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ZEolitic reactor hosting Subphthalocyanines and Metal Oxides as photocatalytic system for opto-electronic applications

Periodic Reporting for period 1 - ZESMO (ZEolitic reactor hosting Subphthalocyanines and Metal Oxides as photocatalytic system for opto-electronic applications)

Reporting period: 2016-09-01 to 2018-08-31

Planet population and with it the energetic demand is increasing, therefore there is the necessity of finding alternative fuel as fossil fuels are finishing. Solar light photocatalytic CO2 reduction to valuable chemicals and fuels is increasingly attracting the attention of the scientific community as one of the “greenest” alternatives to fossil fuels and it could also serve to decrease the levels of atmospheric CO2 emissions, mitigating the greenhouse effect problem. Efficiency values reported so far in the literature are far from optimal. Some of the problems to overcome are the limited wavelength response (frequently limited to only 4% of the total solar light energy), photocorrosion and low quantum efficiencies due to inefficient charge separation.
Most of the reported photocatalysts incorporate precious metals and rare elements, which increase the cost and their low abundance would raise the issue of exhausting its reserves in the future. This proposal aims to address these issues by developing an efficient hybrid photocatalytic system made out of non-critical starting materials and chemicals, able to photocatalyse the CO2 reduction to obtain methane (usable as energy source) using as solely source solar light.

This project allowed to obtain a hybrid photocatalyst constructed from three different materials, a light -harvesting system, metal nanoparticles and zeolite as support, that can be subsequently used to obtain energy. The proposed hybrid photocatalyst have successfully been prepared and fully characterised. In the photoassisted CO2 conversion reaction this photocatalyst proved to be efficient for methane evolution, hence achieving the main goal of this project, green energy production.
The following objectives have been successfully achieved during the period of the action.

Objective 1. Synthesis and characterisation of the [light-harvester]-zeolite hybrid system
Objective 2. Co-incorporation of metal nanoparticles to the zeolite
Objective 3. Evaluation of the photocatalytic activity of a series of synthesised photocatalysts towards CO2 reduction
Objective 4. Deactivation mechanism and operation lifetime studies

Overall, a novel hybrid photocatalyst formed by a catalyst and a light-harvester molecule supported on a zeolite has been synthesized and fully characterized. There are no precedents of this kind of system in the literature, such material is photocatalytically active for photoassisted CO2 conversion. A maximum methane production of 8.55 mmol per gram of metal is obtained.

The photocatalytic stability of the catalyst was also evaluated performing reuses and long-term stability tests. It was observed the catalyst maintaining methane production after 50 hours of irradiation reaching a production value of 11 mmol gCo-1. The maximum production is obtained after 4 hours of irradiation obtaining 1 mmol gCo-1 h-1, decaying the rate for longer times.

Diffuse-reflectance UV spectroscopy was performed in order to gain information about the light absorption properties of the materials. The mechanism of the photocatalytic methane generation was also studied by transient absorption spectroscopy. Evidences for the generation of electrons and holes upon laser excitation in the material were obtained. The charge separation state exhibits long half-life, decaying is in the microsecond range. Quenching experiments were subsequently carried out using electron donor and electron acceptors.

This project has been presented different formal meetings and workshops, it has also been disseminated to the public and students by means of different fairs and events, such the European Researchers Night or visiting schools and high schools. Moreover, the results of this project will lead to their publication in high impact factor journals.
The objectives set in the proposal were achieved by the end of the reporting period. The possibility to open new collaborations with energy-related companies in order to keep exploiting and improving the results obtained in ZESMO are currently being explored, as well as the possibility of applying the synthesized photocatalyst in a pilot plant. Being able to obtain energy from carbon dioxide means the mitigation of the greenhouse effect, which translates into better quality of life and health of humanity. On the other hand, the scaling up of this project will mean the possibility to obtain energy from a sustainable and non-exhausting source such as the sun, allowing the generation of the demanded energy by the population.