Factors affecting the complexation of polyacrylic ... - ResearchGate

Factors Affecting the Complexationof Polyacrylic Acid with Uranyl Ions inAqueous Solutions: A Luminescence StudyARTEM V. DUBOLAZOV, 1 OLGUN GÜVEN, 2 NURSEL PEKEL, 2 GRIGORIY A. MUN, 1 ZAURESH S. NURKEEVA 11 Department of Chemical Physics and Macromolecular Chemistry, Kazakh National University,480012 Almaty, Kazakhstan2 Department of Chemistry, Hacettepe University, Beytepe 06532, Ankara, TurkeyReceived 24 June 2004; revised 1 June 2005; accepted 8 June 2005DOI: 10.1002/polb.20566Published online in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: A study was carried out in aqueous solutions using luminescence techniqueto investigate the effects of pH, salt concentration, and temperature on the polyacrylicacid/uranyl ion (PAA/UO 2þ 2 ) complex formation as well as competitive phenomenaof enhancement and quenching effects on photoexcited state of uranyl ions. Itwas found that excess of H þ and OH is not favorable for complexation betweenuranyl ions and polymer. Added nitrate salts of Na þ and K þ had significant enhancementeffect on emission spectra of PAA/UO 2þ 2 complex. These results indicated thatthe metal ion/polymer chain complex collapsed by addition of salts and then complexbecame more compact with consequent phase separation. No significant effect of temperatureon the PAA/UO 2þ 2 complex stability has been observed between 25–50 8C.The quenching rate constants obtained from Stern–Volmer plots were found to be inthe order of k q (H þ ) >> k q (K þ ) > k q (Na þ ). VC 2005 Wiley Periodicals, Inc. J Polym Sci PartB: Polym Phys 43: 2737–2744, 2005Keywords: luminescence spectroscopy; polyacrylic acid; nonlinear Stern–Volmer;uranyl ionINTRODUCTIONHeavy metal ions tend to form complexes withpolymeric and copolymeric cosolutes in waterthat contain different types of chelating groupsand ligands such as, amine, heterocyclic amine,amidoxime, carboxyl, dithizone, and so forth. 1–5Poly(acrylic acid) (PAA) is the simplest analog ofweak polyelectrolytes, which can be used as flocculantin water treatment. 6,7 Various types ofsmall molecules such as metal ions are complexedto PAA and its derivatives containingCorrespondence to: O. Güven (E-mail: Guven@hacettepe.edu.tr)Journal of Polymer Science: Part B: Polymer Physics, Vol. 43, 2737–2744 (2005)VC 2005 Wiley Periodicals, Inc.hydrophilic carboxyl groups. 8 On the other hand,PAA is used as the water-soluble chelating polymerbecause many comparable data on bindingproperties of PAA have been published in literature.The formation of metal complexes betweenPAA and divalent, trivalent, and tetravalentmetal ions was studied by Roma-Luciow et al. 9For divalent metal ions, the formation constantsdetermined according to the method of Gregoret al. 10 strongly decrease with increasing ligandconcentration in the range of 25–280 mM, butare nearly insensitive to the ligand-to-metal concentrationratio.It has been known that PAA forms complexwith uranyl ions in aqueous solutions. Nishideand his associates 11 as well as Leroy and co-2737

2738 DUBOLAZOV ET AL.workers 12 investigated the process of complexformation between PAA and UO 2þ 2 , using potentiometryand differential pulse polarographytechniques. It was found that polyelectrolyteforms intrapolymer chelates with actinide ionsand complex formation completes with the compositionof UO 2þ2(carboxylate) 2 . The resulting complexformation constants revealed that PAA hasshown much higher complex ability than that oflow-molecular-weight species such as succinicand propionic acids. This phenomena wereexplained by the assumption that the concentrationof ligands is higher in the domain so thatonce the metal ion is attached to one group onthe polymer chain, the other ligands coordinatemore easily. It was also found that PAA formsmore stable complex with uranyl ion than withcopper ion. 11Many researchers have investigated the complexationbehavior between polymer and metalions using ultrafiltration, ion exchange, ionselective electrode potentiometry, and severalspectroscopic techniques. Luminescence spectroscopyin general and time-resolved fluorescencespectroscopy are very sensitive techniques forthe analysis, speciation, and interactions of actinideand lanthanides. 