Microbial Communities on Plastic Polymers in the Mediterranean Sea

Plastic particles in the ocean are typically covered with microbial biofilms, but it remains unclear whether distinct microbial communities colonize different polymer types. In this study, we analyzed microbial communities forming biofilms on floating microplastics in a bay of the island of Elba in the Mediterranean Sea. Raman spectroscopy revealed that the plastic particles mainly comprised polyethylene (PE), polypropylene (PP), and polystyrene (PS) of which polyethylene and polypropylene particles were typically brittle and featured cracks. Fluorescence in situ hybridization and imaging by high-resolution microscopy revealed dense microbial biofilms on the polymer surfaces. Amplicon sequencing of the 16S rRNA gene showed that the bacterial communities on all plastic types consisted mainly of the orders Flavobacteriales, Rhodobacterales, Cytophagales, Rickettsiales, Alteromonadales, Chitinophagales, and Oceanospirillales. We found significant differences in the biofilm community composition on PE compared with PP and PS (on OTU and order level), which shows that different microbial communities colonize specific polymer types. Furthermore, the sequencing data also revealed a higher relative abundance of archaeal sequences on PS in comparison with PE or PP. We furthermore found a high occurrence, up to 17% of all sequences, of different hydrocarbon-degrading bacteria on all investigated plastic types. However, their functioning in the plastic-associated biofilm and potential role in plastic degradation needs further assessment

Advancing the Compositional Analysis of Olefin Polymerization Catalysts with High-Throughput Fluorescence Microscopy

To optimize the performance of supported olefin polymerization catalysts, novel methodologies are required to evaluate the composition, structure, and morphology of both pristine and prepolymerized samples in a resource-efficient, high-throughput manner. Here, we report on a unique combination of laboratory-based confocal fluorescence microscopy and advanced image processing that allowed us to quantitatively assess support fragmentation in a large number of autofluorescent metallocene-based catalyst particles. Using this approach, significant inter- and intraparticle heterogeneities were detected and quantified in a representative number of prepolymerized catalyst particles (2D: ≥135, 3D: 40). The heterogeneity that was observed over several stages of slurry-phase ethylene polymerization (10 bar) is primarily attributed to the catalyst particles' diverse support structures and to the inhomogeneities in the metallocene distribution. From a mechanistic point of view, the 2D and 3D analyses revealed extensive contributions from a layer-by-layer fragmentation mechanism in synergy with a less pronounced sectioning mechanism. A significant number of catalyst particles were also found to display limited support fragmentation at the onset of the reaction (i.e., at lower polymer yields). This delay in activity or "dormancy" is believed to contribute to a broadening of the particle size distribution during the early stages of polymerization. 2D and 3D catalyst screening via confocal fluorescence microscopy represents an accessible and fast approach to characterize the structure of heterogeneous catalysts and assess the distribution of their fluorescent components and reaction products. The automation of both image segmentation and postprocessing with machine learning can yield a powerful diagnostic tool for future research as well as quality control on industrial catalysts

Elucidating the Sectioning Fragmentation Mechanism in Silica-Supported Olefin Polymerization Catalysts with Laboratory-Based X-Ray and Electron Microscopy

Strict morphological control over growing polymer particles is an indispensable requirement in many catalytic olefin polymerization processes. In catalysts with mechanically stronger supports, e. g., polymerization-grade silicas, the emergence of extensive cracks via the sectioning fragmentation mechanism requires severe stress build-up in the polymerizing catalyst particle. Here, we report on three factors that influence the degree of sectioning in silica-supported olefin polymerization catalysts. Laboratory-based X-ray nano-computed tomography (nanoCT) and focused ion beam-scanning electron microscopy (FIB-SEM) were employed to study catalyst particle morphology and crack propagation in two showcase catalyst systems, i.e., a zirconocene-based catalyst (i.e., Zr/MAO/SiO2, with Zr=2,2’-biphenylene-bis-2-indenyl zirconium dichloride and MAO=methylaluminoxane) and a Ziegler-Natta catalyst (i.e., TiCl4/MgCl2/SiO2), during slurry-phase ethylene polymerization. The absence of extensive macropores in some of the catalysts’ larger constituent silica granulates, a sufficient accessibility of the catalyst particle interior at reaction onset, and a high initial polymerization rate were found to favor the occurrence of the sectioning pathway at different length scales. While sectioning is beneficial for reducing diffusion limitations, its appearance in mechanically stronger catalyst supports can indicate a suboptimal support structure or unfavourable reaction conditions

Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts

Kinetics-based differences in the early stage fragmentation of two structurally analogous silica-supported hafnocene- and zirconocene-based catalysts were observed during gas-phase ethylene polymerization at low pressures. A combination of focused ion beam-scanning electron microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy (IR PiFM) revealed notable differences in the distribution of the support, polymer, and composite phases between the two catalyst materials. By means of time-resolved probe molecule infrared spectroscopy, correlations between this divergence in morphology and the kinetic behavior of the catalysts' active sites were established. The rate of polymer formation, a property that is inherently related to a catalyst's kinetics and the applied reaction conditions, ultimately governs mass transfer and thus the degree of homogeneity achieved during support fragmentation. In the absence of strong mass transfer limitations, a layer-by-layer mechanism dominates at the level of the individual catalyst support domains under the given experimental conditions

Unravelling structure sensitivity in CO2 hydrogenation over nickel

Continuous efforts in the field of materials science have allowed us to generate smaller and smaller metal nanoparticles, creating new opportunities to understand catalytic properties that depend on the metal particle size. Structure sensitivity is the phenomenon where not all surface atoms in a supported metal catalyst have the same activity. Understanding structure sensitivity can assist in the rational design of catalysts, allowing control over mechanisms, activity and selectivity, and thus even the viability of a catalytic reaction. Here, using a unique set of well-defined silica-supported Ni nanoclusters (1–7 nm) and advanced characterization methods, we prove how structure sensitivity influences the mechanism of catalytic CO2 reduction, the nature of which has been long debated. These findings bring fundamental new understanding of CO2 hydrogenation over Ni and allow us to control both activity and selectivity, which can be a means for CO2 emission abatement through its valorization as a low- or even negative-cost feedstock on a low-cost transition-metal catalyst

Correction to “Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts”

Figure 1 in the original paper shows d-acetonitrile molecules with four bonds between the N and C atoms. This has been corrected here. new figure to demonstrate a direct correlation between the point spectra and IR maps that were recorded on the given particle cross-section. The main text was adapted as follows: Point spectra, recorded of PE- (i.e., A1 and B1 in Figure 5) and silica-rich regions (i.e., A2 and B2 in Figure 5) as well as reference materials (Figures S10.S12), further helped to assign the imaged phases. A correction to the Supporting Information, section S4.B, was made to reflect that all data were recorded in PiF and not PiFM mode: Atomic force microscopy (AFM) topography images, IR maps and IR point spectra were recorded in dynamic noncontact PiF mode (60 accumulations, 500 ms pixel dwell time, 1 cm.1 spectral resolution) using NCHR Au-coated cantilevers (force constant: 40 N/m). The iFM labels in Figures S7.S9 (Supporting Information) were changed to PiF. Furthermore, the methodology for recording an IR map at a specific wavenumber was described in more detail, both in the Supporting Information and in the main text: Prior to acquiring an IR map at a specific wavenumber, a preliminary low-resolution scan was performed. A point spectrum was then taken in the mapped area to determine the wavenumber of the targeted vibrational band (i.e., the wavenumber at which the band has its maximum intensity). The IR PiFM maps were recorded in noncontact mode26 (amplitude ratio set point of 80%, attractive van der Waals force regime; Table S3) at characteristic wavenumbers for the Si.O stretching vibration46,47 (maps recorded at single wavenumbers in the range of 1050.1030 cm.1, (Si.O), Figure 4) and the symmetric C.H bending vibration of the methylene group37.39 (maps recorded at single wavenumbers in the range of 1472.1460 cm-1, (C.H), Figure 4)