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

• Published in: ACS applied materials & interfaces Vol. 15; no. 33; pp. 39926 - 39945
• Main Authors: Rawool, Sushma A., Pai, Mrinal R., Banerjee, A. M., Nath, S., Bapat, R. D., Sharma, R. K., Jagannath, Dutta, B., Hassan, P. A., Tripathi, A. K.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.08.2023
• Subjects: Surfaces, Interfaces, and Applications; sunlight; carbon nitride; H2 generation; Schottky barrier height; FsTAS; metal/g-C3N4; photocatalysis; supported catalysts; shallow traps
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.3c05833

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 V fb 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, K IET,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.