Fly-Ash-Based Hierarchical MCM-41 Molecular Sieve as an Efficient Adsorbent for Methylene Blue Removal from Wastewater over a Wide pH

The development of cost-effective adsorbents with high sorption capacity and excellent renewability over a wide range of pH is essential for removal of toxic methylene blue (MB) from wastewater. The micro-mesoporous MCM-41 molecular sieve (M-MCM-41) was prepared by coal fly ash (CFA). The low temperature N-2 physical adsorption reveals that the prepared M-MCM-41 has hierarchically micro-mesoporous structure with high surface area (909.5 m(2).g(-1)). As a result, M-MCM-41 possesses superior adsorption presentation towards MB with prominently high sorption capacity of 574.7 mg.g(-1), and rapid sorption rate of 0.29 g.mg(-1).h (13 fold that of CFA). Surprisingly, 95 2 6 of the incipient adsorption capacity remains well after five cycles. More importantly, the M-MCM-41 maintains almost the same maximum sorption capacity in the pH range of 5-9, which is close to the wastewater discharge standard (6 similar to 9) without excessive pH adjustment. The adsorption kinetics and equilibrium data fit well with pseudo-secondorder model and the Langmuir isotherm model, respectively. And the thermodynamic investigations show that the adsorption behavior is spontaneous and exothermic. The M-MCM-41 has well-defined micro-mesoporous porosity and could be used as an effective adsorbent to remove MB from wastewater. This work provides a new sight for the solid waste resource utilization, which is beneficial to the development of recycling economy.

Automated summary

In this study, a cost-effective adsorbent with high sorption capacity and renewability was successfully prepared for the removal of toxic methylene blue from wastewater. The adsorbent exhibited hierarchically micro-mesoporous structure and high surface area, leading to superior adsorption performance. It showed high sorption capacity, rapid sorption rate, and good cyclic stability. Furthermore, the adsorbent maintained excellent adsorption performance over a wide range of pH values, making it suitable for wastewater treatment.