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J. CHEM. soc. DALTON TRANS. 1985 1737Crystal I ine Zi rconi urn (iv) H yd rogenarsenate H yd rogenphosphate Monohydrate:Synthesis, Ion-exchange Properties, and Thermal BehaviourMaria L. Berardelli, Paola Galli. and Aldo. La Ginestra'Dipartimento di Chimica, Universita di Rome, Rome, ItalyMaria A. Massuccilstituto di Metodologie A vanzate Inorganiche del C. N. R., Area della Ricerca di Roma, C. P. I0Montetotondo Scalo, Rome, ItalyKrishna G. VarshneyDepartment of Chemistry, Aligarh Muslim University, Aligarh, IndiaA new crystalline layered inorganic ion-exchanger with formula Zr( HAsO,) (HP0,)-H,O has beenprepared by refluxing the amorphous product. Its ion-exchange properties towards sodium ions andits thermal behaviour, together with that of the pure sodium phases obtained, are reported anddiscussed.The exchanger is very stable to hydrolysis and has a high exchange capacity. Its generalbehaviour is intermediate between that of Zr( H PO,),-H,O and Zr( HAsO,),=H,O.In recent years synthetic inorganic ion-exchangers of the class ofacid phosphates or arsenates of tetravalent metals, with generalformula M(HEO,),mH,O (M = Ge, Ti, Zr, or Sn; E = P orAs; n = 1,2, etc.) have received increasing attention because oftheir potential employment in catalysis.In our investigation on the catalytic properties ofzirconium(1v) hydrogenphosphate and other members of theclass of crystalline layered materials, we have observed that for agiven test reaction, their activity depends on the chemicalcompound, the degree of crystallinity, the structure of the phasepresent during the catalytic process, the thermal pre-treatment,surface area, etc5Since until now only 'single' salts have been investigated inthis field, we were interested in studying the catalytic behaviourof 'mixed' materials [i.e.compounds containing two differenttetravalent metals and a given anion (phosphate or arsenate)or two different anions and a given tetravalent metal], in orderto determine how the gradual substitution of one tetravalentmetal with another or one pentavalent element with anotheraffects the catalytic activity of these materials.Examples of mixed compounds are the crystalline zirconium-titanium phosphates with different compositions and theamorphous arsenate phosphates of tetravalent metal^,^*^ studiedmerely as ion-exchangers.The mixed zirconium-titanium acid phosphates wereprepared by Clearfield and Frianeza6 in an attempt to obtainpure phases with a controlled ion-sieve efficiency and toimprove the poor stability towards hydrolysis of the single a-titanium acid phosphate, a-Ti(HPO4),-H20.The amorphous arsenate phosphates of Ti, Zr, Sn, and Ceproved to be interesting for their selective ion-exchangeproperties. For the amorphous zirconium arsenate phosphate,with molar ratio Zr:As:P = l : l : l , Varshney and co-worker~'*~ found that its ion-exchange capacity, rather low ifcompared to those of the layered crystalline acid phosphates, ismaintained to some extent after ignition at 800 "C.The materialis severely hydrolyzed in slightly alkaline media.'In this paper we report the preparation, the ion-exchange be-haviour towards sodium ions, and the chemical stability ofthe crystalline zirconium arsenate phosphate of formula Zr-(HAsO,)(HPO,)~H,O, together with phase changes withtemperature, with a view to its subsequent employment incatalysis.Comparisons with the single salts a-Zr(HPO,),*H,Oand a-Zr(HAsO,),=H,O are also made.Table 1. Analytical data for crystalline zirconium(1v) hydrogenarsenatehydrogenphosphate monohydrateAnalysis (%)ZrO, P,O, As,O, H,Oh r ?35.65 20.65 33.30 10.4035.70 20.65 33.45 10.2035.70 20.50 33.30 10.5035.60 20.50 33.30 10.60Found for fourrepresentativepreparationsCalculated' 35.65 20.60 33.35 10.45a Calculated for Zr0,(As,0,)o~,(P,0,)o~5~2H,0.ExperimentalChemicals.