TiO2 Photocatalytic Ultrafiltration Membrane Developed with Suspension Plasma Spray Process

Abstract

The suspension plasma spray process was used to fabricate photocatalytic ultrafiltration membranes for potential water and wastewater treatment applications. An aqueous suspension of 30 wt.% titanium dioxide with an average individual particle size of around 30 nm was used as feedstock material. The spray parameters, such as suspension solid content, suspension feed rate, and spray distance, were optimized using an Ar/H2 plasma to retain a fraction of unmelted feedstock nanoparticles as the source of fine pores in the membrane microstructure. The microstructure, porosity, phase composition, and pure water permeability of the membranes were characterized comprehensively. The average pore size of the membrane was around 40 nm, which was very close to the particle size of the pristine titanium dioxide powder. The membranes demonstrated a high water permeability between 2000 and 7200 L m−2 h−1 bar−1, which was inversely proportional to the thickness. They also exhibited significant photocatalytic activity under visible light.

A Comparative Study of the Self-Cleaning and Filtration Performance of Suspension Plasma-Sprayed TiO2 Ultrafiltration and Microfiltration Membranes

“…However, the TiO 2 nanosized particles formed natural agglomerates with d 50 = 3.1 µm in the feedstock suspension used in the SPS process. The presence of these agglomerates proved to be essential to produce nanosized pores within the structure [ 21 ]. On the other hand, the MF membrane was produced using a submicron-sized TiO 2 powder, where the average TiO 2 particle size was 137 ± 40 nm, and the SPS feedstock suspension showed d 50 = 280 nm [ 20 ].…”

“…Recently, suspension plasma spray (SPS) technology was introduced by the authors as a novel method to fabricate TiO 2 membranes with average pore sizes in the range of MF and UF, with a rather high pure water permeability and photocatalytic activity under UV and visible light [ 20 , 21 ]. SPS is a developing thermal spray coating deposition process that can produce thin nanostructured coatings due to using a feedstock of submicron- to nanometer-sized particles suspended in a solvent.…”

“…SPS membranes own a unique porous microstructure, where the porosity depends on the presence of the retained unmelted feedstock particles within the structure, and the average pore size relates to the particle size of the pristine feedstock powder. Additionally, SPS TiO 2 membranes exhibit photocatalytic properties under UV and visible light [ 20 , 21 ]. The photocatalytic activity of TiO 2 membranes under visible light is due to the generation of substoichiometric TiO 2−x under SPS conditions [ 27 ].…”

“…The photocatalytic activity of TiO 2 membranes under visible light is due to the generation of substoichiometric TiO 2−x under SPS conditions [ 27 ]. The presence of oxygen vacancies in the lattice of TiO 2−x in the membrane, known as self-doping, leads to lower bandgap energy [ 21 ]. Consequently, SPS TiO 2 membranes can absorb lower-energy photons in the range of visible illumination.…”

“…The primary emphasis of our earlier works was to investigate the feasibility of creating porous structures with pore sizes in the range of UF and MF membranes suitable to use as filtration membranes. [ 20 , 21 ]. In this study, we aimed to build upon those previous efforts and delve deeper into the performance aspects of the SPS membranes.…”