TAP CHI HOA HOC
DOL: 1015625/0866-7144.2014-0074
T. 52(6) 784-788 T H A N G 12 N A M 2014
NGHIEN CLfU ANN HU'6'NG CUA pH VA HAM LU'QNG NaCI TOI KHA NANG OXI HOA PHENOL Sl> DUNG DIEN CU'C
Ti/SnOz-SbzOg/PbOz
Chu Thi Thu Hiln', Tran Trung', Vu Thi Thu Ha^', Nguyen Nggc Phong' 'Trudng Bgi hgc Sic phgm Ky thugt Himg Yen
^Viin Hda hgc, Viin Hdn Idm Khoa hgc vd Cdng nghi Viet Nam
^ Vien Khoa hgc Vdt lieu, Viin Hdn lam Khoa hgc vd Cong nghi 'Viet Norn Din Tda soan 11-6-2014; Chip nhan dang 4-12-2014
Abstract
This paper presents electrochemical oxidation of phenol compound on home-made Ti/Sb203-SnO2/PbO2 anodic electrode. Investigation of influence of pH solution on this process was studied. It is indicated that the efficiency of phenol oxidadon strongly depends on electrolyte environment. Efficiencies of oxidation processes were evaluated by measurement of chemical oxygen demand (COD). Data showed that in basic enviroment with pH = 8, COD value of initial solution 7.5 g/1 Na2S04 containing phenol 500 mg/1 equals to 38.81 % after 30 minutes of electrolysis on studied Ti/Sb203-Sn02/Pb02 electrode. At the same time, with the presence of sodium chloride at 1 % in this solution, the COD indicator of phenol oxidation reached 96.89 % aiter 6 hours of electrolysis.
Keywords. Ti/Sn02-Sb203/Pb02 anode, phenol oxidation, pH, NaCI presence.
I. GIOI THIEU
Phenol va dan xuat cua nd da dugc sir dung nhieu trong cac ngitnh cdng nghiep nhu nhira foocmandehit, dugc pham, thudc trir sau, det may, thudc nhudm va nha may lgc dau [1-3]. Cdc hgp chat tham cd chiia trong dung djch nudc thai dnh hudng tdi sir sinh trudng va gay ddc cho vi sinh vat trong phan ung xu ly sinh hgc thdng thudng. Do dgc tinh cita phenol, cac hgp chat hiJu co va kha nang tac ddng xau den sir sinh trudng vi sinh vat thdng thudng nen can thiet phai xir ly chiing trong nudc thai [4]. Vi vay, cac phuang phap khac nhau dl xir ly nudc thai cd chiia chat phenol da dugc tap trung nghien ctiu vd sir dung, chiing ban nhu qua trinh oxi hda udt cd sir dung xiic tac nhu kim loai, oxit kim loai hoac zeolit cd mang kim loai [5], hip phu bing than hoat tinh [6], oxi hda hda hgc sii dung tac nhan oxi khdng khi [7], quang xiic tac nhd ZnO [8], xu ly sinh hgc [9], vd qua trinh oxi hda dzdn [10]. Tuy nhien, hieu qua cua viec loai bd cac chit d nhilm hGu ca ddc hai mdi chi cdn rit rit han chi. Oxi hda dien hoa dugc xem la mot phucmg phap hieu qua dl lam giam ham lugng cac chat thai hai hiiu ca dgc trong moi h-udng [4]. Day la mdt phuong phap than thien vdi moi trudng va nhieu hiira hen, ky thuat dan gian, diiu khiln dl dang va tu dgng hda, hieu qud
nang lugng, bleu suat qua trinh oxi hda manh, do do dat hieu qua cao trong xur ly nudc thai hGu ca tap trung [11, 12]. Theo [8], cac dien cue truyin thong, nhu than chi va niken sir dung trong qua trinh dien phan oxi hda phenol cdn cd hieu suat chua cao.
Phenol cd the bi oxi hda nhanh chdng d anot Pt nhung chiing cd the lam cho dien cue nay bj thy dgng nhanh chdng do su kit tiia cua cac kim loai tren dd. Vi?c phat triln cac dien cue nhu cac anot tra (DSA) va irng dyng ^h loai bd phenol bing phuang phap dien hda da kha thanh cdng. Tuy nhien, kha nang lam suy giam phenol trong qua trinh dien phan phu thudc manh vao mdi trudng dien ly. Muc dich cita bai bao nay la khao sat su anh hudng cita pH va ham lugng NaCI tdi kha nang oxi hda dien hoa phenol trong nudc thai nhan tao sii dyng dien cue anot tra Ti/Sn02-Sb203/Pb02 tdng hgp trong phong thi nghiem.
