Photobleaching mechanisms of Radachlorin photosensitizer in aqueous solution

The time dependence of the fluorescence intensity of aqueous solutions of Radachlorin photosensitizer at different concentrations and the influence of the dissolved oxygen concentration on the fluorescence dynamics are analyzed. The experimental results are interpreted based on the numerical solution of the system of kinetic equations describing the photochemical processes that lead to the formation and degradation of singlet oxygen in solution. The influence of possible mechanisms of photosensitizer photobleaching is analyzed. It is shown that the main photobleaching mechanism under our experimental conditions is the chemical reaction between the photosensitizer in the triplet state and dissolved oxygen molecules. Two rate constants of electron-transfer chemical reactions, which are important for understanding the nature of the occurring photoprocesses, are determined.     

The use of dosimeters to measure radical production in aqueous sonochemical systems

The use of two dosimeter systems for quantifying radical production during aqueous sonochemical processes has been investigated. The Fricke (Fe²⁺/Fe³⁺) system was found to be useful at higher concentrations but care must be taken in interpreting the results since radical production is not the only process taking place. There is some reaction even in the absence of ultrasound and this involves dissolved oxygen gas. The concentration of hydroxyl radicals formed was accurately monitored at low concentrations using the terephthalate dosimeter and the limits of its applicability were found. Both systems were used to investigate the effect of varying the ultrasound intensity.     

Dosimetry in sonochemistry: the use of aqueous terephthalate ion as a fluorescence monitor

The generation of HO radicals by acoustic cavitation in water was monitored by their reaction with terephthalic acid (TA) anion to produce fluorescent hydroxyterephthalate ions using a cleaning bath (38kHz) and a probe system (20, 40 and 60 kHz) as different sources of ultrasound. When using the ultrasonic bath as a source of energy for sonochemical studies, the shape of the reaction vessel is important. In the case of HO production from water (50 cm³), reaction in a conical flask (100 cm³) produces 2.75 times more radicals than a round-bottomed flask of the same capacity. The fluorescence yield (fluorescence intensity/ultrasound dosage) obtained using the conical flask and ultrasonic bath was similar to that for a probe operating at 40 kHz on the same volume of solution. For a probe system operating at 20, 40 and 60 kHz the greatest sonochemical efficiency was attained at the highest of these frequencies (60 kHz). For the probe system the fluorescence yield is directly proportional to power input and the concentration of TA. The fluorescence yield decreases as the temperature is increased.     

The effect of dissolve gas concentration in the initial growth stage of multi cavitation bubbles. Differences between vacuum degassing and ultrasound degassing

The sonochemical luminescence intensity from luminol was measured at a sampling rate of several kilohertz. This was noted at three different periods: first, the latent period in which no light emission occurs at all; second, the increased emission period from the start of light emission to the time when a steady state is reached; and third, the steady state period in which light emission occurs at the steady state value. When irradiated with ultrasound of different intensities, the times of the latent period and increased emission period are shorter for higher ultrasound intensities. To know how the dissolved oxygen content is involved in early-stage cavitation growth, an experiment was conducted using solutions with varying dissolved oxygen contents from 100% to 37%. For dissolved air content of 50% or less, it was found that the latent period was 30 times longer in a saturated condition. It was also found that the increased emission period was 10 times longer. However, the emission intensity in the steady state did not change at all even when the initial dissolved gas concentration of the sample was changed. From this, it was found that the reuse of collapsed bubbles takes place efficiently in the steady state. Dissolved oxygen was reduced by the use of a vacuum pump and by the degassing action of ultrasound, and it was discovered that the behavior of transient emission differed for the two ways of degassing.     

Zinc-8-hydroxyquinoline intercalated in calcium bentonite: A promising DO sensor

Zn(II) and 8-hydroxyquinoline were made to react in an in situ solid−solid reaction in the interlayer space of Ca-bentonite from Thailand, resulting in [Zn(8-hydroxyquinoline)₂]²⁺, the well known -Znq₂. X-ray diffraction patterns showed that the interlayer space of the bentonite increased from 1.56 to 1.67 nm on going from Zn(II)-bentonite to Znq₂-bentonite, which confirmed the intercalation of Znq₂ in bentonite. The intercalated Znq₂-bentonite compound was mixed with a solution of polystyrene in toluene and coated as a film on a polystyrene sheet. The fluorescence intensity of Znq₂-bentonite film was measured in the presence of dissolved oxygen (DO). It was found that the fluorescence intensity of the film decreased as dissolved oxygen increased, which is a promising result for developing an optical dissolved oxygen sensor (DO sensor). The fluorescence quenching by oxygen followed the Stern-Volmer plot.     

