Optimizing photocatalytic activity for chromium reduction: the role of MgAl LDH/ triazine covalent organic framework /CdS nanocomposite

Photocatalytic chromium conversion into non-harmful species is an attractive way to reduce pollution and improve the environment. A reasonable design of the optical properties and electronic behavior of photocatalysts is essential to improving catalytic activity. Herein, MgAl layered double hydroxide (LDH) / Covalent Organic Framework (COF) / CdS (MgAl/COF/CdS) nanocomposite as a highly efficient photocatalyst was successfully prepared by a simple step-by-step process for the photocatalytic reduction of strong toxic Cr (VI) to low toxic Cr (III) in visible light and are a candidate for environmental remediation applications. Results verify that the MgAl/COF/CdS nanocomposite exhibited excellent performance in Cr (VI) removal, with a maximum removal capacity of up to 98% in 90 min under visible light irradiation. X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and diffuse reflection spectroscopy (DRS) techniques were employed to characterize the synthesis samples. According to the XRD pattern, the nanocomposite exhibited distinct crystal planes (d₀₀₃, d₀₀₆), which effectively demonstrates the replacement of the covalent organic framework between the layered double hydroxide sheets. Furthermore, the FESEM images clearly illustrate the widespread distribution of the CdS nanoparticles in a hexagonal morphology, and these findings were confirmed by TEM analysis. The UV-vis diffuse reflectance spectrum results reveal that forming the MgAl/COF/CdS nanocomposite heterostructure significantly enhances visible light absorption and facilitates the efficient separation of photogenerated charge carriers. The kinetics and determination of the pH_PZC value supported the catalyst’s reduction of Cr (VI). Additionally, the photostability test demonstrated that the nanocomposite can be reused after four cycles with a minimal decrease in performance.