Tgp chi phdn tich Hda, Ly vd Sinh hgc - Tap 19, Sd 3/2014
DIEN Circ BIEN TINH BANG BITMUT OXIT XAC DINH VET KIM LOAI BANG PHU'ONG PHAP VON-AMPE HOA TAN ANOT
Den tda sogn 23 - 4 - 2014
Nguyen Thi Thu Phirong Khoa Cdng nghe Hda hgc Tru&ngDgi hoc Cdng nghiip Hd Noi
Trinh Xuan Gian Viin Hda hgc
Viin Hdn ldm Khoa hgc vd Cong nghi Viet Nam SUMMARY
BISMUTH OXIDE - MODIFIED ELECTRODE FOR DETERMINATION OF METAL TRACES BY ANODIC STRIPPING VOLTAMMETRY A new chemically modified electrode was constructed for accurate, selective and sensitive simultaneous determination of cadmium (Cd) and indium (In) by anodic stripping voltammetry (ASV). The electrode was prepared by multi-walled carbon nanotubes (58%), parafin oil (35%) and BiiO, (7%) in carbon paste electrode. The linear range between 8.9xl(T''Mto 1.33XW'M for Cdand4.34xW^Mto 2l7xl(r'U for In. The 36 determination limit is l.O/xlO'Mfor Cd and 1.04xlO-^M for In with suitable conditions (buffer acetate and KBr 01 M, pH = 4.5, deposition at -1.2Vfor 180s) The proposed chemically modified electrode was used for the determination of cadmium arui indium in several water samples.
_ , phap cd dp chmh xac, dd nhay cao Do the pic Ep cua hi ya Cd gin sat nhau fliudng dugc su dmig dl xac dinh ham nen vice xac dinh ddng flidi hi va Cd lugng vlt cac khn'loai, Tuy nhien fliuy bang phuong phap Von-Ampe la phuc ngan va mudi cua nd cd ddc tinh cao.
tap. De khac phuc nhugc diem nay cln cho nen da cd nhilu nghien cuu tim CO them chat tao phiic fliich hgp dl tach kilm vat lieu dien cue mdi fliay flil pie [2].Phuang phap Von-Ampe hda tan thuy ngan nhu: cacbon. vang, bac, iridi, su dung dien cue thuy ngan la phuong bitmut, tantali, antimon [3,4]. Trong sd 58
dd, do it ddc, than thien mdi trudng, dien cyc bitmut trong nhieu trudng hgp dugc coi la tot nhit cd thi thay the dien cue thuy ngan vdi khoang the lam viSc tuong ddi rdng, kha nang phan tich dien hda tdt [3,5].
Trong bai bao nay, chiing tdi trinh bay ket qua nghien ciru che tao dien cue paste dng nano cacbon bien tinh bing Bi203 (Bi203 - CNTPE) va ling dung phan fr'ch ddng then ham lugng Cd, In ttong mdt sd mau nudc vdi dung dich nen la dem axetat cd them tac nhan tao phirc KBr de thay ddi tugng ddi the cua In, tach hoan toan hai dmh pic cua In va Cd.
2. THUC NGHIEM
2.1. Thilt bi - Dung cu - Hda chit Thiet bi cue phd da nang 797 VA Computtace do hang Mettohm (ThuySi) san xuat.
- Can phan tich 5 sd TE 214S, sai sd 0,lmg do hang Sartorius (Dire) san xuat; Cac dung cu cdi, chay ma nao (Trung Qudc); ong teflon (Due), dung cu thuy tinh, micropipet (Diic)....
Ong nanocacbon (Han Qudc), dau parafm (Nhat Ban), Bi203 (Dire). Cac dung dich nghien ciiu dugc pha che tir hda chit tinh khilt dung pban tich cua Merck va nudc cit hai lan, sieu sach.
2.2. Che tao dien circ lam viec Vat lieu dien cue bao gdm: dng nanocacbon, diu parafm, Bi203. Chuan bi cac dyng cy che tao dien cyc gdm:
coi chay ma nao, chdt inoc de nhdi hdn hgp vat lieu vao dien cue, gia dd dien cyc, dng teflon, ...(hinh la).
Che tgo vd diin cue: Tien dng teflon cd chilu dai 52 mm, dudng kinh ngoai 3,5
mm, dudng kinh trong 3,0 mm. Phan fren dng cd tien cac doang de gan vdi mdt chdt bang inoc fren thiet b] cyc phd (bg phan dien cyc lam viec). Phin dudi de nhoi vat lieu dien cue.
