Novel synthesis of carbon dots from coconut wastes and its potential as water disinfectant

This paper presents a facile and effective method for the large-scale production of carbon dots (CDs) from diverse coconut wastes (fronds, husk and shell). On comparing two different methods, namely (i) hydrothermal carbonization and (ii) novel sequential synthesis processes (pyrolysis followed by sonication), the latter procedure recorded a higher recovery of CDs (14.0%) over the hydrothermal method (2.33%). Doping agents such as urea, polyethyleneimine (PEI) and hexamethylenetetramine (HMTA) were chosen at varying concentrations to synthesize surface-modified CDs (SMCDs) for enhanced antibacterial properties. Among these SMCDs, urea-doped CDs (1:1) @ 1000 ppm registered significantly higher cytotoxicity (20.6%) against Escherichia coli (E. coli). Subsequently, to assess the applicability of CDs as a disinfectant in water purification systems, two products, namely (i) CD-infused chitosan beads and (ii) pelletized CDs, were developed to ensure the immobilization of CDs. Studies with lab-scale prototypes have revealed that CDs infused chitosan beads reduced the colonies of E. coli from 5.41 × 102 CFU/mL (control group) to 2.16 × 102 CFU/mL, in comparison with pelletized CDs that decreased to 3.30 × 102 CFU/mL. The biosafety of CDs was assessed against Eisenia fetida for 21 days, and the observations revealed no mortality, even at 2000 ppm. Overall, this research demonstrated that a waste biomass can be effectively transformed into a novel water disinfectant. Furthermore, this scientific endeavor opens up research avenues to evolve advanced water purifiers using low-cost and eco-friendly nanomaterials.