IR@CGCRI - Central Glass and Ceramic Research Institute (CSIR)
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NO2 gas sensing performance of Ag-WO3-x thin films prepared by reactive magnetron sputtering process
Get PDFWe have demonstrated a comparative study of NO2 gas sensing behavior of reactive sputtered growth WO3-x nanocrystalline thin films and its functionalization with Ag nanoparticles (Ag-WO3-x) on Si/SiO2 substrates. X-ray diffraction and transmission electron microscope characterizations demonstrate the formation of polycrystalline monoclinic phase of porous WO3-x thin film. X-ray photoelectron spectroscopy experiments reveal that W6+ charge state has higher concentration compared with that of W4+ and W5+. The Ag-WO(3-x )films exhibit a sensitivity of about 70% at 10 ppm, while WO3-x films show 12%, measured at 225(degrees)C with same NO2 gas concentration. The response and recovery time are 2 and 3 min. for Ag-WO3-x films, while these for WO(3-x )films are 3 and 4 min., respectively. This work shows that nano-scale dendritic agglomeration growth of Ag nanoparticles on WO3-x surface can increase active sites for NO2 gas and play an important role in trace-level gas sensing performance
Terahertz sensing of reduced graphene oxide nanosheets using sub-wavelength dipole cavities
Get PDFBecause of extraordinary optoelectronic properties, two-dimensional (2D) materials are the subject of intense study in recent times. Hence, we investigate sub-wavelength dipole cavities (hole array) as a sensing platform for the detection of 2D reduced graphene oxide (r-GO) using terahertz time-domain spectroscopy (THz-TDS). The r-GO is obtained by reducing graphene oxide (GO) via Hummer's method. Its structural characteristics are verified using X-ray diffraction (XRD) and Raman spectroscopy. We also assessed the morphology and chemistry of r-GO nanosheets by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and Fourier Transformed Infrared (FTIR) spectroscopy. Further, we studied the surface plasmon resonance (SPR) characteristics of r-GO nanosheets hybridized dipole cavities using THz-TDS by varying the r-GO thickness on top of the dipole cavities, since these cavities are well known for sustaining strong SPRs. Based on these, we experimentally obtained a sensitivity of 12 GHz/mu m for the porous r-GO film. Thus, a modification in SPR characteristics can be employed towards the identification and quantification of r-GO by suitably embedding it on an array of dipole cavities. Moreover, we have adopted a generic approach that can be expanded to sense other 2D materials like Boron Nitride (BN), phosphorene, MoS2, etc., leading to the development of novel THz nanophotonic sensing devices
Phonons and Thermal Properties of Ge Nanowires: A Raman Spectroscopy Investigation and Phonon Simulations
No full textWe have investigated phonon an harmonicity related thermal properties e.g., coefficient of thermal expansion (alpha), Gruneisen parameter (gamma), and phonon mean free path as limited by Umklapp scattering (lambda(mfp))] for Ge nanowires (NWs) using temperature-dependent Raman spectroscopy as well as phonon dynamics simulations. The experiments were carried out in two types of NW ensembles. One type of NWs has only the native oxide layer on Ge, and the other type has relatively thicker GeO2 on the surface forming a core-shell structure. The temperature-dependent shift of the LO/TO Raman line of Ge (300 cm(-1)) was used to determine the alpha gamma product in the temperature range of 80-800 K. The alpha gamma product is enhanced compared to that observed in the bulk crystalline Ge over the whole temperature range. The experimental work was complimented by phonon simulations with quasi-harmonic approximation using density functional perturbation theory. The simulation allowed us to determine the thermodynamic parameters like bulk modulus, specific heat capacity (C-v), alpha, and gamma. We have determined the anharmonicity coefficients and phonon lifetimes in Ge NWs and also estimated the lambda(mfp) arising from phonon-phonon scattering (Umklapp process). Comparison of the computed thermal parameters with the experimental data allowed us to place a confidence limit on the calculated parameters, which was used to separate out the two parameters alpha and gamma for the NWs from the observed alpha gamma product. The enhancement of alpha, in particular, in the Ge NWs has been explained as arising from significant softening of theta(D) in the NWs as observed from the low temperature C-v calculated from the phonon simulations. Comparison of the computed phonon density of states shows appearance of excess weights in the phonon spectrum, which contributes to enhancement of heat capacity in NWs compared to that in the bulk
