Functionalization of polymeric carbon nitride for solar fuels production
As a low-cost metal-free photocatalyst, polymeric carbon nitride (PCN) has attracted tremendous research attentions due to its visible light activities and tailorable molecular structures. The conventional calcination approach for PCN preparation and modification normally requires high temperature above 500 oC, at which lots of functional groups are not stable. Herein, we have developed a solvothermal approach to synthesize PCN at 200 oC by using cyanuric chloride and other small molecules as precursors. The obtained PCN samples appear as microspheres with surface s-triazine-based functional groups that could contribute additional visible light absorption and promote the overall photocatalytic activities for hydrogen generation. However, if a substrate with silica or metal oxide surface is present in the solvothermal reaction, a smooth PCN film, instead of microspheres, could be grown on the substrate with excellent photoelectrochemical performance for water splitting. Further, owing to mild reaction conditions and homogeneous mixing of precursors, the solvothermal approach allows for uniform elemental-doping and surface functionalization of PCN. In particular, we have demonstrated a copolymerization process to covalently graft pyrene-functional groups on the PCN surface. The resulted pyrene functionalized carbon nitride exhibits unique biphasic photocatalytic activities, which enables efficient CO2 photoreduction in the aqueous solution with simultaneous alkene (C=C) oxidation in the organic phase. The great biphasic activities are attributed to the increased oleophilicity from surface pyrene-functional groups that allows the hydrophobic alkene molecules to readily approach the PCN surface, and be reacted with the hydroxyl radicals created from –OH oxidation by photogenerated holes. By this way, the alkene compounds indirectly consume the photo-holes from the excited PCN, promoting the overall photocatalytic processes. Our studies provide a new strategy of solar fuels production with simultaneous organic synthesis by the oxidization power of photo-holes on amphiphilic metal-free semiconductors.
Dr. Can Xue obtained B.Sc degree at University of Science and Technology of China (USTC) in 2002, and received PhD degree at Northwestern University (IL, USA) in 2007. Afterwards, he moved to Singapore in 2008 as a recipient of the Lee Kuan Yew Research Fellowship, and was appointed as assistant professor in 2009 at Nanyang Technological University, where he got promotion to tenured associate professor in September 2015.