Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions

A considerable amount of research has been carried out in recent years on synthesizing metal nanoclusters (NCs), which have wide applications in the field of optical materials with non-linear properties, bio-sensing, and catalysis. Aside from being structurally accurate, the atomically precise NCs possess well-defined compositions due to significant tailoring, both at the surface and the core, for certain functionalities. To illustrate the importance of atomically precise metal NCs for catalytic processes, this review emphasizes 1) the recent work on Cu, Ag, and Au NCs with their synthesis, 2) the parameters affecting the activity and selectivity of NCs catalysis, and 3) the discussion on the catalytic potential of these metal NCs. Additionally, metal NCs will facilitate the design of extremely active and selective catalysts for significant reactions by elucidating catalytic mechanisms at the atomic and molecular levels. Future advancements in the science of catalysis are expected to come from the potential to design NCs catalysts at the atomic level.

Comparative study of NiO/CuO/Ag doped graphene based materials for reduction of nitroaromatic compounds and degradation of dye with statistical study

In the present work, the Nickel oxide (rGO-NiO), Silver (rGO-Ag), Copper oxide (rGO-CuO) doped Graphene Oxide are reported for catalytic reactions. A comparative study for catalytic activities of these materials are performed with nitroaromatic compound 4-nitroaniline and the results are statistically studied by using univariate analysis of variance and Post Hoc Test through Statistical Package for Social Sciences and it is observed that CuO doped Graphene material is showing better catalytic activity in minimum time. So, further research has been focused on the catalytic acitivity of rGO-CuO only and it is found that it is efficient in reducing other nitro compounds also such as Picric acid and Nitrobenzene. Dye degradation of Methylene blue is also performed using CuO decorated Graphene material and significant changes were observed using UV spectroscopy. The characterization of rGO-CuO is done with Fourier-transform Infrared Spectroscopy, Powder X-ray Diffraction, Thermogravimetric Analysis, Scanning Electron Microscope and Transmission Electron Microscopy.

Nanoarchitected graphene/copper oxide nanoparticles/MoS2 ternary thin films as highly efficient electrodes for aqueous sodium-ion batteries

Sodium-ion batteries (SIBs) operating in aqueous electrolyte are an emerging technology that promises to be safer, cheaper, more sustainable and more efficient than their lithium-based counterparts. One of the great challenges associated with this technology is the development of advanced materials with high specific capacity to be used as electrodes. Herein, we describe an ingenious strategy to prepare unprecedented tri-component nanoarchitected thin films with superior performance when applied as anodes in aqueous SIBs. Taking advantage of the broadness and versatility of the liquid-liquid interfacial route, three transparent nanocomposite films comprising graphene, molybdenum sulphide and copper oxide nanoparticles have been prepared. The samples were characterized using several techniques, and the results demonstrated that depending on the specific experimental strategy, different nanoarchitectures are achieved, resulting in different and improved properties. An astonishing capacity of 1377 mA h g-1 at 0.1 A g-1 and a degree of recovery of 100% were observed for the film in which the interactions among the components were optimized. This is among the highest capacity values reported in the literature and demonstrates the potential of these tri-component materials to be used as anodes in aqueous sodium-ion batteries.

Novel Synthesis of CuO/GO Nanocomposites and Their Photocatalytic Potential in the Degradation of Hazardous Industrial Effluents

Photocatalytic degradation of dyes has been the subject of extensive study due to its low cost, eco-friendly operation, and absence of secondary pollutants. Copper oxide/graphene oxide (CuO/GO) nanocomposites are emerging as a new class of fascinating materials due to their low cost, nontoxicity, and distinctive properties such as a narrow band gap and good sunlight absorbency. In this study, copper oxide (CuO), graphene oxide (GO), and CuO/GO were synthesized successfully. X-ray diffractometer (XRD) and Fourier transform infrared (FTIR) spectroscopy confirm the oxidation and production of GO from the graphene of lead pencil. According to the morphological analysis of nanocomposites, CuO nanoparticles of sizes ≤20 nm on the GO sheets were evenly adorned and distributed. Nanocomposites of different CuO:GO ratios (1:1 up to 5:1) were applied for the photocatalytic degradation of methyl red (MR). CuO:GO(1:1) nanocomposites achieved 84% MR dye removal, while CuO:GO(5:1) nanocomposites achieved the highest value (95.48%). The thermodynamic parameters of the reaction for CuO:GO(5:1) were evaluated using the Van't Hoff equation and the activation energy was found to be 44.186 kJ/mol. The reusability test of the nanocomposites showed high stability even after seven cycles. CuO/GO catalysts can be used in the photodegradation of organic pollutants in wastewater at room temperature due to their excellent properties, simple synthesis process, and low cost.

