Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica
The enhanced adsorption of copper ions onto silica surface from the solution containing 2,2'-bipyridine is explained by ternary surface complex formation. The equilibrium reaction constants of binary and ternary complexes have been calculated using constant capacitance model. The potentiometric...
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| Datum: | 2001 |
|---|---|
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | Englisch |
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Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2001
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Surface| _version_ | 1869291139416195072 |
|---|---|
| author | Vlasova, N. N. Schlapfer, C. -W. Golovkova, L. P. Svezhentsova, A. A. Chuiko, A. A. |
| author_facet | Vlasova, N. N. Schlapfer, C. -W. Golovkova, L. P. Svezhentsova, A. A. Chuiko, A. A. |
| author_institution_txt_mv | [
{
"author": "N. N. Vlasova",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "C. -W. Schlapfer",
"institution": "University of Fribourg"
},
{
"author": "L. P. Golovkova",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "A. A. Svezhentsova",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "A. A. Chuiko",
"institution": "Інститут хімії поверхні НАН України"
}
] |
| author_sort | Vlasova, N. N. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:39Z |
| description | The enhanced adsorption of copper ions onto silica surface from the solution containing 2,2'-bipyridine is explained by ternary surface complex formation. The equilibrium reaction constants of binary and ternary complexes have been calculated using constant capacitance model. The potentiometric titration data were used in order to determine the H*/Cu2+ exchange stoichiometry. The adsorption of 2,2'-bipyridine on a copper-containing silica surface has been studied too. The equilibrium of 2,2'-bipyridine binding to immobilized copper ions are well reproduced by the constants for the formation of ternary surface complexes from an aqueous solution containing copper ions and 2,2'-bipyridine. This indicates clearly that under experimental conditions all reactions are reversible and speciation is controlled by the thermodynamics. |
| first_indexed | 2025-09-24T17:25:23Z |
| format | Article |
| fulltext |
din SURFACЕ COп{PLЕХ I',()RNIATION AT TtIЕ
ADSORPTION 0F Cu2* loNS AND 2,2'-BIPУRIDINЕ oNТo
IIIGIILY DISPЕRSЕ SILIсA
N.N. Vlаsoval, с..w. Sсhliipfel, L.P. Golovkova', A.A. Svеzhеntsoval.
аnd A.A. Сhuikol
Iltlstitute
of Suфсе Сhеmistry, Nаtioпаl Асаtlеmу of Sciепсеs,
G е п. Nаum ov,gtr. ] 7' Kуiv- I 6 1, 0 3 68 0, UKRА INЕ,, -.oi t,, i,lаbаrs@i. сom. uа2!nstitutе o/Inorgаniс Сhеmistry, Universitу of Fribourg, СH-]700 Fribourg,
S|уITZЕRLАND
А bstгасt
Тhе еnhanсеd adsoгption of сoppеr ions оntо siliсa suгfaсе fгom thе solution оontainins
2,2,.bipуridinе is еxplainеd by tегnary suгГaсе сomрlех foгmation. Thе equilibгium .еaсtioi
сonstants оfbinary and tеrnary сomplехes hаvе bеen сalсulatеd using сonstant сapaсitanсe
nrоdеl Thе potеntiomеtгiс titгation data rvеrе usеd in ordег to dЪtеrminе the Fгlcu2t
ехсhangе stоiсhiomеtry. Thе adsoгрtion of 2,2,-bipyгidinе on a сoppег-сontaining siliсa
suгГaсе has bееn sfudiеd too' Тhе еquilibгium af 2,2,-Ьipугidinе binding to immoЪilizеd
соppег ions aге wе1l rеproducеd bу thе сonstаnts fог thе foгmation oГ t.*ury surfaсе
соmplехеs fгom an aquеous solution сontaining сoрper ions and 2,2,-Ьipуniinе. This
indiсates сlеarlу that undеr ехpеrimеntal сonditiоns all rеaсtions arе rеversiblе and
spесiatiоn is сontгollеd bу thе thеrmodynamics'
Introduсtion
The pгesеnсе of
.oгganiс mеtal-сomplех foгming agеnts in solution may signifiсantly
affесt thе adsoгption of mеtal ions onto hydrous oхidе suгГaсe. Bouгg еt аI.\l1 founа
unusual еnhаnсеmеnt of thе adsoгption of Cu2* at thе siliсa suгГaсе bу 2,2'.bipугidinе Тhis
.'rbsегvation was explained by the foгmation of tеrnary suгfaсe сomplехеs. iiris еfгеct is
vеry impoгtant with rеspeсt to many apрliсations bесausе it shows that thе affinity of oхidе
sitгfaсеs сan bе сontrollеd by the adsoгption of mеtal ions. For this геason thе systеm Cu2-,
2,2,-bipyridinе' amorphous siliсa was studiеd by sеvегаl groups sinсе thе sеыnы pup". oi
Bourg et аl|1] aз a modеl systеm foг suгГасе сomрlеx foгmation. Von Zеlewsф and
Bеmtgеn [2] werе thе fiгst onеs that аpрliеd ЕPR to сhaгaсteгizе thе struсture oг tь"
suгГaсе сomplехes, Thеy сould idеntifu a 1:] аnd a 1,'2 Сu2r l2'2'-bipуridine suгfaсе
сompleх. Тhе еquilibгium сonstant еstimatеd from thе spесtгal intеnsitiеs сonfiгmed thе
stзbilization оf thеsе сomplехеs at thе siliсa suгГaсе fоund'nу Bouгg еt аI|1]' Сheahеt аI,
t3] publishеd a dеtailed ХAFS and ЕРR studу whiсh provесl the struсtuге of the tегnaгv
.uгfaсе сomplехеs proposеd in thе еaгliег rvoгk
Тегnary suгГaсе сomplехes aге obtainеd еithег by тhе adsoгption of сomplexes
bеtwееn rnеtal ions and oгganiс ligands formеd in sоlution oг by thе suссеssivе
adsоrption of thе two сomponеnts. In'an еaгliег paрeг Wе гepoгted ttrе preparation of
:еrnary suгГaсе сomplеxеs bеtwееn Сu2- and bipyndinе at a Sloz suгГaсе by thеse two
геaсtion paths .Тhе сomplеxеs havе bееn сhагaсtегizеd Ьу thеiг ЕPR and absoгption
ipесtra [4] No diffегеnсe was oЬsеn'еd bеtwеen thе spесtгa of thе сomplехеs obtainеd by
ihе two diffегеnt rеaсtions, indiсating that thеir struсtЦге is idеntiсаl and doеs not dеpеnd
.ln thе mеthod of prеparation
Iп this paрег we rеpoгt а quantitative study of the adsoгption of Cu2* and
2.2.-binуridinе onto siliсa suгfaсе as a funсtion oГthеiг сonсеntrations and thе pH of thе
14"7
srliсa
lэl, -
siiiоa
i ino
srliсa
's aпd
.