2. THUC NGHIEM
Cac dien cue anot Ti/Sb203-Sn02/Pb02 dugc ehe tao bing phuang phap phan hiiy nhiet va ma dien. Trudc khi phti cac oxit kim logi, nln titan dugc lam sach dau md va tiy hda hgc trong dung dich axit oxalic (15 %). Dung djch de tao Idp pha oxit kim loai dugc chuan bj tii cdc mudi SbClj SnCI 784
TCHH, T. 52(6), 2014
Pb(N03)2, dung mdi isopropanol va mdt sd phu gia khac. Ham lugng cua mdi chit dugc tinh toan chinh xac de dam bao sau qua trinh phan huy nhiet se nhan dugc lap phii Sb20j-Sn02/Pb02 h-en nln titan.
De nghien ctiu anh hudng ctia mdi trudng dien phan tdi kha nang oxi hda phenol bdi dien cue anot da ehe tgo, cac phep do phan circ thi vdng (CV) da dugc thuc hien. He dien hda sii dyng ba dien cue, dien cyc ddi Id thep khdng gi cd dien tich Idn han nhilu lan so vdi dien cue lam viec, dien cue so sanh Calomel bao hda (SCE). Dudng CV dugc khao sat trong khoang the tir 0-2 V (so vdi SCE), tdc do quet 50 mV/s. Mdi trudng dien ly Na2S04 7,5 g/l chira phenol 500 mg/1, nhiet do phdng (30 °C). Mau do la cac tam phang dien tich do dugc khdng ehe la 4 cm'^.
D I xdc dmh hieu qud dien phan hiiy phenol, mau dugc lay sau tirng khoang thdi gian nhat dinh vd dem phan tich nhu cau oxi hda bgc (COD).
De danh gia anh hudng ciia pH den khd nang oxi hda phenol ciia dien cue anot Ti/Sn02-Sb203/Pb02, pH ciia dung dich dugc thay ddi tir 3 den 12. Gia tri pH ndy dugc dieu chinh bang each them dung dich NaOH 5 % hoac H2SO4 5 %.
Anh hudng cua NaCI din qua trinh phan buy dien hda phenol dugc thuc hien trong cac dung dich dien phan cd pH = 8 khi cd NaCI 1 %, 1,5 %, 2 % va khdngcdNaCl.
3. KET QUA v A T H A O L U A N
3.1. Anh hirdng ciia pH din kha nang oxi hoa phenol
Hinh 1 trinh bay ket qud anh hudng cita pH tdi khd nang oxi hda phenol. Cac kit qua cho thay, tin hieu ddng tren cac dudng CV phu thudc rat nhieu vdo pH dung dich.
Hinh la cho thay khi quet CV trong mdi trudng cd pH ^ 3, pic oxi hda phenol khdng xuat hien, chiing td qua trinh oxi hda phan htiy phenol khdng xay ra trong mdi trudng axit. Kit qua nay cd the dugc giai thich bdi kha nang hap phy tmh dien ciia cac hgp chit gdc phenol tren dien cue Ti/Sn02- Sb203/Pb02. Trong mdi trudng axit, phenol hau nhu khdng hi phan ly va tdn tai dudi dang CsHsOH va nguyen tCr oxi trong nhdm chiic OH mang dien ti'ch am.
Khi dien cue phan cue anot, cac phan tu phenol se bj hap phy bdi tuang tac tmh dien giira cac dien tich am vdi dien cue. Khi dien the cita dien cue dat tdi gia tri tbi phan hiiy (Ep,,), qua trinh oxi hda bit diu xay ra va sdn phim tgo thanh la CO2 va H2O
va Thi Thu Hd vd cgng sir (khi phenol bi oxi hda hoan toan) hoac cdc hgp chat gdc quinin (khi qua trinh oxi hda la khdng hoan toan) va ggi chung la "san pham". Qua trinh oxi hda cita phenol cd thi dugc tdm tat nhu sau:
C6H5OH -^ CfiHsOHad -> San phim (1) Hinh lb cho thay, vdi pH = 7, xuat hien mdt pic oxi hda phenol trong khoang the 1,25-1,8 V, tuy nhien d cac vdng quet tilp theo thi pic oxi hda suy bien manh. Dieu nay cd the dugc giai thich la trong mdi trudng trung tinh qua trinh oxi hda phenol la khdng hodn toan, cac sdn pham trung gian dugc tao ra vd tao thdnh cac polyme bao phii be mat dien cue vd lam cho dien cue anot trd nen thy ddng.
