Mechanochemistry Milling of Waste Poly(Ethylene Terephthalate) into Metal-Organic Frameworks.

Converting poly(ethylene terephthalate) (PET) into metal-organic frameworks (MOFs) has emerged as a promising innovation for upcycling of waste plastics. However, previous solvothermal methods suffer from toxic solvent consumption, long reaction time, high pressure, and high temperature. Herein, a mechanochemical milling strategy was reported to transform waste PET into a series of MOFs with high yields. This strategy had the merits of solvent-free conditions, ambient reaction temperature, short running time, and easy scale-up for large-scale production of MOFs. The as-prepared MOFs exhibited definite crystal structure and porous morphology composed of agglomerated nanoparticles. It was proven that, under mechanochemical milling, PET was firstly decomposed into 1,4-benzenedicarboxylate, which acted as linkers to coordinate with metal ions for forming fragments, followed by the gradual arrangement of fragments into MOFs. This work not only promotes high value-added conversion of waste polyesters but also offers a new opportunity to produce MOFs in a green and scalable manner.

Green Synthesis of Carbon Nitride-Based Conjugated Copolymer for Efficient Photocatalytic Degradation of Tetracycline.

Upcycling waste plastics into advanced semiconductor photocatalysts provides a new strategy to reasonably and economically solve the huge amount of waste plastics, which remains challenging. Herein, a carbon nitride-based donor-acceptor (D-A) conjugated copolymer by copolymerization of dicyandiamide and terephthalic acid from discarded polyethylene terephthalate (PET) using Zn(OH)2 as catalyst and template at 360-440 °C is synthesized. The morphology and structure of the conjugated copolymer are well regulated by the calcination temperature. The resultant conjugated copolymer exhibits merits of high light absorption and low electron-hole recombination probability. Consequently, it works excellently in the persulfate-based advanced oxidation process for visible light-driven photocatalytic degradation of tetracycline. The kinetic constant (3.4 × 10-2  min-1 ) is 40.5 and 2.3 times that of the conjugated copolymer system and persulfate system, respectively. Furthermore, the reactive species (including •OH, SO4 •- , •O2 - , 1 O2 , and h+ ) and degradation intermediates of tetracycline are analyzed to expound its degradation process. This work not only pioneers design guidelines on upcycling of waste plastics in a sustainable manner, but also provides a facile strategy to synthesize carbon nitride-based D-A conjugated copolymers for the efficient activation of persulfate-based advanced oxidation process in wastewater treatment.

Upcycling Waste Polyethylene into Carbon Nanomaterial via a Carbon-Grown-on-Carbon Strategy.

Upcycling waste plastics (e.g., polyethylene (PE)) into value-added carbon products is regarded as a promising approach to address the increasingly serious waste plastic pollution and simultaneously achieve carbon neutrality. However, developing new carbonization technology routes to promote the oxidation of PE at low temperature and construct the stable cross-linking network remains challenging. Here, a facile carbon-grown-on-carbon strategy is proposed using carbon black (CB) to convert waste PE into core/shell carbon nanoparticles (CN) in high yields at low temperature. The yield of CN remarkably increases when the heating temperature decreases or the dosage of CB increases. The obtained CN displays turbostratic structure and closely aggregated granular morphology with a size of ≈80 nm. It is found that, prior to the oxidation and carbonization of PE, CB forms a 3D network architecture in the PE matrix. More importantly, CB not only catalyzes the partial oxidation of PE to form PE macromolecular radicals and introduce oxygen-containing groups at low temperature in the early stage, but also favors for the construction of a stable cross-linking network in the latter stage. This work offers a facile sustainable strategy for chemical upcycling of PE into value-added carbon products without post-treatments or usage of metallic catalysts.