The extensive π system in the naphthalene structure and the carboxylic acid group of 1,4-naphthalene dicarboxylic acid (NA) render it an exceptional organic semiconductor for doping TiO₂ using a calcination-free sol-gel method. The resulting catalyst exhibited a significantly improved hydrogen production rate by photolyzing water molecules under visible light, outperforming the efficiency of the calcined material. Read more about the story behind the cover in the Cover Profile and about the research itself (DOI: 10.1002/cplu.202300172).

Abstract

Invited for this month's cover are the collaborating groups of Dr. Jianwei Li at the University of Turku and Prof. Chunman Jia, Kang Yang and Dan Wei at Hainan University. The cover image compares the structure of calcined (left) and non-calcined (right) rutile TiO₂ doped with a molecule NA. The calcination process enlarges the pores in TiO₂, reducing its surface area and hydrogen production efficiency under visible light. The “sad face” symbolizes the damaged pore structure. Conversely, doping TiO₂ with NA without high-temperature calcination forms a covalent bond, resulting in smaller pores, larger surface area, and improved hydrogen production efficiency. The “smiley face” represents the structurally intact TiO₂ hybrid material. More information can be found in the Research Article by Jianwei Li, Chunman Jia, and co-workers.

The cover picture compares the structure of calcined (left) and non-calcined (right) rutile TiO2 doped with a molecule NA. The calcination process enlarges the pores in TiO2, reducing its surface area and hydrogen production efficiency under visible light. The “sad face” symbolizes the damaged pore structure. Conversely, doping TiO2 with NA without high-temperature calcination forms a covalent bond, resulting in smaller pores, larger surface area, and improved hydrogen production efficiency. The “smiley face” represents the structurally intact TiO2 hybrid material. More information can be found in the Research Article by Jianwei Li, Chunman Jia, and co-workers.

The extensive π system in the naphthalene structure and the carboxylic acid group of 1,4-naphthalene dicarboxylic acid (NA) render it an exceptional organic semiconductor for doping TiO₂ using a calcination-free sol-gel method. The resulting catalyst exhibited a significantly improved hydrogen production rate by photolyzing water molecules under visible light, outperforming the efficiency of the calcined material.

Abstract

In recent years, the sol-gel method has been extensively utilized to develop efficient and stable organic semiconductor composite titanium dioxide (TiO₂) photocatalysts. However, the high-temperature calcination requirements of this method consume energy during preparation and degrade encapsulated organic semiconductor molecules, resulting in decreased photocatalytic hydrogen production efficiency. In this study, we found that by selecting an appropriate organic semiconductor molecule, 1,4-naphthalene dicarboxylic acid (NA), high-temperature calcination can be avoided in the sol-gel process, yielding an organic-inorganic hybrid material with stable and effective photocatalytic properties. The uncalcined material displayed a hydrogen production rate of 2920±15 μmol g⁻¹ h⁻¹, which was approximately twice the maximum production rate observed in the calcined material. Likewise, the specific surface area of the uncalcined material, at 252.84 m² g⁻¹, was significantly larger compared to the calcined material. Comprehensive analyses confirmed successful NA and TiO₂ doping, while UV-vis and Mott-Schottky tests revealed a reduced energy bandgap (2.1 eV) and expanded light absorption range. Furthermore, the material maintained robust photocatalytic activity after a 40-hour cycle test. Our findings demonstrate that by using NA doping without calcination, excellent hydrogen production performance can be achieved, offering a novel approach for environmentally friendly and energy-saving production of organic semiconductor composite TiO₂ materials.