siiiсa
:s and
1: п]еnt
:;:s of
,-: -nl -
:. is of
s..\ -
г: sll on
r:s and
ш: I.V.
с:' - siliсa
solutions. Thеsе data allowеd us to dеtеrminе thе еquilibrium сjonstants of thе foгmation of
binary and ternary ,uЬ.. сomplехеs. In^ additiЬп wе measurеd the distribution of
2,2,-bipугidin" ь.t*..n iье sotution and a siliсa suгГaсе which was mоdifiеd bеforеhand bу
thеadsorptionofсoppеrions.Thеmеasцrеdisothегmofbipyridinеiswеllгеproduсеd
with thе сalсulated .q,lirь.i"".' сonstants' This provеs that all the rеaсtions in this sуstеm
aге геversiblе and thе spесiation is оontrollеd by thermodуnamiсs.
Ехpеrimental
Маteriаl;oгphous
higЫу dispеrsе siliсaА.300 (СЫогvinуl,111y:h,Ukгainе) with suгfaсе
aгеa 300 mzlg ' and гeagеnts NaNoз, сuo{oзi.6Hzo, 2,2,.btpуrtd\nе (bipy) ( all p'a.'
Fluka) wеге usеd u, ,...Тu.с. HNoз and NaбH solutions wеге prеparеd from Titrisol
(Мerсk).Allsoiцtionsandsuspеnsionswеrеprеpaгedfromdoublydistillеdwatеr.Thе
tеmDегaturе *u, к.р.
"J",] ^i.Ъi
o z.С and iЬniс Stгrn$h was fixеd with 0 1 M NaNoз
Асid.bаse tilrqliОn of siliса suspеnsiоns
Thе stoсk -",;;;;io;;f siliсa with сonсеntration t0 g/L in 0 1 М NaNo3 was
prеpaгеd and stirrеd io. z *".t.,. А.ftегward, 30 ml of this suspеnsion and 30 ml 2mМ
HNoз weгe plaсеd in spесial thегmostated ,.u..o, еquippеd with a сombinе 8lass .ч:9:
frompH.mеtегмеtгoьm7l3'tipоfautomatiсtitratorDosrmatМеtгohm665,magnеttс
stirrеr,andtubеsfoгaгgonbubblingThеptl-metегandautomatiсtitratorwеrесonnесtеd
andmanagеdwithсomputегbуspеоaltitratiоnprogram'Thismiхturеwastitгatеdwith5
mМ NaoH. Afteг еaсЬ addiiiоn оf basе еquilibrium-was.assumеd if subsequеnt ЕМF
mеasurеmеnts takеn in 15 min intегvals did not diffег bу mоrе than 01 mV. Тhе
сonсеntгationoffieеhуdгogеn1onswasobtainеdfromЕ}ltrmеasurеmеntswithusing
Nегnst equation foг soiutiois with сonstant ioniс strengh. Coеffiсiеnts in this еquation
r"еге dеtегminеd fгom thе сalibгation titration of samtlеs..-ithout of siliсa. Acid.basе
titrationofsuspеnsionsсontainingofсoppеrionsorсoppеrionswith2'2'.bipуidinе(Cu:
bipу 1:l, l:2 and 1:3) wеrе сапiеd out in a.similu, 'uйЪ'.
In thеsе ехpеriments thе rеsult
сonсеntrationofsiliсawas5gll,сoppегion,-osmМandbipy.0.5'1.0andl.5mМ
rrspесt1vеly..ii,o,ptioi
of coppеr ions, bipуridittе апd thеir complехеs
Thе sеries of samplеs Wеге prеparеj ьy **ing 9|]0 ml of stoсk suspеnsion of
siliсa and 10 пn l mМ solutions of сoppеr;й a"аjэ,-ьiw:^1i". *,.'n:
"-ф:|^ll-
dеpеndеnсе oг uo,o.ptJn г,o' ino*lаual solutions. The suspеnsions with thе samе rattos
Cu2- bipу as for potеntiomеtгiс titration werе pгеparеd to study thе adsoгption fгom
mutual solutions.
adjusтed to dеsirable valuеs оvег thе range 3-8.
,n.,. -]lo".o":iilJ;i1Тj}:::ЖТili:;;;;;,;,-stеd, and ,iн"u *u' separatй with
сеntrifugatio" (5 й0.;й rЪ 'iо Thе сЪnсеntrations of сoрpег ions in supеrnatant
solutions *".. o.t",.ii"j u,ing atomiс uь*.p'ion speсtгophоtomеtry (AAS-30, Кarl
Zеiss, Gегmunуi. тi.."on..n.,u,]on, oi bipу Y.'" T:u,,'-.!^-ol
uu spесtrophotomеtry
(SpесoгdМ-40,KaгlZеiss,Gе^rmanу;as.сomplехwithсoppeг.ionsl:1whiсhisfогmеd
with an еxсеSs .*;;;;; cu, ts
"mм)
ano сharactеrizJ with 2 maхima at 300 nm
(в=l5500)and3i0nm(,=rsвoo)[5]Тhесoppеrionandbipуadsorptionvaluеswеге
сalсulatеdasthеditrеrеnсеbеtwееninitialandеquilibгiumсonсentгatlons,
Prеpаrаrion of siliса modфеd bу coppеr ioпs
Thе 5 g siliоa was adсeа to jоo ml of 0'l М NaNoз solution сontaining 2 mМ
Cu(Noз)z. Thе pH was adjustеd to s в-s Ыьi dгop*,isе addition of l mМ NaoH solution
tothеstirrеdsuspеnsion.Thеsuspеnsiоn*usstiггеdundегargon(pгоtесtionГromCoz)
for l wееk. This timе was nесеssary to at|ain еquilibrium bеtwееn dry siliсa and solution
сontaining *ooiu' a,iс .;Ъ;* nitraiеs. Т;; ;н ;.- testеd регi.diсally and readjustеd if
148
l:L Of
: ::. of
.: iby
.,,.^А
s:еm
-jaсe
nя- у -.'
