各种文献研究(表6)已经报道了金属纳米颗粒(NP)在石墨碳氮化物g-C3N4(M/CN)上的分散显著提高了光催化氢气产率。应当理解,金属NP在CN的表面上产生活性位点并充当助催化剂。然而,CN表面不同金属NPs引起的精确变化仍然困扰着我们。这里,我们报告了对形态学的透彻理解和比较,金属-载体相互作用,界面电荷转移动力学,和不同M/CN(M=Pt,Pd,Au,Ag,Cu)与光催化活性相关。在所有金属中,发现Pt/CN在阳光和UV可见光照射下都是最佳性能。在阳光下,在Pt/CN上观察到最大H2@2.7mmol/h/g,其次是Pd/CN>Au/CN>Ag/CN>Cu/CN≈CN。本研究表明,在所有金属中,与其他金属相比,Pt与g-C3N4形成了优异的界面接触。最大肖特基势垒高度(Φb,在Pt/CN处观察到Pt)为0.66V,其次是Φb,Au/CN(0.46V)和Φb,Pd/CN(0.05V)。Pt-XPS中存在缺电子Pt,在VB-XPS中费米能级附近,Pt的d-DOS强度降低,CB尾部状态增加,和MS图中Vfb的阴极位移充分证实了Pt/CN中的强金属-载体相互作用。由于SPR效应,在光沉积过程中,Au和AgNP会团聚和分散不良。精细分散的PtNP(2-4nm,53%的色散)成功地与浅/深陷阱态竞争,并在飞秒瞬态吸收光谱研究的急剧减少的时间段内将光生电子驱动到活性金属位点。通常,界面电子转移速率,KIET,avg,对于Pt/CN,观察到2.5×1010s-1,而在Au/CN中观察到0.087×1010s-1。得出M/CN肖特基结处的能带对准/电势,并且在CB尾态远高于水还原电势的Pt/CN中最有利;但是,在Pd的情况下,这些延伸到远低于H+/H2电位,因此表现得像深陷阱状态。因此,在Pd/CN中(τ0=4200ps,49%)和Ag/CN(3870ps,53%),电子深俘获主导电荷转移到活性位点。本研究将有助于设计未来的新型助催化剂-光催化剂系统。
Various literature studies (Table 6) have reported that dispersion of metal nanoparticles (NPs) on graphitic carbon nitride g-C3N4 (M/CN) has considerably improved the photocatalytic hydrogen yield. It is understood that metal NPs create active sites on the surface of CN and act as a cocatalyst. However, the precise changes induced by different metal NPs on the surface of CN still elude us. Here, we report a thorough understanding and comparison of the morphology, metal-support interactions, interfacial charge transfer kinetics, and band characteristics in different M/CN (M = Pt, Pd, Au, Ag, Cu) correlated with photocatalytic activity. Among all metals, Pt/CN was found to be the best performer both under sunlight and UV-visible irradiation. Under sunlight, maximum H2@ 2.7 mmol/h/g was observed over Pt/CN followed by Pd/CN > Au/CN > Ag/CN > Cu/CN ≈ CN. The present study revealed that among all metals, Pt formed superior interfacial contact with g-C3N4 as compared to other metals. The maximum Schottky barrier height (Φb,Pt) of 0.66 V was observed at Pt/CN followed by Φb,Au/CN (0.46 V) and Φb,Pd/CN (0.05 V). The presence of electron-deficient Pt in Pt-XPS, decrease in the intensity of d-DOS of Pt near the Fermi level in VB-XPS, increase in CB tail states, and cathodic shift in Vfb in MS plots sufficiently confirmed strong metal-support interactions in Pt/CN. Due to the SPR effect, Au and Ag NPs suffered from agglomeration and poor dispersion during photodeposition. Finely dispersed Pt NPs (2-4 nm, 53% dispersion) successfully competed with shallow/deep trap states and drove the photogenerated electrons to active metallic sites in a drastically reduced time period as investigated by femtosecond transient absorption spectroscopy. Typically, an interfacial electron transfer rate, KIET,avg, of 2.5 × 1010 s-1 was observed for Pt/CN, while 0.087 × 1010 s-1 was observed in Au/CN. Band alignment/potentials at M/CN Schottky junctions were derived and most favorable in Pt/CN with CB tail states much above the water reduction potential; however, in the case of Pd, these extend much below the H+/H2 potential and hence behave like deep trap states. Thus, in Pd/CN (τ0 = 4200 ps, 49%) and Ag/CN (3870 ps, 53%), electron deep trapping dominates over charge transfer to active sites. The present study will help in designing futuristic new cocatalyst-photocatalyst systems.