Hierarchical 1-3D titania Hyper-Branched Nanorods (HBNs) thin films for photocatalytic CO2 utilisation applications

Despite our efforts, the concentration of CO2 in the atmosphere is constantly rising at an alarming rate. It is of paramount importance to develop technologies that will expedite the reduction of the rate that CO2 is released into the atmosphere. CO2 utilisation technologies consider CO2 as a valuable carbon building block in a circular carbon economy approach, where the released CO2 is captured, and utilised to produce valuable chemicals. One of these technologies is the photocatalytic utilisation of CO2 for the production of solar fuels and value added chemicals, which has the added advantage of utilising light with mild reaction conditions. However, photocatalysis is limited to the absorbed light energy and CO2 is a very stable molecule which requires a large amount of energy for its conversion. Therefore, designing highly efficient materials as photocatalysts becomes a very important task. The current thesis is concerned with the growth of titania 1-3D hierarchical hyperbranched nanorods (HBNs) on fluorine-doped tin oxide (FTO) conductive glass as thin films to be used as photocatalysts for CO2 reduction reactions. This thesis is focused on investigating the capabilities and photocatalytic behaviour of the titania HBNs material. The HBNs were found to have improved light harvesting when compared to Degussa P25 TiO2 (48.2 to 28.6 μmol m 2 s -1 ), attributed to their 1-3D morphology. P25 is a blend of mainly anatase and traces of rutile phase TiO2, commonly used as a benchmark for photocatalytic applications. P25 was supported on FTO glass and its performance was compared with that of FTO supported HBNs. This thesis is presented as a collection of published bodies of work, where the HBNs are characterised, modified and tested in photocatalytic reactions. In more detail, two reactions are presented, firstly the CO2 photoreduction to produce solar fuels such as CH4 and CO. The HBNs were found to have superior conversion rates (up to 8.7 μmol gcat -1 h -1 ) compared to P25 (6.9 μmol gcat -1 h -1 ) but, more importantly, offer the ability to shift the selectivity of the reaction product from CO to CH4, utilising a facile phase altering treatment. Additionally, the HBNs were loaded with CuO and RuO2 and their performance was investigated and compared. CuO has shown the ability to improve the optical properties of the material, while RuO2 exhibited improved charge separation and suppressed the recombination rate, which led to further improvement in the photocatalytic performance. The second reaction is the CO2 cycloaddition to epoxides, for the photogeneration of cyclic carbonates, which are primarily used as electrolytes in Li-ion batteries amongst others. In the current thesis it is demonstrated that a photocatalytic approach is possible for this reaction. Additionally, RuO2-HBNs are shown to be the best performing photocatalyst in terms of conversion. The main appeal of the photocatalytic approach is the significantly milder reaction conditions (below 55 °C and 200 kPa) when compared to the conditions currently being used in the industry (100-200 °C and 5- 10 MPa).Heriot-Watt University fundin

Investigation of solid base catalysts for biodiesel production from fish oil

The authors would like to acknowledge Innovate UK for funding. Additionally, the authors would like to thank Dr Gavin Peters for the TGA and ICP-OES measurements. Finally, we would like to thank the Engineering and Physical Sciences Research Council, University of St Andrews, and CRITICAT Centre for Doctoral Training for financial support [Ph.D. studentship to M.D.V.T, S.G, and E. B; Grant code: EP/L016419/1].A series of composite CaO-Ca3Al2O6 mixed oxides were investigated as potential catalysts for biodiesel synthesis from waste fish oil. Different Ca/Al ratios, in the range of 1.5 to 6 were studied, alongside pure CaO. The catalysts were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and CO2-Temperature Program Desorption (TPD). The catalytic activity of the materials was studied for the transesterification reaction of cod liver oil with methanol at 65 °C, with 1:12 oil to methanol molar ratio and 10 wt% of catalyst. Over 97% conversion of the triglycerides to methyl esters was achieved for the 6Ca/Al catalyst after 2 h reaction time. This was similar to the performance of CaO. However, 6Ca/Al catalyst was reused successfully for seven consecutive tests, in contrast to CaO that was reused for only five tests, before it deactivated. Therefore, by incorporating the Ca3Al2O6, it was possible to enhance the stability of the catalytically active species and improve the lifetime of the catalyst. Post-test catalyst characterisation showed the formation of an intermediate phase (calcium diglyceroxide) that enhanced the catalyst’s performance and tolerance to air exposure and humidity. Finally, the catalyst deactivation, after seven cycles, took place due to the formation of Ca(OH)2 and CaCO3 species.PostprintPeer reviewe