13 There are however fewpapers in the literature about the complexationbehavior of functional group-containing polymerssuch as PAA with uranyl ions by using luminescencespectroscopy. 14 Both molecular structureand chemical surroundings have an influence onwhether a molecule can produce luminescence.These factors, including chemical structure, temperature,pH, ionic strength, solvent type, concentration,and dissolved oxygen, can affectemission intensity while luminescence occurs. 15The excitation and emission spectra of many fluorophores(fluorescent sensitive molecules) aresensitive to the polarity of their surroundingenvironment. As a consequence, quenching offluorescence is observed if complex affects theelectronic structure of the fluorophore. For somecations, sensing methods were established thatrely on the intrinsic optical properties. Somemetal ions show absorption (ranging from the UVto the near infrared) or luminescence. Examplesare the detection of Cu(II) 16 or the uranyl ion. 14,17Luminescence of hexavalent uranium in solutionand solid state has been known for morethan 150 years. All the electrons in the stronglybonded UO 2þ2structure are paired. Thus, theground electronic level is a singlet. To formhigher-energy electronic states, one of the bondingelectrons is transferred to the 5f nonbondingatomic orbitals of the uranium ion. 18 Thus, thefluorescence spectrum is the result of the transitionsfrom the first excited electronic level to theground singlet and the vibrational levels associatedwith the singlet. Using this fluorescence ofuranyl, the complexation of uranyl ion with someinorganic and organic systems has beenstudied. 13,15 Application of U(VI) luminescenceto speciation of U(VI) however has forwardeddiscrepant results and interpretations. Especiallydependence of fluorescence behavior on pHis discussed in terms of mutually exclusive interpretations.Complexation studies and migrationof radionuclides such as uranium are quiteimportant from environmental pollution andsafety point of view. The advantages of the use ofpolyelectrolytes such as PAA are easy recovery ofthe uranyl ion from aqueous systems.In our previous study 19 the mechanism ofinteraction between PAA and uranyl ions inaqueous solutions and the restrictive role of Coulombicinteractions were confirmed using conductometric,potentiometric, thermal analysis,and FT-IR spectroscopic methods. In this study,we tried to show the effect of some factors suchas pH, salt concentration, and temperature onluminescence properties of UO 2þ2ions complexedwith PAA in aqueous solutions.EXPERIMENTALPAA with weight-average molecular weight (M w )2.3 10 5 was purchased from BDH Chem. Corp.(England) and used without further purification.Uranyl ion stock solutions (c ¼ 0.001 mol/L) wereprepared from hexahydrate of uranyl nitrateUO 2 (NO 3 ) 2 6H 2 O (Merck, Darmstadt, Germany).Inorganic salts (NaNO 3 and KNO 3 ) of analyticalgrade were used as received.The PAA/UO 2þ2solutions were prepared byadding PAA solution (c ¼ 0.002 mol/L on arepeating unit basis) into UO 2þ2stock solutions.In all experiments the [repeating unit of PAA]/[metal] concentration ratio was 2 (stoichiometryof PAA/UO 2þ2complex), keeping the total volumeconstant at 10 mL.To investigate the pH effect on the formationof PAA/UO 2þ2complex, a set of solutions withpH varying from 1.88 to 4.02 were prepared byusing 0.05 M nitric acid or sodium hydroxidesolutions. The pH values of the aqueous mixtureswere determined with a digital pH 211

