摘要:

Calorimetric study of intercalation of n-alkyldiamines into a-titanium hydrogenphosphate Claudio Airoldi* and Sirlei Roca Instituto de Quimica, Universidade Estadual de Campinas, Caixa Postal 6154, 13083-970 Campinas, Sa"oPaulo, Brasil A series of n-alkyldiamines of general formula H,N(CH,),NH, (n=2-9) has been intercalated into the crystalline lamellar compound a-Ti(HPO,),-H,O (TIP) from aqueous solution. The amount intercalated was followed batchwise at 298 _+ 1K and the variation of the original interlayer distance for TIP (756 pm) was followed by X-ray powder diffraction. Linear correlations with good fits were obtained for the interlamellar distance (d)or for the number of moles intercalated (nint)as a function of the number of carbon atoms in the aliphatic chain (nc):d=(883.14f 12.76)+( 108.51 _+2.20)nc and nin,=(5.79_+0.12)-(0.28~0.02)nc. The exothermic enthalpies for the intercalation are related to the monomolecular layer arrangement with a longitudinal axis inclined by 58" to the inorganic sheets.The enthalpies for the overall reaction 2O3P-0H(c) +H,N(CH,),NH,(c, 1)= O,P-O-+H3N(CH2),NH3+ -O-PO,(c); AintH,determined by reaction-solution calorimetry at 298.15 k0.02 K are correlated with the number of carbons in the aliphatic chain or the interlamellar distance, by the equations AintH= -(56.16+0.67)-(2.06+0.12)nC and AintH=-(39.41 f1.41)-(1.80 x lop2kO.10 x 10-')d. The enthalpic value for nc=O gave -56.17 f0.67 kJ mol-' which corresponds to the intercalation of two moles of ammonium cation. Layered hydrogenphosphates of metals in oxidation state +4 ducting polymers and to assemble molecular multilayers at normally exhibit a-crystalline compounds of the general form solid/liquid interfaces." a-M(HPO,),-H,O (M =Zr, Ti, Hf, Sn, Ge, etc.).In the zir- The proposed mechanism for amine intercalation is that the conium compound, whose layered structure was first deter- basic nitrogen group is first protonated by the free hydrogen mined, the metal atoms lie in a plane and are bridged by of the phosphate group and therefore the maximum amount phosphate groups which are located above and below the of intercalated amine should be two moles per unit of metal metal atom plane. Three oxygens of each tetrahedral phosphate phosphate. The quantity of amine intercalated also depends are linked to three zirconium atoms and each metal is octa- on the free area of about 20.0 x lo4 pm' surrounding each hedrally coordinated by six oxygens of six different phosphate phosphate group, which permits the accommodation of one groups.The fourth oxygen of each phosphate group is bonded molecule of amine per phosphate group, for a cross-sectional to a proton which is located in the interlayer space.'.' This area of a trans-trans alkyl chain evaluated as 18.6 x lo4 pm'.'l arrangement of the phosphates groups forms zeolitic type Among the a-metal(1v) phosphates, zirconium phosphate is cavities each containing a water molecule hydrogen bonded to the most explored in organic molecule intercalation processes di-10*15three of the acid phosphate groups on the same layer.This and various features of intercalation of ~oIIo-,~'-~~ and amines have been studied. For the analogous arrangement permits the diffusion of spherical species with a ar~maticl~,'~ The layers are only weakly titanium phosphate, intercalation of only monoamines has theoretical size limit of 264~m.~ The amount of alkylmonoamines interca- held together by dispersion forces. For the corresponding been de~cribed.'~.'~ titanium compound, which is isomorphous with the zirconium lated into the titanium compound corresponds to two moles compound, similar properties can be expected and the proton of amine per mole of the inorganic support with an inclination of the free phosphate group is available for acid-base reactions of the alkyl chain of 55", which is very close to that presented to intercalate bases into the interlamellar region.by zirconium phosphate. During the intercalation of organic molecules into this kind Although intercalation is a well established process, the of layered compound the inorganic host layers interact with great majority of the publications have focused on the struc- the organic guest molecules by increasing the interlamellar tural aspects of these kinds of compounds. The main objective separation. The fully intercalated material consists of regularly of this work is to report some calorimetric determinations alternating organic and inorganic layers and both the physical involving the interaction of a-titanium hydrogenphosphate with n-alkyldiamines (C'-C9), in order to contribute to the nature and the chemical reactivity of the material can be understanding of the energetics of the intercalation.significantly altered.For example, amine intercalation into Thermochemical data related to the intercalation of organic zirconium hydrogenphosphate changes its properties when in molecules into the cavities of lamellar compounds are sparse contact with water. The thin lamellae formed may be reconsti- in the literature.'8~20 These new intercalated compounds have tuted to form thin films which have potential applications in been characterized through physical and thermal methods, the field of ion exchange, chromatography, heterogeneous showing that some data correlate with the energetics of catalysis and as protonic conductor^.