Microcystins (MCs) are toxins produced by cyanobacteria commonly found in harmful algal blooms (HAB) occurring in many surface waters. The presence of MCs in water bodies can endanger aquatic biota, and human exposure to MCs can result in acute or chronic health hazards. Thus, the World Health Organization (WHO) set a guideline of 1 ppb for MC-LR in drinking water. However, conventional methods for removing MC-LR such as membrane filtration and activated carbon are only phase change removal methods and are often expensive in operation and maintenance. It is urgent to develop a rapid, easy-to-use, and cost-effective method for the degradation of MC-LR. In this study, a novel Au-decorated Ni-metal organic framework (Au/Ni-MOF) was newly developed on a hydrophobic carbon paper (2 cm×2 cm) using an air spraying method and applied to the solar-driven (photocatalytic) reactions to remove MC-LR in water. Various water samples (7 mL) containing 20 ppb MC-LR were tested under continuous stirring conditions at 200 rpm at room temperature, and under a controlled simulated sunlight lamp, with an intensity of 1.0 SUN. The test showed degradation of MC-LR with 95%, 99%, and 98% removal efficiency after 4 hours using the Ni-MOF with 0%, 5%, and 10% weight % (wt. %) of Au, respectively, showing that higher wt. % of Au resulted in better MC-LR removal. The Au/Ni-MOF with 20 wt. % of Au showed rapid and complete degradation of MC-LR within the first hour. The first-order degradation reaction rate coefficient (k) of the 20 wt. % of Au was 0.05 min<sup>-1</sup>, which is two times higher than most other recent reported results of MC-LR photodegradation, averaging 0.025 min<sup>-1</sup>. Overall, this study demonstrated the potential for the novel Au/Ni-MOF to effectively reduce the concentration of the MC-LR toxin in the contaminated solution.

Photocatalytic degradation of MC-LR using a novel Au/Ni-MOF

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