Adsorptive Uptake of Acetaminophen by Agricultural Waste-Derived Hydrochar: Kinetics, Isotherms, and Characterization Studies

In this paper, we investigated a hydrochar-derived agricultural waste (AWHC) as a sustainable adsorbent, modified with three types of modification methods (by layer double hydroxides (AWHC-LDH (Mg-Al)), chemical activation method by KOH (AWHC-KOH) and H 3 PO 4 (AWHC-H 3 PO 4 ), and then we used all four different types to remove acetaminophen (ACT) from synthetic solution. The maximum removal of ACT was 87%, 88%, 96%, and 97% for AWHC, AWHC-LDH (Mg-Al), AWHC-KOH, AWHC-H 3 PO 4 , respectively, at pH of 4 for AWHC-LDH (Mg-Al) and 6 for others, with a contact time of 120 min, initial concentration of 80 mg/L, adsorbent dose of 1.1 g, and speed of 200 rpm. The pseudo-second-order kinetic model could fit the adsorption process better (R 2 = 0.953, 0.944, 0.924, and 0.934). The Langmuir model had the highest R 2 for AWHC (0.952), AWHC-LDH (Mg-Al) (0.997), and AWHC-KOH (0.941), indicating its suitability for those hydrochars, while Freundlich isotherm had the highest R 2 for AWHC-H 3 PO 4 (0.946). The characterization results showed that LDH (Mg-Al) and KOH as modifications could effectively make the mesoporous structure. At the same time, H 3 PO 4 developed a macroporous structure, shown by the scanning electron microscopy image supported by the Brunauer–Ettring–Teller and X-ray diffraction findings. The AWHC-LDH (Mg-Al) and AWHC-KOH exhibited better crystallinity and functional groups within the hydrochar matrix. Converting agricultural waste into practicable and sustainable materials for the environment’s benefit is a meaningful topic addressed in this paper.