Green synthesis of Z-scheme CeO2 decorated ZnO nanocomposites for photodegradation of organic pollutants, antioxidant activity and its effects on seed germination

[Display omitted] •A simple cost effective green method was used to synthesized CeO2 decorated ZnO nanocomposites marked as CZ1, CZ2 and CZ3.•CeO2@ZnO nanocomposites is highly effective catalyst for the degradation of MB, CV and RhB dyes via a Z-scheme mechanism.•CZ1 shows better photocatalytic degradation of MB dye than other synthesized samples.•CZ1 also shows better seed germination effect, amylase and protease activities compared with others. The present work aimed to report a green synthesis of CeO2@ZnO nanocomposites via co-precipitation method using azadirachta indica aqueous leaf extract. The characterization of the prepared CeO2@ZnO nanocomposites were done using XRD, FTIR, SEM, EDAX, UV–vis, and PL techniques to examine the structural properties, functional group, morphological and electronic properties. As prepared CeO2@ZnO nanocomposites have been used for photo degradation of Crystal Violet (CV), Methylene blue (MB) and Rhodamine B (RhB) dyes in presence of solar light in aqueous solution. From structural analysis the mean crystallite sizes of the synthesized nanocomposites varied from 27 nm to 9 nm. The degradation of MB, CV and RhB dyes follows pseudo-first order reaction rate with the rate constants k1 for MB is 10.09 × 10−3 min−1, k1 for CV is 8.71 × 10−3 min−1, k1 for RhB is 0.92 × 10−3 min−1. The characterized nanocomposites were used for seedling growth, physiological and biochemical responses during seed germination. In CeO2@ZnO nanocomposites treatments, significantly higher values of shoot length and root length were observed in CZ1 (0.5, and 1 mg/ml) treated seedlings as compared to other samples. Similarly, the activities of ɑ-amylase and protease enzymes were recorded to be maximum for CZ1 nanocomposites. For instance, the increased activity of α-amylase was observed to be 2.12, 2.09, and 1.33 folds higher in CZ1, CZ2, and CZ3 (1 mg/ml) treated seedlings as compared to the control. Similarly, the protease activity was reported to be increased by 0.011 folds in CZ1 nanocomposites (1 mg/ml) treated seedlings as compared to the control. Furthermore, all the CeO2@ZnO nanocomposites have excellent DPPH, and ABTS free radical scavenging activities, confirmed by the Ferric-Reducing Antioxidant Power (FRAP) assay. The CZ1 nanocomposites showed the best results. The CeO2@ZnO nanocomposites were found to have no toxic effects on cellular division confirmed with improved mitotic index under different treatment regimens.