Assembly of 3D printed N-doped biochar as impeller with CaCO3 as sacrificial pore generator for enhanced dye adsorption

Three-dimensional (3D) printed monolithic catalysts/adsorbents have attracted much attention due to their excellent properties. Herein, the rice husk-derived nitrogen-doped biochar (using urea as the nitrogen dopant) was printed into monolithic adsorbents using direct ink writing technology, and then assembled as agitating paddles for organic dye adsorption. To reduce the over-embedding of active sites in the polymeric matrix, CaCO 3 particles in nano-sized or micron-sized were added as sacrificial pore generators to form macropores and expose active sites, leading to an enhanced mass transfer efficiency. Material characterization results confirm the self-sacrificial role of CaCO 3 . The 3D-printed adsorbents with micron-sized CaCO 3 (denoted as 3D-HRSCCm) possessed excellent adsorption performance, as evidenced by a high adsorption capacity and kinetics study. Meanwhile, 3D-HRSCCm adsorbents were mounted as agitating impellers which demonstrated excellent reusability with the adsorption efficiency remaining above 90% after ten cycles. Furthermore, the 3D-HRSCCm exhibited excellent adsorption properties for various dyes such as methylene blue, rhodamine B, crystal violet, and malachite green. Moreover, the numerical simulation confirms that the introduction of CaCO 3 as a pore generator improved diffusion by providing wider channels and facilitated the mass transfer that accelerated the adsorption rates.