Unique Pore Selectivity for Cs⁺ and Exceptionally High NH₄⁺ Exchange Capacity of the Chalcogenide Material K₆Sn[Zn₄Sn₄S₁₇]

Highly selective ion-exchange properties and -exchange capacities of the open framework chalcogenide material K6Sn[Zn4Sn4S17] (1) with Cs+ and NH4+ are reported. Because the structure of this framework is known in great detail, these studies are a rare example where structure/property relationships can be directly drawn. 1 possesses three types of micropore cavities. The largest pore of 1 presents an exact fit for Cs+ and exhibits high selectivity for this ion, as demonstrated by competitive ion-exchange experiments. The next largest pore has a greater capacity (up to four cations) and is well suited for NH4+ ions. This leads to a high ammonium-exchange capacity for 1 of 3.06 mequiv/gr, which is close to the NH4+-exchange capacities of natural zeolites. The single-crystal structures of ammonium-exchanged products at various stages reveal an unusual mechanism for the exchange process of 1 which involves diffusion of ammonium cations from the large cavity to the small ones of the framework. Thermal analysis of one of these ammonium-exchanged products, in combination with mass spectroscopy, showed the decomposition of NH4+ cations to NH3 and H2S with the parallel transformation of the exchanged product to a mixture of crystalline phases. Since K6Sn[Zn4Sn4S17] can be grown in suitably large crystals (much larger than most zeolites), it defines an excellent model system in which ion-exchange processes and products can be characterized and studied in detail in various reaction stages

Unique Pore Selectivity for Cs⁺ and Exceptionally High NH₄⁺ Exchange Capacity of the Chalcogenide Material K₆Sn[Zn₄Sn₄S₁₇]

Highly selective ion-exchange properties and -exchange capacities of the open framework chalcogenide material K6Sn[Zn4Sn4S17] (1) with Cs+ and NH4+ are reported. Because the structure of this framework is known in great detail, these studies are a rare example where structure/property relationships can be directly drawn. 1 possesses three types of micropore cavities. The largest pore of 1 presents an exact fit for Cs+ and exhibits high selectivity for this ion, as demonstrated by competitive ion-exchange experiments. The next largest pore has a greater capacity (up to four cations) and is well suited for NH4+ ions. This leads to a high ammonium-exchange capacity for 1 of 3.06 mequiv/gr, which is close to the NH4+-exchange capacities of natural zeolites. The single-crystal structures of ammonium-exchanged products at various stages reveal an unusual mechanism for the exchange process of 1 which involves diffusion of ammonium cations from the large cavity to the small ones of the framework. Thermal analysis of one of these ammonium-exchanged products, in combination with mass spectroscopy, showed the decomposition of NH4+ cations to NH3 and H2S with the parallel transformation of the exchanged product to a mixture of crystalline phases. Since K6Sn[Zn4Sn4S17] can be grown in suitably large crystals (much larger than most zeolites), it defines an excellent model system in which ion-exchange processes and products can be characterized and studied in detail in various reaction stages

Unique Pore Selectivity for Cs⁺ and Exceptionally High NH₄⁺ Exchange Capacity of the Chalcogenide Material K₆Sn[Zn₄Sn₄S₁₇]

Highly selective ion-exchange properties and -exchange capacities of the open framework chalcogenide material K6Sn[Zn4Sn4S17] (1) with Cs+ and NH4+ are reported. Because the structure of this framework is known in great detail, these studies are a rare example where structure/property relationships can be directly drawn. 1 possesses three types of micropore cavities. The largest pore of 1 presents an exact fit for Cs+ and exhibits high selectivity for this ion, as demonstrated by competitive ion-exchange experiments. The next largest pore has a greater capacity (up to four cations) and is well suited for NH4+ ions. This leads to a high ammonium-exchange capacity for 1 of 3.06 mequiv/gr, which is close to the NH4+-exchange capacities of natural zeolites. The single-crystal structures of ammonium-exchanged products at various stages reveal an unusual mechanism for the exchange process of 1 which involves diffusion of ammonium cations from the large cavity to the small ones of the framework. Thermal analysis of one of these ammonium-exchanged products, in combination with mass spectroscopy, showed the decomposition of NH4+ cations to NH3 and H2S with the parallel transformation of the exchanged product to a mixture of crystalline phases. Since K6Sn[Zn4Sn4S17] can be grown in suitably large crystals (much larger than most zeolites), it defines an excellent model system in which ion-exchange processes and products can be characterized and studied in detail in various reaction stages