Cac dudng cong CV trong dung dich Na2S04 7,5 g/l cd pH = 8 vd pH = 10 dugc trinh bay tren hinh Ic vd Id. Hinh Ic, d cho thay cd xuat hien pic phenol trong khoang the 1,15-1,55 V, d vdng quet dau xuat hien pic cao nhat, dinh pic roi vao gia tri dien the 1,4 V va den cac vdng quet tiep theo thi pic gidm dan den dudng nen. Khi pH = 10, gia trj the ciia pic oxi hda phenol tai nhiing vdng sau ducmg han so vdi nhifng vdng quet dau, chirng td kha nang oxi hda loai bd phenol d nhifng vdng quet sau trd nen khd khan hem. Trong khi tai pH = 8, gid trj thi cita pic oxi hda phenol tai nhifng vdng sau dich chuyen ve phia am han so vdi nhiing vdng quet dau, chiing td khd nang oxi hda loai bd phenol d nhifng vdng quet sau de dang ban.
So sanh dg rdng cita chan pic oxi hda ctia cdc CVl, trong trucmg hgp pH ^ 7, pH = 8 va pH = 10, da cho thay, tai pH = 8 do rdng chan pic dat tdi 0,65V, Idn han nhieu so vdi gia tri 0,5V ciia hai trudng hgp cdn lai. Diiu nay cho thay kha nang oxi hoa phenol trong mdi trudng pH = 8 de dang ban trong mdi trudng pH = 7 va pH = 10. Khi pH = 12 (hinh le), cac dudng CV cd dang gan gidng nhu trong trudng hgp pH = 3, hay dudng nen ciia dien cue trong mdi trudng trung tinh. Cd khac chang Id trong nhifng chu ky dau tdn tai mgt vai nhd dac tnmg cho qua trinh oxi hda phenol xay ra, va vdi dien the bit dau oxi hda 1,19 V/SCE. Nhung din chu ky 10 thi hoan toan mat han.
So sanh vdi ket qua CV do trong dung dich khi khdng cd mat phenol (dudng nen), tren dudng CV (hinh lb, c, d, e) deu chi xuat hien pic oxi hda trudc viing dien the thoat oxi trong qua trinh quet anot.
Nhu vay, ca bdn truimg hgp chit nay deu cd khd nang bi oxi hda true tiep tren dien cue va qua trinh oxi hda nay la qua trinh bat thuan nghich.
Cac thdng sd dien hda dac trung cho cac pic cita phenol dugc tong hgp trong bang 1.
TCHH.T. 52(6),2014 Nghien ciru anh hiring cua pH v.
Hmh 1. Dudng CV ciia qua trinh oxi iioa plienol trong cac moi tnrcmg l<liac nliau.
(a) pH = 3; (b) pH = 7; (c) pH = 8; (d) pH = 10, (e) pH = 12, (0 NSn dicli tlieo can b^ng sau:
Bdng 1: Thong so difin hoa tren duong CV ciia dung dich Na.SO, 7,5 g/l chira phenol 500 mg/l; t6c do
quet thg 50 mV/s pH
3 7 8 10 12
EM, mV 1120 1150 1150 1350
E„„ mV 1650
-
1400 1400 1500
loic, mPJcm^
2,2
-
2,7 1,9 1,9 Bdng 1 cho thay dien the bat dau (Ebd) phan huy ciia phenol phu thugc nhieu vdo pH dung djch, qua trinh oxi hoa phenol trong mdi trudng kilm xay ra tren di$n cue Ti/Sn02-Sb203/Pb02 de dang hem trong mdi trudng axit va mdi trudng trung tinh. Tai pH = 8, mat do ddng pic dat gia tri cao nhat, 2,9 mA/cm^ trong khi tai pH = 7, 10 va 12, gia trj nay la 1,2; 1,9 va 1,9 mA/cm^ tucmg irng.
Ket luan nay cung phit hgp vdi ket qud xac djnh COD ctia dung djch chira phenol trudc va sau khi xCr ly d 30 phiit trong cac moi trudng pH khac nhau (pH
= 3, pH = 7, pH = 8, pH = 10, pH = 12) sir dung phuang phap ddng khdng ddi d i = 50 m/V/cm^. Gia trj COD va do chuyen hda ciia qua trinh xir ly dugc the hien d bang 2.