FACTORS AFFECTING POLYACRYLIC ACID/URANYL ION COMPLEX FORMATION 2739microprocessor pH meter (Hanna Instruments,Germany).The complex solutions with different concentrationsof inorganic salts were prepared by addingcorresponding alkali-metal nitrate to PAAand UO 2þ2solutions separately followed by theirmixing to make up the total solution. Temperatureeffect on the complexation of PAA withuranyl ions was studied by changing the temperatureof complex solution from 25 to 50 8C.UO 2þ2emission spectra were recorded on a PerkinElmerLS 55 luminescence spectrometer (PerkinElmerInstruments, England) under excitationat 310 nm. All measurements were carriedout at ambient temperature within 10 min aftermixing of components for salt concentration andpH investigations. The deconvolution of theemission spectra was performed by resolving thepeaks using a computer program (Peakfit 3.0software).Turbidimetric measurements were carried outwith a Philips model 8715 UV–vis spectrophotometerat 400 nm.RESULTS AND DISCUSSIONThe luminescence properties of uranium speciesin aqueous solutions are known to be stronglyinfluenced by their immediate coordinative environment.20 Earlier 19 we showed the preliminaryresults of very interesting behavior of UO 2þ2emission spectra in the presence of PAA of differentconcentrations: at the concentration ratio[repeating unit of PAA]/[metal] ¼ 2, new hypertransitionshoulder at 483 nm appeared, whichis probably due to complex formation betweenUO 2þ2and PAA.The basic structure of the uranyl nitratehydrates is shown as [UO 2 (NO 3 ) 2 (H 2 O) 2 ]mH 2 O,where m ¼ 0, 1, and 4. 21 Basically, the linearuranyl ion is coordinated to two water moleculesand two bidentate nitrate ions. Other water moleculesin the trihydrate (m ¼ 1) and hexahydrate(m ¼ 4) are linked loosely to the coordinatedwater molecules by means of hydrogen bonding.The removal of the mH 2 O does not affect the fluorescencespectrum significantly. However, it iswell known that the water molecules adjacent tothe uranyl ion affect the fluorescence lifetime.Among the hydrates of uranyl nitrate the hexahydrate,which has the highest number of watermolecules in the unit cell, is expected to lead toan increase in the lifetime.Figure 1. Emission spectra of aqueous UO 2þ2at differentn ¼ PAA on a repeating unit basis /UO 2þ2values:(a) n 2 and (b) (n > 3). k ex ¼ 310 nm.The emission spectra of UO 2þ2aqueous solutionsin the absence and presence of PAA withdifferent concentrations under excitation at310 nm are shown in Figure 1. When n < 2, increasein emission intensity is strongly related toPAA concentration and emission peaks shift tolower wavelengths (Fig. 1a) due to coordinationof UO 2þ2ions by PAA. This can be explained bythe expulsion of some of the water moleculescoordinated to uranyl ions by complex formation.22 It is important to note that the increasein PAA concentration is accompanied by significantchanges in the spectral shape with appearanceof a new shoulder at 483 nm (Fig. 1b) untilstoichiometric ratio reaches the value of n ¼ 2(PAA on a repeating unit basis/UO 2þ2¼ 2:1 Mratio). Formation of shoulders around the mainpeaks of UO 2þ2has also been observed for thecomplexation of uranyl ions with some a-substitutedcarboxylic acids in the work of Moll et al. 23For higher n values however, (PAA on a repeatingunit basis/UO 2þ2>4) decrease in emissionintensity has been observed, which can beexplained by the quenching effect of PAA in

