The Study Of Determination Of Severals Manganese Oxides Electrochemistry

The electrochemistry characteristic of Birnessite(-h), Birnessite(-oh), Cryptomelane, Todorokite and Hausmannite were studied by several methods and the results were compared each other.The most suitable methods were put forward. The main resuls were shown as follow:1. As a classical method ,ST method was suitable to determine the PZC of soil and geothite. It was also can determine the PZC of manganese oxide after improved,.The PZC of birnessite(-h), birnessite(-oh), cryptomelane, todorokite , hausmannite and geothite obtained by improved ST method were 0. 98, 4. 13, 1. 72, 3.31, 5.11 and 8. 41, the order was geothite>hausmannite>birnessite(-oh)> todorokite ,cryptomelane , birnessite(-h);2. The slow stage of pH change was ignored for PT method.lt also suited to determine the PZC of manganese oxide. The PZC of birnessite(-h), birnessite(-oh), cryptomelane, Todorokite , hausmannite and geothite obtained by PT method were 1. 75, 3. 37, 2. 10, 3. 50, 4. 33 and 8. 00, the order was geothite>todorokite > birnessite(-oh) > hausmannite > cryptomelane > birnessite(-h);3. The PZC of birnessite(-h), biraessite(-oh), cryptomelane, todorokite , hausmannite and geothite measured by MT method were 2. 25, 6. 85, 3. 18, 5. 92, 6. 81 and 7. 42, the order was geothite>birnessite(-oh) >hausmannite>todorokite >cryptomelane>birnessite(-h).The results of manganese oxide was bigger than that reported in literature ,as contrary, the results of geothite was smaller.As a new method,the reports and researches about it were less . But it was more handy and speediness,and would has great applied outlook.4. The PZC of oxides which synthesized in acidity condition including birnessite(-h), cryptomelane , obtained by improved ST method were less than theresults of those determined by PT method.The oxides synthesized in alkalescence condition , including hausmannite, birnessite(-oh) and geothite ,were on the contrary. The PZC of manganese oxides determined by MT method was greater than the results of those determined by improved ST or PT, geothite were on the contrary.5.The negative charge of manganese oxides were determined by back-titration and Mehlich method respectively.The results of back-titration showed that the amount of negtive charge of manganese oxides was increased with the raising pH,the order was: birnessite(-h) >birnessite(-oh) >cryptomelane >todorokite. The order abtained by Mehlich method was birnessite(-h) >cryptomelane > todorokite >birnessite(-oh)>hausmannite, expect birnessite(-oh).In general,the back-titration method was more suitable to determine the amount of charge of manganese oxides because of its high preciseness.6.The surface area of birnessite(-h) birnessite(-oh), cryptomelane, todorokite and hausmannite measured by N2 adsorption method was 78.183, 38.038, 98.462, 130.703 and 37.954 (m2/g) respectively,the order was cryptomelane> todorokite> birnessite(-h) >birnessite(-oh) ,hausmannite. Combined with the results of back-titration method,the curve of the charge density versus pH was gained.The curve showed that the order was :birnessite(-h) >birnessite(-oh) > todorokite= cryptomelane from pH 2 to 3.5,and birnessite(-oh) >birnessite(-h) >todorokite> cryptomelane from pH 3.5 to 6,which was not according with the order of the amount of negative charge.