Fabrication of a magnetic composite by CoFe2O4 and an inorganic polymer for simultaneous photo-degradation of organic pollutants under visible LED light: Bandgap engineering, CCD-RSM modeling, and resolving spectral overlap of analytes

[Display omitted] •Designing a magnetic core–shell composite using CoFe2O4 and an inorganic polymer.•Modifying the bandgap of prepared composite by immobilization of Ag nanoparticles.•Simultaneous degradation of two organic pollutants with a severe spectral overlap.•Operating the EXRSM, simple spectrophotometric method, to separate UV–Vis spectra.•Modeling and optimizing the degradation process utilizing the CCD-RSM method. Despite all the progress, photo-catalysts still have some shortcomings, so it is essential to improve them. Herein, we have prepared a magnetic core–shell composite using CoFe2O4 magnetic nanoparticles and poly(chloropropyl-methyl)silsesquioxanes (PCMSQ). Then, its surface was functionalized by NH2 groups to provide favorable conditions for immobilization of Ag nanoparticles. It can lead to adjusting the bandgap energy of the composite and transmitting it to the visible region of light via a plasmonic sensitization process. Consequently, photo-degradation of pollutants can be easily performed by a LED lamp or sunlight. Hence, the degradation of two organic dyes was simultaneously performed to investigate its photo-catalytic properties in simulating actual conditions. However, due to the overlapping of their spectra, it was difficult to monitor the process and determine the concentration of the species using UV–Vis spectrophotometry. Therefore, a new and fast method, namely EXRSM, was employed to solve this problem. The CCD-RSM was also used to optimize, model, and better understand the effect of main factor interactions in the degradation process. For each dye, the adequacy of the model was proven by statistical analyses such as ANOVA and residual plots. The obtained R2, R2adj, and R2pred show a high correlation between experimental and predicted results. The kinetic investigation revealed that the degradation process follows a pseudo-zero-order model, and the Kapp values for MV and MB were calculated to be 0.0156 and 0.0181 (mol·L−1·min−1), respectively. Finally, we analyzed the recycling ability of Ag@PCMSQ@CoFe2O4, in which the photo-catalytic efficiency of the recovered catalyst was only reduced by less than 10%, after five cycles, for each dye.