^ On the other hand, the intercalation.same intercalated materials seem to be useful as precursors in pillaring reaction^'.^ because intercalation produces an increase in the interlayer space, favouring the exchange between the Experimentalintercalated amine and the pillaring agent. Other applications involve the modifications of the host's optical properties, Materials superconducting critical temperature, interlayer magnetic All chemicals used were of reagent grade.Demineralized water coupling and materials Some recent and very interes- was used throughout the experiments. Titanium tetrachloride ting applications involve the use of these materials to modify (Riedel), disodium hydrogenphosphate (Anidrol), hydrochloric electrode surfaces, in the preparation of low-dimensional con- acid (Merck) and phosphoric acid (Carlo Erba) were used for J.Muter. Chem., 1996,6( 12), 1963-1966 1963 preparations The diamines (Aldrich) of the general form H,N(CH,),NH, (n=2-9), I e , 1,2-ethylenediamine (en), 1,3- propylenediamine (pda), 1,4-butylenediamine (buda), 1,5- pentamethylenediamine (pmda), 1,6-hexamethylenediamine (hmda), 1,8-octamethylenediamine(omda) and 1,9-nonamethy- lenediamine (nmda) were used without further purification Preparations The amorphous titanium phosphate was prepared by adding a hydrochloric acid solution of titanium tetrachloride to a phosphoric acid solution containing sodium hydrogenphos- phate l8 The a-titanium hydrogenphosphate (Tip) was pre- pared by refluxing the amorphous material with 12 0 mol dm-3 H,PO, for 160 h at 433 K l8 The crystalline solid was washed until pH 4 0 and dried to constant mass over P,05, and was analysed as described previously '* Intercalation procedure The intercalation process was followed batchwise in aqueous medium at 298 & 1K for diamines H,N(CH,),NH, (n=2-9) Samples of TiP were suspended in variable concentrations of diamine in demineralized water in polyethylene flasks with a solid solution proportion of 10 g 0 10 dm3 The system was mechanically stirred for 6 h The time required to reach equihb- rium was first established through a series of intercalations involving a constant mass of the lamellar compound with the diamines as a function of time Although approximately 4 h were sufficient to attain equilibrium, 6 h was chosen to ensure maximum intercalation At the end of this time, the solid was separated by centrifuging the suspension, and was dried at 373 K From the titration of the supernatant with standard hydrochloric acid, the amount of the diamine intercalated (nlnt) was determined by the expression nInt=(n,-nn,)/m, where n, is the initial number of moles of diamine in solution, n, is the number of moles of diamine in solution in equilibrium with the solid phase and m is the mass of the lamellar compound For each experimental point, the reproducibility was checked by at least one duplicate run Analytical procedures The loss of mass determinations were performed on a DuPont model 1090B thermogravimetric instrument coupled with a model 951 thermobalance, with samples varying in mass from 15 0 to 30 0 mg, using a flux of dry nitrogen and a heating rate of 8 2 x lo-' Ka s-' X-Ray powder patterns were obtained with nickel-filtered Cu-Ka radiation on a Shimadzu model XD3A diffractometer and the interlayer spacings of the com- pounds were calculated from the 002 plane IR spectra were obtained on a Perkin-Elmer FTIR 1600 spectrometer with solid samples ground to obtain a pulverized material The 31P NMR spectra were obtained on an ac 300/P Bruker spec- trometer with magic angle spinning, operating at 121 MHz at room temperature and using 85% H3P04 as reference to calibrate the chemical shift scale Calorimetry An LKB 8700-1 isoperibolic precision calorimetric system was used for all reaction-solution measurements of the intercalation of diamines into lamellar titanium hydrogenphosphate in aqueous media The thermal effects caused by the entrance of the diamine into the lamellar space were determined by breaking thermostatted thin-glass ampoules containing TiP (cu 50 mg) in 0 10 dm3 of diamine solutions of variable concen- tration and the heat produced was recorded During the breaking of the ampoules, the response obtained in the well stirred solution indicated a kinetically favourable system where the baseline was reached rapidly in a few minutes On the other hand, no heat was observed when only TiP samples were broken into the calorimetnc solvent The standard molar enthalpies of intercalation