Heterogeneous Co3O4 catalyst for selective oxidation of aqueous veratryl alcohol using molecular oxygen

Restricted Open-Shell Hartree-Fock Method for a General Configuration State Function Featuring Arbitrarily Complex Spin-Couplings

In this work, we present a general spin restricted open-shell Hartree-Fock (ROHF) implementation that is able to generate self-consistent field (SCF) wave functions for an arbitrary configuration state function (CSF). These CSFs can contain an arbitrary number of unpaired electrons in arbitrary spin-couplings. The resulting method is named CSF-ROHF. We demonstrate that starting from the ROHF energy expression, for example, the one given by Edwards and Zerner, it is possible to obtain the values of the ROHF vector-coupling coefficients by setting up an open-shell for each group of consecutive parallel-coupled spins dictated by the unique spin-coupling pattern of any given CSF. To achieve this important and nontrivial goal, we employ the machinery of the iterative configuration expansion configuration interaction (ICE-CI) method, which is able to tackle general CI problems on the basis of spin-adapted CSFs. This development allows for the efficient generation of SCF spin-eigenfunctions for systems with complex spin-coupling patterns, such as polymetallic chains and metal clusters, while maintaining SCF scaling with system size (quadratic or less, depending on the specific algorithm and approximations chosen).

Selective Depolymerization of Lignin Towards Isolated Phenolic Acids Under Mild Conditions

The selective transformation of lignin to value-added biochemicals (e. g., phenolic acids) in high yields is incredibly challenging due to its structural complexity and many possible reaction pathways. Phenolic acids (PA) are key building blocks for various aromatic polymers, but the isolation of PAs from lignin is below 5 wt.% and requires harsh reaction conditions. Herein, we demonstrate an effective route to selectively convert lignin extracted from sweet sorghum and poplar into isolated PA in a high yield (up to 20 wt.% of lignin) using a low-cost graphene oxide-urea hydrogen peroxide (GO-UHP) catalyst under mild conditions (<120 °C). The lignin conversion yield is up to 95 %, and the remaining low molecular weight organic oils are ready for aviation fuel production to complete lignin utilization. Mechanistic studies demonstrate that pre-acetylation allows the selective depolymerization of lignin to aromatic aldehydes with a decent yield by GO through the Cα activation of β-O-4 cleavage. A urea-hydrogen peroxide (UHP) oxidative process is followed to transform aldehydes in the depolymerized product to PAs by avoiding the undesired Dakin side reaction due to the electron-withdrawing effect of the acetyl group. This study opens a new way to selectively cleave lignin side chains to isolated biochemicals under mild conditions.

Determining surface-specific Hubbard-U corrections and identifying key adsorbates on nickel and cobalt oxide catalyst surfaces

NiO is a popular transition metal oxide (TMO) with high thermal and chemical stability and Co₃O₄ is a relatively more reducible TMO due to weaker metal-oxygen bonds. Both are often used as catalysts in a variety of chemical transformations. Density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) are used to investigate catalysis on TMO surfaces, yet both techniques have their own limitations. The accuracy of DFT highly depends on the choice of Hubbard U correction. The bulk-property optimized U value of 5.3 eV for NiO and different U values for Co₃O₄, without any consensus, are often used in the literature to simulate surface catalysis. However, U values optimized using bulk properties often fail to reproduce surface-adsorbate interactions on TMOs. Similarly, there exists arbitrariness in assigning observed XPS shifts to different surface species on these metal oxides. Hence, a synergistic application of XPS and DFT+U is implemented to determine the surface specific U values for NiO and Co₃O₄, and to identify adsorbed surface moieties corresponding to experimentally observed XPS shifts. For the NiO (100) surface, the U value of ∼2 eV is able to reproduce the experimentally observed XPS O1s core level binding energy shifts correctly, instead of the bulk property optimized and commonly used U value of 5.3 eV. Using this surface specific U value of 2 eV, the experimentally observed XPS shifts are assigned. Similarly, for Co₃O₄ (100) surface, ∼3 eV of U value could successfully predict the experimentally observed XPS shifts and corresponding adsorbates. The surface adsorbates and configurations suggested in this work will help analyze experimental XPS data and the surface specific U values will ensure accurate predictions of adsorption and reaction energetics on these catalysts.