Hierarchical hyper-branched titania nanorods with tuneable selectivity for CO₂photoreduction

Utilising captured CO(2) and converting it into solar fuels can be extremely beneficial in reducing the constantly rising CO(2) concentration in the atmosphere while simultaneously addressing energy crisis issues. Hence, many researchers have focused their work on the CO(2) photoreduction reaction for the last 4 decades. Herein, the titania hyper-branched nanorod (HBN) thin films, with a novel hierarchical dendritic morphology, revealed enhanced CO(2) photoreduction performance. The HBNs exhibited enhanced photogenerated charge production (66%), in comparison with P25 (39%), due to the unique hyper-branched morphology. Furthermore, the proposed HBN thin films exhibited a high degree of control over the product selectivity, by undergoing a facile phase-altering treatment. The selectivity was shifted from 91% towards CO, to 67% towards CH(4). Additionally, the HBN samples showed the potential to surpass the conversion rates of the benchmark P25 TiO(2) in both CO and CH(4) production. To further enhance the selectivity and overall performance of the HBNs, RuO(2) was incorporated into the synthesis, which enhanced the CH(4) selectivity from 67% to 74%; whereas the incorporation of CuO revealed a selectivity profile comparative to P25

Alkali modified P25 with enhanced CO₂adsorption for CO₂photoreduction

To improve the CO(2) adsorption on the photocatalyst, which is an essential step for CO(2) photoreduction, solid solutions were fabricated using a facile calcination treatment at 900 °C. Using various alkalis, namely NaOH, Na(2)CO(3), KOH, K(2)CO(3), the resulted samples presented a much higher CO(2) adsorption capacity, which was measured with the pulse injection of CO(2) on the temperature programmed desorption workstation, compared to the pristine Evonik P25. As a result, all of the fabricated solid solutions produced higer yield of CO under UV light irradiation due to the increased basicity of the solid solutions even though they possessed only the rutile polymorph of TiO(2). The highest CO(2) adsorption capacity under UV irradiation was observed in the sample treated with NaOH, which contained the highest amount of isolated hydroxyls, as shown in the FTIR studies

Investigation of solid base catalysts for biodiesel production from fish oil

A series of composite CaO-Ca3Al2O6 mixed oxides were investigated as potential catalysts for biodiesel synthesis from waste fish oil. Different Ca/Al ratios, in the range of 1.5 to 6 were studied, alongside pure CaO. The catalysts were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and CO2-Temperature Program Desorption (TPD). The catalytic activity of the materials was studied for the transesterification reaction of cod liver oil with methanol at 65 °C, with 1:12 oil to methanol molar ratio and 10 wt% of catalyst. Over 97% conversion of the triglycerides to methyl esters was achieved for the 6Ca/Al catalyst after 2 h reaction time. This was similar to the performance of CaO. However, 6Ca/Al catalyst was reused successfully for seven consecutive tests, in contrast to CaO that was reused for only five tests, before it deactivated. Therefore, by incorporating the Ca3Al2O6, it was possible to enhance the stability of the catalytically active species and improve the lifetime of the catalyst. Post-test catalyst characterisation showed the formation of an intermediate phase (calcium diglyceroxide) that enhanced the catalyst’s performance and tolerance to air exposure and humidity. Finally, the catalyst deactivation, after seven cycles, took place due to the formation of Ca(OH)2 and CaCO3 species

Comparative study of CO₂ photoreduction using different conformations of CuO photocatalyst:Powder, coating on mesh and thin film

The use of CuO-based photocatalysts for CO2 photoreduction has been extensively reported in the literature. However, the comparison of the photocatalytic activity and selectivity from the published results becomes difficult due to different experimental conditions (i.e., synthesis method, configuration of photocatalyst, flow rate of gas, water content, light intensity) and reactor geometry employed. Hence, in this work different conformations of CuO-based photocatalyst, namely powder (i.e., synthesized using precipitation, sonochemical and hydrothermal-microwave treatment), coating on glass fiber mesh, and thin film, were tested using the same photoreactor and experimental conditions. All CuO photocatalysts exhibited 100 % product selectivity towards CH4 over CO and the CuO coating on the glass fiber mesh exhibited the highest production of CH4 (56.3 μmol gcat − 1h− 1). The morphology, particle size, particle dispersity, and presence of impurities/defects within the CuO photocatalysts had a significant effect on photocatalytic activity. A numerical model, which was built using COMSOL, revealed that the experimental data obtained in this simulated photocatalytic activity study fitted well, however, further optimization was needed