Interlayer Water Molecules Research Articles

Detection of Layer Charge Density in Layered Double Hydroxides and Studies on Host‐Guest Interactions

AbstractThe layer charge density of layered double hydroxides (LDHs) significantly affects interlayer spacing, the arrangement of interlayer anions and water molecules, thermal stability, as well as adsorption performance. However, traditional methods for evaluating the layer charge density of LDHs are complex, prone to large errors, and impacted by numerous factors, rendering these methods unable to facilitate direct comparisons of layer charge density across different LDH compositions. Consequently, this study proposes a novel approach based on the host‐guest supramolecular interactions in LDHs to investigate the layer charge density by analyzing changes in the position of the infrared absorption peaks of interlayer guest species. The shifts in infrared absorption peak positions are employed to assess the layer charge density of MgAl‐LDHs with varying molar ratios (M2+/M3+=2, 2.5, 3, 3.5, 4). The validity of using infrared peak position shifts is corroborated through a combination of techniques, including Raman spectroscopy, TG‐DTG, XRD, Zeta potential, and adsorption analyses. Furthermore, the layer charge density of NiAl, CoAl, MgFe, and NiFe‐LDHs are evaluated, confirming the universality of the infrared method. By ranking layer charge density of LDHs with different compositions and ratios, this study resolves the challenge of comparing LDHs with diverse layer compositions.

Expansion of d-spacing of boehmite for enhanced phosphate adsorption via hydrogen bond network

The optimization of the interlayer water content to increase the d-spacing of layered materials has recently attracted interest in pollutant removal. Several studies have explored phosphate adsorption onto boehmite considering its high surface area; however, the influence of its d-spacing on the adsorption performance remains unexplored. Therefore, our study aimed to investigate the impact of the synthesis pH of boehmite on the d-spacing and adsorption performance of phosphate ions. For this purpose, boehmite samples were synthesized under various pH conditions at 100°C to be tested for phosphate adsorption. As a result of this mild synthesis condition, the number of reactive hydroxyl groups in boehmite samples ranged from 7.02 – 9.02mmol/g, nearly four times higher than the reported boehmites. Boehmite prepared under acidic conditions exhibits a relatively high interlayer water content and an enlarged d-spacing from 0.640 to 0.996nm, resulting in superior phosphate adsorption (215mg/g) within one minute. We also confirmed that phosphate adsorption increased the binding energy states of aluminum and oxygen in boehmite, indicating a robust hydrogen bond network with phosphate ions in the inner space. In contrast, the adsorption decreased the binding energy for other types of boehmite, indicating charge interaction. Competitive adsorption tests also showed the strong affinity of boehmite for phosphate ions, even in the presence of fluoride ions. These findings highlight the importance of the interlayer water molecules in controlling the d-spacing of boehmite, indicating their critical role in removing anions from water.

Preparation of Oriented Nanoporous Magnetite Films by a Template-Free Solution Process from Iron Oxyhydroxide Films

Nanoporous oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions. However, a simple, template-free method for their formation remains a challenge. Layered metal hydroxide (LMH) films are a promising precursor for spontaneous formation of nanoporous oxide films.[1-4] LMHs have a layered structure comprising 2D sheets of edge-shared octahedral hydroxide, i.e., brucite structure, with or without interlayer anions and water molecules. Calcination of LMH results in dehydration, anion elimination, and volume shrinkage, leading to the spontaneous formation of nanoporous oxides.In this study, we have prepared nanoporous and ferrimagnetic magnetite (Fe3O4) films by using layered iron hydroxides, namely, green rust (GR), as a precursor. Generally, GR has a brucite-type structure containing Fe2+ and Fe3+ ions, and is highly susceptible to oxidation by oxygen in water and air, leading to the formation of iron oxyhydroxides (FeOOH). Here, GR films were electrochemically deposited on FTO substrates in an aqueous solution containing Fe2+ and NO3 − ions at room temperature. Drying the GR films in air resulted in the formation of two-type FeOOH films, depending on the electrodeposition condition. Characterization using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and FT-IR spectroscopy revealed that one is [010]-oriented γ-FeOOH films, and the other is [001]-oriented δ-FeOOH films. The obtained FeOOH films had a mille-feuille like morphology with 500–700 nm thickness. Heat treatment of these two-type FeOOH films under vacuum at 500 °C resulted in the formation of [110]- and [111]-oriented nanoporous Fe3O4 films. The obtained Fe3O4 films showed a ferrimagnetic behavior in VSM measurements and had a nanoporous structure comprising nanoparticles with 50–100 nm diameter.Finally, a possilble interpretation for the observed orientation relationships between the FeOOH and Fe3O4 was also discussed on the basis of pyrolysis intermediates of FeOOH and similarity in their atomic arrangements. References T. Shinagawa, M. Watanabe, T. Mori, J.-i. Tani, M. Chigane and M. Izaki, Inorg. Chem., 57, 13137 (2018).T. Shinagawa, M. Chigane and M. Izaki, ACS Omega, 6, 2312 (2021).T. Shinagawa, M. Chigane and M. Takahashi, Cryst. Growth Des., 22, 4122 (2022).T. Shinagawa, N. Kotobuki and A. Ohtaka, Nanoscale Adv., 5, 96 (2023). Figure 1