Facile Gram-Scale Synthesis of Co3O4 Nanocrystal from Spent Lithium Ion Batteries and Its Electrocatalytic Application toward Oxygen Evolution Reaction

In this study, we demonstrate a new approach to easily prepare spinel Co₃O₄ nanoparticles (s-Co₃O₄ NPs) in the gram-scale from the cathode of spent lithium ion batteries (SLIBs) by the alkali leaching of hexaamminecobalt(III) complex ions. As-obtained intermediate and final products were characterized with powder X-ray diffraction (PXRD), Ultraviolet-Visible (UV-Vis), Fourier transform infrared (FTIR), and Transmission electron microscopy (TEM). Additionally, the synthesized s-Co₃O₄ NPs showed better electrocatalytic properties toward the oxygen evolution reaction (OER) in comparison to previously reported Co₃O₄ NPs and nanowires, which could be due to the more exposed electrocatalytic active sites on the s-Co₃O₄ NPs. Moreover, the electrocatalytic activity of the s-Co₃O₄ NPs was comparable to the previously reported RuO₂ catalysts. By taking advantage of the proposed recycling route, we would expect that various valuable transition metal oxide NPs could be prepared from SLIBs.

Molten Salt-Assisted Synthesis of Co/N-Doped Carbon Hybrids for Aqueous-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

A resource-efficient and facile method of synthesizing 2,5-furandicarboxylic acid (FDCA) from biomass-derived platform chemical 5-hydroxymethylfurfural (HMF) was explored using cobalt and nitrogen-doped carbon catalysts (Co/N-C). A molten salts-assisted method proved to be effective in improving the surface area of the catalysts as well as uniformity and dispersibility of the Co species. Detailed investigation of different combinations of precursors revealed that the formation of Co-N_x species was imperative for high FDCA selectivity, and the nitrogen-doped carbon matrix enhanced the catalytic activity by providing good electron mobility. A significant observation was made regarding the change in reaction mechanism with the heating rate of Co/N-C. High HMF conversion of 99 % with 68 % FDCA yield was achieved at 120 °C in water at 24 h. This study shows an eco-friendly and cost-effective method of FDCA production with high yield that overcomes the use of precious metal-based catalysts, organic solvents, and severe reaction conditions.

In situ thermal decomposition route: Preparation and characterization of nano nickel, cobalt, and copper oxides using an aromatic amine complexes as a low-cost simple precursor

The main interest now is the development of metallic or inorganic-organic compounds to prepare nanoparticle materials. The use of new compounds could be beneficial and open a new method for preparing nanomaterials to control the size, shape, and size of the nanocrystals. In this article, the thermal decomposition of [M2(o-tol)2(H2O)8] Cl4 (where o-tol is ortho-tolidine compound, M = Ni2+, Co2+, Cu2+) new precursor complex was discussed in solid-state conditions. The thermal decomposition route showed that the synthesized three complexes were easily decomposed into NiO, Co3O4 and CuO nanoparticles. This decomposition was performed at low temperatures (~600°C) in atmospheric air without using any expensive and toxic solvent or complicated equipment. The obtained product was identified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). FT-IR, XRD and EDX analyses revealed that the NiO nanoparticles exhibit a face-centered-cubic lattice structure with a crystallite size of 9–12 nm. The formation of a highly pure spinel-type Co3O4 phase with cubic structure showed that the Co3O4 nanoparticles have a sphere-like morphology with an average size of 8–10 nm. The XRD patterns of the CuO confirmed that the monoclinic phase with the average diameter of the spherical nanoparticles was approximately 9–15 nm.

α-Oxidation of banana lignin with atmospheric oxygen catalyzed by Co3O4

Banana lignin was subjected to oxidation, converting alpha hydroxyl to carbonyl. In this process, atmospheric oxygen acted as an oxidizing agent, CO₃O₄ as a catalyst under mild conditions of temperature and pressure.

