TAP CHl HOA HOC T. 52(3) 376-380 THANG 6 N A M 2014
NGHIEN CU'U T 6 N G H Q P V A T LIEU XUC TAC QUANG HOA AI/AlzOa/TiOz-Ag KHA KIEN U'NG DUNG Ot XCP LY NU'QC 6 NHliM
Dd Phmmg Thao', Trin Thi Thiiy^, Mai Thanh Tiing^, Nguyin Xudn Triromg^*
'Khoa Luyen kim, Trudng Cao ddng Co khi Liiy4tt kim
^ Viin Ky thugt Hda hge, Trudng Dgi hgc Bdch khoa Hd Ngi Din Tda soan 27-11-2013
Abstract
New visible light photocatalyst Al/AUOB/TiOz-Ag is synthesized. The material is characterized using different analytical techniques such as X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), Diffusive Reflectance Spectroscopy (DRS) and Field Emission Scanning Electron Microscopy (FESEM). It is revealed that the Ag doped Al/Al203/Ti02 film drives the catalytic activity from UV to visible region. The environmental application of the photocatalyst is investigated by the degradation of methyl orange (MO) under sunlight. Furthermore, the effect of pH and H2O2 as an oxidizing agent on the degradation efficiency of the material is also studied. The results show the optimal conditions for the photodegradation of the MO 3mg sample are pH 2 and 1ml H2O2 9 % in 6-hour irradiation.
Keywords: Visible light photocatalyst, photodegradation, methyl orange, environmental application, Ag doped Al/Al203/Ti02 film.
1. MO DAU
Nudc thii ciia cac nganh cdng nghiep va khu dan cu chua m§t lupng Idn chat thai huu ca nguy hai khd phan hiiy. Vifc xii ly cac chat d nhiem hiiu ca khd phan buy la mdt vin de khd, ddi hdi su diu tu Idn vl trang thilt bi vi cdng nghe. Trong vai thap ky gan day cd rit nhieu nghien cuu da sir dung chat xiic tie quang hda Ti02 de xir ly nudc d nhiem. TiOz khdng dpc, bin va gii thanh khdng cao phu hop dimg lam chit xiic tac quang hda cho phin ung phan buy cic chat hiru ca d nhiem. Tuy nhien, nhupc diem ciia vat lieu Ti02 dupc dieu che theo phuang phip thdng thudng la cd difn tich be mat khdng Idn v i khd thu hdi xuc tic sau phan ung [I, 6, 7], Mdt nhupc diem Idn khac da hgn che kha nang ung dung trong th\rc te cua vat lifu Ti02 dd la boat tinh quang xiic tie cua nd chi thi hifn khi dupc kich thich bing inh sang tii ngoai [4, 5]. Dilu nay ddng nghTa vdi vifc tieu hao mdt nang lupng dien nhit dinh trong qui trinh sii dung xiic tic. Do dd hifn nay nhilu nghien ciiu tgp trung tdng hop vat lieu Ti02 tren ca sd cac chit mang, pha tap cac nguyen td kim loai va phi kim.... Muc dich de cai thifn dp ben, hoin nguyen xiic tic, ddng thdi md rdng boat tinh quang xuc tac sang viing kha kiln dl cd thi tin dung ngudn nang luong anh sang mat trdi ddi dao [2, 3, 8, 9].
Trong bai bao nay, chiing tdi trinh bay ket qua nghien cuu tdng vat lifu xiic tic quang hda kha kiln Al/Al203/Ti02-Ag. Dong thdi dinh gia khi ning ung dung vat lifu d l xir ly nudc d nhilm thdng qua hifu suit ciia phin dng quang phin hiiy metyl da cam dudi tie dyng ciia inh sang mat trdi.
2. THUC NGHIEM 2.1. Hda chat va thiet bi
Hda chit: Tetra n-butyl octotitanat - TBOT, etanoI-EtOH, H2SO4 98 % (Merck, Dire), HNO, 63%, AgNOj tinh thi, H2O2 30 %, metyl da cam- MO, HjPOj, Cr03 tinh thi (Xilong, Trung Quic), nhdm li be diy 0,5 mm, nudc cit 2 lin.