2740 DUBOLAZOV ET AL.Figure 2. Convoluted emission spectrum of PAA/UO 2þ2complex in aqueous solution. k ex ¼ 310 nm,PAA/UO 2þ2¼ 2, pH ¼ 3.13. Experimental spectrum(—) obtained from UO 2þ2(---) and PAA/UO 2þ2(—)peaks.excess of UO 2þ2complex stoichiometry with nondissociatedgroups of polyelectrolyte.As the emission spectrum shown in Figure 2gives the envelope of individual peaks within thespectral range deconvolution software has beenused to determine peak positions and the exactintensities of PAA/UO 2þ2spectrum. According tothe changes in intensity of uranyl PAA complexband under external stimuli factors we attemptedto use the I/I 0 ratio, where I and I 0 are theluminescence intensity of PAA/UO 2þ2complexband in aqueous solution with and withoutexternally affecting factors such as, H þ or OH ,salt concentration (Na þ and K þ ), and temperature.Relative luminescence intensity of polycomplexband can serve as a qualitative evaluationcriterion of enhancement or weakening of interactionsbetween polymer and metal ions: increaseof I/I 0 value can be interpreted to be asdue to a more compact structure as well as morestable. On the other hand, if I/I 0 value is lowerthan 1 it means that fluorescence properties ofUO 2þ2species are diminished under the quenchingeffect. Contribution of both enhancement(destabilization) and quenching effect to thePAA/UO 2þ2emission spectra under external stimulieffects are separately considered later.pH EffectThe results of the previous studies showed thatchelation of metal ions by polymeric ligandsdepend on the equilibrium pH of medium. Sebastianand coworkers 24 investigated the PAA complexationwith various metal ions at different pHvalues (3.45–6.0). The optimum pH for maximummetal-ion uptake by this polymer was found tobe as follows: 5.4 for Fe(III), 5.4 for Co(II), 6.2for Ni(II), 5.4 for Cr(III), and 6.4 for Zn(II). Thelimitation of pH interval was attributed to themetal hydrolysis and precipitation at higher pH.However, Bodzek et al. 25 investigated the possibilityof removing Cu, Ni, and Zn ions frommodel and real galvanic wastewater at 2–10 pHregion, using PAA as flocculant. In all casesthere was an increase in the permeate flux concomitantwith increasing of pH. This phenomenonwas explained by formation of metal–PAAcomplexes more easily at higher pH.Most of the studies about complexation ofUO 2þ2ions with functional group containing polymersshowed that ion exchange has been consideredas the main mechanism responsible forUO 2þ2ion separation. 26 The ion exchange mechanismfor UO 2þ2ion binding to the polymer is complicatedby the fact that the UO 2þ2ion is hydrolyzedin aqueous solutions within the pH rangeof the studied adsorption system and differenttype of hydrolyzed UO 2þ2ions are formed. At pH4.0, more UO 2 (OH) þ ions exist in the solution. 27Application of fluorescence spectroscopy hasbeen hampered by inconsistent interpretation offluorescence lifetimes observed in solutions withincreasing pH. While it has been well knownthat the UO 2þ2species has a fluorescence lifetimeof about 1 ls in acid solution (pH < 2), a secondlifetime contribution had been reported toappear on increasing the pH value to basic solutions.This second lifetime of about 2.5 ls hasbeen interpreted because of different fundamentalprocesses, for example, intersystem crossingor various hydrolyzed uranyl species formation.18 At pH 4, UO 2þ2is the predominant species(96%), UO 2 (OH) þ is less than 4%; at pH 5, UO 2þ2is around 69%, UO 2 (OH) þ is less than26%, (UO 2 ) 2 (OH) 2þ2is less than 5%; at pH > 5.5,the fractions of UO 2 (OH) þ (35%) and (UO 2 ) 2 (OH) 2þ2are decreased and the fraction of (UO 2 ) 2 (OH) 3þis increased with increasing pH. 28For studying the pH effect on luminescenceproperties of PAA/UO 2þ2complex we investigated1.88–4.02 pH range to avoid hydrolyzed forms ofUO 2þ2. The pH dependence of the relative luminescenceintensity of the complex emission bandis shown in Figure 3a. As it can be seen from figure,I/I 0 values are lower than 1 and reachingthis value only at pH 3.25, which probablymeans that the presence of excess of H þ or OHions is unfavorable for complexation between

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.

