Fe3O4 nanoparticles-mediated solar-driven enzymatic PET degradation with PET hydrolase

Current state and sustainable management of waste polyethylene terephthalate bio-disposal: enzymatic degradation to upcycling

Poly (ethylene terephthalate) (PET) is a widely used plastic that leads to significant environmental pollution due to its durability. Enzymatic degradation of PET presents an eco-friendly disposal approach, with potential scalability for industrial applications. This review examines key crucial factors influencing PET enzymatic degradation, including the catalytic efficiency of PET hydrolase, production scalability of PET hydrolase, and recyclability of degraded PET. We outline major advancements in PET hydrolase development, including discovery techniques, functional enhancement strategies, and degradation optimization. Additionally, it assesses the preparation methodologies for PET hydrolase, covering bacterial expression systems, high-density fermentation technologies, and approaches for sustainable catalytic use. The review also discusses upcycling processes for PET hydrolysates, focusing on repolymerization into new plastics or bioconversion into valuable chemicals. Successful achievement of waste PET bio-disposal in industrial-scale n hinges on balancing degradation costs with revenue from upcycling products. Aim at this target, the review further points out the critical challenges, and proposes targeted solutions and expectations.

Functionalization of amylopectin as a strategy to improve polyethylene terephthalate hydrolase-cross-linked enzyme aggregate (IsPETase-CLEA) in plastic degradation

Polyethylene terephthalate hydrolase-cross-linked enzyme aggregate cross-linked with amylopectin (IsPETase/Amy) was developed and successfully degraded polyethylene terephthalate (PET). However, the low enzyme efficiency of IsPETase/Amy may hamper its industrial application. Hence, the goal of this study is to improve the enzyme efficiency of IsPETase-CLEAs by using novel dialdehyde amylopectin (DAA) from maize as cross-linker. DAA with aldehyde content of 64.3 % was synthesized and used to cross-link IsPETase as IsPETase/DAA. Under best immobilization condition, the activity recovery achieved was 74.3 %. Furthermore, IsPETase/DAA achieved 3.0-, 2.63-, 1.72- and 2.4-fold better thermal stability compared to IsPETase/Amy at 35 °C, 40 °C, 45 °C and 50 °C respectively. Moreover, better pH stability (pH 5-10) was achieved by IsPETase/DAA, and the reusability was enhanced to 7 cycles. Besides, enzyme efficiency of IsPETase/DAA successfully improved 7-fold better than IsPETase/Amy. It was revealed that IsPETase/DAA exhibited better PET degradation that the MHET yield was 66.2 % and 28 % higher than free IsPETase and IsPETase/Amy respectively. Therefore, this study developed a new promising green biocatalyst in PET degradation to be applied in industry.

Scalable nanoplastic degradation in water with enzyme-functionalized porous hydrogels

The prevalence of nanoplastics in water has led to significant environmental and health concerns, yet effective and scalable strategies for mitigating this contamination remain limited. Here, we report a straightforward, efficient, and scalable approach to degrade nanoplastics in water using enzyme-loaded hydrogel granules with an interconnected porous structure and adjustable properties. These porous hydrogels were synthesized via a polymerization-induced phase separation method, allowing easy scaling-up. Our results show that enzyme-functionalized porous hydrogels slightly outperform free cutinase in nanoplastic degradation. Furthermore, immobilized enzymes exhibited enhanced stability under harsh conditions, achieving a 104.1 % higher PET removal rate at pH 5 than free cutinase. Notably, the immobilized enzyme retained 39.9 % of its initial degradation activity after five cycles, demonstrating good reuse stability. This method offers a promising and practical solution for using enzymes to address nanoplastic pollution in aquatic environments.

Toward a Circular Economy of Heteroatom Containing Plastics: A Focus on Heterogeneous Catalysis in Recycling

Plastics play a vital role in modern society, but their accumulation in landfills and the environment presents significant risks to ecosystems and human health. In addition, the discarding of plastic waste constitutes to a loss of valuable material. While the usual mechanical recycling method often results in reduced material quality, chemical recycling offers exciting opportunities to valorize plastic waste into compounds of interest. Its versatility leans on the broad horizon of chemical reactions applicable, such as hydrogenolysis, hydrolysis, alcoholysis, or aminolysis. The development of heterogeneous and supported organocatalysts has enormous potential to enhance the economic and industrial viability of these technologies, reducing the cost of the process and mitigating its global environmental impact. This review summarizes the challenges and opportunities of chemically recycling heteroatom-containing plastics through heterogeneous catalysis, covering widely used plastics such as polyesters (notably PET and PLA), BPA-polycarbonate (BPA-PC), polyurethane (PU), polyamide (PA), and polyether. It examines the potential and limitations of various solid catalysts, including clays, zeolites, and metal-organic frameworks as well as supported organocatalysts and immobilized enzymes (heterogeneous biocatalysts), for reactions that facilitate the recovery of high-value products. By reintroducing these high-value products into the economy as precursors, this approach supports a more sustainable lifecycle for plastics, aligning with the principles of a circular economy.

