Superior Interfacial Contact Yields Efficient Electron Transfer Rate and Enhanced Solar Photocatalytic Hydrogen Generation in M/C3N4 Schottky Junctions

Various literature studies (Table 6) have reported thatdispersionof metal nanoparticles (NPs) on graphitic carbon nitride g-C3N4 (M/CN) has considerably improved the photocatalytichydrogen yield. It is understood that metal NPs create active siteson the surface of CN and act as a cocatalyst. However, the precisechanges induced by different metal NPs on the surface of CN stillelude us. Here, we report a thorough understanding and comparisonof the morphology, metal-support interactions, interfacialcharge 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 undersunlight and UV-visible irradiation. Under sunlight, maximumH(2)@ 2.7 mmol/h/g was observed over Pt/CN followed by Pd/CN> Au/CN > Ag/CN > Cu/CN & AP; CN. The present study revealedthatamong all metals, Pt formed superior interfacial contact with g-C3N4 as compared to other metals. The maximum Schottkybarrier height (& phi;(b,Pt)) of 0.66 V was observed atPt/CN followed by & phi;(b,Au/CN) (0.46 V) and & phi;(b,Pd/CN) (0.05 V). The presence of electron-deficient Pt inPt-XPS, decrease in the intensity of d-DOS of Pt near the Fermi levelin VB-XPS, increase in CB tail states, and cathodic shift in V (fb) in MS plots sufficiently confirmed strongmetal-support interactions in Pt/CN. Due to the SPR effect,Au and Ag NPs suffered from agglomeration and poor dispersion duringphotodeposition. Finely dispersed Pt NPs (2-4 nm, 53% dispersion)successfully competed with shallow/deep trap states and drove thephotogenerated electrons to active metallic sites in a drasticallyreduced time period as investigated by femtosecond transient absorptionspectroscopy. Typically, an interfacial electron transfer rate, K (IET),(avg), of 2.5 x 10(10) s(-1) was observed for Pt/CN, while 0.087 x10(10) s(-1) was observed in Au/CN. Bandalignment/potentials at M/CN Schottky junctions were derived and mostfavorable in Pt/CN with CB tail states much above the water reductionpotential; however, in the case of Pd, these extend much below theH(+)/H-2 potential and hence behave like deep trapstates. Thus, in Pd/CN (& tau;(0) = 4200 ps, 49%) and Ag/CN(3870 ps, 53%), electron deep trapping dominates over charge transferto active sites. The present study will help in designing futuristicnew cocatalyst-photocatalyst systems.