Weakly Hydrated Anion Exchangers Doped with Cu2O and Cu0 Particles—Thermogravimetric Studies

Abstract

Hybrid ion exchangers (HIXs) containing fine Cu2O and Cu0 particles were subjected to thermal analysis in order to determine their hygroscopic water content (with regard to their anomalously low porosity) and to determine the effect of the oxidation state of the copper atom in the deposit on the thermal properties of composite materials. Commercially available anion exchangers, Amberlite IRA 900Cl (macroreticular, M) and Amberlite IRA 402OH (gel-like, G), were used as supporting materials. M/Cu2O, G/Cu2O, M/Cu and G/Cu, containing 4.3–8.4 wt% Cu, were subjected to thermal analysis under respectively air and N2. TG/DTG curves revealed that dry M/Cu and G/Cu contained as little as 7.2% and 4.3% hygroscopic water, while M/Cu2O and G/Cu2O contained respectively 10.6% and 9.4% (Cu0 was a stronger water repellent than Cu2O). The oxidation state of the copper atom in the deposit was found to affect the amount of the forming char, and also Cu0 was found to contribute to the formation of more char than in the pyrolysis of the pure resin (the anion exchanger with no copper deposit). Under air the two kinds of particles transformed into CuO, while under N2 metallic copper and char (from the resin phase) made up the solid residue. This means that in the pyrolysis of the HIXs the inorganic phase participated in char formation and it also transformed itself (undergoing reduction when possible). The above findings provide a basis for in-depth research aimed at the innovative use of copper-containing HIXs and at obtaining usable composite materials with a designed (organic-inorganic) composition.

Copper Rich Composite Materials Based on Carboxylic Cation Exchangers and Their Thermal Transformation

“…Comparing “solid residue” and “Cu content in respective starting sample” ( Table 2 and Table 3 ), it can be estimated that HIX/M pyrolysates contained 70–80% wt% Cu and HIX/G pyrolysates 60–70% wt% Cu. As in the previous research [ 40 , 41 , 60 ], it turned out again that under N 2 , more pyrolysate formed from HIXs than in the case of the same transformation of pure resins (M, G). The research presented here shows that the polymeric matter from which the carboxylic cation exchanger is made (in addition to carbon and hydrogen atoms containing oxygen atoms) during pyrolysis does not give as much carbon char as in the case of a hydrocarbonaceous (oxygen-free) polystyrene matrix of anion exchange resin.…”

“…The first decomposition step up to 132.8 °C (maximum decomposition rate at 78.4 °C) with a mass loss of 4.0% corresponds to the elimination of osmotic water molecules existing in the pores of resin and hydrogen-bonded water (from hydration sites of carboxylic groups). Compared to the ion exchangers of various type [ 40 , 41 , 59 , 60 ], this result is very low and indicates that CCE in the H + form is especially weakly hydrated. The second step up to 282.1 °C (maximum decomposition rate at 237.8 °C) with a mass loss of 11.1% can be assigned to the water elimination between two neighboring carboxylic groups with the creation of some polyacrylic cyclic anhydrides by intermolecular dehydration (5-atom ring such as succinic anhydride type or 6-atom ring such as glutaric anhydride type, Scheme 2 ).…”

“…More precisely, the pyrolysate contains carbon char (a mixture of various high molecular weight organic compounds constituting a product of the decomposition of the polymer’s matrix in air-free conditions) and inorganic matter (mainly deriving from the cupric deposit). Our previous study showed that during pyrolysis, the particles of copper compounds such CuO, Cu (OH) 2 , and Cu 2 O contained in the HIX received from anion exchangers had undergone reduction to Cu 0 [ 40 , 41 ]. Although, in this case, the mass of cupric deposit in the skeleton was several times greater, the result was the same.…”

“…Considering the catalytic properties of copper compounds and also the necessity to develop methods of treatment of the used ion exchangers, we have undertaken research on the synthesis and thermal decomposition of HIXs under air and under N 2 , in which, as host materials for CuO, Cu (OH) 2 , Cu 4 (OH) 6 SO 4 , Cu 2 O, and Cu 0 fine particles, strongly basic anion exchangers with macroreticular and gel-like structure were used [ 37 , 38 , 39 ]. It turned out that copper compounds deposited in the skeleton of such resins significantly altered the results of the thermal analysis in comparison with those of pure resin [ 40 , 41 ]. The differences resulted from the process end temperature, the acceleration of the decomposition steps, the amount of carbonizate in the post-pyrolysis residue, and also the composition of the inorganic phase (CuO after combustion, Cu 0 after pyrolysis).…”