The photocatalytic degradation of various Rhodamine dyes with different functional groups, namely, Rhodamine B (C28H31ClN 2O3), Rhodamine 6G (C28H31ClN 2O3), Rhodamine Blue (C28H32N 2O3), and Rhodamine 6G perchlorate (C28H 31ClN2O7) was investigated under UV irradiation. The kinetics of degradation was determined in the presence of two catalysts: commercial Degussa P-25 and TiO2 synthesized by the combustion solution method. The effect of organic solvents (ethanol and acetonitrile) and metal ions (Cu2+, Fe3+, Zn2+, and Al3+) on the photodegradation of Rhodamine B was investigated. The presence of solvents and metal ions significantly reduced the degradation rate. A detailed Langmuir-Hinshelwood kinetic model was developed to explain the effect of Cu2+ on the rate of photodegradation. It was shown that the degradation rate reduces primarily because of a decrease in electron concentration. © 2007 American Chemical Society.