Studies on the adsorption and kinetics of photodegradation of pharmaceutical compound, indomethacin using novel photocatalytic adsorbents (IPCAs)

Integrated photocatalytic adsorbents (IPCAs) based on TiO2-activated carbon synthesized by an ultrasonic impregnation technique have been used for the photodegradation of indomethacin (IND) in aqueous solutions. The IPCAs in dark adsorption studies had high affinity toward IND with the amount adsorbed proportional to the TiO2 loading. The adsorption capacity increased from 0.597 to 0.657 mmol/g with increase in TiO2 content from 0.5 to 10% in IPCAs. Three adsorption models, Langmuir, Freundlich and Sips, were used to describe the adsorption isotherms while the adsorption kinetic data were fitted to pseudofirst order and pseudosecond order models. The adsorption isotherm study showed that the adsorption followed both Sips and Langmuir models with high regression coefficients (R-2) and low standard error (SE) and sum of residual square error (SSE) values. The adsorption kinetic data are well represented by pseudosecond order model. The kinetics of photocatalytic degradation under UV were found to follow a Langrnuir-Hinshelwood model for the various IPCAs. The adsorption rate constant (K-ads) was considerably higher than the photocatalytic rate constant (k(L-H)), suggesting that the photocatalysis of IND is the rate-determining step during the adsorption/photocatalysis process. The proportion of TiO2 played a significant role upon the photoefficiency of the IPCAs. The photocatalytic efficiency of the 10% TiO2 IPCA remained greater than 70% after five cycles of use.