tailieunhanh - Electrochemically Catalysed Sol-Gel Process Synthesis and Characterizations of TiO2 Anatase

Sol-gel process, a most usefully and effectively process, has a lot of advantage for preparation of a variety of advanced materials in various structures and sizes, via polymerization of metal and semiconductor hydroxides or via hydrolysis and condensation of their alkoxides, since in nucleophilic substitution (SN) reaction and nucleophilic addition (AN) reaction, the substituent with thelargest partial negative charge,is the nucleophile, and in SN reactions the substituent with the largest positive charge, + , is theleaving group or nucleofugal. | Journal of Chemistry Vol. 41 No. 1 P. 125 -133 2003 ELECTROCHEMICALLY CATALYSED SOL-GEL PROCESS SYNTHESIS AND CHARACTERIZATIONS OF TiO2 ANATASE Received 2-8-2002 TRAN TRUNG Department of Electrochemistry Faculty of Chemical Technology HUT summary TiO2 nanostructured film and powder were prepared by electrochemically catalysed sol-gel process in absolutely ethyl alcohol at room temperature. The obtained TiO2 anatase was confirmed by XRD investigation. The morphology and chemically surface characterization were also investigated by using SEM photograph and FTIR measurements. The average particle size was ranged from 20 to 50 nm. The mechanism of the electrochemically catalysed sol-gel process and the presence and origin of a sub-oxide phase of Ti 3-O species incorporated in the obtained TiO2 were discussed. Key words Electrochemically catalysed sol-gel TiO2 anatase XRD SEM FTIR. I - INTRODUCTION Sol-gel process a most usefully and effectively process has a lot of advantage for preparation of a variety of advanced materials in various structures and sizes via polymerization of metal and semiconductor hydroxides or via hydrolysis and condensation of their alkoxides since in nucleophilic substitution SN reaction and nucleophilic addition AN reaction the substituent with the largest partial negative charge Ỗ- is the nucleophile and in SN reactions the substituent with the largest positive charge Ỗ is the leaving group or nucleofugal. Even though sol-gel products in any aspect they are either in powder by sol dispersion or in coating by film preparation the reactions taking place in sol-gel process for example for metal alkoxides popular precursors are quite complex but can be simply represented as follows nMe OR k nk 2 z H2O---- ----- MenOp nk 2- x y H2O z OH x OR y nk-y ROH 1 In any reaction media nucleophiles which attack metal alkoxide molecules and can cause hydrolysis and condensation then are usually water molecules and or hydroxyl groups. Thus the hydrolysis and .