Glycerol Acetylation with Propionic Acid Using Iron and Cobalt Oxides in Al-MCM-41 Catalysts

In this work, Al-MCM-41 molecular sieves were synthesized, containing iron and/or cobalt oxides, impregnated by incipient wetness method, characterized and applied as catalysts in the acetylation reaction of glycerol with propionic acid to produce green glyceryl propionate molecules of high commercial value. According to this, X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Fourier Transform Infra Red (FT-IR), adsorption/desorption N2 isotherms, textural analysis, and Scanning Electron Microscope (SEM) analysis were recorded to evaluate the main characteristics of materials. The presence of Lewis and Brønsted acidic sites and catalysts surface area were observed as important key points to functionalize acetylation reaction. Thus, time reaction, temperature, and glycerol / propionic acid ratio varied to improve the most suitable reaction conditions and behaviors. As a result, glycerol conversion was above 96%, followed by 68% of selectivity to glyceryl monopropionate as well as the formation of glyceryl di- and tri- propionate and a small amount of ethylene glycol dipropionate as an undesired product. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synergistic Effect in Au-Cu Bimetallic Catalysts for the Valorization of Lignin-Derived Compounds

The selective oxidation of veratryl alcohol as lignin-derived compound was studied under mild conditions, using Au-Cu catalysts synthesized from pre-formed nanoparticles with different Au:Cu molar ratios. Bimetallic catalysts show higher activity compared to monometallic counterparts, highlighting a clear synergistic effect. By comparing the physico-chemical surface properties of catalysts supported on carbon and Al2O3, we were able to establish a strong support effect, with alumina-based catalysts being more active than carbon-supported ones. Moreover, TEM and X-ray photoelectron spectroscopy (XPS) analyses showed a different composition of nanoparticles (NPs) and metal exposure, and we established that Au is the active phase of the reaction. The co-presence of Au and Cu species, and their different interaction with the support, enabled obtaining more than 70% conversion of veratryl alcohol to veratryl aldehyde as a unique product. Moreover, the Au1Cu1 supported on alumina catalyst was recovered by filtration and reused without significant loss of activity and selectivity up to four times.

Heterogeneous Catalyzed Thermochemical Conversion of Lignin Model Compounds: An Overview

Thermochemical lignin conversion processes can be described as complex reaction networks involving not only de-polymerization and re-polymerization reactions, but also chemical transformations of the depolymerized mono-, di-, and oligomeric compounds. They typically result in a product mixture consisting of a gaseous, liquid (i.e., mono-, di-, and oligomeric products), and solid phase. Consequently, researchers have developed a common strategy to simplify this issue by replacing lignin with simpler, but still representative, lignin model compounds. This strategy is typically applied to the elucidation of reaction mechanisms and the exploration of novel lignin conversion approaches. In this review, we present a general overview of the latest advances in the principal thermochemical processes applied for the conversion of lignin model compounds using heterogeneous catalysts. This review focuses on the most representative lignin conversion methods, i.e., reductive, oxidative, pyrolytic, and hydrolytic processes. An additional subchapter on the reforming of pyrolysis oil model compounds has also been included. Special attention will be given to those research papers using "green" reactants (i.e., H₂ or renewable hydrogen donor molecules in reductive processes or air/O₂ in oxidative processes) and solvents, although less environmentally friendly chemicals will be also considered. Moreover, the scope of the review is limited to those most representative lignin model compounds and to those reaction products that are typically targeted in lignin valorization.

