Constructing Type-II and S-Scheme Heterojunctions of Cu2O@Cu4(SO4)(OH)6•H2O Polyhedra by In Situ Etching Cu2O with Different Exposed Facets for Enhanced Photocatalytic Sterilization and Degradation Performance

The construction of type-II or S-scheme heterojunctionscan effectivelyaccelerate the directional migration of charge carriers and inhibitthe recombination of electron-hole pairs to improve the catalyticperformance of the composite catalyst; therefore, the constructionand formation mechanism of a heterojunction are worth further investigation.Herein, Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O core-shell polyhedral heterojunctionswere fabricated via in situ etching Cu2O with octahedral,cuboctahedral, and cubic shapes by sodium thiosulfate (Na2S2O3). Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O polyhedral heterojunctionsdemonstrated obviously enhanced sterilization and degradation performancethan the corresponding single Cu2O polyhedra and Cu-4(SO4)-(OH)(6)center dot H2O. WhenCu(2)O with a different morphology contacts with Cu-4(SO4)-(OH)(6)center dot H2O, a built-inelectric field is established at the interface due to the differencein Fermi level (E (f)); meanwhile, the directionof band bending and the band alignment are determined. These leadto the different migration pathways of electrons and holes, and thereby,a type-II or S-scheme heterojunction is constructed. The results showedthat octahedral o-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O is an S-scheme heterojunction; however,cuboctahedral co-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O and cubic c-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O are type-IIheterojunctions. By means of X-ray photoelectron spectroscopy (XPS),ultraviolet photoelectron spectroscopy (UPS), diffuse reflectancespectra (DRS), and Mott-Schottky analyses, the band alignments,Fermi levels, and band offsets (Delta E (CB), Delta E (VB)) of Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O polyhedralheterojunctions were estimated; the results indicated that the catalyticability of the composite catalyst is determined by the type of heterojunctionand the sizes of band offsets. Cubic c-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O has the strongestdriving force (namely, biggest band offsets) to accelerate chargemigration and effectively separate charge carriers, so it exhibitsthe strongest catalytic bactericidal and degrading abilities. An S-scheme heterojunction of octahedralo-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O, and the type-II heterojunctions of cuboctahedral co-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O and cubic c-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O were constructed via in situetchingCu(2)O with octahedral, cuboctahedral, and cubic shapes.The results indicated that c-Cu2O@Cu-4(SO4)-(OH)(6)center dot H2O has the strongest drivingforce (Delta E (CB), Delta E (VB)) to accelerate charge migration and effectively separatecharge carriers, so exhibits the highest catalytic bactericidal anddegrading abilities.