Suresh Mulmi

Magnetically Aligned Iron Oxide/Gold Nanoparticle-Decorated Carbon Nanotube Hybrid Structure as a Humidity Sensor

Functionalized carbon nanotubes (f-CNTs), particularly CNTs decorated with nanoparticles (NPs), are of great interest because of their synergic effects, such as surface-enhanced Raman scattering, plasmonic resonance energy transfer, magnetoplasmonic, magnetoelectric, and magnetooptical effects. In general, research has focused on a single type of NP, such as a metal or metal oxide, that has been modified on a CNT surface. In this study, however, a new strategy is introduced for the decoration of two different NP types on CNTs. In order to improve the functionality of modified CNTs, we successfully prepared binary NP-decorated CNTs, namely, iron oxide/gold (Au) NP-decorated CNTs (IA-CNTs), which were created through two simple reactions in deionized water, without high temperature, high pressure, or harsh reducing agents. The physicochemical properties of IA-CNTs were characterized by ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, a superconducting quantum interference device, scanning electron microscopy, and transmission electron microscopy. In this study, IA-CNTs were utilized to detect humidity. Magnetic IA-CNTs were aligned on interdigitated platinum electrodes under external magnetic fields to create a humidity-sensing channel, and its electrical conductivity was monitored. As the humidity increased, the electrical resistance of the sensor also increased. In comparison with various gases, for example, H2, O2, CO, CO2, SO2, and dry air, the IA-CNT-based humidity sensor exhibited high-selectivity performances. IA-CNTs also responded to heavy water (D2O), and it was established that the humidity detection mechanism had D2O-sensing capabilities. Further, the humidity from human out-breathing was also successfully detected by this system. In conclusion, these unique IA-CNTs exhibited potential application as gas detection materials.

Synthesis and characterization of perovskite-type BaMg0.33Nb0.67−xFexO3−δ for potential high temperature CO2 sensors application

Mixed ionic-electronic conducting BaMg0.33Nb0.67−xFexO3−δ was successfully synthesized by conventional solid state method in air at elevated temperature. Fe-doping helped to increase the total conductivity, while the chemical stability under CO2 at elevated temperatures and under H2O vapour at boiling conditions decreased with increasing Fe content above x = 0.17 in BaMg0.33Nb0.67−xFexO3−δ. Maximum total conductivity of 10−3 S cm−1 at 300 °C was obtained for BMNF33 in air, and further increase in Fe content lowered the electrical conductivity, particularly at low temperatures. Activation energy, in the range of 300–700 °C, for total electrical conduction was found to decrease in air by the incorporation of Fe in BaMg0.33Nb0.67O3 (BMN) (BMN: 0.96 eV; BMNF17: 0.72 eV; BMNF33: 0.25 eV). Furthermore, the x = 0.17 composition demonstrated excellent CO2 sensing characteristics at 700 °C. The investigated perovskite-type metal oxides seem to be promising candidates for monitoring CO2 (ppm level in air) at elevated temperatures.

Thermochemical CO2 splitting using double perovskite-type Ba2Ca0.66Nb1.34−xFexO6−δ

A carbon-neutral fuel is desired when it comes to solving the issues associated with climate change. A smart approach would be to develop new materials to produce such fuels, which could be integrated with renewables to improve the efficiency (e.g., solid oxide fuel cells (SOFCs) in smart grid and concentrated solar fuel technologies). In this study, we report the utilization of nonstoichiometric perovskite oxides, Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) (0 ≤ x ≤ 1), to split CO2 into carbon, carbon monoxide, and oxygen at elevated temperatures. Powder X-ray diffraction shows the chemical stability of double perovskite-type BCNF after being exposed to 2000 ppm CO2 in Ar at 700 °C. Furthermore, all x ≤ 0.66 BCNF members exhibit high chemical stability even under pure CO2 at 700 °C. Scanning electron microscopy coupled with energy dispersive X-ray, Raman spectroscopy, temperature programmed oxidation (TPO) and mass spectroscopy (MS), and DFT analyses confirm the formation of solid carbon upon CO2 exposure, which increases with increasing Fe in BCNF. Mossbauer spectroscopy of the as-prepared BCNF shows the presence of Fe3+, Fe4+ and Fe5+. Upon Ar exposure, the higher valent Fe component is reduced to Fe3+ and subsequent oxidation of Fe3+ seems to promote the CO2 reduction. Overall, these promising results of BCNFs, displaying redox activity at significantly lower temperatures compared to state-of-the-art ceria for CO2 reduction, show great potential for their use in renewable-driven fuel technologies.

Structure, Ionic Conductivity, and Dielectric Properties of Li-Rich Garnet-type Li5+2xLa3Ta2–xSmxO12 (0 ≤ x ≤ 0.55) and Their Chemical Stability

Lithium garnet oxides are considered as very promising solid electrolyte candidates for all-solid-state lithium ion batteries (SSLiBs). In this work, we present a cubic garnet-type Li5+2xLa3Ta2-xSmxO12 (0 ≤ x ≤ 0.55) system as a potential electrolyte for SSLiBs. Powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) were employed to investigate the structural stability of Li5+2xLa3Ta2-xSmxO12. The results from PXRD and SEM suggested structural and morphological transformation as a function of dopant concentration. In addition to Li-ion transport in Li5+2xLa3Ta2-xSmxO12, the dielectric properties were also investigated in the light of electron energy loss functions, which showed some surface energy loss and negligible volume energy loss for the studied garnets. Surface and volume energy loss functions of a mixed conducting LiCoO2 was studied for comparison. The long-term chemical stability of one of members, Li5.3La3Ta1.85Sm0.15O12, was performed on aged sample using PXRD, SEM, and thermogravimetric analysis.