Beyond Mechanical Recycling: Giving New Life to Plastic Waste

Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re‐extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life‐cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.     

Polymer Lamellae as Reaction Intermediates in the Formation of Copper Nanospheres as Evidenced by In Situ X‐ray Studies

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X‐ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre‐nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.     

Analysis of cocaine and its principal metabolites in waste and surface water using solid-phase extraction and liquid chromatography–ion trap tandem mass spectrometry

A validated method based on solid-phase extraction (SPE) and liquid chromatography-ion trap tandem mass spectrometry (LC-MS/MS) is described for the determination of cocaine (COC) and its principal metabolites, benzoylecgonine (BE) and ecgonine methyl ester (EME), in waste and surface water. Several SPE adsorbents were investigated and the highest recoveries (95.7 +/- 5.5, 91.8 +/- 2.2 and 72.5 +/- 5.3% for COC, BE and EME, respectively) were obtained for OASIS HLB(R) cartridges (6 mL/500 mg) using 100 mL of waste water or 500 mL of surface water. Extracts were analysed by reversed-phase (RP) or hydrophilic interaction (HILIC) LC-MS/MS in positive ion mode with multiple reactions monitoring (MRM); the latter is the first reported application of the HILIC technique for drugs of abuse in water samples. Corresponding deuterated internal standards were used for quantification. The method limits of quantification (LOQs) for COC and BE were 4 and 2 ng L(-1), respectively, when RPLC was used and 1, 0.5 and 20 ng L(-1) for COC, BE and EME, respectively, with the HILIC setup. For COC and BE, the LOQs were below the concentrations measured in real water samples. Stability tests were conducted to establish the optimal conditions for sample storage (pH, temperature and time). The degradation of COC was minimal at -20 degrees C and pH = 2, but it was substantial at +20 degrees C and pH = 6. The validated method was applied to a set of waste and surface water samples collected in Belgium.     

Connected Domatic Number in Planar Graphs

A dominating set in a graph G is a connected dominating set of G if it induces a connected subgraph of G. The connected domatic number of G is the maximum number of pairwise disjoint, connected dominating sets in V(G). We establish a sharp lower bound on the number of edges in a connected graph with a given order and given connected domatic number. We also show that a planar graph has connected domatic number at most 4 and give a characterization of planar graphs having connected domatic number 3.     

Optical and redox properties of a series of 3,4-ethylenedioxythiophene oligomers

The optical and redox properties of a series of 3,4-ethylenedioxythiophene oligomers (EDOTn, n=1-4) and their beta,beta'-unsubstituted analogues (Tn, n=1-4) are described. Both series are end capped with phenyl groups to prevent irreversible alpha-coupling reactions during oxidative doping. Absorption and fluorescence spectra of both series reveal a significantly higher degree of intrachain conformational order in the EDOTn oligomers. Oxidation potentials (E(PA1) and E(PA2)) determined by cyclic voltammetry reveal that those of EDOTn are significantly lower than the corresponding Tn oligomers as a consequence of the electron-donating 3,4-ethylenedioxy substitution. Linear fits of E(PA1) and E(PA2) versus the reciprocal number of double bonds reveal significantly steeper slopes for the EDOTn than for the Tn oligomers. This could indicate a more effective conjugation for the EDOTn series, confirmed by the fact that coalescence of E(PA1) and E(PA2) is reached already at relatively short chain lengths ( approximately 5 EDOT units) in contrast to the Tn series (>10 thiophene units). The stepwise chemical oxidation of the EDOTn and Tn oligomers in solution was carried out to obtain radical cations and dications. The energies of the optical transitions of the radical cations and dications as determined by UV/Vis/NIR spectroscopy were similar for the two series. These spectroscopic observations are consistent with quantum-chemical calculations performed on the singly charged molecules. Cooling solutions containing T2.+, T3.+, EDOT2.+, and EDOT3.+ revealed the reversible formation of dimers, albeit with a somewhat different tendency, expressed in the values for the dimerization enthalpy.     

Element specific surface reconstructions of islands during surfactant-mediated growth on Si (111)

The early stages of surfactant- (As, Sb) mediated homoepitaxial growth on Si (111) are examined by scanning tunneling microscopy and extensive ab initio calculations of Si(n) clusters (n相似文献