Sahab Dass

A study on the photoelectrochemical properties of copper oxide thin films

Abstract The photoelectrochemical properties of Copper Oxide thin film, prepared by spray pyrolysis on conducting glass (SnO 2 : F-coated glass) substrate were investigated as a function of film deposition temperature and spray time. The variation in the deposition temperature affected the film morphology. The film deposited at substrate temperature 350°C exhibited better photoresponse than the films prepared at 300°C and 400°C. Creation of large number of dislocations and kink sites at 300°C and 400°C, which act as a recombination center for photogenerated electron has been held as a possible cause for poor photoresponse observed. The rise in photocurrent density with increase in spray time has been attributed to the increase in film thickness, which is probably allowing the film to absorb photons more efficiently. X-ray diffraction patterns of films confirm the presence of cupric oxide (CuO) phase. The films of CuO were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure, on account of incomplete oxidation taking place at a relatively low temperatures (300–400°C).

Deflouridation of water using amended clay

Excessive presence of fluoride (F) in potable water continues to be a serious public health problem in many parts of the world. Hence, the need for a cost effective, simple and user-friendly method for water defluoridation is being felt in such areas. Clay vessels are commonly used in rural parts of India and other developing countries, not only for storing water, but also to get cold potable water during summers. The present study investigates the role of vessels made from locally derived sample of silty clay (C) in water defluoridation. Besides, F sorption by C and its chemically amended forms were also studied to investigate improvement opportunities of clay vessels with regard to their application in water defluoridation. The study revealed C to be a potent F binder and amending it with Al (activated Al2O3), Fe (FeCl3) and/or Ca (CaCO3) significantly improved its F sorption capacity. F sorption by C amended with Al, Fe or Ca, decreased in the same order. C amended simultaneously with 50 mg/g each of Al, Fe and Ca proved to be the most effective F sorbent at pH≈6. F sorption by amended C followed a rapid kinetics with considerable F being removed within 5 min of shaking. The pilot study employing clay vessels to achieve defluoridation of water exhibited encouraging results suggesting the viability of using chemically amended clay vessels for water defluoridation.

Studies on uptake of trivalent and hexavalent chromium by maize (Zea mays)

Pot culture experiments were carried out to study the uptake and translocation of chromium from irrigation water when supplied in its trivalent and hexavalent states to maize plants grown in soil and sand culture. The uptake of chromium was observed to increase with increase in the concentration for both oxidation states of chromium. For the root, the observed order of uptake was CrIII sand > CrVI sand > CrIII soil > CrVI soil, whereas in the lower shoot, upper shoot and fruit the order was CrVI sand > CrVI soil > CrIII sand > CrIII soil. Significantly high uptake of chromium by roots in the sand culture (CrIII treatment) is attributed to the effect of root exudates and degradation products on the mobilization of CrIII. In aerial parts of the plants a higher uptake was observed when the initial supply was CrVI. The trends observed are explained on the basis of the redox behaviour of chromium.

Study of mercury-selenium (HgSe) interactions and their impact on Hg uptake by the radish (Raphanus sativus) plant

Pot culture experiments were conducted to study the effects of selenite and selenate treatment (0.5-6.0 microg/ml) on the uptake and translocation of root-absorbed mercury (Hg) in radish plants irrigated with 2 and 5 microg/ml Hg in sand and soil culture. Statistically significant reductions in mercury uptake with increasing concentrations of selenium (Se) were observed. Both forms of selenium (selenite and selenate) were equally effective in reducing the mercury burden of the plant. The observed reduction in plant uptake of mercury is explained by the formation of an HgSe insoluble complex in the soil-root environment. No significant difference (P > 0.05) in dry matter yields with the various selenium treatments was found, suggesting that no selenium toxicity or salt injury occurred in the plants.

A study on the uptake of trivalent and hexavalent chromium by paddy (Oryza sativa) : possible chemical modifications in rhizosphere

The uptake and translocation of chromium by paddy (Oryza sativa L. Arbario) was studied using radiotracers. Chromium was supplied as Cr III and Cr VI through irrigation water and plants were grown in sand and soil culture. The uptake of chromium for both the oxidation states and culture types was found to increase more or less linearly with the increase in chromium concentration though with different slopes. The rate of increase of the uptake when compared to the increase in feed concentration indicates that the uptake by roots is mediated possibly through a passive mechanism. For a given concentration of feed, values of chromium in μgg−1 dry matter in shoot and grain did not vary significantly either for different oxidation states of feed chromium or culture type. The order of uptake for paddy shows a considerably different pattern when compared to onion, maize and groundnut. This has been qualitatively explained on the basis of the different chemistry of chromium in the rhizosphere of paddy. The amount of chromium translocated to grain was also considerably less compared to the other three crops.

