Fabrication of TiO2-Nanotube-Array-Based Supercapacitors

In this work, a simple and cost-effective electrochemical anodization technique was adopted to rapidly grow TiO₂ nanotube arrays on a Ti current collector and to utilize the synthesized materials as potential electrodes for supercapacitors. To accelerate the growth of the TiO₂ nanotube arrays, lactic acid was used as an electrolyte additive. The as-prepared TiO₂ nanotube arrays with a high aspect ratio were strongly adhered to the Ti substrate. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the TiO₂ nanotube arrays were crystallized in the anatase phase. TEM images confirmed the nanotublar-like morphology of the TiO₂ nanotubes, which had a tube length and a diameter of ~16 and ~80 nm, respectively. The electrochemical performance of the TiO₂ nanotube array electrodes was evaluated using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements. Excellent electrochemical response was observed for the electrodes based on the TiO₂ nanotube arrays, as the cells delivered a high specific capacitance of 5.12 mF/cm² at a scan rate of 100 mV/s and a current density of 100 μA/cm². The initial capacity was maintained for more than 250 cycles. Further, a remarkable rate capability response was observed, as the cell retained 88% of the initial areal capacitance when the scan rate was increased from 10 to 500 mV/s. The results suggest the suitability of TiO₂ nanotube arrays as electrode materials for commercial supercapacitor applications

Effect of Mg on the Structural, Optical and Thermoluminescence Properties of Li3Al3(BO3)4: Shift in Main Glow Peak

The doping of magnesium on lithium aluminium borate phosphor is reported in this study. A solid-state sintering technique was employed as the borate samples were synthesized. This report focuses on the structural, optical, thermoluminescence, and kinetic analyses of the main glow peak. The structural properties of lithium aluminium borates improved due to the magnesium dopants used. Differences in the crystallite size and particle size were 38.85–67.35 nm and 50–60 nm, respectively, and these results were obtained from the analyzed X-ray diffractogram and scanning electron spectroscopy. The energy band gaps obtained from the direct transition of borate phosphor materials were within the range of 3.00–4.40 eV, and the doped samples gave a higher energy band gap. A decrease in the TGA (%) exhibited a weight loss or water loss for the undoped, 0.1% Mg, and 0.3% Mg-doped lithium aluminium borate materials. The glow curve measured at a heat rate of 1 °C·s−1 after irradiation to 50 Gy revealed four peaks related to the magnesium doped lithium aluminium borate. The main glow peak was observed at 86 °C. Activation energy was extracted from the main glow peak by using kinetic analysis which involves the initial rise, deconvolution, and variable heating rate approach, and it was approximately 0.67 ± 0.03 eV. A shift in the main glow peak curve from 86 to 110 °C was recognized for the magnesium-doped lithium aluminium borate when it was irradiated from 1 to 300 Gy

Enhancement of Optical Activity and Properties of Barium Titanium Oxides to Be Active in Sunlight through Using Hollandite Phase Instead of Perovskite Phase

The present study aims to enhance the optical properties of barium titanate through narrowing its band gap energy to be effective for photocatalytic reactions in sunlight and be useful for solar cells. This target was achieved through growth of the hollandite phase instead of the perovskite phase inside the barium titanate crystals. By using solvent thermal reactions and thermal treatment at different temperatures (250 °C, 600 °C, and 900 °C), the hollandite phase of barium titanate was successfully obtained and confirmed through X-ray diffraction (XRD), Raman spectra and scanning electron microscopy techniques. XRD patterns showed a clear hollandite phase of barium titanium oxides for the sample calcined at 900 °C (BT1-900); however, the samples at 600 °C showed the presence of mixed phases. The mean crystallite size of the BT1-900 sample was found to be 38 nm. Morphological images revealed that the hollandite phase of barium titanate consisted of a mixed morphology of spheres and sheet-like features. The optical properties of barium titanate showed that its absorption edge shifted to the visible region and indicated band gap energy tuning ranging from 1.75 eV to 2.3 eV. Photocatalytic studies showed the complete and fast decolorization and mineralization of green pollutants (naphthol green B; NGB) in the prepared barium titanate with hollandite phase after illumination in sunlight for ten minutes. Finally, it can be concluded that the low band gap energy of barium titanate having the hollandite phase introduces beneficial structures for optical applications in sunlight

Structural, Morphological, Electronic Structural, Optical, and Magnetic Properties of ZnO Nanostructures

ZnO nanostructures were grown on a Si(111) substrate using a vapor–liquid–solid (VLS) growth procedure (pristine ZnO) and annealed via a rapid thermal-annealing process in an argon atmosphere at 1100 °C (Ar-ZnO). The synthesized ZnO nanostructures were investigated through structural, electronic structural, morphological, optical, and magnetic characterizations. X-ray diffraction and selective area electron diffraction (SAED) measurements revealed that both samples exhibited the hexagonal wurtzite phase of nanocrystalline ZnO. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy carried out at the O K-edge inferred the presence of the intrinsic-defect states. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy images displayed the formation of ZnO nanostructures. The photoluminescence (PL) spectra demonstrated an emission band in the UV region along with an additional defect band in the visible region. PL spectral analysis confirmed the presence of intrinsic defects in Ar-ZnO nanowires, contributing to the enhanced emission in the visible region. The Raman spectra showed the characteristic band (434 cm−1) corresponding to the vibrational modes of hexagonal wurtzite ZnO, with an additional band attributable to intrinsic defects. DC magnetization measurements showed a ferromagnetic response in both samples with enhanced coercivity in Ar-ZnO (~280 Oe). In brief, both samples exhibited the presence of intrinsic defects, which are found to be further enhanced in the case of Ar-ZnO. Therefore, it is suggested that intrinsic defects have played an important role in modifying the optical and magnetic properties of ZnO with enhanced results for Ar-ZnO

