Innovative Bio-sorption of Pb2+ and Cu2+ from Wastewater Samples using Cannabis sativa L. Buds: Kinetics, Isotherm and Re-usability Studies

Abstract Heavy metal pollution, mainly from industrial wastewater, is an ongoing worldwide concern that threatens water quality. The present study investigated the potential of Cannabis sativa L . buds, both raw and chemically modified with glycine and sodium bicarbonate, to decontaminate Lead (Pb 2+ ) and Copper (Cu 2+ ) ions from wastewater. Fourier transform Infrared spectroscopy results showed that the chemical modification process altered the surface functional groups, as evidenced by shifts in the functional group peak intensities of the modified bio-adsorbents compared to those of the unmodified bio-adsorbent before adsorption. After the adsorption process, a reduction in peak intensities was observed due to adsorption interactions with metal ions. Scanning electron microscopy revealed an irregular and multi-layered surface with interconnected pore network structures of all assessed bio-adsorbents. However, sodium bicarbonate modified cannabis appeared to be more porous than both bio-adsorbents. Energy-dispersive X-ray spectroscopy identified carbon and oxygen as the major elemental components of the bio-adsorbents. X-ray diffraction spectroscopy revealed that the sodium bicarbonate modified bio-adsorbent exhibited a more crystalline form, while thermogravimetric analysis showed that it was more stable than glycine and raw cannabis biomaterial. These findings indicate that bio-adsorbents exhibit an enhanced adsorption capacity, whilst sodium bicarbonate modified cannabis is expected to perform better than the other bio-adsorbents. A batch adsorption method was employed and assessed by varying solution pH, temperature, mass dosage, initial metal concentration, and contact time in a binary system. The optimal adsorption conditions were determined to be a solution pH of 7, reaction time of 10 min, mass dosage of 10 mg, an initial adsorbate concentration of 10 mg/L, and an adsorption temperature of 25 ºC. According to the analysis of variance results, the effects of temperature and adsorbate concentration on the adsorption of metal ions showed the highest (> 61%) and lowest (> 3%) percentage contributions. The adsorption rates of Cu 2+ and Pb 2+ ions fitted a non-linear pseudo-first-order model, and the sorption mechanism was best described by a multilayered surface (the Freundlich isotherm). The metal ion adsorption process was found to be exothermic, spontaneous, and feasible. Sodium bicarbonate modified cannabis showed a larger maximum adsorption capacity (q max ) (31.222–56.875 mg/g) than glycine modified cannabis (28.983–53.888 mg/g) and raw cannabis (26.151–30.527 mg/g) for Cu 2+ and Pb 2+ ions, respectively. The percentage removal efficiency in real wastewater samples was 74–88% for the raw bio-adsorbent, 80–100% for glycine, and 96–100% for the sodium bicarbonate-modified bio-adsorbent for Cu 2+ and Pb 2+ ions, respectively. Though all bio-adsorbents showed good performance in removing both metal ions, sodium bicarbonate-modified cannabis was shown to be superior. This study showed that Cannabis sativa L. buds can be efficiently applied and regenerated at least three times as bio-adsorbents for the removal of metal ions from wastewater samples. Cannabis sativa L . buds offer an efficient, affordable, and eco-friendly alternative for water monitoring compared with conventional adsorbents. Additionally, the potential applicability of Cannabis sativa buds could be further assessed on a large industrial scale analysis.