Aim of investigation is to study the possibility of activating a promising Ni(OH)2, prepared using two-step high-temperature synthesis, by adding 3%, 5% and 10% (mol.) Al3+ to Ni2+. For describing the intercalation of Al3+ into hydroxide structure, "Separate-Solid—Liquid—Solid" mechanism, which included the formation of separate Al-containing phase on synthesis stage, and incorporation of Al3+ into Ni(OH)2 or formation of surface compounds during hydrolysis stage, has been proposed. EDX analysis of precursor confirmed the formation of separate Al-containing phases. By means of PXRD, EDX, SEM, TEM revealed realization of both ways of Al3+ incorporation: at high amounts of Al3+ (5% and 10% mol.), predominantly surface compounds are formed with distorted and altered particle shape and appearance of "core–shell" particles. At low amounts of Al3+ (3% mol.), permeably doping occurs, with partial intercalation of Al3+ into the nickel hydroxide structure. Based on CVA and GCDC results, Al3+ acts as a poison upon the formation of surface compounds have been found. Upon doping of hot hydrolysis samples with aluminum, sample activation was observed, which resulted in an increase of specific capacity by 1.99 times, from 569 Fg−1 (pure Ni(OH)2) to 1112 Fg−1.

The negative thermal expansion material potassium cadmium dicyanoargentate, KCd[Ag(CN) 2 ] 3 , is studied at high pressure using a combination of X-ray single-crystal diffraction, X-ray powder diffraction, infrared and Raman spectroscopy, and density functional theory calculations. In common with the isostructural manganese analogue, KMn[Ag(CN) 2 ] 3 , this material is shown to exhibit very strong negative linear compressibility (NLC) in the crystallographic c direction due to structure hinging. We find increased structural flexibility results in enhanced NLC and NTE properties, but this also leads to two pressure-induced phase transitionsto very large unit cells involving octahedral tilting and shearing of the structurebelow 2 GPa. The presence of potassium cations has an important effect on the mechanical and thermodynamic properties of this family, while the chemical versatility demonstrated here is of considerable interest to tune unusual mechanical properties for application. ■ INTRODUCTION Materials where external stimuli induces an anomalous response, such as expansion upon cooling (negative thermal expansion, NTE 1−3) or on application of hydrostatic pressure (negative linear compressibility, NLC 4,5), have recently received considerable attention. These materials that "break the rules"as a result of specific, and therefore rare, elastic anomalies 6−8 are curious from a fundamental point of view but might also be revolutionary for a range of technologies including interferometric pressure sensors, pressure-controlled or pressure-sensitive electronic devices, and smart actua-tion. 2,4,9−11 The ability to design materials with unusual properties is therefore a key focus of the field: can we understand these elastic anomalies so that we can tune the magnitude and/or range of negative responses? Negative thermal expansion may occur in one, two, or all principal directions without violating thermodynamics. 12,13 Thus, for example, the volume coefficient of thermal expansion (CTE), () V V V T p 1 α = ∂ ∂ , takes large negative values in zirconium tungstate ZrW 2 O 8 and zinc(II) cyanide Zn(CN) 2 over large temperature ranges. 14 Under hydrostatic pressure, however, volume must always reduce and so the volume compressibility (() K V V V p T 1 = − ∂ ∂ , conventionally formulated as the bulk modulus, B = (K V) −1), must be definite and positive. 15 Expansion under pressure can occur in one or two directions, as long as this is coupled to volume reduction. 5,12,16 Therefore, negative linear compressibility (NLC)the expansion in one principal direction of a material under hydrostatic pressureis conceptually and empirically related to linear-NTE. In both cases, anomalous response relies on mechanical anisotropy. The so-called "wine-rack" model is often invoked where mechanical hinging allows linear expansion coupled to volume reduction on increasing pressure or decreasing temperature. 5,8 Attention in this field has focused on a class of materials known as coordination polymers (CPs), in particular due to the very large magnitude of responses found in comparison to conventional oxide-based materials. 7 Examples that show large NTE and NLC include cyanide frameworks such as Ag 3 [Co-(CN) 6 ] (refs 17 and 18), KMn[Ag(CN) 2 ] 3 (refs 19 and 20), Zn[Au(CN) 2 ] 2 (refs 21 and 22), and metal−organic frameworks 23 (MOFs) such as MIL-53 (ref 24), UTSA-16 (ref 25), ZAG-4 (ref 26), and [NH 4 ][Zn(HCOO) 3 ] (ref 27). In many cases, mechanical response can be predicted in these systems by considering the framework as a set of rigid connectors and hinges, sodepending on geometry and topologyNTE or

