Carboxyl and carbonyl groups of carbon dots co-coordinated assembly with Al to emission-enhanced aggregates for sensitive sensing and efficient removal.

It is very challenging to prepare carbon dots (CDs) with aggregation-induced emission (AIE) property for simultaneous sensitive sensing and efficient removal. Herein, blue-emission CDs were facilely prepared by one-step solvothermal treatment of vine tea. Optical characterizations demonstrated that AIE phenomenon of CDs came from the restricted intramolecular motion. Through selected chemical modifications for structure-property relationship analysis, carboxyl and carbonyl groups on CDs were demonstrated as co-coordination active sites to bind with Al for turn-on sensing process. Fluorescence enhancement of CDs by Al chelation could be attributed to synergistic mechanism of AIE and chelation-enhanced fluorescence. Thus, the prepared CDs has been used as a selective, sensitive, and effective fluorescent probe for fast Al sensing (response time, 5 min; linear range, 0.5-30.0 μM; limit of detection, 0.31 μM). More interestingly, high binding affinity between CDs and Al made them assembly into large aggregates via flocculation for Al removal (removal efficiency, 97.5 %) with extraordinary adsorption behavior (adsorption capacity, 1316 mg/g). Furthermore, the proposed CDs were successfully applied in detecting Al in real wastewater samples with acceptable recoveries (98.7-103.0 %) and superior precision (relative standard deviations, less than 3.82 %), and removing Al in spiked samples with satisfactory results. The work thus gives a demonstration of the potential fabrication of CDs with AIE property, and a better understanding of sensing and removal mechanisms for more rational design of CDs with application values.