Synthesis of phosphoric acid-based mesoporous geopolymers from tourmaline tailings for effective adsorption of tetracycline hydrochloride in aqueous environment

Abstract

As a porous material, geopolymers (GPs) have attracted more attention for wastewater purification. Herein, a low-cost and environmentally friendly phosphoric acid-based tourmaline tailings geopolymers (PTMT-GP) were fabricated, and used as adsorbents for removal of tetracycline hydrochloride (TCH) in solution. The morphological and structural evolution of TMT after phosphoric acid attack was confirmed by XRD, SEM and FT-IR. The optimal PTMT-GP0.7 had the largest average pore and specific surface area, which were 3.89 nm and 115.66 m2 g−1, respectively. The observed adsorption process of TCH on PTMT-GP0.7 could be perfectly explained by pseudo-second-order kinetic model, and the maximum theoretical adsorption capacity, obtained from the Langmuir model, was 82.56 mg g−1 at 318 K and pH = 3. Thermodynamics indicated that the adsorption process of TCH on PTMT-GP0.7 was not only endothermic, but also feasible and spontaneous. The removal of TCH in aqueous by PTMT-GP0.7 suggested the combined effect of physical and chemical adsorption, including pore filling, electrostatic, H-bonding and ion exchange interaction. After 5 reuse cycles, PTMT-GP0.7 maintained 86.56% of the first saturated adsorption capacity for TCH, and the adsorption capacity of PTMT-GP0.7 calcined at 400 °C for 2 h decreased by 4.56%. This work will provide a valuable reference for evaluating the adsorption performance of phosphate-based geopolymer materials synthesized from tailings, which are expected to be a low-cost, green and stability adsorbent to remove TCH from wastewater.