Application of Chemiluminescent Probe to Monitoring Superoxide Radicals and Hydrogen Peroxide in TiO₂ Photocatalysis

Abstract

A chemiluminescent probe, luminol, was successfully applied to monitoring superoxide ions (O2 •-) and hydrogen peroxide (H2O2) produced on photocatalytic reaction in aqueous TiO2 suspension. Two chemiluminescent reactions were distinguished from the decay profile after the end of the irradiation, and the reaction mechanism was analyzed. The fast decay component gives information about O2 •- and the slow one provides the amount of H2O2. The rate constant for the reaction of O2 •- with luminol was found to be 1 × 104 M-1 s-1. The amount of O2 •- during the irradiation on TiO2 in alkaline solution could be estimated to be on the order of 10-13 M. Detection of H2O2 in concentrations as small as 10-9 M was demonstrated in the photocatalytic water oxidation.

Time‐resolved chemiluminescence study of the TiO2 photocatalytic reaction and its induced active oxygen species

“…Moreover, the reaction dynamics on the µs-ms timescale is quite different from those on the s and min timescale (15)(16)(17)(18)(19)(20)(21). Thus, further details remain to be investigated.…”

“…Recently, a fluorescence technique with terephthalic acid (TA) has been developed to detect ·OH formed in TiO 2 suspension (14). Besides these methods, luminol chemiluminescence (CL) has also been widely used to detect O 2 ·− and H 2 O 2 in the TiO 2 photocatalytic reaction (15)(16)(17)(18)(19)(20)(21).…”

“…A luminol solution was added either before or after the illumination. By measuring the CL decay, the luminol CL caused by O 2 ·− and H 2 O 2 could be examined on a timescale of seconds (15)(16)(17)(18)(19)(20)(21). However, it was difficult to observe the initial CL dynamics on timescales <1 s in these experiments.…”

Experimental Evidence of the Mobility of Hydroperoxyl/Superoxide Anion Radicals from the Illuminated TiO2Interface into the Aqueous Phase

“…5 However, as the CL signal generated by the presence of H2O2 is approximately 10,000 times less sensitive than that of HO 2 · / O 2 -· , 20 this interference is likely to be negligible. 3,6,9,10 The reaction for the mobility of HO2 · /O2 -· generated from the surface of illuminated TiO 2 particles is illustrated in Figure 5. Briefly, the photocatalysis of In addition, the effective Henry's law constant of HO 2 · /O 2 -· at pH above 4 increases with pH and contributes to increasing solubility, resulting in more desorption from the TiO2 surface and mobility into the available aqueous phase.…”

“…1,2 To date, most of the work in this area has focused on the photocatalytic activity at the TiO2 interface by studying of the oxidation power of photogenerated hole (h + ) and reactive oxygen species such as the hydroxyl radical (·OH). [1][2][3][4] However, recent studies have paid much more attention to the behaviors of hydroperoxyl/ superoxide anion radicals (HO 2 · /O 2 -· , pK a = 4.80) 5 produced as a result of electron transfer from the TiO2 surface to dissolved oxygen (O 2 ), [6][7][8][9][10][11][12] because an understanding of these behaviors is essential to improve the efficiency of TiO 2 photocatalytic reactions by discouraging photoinduced electronhole (e --h + ) recombination. [13][14][15] Nosaka et al 6 have recently developed a chemiluminescence (CL) method to detect O2 · -formation by observing the time dependence of the intensity of luminol dropped on the illuminated alkaline TiO 2 suspension.…”