Surfactant-Assisted Hydrothermal Synthesis of Cobalt Oxide/Nitrogen-Doped Graphene Framework for Enhanced Anodic Performance in Lithium Ion Batteries

Controllable Synthesis of a Porous PEI-Functionalized Co3O4/rGO Nanocomposite as an Electrochemical Sensor for Simultaneous as Well as Individual Detection of Heavy Metal Ions

The present study focuses on the strategy of employing an electrochemical sensor with a porous polyethylenimine (PEI)-functionalized Co₃O₄/reduced graphene oxide (rGO) nanocomposite (NCP) to detect heavy metal ions (HMIs: Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺). The porous PEI-functionalized Co₃O₄/rGO NCP (rGO·Co₃O₄·PEI) was prepared via a hydrothermal method. The synthesized NCP was based on a conducting polymer PEI, rGO, nanoribbons of Co₃O₄, and highly dispersed Co₃O₄ nanoparticles (NPs), which have shown excellent performance in the detection of HMIs. The as-prepared PEI-functionalized rGO·Co₃O₄·PEI NCP-modified electrode was used for the sensing/detection of HMIs by means of both square wave anodic stripping voltammetry (SWV) and differential normal pulse voltammetry (DNPV) methods for the first time. Both methods were employed for the simultaneous detection of HMIs, whereas SWV was employed for the individual analysis as well. The limits of detection (LOD; 3σ method) for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺ determined using the rGO·Co₃O₄·PEI NCP-modified electrode were 0.285, 1.132, 1.194, and 1.293 nM for SWV, respectively. Similarly, LODs of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺ were 1.069, 0.285, 2.398, and 1.115 nM, respectively, by DNPV during simultaneous analysis, whereas they were 0.484, 0.878, 0.462, and 0.477 nM, respectively, by SWV in individual analysis.

Nanocrystalline Cellulose Supported MnO2 Composite Materials for High-Performance Lithium-Ion Batteries

The rate capability and poor cycling stability of lithium-ion batteries (LIBs) are predominantly caused by the large volume expansion upon cycling and poor electrical conductivity of manganese dioxide (MnO₂), which also exhibits the highest theoretical capacity among manganese oxides. In this study, a nanocomposite of nanosized MnO₂ and pyrolyzed nanocrystalline cellulose (CNC) was prepared with high electrical conductivity to enhance the electrochemical performance of LIBs. The nanocomposite electrode showed an initial discharge capacity of 1302 mAh g⁻¹ at 100 mA g⁻¹ and exhibited a high discharge capacity of 305 mAh g⁻¹ after 1000 cycles. Moreover, the MnO₂-CNC nanocomposite delivered a good rate capability of up to 10 A g⁻¹ and accommodated the large volume change upon repeated cycling tests.

Facile Synthesis of Co3O4@CoO@Co Gradient Core@Shell Nanoparticles and Their Applications for Oxygen Evolution and Reduction in Alkaline Electrolytes

We demonstrate a facile fabrication scheme for Co₃O₄@CoO@Co (gradient core@shell) nanoparticles on graphene and explore their electrocatalytic potentials for an oxygen evolution reaction (OER) and an oxygen reduction reaction (ORR) in alkaline electrolytes. The synthetic approach begins with the preparation of Co₃O₄ nanoparticles via a hydrothermal process, which is followed by a controlled hydrogen reduction treatment to render nanoparticles with radial constituents of Co₃O₄/CoO/Co (inside/outside). X-ray diffraction patterns confirm the formation of crystalline Co₃O₄ nanoparticles, and their gradual transformation to cubic CoO and fcc Co on the surface. Images from transmission electron microscope reveal a core@shell microstructure. These Co₃O₄@CoO@Co nanoparticles show impressive activities and durability for OER. For ORR electrocatalysis, the Co₃O₄@CoO@Co nanoparticles are subjected to a galvanic displacement reaction in which the surface Co atoms undergo oxidative dissolution for the reduction of Pt ions from the electrolyte to form Co₃O₄@Pt nanoparticles. With commercial Pt/C as a benchmark, we determine the ORR activities in sequence of Pt/C > Co₃O₄@Pt > Co₃O₄. Measurements from a rotation disk electrode at various rotation speeds indicate a 4-electron transfer path for Co₃O₄@Pt. In addition, the specific activity of Co₃O₄@Pt is more than two times greater than that of Pt/C.

