RESUMO
Layered materials with a robust structure and reversible intercalation behavior are highly sought-after in applications involving energy conversion and storage systems, energy converting devices, supercapacitors, batteries, superconductors, photonic materials, and catalysis involving hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), solar cells and sensors. In the current study, quasi-2D rhombohedral Bi0.775Ln0.225O1.5 (Ln = La, Pr, Nd, Sm, and Eu) samples, synthesized by a solution combustion route, have been demonstrated to intercalate iodine reversibly. A solid-vapor reaction was employed to intercalate iodine at moderate temperatures, and deintercalation occurred on heating at higher temperatures. Expansion of the rhombohedral c-axis by â¼10 Å occurred, and the iodine between the interlayers existed as triiodide ions (I3-) in an unsymmetrical fashion. The amount of intercalated iodide has been determined from thermogravimetric analysis. Electron microscopic analysis confirmed these systems' intercalation and subsequent lattice expansion. In the diffuse reflectance spectra, charge transfer from the triiodide ions to the host oxide was noticed, and it caused the absorption edge to fall beyond the visible region for the intercalated samples. XPS analysis of iodine intercalated Bi0.775Pr0.225O1.5 has shown the mixed valence states for Pr and the existence of I3- along with some IO3- species. The quasi-2D structure was stable during the thermal deintercalation process. The evaluation of iodine intercalated Bi0.775Ln0.225O1.5 (Ln = La, Pr, Nd, Sm, and Eu) samples as anode material in the lithium-ion battery system has given quite promising results, exhibiting fast Li+-ion diffusion, low charge transfer resistance, good reversible capacity, capacity retention (after cycling back to 10 mA g-1), and structural stability (after long cycles).
RESUMO
Recognizing the deficiency in the hole and electron doping outcomes in layered bismuth-based oxyhalides intergrowths, the current study was addressed to the doping of Ca2+ and Zr4+ for Y3+ in Bi2YO4Cl. The samples were rapidly synthesized by a sol-gel auto combustion method and characterized extensively. Up to 30 mol % Y could be substituted with Ca in tetragonal symmetry and without the appearance of any additional phase. The unit cell parameters varied nonlinearly with the elongation of the Y-O bond. The Raman spectra supported the local site distortion. The calcium-substituted samples displayed selected area electron diffraction characteristics similar to those of Bi2YO4Cl. A blueshift of the absorption edge was noticed with increasing calcium content yielding optical band gap values in the 2.40-2.57 eV range. The creation of 10% Bi5+ in Bi2Y0.70Ca0.30O4Cl was established with the help of XPS measurements and redox titrations. The higher reactivity of Bi5+ in an aqueous solution has been demonstrated for the oxidation of As(III) to As(V). Electron doping through Zr4+ incorporation was possible up to 30 mol % in Bi2YO4Cl. The Y-O bonds are contracted, and the Bi-O bonds are elongated with increasing Zr4+ content. Zr4+'s incorporation induced a local distortion. The color of the sample changed from bright yellow to deep yellow with Zr inclusion, resulting in a progressive decrease in optical band gap values. The introduction of electrons caused the reduction of 13.6% of Bi(III) to Bi(0). These results have established the vulnerability of Bi2O2 chains to charge carriers in Bi2YO4Cl. Density functional theory (DFT) calculations were implemented to understand the electronic and optical properties of the pristine and doped compounds. From the band structure calculations, the chosen compounds were found to be indirect band gap semiconductors. The results of the DFT calculations were in good agreement with the experiment; however, for the doped cases, virtual crystal approximation has been used considering uniform doping at the Y-site.