-All reagents were Erba RPE-ACS productsexcept ZrOC12~8H,0, which was a Merck 'pro analysi'product.Preparation of ~-Z~(HASO,)~*H,O rind a-Zr(HPO,),-H,O.Crystalline zirconium(1v) hydrogenphosphate, Zr(HPO,),-H,O, and hydrogenarsenate, Zr(HAsO,),=H,O, were preparedas described by refluxing the amorphous product in 10 moldm-, HJPO, and 4 rnol dm-, H,AsO, respectively, for 100 h.These preparations will be referred to throughout as (10,100)and (4,100) respectively, the first number in each case indicatingthe acid concentration and the second the reflux time.Preparation of Crystalline Zirconium(1v) HydrogenarsenateHydrogenphosphate.-A solution (volume 500 cm3) containingZrOC1,*8H,O (50 g) was added under stirring at roomtemperature to a 500-cm3 solution containing 14.5 mol dm-,H$O, (12 cm3) and 3As20,*5H,0 (40 g): a white gelimmediately formed. The slurry to which was added 14 moldm-3 HNO, (88 cm') was refluxed for 50 h; then, to help thecrystallization process, the suspension was made 4 mol dm-, inHNO, and refluxed for a further 50 h.After cooling, the solidwas filtered off, washed with water till pH 4.5, and dried overP4OI0 under vacuum to constant weight.Analytical data for four preparations of this crystallineproduct are summarized in Table 1 and show it to have thestoicheiometry Zr0,(Asz05)o~,(Pz0,)o~~~2H,0. The first moleof water is lost by 150 "C, the second after heating at 700 "C1738 J.CHEM. soc. DALTON TRANS. 1985hInc a#Ca# >0a9LLc .-c .-.- c4d / % ,2.5 3.0 3.5 4.0 5.0 6.0 7.0 14A . .I 1 I 1 I I I I I I I I: f )r . . . . I . . . . l . . . . I . . . . l . . . . I . . . .35 30 25 20 15 10 5Angle 28/'Figure 1. X-Ray diffraction patterns of samples at different Na'loadings, expressed in molar fraction of sodium content in the solid (f"JTitrution Curue.-The titration of Zr(HAsO,)(HPO,).H,Owas carried out by the batch procedure, equilibrating severalsamples of'exchanger (0.5 g) with 100 cm3 of a 0.1 mol dm-3(NaCl + NaOH) solution. In the range 70-100"/, conversion,the last amounts of titrant were added at intervals to preventhydrolysis. After shaking at 20°C for 3 d, the supernatantliquids were filtered off, analyzed for their arsenate andphosphate content, and their pH measured.Conversion8 0 100 20 LO 609 .o8.07.06 .OI0.5 .O3 .O2 .oMilliequiv.OH-g -1Figure 2. Titration-uptake curve for Zr(HAsO,)(HPO,)*H,O titrant0.1 N NaOH + 0.1 N NaClAnalytical Procedures and Physical Measurements.-TheZr: As: P ratio of crystalline Zr(HAsO,)(HPO,)~H,O wasdetermined as follows: 300 mg of material were dissolved in 1mol dm-3 HF (10 cm3) and the solution diluted to 50 cm3.Zirconium was determined gravimetrically as described,' ' in 10cm3 of this solution. Arsenate was determined iodometricaIly in10 cm3 of solution. Phosphate was determined colorirnetricallyas described,', in 2 cm3 of solution. Since the method is alsovalid for the determination of arsenate, in order to subtract theunavoidable positive interference of this ion, the measurementswere made against a reference solution containing the amountof arsenate present in the same volume, previously determined.A photoelectron DL spectrophotometer was used.The same methods were employed for the determination ofarsenate and phosphate present in the supernatant liquids of thebatch-titration.The solids (at various degrees of exchange) obtained from thetitration were washed and conditioned over saturated BaCl,solution at 20 "C (p/po N 0.9).X-Ray diffraction patterns were taken on a Philips PW 1130diffractometer using nickel-filtered