利用不同波長的光進行藻類有機物的光催化以探討活性物質的產生情形

Abstract

目前將藻類應用於廢水處理程序的研究備受關注，微藻可以經由生物代謝過程去除水中的污染物，且相關研究已證實藻類有機物富含光敏性結構，經光催化後可提高污染物的降解效率。然而，何種波長光源及有機物分子量區間對活性物質的生成影響尚未釐清，故本研究旨在探討不同光源波長及有機物分子量區間對活性物質(三重激發態有機物 3EOM*、單線態氧 1O2及氫氧自由基・OH)的生成影響，以作為未來微藻有機物應用於光催化處理之參考依據。 本研究實驗分為兩階段，第一階段以不同波長光源(紅、黃、藍色LED燈)進行光催化反應，找出活性物質生成效果最佳之光源；第二階段以最佳光源(藍光)及模擬日光作為對照光源，並結合超濾膜過濾裝置將微藻有機物分成三個分子量區間(<10 kDa、10-100 kDa 及>100 kDa)進行光催化，並透過觀測反應速率常數(k'obs)及穩態濃度評估活性物質的生成行為，同時以總有機碳、多醣、蛋白質及螢光激發-發射矩陣(EEM)探討有機物組成變化。 研究結果顯示，活性物質生成速率明顯受光源波長所影響，短波長、高能量的藍光可顯著提升3EOM*及 1O2之生成效率，k'obs分別為 0.0057 h-1及 0.00148 h-1，遠高於黃光及紅光之結果。且1O2的穩態濃度(4.1 × 10-15 M)高於3EOM*，其原因為1O2具有相對較高的反應選擇性及較低的消耗速率。此外，超濾光催化結果顯示，3EOM*和・OH於低分子量區間(<10 kDa)呈現較佳之生成速率。EEM結果指出，活性物質的生成與類腐植酸物質之消耗密切相關，且中高分子量區間(10-100 kDa 及>100 kDa)之類蛋白質物質有助於1O2的生成。而螢光指數(FI)、腐植化指數(HIX)及生物性指數(BIX)變化顯示，光催化過程中會使有機物組成趨於自源性、高生物性與低腐植化特性。整體而言，3EOM*為本研究中兼具高反應性及生成速率之主要活性物質；1O2則展現出反應穩定性且持續生成的能力；而・OH則為系統中生成效率相對較低之活性物質。

The application of microalgae in wastewater treatment processes has attracted considerable attention in recent years. Microalgae can effectively remove pollutants from water through biological metabolism, and previous studies have demonstrated that algal organic matter is rich in photosensitizing structures, which can enhance pollutant degradation efficiency through photocatalytic processes. However, the influence of different light source wavelengths and molecular weight fractions of organic matter on the generation of reactive species remains unclear. Therefore, this study aimed to investigate the effects of light source wavelength and molecular weight fractions of EOM on the generation behavior of reactive species (triplet excited-state organic matter, 3EOM*; singlet oxygen, 1O2; and hydroxyl radicals,・OH), providing a scientific basis for the future application of algal organic matter in photocatalytic wastewater treatment. This study was conducted in two phases. In the first phase, photocatalytic experiments were performed under different light source wavelengths (red, yellow, and blue LEDs) to identify the most effective light source for reactive species generation. In the second phase, the optimal light source (blue light) and simulated sunlight (as the control) were applied, combined with an ultrafiltration system to separate EOM into three molecular weight fractions (<10 kDa, 10-100 kDa, and >100 kDa) for subsequent photocatalytic experiments. The generation behavior of reactive species was evaluated by monitoring the observed reaction rate constants (k'obs) and steady-state concentrations, while changes in organic matter composition were investigated through total organic carbon (TOC), polysaccharides, proteins, and fluorescence excitation-emission matrix (EEM) analysis. The results showed that the generation rate of reactive species was significantly influenced by the light source wavelength. The short-wavelength, high-energy blue light markedly enhanced the generation efficiency of 3EOM* and 1O2, with k'obs values of 0.0057 h-1 and 0.00148 h-1, respectively, which were substantially higher than those observed under yellow and red light. Moreover, the steady-state concentration of 1O2 (4.1 × 10-15 M) was higher than that of 3EOM*, reflecting its relatively higher reaction selectivity and lower consumption rate. The ultrafiltration-photocatalysis results indicated that 3EOM* and ・OH exhibited superior generation rates in the low molecular weight fraction (<10 kDa). EEM analysis revealed that reactive species generation was closely associated with the consumption of humic-like substances, and that protein-like substances in the medium-to-high molecular weight fractions (10-100 kDa, and >100 kDa) contributed to 1O2 generation. Moreover, variations in fluorescence index (FI), humification index (HIX), and biological index (BIX) indicated that the photocatalytic process drove the organic matter composition toward more autochthonous, bioactive, and less humified characteristics. Overall, 3EOM* was identified as the primary reactive species in this system, exhibiting both high reaction rate and generation potential; 1O2 demonstrated stable and sustained generation capability, whereas ・OH contributed relatively less to the system.