Thermal conductivity of polyurethane sheets containing beryllium oxide nanofibers

Polyvinyl alcohol/beryllium sulfate/polyethyleneimine (PVA/BeSO₄/PEI) precursor nanofibers (NFs) was first fabricated to obtain PVA/BeSO₄/PEI electrospun NFs by electrospinning technology, finally manufactured beryllium oxide (BeO) NFs followed by various heat treatment methods. The minimum calcination temperature for pure BeO NFs was 1000 °C, and the minimum specific surface area (5.1 m² g^-1) and pore volumes (0.0128 cm³ g^-1) were at 1300 °C. 46.18% Be and 53.82% O was measured in BeO NFs by X-ray photoelectron spectroscopy. BeO NFs were then impregnated with polyurethane (PU) aqueous solution to make PU/BeO NFs heat-dissipating sheet. This heat-dissipating sheet showed superior thermal conductivity (14.4 W m^-1 K^-1) at 41.4 vol% BeO NFs content. The electrical insulating properties of the heat-dissipating sheet were likewise excellent (1.6 × 10¹² Ω □^-1). In this study, the author attempted to create a thermally conductive but electrically insulating PU/BeO NFs heat-dissipating sheet that could effectively eliminate generated heat from electric equipment.

Sonochemical synthesis of a copper reduced graphene oxide nanocomposite using honey and evaluation of its antibacterial and cytotoxic activities

The combination of graphene-based materials and inorganic nanoparticles for the enhancement of the nanomaterial properties is extensively explored nowadays. In the present work, we used a sonochemical method to synthesize a copper/reduced graphene oxide (Cu/RGO) nanocomposite using Australian honey and vitamin C as capping and reducing agents, respectively. The honey-mediated copper/reduced graphene oxide (H/Cu/RGO) nanocomposite was then characterized through UV-visible, XRD, HRTEM, and FTIR analysis. The copper nanoparticles (Cu-NPs) in the nanocomposite formed uniform spherical shapes with a size of 2.20 ± 0.70 nm, which attached to the reduced graphene oxide (RGO) layers. The nanocomposite could suppress bacterial growth in both types of bacteria strains. However, in this study, the nanocomposite exhibited good bactericidal activity toward the Gram-positive bacteria than the Gram-negative bacteria. It also showed a cytotoxic effect on the cancer colorectal cell line HCT11, even in low concentrations. These results suggested that the H/Cu/RGO nanocomposite can be a suitable component for biomedical applications.

Quasi-HKUST Prepared via Postsynthetic Defect Engineering for Highly Improved Catalytic Conversion of 4-Nitrophenol

HKUST-1 [Cu₃(BTC)₂(H₂O)₃]_n·nH₂OMeOH was submitted to thermolysis under controlled conditions at temperatures between 100 and 300 °C. This treatment resulted in partial ligand decarboxylation, generating coordinatively unsaturated Cu²⁺ sites with extra porosity on the way to the transformation of the initial HKUST-1 framework to CuO. The obtained materials retaining in part the HKUST-1 original crystal structure (quasi-MOFs) were used to promote 4-nitrophenol conversion to 4-aminophenol. Because of the partial linker decomposition, the quasi-MOF treated at 240 °C contains coordinatively unsaturated Cu²⁺ ions distributed throughout the Q-HKUST lattice together with micro- and mesopores. These defects explain the excellent catalytic performance of QH-240 with an apparent rate constant of 1.02 × 10^-2 s^-1 in excess of NaBH₄ and an activity factor and half-life time of 51 s^-1g^-1 and 68 s, respectively, which is much better than that of the HKUST parent. Also, the induction period decreases from the order of minutes to seconds in the presence of the HKUST and QH-240 catalysts, respectively. Kinetic studies fit with the Langmuir-Hinshelwood theory in which both 4-nitrophenol and BH₄^- should be adsorbed onto the catalyst surface. The values of the true rate constant (k), the adsorption constants of 4-nitrophenol and BH₄^- (K_4-NP and K_BH4^-), as well as the activation energy are in agreement with a rate-determining step involving the reduction of 4-nitrophenol by the surface-bound hydrogen species.