- :гisol
.. Тhе
.Noз,
-. was
- ]mМ
: : -..Гode
* .:.notic
...эсted
: .гith 5
..l ЕМF
Thе
::.Цation
. . J.basе
:.е(Cu:
. . геsult
. 5mМ
'" ' using
nесеssary . А-ftеr сеntrifugation thе сonсеntration of adsoгbеd сopper ions was сalсulatеd
fгom thе dесrеasе of Сu,. in thе supегnаtant solution. It was found to bе 0.57 mmoИ or
0'057 mmoVg Sio2 согrеsponding appгoximatеly to З0oА of total amount of Cu2* in thе
suspension' Тhis оoггеsponds to a suгfaсe loading of 1 Cu2. adsorbеd pеr 811 siOH-
8гouр' Thе mеan distanсе bеtwееn two adsoгbеd Cuz* ions is 3.34 nm as сalсulatеd Гrсlm
the arеa availablе fог l Сu2- assuming a homоgeneous distгibution.
Аdsorption of bipу oп siliса modфеd with copper ions
Sampiеs of thе ргepaгеd suspеnsion, 20 ml eaсh, wеrе plaсed in сеntrifugе tubеs.
Aftег сеntrifugation (5000 грпr' 10 min) supегnatant solution was сomplеtеlу removеd
from the solid A knouin amount of a biругidinе solution (0 5 . l0 mmolЛ, рН 6) v;as
addеd to еaсh of thе samрlеs and thе total volume of suspеnsion was сomplеtеd up tо 20
ml Тhе pH valuе of еaсh samp!е iтas сontrollеd and adjustеd to pH 6.0 if nесеssary. Affеr
thе samplеs wеге stirгеd flоr б0 min, the pH was сhесkеd. It did not сhangе signifiсantlу in
all ехpегimеnts. Thеn thе suspеnsion was сеntгifuged and сonсеntrations of bipyridinе and
Сu2* wеre dеtеrminеd in thе sr-rpегnatant еquilibгium solutions.
Spесiаtioп iп |hе soitt|ioп аi|d -'uspе||SiО|l
Тhе spесiatiоn ir sоlutiоns and suspеnsions is сalсulatеd with thе pгogгam GRFIТ
[6J. GRFIТ solvеs sс]utiоn spесiation pгoblеms in hоmo- and hetегоgеnеоus sуstеms. It is
spесiallу wгittеn fоr еr,аluating сonсеntгations, thегmоdynamiсai equilibгium сonstants and
саpaсitiеs, or sitе dеnsitiеs, dеpеnding on thе сhosen doublе-layеr modеl, We сhoosе as a
modеl of suгfaсе ionizatiоn and сomplех foгmation thе сonstant оapaсitanое model (СCМ)
[7] bесau:e all our ехрегimеnts weге madе at strong сonstant ioniс stгength At thе
tгеatmеnt of thе pоtеntiomеtriс titгatiоn data йth GRFIT ргogram thе сonсеntrations оf
aсtivе suгfaсе gгoups and сaрaсitanсе ofdouble еleсtгic layег arе fittеd. Thеn, thеsе valuеs
arе usеd in thе саlсulаtions of еquiiibгium гeaсtion сonstants. Тhе suгГaсе геaсtiоns and
сoггеsponding еquilibгium сonstants сan be dеsсгibed as
=SioH + pCu]* ; il'оipУ <-+ =SioH.* Сuo(bipy)'(2P.^)* + и}I"
{:SioЕL' Cuoфipy)"(2p..)*} [н*]'
g : ------_---------_-:-_ е
(2P. п) F.yд'т
{=sioн} [ Сu,']P [bipy]"
wЬere m=O, 1,2, tt =О'1,2; p =o,l.
Morеovег this pгogram allows us to сalсulatе thе сonсеntration of thе spесiеs in
solution and on thе suгfaсе if thе сomposition of thе systеm (total сonсеntгations and pH)
and the chеmiсal modеl (геaсtion stoiоhiomеtry) arе known.
Rеsults and disсussion
Тhе results of рotentiometric titration of thе siliсa suspеnsion (in absеnсе and
pгеsenсе of сoppеr iоns and bipy) wеге usеd foг the calсulation of thе quantity of protons
adsorbеd on suгfaсе oг rеlеasеd from suгГaсе at thе dissoсiation (Q, mmol/l) :
У1A - l,в B + (vo * ve + vд )х ( K"/ [H-] _ tн'] )
a = -(;;;;'--;;;; ---'-
whеre v7 , vд aге th€ volumes of added aсid or basе with сonсеntгations A and B'
геspeсtivеly, vp is thе initial volume of siliсa suspension (in l ); K* = [I]-l[oн.]
l0-13.78 and [Н-] - сonсеntгation of pгotons dеtегminеd fгom ЕМF mеasuгеmеnts' Тhе
сurves Q as funсtions of pH arе shown in Fig.l. In this figuгe thе positivе valuеs of Q
nеan thе геlеasing of protons frоm suгfaсе and negativе values of Q mеan thе uptakе of
эгotons fгоm solution' Thе ргoton adsoгptiоn on siliсa suгfaсe in thе pН rаngе bеing
, - sion of
: of PH-
,__ з ratios
r fгom
...gе 3-8.
