M. Kamruddin

Plasmon-mediated, highly enhanced photocatalytic degradation of industrial textile dyes using hybrid ZnO@Ag core–shell nanorods

Hybrid ZnO@Ag core–shell heterojunction nanorods were synthesized using a novel, facile two-step process based on hydrothermal and seed mediated growth techniques. The material was characterized by UV-visible spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), room temperature photoluminescence spectroscopy (RTPL), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The hybrid ZnO@Ag core–shell nanorods were comprised of one-dimensional (1D) ZnO nanorods serving as a core material, over which surface-doped Ag nanoclusters (∼2.5 nm) were anchored as a heterogeneous shell. The presence of oxygen vacancies and Zn interstitials were confirmed by RTPL and Raman spectroscopic analysis. The photocatalytic activity of the hybrid ZnO@Ag core–shell nanorods was studied in comparison to bare ZnO nanorods using standard R6G dye and industrial textile dyes such as Congo red and Amido black 10B under UV and visible light (solar) irradiations. Moreover, the material was tested for real time industrial textile effluents under ambient conditions and was found to be highly efficient. The enhanced photocatalytic property observed for ZnO@Ag hybrid core–shell nanorods is attributed to a phenomenal increase in oxygen related defects in the core that generate photo-induced charge carriers and the presence of plasmonic Ag nanoclusters in the shell, which act as a sink for the photo-induced charge carriers.

Nanocrystalline and metastable phase formation in vacuum thermal decomposition of calcium carbonate

Abstract Well characterised, polycrystalline powders of commercially procured CaCO 3 were thermally decomposed in the vacuum as well as in the flowing gas atmosphere for the purpose of studying solid state transformations. The characterisation of the end product CaO, obtained from the thermal decomposition, revealed contrasting features in the powder X-ray diffractograms. While the flowing gas method, conducted inside a thermogravimetric analyser (TGA), indicated formation of stable microcrystalline calcia, the decomposition under dynamic vacuum revealed formation of metastable-nanocrystalline calcia. The latter study was carried out in an evolved gas analysis-mass spectrometry (EGA-MS) facility. Experiments were also conducted inside the high temperature XRD (HTXRD) machine. The paper attempts to bring out possible mechanisms responsible for formation of these end products with such glaring structural contrast. Non-equilibrium conditions prevalent under dynamic vacuum condition as well as misfit strain energy available from CaCO 3 /CaO interface are presumed to be the reason behind such metastable transformations. Kinetic analysis of the transformation revealed prevalence of nucleation and growth phenomena. Corresponding Arrhenius factors were also calculated.

Thermogravimetry-evolved gas analysis-mass spectrometry system for materials research

Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA-MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA-EGA-MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for (i) temperature programmed decomposition (TPD), (ii) synthesis of nanocrystalline materials, (iii) gas-solid interactions and (iv) analysis of gas mixtures. The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA-MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas-solid interactions are also described.

Temperature programmed decomposition of uranyl nitrate hexahydrate

Abstract Temperature programmed decomposition (TPD) of uranyl nitrate hexahydrate has been studied using evolved gas analysis mass spectrometry (EGA-MS) in the temperature range 300–1400 K. Thermogravimetric (TGA) investigations were performed in the temperature range 300–1100 K. An attempt has been made to resolve the complexity of decomposition behaviour through suitable comparison of TGA and EGA-MS data. Kinetic control regimes for various decomposition stages could be deduced from EGA-MS data. The corresponding activation energies and frequency factors were also evaluated. Kinetics based on random nucleation and diffusion was found to be rate controlling. The residue left over after each decomposition stage was analysed by XRD and XPS to determine structure and composition. The ultimate product was found to be a mixture of UO 3 H 1.17 and U 3 O 8 : the former being a topotactic hydrogen spill over compound of UO 3 . Complete conversion of this residue to U 3 O 8 was noticed during ion beam exposure of the residue which was performed in the course of XPS investigations.

