“Nanocomposites and nanomaterials”

Structural, morphological, and catalytic properties of cryptomelane
T.L. Rakitskaya, A.S. Truba, N.I. Zhekova, V.Y. Volkova
Faculty of Chemistry and Pharmacy, Odessa I.I. Mechnikov National University.
St. Dvoryanskaya 2, 65082, Odessa, Ukraine. E-mail: tlr@onu.edu.ua
Tunnel-structured (22) manganese dioxide (-MnO2 or cryptomelane) is extensively used as a catalyst of various redox reactions including the low-temperature ozone decomposition. The cryptomelane samples were synthesized by potassium permanganate reduction: with manganese acetate (solid-phase reaction) – 1S-Mn sample, with manganese sulfate (reflux method) – 2S-Mn sample, with maleic acid (sol-gel method) – 3S-Mn and also by KNO3 and MnSO4 melting together – 4S-Mn sample. All the samples thus obtained were characterized by XRD method, SEM, FT-IR spectroscopy, thermogravimetric (DTA-DTG) analysis, N2 and water vapour adsorption, and also by pH-metry. As can be seen from Table, the phase composition, texture (Ssp and dm) as well as the crystallite sizes, D, of the samples depend on the methods of their synthesis. 
Sample	Phase (content, %)	Ssp, m2/g	dm, nm	D, nm	Qsp103, mol/g	
1S-Mn	-MnO2 (85.3)	63.6	17.85	16	0,22	
	-MnO2 (14.7)			28		
2S-Mn	-MnO2 (90.5)	112.0	34.51	15	1,44	
	Mn2O3  (9.5)			66		
3S-Mn	-MnO2 (100.0)	47.6	16.92	36	1,62	
4S-Mn	-MnO2 (100.0)	105.0	34.91	14	2,38	

We assumed that the changes in above mentioned properties will affect the catalytic activity of cryptomelane in the reaction of O3 decomposition. To be sure of this assumption, the cryptomelane samples (0.5 g each) were tested at 20 °C, an initial ozone concentration in the ozone air mixture (OAM) of 100 mg/m3, and an OAM flow rate of 16.6 cm3/s. The catalytic activity of cryptomelane samples defined as a specific amount of ozone reacted over a time period of 600 min allows to rank the cryptomelane samples in the order: 4S-Mn3S-Mn2S-Mn1S-Mn.