Multiple Modification of Titanium Dioxide to Enhance Its Photocatalytic Performance

A Calcination-Free Sol-Gel Method to Prepare TiO2 -Based Hybrid Semiconductors for Enhanced Visible Light-Driven Hydrogen Production

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.

Property-governed performance of platinum-modified titania photocatalysts

Titania is probably the most widely investigated semiconductor photocatalyst because of various advantages, such as high activity, thermal and chemical stability, low price, abundance, and negligible toxicity. However, pristine titania is also characterized by charge carriers’ recombination, and thus lower quantum yields of photocatalytic reactions than theoretical 100%. Moreover, its wide bandgap, despite being recommended for excellent redox properties, means also inactivity under visible part of solar radiation. Accordingly, titania has been surface modified, doped and coupled with various elements/compounds. For example, platinum deposited on the surface of titania has shown to improve both UV activity and the performance under vis. Although the studies on titania modification with platinum started almost half a century ago, and huge number of papers have been published up to now, it is unclear which properties are the most crucial and recommended to obtain highly efficient photocatalyst. In the literature, the opposite findings could be found on the property-governed activities that could result from huge differences in the reaction systems, and also examined photocatalysts. Considering the platinum properties, its content, the size of nanoparticles and the oxidation state, must be examined. Obviously, the characteristics of titania also influence the resultant properties of deposited platinum, and thus the overall photocatalytic performance. Although so many reports on Pt/TiO₂ have been published, it is hardly possible to give indispensable advice on the recommended properties. However, it might be concluded that usually fine platinum NPs uniformly deposited on the titania surface result in high photocatalytic activity, and thus in the low optimal content of necessary platinum. Moreover, the aggregation of titania particles might also help in the lowering the necessary platinum amount (even to 0.2 wt%) due to the interparticle electron transfer mechanism between titania particles in one aggregate. In respect of platinum state, it is thought that it is highly substrate-specific case, and thus either positively charged or zero valent platinum is the most recommended. It might be concluded that despite huge number of papers published on platinum-modified titania, there is still a lack of comprehensive study showing the direct correlation between only one property and the resultant photocatalytic activity.