Manoj Kumar Khanna

Increasing the urea content of microwave-synthesized citric acid–urea carbon quantum dots raises their nitrogen content and surface-to-bulk nitrogen ratio, and introduces nitrogen- and oxygen-related sub-gap states that their emission follows.

This study theoretically investigates an optical fiber structure coated with a bilayer film of zinc oxide (ZnO) and lithium fluoride (LiF) for ethanol detection. The ZnO thin film exhibits lossy mode resonance (LMR) in the visible and near-infrared spectrum (400 – 1500nm), which serves as the basis for designing a refractive index (RI) sensor by appropriately selecting the ZnO thickness. To further enhance the resonance characteristics, a dielectric layer of LiF is introduced between the unclad fiber core and the ZnO coating. It Improves phase matching and generates sharper LMR dips with a narrower full width at half maximum. The proposed structure is also analyzed using two different core materials: pure silica and 4% Ge-doped silica. A comparative study of their sensing performance is also presented. Its sensing performance is examined by varying the thicknesses of the ZnO and LiF layers to identify the optimal structural parameters. The designed fiber-optic sensor is then evaluated for detecting ethanol concentrations in ethanol–water mixtures (RI =1.33 for 0% ethanol and RI =1.36 for pure ethanol) using both s- and p -polarized incident light. Calibration curves demonstrating the relationship between resonant wavelength shifts and the RI of the sample are presented. This sensor achieves excellent sensitivities of 1163 nm RIU ⁻¹ for s -polarization and 1475 nm RIU ⁻¹ for p -polarization, making it promising for the development of High-Figure of Merit biochemical sensors for potential applications.

In this paper, an ultra-wideband (UWB) terahertz Metamaterial Perfect Absorber (MPA) based on the phase change feature of vanadium dioxide (VO₂) is proposed. The proposed absorber consists of two square loops of vanadium dioxide (VO₂), silicon dioxide (SiO₂) as the dielectric substrate and a layer of gold (Au) acting as the ground. Phase transition material VO₂ changes the conductivity (conductivity is changed from 200 to 2 × 10⁵ S m⁻¹, concerning temperature 300 K to 341 K) by several orders of magnitude at temperatures above 340 K by shifting from an insulating to a metallic state. The absorption of this suggested absorber can be adjusted from 4% to 100% within the conductivity range of 200 to 2 × 10⁵ S m⁻¹, which corresponds to temperatures between 300 K and 341 K. In the 2.2–6.8 THz range, with a bandwidth of up to 4.6 THz, more than 80% absorption is observed. The absorber design we proposed is polarization insensitive, simple and easily integrable. There are numerous uses for the suggested absorber in communication-related futuristic devices.

This manuscript explores the removal of eosin yellow dye, a toxic color substance contributing to water pollution, from aqueous solutions. For this purpose, iron-zirconia binary oxide (Fe₂O₃-ZrO₂) was functionalized with eugenol oil, a natural phenolic aromatic compound extracted from the clove plant. The functional groups developed in the binary oxide were confirmed by Fourier transform infrared spectroscopy (FT-IR), and its crystal structure was determined via X-ray diffraction (XRD). The grain size analyzed by the XRD pattern was found to be 45 nanometers. The morphological analysis revealed nanoparticles of quasi-spherical type with a size ranging from 4 to 5 nanometers. The consistency between SEAD and XRD further confirmed that the material formed was iron-zirconia binary oxide. The obtained material, which was insoluble in water, was used as an adsorbent. Through the adsorption study of eosin yellow dye, the maximum monolayer adsorption capacity of approximately 91.0 mg/g at 27 °C and pH = 7.0 for the functionalized adsorbent was determined. The process was exothermic, feasible, and spontaneous. At a dose of 1.0 g/L, the adsorbent was responsible for removing more than 90% of eosin yellow with 10–70 mg/L initial concentration, while about 56% removal was achieved at a higher concentration of 150 mg/L at 27 °C and pH = 7.0. These results highlight the potential of functionalized Fe₂O₃-ZrO₂ as an effective adsorbent for water purification applications.

