Photoreactive Carbon Dots Modified g-C[sub.3]N[sub.4] for Effective Photooxidation of Bisphenol-A under Visible Light Irradiation

A series of carbon dots (CDs) modified g-C[sub.3]N[sub.4] (xCDs/g-C[sub.3]N[sub.4]; x = 0.5, 1.0, and 1.5 mL CDs solution) was synthesized via the microwave-assisted hydrothermal synthesis method for the photooxidation of bisphenol-A (BPA) under visible light irradiation. The X-ray diffraction (XRD) analysis indicates that the CDs may have a turbostratic structure and the resulting photocatalysts have distorted crystal structure, as compared with pure g-C[sub.3]N[sub.4]. The high-resolution transmission electron microscope (HR-TEM) analysis revealed amorphous, mono-disperse, spherical CDs with an average particle size of 3.75 nm. The distribution of CDs within the matrix of g-C[sub.3]N[sub.4] appear as small dark dot-like domains. The N[sub.2] adsorption-desorption analysis indicates that the nanocomposites are mesoporous with a density functional theory (DFT) estimate of the pore size distribution between 2-13 nm. The CDs quantum yield (QY) was determined to be 12% using the UV-vis spectral analysis, where the CDs/g-C[sub.3]N[sub.4] has improved absorption in the visible region than g-C[sub.3]N[sub.4]. The higher BET surface area of CDs/g-C[sub.3]N[sub.4] provided more adsorption sites and the ability to yield photogenerated e[sup.−]/h[sup.+] pairs, which caused the 1.5 CDs/g-C[sub.3]N[sub.4] to have better photocatalytic efficiency compared to the rest of the systems. The highest removal, 90%, was achieved at the following optimum conditions: BPA initial concentration = 20 mg L[sup.−1], catalyst dosage = 30 mg L[sup.−1], and pH = 10. The photooxidation process is mainly driven by photogenerated holes (h[sup.+]) followed by [sup.*]OH and O[sub.2] [sup.*−]. The synthesis of the 1.5 CDs/g-C[sub.3]N[sub.4] system is simple and cost-effective, where this photocatalyst is highly stable and reusable versus other systems reported in the literature.