Interlaboratory Comparison Reveals State of the Art in Microplastic Detection and Quantification Methods

\ua9 2025 The Authors. Published by American Chemical Society. In this study, we investigate the current accuracy of widely used microplastic (MP) detection methods through an interlaboratory comparison (ILC) involving ISO-approved techniques. The ILC was organized under the prestandardization platform of VAMAS (Versailles Project on Advanced Materials and Standards) and gathered a large number (84) of analytical laboratories across the globe. The aim of this ILC was (i) to test and to compare two thermo-analytical and three spectroscopical methods with respect to their suitability to identify and quantify microplastics in a water-soluble matrix and (ii) to test the suitability of the microplastic test materials to be used in ILCs. Two reference materials (RMs), polyethylene terephthalate (PET) and polyethylene (PE) as powders with rough size ranges between 10 and 200 μm, were used to press tablets for the ILC. The following parameters had to be assessed: polymer identity, mass fraction, particle number concentration, and particle size distribution. The reproducibility, SR, in thermo-analytical experiments ranged from 62%-117% (for PE) and 45.9%-62% (for PET). In spectroscopical experiments, the SR varied between 121% and 129% (for PE) and 64% and 70% (for PET). Tablet dissolution turned out to be a very challenging step and should be optimized. Based on the knowledge gained, development of guidance for improved tablet filtration is in progress. Further, in this study, we discuss the main sources of uncertainties that need to be considered and minimized for preparation of standardized protocols for future measurements with higher accuracy

Water-Dispersible Copper Sulfide Nanocrystals via Ligand Exchange of 1-Dodecanethiol

In colloidal Cu2–xS nanocrystal synthesis, thiols are often used as organic ligands and the sulfur source, as they yield high-quality nanocrystals. However, thiol ligands on Cu2–xS nanocrystals are difficult to exchange, limiting the applications of these nanocrystals in photovoltaics, biomedical sensing, and photocatalysis. Here, we present an effective and facile procedure to exchange native 1-dodecanethiol on Cu2–xS nanocrystals by 3-mercaptopropionate, 11-mercaptoundecanoate, and S2– in formamide under inert atmosphere. The product hydrophilic Cu2–xS nanocrystals have excellent colloidal stability in formamide. Furthermore, the size, shape, and optical properties of the nanocrystals are not significantly affected by the ligand exchange. Water-dispersible Cu2–xS nanocrystals are easily obtained by precipitation of the nanocrystals capped by S2–, 3-mercaptopropionate, or 11-mercaptoundecanoate from formamide, followed by redispersion in water. Interestingly, the ligand exchange rates for Cu2–xS nanocrystals capped with 1-dodecanethiol are observed to depend on the preparation method, being much slower for Cu2–xS nanocrystals prepared through heating-up than through hot-injection synthesis protocols. XPS studies reveal that the differences in the ligand exchange rates are due to the surface chemistry of the Cu2–xS nanocrystals, where the nanocrystals prepared via hot-injection synthesis have a less dense ligand layer due to the presence of trioctylphosphine oxide during synthesis. A model is proposed that explains the observed differences in the ligand exchange rates. The facile ligand exchange procedures reported here enable the use of high-quality colloidal Cu2–xS nanocrystals prepared in the presence of 1-dodecanethiol in various applications

Size-Dependent Band-Gap and Molar Absorption Coefficients of Colloidal CuInS2 Quantum Dots

The knowledge of the quantum dot (QD) concentration in a colloidal suspension and the quantitative understanding of the size-dependence of the band gap of QDs are of crucial importance from both applied and fundamental viewpoints. In this work, we investigate the size-dependence of the optical properties of nearly spherical wurtzite (wz) CuInS2 (CIS) QDs in the 2.7 to 6.1 nm diameter range (polydispersity ≤10%). The QDs are synthesized by partial Cu+ for In3+ cation exchange in template Cu2-xS NCs, which yields CIS QDs with very small composition variations (In/Cu= 0.91±0.11), regardless of their sizes. These well-defined QDs are used to investigate the size dependence of the band gap of wz CIS QDs. A sizing curve is also constructed for chalcopyrite CIS QDs by collecting and reanalyzing literature data. We observe that both sizing curves follow primarily a 1/d dependence. Moreover, the molar absorption coefficients and the absorption cross-section per CIS formula unit, both at 3.1 eV and at the band gap, are analyzed. The results demonstrate that the molar absorption coefficients of CIS QDs follow a power law at the first exciton transition energy (ε_(E_1 )=5208 d^2.45), and scale with the QD volume at 3.1 eV. This latter observation implies that the absorption cross-section per unit cell at 3.1 eV is size-independent, and therefore can be estimated from bulk optical constants. These results also demonstrate that the molar absorption coefficients at 3.1 eV are more reliable for analytical purposes, since they are less sensitive to size and shape dispersion

