Determination of Band Alignment in the Synergistic Catalyst of Electronic Structure-Modified Graphitic Carbon Nitride-Integrated Ceria Quantum-Dot Heterojunctions for Rapid Degradation of Organic Pollutants

다국어 초록 (Multilingual Abstract)

<P>We engineered novel heterojunction ceria (CeO<SUB>2</SUB>) QDs decorated on the surfaces of graphitic carbon nitride (g-C<SUB>3</SUB>N<SUB>4</SUB>) nanosheets by a facile in situ hydrothermal synthetic route. Using core-level/valence-band X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy, and work function measurements of the materials, we constructed the energy band alignment at the heterojunction. The band alignment has a Type-II alignment between organic (g-C<SUB>3</SUB>N<SUB>4</SUB>) and inorganic (CeO<SUB>2</SUB> QDs) semiconductors junction with valence/conduction band offsets (VBO/CBO) of −0.07/–0.31 eV. The calculated band alignment parameters of the heterojunction were compared with the experimental values of g-C<SUB>3</SUB>N<SUB>4</SUB>/CeO<SUB>2</SUB> QD composite and a new energy band diagram was proposed for the electronic structure-modified g-C<SUB>3</SUB>N<SUB>4</SUB>/CeO<SUB>2</SUB> QDs heterojunction. The newly constructed heterojunction is formed by carbon-vacancy-promoted g-C<SUB>3</SUB>N<SUB>4</SUB> coupled to lower defect-mediated (oxygen vacancies) CeO<SUB>2</SUB>, as determined by high-resolution XPS analysis. Moreover, the CeO<SUB>2</SUB> QD distribution on g-C<SUB>3</SUB>N<SUB>4</SUB> sheets using HR-TEM and the lattice parameter variations of g-C<SUB>3</SUB>N<SUB>4</SUB>/CeO<SUB>2</SUB> QDs as compared with those of pristine CeO<SUB>2</SUB> QDs from Rietveld refinement were investigated. To demonstrate the ability of the proposed heterojunction as a catalyst, we tested the catalytic activity of the composite junction for the degradation of Rhodamine B (RhB) in the presence of NaBH<SUB>4</SUB> as an example. The band alignment mechanism is useful for promoting the catalytic activity of the graphitic carbon nitride-based organic semiconductor and will attract researchers’ attention for developing new composite heterojunction catalysts for multifunctional applications.</P><P><B>Graphic Abstract</B>
<IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2017/jpccck.2017.121.issue-45/acs.jpcc.7b08568/production/images/medium/jp-2017-08568k_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b08568'>ACS Electronic Supporting Info</A></P>