Depolymerization of plastics by means of electrified spatiotemporal heating.

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Genome-wide investigation of multiplexed CRISPR-Cas12a-mediated editing in rice.

Clustered regularly interspaced short palindromic repeats (CRISPR) nucleases like Cas9 and Cas12a are revolutionizing plant basic research and crop breeding. A major advantage of CRISPR over earlier nucleases systems is its capability of multiplexed genome editing. However, it remains unknown about the potential off-target effects when multiple concurrent DNA double-strand breaks (DSBs) are induced in a crop genome. Here, we investigated this important question in rice (Oryza sativa) using a highly multiplexed CRISPR-Cas12a system. With whole-genome sequencing, we first revealed high genome editing specificity of Mb2Cas12a and protospacer adjacent motif promiscuity of LbCas12a. We discovered large chromosomal rearrangement events in edited rice plants that endured many (e.g., >50) simultaneous DSBs, but not in plants that endured lower order DSBs (e.g., <10). Our results shed important light on the analysis and regulation of engineered crops derived from CRISPR-Cas mediated multiplexed genome editing.