Giant exchange bias in antiferromagnetic Pr2CoFe0.5Mn0.5O6: a structural and magnetic properties study
No full textAntiferromagnetic (AFM) materials with a colossal exchange bias (EB) effect find applications as high-density spintronic devices. We report structural (geometrical and electronic) and magnetic studies in the polycrystalline Pr2CoFe0.5Mn0.5O6 double perovskite system. The observed lack of training effect suggests the existence of robust EB. In addition, the detailed magnetic studies and Raman studies unravel the Griffith-like phase along with the spin-phonon coupling in the present system. The x-ray photoemission spectroscopy (XPS) analysis supports more than one valence state of B-site elements, which is accountable for the competition between ferromagnetic (FM) and AFM interactions in addition to the anti-site disorder in the system. The neutron measurement confirms the G-type AFM spin arrangement, accredited by the DFT calculation. The magnetic studies have correlated with the electronic structure, neutron study, and theoretical first principle calculations
A Ni(II) Metal-Organic Framework with Mixed Carboxylate and Bipyridine Ligands for Ultrafast and Selective Sensing of Explosives and Photoelectrochemical Hydrogen Evolution
No full textWe report a Ni-MOF (nickel metal-organic framework), Ni-SIP-BPY, synthesized by using two linkers 5-sulfoisophthalic acid (SIP) and 4,4'-bipyridine (BPY) simultaneously. It displays an orthorhombic crystal system with the Ama2 space group: a = 31.425 angstrom, b = 19.524 angstrom, c = 11.2074 angstrom, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, and two different types of nickel(II) centers. Interestingly, Ni-SIP-BPY exhibits excellent sensitivity (limit of detection, 87 ppb) and selectivity toward the 2,4,6-trinitrophenol (TNP)-like mutagenic environmental toxin in the pool of its other congeners via ``turn-off'' fluorescence response by the synergism of resonance energy transfer, photoinduced electron transfer, intermolecular charge transfer, pi-pi interactions, and competitive absorption processes. Experimental studies along with corroborated theoretical experimentation, vide density functional theory studies, shed light on determining the plausible mechanistic pathway in selective TNP detection, which is highly beneficial in the context of homeland security perspective. Along with the sensing of nitroaromatic explosives, the moderately low band gap and the p-type semiconducting behavior of Ni-SIP-BPY make it suitable as a photoanode material for visible-light-driven water splitting. Highly active surface functionalities and sufficient conduction band minima effectively reduce the water and result in a seven times higher photocurrent density under visible-light illumination
Trapped Exciton-Enhanced Response of n-TiO2(110)/p-Si(111) Nanostructures as Photodetectors
No full textA p-type Si(111)/n-TiO2(110) heterojunction photodetector device has been fabricated for broad spectral range detection. An environmentally friendly NaCl assisted hydrothermal route was employed for synthesizing an n-type TiO2(110) hierarchical nanostructure powder. A 1 mu m thick film of TiO2 was then deposited by spin coating on the top of p-type Si(111). The role of NaCl in tuning both anionic (oxygen vacancy) and cationic (Ti mono- and divacancy, Ti interstitials) defects has been investigated. The vacancies posed a significant effect on photoresponse and junction characteristics of the device, viz., dark current, barrier height, photosensitivity, detectivity, and photoresponse gain. The TiO2 n-type layer fabricated at higher NaCl concentrations has been found to exhibit maximum responsivity of similar to 550 A/W, gain of similar to 2.00, specific detectivity of similar to 1.27 x 1011 Jones, and fast response and recovery times of 38 and 43 ms, respectively. The device has been highly repeatable (for 12 cycles) with a stability of 60 days. These have been ascribed to the exciton, formed at the bridged oxygen adjacent to the Ti vacancy at the (110) surface. We have also resolved that the charge carrier-phonon interaction facilitates exciton stabilization, while the charge transfer across the interface follows the adiabatic process. To explain the variation of device performance with defects, a mathematical model has been proposed to correlate the device responsivity to the different vacancies
Room-temperature multiferroicity in GaFeO3 thin film grown on (100)Si substrate
