MPTS Modified ZnS-Mn2+ Quantum Dot Probes for Cu2+ Ions Fluorescent Sensing in Aqueous Solution

Water pollution due to heavy metal ions is a global issue which requires proper attention to maintain the water quality demands. Surplus amounts of copper in aqueous systems coming from industrial waste and domestic sewage could have bad influence on the surrounding ecosystem and pose a serious threat to human health. We have developed a novel, simple, cost-effective method for the detection of heavy metal ion Cu 2+ using eco-friendly (3-mercaptopropyl)trimethoxysilane ( MPTS ) functionalized ZnS-Mn 2+ quantum dots ( QDs ) through rapid fluorescent analysis. The QDs were synthesized, and the surface was modified with a non-toxic functionalizing agent MPTS through microwave assisted aqueous route. Such surface modified QDs were then employed as a fluorescent sensor for the detection of Cu 2+ even at very low concentration. The optical properties and structural features of the QDs have been characterized by absorption spectra, fluorescence spectra, TCSPC lifetime studies, pH studies, XRD, FTIR, TEM, and zeta potential. The sensing action is based on the fluorescent quenching of MPTS capped ZnS-Mn 2+ QDs which is possibly due to the effective electron transfer from QDs to Cu 2+ ion. The sensing ability of the synthesized QDs was confirmed by UV-visible absorption and fluorescence spectroscopic studies. The XRD studies and FTIR spectra also confirmed the interaction of QDs with Cu 2+ ions which are responsible for the sensing action. Under the optimum conditions, the Stern–Volmer plot of Cu 2+ showed a good linearity within the concentration range of 0 to 4 × 10 –6 M. The K SV was found to be 0.561 × 10 6 M –1 with the detection limit of 2.3 × 10 –8 M. Selectivity studies were conducted, and the fluorescence quenching of MPTS capped ZnS-Mn 2+ QDs was found to be more sensitive to Cu 2+ ions even when the cationic concentrations were 100 times higher than that of Cu 2+ ion. Hence, the detection of heavy metal ion Cu 2+ can be performed more easily and rapidly by this fluorescent sensor, and it provides a novel green concept in the field of sensing mechanisms.