Quy trinh che tgo: Can chinh xac hdn hgp gdm dng nanocacbon (CNT), Bi203,dlu parafin theo ti le thich hgp cho vao cdi ma nao, trdn deu bang chay ma nao. Hdn hgp vat lieu (hinh lb) thu dugc dem say d 105°C frong 2 gid. Lap dng dien cue teflon vao gia dd dien cyc, diing chdt nhdi bang inoc nhdi hdn hgp thu dugc vao dng dien cue teflon, mai bdng bl mat dien cue tren giay lgc am dugc dien cue Bi203 - CNTPE hoan chinh (hinh lc). Lap dien cyc vao v] tri dien cyc lam viec (WE) cua thiet b] cue phd.
3. KET QUA VA T H A O LUAN 3.1. Nghien cuu anh hirdng cua ti le khoi lirgng vat li^u tron tdi tin hieu do ciia Cdviiln
De khao sat ti le khdi lugng cua vat lieu frgn den tin hieu ciia Cd va In, chiing tdi frgn cac ti le khdi lugng khac nhau cua hdn hgp dng nanocacbon, diu parafin, Bi203. Theo [5], ndng dp Bi203 thich hgp de che tao dien cyc cacbon bien tinh bing BiiOs la 0,5 % din 7 %. Vi vay chung tdi tien hanh che tao dien cyc vdi nong dp Bi203 tir 0,2 % din 8 %, sau dd ghi do ddng Ip cua dung dich gdm [Cd^*] 4,5.10"* M, [In^*] = 7.8.10'* M frong dung dich nin dem axetat va KBr 0,1 M, pH = 4,5 fren dien cyc che tao dugc. Ket qua cho thiy khi ti le dng nanocacbon, Bi203,dlu parafin
59
la 58:7:35 hoac 58:5:37 (tmh flieo phan fram vl khdi lugng) cho tm hieu Ip cua Cd'* %a hi'* tuong ddi cao, pic thu dugc can ddi nen chung tdi chgn cac ti le nay dl chl tao dien cue. Cac nghien Cliu tilp flieo su dung dien cyc cd thanh phin dng nanocacbon, Bi203,dlu parafin la 58:7:35 .
3.2. Nghien ciru clu triic bl mat dien cue
D I tim hilu can tnic bl mat cua dien cyc chl tao dugc, chiing tdi tien hanh chup anh hiln vi dien hi quet (SEM)
, ^
cua 2 mau: mau flng nanocabon \ a mau dien cyc Bi203-CNTPE. Ket qua cho thSy 6ng nanocacbon ban dau co kich
\h\x6c sieu nho cof khoang 50 nm. sau khi dugc sii dung de che lao dien circ BiiOs-CNTPE, tfencuc mcd co kich thuoc CO khoang 500 nm, be mat tuong doi ddng deu tao dieu kien cho qua trinh tao mang bitmut cung nhu qua trinh lam giau kim loai tren lop mang bitmut dugc hieu qua hem.
Hon hop vat lieu
/
Chot kjmloai
I
Hinh la. Cdc dung cu de Hinh lb. Hdn hgp vdt Hinh lc. Hlnh dnh dien chi tgo diin cue liiu sau khi dugc trgn deu circ BijOs - CNTPE 3.3.Nghien ciru khoang the lam viec
ciia di^n cyc va chon nen.
Khao sat khoang the lam viec ciia dien cue trong 3 mdi trudng khac nhau: HCI O.IM: NaOH 0,1M; dem axetat •^ KBr O.IM (pH =4.5). Ket qua cho thiy nin dem axetat + KBr cd khoang thi lam
\ iec rpng nhat. Dieu nay dugc giai thich la do frong mdi trudng axit HCI 0,1M cd flie xay ra sy khii hidro tao bgt khi Hi bam len be mat dien cyc lam viec va ttong mdi Uirdng NaOH O.IM cd thi 60
tao Bi(0H)3 lam giam lugng Bi tren be mat dien cue, do dd giam khii nang lam giau cua kim loai. Mat khac, khi khao sat tin hieu Ip cua dung dich gdm ]Cd" ]
= 4,5.10'*M, [In^"] = 8.7,10"''M lln lugt trong mdt sd nen do nhu dem axetat 0,1M (pH = 4,5): dem axetat va KCI 0,1M, dem axetat va NaNOs O.IM. dem axetat va KBr 0,1M (pH =4.5) thi chi co nindem axetat 0,1M \a KBr O.IM (pH
= 4,5) cho 2 dmh pic cua 2 kim loai tach rieng biet, pic thu dugc cao \a can
ddi. cac nen cdn lai cd sy chen lan pic cua 2 ion. Dieu nay dugc giai thich la do Cd va In cd the gan nhau nen d cac nin KCI 0,1M, NaN03 0,IM, dem axetat 0,1M (pH = 4,5) cd sy chen lln pic ciia 2 ion: ttong nen dem axetat va KBr, KBr da tao phiic vdi indi lam thay ddi the dinh pic cua indi nen da tach hoan toan 2 pic ciia In va Cd ra khdi nhau. Chinh vi the chiing tdi chpn nen dem axetat 0,1M+ KBr 0,1M (pH = 4,5) cho cac nghien ciiu tiep theo.
