“Nanocomposites and nanomaterials”

Adsorption and protolytic properties of nanocryptomelane and its activity in ozone decomposition reaction 
Rakitskaya T.L., Truba A.S., Sokolova Z.V., Slobodianyk I.O.
Faculty of Chemistry and Pharmacy, Odesa I.I. Mechnikov National University,2, St. Dvoryanska, 65082, Odesa, Ukraine. 
E-mail: email.of corresponding truba@onu.edu.ua

Activity of polymorphic nanooxide forms of manganese(IV) in ozone decomposition reaction significantly depends on relative humidity of ozone–air mixture and residual content of hydrogen ions on the samples’ surface. The influence of these two factors on the catalytic properties of manganese nanooxides is practically not discussed in the literature. Cryptomelane samples were synthesized by different methods: reflux method (I), melting together (II), sol-gel method (III), solid-phase reaction (IV). All the samples were characterized by XRD method, SEM, FT-IR spectroscopy. We studied the protolytic (pHs) and adsorption properties of these samples in relation to water vapor. Based on isotherms of water vapor adsorption by above cryptomelane samples at a constant adsorption value a = 2.0 mmol/g the thermodynamic activity of adsorbed water aH2O = P/Ps and pH values were determined. These values​ depend significantly on the origin of cryptomelane (method of synthesis). So the pHs values increases in a row I < II < III < IV, and corresponding аН2О values are in the range of 0.76-0.92. The activity of these samples in ozone decomposition reaction was characterized using two parameters: MPC (time of protective action) and Qsp (specific amount of ozone, which decomposed into half-life of ozone). The combined effect of the activity of water and hydrogen ions on the МРС and Qsp values was estimated using the values of the GTP = lgаН2О/аН3О+ (table). It was found that sample II with GTP = 5.40 is characterized by the maximum values ​​of MPC and Qsp. 

Characteristics of nanocryptomelan samples and their activity
in ozone decomposition reaction
Sample	I	II	III	IV	
GTP	2.87	5.40	7.10	11.50	
Qsp103, moles of О3/g	2.20	4.86	1.73	0.22	
MPC, min	30	1055	1	1