Tir cac ket qua do dudng CV (hinh 1) vd chi sd COD (bdng 2) cho thay qua trinh oxi hoa phenol trong mdi trudng kiem xay ra tren dien cue Ti/SnOj- Sb203/Pb02 de dang han trong mdi trudng axit va mdi trudng trung tinh. Su khac biet nay cd thi giai thich la do su xuat hien ciia ion phenolat trong dung
CfiHs-OH t ; CfiHs- O" + iT (2) Bdng 2: Do chuyen hda COD d cac mdi trudng pH
khac nhau pH
Gia tri COD (nigb,/l) Do chuy6n
hoa COD
(%)
6 (ban dSu) 1675
0 3 1658
2,81 7 1487
11,23 8 1025
38,81 10 1125
32,86 12 1268
24,30
Di^u nay cd the da dan den ndng do cua cac hgp chat phenol cao ban trong lap dien tich kep va cQng ddng nghTa Id qua trinh oxi hda true tiep ciia phenol trong mdi trudng pH = 8 trd nen tot hon. Su xuat hien ctia ion phenolat dugc thiy rd rdng ban trong mdi trudng pH = 8, 10. Phenol la axit yeu nen trong mdi trudng kiem cac chit nay se tham gia phan iing:
R-OH + OH^ ^ R - 0 " + H2O (3) Qua trinh ox! hda cac hgfp chat hiiu co trong dung dich nudc cd budc phd htiy phan tii nudc tao gdc hap phy HO* va HO' sinh ra se pha buy phenol:
Pb02 + H20-»Pb02[ HO'] + H*+ e" (4)
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Ngoai ra, qua trinh oxi hda phenol tao thanh cac san pham trung gian: catechol, benzoquinon, axit fomic, axit oxalic vd cudi ciing bi khoang hda thanh CO2, H2O cd sinh ra H*, nen d mdi trudng axit do chuyen hda phenol thip han so vdi mdi trudng kiem.
Tuy nhien, neu mdi trudng cd pH qua cao se dan den pha htiy dien cue Pb02 va lam gidm hieu suat qua trinh oxi hoa phenol.
3.2. Anh hudng ciia NaCI tdi kha nang oxi hoa phenol
Diem quan trgng trong viec ap dung phuang phap dien hoa de xir ly nudc thai la sir tuang hgp cua qua trinh dien hoa vdi ion CI' trong dung djch, vi oxi hoa dien boa dung dich chira ion CI" se tao thanh hypochlorit C10~ va d o (thudng dugc ggi la nudc gia ven). Chinh nhung chat oxi boa nay cd the oxi hoa cac chat hu'u ca hda tan trong dung dich hoac nhiing san pham oxi hda trung gian.
Hinh 2 la dudng CV trong dung dich phenol cd bd sung them NaCI 1 %, 1,5 % va 2 % tai pH = 8.
Khac vdi cac kit qua CV khi khdng cd mat phenol, tren do thj xuat hien mgt pic oxi hda trong qua trinh quet the thuan (quet anot) va mdt pic khu trong qua trinh quel the ngugc (quet catot).
Hmh 2: Pho CV cua qua trinh oxi hda phenol anh hudng bdi cac ndng do ciia NaCI Su xuat hien cita pic oxi hda cd the Id do phan ling oxi hda:
C r + H2O - 2e -> CIO" + 2H^ (5) Sir xuit hien cita pic khu cd the la do phan ting khu: '
CIO" + 2 e + H 2 0 ^ C r + 20H" (6) Khi trong dung dich cd mat ddng thdi phenol va NaCI thi dd thj CV trong dung djch thay ddi rit nhilu (hinh 2). ^
So sanh cac dudng CV ta thay khi bo sung NaCI
va Thi Thu Hd vd cdng su gia trj ddng pic oxi hda cao hem ban so vdi tirng trudng hgp rieng re chi cd NaCI hay phenol. Hon nifa dang pic cung thay ddi trd nen tit ban, trai tren mgt viing dien thi Idn hem. Nhu vay khi quet anot trong dung djch cd phenol va NaCI thi pic oxi hda thu dugc tich hgp bdi hai qua trinh oxi hda: Oxi hda phenol va oxi hda CI". Them nifa, so sanh dudng CV cita dung djch chi cd NaCI 1 %, trong cac CV ciia dung dich phenol cd bd sung them NaCI khdng cd pic khir. Dieu nay chirng td da cd su tuong tac giifa phenol va cac gdc CIO . Ben canh qua trinh oxi hda true tiep tren be mat dien cue, cac phan tir phenol hap phu va cac san pham ciia qua trinh oxi hda tren be mat dien cue da tiep tyc bj oxi hda gian tiep bdi gdc CIO" vira dugc tao ra tren be mat dien cue. Cac phan tir hifu ca trong dung dich nam d lan can be mat dien cue cung se tham gia vdo qua trinh oxi hda gian tiep nay. Hau nhu toan bg gdc CIO" dugc tao ra da tham gia vao phan iing oxi hda gian tiep cac hgp chat hifu ca. Dieu nay giai thich su bien mat cita pic khir trong qua trinh quet ngugc tren dd thj CV khi cd mat ddng thdi cd phenol va NaCI.
