Objective of the experiments reported by the authors was to increase the stability of the nanoparticles, as well as the adsorption capacity of CO2 on their surface, thus improving the efficiency of synthetic photosynthesis

A group of scientists from the FAPESP Shell Research Centre for Gas Innovation (RCGI) has recently published an article in the Journal of Physical Chemistry C, which represents a huge advance in how to design more stable ceramic photocatalysts for artificial photosynthesis and water photolysis. The team is led by Professor Douglas Gouvêa, of the Department of Metallurgical and Materials Engineering of the Polytechnic School of the University of São Paulo (Poli-USP), and the main author of the article is Andre Luiz da Silva, a post-Doctoral student in the same institution. Both belong to the RCGI team and work on a project that seeks to transform CO2 into organic products with the use of nanoparticles.

“The Journal of Physical Chemistry C is an outstanding magazine, with many readers, and its purpose is specifically to publish physical-chemistry articles related to the phenomena of surfaces, interfaces, nanomaterials, and catalysis, which is directly associated with what we are doing in the RCGI’s Project 31. It is the first publication of the project team and others are being finished,” Gouvêa said. Project 31 is a part of the RCGI’s Carbon Abatement Program.

In the program, the researchers plan to reproduce, with semiconductor oxide nanoparticles, what nature does during the photosynthesis process, starting from the absorption of light, CO2, and water. In natural photosynthesis, chlorophyll absorbs light, transforms water into oxygen and protons, and uses the resulting electrons to make other transformations within the cell. Electrons and protons are taken to another organic cycle, where the system absorbs CO2, and later transforms it into sugar, that is, the carbon assimilated from the atmosphere was transformed and used for other applications.

In order to achieve this objective, the first step was to study the stability of these nanoparticles, which is the subject of the recently published paper (click here to access it). The team focused on improving the catalytic capacity of the titanium oxide nanoparticles, by adding such substances as barium oxide (later, magnesium oxide, calcium oxide, and strontium oxide, will also be tested), to increase the effectiveness of the artificial photosynthesis process.

“The objective of the series of innovative experiments performed by the group was to increase the stability of the nanoparticle and also its surface capacity for adsorption of CO2. Titanium has a tendency to adsorb water and, barium, to adsorb CO2. When barium is applied to the nanoparticle, most of it goes to the surface of the particle. This, it is possible to increase the efficiency of synthetic photosynthesis, which is directly connected with the efficiency of the adsorption of CO2 by the particle,” Andre Luiz da Silva explained.

The scientists worked with such concepts as surface segregation (which is the capacity of the applied material to migrate to the surface of the particle), border segregation of the particle (the ability of the applied material to deposit itself on the interface between particles that touch each other), and surface energy (a measurement of particle stability).

“For the first time, it was experimentally shown that surface segregation, border segregation of the particle, and surface energy are truly interconnected. The quantification of these three numbers had never before been reported experimentally in the same article,” Silva stated.

“This is the first publication in which we were able to fully distinguish the system. We showed that barium goes to the surface of the material (segregation) and that this has an energy effect on the system,” Gouvêa summarized.

According to him, the paper published in the Journal of Physical Chemistry C is important, because it helps understand how thermodynamics are important for the stabilization of particles and how this stabilization is essential to the photocatalyst process. The impact of the article is already being felt: the American Ceramic Society wrote an article on the work and published it in Ceramic Tech Today (click here to see it).

According to the researchers, the quantification and the measurements involved other institutions and show team work: the University of California, Davis (UC/Davis), and the National Nanotechnology Laboratory, in Campinas, SP.

“All of the surface energy and adsorption measurements were made at UC/Davis. They specialize in calorimetry, including adsorption, and have instruments that very few institutions in the world have. And here, at the Luz Synchrotron Laboratory, we quantified segregation,” said the Poli Professor.

Andre Silva revealed that a micro-reactor is under construction, for testing the efficiency of the nanoparticles. “In the future the perspective is to create portable systems, like panels of activated nanoparticles that can be used everywhere. But it is necessary to first test the efficiency of the nanoparticles in photocatalysis and only after that to think about any form of prototype.”