Regulating the Surface State of Carbon Dots as Ultrahigh‐Capacity Adsorbents for Water Treatment

Adsorption is one of the most widely researched and highly effective methods for mitigating the environmental threat posed by recalcitrant dyes in aqueous solutions. This paper presents a solvent‐free synthesis method for the rapid and large‐scale production of nitrogen (N) and phosphorus (P) co‐doped carbon dots (N, P‐CDs) which possess specific surface states and outstanding dye adsorption properties. Compared to the undoped CDs, the N, P‐CDs not only exhibit a higher yield of solid‐state luminescence but also endow them with the efficient adsorption and removal of Congo red (CR) from water. Due to the synergistic effects of π–π stacking, hydrogen bonding and electrostatic attraction, the N, P‐CDs exhibit an ultra‐high adsorption capacity (3118.87 mg g−1) and a removal efficiency (97.4%, at 500 mg L−1) for CR, and also display excellent selective adsorption in both single‐dye and dual‐dye systems. This method offers a rational strategy for synthesizing novel CDs‐based adsorbents for CR, which provides a demonstration for future dye adsorption studies and practical wastewater treatment applications of CDs. Strong green‐emitting N, P‐CDs powders are obtained by heating 3‐Hydroxy‐2‐naphthoic acid and a single dopant (piperazine phosphate) using a solvent‐free method. Based on the synergistic effects of π–π stacking, hydrogen bonding and electrostatic attraction, the N, P‐CDs exhibits an ultra‐high adsorption (3118.87 mg g−1) and a removal efficiency (97.4% at 500 mg L−1) of Congo red (CR) from water.