Novel versatile 5-aminoisophthalic acid modified chitosan nanofiber pads for adsorption toward Congo red, methyl orange, crystal violet, and methylene blue

Abstract

To structure novel nanofiber pads for organic dye removal from dye-polluted water, we previously prepared CSP nanofiber pads by chitosan (CS) and polyethylene oxide (PEO) via electrospinning, followed by preparation of CSRP nanofiber pads through partial PEO removal from CSP, and the subsequent fabrication of CS-A nanofiber pads via grafting 5-aminoisophthalic acid (5-AIPA) to CSRP. FTIR, XRD, and elemental analyses confirmed the successful synthesis of CS-A nanofiber pads (crosslinking and crystalline degrees of 36.64 % and 4.57 %). CS-A nanofiber pads had porous nanofiber structures (diameter and pore size of 153.46 and 3.82 nm), high specific surface area (102.06 m2/g), great thermal stability (total mass loss of 50.2 %), excellent hydrophilicity (water contact angle of 12.0°), superior swelling performance (2331 %), good pH stability (pH of 3.0–11.0), and 6.8 of pHpzc, evidenced by SEM, Brunauer-Emmett-Teller (BET), thermogravimetric (TG), differential thermogravimetric (DTG), wettability, swelling, and solid addition tests. Optimum adsorption parameters (e.g., pH, dosage, and initial concentration) were selected by batches of tests on adsorption toward four organic dyes. CS-A’s surfaces were heterogeneous, and the adsorption belonged to spontaneous endothermic chemical adsorption, confirmed by kinetic and isothermal models and thermodynamic results. CS-A nanofiber pads were of great reusability and easy to be separated. Adsorption mechanisms involved electrostatic attractions, hydrogen bondings, π-stacking interactions, and pore fillings. Dynamic adsorption toward Congo red showed the Thomas model well fitted the breakthrough curves (R2 > 0.9971), showing the maximum adsorption capacity of 949.15 mg/g. Totally, CS-A nanofiber pads were effective adsorbents suitable for organic dye-containing wastewater purification.