Research Article Hydrothermal Synthesis of Ni/Al Layered Double Hydroxide Nanorods

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1 Nnotehnology Volume 2011, Artile ID , 6 pges doi: /2011/ Reserh Artile Hydrotherml Synthesis of Ni/Al Lyered Doule Hydroxide Nnorods Yun Zho, Fenfei Xio, nd Qingze Jio Shool of Chemil Engineering nd Environment, Beijing Institute of Tehnology, Beijing , Chin Correspondene should e ddressed to Yun Zho, zhoyun@it.edu.n Reeived 7 Mrh 2011; Aepted 11 April 2011 Ademi Editor: Mllikrjun Ndgoud Copyright 2011 Yun Zho et l. This is n open ess rtile distriuted under the Cretive Commons Attriution Liense, whih permits unrestrited use, distriution, nd reprodution in ny medium, provided the originl work is properly ited. Ni/Al lyered doule hydroxide (LDH) nnorods were suessfully synthesized y the hydrotherml retion. The rystl struture of the produts ws hrterized y X-ry diffrtion (XRD). The morphology of the produts ws oserved using trnsmission eletron mirosopy (TEM) nd field emission snning eletron mirosopy (SEM). The influenes of retion time nd ph vlue on the morphology of the Ni/Al LDHs were investigted. The result showed tht the well-rystllized nnorods of Ni/Al LDHs ould e otined when the ph vlue ws out 10.0 with long retion time (12 18 h) t 180 C. 1. Introdution Lyered doule hydroxides (LDHs) or LDH-type ompounds elong to lrge lss of nioni lys. They n e represented y the generl formul [M(II) 1 x M(III) x (OH) 2 ] x+ [A n ] x/n mh 2 O[1], where M(II) is divlent metl tion, suh s Mg, Mn, Ni, Zn, nd Cu; M(III) is trivlent metl tion, suh s Al, Fe, Co, nd Cr; [1] A n is n exhngele nion, suh s F,Cl,NO 3,CO 3, SO 4,ndPO 4 3 [2, 3]. The vlue of x is etween 0.2 nd 0.34 generlly. LDHs re lyered struture with positively hrged ruite-like sheets, where M(II) nd M(III) re othedrlly oordinted. The exess hrge is lned y nions in the interlyer, together with wter moleules. Reently, LDHs hve ttrted muh ttention euse of their unique pplitions in mny fields. For exmple, they n e used s tlysts, tlyst supports, ion exhngers, dsorents, nd pigments nd lso e used in sensor nd mgneti tehnologies [1, 4, 5]. Sotter nd ken B, prepred Ni/Al, Mg/Al, Co/Al, Cu/Al LDHs nd used them s the tlysts of the stem reforming of methnol to produe hydrogen [6]. Alejndre et l. used Cu/Ni/Al LDHs s preursors of tlysts for the wet ir oxidtion of phenol queous solutions [7]. Most of these dvned funtions depend strongly on the omposition, size, nd morphology. So nnostrutures of LDHs will e of prtiulr interest for the pplitions. In the lst dede, 1-D nnostrutures hve een pid more ttention due to their unique physil nd hemil properties nd their potentil pplitions in siene nd engineering. The suessful synthesis of nnotues suh s BN, WS 2,ndMoS 2 hs een reported [8]. Mny hydroxide nd oxide nnorods or nnotues hve lso een prepred [9 15]. However, there is little report relting to LDH nnorods. A vriety of Ni-sed LDHs suh s Ni/Al, Ni/Co, Ni/Fe, nd Ni/Mn hve een studied s thode mterils nd tlysts [16, 17]. If Ni/Al LDHs were frited in the form of one-dimensionl (1-D) nnostruture, they would hold promise s highly funtionlized mterils. In this pper, Ni/Al LDH nnorods were suessfully synthesized y hydrotherml retion. In prtiulr, the effet ftors on the morphology of the LDHs were investigted suh s retion time nd ph vlue. 2. Experimentl A series of Ni/Al LDHs with nominl Ni 2+ /Al 3+ tomi rtio of 3/1 were prepred y hydrotherml retion t 180 C. All of them were prepred s follows: pproprite mounts of NiSO 4 6H 2 OndAl 2 (SO 4 ) 3 18H 2 O(Ni 2+ /Al 3+ = 3/1 (molr rtio)) were dissolved in deionized wter (40 ml). Then queous solution of mmonium hydroxide ws dded to the ove solution drop y drop with vigorous stirring to djust