Cu-K, radiation.The water content of Zr(HAsO,)(HPO,)-H,O, and of thepure phases formed during the titration, was determined fromthe weight losses during heating up to 900 "C.Thermogravimetric (t.g.) and differential thermal analysis(d.t.a.) measurements were carried out on a Stantonsimultaneous thermoanalyzer, model STA 78 1, with a heatingrate of 5 "C min-', Pt/Pt-Rh (87 : 13) thermocouples, andplatinum crucibles.Results and DiscussionAlthough the structure of the new compound is not known, itsX-ray powder diffraction pattern shown in Figure l(a) (thecorresponding d values are listed in Table 2) shows a greatsimilarity with those of a-Zr(HP04),-H20 l 3 and a-Zr(HAsJ.CHEM. soc. DALTON TRANS. 1985 1739Table 2. X-Ray powder diffraction spectra of the ZrH,(AsO,)(PO,) forms and their dehydration productsZrH ,(As04)( PO,)-H , 0 a Layered ZrAsPO,b Cubic ZrAsPO,' ZrH,(AsO,)(PO,)~nH,Od - & - 1dlA7.734.564.504.303.623.562.672.532.432.372.132.061.901.891.80u771002514589424451157511107dlA6.234.524.363.703.142.682.60I/%463177100235431dlA4.834.193.743.412.962.522.3 1a Dried over P,Olo.After heating at 650 "C. After heating at 800 "C. As prepared.I/%1410050432745134 A10.645.525.374.784.504.304.2 13.813.493.403.072.902.8 12.772.712.672.522.412.36I/%10085131530283745371878231828855Table 3. X-Ray powder diffraction spectra of sodium half-exchanged ZrH,(AsO,)(PO,)-H,O and its dehydration productsZrHNa(AsO,)( P04)-4H,0 ZrHNa(AsO,)(PO,)*H,O ZrHNa(AsO,)(PO,) 'dlA10.715.304.654.554.364.234.033.523.253.032.742.662.462.402.172.1011/77100816108586578517355888IdIA8.004.404.2 13.863.553.333.192.972.862.8 12.732.591I/%8043100871269118141448514 A7.194.644.414.033.953.853.262.852.792.59II/%501010253710015373725dlA6.464.634.493.873.222.912.602.592.3 12.2 12.142.1 12.052.011.971.951.931Il%4844461004110021465125521107331Conditioned at WA relative humidity.Dried over P4010. ' After heating at 300 "C.After heating at 700 "C.0,)2=H20.14 These data together with the ion-exchange andthermal behaviour given below, strongly support the hypothesisthat the material possesses an a-type layered structure. As aconsequence, we assign the new compound the formulaZr(HAsO,)(HPO,)-H20 and assume the first d value of 7.73 8,as the distance between two adjacent planes of zirconium atoms(d0*2).Ion-exchange Properties of Crystalline Zr(HAsO,)(HPO,)-H 2 0 towarb Sodium lons.-Figu_re 2 shows the titration anduptake curves for the Na+ - H+ process.* The curves arepractically coincident since only negligible amounts of arsenateand phosphate ions were found in the solutions below pH 10.All data refer to 1 g of exchanger.The titration process occurs in two stages, each stagerequiring CQ.2.95 milliequiv. of OH- ions. The total amount of* Na' - fi' represents Na' replacing H+ in the exchanger.NaOH employed (5.85 milliequiv.) is in good agreement withthe theoretical ion-exchange capacity of the exchanger (5.80milliequiv. g-l) calculated by considering two exchangeablehydrogens per mole formula.X-Ray patterns of the samples at various degrees of Na+uptake (Figure 1) completely agree with the shape of thetitration curve. In the plateaux (constant pH 3.3 and 6.3respectively) two phases are present, while along the slopes onlyone phase is found, in agreement with the phase rule." Up to3% Na+ uptake, the solid maintains the structure of thedihydrogen form, then, in the range of 6 3 0 % Na+ loading, anew phase with an interla er distance of 10.64 A co-exists withthe phase at dooz = 7.73 1, the former increasing and the latterdecreasing in intensity with Na+ uptake [Figure l(6) and (c)].At the end of the plateau ( N 30% of Na+ exchanged) only the'10.64 A' phase is present.The subsequent sodium uptake up to50% occurs with the formation of a solid solution since no otherphases appear: the interlayer distance of the phase presentgradually shifts from 10.64 to 10.71 A1740 J. CHEM. soc. DALTON TRANS. 