One-pot laccase@MOF biocatalysts efficiently remove bisphenol A from water

The presence of bisphenol A (BPA) in wastewater, its toxicity and the hardness for its complete degradation constitutes a serious environmental problem and a scientific challenge. The enzyme laccase is an oxidoreductase capable of oxidizing phenolic compounds, being one of the most efficient biocatalysts for BPA removal. The immobilization of laccases to lead solid biocatalysts is essential for their applications as it allows their stabilization and easy recovery from the liquid reaction media and subsequent reuse. This work compares the efficiency of siliceous-type supports, which have traditionally been used for this purpose, with the use of MOF-type supports. Thanks to the versatility in the synthesis methods offered by MOFs, MOF-type biocatalysts can be prepared in a one-pot using an in-situ procedure ([email protected]2-MIL-53(Al)) under conditions compatible with enzymatic activity (room temperature, aqueous solution and moderate pH values). The resulting biocatalyst displays a high enzyme loading of 100 mg.g-1 which is also permanent: free of enzyme leaching. As opposed, post-synthesis in two steps: Lac#NH2-MIL-53(Al) (with low enzyme loading) and Lac#Amorphous silica-NH2 (100 mg.g-1 enzyme loading, but high rate of enzyme leaching) were also prepared and compared. In contrast to the elimination of 90% of BPA in 60 min obtained with Lac#Amorphous silica-NH2, the one-pot immobilization of laccase on MOFs resulted much more efficient. The own enzyme-free MOF-type support (NH2-MIL-53(Al)) removed more than 90% of BPA from aqueous solution in 30 min, but such performance was widely surpassed by the biocatalyst [email protected]2-MIL-53(Al) (100% in just 3 min). The significant improvement of BPA degradation was attributed to the mutual and simultaneous contribution of both support and enzyme. In addition, the biocatalyst [email protected]2-MIL-53(Al) was able to remove BPA in five successive cycles with efficiency higher than 85% at the end of the last batch.