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A photo-catalytic composite material incorporating rice husk ash (RHA) and TiO2 (RHA:TiO2 = 75:25 and 50:50) has been developed and used to investigate the photodegradation of the well-known dye pollutant, methylene blue (MB). Photodegradation was monitored in the dark and under illumination using a halogen lamp as well as sun light to facilitate photodegradation. Both the dark reaction and photo- mineralization processes were evaluated in terms of kinetic study which revealed the validation of first-order kinetics. A parallel measurement of chemical oxygen demand (COD) was also performed for a better understanding of the degradation process. The higher degradation rate in the sun light offers an easy-to-use and environment friendly approach for the treatment of dye stuffs. However, the overall phototdegradation mechanism involved the participation of both the anodic (h+ consumption) and cathodic (e- consumption) processes which were responsible for the degradation of MB and consumption of dissolved oxygen respectively. Key words: Photo-degradation; Composite plate; Rice husk ash, Methylene blue; Adsorption. DOI: http://dx.doi.org/10.3329/bjsir.v46i1.8100 Bangladesh J. Sci. Ind. Res. 46(1), 17-26, 2011

Organic Polymer carboxymethyl cellulose (CMC) (0.25, 0.50 and 1.5% solution) was incorporated in Ordinary Portland Cement (OPC) and its effect on compressive strength, setting time, porosity, corrosive resistance, density and water absorbance have been studied. Organic polymer retards the setting time and a small increase in compressive strength was observed after 90 days for 0.5% CMC. Addition of polymer has been found to be effective in improving the acid resistance of OPC. Interaction of CMC with OPC causes decrease in water absorption, porosity and chemically bound water. X-ray diffraction of OPC-CMC pastes after 4 months and 1 year display some new peaks as well as disappearance of few peaks showing interaction of CMC with hydrated cementitious pastes. Examination of microstructure reveals that fibre types of matters were formed in hardened cement paste.

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Various physico-chemical properties such as particle size distribution, specific gravity, specific surface area, chemical composition, solubility of Fly Ash (FA) in NaOH and pozzolanic activity of fly ash towards lime have been investigated. Chemical analysis of FAreveals that the FA used in this present investigation belongs to class F type of fly ash. XRD investigation of FA depicts the presence of crystalline mullite and quartz phases. Pozzolanic activity of fly ash was investigated by pH and electrical conductivity measurement, by determining the amount of calcium reacted with fly ash and by the amount of Insoluble Residue (IR) observed in FA-lime paste. XRD investigation of ash-lime paste identified the Calcium Silicate Hydrate (C-S-H) phase. The results obtained from these studies suggested that fly ash possesses pozzolanic activity. Key words: Pozzolanic activity; Fly ash (FA); Rice husk ash; Ordinary Portland Cement (OPC); Insoluble residue (IR); Calcium hydroxide (CH); Calcium silicate hydrate (C-S-H); Kinetics; XRD. DOI: 10.3329/bjsir.v45i4.7326 Bangladesh J. Sci. Ind. Res. 45(4), 303-308, 2010