1985Table 4. X-Ray powder diffraction spectra of sodium fullexchanged ZrH,(AsO,)(PO,).H,O and its dehydration productsZrNa,(AsO,)( PO,).3 H ,O ardlA9.934.524.203.763.533.443.302.962.742.632.593I/%1009291393871320139ZrNa,(AsO,)(PO,)-H,O - 9.76 1007.89 74.50 154.18 473.74 203.52 43.42 383.27 43.21 42.97 202.72 232.6 1 25dlA II%a Conditioned at 90% relative humidity.Dried over P4OI0. ' After heating at 700 "C.ZrNa,(AsO,)(PO,)&7.10 204.60 154.48 144.38 223.95 1003.86 303.21 153.16 222.97 902.9 1 352.64 452.60 172.27 71.97 35dlA 11%At 50% Na+ conversion the phase has the compositionZrHNa(As0,)(P0,)4H20. Its X-ray pattern is shown inFigure l(d), while the d values are reported in Table 3.The same reasoning applies between 50 and 100% ofexchange. Here the new phase, possessing an interlayer distanceof 9.93 A, co-exists with the half-sodium form until at cu. 85%Na+ loading [Figure l(e)J; after this point it is the only onepresent.At the end of the process the new phase, still withdOo2 = 9.93 A, has a composition ZrNa2(As04)(P0,)-3H,0since the degree of hydrolysis is negligible. Its X-ray diffractionpattern is shown in Figure 1 0 and the corresponding d valuesare reported in Table 4.The ion-exchange behaviour of Zr(HAsO,)(HPO,)=H,Otowards sodium ions is very similar to that found on titrating a-Zr(HAsO,),*H,O (4,100) '' and a-Zr(HP04)2-H20(10,100),'6the only difference is that the new exchanger exhibits shorterplateaux and wider slopes.It is known that, for a given exchanged cation, the shape ofthe titration curve for these layered materials depends on thedegree of crystallinity:' 7*18 the lower the degree of crystallinity,the shorter is the plateau and therefore the wider is the stepinvolving the solid solution formation (slope).18*19In order to obtain information on the degree of crystallinityof Zr(HAs04)(HP0,)*H20, the procedure of Alberti et ~ 1 . ~ 'was employed. These authors found that the back-titration ofthe half-sodium form of the a-Zr(HPO,),-H,O with thehighest degree of crystallinity restores the monohydrateddihydrogen form, Zr(HP04)2*H,0 (do,, = 7.56 A), whilezirconium(rv) hydrogenphosphates with gradually decreasingcrystallinities give mixtures of a '7.56 A phase,' andZr(HP04),*6H20 (tioo2 = 10.4 A) (termed 6-ZP by Clearfieldet al."), or Zr(HPO,),.6H2O and a hydrogen phase withdOo2 = 11.5 A. Pure Zr(HPO4),-6H2O was obtained from thehalf-sodium form of a-Zr(HP0,)-H,O (10,100), which has amedium-to-low degree of crystallinity.This procedure appliedon Zr(HAsO,)(HPO,)-H,O and a-Zr(HAsO4),-H,O (4,100)gave pure dihydrogen forms Zr(HAsO,)(HPO,).nH,O andZr(HAsO,),-nH,O (n % 1) respectively. Left in air, thematerials lose water and the monohydrated dihydrogen formsare rapidly re-obtained as for Zr(HPO4),-6H,O. The dvalues ofthe highly hydrated Zr(HAsO,)(HPO,) are given in Table 2.From these experiments, it can be supposed that Zr(HAs0,)-(HPO,).H,O, prepared by refluxing the amorphous product for100 h, should possess a degree of crystallinity comparable tothat of a-Zr(HPO,),=H,O (10,100) and a-Zr(HAsO,),*H2O(4, m.0X 0CI tat0C0,01020- 0 s2 10E .0-0 -0 .-5 l o010I l r l r l l l l l r l r l l l l100 200 300 400 500 600 700 800T / " CFigure 3. (a) D.t.a. and (b) t.g. curves of (i) ZrH,(PO,),*H,O, (ii)ZrH,(AsO,)(PO,)-H,O, (iii) ZrH,(AsO,),~H,O, and (io) ZrH,(As-O,)( PO,)=nH,O (regenerated)Thus the shorter plateaux and wider slopes observed in thetitration curve of Zr(HAsO,)(HPO,)~H,O could be due eitherto the low degree of crystallinity or to a greater tendency of themixed exchanger to give solid solutions because of the presencJ. CHEM. SOC. DALTON TRANS. 