Tunable Photodeposition of MoS₂ onto a Composite of Reduced Graphene Oxide and CdS for Synergic Photocatalytic Hydrogen Generation

Recently, MoS₂ as an excellent cocatalyst for hydrogen evolution reaction (HER) has attracted extensive attention. In this work, MoS₂ was controllably loaded on the composite of reduced graphene oxide (rGO) and CdS (rGO/CdS) by a facile photoreduction method at different pHs. At low pH 7, MoS₂ deposits on the surface of the CdS particles of the composite. However, at high pH 11, it loads on the exposed rGO. When MoS₂ is on the rGO, the transfer of the photoexcited electron from CdS to rGO is compatible with the HER at MoS₂ (synergic effect), whereas the transfer is incompatible with the HER when it is on the CdS (antisynergic effect). Moreover, the MoS₂ deposited on the CdS decreases the photoabsorption and photoactivity of CdS, and the effect is avoided when MoS₂ is on the rGO. The photocatalytic HER rate under the synergic condition is 4.3 times as high as that under antisynergic condition. This work would open a promising way to design and fabricate the efficient composite photocatalysts

Facile Synthesis of Graphene Sponge from Graphene Oxide for Efficient Dye-Sensitized H₂ Evolution

Graphene is an advanced carbon energy material due to its excellent properties. Reduction of graphene oxide (GO) is the most promising mass production route of graphene/reduced graphene oxide (rGO). To maintain graphene’s properties and avoid restacking of rGO sheets in bulk, the preparation of 3-dimensional porous graphene sponge via 2-dimensional rGO sheets is considered as a good strategy. This article presents a facile route to synthesize graphene sponge by thermal treating GO powder at low temperature of 250 °C under N₂ atmosphere. The sponge possesses macroporous structure (5–200 nm in size) with BET specific surface area of 404 m² g^–1 and high conductivity. The photocatalytic H₂ production activity of the rGO sponge with a sensitizer Eosin Y (EY) and cocatalyst Pt was investigated. The rGO sponge shows highly efficient dye-sensitized photocatalytic H₂ evolution compared to that obtained via a chemical reduction method. The maximum apparent quantum yield (AQY) reaches up to 75.0% at 420 nm. The possible mechanisms are discussed. The synthesis method can be expanded to prepare other graphene-based materials

Facile Synthesis of Amorphous NiO/Reduced Graphene Oxide as a Cocatalyst for Enhanced Dye-Sensitized Photocatalytic H₂ Evolution

It is still a challenge to develop efficient catalysts for hydrogen evolution reaction (HER) via a low-cost and simple method. Herein, we report an amorphous NiO/reduced graphene oxide (A-NG) composite as a cocatalyst for enhanced photocatalytic H2 evolution via dye sensitization. The A-NG composite is facilely fabricated by calcinating the NiCl2/GO precursor at a low temperature of 250 °C. The detailed characterizations show that amorphous NiO presents as tiny nanoparticles highly dispersed on graphene sheets, and nickel carbide is formed at the NiO/graphene interface, which demonstrates the strong interaction between Ni and the defective carbon of graphene. Compared with crystalline NiO/rGO (C-NG), the A-NG cocatalyst shows much enhanced dye-sensitized photocatalytic HER activity because the amorphous NiO nanoparticles can effectively adsorb the dye. As a result, highly dispersed amorphous NiO accelerates the photoinduced electron transfer from the excited dye to the cocatalyst, namely, the amorphous nickel carbide formed between NiO and rGO. This work provides a low-cost and simple method to develop efficient cocatalysts for photocatalytic H2 evolution