Reaction kinetics of dye decomposition processes monitored inside a photocatalytic microreactor

Abstract

The photocatalytic decomposition processes of several kinds of dyes were monitored in real-time, in a TiO(2)-immobilized microcapillary. Their fluorescence spectra were measured directly from the UV-irradiated area. The photocatalytic reactions proceeded two orders of magnitude faster in the microcapillary than in a bulk reaction, and intermediate species were easily observed, due to their high concentrations compared with those of the reactants. Even for molecules that were not originally fluorescent, fluorescence was detected for the reactants or intermediate species of all the molecules studied. Photocatalytic reactions are typically analyzed in terms of pseudo-first-order or Langmuir-Hinshelwood reaction mechanisms, but it was ascertained that all of the dyes investigated in this study decomposed via a multi-step reaction such as a simple multi-step reaction, a self-catalytic reaction, and further, a more complicated reaction, depending on the molecular structure. These reactions were simulated using models based on the reaction kinetics, and reaction mechanisms were assigned to each type of dye. The fact that intermediate species (which are difficult to observe using conventional analytical methods) were successfully detected meant that mechanisms for different dyes could be further clarified.

Kinetic Modeling of Advanced Oxidation Processes Using Microreactors: Challenges and Opportunities for Scale-Up

“…However, this assumption is not often adequately justified. Tsuchiya et al [60], for example, used a fused silica circular capillary with immobilized TiO 2 for the removal of several dyes from water, and they claim that mass transfer limitations are negligible for an internal diameter of 530 µm, without giving any indication of the adopted length and flow rates and of the relative order of magnitude of the different transport phenomena in the system. On the other hand, in a recent study, Satuf et al [44] report a fully characterized microdevice, giving a mathematical derivation for the estimation of intrinsic kinetic parameters when the reactor is operated under a kinetic regime, i.e., in the absence of external mass limitations.…”

Anodized titania nanotube array microfluidic device for photocatalytic application: Experiment and simulation

“…In their study, the photocatalytic experiments were performed in a batch reactor configuration. Most of the current literature on photocatalytic microfluidic systems involve TiO 2 nanoparticle film as a photocatalyst [14,15,3,16,17]. Subsequently, a more efficient degradation system could be realized by integrating TNA in a microfluidic system.…”

Zinc oxide nano-enabled microfluidic reactor for water purification and its applicability to volatile organic compounds

“…First, most previous reports relate to the use of thin films as the photocatalytic material. Only a few reports relate to nanomaterials [12][13][14] and most often than not, the photocatalytic material is TiO 2 [15][16][17][18] . ZnO is an interesting alternative to TiO 2 , many research groups all over the world focused on this promising research field: developments of ZnO-based photocatalyst in water treatment technology [19][20][21][22][23][24][25][26] .…”