β-Ge3N4 loaded with nanoparticulate RuO2 as a cocatalyst is the first successful non-oxide photocatalyst for overall water splitting.To get an insight into the working mechanism of this particular photocatalytic syst...β-Ge3N4 loaded with nanoparticulate RuO2 as a cocatalyst is the first successful non-oxide photocatalyst for overall water splitting.To get an insight into the working mechanism of this particular photocatalytic system,we have calculated geometrical structures of low-index surfaces forβ-Ge3N4.Analysis of surface energies indicates that the most preferentially exposed surface is(100).The band gap of surface is narrower than that of bulk due to the dangling bonds.Dissociative water adsorption on(100)surface is thermodynamically favorable.The adsorption behavior of(RuO2)n(n=2,3,and 4)clusters on theβ-Ge3N4(100)surface has been explored.It is found that all the clusters bind to(100)surface strongly by forming interfacial bonds so that the adsorptions are exothermic processes.The calculation on density of states forβ-Ge3N4(100)surface loaded with(RuO2)nclusters reveals that photo-induced electrons tend to accumulate on(RuO2)nclusters and holes tend to stay inβ-Ge3N4.Based on the theoretical indication of Type-II staggered band alignment,we have proposed that in photocatalytic water splitting reaction,oxygen evolution reaction is inclined to occur on the surface ofβ-Ge3N4 while hydrogen evolution reaction is apt to occur on(RuO2)nclusters.In a word,loading RuO2 nanoparticles as a reduction cocatalyst benefits the charge separation inβ-Ge3N4.Furthermore,attaching(RuO2)nclusters ontoβ-Ge3N4(100)surface results in the redshift of absorption edge and the increase of absorption intensity.Our calculations have reasonably explained the experimental observation on the decomposition of water into H2 and O2 after loading RuO2 cocatalyst inβ-Ge3N4 photocatalyst.展开更多
The rational fabrication of heterostructures is one of efficient strategies for improving photocatalytic performance of semiconductor photocatalysts.Very recently,Domen and co-workers found that Ta_(3)N_(5) single cry...The rational fabrication of heterostructures is one of efficient strategies for improving photocatalytic performance of semiconductor photocatalysts.Very recently,Domen and co-workers found that Ta_(3)N_(5) single crystals grown on the surface of KTaO_(3) can accomplish photocatalytic overall water splitting for the first time.In order to comprehend the underlying mechanism of this photocatalytic system,we have performed a systematic study based on density functional theory first-principles calculations.Ta_(3)N_(5)(010)/KTaO_(3)(110)slab models have been built according to experimental observations by considering two common terminations of KTaO_(3)(110)surface,named as Ta_(3)N_(5)/O_(2) and Ta_(3)N_(5)/KTaO.The formations of interfacial bonds are thermodynamically stable,showing a covalent interaction between two components of a heterostructure.Ta_(3)N_(5)/O_(2) has a higher mobility of photogenerated charge carriers and lower recombination rate of charge carriers than Ta_(3)N_(5)/KTaO.The light absorption of heterostructures displays the feature of KTaO_(3) in the short wavelength region and the characteristic of Ta_(3)N_(5) in the long wavelength region.The calculated band offsets show that Ta_(3)N_(5)/O_(2) and Ta_(3)N_(5)/KTaO have distinct Type-II band alignments,with Ta_(3)N_(5) as the accumulator of photoinduced electrons in the former and the collector of photogenerated holes in the latter,respectively.The difference in charge density and electrostatic potential between two components acts as a driving force to promote the transfer of electrons and holes to different domains of the interface,which is beneficial to extend the lifetime of photoinduced carriers.Our results demonstrate that the function of Ta_(3)N_(5) in Ta_(3)N_(5)/KTaO_(3) photocatalytic system is determined by the termination property of KTaO_(3)(110)surface,which provides a likely reason of the observed photocatalytic activity of overall water splitting achieved by Ta_(3)N_(5) synthesized by using KTaO_(3) as a precursor for the nitridation reaction.展开更多
Ni self-assembly has been performed on Ga N(0001), Si(111) and sapphire(0001) substrates. Scanning electron microscopy(SEM) images verify that the Si(111) substrate leads to failure of the Ni assembly due to Si–N int...Ni self-assembly has been performed on Ga N(0001), Si(111) and sapphire(0001) substrates. Scanning electron microscopy(SEM) images verify that the Si(111) substrate leads to failure of the Ni assembly due to Si–N interlayer formation; the GaN(0001) and sapphire(0001) substrates promote assembly of the Ni particles. This indicates that the GaN/sapphire(0001) substrates are fit for Ni self-assembly. For the Ni assembly process on Ga N/sapphire(0001) substrates,three differences are observed from the x-ray diffraction(XRD) patterns:(i) Ni self-assembly on the sapphire(0001) needs a 900?C annealing temperature, lower than that on the GaN(0001) at 1000?C, and loses the Ni network structure stage;(ii) the Ni particle shape is spherical for the sapphire(0001) substrate, and truncated-cone for the GaN(0001) substrate; and(iii) a Ni–N interlayer forms between the Ni particles and the GaN(0001) substrate, but an interlayer does not appear for the sapphire(0001) substrate. All these differences are attributed to the interaction between the Ni and the Ga N/sapphire(0001) substrates. A model is introduced to explain this mechanism.展开更多
基金the National Natural Science Foundation of China under Grant 21473183the open fund of Key Laboratory of Computational Physical Sciences(Fudan University),Ministry of Education.