3.4. Dac tinh Von-Ampe hoa tan cua Cd(II), In(III) tren dien cue Bi203- CNTPE
Khao sat dudng Von-Ampe vdng (hinh 2) trong 2 trudng hgp: (1) nin dem axetat va KBr O.IM (pH = 4,5); (2) nhu (1) nhung cho fliem [hi'*] = 3,05.10'' M; [Cd^*] = 3.12.10'' M.Klt qua cho thay d (I): chi xuat hien dinh ciia kim loai Bi tai Ep = +0,004 V chiing td frong khoang the nghien cihi, fren dien cue lam viec nen dem axetat khdng gay ra phan irng dien hda nao khac ngoai phan ling dien hda cua Bi nen khdng anh hudng din tin hieu hda tan ciia Cd, In.
a (2): xult hien 3 dinh pic ciia Bi, Cd, In vdi till dinh Ep(Cd) -0.746V, Ep(In) = -0,645V, Dmh hda tan ciia Cd, In kha ldn nen hoan toan cd thi ap dung
de dinh lugng Cd, In frong dung dich, 3.5. Nghien cihicac dieu kien ghi do De xay dyng quy frinh xac dinh ham Iugng Cd, In bang phuang phap Von- Ampe hoa tan, chiing tdi tien hanh nghien ciru cac thdng sd ghi do thich hgp nhu: khoang quet the, tdc do quet the, the lam sach, thdi gian lam sach, thdi gian nghi, bien dd xung (hlnh 3a), thdi gian tao xung, tdc dd quay dien cue, thdi gian sue khi nito (hinh 3b).
Ket qua nghien ciiu cac Ardng Von- Ampe hoa tan anot xung vi phan thu dugc khi ghi do dung dich chiia [Cd ^ = 1,78.10"*M, [hi^*] = 8,7.10"*M frong nen dem axetat (CH3COOH 0,1 M va NaOH 0,1 M pH = 4,5) va KBr 0,1 M cho flily cac dieu kien thich hgp ghi do la:
The dien phan lam giau: -1,2 V Thdi gian dien phan lam giau: 180 s Khoang quet till tir: -1,2 din +0,3 V Tdc dp quet till: 0,015 V/s The lam sach: +0,3V Thdi gian lam sach: 30 s Thdi gian nghi: 10 s Bien do xung: 0,03 V Thdi gian tao xung: 0,04 s Tdc do quay dien cue: 2000 vdng/phiit
Thdi gian sue khi nito: 350 s
ITuih2FhdSghidotinhieu /p dia Cdvd In bdngphuong
phep Von-Ampe vong (CV)
Hmh 3aPhd dd DP-ASV tm cac bien dp xung khdc rfiau (0.02 V; 0.03 V; 0,05 V)
Hmh 3bFhd do DP-ASV tgi cdc th&i gicm duoi oxi Ididc
nhau (60s; 250 s; 350 s) 61
3.6. Khoang tuyen tinh,d6 lap lai, do nhay, gidi han phat hien va gidi ban dinh lirgng
Bang thuc nghiem, khi dien phan dung dich chiia Cd, In d thi -1,2 V chiing tdi da xac dinh dugc Ip phu thudc tuyen tmh vao ndng dp cua Cd tir 8,9.10" M den 1,33.10"' M va ndng dp ciia In tir 4,34.10"* M din 2,17.10"' M (hinh 4).
Lap phuong trinh dudng chuan cua 2 ion nghien ciiu trong khoang tuyen tinh nay dugc cac phuang trinh dudng chuan vdi he sd R^ tuang ung (hinh 5a, 5b).
Tien hanh ghi do lap lai 8 lan dung dich chiia [Cd^l = 1,78.10'* M, [hi'^
8,7.10'* M titu dugc RSDcd = 2,42 %;
RSDi„ = 3,66%.