. .:еd with
. : еrnatant
. : ), Karl
. .:omеtry
foгmеd
100 nm
- -еs werе
;2mМ-
solution
nCOz)
sоlution
зjustеd if
t49
studiеd is pгaсtiсallу not obsегvеd Тhе геleasing of protons is a rеsult of dissoсiation of
silanol groups and thе intrinsiс dissoсiation сonstant dеtеrminеd bу еquation is сalсulatеd:
:SiOH ++ =SiO- * H- ; k int =
{=sio'} [H']
ехp (-FY/RT)
{=Sioн}
Y is thе suгfaсе potential. Тhе сalсulatеd valuе of dissoсiatiоn сonstant оf silanol gгouрs
(log k;"1 = -6.90+ 0 03) is in a good agгееmеnt йth liteгaturе data [8,9]. This соnstant was
fiшеd with using of сonсentration of silаnolgroups 0 5 mМ/g and сaрaсitanсе 1.2 F m.,.
As Гoг pоint of zего сhargе (РZC) ivе observе an intеrve] in thе рН rangе 2 . 3 in whiсh
siliсa suгfaсе is pгaсtiсallу еlесtгonеutral оn thе wholе' Thе valuе oГPZС fгom 2 [8-l l] to
2.9 L]'2 ] aге quotеd
In Fig' l potentiomеtгiс titгation data
of siliоa suspеnsion in prеsеnсe of сoрpег
ions oг сoppеr- bipуridinе соmplехеs are 2,a
also pгеsent' Thе соmpaгison of thesе
titration сuгvеs with titгatiоn сuгve oГ siliсa 1.5
aiсlnе allowеd us to сalсulate the
сonсеntrations of protons геlеasеd at thе E ,' .
adsoгption of сoppег ions oг thеiг Е
сomplехеs with bipу on siliсa suгfaсе. d
Тhе сonсеntгation of еaсh spесiеs 0'5
in solution (in thе absеnсе of silica) was
сalоulatеd (GRFIT' ..Solution spесiation'')
as a funсtion of pН using thе сomplех
foгmation and aсidity сonstants геpгеsentеd
in Tаblе l This сalсulation shows that in
solution with гatio Cu : bipу 1:l thе main
сomplех is Cu(bipу)z* , and in solutions
with гatios Cu : bipy |.. 2 and 1:3 thе
pгеdominant spесiеs is сomplех
Cu(bipy)2,- оvег thе rangе ofpH 3-8.
Thе геsults of adsoгрtion studу of Cu2* and bipy onto siliсa suгfaсе arе shown in
Figs.2 and 3. The adsoгption data weге usеd to fit adsoгption сonstants of thr suгfaсе
соmplех formation rеaсtions using thе valuеs of sitе dеnsitу and doublе layег сapaоitanсе
fittеd at thе titгation of siliсa suspеnsion,
Аdsorplioп of Сu2* ions
Тhе сopрег ions adsoгption as a funсtion of pH is shown in Fig.2 The adsorption
of сoppеr ions bеgins at pH >4 and abruptly inсreasеs at p}Ь 5. We suрposеd that suгfaсе
сomрlеxation of Сu2* ions by siliсa involves bond foгmation with suгГaсe silanоl gгoups and
Droton releasе :.
=Sioн + Cu2* <+ =SioFLt Cu- + нt
=SiOH + Cu2* t+ =SiOH-z Cu + 2]F-r
Thе сalсulated еquilibгium сomplех foгmation сonstants for геaсtions (1) and (2) and all
other onеs aге rеpгеsentеd in Table 1.
0,0
pH
Fig.1 Potеntiоmеtriс titгation of siliсa
susDеnsion and its mixturе with solutions
сontaining Cuz*, and Cu2-. bipyгidinе
with ratios 1:l and l:2
(i)
(2)
150
Tаblе 1
Thе сomplех foгmation rеaсtions in
еquilibгium сonstants
solution and onto siliсa suгfaсе and сorгеspondins
rrion of
:ulatеd:
)
qгouрs
ent was
I F m-2.
r rvhiсh
3-i l] tо
Rеaсtiсln logК'nt
Bipу + H- <+ Ьipy}I-
Bipу * 2H. ++ biрy}I2l.
Сu2 + bipу ++Сu(bipy),.
Сu, .н 2 bipy ++ Cu(bipy)22.
Cr:, +3bipy э Сu(bipv).z'
.SioН +* =Sio - l{t
=SioН - Сu2- ++ =SioСu. + ij-
=SioH - Сu,' * Hzo ++ =SioСuoН -t 2H-
-sioн + biPУ +} =SioH(biр1,)
=SiOН + }{.l. .biру-
t.> =Siol{(Hoipу)-
=SiOН + Сu2' + biРУ +.* =SioНСu("ЬIр.;)-
=SioH + Сu2- + biРУ ++ =SrQfц16io.,,. + }I-
-siOH+Сu2"+ biPУ+H:o э=SioCuoH(bipу) + 2I7.
