Valorization Strategies in CO2 Capture: A New Life for Exhausted Silica-Polyethylenimine.

The search for alternative ways to give a second life to materials paved the way for detailed investigation into three silica-polyethylenimine (Si-PEI) materials for the purpose of CO2 adsorption in carbon capture and storage. A solvent extraction procedure was investigated to recover degraded PEIs and silica, and concomitantly, pyrolysis was evaluated to obtain valuable chemicals such as alkylated pyrazines. An array of thermal (TGA, Py-GC-MS), mechanical (rheology), and spectroscopical (ATR-FTIR, 1H-13C-NMR) methods were applied to PEIs extracted with methanol to determine the relevant physico-chemical features of these polymers when subjected to degradation after use in CO2 capture. Proxies of degradation associated with the plausible formation of urea/carbamate moieties were revealed by Py-GC-MS, NMR, and ATR-FTIR. The yield of alkylpyrazines estimated by Py-GC-MS highlighted the potential of exhausted PEIs as possibly valuable materials in other applications.

Determination of polyurethanes within microplastics in complex environmental samples by analytical pyrolysis.

Polyurethanes (PUR) are a group of polymers synthesized from different diisocyanate and polyol monomers resulting in a countless number of possible structures. However, the large market demand, and the variety of application fields justify the inclusion of PUR in microplastic (MP) investigation. This study aimed at providing comprehensive information on PUR within MP analysis by pyrolysis-gas chromatography-mass spectrometry to clarify whether (i) it is possible to make a reliable statement on the PUR content of environmental samples based on a few pyrolysis products and (ii) which restrictions are required in this context. PUR were managed as subclasses defined by the diisocyanates employed for polymer synthesis. Methylene diphenyl diisocyanate (MDI)- and toluene diisocyanate (TDI)-based PUR were selected as subclasses of greatest relevance. Different PUR were pyrolyzed directly and under thermochemolytic conditions with tetramethylammonium hydroxide (TMAH). Distinct pyrolytic indicators were identified. The study supported that the use of TMAH greatly reduced the interactions of pyrolytic MP analytes with the remaining organic matrix of environmental samples and the associated negative effects on analytical results. Improvements of chromatographic behavior of PUR was evidenced. Regressions (1-20 µg) showed good correlations and parallelism tests underlined that quantitation behavior of different MDI-PUR could be represented by the calibration of just one representative with sufficient accuracy, entailing a good estimation of the entire subclass if thermochemolysis were used. The method was exemplary applied to road dusts and spider webs sampled around a plastic processing plant to evaluate the environmental spread of PUR in an urban context. The environmental occurrence of MDI-PUR as MP was highly influenced by the proximity to a potential source, while TDI markers were not observed.

Bioplastic leachates characterization and impacts on early larval stages and adult mussel cellular, biochemical and physiological responses.

Bioplastics are promoted as safer alternatives to tackle the long-term persistence of conventional plastics. However, information on the potential release of additives and non-intentionally added substances (NIAS) in the surrounding environment is limited, and biological effects of the leachates have been little studied. Leachates produced from three bioplastics, i.e. compostable bags (CB), bio-polyethylene terephthalate bottles (bioPET) and polylactic acid cups (PLA), and a control polymeric material, i.e. rubber tire (TR), were examined. The chemical nature of bioplastic polyesters PET, PLA and poly (butylene adipate-co-terephthalate) (PBAT) in CB, was confirmed by analytical pyrolysis. Fragments were incubated in artificial sea water for 14 days at 20 °C in darkness and leachate contents examined by GC-MS and HPLC-MS/MS. Catalysts and stabilizers represented the majority of chemicals in TR, while NIAS (e.g. 1,6-dioxacyclododecane-7,12-dione) were the main components of CB. Bisphenol A occurred in all leachates at a concentration range 0.3-4.8 µg/L. Trace metals at concentrations higher than control water were found in all leachates, albeit more represented in leachates from CB and TR. A dose response to 11 dilutions of leachates (in the range 0.6-100%) was tested for biological effects on early embryo stages of Mytilus galloprovincialis. Embryotoxicity was observed in the whole range of tested concentrations, the magnitude of effect depending on the polymers. The highest concentrations caused reduction of egg fertilization (CB, bioPET, TR) and of larvae motility (CB, PLA, TR). TR leachates also provoked larvae mortality in the range 10-100%. Effects on adult mussel physiology were evaluated after a 7-day in vivo exposure to the different leachates at 0.6% concentration. Nine biomarkers concerning lysosomal functionality, neurotransmission, antioxidant and immune responses were assessed. All lysosomal parameters were affected, and serum lysozyme activity inhibited. Harmonized chemical and biological approaches are recommended to assess bioplastic safety and support production of sustainable bioplastics.

Changes of dissolved oxygen in aqueous solutions of caffeine oxidized by photo-Fenton reagent.

ABSTRACT Formation of oxygen in the caffeine aqueous solutions occurs through self-decomposition reactions of the hydrogen peroxide, used as an oxidant in the photo-Fenton treatment. The total concentration of hydrogen peroxide used in the treatment would be the contribution of the stoichiometric concentration that reacts with the organic matter ([H2O2]0 = 2.0 mM) and the excess of oxidant that decomposes to oxygen, through radical mechanisms, according to a ratio of 0.8164 mmol H2O2 mg-1 O2. When operating at concentrations lower than [H2O2]0 = 2.0 mM, oxygen is not released because there is no excess of oxidant. Moreover, it is verified that the ferrous ion catalyst is oxidized to ferric ion and its subsequent regeneration to ferrous ion. Working at concentrations higher than [H2O2]0 = 2.0 mM, oxygen is released in the water, verifying that the catalyst remains as ferric species, which does not regenerate. The reaction time in which oxygen evolution happpens depends on the concentration of catalyst used in the oxidation, verifying that the highest oxygen generation rates are obtained when applying [Fe]0 = 10.0 mg L-1. Once generated in the water, the maximum concentration of oxygen begins to decrease as the hydrogen peroxide is consumed, until reaching a constant value. The stages of formation and decrease of oxygen are adjusted to zero-order kinetics, estimating the kinetics constants as a function of the catalyst concentration: k f = 29.48 [Fe]0 -1.25 (mg O2 L-1 min-1) and k d = -0.006 [Fe]0 2.0 + 0.244 [Fe]0-3.69 (mg O2 L-1 min-1).