2742 DUBOLAZOV ET AL.takes place, but in the latter case there is only adistribution of Me þ metal ions near the polymerchain and no real binding of monovalent metalions. 30 Attraction between PAA and Me þstrongly affects the electric field of polymer surface,which can lead to the rearrangement ofPAA structure. As a general rule the increase insalt concentration of the medium changes theconformation of the polymer chains to a morecompact form. 31 In our case this factor probablyleads to the enhancement of hydrophobicity aswell as stability of PAA/UO 2þ2complex.Recently Iida observed the similar effect ofKCl on activity of Ca 2þ in aqueous PAA solution,using a Ca 2þ ion sensitive electrode. The Ca 2þactivity in the PAA solution at the low degree ofneutralization was increased by the presence ofdilute KCl and decreased by the presence of concentratedKCl. 32The size effect seems to be obvious explanationfor the influence of Me þ nature on thestability of PAA/UO 2þ2polycomplex. Kim and coworkers31 found that in the solutions containingalkali metal ions, aggregation of PAA wasincreased in the order Li þ < Na þ < K þ < Cs þ ,which means that the hydrophobicity of thechain decreases with increasing solvated radiusof the counterion. As it can be seen from Figure4, the addition of KNO 3 has more pronouncedeffect on increasing of I/I 0 value than NaNO 3 aswell as on the critical concentration of complexprecipitation (see Fig. 5). Indeed, the radius ofhydrated Na þ (R H 4Å) is bigger than that ofK þ (R H 3Å). 33 Therefore in our case condensationforce is higher for K þ , which can stabilizeand favor the aggregation of PAA/UO 2þ2polycomplexat lower concentrations than Na þ . Consideringthe difference in the critical concentration ofcomplex aggregation at the onset of phase separation,we conclude that the PAA/UO 2þ2 /KNO 3complex is more hydrophobic and stable thanPAA/UO 2þ2 /NaNO 3.The effect of concentrations of H þ , NaNO 3 ,and KNO 3 on quenching the luminescent intensityof UO 2þ2complexed with PAA has been analyzedby constructing relevant Stern–Volmerplots, namely, I 0 /I versus quencher concentrations,using the following relation:Figure 5. Effect of inorganic salts NaNO 3 (1) andKNO 3 (2) on the turbidity of PAA/UO 2þ2aqueous solutions.k ¼ 400 nm, pH ¼ 3.13, PAA/UO 2þ2¼ 2.I 0 =I ¼ I þ k q hs 0 i½QŠwhere I 0 and I are luminescent intensities in theabsence and presence of quencher, k q quenchingrate constant, hs 0 i average lifetime of the uranylion in water and [Q] concentration of quencher.The data presented in Figures 3a and 4 weretherefore used to prepare Figure 6. The inset inthis figure is for H þ ions. Ascending parts of thecurves correspond to quenching of luminescenceby corresponding salts or acid. By taking the hs 0 ivalue as 5 ls, which is typical average lifetime ofUO 2þ2in aqueous solutions, 14 and using the slopeof ascending parts of the curves of Figure 6quenching rate constant k q was calculated andlisted in Table 1. By analogy to the effect ofquenching, the descending parts of the curveswere evaluated similarly to calculate the rateconstants for enhancement effect, where thecoefficient k q in above given equation is replacedby k e . Both results are listed in Table 1. Thequenching rate constant k q ¼ 1.7 10 8 M 1 s 1determined for H þ is in very good accordanceFigure 6.3a and 4Stern–Volmer plot of the data of Figures

