Removal of Methylene blue dye from contaminated wastewater using lignocellulosic biomasses: A comparative study

In this study, lupine seed (Lu-SP) and pumpkin seed shells (PSSP) biomasses were used to create alternative and effective adsorbents. Methylene blue (MB) dye was removed from wastewater using the as-prepared adsorbents at variables solution pH 2.0 –11.0, contact period (0–180 min), and adsorbent mass (0.2–2.0 g/L). The solution pH had a synergistic effect on the improved removal of MB and the optimal adsorption removal for both adsorbents occurred at pH 8.0 and 120 min. The adsorption isotherm modelling results showed a good fit with the Langmuir model, with a maximum monolayer adsorption capacity of 48.98 and 77.48 mg/g for PSSP and Lu-SP, respectively. Similarly, the pseudo-first-order (PFO) model is regarded as the best-fit kinetic model for both adsorbents and suggests the predominance of physisorption via interfacial diffusion. Mechanistic investigation of the present system suggests that both intraparticle diffusion and surface sorption mechanisms control the adsorption rate. Notably, the Lu-SP with a lower surface area (54.013 m²/g) outperformed the PSSP (235.992 m²/g) in terms of adsorption capacity under varying pH. Therefore, in addition to electrostatic interaction, adsorption into the micropores via volume filling is considered one of the adsorption mechanisms. This study, therefore, revealed that the PSSP and Lu-SP may be very helpful for removing cationic MB dye from contaminated wastewater.