=Slol{ + Сu2" -r 2bip:t *э =SiOl{Сu(bipу),
=SioFl + Сu2- - 2ь\pУ <+ =SioСrr(biрv)z. .l. H-
=SioН + Сu2. + 2bipу rДlo +} =SioСuoHQP9зj_щ:
Тhе tFI"]/{Cuzt} eхсhangе stoiсhiоmеtry of thеsе геaсtions wеге dеtегminеd usins
::lе pоtеntiom.еtгiс titгation data' Thе potеntiomеtгiс сuгvе (Fig.1) of siliсa suspеnsioi
'оntaining Cu2* ions рassеs highег than a сuгvе of siliса titгation] whiсh is еvidеnсе of.jгoton геlеasе at thе Cu,t iоn adsoгption onto thе siliсa strгГaсе. Тo dеtеrminе the rаtio of
Ц. геlеasеd соnсеntгation to Сu2- iоn adsorbеd сonоеntration we mоdеlеd thе titration
:un'е with thе GRFIT program Wе took into aссount ргoton rеlеasе at thе dissoсiation of
'iliсa itsеlf and trr'o rеaсtiоns of Cu2* ion binding with silanol gгoups on Еqs' (1) and (2)
l.l,е bеst agгееmеnt bеtweеn expегimеntal and сalсulatеd titration сuгvеs as wеll as
aqrеemеnt bеtwееn ехpегimеntal and сalсulatеd adsoгption сuгvеs wеге obsеrvеd at thе
:згmatiоn on thе suгГaсе both сomplехеs . on thе onе hand, wе supposеd that a sесond
]гoton was fогmеd at thе hуdrolysis of adsoгЬed сoppеr ions that is геlеasеd from water
:lolесulеs in thе сoordination sphеге о| a hуdгatеd сu2- ion' Thе possibility of foгmation
:f suсh соmplехеs is сonfiгmеd hу us [4] and othегs Il4] on ЕSR spесtгa of сopрег ions
зdsorbеd on siliса. Тhе intеnsity of thе ЕSR signal in suсh speсtгa is lеss than сould bе
:\pесtеd fгоm tоtal сonсеntгation оГ adsoгbed сoppег' Apparеntly somе paгt of сoppeг
зхists оn thе suгfaсе as hуdroхoсomplехеs whiсh arе inсlined to formation of polynuсlеaг
:lamagnеtiс сlusters, on thе otliег hаnd, thе сonсеntгatiоn of silanol gгoups 0.5 mlWg
:orгesponds to thеiг distгibution , 1 sioH l nm2, and thе distanсе bеtwееn two silanol
]гouрS appгохimatеlу 1 13 nm, Тhis distanсе is largеr than nесеssary for the fогmation of
:оmplеx rvith рaгtiсipation of ti,.''о silаnol groups. AJthough it is impossible to ехсludе thе
l5t
4 '4З L|3J
s e3 П31
8 00 ш31
lз.50 [lз]
r6 e0 П31
-6.90t0 0з
-4 20t0 c3
- 10.3610,03
201t003
6'49+ О Оц
988t00з
502+00з
-3'2б t 0 08
1567r003
10201003
2 26 ! 0.О9
: siliсa
: .,rtions
.:nе
i:.оwn in
е suгГaсе
;.сitanсе
с.icгption
a: surfaсе
г:.рs and
I .nd all
iггеgulaг distribution ofsilanol groups on thе suгfaсе and
сlosег aггangеment of thеsе groups So wе сan maгk
{:SioCuoн}.
thе pгesеnсе of suгfaсе arеa йth
this сompleх as {=Sio}Lz Сu) or
ё
4о
20 -*-+
.l
pн
Fig.2 Adsorption of Cu2* and bipу from
individual aquеous solution as a funсtion
oГpH (C*: O 5 mМ' C6;p.;:0 5 mJvl,
Сs;oz: 5 8Л )
10о
pР|
Fig.3 Adsorption of Cuz- ions and bipy Гrom
soiutions with diffеrеnt гatios as a funсtion of
pн (с* = 0,5 mМ, С6io, = 0.5;1,0; and 1.5 mМ'
Cslоu = 5 c/\)
Аdsсsrptiotl of 2,2'-bipуridinе
Тhе bipугidinе adsоrption оn siliсa surfaсе frоm aquеous solutions as a funсtion of
pH is shоwn in гig'z. Wе assumеd foгmation of 2 binary сomplехes and сalсulatеd thеiг
equiiibгium геaсtion оonstants aссогding йth еquations (3) and (4) with using GRFIT
progгam :
=SioH + bipу <-.) =SioH(bipу) (з)
=SioН + Hbipу- ++ =SioН(Hbipу)-
(4)
ТhеfoгmationofthеsесomplехеsisсonfirmеdbyUVrеflесtanсeabsoгption
spесtra. Wе isolatеd ,"u..ut samplеs of adsoгbеd bipyridinе fгom solutions йth diffеrеnt
pI{ ;;; obsегvеd in UV геflесtanсе spесtra absorption band at -280 nm whiсh is
сhaгaсtеristiс foг nеutral bipу mоleсulе and at -300 nm inhегеnt foг protonated foгm oГ
bipугidinе
Аdsorption of сoppеr . 2,2'-bipуridiпе complехеs
Thе rеsuits of thе adsЫption study of сoppеr ions and bipyгidinе from soiutions
with moiar гatio 1:1, 1:2 and l:3 arе pгesеnt in Fig.3. At thе adsoгption from mutual
solutions an еssеntial in"..u,. in сoppеi ion adsoгption is observеd. At low pН 3 - 5 the
;;;.; оonсеntrations Cu2* and bipy rеmain almost сonstant. At pН > 5 thе prгсеntagе
of adsorbеd сoppег ions and ьipу гailаtу inсrеasеs with pH. Thе almost full agreеment
of Cuz* and bipу adsoгption гl.o' soiution with гatio i;1 suggests that thе main adsoгbed
spесiеs is the сomplе* ёutЬ,pуl,t Тhе-fraсtion of adsoгbеd bipy from solution with ratio
ili is stigьttу lеsi than tйai-of adsorbеd сoppеr ions- It'сan aгisе from simultaneous
"а,й'i"i
oi сu(ьipуf- and Сu(bipy),,-. тьЪ molar fraсtion adsorption of biрy fгom
solution with гatio 1:3 is approximaiеiу lеss bу a faсtoг of l.5 than adsoгption of сoppег
ions suggеsting tnat сomp1.еi ёuФipу),,- is. pгеdominantlу adsorbеd on si1iсa suгfaсе. Тhe
сompaгison of thesе oatu.йtь poi.ntio'"t'li data indiсatеs that thе intегaсtion of сomplех
152
i .\ith
.j.oг
с' ffom
u;i:cn of
i'5mМ'
:.;n of
г thеiг
с.].FIT
:
к:ption
t.jегеnt
r:.:сh is
::m of
Е. ]tlons
r :utual
j.5thе
r: зntagе
Е:еmеnt
ш'sorbеd
г:.: гatio
!;: з1eous
в ' from
в :oppег
Ё:е Thе
i'::nplех
ions with suгfaсe in pH гangе from 3 to 4 is not.aссompaniеd by rеlеasе of pгotons, at thеinсгеasе of pH onе pгoton rеlеasеs pег аdsoгbed .opp". ion lJ.ut pH > 6 5 slightiyеnhanсеment of rеlеasеd proton сonсеntгation is ЬЬsеrvеd' The last is еvidеnсе thаtreaсtion with геlеasе of 2 protons is possiblе.
