Enhanced Activity And Mechnism Of Potassium And Iodine Co-doped G-C₃N₄ For Photocatalytic Hydrogen Evolution

Semiconductor photocatalytic water splitting using solar energy has been considered one of the most promising ways to deal with the global energy crisis.Semiconductor-based photocatalyst with high activity and good stability is the most important factor influencing photocatalytic activity.Graphitic carbon nitride?g-C₃N₄?has been confirmed as a promising photocatalyst for hydrogen evolution,on account of its advantages of visible light response and good stability.However,there are some drawbacks that limit its application,such as relatively large band gap,fast charge carrier recombination and low specific area.Apparently,it is urgent to develop novel g-C₃N₄-based photocatalysts which overcome the shortcomings mentioned.In the current work,potassium and iodine co-doped graphitic carbon nitride?CN-KI?photocatalysts were prepared via thermal polymerization.Several techniques were employed to characterize the CN-KI photocatalysts and elucidate the mechanisms of the K and I co-doping.It was found that both the doped potassium and iodine play a vital role in the improvement in photocatalytic activity,the former of which accelerates charge transport,and the latter conduces to visible light response.The K and I co-doped g-C₃N₄ photocatalyst exhibited advantageous photocatalytic activity over the K doped and I-doped ones on account of the synergistic effect of K and I doping.In addition,an optimal mass fraction of KI was ensured to be 0.06 via a series of photocatalytical activity tests.Based on the research above,the potassium and iodine co-doped mesoporous g-C₃N₄-based photocatalyst?MP-CN-KI?was constructed via the one pot thermal polymerization of a mixture using dicyandiamide as precusor,KI?the optimal mass ratio?as dopant,and SBA-15 as the hard template.It was shown that MP-CN-KI consists of ordered mesoporous channels,which enlarged surface area of the photocatalyst.A blue shift of the optical absorption band edge originated from the mesoporous structure was compensated for by the red shift induced by the co-doping with K and I.Besides,MP-CN-KI exhibits longer life time of carries,faster charge transport,and higher photocurrent density thanks to a synergistic effect between the formation of the mesoporous structure and the co-doping with K and I.The synergistic effect make the K and I co-doped mesoporous g-C₃N₄ photocatalyst achieves a high hydrogen evolution rate of 80.58 ?mol /h,9.7 times as high as that for pristine g-C₃N₄.In a word,cation-anion co-doping could provide an effective method for improving the photocatalytic activity of g-C₃N₄-based photocatalysts.Furthermore,the integration of different modification strategies,such as morphology control and cation-anion co-doping,can be a feasible way to develop novel g-C₃N₄-based photocatalysts with much enhanced photocatalytic activity.