Dung cu va thilt bi: Difn c\rc titan, miy khuiy t&
gia nhift, ngudn difn mpt chilu, may do pH, cin phin tich. Id nung.
2.2. Tong hpp vat lifu AI/AliO/FiOi-Ag 2.2.1. Tdng hgp vdt li^u mang Al/AhOj bdng phuang phdp di^n hda
Miu Al dupc lau sach dau md bing giiy lpc tim axeton, rira nudc ndng, rua nudc Ignh roi ngim trong dung djch tay bdng nhdm (H2SO4 28 %,
TCHH, T. 52(3), 2014
HjP04 50 %, C1O3 4 %. nudc 18 %) d 80-90 "C trong2-4phut[7].
Mau Al sau dd dupc rua Igi bing nudc cit va mic vao binh difn phan. Anot li mlu Al cdn catot la difn c ^ titan nguyen chat. Dien phan vdi mat dp ddng 1,5 A/dm^ trong dung dich H2SO4 2 M vdi thdi gian 30 phut
2.2.2. Tdng hgp vdt li^u Al/AhO/TiOrAg bang phuang phdp nhung phit sol - gel
Trudc hit, chuin bj dung dich sol theo ty le vl mol nhu sau: TB0T:H2O:Et6H:HNO3:AgN0j = 1:1:8:0,27:0,03 [3, 4]. Theo ty If mol niy, lupng Ag/Ti02 tuang dng ve phin tram khdi lupng la 1,5
%. Hdn hpp ludn dupc khuiy diu d 0 "C. Sau do, nhiSng vgt lifu AI/AI2O3 vio dung djch sol, nung d 500 °C trong 10 phiit. Qui Uinh nhung va nung duoc lap lai 2 lin, nung lin thd 2 thuc hien trong 30 phiit [3,4].
2.3. Danh gia hoat tinh xuc tac quang hoa ciia vat lifu
Hogt tinh quang xuc tac ciia vat lieu Al/Al203/Ti02-Ag dupc dinh gii bing phin iing quang phin hiiy mpt lupng khdng ddi 3 mg MO trong nudc, difn tich be mat eCia xuc tic la 24 cm^, dudi tac dyng ciia inh sang mat trdi. Hifu suit ciia phin img phin hiiy MO dupc tinh theo cdng thirc [9]:
H(%)=^~^'x\00.
Trong dd AQ va A, li dp hip thy ciia MO ban diu va thdi dilm t.
Dp hap thy ciia MO dupc xac djnh theo phuong phip do quang tren may UV-Vis Agilent 8453. Vdi mdi trudng pH = 7 vi pH = 8, dp hap thu quang dupc do tgi budc sdng X^^ = 464 nm. Mat khac, vdi
Nguyin Xudn Trudng vd cgng s{r pH = 2, A dupc do tai budc sdng x^ = 508 nm.
3. KET QUA VA THAO LUAN 3.1. Gian do nhieu xa tia X - XRD
Phd XRD (hinh 1) ciia c i vat lieu AI/AIjOj/TiOz (hinh la) vi Al/AljOj/TiOj-Ag (hinh lb) diu cho thay Ti02 tdn tai d dgng pha anatase. Ngoai ra, cdn thiy cd nhimg tin hieu ciia pha kim logi Ti (28 = 38,44", 40,18°, 53,02°) [12] v i Al (28 = 44,6r, 65,02°) [U]. Do su pha tap Ag, cudng dp cic pic cua pha anatase tang len rd rft (cic pic die trung cua pha anatase tgi 28 = 25,3°, 37,1°, 48,19°, 55°, 62,79° va 68,77°) [5, 10]. Them vio dd xuit hifn nhiing pic mdi d 28 = 31,5°, 51,5° [4]. Khdng tim thay tin hifu nhieu xg ciia Ag rieng re, chirng td lupng Ag da dupc phan tin rat ddng diu vio cac trung tam hogt tinh ciia cac hgt Ti02 va ngan cin sy phat trien cd djnh hudng cQa cic hat Ti02. Cudng dp nhieu xa tang len chung td su tgo thanh cic tinh the anatase Idn han khi pha tap Ag.
