Papers by Author: Nageswara Rao Neti

Abstract: Carbonate is a common pollutant in water and wastewater. A study to understand its influence on the photodegradation rates is necessary especially when TiO₂/UV technique is emerging as an advanced technology for pollution abatement. In the present investigation, we report surface modification of titanium dioxide using carbonate ions, characterization of carbonate modified titanium dioxide (CMT) and photocatalytic application of carbonate modified TiO₂. Titanium dioxide from two different sources namely BDH, Mumbai and Degussa AG, Germany was used as photocatalyst. The CMT catalysts were characterized using potentiometry, FT-IR and XPS. Approximately, 18.9 mg CO₃/g CMT(BDH) and 8.13 mg CO₃/g CMT(Degussa) was found loaded as determined by potentiometry. The C 1s and O 1s binding energies observed at 289.2 and 531.3 eV, respectively were attributed to surface carbonate species. The adsorption and photodegradation of Acid Blue I dye examined using neat TiO₂ as well as CMT catalysts revealed that carbonate inhibits catalytic activity for color and Chemical Oxygen Demand (COD) removal. The photo degradation rate constant (k, s^-1) decreases gradually with increasing concentration of carbonate. Thus, in the absence of carbonate k_dye is 5.45 × 10^-4 s^-1 (R² = 0.97) and k_COD is 3.50 × 10^-5 s^-1 (R² = 0.97). At 100 mg/L CO₃^2-, k_dye is 0.16 × 10^-4 s^-1 (R² = 0.96) and k_COD is 2.66 × 10^-5 s^-1 (R² = 0.98). In addition, the carbonate spiking studies revealed the onset of inhibition soon after the addition of carbonate into reacting suspensions of TiO₂. The results suggest that carbonate inhibits catalytic activity through formation of strong surface complex under suitable pH by displacing OH₂⁺ and OH groups from TiO₂ surface. This results not only in fewer (OH)_surface groups available for h⁺ trapping for oxidation into OH radicals but also in non-availability of adsorption sites for the dye molecules. A pretreatment to remove carbonate from (waste) water appears necessary prior to application of TiO₂/UV technique

Abstract: Development of photocatalysts and photoreactors for treatment of industrial effluents is considered important to harness solar energy for environmental clean up. The photocatalytic method of decolorization of textile dyes utilizes UV component of sunlight (3-5%) and the only solid phase (TiO₂ catalyst) can be recycled on a technical scale. Moreover, the method does not produce any sludge unlike adsorption and coagulation methods. These attributes of the photocatalytic method are attractive for possible application in industry. Our group is presently working on pilot scale photoreactors and exploring feasibility of industrial application of this technique. We have developed a few TiO₂ based photocatalysts (P-25 TiO₂, ZnO, TiO₂ (bulk) and rare earth metal (In₂O₃, Nd₂O₃, Yb₂O₃ and Sm₂O₃) doped TiO₂), photo catalyst bearing supports (e.g., acrylic sheet) and photoreactors (annular immersion well type, falling film type and shallow slurry photoreactors) for use with UV & sunlight. We have carried out a few tests with Solar Slurry Photoreactor (SSPR) in field using actual textile wastewater with encouraging results. The SSPR developed under this study was capable of decolorizing textile wastewater under specified conditions approximately with a treatment rate of 9.0 Lh^-1. The reactor area exposed to sunlight was approximately 1 m². Thus, a reactor having 18-20 m² exposed area would treat about 1.0 m³ textile wastewater at a rate approximately equal to180 Lh^-1. The present data suggest that it may be possible to apply this technique initially for the color treatment of textile wastewater from small dyeing operations. However, the details of techno-economic feasibility need to be assessed beforehand. The proposed book chapter would present details of all the above-mentioned efforts. It would be targeted to bring out inadequacies associated with the photocatalytic technology for wastewater treatment.