1985 17410X ia c 0UC u0100 -2 10v)0- 0 rL m g 101 1 1 1 1 1 1 1 1 , 1 1 1 , 1 1 1100 200 300 400 500 600 700 800 900T J " CFigure 4. (a) D.t.a. and (6) t.g. curves of ( i ) ZrHNa(PO,),~SH,O, (ii)ZrHNa(As04)(P0,)4H,0, (iii) ZrHNa(As04),-3H,0, and (iv)ZrNa,(AsO,)( P04).3H,0in the lattice layer of atoms (P and As) with analogous chemicalcharacteristics but different dimensions.Thermal behaviour of Zr(HAsO,)(HPO,).H,O and theSodium-exchanged Phases.-In order more completely tocharacterize the new ionexchanger, the thermal behaviour ofthe dihydrogen and sodium forms of Zr(HAsO,)(HPO,)~H,Owas studied and the results compared with those for thecorresponding a-Zr(HPO,),-H,O and ~-Z~(HASO,)~*H,Ophases.Figure 3 shows the t.g.and d.t.a. curves obtained fromZrH,(As0,)(P04)*H20, ZrH,(AsO,),~H,O, and ZrH,-(P04),-H20. ZrH,(AsO,)(PO,)-H,O loses the mole ofhydration water in the range 40---150"C, and the relatedendothermic effect is narrower than those of ZrH,(AsO,),~H,Oand ZrH,(P0,),*H20. The second endothermic effect (which isconnected with a reversible phase transition) is thus betterresolved than in the case of the other two exchangers.,, It mustbe pointed out that in the case of ZrH,(AsO,)(PO,)~H,O thephase transition occurs on the anhydrous phase, whilst for theother two materials it occurs on not completely dehydratedphases.The third endothermic effect is related to the condensation ofthe =As-OH and =P-OH groups and the process takes place inthe range 340-470 "C.The analogous processes for ZrH,-(AsO,), and ZrH,(PO,), occur in the ranges 300-370 and450-600 "C, respectively. Therefore, the thermal stability ofthese dihydrogen phases decreases as the phosphate groups aresubstituted with the arsenate ones.After the condensation process, a layered zirconiumpyroarsenophosphate is formed, above 800 "C, this transformsinto a cubic pyro-compound (Table 2) behaving in exactly thesame fashion as do ZrH,(PO,),*H,O and the o%er layeredexchangers of this class.23Figure 4 shows the t.g.and d.t.a. curves of ZrHNa(As-0,)(P0,)4H20, together with those of ZrHNa(As0,),-3H20and ZrHNa(P0,),4H20 for comparison.The three half-exchanged materials lose their hydration waterbetween 40 and 200 "C. The process occurs in two steps. The firstweight loss leads to monohydrated phases, the second toanhydrous phases. Each monohydrated or anhydrous phasepossesses a well defined interlayer spacing, which decreases withthe decreasing water content.The X-ray diffraction analysis shows that below 400 "C, allthe materials maintain the layered structure.For theZrHNa(AsO,)(PO,) forms, dooz varies from 10.71 %( for thetetrahydrated compound, to 7.19 %( for the anhydrous phaseheated at 300 "C.In the range 400-500 "C, ZrHNa(AsO,)(PO,) undergoesthe condensation process. At 500 "C the solid is amorphous,then, at ca. 600 "C (after the occurrence of the exothermic peakin the d.t.a. curve) a recrystallization takes place with theformation of a new phase, isostructural with NaZr,(PO,), andNaZr,(AsO,), obtained by heating ZrHNa(PO,), andZ~HN~(ASO,),~' at 650 "C. The new phase should correspondto a sodium dizirconium tris(arsenate phosphate) with formulaThe X-ray patterns of the various phases obtained fromZrHNa(AsO4)(PO,)-4H,O are reported in Table 3.The t.g.and d.t.a. curves of ZrNa,(AsO4)(PO,)~3H,O arealso shown in Figure 4. The dehydration process is quite similarto that observed in the case of ZrNa,(P0,),-3Hz0.24 The threemoles of water are lost in two steps: two moles between 50 and150 "C and the last mole between 150 and 200 "C. From 200 upto 780"C, neither weight