The global scarcity of freshwater and its increasing microbial contamination pose significant public health risks. Traditional disinfection methods like UV, ozone, and chlorination have limitations, including the generation of harmful byproducts and limited effectiveness against certain biohazards. Advanced oxidation processes (AOPs), particularly those using persulfate, offer a promising alternative due to their superior inactivation capabilities and reduced byproduct formation. Peroxymonosulfate (PMS), activated by transition metal catalysts, is particularly attractive for its wide pH adaptability and ease of activation. Cobalt-based catalysts are highly effective but suffer from leaching and recovery issues. Homogeneous catalytic systems, which use soluble cobalt, are undesirable due to the high toxicity of cobalt and the difficulty of separation from the purified water. This work focused on developing a heterogeneous cobalt catalyst that overcomes these limitations using a membrane system for easy recycling. The specific aims were to address cobalt leaching and create a scalable and stable AOPs system. Heterogeneous cobalt-based catalysts have been developed to reduce metal leaching, however these typically involve cumbersome and expensive recovery methods such as magnetic separation or filtration. The use of carbonaceous materials, particularly nitrogen-doped carbon materials, has been explored to further reduce the leaching problem and improve the catalytic performance of the process. The work developed a continuous flow reactor to address the scalability issues typically associated with previous AOPs systems, which greatly limited their applicability.

The literature extensively supports the efficacy of PMS-based AOPs for water disinfection. However, challenges remain in catalyst stability and the efficient recovery of metal catalysts. Existing heterogeneous catalysts often exhibit limited stability, and recovery processes are cumbersome and costly. The combination of metal and nitrogen-doped carbon has shown promise in preventing metal ion leakage and enhancing catalytic activity, addressing the limitations of previous approaches. This approach, while showing potential, has not been thoroughly explored in a continuous flow reactor system for efficient water treatment.

The researchers synthesized Co-NC membranes via a chemical vapor deposition (CVD) method, involving polydopamine coating of carbon cloth, cobalt ion soaking, CVD pyrolysis, and acid corrosion. For comparison, Co+NC membranes (without DCA and acid corrosion) were also prepared. Characterization techniques included X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. A custom-built flow reactor was designed to evaluate membrane performance, enabling continuous operation and easy membrane replacement. The reactor's efficiency in removing Rhodamine B (RhB) as a model organic pollutant and its long-term stability were tested at different flow rates. The sterilization capability was evaluated using *Escherichia coli* (E. coli) and *Staphylococcus aureus* (S. aureus) as model microorganisms. The concentration of leached Co ions was measured using Inductively Coupled Plasma (ICP) spectroscopy. The influence of various experimental conditions—including PMS concentration, pH, flow rate, presence of inorganic anions, humic acid concentration, and different water sources (deionized water, river water, lake water)—on bacterial inactivation was systematically investigated. Fluorescence microscopy, SEM, and various biochemical assays were used to elucidate the mechanism of bacterial inactivation. Reactive oxygen species (ROS) scavenging experiments identified the dominant active species. HPLC was used to quantify PMSO and PMSO2 to confirm the role of high-valence cobalt.

The Co-NC membrane exhibited superior catalytic activity and stability compared to Co+NC membranes. The Co-NC membrane demonstrated a remarkable 99.9999% sterilization efficiency against *E. coli* with minimal cobalt leaching (below the detection limit of ICP after six filtration cycles). After 40 repeated cycles (240 filtration cycles), the membrane retained 96.29% of its initial activity, demonstrating excellent long-term stability. The high performance of the system was maintained even at high flow rates (up to 1448 L m⁻²h⁻¹). The system demonstrated effective RhB degradation (100% after one filtration cycle). In contrast, Co+NC exhibited significant Co leaching and reduced stability after 40 cycles. The system showed effective sterilization against both Gram-negative (*E. coli*) and Gram-positive (*S. aureus*) bacteria. Experiments with varying PMS concentrations, flow rates, and the presence of various inorganic anions (Cl⁻, NO₃⁻, SO₄²⁻, PO₄³⁻) indicated that the system maintained high efficiency under different conditions; however, increasing the flow rate reduced the disinfection efficiency. The presence of humic acid and varying water sources (deionized water, river water, and lake water) had little effect on the performance of the system. Mechanistic studies indicated that high-valence cobalt (Co=O) is the primary active species responsible for bacterial inactivation, initiating lipid peroxidation and subsequent cell membrane damage, also resulting in DNA leakage, K+ leakage, and ATP depletion. The system was successfully tested in real river water samples (Qiuxi River), achieving consistent high sterilization and organic pollutant removal efficiency for up to 12 hours of continuous operation. The results suggest the high valence cobalt-oxygen species is the dominant active specie, which attacks the cell membrane and destroys intracellular components of *E. coli*.

The findings demonstrate the successful development of a highly efficient and stable heterogeneous catalyst for PMS activation in water disinfection. The Co-NC membrane's superior performance compared to the Co+NC membrane highlights the importance of nitrogen doping and the encapsulation of cobalt nanoparticles within the carbon nanotubes in preventing cobalt leaching and enhancing catalytic activity. The continuous flow reactor design addresses scalability concerns, making this technology suitable for practical applications. The system's resilience to various water conditions, including the presence of inorganic anions and humic acid, suggests broad applicability. The mechanistic studies provide valuable insights into the role of high-valence cobalt species in bacterial inactivation. The successful application of the Co-NC/PMS system in real river water demonstrates the system's potential for large-scale water treatment applications.

This study successfully developed a highly efficient and stable Co-NC membrane for water disinfection using PMS-based AOPs. The continuous flow reactor design and the membrane's resilience to various water conditions and long-term operation indicate its suitability for large-scale industrial applications. Future research could focus on optimizing the membrane synthesis process, exploring other metal-carbon composites, and conducting long-term field studies to assess the technology's real-world performance and environmental impact.

While the study demonstrates excellent performance under controlled conditions, further research is necessary to fully assess the system's long-term durability in diverse real-world scenarios, including different types of water matrices, varying temperatures, and the presence of other pollutants. Cost-effectiveness and scalability for industrial implementation also need comprehensive evaluation. The study primarily focused on *E. coli* and *S. aureus*; a broader range of microorganisms needs to be tested for a complete assessment of the system's efficacy.