In this research, a tungsten oxide was prepared via a green (biogenic) synthesis route where sodium tungstate dihydrate and Punica granatum peel extract were used as a precursor and a reducing/capping agent, respectively. The characterization of the prepared tungsten oxide was performed through various spectroscopic and microscopic techniques. The characterization results revealed the preparation of highly crystalline and nanorod-shaped (length = 123 nm and width = 31.3 nm) tungsten oxide with a probable chemical formula of W₅O₁₄. Various functional groups on the W₅O₁₄ surface were also reported. The prepared nanorods were further used for the removal of Bismarck Brown R (BBR) dye from water in a batch manner. By varying the dose of nanorods (0.5–3.0 g L⁻¹), BBR solution pH (2−10), contact time (15–120 min), BBR concentration in solution (10–60 mg L⁻¹), and temperature of BBR solution (30, 40, and 50 °C), the optimized condition for maximum adsorption efficiency was measured. The results revealed that 2.0 g L⁻¹ amount of nanorods of tungsten oxide were used to remove ~98% of BBR dye from its 10 mg L⁻¹ at 30 °C and 7.0 pH. The temperature-dependent adsorption data were fitted to different types of non-linear isotherm models (e.g., Langmuir and Freundlich) to assess the adsorption potential and adsorption mechanisms in relation to temperature impacts. The synthesized nano-adsorbent fits the Langmuir as well as the Freundlich isotherm model with a maximum adsorption capacity of 17.84 mg g⁻¹. Pseudo-first-order, pseudo-second-order, and Elovich kinetic models were used for the study of adsorption kinetics. BBR adsorption onto the W₅O₁₄ nanorods follows the pseudo-second-order rates. The present adsorption is governed by physico-chemical adsorption with predominant chemical interactions.

Attenuation characteristics of germanium (Ge) film clad planar optical waveguide are theoretically studied at the spectral wavelength of 0.6328 μm. Thin films of Ge are found to possess greater attenuation values than the other recognized materials. The existence of these greater attenuations is caused by lossy modes that are sustained by these films. It has been shown that the attenuation of the TM mode can be greatly increased by adding a high-index buffer layer between the Ge layer and the dielectric guide. It occurred because of the resonant coupling between the lossy modes supported by the Ge layer and the waveguide modes. Moreover, it is claimed that by adding a dielectric superstrate layer above the Ge thin film, the strength of the TM mode in the proposed structure can be further attenuated to an ultra-high value. In this study, a TE pass polarizer is proposed having a high extinction ratio of 30582.15 dB. Attenuation results are presented, after optimization of several parameters like thicknesses of Ge, buffer, and superstrate layers along with environmental stability of the suggested structure. The generated field distribution profiles are also in good agreement with the obtained attenuation results.

The objective of the present investigation is to optimize the thickness of Pulse Laser Deposition (PLD)-grown CoFe thin films to achieve minimal effective Gilbert damping (αeff) for potential spintronics applications. The effect of the thickness (5-30 nm) of CoFe ultra-thin films on the Si/SiO2 substrate on the structural, morphological and magnetic properties has been reported. The X-ray diffraction (XRD) peak at 44.5° shows the growth of CoFe along the (110) crystal plane. A nearly square M-H loop with high saturation magnetization (Ms) suggests good crystalline growth of CoFe film. A high coercive field (Hc) observed in the thinnest 5 nm film is due to defects such as dislocations and stacking faults that appear at very low thickness. These defects gradually decrease with an increase in CoFe film thickness, as evident from a decrease in the Hc and an increase in the Ms. The value of αeff is largest for the thinnest 5 nm film due to defects and magnetic inhomogeneities present at this thickness. The damping is reduced by approximately one-third for the 10 nm thin film in comparison to the 5 nm film, which signifies a good quality film with fewer disorders.

Hydrogen (H₂) is a well-known renewable energy source that produces water upon its burning, leaving no harmful emissions. Nanotechnology is utilized to increase hydrogen production using sacrificial reagents. It is an interesting task to develop photocatalysts that are effective, reliable, and affordable for producing H₂ from methanol and acetic acid. In the present study, CuO, CdWO₄, and CuO–CdWO₄ nanocomposite heterostructures were prepared using a cost-efficient, enviro-friendly, and facile green chemistry-based approach. The prepared CuO, CdWO₄, and CuO–CdWO₄ nanocomposites were characterized using X-ray diffraction pattern, Fourier-transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction (SAED) pattern, N₂ physisorption, photoluminescence, and X-ray photoelectron spectroscopy techniques. The synthesized photocatalysts were utilized for photocatalytic H₂ production using aqueous methanol and acetic acid as the sacrificial reagents under visible light irradiation. The influence of different variables, including visible light irradiation time, catalyst dosage, concentration of sacrificial reagents, and reusability of catalysts, was studied. The maximum H₂ was observed while using methanol as a sacrificial agent over CuO–CdWO₄ nanocomposite. This enhancement was due to the faster charge separation, higher visible light absorption, and synergistic effect between the CuO–CdWO₄ nanocomposite and methanol.