Molecular dynamics study of Gr(GO)/C-A-S-H composites at different temperatures: optimization of structural, dynamic and mechanical properties of civil engineering materials

In recent years, composites have been widely used in engineering fields, where nanomaterials such as graphene (Gr) and graphene oxide (GO) have potential advantages as interfacial modifiers in enhancing the properties of composites. However, the relationship between the interfacial structure and the mechanical properties of the nanocomposites is not clear, and the behavior of the composites may differ significantly at different temperatures. This study aims to investigate in depth the interfacial structure, dynamics, and mechanical properties of Gr, epoxy group-containing (-O) and hydroxyl group-containing (-OH) graphene oxide and calcium aluminosilicate hydrate (C-A-S-H) composites at different temperatures using molecular dynamics. The effect of nanomaterial composition on the interfacial chemical bonding network is revealed. The local chemical structures of bridging aluminum [Al(Q2b)] and interlayer aluminum (Alw) show different changes at different temperatures. Elevated temperature promotes the hydrolysis of interlayer water molecules to form hydroxyl groups, which affects the formation of chemical bonding networks.Al(Q2b) favors Gr and C-A-S-H linkages, whereas Alw favors GO and C-A-S-H bonding. Temperature changes lead to different chemical bonding connections and altered atomic motions. At the interface, Al atoms form a more stable chemical bonding network, which improves the interaction strength at the interface. Different composite models exhibited different mechanical properties at high temperatures and introducing epoxy and hydroxyl groups enhanced the plastic deformation of the composites. Structural analyses showed that temperature changes affected the molecular structure and interfacial bonding effects of the composites, which in turn affected the mechanical properties of the materials. At different temperatures, GO-O/C-A-S-H has higher tensile strength and Young's modulus, which can resist the degradation of performance caused by thermal expansion to a certain extent, and ensure the stability and safety of the structure, so it is more practical. These findings provide important insights to deepen the understanding of composite properties and have positive implications for future composite design and applications.

Frictional mechanisms of hydrated montmorillonite under normal loading

The friction behavior of clay particles plays an essential role in controlling its mechanical properties, but remains unclear in microscale. As one of the major clay particles, the nanoscale friction properties of hydrated montmorillonite have been studied using steered molecular dynamics (SMD) simulation method, considering the coupling effect of water content of 0 ∼ 30 % and normal load of 1 atm ∼ 10 GPa. The SMD friction along the y-direction has been performed to investigate the frictional mechanism of hydrated montmorillonite and its structural properties of interlayer water. The evolution of average friction load with water content, friction coefficients, and the distribution of interlayer water molecules were obtained. Furthermore, the SMD pulling along the z-direction was conducted to study the effect of interlayer water molecules on the interaction between montmorillonite layers. All simulation results showed that more energy and a higher friction load were required to slide at a higher normal load. The friction coefficient of 0.058 ∼ 0.17 and internal friction angle of 3.3°∼9.6° for hydrated montmorillonite agreed well with previous studies in microscale, showing the weak friction properties. The evolution of friction coefficient with water content was different at different normal loads, where the friction coefficient of 5 % hydrated montmorillonite was the highest at 3 ∼ 10 GPa. Moreover, the increasing normal load could change the distribution of interlayer water molecules.

Monitoring Ti3C2Tx MXene Degradation Pathways Using Raman Spectroscopy.

Extending applications of Ti3C2Tx MXene in nanocomposites and across fields of electronics, energy storage, energy conversion, and sensor technologies necessitates simple and efficient analytical methods. Raman spectroscopy is a critical tool for assessing MXene composites; however, high laser powers and temperatures can lead to the materials' deterioration during the analysis. Therefore, an in-depth understanding of MXene photothermal degradation and changes in its oxidation state is required, but no systematic studies have been reported. The primary aim of this study was to investigate the degradation of the MXene lattice through Raman spectroscopic analysis. Distinct spectral markers were related to structural alterations within the Ti3C2Tx material after subjecting it to thermal- and laser-induced degradation. During the degradation processes, spectral markers were revealed for several specific steps: a decrease in the number of interlayer water molecules, a decrease in the number of -OH groups, formation of C-C bonds, oxidation of the lattice, and formation of TiO2 nanoparticles (first anatase, followed by rutile). By tracking of position shifts and intensity changes for Ti3C2Tx, the spectral markers that signify the initiation of each step were found. This spectroscopic approach enhances our understanding of the degradation pathways of MXene, and facilitating enhanced and dependable integration of these materials into devices for diverse applications, from energy storage to sensors.

