Search Results (19)

Palladium (Pd), a noble metal, has unique properties for C-C bond formation in reactions such as the Suzuki and Heck reactions. Besides Pd-based complexes, Pd NPs have also attracted significant attention for applications such as fuel cells, hydrogen storage, and sensors for gases such as H₂ and non-enzymatic glucose, including catalysis. Additionally, Pd NPs are catalysts in environmental treatment to abstract organic and heavy-metal pollutants such as Cr (VI) by converting them to Cr(III). In terms of biological activity, Pd NPs were found to be active against Staphylococcus aureus and Escherichia coli, where 99.99% of bacteria were destroyed, while PVP-Pd NPs displayed anticancer activity against human breast cancer MCF7. Hence, in this review, we attempted to cover recent progress in the various applications of Pd NPs with emphasis on their application as sensors and catalysts for energy-related and other applications. Full article

The utilization of heterogeneous catalysts during the production of biodiesel potentially minimize the cost of processing due to the exclusion of the separation step. The (X wt%)Ni–ZrO₂ (where X = 10, 25 and 50) catalysts prepared through a hydrothermal process were tested for the production of biodiesel by the transesterification of waste cooking oil (WCO) with methanol. The influences of various reaction parameters were systematically optimized. While the physicochemical characteristics of the as-synthesized catalysts were examined using numerous techniques such as FTIR, XRD, TGA BET, EDX, SEM, and HRTEM. Among all the catalysts, (10 wt%)Ni–ZrO₂ exhibited high surface area when compared to the pristine ZrO₂, (25 wt%)Ni–ZrO₂ and (50 wt%)Ni–ZrO₂ nanocatalysts. It may have influenced the catalytic properties of (10 wt%)Ni–ZrO_2, which exhibited maximum catalytic activity with a biodiesel production yield of 90.5% under optimal conditions. Such as 15:1 methanol to oil molar ratio, 10 wt% catalysts to oil ratio, 8 h reaction time and 180 °C reaction temperature. Furthermore, the recovered catalyst was efficiently reused in several repeated experiments, demonstrating marginal loss in its activity after multiple cycles (five times). Full article

This work demonstrates hydrazine electro-oxidation and sensing using an ultrathin copper oxide nanosheet (CuO-NS) architecture prepared via a versatile foam-surfactant dual template (FSDT) approach. CuO-NS was synthesised by chemical deposition of the hexagonal surfactant Brij^®58 liquid crystal template containing dissolved copper ions using hydrogen foam that was concurrently generated by a sodium borohydride reducing agent. The physical characterisations of the CuO-NS showed the formation of a two-dimensional (2D) ultrathin nanosheet architecture of crystalline CuO with a specific surface area of ~39 m²/g. The electrochemical CuO-NS oxidation and sensing performance for hydrazine oxidation revealed that the CuO nanosheets had a superior oxidation performance compared with bare-CuO, and the reported state-of-the-art catalysts had a high hydrazine sensitivity of 1.47 mA/cm² mM, a low detection limit of 15 μM (S/N = 3), and a linear concentration range of up to 45 mM. Moreover, CuO-NS shows considerable potential for the practical use of hydrazine detection in tap and bottled water samples with a good recovery achieved. Furthermore, the foam-surfactant dual template (FSDT) one-pot synthesis approach could be used to produce a wide range of nanomaterials with various compositions and nanoarchitectures at ambient conditions for boosting the electrochemical catalytic reactions. Full article

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. Full article

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. Full article

Plant extract of Pulicaria undulata (L.) was used as both reducing agent and stabilizing ligand for the rapid and green synthesis of gold (Au), silver (Ag), and gold–silver (Au–Ag) bimetallic (phase segregated/alloy) nanoparticles (NPs). These nanoparticles with different morphologies were prepared in two hours by stirring corresponding metal precursors in the aqueous solution of the plant extracts at ambient temperature. To infer the role of concentration of plant extract on the composition and morphology of NPs, we designed two different sets of experiments, namely (i) low concentration (LC) and (ii) high concentration (HC) of plant extract. In the case of using low concentration of the plant extract, irregular shaped Au, Ag, or phase segregated Au–Ag bimetallic NPs were obtained, whereas the use of higher concentrations of the plant extract resulted in the formation of spherical Au, Ag, and Au–Ag alloy NPs. The as-prepared Au, Ag, and Au–Ag bimetallic NPs showed morphology and composition dependent catalytic activity for the reduction of 4-nitrophenol (4-NPh) to 4-aminophenol (4-APh) in the presence of NaBH₄. The bimetallic Au–Ag alloy NPs showed the highest catalytic activity compared to all other NPs. Full article

