Structure Design Of Graphite-like Carbon Nitride For Photocatalytic Hydrogen Production

Nowadays,greenhouse gases,carbon sinks,air pollution,global temperature warming are hot topics.As a large number of fossil fuels are consumed,a series of environmental issues frequently remind people of green development.Therefore,formulating an action plan for peaking carbon emissions and optimizing the energy structure has become one of the development plans of many governments.Using semiconductor photocatalytic technology to convert solar energy into hydrogen energy is one of the potential solutions for optimizing the energy structure in the future.As a layered conjugated polymer material,graphite-like carbon nitride（g-C₃N₄）has attracted wide interest due to its unique structure,stability and suitable band gap.However,the realization of high-efficiency photocatalytic water splitting requires a series modification of g-C₃N₄ to overcome shortcomings such as severe photo-generated electron/hole recombination and low visible light utilization.Based on the construction of the electronic push-pull unit,this paper constructed a sp hybrid carbon bridged g-C₃N₄-based D-π-A photocatalysts;then constructed the electronic push-pull unit and the nickel complex as hydrogen release center on g-C₃N₄ to achieve Non-noble metals assist photocatalytic hydrogen release.The main contents are as follows.（1）The sp hybrid carbon bridged g-C₃N₄-based D-π-A photocatalyst（UCN-BTD）was synthesized by successive coupling bromopropyne and benzothiadiazole into g-C₃N₄ terminal amino groups during two-step process at mild conditions.The conjugated structure of the alkynyl group not only facilitates the charge transfer between the donor and the acceptor,but also promotes the dispersion and deposition of the co-catalyst.Modulating terminal receptors can effectively improve the light response and surface carrier transfer of g-C₃N₄.The optimized UCN-BTD exhibited a remarkably H₂ evolution rate(122μmol h^-1),which is nearly five times of that of the pristine g-C₃N₄.Moreover,it is found that the stronger electronegativity of the acceptor unit exhibits an adverse effect on the activity of hydrogen production.（2）The CN-NiL₂ composite photocatalyst was successfully synthesized by grafting nickel molecular catalyst（NiL₂）into g-C₃N₄ terminal amino groups through amidation.The terminal carbonyl thiophene not only forms an electron push-pull structure with g-C₃N₄ to accelerate the separation of photogenerated electrons and holes,but also provides O and S coordination sites to construct a non-noble metal hydrogen release catalytic center.The optimized CN-NiL₂catalyst exhibited excellent photocatalytic hydrogen production performance(20.7μmol·h^-1)and high stability without precious metal co-catalyst.