Tuning of excitation wavelength to achieve dual-channel detection of Cr(VI) by cellulose-based carbonized polymer dots.

Carbonized polymer dots (CPDs), a new nanofluorescent materials inheriting the advantages of CDs, have been widely studied for their excellent physicochemical stability and tunable fluorescence properties, and have extensive application in the fields of optoelectronic devices and environmental monitoring. In this study, nitrogen-doped CPDs (CMC-M-CPDs) were synthesized via hydrothermal reaction using carboxymethyl cellulose (CMC) and melamine (M), which allowed N doping to improve the luminescence of CPDs through cross-linking and reduction of the energy gap. Due to the excitation-dependent, the luminescence wavelength of CPDs can be tuned, so these CPDs exhibit two optimal emission centers in the fluorescence spectra, which originate from the carbon core and the surface, respectively. A significant quenching effect on the luminescence of CMC-M-CPDs at 457 nm and 515 nm was exhibited due to static quenching of Cr(VI). Therefore, dual-channel fluorescence detection of Cr(VI) can be achieved, allowing detection using both excitation wavelengths to be carried out concurrently and mutually verified in complex environments. This improves the accuracy of detection, with limits of detection (LOD) of 60.15 nM and 93.95 nM, respectively. The CMC-M-CPDs demonstrate excellent selectivity and anti-interference in the detection of Cr(VI), with a quenching response occurring within 1 s. This dual-channel fluorescent probe can also be applied for sensitive detection in tap water and Songhua River water. Furthermore, the fluorescence of quenched CPDs can be restored by adding ascorbic acid (AA), achieving a maximum recovery efficiency of 96.6 %.