Synthesis, Characterization and Photodegradation Studies of Copper Oxide–Graphene Nanocomposites

In this work, a simple hydrothermal method was employed to prepare a pristine sample of copper oxide (CuO) and three samples of copper oxide–graphene nanocomposites (CuO-xG) with x = 2.5, 5, and 10 mg of graphene. The synthesized samples were characterized using X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV-Vis) spectroscopy. The XRD patterns of CuO-xG nanocomposites exhibited the diffraction peaks related to the crystal planes of monoclinic CuO and hexagonal graphite. The surface morphology of the prepared samples was investigated using FESEM images. EDX analysis was used to investigate the chemical composition of the synthesized samples. FTIR spectroscopy identified the vibrational modes of the covalent bonds present in the samples. The allowed direct optical bandgap energy was calculated for all prepared samples using UV-Vis absorption spectra. The small bandgap of CuO-xG nanocomposites indicates their potential use as an effective photocatalyst in the presence of visible light. Photocatalytic activity of the samples was explored for the degradation of methylene blue (MB) dye contaminant under visible light irradiation. The results showed that the CuO-5G sample has the highest photodegradation efficiency (~56%).

Synthesis of sub-nanometric Cu2O catalysts for Pd-free C–C coupling reactions

The current template route provides Cu₂O nanocrystals with various shapes and depends on the homologues of glucose. These morphology-controlled Cu₂O nanocrystals show high activity for the external base-free Ullmann homocoupling of aryl halides.

Graphene oxide decorated with cellulose and copper nanoparticle as an efficient adsorbent for the removal of malachite green

In this study, the graphene oxide surface was modified by grafting of nanocellulose and copper nanoparticles to promote the surface charge and adsorption efficiency for malachite green (MG). The structural and configurational properties of GO-CEL-Cu were verified by UV/Vis, SEM, TEM, EDX and FTIR spectroscopy and confirmed the electrostatic interaction and hydrogen bonding between GO, CEL and Cu-NPs. TEM images confirmed the deposition of Cu-NPs size between 24 and 37 nm on the GO surface. The uniform fine particles size makes strong interfacial interaction with GO sheets result in efficient load transfer from the matrix to the hybrid. The variable parameters such as adsorbent amount, MG concentration, pH, time and temperature were investigated to achieve optimum experimental condition. The experimental data was justified by Langmuir isotherm model with adsorption capacity for GO, GO-Cu, GO-CEL, GO-CEL-Cu as 127.3, 149.2, 156.8 and 207.1 mg/g, respectively. The spontaneity and endothermic nature of the process were confirmed by negative Gibbs free energy and followed the pseudo-second-order rate equation. Additionally, positive values of enthalpy and entropy suggesting endothermic process and increase randomness during process, respectively. In conclusion, nanocomposite is capable to adsorb the toxic dye due to its well economic, eco-friendly, well adsorption rate and regeneration ability.

