Band Structure Engineering of Carbon Nitride: In Search of a Polymer Photocatalyst with High Photooxidation Property

The electronic band structure of a semiconductor photocatalyst intrinsically controls its level of conduction band (CB) and valence band (VB) and, thus, influences its activity for different photocatalytic reactions. Here, we report a simple bottom-up strategy to rationally tune the band structure of graphitic carbon nitride (g-C₃N₄). By incorporating electron-deficient pyromellitic dianhydride (PMDA) monomer into the network of g-C₃N₄, the VB position can be largely decreased and, thus, gives a strong photooxidation capability. Consequently, the modified photocatalyst shows preferential activity for water oxidation over water reduction in comparison with g-C₃N₄. More strikingly, the active species involved in the photodegradation of methyl orange switches from photogenerated electrons to holes after band structure engineering. This work may provide guidance on designing efficient polymer photocatalysts with the desirable electronic structure for specific photoreactions

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe₂O₃ Core–Shell Nanowire Array as Photoanode

Hematite (α-Fe₂O₃) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe₂O₃ limits the performance of α-Fe₂O₃ photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe₂O₃ nanocrystal shell (ITO@α-Fe₂O₃) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe₂O₃ nanocrystal film using chemical bath deposition (CBD) method. The <i>J</i>–<i>V</i> curves and IPCE of ITO@α-Fe₂O₃ core–shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe₂O₃ on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe₂O₃ nanocrystals in the core–shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe₂O₃ and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe₂O₃ core–shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40 000 s