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TNG HP THY NHIT V NGHIN CU TNH CHT CA CC HT VI CU V NANO HNH CU XP ZnS

Nguyn Tr Tun1, Nguyn Vn t2, Nguyn Th Phng Em3 v L Vn Nhn4 ABSTRACT

ZnS nanoparticles were hydrothermally synthesized at 200 C for 4 and 7 hours using sodium thiosulfate (Na2S2O3) and zinc chloride as initial materials. Scanning electron microscopy (SEM) images showed the co-existance of individual ZnS nanoparticles and microspheres formed by the nanoparticles. When acrylamide was added to the hydrothermal synthesis process as a surfactant, ZnS porous nanospheres were obtained. X-ray diffraction (XRD) revealed that the average size of ZnS nanocrystallites, estimated by the Debye-Sherrer formula, was about 4 nm. Photoluminescence excited (PLE) spectra of the material exhibited two blue shifts (~ 64 nm and ~ 24 nm) compared with the Photoluminescence (PL) peak of bulk ZnS. It is known to arise due to quantum confinement effect. Keywords: Nanoparticles; porous nanospheres; microspheres; hydrothermally synthesis Title: Hydrothermal synthesis and study on properties of ZnS micropheres and porous nanospheres

TM TT Cc ht nano tinh th ZnS c tng hp thy nhit 200 oC trong 4 gi v 7 gi, bng cch s dng cht Na2S2O3 (sodium thiosulfate) and ZnCl2 lm vt liu ban u. nh hin vi in t qut cho thy s tn ti ng thi cc ht nano ZnS ring r v cc ht vi hnh cu c to thnh bi cc ht nano. Khi cht acrylamide (cht hot ng b mt) c cho thm vo trong qu trnh tng hp thy nhit, cc nano hnh cu xp ZnS c to thnh. S dng phng php nhiu x tia X (XRD) o kch thc trung bnh ca nano tinh th ZnS bng cng thc Debye-Sherrer, c gi tr khong 4 nm. Ph kch thch hunh quang (PLE: photoluminescence-excitation) ca vt liu cho thy rng c 2 dch chuyn rt mnh (~64 v 24 nm) v pha bc sng ngn (blue shift) so vi nh hunh quang (PL:Photoluminescence) ca ZnS khi. S dch chuyn ny do nh hng ca hiu ng giam gi lng t. T kha: ht nano, nano hnh cu xp, vi hnh cu, tng hp thy nhit

1 GII THIU ZnS l mt bn dn II-VI quan trng, c nng lng vng cm ln, khong 3.7 eV 300 K, n c s dng lm vt liu hunh quang cho ng tia cathode [1], bt phosphor cho mn hnh phng v trong linh kin in hunh quang mng mng [2]. Gn y, nhiu nhm nghin cu quan tm n vt liu nano c hnh dng c bit v cc tnh cht mi c mong i ca n. Vt liu nano ZnS mt chiu c ch to nh l que nano [3], dy nano [4-7], ai nano [8], ng nano [9], hnh 1 B mn Vt l, Khoa Khoa hc t nhin, Trng i hc Cn Th 2 B mn Ha hc, Khoa Khoa hc, Trng i hc Cn Th 3 Khoa c bn, Trng i hc Tin Giang 4 B mn Vt l S phm, Khoa S phm, Trng i hc Cn Th

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cu nano [10-12]. Hnh cu nano xp c th ng dng dng lm vt liu nh l tinh th quang t, b lc, xc tc,... V cc kh nng ng dng ca vt liu ny, nn chng ti ch to ht nano hnh cu xp ZnS bng phng php thy nhit 200 C trong 4 gi v 7 gi, khi cht acrylamide (cht hot ng b mt) cho thm vo trong qu trnh phn ng.