Functional Channel of SWCNTs/Cu2O/ZnO NRs/Graphene Hybrid Electrodes for Highly Sensitive Nonenzymatic Glucose Sensors

The hybrid electrode of single-wall carbon nanotubes (SWCNTs)/Cu₂O/ZnO nanorods (NRs)/graphene used on the current-response nonenzymatic glucose sensor was investigated herein, regarding the mechanism of the formation of functional channel. The synthesis of the hybrid electrode involved four steps. First, the graphene was grown by chemical vapor deposition (CVD) and then wet-transferred onto indium transparent oxide (ITO) glass. Second, a zinc oxide (ZnO) seed layer was sputtered onto the graphene/ITO glass, and ZnO NRs were gradually grown by the hydrothermal method. Third, the ZnO NRs were clad with cuprous oxide (Cu₂O) by the electrochemical method. Fourth, the SWCNTs were dropped onto the Cu₂O surface, with a Nafion surfactant. X-ray diffraction spectra, scanning electron microscopy spectra, Raman spectra, cyclic voltammograms, and amperometric response diagrams were used to verify the performance of the device. Results showed that sensitivity increased significantly from 11.2 to 289.8 μA mM^-1 cm^-2, linear range increased significantly from 0.6 to 11.1 mM, and the coefficient of determination (R²) increased from 0.9766 to 0.9923, all by the addition of the SWCNTs/Cu₂O functional channel mechanism and without graphene. When the graphene was added to the functional channel electrode, sensitivity increased again from 289.8 to 466.1 μA mM^-1 cm^-2 at low concentrations.

Cu–Fe Incorporated Graphene-Oxide Nanocomposite as Highly Efficient Catalyst in the Degradation of Dichlorodiphenyltrichloroethane (DDT) from Aqueous Solution

Abstract

Fe/graphene oxide and Cu–Fe/graphene oxide nanocomposite were synthesized by the atomic implantation method to study the photocatalytic degradation of dichlorodiphenyltrichloroethane (DDT). The synthesized nanocomposites were characterized by the XRD, N2 isotherms, SEM with EDX, TEM and XPS analysis. Characterization results have reported that oxides of Cu and Fe were uniformly distributed on graphene oxide and exited in the form of Cu+ and Fe2+ ions in Cu–Fe/graphene oxide nanocomposite. The high photocatalytic DDT removal efficiency 99.7% was obtained for Cu–Fe/graphene oxide under the optimal condition of 0.2 g/L catalyst, 15 mg/L H2O2 and pH 5. It was attributed to the reduction of Fe3+ to Fe2+ by Cu+ ions and –OH radicals formation. However, it was dropped to 90.4% in the recycling study by leaching of iron and without a change in phase structure and morphology.

Graphic Abstract

Sea-Island-Like Morphology of CuNi Bimetallic Nanoparticles Uniformly Anchored on Single Layer Graphene Oxide as a Highly Efficient and Noble-Metal-Free Catalyst for Cyanation of Aryl Halides

Aryl nitriles are versatile compounds that can be synthesized via transition-metal-mediated cyanation of aryl halides. Most of the supported-heterogeneous catalysts are noble-metals based and there are very limited numbers of efficient non-noble metal based catalysts demonstrated for the cyanation of aryl halides. Herein, bimetallic CuNi-oxide nanoparticles supported graphene oxide nanocatalyst (CuNi/GO-I and CuNi/GO-II) has been demonstrated as highly efficient system for the cyanation of aryl halides with K₄[Fe(CN)₆] as a cyanating agent. Metal-support interaction, defect ratio and synergistic effect with the bimetallic nanocatalyst were investigated. To our delight, the CuNi/GO-I system activity transformed a wide range of substrates such as aryl iodides, aryl bromides, aryl chlorides and heteroaryl compounds (Yields: 95-71%, TON/TOF: 50-38/2 h^-1). Moreover, enhanced catalytic performance of CuNi/GO-I and CuNi/GO-II in reduction of 4-nitropehnol with NaBH₄ was also confirmed (k_app = 18.2 × 10^-3 s^-1 with 0.1 mg of CuNi/GO-I). Possible mechanism has been proposed for the CuNi/GO-I catalyzed cyanation and reduction reactions. Reusability, heterogeneity and stability of the CuNi/GO-I are also found to be good.