Cd the thay viec pha tgp Ag vio TtOj ddng vai trd quan trpng, dilu khien qui trinh tinh thi hda chpn lpc cho pha anatase trong qua trinh sol-gel. Do Ag c6 ban kinh ion (1,26 A) Idn han so vdi Ti (0,605 A) nen khi dupc pha tap vao mgng tinh thi Ti02, chiing thay the T i ' , dim may difn tir trong Ti02 se lien ket idng leo hem, thich hpp cho sy tgo thanh pha anatase (ngupc Iai vdi cau triic sip xep chat che thich hpp cho sy tgo thanh pha rutile) [4, 5]. Giira 2 dgng tinh thi chinh cua Ti02 anatase vi rutile, thi pha anatase the hifn hogt tinh quang xiic tac cao khi phan hiiy hau het cae chit hiiu co d nhilm trong nudc va khdng khi, trong khi hogt tinh nay yeu vdi pha rutile.
Nhu vay, vat lifu Al/Al203/Ti02-Ag vdi so lupng va kich thudc tinh the pha anatase Idn li mpt trong nhirng nguyen nhan Iam cho vgt lifu cd hogt linh quang xuc tic cao.
: U^.^Niatil'\v^^r*-W^ *^^^ ^''''^'ii'^M^.tV^^ ^''t*!^
I - i t I LiJ -1
Hmh I: Gian dd XRD eua vat lifu AI/AbOjATiO, (a) va AI/AliO/TiOi-Ag (b)
TCHH, T. 52(3), 2014 Nghiin dm Idng hgp vgt U?uxuc lac...
(a) (b) Hmh 2: Anh FESEM bl mat AI/AI2O3 (a) va Al/AbOj/TiOj-Ag (b)
3.2. Pho tan xa nang luwng tia X-EDS Phd EDS ciia miu Al/AhOj/TiOj-Ag (hinh 3) cho thiy pic cua Ag cimg vdi pic cua cic nguyen td CO ban khac Ti, O va Al. Dilu nay chiing td phuang phap nhimg phii sol-gel da pha tap thanh cdng Ag tren mang AI/Al203/Ti02.
: 1
0.4-
1 : 1
O J -
0 , , 0
i
^
0
1 1 1 2 4 6
3.4. Phd tan xa phan xa - DRS
Kit qua ghi phd DRS (hinh 4) cho thay, vgt lifu Al/Al203/Ti02-Ag cd dp phan xg giam manh d vung khi kiln 400-700 nm so vdi vit lifu Al/AljOj/TiO^
Dilu dd chung td dO hip thy quang cua vgt lifu Al/Al203/Ti02-Ag tang manh trong viing nay. Noi each khie, da cd sy dich chuyin viing hap thy ciia vit lieu Xlic tie quang Al/A^Os/TiOz-Ag tir vung inh sang tir ngogi UV sang viing inh sang kha kiln Vis. Nhu vay, vifc pha tap Ag ddng vai trd quan trpng tgo nen vgt lifu xiic tie quang hda kha kien Ai/Al203n"i02-Ag.
Phd DRS Cling cho thiy, vat lifu xiic tie quang hda khi kiln rit phii hpp diing cho phan iing quang phan hiiy MO vdi cic eye dai hip thy d budc sdng 464 vi 508 nm.
Hmh 3: Anh EDS miu Al/AljOj/TiOj-Ag 3.3. Anh hien vi dien tir quet - FESEM
Hinh 2a cho thiy, qua trinh anot hda cho be mat AI2O3 cd dp ddng nhit cao. Ldp ming AI2O3 dat dupc cd cau triic Id xdp ddng nhat, dp trat ty cao va hiu nhu cd ciu triic hexagonal [7, 8]. Cau true lo xdp tgo thanh nay chinh la ca sd cin thilt v i thuan lai cho dung dich sol bim vao be mgt AI/AI2O3 va sau dd li cac hgt Ti02-Ag [1]. Quan sit hinh 2b, sau khi phii ldp dung djch sol vio cac Id xdp AI2O3 va tien hanh nung luyen thu dupc cac hat Ti02 cd cau tnic bit difn. Cac hgt nay cd kich thudc thay ddi tiir nhd tdi Idn. Hgt nhd bam chac vao cau tnic Id xdp ciia AI2O3. Nhirng hat Idn han tren be mat kha ning bam chac kem ban.
