Aligned α-FeOOH nanorods anchored on a graphene oxide-carbon nanotubes aerogel can serve as an effective Fenton-like oxidation catalyst

Abstract

The self-assembled synthesis of a hierarchical graphene oxide (GO)-carbon nanotubes (CNTs)-α-FeOOH decorated composite aerogel (α-FeOOH@GCA) through a facile in-situ hydrolysis route is reported for the first time and the materials was tested for its performance as Fenton-like catalyst. The introduction of GO-CNTs clearly mediated the morphology to aligned α-FeOOH nanorods (ca. 100nm) within aerogel matrix comparing with pristine urchin-like α-FeOOH three-dimensional microstructures (ca. 1μm). This three dimensional porous aerogel network provided efficient charge/mass-transfer leading to great enhancement of the catalytic activity of α-FeOOH. The outstanding catalytic performance of this composite in degradation of organics with different charge and structure, i.e. Orange II (OII), rhodamine B (RhB), methylene blue (MB), phenol and endocrine disruptor bisphenol A (BPA) was demonstrated. For example, the discoloration of OII with pseudo first-order rate constant of 0.10min−1 significantly exceeded that of pristine α-FeOOH. At relatively low concentration of α-FeOOH@GCA catalyst (125mgL−1) and H2O2 (0.55mM) showed excellent catalytic activity for efficient (∼99%) discoloration of OII (40mgL−1) under a 60min UV365 irradiation in the pH range 3–10. The different charge of five target contaminats greatly determined the surface-catalyzed degradation kinetics at natural solution pH in the order of cationic>neutral>anionic organics due to the negatively charged carbon-based aerogel matrix. The new identified desulfonation intermediates elucidated through UPLC–MS analysis indicated two reaction pathways: 1) hydroxylation and 2) desulfonation by-products followed by cleavage of the azo bond as the predominant degradation pathway of OII. The elimination of the acute toxicity of the parent contaminant to luminescent bacterium Q67 was consistent with the formation of less toxic degradation by-products identified. Free radical quenching studies accessed the role of hydroxyl radical (OH), superoxide anion radical (O2−) and singlet oxygen (1O2) as the dominating reactive oxygen species (ROS). The quantitative studies to measure radical concentrations using relative molecular probes showed the effective activation of H2O2 led to high rate production of ROS accounted for OII degradation. The greatly enhanced photocatalytic property of this hybrid was correlated with the efficient conversion between Fe2+/Fe3+ and synergistic coupling between α-FeOOH and carbon-based aerogel matrix evidenced through the formation of FeOC chemical bonds was verified by X-ray photoelectron (XPS) analysis. Based on its simple and scalable preparation route as well as its excellent UV365 or visible light-responsive catalytic performance, this hybrid exhibits a high potential to be used as an efficient and environmental-friendly catalyst for water remediation.