A comparative account of glucose yields and bioethanol production from separate and simultaneous saccharification and fermentation processes at high solids loading with variable PEG concentration

A process strategy to aid in optimal enzymatic hydrolysis through the addition of polyethylene glycol (PEG6000) was tested for separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). Pretreated wheat straw at 30% solids (w/w) loading was enzymatically hydrolyzed with 0, 0.5, 1, 1.5, 2 and 2.5% of PEG6000 through SHF and SSF. During SHF, bioethanol concentration of 107.5 g/L (2.5% PEG6000) was achieved. SSF ethanol concentration were about 113 g/L at 1.5% PEG6000 addition. A technoeconomic feasibility showed a return on investment (ROI) of 8.13% using 0.5% PEG6000 for SHF (96 h) and 12.25% ROI for SSF control (72 h). Life cycle assessment for the various scenarios indicated higher environmental gains for best cases of SSF over SHF. The study shows the SSF approach (0% PEG6000; 72 h) facilitates higher process efficiencies; technoeconomic gains and high environmental sustainability for future scale-up and commercial realization.

Self-supporting Co3O4/Graphene Hybrid Films as Binder-free Anode Materials for Lithium Ion Batteries

A self-supporting Co₃O₄/graphene hybrid film has been constructed via vacuum filtration of Co(OH)₂ nanosheet and graphene, followed by a two-step thermal treatment. Within the hybrid film, Co₃O₄ nanoparticles with size of 40~60 nm uniformly in-situ grew on the surface of graphene, forming a novel porous and interleaved structure with strong interactions between Co₃O₄ nanoparticles and graphene. Such fascinating microstructures can greatly facilitate interfacial electron transportation and accommodate the volume changes upon Li ions insertion and extraction. Consequently, the binder-less hybrid film demonstrated extremely high reversible capacity (1287.7 mAh g⁻¹ at 0.2 A g⁻¹), excellent cycling stability and rate capability (1110 and 800 mAh g⁻¹ at 0.5 and 1.0 A g⁻¹, respectively).

Direct Electrophoretic Deposition of Binder-Free Co3O4/Graphene Sandwich-Like Hybrid Electrode as Remarkable Lithium Ion Battery Anode

Co₃O₄ is emerging as a promising anode candidate for lithium ion batteries (LIBs) with high theoretical capacity (890 mAh g^-1) but suffers from poor electrochemical cycling stability resulting from the inferior intrinsic electronic conductivity and large volume changes during electrochemical cycling. Here, a new electrophoretic deposition Co₃O₄/graphene (EPD Co₃O₄/G) hybrid electrode is developed to improve the electrochemical performance. Through EPD, Co₃O₄ nanocubes can be homogeneously embedded between graphene sheets to form a sandwich-like structure. Owing to the excellent flexibility of graphene and a large number of voids in this sandwich-like structure, the structural integrity and unobstructed conductive network can be maintained during cycling. Moreover, the electrode kinetics has proved to be a fast surface-controlled lithium storage process. As a result, the Co₃O₄/G hybrid electrode exhibits high specific capacity and excellent electrochemical cycling performance. The Co₃O₄/G hybrid electrode was also further studied by in situ electrochemical XRD to understand the relationship of its structure and performance: (1) The observed Li_xCo₃O₄ indicates an intermediate of possible small volume change in the first discharging. (2) The theoretical capacity achievement of the Co₃O₄ in hybrid electrode was evidenced. (3) The correlation between the electrochemical performance and the structural evolution of the Co₃O₄/G hybrid electrode was discussed detailedly.

Nitrogen doped RGO-Co3O4 nanograin cookies: highly porous and robust catalyst for removing nitrophenol from waste water

The fabrication of nanograins with a uniform morphology wrapped with reduced graphene oxide (RGO) in a designed manner is critical for obtaining a large surface, high porosity and efficient catalytic ability at mild conditions. Hybrid structures of metal oxides decorated on two-dimensional (2D) RGO lacked an interface and channels between the individual grains and RGO. The present work focuses on the synthesis of RGO-wrapped Co₃O₄ nanograin architecture in micron-sized polyhedrons and the ability to reduce aromatic nitro compounds. Doping N in the designed microstructure polyhedrons resulted in very large surface area (1085.6 m² g^-1) and pore density (0.47 m³ g^-1) microcages. Binding energies from x-ray photoelectron spectroscopy (XPS) and Raman intensities confirmed the presence of doped N and RGO-wrapped around Co₃O₄ nanograins. However, the morphology and microstructure was supported by FESEM and HRTEM images revealing the fabrication of high integrity RGO-Co₃O₄ microstructure hybrids composed of a 10 nm grain size with narrower grain size distribution. Ammonia treatment produced interconnected channels and dumbbell pores that facilitated ion exchange between the catalyst surface and the liquid medium at the grain boundary interfaces, and offered less mass transport resistance providing fast adsorption of reactants and desorption of the product causing surface renewal. Prepared N-RGO-Co₃O₄ shows the largest percentage reduction (96%) of p-nitrophenol (p-NP) at room temperature as compared to pure Co₃O₄ and RGO-Co₃O₄ nanograin microstructures over 10 min. Fabricated architectures can be applied effectively for fast and facile treatment of industrial waste streams with complex organic molecules.