Solar Energy-Promoted Bisphenol A Degradation with Immobilized Laccase in an Fe3O4-Embedded Metal-Organic Framework

Bisphenol A (BPA) is a well-recognized endocrine-disrupting chemical that poses risks to both human health and the environment. Laccase can effectively biodegrade bisphenol A, but the low environmental temperature (∼25 °C) restricts the biodegradation efficiency. In this study, the enzyme laccase and Fe3O4 with solar-thermal conversion capability were coimmobilized into zeolitic imidazolate framework-8 (Lac@ZIF-8-Fe3O4) to facilitate efficient biodegradation of bisphenol A under simulated solar irradiation. Compared to free laccase, Lac@ZIF-8-Fe3O4 exhibited high activity recovery (115.5%), an ∼39% increased catalytic constant, more effective bisphenol A biodegradation (up to 24-fold) at extensive bisphenol A concentrations (5-100 mg/L), excellent thermal stability (50 °C, 12 h), acid-tolerance (pH 3), and storage ability in 10 days. Simulated solar irradiation (1 kW/m2) increased the temperature of Lac@ZIF-8-Fe3O4 solution (10 μg laccase/mL) from 25 to 42.5 °C within 15 min, resulting in 96.4% biodegradation of bisphenol A within 60 min, nearly double the biodegradation efficiency under dark condition (55.9%). Furthermore, Lac@ZIF-8-Fe3O4 maintained 99.0% biodegradation efficiency even after 12 recycles of use under simulated solar irradiation (5 mg/L bisphenol A, 80 min/cycle). This work has thus offered efficient biocatalysis for integrating solar-energy promotion and enzymatic catalysis in treating environmental BPA pollutants. Further, the experimental findings benefited from the development of more sustainable and high-performance immobilized enzyme preparations for pollutant treatment via solar-thermal promotions.

Catalytic and biocatalytic degradation of microplastics

In recent years, there has been a surge in annual plastic production, which has contributed to growing environmental challenges, particularly in the form of microplastics. Effective management of plastic and microplastic waste has become a critical concern, necessitating innovative strategies to address its impact on ecosystems and human health. In this context, catalytic degradation of microplastics emerges as a pivotal approach that holds significant promise for mitigating the persistent effects of plastic pollution. In this article, we critically explored the current state of catalytic degradation of microplastics and discussed the definition of degradation, characterization methods for degradation products, and the criteria for standard sample preparation. Moreover, the significance and effectiveness of various catalytic entities, including enzymes, transition metal ions (for the Fenton reaction), nanozymes, and microorganisms are summarized. Finally, a few key issues and future perspectives regarding the catalytic degradation of microplastics are proposed.

Simulation Study of Polyethylene Terephthalate Hydrolase Adsorption on Self-Assembled Monolayers

Polyethylene terephthalate (PET) hydrolase, discovered in Ideonella sakaiensis (IsPETase), is a promising agent for the biodegradation of PET under mild reaction conditions, yet the thermal stability is poor. The efficient immobilization and orientation of IsPETase on different solid substrates are essential for its application. In this work, the combined parallel tempering Monte Carlo simulation with the all-atom molecular dynamics simulation approach was adopted to reveal the adsorption mechanism, orientation, and conformational changes of IsPETase adsorbed on charged self-assembled monolayers (SAMs), including COOH-SAM and NH2-SAM with different surface charge densities (SCDs). The results show that the protein adsorption orientation was determined not only by attraction interactions but also by repulsion interactions. IsPETase is adsorbed on the COOH-SAM surface with an "end-on" orientation, which favors the exposure of the catalyzed triplet to the solution. In addition, the entrance to the catalytic active center is larger on the COOH-SAM surface with a low SCD. This work reveals the controlled orientation and conformational information on IsPETase on charged surfaces at the atomistic level. This study would certainly promote our understanding of the mechanism of IsPETase adsorption and provide theoretical support for the design of substrates for IsPETase immobilization.