were obtained by breaking at least five ampoules at 298 15 &O 02 K The heat of of empty ampoule breaking was found to be negligible ''22 Details of the oper- ational procedure, calculations and accuracy of the apparatus have been previously described 23 After the thermochemical measurements, the resulting solution was filtered and aliquots of the supernatant were titrated with standard hydrochloric acid solution The isolated solid was dried and submitted to thermogravimetry, IR and X-ray measurements Results and Discussion The lamellar TiP compound can intercalate various kinds of polar organic molecules which are accommodated in the interlayer space Before intercalation, an interlamellar distance of 756pm was obtained by X-ray measurements and are in accord with previous measurements An ion exchange capacity of 7 70 mmol g-' was obtained from the exchange with an aqueous solution of n-butylamine l8 The thermogravimetric curve indicated a 14% total mass loss in two distinct steps The hydrated water was eliminated in the range 313-360K, which was followed in the range of 490-600 K by the removal of water of condensation due to the interaction of phosphate groups to produce pyrophosphate l8 The IR spectrum showed the presence of characteristic peaks at 3555 and 3010 cm-', demonstrating the presence of water and the main P-0 stretching vibration at 1033 cm-' l8 The 31P NMR CP MAS spectrum showed only a narrow and intense peak at 6 -18 4, which was attributed to protonated phosphate 24 26 The number of moles of n-alkyldiamines intercalated is shown in Table 1 These values, which were obtained through a batchwise process, decreased with increasing alkyl chain length of the diamine From the analysis of the intercalated compound, the general formula can be written as Ti( P04)H2 -,[H3N(CH,),NH3],H2 -,(O4P)Ti HzO, where x was determined by the titration of the supernatant after intercalation, and can be compared with thermogravimetric measurements Although the number of moles intercalated decreased with increasing chain length, the relationship between the number of moles of diamine and the number of moles of the lamellar compound was always close to unity For example, for pmda and hmda which differ by only one carbon atom, the number of moles intercalated were 4 31 and 4 08 mmol g-' respectively, corresponding to a molar ratio of diamine/intercalated compound of 1 11 and 105, respectively The decrease in the amount of the diamine intercalated with increasing chain length can be correlated with the size of the n-alkyl chain since larger diamines have less freedom to diffuse into the interlayer space to interact easily with the avail- able pendant protons distributed on the inorganic support The smallest molecule, en, contrasts to the longest n-alkyldiamine, nmda, in its degree of intercalation, the values being 1 36 and 0 89 mmol g-', respectively Moreover, when a diamine is bonded to a phosphate group, this concomitantly renders an adjacent site unavailable for bonding due to the Table 1 The number of moles of diamine intercalated (n,,,), interlamel-lar distance (d), and x values in the formula Ti(P0J2H2 2x [H,N(CH,),NH,], -H,O, where xtlt and xthemwere obtained by titration and thermogravimetry, respectively diamine n,,,/mmol g d/pm Xtlt Xtherm en 5 29 1090 136 138 Pda 5 14 1210 132 130 buda 4 50 1318 116 113 pmda hmda 4 31 4 08 1424 1549 111 105 111 104 omda 3 53 1766 0 91 0 89 nmda 3 41 1839 0 88 0 88 1964 J Muter Chern, 1996, 6(12), 1963-1966 fact that it covers this site.26 This behaviour is reflected directly in the number of moles intercalated, which is lower than the maximum capacity of the available protons as determined by intercalation of monoamines.The quantity of intercalated organic molecules determined from titration data agreed closely with the thermogravimetric results, as shown in Table 1.The intercalated materials showed two mass losses: one, centred at 340 K, due to loss of water of hydration and the second, between 480 and 700 K, comprising the loss of diamine and water of condensation. The intercalation process induces an increase in the inter- layer distance to accommodate the diamines in the free space of the cavity. This behaviour can be followed via the X-ray data shown in Table 1. The interlamellar distance increased with increasing length of the alkyl chain but also depended in the opposite manner on the degree of intercalation.For ex- ample, the end member diamines en (n=2) andnmda (n=9) with degrees of intercalation of 1.36 and 0.88 mmol g-l, showed interlamellar distances of 1090 and 1839 pm, respectively. Both the numbers of moles intercalated and interlamellar distance correlated linearly with the number of carbons in the aliphatic chain, as illustrated in Fig. 1 and 2 and according to eqn. (1) and (2). nf= (5.79 f0.12) -(0.28 & 0.02)nc (r=0.997) (1) d=(883.14f 12.76)+( 108.51 +2.20)nc (r=0.999) (2) From the interlamellar distance correlation shown in Fig. 2, the angular coefficient value enables an estimation of the inclination of the diamine molecule, as well its arrangement in either a mono-or a bi-layer manner.For a sequence of diamines the increment of one additional carbon atom in an all-trans alkyl chain length was, as expected, 127pm. If the Fig. 1 Number of moles intercalated (nint)as a function of the number of carbons (n,) of n-alkyldiamine t' ,"'1 ,/' Y' ,d' A" m+. , . , . 