Toxics, Vol. 11, Pages 30: A Novel Chemiluminescent Method for Efficient Evaluation of Heterogeneous Fenton Catalysts Using Cigarette Tar

We have previously studied the CL behavior of tobacco-methanol extract (TME) with the Fe2+/H2O2 system [26]. Herein, the CL characteristics of CTME with the Fe2+/H2O2 system were also investigated. As shown in Figure 1a, the CL emissions of CTME with the Fe2+/H2O2 system were generated at different pH levels ranging from 0 to 14. Results indicated that CTME could undergo CL reactions with Fe2+/H2O2 system in acidic, neutral, and alkaline media as with the TME [26]. CTME exhibited slow CL reactions, which had almost a plateau of long-lasting weak emissions at pH ≤ 2, while there were fast CL reactions for TME, and the CL intensity reached the maximum at pH = 1 [26]. As pH increased, however, the CL intensity of CTME increased until pH 4 and remained stable from pH 4 to 10. From pH 11 to 14, the CL intensity of CTME escalated and then declined drastically. The maximum of CL intensity for CTME was at pH = 12, which was about three times higher than at pH 4 through 10. In contrast, the CL intensity for TME began to decrease at pH > 1 and increased to the maximum at pH = 9 once again [26]. Thereafter, the CL intensity declined [26]. The results show the different CL characteristics between CTME and TME, indicating that the chemiluminophores within CTME and TME were probably different in quantity and type. In addition, the luminescent efficiency of CTME and TME was also examined (Figure S1). The CL intensity of CTME was about two to three times greater than TME at the same mass concentration. This further implied that the process of combustion that generated cigarette tar from tobacco probably changed the chemiluminophores both in quantity and types, which lead to higher luminescent efficiency of CTME than TME.To further examine the CL behavior of CTME with Fe2+/H2O2, CL spectrums of CTME-Fe2+/H2O2 were conducted in acidic, neutral, and alkaline media, respectively (Figure 1b–d). In an acidic medium with 0.1 mM of H2SO4 solution, there were two peaks, one centered at 490 nm and the other at 575 nm (Figure 1b). In H2O as the neutral medium, two maximum peaks appeared at about 490 nm and 590 nm (Figure 1c). The variation of wavelength shifted from 575 nm in an acidic medium to 590 nm in a neutral medium, which could probably be attributed to the change in pH value. In the 0.01 mol/L of NaOH solution representative of the alkaline medium, there was an additional peak relative to the two peaks at 490 nm and 590 nm that emerged at 535 nm (Figure 1d). Furthermore, the CL intensity of peak at 490 nm escalated as pH increased, while the CL intensity at 590 nm in neutral and alkaline media was almost identical but larger than that at 575 nm in the acidic medium. The CL intensities at 590 nm (or 575 nm in an acidic medium) were larger than those at 490 nm regardless of the pH value. CL intensity at 535 nm in an alkaline medium was higher than those both at 490 nm and 590 nm, which is most likely the reason that there was a maximum CL intensity in the 0.01 mol/L of NaOH solution. Overall, approximately three kinds of potential emitting species in CTME participated in CL reactions with Fe2+/H2O2, and the emission wavelength at 490 nm and 590 nm could undergo CL reactions regardless of the pH value for some of the species. This is intriguing given that the conventional CL reactions are usually restricted by pH value. Meanwhile, the emitting species corresponding to the emission wavelength at 535 nm tended to take place CL reaction in alkaline media (e.g., pH = 12), but not in acidic and neutral solutions.

留言 (0)

沒有登入
gif