Group led by a Poli/USP Professor wants to remove carbon dioxide from the atmosphere and transform it into organic products by using nanoparticle oxides

Reproduce the natural photosynthesis process whereby organic molecules are synthetized by absorption of light, CO2, and water from the atmosphere by metal oxide semiconductor nanoparticles: this is, in general terms, the main goal of the Project 31, as a part of the CO2 Abatement Program driven by FAPESP-Shell- Research Centre for Gas Innovation (RCGI). Production of organic molecules from CO2 and H2O by nano oxide photocatalysis project is coordinated by Professor Douglas Gouvêa, of the Department of Metallurgical and Materials Engineering of the Polytechnic School of the University of São Paulo (Poli-USP). Use CO2 as a raw-material transforming it into an organic product which can be used later for other purposes is the central idea behind the proposal. According to Gouvêa, the “ace in the hole” to achieve this goal is to use the knowledge developed by his team in nanostructure and physico-chemistry of interface.

“To that end, we want to use our knowledge regarding the composition of the interfaces and the stability of nanoparticles – that is the particularity of our proposal, although it is no original, because many people want to use nanoparticles to reproduce natural phenomena.”

He explains that, in the photosynthesis performed by plants, chlorophyll absorbs a given amount of light, transforms water into oxygen and protons and uses the resulting electrons to make other reactions, within the cell itself.

“These electrons and protons are taken to another organic cycle, in which the system absorbs CO2, transforming it into sugar. That is: the carbon assimilated from the atmosphere was transformed and used for other purposes.” Gouvêa said.

That is what he and his team of seven researchers are attempting to reproduce, based on nanoparticles of zinc oxide and titanium oxide, which are “broadband” semiconductor materials (that absorb ultraviolet light from the Sun).

The researcher explains that it is possible to generate electronic charges in these semiconductors by absorbing light that promotes the electron from the valence band to the conduction band.

“When separating these charges, we transform the electron into a reductant and its absence into an oxidant. The nanoparticles of semiconductors absorb sunlight and are able to make this separation of charges.”

According to Gouvêa, when the charges are separated, the next step is to concentrate the holes in a given region of the system, and the electrons in another region.

“When the water in the environment, existing as vapor, is adsorbed on the surface of the particle where the “holes” are, its molecular structure will be weakened making possible the reaction that will transform it into H+ and O2. This releases oxygen in gaseous form and is the first phase of photosynthesis. The CO2 will also be adsorbed, but that happens on the area of the particle that contains the electrons; its molecular structure will weaken, and will combine with the electron and the H+ originating from the previous reaction, and it is transformed into an organic acid: formic acid. This acid can then be converted into alcohol, for example. Thus, what we are promoting is the removal of CO2 from the atmosphere and its transformation into an organic compound by using sunlight, as is done in nature, except that this is generating more interesting chemical precursors.”

This project has the collaboration of Professor Ricardo Castro of the University of California, Davis, a specialist in adsorption calorimetry, and of Professor Guilherme Lens of the Metallurgy and Materials Department of the Polytechnic School, a specialist in graphite nanotubes. The intent is to elaborate stable nanoparticles with the chemical composition of the modulated surface to allow the adsorption of the species and the reactions with the adsorbed gases and the chemical composition of the particle surfaces that allow the free transfer of the electrical charges between the nanoparticles in a more efficient manner than is currently known.

A long-term objective of the project is the production of a photocatalysis cell, in a controlled environment, for testing. Gouvêa believes that, in the future, it will be possible to think about local, portable systems – something like nanoparticle plates with additives, which can be placed in a variety of environments: homes, offices, etc., for transforming CO2 from the atmosphere into an organic compound to be used for other purposes.

“Water, CO2, and light exist everywhere in the world. Therefore, our optimistic vision for the future is to create a source for storing chemical energy that can be used anywhere on the planet. The dimensions would be adjustable – like a solar panel, for example, which can be made in adjustable sizes.”

The abatement of carbon emissions is one of the objectives of the RCGI, which was created about two years ago with the funding of the Research Support Foundation of the State of São Paulo (FAPESP) and of Shell. Currently, the RCGI has a portfolio of 45 research projects divided into four programs: Engineering; Physicochemical; Energy and Economic Policies; and CO2 Abatement.