Reactive Crystallization via Metal–Organic-Framework Formation Enables Separation of Terephthalic Acid from Textile Impurities

Abstract

Polyethylene terephthalate (PET) fibers are among the largest plastics in production. Used commonly in textiles, PET fibers are often blended with non-PET components such as cotton, dyes, and additives. As these non-PET components generate impurities during depolymerization, extracting a high-purity terephthalic acid (TPA) monomer from the chemical recycling of textiles is challenging. Here, we demonstrate the extraction of high-quality TPA from the impure crude digestion mixtures containing depolymerized PET fibers and non-PET components. Our approach uses reactive crystallization to turn TPA into a metal−organic framework (MOF). As TPA is the only component in the mixture capable of forming an extended, crystalline structure, TPA monomers are separated from impurities as MOF crystallizes. We demonstrate this concept on recycled TPA (rTPA) extracted from a polyester−cotton blend textile through alkaline hydrolysis, where the impure rTPA was used as an organic linker to prepare MOF . This MOF crystallization removed the trapped impurities. After MOF disassembly, colorless TPA, reminiscent of a virgin-grade monomer, was obtained (yield: 78%). These results demonstrate self-assembly-induced crystallization as a new strategy to selectively recover monomers from complex mixtures.

Synthesis of Metal–Organic Frameworks through Enzymatically Recycled Polyethylene Terephthalate

“…Those impurities in the PET degradation supernatant could impede the MOF synthesis (SI, Section S5), and one-pot MOF synthesis using enzymatically recycled TPA requires further optimization. Therefore, following the reported methods, , both bac-TPA and enz-TPA were protonated, washed, and collected for the MOF synthesis (SI, Section S6).…”

“…Polyethylene terephthalate (PET), as one of the most produced plastics, is extensively employed in single-use bottles, textiles, packaging, etc. Notably, it may take up to 48 years to degrade PET bottles under ambient conditions, leading to a huge burden on the environment. , Current PET recycling is through mechanical, thermal, or chemical approaches. − These methods can be energy-consuming or generate secondary pollutants. , Consequently, enzymatic recycling of PET has raised massive attention ever since the discovery of PET depolymerase ( Is PETase) from Ideonella sakaiensis in 2016, as this process could depolymerize PET into its monomers terephthalic acid (TPA), 2-hydroxyethyl terephthalic acid (MHET), and ethylene glycol (EG) with high specificity in mesophilic conditions . Efforts have since been made to elevate the efficiency of PETase through rational designing, directed evolution, and machine learning, as the cost of enzymatically recycled TPA ($1.93/kg) is predicted to be comparable to that of the virgin TPA ($1.0–1.5/kg) .…”

Chemical recycling of polyester textile wastes: shifting towards sustainability

“…311 More elaborated products were also directly produced from (dyed) PET textiles, such as (MOFs). [312][313][314] The many upcycling developments deployed for bottle PET will certainly be applied soon more largely to textiles, supporting circular economy and reducing environmental pollution.…”

“…311 More elaborated products were also directly produced from (dyed) PET textiles, such as (MOFs). 312–314…”

Synergistic Interfacial Reconstruction and Surface Polarization in a Compact ZnIn2S4–CdIn2S4 Heterojunction for Enhanced Photocatalytic H2O2 Production

“…So far, the research on artificial photosynthesis of H 2 O 2 is undergoing a phase of robust development, with a primary focus on enhancing the properties and efficiency of photocatalysts . Among them, zinc indium sulfide (ZnIn 2 S 4 ) has also been proven to be a superior candidate for PO due to its visible-light responsiveness, higher physiochemical stability, and less toxicity. − However, like above, awkwardness persists with conventional catalysts. The photocatalytic performance of ZnIn 2 S 4 further remains a substantial improvement space. , To tackle the predicament, various strategies, such as metal doping, morphological control, and cocatalyst modification construction, are adopted. − Among those modification tactics, constructing heterojunction holds an appealing choice for facilitating electron and hole separation and adjusting redox capacity. − The bimetallic sulfide material, chromic indium sulfide (CdIn 2 S 4 ), exhibits exceptional photostability, an appropriate bandgap, easy preparation, cost-effectiveness, and high durability.…”