped MnO2, which is further codoped with nitrogen-doped graphene (N-DG) [i.e., (X %)N-DG/MnO2-(1% Ag2O)] using physical milling of separately prepared N-DG and Ag2O NPs-MnO2 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 (O2 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 MnO2-(1% Ag2O) [i.e., undoped catalyst] and MnO2-(1% Ag2O) 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/MnO2-(1% Ag2O) 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 MnO2-(1% Ag2O) 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/MnO2-(1% Ag2O). Interestingly, it is also found that the N-DG/MnO2-(1% Ag2O) 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.

Large-scale production of myco-fabricated ZnO/MnO nanocomposite using endophytic Colonstachys rosea with its antimicrobial efficacy against human pathogens

In this study, a ZnO/MnO nanocomposite was myco-fabricated using the isolated endophytic Clonostachys rosea strain EG99 as the nano-factory. The extract of strain EG99, a reducing/capping agent, was successfully titrated with equal quantities of Zn(NO3)2·6H2O and Mn(NO3)2·6H2O (precursors) in a single step to fabricate the rod-shaped ZnO/MnO nanocomposite of size 6.22 nm. The ZnO/MnO nanocomposite was myco-fabricated in 20 min, and the results were validated at 350 and 400 nm using UV-Vis spectroscopy. In a 7-L bioreactor, an industrial biotechnological approach was used to scale up the biomass of this strain, EG99, and the yield of the myco-fabricated ZnO/MnO nanocomposite. A controlled fed-batch fermentation system with a specific nitrogen/carbon ratio and an identical feeding schedule was used in this production process. Higher yields were obtained by adopting a controlled fed-batch fermentation approach in a 7-L bioreactor with a regular feeding schedule using a nitrogen/carbon ratio of 1:200. Overall, the fed-batch produced 89.2 g/l of biomass at its maximum, 2.44 times more than the batch's 36.51 g/l output. Furthermore, the fed-batch's maximum ZnO/MnO nanocomposite yield was 79.81 g/l, a noteworthy 14.5-fold increase over the batch's yield of 5.52 g/l. Finally, we designed an innovative approach to manage the growth of the endophytic strain EG99 using a controlled fed-batch fermentation mode, supporting the rapid, cheap and eco-friendly myco-fabrication of ZnO/MnO nanocomposite. At a dose of 210 µg/ml, the tested myco-fabricated ZnO/MnO nanocomposite exhibited the maximum antibacterial activity against Staphylococcus aureus (98.31 ± 0.8%), Escherichia coli (96.70 ± 3.29%), and Candida albicans (95.72 ± 0.95%). At the same dose, Staphylococcus aureus biofilm was eradicated in 48 h; however, Escherichia coli and Candida albicans biofilms needed 72 and 96 h, respectively. Our myco-fabricated ZnO/MnO nanocomposite showed strong and highly selective antagonistic effects against a variety of multidrug-resistant human pathogens. Therefore, in upcoming generations of antibiotics, it might be employed as a nano-antibiotic.

High-Loading, Well-Dispersed Phosphorus Confined on Nanoporous Carbon Surfaces with Enhanced Catalytic Activity and Cyclic Stability

Phosphorus-doped carbon materials are promising alternatives to noble metal-based catalysts for the highly selective oxidation of benzyl alcohol to benzaldehyde, but it is challenging to achieve high loadings of high-activity P dopants in metal-free catalysts. Here, the preparation of high-loading and well-dispersed P atoms confined to the surfaces of cellulose-derived carbon via a dissolving-doping strategy is reported. In this method, cellulose is dissolved in phosphoric acid to generate a cellulose-phosphoric supramolecular collosol, which is then directly carbonized. The as-prepared carbon possesses a high specific surface area of 1491 cm³ g^-1 and a high P content of 8.8 wt%. The P-doped nanoporous carbon shows a superior catalytic activity and cyclic stability toward benzyl alcohol oxidation, with a high turnover frequency of 3.5 × 10^-3 mol g^-1 h^-1 and a low activation energy of 35.6 kJ mol^-1 . Experimental results and theoretical calculations demonstrate that the graphitic C₃ PO species is the leading catalytic active center in this material. This study provides a novel strategy to prepare P dopants in nanoporous carbon materials with excellent catalytic performance.

Enhanced Apoptosis by Functionalized Highly Reduced Graphene Oxide and Gold Nanocomposites in MCF-7 Breast Cancer Cells

