Nanoconfinement in advanced oxidation processes

Advanced oxidation processes (AOPs) based on the generation of reactive radicals are widely accepted to be effective technologies for mineralizing refractory organic contaminants or pretreating bio-recalcitrant compounds. The efficiencies of AOPs suffer from the low availability of ultrashort lifetime radicals due to their rapid self-quenching, mass transfer and nonselective limitations. Heterogeneous AOPs are hampered due to the declining activity and stability of catalysts resulting from aggregation, leakage and poisoning. The effectiveness, selectivity and reactivity of highly reactive species of AOPs can be greatly enhanced when the oxidation reactions are conducted in confined nanospaces. The stability, accessibility, variety and activity of nanoconfined catalysts would be improved by confining the nanoparticle catalysts inside porous scaffolds or substrates. Other confined systems, such as surface confinement, quantum confinement and electron confinement, have also been applied in different AOPs to improve the contaminant degradation performance. The above-mentioned nanoconfinement applications in AOPs are systematically summarized in this critical review. Prospects and challenges are presented to stimulate future interest and breakthroughs for nanoconfinement in AOPs.