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

摘要

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 N2 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~(-1) (13 fold that of CFA). Surprisingly, 95% 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 (6～9) without excessive pH adjustment. The adsorption kinetics and equilibrium data fit well with pseudo-second-order model and the Langmuir isotherm model, respectively. And the thermodynamic investigationes 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.