Introduction

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^[1] because its degradation time is more than 100 years, even 500 years^[2]. In addition, plastic waste may put a threat to human health^[3][4]. 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^[2]. The traditional methods of PET waste disposal are incineration and landfills^[5]. However, a large number of toxic gases such as dioxins^[6], 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^[7].

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^[8]. Enzymatic degradation of PET has become a hit for its environmental friendliness and sustainability^[9].

It has been reported various PET enzymes have excellent properties for the biodegradation of PET plastics^[10].In 2016, Yoshida et al. derived PET hydrolase (PETase) from Ideonella sakaiensis^[11], 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^[12]. 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^[13]. 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^[14][15].

We proposed solar-driven enzymatic PET degradation with DuraPETase-4M^[16], a high-efficiency mutant of PETase, and MG8^[17], 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^[18][19]. 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^[16],while MG8 shows excellent catalytic activity of crystalline PET^[17].By combining them, PET can be more thoroughly degraded.