Uniaxial tensile study of calcium aluminosilicate hydrate (C-A-S-H): Structure, dynamics and mechanical properties

Calcium aluminosilicate hydrate (C-A-S-H) is the main hydration product of environmentally friendly concrete, which uses aluminum-rich industrial waste residue to partially replace cement raw materials. In order to understand the structure and properties of C-A-S-H gel at the molecular level. The structure, dynamics and mechanical properties of C-A-S-H gel at different Al/Si ratios were studied by reactive molecular dynamics simulation. The results showed that the doping of aluminates substances caused changes in the silicate-aluminate skeleton and inter-layer water molecules in C-A-S-H gels. As the Al/Si ratio increased, more water molecules dissociated and associated with Al atoms to produce Al-O(H)-Si and Al-OH. In addition, the presence of Al-O-Si chains not only imposed geometrical constraints on the inter-layer water molecules, but also increased the attraction of the substrate for water molecules. Furthermore, the mechanical behavior and deformation mechanism of C-A-S-H gels were investigated based on uniaxial tensile tests. The inter-layer bond strength and stiffness of C-A-S-H gels increased significantly with increasing tensile load and aluminate branching structure.

Stepless IR Chromism in Ti3 C2 Tx MXene Tuned by Interlayer Water Molecules.

Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3 C2 Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3 C2 Tx . This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3 C2 Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Nickel pre-intercalated bilayer vanadium pentoxide hydrate for reversible structural evolution in Na-ion battery cathode

Layered vanadium oxides, due to their high specific capacity and the multiple oxidation states of vanadium, are attractive candidates as cathode materials for sodium-ion batteries (SIBs). To meet the requirements of increasing interlayer spacing and significantly improving structural stability, herein, nickel pre-intercalated bilayer vanadium pentoxide hydrate, Ni0.28V2O5∙0.62 H2O (referred to as NVO) is synthesized successfully. The interlayer water molecules significantly increase the interlayer distance of the bilayer vanadium pentoxide. At the same, by forming a stable interlayer NiO6 octahedron, the intercalated Ni atoms effectively relieve the big change of volume during the Na ions insertion/extraction process and effectively inhibit the interlayered water molecules escape in charge/discharge process. Due to the big interlayer distance and excellent structural stability, the NVO electrode exhibits an excellent electrochemical performance. Except for the first few cycles, a high reversible capacity of about 260 mAh g−1 is obtained and the mean fade is only 0.5% per cycle. In addition, the excellent Na storage mechanism of the NVO electrode is also explored in detail by in situ XRD.

Investigation of the interface stick-slip friction behavior of clay nanoplatelets by molecular dynamics simulations

As lamella and porous materials, the failure of clay soil is closely related to the microscale friction features between nano minerals sheets. This study delves into the microscale interface stick-slip friction behavior of clay minerals, with a particular focus on kaolinite and halloysite models, under varying hydrostatic pressure conditions. The research unveils several significant discoveries. Firstly, under hydrostatic pressure, the mechanical properties of clay minerals perpendicular to the mineral platelet weaken, accompanied by a gradual reduction in the space occupied by interlayer water molecules. As pressure increases, these molecules assemble into "water molecular clusters", resulting in the formation of two or three layers of water molecular films. At 6 GPa, interlayer water nearly reaches a state of stagnation. Secondly, both kaolinite and halloysite exhibit "stick-slip friction behavior" during shearing, with rising hydrostatic pressure intensifying interatomic interactions and augmenting shear stress fluctuations. Lastly, the calculated friction coefficients (μ) for the three systems (kaolinite –7 Å, halloysite –8.6 Å, and halloysite –10 Å) are 0.035, 0.048, and 0.033, respectively, while the friction angles (φ) are 2.270, 2.900, and 2.263. The cohesion values (C) for these systems, obtained through different methods, demonstrate consistency. These findings advance the understanding of clay mineral behavior under varying conditions and contribute valuable insights to the microscale failure mechanism of clay soil.

Designing artificial ion channels with strict K+/Na+ selectivity toward next-generation electric-eel-mimetic ionic power generation.