In Situ Decoration of Gold Nanoparticles on Graphene Oxide via Nanosecond Laser Ablation for Remarkable Chemical Sensing and Catalysis

Gold decorated graphene-based nano-hybrids find extensive research interest due to their enhanced chemical catalytic performance and biochemical sensing. The unique physicochemical properties and the very large surface area makes them propitious platform for the rapid buildouts of science and technology. Graphene serves as an outstanding matrix for anchoring numerous nanomaterials because of its atomically thin 2D morphological features. Herein, we have designed a metal-graphene nano-hybrid through pulsed laser ablation. Commercially available graphite powder was employed for the preparation of graphene oxide (GO) using modified Hummers' method. A solid, thin gold (Au) foil was ablated in an aqueous suspension of GO using second harmonic wavelength (532 nm) of the Nd:YAG laser for immediate generation of the Au-GO nano-hybrid. The synthesis strategy employed here does not entail any detrimental chemical reagents and hence avoids the inclusion of reagent byproducts to the reaction mixture, toxicity, and environmental or chemical contamination. Optical and morphological characterizations were performed to substantiate the successful anchoring of Au nanoparticles (Au NPs) on the GO sheets. Remarkably, these photon-generated nano-hybrids can act as an excellent surface enhanced Raman spectroscopy (SERS) platform for the sensing/detection of the 4-mercaptobenzoic acid (4-MBA) with a very low detection limit of 1 × 10-12 M and preserves better reproducibility also. In addition, these hybrid materials were found to act as an effective catalyst for the reduction of 4-nitrophenol (4-NP). Thus, this is a rapid, mild, efficient and green synthesis approach for the fabrication of active organometallic sensors and catalysts.

Ni nanoparticle supported reduced graphene oxide as a highly active and durable heterogeneous material for coupling reactions

We report the loading of highly air stable Ni(0) nanoparticles (average particle size = 11 nm) on the surface of a reduced graphene oxide (RGO) material. The material was characterized using different techniques, including Raman spectroscopy, XRD, TEM, SEM, and HRTEM analysis. The Ni(0)@RGO catalyst showed superb efficiency towards Kumada-Corriu C-C cross-coupling reactions, with 92% yield of 4-methoxybiphenyl at 60 °C. The recycled material can be reused up to the 5^th cycle after regeneration by calcination, without loss of activity.

Copper oxide-graphene oxide nanocomposite: efficient catalyst for hydrogenation of nitroaromatics in water

A low-cost nanocomposite catalyst containing copper oxide (CuO) nanoparticles (NPs) on graphene oxide (GO) was fabricated by a facile hydrothermal self-assembly process. The segregated CuO NPs and GO exhibited negligible catalytic activities for the reduction of nitroaromatics. However, their hybrid composite accomplished facile reduction with high conversions for several substituted nitroaromatics in aqueous NaBH4 solution; synergetic coupling effect of CuO NPs with GO in the nanocomposite catalyst provided excellent catalytic activity. The nanocomposite catalyst could be separated from the reaction mixture and recycled consecutively.

Copper Oxide/Reduced Graphene Oxide Nanocomposite-Catalyzed Synthesis of Flavanones and Flavanones with Triazole Hybrid Molecules in One Pot: A Green and Sustainable Approach

An efficient, green, and sustainable synthesis of new hybrid molecules containing flavanone with triazole by merging the Michael addition and Click reaction using a copper oxide/reduced graphene oxide nanocomposite in one pot is reported. The catalyst can easily be recycled and reused in seven consecutive runs without compromising the product yields. Other notable advantages include using water as a reaction medium and obtaining good to excellent yields, low catalyst loading, high atom efficiency, high substrate variation, and good results in the gram scale reaction.

High-performance Cu nanoparticles/three-dimensional graphene/Ni foam hybrid for catalytic and sensing applications

A novel hybrid of Cu nanoparticles/three-dimensional graphene/Ni foam (Cu NPs/3DGr/NiF) was prepared by chemical vapor deposition, followed by a galvanic displacement reaction in Ni- and Cu-ion-containing salt solution through a one-step reaction. The as-prepared Cu NPs/3DGr/NiF hybrid is uniform, stable, recyclable and exhibits an extraordinarily high catalytic efficiency for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with a reduction rate constant K = 0.056 15 s^-1, required time ∼30 s and excellent sensing properties for the non-enzymatic amperometric hydrogen peroxide (H₂O₂) with a linear range ∼50 μM-9.65 mM, response time ∼3 s, detection limit ∼1 μM. The results indicate that the as-prepared Cu NPs/3DGr/NiF hybrid can be used to replace expensive noble metals in catalysis and sensing applications.

