Carbon Quantum Dot-Anchored Bismuth Oxide Composites as Potential Electrode for Lithium-Ion Battery and Supercapacitor Applications

The present investigation elucidates a simple hydrothermal method for preparing nanostructured bismuth oxide (Bi₂O₃) and carbon quantum dot (CQD) composite using spoiled (denatured) milk-derived CQDs. The formation of the CQD-Bi₂O₃ composite was confirmed by UV-vis absorption, steady-state emission, and time-resolved fluorescence spectroscopy studies. The crystal structure and chemical composition of the composite were examined by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The surface morphology and the particle size distribution of the CQD-Bi₂O₃ were examined using field emission scanning electron microscope and high-resolution transmission electron microscope observations. As an anode material in lithium-ion battery, the CQD-Bi₂O₃ composite exhibited good electrochemical activity and delivered a discharge capacity as high as 1500 mA h g^-1 at 0.2C rate. The supercapacitor properties of the CQD-Bi₂O₃ composite electrode revealed good reversibility and a high specific capacity of 343 C g^-1 at 0.5 A g^-1 in 3 M KOH. The asymmetric device constructed using the CQD-Bi₂O₃ and reduced graphene oxide delivered a maximum energy density of 88 Wh kg^-1 at a power density of 2799 W kg^-1, while the power density reached a highest value of 8400 W kg^-1 at the energy density of 32 Wh kg^-1. The practical viability of the fabricated device is demonstrated by glowing light-emitting diodes. It is inferred that the presence of conductive carbon network has significantly increased the conductivity of the oxide matrix, thereby reducing the interfacial resistance that resulted in excellent electrochemical performances.

Facile Construction of Novel 3-Dimensional Graphene/Amorphous Porous Carbon Hybrids with Enhanced Lithium Storage Properties

Presently, porous materials have become essential to many technological applications. In this account, 3-dimensional skeleton composite materials consisting of a core-shell amorphous porous carbon/multilayer graphene are synthesized by chemical vapor deposition on Ni foam using a facile one-step growth method. The data suggest that these composites have not only outstanding electrical and mechanical properties of the multilayer graphene but also the mesoporous characteristics of the amorphous carbon. Moreover, the composited carbon materials perfectly inherit the macroporous structure of Ni foam, and the amorphous carbon core in the skeleton serves as a cushion to buffer the volume variation after the removal of Ni. The carbon composites reveal ultralow density (4.45 mg cm^-3) and high conductivity (45 S cm^-1), essentially issued from the perfectly preserved structural integrity of graphene. The novel carbon composites can be used as anodes for lithium ion batteries. After these carbon composites are incorporated with NaBiO₃, superior electrochemical activities above 2 V can be achieved with a discharge capacity of ∼300 mAh g^-1.

Bi2(C2O4)3·7H2O and Bi(C2O4)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth

Two bismuth oxalates, namely, Bi₂(C₂O₄)₃·7H₂O and Bi(C₂O₄)OH, were studied in terms of synthesis, structural characterization, particle morphology, and thermal behavior under several atmospheres. The oxalate powders were produced by chemical precipitation from bismuth nitrate and oxalic acid solutions under controlled pH, then characterized by X-ray diffraction (XRD), temperature-dependent XRD, IR spectroscopy, scanning electron microscopy, and thermogravimetric differential thermal analyses. New results on the thermal decomposition of bismuth oxalates under inert or reducing atmospheres are provided. On heating in nitrogen, both studied compounds decompose into small bismuth particles. Thermal properties of the metallic products were investigated. The Bi(C₂O₄)OH decomposition leads to a Bi-Bi₂O₃ metal-oxide composite product in which bismuth is confined in a nanometric size, due to surface oxidation. The melting point of such bismuth particles is strongly related to their crystallite size. The nanometric bismuth melting has thus been evidenced ∼40 °C lower than for bulk bismuth. These results should contribute to the development of the oxalate precursor route for low-temperature soldering applications.

Nanostring-cluster hierarchical structured Bi2O3: synthesis, evolution and application in biosensing

A new Bi₂O₃ with a nanostring-cluster hierarchical structure was employed for glucose enzyme immobilization and was designed for biosensors.

Structural, compositional and textural properties of monoclinic α-Bi₂O₃ nanocrystals

Perfect α-Bi2O3 nanocrystals were successfully synthesized via green synthesis method. X-ray diffraction studies clearly revealed a single phase α-Bi2O3 nanocrystal without any secondary phase. The strong XPS peaks observed at 160 and 165 eV were assigned to Bi4f5/2 and Bi4f7/2 and clearly revealed Bi(3+) valence states of bismuth ions. Photoluminescence spectra revealed the perfect α-Bi2O3 crystal nature without having inter band transitions between defects, impurity and different valence states of bismuth ions. Out of thirty expected modes, the symmetry assignments of Raman bands correlated to Bg(4), Ag(5), Bg(5), Bg(6), Ag(7), Ag(8), Ag(9), Ag(10), Ag(12) and Ag(14) modes revealed perfect α-Bi2O3 nanocrystals. Transmission electron microscopy studies combined with a selected area electron diffraction pattern recorded on α-Bi2O3 nanocrystals show monoclinic structure preferential orientation with sizes approximately 200 nm in diameters and 500 nm in length.