Versatile P-doped carbon quantum dots derived from green precursor: an efficient metal ion sensor and photocatalytic behaviour in aqueous environment

The contamination of water by hazardous industrial discharges and harmful bacteria has evolved into a pressing concern, inflicting considerable harm on both the environment and human well-being. It is imperative that decisive measures are taken to mitigate and eradicate industrial wastewater pollution. In this study, we applied (phosphorus) P-doped carbon quantum dots simultaneously for metal ion sensing and photocatalytic without any post-treatment. P-doped carbon quantum dots (CQDs) were prepared from a green precursor microwave irradiation method. Our investigation delved into the structural, morphological, chemical, and elemental composition through various techniques. The P-CQD presented abundant functional groups on the surface with about 5 nm size. The P dopant and P–O–P bonds confirm the presence of P on CQDs. We investigated the influence of P-doping on the absorption, adsorption, and fluorescence characteristics in detail using UV–visible and photoluminescence (PL) spectroscopy. Our findings revealed that the PL emission in blue region is intricately linked to the excitation and pH levels. A noticeable 33% PL quantum yield was found. PL phenomenon attributed to the functional groups presents on the surface of the CQDs. Further, the potential of P-CQDs for the detection of metal ions specifically Fe³⁺ and Hg²⁺ in an aqueous environment was investigated, by employing a fluorescence quenching mechanism. The main factors driving quenching are the energy transfer interaction between carbon dots and metal ions facilitated by a certain interaction involving functional groups and surface traps. Impressively, P-CQDs exhibited a low detection limit of 51 nM for Fe³⁺ and 81 nM for Hg²⁺. It is worth noting that the P-CQDs exhibited superior quenching efficiency when exposed to Fe³⁺ and Hg²⁺ ions compared to other cations. Additionally, it displayed the ability to degrade methyl orange dye, achieving 70% degradation efficiency within a mere 240 min under ordinary visible light without any further integration with other materials. Thus, our study on P-CQDs demonstrates immense dual potential and efficiency for environmental applications.