Bang 3 bieu dien cac thdng sd dien hda cua cac pic oxi hda tren phd CV. Khi gia tri bd sung them NaCI, kich thudc cua pic oxi hda ciia cac hgp chat phenol ciing tang len vd gia trj di^n the oxi hda cung djch vl phia am ban.
Nhu vay, khi cd mat NaCI trong dung dich dien phan the chuyen ve gia tri am han va pic oxi hda xuat hien rd rang, kha nang oxi hda phenol trd nen de ddng ban khi khdng bd sung them NaCI, dac biet ddi vdi trudng hgp bd sung them NaCI 1 %. Do dd ndng dg NaCI 1 % dugc lira chgn de bd sung them vao dung djch dien phan phenol.
Bdng 3: Thdng sd dien hda ctia cac hgp chdt phenol tren phd CV frong dung dich Na2S04 7,5 g/l, chiia 500 mg/1 phenol, pH = 8 vd cd bd sung NaCI, tdc do
quet thi 50 mV/s Nong do
NaCI, % 0 1 1,5 2
Eta, mV 1150 1150 1150 1150
Ep,„ mV 1450 1300 1400 1400
mA/cm 2,0 2,3 2,5 2,4 Xac djnh chi sd COD ctia dung dich dien phan theo thdi gian dien phan cho thay, chi sd COD giam manh theo thdi gian dien phan khi cd mat them NaCI trong dung dich dien phan (tir 1768 mg02/l xudng 55 mg02/l sau 6 gid dien phan), dg chuyen hda COD la 96,89 %. Nghien ciiu d day cho thay vdi ndng do NaCI 1 %, qua frinh di?n phan xir ly phenol gin nhu kit thiic sau 6 gid dien phan. Hau hit cac chit hifu
TCHH, T. 52(6), 2014
ca t6n tgi trong dung dich ndy da dugc oxi hda thdnh cdc san phim cuoi ciing Id COi, nudc vd cdc hgp chat trung gian.
Nhu vay, su cd mat ciia NaCI frong dung djch cd tdc dyng*xiic tac cho qua frinh dien phan phan hity cac chit hiiu ca. Su xiic tac nay dugc gidi thich do su tgo thanh gdc CIO' tir ion CI".
Trong khi dien phan, tren bl mat dien c\rc andt Ti/Sn02-Sb203/PbO2, ion CI" (do NaCI tgo ra) dugc oxi hod tgo thanh hypoclorit CIO :
c r + 20H" - 2e ^ CIO" + HjO (7) vd tir CIO" cd the tao thanh clorat:
6C10"+3H20 -6e->2C103"+4Cr+6ir+3/202 (8) CIO" sinh ra se tham gia vao qua frinh oxi hod phenol va bien ddi Igi thanh CV.
4. KET LUAN
1. Phenol cd the bi oxi hda dien hda tren di?n circ anot Ti/Sb203-Sn02/Pb02 tu chi tao. Kha nang oxi hda phenol hi?u qua nhit trong mdi trudng kilm pH = 8, sau 30 phiit dien phan vdi do chuyen hda COD dat dugc la cao nhit (38,81 %).
2. Khi cd mgt NaCI trong dung dich dien phan thi kha nang oxi hda phenol tdt ban khi khdng cd NaCI vd tdt nhat khi ndng dg NaCI la 1 %, chi sd COD cua dung dich dat 96,89 % sau 6 gid di?n phan.
3. Khi cd mat NaCI trong dung dich dien phan phenol khdng nhung b| oxi hda dien hda fryc tiep tren di?n cyc anot Ti/Sb203-Sn02/Pb02 ma cdn bi oxi hda gidn tiep bdi chit oxi hda manh CIO" dugc tgo ra frong qua trinh di^n phan.
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Liin h?: Vu Thi Thu Ha Vien Hda hgc
Vi^n Han lam Khoa hgc va Cdng ngh? Vi^t Nam Sd 18, Hoang Qudc Vi?t, Cau Giiy, Ha Ngi E-mail: [email protected].
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