Caffeine-alginate immobilized CeTiO4 bionanocomposite for efficient photocatalytic degradation of methylene blue

Abstract

The degradation of colored dyes through the photocatalysis process has been proved to be a promising technique for wastewater treatment. Herein, we report the synthesis of cerium titanate (CeTiO4) nanoparticles (NPs) immobilized with a blend of caffeine (Caf) grafted alginate (Alg) biopolymer resulting in the formation of Caf–Alg@CeTiO4 bionanocomposite (BNC) material. The material was characterized by various instrumental techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning electron microscope– Electron dispersive X-ray (SEM-EDX), Transmission electron microscope (TEM), Brunauer, Emmett and Teller (BET), X-ray photoelectron spectroscopy (XPS) and Ultraviolet–visible (UV–VIS) spectroscopy. The XRD data and results suggested the presence of anatase phase of TiO2 which is a little bit mitigated due to doping of Ce4+ at the grain sides resulting in an orthorhombic structure with 16.23 nm crystallite size. Further, the material was probed as a photocatalyst to degrade methylene blue (MB) under visible solar radiation. The antagonistic and synergistic effects of reaction variables like irradiation time (30–60 min), pH (6–10), MB concentration (50–100 mg L−1), and catalyst dose (0.5–1.5 g L−1) on MB degradation was designed by a combination of statistical model response surface methodology (RSM) and Box-Behnken design (BBD). The statistically optimized results with minimum error were computed as irradiation time as 50 min, pH as 6.6, MB concentration as 98.60 mg L−1 and catalyst dose as 0.57 g L−1 with maximum MB degradation of 98%. The kinetic studies revealed that the photocatalytic degradation process followed pseudo-first-order path associated with Langmuir- Hinshelwood (L-H) kinetic model. The values of intrinsic coefficient (kr) and adsorption constant (ks) were found to be 0.22 mg L−1 min−1and 0.48 L mg−1 respectively. Trapping experiments revealed peroxide radical (O2− radicals) as primary reactive oxygen species (ROS) for 98% degradation of MB under visible solar radiation.