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Globally, researchers have devoted consistent efforts to producing excellent coating properties since coating plays an essential role in enhancing electrochemical performance and surface quality. In this study, TiO2 nanoparticles in varying concentrations of 0.5, 1, 2, and 3 wt.% were added into the acrylic-epoxy polymeric matrix with 90:10 wt.% (90A:10E) ratio incorporated with 1 wt.% graphene, to fabricate graphene/ TiO 2 -based nanocomposite coating systems. Furthermore, the properties of the graphene/ TiO 2 composites were investigated by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), ultraviolet-visible (UV-Vis) spectroscopy, water contact angle (WCA) measurements, and cross-hatch test (CHT), respectively. Moreover, the field emission scanning electron microscope (FESEM) and the electrochemical impedance spectroscopy (EIS) tests were conducted to investigate the dispersibility and anticorrosion mechanism of the coatings. The EIS was observed by determining the breakpoint frequencies over a period of 90 days. The results revealed that the TiO 2 nanoparticles were successfully decorated on the graphene surface by chemical bonds, which resulted in the graphene/ TiO 2 nanocomposite coatings exhibiting better dispersibility within the polymeric matrix. The WCA of the graphene/ TiO 2 coating increased along with the ratio of TiO 2 to graphene, achieving the highest CA of 120.85° for 3 wt.% of TiO2. Excellent dispersion and uniform distribution of the TiO 2 nanoparticles within the polymer matrix were shown up to 2 wt.% of TiO2 inclusion. Among the coating systems, throughout the immersion time, the graphene/ TiO 2 (1:1) coating system exhibited the best dispersibility and high impedance modulus values ( Z 0.01   Hz ), exceeding 10 10 Ω   cm 2 . [ABSTRACT FROM AUTHOR]

Graphene‐based nanocomposites with inorganic (metal and metal oxide) nanoparticles leads to materials with high catalytic activity for a variety of chemical transformations. Graphene and its derivatives such as graphene oxide, highly reduced graphene oxide, or nitrogen‐doped graphene are excellent support materials due to their high surface area, their extended π‐system, and variable functionalities for effective chemical interactions to fabricate nanocomposites. The ability to fine‐tune the surface composition for desired functionalities enhances the versatility of graphene‐based nanocomposites in catalysis. This review summarizes the preparation of graphene/inorganic NPs based nanocomposites and their use in catalytic applications. We discuss the large‐scale synthesis of graphene‐based nanomaterials. We have also highlighted the interfacial electronic communication between graphene/inorganic nanoparticles and other factors resulting in increased catalytic efficiencies. [ABSTRACT FROM AUTHOR]

Graphene–metal nanocomposites have been found to remarkably enhance the catalytic performance of metal nanoparticle‐based catalysts. In continuation of our previous report, in which highly reduced graphene oxide (HRG)‐based nanocomposites were synthesized and evaluated, we present nanocomposites of graphene oxide (GRO) and ZnO nanoparticle‐doped MnCO3 ([ZnO–MnCO3/(1%)GRO]) synthesized via a facile, straightforward co‐precipitation technique. Interestingly, it was noticed that the incorporation of GRO in the catalytic system could noticeably improve the catalytic efficiency compared to a catalyst (ZnO–MnCO3) without GRO, for aerial oxidation of benzyl alcohol (BzOH) employing O2 as a nature‐friendly oxidant under base‐free conditions. The impacts of various reaction factors were thoroughly explored to optimize reaction conditions using oxidation of BzOH to benzaldehyde (BzH) as a model substrate. The catalysts were characterized using X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, Energy dispersive X‐ray spectroscopy (EDX), Brunauer‐Emmett‐Teller (BET), and Raman spectroscopy. The (1%)ZnO–MnCO3/(1%)GRO exhibited significant specific activity (67 mmol.g−1.hr−1) with full convversion of BzOH and >99% BzH selectivity within just 6 min. The catalytic efficiency of the (1%)ZnO–MnCO3/(1%)GRO nanocomposite was significantly better than the (1%)ZnO–MnCO3/(1%)HRG and (1%)ZnO–MnCO3 catalysts, presumably due to the existence of oxygen‐possessing groups on the GRO surface and as well as a very high surface area that could have been instrumental in uniformly dispersing the active sites of the catalyst, i.e., ZnO–MnCO3. Under optimum circumstances, various kinds of alcohols were selectively transformed to respective carbonyls with full convertibility over the (1%)ZnO–MnCO3/(1%)GRO catalyst. Furthermore, the highly effective (1%)ZnO–MnCO3/(1%)GRO catalyst could be successfully reused and recycled over five consecutive runs with a marginal reduction in its performance and selectivity. [ABSTRACT FROM AUTHOR]