Optimum Preferential Oxidation Performance of CeO2-CuO x-RGO Composites through Interfacial Regulation

Interfacial regulation offers a promising route to rationally and effectively design advanced materials for CO preferential oxidation. Herein, we initiated an interfacial regulation of CeO₂-CuO _x-RGO composites by adjusting the addition sequence of the components during the support formation. The presence of RGO along with the sequence tuning of the components is confirmed to survey the changes of the oxidation state of copper species, the content and distribution of the Cu⁺ site, and the synergistic interactions between Cu-Ce mixed oxides and reduced graphene oxide (RGO) over the catalysts. These catalysts were systematically characterized by inductively coupled plasma, X-ray diffraction, transmission electron microscopy/high-resolution transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectra, thermal gravimetric analysis, Raman spectra, and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements. The results show that RGO is favorable for the generation of Cu⁺ and the dispersion of copper-cerium species in the as-prepared catalysts. Furthermore, by multi-interfacial regulation of the CeO₂-CuO _x-RGO composites, the catalyst CeO₂/CuO _x-RGO exhibits a strikingly high catalytic oxidation activity at a low temperature coupled with a broader operation temperature window (i.e., CO conversion >99.0%, 140-220 °C) in the CO-selective oxidation reaction, which has been attributed to the high content of the active species Cu⁺ enriched on the surface, the highly dispersed copper oxide clusters subjected to a strong interaction with ceria, and the synergistic interactions between Cu-Ce mixed oxides and RGO.

The influence of copper addition on the electrical conductivity and charge transfer resistance of reduced graphene oxide (rGO)

The possible explanations on how the existence of copper, CuO, or Cu₂O influences the electrical conductivity and electrochemical properties of rGO.

Photo-reduced Cu/CuO nanoclusters on TiO2 nanotube arrays as highly efficient and reusable catalyst

Non-noble metal nanoparticles are becoming more and more important in catalysis recently. Cu/CuO nanoclusters on highly ordered TiO₂ nanotube arrays are successfully developed by a surfactant-free photoreduction method. This non-noble metal Cu/CuO-TiO₂ catalyst exhibits excellent catalytic activity and stability for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with the presence of sodium borohydride (NaBH₄). The rate constant of this low-cost Cu/CuO based catalyst is even higher than that of the noble metal nanoparticles decorated on the same TiO₂ substrate. The conversion efficiency remains almost unchanged after 7 cycles of recycling. The recycle process of this Cu/CuO-TiO₂ catalyst supported by Ti foil is very simple and convenient compared with that of the common powder catalysts. This catalyst also exhibited great catalytic activity to other organic dyes, such as methylene blue (MB), rhodamine B (RhB) and methyl orange (MO). This highly efficient, low-cost and easily reusable Cu/CuO-TiO₂ catalyst is expected to be of great potential in catalysis in the future.

Graphene oxide based planar heterojunction perovskite solar cell under ambient condition

Herein, we developed a highly stable planar heterojunction perovskite solar cell (PSC) with a novel architecture (ITO/GO/PEDOT:PSS/MAPbI₃/PCBM/carbon tape).

Palladium-modified functionalized cyclodextrin as an efficient and recyclable catalyst for reduction of nitroarenes

A kind of palladium-modified functionalized cyclodextrin catalytic system was synthesized and characterized. It showed high activity in the reduction of nitroarenes with the absence of sodium borohydride in water at room temperature.

Direct access to stabilized CuI using cuttlebone as a natural-reducing support for efficient CuAAC click reactions in water

Cuttlebone@CuCl₂ as a highly active, versatile, and green heterogeneous catalyst was investigated for the efficient preparation of 1,4-disubstituted 1,2,3-triazoles through the one-pot Huisgen 1,3-dipolar cycloaddition reaction in water.