Recent Advances in Nanozyme Research

As a new generation of artificial enzymes, nanozymes have the advantages of high catalytic activity, good stability, low cost, and other unique properties of nanomaterials. Due to their wide range of potential applications, they have become an emerging field bridging nanotechnology and biology, attracting researchers in various fields to design and synthesize highly catalytically active nanozymes. However, the thorough understanding of experimental phenomena and the mechanisms beneath practical applications of nanozymes limits their rapid development. Herein, the progress of experimental and computational research of nanozymes on two issues over the past decade is briefly reviewed: (1) experimental development of new nanozymes mimicking different types of enzymes. This covers their structures and applications ranging from biosensing and bioimaging to therapeutics and environmental protection. (2) The catalytic mechanism proposed by experimental and theoretical study. The challenges and future directions of computational research in this field are also discussed.

Microwave-Assisted Catalytic Solvolysis of Lignin to Phenols: Kinetics and Product Characterization

Lignin, a major component of lignocellulosic biomass, is a valuable source of phenolic and aromatic compounds. It is, therefore, vital to develop strategies to selectively deconstruct lignin to valuable chemicals. This study focuses on the kinetics of depolymerization of lignin and the production of phenols via a microwave-assisted catalytic process at mild conditions of 80 °C in dimethyl sulfoxide/water medium. Four different catalysts used in this study, viz., Fe2O3, LaFeO3, ZrO2, and zeolite-Y hydrogen (ZYH), were characterized for structure, specific surface area, and surface morphology. The molecular weight reduction of lignin and the evolution of phenolic monomers and oligomers were monitored using various techniques, and the rate constants of lignin degradation in the presence of different catalysts were determined using a continuous distribution kinetics model, assuming scission of the lignin macromolecule at any random position. The rate constants (min-1) followed the trend: ZYH (26 × 10-4) ≈ LaFeO3 (25 × 10-4) > ZrO2 (22 × 10-4) > Fe2O3 ≈ no catalyst (16 × 10-4). Vanillic acid (15 mg g-1) and methyl phenol (17 mg g-1) were the major phenolics obtained with LaFeO3, whereas coniferaldehyde (13 mg g-1) was the major phenolic compound with Fe2O3. Vanillin was produced at ca. 11 mg g-1 with both Fe2O3 and ZYH. LaFeO3 is shown to be a promising catalyst for both molecular weight reduction of lignin and the production of monomeric phenols, whereas the use of Fe2O3 results in the formation of only phenols, possibly via specific end-chain depolymerization. The selectivities of the monomeric phenols were higher with these two catalysts, whereas with ZYH and ZrO2, the selectivities of the oligomers were better. The reusability of the catalysts and the effect of catalyst loading on kinetics of lignin depolymerization were also evaluated.

Mixed-Oxide Catalysts with Spinel Structure for the Valorization of Biomass: The Chemical-Loop Reforming of Bioethanol

This short review reports on spinel-type mixed oxides as catalysts for the transformation of biomass-derived building blocks into chemicals and fuel additives. After an overview of the various methods reported in the literature for the synthesis of mixed oxides with spinel structure, the use of this class of materials for the chemical-loop reforming of bioalcohols is reviewed in detail. This reaction is aimed at the production of H2 with intrinsic separation of C-containing products, but also is a very versatile tool for investigating the solid-state chemistry of spinels.

Role of cobalt cations in short range antiferromagnetic Co3O4 nanoparticles: a thermal treatment approach to affecting phonon and magnetic properties

We report the phonon and magnetic properties of various well-stabilized Co₃O₄ nanoparticles. The net valence in cobalt (II)/(III) cation can be obtained by subtracting the Co²⁺ ions in tetrahedral interstices and Co³⁺ ions in the octahedral interstices, respectively, which will possess spatial inhomogeneity of its magnetic moment via Co²⁺ in tetrahedra and Co³⁺ in octahedral configurations in the normal spinel structure. Furthermore, the distribution of Co²⁺/Co³⁺ governed by various external (magnetic field and temperature) and internal (particle size and slightly distorted CoO₆ octahedra) sources, have led to phenomena such as a large redshift of phonon-phonon interaction and short-range magnetic correlation in the inverse spinel structure. The outcome of our study is important in terms of the future development of magnetic semiconductor spintronic devices of Co₃O₄.