Тogеthег with binary сompleх foгmatiоn rеaсtions for Cu2* (1), (2) and ibг bipу(3)' (4) on siliсa suгГaсе we assumеd the Гollowing гeaсtions of tегnary сompleх {brmationsand сalсulatеd thе сoпеsponding equilibгium
"on*uun.,.=SioН + Cu2- + 61p, € =SioHCu(bipy),- (5)
=SioFI * Cuz* + biPУ Ф
=sioF{ + Сu2. + biPУ + Hzo +>
=SioH + сu2* + zЬipУ Ф
=SioH * Cu2t + zbipy Э
=SioH + Cu2t + 2bipу + Hzo <->
Fig.4 Suгface speсiation of сoppeг-
bipyгidinе сomplеxеs'
=SiOCu(bipy). + ffu (6)
=SioCuoН(bipу)
=SiOHCu(bipy)22.
=SioCu(bipу)2' J т-I*
' ll
=SiOCuOH(bipy), + 211- ( l0)
(8)
/q\
Using thеsе сonstants wе сalсuiatеd
thе сomрosition оf adsоrptiоn leуег опtо
siliсa suгtасе in dереndеnсе of pH and
сomposition оf solutiоns соntaining Сu2
and bipy (Frg a). It was found that at thс
adsогption ltоm solutiоns соntajпIng сoрpег
ions and biрv iп diffегеnt rаtiоs оnly tегnani
сomplехеs аге foгmеd onto silrсa suггaсе
Wе obsеп'еd in thе геflесtanсе spесtra of
thеsе samplеs in UV-rеgion thе aЬsoгptiоn
bands inhеrеnt to сomplех iоns Сu(biрy)2-^
and in visiblе гegion - absогption bands of d-
d transitions of сoppег ions сontainins the
nitrogеn donoг atoms in сoоrdination ,o.h...
t4l
Аdsorption of 2,2,-bipуridiпе аt thе
siliса modфеd with copреr ioпs
The геsults of thе adsoгption.
mеasuгеd for 2,2 -bipугidjnе on thе suгfaсе
оf siliса modifiеd u'ith сoppег iоns aге
prеsеnted in Тablе 2' Тhе еxpегimental data
aге. thе сonсеntгatiсlns of 2,2,.bipyгidinе and
Cu2* in thе еquilibnum soiцtions aftег
adsorption. Thе valuеs shоw that with
inсгeasing thе 2,2.-bipугidinе total
сonсеntгation thе arnount of adsoгbеd
сopреr ions dеcrеasеs' Thе rеasоn fоr thе
deloгрtion ofCuz. is thе dесгеasе оfthе fгее
Cu"- сonсеntгation duе to thе fогmation оf
геlativеly stablе сoppег - 2,2.-bipугidinе
сompleхes in solutiоn, Thе ггее
-
bipv
сonсеntгations [bipy], r-r,hiсh arе alsti sivеn in
s|oсUoньlp
sioнсU(blру).l.
sioсU(ь|py),
s|oнсU(Ьlpу)ll.
сu,ЬjPу 1,3
s io с uo н (ь.Pу
I.5-j
Table2, aге сalсulatеd from mеasuгеd total сonсentгation of Cu2* and 2,2'-Ьipyгidinе and
* ;" of the solution using the еquilibгium сonstants of thе protonаtion of bipy and the
"o*pl"*
foгmation rеaсtions with сopper ions Il3]'
Tablе 2
initi"t unа еquilibrium сonсеntrations of bipу and соppеr ions
iisioнj = i mmoИ; {Cu} =o sт-mцoyt;,p,н.о; 0.t LtlчNo..)
Co'o,',,,.,,o,Ы'oolequilibriumTotalеquilibпum-logtьily1
mmol/l сonсеntration, сonсеntгation,
mmoUl mmol/l
0.50
0.56
0б0
0.7 5
0.84
1 i5
1.30
170
2.00
з.20
4.00
6.00
8.00
10.0
0.8'7',7
0.982
1 053
1.з 1б
1.4',7 4
2 018
2.280
2.982
3.510
5.614
7 018
l 0.526
14 035
t7.544
0.108
0.126
О |42
0 211
0.255
0 4з9
0 569
0.960
1.275
2.3 08
з.02
4.68
б.3 5
8.062
0.1 57
0.lз5
0.133
0.r50
0.1 56
0 192
0.216
0.264
0.307
0.380
04з1
0.470
0.515
0.522
I. t6
'7.12
6.4',7
5.62
5.з.7
446
400
350
2.90
2.15
2.50
,?o
2.20
* - сalсulatеd from еxpегimеntal total еquilibrium сonсеntrations bipу and Сu(II) using thе
program GRFIT.
Еarliегweassumеdthattheadsoгptionofсopperiоnsonsiliсasuгfaсеfrom
solutions at pH > 4 сould bе modеled postulating the foгmation of two suгГaсe сompleхes
with thе stoiсhiometry {=SioH.rCu-} and {=SioH.zCu} if .
thе surfaое сovегage was
lowеr than o.2з уoof monolayer. Wе shouljmеntion that at highеr Cu2* loading suгГaсe
prесipitation oг.opp., ьydroxidе :P:.l.,tyu'obsегvеd
еvrn at a surfaсе сoveragе as
low as 0.s % [14]. A;;й о 1= sioСut} aссounts appгoximatе|у 6О% of total amount of
adsoгbеd сopper ion,..-
.