Co_xO_y–manganese carbonate (X%)(Co_xO_y–MnCO₃ catalysts (X = 1–7)) were synthesized via a straightforward co-precipitation strategy followed by calcination at 300 °C. Upon calcination at 500 °C, these were transformed to Co_xO_y–dimanganese trioxide i.e., (X%)Co_xO_y–Mn₂O₃. A relative catalytic evaluation was conducted to compare the catalytic efficiency of the two prepared catalysts for aerial oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using O₂ molecule as a clean oxidant without utilizing any additives or alkalis. Amongst the different percentages of doping with Co_xO_y (0–7% wt./wt.) on MnCO₃ support, the (1%)Co_xO_y–MnCO₃ catalyst exhibited the highest catalytic activity. The influence of catalyst loading, calcination temperature, reaction time, and temperature and catalyst dosage was thoroughly assessed to find the optimum conditions of oxidation of benzyl alcohol (BzOH) for getting the highest catalytic efficiency. The (1%)Co_xO_y–MnCO₃ catalyst which calcined at 300 °C displayed the best effectiveness and possessed the largest specific surface area i.e., 108.4 m²/g, which suggested that the calcination process and specific surface area play a vital role in this transformation. A 100% conversion of BzOH along with BzH selectivity >99% was achieved after just 20 min. Notably, the attained specific activity was found to be considerably larger than the previously-reported cobalt-containing catalysts for this transformation. The scope of this oxidation reaction was expanded to various alcohols containing aromatic, aliphatic, allylic, and heterocyclic alcohols without any further oxidation i.e., carboxylic acid formation. The scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) specific surface area analytical techniques were used to characterize the prepared catalysts. The obtained catalyst could be easily regenerated and reused for six consecutive runs without substantial decline in its efficiency. Full article

Recently, the development of eco-friendly mechanochemical approaches for the preparation of novel catalysts with enhanced activity and selectivity has gained considerable attention. Herein, we developed a rapid and solvent-less mechanochemical method for the preparation of mixed metal oxide (Ag₂O–MnO₂) decorated graphene oxide (GRO)-based nanocomposites (Ag₂O–MnO₂/(X wt.%)GRO), as the Ag₂O–MnO₂/(X wt.%)GRO nanocomposite was fabricated by the physical grinding of freshly prepared GRO and pre-annealed (300 °C) mixed metal oxide nanoparticles (NPs) (Ag₂O–MnO₂) using an eco-friendly milling procedure. The as-prepared nanocatalysts were characterized by using various techniques. Furthermore, the nanocomposites were applied as a heterogeneous catalyst for the oxidation of alcohol by employing gaseous O₂ as an eco-friendly oxidant under base-free conditions. The mechanochemically obtained GRO-based composite exhibited noticeable enhancement in the surface area and catalytic performance compared to the pristine Ag₂O–MnO₂. The results revealed that (1%)Ag₂O–MnO₂/(5 wt.%)GRO catalyst exhibited higher specific performance (13.3 mmol·g⁻¹·h⁻¹) with a 100% conversion of benzyl alcohol (BnOH) and >99% selectivity towards benzaldehyde (BnH) within 30 min. The enhancement of the activity and selectivity of GRO-based nanocatalyst was attributed to the presence of various oxygen-containing functional groups, a large number of defects, and a high specific surface area of GRO. In addition, the as-prepared nanocatalyst also demonstrated excellent catalytic activity towards the conversion of a variety of other alcohols to respective carbonyls under optimal conditions. Besides, the catalyst ((1%)Ag₂O–MnO₂/(5 wt.%)GRO) could be efficiently recycled six times with no noticeable loss in its performance and selectivity. Full article

Graphene and its nanocomposites are showing excellent potential in improving the catalytic performances of different materials. However, the synthetic protocol and its form, such as graphene oxide (GRO) or highly reduced graphene oxide (HRG), influence the catalytic efficiencies. Here, we present, a facile synthesis of graphene oxide (GRO) and ZrO_x-MnCO₃-based nanocomposites [(1%)ZrO_x–MnCO₃/(x%)GRO] and their outcome as an oxidation catalyst for alcohol oxidation under mild conditions using O₂ as a clean oxidant. The ZrO_x–MnCO₃/GRO catalyst prepared by incorporating GRO to pre-calcined ZrO_x-MnCO₃ using ball milling showed remarkable enhancement in the catalytic activities as compared to pristine ZrO_x–MnCO₃, ZrO_x–MnCO₃ supported on HRG or ZrO_x–MnCO₃/GRO prepared by in-situ growth of ZrO_x–MnCO₃ onto GRO followed by calcination. The catalyst with composition (1%)ZrO_x–MnCO₃/(1%)GRO exhibited superior specific activity (57.1 mmol/g·h) with complete conversion and >99% selectivity of the product within a short period of time (7 min) and at a relatively lower temperature (100 °C). The catalyst could be recycled at least five times with a negligible decrease in efficiency and selectivity. The catalytic study was extended to different aromatic as well as aliphatic alcohols under optimized conditions, which confirmed the efficiency and selectivity of the catalyst. Full article

