A novel structured graphene oxide@microalgae nanohybrids as adsorbents for removal of Cr(VI) ions in aqueous solutions

Novel structured graphene oxide@microalgae-based nanohybrids have been prepared by incorporating green microalgae biomass (Algae) with graphene oxide (GO) or N-doped graphene oxide (NGO) in different ratios (e.g., 3:1, 1:1 and 1:3). Biogenic GO-Algae and NGO-Algae nanohybrids were synthesized via a self-assembly method. Morphological and structural characterizations and adsorption performance of the nanostructured material towards Cr(VI) species were studied extensively. The removal of Cr(VI) species by GO-Algae and NGO-Algae nanohybrids was highly pH dependent, with the maximum adsorption removal occurring at pH 2. The results indicate that the adsorption of Cr(VI) by GO-Algae and NGO-Algae nanohybrids was as follows: GO@Algae-3:1 (90.5%) < GO@Algae-1:1 (98.7%) < GO@Algae-1:3 (99.6%) and NGO@Algae-3:1 (79.2%) < NGO@Algae-1:1 (82.3%) < NGO@Algae-1:3 (92.6%), respectively. The GO: Algae-1:3 and NGO: Algae-1:3 nanohybrids with a high microalgae content ratio exhibited high maximum removal, owing to the presence of more active sites within their lattice compared to their counterparts. On the other hand, pseudo-first-order, pseudo-second-order, intraparticle diffusion, Langmuir, and Freundlich models adequately simulated adsorption mechanisms, suggesting that the adsorption process involved a combination of external mass transfer and chemisorption, with electrostatic and complexation interactions being the dominant mechanisms for Cr(VI) removal. Additionally, GO@Algae-1:3 and NGO@Algae-1:3 displayed outstanding reusability. Therefore, these structured graphene@microalgae-based nanohybrids can simultaneously serve as adsorbents for Cr(VI) removal from wastewater and contaminated water sources.