卤素离子对溶解性黑碳光化学活性的影响

溶解性黑碳(DBC)是天然有机质的重要组分,但其在河口水环境中的光化学活性尚不清楚.为解决这个问题,以大豆秸秆溶解性黑碳为目标物,使用山梨酸能量转移同分异构方法研究河口水卤素离子浓度条件下激发三重态DBC (³DBC^*)的生成速率(F_T)、淬灭速率(k_s')、稳态浓度(T]_ss)变化规律,并使用2,4,6-三甲基苯酚电子转移探针方法研究卤素离子对³DBC^*电子转移过程的影响.结果表明,卤素离子及其离子强度作用对F_T无显著影响,但k_s'因离子强度和Br^-重原子效应而减小,导致³DBC^*的T]_ss增加.高浓度DBC光化学实验证实离子强度作用引起DBC分子聚集,导致³DBC^*的电荷转移过程减弱,从而抑制³DBC^*的淬灭.山梨酸探针实验表明,卤素离子及其离子强度作用对³DBC^*的能量转移无直接影响,主要是通过抑制³DBC^*的淬灭,增加T]_ss.进一步研究发现卤素离子及其离子强度作用对低能态³DBC^*(E_T < 250kJ/mol)无显著影响,但抑制高能态³DBC^*(E_T > 250kJ/mol)的电子转移,且随卤素离子和离子强度的增加而愈发明显.

Effect of halogen ions on photochemical activity of dissolved black carbon

Dissolved black carbon (DBC) is regarded as an important part of natural organic matter, however, its photochemical activity in the estuary is not clear. Here, the soybean straw DBC as the target, the changes in the formation rate (F_T), the loss rate constants (k_s’), and the steady-state concentrations (T]_ss) of ³DBC^* in the presence of halogen ions in the estuary was explored by energy transfer isomerization of sorbic acid. The effects of halogen ions on ³DBC^* electron transfer were studied by 2,4,6-trimethylphenol method. The results showed that halogen ions and ionic strength did not affect F_T, but k_s’ was decreased due to ionic strength and heavy atom effect of Br^-, which increased T]_ss. The photochemical experiment of high concentration DBC confirmed that the ionic strength effect caused the aggregation of DBC molecules, which weakened the charge transfer of ³DBC^* and inhibited the quenching of ³DBC^*. For energy transfer of ³DBC^*, it was not directly affected by halogen ions and ionic strength, but by the increase of T]_ss. Moreover, it was further found that halogen ions and ionic strength had no significant effect on the low-energy (E_T < 250kJ/mol) ³DBC^*, but only on high-energy ³DBC^*and became obviously with the increase of the concentrations of halogen ions and ionic strength.