Effect of Morphological Modification over g-C3N4 on Photocatalytic Hydrogen Evolution Performance of g-C3N4-Pt Photocatalysts

Abstract

In this study, the morphological properties of g-C3N4 in g-C3N4-Pt photocatalysts were modified by a simple hydrothermal treatment for photocatalytic hydrogen evolution. In addition, the morphological modification effect of g-C3N4 on the hydrogen evolution performance was investigated. The long-time hydrothermal treatment clearly changed the morphology of g-C3N4 by building extended melem units with more oxygen functional groups at the defect edges of the extended melem units, which was evidenced by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) measurements. The different morphological features of g-C3N4 resulted in lower photoluminescence (PL) emission intensity in PL spectra and a smaller semicircle radius in electrochemical impedance spectroscopy (EIS) data. This indicates the more efficient charge separation of the g-C3N4-Pt photocatalyst with a modified morphology. Consequently, morphologically modified g-C3N4-Pt showed a higher photocatalytic hydrogen evolution rate due to the better charge separation efficiency.

Enhanced Visible-Light H2O2 Production over Pt/g-C3N4 Schottky Junction Photocatalyst

“…The FTIR spectra of g-C 3 N 4 and Pt0.05/g-C 3 N 4 are displayed in Figure . In the g-C 3 N 4 spectrum, the absorption peak at 808 cm –1 corresponds to the heptazine unit in the g-C 3 N 4 structure, and the absorption peak at 1200–1700 cm –1 is for the aromatic CN or C–N stretching vibration. , The broad peak at 3000–3500 cm –1 corresponds to the stretching vibration of O–H in adsorbed H 2 O and the N–H in –NH/–NH 2 groups . For Pt0.05/g-C 3 N 4 , the characteristic absorption peak is similar to that of g-C 3 N 4 .…”

“…The high-resolution Pt 4f spectra of Pt0.05/g-C 3 N 4 (Figure e) can be deconvoluted into a double peak. The peaks at 71.22 and 74.37 eV can be attributed to the 4f 7/2 and 4f 5/2 orbits of zero-valence Pt. , Notably, the metal Pt nanoparticles can activate O 2 molecules and transport electrons generated by photocatalysis, ,, therefore, benefiting photocatalytic H 2 O 2 production.…”

“…Based on the above analysis, the possible mechanism for photocatalytic production of H 2 O 2 over Pt/g-C 3 N 4 was posed and displayed in Figure . Under the irradiation of visible light on the Pt/g-C 3 N 4 photocatalyst, the electrons on the valence band of g-C 3 N 4 are excited to the conduction band, the photogenerated holes remained in the valence band (eq ), and the photogenerated electrons on the conduction band can migrate to the Pt nanoparticles and reduce O 2 in the system to • O 2 – (eq ), and here Pt nanoparticles improve the separation efficiency of photogenerated carriers, reduce the resistance of electron migration and promote the adsorption and activation of O 2 . ,, The • O 2 – radicals further combine with H + in the system to form H 2 O 2 (eq ). ,,,,,, How does the • O 2 – radical change into H 2 O 2 in eq ?…”

“…To investigate the source of oxygen in the reaction system, here, the reactive solution was bubbled with airflow for 0.5 h − (eq 3), and here Pt nanoparticles improve the separation efficiency of photogenerated carriers, reduce the resistance of electron migration and promote the adsorption and activation of O 2 . 26,31,39 The • O 2 − radicals further combine with H + in the system to form H 2 O 2 (eq 4). 17,19,25,43,44,68,69 .…”

“…To address these issues and improve its performance, various strategies such as introducing defects, element doping, , heterojunction engineering, , and noble-metal modification − have been investigated. Noble-metal modification was proved to be an effective strategy to improve the photocatalytic activity due to the high conductivity, low activation energy, and high work function of noble metals. − In particular, metal platinum (Pt) nanoparticles as a cocatalyst were deposited on the surface of g-C 3 N 4 to capture electrons to improve the separation efficiency of photocatalytic carriers and photocatalytic performance for H 2 O 2 production. , However, the contents of Pt in photocatalysts are generally higher than 0.5 wt % in the literature, − which severely limits its practical application owing to their low earth abundance and high price. In addition, the roles of Pt as a cocatalyst in H 2 O 2 production should be considered in detail.…”