Zeolite/polyaniline composite: synthesis and adsorptive properties regarding Cr(VI) from aqueous solutions

Abstract

The article is devoted to the chemical synthesis of a zeolite/polyaniline (Zt/PAn) composite and a comparative (relative to polyaniline, PAn) study of some of its physicochemical properties, in particular, structural, thermal, and adsorptive (regarding Cr(VI)) characteristics. The results of the studies of spectral, thermal and electrical properties of the initial natural filler mineral (zeolite), synthesized individual samples of polyaniline and Zt/PAn confirmed that the latter are a composite. It was determined that the structure of the polymer in the synthesized samples of both individual polyaniline and the zeolite/polyaniline composite is mostly amorphous and corresponds to the emeraldine salt of sulfuric acid, which is deposited in the form of a thin film on the surface of polycrystalline particles of a finely dispersed mineral. The study of the thermal properties of the samples of individual polyaniline and composite showed that the polymer content in the composite is approximately 50%. The results of studying the adsorption capacity of PAn and Zt/PAn samples proved their high efficiency (98–99%) in removing of Cr(VI) from aqueous solutions. The study of the Cr(VI) adsorption kinetics at its content in the initial solutions of 200–500 mg/L showed that the process is two-stage, and the adsorption capacity of both samples of individual polyaniline and the zeolite/polyaniline composite depends on the concentration of the initial solutions. An increasing of the initial concentration of Cr(VI) in the solutions leads to a certain decreasing in absorption degree and values of adsorption at the first stage of the process by both samples of the PAn and the Zt/PAn. The course of the second stage of sorption, which obviously has the nature of absorption, is longer, but it is during this stage that almost 98–99% removal of Cr(VI) from the investigated solutions is achieved. In particular, it was established that with a Cr(VI) content of 500 mg/L in the investigated solution, the adsorption capacity of zeolite/polyaniline composite samples is 49 mg on 1 g of adsorbent. At the same time, additional studies showed that the adsorption capacity of polyaniline in the sample of the Zt/PAn composite (i. e., without taking into account the mass of finely dispersed mineral filler) reaches 93 mg/g for the identical content of Cr(VI) in the adsorption solution.