3.11.2 Effects Of Ph

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3.11.2. Effects of pH
The pH is a very important parameter which controls the extent of photoassisted degradation. The effects of pH on degradation of CR were investigated using 15.0 mg of
LDH; 1x10-5 M CR solution in the pH range of 4.0 to 11.0, adjusted by addition of either 0.1 M HCl or NaOH. The plot of C/C0 vs. irradiation time of aqueous CR is presented in Fig.12(B). The efficiency of photodegradation of aqueous CR was found to be higher in the acidic medium particularly at pH 4 (~99.7%) because Co/Ti LDH surface was highly positive at this pH, indicated by the zeta potential results, creating strong electrostatic interaction with the negatively charged CR ions. At pH > pHzpc, the
LDH surface is negatively charged, repelling the dye anions
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12. (A) Effects of catalyst amount and (B) Effects of pH on photodegradation of aqueous Congo Red
3.11.3. Effects of initial dye concentration
The effects of dye concentration are very important from the application point of view.
Maximum efficiency was observed at pH 4 with 15.0 mg of Co/Ti-LDH [Fig.13(A)]. At the dye concentration of 1x10-5 M, 99.7% degradation could be achieved with aqueous
CR at room temperature (~300C). The degradation decreased to 80% and 71% for aqueous CR of 1x10-4 M and 1x10-3 M concentrations respectively.
The decreased degradation of the dye with increasing concentration may be due to
(a) high dye concentration may act as an inner filter which shunts the photons away from the LDH surface, (b) may lead to the non-availability of oxidative free radicals associated with the degradation process and (c) most of the dye molecules get adsorbed on the LDH surface blocking the active surface sites in the LDH. The maximum photodegradation efficiency was obtained at the dye concentration of 1 x 10-5 M.
3.11.4. Recyclability of 2:1 Co/Ti LDH
After each degradation cycle, the LDH was separated from the reaction system, was regenerated by washing it three times with de-ionized water followed by drying,

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