Optimization of post-treatment variables to produce hierarchical porous zeolites from coal gangue to enhance adsorption performance

[Display omitted] •Hierarchical porous zeolites are prepared by using coal gangue as the raw materials.•The post-treatment variables of zeolites have been optimized.•The adsorbabilities of Cu2+ and Rh-B have been improved to 83.5% and 95.1%.•Post treatments of zeolites are found to increase surface adsorption efficiencies. Our research data indicates that a cost-effective hydrothermal synthesis with optimized post-treatment variables can provide a feasible paradigm to convert the coal gangues into valuable zeolites. It is found the integrity of skeleton structure of these cubic zeolites is well maintained upon series of post-treatments. The effects of these treatment parameters indicate concentration of NaOH solution (3.0 mol/L), alkaline treatment time periods (2 h) and temperature (90 °C), and ultrasonication time duration (40 min) collectively affect on the crystal structure, morphology, and adsorption performance of these zeolites. The specific surface area of treated zeolite is measured to be 162.29 m2/g and significantly increases compared with the untreated one (64.28 m2/g). The mechanistic study of zeolites post-treatment suggests that the erosion of parts of Al-OH and Si-OH bonds and the expansion of pore size will lead to a formation of hierarchical mesopores. As a consequence, the removal efficiencies of these modified zeolites have been greatly improved to 83.5% and 95.1% for Cu2+ ions and Rhodamine B (Rh-B), respectively. It is critical to point out that the subsequent alkaline and ultrasonic post-treatments greatly improve the adsorption performance of multiple mesoporous zeolites prepared from coal gangue. The post synthetic treatment can provide a platform of environmental cleanup applications such as industrial water remediation and solid waste handling by conversion of mining wastes into a value-added product.