TiO2-chitosan-cyclodextrin polymers based on subject-object recognition for adsorption-assisted photocatalytic degradation of Congo red.

Water pollution caused by anionic dyes, particularly exemplified by Congo Red (CR), poses a serious threat to ecosystems. To address this, a TiO2-chitosan-cyclodextrin polymer (CS-β-CDP/TiO2) was prepared via a host-guest recognition strategy. Its unique structure not only prevented the aggregation of TiO2 but also endowed it with an adsorption-photocatalytic synergistic effect, enabling the effective removal of CR. Detailed characterization (FTIR, XRD, XPS, TEM, TGA) confirmed the successful integration of anatase TiO2 nanoparticles (ca. 6-15 nm) onto the chitosan-cyclodextrin polymer (CS-β-CDP), with a TiO2 loading of 53%. The introduction of TiO2 led to a substantial increase in the BET surface area, which reached 15.597 m2·g-1. The corresponding adsorption capacity of CS-β-CDP/TiO2 was 124.2 mg·g-1 under optimized conditions. The adsorption process was well described by the Langmuir isotherm model and obeyed the pseudo-second-order kinetic expression. Furthermore, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) analyses confirmed the photocatalytic activity of CS-β-CDP/TiO2. Remarkably, the photocatalytic degradation rate was 99.5% under UV irradiation, the TOC (total organic carbon) analysis confirmed the effective mineralization of the dye. Importantly, possible pathways for CR degradation were proposed based on the results of LC-MS analysis and trapping experiments. Furthermore, the composite material demonstrated excellent stability with low Ti ion leaching (5.089 mg/L) and retained high performance over five adsorption-photocatalytic regeneration cycles. This demonstrates a new approach for the combined application of chitosan and TiO2, highlighting the potential of CS-β-CDP/TiO2 as a green, recyclable solution for wastewater remediation.