Sustainable dye wastewater treatment: utilizing duckweed-derived adsorbents for efficient methylene blue removal

Invasive plants threaten natural ecosystems due to their rapid spread and growth. This study used duckweed (DW) to develop a low-cost and sustainable adsorbent to remove methylene blue (MB) from aqueous solution. The adsorbent was analysed using various techniques. Fourier transform infrared spectroscopy (FT-IR) identified oxygen-containing functional groups on the DW surface that enhanced its adsorption capacity. Optimal adsorption conditions were achieved with an adsorbent amount of 20 mg, a pH of 10, and an initial MB concentration of 10 mg/L. Experimental data matched the pseudo-second-order (PSO) model across all concentrations, including 10 mg/L (Q_e = 73.53 mg/g), 20 mg/L (Q_e = 183.15 mg/g), and 50 mg/L (Q_e = 200.80 mg/g). The Temkin isotherm model fit the data better than the Langmuir and Freundlich models. Adsorption decreased with increasing temperatures (ΔG^o =  − 7.56 to − 8.06 kJ/mol, ΔH^o =  − 4.93 kJ/mol, ΔS^o =  − 6.76 kJ/mol). The primary adsorption mechanisms included electrostatic interactions, hydrogen bonding, and π-π electron interactions. The production cost of the DW adsorbent was estimated at RM 14.40 per kg, making it a more affordable alternative. With its high adsorption capacity and wide availability, DW is a promising material for controlling dye pollution in wastewater.