Nitrogen-doped graphene (NDG)-palladium (Pd)-based nanocatalysts (NDG@Pd) can be potentially applied as an efficient catalyst for the preparation of biaryls in a Suzuki–Miyaura coupling reaction. Herein, we report the one-pot facile synthesis of an NDG@Pd nanocatalyst, wherein the nanocatalyst was prepared by the simultaneous reduction of graphene oxide (GRO) and PdCl₂ in the presence of hydrazine hydrate as a reducing agent, while ammonium hydroxide was used as a source of “N’’ on the surface of graphene. The as-synthesized NDG@Pd nanocatalyst, consisting of smaller-sized, spherical-shaped palladium nanoparticles (Pd-NPs) on the surface of NDG, was characterized by several spectroscopic and microscopic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The nanocatalyst displayed outstanding catalytic activity in the Suzuki–Miyaura cross-coupling reactions of phenyl halides with phenyl boronic acids under facile conditions in water. The catalytic activity of NDG@Pd was found to be a more efficient catalyst when compared to pristine highly reduced graphene oxide (HRG) based Pd nanocatalyst (HRG@Pd). Furthermore, the reusability of the catalyst was also tested by repeatedly performing the same reaction using the recovered catalyst. The N-doped catalyst displayed excellent reusability even after several reactions. Full article

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). Full article

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. Full article

Plant-mediated green synthesis of nanomaterials has been increasingly gaining popularity due to its eco-friendly nature and cost-effectiveness. In the present study, we synthesized silver nanoparticles (AgNPs) by using an aqueous solution of Saudi Origanum vulgare L. plant extract as a bioreducing agent. The as-synthesized AgNPs were characterized using various microscopic and spectroscopic techniques. The results indicated the formation of crystalline face-centered cubic (fcc) AgNPs. Additionally, FT-IR study confirmed that the O. vulgare L. extract not only functioned as a bioreductant but also stabilized the surface of the AgNPs by acting as a capping agent. Moreover, the effect of the amount of the plant extract on the size and the antimicrobial activity of the NPs was also assessed. It was found that with increasing amounts of plant extract, the size of the NPs was decreased. Moreover, as-synthesized AgNPs as well as O. vulgare L. plant extract were separately tested to examine their antimicrobial activities. The activities were tested against various bacterial and fungal microorganisms including Shigella sonnei, Micrococcus luteus, Escherichia coli, Aspergillus flavus, Alternaria alternate, Paecilomyces variotii, Phialophora alba, and so on. These results evidently show that the inclusion of O. vulgare L. extracts improves the solubility of AgNPs, which led to a significant enhancement in the toxicity of the NPs against the assessed microorganisms. Full article

Nanocomposites of highly reduced graphene oxide (HRG) and ZnO_x 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., ZnO_x(1%)–MnCO₃/(X%)HRG (where X = 0–7), calcination at 400 °C and 500 °C, yielded different manganese oxides i.e., ZnO_x(1%)–MnO₂/(X%)HRG and ZnO_x(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 ZnO_x(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 ZnO_x(1%)–MnCO₃/(X%)HRG nanocomposites possess several application prospect in other organic chemistry reactions. Full article

The synthesis of Palladium (Pd) nanoparticles by green methods has attracted remarkable attention in recent years because of its superiority above chemical approaches, owing to its low cost and ecological compatibility. In this present work, we describe a facile and environmentally friendly synthesis of Pd nanoparticles (Pd NPs) using an aqueous extract of aerial parts of Origanum vulgare L. (OV) as a bioreductant. This plant is available in many parts of the world as well as in Saudi Arabia and is known to be a rich source of phenolic components, a feature we fruitfully utilized in the synthesis of Pd NPs, using various concentrations of plant extracts. Moreover, the OV extract phytomolecules are not only accountable for the reduction and progression of nanoparticles, but they also act as stabilizing agents, which was confirmed by several characterization methods. The as-synthesized Pd nanoparticles (Pd NPs) were analyzed using ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and thermal gravimetric analysis (TGA). Further, FT-IR study has proven that the OV not merely represents a bioreductant but also functionalizes the nanoparticles. Furthermore, the green synthesized metallic Pd NPs were successfully applied as catalysts for selective oxidation of alcohols. Full article