A facile and chemical specific method to synthesize highly reduced graphene oxide (HRG) and Pd (HRG@Pd) nanocomposite is presented. The HRG surfaces are tailored with amine groups using 1-aminopyrene (1-AP) as functionalizing molecules. The aromatic rings of 1-AP sit on the basal planes of HRG through π–π interactions, leaving amino groups outwards (similar like self-assembled monolayer on 2D substrates). The amino groups provide the chemically specific binding sites to the Pd nucleation which subsequently grow into nanoparticles. HRG@Pd nanocomposite demonstrated both uniform distribution of Pd nanoparticles on HRG surface as well as excellent physical stability and dispersibility. The surface functionalization was confirmed using, ultraviolet–visible (UV–Vis), Fourier transform infra-red and Raman spectroscopy. The size and distribution of Pd nanoparticles on the HRG and crystallinity were confirmed using high-resolution transmission electron microscopy and powder X-ray diffraction and X-ray photoelectron spectroscopy. The catalytic efficiency of highly reduced graphene oxide-pyrene-palladium nanocomposite (HRG-Py-Pd) is tested towards the Suzuki coupling reactions of various aryl halides. The kinetics of the catalytic reaction (Suzuki coupling) using HRG-Py-Pd nanocomposite was monitored using gas chromatography (GC). [ABSTRACT FROM AUTHOR]

Zirconia nanoparticles doped MnCO3 have been successfully immobilized on various percentages of highly reduced graphene oxide (HRG)[(X%)HRG/MnCO3-(1%)ZrOx](where, X=0-7)],via a facile and straight forward co-precipitation method. Upon calcination, the as-obtained materials have yielded different types of HRG/manganese oxide nanocomposites at different temperatures i.e.[(X%)HRG/MnO2-(1%)ZrOx] and [(X%)HRG/Mn2O3-(1%)ZrOx]. A detail investigation was carried out to compare the catalytic performance of carbonates and oxides based nanocomposites for the selective oxidation of secondary alcohols. For this purpose, molecular oxygen was employed as an environmentally benign oxidant under basefree conditions. The reaction conditions were optimized with different weight percentages of HRG, reaction times, calcination temperatures, catalyst dosages, and reaction temperatures using 1-phenylethanol as a substrate model. The catalytic performance of the nanocomposites was enhanced significantly due to the presence of HRG as a support material. The catalyst with (1%)HRG/MnCO3-(1%)ZrOx exhibited outstanding performance as well as excellent selectivity in the aerobic oxidation of 1-phenylethanol. In this case, 100% conversion in 4 min with more than 99% selectivity was achieved with excellent specific activity of 60.0 mmol.g-1.h-1. Moreover, catalyst can be efficiently reused 5 times without discernible decrease in its activity and selectivity. Apart from this, various other alcohols were also selectively oxidized to their corresponding carbonyls with complete conversion in short reaction times under optimal conditions without over-oxidation to the carboxylic acids. [ABSTRACT FROM AUTHOR]

