Multifunctional halogen doped carbon quantum dots for photo-degradation of methylene blue and selective detection of Cu2+ ions

Urbanization and rising demand lead to hazardous industrial residue, particularly organic dyes and chemicals, polluting water bodies. This study explores halogen-doped carbon dots for photocatalytic degradation of carcinogenic methylene blue. Electron-withdrawing halogen ions were found to enhance the photocatalytic degradation of MB dye. The paper systematically examines the influence of chlorine, fluorine, iodine, and bromine doping on methylene blue photodegradation. Halogen doping increased sample crystallinity and reduced particle size, causing a blue shift in absorption spectra. A wider band gap potentially reduced charge carrier recombination, improving separation. Iodine-doped carbon dots exhibited the highest methylene blue adsorption. Bromine doping boosted the photocatalytic degradation efficiency of undoped carbon dots from 90 % to 98.7 % under 60 min of UV irradiation. LC-MS studies elucidated the degradation mechanism. Detailed optical, luminescent, compositional, and morphological analyses were conducted. Intrinsic carbon dots were also utilized as fluorescent probes for selective sensing of Cu²⁺ ions in aqueous solution. Carbon dots were found to selectively detect the presence of Cu²⁺ ions out of Fe³⁺, Fe²⁺, Cr²⁺, Sn⁴⁺, Co²⁺, Hg²⁺ and Pb²⁺ ions. Cu²⁺ ions get adsorbed on the oxygen-functional groups on the carbon dot surface and form a ground state complex, resulting in static quenching of blue luminescence of carbon dots.