Robust and porous 3D-printed multifunctional hydrogels for efficient removal of cationic and anionic dyes from aqueous solution

A porous multi-layered nanocomposite hydrogel, made of poly (ethylene oxide) (PEO) and cellulose nanocrystals (CNCs), suitable for the selective adsorption of different organic dyes has been developed via 3D printing. To obtain cationic and anionic CNCs and to facilitate the adsorption of positive and negative dyes, CNCs were modified. The cross-linked nanocomposite bioink was 3D printed to form a porous multilayered hydrogel with oppositely charged layers. SEM images revealed that surface charge has a predominant effect on the porous structure of hydrogel layers. The cationic hydrogel layer exhibited a large degree of randomness in pore size and geometry, however, ionic layers displayed well-organized pore structure. The cationic and anionic layer pre-sented pore size in the range of 10-40 mu m, and 10-30 mu m, respectively. Surprisingly, the observed distance between adjacent layers and delamination phenomenon suggested missing adherence between layers due to long printing time, cooling temperature, and different chemical structures in adjacent layers. 3D printed hydrogels exhibited high equilibrium swelling ratios at different levels of pH (i.e., 4, 5, 8, and 9), while fastest swelling was observed at pH 8 and pH 9.An approximate 75% of maximum adsorption ratios was observed within the first 3 h of exposure. The hydrogel exhibited almost twice the adsorption capacity for MB in comparison with MG in the pH levels studied in this work. The maximum adsorption capacity for MB and MG was observed at pH 9 for 95.23 and 82.39%, respectively. The kinetics of adsorption was analyzed via pseudo-first and second orders, and Langmuir models. The adsorption kinetics followed the pseudo-second-order model well while equilibrium adsorption from the pseudo-first order and Langmuir exhibited a large difference with experimental data. The work provides promising results for the development of CNC-PEO materials as a multilayered adsorbent for effective and efficient dye decontamination of the wastewater.

Automated summary

A porous multi-layered nanocomposite hydrogel featuring selective adsorption of organic dyes has been developed via 3D printing. The surface charge of the hydrogel has a predominant effect on the porous structure, with layers of opposite charges showing different pore characteristics.