0 2 4 B1 nC Fig. 2 Interlamellar distance (d) after intercalation as a function of the number of carbons of n-alkyldiamine (n,) diamines are present as a monomolecular layer of extended molecules, their longitudinal axes are inclined at an angle of arcsin (108/127)=58" to the plane of the inorganic sheet. This same behaviour was found for zirconium phosphate, where the arrangement of the diamines was in monolayers with an angle of 58", the same value found here."^'^ For an extrapolated diamine with no carbon atom (nc=O), the above correlation gives an interlamellar distance of 883 pm, greater than that found for pure TiP, which can be attributed to the intercalation of two NH3' species into the lamellar compound.A very similar behaviour was found for the inter- lamellar distance for hydrazine ions in zirconium phosphate, the value of which (850 pm) is comparable with our experimen- tal value.'O The IR spectra of the intercalated materials showed a broad peak in the range 3200-2000cm-' attributed to N-H and NH3+ stretching, hydrogen bridging and C-H stretching. The characteristic peak at 1540 cm-' can be attributed to NH3+ bending.A similar spectrum was also observed in the intercal- ation of amines into zirconium ph~sphate.'~ The 31P MAS NMR spectra of intercalated compounds showed peaks at 6-18.4 and -14.9, which can be attributed to protonated and deprotonated phosphate, re~pectively.'~-~' The former peak can be assigned to unreactive phosphate groups, which are blocked by intercalated amines or are located in the bulk of the inorganic matrix and consequently are inaccessible to the reaction with the diamines. In acquiring information about the thermodynamics of intercalation, the organic molecules were interacted with the inorganic matrix in aqueous solution and enthalpy changes were obtained by reaction-solution calorimetry. All data clearly showed that the process of intercalation of n-alkyldiamines in TIP can be interpreted as an acid-basic solid-state reaction between a layered acid host 03P-OH and Brsnsted-base guests according to eqn.(3).15 20,P-OH(c) +HZN(CH,),NHz(c,l) =03P-0-+ H3N(CH2),NH3 -0-P03(c); A,,,Jl + The standard enthalpy of intercalation of diamines in the condensed phase of the above process was calorimetrically determined and the values obtained are listed in Table 2, as well as the number of experiments conducted. The results show that an increase in carbon number in the alkyl chain induces a corresponding enhancement in the exo- thermicity of the enthalpy of intercalation. For example, for en and nmda, the values of enthalpy of intercalation are -60.37f 1.99 and -74.22f 1.75 kJ mol-', respectively.These standard enthalpies are linearly correlated with the number of carbons of the diamine (n,) and with the interlamellar distance (d),as illustrated in Fig. 3 and 4, and can be expressed in terms of eqn. (4) and (5). AintH=-(56.16f0.67)-(2.06~0.12)nc (r=0.992) (4) AintH=-(39.41+1.41) -(1.80~10-2$0.10~ 10-')d (r=0.994) (5) Table 2 Values of enthalpy of intercalation (Ai,,Jf) and number of experiments (N)for all n-alkyldiamines diamine -Ai,,H/kJ mol-' N ~ ~~ en 60.37 i1.99 7 Pda 61.91 k4.99 5 buda 63.81 k2.07 6 pmda hmda 66.70 k4.31 69.85i3.16 6 9 omda 72.39i1.70 8 nmda 74.22i1.75 6 J. Muter. Chem., 1996, 6(12), 1963-1966 1965 standing of these types of system.The linear correlations observed suggest that enthalpic values can be inferred for other intercalated species by using these linear correlations for n-alkyldiamines and can be readily estimated from the number of carbons in the alkyl chain or from the interlamellar distance. The authors are indebted to PADCT and FAPESP for financial support and gratefully acknowledge CNPq for fellowships. References 1 G. Alberti, P. C. Galli, U. Costantino and E. Torracca, J. Inorg. Nucl. Chem., 1967, 29, 571. 2 A. Clearfield, Inorganic Ion Exchange Materials, CRC Press, Boca Raton, FL, 1982. 3 M. Suarez, J. R. Garcia and J. Rodriguez, J. Phys. Chem., 1984, 88, 159. 4 G. Alberti, M.Casciola and U. Costantino, J. Colloid Interface Sci., 1985,107,256. 5 A.Clearfield and B. D. Roberts. InorP. Chem.. 1988.27.3237. 6 P. Oliveira-Pastore, A. J. Lopes, P.-M. Torres, E. C. Rodrigues, A. A. G. Tomlinson and L. Alagna, J. Chem. Soc., Chem. Commun., 1989,751. 7 Intercalation Chemistry, ed. M. S. Whittingham and A. J. Jacobson, Academic Press, New York, 1982. 8 R. Schollhorn, Inclusion Compounds, Academic Press, London, 1984. 