Acid–Base Interaction Induced Removal of Methylene Blue From Wastewater by Using Ring Cross-Linked Polyphosphazene Material

Abstract

Dye-containing wastewater (DCW) has become a serious environmental issue worldwide. In this work, thepoly(cyclotriphosphazene-co-2,4-diamino-6-phenyl-1,3,5-triazine) (PBMA) material was synthesized by precipitation polymerization method to probe the adsorptive removal of methylene blue (MB) from DCW. The adsorption conditions were optimized as pH = 7, initial MB concentration = 100 mg L⁻¹, and adsorption time = 800 min. Based on the acid–base interaction, the MB molecules in the DCW was adsorbed over the surface of PBMA. The surface morphology, surface elemental composition and surface functional group changes of PBMA were monitored by scanning electron microscopy images, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy, respectively. The thermodynamic analysis showed that the removal of MB prefers a single-layer adsorption over PBMA surface according to the good fitness of the adsorption results by using Langmuir isotherm (R ² = 0.9906). The kinetic analysis revealed that the adsorptive removal of MB follows the pseudo-second-order kinetics, with intra-particle diffusion and external diffusion as the dominant factors. The PBMA maintained a high adsorption capacity even after undergoing five consecutive adsorption–desorption experiments (Over 90%). The development of polyphosphazene material provides potential application in the field of dye removal from DCW.