Several parameters have been studied in this manuscript to investigate the effect of certain conditions on the removal and the decolorization of the textile dyes: reactive yellow 14 (RY 14) and reactive green (RG) dyes from aqueous solution. Parameters such as temperature, initial concentration of dye and initial pH were taken into consideration to reach the perfect removal and decolorization for both dyes. This work was achieved in both dark and photoreaction processes.
In dark reaction, the type of adsorption was determined based on Gibb's free energy values, activation energies and change in enthalpies, which were found that the physical adsorption for removal of both dyes is predominated, and the reaction is exothermic . The adsorption capacity and percentage of removal both dyes elevated with raised the dye concentration. The best initial pH for removal of RY 14 and RG dyes dyes was conducted and found equal to 5.14 and 9.75 respectively. The raised in temperature is not enhanced the adsorption process, that due to the dark reaction for both dye is exothermic. The small negative values of change in entropies are proved the associative mechanism of both dyes on ZnO surface.
On the other hand, the results under the percent UV-light showed, that the optimal conditions were found at 303.15 K, with 25 ppm and optimum pH=11.01 for reactive green(RG) dye, while the optimum conditions were appearing at 50 ppm and best pH= 6.075 for reactive yellow 14 at same temperature. The decolorization process for both studied dyes was found to be a pseudo-first-order kinetic, fast (low activation energies), endothermic reaction (positive change in enthalpies), non- spontaneous (positive change Gibbs free energies) and less random (negative change in entropies). The photoreaction is a completed to removal process to depress the toxicity for these studied textiles dyes.