Groundwater Quality Assessment of Tehsil Kheragarh, Agra (India) with Special Reference to Fluoride

Fluoride concentration and other parameters in groundwater from 261 villages in Tehsil Kheragarh of District Agra were assessed and attempts were made to observe the relationship between fluoride and other water quality parameters. Of 658 groundwater samples (collected from separate sources) analysed for fluoride, 27% were in the range of 0–1.0 mg/L, 25% in 1.0–1.5 mg/L, 32% in1.5–3.0 mg/L and 16% above 3.0 mg/L. The highest fluoride concentration recorded was 12.80 mg/L. Significant correlation of fluoride with pH, alkalinity, Na, SiO2 and PO4 were observed. Factor analysis was also attempted in order to identify the contributing sources.

Improved photoelectrochemical response of haematite by high energy Ag9+ ions irradiation

Haematite (?-Fe2O3) thin films deposited on a conducting glass substrate were irradiated with 120?MeV Ag9+ ions with increasing ion fluences. Their structural evolution was determined by x-ray diffraction and Raman spectroscopy. The irradiation of the samples of ?-Fe2O3 was found to be effective in improving its photoelectrochemical response. The film irradiated at a fluence of 1 ? 1013?ions?cm?2 showed a significantly higher photocurrent density than the unirradiated ?-Fe2O3. This effect is correlated with the transition from the ?-Fe2O3 to the Fe3O4 phase and the reduction in grain size that were observed on irradiation with Ag9+ ions. The measured flatband potential and donor density of the sample were also maximum at a fluence of 1 ? 1013?ions?cm?2.

A Study on Fluoride Sorption by Montmorillonite and Kaolinite

Fluoride (F) sorption by acidified montmorillonite, montmorillonite and kaolinite has been investigated as a function of period of agitation, pH, initial fluoride concentration and clay amount. In case of montmorillonite and kaolinite, F sorption is insignificant at pH > 7, while it is maximum at pH 4. Enhanced F sorption by acidified montmorillonite is noted at pH < 10, maximum being at pH 6. Significant concentration of Al3+,Fe3+ and silica are released from acidified montmorillonite lattice (pH ≈ 2; 1:10 w/v), which decreased considerably owing to the formation of hydroxy (Al and Fe) silicates on subsequent base addition. Soluble fluoro-complexes at pH ≈ 2 and chemical interaction of F with hydroxy (Al and Fe) silicates at pH > 4, are potent sink for F in case of acidified montmorillonite. Soluble fluoro-complexes are also detected in case of montmorillonite and kaolinite at pH ≈ 4. Saturation indices (SIs) for acidified montmorillonite, over the studied pH range (2–10) has also been computed.

Studies on aluminium leaching from cookware in tea and coffee and estimation of aluminium content in toothpaste, baking powder and paan masala.

Studies were conducted in order to assess the level of aluminium (Al) in samples of Indian tea, coffee, toothpaste, paan masala (mouth freshener) and baking powder. Leaching of Al from cookware while preparing tea and coffee was also studied. Experiments were also conducted to study the sequential leaching of Al from cookware by preparing tea and coffee in the presence of standard size Al sheets (coupons). A small amount of Al was found to have leached from coupons during preparation of tea. Tea leaves, were found to be a rich source of Al and a maximum of 2.2% Al is extracted in tea infusions. Coffee powder on the other hand was not found to be a rich source of Al. Baking powder was found to be a rich source of Al and 1 kg of cake prepared with 1-3 teaspoon of baking powder may contain 2-12.7 mg of Al in each serving (25 g). Toothpaste also contains a significant quantity of Al, more so, when packed in Al tubes. Ingestion pattern of Al from these items by humans is also discussed.

Plant uptake of fluoride in irrigation water by ladyfinger (Abelmorchus esculentus)

Because of suggestions that food is a rich source of fluoride to humans and the absence of permissible and upper limits of fluoride for irrigation water, plant uptake studies were conducted using fluoride-rich irrigation water. Ladyfinger was grown in sand and soil cultures for 18 wk and the accumulation of fluoride in various plant parts was studied. The potential for ingestion of fluoride by humans through this route was also considered. The percentage uptake was greater in sand-cultured plants than in soil-cultured plants. The root accumulates most of the fluoride supplied through irrigation water and the fruit accumulates the least. Up to 120 mg fluoride/litre of irrigation water did not harm the plants. The ingestion of fluoride by humans from plants irrigated with water containing 10 mg fluoride/litre would be 0.20 mg per 100 g ladyfinger.