2 2 Nnotehnology Tle 1: Chemil formuls nd interlyer distnes of Ni/Al LDH prepred t different ph vlues. ph vlue Interlyer distnes (nm) Ni/Al (molr rtio) Composition of LDHs [Ni 0.63 Al 0.37 (OH) 2 ](SO 4 ) H 2 O [Ni 0.74 Al 0.26 (OH) 2 ](SO 4 ) 0.13 (CO 3 ) H 2 O [Ni 0.75 Al 0.25 (OH) 2 ](SO 4 ) 0.16 (CO 3 ) H 2 O Trnsmittne (%) 1367 TheTEMmirogrphswerereordedonHithiH-800 instrument. The SEM imges were tken on Hithi S4800 field emission snning eletron mirosopy. Metls nd S nlysis ws performed on Perkin-Elmer Optim 3300 DV indutively oupled plsm-tomi emission spetrometer instrument. Mironlysis (% C, H, N) dt were olleted using LECO CHN-900 nlyzer. IR spetr were reorded on Bruker Vetor 22 spetrometer using KBr pellets Results nd Disussion Wvenumer (m 1 ) 1000 Figure 1: IR spetr of Ni/Al LDHs prepred t different ph vlues : 5.5; : 8.5; : I (CPS) 0 (003) 10 (006) (009) (015) (018) θ (deg) Figure 2: XRD powder ptterns of the produts prepred t different ph vlues : 5.5, : 8.5, : the ph vlue of the solution. After tht, the suspension ws trnsferred into 50 ml stinless Teflon-lined utolve nd heted t 180 C for pproprite time, then ooled to room temperture nturlly. The resulting produts were filtrted nd wshed severl times with distilled wter nd solute ethnol. The pple-green solid ws then olleted nd dried t room temperture for 12 h. XRD powder nlysis ws rried out with Rigku D/ mx-rb12kw X-ry diffrtometer using Cu K α1 rdition (λ = Å) in the 2θ rnge of 4 80 t room temperture. (110) 60 (113) Influene of ph Vlue on the Struture nd the Morphology of LDHs. Chemil formuls for LDHs prepred t different ph re given in Tle 1 sed on the metls, S nlysis, nd mironlysis (% C, H, nd N) dt. A Ni/Al rtio of 3 for Ni/Al LDHs otined t ph of 8.5 nd 10.0 is onsistent with the Ni/Al rtio used in the strting solutions. The Ni/Al rtio of 1.7, however, suggests the inomplete preipittion of Ni 2+ ions t ph of 5.5. The elementl nlyses indited tht the LDH smples prepred t ph of 8.5 nd 10.0 ontin oth sulfte nd ronte nions within the interlyer, however, sulfte nions re the dominnt interlyer nion. It n lso e onfirmed y IR spetrum (Figure 1). The nd t 1111 m 1 n e ttriuted to υ 3 virtion of SO 4,ndthe nd t 1367 m 1 n e ssigned to υ 3 virtion of CO 3. The introdution of ronte n e ttriuted to the CO 2 in queous solution of mmonium hydroxide in the proess of prepring LDHs. LDHs prepred t ph = 5.5 ontin only sulfte nions in the interlyer due to using the smllest mount of queous solution of mmonium hydroxide. The powder XRD ptterns for the Ni/Al LDHs prepred t different ph vlue re shown in Figure 2. AlltheXRD ptterns exhiit the hrteristi refletions of LDHs mteril. They show two groups of very lose (003), (006), nd (009) refletions for LDHs prepred t ph of 8.5 nd 10.0 due to ontining oth sulfte nd ronte nions within the interlyer. No impurity n e deteted in the XRD nlysis. Therefore pure Ni/Al LDHs must hve een otined t ph of 5.5, 8.5, nd The lower diffrtion intensity for LDHs otined t ph of 8.5 is oserved. This indites their lower rystllinity. The diffrtion peks of LDHs synthesized t ph of 10.0 re nrrow nd shrp, whih suggest tht Ni-Al LDHs prepred t ph = 10.0 re well rystllized. Compring the positions of 003 nd 006 refletions of smples prepred t different ph vlue, we n see tht they shift oviously towrd lower 2θ ngle with the derese of ph vlue. This indites tht when the ph vlues dereses to 5.5, the distne from the enter of one lyer to the next for Ni/Al LDHs inreses (see Tle 1), whih is relted to the tul Ni/Al molr rtio of the LDHs smples.

