Conference Agenda

Photochemical reactions are emerging as transformative tools for sustainable chemical manufacturing, offering energy-efficient pathways to synthesize fine chemicals, pharmaceuticals, and renewable fuels while minimizing waste and fossil fuel dependence. However, their industrial adoption hinges on overcoming critical scalability challenges tied to photon and mass transport and eventually reactor design. Due to the complex interaction of the different transport processes, the transfer of photochemical processes from laboratory to industrial scale remains a considerable challenge.

The availability of photons to drive reactions is governing not only the reaction rate but also determines selectivity and lifetime of catalytic systems. End-point analysis, for instance with gas chromatography, often only provides information on the overall activity after the catalytic system is not active anymore, without the possibility to conclude on the reasons of e.g. deactivation or observed selectivity. Online spectroscopy allows to bridge the gap between the macroscopically observed activity and the underlying chemical reasons as time-resolved, i.e. kinetic, information can be obtained.

This contribution will discuss recent results on the effect of dynamic irradiation on the efficiency of light-driven water splitting. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 31 referring to the external energy efficiency by controlling the local availability of photons. Detailed insights into the mechanism of light driven water oxidation could be obtained using complementary methods of investigation like Raman, IR, and UV/Vis/emission spectroscopy, unraveling the importance of avoiding high concentrations of excited photo-sensitizers.

Spectroelectrochemistry, particularly the combination of electrochemical techniques with vibrational spectroscopy, such as Raman or mid-IR spectroscopy, has gained significant interest. This is because it provides molecular information on electrochemically or interfacially driven processes at the solid/electrolyte interface, offering selectivity, sensitivity and, depending on the combined platform, temporal and spatial resolution [1, 2]. Various approaches have been employed in the development of experimental setups, including hybrid analytical platforms that combine electrochemical and/or molecularly specific information with spatially resolved measurements. Boron-doped diamond (BDD) is highly suitable for spectroelectrochemical investigations in the mid-IR region as an IR-transparent electrode. It is characterized by a large potential window, a broad spectroscopic window, chemical inertness and favorable signal-to-noise ratios [3]. BDD's excellent chemical and physical properties, and the ability to fabricate BDD-modified diamond ATR crystals, render it highly suitable for spectroelectrochemical applications. Examples of such combined measurements include the electrochemical deposition of conducting polymers, which was investigated via AFM and IR-ATR. AFM provides the advantage that additional information, such as adhesion forces, can be obtained. To improve electrochemical sensitivity and take advantage of surface-enhanced infrared absorption (SEIRA), BDD can be modified electrochemically with metal nanoparticles, such as gold and silver (NPs) [4].

This contribution presents combined scanning probe techniques with mid-IR ATR spectroscopy for in situ investigations of processes occurring at BDD or Au nanoparticle-modified BDD surfaces. Additionally, the potential of mid-IR spectroelectrochemistry to provide mechanistic insight into light-driven water oxidation catalysis (WOC) is explored [5].

Solar radiation is the principal source of energy on Earth and has unmatched potential for the synthesis of organic material from primordial molecular building blocks. Providing the energy for photochemical synthesis of (proto)biomolecules, light has also been found to often provide remarkable selectivity in these processes. Reactivity and selectivity in photochemical prebiotic synthesis is a topic of long interest.[1-6]

There is much evidence suggesting that HCN (hydrogen cyanide, or formonitrile) was important in prebiotic synthesis.[7] Diaminomaleonitrile (DAMN, chemical formula C₄N₄H₄) is the most prominent low molecular weight product formed during the condensation of HCN to oligomers.[8, 9] The major interest in DAMN is concerned with its significance in the prebiotic synthesis of adenine (chemical formula C₅N₅H₅) and other heterocycles under the primitive Earth conditions.[9, 10]

In the present work we explore the UV-induced photochemistry of DAMN monomers isolated in a cryogenic inert matrix.[11] Photoinduced hydrogen-atom transfer was found to be the major process occurring upon UV-irradiations of DAMN. The transfer of a hydrogen atom from NH₂ group to a nitrile fragment resulted in isomerization to another open-ring tautomer of DAMN involving a ketenimine group. Another photoinduced reaction resulted in the formation of the heterocyclic compound, amino-imidazole-carbonitrile (AICN, chemical formula C₄N₄H₄). Hereby we proved that the light-induced cyclization of DAMN is its intrinsic property, which occurs on the monomeric level and without any solvent involved. We also show that the ring-closure photochemistry of DAMN, via ketenimine isomer, is selective and leads to only one specific tautomeric form of AICN. The mechanistic analysis of the observed transformations will be presented.[11]

Funding

Funded by the European Union, project H2OforAll: Innovative Integrated Tools and Technologies to Protect and Treat Drinking Water from Disinfection Byproducts (Grant Agreement GA101081953). The Research Centre on Chemical Engineering and Renewable Resources for Sustainability (CERES) is supported by the Portuguese Science Foundation (“Fundação para a Ciencia e a Tecnologia”, FCT) through FCT projects UIDB/EQU/00102/2020, DOI: https://doi.org/10.54499/UIDB/00102/2020 and UIDP/EQU/00102/2020, DOI: https://doi.org/10.54499/UIDP/00102/2020 (National Funds).

References

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