الفهرس | Only 14 pages are availabe for public view |
Abstract Its known that in acidic solutions the surfaces of photocatalysts are positively charged this means that it cannot provide hydroxyl group which are needed for hydroxyl radical formation. and the surface of photocatalysis become negatively charged in alkaline solutions. Predicting that degradation efficiency on the surface of alkaline solution increased as this higher pH value can provide higher concentration of hydroxyl ions to react with the holes to form hydroxyl radicals in this work the effect of pH on methylene blue degradation was studied by varying the pH from 2 to 12. Figure 3.30 showed that at high pH12 degradation efficiency decreased to 85% and in acidic medium degradation efficiency also decreased to 61% as in acidic medium There was an increase in H+ concentration , adsorption of cationic dyes will be low due to repulsive forces causing the reduction of degradation efficiency (138,139) on the other hand in alkaline medium the degradation of dyes is inhibited as the hydroxyl ions compete with dyes molecules in adsorption on the surface of photocatalysts[144] It was observed that the removal of dye by 1% Cu2+/CdS was maximum at pH 6.5 to 7.5. |