Sanchezia nobilis leaves derived N, O co-doped carbon activated by magnesium chloride for enhanced chromium removal

• N, O co-doped carbons (MgBC) is achieved by pyrolysis of sanchezia nobilis and MgCl 2 . • MgBC is featured by high surface area, abundant mesopores , and suitable N, O co-doping. • MgBC exhibits a supercolossal Cr(VI) adsorption capacity of 27.77 mg g −1 . • Although chemical processes are involved, physical single-layer adsorption is dominant. • Adsorption mechanism is mainly through electro-attraction, complexation and reduction. Chromium contamination persists as a pressing environmental issue, prompting ongoing endeavors to devise economical and efficient adsorbents for Cr(VI) eradication. Herein, N, O co-doped carbons (MgBC) were successfully synthesized through a single-step pyrolysis process, employing sanchezia nobilis as the raw material and magnesium chloride as the activator. Characterization results revealed that, under optimal conditions, specifically a biomass-to-activator mass ratio of 1:2 and a carbonization temperature of 600 °C, the MgBC possessed a specific surface area of 267.18 m 2 g −1 , a nitrogen content of 3.65 at%, and an oxygen content of 8.72 at%. In addition, diverse parameters, encompassing carbonization temperature, activator dosage, initial Cr(VI) concentration, adsorption duration, and solution pH, were systematically investigated to evaluate their impact on the adsorption performance of MgBC for Cr(VI) removal. The optimal MgBC demonstrated rapid kinetics and substantial adsorption capacity, achieving a Langmuir maximum capacity of 27.77 mg g −1 at a solution pH of 7. The superior performance of MgBC can be ascribed to its augmented specific surface area, optimized porosity, and heightened N, O content. The adsorption data adhered well to the pseudo-second-order model and Langmuir model suggested that physical adsorption with monolayer coverage predominated, albeit with some involvement of chemical processes. Additional mechanistic analysis confirmed that the attachment of Cr(VI) to MgBC primarily resulted from a synergistic interaction of electrostatic attraction, surface complexation and reduction. This work not only proposes a new approach for the development of heavy metal adsorbents, but also provides theoretical support for environmental remediation strategies.