Abstract
In an endeavor to tackle environmental problems, the photodegradation of microcystin-LR (MC-LR), one of the most common and toxic cyanotoxins, produced by the cyanobacteria blooms, was examined using nanostructured TiO2 photocatalysts (anatase, brookite, anatase–brookite, and C/N/S co-modified anatase–brookite) under UV-A, solar and visible light irradiation. The tailoring of TiO2 properties to hinder the electron–hole recombination and improve MC-LR adsorption on TiO2 surface was achieved by altering the preparation pH value. The highest photocatalytic efficiency was 97% and 99% with degradation rate of 0.002 mmol L−1 min−1 and 0.0007 mmol L−1 min−1 under UV and solar irradiation, respectively, using a bare TiO2 photocatalyst prepared at pH 10 with anatase to brookite ratio of ca. 1:2.5. However, the bare TiO2 samples were hardly active under visible light irradiation (25%) due to a large band gap. Upon UV, solar and vis irradiation, the complete MC-LR degradation (100%) was obtained in the presence of C/N/S co-modified TiO2 with a degradation rate constant of 0.26 min−1, 0.11 min−1 and 0.04 min−1, respectively. It was proposed that the remarkable activity of co-modified TiO2 might originate from its mixed-phase composition, mesoporous structure, and non-metal co-modification.
Highlights
IntroductionCyanobacteria (blue-green algae) are naturally present in aquatic environments. The increase in nutrient concentration, global water temperature, and sunlight intensity results in cyanobacterial blooms, named harmful algal blooms (HABs) [1]
Cyanobacteria are naturally present in aquatic environments
It should be pointed that, besides a decrease in ecosystem stability, harmful algal blooms (HABs) might cause a production of highly active toxic compounds, known as cyanotoxins, during cell lysis, which is of special concern for drinking water sources [1,2,3]
Summary
Cyanobacteria (blue-green algae) are naturally present in aquatic environments. The increase in nutrient concentration, global water temperature, and sunlight intensity results in cyanobacterial blooms, named harmful algal blooms (HABs) [1]. The intoxication resulting from cyanotoxins, present in drinking water, has been reported worldwide [3,4]. Cyanotoxins represent a significant threat to all living organisms on the earth since they can poison and even kill animals and humans. They can accumulate in various animals, such as fish and shellfish, and cause toxemia, such as shellfish poisoning [5]. In China, cyanotoxins were suspected of liver cancer resulting from drinking of polluted water [7,8,9]. Microcystins (MCs), strong hepatotoxin, are considered the most widespread cyanotoxin in different environments [11,12]. The provisional guideline value for MCLR in drinking water should be lower than 1.0 μg L−1 , as proposed by the World
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