3D coaxial printing of porous construct stacked with hollow filaments for heavy metal removal

Biopolymers-based hydrogels/aerogels have been widely used for removing heavy metals from water. However, the adsorption efficiency is limited by the monolithic macroscopic structure due to low exposed adsorption sites and ion diffusion rate. In this study, we report a proof-of-concept micro-extrusion-based 3D coaxial printing technology to solve the aforementioned problems in heavy metal removal. The 3D printed grid-like architectures stacked with hollow filaments prepared by alginate and cellulose nanocrystal showed excellent heavy metals (including Cu, Zn, Cr, and Cd) removal performance over other common adsorbents. The Cu(II) adsorption was greatly influenced by the initial pH and ionic strength. It followed pseudo-second order kinetics and Langmuir isotherms models. The maximum adsorption capacity of the porous construct was found to be 97.22 mg∙g −1 at room temperature. Moreover, the equilibrium adsorption capacity and adsorption rate of Cu(II) in the hierarchical porous adsorbents (~68 mg∙g −1 , 2.29 × $\times$ 10 −3  g∙mg −1 ∙min −1 ) were much higher than that in its corresponding solid chunk hydrogel (~48 mg∙g −1 , 7.27 × $\times$ 10 −4  g∙mg −1 ∙min −1 ). It exemplifies that the 3D coaxial printing strategy for wastewater treatment enables shape-specific applications of functional hierarchical porous adsorbents.