Elucidating the role of adsorption during artificial photosynthesis: H2O and CO2 adsorption isotherms over TiO2 reveal thermal effects under UV illumination

Adsorption measurements of CO2 and H2O over TiO2 surfaces in dark and under illumination were carried out to reveal the ensuing bottlenecks of the initial steps of the artificial photosynthesis reaction. When the adsorption isotherms of both CO2 and H2O were measured under illumination, the results were comparable to isotherms measured at higher temperatures in dark. This evidence is interpreted as the presence of hot spots, due to charge carrier recombination reactions. Differential heat of adsorption measurements revealed that H2O adsorption on TiO2 is stronger, and with a higher coverage than that of CO2. Dissociation of water is an energetically uphill reaction, and the local hot spots due to charge carrier recombination in indirect bandgap semiconductors can enhance the reaction probability. At higher temperatures, higher reaction probabilities are expected and estimated by a thermodynamic analysis for water splitting reaction. The potential role of these hot spots during natural and artificial photosynthetic reactions is discussed.


Elucidating the role of adsorbed states of hydrogen, water and carbon dioxide over TiO2 and Pd/TiO2
Yılmaz, Begü; Üner, Deniz; Department of Chemical Engineering (2020)
Artificial photosynthesis studies aim to utilize solar energy for conversion of CO2 into valuable organics using H2O; however, developments in the area are far from realistic level applications due to the low production rates. In order to understand the mechanism, CO2 and H2O adsorption isotherms over TiO2 P25 were investigated by using a volumetric chemisorption technique with and without an illumination source. Adsorption isotherms revealed indirect evidences on local temperature rise on the surface indic...
Elucidating the Barriers on Direct Water Splitting: Key Role of Oxygen Vacancy Density and Coordination over PbTiO3 and TiO2
METE, ERSEN; Ellialtioglu, Sinasi; GÜLSEREN, Oğuz; Üner, Deniz (2021-01-01)
In this work, using the state-of-the-art first-principles calculations based on density functional theory, we found that the concentration and coordination of surface oxygen vacancies with respect to each other were critical for the direct water-splitting reaction on the (001) surfaces of PbTiO3 and TiO2. For the water-splitting reaction to happen on TiO2-terminated surfaces, it is necessary to have two neighboring O vacancies acting as active sites that host two adsorbing water molecules. However, eventual...
A periodic DFT study of water and ammonia adsorption on anatase TiO2 (001) slab
Erdogan, Rezan; Ozbek, Olus; Önal, Işık (2010-06-15)
Water and ammonia adsorption mechanisms on anatase TiO2 (001) slab surface are investigated by means of periodic DFT approach. Molecular and dissociative adsorption energies for water are calculated to be -15 kcal/mol and -32 kcal/mol, respectively. Similarly, molecular and dissociative adsorption energies of ammonia on the same surface are found as 25 kcal/mol and 20 kcal/mol. A reverse result in this order is reached for the previous case of ONIOM cluster study (23 kcal/mol and 37 kcal/mol, respectively)....
Assessment of diffusive and convective mechanisms during carbon dioxide sequestration into deep saline aquifers
Özgür, Emre; Gümrah, Fevzi; Department of Petroleum and Natural Gas Engineering (2006)
The analytical and numerical modeling of CO2 sequestration in deep saline aquifers having different properties was studied with diffusion and convection mechanisms. The complete dissolution of CO2 in the aquifer by diffusion took thousands, even millions of years. In diffusion dominated system, an aquifer with 100 m thickness saturated with CO2 after 10,000,000 years. It was much earlier in convective dominant system. In diffusion process, the dissolution of CO2 in aquifer increased with porosity increase; ...
The deactivation behavior of the TiO2 used as a photo-catalyst for benzene oxidation
Üner, Deniz (1999-01-01)
In this study, the deactivation behavior of TiO2 as a photocatalyst for benzene decomposition to carbon dioxide and water was investigated. The effect of space time on the benzene and carbon dioxide conversions were monitored. Benzene conversion and carbon dioxide production rates were not correlated, indicating accumulation of a carbon containing intermediate on the surface. This intermediate was blocking the active sites at a stiochiometry of 1 C:1 site. High space times favored the production of carbon d...
Citation Formats
D. Üner and B. Yılmaz, “Elucidating the role of adsorption during artificial photosynthesis: H2O and CO2 adsorption isotherms over TiO2 reveal thermal effects under UV illumination,” PHOTOSYNTHESIS RESEARCH, pp. 0–0, 2022, Accessed: 00, 2022. [Online]. Available: https://hdl.handle.net/11511/99267.