Preparation and Photocatalytic Hydrogen Production of Pt-Graphene/TiO₂ Composites from Water Splitting

Abstract

Hydrogen is considered as a promising energy source with its high energy yield, renewable, environment friendly properties. TiO2 modified with noble metal and nonmetal is widely used. In this study, Pt and graphene (GN) were used to modify TiO2 nanoparticles. GN/TiO2 (TG), Pt-TiO2 (PT), Pt-GN/TiO2 (PTG) was successfully synthesized by modified Hummers' method, alcohol thermal and photodeposition method, respectively. The characterizations of the synthesized catalysts by UV-vis/DRS, components analysis, XRD and TEM analysis were conducted. Results showed the maximum hydrogen production rate was approximately 4.71 mmol h-1 g-1 when the Pt content was 1.0 wt.%. Higher and lower than 1.0 wt.% of Pt loading content both result in low efficiency of hydrogen production. The situation of graphene is similar to Pt. The optimal ratio for grapheme is 10 wt.%. The highest hydrogen production rate is 6.58 mmol h-1 g-1 by 1.5 wt.% Pt-5 wt.% GN/TiO2 (1.5PTG5), which is about 1.4 and 2.2 times higher than that of Pt-TiO2 and GN/TiO2 binary composites, respectively. The utilization of low-cost graphene can reduce the use of noble metal Pt in photocatalytic hydrogen production. The mechanism of Pt-GN/TiO2 for the improved photocatalytic activity is proposed. 0.1 g L-1 is found to be the optimum catalyst concentration for optimal hydrogen production.

Biomimetic Catalysts Based on Au@ZnO–Graphene Composites for the Generation of Hydrogen by Water Splitting

“…Incorporation of gold and graphene greatly increased hydrogen production in both the UV and visible regions of all the composites. The presence of co-catalysts such as Au and graphene improve the charge separation and suppresses the recombination of excited photogenerated carriers, resulting in a better evolution of H 2 [ 26 ]. Different studies [ 45 , 46 , 47 ] have demonstrated that when semiconductors, such as ZnO, are doped with noble metal or metal ions, they exhibit a negative shift in the Fermi level that implies a greater degree of electron accumulation in Au-loaded.…”

“…These improvements are in turn associated with a considerable enhancement of the electric near-field [ 45 ]. This activity relates strongly to the size and shape-dependent surface charge oscillation known as surface plasmon resonance (SPR) in the presence of light irradiation [ 26 ]. Furthermore, the incorporation of graphene on semiconductors creates the p–n junction, which also improves the separation of photogenerated charges [ 26 , 48 ].…”

“…This activity relates strongly to the size and shape-dependent surface charge oscillation known as surface plasmon resonance (SPR) in the presence of light irradiation [ 26 ]. Furthermore, the incorporation of graphene on semiconductors creates the p–n junction, which also improves the separation of photogenerated charges [ 26 , 48 ]. The photogenerated holes that were created are then scavenged by the sacrificial agent (S 2– /SO 3 2– ), and the electrons are excited to the conduction band.…”

“…The photogenerated holes that were created are then scavenged by the sacrificial agent (S 2– /SO 3 2– ), and the electrons are excited to the conduction band. Electrons transferred from the conduction band of the semiconductor are injected into the graphene because graphene has a slightly lower redox potential than the semiconductor conduction band [ 26 , 48 ]. Graphene has a high charge carrier transfer and mobility as a result of its π-conjugated structure, and hence Au nanoparticles dispersed on the graphene can also accept electrons and act as active sites to react with adsorbed H + ions for H 2 evolution [ 26 , 48 ].…”

“…Graphene has unique properties such as high thermal conductivity, excellent mobility of charge carriers, large surface area, and good mechanical stability [ 25 ]. As a co-catalyst, graphene has significant advantages, including that it (i) provides a support for anchoring well-dispersed metallic or oxide nanoparticles; (ii) works as a highly conductive matrix for enabling good contact throughout the matrix; (iii) induces an easy electron transfer from the conduction band of the semiconductor to graphene because of the large energy level offset formed at the interface, leading to an efficient charge separation; and (iv) acts as an efficient co-catalyst for H 2 evolution because of its large specific surface area and superior electron mobility [ 26 ].…”