Rohit Shrivastav

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.

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.

Enhanced Photoelectrochemical Response of Zn-Dotted Hematite

Photoelectrochemical response of thin films of α-Fe2O3, Zn doped α-Fe2O3, and Zn dots deposited on doped α-Fe2O3 prepared by spray pyrolysis has been studied. Samples of Zn dots were prepared using thermal evaporation method by evaporating Zn through a mesh having pore diameter of 0.7 mm. The presence of Zn-dotted islands on doped α-Fe2O3 surface exhibited significantly large photocurrent density as compared to other samples. An optimum thickness of Zn dots ∼230 A is found to give enhanced photoresponse. The observed results are analyzed with the help of estimated values of resistivity, band gap, flatband potential, and donor density.

Studies on leaching of Cr and Ni from stainless steel utensils in certain acids and in some Indian drinks

Leachates of Cr and Ni from stainless steel utensils viz., frying pans, bowls and tumblers, have been investigated, by exposing the utensils to decinormal solutions of citric, tartaric and lactic acids and to some common Indian drinks. A comparison of observed results indicate that the complexation of metal ions with organic acid anions is most vital and metal leaching is largely a function of the availability of free anions. The intake of Cr and Ni by human beings has also been calculated.

Morphological, optical and photoelectrochemical properties of Fe2O3–GNP composite thin films

The ever increasing demand for energy and increased environmental pollution has led to the search for new and renewable energy sources. Harnessing solar energy for the production of clean hydrogen is a very attractive method. This paper focuses on the synthesis of iron oxide photoanodes modified with graphene nanoplates (Fe2O3–GNP) as conducting scaffolds for the efficient generation of hydrogen in a photoelectrochemical (PEC) cell using solar energy. These GNP modified α-Fe2O3 samples were found to exhibit an enhanced photoresponse, which has been mainly attributed to: (i) efficient charge transfer at the semiconductor/electrolyte junction, and (ii) a red shift in the UV-vis spectra of the composite Fe2O3–GNP thin films with respect to the pristine α-Fe2O3 sample. The highest photocurrent density of 2.5 mA cm−2 at 0.75 V/SCE was observed for the 0.2 wt% GNP modified α-Fe2O3 sample, with a solar to hydrogen conversion efficiency of 1.8%. The flat band potential (−0.83 V/SCE) and donor density (1.09 × 1021 cm−3) were found to be maximized for the same sample. In virtue of their superior photoelectrochemical performance, GNP modified α-Fe2O3 thin films have substantial potential for use in PEC water splitting reactions.