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[Display omitted] • Cobalt doped Fe 2 O 3 nanospheres were synthesised via a solvothermal route. • 3% cobalt doping was most efficient for peroxymonosulfate activation in degradation of p-hydroxybenzoic acid. • Identification of free radicals was done by quenching tests and electron paramagnetic resonance spectra. • Detailed mechanistic studies on peroxymonosulfate activation and degradation pathways were performed. Environmental remediation has become more effective when using nanotechnologies. In this study, iron oxide (α-Fe 2 O 3) nanospheres with different cobalt doping levels (xCo-Fe 2 O 3) were synthesised and applied in the heterogeneous activation of peroxymonosulfate (PMS) for the degradation of p-hydroxybenzoic acid (p-HBA). The catalyst (3Co-Fe 2 O 3) with 3% Co doping exhibits the best performance for PMS activation, possibly because of the larger specific surface area and the tailored catalyst surface as confirmed by X-ray photoelectron spectroscopy (XPS). Reaction parameters were investigated to optimise the degradation efficiency. The metal ions leaching tests confirmed the higher stability of the catalyst, thanks to the leaching suppression by the doping of Co2+. The main contribution of free radicals (SO 4 •- and •OH) was confirmed by electron paramagnetic resonance (EPR) spectra, whereas partial contribution of oxygen anions and singlet oxygen (O 2 •-, 1O 2) was observed during the quenching tests. Finally, a radical based degradation mechanism was proposed for the removal of p-HBA. It is expected to open up a novel perspective for the application of iron oxide as a potential catalyst for the removal of emerging contaminants. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel g-C 3 N 4 /Fe 2 O 3 /rGO ternary composite was synthesised using a hydrothermal process. • The catalyst exhibits a high photocatalytic oxidation efficiency for the removal of sulfamethoxazole. • Reactive oxygen species were identified by quenching tests and electron paramagnetic resonance spectra. • Detailed mechanistic studies were performed to deduce the radical and non-radical degradation pathways. Rational design of semiconductor photocatalysts is an effective way to achieve efficient visible-light-driven environmental remediation. Herein, a series of graphitic carbon nitride (g-C 3 N 4) engineered hematite (Fe 2 O 3)/reduced graphene oxide (rGO) photocatalysts were synthesised and employed in visible-light-driven photo-Fenton-like degradation of sulfamethoxazole (SMX). The exceptional performance of the optimal photocatalyst (0.4-FerGCN-3) was achieved because of the successful structural integration of g-C 3 N 4 /Fe 2 O 3 /rGO for efficient separation and migration of photoinduced charge carriers (e−/h+). Photochemical decomposition efficiency was also optimised by analysing the important reaction parameters such as initial catalyst loading, initial H 2 O 2 dosage, pH, and reaction temperature. Detailed studies on the generation of reactive species and degradation intermediates were performed to propose a possible mechanism for SMX degradation. The findings may provide not only a strategy for nanostructure engineering of semiconductor photocatalysts but also insights into the effective remediation of emerging contaminants such as SMX. [ABSTRACT FROM AUTHOR]

Over the past few years, advanced oxidation processes (AOPs) have shown promising efficiencies for wastewater remediation. Carbocatalysis, in particular, has been exploited widely thanks to its sustainable and economical properties but has an issue of recovery and reusability of the catalysts. To address this, three-dimensional (3D) binary and ternary graphene-based composites in the form of macro discs were created to activate peroxymonosulfate (PMS) for catalytic oxidation of sulfamethoxazole (SMX). Graphene oxide served as the base, while graphitic carbon nitride (g-C 3 N 4) and/or single-walled carbon nanotubes (SWCNTs) were added. Among the various discs synthesized, rGNTCN discs (ternary composite) were proven to be the most efficient by completely degrading SMX in 60 min owing to their large surface area and nitrogen loading. The catalytic system was further optimized by varying the reaction parameters, and selective radical quenching and electron paramagnetic resonance tests were performed to identify the active radical, revealing the synergistic role of both radical and non-radical pathways. This led to the development of possible SMX degradation pathways. This research not only provides insights into ternary carbocatalysis but also gives a novel breakthrough in catalyst recovery and reusability by transforming nanocatalysts into macro catalysts. [Display omitted] • Novel graphene-based binary and ternary macro discs were fabricated. • The discs can activate peroxymonosulfate (PMS) for catalytic oxidation. • The identification of dominant reactive species was conducted. • PMS activation and sulfamethoxazole degradation pathways were illustrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-doped reduced graphene oxide beads (NrGOb) were fabricated by a one-step self-assembly strategy. • The lightweight NrGOBs and peroxymonosulfate system presented high activity in oxidative degradation of organic pollutants. • The catalytic beads were packed in a fixed-bed column reactor to maintain a continuous process. • Reactive radicals were identified by the quenching tests and electron paramagnetic resonance spectra. • Mechanistic studies on peroxymonosulfate activation and degradation pathways of hydroxybenzoic acid were performed. Metal-free graphene-based catalysts have demonstrated excellent performance in advanced oxidation processes (AOPs). However, the recovery and reusability of these nanocatalysts are still a major issue. In this study, three dimensional (3D) nitrogen-doped reduced graphene oxide beads (NrGOb) were synthesized via a self-assembly method and then applied in heterogeneous activation of peroxymonosulfate (PMS) for the oxidation of hydroxybenzoic acid (HBA). The materials (NrGOb) were annealed at various temperatures ranging from 500 to 1000 °C, and the resulting NrGOb derived from 800 °C (NrGOb-800) exhibited the best performance for PMS activation. To avoid the challenging recovery, the degradation experiments were also performed in a packed-bed catalytic reactor. Various reaction parameters were investigated to optimize the efficiency of the system. Electron paramagnetic resonance (EPR) and quenching tests were carried out to differentiate the contribution of reactive radicals (SO 4 •- and •OH) in the degradation process and then aided in illustrating the degradation mechanism. Finally, the stability and reusability of the catalytic beads were investigated. The efficiency slightly declined with increased cycles; however, catalyst regeneration would be able to partially restore the active sites. The results suggest the feasibility of exploiting graphene-based macrostructures on the AOPs platform for the degradation of organic pollutants in commercial wastewater treatment plants. [ABSTRACT FROM AUTHOR]