An affordable co-precipitation procedure has employed for the preparation of ZnOx nanoparticles doped MnCO3 supported on different percentages of highly reduced graphene oxide (HRG) nanocomposites (X%)HRG/MnCO3-(1%)ZnOx (where x = 0-7) calcined at 300°C. Upon calcination at 400 and 500°C, manganese carbonate is converted to different manganese oxides, i.e. manganese dioxide (MnO2) and manganic trioxide (Mn2O3), respectively. A comparative catalytic study was performed to assess the catalytic efficiency of the manganese carbonates and manganese oxides for the selective oxidation of secondary alcohols in the presence of molecular O2 as a clean oxidant under base-free condition. Effects of several parameters were systematically studied using oxidation of 1-phenyl-ethanol into acetophenone as a reaction model. It was found that the efficiency of the catalytic system has improved significantly after doping the catalyst with graphene for the aerial oxidation of secondary alcohols. Furthermore, the promotion role of HRG support in the adsorption of reactant alcohol and oxygen near the ZnOx NPs as well as graphene support possesses extremely high surface area. The as-fabricated catalysts were characterised by EDX, SEM, XRD, TGA, Raman, FTIR and BET techniques. (1%)HRG/MnCO3-(1%)ZnOx nanocomposite exhibited outstanding specific activity (66.67 mmol g-1 h-1) with complete conversion along with <99% acetophenone selectivity within only 6 min. Notably, the achieved specific activity is much higher than the specific activity of the previously reported catalytic systems. The scope of the oxidation reaction is expanded to different types of alcohols such as benzylic, aliphatic, allylic and heteroatomic alcohols with 100% convertibility without over-oxidation to the carboxylic acids under mild conditions. [ABSTRACT FROM AUTHOR]

Nanocomposites of highly reduced graphene oxide (HRG) and ZnOx nanoparticles doped manganese carbonate containing different percentages of HRG were prepared via a facile co-precipitation method. The prepared sample calcined at 300 °C yielded i.e., ZnOx(1%)-MnCO3/(X%)HRG (where X = 0-7), calcination at 400 °C and 500 °C, yielded different manganese oxides i.e., ZnOx(1%)-MnO2/(X%)HRG and ZnOx(1%)-Mn2O3/(X%)HRG respectively. The prepared catalyst were subjected to catalytic evaluation and a comparative catalytic study between carbonates and oxides for the liquid-phase aerobic oxidation of benzylic alcohols to corresponding aldehydes using molecular oxygen as an eco-friendly oxidant without adding additives or bases. The influence of various parameters such as percentage of HRG, reaction time, catalyst amount, calcination and reaction temperature was systematically examined to optimize reaction conditions using oxidation of benzyl alcohol as a substrate model. It was found that the catalytic performance is remarkably enhanced after using HRG as catalyst co-dopant for the aerobic oxidation of alcohols, possibly owing to the presence of carbon defects and oxygenated functional groups on HRG surface. The as-synthesized catalysts were characterized by SEM, EDX, XRD, Raman, TGA, BET, and FT-IR. Under optimal conditions, the catalyst with composition ZnOx(1%)-MnCO3/(1%)HRG calcined at 300 °C exhibited remarkable specific activity (57.1 mmol·g-1·h-1) with 100% conversion of benzyl alcohol and more than 99% product selectivity within extremely short time (7 min). The as-prepared catalyst was re-used up to five consecutive times without significant decrease in its activity and selectivity. To the best of our knowledge, the achieved specific activity is the highest so far compared to the earlier reported catalysts used for the benzyl alcohol oxidation. A wide range of substituted benzylic and aliphatic alcohols were selectively oxidized into their corresponding aldehydes with complete convertibility and selectivity in short reaction times without over-oxidation to the acids. Due to their significant low cost, superior reproducibility, excellent catalytic efficiency, the ZnOx(1%)-MnCO3/(X%)HRG nanocomposites possess several application prospect in other organic chemistry reactions. [ABSTRACT FROM AUTHOR]

