Hierarchically structured, well-dispersed Ti4+ cross-linked chitosan as an efficient and recyclable sponge-like adsorbent for anionic azo-dye removal

Abstract

Porous macro- and hierarchically structured materials with desired morphologies and high adsorption capacities are of great interest because of their potential applications in realistic environmental pollutant treatment. In this study, sponge-like Ti⁴⁺ cross-linked chitosan (SL-TiCs) was synthesized using a chitosan solution and titanium metal salt as precursors. The as-prepared product was characterized via FE-SEM, HR-TEM, EDS, EMI, FT-IR and XPS. The results demonstrate that SL-TiCs is composed of multiple nano-layer twisted sheets and a high content of well-dispensed Ti⁴⁺ on its surface, which provide plenty channels for mass transfer and active sites for pollutant adsorption. The hierarchical structure of SL-TiCs exhibits a high adsorption capacity for Orange II with a fast adsorption rate and good recyclability. The adsorption performance can be described by the pseudo-second order and Langmuir isotherm models. The maximum adsorption capacity is 1120 mg g⁻¹, which is much higher than that of many other adsorbents. It is speculated that the probable mechanisms involve ligand exchange (44.6%) between Cl⁻ and dye–SO₃⁻ and electrostatic attraction (55.4%) between Ti–OH₃⁺ and dye–SO₃⁻ anions in the adsorption process. This study implies that SL-TiCs can be a potential adsorbent for the adsorption and separation of anionic dyes from large volumes of industrial dye wastewater.