No full textRoom-temperature magnetoelectric multiferroicity has been observed in c-axis oriented GaFeO3 thin films (space group Pna2(1)), grown on economic and technologically important (100)Si substrates by a pulsed laser deposition technique. Structural analysis and comprehensive mapping of the Ga:Fe ratio across a length scale range of 10(4) reveals coexistence of epitaxial and chemical strain. It induces formation of finer magnetic domains and large magnetoelectric coupling-a decrease in remanent polarization by similar to 21% under similar to 50 kOe. Magnetic force microscopy reveals the presence of both finer (<100 nm) and coarser (similar to 2 mu m) magnetic domains. Strong multiferroicity in epitaxial GaFeO3 thin films, grown on a (100)Si substrate, brighten the prospect of their integration with Si-based electronics and could pave the way for development of economic and more efficient electromechanical, electrooptic, or magnetoelectric sensor devices. Published under an exclusive license by AIP Publishing
A Review on Conversion of Biomass to Liquid Fuels and Methanol through Indirect Liquefaction Route
No full textGlobal urbanization and industrialization are energy-intensive processes. Among different energy resources, fossil fuels meet more than 80 % of the energy demand. The factors such as the depletion of fossil fuel reserves, the unstable price of fossil fuels, and the emission of greenhouse gases (GHGs) due to the burning of fuels draw researchers' attention towards the development of renewable and sustainable fuels. In this context, biomass may fill the gap between energy demand and petroleum availability in the foreseeable future. Moreover, half of this bioenergy comes from conventional uses of biomass, primarily in cooking and heating, as well as within small-scale industries (such as charcoal kilns and brick kilns). The Biomass-to-Liquid (BTL) technology using Fischer-Tropsch synthesis (FTS) and the Methanol process offers advantages over the traditional use of biomass. The FT/Methanol process is a propitious route to produce carbon-neutral, ultra-clean fuels that generate regulated emissions, including NOx, SOx, and PM. In this article, we have reviewed the processes of biomass gasification, syngas cleaning and conditioning, FTS and methanol synthesis
Sustainable conversion of textile industry cotton waste into P-dopped biochar for removal of dyes from textile effluent and valorisation of spent biochar into soil conditioner towards circular economy
No full textEffective immobilization of industrial waste into biochar development could be one of the most promising technologies for solid waste management to achieve circular economy. In this study, post-industrial cotton textile waste (PICTW), a cellulose rich industrial waste, was subjected to slow pyrolysis to develop a surface engineered biochar through phosphoric acid impregnation. Biochar produced at 500 degrees C designated as PICTWB500 showed a maximum methylene blue number (240 mg g-1) with remarkable specific surface area of 1498 m2 g-1. FESEM, FTIR, XRD and Raman spectra analysis were performed to investigate the surface texture and functionalities developed in the biochar. Adsorption efficiency of the biochar was assessed using drimarene red, blue, violet, and black dyes as model dye pollutants in batch mode at different biochar dose, pH and contact time. The maximum monolayer adsorption capacity was obtained in the range 285-325 mg g-1 for different dyes, determined from Langmuir adsorption model. The kinetic behaviour was more favourable with the pseudo second-order model. The recycling ability of PICTWB500 was proven to be effective up to 6th cycle without compromising its adsorption efficiency significantly. This study demonstrated an excellent adsorption capability of the biochar in dye laden real textile effluent and recycling of spent biochar as a precursor of bio compost. Hence, this study established a dual win strategy for waste utilization in textile industry using a closed loop approach with substantial techno-economic feasibility that may have potential applications
Impact of melt solidification rate on structural and thermoelectric properties of n-type Bi2Te3 alloy
No full textAlloys based on bismuth telluride (Bi2Te3) form an important class of thermoelectric materials used in Peltier cooling devices and thermoelectric generators. In this work, polycrystalline n-type Bi2Te3 alloy was prepared by a melt-quenching process using different quenching mediums: alkaline ice water, ice water, normal water, liquid nitrogen, and air-cooling. The relation between melt solidification rate and structural and thermoelectric transport properties of Bi2Te3 alloy were studied. The pure phase of Bi2Te3 is confirmed by structural characterizations: XRD and Raman. This study showed that the melt solidification rate has a consequential role in modulating the microstructure and thermoelectric transport properties. The moderate cooling rate of melt solidification showed the highest zT of similar to 0.06 at 423 K due to higher defect density. This study attempts to explain the different zT values observed for different quenching mediums