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SYNTHESIS OF NOVEL NANOSTRUCTURED METAL-SUPPORTED PHOTOCATALYSTS: CHARACTERIZATION AND PROMISING APPLICATIONS IN THE PRODUCTION OF HIGH VALUE CHEMICALS FROM LIGNOCELLULOSIC BIOMASS

Final Report Summary - PHOTOBIO23JC (SYNTHESIS OF NOVEL NANOSTRUCTURED METAL-SUPPORTED PHOTOCATALYSTS: CHARACTERIZATION AND PROMISING APPLICATIONS IN THE PRODUCTION OF HIGH VALUE CHEMICALS FROM LIGNOCELLULOSIC BIOMASS)

Since the beginning of the project the work performed has been completed with success. There is a very good number of scientific papers in high impact journals not only dedicated to the research area of the project (such as Applied Catalysis B: Environmental, Journal of Molecular Catalysis and similar ones) but in journals and books for a broad scientific community (e.g. Chemical Society Reviews, Bioresource Technology, Taylor and Francis Books). Additionally, the dissemination/socialization/popularization of the project findings were amazing spread through the fellow participation in an important number of conferences/seminars as well as by his participation in the preparation of two press releases and other forms of science popularization (e.g. a well-designed and easy-to-surf project website: http://photo-catalysis.org/).
It was organized a successful research collaborative visit in Colombia and Spain (Cordoba) where several meetings took place with representatives of institutions from these countries. The research visit in Spain was very fruitful from the academic point of view (one of the important things to highlight from this visit is the pilot-plant tests of our photocatalysts) but also the strengthening of academic/personal skills of Dr Colmenares and his PhD student (Ms Magdziarz) was of great value.

The main research findings achieved in the frame of this MC project can be summarized as follows:

• Glucose was selectively oxidized in presence of TiO2 photocatalysts synthesized by an original ultrasound-promoted sol-gel method (TiO2(US)). The catalysts were more selective towards glucaric acid, gluconic acid and arabitol (total selectivity approx. 70%) than the most popular photocatalyst, Evonik P-25. In terms of phenol mineralization, 1.5 hours are good enough for total degradation of phenol in presence of TiO2(US) and bubbling air through 50 ppm phenol solution.

• The results concerning the study of the Strong Metal Support Interaction (SMSI) effect of Pd/TiO2 and Pt/TiO2 on the photocatalytic reforming of glucose in aqueous solution to biohydrogen. In this investigation, these two different photocatalytic systems prepared by ultrasound-promoted sol-gel method were submitted to diverse oxidative and reductive calcinations post-treatments and tested for the above-mentioned reaction. Oxidation and reduction at 850º C resulted in better photocatalysts for hydrogen production than Evonik P-25 and the ones prepared at 500º C, despite the fact that the best photocatalyst (Pt/TiO2) consisted in very low surface area (6 – 8 m2/g) rutile titania specimens. The Pt-containing systems prepared at 850º C gave the most active catalysts (ca. 4.8 mmol of hydrogen after 9 hours of irradiation). By XPS analyses, it was concluded that the greater SMSI effect, the better the catalytic performance.

• The photocatalysts designed and synthesised at the IPC PAS are activated by solar or UV light, and the actual chemical reaction can take place at a temperature of about 30°C and under normal pressure. Such conditions naturally occur in many places on Earth. The crucial component of the new photocatalysts is titanium dioxide doped with small amount of iron or chromium atoms. All these materials are commonly available and cheap. The photocatalysts are deposited on appropriate supports – fumed silica or zeolites (crystalline aluminosilicates of Y type) – using common laboratory equipment: a rotary evaporator and an ultrasonic bath. Ultrasonic irradiation of a solution containing precursors of titania and chromium or iron generates microbubbles of high pressure and temperature. We could manage these conditions and prepare nanocomposite materials which were very stable and photocatalytic active.

• Silica supported photocatalysts (modified with iron or chromium) turned out to be particularly effective in phenol mineralization, leading to a high degree of phenol oxidation and yielding water and carbon dioxide as the reaction products. Zeolite supported systems (modified with iron or chromium) catalysed glucose partial degradation (glucose is a monomer forming cellulose polymer chains) resulting in formation of gluconic and glucaric acids with high selectivities (>85%). These carboxylic acids are important intemediates used in food, pharmaceutical and cosmetic industries. What's particularly important is that the analyses performed by Dr Colmenares' group clearly prove that there is no release of chromium or iron atoms to water during the entire cleaning process. After the reaction is completed, the photocatalyst can be easily recovered. Due to durable deposition on silica or zeolite particles of relatively large (micrometric) size, it's enough to filter water to get the catalyst back. The recovered powder can be reused, and multiple repetition of the cycle does not significantly affect the catalyst performance.

• In terms of plausible application of project results, it can be stated that: many areas worldwide are affected by the problem of growing water pollution by wastes from wood and paper industries, including cellulose and phenol derivatives and the removal of these agents from water can be easier in future due to low cost and easy-to-produce photocatalysts developed by Dr Juan Carlos Colmenares' group from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw. Coatings manufactured of these materials have sufficient mechanical strength to be used, e.g. as swimming pool accessories. With good solar insolation, water in a swimming pool constructed with the use of such materials would be subject to continuous self-cleaning process. Essential advantages of our photocatalysts include simplicity of production, low manufacturing costs and convenience of performing chemical reactions under natural conditions. Equally important is that our materials allow to stop oxidizing water pollutants at desired stage and to obtain substances important for the industry (e.g. carboxylic acids).
We believe that the effectiveness of this innovative idea in the removal of organic contaminants in water with the parallel biomass conversion into useful molecules will contribute to the global fight against water pollution and the energy crisis. Based on the fact that over one billion people in the world suffer from lack of access to clean water, it is no doubt that the goals of this project are very important.

Thanks to the funding support of Marie Curie International Reintegration Grant (European Commission) and the Polish Ministry of Science and Higher Education (grant nr. 473/7.PR/2012) photocatalysis has been systematically developed and adapted to the needs of the Institute of Physical Chemistry of PAS. The host institution approved (IPC-PAS Research Council decision on June 2013) to open a new research team related to the research topics of this project and under the leadership of Dr Colmenares (the fellow). The new research team under the name of “Catalysis for sustainable energy production and environmental protection” (http://photo-catalysis.org/) is officially operating since the beginning of 2014 and is constituted by two Ph.D. students and one technician.