Biosorption of pollutants by plant leaves: An empirical review

In recent years, research focus has been shifting towards the development of environmentally friendly systems for the removal of pollutants from effluents. The use of green adsorbents from tree leaves is a key research domain in this regard. In this empirical review, plant leaves biosorption studies within the last two decades were considered. The numerous source plants, preparation and modification techniques and adsorbent improvement findings were elucidated. The basic steps of preparation were found to be similar for most studies and it involves pre-cleaning, drying, grinding and sieving. In some studies, further chemical modification was conducted. Comprehensive catalogues of empirical findings were presented for removal efficiency, adsorption capacity, factor optimal, equilibrium, kinetics and thermodynamic studies. In these areas, a variety of findings were deduced by researchers with the peculiarity of obtained results being consequent on the type and nature of the pollutant and plant precursor. The desorption methodology and reusability potential was also considered and key knowledge gaps elucidated. Real wastewater treatment, pilot and full-scale applications, column studies, disposal and treatment ways of the exhausted adsorbents are fallow areas needing more extensive exploration. It can be surmised that plant leaves are excellent, eco-friendly, cost-effective and easy-to-prepare precursors for the development of biosorbents effective in removing heavy metals, dyes, cations and other chemical species from aqueous solutions.