Do nhay cua phuong phap tuang dli frong khoang tir 0,77 = 1,87 pA/ppb vdi Cd va tir 0,028 - 0,388 pA/ppb vdi hi.
Gidi ban phat hien (LOD) va gidi ban dinh lugng (LOQ) ciia phucmg phap xac dinh tiieo qui tic 3g la LODcd = 1,07.10' ' M; LOD|„ =1,04.10'* M va LOQcd = 3 , 5 7 . 1 0 ' ' M ; LOQI„ = 3,48.10"*M.
O.l 015
Hinh 4.Phd ddd DP-ASV ghi H-mh5aDir&ngclnAxdcdi,ii '^'^ SbDudng chudnx&;
nh khoang tuyen ^2- dinhlrT do xdc dinh khodng tuyin ^,
tinh cita Cd''. In^^
3.7.Ket qua phan tich mlu that Mau nudc phan tich la mau nudc Hd Tay (la\ vl tir ngay 24/01/2014 26/01/2014) va mlu nudc thai khu Cdng nghiep Yen Phong, huyen Yen Phong, tinh Bic Ninh (ily ve tir ngay 20/3/2014 = 26/3/2014). Mlu nudc sau khi ily vl, xir ly. lgc. Nudc lpc thu dugc dem xac dinh ham lugng Cd, In bang phuang phap DP-ASV fren may cyc phd da nang 797 VA Computrace.
Ket qua phan tich cac mlu nudc theo 52
phuang phap them chuan cho thiy: cac mau nudc hd Tay deu cd ham lugng hi nhd hon LOD, ham lugng ciia Cd nam trong khoang tir 0,82 pg/1 din 3,44 ng/1;
cac miu nudc khu Cdng nghiep Yen Phong diu cd Cd, ham lugng Cd nim trong khoang tir 3,89 pg/l den 8,42 pg/1, chi cd mdt mlu cd In (ham lugng 0,97 (ig/l (hinh 6)), cac mau cdn lai ham lugng In diu nhd ban LOD.
Hinh 6. Phd do ghi do DP-ASV phdn tich mdu that 4. KET LUAN
Da nghien curu che tao thanh cdng dien cyc paste dng nano cacbon bien tinh bang Bi203 (Bi203-CNTPE) vdi khdi lugng bitmut la 7 %; xay dung cac dilu kien thich hgp cho qua frinh phan tich ham lugng In'* va Cd^* bang phuong phap DP-ASV. Cac dilu kien thich hgp bao gdm: dien phan d the -1,2 V frong thdi gian 180 s, bien do xung 30 mV;
toe do quet the 0,015 V/s; tdc do quay dien cyc 2000 vdng/phiit, thdi gian sue khi nito la 350 s, thi lam sach dien cue la 0,3 V trong 30 s, tiidi gian nghi la 10 s Kit qua nghien ciiu thu dugc cho thiy khoang tuyin tinh giira Ip va ndng dp tuong ddi rdng, dp lap lai tdt, gidi ban phat han va gidi han dinh lugng deu thip. Dien cyc chl tao da dugc iing dung dl phan tich Cd^* va Zn'* frong miu nudc Hd Tay va nudc thai cho kit qua tdt.
TAI LIEU THAM KHAO 1. Cao van Hoang. Nghien ciiu che tao dien cue mang bitmut fren nen paste nano cacbon de xac dinh ddng thdi cadimi, indi va chi trong nudc tu nhien bang phuong phap Von-Ampe hda tan, Ludn dn tiin sy hda hgc, Vien Han lam Khoa Hpc va Cdng nghe Viet Nam, 28- 33(2012).
2. A. Charalambous, A. Economou, A study on the utility of bismuth-film electrodes for the determination of In(III) in the presence of Pb(II) and Cd(II) by square wave anodic stripping voltammetry, Analytica Chimica Acta 547, 53-58(2005).
3. Y. Tian, L. Hu, S. Han, Y, Yuan, J, Wang, G, Xu, Electrodes with extremely high hydrogen overvoltages as substrate electrodesfor stripping analysis based on bismuth-coated electrodes, AnalyticaChimicaActalSS, 41^4(2012).
4. G. G. Wildgoose, C. E. Banks, H. C.
Leventis, and R. G. Compton, Chemically modified carbon nanotubes for use in electroanalysic,A/ic/-oc/zim Acta, 152, 187-214(2006).
5. N. Serrano, A. Alberich, J. M. Diaz- Cruz, C. Ariiio, M. Esteban. Coating methods, modifiers and applications of bismuth screen-printed electrodes, Trends in Analytical Chemistry, 46, 15- 29(2013).
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