9 C. A. Formstone, E. T. Fitzgerald, D. OHare, P. A. Cox, M. Kurmoo, J. W. Hodby, D. Lillicrap and M. Goss-Custard, J. Chem. Soc., Chem. Comrnun., 1990,501. Fig. 3 Standard enthalpy of intercalation (A,ntH)of n-alkydiamines into cc-titanium hydrogenphosphate as a function of the number of carbons (n,) -72.Jh . , . , , . .,, ,=, 10 M. Casciola, U.Costantino and F. Marmottini, Solid State lonics, 1989,35, 67. 11 A. I. Kitaigorodsy, Molecular Crystals and Molecules, Academic Press, New York, 1973. -76.00 12 F. Menedez, A. Espina, C. Trobajo and J. Rodrigues, Muter. Res. 1200 1400 1600 1800 Bull., 1990, 25, 1531. dlpm 13 M. Casciola, E. K. Andersen and J. G. K. Andersen, Acta Chem. Scand., 1990,44, 459. Fig. 4 Standard enthalpy of intercalation (A,ntH)of n-alkyldiamines into a a-titmium hydrogenphosphate as a function of the interlamellar distance (d I 14 15 16 U. Costantino, J. Chem. Soc., Dalton Trans., 1979,402. M. Casciola, U. Costantino, L. DiCroce and F. Marmottini, J. Incl. Phenom., 1988,6,291. L. E. Depero, M. Zocchi, A. La Ginestra and M. A. Massucci, The contribution to the enthalpy of each carbon added to the aliphatic chain of the diamine corresponds to -2.06 kJ mol-' and, in terms of the variation in interlamellar spacing, this corresponds to 1.80 x low2kJ mol-' pm-'.Extrapolating the linear behaviour of these correlations to n, =0, the enthalpy of intercalation of two moles of ammonium cations per mole of the inorganic matrix has a value of 17 18 19 20 21 22 Struct. Chem., 1993, 4, 317. A. L. Blumenfeld, A. S. Golup, G. Protsenko, Y. N. Novikov, M. Casciola and U. Costantino, Solid State lonics, 1994,68, 105. C. Airoldi and S. F. Oliveira, Struct. Chem., 1991,2,41. F. Menedez, A. Espina, C. Trobajo, J. R. Garcia and J. Rodrigues, J. Incl. Phenom., Mol. Recogn. Chem., 1993, 15, 215. T. Kijima and M. Goto, Thermochim. Acta, 1983,63, 33. C. Airoldi and S. Roca, J. Solution Chem., 1993,22, 707. I. Wadso, Science Tools, 1966,13, 33. -56.16k 0.67 kJ mol-'. When same procedure was used for the intercalation of alkylmonoamines into titanium hydrogen- phosphate, a value of -28.04k0.88 kJ mol-' was obtained." However, since monoalkylamines intercalate as double layers into the host, this value should be doubled, resulting in an enthalpic value of -56.08 k1.76 kJ mol-', very close to the value found here. 23 24 25 26 27 C. Airoldi and E. A. Digiampietri, J. Chem. Thermodyn., 1992, 24,33. N. J. Clayden, J. Chem. Soc., Dalton Trans., 1987, 1877. D. J. MacLachlan and K. R. Morgan, J. Phys. Chem., 1992, 96, 3458. D. J. Maclachlan and K. R. Morgan, J. Phys. Chem., 1990,94,7656. U. Costantino, J. Inorg. Nucl. Chem., 1981,43, 1895. The sequence of the enthalpies determined here with a Paper 6/03541H; Received 21st May, 1996 limited number of n-alkyldiamines contributes to the under- 1966 .I.Muter. Chern., 1996, 6(12), 1963-1966

ISSN:0959-9428    

DOI:10.1039/JM9960601963

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

MATERIALS CHEMISTRY COMMUNICATION Enhanced fluorescence of coumarin laser dye in the restricted geometry of a porous nanocomposite P. Wlodarczyk, S. Komarneni,* R.Roy and W. B. White Intercollege Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA We report here the dramatic increase in fluorescence intensity of 7-diethylamino-4-methylcoumarin(coumarin 1) laser dye in the restricted geometry of a pillared clay nanocomposite. The fluorescence intensity of the alumina-pillared fluorphlogopite- coumarin complex is about 6 times greater than that of the fluorphlogopite-coumarin complex. The prevention of dye aggregation and the change of the crystal field surrounding the coumarin dye molecules in the compartments between pillars apparently lead to this fluorescence enhancement. The positive results obtained here may lead to the potential application of dye-intercalated nanocomposite clays in linear and non-linear optics.Lasers depend on an amplifying medium for their operation. In dye lasers this medium is a solution of an organic dye. The original dye laser employed a phthalocyanine solution,' but this solution was soon replaced by rhodamine 6GZ which is still one of the most widely used amplifying dyes today. After the development of the dye laser, thousands of dyes were investigated for this purpose. With such intensive investigation of available dye sources, it was determined that only four additional and previously commercially available dyes, pyronin B, rhodamine S, 9-aminoacridine hydrochloride and benzyl j-methylumbelliferone, were useful in the dye laser.3 A vast amount of research has been carried out to date on the structure and fluorescence of laser dyes and these properties are well established.It is well known that fluorescence efficiency is high in dye molecules with rigid, planar structures4 and that aggregation of dye molecules has a major role in fluorescence quenching. Dyes that form dimers and larger aggregates will often have distinctly different