文摘β-Ge3N4 loaded with nanoparticulate RuO2 as a cocatalyst is the first successful non-oxide photocatalyst for overall water splitting.To get an insight into the working mechanism of this particular photocatalytic system,we have calculated geometrical structures of low-index surfaces forβ-Ge3N4.Analysis of surface energies indicates that the most preferentially exposed surface is(100).The band gap of surface is narrower than that of bulk due to the dangling bonds.Dissociative water adsorption on(100)surface is thermodynamically favorable.The adsorption behavior of(RuO2)n(n=2,3,and 4)clusters on theβ-Ge3N4(100)surface has been explored.It is found that all the clusters bind to(100)surface strongly by forming interfacial bonds so that the adsorptions are exothermic processes.The calculation on density of states forβ-Ge3N4(100)surface loaded with(RuO2)nclusters reveals that photo-induced electrons tend to accumulate on(RuO2)nclusters and holes tend to stay inβ-Ge3N4.Based on the theoretical indication of Type-II staggered band alignment,we have proposed that in photocatalytic water splitting reaction,oxygen evolution reaction is inclined to occur on the surface ofβ-Ge3N4 while hydrogen evolution reaction is apt to occur on(RuO2)nclusters.In a word,loading RuO2 nanoparticles as a reduction cocatalyst benefits the charge separation inβ-Ge3N4.Furthermore,attaching(RuO2)nclusters ontoβ-Ge3N4(100)surface results in the redshift of absorption edge and the increase of absorption intensity.Our calculations have reasonably explained the experimental observation on the decomposition of water into H2 and O2 after loading RuO2 cocatalyst inβ-Ge3N4 photocatalyst.
基金financially supported by the Natural Science Foundation of Liaoning Province(Grant No.2019-ZD-0304)the Educational Department of Liaoning Province(Grant No.LJ2019009)+1 种基金Liaoning BaiQianWan Talents Program,Doctoral Start-up Foundation of Liaoning Province(Grant No.20170520231)the open fund of the State Key Laboratory of Molecular Reaction Dynamics in Dalian Institute of Chemical Physics(Grant No.SKLMRDK202001),Chinese Academy of Sciences。
文摘The rational fabrication of heterostructures is one of efficient strategies for improving photocatalytic performance of semiconductor photocatalysts.Very recently,Domen and co-workers found that Ta_(3)N_(5) single crystals grown on the surface of KTaO_(3) can accomplish photocatalytic overall water splitting for the first time.In order to comprehend the underlying mechanism of this photocatalytic system,we have performed a systematic study based on density functional theory first-principles calculations.Ta_(3)N_(5)(010)/KTaO_(3)(110)slab models have been built according to experimental observations by considering two common terminations of KTaO_(3)(110)surface,named as Ta_(3)N_(5)/O_(2) and Ta_(3)N_(5)/KTaO.The formations of interfacial bonds are thermodynamically stable,showing a covalent interaction between two components of a heterostructure.Ta_(3)N_(5)/O_(2) has a higher mobility of photogenerated charge carriers and lower recombination rate of charge carriers than Ta_(3)N_(5)/KTaO.The light absorption of heterostructures displays the feature of KTaO_(3) in the short wavelength region and the characteristic of Ta_(3)N_(5) in the long wavelength region.The calculated band offsets show that Ta_(3)N_(5)/O_(2) and Ta_(3)N_(5)/KTaO have distinct Type-II band alignments,with Ta_(3)N_(5) as the accumulator of photoinduced electrons in the former and the collector of photogenerated holes in the latter,respectively.The difference in charge density and electrostatic potential between two components acts as a driving force to promote the transfer of electrons and holes to different domains of the interface,which is beneficial to extend the lifetime of photoinduced carriers.Our results demonstrate that the function of Ta_(3)N_(5) in Ta_(3)N_(5)/KTaO_(3) photocatalytic system is determined by the termination property of KTaO_(3)(110)surface,which provides a likely reason of the observed photocatalytic activity of overall water splitting achieved by Ta_(3)N_(5) synthesized by using KTaO_(3) as a precursor for the nitridation reaction.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61473266 and 61673404)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.16HASTIT033)+2 种基金the Science and Technique Foundation of Henan Province,China(Grant Nos.132102210521,152102210153,182102210516,and 172102210601)the Key Program in Universities of Henan Province,China(Grant No.17B520044)the Science and Technique Project of the China National Textile and Apparel Council(Grant No.2018104)
文摘Ni self-assembly has been performed on Ga N(0001), Si(111) and sapphire(0001) substrates. Scanning electron microscopy(SEM) images verify that the Si(111) substrate leads to failure of the Ni assembly due to Si–N interlayer formation; the GaN(0001) and sapphire(0001) substrates promote assembly of the Ni particles. This indicates that the GaN/sapphire(0001) substrates are fit for Ni self-assembly. For the Ni assembly process on Ga N/sapphire(0001) substrates,three differences are observed from the x-ray diffraction(XRD) patterns:(i) Ni self-assembly on the sapphire(0001) needs a 900?C annealing temperature, lower than that on the GaN(0001) at 1000?C, and loses the Ni network structure stage;(ii) the Ni particle shape is spherical for the sapphire(0001) substrate, and truncated-cone for the GaN(0001) substrate; and(iii) a Ni–N interlayer forms between the Ni particles and the GaN(0001) substrate, but an interlayer does not appear for the sapphire(0001) substrate. All these differences are attributed to the interaction between the Ni and the Ga N/sapphire(0001) substrates. A model is introduced to explain this mechanism.