Plastic waste is currently generated at a rate approaching 400 Mt year–1. The amount of plastics accumulating in the environment is growing rapidly, yet our understanding of its persistence is very limited. This Perspective summarizes the existing literature on environmental degradation rates and pathways for the major types of thermoplastic polymers. A metric to harmonize disparate types of measurements, the specific surface degradation rate (SSDR), is implemented and used to extrapolate half-lives. SSDR values cover a very wide range, with some of the variability arising due to degradation studies conducted in different natural environments. SSDRs for high density polyethylene (HDPE) in the marine environment range from practically 0 to approximately 11 μm year–1. This approach yields a number of interesting insights. Using a mean SSDR for HDPE in the marine environment, linear extrapolation leads to estimated half-lives ranging from 58 years (bottles) to 1200 years (pipes). For example, SSDRs for HDPE and polylactic acid (PLA) are surprisingly similar in the marine environment, although PLA degrades approximately 20 times faster than HDPE on land. Our study highlights the need for better experimental studies under well-defined reaction conditions, standardized reporting of rates, and methods to simulate polymer degradation using.

In this study, we demonstrated that a reduction in solely the concentration of the polymer solution for preparation of the support layer effectively enhances the water flux of a thin-film composite (TFC) reverse osmosis (RO) membrane. However, a decrease in the polymer concentration caused the sub-surface structure of the support layer to become too porous, which unavoidably weakened the mechanical strength of the support layer. To overcome the problem, we prepared a highly porous support layer with improved mechanical strength by incorporating graphene oxide (GO) platelets. The thickness of the GO platelets was controlled by adjusting the mechanical energy input per volume of precursor solution. We confirmed that well-exfoliated GO platelets (mean thickness; about 1.5 nm) are more effective in enhancing mechanical properties of the support layer. The TFC RO membrane made of the GO composite support layer had almost 1.6 to 4 times higher water flux with comparable salt rejection compared to both the current upper bounds of the RO membranes prepared by modification of the active layer and the commercial RO membranes. Fig. 5 (a) Water flux and (b) salt rejection of the RO membranes prepared using the 15 wt% support layer (TFC-15), the 10 wt% support layer without and with 0.9 wt% 1-GO (TFC-10 and TFC-1-GO, respectively). Error bar: standard deviation (n=2).

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Oxorhenium catalysts effectively transform biomass-derived polyols into corresponding alkenes via deoxydehydration (DODH) with a secondary alcohol as a hydrogen donor. This study describes the preparation of unsupported rhenium oxide nanoparticles (ReO x NPs), their use as DODH heterogeneous catalyst, and changes in the speciation and structure of Re during catalysis leading to a possible mechanism for DODH by a heterogeneous catalyst. The unsupported nanoparticles catalyze various polyols transformation to produce alkenes with high efficiency and recyclability. X-ray spectroscopy analysis shows that the structure of as-prepared ReO x NPs is similar to perrhenate with oxidation state between Re­(VI) and Re­(VII). Under reaction conditions and postcatalysis, the ReO x NPs are reduced by approximately two oxidation units. Kinetic isotope effect demonstrates that dissociation of a C–H bond during reduction of ReO x NPs by 3-octanol is part of the rate-determining step. Based on all experimental observations, the mechanism of DODH catalysis with unsupported ReO x NPs involving a Re­(VII)/Re­(V) redox pair is proposed.

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Renewable adipic acid is a value-added chemical for the production of bioderived nylon. Here, the one-step conversion of mucic acid to adipates was achieved in high yield through deoxydehydration (DODH) and catalytic transfer hydrogenation (CTH) by a bifunctional Pt-ReO x /C heterogeneous catalyst with isopropanol as solvent and reductant. The Pt-ReO x /C catalyst is reusable and was regenerated at least five times. The catalyst exhibits a broad substrate scope of various diols. Spectroscopic studies of Pt-ReO x /C revealed Re VII and Pt 0 as the relevant species for DODH and CTH, respectively. Isotope labeling experiments support a monohydride mechanism for CTH over Pt. This work demonstrates a reusable bifunctional catalyst for a one-step valorization of sugar acids to a practical monomer, which opens the door to multifunctional catalysis streamlining valorization of biomass-derived molecules.