absorption bands. Some may have weak or no fluorescence at all. In general, dyes aggregate to a greater extent in water than in organic solvents. Aqueous concentrated dye solutions show less aggregation in the presence of alcohol or glycerol5 Where an aqueous solution is desired for xanthine dyes, surfactants such as hexadecyltrimethylammonium bro- mide, Triton X, sodium lauryl sulfate and potassium oleate have been studied with varying degrees of success.6 One of the effective ways to prevent dye aggregation is to isolate the molecules in a matrix.In the last decade, several studies of the effects of restrictive geometries on optical dyes have been performed. The majority of these studies used sol-gel-processed alumina films and silicate gels as the host matrices for the dye.'-'O In these studies, sols were doped with various organic dyes and gelled to trap the dye within the microporous gel structure. Other studies were performed on swelling clays with organic dyes intercalated within the 2: 1 structure of the phyllosilicate." The concentration of dye solutions and cation- exchange capacity of the clay were the controlling factors for the amount of intercalated dye.The novel crystal-field environ- ment of the gels and clays in these studies was reported to increase the melting temperature and to affect the fluorescence intensity and photostability of the intercalated dyes. The conceptual innovation in the present work was to create a nanocomposite of dye molecules in the restricted compartments in a porous, pillared clay. Natural phyllosilicates, including montmorillonite from three different sources, a saponite, a hectorite, a synthetic lithium fluorhectorite (Corning) and a synthetic sodium fluorphlogopite (Kunimine), were intercalated with the Al13 polymer { [A11304(OH)24(H20)1z]7t} precursor and calcined to yield alumina-pillared clay nanocomposites.The pillaring of clays is now an established pro~ess.'~-'~ Successful pillar formation was tested by X-ray analysis. Basal !pacings of the pillared phyllosilicates ranged from 16.9 to 18.1 A after pillaring and heating at 450°C for 5 h (Table 1). These basal spacings are typical of clays pillared with alumina. Both the original phyllosilicates and their corresponding pillared nanocomposites were intercalated with the laser dyes, 7-diethylamino-4-methylcoumarin(coumarin 1; hereafter cou- marin), pyronin Y, rhodamine B and rhodamine 6G in solu- tions of ethanol.Equivalent processing techniques were employed for all samples to introduce the laser dyes into the interlayer. The only significant differences in intercalation were introduced in the dye solution concentrations to accommodate the difference in cation-exchange capacities (CECs) between pillared samples and the corresponding non-pillared compo- nent phyllosilicates. Table 1 lists the CEC values determined by a standard procedure" for each phyllosilicate and sub- sequent nanocomposite used. It is apparent that between 60 and 87% of the CEC was satisfied by pillar species in the Table 1 Cation-exchange capacity (CEC) of pillared and non-pillared phyllosilicates CEC of sample phyllosilicate 1 Kunipia montmorillonite (Japan) 2 saponite (CA) 3 lithium fluorhectorite (synthetic) 4 sodium fluorphlogopite (synthetic) 5 Texas montmorillonite (TX) 6 hectorite (CA) 7 Arizona montmorillonite (AZ) non-pillared/ mequiv (100 g)-' pillared/mequiv (100 g)-' basal spacing pf pillared clay/A 126 22 17.6 101 40 16.9 200 59 17.3 19 25 18.1 128 17 17.3 92 31 16.9 115 21 11.7 J.Mater. Chem., 1996,6( 12), 1967-1969 1%7 interlayer The CEC remaining in the phyllosilicate layers aids in the intercalation of the dye molecules which are cationic in solution The uptake mechanism of neutral dyes such as coumann (although charge can develop with pH changes) is not understood but could be due to the hydrophobic nature of the interlayer surface The dye intercalation procedure used was as follows Ethanol-water solutions of each laser dye (0 16 mol 1-') were prepared to satisfy 200% of the CEC in the highest-charged phyllosilicate, fluorhectonte The other phyllosilicates were treated with the same concentration of laser dye, assuming any excess dye would be removed by washing pnor to optical and thermal analysis Similarly, a 0 048 mol 1-' solution of dye and EtOH-H,O (95 5, v/v) was prepared to satisfy 200% of the CEC remaining in the highest-charged pillared phyllosil- icate, fluorhectonte, and in excess for the other pillared samples Pnor to solution preparation, it was determined that the solubility of these solutions was better in ethanol than in water Each dye solution was stirred in a sealed container for several hours to ensure good dissolution Approximately 0 2 g of each onginal and pillared phyllosilic- ate were weighed and placed in 35 ml plastic bottles for each of the four dye solutions The dye solutions (0 16 mol 1-', 25 ml) were pipetted into each onginal phyllosilicate