Preparation of low-cost adsorbents from Bidens pilosa L. weed using H₃PO₄ and KOH as activating agents and assessment of their organic dyes adsorption

Abstract

The present study produced activated carbons (AC) derived from chemically treated Bidens pilosa weed (BPW) through traditional pyrolysis. The ACs were used to treat dyes, such as rhodamine B (RhB), methyl orange (MO), and methyl red (MR), from aqueous solutions. The influence of impregnated ratios (1:0.5, 1:1, 1:1.5, and 1:2) of potassium hydroxide (KOH) and phosphoric acid (H₃PO₄) as chemical activation agents on adsorption efficiency was investigated. The results showed that for all investigated dyes, the carbon activated by the H₃PO₄ agent at an impregnated ratio of 1:2 (ACH4) exhibited the best adsorbent for dye removal. After 300 min of uptake experiments, the adsorption reached equilibrium, with adsorption efficiencies of 98.6%, 95.5%, and 96.0% for RhB, MO, and MR, respectively. ACH4 was analyzed using Fourier-transform infrared spectroscopy (FTIR) spectra and scanning electron microscopy (SEM). The SEM image revealed a progressive development of pores resulting from removing volatile substances and impurities. FTIR analysis indicated the predominance of acidic surface functional groups, which favored the adsorption process. Therefore, ACH4 prepared from Bidens pilosa weed is a promising adsorbent for removing dyes from an aqueous solution.