Three-dimensional composite of Co3O4 nanoparticles and nitrogen-doped reduced graphene oxide for lignin model compound oxidation

3D composite of Co₃O₄ nanoparticles and N-doped reduced graphene oxide can effectively catalyze the oxidation of lignin model compounds.

Catalytic Oxidation of Lignin in Solvent Systems for Production of Renewable Chemicals: A Review

Lignin as the most abundant source of aromatic chemicals in nature has attracted a great deal of attention in both academia and industry. Solvolysis is one of the promising methods to convert lignin to a number of petroleum-based aromatic chemicals. The process involving the depolymerization of the lignin macromolecule and repolymerization of fragments is complicated influenced by heating methods, reaction conditions, presence of a catalyst and solvent systems. Recently, numerous investigations attempted unveiling the inherent mechanism of this process in order to promote the production of valuable aromatics. Oxidative solvolysis of lignin can produce a number of the functionalized monomeric or oligomeric chemicals. A number of research groups should be greatly appreciated with regard to their contributions on the following two concerns: (1) the cracking mechanism of inter-unit linkages during the oxidative solvolysis of lignin; and (2) the development of novel catalysts for oxidative solvolysis of lignin and their performance. Investigations on lignin oxidative solvolysis are extensively overviewed in this work, concerning the above issues and the way-forward for lignin refinery.

Co₃O₄@CoS Core-Shell Nanosheets on Carbon Cloth for High Performance Supercapacitor Electrodes

In this work, a two-step electrodeposition strategy is developed for the synthesis of core-shell Co₃O₄@CoS nanosheet arrays on carbon cloth (CC) for supercapacitor applications. Porous Co₃O₄ nanosheet arrays are first directly grown on CC by electrodeposition, followed by the coating of a thin layer of CoS on the surface of Co₃O₄ nanosheets via the secondary electrodeposition. The morphology control of the ternary composites can be easily achieved by altering the number of cyclic voltammetry (CV) cycles of CoS deposition. Electrochemical performance of the composite electrodes was evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The results demonstrate that the Co₃O₄@CoS/CC with 4 CV cycles of CoS deposition possesses the largest specific capacitance 887.5 F·g⁻¹ at a scan rate of 10 mV·s⁻¹ (764.2 F·g⁻¹ at a current density of 1.0 A·g⁻¹), and excellent cycling stability (78.1% capacitance retention) at high current density of 5.0 A·g⁻¹ after 5000 cycles. The porous nanostructures on CC not only provide large accessible surface area for fast ions diffusion, electron transport and efficient utilization of active CoS and Co₃O₄, but also reduce the internal resistance of electrodes, which leads to superior electrochemical performance of Co₃O₄@CoS/CC composite at 4 cycles of CoS deposition.

Peroxidase-like activity of the Co3O4 nanoparticles used for biodetection and evaluation of antioxidant behavior

Nanostructured enzyme mimics are of great interest as promising alternatives to artificial enzymes for biomedical and catalytic applications. Studying the chemical interactions between antioxidants and nano-enzymes may result in a better understanding of the antioxidant capability of antioxidants and may help improve the function of artificial enzymes to better mimic natural enzymes. In this study, using Co3O4 nanoparticles (NPs) as peroxidase mimics to catalyze the oxidation of chromophoric substrates by H2O2, we developed a platform that acts as a biosensor for hydrogen peroxide and glucose and that can study the inhibitory effects of natural antioxidants on peroxidase mimics. This method can be applied specifically to glucose detection in real samples. Three natural antioxidants, gallic acid (GA), tannic acid (TA), and ascorbic acid (AA), were compared for their antioxidant capabilities. We found that these three antioxidants efficiently inhibit peroxidase-like activity with concentration dependence. The antioxidants showed different efficiencies, in the following order: tannic acid > gallic acid > ascorbic acid. They also showed distinct modes of inhibition based on different interaction mechanisms. This study serves as a proof-of-concept that nano-enzyme mimics can be used to evaluate antioxidant capabilities and to screen enzyme inhibitors.

