Effect of Oxygen in a Thin-Film Rotating Disk Photocatalytic Reactor

Abstract

A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.

Visible‐Light Photocatalytic Degradation of Methylene Blue Using SnO2/α‐Fe2O3 Hierarchical Nanoheterostructures

“…Consequently, the interfacial electron-hole pair separation in the SHNHs would be bidirectional, as illustrated in Figure S13. This is probably because the photocatalyst possesses an unusual hierarchical nanostructure: [39][40][41] 1) the obtained netlike substructures of the nanosheets in the SnO 2 /a-Fe 2 O 3 SHNHs can serve as "electron-transfer channels", which can reduce the recombination of photogenerated electron-hole pairs and be of great benefit to the photocatalytic reaction; 2) highly porous structures can be considered as transport routes for molecules of MB and products moving in or out of the material. The pore size (5.61 nm) of the SnO 2 /a-Fe 2 O 3 SHNHs is bigger than that of P25 (TiO 2 ) (3.85 nm), providing much more suitable space; 3) the SnO 2 /a-Fe 2 O 3 SHNHs allow multiple reflections of UV light in the nanopetals, facilitating more efficient use of the light source.…”

Nanocrystalline TiO2 Photocatalytic Membranes with a Hierarchical Mesoporous Multilayer Structure: Synthesis, Characterization, and Multifunction

“…In fact, TiO 2 photocatalysis has been found to be extremely effective for complete mineralization of virtually all organic compounds and for inactivation of pathogenic microorganisms present in contaminated water. [11][12][13][14] An inorganic membrane generally consists of a macroporous substrate providing mechanical strength for an overlying thin active layer. [15,16] It is known that the quality of the underlying support layer determines, to a large extent, the quality of the top skin mesoporous titania membrane.…”

Diffusion-controlled growth of CuAl2O4 nanoparticles: effect of sintering and photodegradation of methyl orange

“…In low-bandgap photocatalysts the recombination of photoinduced electrons and holes decrease the availability of OH • [55,56] consequently reducing the photocatalytic efficiency. Thus, it is desirable to suppress this recombination for increased photocatalytic efficiency, which can be achieved using electron acceptors such as H 2 O 2 .…”