80-|
70- 60- 50- g? « • Q!
30 10 10
- — Al/Al203/Ti02-Ag Al/AljOj/TiOj
100 300 400 SOO 600 TOO 800
y
il,nm
Hinh 4: Phd tin xg phan xg DRS cua vgt lifu Al/Al203A'i02 va Al/A!203/Ti02-Ag 3.5. Su cd mat ciia Ag anh hudnng d i n ho^t tiob quang xiic tac
Hinh 5 dua ra ket qui khio sat hifu suit cua
TCHH, l.DA-*).^U14
phin ling quang phan hiiy MO dudi tic dung cua inh sang ni$t trdi tren hai mau vgt lifu: khdng pha tgp Ag (Ml) va cd pdu tgp Ag (M2). Nhgn thiy, vdi sy pha tgp kim logi Ag, hifu suit (H) cua phin dng quang phan huy MO ting Idn ro rft. H > 10 % sau 2 gid va dgt ~ 22 % sau 10 gid. Sy tang mgnh hifu suit phan
^ g cua vgt lifu quang xiic tac Al/Al203/Ti02-Ag cd thi dupc giii thich nhu sau: kim loai chuyin tilp Ag dupc dua vio Ti02 cd tic dung lim hep dp rpng vimg cam do sy Iai hda cic orbitan d giiia Ti va nguyen td Ag. Mat khac chung ddng vai trd nhu cic
"bly"_difn tii vi "bay" Id trdng, tang cudng sy chia tich Id trdng ~ dien tii. Cac difn tir bi mic ket tren biy difn tii tuang tic vdi O2 tao thinh cac phin tu hogt dpng (02*, 'OH) [6]. Do dd lim tang hifu suit phin ling quang xuc tic phan hiiy MO. Nhung mat khie, khi nong dp pha tap dat din gii tri nao dd tlii cic "bay" difn tii lgi ddng vai trd nhu cae tam tai hpp ciia cic cap "dien tu - Id trdng" lim giam khi nang quang xuc tic cua vgt lifu [6]. Vdi vat lieu nghien ciiu d day, him lupng Ag pha tap 1,5 % cho hifu qui quang xiic tic tdi uu nhat.
Nguyin Xudn Trudng vd cgng su Al/AljOj/TiOi-Ag va H2O2 cho hifu qui cao ban ding kl, H dgt tdi ~ 42 % sau 10 gid.
51
40
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- * - M 3 - • - M I
— • - M I
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Hinh 6: Anh hudng cua H2O2 din hogt tinh quang xuc tic ciia vit lieu. M1: Al/Al203/Ti02-Ag;
M2: 1 ml H2O2 9%; M3: M H M2
2Sn
20-
15
K 10
S'
0-
1 — • - M Z 1
0 2 4 £ 8 10 t , h
Hinh 5: Sy cd mat cua Ag anh hudng din hogt tinh quang xiic tic ciia vat lifu. M1: Al/Al203/Ti02;
M2: Al/Al2O3/Ti02-Ag
3.6. Anh huong cua H2O2 den boat tinh quang Xlic tic
Hinh 6 trinh biy kit qui khio sit hifu suit ciia phin umg quang phin hiiy MO dudi tac dyng ciia inh sing mjt trdi vdi 3 miu. Miu Ml chi cd vgt lifu AI/Al203/TiO2-Ag, M2 chi them H2O2 vi M3 gom ci Ml vi M2. Vdi miu MI, H dgt - 22 % sau 10 gid. Vdi miu M2, hifu suit phin img phin buy thip htm, H chi dgt - 14 % sau 10 gid. Trong khi dd, vdi mlu M3 sii dyng td hpp vgt lifu xiic tic
Hieu suit quang phin hiiy mlu chira 3 mg MO li toi uu khi kit hpp vat lifu Al/Al203/Ti02-Ag 24 cm^ vi I ml H2O2 9 %. Tuy nhien khi them lupng H2O2 Idn han, khdng thiy hifu qui cao hem. Nguyen nhan la do sy cd m^t nhilu ciia goc 'OH se dan tdi su tai kit hpp cac goc ty do 'O2", 'OH, *0H2 tgo thanh nudc, ben cgnh dd H2O2 se tuang tie vdi 'OH lim giam mpt phan lupng 'OH [8].
