Removal of heavy metals by leaves-derived biosorbents

Among various remediation technologies, biosorption is promising for the removal of heavy metals from water and wastewater, since in many cases, it is fast, selective, and with elevated efficiency. Other advantages such as applicability against various types of pollutants, simplicity, low cost and ease of operation, as well as the reusability potential of the adsorbents, make it beneficial. Nowadays, more green materials, raw or modified, are explored instead of conventional adsorbents, within the concept of Green Chemistry'. This review focuses on the use of leaves-based biosorbents in raw or modified forms to sequestrate heavy metals from waters and wastewaters. It can be concluded that: (1) chemical modifications led to a satisfactory improvement of the removal capability of leaf-based adsorbents, (2) the maximum monolayer adsorption, obtained from Langmuir isotherm, ranged between 3.9-300 and 7.8-345mg/g for raw and modified leaf biosorbents, respectively, (3) in most cases the Langmuir isotherm and pseudo-second-order kinetic model gave the best fit, (4) thermodynamic studies showed that the adsorption was in all studied cases spontaneous and mainly endothermic with increased randomness at the solid-liquid interface during adsorption, and (5) an enthalpy-entropy compensation effect was observed.