In clean, renewable energy resource research, photocatalytic H₂ production in an aqueous solution has received considerable attention. We have reported that water splitting over a semiconductor photocatalyst by using solar energy can produce H₂ and O₂ which has a high degree of sustainability, but the back reactions of the products on the catalyst surfaces result in inefficient photocatalytic H₂ generation. Regarding the renewability of H₂ resources, photocatalytic reforming of biomass materials, such as glucose (C₆H₁₂O₆), sugar (sucrose, C₁₂H₂₂O₁₁), and cellulose ((C₆H₁₀O₅)_n) represents a promising counterpart to photosynthesis for achieving a sustainable carbon cycle that produces clean solar fuels. Most studies have used TiO₂ as the photocatalyst for reforming glucose or sugar to produce H₂, but TiO₂ has its limitation in solar light absorption. Carbon- or graphene-based photocatalysts, which are environmentally benign and sensitive to visible light, are considered as ideal media for producing clean and renewable H₂. Performance of carbon- or graphene-based photocatalysts in the reforming of glucose, sugar, or cellulose for H₂ production requires exploration. Our research efforts have proved that graphene dots are a promising catalyst for photoreforming of biomass materials into H₂ in a practical manner; we achieved a H₂-evolution apparent quantum yield of >20% under monochromatic irradiation at 420 nm. 

In clean, renewable energy resource research, photocatalytic H₂ production in an aqueous solution has received considerable attention. Water splitting over a semiconductor photocatalyst by using solar energy to produce H₂ and O₂ has a high degree of sustainability, but the back reactions of the products on the catalyst surfaces result in inefficient photocatalytic H₂ generation. Regarding the renewability of H₂ resources, photocatalytic reforming of biomass materials, such as glucose (C₆H₁₂O₆), sugar (sucrose, C₁₂H₂₂O₁₁), and cellulose ((C₆H₁₀O₅)_n) represents a promising counterpart to photosynthesis for achieving a sustainable carbon cycle that produces clean solar fuels. Most studies have used TiO₂ as the photocatalyst for reforming glucose or sugar to produce H₂. Carbon- or graphene-based photocatalysts, which are environmentally benign and sensitive to visible light, are considered as ideal media for producing clean and renewable H₂. Performance of carbon- or graphene-based photocatalysts in the reforming of glucose, sugar, or cellulose for H₂ production requires exploration. 

Graphene is a flat monolayer comprising sp²-bonded carbon atoms tightly packed into a two-dimensional honeycomb lattice. The lack of a band gap limits the applicability of graphene in photoenergy conversion, which requires semiconducting materials with a finite band gap. Graphene oxide (GO) is a form of graphene that has a band gap and contains various oxygen functional groups on the basal plane and sheet edge. The tunable electronic properties of graphene oxide (GO) nanomaterials make them interesting candidates for photoenergy conversion applications, including photoluminescence, photovoltaics and photocatalysis for water splitting. 

The oxygen functionalities on the graphene substrate enlarge the band gap and enable GO to easily disperse in an aqueous solution. Doping heteroatoms into GO matrices repairs the defects and modulates the electronic structure to increase their photocatalytic activity. We reported photocatalytic reforming of water into H₂ and O₂ over nitrogen-doped GO quantum dots (NGODs), which are based on the abundant elements C, H, O, and N. The NGODs exhibited both p- and n-type conductivities, with electronic properties similar to those of a p-n photochemical diode. The water-reforming mechanism was analogous to that of biological photosynthesis.  

We reported that S and N can be introduced into the GO matrix to effectively repair the vacancy defects and facilitate the separation of photogenerated charges for interfacial reactions over the catalysts. S and N co-doped GO dots (SNGODs) exhibited a high content of graphitic N that was located inside the graphene sheets and repaired the vacancy defects of the basal plane. The peripheral N and S functionalities of the SNGODs produced electron resonance between the graphitic-π orbital and nonbonding states of the N and S atoms, resulting in the reduction of the band gap and the extension of the photogenerated charge lifetime. Pt-deposited SNGODs were stable in photocatalytic reforming of sugar and glucose into H₂, with apparent quantum yields of 11% and 7.4%, respectively, under monochromatic irradiation at 420 nm. The high quantum yields in H₂ production demonstrated the superiority of using graphene dots in the photocatalytic reforming of biomass into H₂.

For practical applications, we have demonstrated the high efficiency of photocatalytic reforming of cellulose for H₂ evolution over the SNGODs. Cellulose is the main constituent of biomass, a homopolymer consisting of glucose units, and is not completely soluble in aqueous solutions. With a pretreatment on cellulose, we achieved a H₂-evolution apparent quantum yield of 23% under monochromatic irradiation at 420 nm.