Rajani Ramawat, Poonam Sandu and Rajendra Mathur
Abstract
Cellulose, a widely available carbon polymer found in various plant, animal, and bacterial sources, constitutes a significant portion of fruit and vegetable waste also. In tune with the current research, cellulose is also being extensively developed as a nano material, i.e. nano cellulose crystals (CNC). CNCs are advanced version of cellulose particles at nanometer scale and have additional properties other than natural and biodegradable attributes like high surface area, nano size effect, non-toxic, high mechanical strength, thermal stability, hydrophilic, possibility of functionalization due to presence of hydroxyl groups on surface. Nano cellulose has been extensively used in the field of food packaging materials, wastewater treatment, and drug delivery and as a catalyst. Nano cellulose and its hybrid nano composites are among the emerging nanomaterials of this century employed for wastewater remediation application specifically to remove heavy metals from industrial effluents. Recently, with the modification of surface properties of CNC with metal or metal oxide nanoparticles via ex-situ simple blending method, metal-organic framework based hybrid nano composites are synthesized for abundant application worldwide. Biodegradable watermelon peel waste derived nano cellulose (CNC)/nano silver (AgNPs) nano composite synthesized herein is applied as an adsorbent for the removal of heavy metals to purify waste water or textile effluent, mitigating problem of water pollution as well as solid fruit peel waste management. During the study, CNCs were prepared by ultrasonication and acid hydrolysis of isolated cellulose. Pure Cellulose is isolated from natural watermelon peel waste through chemical pre-treatment in which all non-cellulosic components were removed subsequently. Silver nanoparticles (AgNPs) were also synthesized by green biological method from leaf extract of Nyctanthus arbour tristis. CNCs were characterized by FTIR, XRD and FESEM to analyze purity of cellulose, crystallinity of CNCs and morphology and size of CNCs respectively. Excellent potential of CNC/AgNPs hybrid nano composites towards water purification application is successfully explored in this study via AAS adsorption estimates and FESEM and EDX analysis of CNCs/AgNPs adsorbent (before and after adsorption of heavy metal ions). Adsorption of heavy metals such as lead, cadmium and copper from textile effluent by CNCs/AgNPs is estimated with 88.68%, 35.44% and 88.04% removal efficiency. This recent development on low cost, natural waste derived sustainable production of novel metal-organic framework based CNCs/AgNPs adsorbent encourages sustainable waste management practices specially towards circular economy concept (3Râs) which suggests waste reduction, recycling, and reuse of waste in the production of eco-friendly materials for cleaner environment.