Graphene nanocomposites have gained significant interest in a variety of biological applications due to their unique properties. Herein, we have studied the apoptosis-inducing ability and anticancer properties of functionalized highly reduced graphene oxide (HRG) and gold nanoparticles (Au NPs)-based nanocomposites (AP-HRG-Au). Samples were prepared under facile conditions via simple stirring and ultrasonication. All the samples were tested for their anticancer properties against different human cancer cell lines including lung (A549), liver (HepG2), and breast (MCF-7) cancer cells using doxorubicin as a positive control. In order to enhance the solubility and bioavailability of the sample, HRG was functionalized with 1-aminopyrene (1-AP) as a stabilizing ligand. The ligand also facilitated the homogeneous growth of Au NPs on the surface of HRG by offering chemically specific binding sites. The synthesis of nanocomposites and the surface functionalization of HRG were confirmed by UV-Vis, powder X-ray diffraction, and Fourier transform infrared spectroscopy. The structure and morphology of the as-prepared nanocomposites were established by high-resolution transmission electron microscopy. Because of the functionalization, the AP-HRG-Au nanocomposite exhibited enhanced physical stability and high dispersibility. A comparative anticancer study of pristine HRG, nonfunctionalized HRG-Au, and 1-AP-functionalized AP-HRG-Au nanocomposites revealed the enhanced apoptosis ability of functionalized nanocomposites compared to the nonfunctionalized sample, whereas the pristine HRG did not show any anticancer ability against all tested cell lines. Both HRG-Au and AP-HRG-Au have induced a concentration-dependent reduction in cell viability in all tested cell lines after 48 h of exposure, with a significantly higher response in MCF-7 cells compared to the remaining cells. Therefore, MCF-7 cells were selected to perform detailed investigations using apoptosis assay, cell cycle analysis, and reactive oxygen species measurements. These results suggest that AP-HRG-Au induces enhanced apoptosis in human breast cancer cells.

Electro-Oxidation of Ammonia at Novel Ag2O−PrO2/γ-Al2O3 Catalysts

An Ag2O(x)−PrO2(y)/γ-Al2O3 electrocatalyst series (X:Y is for Ag:Pr from 0 to 10) was synthesized, to use synthesized samples in electrochemical applications, a step in fuel cells advancements. Ag2O(x)−PrO2(y)/γ-Al2O3/Glassy-Carbon was investigated for electrochemical oxidation of ammonia in alkaline medium and proved to be highly effective, having high potential utility, as compared to commonly used Pt-based electrocatalysts. In this study, gamma alumina as catalytic support was synthesized via precipitation method, and stoichiometric wt/wt.% compositions of Ag2O−PrO2 were loaded on γ-Al2O3 by co-impregnation method. The desired phase of γ-Al2O3 and supported nanocatalysts was obtained after heat treatment at 800 and 600 °C, respectively. The successful loadings of Ag2O−PrO2 nanocatalysts on surface of γ-Al2O3 was determined by X-rays diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR), and energy dispersive analysis (EDX). The nano-sized domain of the sample powders sustained with particle sizes was calculated via XRD and scanning electron microscopy (SEM). The surface morphology and elemental compositions were examined by SEM, transmission electron microscopy (TEM) and EDX. The conductive and electron-transferring nature was investigated by cyclic voltammetry and electrochemical impedance (EIS). Cyclic voltammetric profiles were observed, and respective kinetic and thermodynamic parameters were calculated, which showed that these synthesized materials are potential catalysts for ammonia electro-oxidation. Ag2O(6)−PrO2(4)/γ-Al2O3 proved to be the most proficient catalyst among all the members of the series, having greater diffusion coefficient, heterogeneous rate constant and lesser Gibbs free energy for this system. The catalytic activity of these electrocatalysts is revealed from electrochemical studies which reflected their potentiality as electrode material in direct ammonia fuel cell technology for energy production.

Eco-Friendly and Solvent-Less Mechanochemical Synthesis of ZrO2–MnCO3/N-Doped Graphene Nanocomposites: A Highly Efficacious Catalyst for Base-Free Aerobic Oxidation of Various Types of Alcohols

In recent years, the development of green mechanochemical processes for the synthesis of new catalysts with higher catalytic efficacy and selectivity has received manifest interest. In continuation of our previous study, in which graphene oxide (GRO) and highly reduced graphene oxide (HRG) based nanocomposites were prepared and assessed, herein, we have explored a facile and solvent-less mechanochemical approach for the synthesis of N-doped graphene (NDG)/mixed metal oxide (MnCO3–ZrO2) ((X%)NDG/MnCO3–ZrO2), as the (X%)NDG/MnCO3–ZrO2 nano-composite was synthesized using physical grinding of separately synthesized NDG and pre-calcined (300 °C) MnCO3–ZrO2 via green milling method. The structures of the prepared materials were characterized in detail using X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), Raman, Thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm analysis. Besides, the obtained nanocomposites were employed as heterogeneous oxidation catalyst for the alcohol oxidation using green oxidant O2 without involving any surfactants or bases. The reaction factors were systematically studied during the oxidation of benzyl alcohol (PhCH2OH) as the model reactant to benzaldehyde (PhCHO). The NDG/MnCO3–ZrO2 exhibits premium specific activity (66.7 mmol·g−1·h−1) with 100% conversion of PhCH2OH and > 99.9% selectivity to PhCHO after only 6 min. The mechanochemically prepared NDG based nanocomposite exhibited notable improvement in the catalytic efficacy as well as the surface area compared to the pristine MnCO3–ZrO2. Under the optimal circumstances, the NDG/MnCO3–ZrO2 catalyst could selectively catalyze the aerobic oxidation of a broad array of alcohols to carbonyls with full convertibility without over-oxidized side products like acids. The NDG/MnCO3–ZrO2 catalyst were efficiently reused for six subsequent recycling reactions with a marginal decline in performance and selectivity.