Temperature programmed decomposition of thorium oxalate hexahydrate

Temperature programmed decomposition (TPD) of thorium oxalate hexahydrate (TOH) was studied by evolved gas analysis-mass spectrometry (EGA-MS), thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). The microcrystalline solid exhibited sequential dehydration. The anhydrous compound yielded amorphous phase Th(CO 3 ) 2 upon CO release arising out of the bond cleavage. The Th(CO 3 ) 2 phase transformed to nano-crystalline thoria upon decomposition through an oxycarbonate intermediate. The mechanism underlying various conversion stages exhibited control by random nucleation, diffusion and phase boundary interface motion. From the fractional extent of decomposition data, Arrhenius factors like activation energy and pre-exponential factors were evaluated. Based on these studies, a chemical pathway is proposed for the entire decomposition process.

Mass spectrometry based evolved gas analysis system for thermal decomposition studies

An experimental facility for evolved gas analysis by mass spectrometry (EGA-MS) has been built in-house and extensively used to study the temperature programmed decomposition (TPD) of a number of inorganic solids. Fractional extent of reactionα acquired from real time multiple ion detection trend analysis mass spectra of gases released from thermally impressed specimen has been used to obtain functional transformf(α) of non-isothermal solid state kinetic rate expressions. The corresponding model integral functionsg(α) based on mechanisms like random nucleation, diffusion and interface motion have been used to establish kinetics control regimes for specific decomposition sequences. From ln[g(α)/T2] vs 1/T plots Arrhenius parameters like activation energy and pre-exponential factor could be determined. Signature of the rate controlling mechanism governing the gas release behaviour was found in the crystallographic transformation brought about by the temperature programme. This paper describes the scope and capabilities of our EGA-MS facility with typical results on temperature programmed decomposition of CuSO4·5H2O and AlNH4(SO4)2·12H2O.

Evolved Gas Analysis by Mass Spectrometry

Abstract A quadrupole mass spectrometer based evolved gas analyser has been built in our laboratory with necessary UHV hardware, computer interface and software for conducting real-time multiple ion detection mass spectrometry over a wide dynamic pressure regime. Thermal decomposition behaviour of model salts CaCO3, CuSO4.5H2O, Pb(NO3)2 and AlNH4(SO4)2.12H2O has been studied to standardise this system. Reaction parameters for the dehydration and decomposition of CuSO4 5H2O are computed and found to be in agreement with the reported literature values.

Conductive atomic force microscopy studies on dielectric breakdown behavior of ultrathin Al2O3 films

Ultrathin films of Al2O3 prepared by atomic layer deposition have been subjected to local electrical stress analysis using conducting atomic force microscopy. The loss of local dielectric integrity through current leakage in these extremely thin films is studied using scanning spreading resistance imaging. Our experimental results shows that repeated voltage stress progressively increases number of leakage spots. While the density of leakage spots increase with higher applied bias for thin oxide films, initial increase and reduction in leakage spots are observed for thick films.

Non-isothermal kinetics of decomposition of AlNH4(SO4)2.12H2O by EGA-MS

Abstract Real-time multiple-ion detection trend analysis mass spectrometry has been employed to study the temperature-programmed decomposition of AlNH 4 (SO 4 ) 2 · 12H 2 O in the temperature range 300–1200 K. Significant correlations are established with certain non-isothermal solid state kinetic rate expressions through the use of fraction release plots obtained from Evolved Gas Analysis Mass Spectra (EGA-MS). The EGA mass spectra clearly resolve the dehydration stage and various other stages associated with the thermal decomposition. The dehydration step is concomitant with stage I of a three-stage ammonia release followed by the final decomposition of Al 2 (SO 4 ) 3 . These stages are found to comply with models based on random nucleation and diffusion approaches. A change in rate-governing mechanism was noticed with increase in the heating rate for the dehydration step. Relevant Arrhenius parameters such as the activation energy and pre-exponential factor were determined for all the decomposition stages. The ultimate product resulting from the decomposition was confirmed as γ-alumina by X-ray diffraction studies.

Real time mass spectrometric study of temperature programmed decomposition of CuSO4·5H2O

A facility based on real time multiple ion detection trend analysis mass spectrometry has been set up in our laboratory for studying thermal decomposition behaviour of inorganic solids. The system has been used for studying decomposition of CuSO4· 5H2O. Non-isothermal kinetic rate expressions based on random nucleation and 3-d phase boundary migration (for dehydration stage), 3-d diffusion and 3-d phase boundary migration (for decomposition stage) were found to have significant correlations with Evolved Gas Analysis (EGA) data. Brief description of the experimental facility along with physical explanations behind compliance of EGA data to above models are discussed.