3.7. Anh hurdng ciia pH den hoat tinh quang xiic tac
Nghien ciiu nay khao sit anh hudng cua pH din hieu suit phan Omg quang phin hiiy MO bdi vgt lifu Al/Al203/Ti02-Ag vdi sy cd mit ciia H2O2 dudi tic dung ciia inh sang mat trdi. Ket qua (hinh 7) cho thiy tdc dp va hifu suit phan iing trong mdi trudng axit pH = 2 eao hon han so vdi trong mdi trudng trung tinh pH = 7 va mdi trudng kiem pH = 8. Tgi pH = 2, chi sau 6 gid, H da dgt tdi - 86 %. Trong khi tai pH = 8, H dat dupc > 50 % va tgi pH = 7, H chi dgt ~ 42 % sau 10 gid. Tdc dp va hifu suit phin img cao trong mdi trudng axit la do ting cudng sy hap phu ciia MO len be mat TiO: mang difn duang.
Them vao dd, sy tii ket hpp electron - Id trdng dupc giim thieu. Trong mdi trudng kiem va trung tinh, ci MO va be mit Ti02 mang difn tich am do dd toe dp va hieu suit quang phan hiiy giam di [5].
Mat khac, trong mdi trudng pH = 7, AI(0H)3 cd the dupc tgo thanh tren bl mgt xiic tic dan tdi thy dpng hda va lam giim hogt tinh xiic tic quang [8].
Trong mdi trudng kiem yeu pH = 8, giai dogn diu 379
TCHH, T. 52(3), 2014
tdc dp tgo thinh AI(0H)3 Idn han, nen trong 6 gid diu tdc dp phan umg quang xuc tic thip han. Sau dd Al(OH)3 nay Igi bj hda tan dan trong kilm, nen b l mat xuc tac lgi trd nen hogt tinh [7].
100-.
80-
60-
= 4..
20-
0-
- • - M l
0 1 4 6 8 10 t,h
Hmh 7: Anh hudng cua pH den hoat tinh quang xiic tic ciia vat lieu.
MI: pH = 2; M2: pH = 7; M3: pH = 8 4. KET LUAN
Da tdng hpp thanh cdng vgt lifu xiic tic quang hda khi kien Al/Al203/Ti02-Ag. Chat mang AI/AI2O3 dupc tdng hpp bing phuang phip dien hda cd ciu triic Id xop ddng deu, dp trat ty eao. Ming Ti02-Ag dupc tdng hpp bang phuang phap sol-gel cd cau triic pha tinh the dgng anatase. Vdi lupng pha tap tdi uu 1,5 % Ag, sy hip thy quang ciia vit lifu dich chuyen tir vimg inh sing tu ngogi sang vung anh sang khi kiln.
Vgt lieu xiic tac quang hda khi kiln Al/Al2O3/Ti02-Ag cd hieu suit quang phan hiiy mlu ehiia 3 mg MO tdi 86 % trong dieu kien: mdi trudng axit pH 2, difn tich be mat xuc tac 24 cm^, them 1 ml H2O2 9 %, vi sau 6 gid dudi inh sing ty nhien.
Vat lifu Xlic tac quang hda kha kiln Al/Al203/Ti02- A g j i t phii hpp diing de xOr ly cac chit huu ca d nhiem khd phan huy, hiia hen dl triln khai ung dyng trong thyc tl cho hifu qui kinh t l cao.
TAI LlgU THAM KHAO
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