Unique Pore Selectivity for Cs⁺ and Exceptionally High NH₄⁺ Exchange Capacity of the Chalcogenide Material K₆Sn[Zn₄Sn₄S₁₇]

Highly selective ion-exchange properties and -exchange capacities of the open framework chalcogenide material K6Sn[Zn4Sn4S17] (1) with Cs+ and NH4+ are reported. Because the structure of this framework is known in great detail, these studies are a rare example where structure/property relationships can be directly drawn. 1 possesses three types of micropore cavities. The largest pore of 1 presents an exact fit for Cs+ and exhibits high selectivity for this ion, as demonstrated by competitive ion-exchange experiments. The next largest pore has a greater capacity (up to four cations) and is well suited for NH4+ ions. This leads to a high ammonium-exchange capacity for 1 of 3.06 mequiv/gr, which is close to the NH4+-exchange capacities of natural zeolites. The single-crystal structures of ammonium-exchanged products at various stages reveal an unusual mechanism for the exchange process of 1 which involves diffusion of ammonium cations from the large cavity to the small ones of the framework. Thermal analysis of one of these ammonium-exchanged products, in combination with mass spectroscopy, showed the decomposition of NH4+ cations to NH3 and H2S with the parallel transformation of the exchanged product to a mixture of crystalline phases. Since K6Sn[Zn4Sn4S17] can be grown in suitably large crystals (much larger than most zeolites), it defines an excellent model system in which ion-exchange processes and products can be characterized and studied in detail in various reaction stages

Unique Pore Selectivity for Cs⁺ and Exceptionally High NH₄⁺ Exchange Capacity of the Chalcogenide Material K₆Sn[Zn₄Sn₄S₁₇]

Highly selective ion-exchange properties and -exchange capacities of the open framework chalcogenide material K6Sn[Zn4Sn4S17] (1) with Cs+ and NH4+ are reported. Because the structure of this framework is known in great detail, these studies are a rare example where structure/property relationships can be directly drawn. 1 possesses three types of micropore cavities. The largest pore of 1 presents an exact fit for Cs+ and exhibits high selectivity for this ion, as demonstrated by competitive ion-exchange experiments. The next largest pore has a greater capacity (up to four cations) and is well suited for NH4+ ions. This leads to a high ammonium-exchange capacity for 1 of 3.06 mequiv/gr, which is close to the NH4+-exchange capacities of natural zeolites. The single-crystal structures of ammonium-exchanged products at various stages reveal an unusual mechanism for the exchange process of 1 which involves diffusion of ammonium cations from the large cavity to the small ones of the framework. Thermal analysis of one of these ammonium-exchanged products, in combination with mass spectroscopy, showed the decomposition of NH4+ cations to NH3 and H2S with the parallel transformation of the exchanged product to a mixture of crystalline phases. Since K6Sn[Zn4Sn4S17] can be grown in suitably large crystals (much larger than most zeolites), it defines an excellent model system in which ion-exchange processes and products can be characterized and studied in detail in various reaction stages

Factors Controlling the Enhanced Mechanical and Thermal Properties of Nanodiamond-Reinforced Cross-Linked High Density Polyethylene