Similarly, 25 ml of 0 048 mol 1-' dye solutions were pipetted into each pillared phyllosilicate All of the samples were shaken vigor- ously for 1 min and placed in a test-tube rack rotator for more than 1 day in a closed cabinet to decrease any light degradation of the dye molecules in solution The 28 samples were then placed in a 65 "C water bath for 1 week, and again protected from light exposure Upon removal from the water bath, each sample was vacuum-filtered and rinsed with ethanol several times until the filter run-off appeared clear, indicating the removal of most of the excess dye that was not held in the interlayer The pillared phyllosilicate-dye and phyllosilicate- dye complexes were left upon the PTFE membrane filter and placed in a closed cabinet to dry in the air at room temperature for more than 24 h The dye-intercalated samples were then placed in small glass vials and sealed for later testing The optical properties of bulk dye solutions and dye- phyllosilicate complexes were analysed using a Hitachi fluorescence spectrophotometer, model number F-4010 Dye solutions used for the intercalation procedure were analysed first Dilute solutions, ca mol I-', of dye and ethanol show the least amount of quenching due to dimer and trimer formation With this in mind, the 0 048 mol 1-' dye solutions were placed in quartz vials and analysed several times with continuous dropwise dilution and agitation All of the dye solutions exhibited a slight blue shift and peak intensity increase with dilution When this behaviour ceased, the spectra obtained were stored The excitation wavelengths, A,,,, of incident light used for coumarin, pyronin Y, rhodamine B and rhodamine 6G were 370, 360, 550 and 530nm, respectively The reported A,,, values were adjusted to produce the most intense peak by running the dye solutions at the given wave- length and investigating 5 nm shifts about the value, totalling a 50nm span to each side The ethanol solution used to produce the dye solutions was tested at each of the four excitation wavelengths, to ensure that any Raman peaks due to the solvent were not misinterpreted as dye fluorescence A Raman peak was only evident in the pyronin Y solution at 431 nm, this peak was much less intense than the fluorescence peak at 588nm and was disregarded in further testing of pyronin Y complexes Dye complexes of phyllosilicate and pillared phyllosilicate were analysed at the excitation wavelengths attained in the dye solution study Each sample was placed in a solid sample holder behind a quartz window and fluorescence spectra collected, again in the range 220-700nm Data were also collected for the phyllosilicates and nanocomposites that were not dye-intercalated at the four excitations used in the dye studies Owing to the temperature dependence of fluores- cence, room temperature was monitored dunng analysis Temperatures were 19k 1 "C for the duration of the data collection and significant fluctuations in fluorescence were not detected Differential thermal analysis (DTA) was used to investigate the changes in melting and decomposition temperature of intercalated dyes A platinum sample cup was filled with each of the dye-intercalated samples and the bulk dye in powder form and run from 50 to 650°C at a rate of 10°C min-' us an aluminium oxide standard A Perkin-Elmer DTA model 1700 in tandem with a system 7/4 thermal analysis controller and a data station equipped with Perkin-Elmer TADS software was used to collect all data Detailed fluorescence results of the various dye-clay and dye-pillared clay complexes, apart from the coumarin com- plexes, do not justify detailed presentation The results show that pyronin Y exhibited no fluorescence in complexes of pillared and non-pillared phyllosilicates while rhodamine B and rhodamine 6G intercalates in either unpillared or pillared clays showed no fluorescence improvement All the unpillared clay-coumarin dye complexes exhibited relative intensity increases over the unpillared clay-dye com-posites when fluorescence tested at AeXc= 370 nm Maximum fluorescence intensity occurred between 443 and 498 nm Each set of spectra was obtained at an excitation and emission bandpass to maximize the fluorescence emission without satu- rating the detector Therefore intensities within each data set can be compared Table 2 summarizes the fluorescence data obtained for coumarin The fluorescence peak width at half maximurn intensity (FWHM) was measured from each curve (within &2 nm) Because the actual molecular concentration of dye molecules in the original and pillared clays is not known, quantum efficiencies cannot be calculated Because of the differences in scattering characteristics and the unknown concentrations, it is likewise not possible to compare the fluorescence intensities of dye-clay complexes with the dye solutions However, with care in packing the clays into the sample cell and making the measurements with