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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] • Novel nitrogen-doped graphene cubes (NGCs) were synthesised. • The lightweight NGCs were employed for sulfamethoxazole (SMX) degradation. • Identification of reactive oxygen species was conducted. • Comprehensive mechanistic studies on SMX degradation were performed. As a sustainable and green approach, carbocatalysis, a metal-free strategy, has shown exceptional results in advanced oxidation processes (AOPs). Nonetheless, the recovery of these catalysts has been a major shortcoming over the years. Herein, three-dimensional nitrogen-doped graphene macrostructures (3D-NGMs), in the form of macro cubes, were synthesised by a simple cross-linking and thermal annealing procedure, after which they were employed in the activation of peroxydisulfate (PS) for the degradation of sulfamethoxazole (SMX). The catalytic cubes were loaded with different amounts of nitrogen precursor to investigate the role of nitrogen configuration in the sp2 hybridised carbon network on AOPs. NGC3 cubes with optimum N-loading exhibited outstanding performance for SMX degradation owing to their optimum N/C ratio. Various reaction parameters were studied to optimise the catalytic system. Comprehensive studies on the radical generation were done and illustrated the dominance of the non-radical pathway leading to the proposal of a possible reaction mechanism for SMX. This study not only suggests the role of nitrogen doping on graphene macrostructures but also provides novel insights into macro catalysis to overcome the recovery challenges posed by nano catalysis. [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]