Recently metal-free catalysts become very promising in environmental catalysis own to the nature of being free of metals for avoiding metal leaching-related secondary contamination. Herein, a series of boron and nitrogen co-doped graphene nanotubes were first synthesised by thermal treatment of urea, boric acid, and polyethene glycol (PEG, 2000). The materials fabricated under varied thermal conditions, e.g., different pyrolysis temperature and retention time, were characterised through advanced physiochemical techniques. The as-prepared materials showed outstanding catalytic activity for degradation of 4-hydroxybenzoic acid (HBA) via peroxymonosulfate (PMS) activation, whereas the catalyst pyrolysed at 1100 ​°C for 6 ​h (BNG-1100-6h) was found to be the best candidate for environmental remediation, thanks to its engineered surface, exposed active sites, and well-tuned functional groups. Based on the optimal carbocatalyst, reaction conditions such as catalyst loading, PMS dosage, solution pH, and reaction temperature were thoroughly investigated to make it a cost-effective catalytic system. A thermal regenerative path was adopted to enhance the catalyst stability and reusability. Quenching tests and electron paramagnetic resonance (EPR) spectroscopic analysis further revealed the dominant role of singlet oxygen (¹O₂), a non-radical reactive species, in the degradation of HBA. The current research work will not only provide a facile strategy for development of a carbocatalytic system but also open a new perspective for degradation of emerging contaminants such as HBA via a non-radical route.

Two−dimensional (2D) supports confined single−atom catalysts (2D SACs) with unique geometric and electronic structures have been attractive candidates in different catalytic applications, such as energy conversion and storage, value−added chemical synthesis and environmental remediation. However, their environmental applications lack of a comprehensive summary and in−depth discussion. In this review, recent progresses in synthesis routes and advanced characterization techniques for 2D SACs are introduced, and a comprehensive discussion on their applications in environmental remediation is presented. Generally, 2D SACs can be effective in catalytic elimination of aqueous and gaseous pollutants via radical or non−radical routes and transformation of toxic pollutants into less poisonous species or highly value−added products, opening a new horizon for the contaminant treatment. In addition, in−depth reaction mechanisms and potential pathways are systematically discussed, and the relationship between the structure−performance is highlighted. Finally, several critical challenges within this field are presented, and possible directions for further explorations of 2D SACs in environmental remediation are suggested. Although the research of 2D SACs in the environmental application is still in its infancy, this review will provide a timely summary on the emerging field, and would stimulate tremendous interest for designing more attractive 2D SACs and promoting their wide applications.