Size-Dependent Band-Gap and Molar Absorption Coefficients of Colloidal CuInS2 Quantum Dots

The knowledge of the quantum dot (QD) concentration in a colloidal suspension and the quantitative understanding of the size-dependence of the band gap of QDs are of crucial importance from both applied and fundamental viewpoints. In this work, we investigate the size-dependence of the optical properties of nearly spherical wurtzite (wz) CuInS2 (CIS) QDs in the 2.7 to 6.1 nm diameter range (polydispersity ≤10%). The QDs are synthesized by partial Cu+ for In3+ cation exchange in template Cu2-xS NCs, which yields CIS QDs with very small composition variations (In/Cu= 0.91±0.11), regardless of their sizes. These well-defined QDs are used to investigate the size dependence of the band gap of wz CIS QDs. A sizing curve is also constructed for chalcopyrite CIS QDs by collecting and reanalyzing literature data. We observe that both sizing curves follow primarily a 1/d dependence. Moreover, the molar absorption coefficients and the absorption cross-section per CIS formula unit, both at 3.1 eV and at the band gap, are analyzed. The results demonstrate that the molar absorption coefficients of CIS QDs follow a power law at the first exciton transition energy (ε_(E_1 )=5208 d^2.45), and scale with the QD volume at 3.1 eV. This latter observation implies that the absorption cross-section per unit cell at 3.1 eV is size-independent, and therefore can be estimated from bulk optical constants. These results also demonstrate that the molar absorption coefficients at 3.1 eV are more reliable for analytical purposes, since they are less sensitive to size and shape dispersion

Nature of cobalt species during the in situ sulfurization of Co(Ni)Mo/Al2O3 hydrodesulfurization catalysts

The evolution in local structure and electronic properties of cobalt was investigated during in situ sulfurization. Using a combination of 1s X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (RIXS), the valence, coordination and symmetry of cobalt ions were tracked in two cobalt-promoted molybdenum oxide precursors of the hydrodesulfurization catalyst system, namely Co-Mo/Al2O3 and Co-Ni-Mo/Al2O3. Extended X-ray absorption fine structure shows that the CoO bonds were replaced with CoS bonds as a function of reaction temperature. The cobalt K pre-edge intensity shows that the symmetry of cobalt was modified from Co3+Oh and Co2+Oh to a Co2+ ion where the inversion symmetry is broken, in agreement with a square-pyramidal site. The 1s3p RIXS data revealed the presence of an intermediate cobalt oxy-sulfide species. This species was not detected from XAS and was determined from the increased information obtained from the 1s3p RIXS data. The cobalt XAS and RIXS data show that nickel has a significant influence on the formation of the cobalt oxy-sulfide intermediate species prior to achieving the fully sulfided state at T > 400 degrees C

Synthesis and Formation Mechanism of Colloidal Janus-Type Cu2 -xS/CuInS2Heteronanorods via Seeded Injection

Colloidal heteronanocrystals allow for the synergistic combination of properties of different materials. For example, spatial separation of the photogenerated electron and hole can be achieved by coupling different semiconductors with suitable band offsets in one single nanocrystal, which is beneficial for improving the efficiency of photocatalysts and photovoltaic devices. From this perspective, axially segmented semiconductor heteronanorods with a type-II band alignment are particularly attractive since they ensure the accessibility of both photogenerated charge carriers. Here, a two-step synthesis route to Cu2-xS/CuInS2 Janus-type heteronanorods is presented. The heteronanorods are formed by injection of a solution of preformed Cu2-xS seed nanocrystals in 1-dodecanethiol into a solution of indium oleate in oleic acid at 240 °C. By varying the reaction time, Janus-type heteronanocrystals with different sizes, shapes, and compositions are obtained. A mechanism for the formation of the heteronanocrystals is proposed. The first step of this mechanism consists of a thiolate-mediated topotactic, partial Cu+ for In3+ cation exchange that converts one of the facets of the seed nanocrystals into CuInS2. This is followed by homoepitaxial anisotropic growth of wurtzite CuInS2. The Cu2-xS seed nanocrystals also act as sacrificial Cu+ sources, and therefore, single composition CuInS2 nanorods are eventually obtained if the reaction is allowed to proceed to completion. The two-stage seeded growth method developed in this work contributes to the rational synthesis of Cu2-xS/CuInS2 heteronanocrystals with targeted architectures by allowing one to exploit the size and faceting of premade Cu2-xS seed nanocrystals to direct the growth of the CuInS2 segment

