Molecular Structure Regulation Of Graphitic Carbon Nitride For Photocatalytic Hydrogen Evolution

Nowadays,environmental pollution and energy shortage emerge with the development of society.It is essential to develop a kind of green and renewable energy to replace traditional fossil fuel.As a clean energy carrier,hydrogen has the advantages of non-toxic,non-polluting,renewable,and high combustion heat,with product of water only after burning.By virtue of the above-mentioned merits,hydrogen energy can meet the sustainable development needs of today's society.To date,semiconductor photocatalysis technology can transform the continuous solar energy into hydrogen,which is acknowledged to a very worthwhile way to obtain hydrogen energy.A key component of the technology is to find an environmentally friendly and efficient semiconductor catalyst.Graphite-like carbon nitride?g-C₃N₄?,as a kind of non-metallic organic semiconductor material,has attracted tremendous attentions of scientific community with the characteristics of visible light response,high thermal stability and chemical stability.However,g-C₃N₄suffers from the following shortcomings:weak light absorption,small specific surface area and fast recombination of photogenerated electron-hole pairs.In view of the defects of g-C₃N₄,aniline,2-aminopyridine and o-phthalimide were used to graft on g-C₃N₄in order to modify the molecular structure of carbon nitride.Therefore,semiconducting photocatalysts with strong light absorption ability and high separation efficiency of photogenerated electron-hole pairs were prepared.The main research work of this paper is as follows:?1?The extended?-conjugated g-C₃N₄catalysts?UCN-AB,UCN-APy?were obtained by incorporating 3-Aminobenzoic acid?AB?and 6-aminopyridinecarboxylic acid?APy?into the g-C₃N₄framework during one-step process at low temperature.The chemical composition and morphology of the catalysts were characterized using FTIR,XPS,EA,XRD,¹³C NMR,SEM and TEM.Benefiting from the enhanced absorption ability induced by the conjugated effect,UCN-AB and UCN-APy showed higher photocatalytic activity than UCN.In addition,APy can quickly capture the photogenerated charge from g-C₃N₄due to the electron pulling effect,thus effectively separating the photogenerated electrons and holes.Upon modification of the molecular structure,the highest hydrogen production rates of UCN-APy and UCN-AB catalysts are 133.2 and 104.0?mol·h^-1,which are 5 and 4 times of that of pure carbon nitride,respectively,without obvious attenuation within 16 h,showing high stability.?2?A new composite photocatalyst CCN-Ni PI?SCN?was successfully prepared by amide condensation between phthalimide?PI?and g-C₃N₄,followed by complexation with Ni²⁺and SCN^-at low temperature.The chemical composition and morphology of the catalysts were assayed by FTIR,XPS,XRD,SEM and TEM.The PI molecule can adjust the band structure by the positive shift of VB,then reduce the bandgap and improve the visible light response.After the combination,there is a new internal electric field that promotes the electron migrate from CN to PI and Ni²⁺.Based on the above analysis,the photocatalytic activity can be improved theoretically by the enhanced optical properties and accelerated charge transfer rate.Under the irradiation of visible light,pure carbon nitride exhibits no photocatalytic activity for hydrogen production.However,the CCN-Ni PI?SCN?catalyst shows higher hydrogen production performance,up to 21.6?mol h^-1,and has no obvious attenuation within16 h.