Unexplored role of nanoconfinement in regulating contaminant oxidation pathways for water decontamination: Confined energy driving low-carbon route

Advanced oxidation processes (AOPs) are highly effective for removing emerging contaminants from water. However, their efficiency is often limited by sluggish catalytic oxidation, excessive input of chemicals and energy for organic mineralization, and undesirable carbon emission. Current improvements mainly focus on enhancing catalyst activation, often neglecting the elimination step of contaminants. This study presents a confined energy-drive strategy to shift the removal pathway of 2,4,6-trichlorophenol (TCP) from degradation mineralization to oxidative coupling polymerization. Nanosphere catalysts (Fe-NC-x, where x = 1, 2, 3, 4) with varying channel diameters were developed by loading iron into nanochannels of different sizes. The confined Fe-NC-1 catalytic system achieved a remarkable 99 % TCP removal within 40 min, in contrast to the 69 % removal observed with the non-confined Fe-NC-0 catalytic system. As the channel confinement decreased, the TCP removal efficiency increased. This enhanced performance is attributed to the in-situ confined energy generated by Fe-NC-1 nanochannels (< 5 nm), which promotes peroxydisulfate pre-adsorption and accelerates electron transfer between peroxydisulfate and the catalyst. Furthermore, the confined energy stabilizes the oxidation transition state of TCP, favoring the low-energy barrier coupling polymerization pathway. This study provides a green and sustainable strategy for AOPs through confined energy-driven, low-carbon methods for water purification and organic carbon recovery.