Zinc oxide nanoparticles doped manganese carbonate catalysts [X% ZnOx–MnCO3] (where X = 0–7) were prepared via a facile and straightforward coprecipitation procedure, which upon different calcination treatments yields different manganese oxides, that is, [X% ZnOx–MnO2] and [X% ZnOx–Mn2O3]. A comparative catalytic study was conducted to evaluate the catalytic efficiency between carbonates and oxides for the selective oxidation of secondary alcohols to corresponding ketones using molecular oxygen as a green oxidizing agent without using any additives or bases. The prepared catalysts were characterized by different techniques such as SEM, EDX, XRD, TEM, TGA, BET, and FTIR spectroscopy. The 1% ZnOx–MnCO3 calcined at 300°C exhibited the best catalytic performance and possessed highest surface area, suggesting that the calcination temperature and surface area play a significant role in the alcohol oxidation. The 1% ZnOx–MnCO3 catalyst exhibited superior catalytic performance and selectivity in the aerial oxidation of 1-phenylethanol, where 100% alcohol conversion and more than 99% product selectivity were obtained in only 5 min with superior specific activity (48 mmol·g−1·h−1) and 390.6 turnover frequency (TOF). The specific activity obtained is the highest so far (to the best of our knowledge) compared to the catalysts already reported in the literatures used for the oxidation of 1-phenylethanol. It was found that ZnOx nanoparticles play an essential role in enhancing the catalytic efficiency for the selective oxidation of alcohols. The scope of the oxidation process is extended to different types of alcohols. A variety of primary, benzylic, aliphatic, allylic, and heteroaromatic alcohols were selectively oxidized into their corresponding carbonyls with 100% convertibility without overoxidation to the carboxylic acids under base-free conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Degradation of organic dyes and their byproducts by heterogeneous photocatalysts is an essential process, as these dyes can be potentially discharged in wastewater and threaten aquatic and xerophyte life. Therefore, their complete mineralization into nontoxic components (water and salt) is necessary through the process of heterogeneous photocatalysis. In this study, Zr/CrO2 (Zirconium-doped chromium IV oxide) nanocomposite-based photocatalysts with different compositions (1, 3, 5, 7 & 9 wt.%) were prepared by an environmentally friendly, solid-state reaction at room temperature. The as-prepared samples were calcined under air at 450 °C in a furnace for a specific period of time. The synthesis of Zr/CrO2 photocatalysts was confirmed by various techniques, including XRD, SEM, EDX, FT-IR, UV-Vis, and BET. The photocatalytic properties of all samples were tested towards the degradation of methylene blue and methyl orange organic dyes under UV light. The results revealed a concentration-dependent photocatalytic activity of photocatalysts, which increased the amount of dopant (up to 5 wt.%). However, the degradation efficiency of the catalysts decreased upon further increasing the amount of dopant due to the recombination of holes and photoexcited electrons. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study addressed the limitations of lead-based radiation shields by developing lead-free, non-toxic, lightweight, and flexible shielding materials with high attenuation efficiency. To achieve this, single and triple layers of Bi2O3-BaTiO3/PVP-PEG nanocomposite films were synthesized. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) polymers (2:1 ratio) were used as the polymeric matrix in which fillers of Bi2O3 and BaTiO3 nanoparticles (NPs) with particle sizes ranging from 90 to 210 nm and <100 nm, respectively, were embedded. Four single-layer samples with 20%, 30%, 40%, and 50% NP concentrations were prepared; the samples were 1.05, 1.09, 1.27, and 1.42 mm thick, respectively. Two samples of triple-layered films were prepared with 30% and 50% NPs, measuring 3.78 and 4.23 mm in thickness, respectively. The attenuation efficiency of these films was investigated using X-ray tube voltages from 10 to 120 kVp. Further, the flexibility of the synthesized films was tested by manual handling. All single- and triple-layer nanocomposites exhibited effective radiation attenuation and desirable flexibility. Specifically, at the lowest tube voltage, all samples exhibited 100% attenuation, while at the highest tube voltage, the attenuation ranged from 27% to 84%, depending on the NP concentration and number of layers of the sample. The highest attenuation ratio, observed in the 50% triple-layer sample, reached 100% up to approximately 60 kVp and 84% at 120 kVp. Consequently, the most optimal film synthesized in this study had a triple-layer configuration with 50% Bi2O3-BaTiO3 NPs embedded in a PVP-PEG polymer with an average attenuation of 95.5% for all tube voltages (10–120 kVp). Therefore, this shielding is suitable for various diagnostic applications, such as mammography, dental X-rays, computerized tomography, and fluoroscopy.Highlights Single- and triple-layered nanocomposite Bi2O3-BaTiO3/PVP-PEG films were synthesizedThe attenuation efficiency of the films against X-rays was investigatedA triple-layer configuration with 50% Bi2O3-BaTiO3/PVP-PEG was suitable for various diagnostic applicationsSingle- and triple-layered nanocomposite Bi2O3-BaTiO3/PVP-PEG films were synthesizedThe attenuation efficiency of the films against X-rays was investigatedA triple-layer configuration with 50% Bi2O3-BaTiO3/PVP-PEG was suitable for various diagnostic applications [ABSTRACT FROM AUTHOR]

