Montmorillonite/cellulose-chitosan foam for selective removal of methyl blue from wastewater based on electrostatic interaction and size matching effects.

The selective removal of specific dyes from mixed dye solutions faces great challenges. This work fabricated an eco-friendly, structure-controlled montmorillonite/cellulose-chitosan foam (NaMt/CNC-CS) through Pickering emulsion templating combined with freeze-drying technology for selective adsorption of methyl blue (MB). Under the conditions of pH 3 and an initial MB concentration of 60 mg/L, the NaMt/CNC-CS achieved a MB removal efficiency of 99.10 % with a maximum adsorption capacity of 1019.06 mg/g. Coexisting heavy metal cations and anions such as Cr3+, Pd2+, Cl- and NO3- in such system does not have a significant impact on the adsorption selectivity of NaMt/CNC-CS for MB (removal efficiency over 95 %). Furthermore, in a binary methyl blue/rhodamine B (MB/Rh B) mixed system, the NaMt/CNC-CS exhibited a removal efficiency of 89.72 % for MB compared to only 2.35 % for Rh B. Additionally, after undergoing 5 cycles of adsorption/regeneration, the MB removal efficiency of NaMt/CNC-CS remained at 85.46 %. NaMt/CNC-CS enhances MB-selective adsorption through the synergistic effects of electrostatic interaction, hydrogen bonding and n-π conjugation, and pore size matching. Moreover, spent NaMt/CNC-CS foam was pyrolyzed into mineral-biochar, which can promote the growth of soybeans. This study guides green bio-adsorbent design for specific dyes and advances utilization of cellulose, minerals, and spent adsorbents.