Porous Organic Salts Composed of Terphenyl Sulfonic Acid and Their Bottleneck Designability

Porous organic salts (POSs) are constructed through a strong charge-assisted hydrogen bond between sulfonic and amino groups. The molecular design of sulfonic acid, the linker part, enables various porous structures. In the current work, we synthesized p-terphenyl-4,4’’-disulfonic acid (TPDS), whose molecular structure can be easily modified by organic synthesis. Combining of TPDS and bulky tri-p-tolylmethanamine (TPMA-Me), which has three methyl groups at each para-position of the phenyl groups of triphenylmethylamine (TPMA), gave POS with one-dimensional pore channels having two different types of bottlenecks. The central benzene ring of TPDS is exposed on the surface of the pore. Therefore, we combined 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzenesulfonic acid (BTDBS) containing 2,1,3-benzothiadiazole (BT) with TPMA-Me, and successfully constructed a one-dimensional pore channel with a bottleneck of 3.5 Å, by exposing BT to the surface of the pore. BTDBS/TPMA-Me exhibited a large adsorption/desorption hysteresis of nitrogen because of the bottleneck, electronic state of BT, and larger oxygen adsorption than the isostructural TPDS/TPMA-Me. Systematic and intended modulation of the pore structure of POS based on the modification of sulfonic acid was demonstrated, and for the first time, we established a precise design methodology for a one-dimensional pore channel with a bottleneck and high crystallinity in metal-free porous organic materials.     

Flux-Assisted Synthesis of Y2Ti2O5S2 for Photocatalytic Hydrogen and Oxygen Evolution Reactions

Photocatalytic water splitting is an ideal means of producing hydrogen in a sustainable manner, and developing highly efficient photocatalysts is a vital aspect of realizing this process. The photocatalyst Y₂Ti₂O₅S₂ (YTOS) is capable of absorbing at wavelengths up to 650 nm and exhibits outstanding thermal and chemical durability compared with other oxysulfides. However, the photocatalytic performance of YTOS synthesized using the conventional solid-state reaction (SSR) process is limited owing to the large particle sizes and structural defects associated with this synthetic method. Herein, we report the synthesis of YTOS particles by a flux-assisted technique. The enhanced mass transfer efficiency in the flux significantly reduced the preparation time compared with the SSR method. In addition, the resulting YTOS showed improved photocatalytic H₂ and O₂ evolution activity when loaded with Rh and Co₃O₄ co-catalysts, respectively. These improvements are attributed to the reduced particle size and enhanced crystallinity of the material as well as the slower decay of photogenerated carriers on a nanosecond to sub-microsecond time range. Further optimization of this flux-assisted method together with suitable surface modification is expected to produce high-quality YTOS crystals with superior photocatalytic activity.