FACTORS AFFECTING POLYACRYLIC ACID/URANYL ION COMPLEX FORMATION 2743Table 1. Quenching and Enhancement Effectsof Some Ions on Luminescence Properties ofPAA-Bonded UO 2þ2Ion k q (M 1 s 1 ) k e (M 1 s 1 )H þ 1.7 10 8 1.1 10 9Na þ 7.6 10 4 1.8 10 7with data reported in the literature 2.8 10 7 ,2.7 10 8 for acrylic acid and methacrylic acidmonomers. 14Stern–Volmer plots obtained in the presenceof Na þ and K þ , and as a function of H þ shownonlinear behavior (Fig. 6). The curves given inthis figure can be considered to be composed oftwo parts; an initial enhancement effect up to acertain salt or H þ concentration, followed by aquenching effect. I 0 /I vs. concentration patternsfor all three quenchers used are quite similar.These type of nonlinear Stern–Volmer plots havebeen also observed with monovalent alkalinesalts (Na þ and K þ ) in another fluorescencequenching study. 34 Such nonlinear behavior hasbeen generally explained to be due to combinedeffects of dynamic and static quenching mechanisms.As it is seen directly from the slopes ofquenching part of the curves corresponding tohigher salt concentrations in Figure 6, and fromthe calculated quenching constants k q given inTable 1, K þ is more effective than Na þ . This canbe due to smaller hydrated ion size of K þ comparedto that of Na þ . A similar effect on quenchingefficiency of ions has been observed in thecase of interactions of monovalent salts (NaCland KCl) with a fluorescent probe. 34are relatively temperature stable in 25–50 8Crange. Rao et al. 35 studied the complexation ofuranium (VI) with malonate using UV–visabsorption and luminescence spectra at differenttemperatures, and provided qualitative informationon the temperature effect. No significantshifts in the positions of the luminescence emissionbands were observed when the temperatureof the uranyl malonate solutions was increasedfrom 25 to 70 8C. However, the overall intensitiesof the bands decreased by about ten times at70 8C, compared to those at 25 8C.CONCLUSIONSThe complexation behavior of UO 2þ2ions withpoly(acrylic acid) (PAA) has been studied byusing fluorescence spectroscopy in the presenceof varying external factors such as pH, salt concentration,and temperature. Following are theconclusions reached from this work:1. UO 2þ2ions form various hydrolyzed speciesdepending on the pH of medium. In acidicsolutions generally UO 2þ2ions are predominant,while the hydrolyzed species predominatewith increasing pH. Fluorescenceemission intensities of PAA/UO 2þ2complexdecreased in strong acidic solutions (pH ¼2.0–3.25) because of the destabilization ofthe complex between uranyl ions and PAAby H þ ions, whereas at pH > 3.25 forma-K þ 1.2 10 6 4.6 10 6 Figure 7. Effect of temperature on the relativeTemperature EffectThe temperature effect on the stability of PAA/UO 2þ2complex is shown in Figure 7. Variation oftemperature from 25 to 50 8C affects I/I 0 value ofcomplex emission band (483 nm) by slightdecreasing of relative emission intensity of complexband (curve 1). It is known that the lifetimeof excited uranyl (VI) ion in aqueous solutionalso decreased with temperature from 1.6 to0.6 ls at 20–50 8C temperature range. 18 Resultsobtained confirmed the absence of enhancementeffect, as well as existing of slight increase ofquenching with increase in temperature (curves2 and 3). Therefore taking into account this factwe concluded that PAA/UO 2þ2complex particlesluminescence intensity of PAA/UO 2þ2(1) and maximumUO 2þ 2 bands in the absence (2) and presence of PAA(3). k ex ¼ 310 nm, pH ¼ 3.13, [UO 2þ2] ¼ 0.001 mol/L,PAA/UO 2þ2¼ 2.

