Photodegradation of Azo Dyes in Sunlight Promoted by Nitrogen- Sulfur-Phosphorus Codoped Carbon Dots

Removal of organic contaminants such as azo dyes is highly desirable because of their toxicity, stability, and mutagenic properties. Herein an efficient method for the photodegradation of two well-known model azo dyes, namely metanil yellow (MY) and methyl orange (MO), under sunlight by multiple-heteroatom-doped carbon dots (CD) (nitrogen-, sulfur-, and phosphorus-doped-CD (NSP-CD)) is presented. The photodegradation results favored sunlight as a sustainable light source, as its value of t(1/2) is significantly less than that of artificial light (100 IV tungsten bulb). Various parameters, such as the concentrations of individual dyes (20-100 ppm), a mixture of both dyes, changes in pH, and foreign/interfering ions, were investigated to understand the photo-catalytic activity of NSP-CD. Under sunlight, photo-degradation of similar to 20 ppm of dye was observed in , similar to 60 min (for MY) and similar to 90 min (for MO), respectively. A comparative NMR investigation was performed to confirm the photodegradation of the complex structural framework of azo dyes by NSP-CD. Moreover, to explore the real-life utility of the process, sunlight-promoted photodegradation experiments were conducted by externally spiking four different types of industrial samples. Spiking of MY and MO dyes with concentrations in the range of similar to 15-23 ppm showed similar results of photodegradation.

Automated summary

The study demonstrates an efficient method for the photodegradation of azo dyes using NSP-CD under sunlight, which is a sustainable light source with faster degradation rates compared to artificial light. NMR investigations confirm the photodegradation of the complex structural framework of azo dyes by NSP-CD. Sunlight-promoted photodegradation experiments show potential real-life applications in industrial samples.