й a stuаy of thе intеraсtion of 2,2..bipyridinе with a suгГaсе
modifiеd bу .adsorbеd сu]i on. has in addition to thе foгmation of thе tеrnary Cu2t -
2,2,.Ь\pуridlnе sцгfaсе .o'pi.*., to сonsidеr thе adsorption of 2,2,.Ьipуridinе bу aсtivе
sitеs of thе siliсa suгfaсе. Tйe stoiсhiomеtry and thе еquilibrium сonstants for this pгoсеss
were detеrminеd in ." i"o.p."с"nt eхpегiЬent by mеasuгinc Ц".adsoгption
of bipy as a
funсtion of pH. Using the сonstants -in
TabtЬ 1 wе сalсulatеd the isothегm for
2,2,-bipуr\dtnе and с"?- uа,o,p'ion in this ехpeгimеnt. Figuге 5 shows thе еxpеrimеnta1
data points and thе .;;."й;;; ;;e (so1id tinе;. тье good agreеmеnt сlеaгly indiсates
that, undеr thе сonditions of our ехpеrimеnt, pн 6, [Cu,t 1,o..< 9 {sioн}ьt , all thе
rеaсtlons arе геvегsiblе at thе siliсa suгfacе and ihe spесiation is сontrollеd bу
il,.i'ooуnu'iсs within thе timе sсalе of thе ехpеrimеnt.
ts4
:cinе and
:.' and thе
:g[bipy]
iее *
Фt
I
(.rt
I
B
+
(bipy)*
5
-loslыpу]
Fig.5 Ехpегimеntal (points) and
Calсulatеd (solid linе) isotheгm of
Bipyridinе adsoгption on сoppег.
Containing siliсa suгГaсe: {SioFI} =
0.5 mmoVg, {Cu} = 0.57mmoUg,
{bipу}юиr = 0.5 - 10 mmoИ, pH 6 0.
Fig.6 The suгfaсе distributiоn of bipугidinе
сomplеxеs onto сoppег-сontaining siliсa
(tsioЕI) = 0.5 mmoVg' {сui :0.057 mmol/g'
pн 6.0 ).
r78
-12
r +/
562
I J/
r00
r50
_90
_ I>
_JU
-20
Тhе distribution of surfaсe bipy сomplехеs as a funсtion of fгее bipy сonсentгation
is shown in Fig.6. Diffеrеnt сomplеxеs of bipy arе foгmеd at thе suгГaсe oГ сoppег-
сontaining siliсa as a funоtion of inсгеasing bipу сonсentration. At low biрy сonсеntrations,
iowег oг about еqual to the amount of adsoгbеd Cu2-, thе сomplех {=SioCubipy-} is
foгmеd' Under thеse сonditions thе adsoгptiоn of bipу is stгongly еnhanсеd bу thе сu2- at
thе suгfaсе. At highеr bipy сonсentгations thе сomplех {=SioCu(bipУ)z-) is formed оn thе
suгГaсе. Howеvег, thе amount of this spесiеs at thе suгfaсе is small, bесause a signifiсant
paгtofadsoгbеdсoppeгions goеsintosolutionasCu(bipу)'2* (n: l,2,3)' Atеvеnhighег
bipу conсеntгations thе сoppeг ions disappеar praсtiсallу сompletеly from thе suгГaсе
and eхсеss bipyridinе foгms thе binаry suгГaсе spесiеs {=SioHbipy} and {=SioH t{bipy-}
with suгГaсе silanol groups' Thе UV геflесtanсе spесtra of thе samplеs also сonfiгm thе
formation of thesе сomplехеs. Wе isolatеd sevегal samplеs that сoгrеspond to diffегеnt
сompositions of adsoгption layer and obsеrvеd in UV spесtra two adsoгption bands at з00
and 3l0 nm inhеrеnt foг сomplехes Сu(bipy)2t and Cu(bipy)22- and onе band at 280 nm,
whiсh is сhaгaоteгistiс foгbipyгidinе not bound with сoppег ions [15].The сonсеntrations
of сomplеxеs in whiсh bipy is bound to the сomplех {=SioCuoН} are vеry small; they
nеveгeхсееd 0.1 рmoUg.
Fгom thе гesults of ouг mеasurеmеnts, wе сan dеduсе thе еquilibгium сonstants fоr
the binding of bipyridine onto Cuz* immobilizеd to thе siliсa suгfaсе bv thегmodynamiс
сyсlе. Thе сonstants show that thе bipугidinе pгеfеrs stгonglу tо bе bound to Cu2* at thе
suгfaсе rathег than diгесtly to thе SioH sitеs .
{=SiOCu') + biРУ ё {=SioCubipу" ) IogK: 9.22
{=SioCubipу}- + bipy Э {=SioCu(bipy)2-} lоgK= 5l8
A сompaгison with the сoгresponding сomplеx foгmation сonstants in solutiоn
indiсatеs that thе 1.1 сomplех foгmation is moге favorablе at thе suгfасe (logK : 9 22)
.l:lg thе
: fгom
^ plехes
::е was
s lгfaсе
.1-]е as
- -:nt of
. . -rгГaсе
tt -
зсtivе
]:cсеss
:. as a
,r for
.:.еntal
.:lэates
:., thе
.: by
1.55
than in solution ( logK = s 00). This rеsult is diгесt еvidenсе of thе additional stabilitу
of thе tегnary suгfaсе сomplехеs. Thе affinitу foг thе sесond bipy moleсule is slightiу lеss
favorablе than that in solution. Thе introduсtion of sесond bipу molесulе into сoordination
sphеге of thе сomplех {=SioCubipyt} is stегiсallу hindеred аnd requiгеs of sцbstantial
геaгrangеmеnt of thе struсtuге of tегnary suгfaсе сomplех.
Алother intеrеsting еquilibгium сonstant that might be dеduсеd from thе rеsults, is
thе onе fоr thе formation of thе tегnary suгfaсе сomplехеs of Cu,' and bipу, staгting from
adsoгbed bipyridine and adsoгbеd Cu2-. This rеaсtion сoпеsponds to a redistribution of
thе molесulеs at thе suгfaсе, In thеsе геaсtion thе numbеr of еduсt spесiеs is еqual to thе
numbеr of pгoduсt spесies. Hеnсе, the еquilibгium сonstants for this геaсtiоn is
indеpеndеnt оfthе сonсеntration sсalе геspесtivеlу thе standard statе usеd:
{=SioСut} + {=SioHbipу} э {=SioCubipу- } + {=SiOH} logK1''u,= 1.2
{=SioCubipу. ) {=sioH-}
logKt'..,'г
{=SiOCu' } { =SiOllbioYi
{=SioCubipу-}+ {=SioHbipy} ++ {=SioCu(bipу)z-i - t=Sioн} logK2,,u6= 3.2
{=SioCu(bipy),-} {=Sioн}
loBKZ,su.i =
{ =SioCubipy- } { =Siol]biрy}
Thе сonstants ofthе reaсtion at thе suгfaсе are smallег than thosе foг thе rеaсtions
in solution, This givеs somе hint into thе influеnсе of thе sol.;ation on сompleх foгmation.
