Homodispersed B-CN/P-CN S-scheme homojunction for enhanced visible-light-driven hydrogen evolution

Proper interface and band alignment always play essential roles in the separation of photoexcited charge of photocatalysts.In this work,we prepared a homodispersed S-scheme carbon nitride homojunction with local electron structure difference by a facile pre-doping and two-step calcination approach.Boron doping into heptazine created extra acceptor impurity,and phosphorus doping into heptazine created extra donor impurity,which eventually modulated the electronic structure of carbon nitride.As heptazines with different element doping were integrated into carbon nitride by recalcination,B-CN and P-CN formed a homodispersed homojunction and thus produced a rich interface.Meanwhile,caused by Fermi energy levels equilibrium,the band bending constructed an S-scheme homojunction,which stimulated photogenerated electrons to transfer from CB of B-CN to VB of P-CN.The homodispersed S-scheme homojunction structure led to efficient suppression of recombination of photoinduced charge and retained stronger redox charge.Consequently,the photocatalytic performance was dramatically boosted to 2620 μmol g^(-1) from 60 μmol g^(-1) of pure CN in 4-h hydrogen evolution from water.This novel method for electron structure engineering helped to provide a new strategy for designing homojunction photocatalysts with excellent photocatalytic performance.

One step method of structure engineering porous graphitic carbon nitride for efficient visible-light photocatalytic reduction of Cr(Ⅵ)

Porous g-C_(3)N_(4)nanosheets(PCN)were prepared by the nickel-assisted one-step thermal polymerization method.Hydrogen(H2)which was produced by the reaction between nickel(Ni)foam and ammonia(NH3)defined the structure and properties of PCN.During the formation of PCN,the participation of H2 not only enhanced the spacing between layers but also boosted the specific surface area that more active sites were exposed.Additionally,H2 promoted pores formation in the nanosheets,which was beneficial to the transfer of photons through lamellar structure and improved the absorption efficiency of visible light.Remarkably,the obtained PCN possessed better Cr(Ⅵ)photocatalytic reduction efficiency than pure g-C_(3)N_(4).The reaction rate constant(k)of PCN(0.013 min-1)was approximately twice that of bare g-C_(3)N_(4)(0.007 min-1).Furthermore,the effects of original pH and concentration of Cr(Ⅵ)-containing solution on re moval efficiency of Cr(Ⅵ)were explored.A possible photocatalytic mecha nism was proposed based on the experiments of radical scavengers and photoelectrochemical characterizations.

One-step fabrication of nitrogen-deficient carbon nitride through pyrolysis of melamine and 1,2,4-triazole for its enhanced photocatalytic degradation

The construction of defects in semiconductor photocatalysts,as a kind of modification methods,plays an indispensable role in the enhancement of the photocatalytic performance.Herein,nitrogen defects were successfully introduced into the framework of graphite carbon nitride(CN-T_(x))through thermal polymerization with melamine and 1,2,4-triazole as precursors.The existence of nitrogen defects in CN-T_(x) were confirmed to be located at the two-coordinated(N_(2c))C■N-C lattice sites,which resulted in the destruction of its planar structure and the initiation of n-π^(*)electron transition that greatly expanded the response range to visible light and improved the separation efficiency of photogenerated charge carrier.More significantly,CN-T_(x) could enhance photocatalytic water purification activity towards different kinds of pollutants.The photocatalytic rates of CN-T_(3) were estimated to be 2.54(tetracycline)and 2.31(2-hydroxynaphthalene)times higher than those of pristine g-C3N4.Furthermore,the possible photocatalytic degradation mechanism over CN-T_(x) photocatalyst was proposed by free radical trapping experiments combined with ERS characterization.This work provides an in-depth understanding of the important role of nitrogen defects in the electronic structure and chemical properties of g-C3N4 and its photocatalytic water purification performance.