QuoteMany people are familiar with the haunting images of wildlife — including sea turtles, dolphins and seals — tangled in abandoned fishing nets.
The main issue behind Nylon-6, the plastic inside these nets, carpet and clothing, is that it's too strong and durable to break down on its own. So, once it's in the environment, it lingers for thousands of years, littering waterways, breaking corals and strangling birds and sea life.
Now, Northwestern University chemists have developed a new catalyst that quickly, cleanly and completely breaks down Nylon-6 in a matter of minutes — without generating harmful byproducts. Even better: The process does not require toxic solvents, expensive materials or extreme conditions, making it practical for everyday applications.
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Rational tailoring of catalytic systems offers highly desirable transformations targeting the growing environmental challenges associated with plastics pollution. For example, the identification of efficient catalysts to address alarming end-of-life Nylon pollution remains underexplored.
Nylon-6 is a non-biodegradable high-performance engineering plastic with centuries of chemical persistence, resulting in millions of tons of waste accumulation. Here we report the rational manipulation of organolanthanide catalyst structure to achieve an exceptionally efficient, solventless, and scalable Nylon-6 depolymerization process, affording monomer ε-caprolactam in ≥99% yield.
Specifically, catalyst Cp*2LaCH(TMS)2 (Cp* = η5-C5Me5, TMS = SiMe3) operates at catalyst loadings as low as 0.2 mol% and temperatures as low as 220 °C. For efficient deconstruction of more recalcitrant commodity Nylon-6 end-of-life articles such as fishing nets, carpets, and clothing, the robust, thermally stable ansa-metallocene catalyst Me2SiCp''2YCH(TMS)2, (Cp'' = η5-C5Me4) effects >99% conversion of these items into ε-caprolactam.
The collected product can be readily re-polymerized to afford pristine Nylon-6 with higher molecular masses and comparable structural regularity, providing a superior upcycling pathway for end-of-life Nylon plastics. Experimental mechanistic studies reveal intriguing and effective depolymerization pathways, such as catalytic intrachain "unzipping" enabled by the catalyst π-ancillary ligand steric constraints. Effective interchain "hopping" mechanisms, as well as chain-end deactivation are also demonstrated and supported by DFT analyses.
QuoteEver since the spooky phenomenon of superconductivity was discovered in 1911, scientists have been searching for superconducting materials that work under practical conditions.
If only they could find a compound in which electrical resistance vanishes at room temperature and ambient pressure – not extreme cold and ultrahigh forces – then we could finally step into the world they envisage of ultrafast computer chips, levitating trains, and superefficient energy grids.
For a hot minute, it looked like 2023 was going to be the year where physicists' pursuits broke through the room-temperature barrier. But those hopes – which were doused in skepticism from the start – were dashed not once, but twice in the space of a few months.
Now, the findings from a team of materials scientists at the Chinese Academy of Sciences (CAS) have been peer-reviewed, putting another nail in the coffin of LK-99, the material a South Korean team claimed in July was a room-temperature superconductor.
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To recap, Zhu and colleagues synthesized two kinds of LK-99 with different copper(I) sulfide (Cu2S) content and investigated the samples' material properties.
Firstly, they showed the electrical resistance of Cu2S alone plummeted around 112 °C (385 K) and they saw a similar effect in LK-99 samples with lots of copper sulfide impurities.
That 'transition' temperature is not far off 105 °C – the temperature at which the South Korean team reported LK-99's superconductivity properties emerged.
But Zhu and colleagues argue that LK-99's superconductor-like properties most likely originate from the Cu2S, which morphs from a hexagonal structure to a monoclinic one near 126 °C (400 K). Their impure LK-99 samples also didn't show zero resistivity like a true superconductor would.
This "strongly suggests that the superconductivity-like behavior in LK-99 reported by Lee et al. is caused by the structural phase transition of the impurity Cu2S" the researchers write.
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Lee et al. reported that the compound LK-99, with a chemical formula of Pb10xCux(PO4)6O (0.9<x<1.1), exhibits room-temperature superconductivity under ambient pressure. In this study, we investigated the transport and magnetic properties of pure Cu2S and LK-99 containing Cu2S.
We observed a sharp superconducting-like transition and a thermal hysteresis behavior in the resistivity and magnetic susceptibility. However, we did not observe zero-resistivity below the transition temperature. We argue that the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by the first order structural phase transition of Cu2S at around 385 K, from the β phase at high temperature to the γ phase at low temperature.