Scheme. PET degradation and Co-immobilized enzyme 4M-MG8@Fe3O4NPs recycle.
Recent years, the enormous waste plastic has become a severe environmental issue with the wide abuse of plastic products. Waste plastic showed a great negative impact on the ecological environment because its degradation time is more than 100 years, even 500 years. In addition, plastic waste may put a threat to human health. For instance, it has been reported that microplastics smaller than 5mm can accumulate in the human body in different ways. Polyethylene terephthalate (PET) accounts for 12% of global solid waste. The traditional methods of PET waste disposal are incineration and landfills. However, a large number of toxic gases such as dioxins, and carbon monoxide produced by incineration will cause damage to the atmosphere. Meanwhile, landfill treatment will occupy land resources and cause severe contamination of groundwater.
Fortunately, biodegradation of PET plastic has been discovered. Therefore, circular carbon economy for PET could theoretically be achieved through rapid enzymatic depolymerization followed by repolymerization or conversion into other products. Enzymatic degradation of PET has become a hit for its environmental friendliness and sustainability.
It has been reported various PET enzymes have excellent properties for the biodegradation of PET plastics.In 2016, Yoshida et al. derived PET hydrolase (PETase) from Ideonella sakaiensis, which can effectively degrade PET into bis (2-hydroxyethyl) terephthalic (BHET), mono (2-hydroxyethyl) terephthalate (MHET), TPA, and EG. At moderate temperature (30–40◦C), due to its unique PET substrate binding pocket. IsPETase has immediately become one of the most promising PET plastic degradation enzymes. However, this poor thermal stability of wild-type IsPETase limited its application for PET degradation. Until now, the improvement of thermal stability and biodegradation capacity is the main research direction of PETase. And many kinds of engineering enzyme are based on IsPETase.
We proposed solar-driven enzymatic PET degradation with DuraPETase-4M, a high-efficiency mutant of PETase, and MG8, a new PET hydrolase from the human saliva metagenome, by using Fe3O4 nanoparticles (NPs) as a solar-to-thermal convertor. Solar irradiation could elevate the temperature of Fe3O4 NPs for the effective PET degradation. Also, by covalently binding to Fe3O4 NPs, enzymes can easily be recycled, which will make a contribution to cost reduction. DuraPETase-4M is mainly good at the degradation of amorphous PET,while MG8 shows excellent catalytic activity of crystalline PET.By combining them, PET can be more thoroughly degraded.
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