2744 DUBOLAZOV ET AL.tion of UO 2 (OH) þ alters the complexationbehavior of PAA, thus reducing the emissioncoming from PAA/UO 2þ2complex. Onlyat pH 3.25, H þ has no significant effect onthe complexation of uranyl with PAA.2. The influence of salt concentration hasbeen studied by using sodium and potassiumnitrate salts. The fluorescence intensitywas first observed to increase withincreasing salt concentration and thendecreased. The decrease in intensity wasassumed to be mostly due to the collapse ofPAA chains, as observed by the increasingturbidity of solutions at higher salt concentrations.3. Temperature has limited effect on fluorescenceintensity of complex within therange of 25–50 8C.4. The luminescence quenching rate constantof H þ , k q ¼ 1.7 10 8 M 1 s 1 determinedfrom Stern–Volmer plot was found to be invery good accordance with the reported literaturevalues. The order of quenching efficienciesof the ions were found to be k q (H þ )>> k q (K þ ) > k q (Na þ ). Because of the combinedeffects of dynamic and static quenchingprocesses a nonlinear Stern–Volmerplot was observed for the salts studied.REFERENCES AND NOTES1. Pekel, N.; S˛ ahiner, N.; Güven, O. Radiat PhysChem 2000, 59, 485–491.2. S˛ ahiner, N.; Pekel, N.; Güven, O. Reactive FunctPolym 1999, 39, 139–146.3. S˛ ahiner, N.; Pekel, N.; Akkas˛, P.; Güven, O.;J Macromol Sci, Pure and Appl Chem 2000, 37A,1159–1172.4. Choi, S. H.; Nho, Y. C. Rad Phys Chem 2000, 57,187–193.5. Beavais, R. A.; Alexandratos, S. D. ReactiveFunct Polym 1998, 36, 113–123.6. Morlay, C.; Cromer, M.; Mouginot, Y.; Vottori, O.Talanta 1999, 48, 1159–1166.7. Morlay, C.; Cromer, M.; Mouginot, Y.; Vottori, O.Talanta 1998, 45, 1177–1188.8. Molyneux, P. Water-Soluble Synthetic Polymers:Properties and Behavior, Vol. 2; CRC Press: BocaRaton, 1982.9. Roma-Luciow, R.; Saraff, L.; Morcellet, M. PolymBull 2000, 45, 411–418.10. Gregor, H. P.; Luttinger, L. B.; Loebl, E. M.J Phys Chem 1955, 59, 34–39.11. Nishide, H.; Oki, N.; Tsuchida, E. Eur Polym J1982, 18, 799–802.12. Leroy, D.; Martinot, L.; Jerome, C.; Jerome, R.Polymer 2001, 42, 4589–4596.13. Saito, T.; Nagasaki, S.; Tanaka, S. RadiochimActa 2002, 90, 27–33.14. Watanabe, C. N.; Gehlen, M. H. J PhotochemPhotobiol A: Chem 2003, 156, 65–68.15. Rustenholtz, A.; Billard, I.; Duplâtre, G.; Lützenkirchen,K.; Sémon, L. Radiochim Acta 2001, 89,83–89.16. Szintay, G.; Horváth, A. Inorg Chim Acta 2001,324, 278–285.17. Addleman, R. S.; Carrott, M.; Wai, C. M.; Carleson,T. E.; Wenclawiak, B. W. Anal Chem 2001,73, 1112–1119.18. Meiranth, G. Aquatic chemistry of uranium, FreibergOn-line Geoscience 1998, 1; available at http://www.geo.tu_freiberg/fog (June 19, 2003).19. Dubolazov, A. V.; Güven, O.; Pekel, N.; Azhgozhinova,G. S.; Mun, G. A.; Nurkeeva, Z. S.J Polym Sci Part B: Polym Phys 2004, 42,1610–1618.20. Kato, B. Y.; Meinrath, G.; Kimura, T.; Yoshida, Z.Radiochim Acta 1994, 64, 107–113.21. Leung, A. F.; Hayashibara, L.; Spadaro, J. J PhysChem Solids 1999, 60, 299–304.22. Nagata, I.; Okamoto, Y. Macromolecules 1983, 16,749–753.23. Moll, H.; Geipel, G.; Reich, T.; Bernhard, G.; Fanghanel,T.; Grenthe, I. Radiochim Acta 2003, 91,11–20.24. Sebastian, N.; George, B.; Mathew, B. PolymDegrad Stab 1998, 60, 371–375.25. Bodzek, M.; Korus, I.; Loska, K. Desalination1999, 121, 117–121.26. Schiewer, S.; Volesky, B. Environ Sci Technol1995, 29, 3049–3058.27. Yang, J.; Volesky, B. Internat BiohydrometallSymp Proc B 1999, 483–492.28. Hongxia, Z.; Zuyi, T. J Radioanal Nucl Chem2002, 254, 103–107.29. Moulin, C.; Decambox, P.; Trecani, L. Anal ChimActa 1996, 321, 121–126.30. Morawetz, H. Macromolecules in Solution, Wiley:New York 1975, p 366.31. Kim, G. H.; Lee, J. H.; Lee, H. B.; John, M. S.J Colloid Interface Sci 1993, 157, 82–87.32. Iida, S. Biophys Chem 1996, 57, 133–142.33. Weast, R. C. Handbook of Chemistry andPhysics, 53rd ed.; The Chemical Rubber Co.:Ohio, 1973.34. Adenier, A.; Aaron, J. J. Spectrochim Acta A 2002,58, 543–551.35. Rao, L.; Jiang, J.; Zanonato, P. L.; Bernardo, P.D.; Bismondo, A.; Garnov, A. Y. Radiochim Acta2002, 90, 581–588.