A systematic investigation of the factors influencing the notable enhancement of the mechanical and thermal properties of nanodiamonds (NDs)-reinforced cross-linked high density polyethylene (PEX) is presented in this work. The effects of crystal structure and molecular conformation as well as filler dispersion and adhesion with the matrix were found to govern the mechanical properties of the final composites. A considerable increase in the strength, toughness, and elastic modulus of the materials was found for the composites with filler content below 1 wt %. For higher NDs concentrations, the properties degraded. When filler concentration does not exceed 1 wt %, enhanced adhesion with the matrix is achieved, allowing a more successful load transfer between the filler and the matrix, thus enabling an effective reinforcement of the composites. The higher degree of crystallinity along with larger crystal size are also positively influencing the mechanical properties of PEX. Higher filler concentrations, on the other hand, lead to the formation of larger aggregates, which lead to lower adhesion with the matrix, while they also constitute stress concentrators and therefore reduce the positive reinforcement of the matrix. The thermal conductivity of the composites was also found to be significantly increased for low-filler concentrations. This enhancement was less significant for higher NDs concentrations. It is concluded that this reinforcement is due to the heat capacity increase that NDs incorporation causes in PEX. Additionally, a thermal stability enhancement was found for the composite with minimum filler content

Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties

In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly­(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (<i>f</i>-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % <i>f</i>-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. <i>f</i>-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30–40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy

Multistates and Polyamorphism in Phase-Change K₂Sb₈Se₁₃

The phase-change (PC) materials in the majority of optical data storage media in use today exhibit a fast, reversible crystal → amorphous phase transition that allows them to be switched between on (1) and off (0) binary states. Solid-state inorganic materials with this property are relatively common, but those exhibiting an amorphous → amorphous transition called <i>polyamorphism</i> are exceptionally rare. K₂Sb₈Se₁₃ (KSS) reported here is the first example of a material that has both amorphous → amorphous polyamorphic transition and amorphous → crystal transition at easily accessible temperatures (227 and 263 °C, respectively). The transitions are associated with the atomic coordinative preferences of the atoms, and all three states of K₂Sb₈Se₁₃ are stable in air at 25 °C and 1 atm. All three states of K₂Sb₈Se₁₃ exhibit distinct optical bandgaps, <i>E</i>_g = 1.25, 1.0, and 0.74 eV, for the amorphous-II, amorphous-I, and crystalline versions, respectively. The room-temperature electrical conductivity increases by more than 2 orders of magnitude from amorphous-I to -II and by another 2 orders of magnitude from amorphous-II to the crystalline state. This extraordinary behavior suggests that a new class of materials exist which could provide multistate level systems to enable higher-order computing logic circuits, reconfigurable logic devices, and optical switches

Multistates and Polyamorphism in Phase-Change K₂Sb₈Se₁₃

The phase-change (PC) materials in the majority of optical data storage media in use today exhibit a fast, reversible crystal → amorphous phase transition that allows them to be switched between on (1) and off (0) binary states. Solid-state inorganic materials with this property are relatively common, but those exhibiting an amorphous → amorphous transition called <i>polyamorphism</i> are exceptionally rare. K₂Sb₈Se₁₃ (KSS) reported here is the first example of a material that has both amorphous → amorphous polyamorphic transition and amorphous → crystal transition at easily accessible temperatures (227 and 263 °C, respectively). The transitions are associated with the atomic coordinative preferences of the atoms, and all three states of K₂Sb₈Se₁₃ are stable in air at 25 °C and 1 atm. All three states of K₂Sb₈Se₁₃ exhibit distinct optical bandgaps, <i>E</i>_g = 1.25, 1.0, and 0.74 eV, for the amorphous-II, amorphous-I, and crystalline versions, respectively. The room-temperature electrical conductivity increases by more than 2 orders of magnitude from amorphous-I to -II and by another 2 orders of magnitude from amorphous-II to the crystalline state. This extraordinary behavior suggests that a new class of materials exist which could provide multistate level systems to enable higher-order computing logic circuits, reconfigurable logic devices, and optical switches