Template free mild hydrothermal synthesis of core-shell Cu₂O(Cu)@CuO visible light photocatalysts for N-acetyl-para-aminophenol degradation

Solar photocatalytic processes are a promising approach to environmental remediation, however their implementation requires improvements in visible light harvesting and conversion and a focus on low cost, Earth abundant materials. Semiconducting copper oxides are promising visible light photocatalysts for solar fuels and wastewater depollution. Here we report the mild, hydrothermal (template-free) synthesis of core-shell Cu₂O(Cu)@CuO photocatalytic architectures for the visible light photocatalytic degradation of N-acetyl-para-aminophenol (APAP). Hollow and rattle-like core-shell nanosphere aggregates with diameters between 200 nm and 2.5 μm formed under different synthesis conditions; all comprised an inner Cu₂O shell, formed of 10-50 nm nanoparticles, surrounded by a protective corona of CuO nanoparticles. High reductant and structure-directing agent concentrations promoted the formation of a yolk-like Cu₂O/Cu core, associated with improved photophysical properties, notably a high oxidation potential and suppressed charge carrier recombination, that correlated with the highest apparent quantum efficiency (8%) and rate of APAP removal (7 μmol g^-1 min^-1). Trapping experiments demonstrated hydroxyl radicals were the primary active species responsible for APAP oxidation to quinones and short chain carboxylic acids. Rattle-like core-shell Cu₂O/Cu@CuO nanospheres exhibited excellent physiochemical stability and recyclability for APAP photocatalytic degradation.