3D-Cobalt-Dicyanamide-Derived 2D-Layered-Co(OH)2-Based Catalyst for Light-Driven Hydrogen Evolution

Derivation of 3D coordination polymers to produce active catalysts has been a feasible strategy to achieve a precise coordination sphere for the catalytic site. This study demonstrates the partial conversion of a 3D cobalt dicyanamide coordination polymer, Co-dca, to a 2D layered hydroxide-oxyhydroxide structure under photocatalytic conditions. The catalyst exhibits an activity as high as 28.3 mmol h-1 g-1 in the presence of a [Ru(bpy)3]2+/triethylamine (TEA) couple to maintain it for at least 12 h. Photocatalytic and characterization studies reveal that the dicyanamide ligand within the coordination polymer is crucial for governing modification and achieving a superior H2 evolution rate. Moreover, we observed the critical role of TEA as the hydrolyzing agent for the transformation process. This study displays that the metal dicyanamides can be utilized as templates for preparing active and robust catalysts.

Production of γ-valerolactone over mesoporous CuO catalysts using formic acid as the hydrogen source

In the present study, the conversion of levulinic acid (LA), butyl levulinate (BL), and ethyl levulinate (EL) to valuable biomass-derived compound γ-valerolactone (GVL) is studied.

Selective Hydroperoxygenation of Olefins Realized by a Coinage Multimetallic 1-Nanometer Catalyst

The science of particles on a sub-nanometer (ca. 1 nm) scale has attracted worldwide attention. However, it has remained unexplored because of the technical difficulty in the precise synthesis of sub-nanoparticles (SNPs). We recently developed the "atom-hybridization method (AHM)" for the precise synthesis of SNPs by using a suitably designed macromolecule as a template. We have now investigated the chemical reactivity of alloy SNPs obtained by the AHM. Focusing on the coinage metal elements, we systematically evaluated the oxidation reaction of an olefin catalyzed by these SNPs. The SNPs showed high catalytic performance even under milder conditions than those used with conventional catalysts. Additionally, the hybridization of multiple elements enhanced the turnover frequency and the selectivity for the formation of the hydroperoxide derivative. We discuss the unique quantum-sized catalysts providing generally unstable hydroperoxides from the viewpoint of the miniaturization and hybridization of materials.

Selective cyclohexene oxidation with O2, H2O2 and tert-butyl hydroperoxide over spray-flame synthesized LaCo1−xFexO3 nanoparticles

A series of spray-flame made LaCo_1−xFe_xO₃ nanoparticles showed promising activity for liquid-phase cyclohexene oxidation. Various oxidizing agents, i.e., O₂, H₂O₂ and tert-butyl hydroperoxide, led to different product selectivities.

Characterization of Hydrothermal Deposition of Copper Oxide Nanoleaves on Never-Dried Bacterial Cellulose

Bacterial cellulose (BC) has attracted a great deal of interest due to its green synthesis and biocompatibility. The nanoscale dimension of BC nanofibers generates an enormous surface area that enhances interactions with water and soluble components within aqueous solution. Recent work has demonstrated that BC is a versatile platform for the formation of metal/metal oxide nanocomposites. Copper oxide (CuO) is a useful material to compare nanomaterial deposition on BC with other cellulosic materials because of copper’s colorimetric reaction as it forms copper hydroxide (Cu(OH)₂) and transitions to CuO. In this research, we found that never-dried BC readily deposits CuO into its matrix in a way that does not occur on cotton, dried BC, or regenerated cellulose fibers. We conclude that hydroxyl group availability does not adequately explain our results and that intrafibrillar pores in never-dried BC nanofibers play a critical role in CuO deposition.

Magnetically separable and reusable rGO/Fe3O4 nanocomposites for the selective liquid phase oxidation of cyclohexene to 1,2-cyclohexane diol