Effect of zinc : cobalt composition in ZnCo2O4 spinels for highly selective liquefied petroleum gas sensing at low and high temperatures

Nano ZnCo₂O₄ spinels were synthesized at varying zinc and cobalt ratios such as 1 : 1, 1 : 1.5, 1 : 2, 1 : 2.5 and 1 : 3.

Co3O4/graphene nanocomposite: pre-graphenization synthesis and photocatalytic investigation of various magnetic nanostructures

For the first time, a novel technique for preparing cobalt(ii) acetyl acetonate [Co(acac)₂] nanostructures has been developed by using the sublimation process.

Magnetic Co3O4/reduced graphene oxide nanocomposite as a superior heterogeneous catalyst for one-pot oxidative esterification of aldehydes to methyl esters

Magnetic Co₃O₄/reduced graphene oxide nanocomposite as a superior heterogeneous catalyst for one-pot oxidative esterification of aldehydes to methyl esters.

Design synthesis of polypyrrole-Co3O4 hybrid material for the direct electrochemistry of Hemoglobin and Glucose Oxidase

We designed and synthesized a novel organic-inorganic hybrid material polypyrrole-Co3O4 (Ppy-Co3O4), then mixed it with ionic liquid (IL) to form stable composite films for the immobilization of Hemoglobin (Hb) and Glucose Oxidase (GOD). The combination of Ppy and Co3O4 as well as IL created a platform with exceptional characteristics, and the content of Ppy had an effect on the direct electron transfer (DET) of Hb/GOD. Notably, when weight percentage of pyrrole monomer was 20%, the heterogenous electron transfer rate constant (ks) for Hb and GOD was estimated to be 1.71s(-1) and 1.67s(-1), respectively. In the meantime, electrochemical and spectroscopic measurements showed that Hb/GOD remained their bioactivity, and achieved fast electron transfer on the Ppy-Co3O4/IL composite film modified electrode. Furthermore, the Ppy-Co3O4/IL/Hb composite film modified electrode was used as a biosensor, and exhibited a long linear range and lower detection limit to H2O2. The apparent Michaelis-Menten constant (Km) was found to be 0.53mM. The sensing design based on the Ppy-Co3O4 hybrid material was demonstrated to be effective and promising in developing protein and enzyme biosensors.

Co₃O₄ nanoparticles with multi-enzyme activities and their application in immunohistochemical assay

Co3O4 nanoparticles (Co3O4 NPs), synthesized by the coprecipitation method, showed intrinsic catalase-like, peroxidase-like, and SOD-like activity. The catalytic activity of Co3O4 NPs was much higher than analogous Fe3O4 NPs. Co3O4's mechanisms of catalytic activity were analyzed in detail using the electron spin resonance (ESR) method, which confirmed that Co3O4 NPs don't follow the classical Fenton reactions with hydrogen peroxide the way Fe3O4 NPs do. The high redox potential of Co(3+)/Co(2+) was supposed to be the leading cause of the differences in both activity and mechanism with Fe3O4. Based on the high, peroxidase-like activity, a new immunohistochemical assay was designed in which the avastin antibody was conjugated onto the surface of Co3O4 NPs. The conjugates obtained were used to detect vascular endothelial growth factor (VEGF) that was overexpressed in tumor tissue. When the experimental and control groups were stained, there were clear distinctions between them. This study showed that there are many opportunities to improve the enzyme-like activities of nanomaterials and also to improve their potential applications for biocatalysis and bioassays, especially in relatively harsh conditions.

A green process for efficient lignin (biomass) degradation and hydrogen production via water splitting using nanostructured C, N, S-doped ZnO under solar light

Simultaneous photocatalytic hydrogen production (water splitting) and waste lignin (biomass) degradation under visible light has been demonstrated using C, N, S-doped ZnO/ZnS.

Solvothermal synthesis of mesoporous manganese oxide with enhanced catalytic activity for veratryl alcohol oxidation

Solvothermally prepared Mn₃O₄ showed excellent performance for veratryl alcohol oxidation to veratraldehyde due to formation of monoclinic and hausmannite phases.