Studies on TiO(2)/ZnO photocatalysed degradation of lignin.

The photocatalytic degradation of lignin obtained from wheat straw kraft digestion has been investigated by using TiO(2) and ZnO semiconductors. ZnO has been found to be a better photocatalyst than TiO(2). The different variables studied, include catalyst dose, solution pH, oxidant concentration and initial concentration of the substrate. The degradation of lignin was favorable at pH 11. Optimum values of catalyst dose and oxidant concentration were found to be 1g/l and 12.2 x 10(-6) M, respectively. The degradation of the organic compound was also evaluated as COD removal and increase in the COD removal was observed with increase in degradation rate. An attempt has also been made to explore the applicability of ZnO in immobilized mode for the degradation of lignin under solar light for industrial scale application. Further the comparative evaluation of ZnO in slurry/immobilized mode has been carried out.

Studies on photodegradation of two commercial dyes in aqueous phase using different photocatalysts.

The present study involves the photocatalytic degradation of Methyl Orange (MO) and Rhodamine 6G (R6G), employing heterogeneous photocatalytic process. Photocatalytic activity of various semiconductors such as titanium dioxide (TiO(2)), zinc oxide (ZnO), stannic oxide (SnO(2)), zinc sulphide (ZnS) and cadmium sulphide (CdS) has been investigated. An attempt has been made to study the effect of process parameters viz., amount of catalyst, concentration of dye and pH on photocatalytic degradation of MO and R6G. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with UV and solar light. The rate of decolorization was estimated from residual concentration spectrophotometrically. Similar experiments were carried out by varying pH (2-10), amount of catalyst (0.25-2.0g/l) and initial concentration of dye (5-200mg/l). The experimental results indicated that the maximum decolorization (more than 90%) of dyes occurred with ZnO catalyst and at basic pH and the maximum adsorption of MO was noticed at pH 4 and of R6G at pH 10. The percentage reduction of MO and R6G was estimated under UV/solar system and it was found that COD reduction takes place at a faster rate under solar light as compared to UV light. In case of R6G, highest decolorizing efficiency was achieved with lower dose of catalyst (0.5g/l) than MO (1g/l) under similar conditions. The performance of photocatalytic system employing ZnO/solar light was observed to be better than ZnO/UV system.

Role of water-soluble matrix fraction, extracted from the nacre of Pinctada maxima, in the regulation of cell activity in abalone mantle cell culture (Haliotis tuberculata).

In mollusks, the mantle is responsible for the secretion of an organic matrix that mineralizes to form the shell. A model of mantle cell culture has been established from the nacreous gastropod Haliotis tuberculata. First, viability of cells, quantified by the MTT (3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide) reduction assay, was monitored in order to determine a cell density and a time-culturing period in order to investigate biomineralization processes in vitro. During the first 11 days of culture, an increase of MTT response demonstrated an activation of cultured cells mitochondrial activity as confirmed by the total protein content assay. The effect of a water-soluble extract from the organic matrix of Pinctada maxima (WSM) was tested on this cell culture system for 11 days-period exposure. WSM reduced the global viability of mantle cells in a dose-dependent way which corresponded to a cell death. Alkaline phosphatase activity normalized to total protein content increased in the presence of WSM. This increase may be due to an activation of cells and a selection of one (or a few) cell type(s). Further investigations will help us to determine this selectivity issue.