Functional properties and continuous adsorption process of Arenga pinnata shell and its porous biochars for aqueous methylene blue removal

Abstract

Arenga pinnata shell, an agricultural-processing residue, was used as an alternative precursor for synthesizing Arenga pinnata shell particles (ASP), Arenga pinnata shell biochar (ASB), and Arenga pinnata shell activated biochar (ASAB) for methylene blue (MB) adsorption. Optimized adsorbent was observed for ASAB fabricated via an impregnation ratio of KOH to ASP of 0.5:1 (w/w) at 700 °C for 30 min of activation time under N2 pyrolysis, with a surface area, pore volume, and average pore diameter of 967 m2/g, 0.572 cm3/g, and 2.47 nm, respectively. The adsorbent also possesses the largest carbon constituent (90.4 %), negative surface charge (−36.4 mV), and abundant oxygen-containing functional groups. Dynamic MB adsorption properties on the adsorbents from the aqueous environment under continuous mode at 25 °C were determined using the Thomas and Yoon-Nelson models. Although the ASP and ASB presented comparatively favorable adsorption properties, the optimum adsorption performance was observed for the ASAB. Its superior functional features contributed to the largest adsorption capacity of 203.86 mg/g. The elemental composition analysis indicated the presence of sulfur on the ASAB surface, which supported the findings. This research demonstrates the utility of Arenga pinnata shell as an eco-friendly precursor for high-performance adsorbent fabrication with excellent MB adsorption properties.