Title : Undoped and Co-doped anatase-brookite catalysts – An experimental/theoretical study of the less-studied TiO2 mixed phase
Organic pollutants (OrPo) removal from wastewater is challenging, due to their unique behaviour, mechanisms and side effects. Advanced oxidation process (AOPs) is a group methods based on pollutants mineralization by generating highly reactive oxygen species (ROS), such as hydroxyl radicals (•OH). The diffusion distance of •OH ROS was determined to be between 1.3 and 2.4 nm (after the catalytic surfaces). Therefore, maintaining the OrPo inside the •OH ROS attack range (1.3-2.4 nm) is crucial. Molecular recognition (MRec) is an essential requirement in the initial stage of organic reactions. After the MRec, molecular-orientations and molecular-orbitals energy-levels (MOrbE) will occur. In the photocatalytic systems, MRec will be performed in the catalyst-environment interface (restricted by •OH ROS at 1.3-2.4 nm above catalytic surface). This interface has been studied using a variety of theoretical approaches due to its complexity. Molecular dynamics (MD) simulation is a powerful tool employed to explore the interface nature by assessing the surface/environment energy affinities (Ebinding) related with MRec. Thus, if the MRec is also taken into consideration as a key component, the understanding of photocatalytic systems used in AOPs wastewater treatment would be increased.
This experimental/theoretical study focused to provide additional parameters to comprehend less studied anatase-brookite mixed-phase (doped and undoped), in H2O (aerobic/anaerobic) environments, Vis-light and OrPo methyl orange (MO). Nanoparticles of anatase-brookite mixed-phase (TiO2NP) and anatase-brookite mixed-phase doping with 0.1 at% of Co (TiO2NP-Co) photocatalysts were obtained using the sol-gel technique. Several methods (XRD, BET, SEM, HR-TEM and FT-IR) were used to characterize the morphologies and surfaces. UV-vis DRS and PL, respectively, were employed to study photo-response and electron-hole pair (e--h+) recombination. The position of the conduction-band (CB) and valence-band (VB) was determined using the Mott-Schottky plot. Finally, MD simulation was used to study the MRec of the systems, focusing on the second-order interactions (van der Waals and Hydrogen bonds) between catalysts-environments.
The results exhibit that the photoactivity in Vis-light is boosted by anatase-brookite mixed-phase. But distinct MO degradation rates in TiO2NP and TiO2NP-Co were exhibited, indicating that their •OH ROS generation and MO degradation behaviours are unique. The Mott-Schottky plot suggests that TiO2NP band is thermodynamically favourable for water splitting, whereas TiO2NP-Co is favourable toward oxygen reduction. As result, TiO2NP-Co is favored by an aerobic environment (O2 rich) because oxygen molecules remove electrons from CB to produce •O2- ROS which will transform into •OH ROS.
The DM results revealed that the doping-free surfaces (121-brookite and 101-anatase) possessed an advantageous surface affinity. According to TiO2NP Ebinding values of, anatase is the phase that generates •OH ROS via H2O oxidation, while brookite is the phase that strongly attracts the MO molecule toward the reaction zone (favourable MRec between MO and surfaces). The TiO2NP-Co Ebinding values show a reduction in affinity toward MO, indicating that MO will be less attracted to the reactive zone in this catalyst. TiO2NP experimental/theoretical results exhibit remarkable photocatalytic degradation toward MO in both aerobic and anaerobic environments.
What will audience learn from your presentation?
The crucial function of molecular recognition.
A deep comprehension of the catalytic interface.
The Interpretation of binding energies in photocatalytic systems.
- Explain how the audience will be able to use what they learn?
- The catalyst plays an unquestionable role, but the media on the catalytic surface is the other component of the system. The OrPo behavior will play a key role, as well as, the reactive media. If the surfaces are not compatible with the components in the reactive media, the photocatalytic system won't be efficient. The first approximations of the different components are equally important that the energy-levels of the catalysts.
- How will this help the audience in their job?
- This contribution has been addressed to analyze the photocatalytic systems (applied in wastewater treatment) from multiples point of view. The different theoretical sceneries can offer different insights on their works.
- Is this research that other faculty could use to expand their research or teaching? Yes
- Does this provide a practical solution to a problem that could simplify or make a designer’s job more efficient? No
- Will it improve the accuracy of a design, or provide new information to assist in a design problem? Yes
- List all other benefits
- Multiple characterizations were employed to design/build the theoretical models, which exhibited the influence of the environments in the interface space. The feedback between theoretical and experimental results was established. This theoretical and experimental analysis can be applied to different systems.