A series of magnetically separable rGO/Fe₃O₄ nanocomposites with various amounts of graphene oxide were successfully prepared by a simple ultrasonication assisted precipitation combined with a solvothermal method and their catalytic activity was evaluated for the selective liquid phase oxidation of cyclohexene using hydrogen peroxide as a green oxidant. The prepared materials were characterized using XRD, FTIR, FESEM, TEM, HRTEM, BET/BJH, XPS and VSM analysis. The presence of well crystallized Fe₃O₄ as the active iron species was seen in the crystal studies of the nanocomposites. The electron microscopy analysis indicated the fine surface dispersion of spherical Fe₃O₄ nanoparticles on the thin surface layers of partially-reduced graphene oxide (rGO) nanosheets. The decoration of Fe₃O₄ nanospheres on thin rGO layers was clearly observable in all of the nanocomposites. The XPS analysis was performed to evaluate the chemical states of the elements present in the samples. The surface area of the nanocomposites was increased significantly by increasing the amount of GO and the pore structures were effectively tuned by the amount of rGO in the nanocomposites. The magnetic saturation values of the nanocomposites were found to be sufficient for their efficient magnetic separation. The catalytic activity results show that the cyclohexene conversion reached 75.3% with a highest 1,2-cyclohexane diol selectivity of 81% over 5% rGO incorporated nanocomposite using H₂O₂ as the oxidant and acetonitrile as the solvent at 70 °C for 6 h. The reaction conditions were further optimized by changing the variables and a possible reaction mechanism was proposed. The enhanced catalytic activity of the nanocomposites for cyclohexene oxidation could be attributed to the fast accomplishment of the Fe²⁺/Fe³⁺ redox cycle in the composites due the sacrificial role of rGO and its synergistic effect with Fe₃O₄, originating from the conjugated network of π-electrons in its surface structure. The rapid and easy separation of the magnetic nanocomposites from the reaction mixture using an external magnet makes the present catalysts highly efficient for the reaction. Moreover, the catalyst retained its activity for five repeated runs without any drastic drop in the reactant conversion and product selectivity.

A series of magnetically-separable and reusable rGO/Fe₃O₄ nanocomposites were successfully synthesized for the selective liquid-phase oxidation of cyclohexene to 1,2-cyclohexane-diol.

Synthesis of Heart/Dumbbell-Like CuO Functional Nanostructures for the Development of Uric Acid Biosensor

It is always demanded to prepare a nanostructured material with prominent functional properties for the development of a new generation of devices. This study is focused on the synthesis of heart/dumbbell-like CuO nanostructures using a low-temperature aqueous chemical growth method with vitamin B₁₂ as a soft template and growth directing agent. CuO nanostructures are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. CuO nanostructures are heart/dumbbell like in shape, exhibit high crystalline quality as demonstrated by XRD, and have no impurity as confirmed by XPS. Apparently, CuO material seems to be porous in structure, which can easily carry large amount of enzyme molecules, thus enhanced performance is shown for the determination of uric acid. The working linear range of the biosensor is 0.001 mM to 10 mM with a detection limit of 0.0005 mM and a sensitivity of 61.88 mV/decade. The presented uric acid biosensor is highly stable, repeatable, and reproducible. The analytical practicality of the proposed uric acid biosensor is also monitored. The fabrication methodology is inexpensive, simple, and scalable, which ensures the capitalization of the developed uric acid biosensor for commercialization. Also, CuO material can be used for various applications such as solar cells, lithium ion batteries, and supercapacitors.

Tailoring the reducibility and catalytic activity of CuO nanoparticles for low temperature CO oxidation

Copper oxide (CuO) nanoparticles have received considerable interest as active and inexpensive catalysts for various gas-solid reactions. The CuO reducibility and surface reactivity are of crucial importance for the high catalytic activity. Herein, we demonstrate that the reducibility and stability of CuO nanoparticles can be controlled and tailored for the high catalytic activity of CO oxidation. The synthesized CuO nanoparticles possessed enhanced reducibility in CO atmosphere at lower reduction temperature of 126 °C compared to 284 °C for that of reference CuO particles. Moreover, the CuO catalysts with tailored reducibility demonstrated a reaction rate of 35 μmol s-1 g-1 and an apparent activation energy of 75 kJ mol-1. Furthermore, the tailored catalysts exhibited excellent long-term stability for CO oxidation for up to 48 h on stream. These readily-reducible CuO nanoparticles could serve as efficient, inexpensive and durable catalysts for CO oxidation at low temperatures.

Competitive Inhibition of the Enzyme-Mimic Activity of Gd-Based Nanorods toward Highly Specific Colorimetric Sensing of l-Cysteine

Gd-based nanomaterials offer interesting magnetic properties and have been heavily investigated for magnetic resonance imaging. The applicability of these materials beyond biomedical imaging remains limited. The current study explores the applicability of these rare-earth nanomaterials as nanozyme-mediated catalysts for colorimetric sensing of l-cysteine, an amino acid of high biomedical relevance. We show a facile solution-based strategy to synthesize two Gd-based nanomaterials viz. Gd(OH)₃ and Gd₂O₃ nanorods. We further establish the catalytic peroxidase-mimic nanozyme activity of these Gd(OH)₃ and Gd₂O₃ nanorods. This catalytic activity was suppressed specifically in the presence of l-cysteine that allowed us to develop a colorimetric sensor to detect this biologically relevant molecule among various other contaminants. This suppression, which could either be caused due to catalyst poisoning or enzyme inhibition, prompted extensive investigation of the kinetics of this catalytic inhibition in the presence of cysteine. This revealed a competitive inhibition process, a mechanism akin to those observed in natural enzymes, bringing nanozymes a step closer to the biological systems.