Influence of complex formation upon inclusion of Mn(II), Co(II), Ni(II), and Cu(II) in ZnC₂O₄·2H₂O

Abstract

The inclusion of 3d-impurities Mn(II), Co(II), Ni(II) and Cu(II) in a crystalline precipitate of ZnC 2 O 4 .2H 2 O is investigated. This study is a part of the systematic one deal with the mechanism of inclusion of 3d-ions in sparingly soluble oxalate systems. The experiments are carried out in bi-end multi-component systems at two different mediums -one with deficiency of oxalate ions, another with excess. Good agreement between included impurity and the concentration of its complex in the solution is established. The stability constant of monooxalato complex affects the impurity inclusion. This effect depends on the medium nature. In the deficiency of oxalate ions the factor determining the inclusion is thermodynamic one -stability of monooxalato complexes. In the excess of oxalate ions inserted amount depends on kinetic factor -the formation rate of these complexes. In the term of that the insertion of Mn(II) is definitely different in the two mediums while that of the Ni (II) does not depend on the medium. The copper shows deviation from overall dependence in the two mediums due to the Jahn-Teller distortion. Its double decreasing insertion in the excess of oxalate ions is related with stabilization of [Cu(C 2 O 4 )2] 2-. The conclusions presume that by varying the background medium and taking in view the ions present in the solution, the amount of inserted impurities can be predicted and controlled. IntroductionThe study of the sparingly soluble oxalate systems is related to their use as precursors in the synthesis of hightemperature superconductive ceramic materials, in the preparation of nanomaterials and a number of other new materials due to the fact that the precipitation processes provide the possibility of controlling the chemical and physical properties of the final products. Oxalate systems are traditionally used for the separation and concentration of elements, especially rare earth and transuranium elements. Detailed studies on the insertion of impurities upon the spontaneous crystallization of sparingly soluble oxalate systems are limited. Some of them are directed to the investigation of the effect of impurities on the properties of the materials [1][2][3][4]. Others deal with the effect of the process kinetics on the inserted amount of impurities [5][6][7] and with the determination of the distribution coefficients [8][9][10][11][12][13]. However, all these studies are carried out on bicomponent systems, comprising just a macro-and a micro-component. For this reason, a detailed investigation of the kinetics of the cocrystallization in oxalate systems directed to the elucidation of the mechanism of inclusion of impurities would clear up this problem. It would undoubtedly help the elucidation of the mechanism of the coprecipitation processes as well, since "the chemistry of oxalate coprecipitatiom processes and the nature of the products have not been well defined" [14]. The present study deals with the sparingly soluble compound ZnC 2 O 4 .2H 2 O, which is used as a starting material for the pr...

Investigation on the catalytic activity of doped low-percentage oxide catalysts Mn/ZnO obtained from oxalate precursor

“…The results show that precursors with a low manganese content ≤ 0.07% Mn are obtained. As it could be expected in view of the previous investigations on the mechanism of co-crystallization of Mn in ZnC 2 O 4 ·2H 2 O the amount of included dopant depends on the ratio of Zn 2+ :C 2 O 4 2-, in spite of the fact that the applied initial concentrations of the admixture ions are the same for both the series [21]. The excess of oxalate ions in case of the (1:2) series leads to inclusion of a higher amount of manganese.…”

“…For this reason Mn is slightly included, mainly by participating in the ion exchange with the first subsurface layer (called Panet layer). In case of oxalate ions excess (series 1:2) the manganese forms neutral complexes, whereupon it can participate directly both in the process of crystal formation and in the growth of the crystalline phase by substituting the zinc neutral complexes in the adsorption layer (Volmer's layer) [21][22][23]. The expectation is in this way a considerably more uniform distribution in the crystal lattice is achieved, which passes over to the oxide product.…”

“…Our previous investigations on the mechanism of cocrystallization of Mn, Co, Ni and Cu in ZnC 2 O 4 ·2H 2 O crystals [21][22][23] have shown that the different concentrations of the oxalate ions in the initial system determine both a different amount of included admixture and a different mechanism of their inclusion. Therefore the synthesis of the Zn-Mn precursor, studied in the present work, was carried out under conditions, analogous to those used in [21] -from solutions of ZnSO 4 and K 2 C 2 O 4 at initial ratio Zn 2+ :C 2 O 4 2-= 1:1 and 1:2.…”

“…Therefore the synthesis of the Zn-Mn precursor, studied in the present work, was carried out under conditions, analogous to those used in [21] -from solutions of ZnSO 4 and K 2 C 2 O 4 at initial ratio Zn 2+ :C 2 O 4 2-= 1:1 and 1:2. The admixture, included in the precursor by different mechanisms, would in different ways affect the activity of the support.…”

Rare earth cerium doping effects in nonlinear optical materials: potassiumhydrogen phthalate (KHP) and tris(thiourea)zinc(II) sulfate (ZTS)

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In the recent past we have reported a few important investigations on the effect of doping in nonlinear optical (NLO) materials which enhanced the crystalline perfection followed by the enhancement of second harmonic generation efficiency. 1,2,14 Ce doping in a good number of materials has been investigated.…”