Optimization of hydrothermal synthesis conditions of Bidens pilosa-derived NiFeO@AC for dye adsorption using response surface methodology and Box-Behnken design.

The presence of stable and hazardous organic dyes in industrial effluents poses significant risks to both public health and the environment. Activated carbons and biochars are widely used adsorbents for removal of these pollutants, but they often have several disadvantages such as poor recoverability and inseparability from water in the post-adsorption process. Incorporating a magnetic component into activated carbons can address these drawbacks. This study aims to optimizing the production of NiFeO-loaded activated carbon (NiFeO@AC) derived from a Bidens pilosa biomass source through a hydrothermal method for the adsorption of Rhodamine B (RhB), methyl orange (MO), and methyl red (MR) dyes. Response surface methodology (RSM) and Box-Behnken design (BBD) were applied to analyze the key synthesis factors such as NiFeO loading percentage (10-50%), hydrothermal temperature (120-180 °C), and reaction time (6-18 h). The optimized condition was found at a NiFeO loading of 19.93%, a temperature of 135.55 °C, and a reaction time of 16.54 h. The optimum NiFeO@AC demonstrated excellent sorption efficiencies of higher than 92.98-97.10% against all three dyes. This adsorbent was characterized, exhibiting a well-developed porous structure with a high surface area of 973.5 m g. Kinetic and isotherm were studied with the best fit of pseudo-second-order, and Freundlich or Temkin. Q values were determined to be 204.07, 266.16, and 177.70 mg g for RhB, MO, and MR, respectively. By selecting HCl as an elution, NiFeO@AC could be efficiently reused for at least 4 cycles. Thus, the Bidens pilosa-derived NiFeO@AC can be a promising material for effective and recyclable removal of dye pollutants from wastewater.