Factors affecting the complexation of polyacrylic ... - ResearchGate

FACTORS AFFECTING POLYACRYLIC ACID/URANYL ION COMPLEX FORMATION 2741appearance of first uranyl hydroxide complexUO 2 (OH) þ at pH 4, which probably has less tendencyto form complexes with PAA than withUO 2þ2(aq.).Figure 3. (a) Effect of pH on the relative luminescenceintensity of PAA/UO 2þ2complex band. k ex ¼ 310nm, PAA/UO 2þ2¼ 2. (b) Effect of concentration of H þ onthe relative luminescence intensity of maximumUO 2þ2band in the presence and absence of PAA. k ex ¼310 nm, [UO 2þ 2 ] ¼ 0.001 mol/L.Salt EffectFigure 4 shows the plot of relative luminescenceintensity of PAA/UO 2þ2complex band against concentrationof sodium nitrate and potassium nitrate.It is seen that I/I 0 value increases withincrease in the concentration of NaNO 3 (achievingthe maximum point at c ¼ 0.03 M of salt)and drastically increases in the presence ofKNO 3 (maximum I/I 0 value at c salt ¼ 0.01 M). Athigher salt concentrations phase separation wasobserved, which was confirmed by turbidimetricmeasurements of PAA/UO 2þ2 /MeNO 3 mixtures,Figure 5.This experimental result suggests that thepresence of inorganic salt in PAA/UO 2þ2complexaqueous solutions enhances the hydrophobicityof polycomplex particles because of an increasein luminescence intensity. 22 It should be notedthat in both cases I/I 0 values are higher than 1,indicates that luminescence intensity of the complexhas been governed by enhancement effect.It is known that ‘‘complexation’’ term is usedfor the binding of PAA with multivalent metalions (Cu 2þ , Zn 2þ , Ca 2þ , Mg 2þ , Tb 3þ , etc) and‘‘condensation’’ is conventionally used for thebinding of PAA with monovalent ions (Li þ ,Na þ ,K þ , etc). In both cases electrostatic interactionUO 2þ2and PAA ligands. On the other hand, quenchingeffect of excess H þ cannot be ignored. Figure3b represents curves of I/I 0 values for maximumuranyl bands of uranyl spectrum in the presenceand absence of PAA versus concentration ofnitric acid, which confirms the fact of quenchingeffect. 29 Therefore we propose that protons andUO 2þ2ions compete for the same binding sitesalong PAA chains. The possible mechanism ofcomplex formation between PAA chains andUO 2þ2ions were given in our previous paper. 19As shown in Figure 3a the complex formationability increased with increase in pH, reachingmaximum values at 3.25 and then decreased.Depression in I/I 0 value can be attributed to theFigure 4. Dependence of I/I 0 value of PAA/UO 2þ2band on the concentration of NaNO 3 (1) and KNO 3(2). k ex ¼ 310 nm, pH ¼ 3.13, PAA/UO 2þ2¼ 2.