Synthesis of a chitosan-clay nanomembrane by pH control and its thermal stability in aqueous environments

Nanofiltration is a promising technology for the treatment of industrial effluents containing organic contaminants and large divalent ions. The development of green nanomembranes is hence crucial for advancing this technology. This work aims to synthesize a novel chitosan-montmorillonite (CTS-MMT) nanomembrane concerning pH effects and to evaluate its structural stability under a wide range of operating temperatures in aqueous solution. Molecular dynamics method is conducted here and the INTERFACE-PCFF force field was employed in the biopolymer-organic system. Results show that water and counterions play a hindering role in the coating process. The higher protonation rate of chitosan can achieve higher adhesiveness and a more uniform distribution on the MMT surface after complete drying. This behaviour is due to the CTS-MMT interaction, mainly generated by -NH3+ via electrostatic and hydrogen bonding interactions, while OH and NH2 groups exhibit negligible contributions. Both water-induced peeling as well as temperature-dependent peeling were analyzed basically according to the adhesion rate of NH3+ groups. Water evaporation is observed at around 550 K and no decisive desorption of chitosan from the clay substrate can be found even at extremely high temperatures up to 800 K. The high thermal stability of the CTS-modified organoclay nanomembrane in water proves that they will not generate secondary pollutants. This study can therefore provide insight into the fabrication and design of the proposed new type of membrane within clay nanocomposites.