Microfluidic fabrication of hollow photocatalytic fiber for gas purification and water recovery

Abstract

It has become imminent to address the environmental and energy challenges, owing to the increasing population and energy crisis in recent years. In order to produce sustainable energy efficiently, photocatalysis is an attractive way forward. Extensive amount of research investigations has been explored with a focus on fabricating new photocatalysts or combining different photocatalysts for heterojunction composites, but the difficult problem of photocatalyst recovery after use has been ignored. In practical applications, macroscopic materials with millimeter or centimeter scales are more easily to manipulate and recycle in the process. In addition, among different structures, hollow structures that exhibit unique characteristics of flexibility and large specific surface area, have attracted increasing attentions.
In recent decades, microfluidics has become a family of alternatives of preparation methods due to its stable and controllable properties. Thus, the large-sized hollow fibers could be selected, designed and obtained through microfluidic method for loading different kinds of photocatalysts, overcoming the easy agglomeration problem of traditional powder. Apart from that, functional hollow fibers and tubes can also be used for environmental protection and energy conversion. This thesis aims to prepare different types of functional hollow fibers or tubes with special structures through microfluidic approach and microfluidic-assisted method, and endow them to be applied in gas treatment area such as NO removal, H2 generation, and also water recovery from condensation. The details are listed below:
(1) A novel hollow Ca-alginate microfibers containing CNT/TiO2 hetero-structure photocatalysts were successfully synthesized through a facile and stable microfluidic method. The formation conditions for hollow fibers have been investigated and explained. Hollow Ca-alginate microfibers with diameter of around 1000 µm were then used as the ideal support for powder CNT/TiO2. Optimal CNT(10%)/TiO2 microfibers exhibited superior performance with NO removal efficiency of 44.3% under visible light.
(2) Simulation and experimental study of heat transfer performance based on hollow tubes with different wettability have been investigated, in which microfluidics-assisted and 3D printing methods were used for preparing surfaces of hydrophilicity and hydrophobicity, respectively. A detailed model was designed for exploring the condensation of vapor. In experimental observation, the overall heat flux can be improved by optimizing the parameters of tube wall thickness, cooling water flow velocity and chamber heating temperature. Highest amount of condensate water is generated when the flow velocity of cooling water is 0.2 m/s and the velocity of vapor is 0.1 m/s.
(3) A novel large-sized nanofilm-constructed hierarchical porous SiO2 (LNCHPS) fiber was successfully synthesized through templating and microfluidic method, showing the improved performance as a candidate to support g-C3N4. The g-C3N4/LNCHPS exhibited high RhB photocatalytic degradation performance, which is 6.0 times that of bulk g-C3N4, and high stability after 4 cycles. The g-C3N4/LNCHPS also leads to great H2 production amount of 200 µmol after 5 h in a single run.
In summary, this thesis has introduced microfluidics method or microfluidics-assisted method for synthesizing several types of functional hollow fiber or tube materials. They have exhibited considerable activity and properties in different applications. In addition, the relationship between the performance and the structure morphology has been further demonstrated.

Date of Award	17 Mar 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Yong Ren (Supervisor), Xinyu Zhang (Supervisor) & Yuying Yan (Supervisor)