Photoreforming of Organic Waste into Hydrogen Using a Thermally Radiative CdO/CdS/SiC Photocatalyst

To achieve superior efficiency for photocatalytic reactions, it is necessary to utilize visible light, which accounts for most of the solar energy. Herein, by applying a photocatalytic reaction, we aimed to develop a method for generating hydrogen by reforming organic waste, which is discharged as part of domestic, agricultural, forestry, and industrial practice. In the prepared CdS/SiC composite photocatalyst, etching of the oxide film of SiC and oxidation of the atomic-level surface of CdS proceeded in an alkaline reaction solution to form a CdO/CdS/SiC composite. This composite is stable under light irradiation in a high-temperature alkaline reaction solution and can steadily promote hydrogen production. CdO/CdS/SiC exhibits absorption in the entire ultraviolet and visible light region. In particular, the visible light region on the long-wavelength side, which is derived from the crystal defect of SiC, was used for heat radiation, and it was effective in increasing the temperature of the reaction solution. The high-temperature alkaline reaction solution promoted the hydrolysis of organic wastes with high molecular weight. Elution of small organic molecules by this process facilitated the progress of photocatalytic reactions and improved the rate of hydrogen production. Furthermore, in the absorption region derived from the interband transition below 580 nm, electron transfer between SiC and CdS suppressed recombination and improved the photocatalytic activity. Particularly, we achieved a high quantum yield of almost 20% in the ultraviolet region of 380 nm, where electron transfer from SiC was remarkable. Even in the visible light region, 2.0% was achieved at 420 nm, indicating an activity superior to that of conventional photoreforming systems. Using the developed photocatalytic system, we succeeded in producing hydrogen by photoreforming organic waste, such as cellulosic biomass, animal biomass, and plastic, under sunlight. Therefore, it is possible to solve waste disposal, environmental, and energy problems using sustainable photocatalytic processes.