Polyaniline modified fly ash based MCM-48 as a highly effective and raspberry-shaped adsorbent for Cd2+, Co2+, and Cu2+

With the aim of both reducing pollution and improving the utilization of coal by–products, a fly ash desilication solution is proposed as the silicon source for the preparation of the mesoporous molecular sieve MCM-48. A series of a highly effective and raspberry-shaped adsorbents for treating wastewater contaminated with heavy metal ions are obtained by modifying the MCM-48 with polyaniline (PANI) through a hydrothermal synthetic strategy. The results of experimental studies show that MCM-48/1PANI has removal efficiencies for Cd²⁺, Co²⁺, and Cu²⁺ of 97.67 %, 94.35 % and 87.26 %, respectively, which are significantly better than those of raw MCM-48. The adsorption behavior fits well with the proposed second-order kinetic equation and the Langmuir isothermal adsorption model. It is shown that the adsorbent shares electrons or electron transfer with the metal ions and forms a homogeneous monolayer adsorption on the adsorbent surface. In an experiment on adsorption of ions coexisting in solution, the selectivity of adsorption is found to be Cd²⁺ > Co²⁺ > Cu²⁺, with the differences being ascribed to the different hydration radii of metal ions. A test of cyclic regeneration performance shows that the MCM-48/1PANI adsorbent exhibits excellent stability after five cycles. Thus, this work provides not only a way for preparing MCM-48/PANI from fly ash, but also an efficient method for removal of heavy metal ions from wastewater.