Additional treatment with NaOH of acid activated vermiculite results in even higher increase in the adsorption capacity in comparison to samples modified only in acidic solution (first step of activation) with respect to raw material. Optimization of treatment conditions and adsorption capacity for two cationic dyes (methylene blue (MB) and astrazon red (AR)), also as binary mixture, was evaluated. The capacity, based on column studies, increased from 48 ± 2 to 203 ± 4 mg g in the case of methylene blue and from 51 ± 1 to 127 ± 2 mg g in the case of astrazon red on starting and acid-base treated material, respectively. It was shown that adsorption mechanism changes for both cationic dyes after NaOH treatment and it results in decrease of adsorption rate. In binary mixtures methylene blue is bound stronger by adsorbent and astrazon red may be removed in initial stage of adsorption. Extensive studies on desorption/regeneration process proved high efficiency in recyclable use of all materials. Although cation exchange capacity decreases due to acid treatment, after base treatment exchange properties are used more efficiently. On the other hand, increased specific surface area has less significant contribution into the adsorption potential of studied materials. Obtained adsorbents worked efficiently in 7 adsorption-regeneration cycles and loss of adsorption capacity was observed only in two first cycles.
The self-assembly of copper(ii) complexes with two Schiff base ligands: L1 = N and L2 = N and octacyanidomolybdate(iv) ions yields two discrete molecules of odd nuclearity, namely pentametallic [Cu(L1)(py)][Mo(CN)]·14HO (1), CuMo and trimetallic [Cu(L2)][Mo(CN)]·9HO (2), CuMo. Both molecular systems have been characterised structurally and magnetically, revealing a photomagnetic effect. In the case of (1) a metal-to-metal charge transfer (MMCT) mechanism is proposed. The analysis of magnetic interactions in the photogenerated state of (1) assumes the formation of the metastable cluster CuCuMo where metal centres in Mo-CN-Cu linkages are ferromagnetically coupled with J = 104(3) cm. In (2) the increase in the magnetisation is due to the singlet-triplet transition on the Mo centre leading to the formation of the metastable CuMo. The presence of the paramagnetic Mo (S = 1) centre linking the Cu (S = 1/2) centres allows for effective ferromagnetic interaction of 3 paramagnetic centres with coupling constant J = 20.2(7) cm.
Wet fine milling, as a pretreatment step to acid activation of vermiculite, was applied in order to decrease the environmental impact of the procedure commonly used to increase the mineral's adsorption capacity. Milling caused fragmentation of the material and several changes in its structure: edges of the flocks became frayed, the surface cracked, cation exchange capacity (CEC) increased, and most of the iron in oligonuclear and bulk form was removed. At the same time the specific surface area, crystallinity, chemical composition and adsorption capacity did not change significantly. Fine ground material was more susceptible to acid activation, which caused a decrease in the crystallinity and CEC, development of meso-and microporosity, an increase in the total volume of pores, in the specific surface and external surface areas. Micropores were developed faster in lower acid concentrations in the rough ground material, while the external surface area and total pores volume increased faster in the fine ground vermiculite. The latter material also had a higher CEC. Application of 0.5 mol L −1 HNO 3 to rough ground vermiculite did not change its adsorption capacity, however it changed from 55 ± 7 to 110 ± 8 mg g −1 when the material was fine ground. The optimal treatment conditions for both materials were obtained for 1.0 mol L −1 HNO 3 , however the adsorption capacity for the fine ground vermiculite increased more (i.e., from 55 ± 7 to 136 ± 7 mg g −1) than for its rough ground counterpart (i.e., 52 ± 7 to 93 ± 7 mg g −1). Concentrations higher than 1.0 mol L −1 resulted in deterioration of the adsorption capacities in both cases. Considering all the experimental outcomes, it can be concluded that the environmental impact of acid activation of vermiculite may be diminished by application of fine grinding of the material before the chemical activation process. Such treatment resulted in higher adsorption capacity at a given acid concentration compared to the rough ground material.
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