The variety of H bond (HB) interactions is a source of inspiration for bottom-up molecular engineering through self-aggregation. Non-conventional intermolecular HBs between N,N0disubstituted urea and thiourea are studied in detail by vibrational spectroscopies and ab initio calculations. Raman and IR mode assignments are given. We show that it is possible to study selectively the different intermolecular bifurcated intra-and inter-dimer HBs with the two types of HB acceptors. Through the ab initio calculation, the thioamide I mode, a specific marker of N-H … S=C HB interactions, is unambiguously identified.

Au-covered hollow urchin-like ZnO nanostructures were prepared with controlled size by combining nanosphere lithography (NSL), atomic layer deposition (ALD), electrodeposition, and electron beam (e-beam) evaporation. The optimal Au film thickness for sensing applications was determined by measuring the surface-enhanced Raman scattering (SERS) intensities of the substrates. Furthermore, the sensing performances of these hybrid nanostructures have been investigated by using chemical and biological molecules: thiophenol and adenine, respectively. Limits of detection (LOD) of 10 À8 M and 10 À6 M were found for the detection of thiophenol and adenine, respectively. Additionally, the excellent uniformity and batch-to-batch reproducibility of the substrates make them excellent candidates for reliable SERS sensing and biosensing.

We demonstrate that weak CH⋅⋅⋅O hydrogen bonds (HBs) are important host−guest interactions in zeolite assemblies involving structure directing organocations. This type of HB is identified between alkyl groups of the organic structure directing agent (OSDA) and the silica framework in as‐synthesized silicalite‐1 of complex topology (MFI) using a combination of experimental and theoretical data obtained at low and room temperatures. The 28 weak CH⋅⋅⋅O HBs, evidenced along dynamics simulation at room temperature, represent 30 % of the energy of the Coulomb electrostatic interaction between OSDA and the zeolite framework. The strongest and most stable HB found here connects the OSDA to the [415262] cage containing F atoms and should contribute to preserve zeolite topology during crystal growth. An inspection of other as‐synthesized zeolites of very different framework topology indicates that the directional CH⋅⋅⋅O HBs have to be considered when discussing zeolite structure directing phenomena.

Low-dimensional materials have been examined as electrocatalysts for the hydrogen evolution reaction (HER). Among them, two-dimensional transition metal dichalcogenides (2D-TMDs) such as MoS2 have been identified as potential candidates. However, the performance of TMDs toward HER in both acidic and basic media remains inferior to that of noble metals such as Pt and its alloys. This calls for investigating the influence of controlled defect engineering of 2D TMDs on their performance toward hydrogen production. Here, we explored the HER activity from defective multilayered MoS2 over a large range of surface S vacancy concentrations up to 90%. Amorphous MoS2 and 2H MoS2 with ultrarich S vacancies demonstrated the highest HER performance in acid and basic electrolytes, respectively. We also report that the HER performance from multilayered MoS2 can be divided into two domains corresponding to "point defects" at low concentrations of surface S vacancies (Stage 1) and large regions of undercoordinated Mo atoms for high concentrations of surface S vacancies (Stage 2). The highest performance is obtained for Stage 2 in the presence of undercoordinated Mo atoms with a TOF of similar to 2 s(-1) at an overpotential of 160 mV in 0.1 M KOH which compares favorably to the best results in the literature. Overall, our work provides deeper insight on the HER mechanism from defected MoS2 and provides guidance for the development of defect-engineered TMD-based electrocatalysts.

Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS2) nanosheets. The functionalized MoS2 membranes demonstrate >90% and similar to 87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS2 membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability