TAP CHI H 6 A HOC T. 50(4) 455^60 THANG 8 NAM 2012
CH§ TAO VA DAC TRLCNG CAU TRUC CClA VAT LIEU NANO MgAI HYDROTALXIT. ANH HU-d^NG C O A T ? LE KIM LOAI Mg/AI VA ANION
XEN CAI TRONG LOP KEP
Nguyen Thj Dung'*,Tr^n Bpi An', Phan Ngpc Hda^ Nguyen Quang Hai^ Nguyen Thj Ngan Hd^
Tran T\\\ Bipp^
' Vien Cdng ngh4 Hda hgc. Vi^n Khoa hgc vd Cdng ngh4 Vi^t Nam
^Trudng Dgi hgc Bdch khoa. DHQG Thdnh pho Hd Chi Minh 'Vi^n Ndng hda Thd Nhudng, Vi4n Khoa hgc vd Ndng nghipp Vi^t Nam Hd Ngi
^Khoa Khoa hgc. Trudng Dgi hgc Cdn Tho Den Tdasogn 3-4-2012 Abstract
A senes of Layered Double Hydroxides (LDHs) - Hydrotalcite with varying ratio of Mg/Al (2,3,4) were prepared by the co-precipitation method with the solution of Mg^* and Al'* in the medium containing different anions (CO3- and NO3-) and synthesis conditions (aqueous ammonium solution or sodium hydroxide to control pH of the reaction) followed by the calculations at different tenperature (350-550°C). The sanq>les were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and infrared spectroscopy (FTIR). The XRD patterns shown that pure Hydrotalcite phase were obtamed for all san:q)les and layered structure is still maintained up to 3S0°C. However further heating at higher temperature the collapse of the layered structure was taken. The effect of the intercalated anion (NO3, CO3) and Mg/Al ratio on the structural and textural properties have been investigated. It was shown that the nitrate form Hydrotalcite MgAl-NOs has higher basal spacing compared with the carbonate form about 0.5 A at the same Mg/Al ratio. The crystalline size calculated by Sheerer's equation for all prepared sanq)les was below 10 nm. The particle sheet size of Hydrotalcite with carbonate intercalated anion was smaller than that of nitrate anion. Tbe PZC of the obtained Hydrotalcite has maiiUy similar value (10-11) for the both form at the same Mg/Al ratio. This is indicated that the synthesis condition and nature of intercalate anion NO5 and CO3 have no signifrcant e^ect on PZC. The lower Mg/Al ratio the higher value of PZC. The calcined hydrotalcite can be restmctured easy in die anionic solution.
Keywords: Layered double hydroxide-hydrotalcite, basal space, Mg/Al ratio, mtercalated anion.
1, Md DAU Ti Ip M^*/M** thudng trong khoang 0,1 < x <
0,5 [1-3, 4]. Trong thien nhi8n, hydrotalxit Id mgt Vgt lipu hydroxit lap kep (Layered double hydrocarbonate cua magie va nhdm [4-7] vdi cdng Hydroxide - LDHs) la hdn hgp hydroxit cua kim thuc [M6^^AU*^(OH),6]^*C03^'.4H2O [8-10]. Cdc logi hda tri n va kim loai hda trj m, tgo thanh cac logi vgt lipu hydroxit Idp kep cd thS dieu che dugc d Idp bat dipn mang dipn tich ducmg. De cau true qui md phdng thi nghipm va cd qui md cdng nghipp trung hda ve difn tich, cdc anion hydrat hda dugc trong dd LDHs-MgAl dugc nghien cihi vd ung dyng dan xen vao khoang trdng giua hai Idp bdt dipn. nhilu nhat vi tinh chat md phdng tu nhien vugt trpi Cdng thurc tong qua ciia hydrotalxit cd dgng ciia nd [2,4-7,11].
[M(,.j)"Lx'"(0H)2X;i,m'^.H20], trong dd M la cdc kim Vdi d^c trung cau tnic la mpt hydroxit Idp cd logi hda tri II: Ca^*, Mg^*, Zn^*, Ni^*, Co^*, Mn^* khd nang luu giij- vd trao doi cdc anion ben trong Idp hogc Fe^*; L la cac kim logi hda trj HI: Al**, Cr**, kep nay vdi anion mdi trudng ngodi, cho nen vat Mn**, Fe^, Co** hogc Ni*"*... X Id cdc anion xen cdi lieu hydrotalxit hipn nay dugc nghien cuu rat mgnh CO thS la cdc anion vd ccr nhu hda tri m nhu: CO^', vd irng dyng trong nhieu ITnh vgc khac nhau nhu:
NOs', P04^', S04^" hogc CI" hodc hiru ca: oxalat, trong y dugc dugc dimg lam chat mang cho nhihig phenolat, cacboxylat, sulfonat loai thu6c, antipeptin, chat trung hda pH cho thudc dau dg ddy, trong cdng nghipp dugc ung dyng lam
TCHH, T. 50(4), 2012
chat tdng cudng, chat ben nhipt ch^t on djnh cho PVC, lam vgt lipu hap phy xir ly mdi trudng; chat xue tac the he mdi, vgt lipu lai organic-inorganic xiic tac enzym [8-12],
Trong ndng nghipp, phdn dgm N dugc sir dyng rat nhieu. Tuy nhien, du lugng N dgng NGj trong ddt anh hudng den ngu6n nude dkn den sy tich luy trong cay trong Id nguyen nhdn cua hpi chumg Baby bluedtreem [13]. Dodo hipn nay cdc nhd khoa hpc rat quan tam tdi vi$c kiem sodt hdm lugng NO3 thai ra mdi trudng. Phan bdn nhd chdm tren nen hydrotalxit cd kha ndng nhd dan lugng NO3 de nudi cay trong, dong thdi thyc hipn phan irng trao doi anion vdi cac anion mdi trudng, giiJ Igi trong c4u tnic cua cac anion nhu CI la nguyen nhan lam chua dat. Ddy la mpt hudng nghien cim kha ly thu trong tuong lai hudng tdi nen sdn xuat ben vCrng vd than thien mpi trudng.
Tiiy theo myc dich sir dyng yeu cau LDHs cd cau tnic ciia phii hgp, trong dd thdng so ve khoang each giira cac Idp kep va kha ndng trao doi anion ciing nhu tai cau tnic la rat quan trgng. Cd nhicu phuang phdp de dilu che vgt lipu hydrotalxit, trong do pho bien nhat la phuang phdp ddng ket tiia [4, 8, 10, 11, 14, 15]. Uu diem ciia phuang phap ndy Id dan gian de thgc hipn cd the dieu chinh dpc Igp cac thong sd khac nhau trong qud trinh tdng hgp (nhipt dp, pH ciia mdi trudng, ndng do muoi kim logi, vd cac anion khac nhau....) de tao ra dugc vat Iipu LDHs mong mudn.
Trong cdng trinh nay myc tieu dugc ddt ra la nghien cim anh hudng ciia dieu kipn che tao nhu:
ban chdt cua cdc anion xen cai NOj" vd COs^", mdi trudng ddng ket tiia, nhipt dg nung, ty le kim logi din khoang each va tinh chdt ly hda cung nhu kha nang tai cdu tnic ciia LDHs Mg-AI Idm ca sd de dieu che LDHs thich hprp cho cac myc dich sir dyng khdc nhau.
2.THUCNGHI$M 2.1. Hoa chat
Cac hda chdt dugc sii- dyng bao gdm: Nhdm nitrat-AI(N03)3.9H20, magie nitrat- Mg(N03)2.6H20, natri cacbonat-Na2C03, natri nitrat - NaN03, HNO3 va NaOH 3 M. Nhihig hda chat ndy Id nhCmg hda chat tinh khiet nhdm hgn che nhihig anh hudng ciia cdc tgp chat va cac ion Ig.
2.2. Tong hop vat lipu hydrotalxit (HT) Hydrotalxitdugc di6u che bdng phuang phdp ddng ket tua hdn hgp dung djch 2 muoi trong mdi
Nguyin Thi Dung va cgng sir
I
Irudng dung djch chiira ion c^n xen cdi vao lop k^trong dieu ki^n cd khu^y trpn lien tyc d nhipt dp phdng vd pH on djnh. Cy the nhu sau: chuan bj hai dung djch; A (500 ml hon hgp dung djch 2 mu^i A1(N03)3 vd Mg(N03)2 vd 500 ml dung djch B Na2C03 hodc NaNO] (mdi trudng dong ket tiia chija cdc anion c^n xen cdi COs^' hodc NO3'). Dung djch A: muoi AI(N03)3 vd Mg(NO])2 vdi lugng can theo ti Ip mol Mg/Al = 2/1, 3/1 vd 4/1 sao cho n^ng dO t6ng cua hai muoi Id 1 M. Dieu chinh pH ciia dung djch B theo thir ty nhu sau: bdng NaOH 3 M vdi pH khoang 8,5-9 khi diing mdi trudng Id Na2C03; va NI l^OH (25%) vdi mdi trucmg Id NaN03 vdi pH = 10-10,5. 6n djnh pH ciia dung djch B trong thin gian 10 phut vd khuay trgn h5n hgp, sau dd bdt dau nhd tir tir hon hgp dung djch A vdo dung djch B dong thdi cung nhd dung djch NaOH ho$c NH^OH de giii' pH on djnh. Sau khi dung djch A dugc cho het vao dung djch B (trong thdi gian khoang 60 phut) cdc ket tiia tgo thdnh dugc khuay trgn them 30 phiit sau dd bdt dau gia nhipt de gid hda d SOX trong 24 gid. Ket thiic qua trinh gid hda, ket tiia dugc rira nhieu lan bdng nude cat cho sgch cdc mudi du vd tach Igc bdng mdy ly tdm, say d 80°C trong 10 gid. Cdc mdu dugc luu trir trong binh kin va ky hi$u theo ion xen cdi HT-NO3, HT-CO3 de cho cac nghien cuu tiep theo.
2.3. Xir ly nhipt vd tdi cau true vat lipu Hydrotalxit thu dugc d cdc thi nghipm tren dugc nung d nhi?t_ dp khdc nhau: 350-550T, thoi gian 4 gid. Cac mdu sau khi nung dugc ky hipu la HTC (Hydrotalcite Calcined). De nghien cuu kha ndng tai cau tnic ciia vgt lipu cdc mau sau khi nung dugc ngam trong dung djch NajCOs 0,1 N hojc NaNOj 0,1 N trong 24 gid.
Cy the nhu sau: lay 1 g vgt Iipu HTC ngdmfrong 40 ml dung djch Na2C03 0.1 N ho§c NaNOj0,l N, de tren mdy ldc d nhipt dg phdng trong thdi gian 24 gid.
2.4. Dac tru-ng vat lipu hydrotalxit
Vgt lipu hydrotalxit sau khi che tao dugc phan tich cau tnic va thanh phan pha bdng phuong phap XRD tren thiet bj D8 Advance - Brucker (Diic) v(Si birc xg CuK^ (1,5406 A) d 40 kV va 30 mA gdc quet 26 tir 5° den 70°, pho hong ngogi FTIR dugc phan tich tren thiet bj Brucker-EQUINOX-SS tgi Vi^
Khoa hpc Vgt lipu tmg dyng, dnh SEM cua cdc mau XLic tac dugc chyp tren mdy JEOL (Nhgt Ban) Vi^n Cdng nghp Hda hgc.
TCHH, T. 50(4), 2012 3. KET QUA VA T H A O LUAN
3.1. Anh hudng ciia ti 1$ Mg/Al den d^c trirng cau triic va tinh chat hoa ly ciia v$t lipu
Ket qud phan tich pho XRD d6 xdc djnh cau triic cud cdc mau vgt H^u ch^ tgo vdi ty Ip Mg/AI va mdi trudng tgo pH khdc nhau dugc trinh bdy trong bang 1 vd hinh 1.
Tir hinh 1 cho thay pho XRD cua cdc mdu thu dugc Id cd cdu triic dgc trung cua vgt lipu Hydrotalxit vdi cdc pic phan xg (003), (006), (012), (015), (018), (110), (113). TCr phd XRD cua cdc mlu HT cho cdc sd li^u v6 cdc thdng so cau tr6c Idp ciia chiing. Kit qua cho thay sg khac nhau giiJa cdc HT vdi anion xen cdi dua vdo mgng.
Khoang each cg bdn (d-spacing) d6i vdi mlu HT-COj Id khodng 7,8 A vd mau HT-NOj Id 8,7 A.
Di^u ndy khd phit hgp vdi cdng bo ciia cdc tdc gid khdc [16]. Su khdc nhau ve khodng cdch cabdn gi&a hai logi HT cd anion xen cdi khdc nhau cd th^ giai
Che tgo vd dgc trung cdu tnic cua ...
thich la do kich thudc cua cdc anion khdng bdng nhau.
Ty Ip Mg/Al tang tir 2-4 cudng dg pic 003 vd 006 gidm vd cd hinh dgng rgng, tii han so vdi mlu cd ty Ip Mg/Al thap. Dieu nay cho thay muc dO tinh the hda ciia chung thap hem.
Hinh 1: Pho XRD ciia vgt lipu hydrotalxit Mg-AI- CO]^" vdi cdc ti Ip Mg/AI khac nhau;
(a) Mg/Al = 2/1; (b) Mg/AI = 3/1; (c) Mg/AI = 4/1 Bdng 1: Cdc thdng so ddc trung cau triic ciia vgt lipu hydrotalxit
Ki hieu mau HT2-COj HT3-CO3 HT4-COj HT2-NO3 HT3-NO3 HT4-NOj
Tile mol Mg/AI
2/1 3/1 4/1 2/1 3/1 4/1
Moi tnrcmg ket tiia NaiCOj
NaOH NaiCOj NaOH NajCOj NaOH NaNOj NRiOH NaNOj NH4OH NaNOj NHiOH
Khoang each lop
chinh (003), A
7,62 7,71 7,93 S,60 8,91 8,98
Khoang each lop hidroxit (006), A
3,79 3,84 3,98 4,33 4,47 4,38
Khoang each giira 2 I6p hydroxit, A 3,82 3,86 3,96 4,27 4,44 4,60
Kieh thir6c tinh the,
nm 7,7 5,2 5,8 7,9 5,3 6,2
Diem dang dien PZC 11,7 11,4 10,4 11,5 11,3 10,2 Mgt khdc do dg du dipn tich duong ciia cac mdu
giau Al cao ban cho nen lugng anion bii trir NO3' hogc COs^" nhiSu ban. Theo cdc tdc gid Wang vd cdc dong sy [13], sg sdp x^p cac anion xen cdi phy thugc vao ndng dg ciia chiing. CJ ndng dg cao xu hudng xdp xe[> thdng vudng gdc vdi mat phdng Idp hidroxit sS chilm uu th8 cdn d ndng d$ thap sS Id xu hudng song song. Kich thudc tinh th€ ciia cac mdu HT tinh theo cdng thirc Scherrer (bang 1) trong khoang 50-80 nm khdng phy thugc vdo ty 1? Mg/Al cung nhu mdi trudng on djnh pH la NH4OH hay NaOH.
Cac so lieu tur bang 1 cho thay, hydrotalxit vdi anion xen cdi NOs' trong mdi tnrcmg ket tua dugc on
djnh pH bdng dung djch NH4OH cd khodng cdch giiJa hai Idp hidroxit ldn hon khodng 0,5 A so vdi vgt lipu dugc dieu che vdi anion xen cai la COs^' vd 6n djnh pH bdng dung djch NaOH. Tiiy theo ty 1^
Mg/Al sy khac biet nay se thay doi va tang 0,45, 0,58,0,60 A khi ty Ip Mg/Al tang 2,3,4 tuang img.
DiSm dang dien PZC ciia cdc mau vdi anion COs^" trong khoang 10,5-11,7 cdn vdi cac mdu vdi anion NO3' Id 10,2-11,5 tiiy theo ty Ip ciia Mg/Al.
KSt qud cho thdy PZC ciia cac mau khdng khac nhau nhieu vd hdu nhu khdng bj dnh hudng bdi cdc anion xen cai khdc nhau. Mlu vgt lipu cd ham lugng Al cdng cao thi gid tri PZC cang ldn do mdi ion Al^**
thay the vdo cdc vj tri ciia mdi ion Mg^^ lam du 1
TCHH, T. 50(4), 2012
dipn tich duang, din den dipn tich be m$t cdng duang han so vdi mdu cd ty Ip Al thap.
Gid tri PZC Id mgt thdng so rat quan trgng dui vdi vgt lipu rdn, theo dd neu moi trudng dung djch cd pH nhd ban PZC thi be mjl vgt lipu sS mang dipn tich duang vd neu Idn han s2 mang dipn tich am.
Dieu nay dan den vipc hap phy cac ion trdi d^u trong dung djch sc thugn Igi hay khd khdn ban.
Nguyin Thi Dung vd cgng si/
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I I I • • • \ v |i
Hinh 3: Pho IR ciia vgt lipu hydrotalxit (a) HT-NO,: (I) Ty Ip Mg:Al = 3:1; (2) Ty ip Mg;Al
= 2:1; (b) HT-COj: (I) Ty Ip Mg:Al =2:1; (2)Ty I?
Mg:Al = 3:1; (3) Ty ip Mg:Al = 4:1 3.2. Anh hirdug ciia nhipt dg nung
Nghien ciru nay thyc hipn \ u ly nhipt cdc mau HT d nhipt dp 350°C, 4 5 0 ^ va 550°C nh§m xac djnh nhipt dp thich hgp nhdt.
Hinh 2: Anh SEM ciia vat lipu hydrotalxit (a) HT2-CO3; (b) HT2-NO3 Hinh anh SEM ciia hai vdt lieu hydrotalxit dugc dieu che vdi hai anion CQ^' vd N03 cho thay deu cd dgng Ic^ phien mdng tuy vgy su khdc nhau ve hinh thai kha rd. Ddi vdi HT-CO3, vgt lipu cd dgng vay xdp cd kich thudc va dp day Idp phien nhd ban (83 nm) so vdi HT-NO3 (1041 nm).
Phd IR tir hinh 3 cho thdy trong cau triic vgt lipu cd sy cd mat ciia nhdm -OH the hipn cdc pic d budc sdng v = 3500-3400, va nude cau tnic ndm trong Idp kep the hipn d cac budc sdng v = 1650-1600. Dong thdi ciing xuat hipn cac pic trong khoang budc sdng V = 793, 671, 559 Id cdc dao dgng ciia lien ket oxit kim loai M-O (Mg-0 va Al-0).
Hinh 3a cd su xuat hipn cac pic dgc trung ciia nhdm NO3" vdi cac budc sdng v = I380-I440; 1030- 1080, 810-850, 720-760. Hinh 3b cd xudt hipn cac pic ddc trung ciia nhdm C03^" vdi cac budc sdng v = 1380-1350, 880-850, 690-670. Nhirng thong tin ndy chimg minh dugc vipc dieu che thdnh cdng vgt lipu Hydrotalxit tir 2 he Mg-Al-COj va Mg-AI-NOj.
Hinh 4: Pho XRD ciia hydrotalxit tnrdc vd sau khi xu ly nhipt (a) hydrotalxit Mg-Al-COj chua nung;
(b) hydrotalxit nung d 350*'C; (c) hydrotalxit nungcf 450°C; (d) hydrotalxit nung d 5 5 0 ^ Pho XRD tir hinh 4 cho thay, d nhipt dp nung 350°C, vat lipu vIn cdn giii dugc cdu tnic cua hydrotalxit, tuy vgy cudng dg cdc pic dgc tnmg 0 va 006 thap ban va dan rgng hon. Khi nang MTI^M dp 450°C vd 550°C cau tnic lap cua HT da thayf va cd hipn tugng sgp mgng la do sg khu nude lien ket vdi cdc cation va sg tdch cdc anion xen cdi trp||
Idp HT. NSu d nhipt dg nung thap < SSO^C thi kh"^
nude d be mdt s6 xdy ra Id chu yeu, cdn d nhi^ 1I6
TCHH, T. 50(4), 2012
cao ban (450-550) nude cau tnic se bj khii, mgng HT bj sgp va tgo thanh cdc oxit ciia Mg, Al (pic d 29
= 46°). Tren phd XRD cCia mau HT dugc sir ly nhipt d nhipt dp 450°C vd 550''C hau nhu khdng cd gi khac bipt chumg td khdng cd sy thay ddi ndo vk thanh phdn pha vd cau tnic trong khoang nhipt dg nay do vay nhi^t dp xijr ly thich hgp s6 dugc chpn Id 450''C. K6t qud ndy ciing khd phii hgp vdi nhiJng cdng bd ciia cac tdc gia [7, 10, 11].
3.3. Tai cau true v^t lipu
Vdt lipu HT cd kha ndng tdi cau tnic ban d4u khi dugc bSp xiic vdi dung djch chira cdc anion xen cai ddu tien hogc cac anion khdc. Day Id mgt ddc tmh kha ly thii va cung Id uu diem vugt tr^i cua logi
Che tgo vd ddc trung cdu true cua ...
vgt Iipu nay.
Trong bai bdo nay, chiing tdi thyc hipn khdo sat qud trinh tai c^u tnic vdt li^u hydrotalxit vdi dung djch NaNOj va KBr. KSt qud dugc trinh bdy trong hinh 5.
Tir hinh 5 cho thdy, sau khi tdi cau tnic vat lieu trd lgi cau tnic cua hydrotalxit vdi cdc pic ddc trung.
Sau khi nung, vgt Hpu bj mat cau tnic Idp do cac phdn tir nude trong cau tnic Idp thoat khdi cau tnic vgt Iipu, lam cac Idp xd Ipch ldn nhau. Khi ngam trong dung djch cd chira cac anion can xen cdi vdo cau tnic Idp, md trong trudng hgp nay Id anion CO3" vd NOs", thi vat lipu dugc cung cap trd lgi cac phdn tir nude vd cdc phan tir anion cdn thiet dk tai Igp Igi cau true ban dau. Va kit qud cho thdy, vat hpu dd dugc tai cau tnic thdnh cdng.
Hinh 5: Phd XRD ciia vgt lieu hydrotalxit
(a) Vat lieu HT-C03^": (1) HT-C03^" ban dau; (2) HT-C03^" tdi cdu tnic; (3) HT-C03^" nung d 450°C (b) Vat lieu HT-NO3": (1) HT-NO3' ban ddu; (2) HT-NO3" tai cdu tnic; (3) HT-NO3" nung d 450°C 4. KET LUAN
Da che tao cdc mau nano HT (5-9 nm) vdi anion xen cai COs^' va NO3" vd ty Ip Mg/Al khac nhau (2.3.4) bang phuang phdp ddng ket tiia tir cac mudi ldm logi trong mdi trudng pH dn dinh bdi NaOH hogc NH4OH. Ket qua nghien cim cho thdy, ty le kim logi MgAI va tinh chat cua cac anion xen cdi trong lap ciing nhu mdi trudng ket tiia cd anh hudng Idn den khoang each ca bdn ciia Idp cdu tnic (d- spacing) va dac trung ly hda ciia hydrotalxit. Ty Ip Mg/Al cdng cao khoang each ca ban ciia Idp cau true cang tang, diem ddng dien PZC cdng giam.
Anion xen cdi Id NO3' cho khoang each lap cao ban khoang 0,5 A so vdi anion COs^" cd cimg ty Ip Mg/Al. Kich thudc cac hgt Idp phien cua HT-COs^' nhd ban so vdi HT-NO3" (KT-COi^': 83 nm; HT- NO3'; 1041 nm). Nhi$t dO nung thich hgp dk tgo vat lipu bin tdi cdu tnic Id 450*'C. Vgt lipu sau khi ngdm vdi dung djch chiia ion khac loai da tdi cdu tnic Idp nhu cdc mau ban dIu.
Nhihig nghiSn cihi biln tinh vat lieu vdi cac anion khdc de thay d6i vd tdng khoang cdch lap ca
bdn (d-spaeing) vd khd nang trao doi anion dang dugc tilp tyc nghien cuu va se cdng bd d nhiing bdi bdo sau.
Loi cam on: Cdc tdc gid chdn thdnh cdm on Truong DH QG Tp HCM dd tdi trg kinh phi cho de tdi md sdB2012-20-08TD vd Vi^n Cdng nghe Hda hgc da tgo dieu kien di thm: hi^n nghien ciru ndy.
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Lien h4: Nguyen Thj Dung
Vien Cdng nghe Hda hpc, Vipn Khoa hpc va Cdng nghp Vipt Nam So 1 Mgc Dmh Chi, phuong Ben Nghe, qugn 1, Thanh pho Ho Chi Minh Email: [email protected].
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