Water-Dispersible Copper Sulfide Nanocrystals via Ligand Exchange of 1-Dodecanethiol

In colloidal Cu2–xS nanocrystal synthesis, thiols are often used as organic ligands and the sulfur source, as they yield high-quality nanocrystals. However, thiol ligands on Cu2–xS nanocrystals are difficult to exchange, limiting the applications of these nanocrystals in photovoltaics, biomedical sensing, and photocatalysis. Here, we present an effective and facile procedure to exchange native 1-dodecanethiol on Cu2–xS nanocrystals by 3-mercaptopropionate, 11-mercaptoundecanoate, and S2– in formamide under inert atmosphere. The product hydrophilic Cu2–xS nanocrystals have excellent colloidal stability in formamide. Furthermore, the size, shape, and optical properties of the nanocrystals are not significantly affected by the ligand exchange. Water-dispersible Cu2–xS nanocrystals are easily obtained by precipitation of the nanocrystals capped by S2–, 3-mercaptopropionate, or 11-mercaptoundecanoate from formamide, followed by redispersion in water. Interestingly, the ligand exchange rates for Cu2–xS nanocrystals capped with 1-dodecanethiol are observed to depend on the preparation method, being much slower for Cu2–xS nanocrystals prepared through heating-up than through hot-injection synthesis protocols. XPS studies reveal that the differences in the ligand exchange rates are due to the surface chemistry of the Cu2–xS nanocrystals, where the nanocrystals prepared via hot-injection synthesis have a less dense ligand layer due to the presence of trioctylphosphine oxide during synthesis. A model is proposed that explains the observed differences in the ligand exchange rates. The facile ligand exchange procedures reported here enable the use of high-quality colloidal Cu2–xS nanocrystals prepared in the presence of 1-dodecanethiol in various applications

Nature of cobalt species during the <i>in situ</i> sulfurization of Co(Ni)Mo/Al₂O₃ hydrodesulfurization catalysts

The evolution in local structure and electronic properties of cobalt was investigated during in situ sulfurization. Using a combination of 1s X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (RIXS), the valence, coordination and symmetry of cobalt ions were tracked in two cobalt-promoted molybdenum oxide precursors of the hydrodesulfurization catalyst system, namely Co–Mo/Al2O3 and Co–Ni–Mo/Al2O3. Extended X-ray absorption fine structure shows that the Co—O bonds were replaced with Co—S bonds as a function of reaction temperature. The cobalt K pre-edge intensity shows that the symmetry of cobalt was modified from Co3+ O h and Co2+ O h to a Co2+ ion where the inversion symmetry is broken, in agreement with a square-pyramidal site. The 1s3p RIXS data revealed the presence of an intermediate cobalt oxy-sulfide species. This species was not detected from XAS and was determined from the increased information obtained from the 1s3p RIXS data. The cobalt XAS and RIXS data show that nickel has a significant influence on the formation of the cobalt oxy-sulfide intermediate species prior to achieving the fully sulfided state at T &gt; 400°C.</jats:p

Synthesis and Formation Mechanism of Colloidal Janus-Type Cu2 -xS/CuInS2Heteronanorods via Seeded Injection

Colloidal heteronanocrystals allow for the synergistic combination of properties of different materials. For example, spatial separation of the photogenerated electron and hole can be achieved by coupling different semiconductors with suitable band offsets in one single nanocrystal, which is beneficial for improving the efficiency of photocatalysts and photovoltaic devices. From this perspective, axially segmented semiconductor heteronanorods with a type-II band alignment are particularly attractive since they ensure the accessibility of both photogenerated charge carriers. Here, a two-step synthesis route to Cu2-xS/CuInS2 Janus-type heteronanorods is presented. The heteronanorods are formed by injection of a solution of preformed Cu2-xS seed nanocrystals in 1-dodecanethiol into a solution of indium oleate in oleic acid at 240 °C. By varying the reaction time, Janus-type heteronanocrystals with different sizes, shapes, and compositions are obtained. A mechanism for the formation of the heteronanocrystals is proposed. The first step of this mechanism consists of a thiolate-mediated topotactic, partial Cu+ for In3+ cation exchange that converts one of the facets of the seed nanocrystals into CuInS2. This is followed by homoepitaxial anisotropic growth of wurtzite CuInS2. The Cu2-xS seed nanocrystals also act as sacrificial Cu+ sources, and therefore, single composition CuInS2 nanorods are eventually obtained if the reaction is allowed to proceed to completion. The two-stage seeded growth method developed in this work contributes to the rational synthesis of Cu2-xS/CuInS2 heteronanocrystals with targeted architectures by allowing one to exploit the size and faceting of premade Cu2-xS seed nanocrystals to direct the growth of the CuInS2 segment