Inderpreet Singh Grover

Priority PAHs in orthodox black tea during manufacturing process

Orthodox black tea is obtained from fresh leaves followed by withering, rolling, fermentation and drying. The presence of 16 priority polycyclic aromatic hydrocarbons (PAHs) was studied in fresh leaves and at various stages of manufacturing. Benzo(a)pyrene (2A: probable human carcinogen) was found in dried tea leaves only whereas, naphthalene (2B: probable human carcinogen) was present during all the stages of manufacturing. Dry tea leaves showed higher content of total 16 PAHs (∑PAHs) about 3 and 211 times than present in withered and dried leaves, respectively. Chrysene, benzo[g,h,i]perylene, indendo[1,2,3-c,d]pyrene, dibenzo[a,h]pyrene and benzo[a]antracene were not found during manufacturing stages of tea.

Stable anatase TiO2 formed by calcination of rice-like titania nanorod at 800 °C exhibits high photocatalytic activity

This paper demonstrates the complete retention (>98%) of anatase TiO2 crystalline phase after high temperature (800 °C) thermal treatment of rice-like TiO2 nanorods (length = 81–134 nm, diameter = 8–13 nm) relative to 100% conversion of the rutile phase after calcination of P25-TiO2 under similar conditions. The existence of the anatase phase at >800 °C was further confirmed by the presence of characteristic vibrational bands (144, 395, 513 and 639 cm−1) in the Raman spectra. It was found that TiO2 nanorods undergo fragmentation to a highly crystalline irregular morphology (60–70 nm), nanopolygons (91–110 nm) and smaller rod-shaped particles (length = 60–110 nm and diameter = 7–12 nm), accompanied by a gradual increase in their crystallite size (from 16 to 40 nm) and decrease in surface area (from 79 to 31 m2 g−1) with increased calcination temperatures from 200 to 900 °C. This TiO2 anatase phase displayed enhanced photocatalytic oxidation rate (∼2–11 times higher than rutile TiO2) for methyl parathion (a neurotoxic pesticide) degradation to various intermediate products and ultimately to CO2, whereas 1.0 wt% Au–TiO2 significantly improved the photoactivity.

Influence of thermal treatment and Au-loading on the growth of versatile crystal phase composition and photocatalytic activity of sodium titanate nanotubes

A coalescence influence of Au-loading followed by calcination at 800 °C led to a notable change in crystal-structure, morphology, phase composition and photocatalytic activity of titanate-nanostructures. After calcination at 800 °C, bare sodium titanate nanotubes (TNT) having a BET surface area (SBET) of 176 m2 g−1 is transformed into sodium titanate nanorods of SBET = 21 m2 g−1, whereas calcination of Au-loaded (Au+3, Au0 and Au-nanoparticle (AuNP)) TNT at 800 °C led to a variety of fragmented particles having different crystal structures, SBET (21–39 m2 g−1), shape and sizes (50–75 nm), attributed to strain induced thermal decomposition of TNT after Au-loading, and the oxidation state of Au is determined by XPS analysis. The comparative photocatalytic activity of these as-prepared catalysts to that of P25-TiO2 under UV-light were evaluated for the photooxidation of the insecticide imidacloprid which gradually degraded to various intermediate photoproducts and finally decomposed to CO2. The degradation of imidacloprid follows pseudo-first order kinetics, where 0.5 wt% Au0-deposited-TNT after calcination exhibits the highest photocatalytic activity (rate constant k = 8.9 × 10−3 min−1), which is comparatively explained on the basis of their crystal phase, surface-area, morphology and the relaxation time of photoexcited electron–hole pairs, as measured by time resolved spectroscopy.

Photodegradation of imidacloprid insecticide by Ag-deposited titanate nanotubes: a study of intermediates and their reaction pathways.

The present work demonstrates the influence of Ag-loading (0.2-1.0 wt %) onto sodium titanate nanotubes (TNT) for complete photomineralization of the neurotoxic imidacloprid (IMI) insecticide under UV light illumination. It has been observed that degradation of IMI follows pseudo-first-order kinetics, where 0.5 wt % Ag-loaded TNT exhibited highest apparent rate constant (2.2 × 10(-2) min(-1)) and corresponding least half-life (t1/2) of 31 min for IMI relative to bare P25-TiO2 (3.4 × 10(-3) min(-1), t1/2 = 230 min). The mineralization of IMI intermediates to CO2 during its photooxidation has been described by time course GC-MS and GC analysis and has been correlated with the kinetic analysis. The investigation for the role and quantitative estimation of the fate of heteroatoms (N, O, and Cl) present in IMI revealed an increase in the amount of nitrate, nitrite, and chloride ions with time during its photooxidation. On the basis of these results a mechanistic pathway for photomineralization of IMI is proposed.

Influence of Thermal Treatment and Fe-Loading on Morphology, Crystal Structure, and Photocatalytic Activity of Sodium Titanate Nanotubes

An understanding of collective influence of Fe-loading and calcination on changes in the crystal structure, morphology, phase composition, and photocatalytic activity of titanate-nanostructures is investigated here. Bare sodium-titanate nanotubes (TNT) having a BET-surface-area (SBET) of 176 m2 g−1 were transformed to sodium-titanate nanorods (TNT(S)) of SBET = 21 m2 g−1 when calcined at 800°C. Whereas, calcination of Fe-loaded-TNT at 800°C led to a variety of fragmented particles having different crystal structures, SBET (21–39 m2 g−1), shape, and sizes (50–70 nm) attributed to the strain induced thermal-decomposition of TNT after Fe-loading. The comparative photocatalytic activity of as-prepared catalysts under UV-light irradiation was evaluated by photooxidation of naphthalene to CO2, with the identification of its photoproduced intermediates by GC-MS analysis. These results are well explained in correlation with the surface area, size, and shape of as-prepared catalysts.