A single-step solvothermal approach to prepare stabilized cubic zirconia (ZrO2) nanoparticles (NPs) and highly reduced graphene oxide (HRG) and ZrO2 nanocomposite (HRG@ZrO2) using benzyl alcohol as a solvent and stabilizing ligand is presented. The as-prepared ZrO2 NPs and the HRG@ZrO2 nanocomposite were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD), which confirmed the formation of ultra-small, cubic phase ZrO2 NPs with particle sizes of ~2 nm in both reactions. Slight variation of reaction conditions, including temperature and amount of benzyl alcohol, significantly affected the size of resulting NPs. The presence of benzyl alcohol as a stabilizing agent on the surface of ZrO2 NPs was confirmed using various techniques such as ultraviolet-visible (UV-vis), Fourier-transform infrared (FT-IR), Raman and XPS spectroscopies and thermogravimetric analysis (TGA). Furthermore, a comparative electrochemical study of both as-prepared ZrO2 NPs and the HRG@ZrO2 nanocomposites is reported. The HRG@ZrO2 nanocomposite confirms electronic interactions between ZrO2 and HRG when compared their electrochemical studies with pure ZrO2 and HRG using cyclic voltammetry (CV). [ABSTRACT FROM AUTHOR]

Ag2O nanoparticles-doped MnO2 decorated on different percentages of highly reduced graphene oxide (HRG) nanocomposites, i.e., (X%)HRG/MnO2–(1%)Ag2O (where X = 0–7), were fabricated through straight-forward precipitation procedure, and 400 °C calcination, while upon calcination at 300 °C and 500 °C temperatures, it yielded MnCO3 and manganic trioxide (Mn2O3) composites, i.e., [(X%)HRG/MnCO3–(1%)Ag2O] and [(X%)HRG/Mn2O3–(1%)Ag2O], respectively. These nanocomposites have been found to be efficient and very effective heterogeneous catalysts for selective oxidation of secondary alcohols into their respective ketones using O2 as a sole oxidant without adding surfactants or nitrogenous bases. Moreover, a comparative catalytic study was carried out to investigate the catalytic efficiency of the synthesized nanocomposites for the aerobic oxidation of 1-phenylethanol to acetophenone as a substrate reaction. Effects of several factors were systematically studied. The as-prepared nanocomposites were characterized by TGA, XRD, SEM, EDX, HRTEM, BET, Raman, and FTIR. The catalyst with structure (5%)HRG/MnO2–(1%)Ag2O showed outstanding specific activity (16.0 mmol/g·h) with complete conversion of 1-phenylethanol and >99% acetophenone selectivity within short period (25 min). It is found that the effectiveness of the catalyst has been greatly improved after using graphene support. A broad range of alcohols have selectively transformed to desired products with 100% convertibility and no over-oxidation products have been detected. The recycling test of (5%)HRG/MnO2–(1%)Ag2O catalyst for oxidation of 1-phenylethanol suggested no obvious decrease in its performance and selectivity even after five subsequent runs. [ABSTRACT FROM AUTHOR]