the same instrument settings, the phyllosilicate of dye complex 1 orignal, pillared 2 ongmal, pillared 3 origmal, pillared 4 ongmal, pillared 5 onginal, pillared 6 ongmal, pillared 7 ongmal, pillared Table 2 Fluorescence data for clay-coumann complexes L"/nm intensityb enhancementc FWHM/nm 469,451 467,455 66,135 343,644 -, 205 -, 188 62,51 55,51 469, 452 370,2590 -, 70 52, 78 465,443 1303,7829 -, 601 49, 80 474, 452 498,445 458,453 265,1417 528,2916 189,350 -, 5 35 -, 5 52 -, 185 52, 56 51, 56 51, 60 "Wavelength at maximum intensity 'Relative intensities for all specimens measured in the same way with the same instrument settings '(Fluorescence intensity of pillared clay)/(fluorescence intensity of ongnal clay-coumann complex) 1968 J Muter Chem , 1996, 6(12), 1967-1969 Alnm Fig.1 Fluorescence emission spectra for (A) sodium fluorphlogopite- coumarin complex (intensity magnified 5 x) and (B) pillared sodium fluorphlogopite-Coumarin complex. Excitation wavelength =370 nm. Table 3 Bulk dye and dye-complex melting temperatures sample complete melting“/”C melting temp. increasea*b/oC bulk coumarin dye dye-1 complex dye-2 complex dye-3 complex dye-4 complex dye-5 complex dye-6 complex dye-7 complex 85 92; 157 176; 177 198; 154 120; 163 112; 146 183; 168 93; 100 7; 72 91; 92 113; 69 8; 15 35; 78 27; 61 98; 83 bulk pyronin Y dye dye-1 complex 280 320; 316 40; 36 bulk rhodamine B dye dye-1 complex 210 253; 270 43; 60 bulk rhodamine 6G dye dye-1 complex 264 275; 270 11; 6 “Original; pillared.’Increase over bulk dye melting temperature. comparison between the pillared clays and the original clays should be reasonably accurate. Fluorescence intensity was greatly enhanced in all pillared phyllosilicate-coumarin complexes (Table 2). The pillared fluorhectorite-coumarin complex exhibited an intensity ca. 7 times that of the non-pillared fluorhectorite-coumarin com- plex, and over 6 times that of the non-pillared fluorphlogopite- coumarin complex was attained in the pillared sodium fluorphlogopite-coumarin complex (Fig. 1; Table 2). This dramatic enhancement in fluorescence may be attributed to the isolation of coumarin molecules in the compartments between pillars with little or no interaction between the molecules.The pillaring of layers also leads to a lower CEC and therefore, the number of molecules that enter the interlay- ers is also limited. The smaller number of molecules coupled with their isolation in the compartments appears to cause this dramatic increase in fluorescence. The red shift evident in the non-pillared phyllosilicate-coumarin complexes (Table 2; Fig. 1) is an indication that the adsorbed dye is located in the interlayer space of the phyllosilicate. Similar red-shift changes were reported by Endo et al.” for pyronin Y and rhodamine 590 intercalated in montmorillonite. Thermal analysis showed that the intercalated dye molecules in pillared clay nanocomposites have substantially higher thermal stability than those intercalated in non-pillared clays (Table 3).In general, dye molecules intercalated in clays have a higher thermal stability than those in dye alone. Although the positive results presented in this research are limited to coumarin complexes, the data provided suggest several potential applications of dye-intercalated nano-composites as laser light guides and filters in linear and non-linear optics. This research was supported by the Division of Materials Science, Office of Basic Energy Sciences, US Department of Energy under grant no. DE-FG02-85ER45204. References 1 P. P. Sorkin and J. R. Lankard, IBM J. Res. Develop., 1996,10,162. 2 P. P. Sorkin, J. R. Lankard, E.C. Hammond and V. L. Moruzzi, IBM J. Res. Develop., 1967, 11, 130. 3 D. W. Gregg and S. J. Thomas, IEEE J. Quant. Electr., 1969,5302. 4 Th. Foster, Fluoreszenz Organischer Verbindungen, Vandenhoeck and Ruprecht, Gottingen, 1951,pp. 94-124. 5 0. Valdes-Aguilera and D. C. Neckers, Acc. Chem. Res., 1989, 22, 171. 6 V. K. Kelkar, B. S. Valaulikar, J. T. Kunjappu and C. Manohar, Photochem. Photobiol., 1990,52,717. 7 D. Avnir, D. Levy and R. Reisfeld, J. Phys. Chem., 1984,88, 5956. 8 J. Warnock, D. D. Awschalom and M. W. Shafer, Phys. Rev., 1986, 34,475. 9 J. C. Pouxviel, S. Parvaneh, E. T. Knobbe and B. Dunn, Solid State Ionics, 1989,32133,646. 10 H. Tanaka, J. Takahashi and J. Tsuchiya, J. Non-Cryst. Solids, 1989,109,164. 11 T. Endo, N. Nakada, T. Sat0 and M. Shimada, J. Phys. Chem. Solids, 1988,49, 1423. 12 S. Yamanaka, Ceram. Bull., 1991,70, 1056. 13 P. Malla, S. Yamanaka and S. Komarneni, Solid State Ionics, 1989, 32133,354. 14 P. B. Malla and S. Komarneni, Clays Clay Miner., 1990,38, 363. 15 M. L. Jackson, Soil Chemical Analysis-Advanced Course, 2nd edn., The University of Wisconsin, Madison, WI, 1979, p. 895. Communication 6/05603B; Received 12th August, 1996 J. Muter. Chem., 1996,6( 12), 1967-1969 1969

ISSN:0959-9428    

DOI:10.1039/JM9960601967

出版商:RSC    

年代:1996

数据来源: RSC