2 THC NGHIM 2.1 Tng hp nano tinh th ZnS Trong th nghim ny, 4.08 g ZnCl2 khan v 7.44 g Na2S2O3.5H2O c vo Teflon ca bnh thy nhit c th tch 150 ml cng vi nc kh ion, chim tng cng th tch 120 ml (80%) ca Teflon. Bnh thy nhit c ng kn nhit 200 oC trong 4 v 7 gi. Sau khi thi gian phn ng ht, kt qu thu c l cht lng trng c. Dung dch ny c em quay ly tm, lc ra 2 ln bng nc kh ion v cn tuyt i, sau em sy kh trong chn khng (10-2 10-3 Torr) nhit 70 oC trong 15 gi. Kt qu, sn phm thu c l bt nano tinh th ZnS. 2.2 Tng hp nano hnh cu xp ZnS Tng hp nano hnh cu xp ZnS, 3.6 g acrylamide s dng nh cht hot ng b mt, c thm vo th nghim trn, nhit 200 oC trong 4 gi. Phng php tng hp ny tng t nh phng php ca Changlong Jiang v cng s [10]. 2.3 Cc phng php kho st thc nghim Cc mu thu c sau khi tng hp c kho st tnh cht cu trc bng gin nhiu x tia X (D8 Advance Bruker- c) ti Khoa Ha hc, Trng i hc Khoa hc T nhin, i hc Quc gia H Ni. Kch thc v hnh thi cu trc ca mu c kho st bng nh hin vi in t qut (FESEM) v nh hin vi truyn qua (TEM) ti Vin v sinh Dch t trung ng. Tnh cht quang ca vt liu c o bng my o ph hunh quang FL3-22 (Jobin Yvon-Spex, M) ti Trung tm Khoa hc Vt liu- HKH T nhin H Ni.

3 KT QU 3.1 Tnh cht cu trc Hnh 1 l gin nhiu x tia X ca ca mu nano tinh th ZnS nhn c sau qu trnh tng hp bng phng php thy nhit, 200 oC trong 4 gi (4 h), 7 gi (7 h) v 4 gi (4 h(a)) c cht hot ng b mt acrylamide (a).

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Hnh 1: Gin nhiu x tia X ca mu nano tinh th ZnS tng hp thy nhit

200 oC trong 7h, 4 gi v 4 gi c cht hot ng b mt acrylamide C th thy trong hnh 1, gin nhiu x tia X c c trng bi 3 nh nhiu x c cng yu v rng bn ph ln. V tr cc nh ny l hon ton tng ng vi nhiu x trn 3 mt (111), (220) v (311) ca ZnS c cu trc lp phng gi km. Kt qu ny khng nh bt nhn c t quy trnh tng hp ca chng ti l ZnS. Cng yu v rng bn ph ln ca cc nh nhiu x cho thy cc tinh th nhn c c kch thc nh v kt tinh thp. Da vo gin nhiu x tia X v cng thc Debye-Sherrer, chng ti tnh c kch thc tinh th ca nano ZnS ca mu 1, 2 v 3 c biu din bng 1. Da vo bng 1, chng ti thy kch thc tinh th ca nano ZnS ca mu 1 v 2 l thay i khng nhiu. i vi mu 3, kch thc tinh th ca nano ZnS l ~3 nm, nh hn so vi hai mu trn. Bng 1: Kch thc trung bnh ca ht nano tinh th ZnS c tng hp thy nhit

200 oC trong 4 gi, 7 gi v 4 gi c cht hot ng b mt acrylamide Mu 1 2 3

Thi gian thy nhit 4 gi 7 gi 4 gi (a) Kch thc tinh th ~9 nm ~12 nm ~3 nm

nh FESEM ca mu 1 v 2 c biu din hnh 2. Hnh 2a l nh FESEM mu 1, cho thy nh ca mt ht vi cu c ng knh khong 1m, b mt ca ht vi cu ny nhm, khng c nhn. Hnh 2b l nh FESEM ht vi cu c phng to ln hai ln, cho thy cc ht nano b mt ca ht vi cu c kch thc khong 15 nm, ln hn kch thc c tnh ton da trn gin nhiu x tia X.

Hnh 2: nh FESEM ca ht nano tinh th ZnS c tng hp thy nhit nhit 200 oC trong 4 gi v 7h

a cb d

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iu ny chng t cc ht tinh th nano ZnS to thnh cc ht vi cu ZnS. Hnh 2c l nh FESEM mu 2, cho thy ngoi cc ht vi cu ZnS c ng knh khong 1-5 m, cn c ln cc ht nano c kch thc trung bnh khong 20 nm c biu din hnh 2d. Nh vy, khi tng hp thy nhit mu 2 (200 oC, 7 gi), c thi gian ln hn mu 1 (200 oC, 4 gi), th kch thc trung bnh ca cc ht nano tinh th ZnS ln hn v kch thc khong 5 nm, iu chng t cc ht b kt m khi thi gian tng hp thy nhit lu hn 4 gi. nh FESEM ca mu 3 c biu din hnh 3. Hnh 3a cho thy nh cc ht nano ZnS c dng hnh cu xp, ng knh ca cc ht nano hnh cu xp c kch thc khong 130-230 nm. Nguyn nhn to ra ht nano hnh cu xp, c th l do cc bt kh SO2 to ra trong qu trnh phn ng, bay ln lm cho cc ht nano hnh cu c nhng l nh to nn hnh cu xp. Hnh 3b cho thy cc ht nano ZnS c kch thc khong 10 nm cu thnh cc ht nano hnh cu xp, khi tng hp thy nhit mu 3 do c cht xc tc b mt acrylamide thm vo trong mu, ngn khng cho ht kt t ln ln c.