3 Nnotehnology nm () () () Figure 3: TEM imges for Ni/Al LDHs synthesized t different ph vlues. () 5.5; () 8.5; () Tle 2: Chemil formuls of Ni/Al LDH prepred t different retion times. Retion times (h) Ni/Al (molr rtio) Composition of LDHs [Ni 0.72 Al 0.28 (OH) 2 ](SO 4 ) 0.13 (CO 3 ) H 2 O [Ni 0.73 Al 0.27 (OH) 2 ](SO 4 ) 0.12 (CO 3 ) H 2 O [Ni 0.75 Al 0.25 (OH) 2 ](SO 4 ) 0.16 (CO 3 ) H 2 O [Ni 0.75 Al 0.25 (OH) 2 ](SO 4 ) 0.16 (CO 3 ) H 2 O d Trnsmittne (%) d 1367 I (CPS) Wvenumer (m 1 ) Figure 4: IR spetr of Ni/Al LDHs prepred with different retion times:2h;:6h;:12h;d:18h θ (deg) As shown in Tle 1, the rel Ni/Al molr rtio of the LDHs smples dereses with deresing ph vlue. The morphologies of the s-prepred Ni/Al LDHs were exmined with trnsmission eletron mirosopy (TEM). In Figure 3, theeffet of ph vlue on the morphology of LDHs is demonstrted. It n e seen tht nnoprtiles nd nnorods oexist in Ni/Al LDHs otined t ph of 5.5 nd 8.5. However, only nnorods were formed when the ph vlue ws inresed to They re nm in dimeter nd nm in length. Figure 5: XRD ptterns of the produts prepred t different retiontimes:2h;:6h;:12h;d:18h. It is ler tht the ph of 10.0 is suitle for the formtion of well rystllized Ni/Al LDH nnorods. So the influene of retion time on the struture nd morphology of Ni/Al LDHs ws investigted t ph of Influene of Retion Time on the Struture nd the Morphology of LDHs. Chemil formuls for LDHs prepred

4 4 Nnotehnology () () () (d) Figure 6:TEMimgesforNi/AlLDHswithdifferent retion times, () 2 h; () 6 h; () 12 h; (d) 18 h. t different times re given in Tle 2 sed on the metls, S nlysis nd mironlysis (% C, H, N) dt. The elementl nlyses, nd IR spetrum (Figure 4) yield evidene of the formtion of ronte nd sulfte-ontining LDHs t different times: 2, 6, 12, nd 18 h. The powder XRD ptterns for Ni/Al LDHs synthesized t 180 Cfordifferent retion times (2, 6, 12 nd 18 h) re shown in Figure 5. In eh se, the XRD ptterns exhiit the hrteristi refletions of n LDHs mteril with sl pek. They lso show two groups of very lose (003), (006), nd (009) refletions for LDHs prepred t different times due to ontining oth sulfte nd ronte nions within the interlyer. The intensity of the LDH diffrtion peks inreses with inresing the retion time, inditing tht, s expeted, the rystllinity of the rystllites inrese with inresing the retion time. From Figure 6, it n e found tht the retion time hs lrgeeffet on the morphology of Ni/Al LDHs. When the retion time ws lower thn 2 h, only nnoprtiles with the size of nm were otined. If the retion time ws up to 6 h, short nnorods were formed nd the length ws out nm. With the inrese of the retion time, nnorods with high spet rtio were oserved. As n e seen from Figure 4(), nnorods of Ni/Al LDHs with retion time of 12 h were nm in dimeter nd nm in length. When the time ws prolonged to 18 h, the nnorods inresed in length nd width. They hd dimeter of nm nd length of 1 3 μm. Ni/Al LDHs prepred for 12 h nd 18 h were lso oserved using SEM. As shown in Figure 7, lrgemount of Ni/Al LDHs nnorods with muh higher spet rtios were otined. It onfirmed tht Ni/Al LDHs nnorods were suessfully prepred y hydrotherml retion t 180 Cnd