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For the realization of a sustainable energy economy, it is of great importance to develop CO2 -neutral methods producing multi-carbon organic chemicals used as feedstock in the chemical industry as well as carbon-neutral fuels. A promising method to alleviate the greenhouse effect and thereby forming value-added chemicals or syngas as an energy carrier, is through the electrochemical CO2 reduction reaction (CO2RR). In this work, a bioelectrotechnological approach is developed, in which the CO2RR reaction products (CO and H2) are directly fed to bacteria (acetogens), who use them as “reduction equivalents” to further metabolize CO2 to valuable carbon compounds. Therefore, a bio-electrochemical system consisting of a bioreactor coupled to a CO2 electrolysis cell will be established. Currently, scarce catalysts such as Ag and Au are used as for the CO2RR which may hamper the use of decentral CO2 conversion technology for cost reasons.
The technological viability of the bacteria-assisted electrolysis depends on the usage of efficient, biocompatible, and selective electrocatalysts prepared from inexpensive precursors. Porous transition metal and nitrogen co-doped carbons (M-N-Cs) have emerged as precious-metal free electrocatalysts for the direct electrochemical reduction of CO2 into CO and are excellent candidates for scale-up and deployment in technological applications. Furthermore, Co/Ni/Zn functioning as the catalytically active sites will be used, as they are expected to depict non-bactericidal properties in contrast to Cu and Ag catalysts. The non-bactericidal property could e.g., allow for application within the hybrid device (bio-electrochemical system), without the need to separate bacteria and cathode catalyst. The MNCs with the most promising electrocatalytic activity and selectivity will be evaluated in abiotic conditions in the hybrid bio-electrochemical reactor system.
Singlet oxygen generation potential of two novel free-base-porphyrin photocatalysts was investigated. The freebase-porphyrin-sensitized Fe3O4 magnetic nanoparticles (MNPs) were tested for the degradation of the model pollutant Bisphenol A (BPA) in aqueous solution, for the first time. MNPs with either cubic or spherical shape were synthesized using the sonochemical approach, followed by sensitizing with photoactive 4,4′,4′′,4′′′- (Porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (TCPP). The resulted photocatalysts were characterized in detail by scanning and transmission electron microscopy, Brunauer–Emmett–Teller analysis, spectral techniques and vibrating sample magnetometry. The electron spin resonance experiments have confirmed the high activity of the photocatalysts through the efficient formation of singlet oxygen in solution. The optimum operational parameters for BPA degradation were established as follows: 1.0 μmol L−1 BPA, 1.0 g L−1 of photocatalyst, 100 μmol L−1 H2O2, under UVA irradiation. In these conditions, the results for both photocatalysts revealed that after only 10 min of reaction, over 64% and ca. 90% of BPA have been removed from solution in the absence and presence of H2O2, respectively. Whereas after 60 minutes of treatment, only 24% of BPA in real wastewater effluent samples were removed under UVA irradiation in the absence of H2O2, showing the high complexity of real wastewater. Moreover, both photocatalysts were successfully used for BPA removal in three consecutive runs, without significant loss of catalytic features.
Three types of hybrid modified magnetite (Fe₃O₄) nanoparticles, functionalized with either chitosan, chitosan/iron (II) oxalate or chitosan/iron (III) citrate, were synthesized by chemical precipitation method.
The obtained nanomaterials were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, scanning and Transmission electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometry. The prepared composites were further tested as magnetic catalysts for the removal of bisphenol A (BPA) in aqueous media. The kinetic Degradation experiments were performed at laboratory scale, while the best operational parameters for all three materials were established: 1.00 g L⁻¹ of catalyst, 10 mmol L⁻¹ H₂O₂, under simulated solar light irradiation.
After 15 min of UVA irradiation under the experimental conditions mentioned above, it was possible to decompose up to 99% of the micropollutant over all catalysts. Fe₃O₄/chitosan/iron oxalate catalyst showed the highest and fastest catalytic activity in BPA removal. Catalytic wet peroxide oxidation of non-biodegradable micropollutants on such iron-based hybrid nanoparticles can be a suitable pre-treatment method for wastewater decontamination, as an environment-friendly simplified Approach for water clean-up.