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

Abstract

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-heteroatomdoped carbon dots (CD) (nitrogen-, sulfur-, and phosphorusdoped-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 W 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 photocatalytic activity of NSP-CD. Under sunlight, photodegradation of ∼20 ppm of dye was observed in ∼60 min (for MY) and ∼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 ∼15−23 ppm showed similar results of photodegradation.

Visible-Light-Promoted Photocatalytic Applications of Carbon Dots: A Review

“…94 Also, NSP-CD were prepared using PEG, H 3 PO 4 , and Lcysteine as C, P, and N/S sources and photocatalytic activities toward the degradation of MO and methanine yellow (MY) dyes were analyzed. 95 Li et al prepared NSP-tri doped CD via the hydrothermal method using H 3 PO 4 and sulfonamide with a QY of ∼33%. A UV absorption spectra of NSP-CD is shown in Figure 5f, and the inset is the images of NSP-CD solution under daylight and UV-light showing fluorescence.…”

“…Recently, multiple-heteroatom doped CD (NSP-CD) was used to degrade azo dyes (MO and MY) in acidic medium. 95 A light-assisted comparative study was also performed in the presence of a 100 W bulb light and under sunlight. The obtained result showed that NSP-CD has great photodegradation ability under sunlight in comparison to bulb light, and as the rate increases (K sunlight > K bulb-light ), the half-life t 1/2 decreases (∼10 times) as shown in Figure 9c,d The photogenerated e − in the CB of SnS 2 can easily be inserted into the CD with the destruction of charge recombination followed by an improved photocatalytic activity.…”

“…for N,S-CD synthesis using the same N,C precursor and thiourea as a S source for Cr­(VI) reduction reaction under sunlight . Also, NSP-CD were prepared using PEG, H 3 PO 4 , and l -cysteine as C, P, and N/S sources and photocatalytic activities toward the degradation of MO and methanine yellow (MY) dyes were analyzed . Li et al.…”

“…(c–e,g) MO and MY dye degradation using NSP-CD in the different light source; bar diagram of the half-life of MO and MY dye degradation under bulb-light and sunlight; proton NMR of MY dye degradation using NSP-CD (insets are zoomed images of a yellow rectangular box and chemical structure of MY dye); digital images of MY dye before and after degradation, respectively. Reproduced from ref . Copyright 2021 American Chemical Society.…”

“…The NMR results show that the complex organic framework breaks down after degradation, as shown in Figure9f. The real photographic images of MY and MB dye before degradation and after degradation is shown in Figure9g,h 95,57. 4.2.…”