ph of 10.0 for longer retion time (12 18h). On the sis of the reports [8, 10, 14], mny 1-D nnostrutures (nnotues or nnorods) hve een suessfully synthesized from lyered strutures, the so-lled 2- D strutures suh s Ni(OH) 2 nd Mg(OH) 2. Ni/Al LDHs re lyered ompounds, therefore, we my suppose tht the formtion of Ni/Al LDHs nnorods might e relted to the nture of its lmellr 2-D strutures. However the struture of Ni/Al LDHs is different from Ni(OH) 2 nd Mg(OH) 2 with simple lyered strutures. The struture of Ni/Al lyered doule hydroxides (LDHs) n e desried s ontining ruite (Mg(OH) 2 )-like lyers in whih some of the divlent tions (Ni 2+ ) hve een repled y trivlent ions (Al 3+ ) giving positively hrged sheets. This hrge is lned y interltion of CO 3 or SO 4 nions in the hydrted interlyer regions. It is ovious tht Ni/Al LDHs possess omplited lyered struture. Bsed on the report [18], highly symmetril mterils, whih hve hexgonllyered strutures, n e grown

5 Nnotehnology 5 BACPCS kv 8.5 mm x40.0 k 3/1/ μm BACPCS kv 8.5 mm x100 k 3/1/ nm () () BACPCS kv 8.5 mm x20.0 k 3/1/ μm BACPCS kv 8.5 mm x40.0 k 3/1/ μm () (d) Figure 7: SEM imges for Ni/Al LDHs with different retion times. (, ) 12 h; (, d) 18 h. into low-symmetril rystllites suh s one-dimensionl nnorods. LDHs, whose si lyered unit possesses hexgonl symmetry, represent group of highly symmetril mterils tht show peulir one-dimensionl growth nisotropy. Under the present hydrotherml ondition, the nuletion of LDHs would our nd there ws n intrinsi tendeny to grow into rod-like nnoprtiles due to its ntistropi hexgonl struture. So, formed LDH nnorods re stle geometril morphologies in the surfe hemistry ontext, euse with this shpe LDHs hve low system energy [15, 18]. The TEM imges with different retion times showed tht the growth of Ni/Al LDH nnorods is forming nnoprtiles first, then growing to short nnorods, nd finlly to long nnorods. 4. Conlusions In summry, nnoprtiles nd nnorods of Ni/Al LDHs with size nd morphologil ontrols hve een synthesized y hydrotherml retion. The effet ftors suh s ph vlue nd retion time on the morphology of the LDHs were investigted. Ni/Al LDH nnorods were suessfully prepred y hydrotherml retion t 180 C nd ph of 10.0 for 12 h 18 h. Ni/Al LDH nnorods with retion time of 12 h hd dimeter of nm nd length of nm. When the time prolonged to 18 h, longer nd wider nnorods were otined with dimeter of nm nd length of 1 3 μm. The suessful growth of nnorods will provide promising route to low-dimensionl nnostrutures of other LDHs. Aknowledgment This work ws supported y Beijing Muniipl Nturl Siene Foundtion (Grnt no ). Referenes [1] F. Cvni, F. Trifirò, nd A. Vri, Hydrotlite-type nioni lys: preprtion, properties nd pplitions, Ctlysis Tody, vol. 11, no. 2, pp , [2] S. Miyt, Physio-hemil properties of syntheti hydrotlites in reltion to omposition, Clys nd Cly Minerls, vol. 28, no. 1, pp , [3] A. Ookuo, K. Ooi, nd H. Hyshi, Preprtion nd phosphte ion-exhnge properties of hydrotlite-like ompound, Lngmuir, vol. 9, no. 5, pp , [4] S. Miyt, Properties nd dsorption hrteristis of hydrotlites, Gipsum & Lime, vol. 187, p. 333, 1983.

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