Hnh 3: nh FESEM ca ht nano tinh th ZnS c tng hp thy nhit nhit 200 oC trong 4 gi c cht hot ng b mt acrylamide

xc nh kch thc v hnh thi hc ca ht chnh xc hn, chng ti chp nh TEM ca mu. Hnh 4 l nh TEM ca cc ht nano c thy nhit 200 oC khng c cht acrylamide, cc ht ny c kch thc ~10 nm v kt m li vi nhau. Kch thc ht ny kh ph hp vi kch thc tnh bng gin tia X.

Hnh 4: nh TEM ca ht nano tinh th ZnS c tng hp thy nhit nhit 200 oC trong 4 gi, khng c acrylamide

a b

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Hnh 5 l nh TEM ca ht nano tinh th ZnS c tng hp thy nhit nhit 200oC trong 4 gi, c cht hot ng b mt acrylamide.

Hnh 5: nh TEM ca ht nano tinh th ZnS c tng hp thy nhit nhit 200 oC -4 gi, c cht hot ng b mt acrylamide

Da vo hnh 5a, cho thy cc ht nano ny c kch thc kh nh ~2-3 nm, do cht hot ng b mt bm vo b mt ca cc ht nano khng cho cc ht kt t li vi nhau. Hnh 5b, cho thy cc ht nano cu thnh cc nano hnh cu xp ZnS, c kch thc trung bnh ~30-80 nm. Kch thc ca cc ht nano Zns ny tng i ph hp vi kch thc tnh bng gin nhiu x tia X v nh FESEM. 3.2 Tnh cht hunh quang Hnh 6, l ph kch thch hunh quang ca ht nano v ht nano hnh cu xp ZnS c tng hp thy nhit 200 oC trong 4 gi v 7 gi khng c cht acrylamide v 4 gi c cht acrylamide. Vng ph PLE rng t 250-350 nm, hai nh chnh nhn c bao gm hai vng ph c trng vi cc i tng ng ~280 v ~320 nm, so vi ph kch thch hunh quang ca ZnS khi 344 nm [13], c s dch chuyn v pha bc sng ngn, c nng lng cao (blue shift) rt mnh ~64 nm v 24 nm tng ng. Hin tng dch chuyn ny lin quan n hin hiu ng giam gi lng t mnh, khi kch thc ht gim xung 2-3 nm. T hnh 6, ph hunh quang ca cc mu ZnS khng c v c cht hot ng b acrylamide c tng hp thy nhit, chng ti quan st thy vng pht x rng ~400-500 nm, c nh hunh quang cc i 436 nm. nh pht x ny thng l do cc sai hng v trng thi b mt ca nano ZnS gy nn.

Hnh 6: Ph PLE v PL ca nano tinh th ZnS c tng hp thy nhit, vi em: 440 nm v ex: 280 nm

30 nm

60 nm

80 nm

a b

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Theo cc cng b gn y, nh hunh quang mu xanh dng (blue) thng c quan st thy cc mu nano tinh th ZnS vi di ph khong 430-464 nm [6,14]. y c xem nh l nh pht x lin quan n sai hng ca ZnS. Mt s cng trnh gii thch nguyn nhn ca pht x xanh dng ca ZnS l do cc nt khuyt S [15].

4 KT LUN Trong bi bo ny, chng ti trnh by qui trnh thy nhit ch to cc ht nano v vi cu ZnS 200 oC trong 4 gi v 7 gi. ng thi trnh by k thut ch to ht nano hnh cu xp ZnS 200 oC trong 4 gi khi thm vo cht hot ng b mt acrylamide, nano hnh cu xp ZnS c hnh thnh khi c bong bng kh SO2 trong sut qu trnh phn ng. Tnh cht quang ca nano hnh cu xp ZnS c nghin cu bng ph PLE v PL. nh ph kch thch hunh quang dch chuyn v pha bc sng ngn (blue shift) rt mnh ~64 v 24 nm so vi nh ca ZnS khi. Phng php ny ang c p dng ch to cc ht nano hnh cu xp v c khc.

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