losses nor other phenomena areobserved and the solid maintains the layered structure. At ca.850 "C, after the occurrence of an exothermic peak in the d.t.a.curve, besides the layered phase, a new phase begins to form, theevolution of which cannot be followed because the materialdecomposes after 950 "C, with gradual elimination of As,O,.The X-ray patterns of the various phases obtained fromZrNa,(AsO4)(PO4)=3H,O are given in Table 4.NaZrZ(AsO.5 S04)3-ConclusionsIt is possible to prepare reproducibly, as a single crystallinephase, a layered mixed inorganic ion-exchanger containing twoanions in a 1 : 1 ratio, Le. Zr(HAsO,)(HPO,)~H,O, which isisostructural with Zr(HPO,),-H,O and Zr(HAsO,),~H,O, andposseses an interlayer spacing of 7.73 A, intermediate betweenthose of the last two compounds.We believe that obtaining a single phase with the leastfavourable molar ratio (As: P = 1 : 1) presumably indicates thatthe Zr arsenate phosphate system shows a wide, if not complete,miscibility.The substitution of P with As allows not only the variationsin the ion-exchange and thermal properties of these materials tobe gradually followed, but also the strength of their acidic siteswhen employed as acid catalysts.A study in this area is inprogress.'References1 F. Nozaki, T. Itoh, and S. Ueda, Nippon Ggaku Kuishi, 1973,4,474.2 T. Kalman and A. Clearfield, Proc. 3rd Int. Symp. Chem. React. Eng.3 A. Clearfield and D. S. Thakur, J. Cataf., 1980,65, 185.4 M. Iwamoto, Y. Nomura, and S. Kagawa, J. Curuf., 1981,69, 234.Adv. Chem., 3rd Series, 1974,65, 1331742 J. CHEM. SOC. DALTON TRANS. 19855 A. La Ginestra, P. Patrono, M. L. Bernardelli, P. Galli, M. A.Massucci, C. Ferragina, and P. Ciambelli, XVII Congress0Nasionale di Chimica Inorganica, October 1984, Cefalir, Italy.6 A. Clearfield and T. N. Frianeza, J.Znorg. Nucl. Chem., 1978,40,1925.7 K. G. Varshney and A. Premadas, Sep. Sci. Technol., 1981,16, 793.8 K. G. Varshney and A. A. Khan, J. Znorg. Nucl. Chem., 1979,41,241.9 G. Alberti, U. Costantino, S. Allulli, and M. A. Massucci, J. Znorg.10 E. Torracca, U. Costantino, and M. A. Massucci, J. Chromatogr.,I 1 G. Alberti, A. Conte, and E. Tonacca, J. Znorg. Nucl. Chem., 1966,28,12 D. N. Bernhart and A. R. Wreath, Anal. Chem., 1955,27,440.13 A. Clearfield and Y. D. Smith, Znorg. Chem., 1969,8,431.14 A. Clearfield and W. L. Duax, Acta Crystallogr., Sect. B, 1969, 25,2658.15 A. Clearfield, W. L. Duax, J. M. Garces, and A. S. Medina, J. Znorg.Nucl. Chem., 1973,34, 329.16 G. Alberti, S. Allulli, U. Costantino, P. Galli, M. A. Massucci,R. Platania, and E. Torracca, 2nd Symposium on Ion Exchange, ed.J. A. Mikes, Magyar, Budapest, 1969, vol. 1.Nucl. Chem., 1973,38, 1339.1967,30, 584.225.17 A. Clearfield, in ‘Inorganic Ion Exchange Materials,’ ed. A.Clearfield, CRC Press Inc., Boca Raton, Florida, 1981, ch. 1.18 G. Alberti, U. Costantino, S. Allulli, M. A. Massucci, and M.Pelliccioni, J. Znorg. Nucl. Chem., 1973, 35, 1347.19 A. Clearfield, A. Oskarsson, and C. Oskarsson, Zon Exch. Membr.,1972, 1, 9.20 G. Alberti, U. Costantino, and J. S . Gill, J. Znorg. Nucl. Chem., 1976,38, 1783.21 A. Clearfield, A. L. Landis, A. S. Medina, and J. M. Troup, J. Inorg.Nucl. Chem., 1973, 35, 1099.22 A. La Ginestra, C. Ferragina, M. A. Massucci, and N. Tomassini,Proc. 3rd Znt. Conf. Therm. Anal., Akadimiai Kiado, Budapest, 1974,1, 631.23 U. Costantino and A. La Ginestra, Thermochim. Acta, 1982,58, 179.24 A. Clearfield, W. L. Duax, A. S. Medina, G. D. Smith, and J. R.25 G. Alberti, U. Costantino, and M. A. Massucci, unpublished work.Thomas, J. Phys. Chem., 1969,73, 3424.Received 2nd July 1984; Paper 4/ 1 1 2

ISSN:1477-9226    

DOI:10.1039/DT9850001737

出版商:RSC    

年代:1985

数据来源: RSC