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Sesiunea științifică “Tailoring the activity of photocatalysts: from hollow structures to shape-tailored nanoparticles”

În 3 decembrie 2020, Institutul STAR-UBB organizează, prin programul Advanced Fellowship, sesiunea științifică cu titlul: “Tailoring the activity of photocatalysts: from hollow structures to shape-tailored nanoparticles”. Prezentările vor fi în limba engleză, iar programul și descrierea detaliată a sesiunii sunt prezentate mai jos:

14:00-14:05 – Opening words

14:05-14:50 – Prof. Dr Klára Hernádi, University of Szeged

Fabrication of semiconductor hollow structures – advantages in photocatalysis

14:50-15:35 – Dr. Zsolt Pap, Babeș-Bolyai University

Calcination and solvothermal crystallization – tools to obtain TiO2 the VIP photocatalyst

Link Goggle Meet: https://meet.google.com/vot-akxz-tnn

Fabrication of semiconductor hollow structures – advantages in photocatalysis

Klára HERNÁDI

University of Szeged, Department of Applied and Environmental Chemistry, H-6720 Szeged, Rerrich B. ter 1. Hungary

            Heterogeneous photocatalysis has recently emerged as one of the most effective and “greener” technique for the solution of certain environmental concerns. The photocatalytic activity of semiconductor materials can be dependent on various parameters such as the crystal phase composition, the crystallite size, the orientation of the crystal facets, structural hierarchy etc.

            As it was demonstrated earlier1, multiple reflections within a hollow cavity can lead to the enhanced utilization of the light source resulting in the production of more photogenerated charge carriers, thus increasing the photocatalytic efficiency of the semiconductor. Therefore, semiconductor hollow structures are of growing interest in the field of photocatalysis, too. These objects are interesting not just because of their unique optical properties but also their low apparent density. However, their reproducible fabrication can be challenging. 

            For the synthesis of either carbon-metal oxide composites or hollow semiconductor structures, nanometer sized carbon spheres (CS) were prepared by mild hydrothermal treatment of ordinary table sugar (sucrose). CSs were successfully coated with TiO2 and ZnO via either sol-gel method or atomic layer deposition2

            The unique hollow sphere morphology proved to enhance the photocatalytic activity (six times) as well as TOC removal efficiency (twelve times) compared to the reference sample. Combining the hollow spherical morphology with the deposition of noble metals, results revealed that both gold-deposited sample and platinum-deposited TiO2-s showed higher photocatalytic activity in phenol or oxalic acid decomposition under UV light irradiation.

Calcination and solvothermal crystallization – tools to obtain TiO2 the VIP photocatalyst

Zsolt PAP

Babeș-Bolyai University, Interdisciplinary Research Institute on Bio-Nano Sciences, RO-400271 Treboniu Laurian 42, Romania

            To obtain any novel photocatalytic materials an efficient reproducible synthesis procedure should be developed. However, the cost of “rushing and jumping” into seemingly efficient and adequate solutions is extremely high and affects the scientific community by flooding the literature with inconsistent data. The most representative material is TiO2 which is widely covered in the photocatalysis literature. There are numerous ways to obtain these materials including sol-gel based methods, solvothermal crystallization etc.

            As the controlled crystallization requires energy it is very important to know the crystallization parameters, which can be differentiated based on the chosen crystallization procedure. When the calcination is the final step to obtain nanocrystalline titania, the time/duration, the calcination atmosphere and the heating rate of the furnace (for both muffle and tube furnaces) are those parameters which define the final properties of the material and some of them are systematically ignored (e.g. duration of the calcination), generating knowledge voids and misconceptions.

            When a solvothermal crystallization is considered, the same parameters may be valid, however completed with the issues of crystallization media related chemistry, such as the acidity, polarity of the solvents, ionic strength, the presence of different shape-tailoring agents. Some of the simplest issue are also not quite considered here, namely the complex interaction of crystallization nuclei with the media, which may result in materials with complex structure and properties.

            The two examples mentioned above are just a few drops in the ocean of scientific results and due to the rush to publish as soon as possible most of the appearing issues will remain unsolved, making the work of scientists harder later on.