Structural, Electrical and Optical Properties of TM (Mn and Cr) Doped BiFeO₃ Nanoparticles

In this paper, the sol-gel technique has been employed to prepare the pure and TM (Mn, Cr) doped BiFeO3 nanoparticles. The synthesized nanoparticles were characterized using X-ray diffraction, UV-vis spectroscopy, photoluminescence, and dielectric measurements. Crystal structural analysis infers that pure and TM-doped BiFeO3 nanoparticles displayed a rhombohedral distorted perovskite structure with R3c space group, along with a minor phase of Bi2Fe4O9. Lattice parameters have been found to decrease with TM doping. The particle size, measured with the help of the XRD spectra, was found to decrease from 54.4 nm to 38.7 nm with TM doping. The bandgap, determined using the UV-vis spectra, was observed to be 1.92, 1.66, and 1.54 eV for undoped, 5% Mn, and 5% Cr-doped BiFeO3 nanoparticles, respectively. The dielectric constant shows a normal dispersion behavior at room temperature and its value increases with TM doping. The ac conductivity also increases with TM doping in BiFeO3 nanoparticles

Hybrid Density Functional Investigation of Cu Doping Impact on the Electronic Structures and Optical Characteristics of TiO₂ for Improved Visible Light Absorption

We report a theoretical investigation of the influence of Cu doping into TiO2 with various concentrations on crystal structure, stability, electronic structures and optical absorption coefficient using density functional theory via the hybrid formalism based on Heyd Scuseria Ernzerhof. Our findings show that oxygen-rich environments are better for fabricating Cu-doped materials and that the energy of formation for Cu doping at the Ti site is lower than for Cu doping at the O site under these environments. It is found that Cu doping introduces intermediate bands into TiO2, narrowing the band gap. Optical absorption curves show that the Cu-doped TiO2 can successfully harvest visible light. The presence of widely intermediate bands above the valence-band edge could explain the increase in the visible light absorption range. However, the intensity of visible light absorption rises with the increase in doping concentration

Conversion of Non-Optical Material to Photo-Active Nanocomposites through Non-Conventional Techniques for Water Purification by Solar Energy

Development of optical materials has attracted strong attention from scientists across the world to obtain low band gap energy and become active in field of solar energy. This challenge, which cannot be accomplished by the usual techniques, has overcome through the current study using non-conventional techniques. This study has used explosive reactions to convert non-optical alumina to series of new optical nanocomposites with very low band gap energy for the first time. In this trend, alumina nanoparticles were prepared and modified by explosive reactions using ammonium nitrate as a solid fuel. By using methanol or ethanol as a source of carbon species, three nanocomposites were produced indicating a gradual reduction of the band gap energy of alumina from 4.34 eV to 1.60 eV. These nanocomposites were obtained by modifying alumina via two different carbon species; core-shell structure and carbon nanotubes. This modification led to sharp reduction for the band gap energy to become very sensitive in sunlight. Therefore, these nanocomposites caused fast decolorization and mineralization of green dyes after illuminating in sunlight for ten minutes. Finally, it can be concluded that reduction of the band gap energy introduces new optical materials for developing optical nano-devices and solar cells

Thermally stable Au decorated silica-titania mesoporous nanocomposite for pH sensing evaluation

Herein, doping/decoration of gold nanoparticles (AuNPs) within mesoporous silica-titania nanocomposite is achieved via a facile and co-assembly sol-gel method. Polyethylene glycol is used as a co-structure-directing-agent. For sensing analysis, a mixture of organic dyes i.e., bromophenol blue, phenol red, and cresol red is encapsulated in the AuST nanocomposite matrix. FESEM/EDX analysis shows a crack-free surface, porous network and uniform distribution of Au, Ti, Si, along with dye species. FTIR and XRD suggested the heterogeneous chemical bonding and crystallite size 24 nm after encapsulation. AuST nanocomposite shows thermally stable behavior after 450 °C even after co-dyes encapsulation. High surface area 322 ± 2.5 m2/g, pore diameter 30.2 Å, and pore volume 0.24 cm3/g, average surface roughness 10 nm, and refractive index 1.29 is advantageous for good sensing response at pH 1–12. The sensitivity is measured as 10 counts/pH at 441 nm. Moreover, good reversible response, fast response time 2.1 sec in acidic media, and 0.9 sec in basic media is observed

One-step spin-coating of methylammonium lead iodide on SILAR-deposited tin oxide, SnO2 films for effective electron transport

Tin oxide (SnO2) materials were prepared via successive ionic layer adsorption and reaction (SILAR) technique at varying deposition times. The synthesized tin oxide layer served as an electron transport layer for the deposition of a perovskite layer via spin coating method. The morphology, structure, elemental, optical features and vibration modes of the prepared samples have been studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray spectroscopy (EDX), UV–vis spectrophotometry, and Raman spectrophotometry, respectively. The films revealed granular-shaped nanograins with a maximum average grain size of 197.03 nm. XRD results showed a cassiterite pure-phase crystal structure with several prominent peaks. EDX studies confirmed the as-deposited elemental constituents with good optical properties obtained from the optical studies. The band gap energies ranged from 4.01 to 4.24 eV at increasing deposition times. The phonon modes and crystal structures were also revealed from the Raman studies. The materials find applications in solar cells and electronic devices