Quantum Chemical Study of Molecular Cluster of Silica

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Addis Ababa Universty


The. Ut.le. st.udy w .... unde.r-t.ake.n t.o an e.lablJr-at.e.d clust.e.» mode.l of' silica ge.l and t.o inve.sUgat.e. adso»pt.ion comple.xe.s of pr-ope.ne. wit.h silica using INDO me.t.hod and opt.imizat.ion of geomet.»y. The. basic idea of clust.ermode. ling ent.ails sub .. Ut.ut.ion of t.he. bUlk of sUica by t.e.r-minal is-at.oms t.he quant.um-che.mical INDO of which ar-e st.r-ict.ly opt.imized t.o give adequat.e de.scr-ipt.ion of t.he. dist.r-ibut.ions in silica. The.or-et.ical r·esuIt.s par-ame.t.e.r-s, e.lect.l'onic t.he. mode.l st.udie.d found t.o be. in fab'ly good agr-ee.me.nt. wit.h e.xist.tng expe.r-ime.nt.al dat.a. Thl'ee st.ages of clusr-t.el' mode.ling conside.l'ed. The. simple.st. mode.l hiy®oxylat.ed adsor-be.nt.s is: t.he. hydr-oxide. anion. In t.he. second st.age. o:r-t.hosUicic acid is: use.d as a mode.l of silica but. t.he. model has a basic dl'awback be.cause. t.he.r-e. ar-e. no sUoxane br-idges in it.. The. t.hl:r-d st.age. of modeling p:r-esupposes t.he. blco»po:r-at.ion of t.he. siloxane in t.he clust.el's. The clust.el' is char-act.e:r-ize.d by non-unffo:r-m e.lect.:r-onio diSt.l'ibut.ion in t.he bulk phase of s11ica and also gives inadequat.e de.scl'ipt.ion of t.he band St.l'UCt.U1'e. of sUioa whUe t.he ClUSt.e.l' 8i(08iH:) 4 leads t.o mOl'e aC<lul'at.e and I'eliable desa:r-ipt.ion of t.he. eleat.l'onic and band stl'uct.ul'e of sUi Ca. ill The. clust.el' mode.l S1(OSiH9 ) 4 is found t.o be opUmum.



Molecular Cluster of Silica