Abstract
M.Tech. (Chemistry)
The dissertation reports on the preparation, characterization and applications of quaternized adsorbents for the adsorption and subsequent reduction of Cr(VI) and cyanide ions (CN-). The quaternized materials were based on poly(vinyl pyridine) and its polyacrylic acid copolymer deposited on activated carbon. The quaternization of the PVP-based adsorbents was done in order to modulate the charge on the nitrogen atom of the pyridine ring for better selectivity towards the anionic pollutants (Cr(VI) and CN- ions). Further modulation of the cationic centre was achieved through copolymerization of vinylpyridine and acrylic acid via radical polymerization to form 4PVP-co-PAA. On the other hand, these adsorbents were incorporated with TiO2 for the photo-reduction and photo-oxidation of Cr(VI) and CN- respectively. The main findings of the research are outlined below.
All the prepared materials were characterized using a variety of techniques. Characterization using FTIR confirmed the formation of the polymer adsorbents and their subsequent quaternization as indicated by the appearance of new bands at certain specific wavenumbers. The XRD and Raman spectroscopy showed the presence of both TiO2 and activated carbon, which proves the successful incorporation of the photocatalyst in the adsorbent materials. Microscopy (SEM and TEM) studies showed that TiO2 particles were uniformly dispersed when incorporated in activated carbon and polymeric materials.
The adsorbents were tested for the removal of Cr(VI) and its photo-reduction. It was found that the use of quaternized adsorbents for adsorption of Cr(VI) was optimal at pH 3 with up to 93%, e.g. removal of 93% and 90% were observed for AC/QP4VP (activated carbon supported quaternized poly-4-vinylpyridine) and AC/QP4VP-co-PAA (activated carbon supported quaternized polyvinylpyridine-co-polyacrylicacid) respectively. The adsorption was due to the positively charged nitrogen, which interacted with the negatively charged HCrO4- ion through electrostatic attraction. Using photo-reduction, the removal of Cr(VI) in solution was increased to 98% within 180 minutes. The chemistry between the 4-VP with Cr(VI) ions was interrogated using the UV-Vis spectroscopy. The coordination of the chromate ions to the...