应用于FAGE技术测量OH自由基的激光器波长修正方法研究

研究了一种应用于气体扩张激光诱导荧光(FAGE)技术测量OH自由基的染料激光器波长修正方法。该方法采用镍铝丝热解水汽产生稳定的高浓度OH自由基,利用重复频率为8500 Hz的染料激光器输出波长约282 nm激光作为光源.激发低压腔内热解产生的高浓度高稳定性OH自由基产生荧光,由普通光电倍增管和光电二极管分别探测激发荧光和出腔激光强度。通过延时信号发生器统一触发激光器和高速数据采集卡并结合LabVIEW软件处理得到单位激光强度的荧光积分强度数据。连续两次扫描激光波长,当第二次扫描的荧光积分强度达到第一次最大值的0.95倍时,停止波长扫描,此时的激光器波长位置即为激发线位置。本文首先扫描激光波长,研究了282 nm激发机制下的OH自由基激发谱;然后在Q_1 2激发线位置探究了气体湿度、氧气含量、进气量以及抽速对荧光积分强度和寿命的影响;并分析了镍铝丝热解水的反应机理,初步认为热解中OH自由基主要来源于氧原子与水的反应。在以上荧光积分强度和寿命影响因素的研究基础上,优化了系统参数,使荧光积分强度波动小于±1.9%。连续多次进行波长修正,修正偏差为0.1pm。该方法能够满足气体扩张激光诱导荧光(FAGE)技术定量精确测量大气OH自由基对波长的要求。     

基于单光源频域荧光寿命的水体溶解氧浓度检测方法

现有的光学溶解氧浓度检测方法中光路及电路结构复杂,本文提出了一种单路光源的频域荧光寿命的溶解氧检测方法.采用单路光源的光学结构实现水体溶解氧浓度的检测,简化了光路及电路结构,改进了溶解氧浓度检测算法,降低了整体检测过程的计算量.设计对比实验对方法进行验证,实验结果表明:单光源的频域荧光寿命的检测方法与DOP1光学溶解氧分析仪相比,在0~9mg/L范围内,实际检测误差降低至0.04mg/L;衡量稳定性的检测标准偏差为0.007mg/L,同比降低了36%;采用快速傅里叶变换以及改进的溶解氧浓度计算方法,配合优化的电路及光路结构,在达到90%稳态时响应时间平均缩短了12s,浓度上升和下降时的响应速度分别提升为40%和28%.该方法具有较好的检测精度、稳定性以及响应速度.     

不同水体中有色可溶性有机物质荧光光谱定量分析研究

有色可溶性有机物(CDOM)是指水体中对紫外及可见光均有光吸收的溶解有机物,能对水色产生影响,是自然生态系统、水色光学遥感、水体碳循环研究中必不可少的环境因素。由于CDOM具有荧光特性,荧光光谱技术已成为开展CDOM研究的重要手段,被用于CDOM的来源、分布及其变化规律的研究。文章主要利用荧光检测技术,研究了不同水体CDOM的发射荧光光谱峰面积、荧光峰强度与其浓度间的变化关系,发现在低浓度范围内,发射光谱峰面积和荧光强度与CDOM浓度具有良好的线性关系(r2＞0.98);不同浓度的CDOM水溶液的发射光谱峰面积及其荧光强度随浓度的变化趋势是一致的。文章首次利用低浓度下CDOM的发射光谱峰面积与浓度间的线性关系,建立了适合于水体中组成复杂的CDOM的定量分析方法,拓展了荧光分析技术在CDOM研究中的应用。     

Frequency and power dependence of ultrasonic degassing

We investigated the time variation of ultrasonic degassing for air-saturated water and degassed water with a sample volume of 100 mL at frequencies of 22, 43, 129, 209, 305, 400, 514, 1018, and 1960 kHz and ultrasonic power of 15 W. Ultrasonic degassing was evaluated by dissolved oxygen concentration. Ultrasonic degassing was also investigated at a frequency of 1018 kHz and ultrasonic powers of 5, 10, 15, and 20 W. The dissolved oxygen concentration varied with the ultrasonic irradiation time and became constant after prolonged ultrasonic irradiation. The constant dissolved oxygen concentration value depended on the frequency and ultrasonic power but not the initial dissolved oxygen concentration. The degassing rate at 101.3 kPa was higher in the frequency range of 200 kHz to 1 MHz. The frequency dependence of the degassing rate was almost the same as that of the sonochemical efficiency obtained by the potassium iodide (KI) method. Ultrasonic degassing in the frequency range of 22–1960 kHz was also investigated under reduced pressure of 5 kPa. Degassing was accelerated when ultrasonic irradiation was applied under reduced pressure. However, under a reduced pressure of 5 kPa, the lower the frequencies, the higher is the degassing rate. The sonochemical reaction rate was examined by the KI method for varying dissolved air concentrations before ultrasonic irradiation. Cavitation did not occur when the initial dissolved oxygen concentration was less than 2 mg·L⁻¹. Therefore, the lower limit of ultrasonic degassing under 101.3 kPa equals 2 mg·L⁻¹ dissolved oxygen concentration. A model equation for the time variation of dissolved oxygen concentration due to ultrasonic irradiation was developed, and the degassing mechanism was discussed.