Adsorptive Removal of Nitrophenols from Water by Biomass-Derived Carbon Nano-Onions

In light of accelerated industrialization, the quality of human life, and the crisis of clean water, the treatment of wastewater is particularly significant. Nitrophenols are high-priority and most noticeable industrial contaminants due to their high toxicity and resistance to biodegradation. Low-cost and green nanomaterials can effectively eliminate nitrophenols from contaminated water and play a vital role in protecting human life and the environment. In this work, low-cost, sustainable, and green carbon nano-onions (CNOs) were synthesized from low-quality flaxseed oil via a simple and economical flame pyrolysis procedure. The synthesized CNOs were used for the elimination of nitrophenols from water via the adsorption method. Adsorption of nitrophenols was carried out systematically at various conditions such as the dose of adsorbent, variation in pH, adsorption time, and temperature. The removal efficiencies of nitrophenols were 90, 85, and 95% for 2-NP, 3-NP, and 4-NP by CNOs and reached the equilibrium state within 25 min at a dosage level of 10 mg for 10 mL of 20 mg L-1 nitrophenol solution at neutral pH and ambient temperature (25 degrees C). The adsorption kinetics of nitrophenols over CNOs can be explained with the help of a Langmuir adsorption isotherm, which follows the pseudo-second-order kinetics (R-2 = 0.99) via monolayer adsorption. The thermodynamic parameters were also investigated, which showed that nitrophenol adsorption is spontaneous and exothermic. Furthermore, the practical applicability of CNOs toward the elimination of nitrophenols was validated in various real wastewater sources and showed removal efficiencies for 2-NP, 3-NP, and 4-NP of 90, 85, and 94% from dam water, 85.05, 80.85, and 92.02% from tap water, and 89, 82.50, and 90.15% from lake water, respectively. Besides, the CNOs demonstrated good recyclability and easy separation, showing high potential in wastewater treatment.