Wе think that this dесгеasе оf thе stability is mainly duе to a геduсеd hydrophоbiс еffесt оf
bipy in thе suгГaсе laуег. The fгее bipуridinе mоlесulеs in whiсh the aгomatiс сyсlе arе
hуjrophobiс aге dеstabilizеd bу unfavorable solvation in аqueous solution, whiсh suppoгts
.Ь.pi.* foгmation undег thеsе сonditiоns. This еffесt is lеss pгоnounсеd Гoг bipугidinе
adsоrbеd onto siliсa suгfaсе.
Summary
ouг measurеmrnts of adsorption of 2,2,-Ьipуridinе onto a hydrous siliсa suгfaсе,
whiсh prейously modifiеd by Cu2- , sho*s с1еariy that thе equilibria arе сontrollеd bу thе
samе еquilibrium сonstant, uЪ t.l.nury suгfaсе сomplех foгmation. This indiсatеs that all thе
suгfaсе геaсtions in this sуstеm arе thегmodynamiсallу сontrollеd, at lеast undег thе
сonditions of ouг ехpегimеnt. This mеans еspесially low сoppеr ions suгГaсе сovеragе to
,upp,",, thе foгmaiion of Cu(oH)2 phasеs at thе surfaсе. Undеr thеsе сonditions
еquilibrium сonstants foг many diffeгent suгfaсе pгoсеsses сan be obtained using
thеrmodynamiс сусle.
Aсknоwle.dgemеnt
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| id | oai:ojs.pkp.sfu.ca:article-54 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-09-24T17:44:39Z |
| publishDate | 2001 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/68/9046cc3452ff44ab9bd16a2249852268.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-542018-11-27T09:42:39Z Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica Vlasova, N. N. Schlapfer, C. -W. Golovkova, L. P. Svezhentsova, A. A. Chuiko, A. A. The enhanced adsorption of copper ions onto silica surface from the solution containing 2,2'-bipyridine is explained by ternary surface complex formation. The equilibrium reaction constants of binary and ternary complexes have been calculated using constant capacitance model. The potentiometric titration data were used in order to determine the H*/Cu2+ exchange stoichiometry. The adsorption of 2,2'-bipyridine on a copper-containing silica surface has been studied too. The equilibrium of 2,2'-bipyridine binding to immobilized copper ions are well reproduced by the constants for the formation of ternary surface complexes from an aqueous solution containing copper ions and 2,2'-bipyridine. This indicates clearly that under experimental conditions all reactions are reversible and speciation is controlled by the thermodynamics. The enhanced adsorption of copper ions onto silica surface from the solution containing 2,2'-bipyridine is explained by ternary surface complex formation. The equilibrium reaction constants of binary and ternary complexes have been calculated using constant capacitance model. The potentiometric titration data were used in order to determine the H*/Cu2+ exchange stoichiometry. The adsorption of 2,2'-bipyridine on a copper-containing silica surface has been studied too. The equilibrium of 2,2'-bipyridine binding to immobilized copper ions are well reproduced by the constants for the formation of ternary surface complexes from an aqueous solution containing copper ions and 2,2'-bipyridine. This indicates clearly that under experimental conditions all reactions are reversible and speciation is controlled by the thermodynamics. The enhanced adsorption of copper ions onto silica surface from the solution containing 2,2'-bipyridine is explained by ternary surface complex formation. The equilibrium reaction constants of binary and ternary complexes have been calculated using constant capacitance model. The potentiometric titration data were used in order to determine the H*/Cu2+ exchange stoichiometry. The adsorption of 2,2'-bipyridine on a copper-containing silica surface has been studied too. The equilibrium of 2,2'-bipyridine binding to immobilized copper ions are well reproduced by the constants for the formation of ternary surface complexes from an aqueous solution containing copper ions and 2,2'-bipyridine. This indicates clearly that under experimental conditions all reactions are reversible and speciation is controlled by the thermodynamics. Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2001-06-10 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/54 Surface; No. 4-6 (2001): Chemistry, Physics and Technology of Surface; 147-159 Поверхность; № 4-6 (2001): Химия, физика и технология поверхности; 147-159 Поверхня; № 4-6 (2001): Хімія, фізика та технологія поверхні; 147-159 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/54/53 Авторське право (c) 2001 N.N. Vlasova, C.-W. Schlapfer, L.P. Golovkova, A. A. Svezhentsova, and A. A. Chuiko |
| spellingShingle | Vlasova, N. N. Schlapfer, C. -W. Golovkova, L. P. Svezhentsova, A. A. Chuiko, A. A. Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_alt | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_full | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_fullStr | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_full_unstemmed | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_short | Surface complex formation at the adsorption of Cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| title_sort | surface complex formation at the adsorption of cu2+ ions and 2,2'-bipyridine onto highly disperse silica |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/54 |
| work_keys_str_mv | AT vlasovann surfacecomplexformationattheadsorptionofcu2ionsand22bipyridineontohighlydispersesilica AT schlapfercw surfacecomplexformationattheadsorptionofcu2ionsand22bipyridineontohighlydispersesilica AT golovkovalp surfacecomplexformationattheadsorptionofcu2ionsand22bipyridineontohighlydispersesilica AT svezhentsovaaa surfacecomplexformationattheadsorptionofcu2ionsand22bipyridineontohighlydispersesilica AT chuikoaa surfacecomplexformationattheadsorptionofcu2ionsand22bipyridineontohighlydispersesilica |