A biological potassium channel is >1000 times more permeable to K+ than to Na+ and exhibits a giant permeation rate of ∼108 ions/s. It is a great challenge to construct artificial potassium channels with such high selectivity and ion conduction rate. Herein, we unveil a long-overlooked structural feature that underpins the ultra-high K+/Na+ selectivity. By carrying out massive molecular dynamics simulation for ion transport through carbonyl-oxygen-modified bi-layer graphene nanopores, we find that the twisted carbonyl rings enable strict potassium selectivity with a dynamic K+/Na+ selectivity ratio of 1295 and a K+ conduction rate of 3.5×107 ions/s, approaching those of the biological counterparts. Intriguingly, atomic trajectories of K+ permeation events suggest a dual-ion transport mode, i.e. two like-charged potassium ions are successively captured by the nanopores in the graphene bi-layer and are interconnected by sharing one or two interlayer water molecules. The dual-ion behavior allows rapid release of the exiting potassium ion via a soft knock-on mechanism, which has previously been found only in biological ion channels. As a proof-of-concept utilization of this discovery, we propose a novel way for ionic power generation by mixing KCl and NaCl solutions through the bi-layer graphene nanopores, termed potassium-permselectivity enabled osmotic power generation (PoPee-OPG). Theoretically, the biomimetic device achieves a very high power density of >1000W/m2 with graphene sheets of <1% porosity. This study provides a blueprint for artificial potassium channels and thus paves the way toward next-generation electric-eel-mimetic ionic power generation.

Study on the crystal structure using the powder method for XRD refinement and the hydration state of halloysite

Halloysite is an intelligent nano-mineral material available in abundance and at a low price. However, due to the poor crystallization performance, the current data on the crystal structure of halloysite are insufficient. This paper will compare and analyze the crystal structure of halloysite and kaolinite in the kaolin subgroup. Using the x-ray powder diffraction data, the crystal structure of halloysite is refined by Rietveld’s least square full spectrum fitting method. Compared with the crystal structure of kaolinite, the crystal structure of halloysite contains a small amount of interlayer water molecules. Through structural refinement verification, each unit cell contains 0.121 interlayer water molecules, and the water molecules are at the center of the interlayer area corresponding to the hexagonal ring of the tetrahedron layer.

Influence of inorganic and organic salts on the hydration mechanism of montmorillonite based on molecular simulation

The molecular dynamics method is used to further reveal, from the molecular point of view, the mechanisms of salt inhibiting the hydration of Na-MMT. The interaction between water molecules, salt molecules, and montmorillonite are calculated by establishing the adsorption models. According to the simulation results, the adsorption conformation, interlayer concentration distribution, self-diffusion coefficient, ion hydration parameters, and other data are compared and analyzed. The simulation results show that the volume and basal spacing increase in a stepwise manner with the increase of water content, and water molecules have different hydration mechanisms. The addition of salt will enhance the hydration properties of compensating cations of montmorillonite and affect the mobility of particles. The addition of inorganic salts mainly reduces the adsorption tightness between water molecules and crystal surfaces, thereby reducing the thickness of water molecules layer, while the organic salts can better inhibit migration by controlling interlayer water molecules. The results of molecular dynamics simulations reveal the microscopic distribution of particles and the influence mechanism when the swelling properties of montmorillonite are modified by chemical reagents.

Crystallization kinetics and crystallization process of pseudoboehmite from ammonium aluminum sulfate solution

In this work, the crystallization kinetics of pseudoboehmite was studied by intermittent crystallization method. The kinetic model of pseudoboehmite process was established based on particle number equilibrium. The results show that the nucleation is mainly caused by crystal collision, the main speed control step is diffusion process, and the enlargement of crystals mainly originates from the growth. Reducing the temperature of system can obtain pseudoboehmite crystals which have larger particle size and more uniform particle size distribution. Two parallel octahedral units connected by hydroxyl groups are preferentially stacked along the (020) crystal plane. Excessive interlayer water molecules between (020) crystal planes lead to an increase in the interlayer distance. The increased distance between (020) layers will weaken the hydrogen bond between layers, as well as the electrostatic forces and van der Waals forces, resulting in the formation of folded layers with holes. Finally, the irregularly sheets of pseudoboehmite are stacked to form porous spherical structures.

Improving the adsorption capacity of amino-modified Mg-Al LDH using a combined DFT and experiment

The adsorption of CO2 using layered double hydroxides (LDHs) such as Mg-Al LDH is both technically feasible and economical. Although some approaches to the modification of LDHs have proved fruitful, there is still a need for further improvement in the adsorption capacity of modified LDHs. Here, a new optimization direction for amino-modified Mg-Al-LDHs is proposed based on using DFT and AIMD simulations to elucidate the mechanism of CO2 diffusion. The proposed approach was then evaluated experimentally. Theoretical calculations showed that the adsorption energy of ordinary amino-modified LDHs was low, at − 0.56 eV. DFT simulations showed that the number of interlayer water molecules affects the CO2 adsorption energy, with the optimum adsorption energy of − 0.78 eV obtained in the presence one interlayer water molecule. Experimental analysis showed that the drying time affects the amount of interlayer water and thus the CO2 adsorption capacity, with the maximum adsorption capacity of 1.7424 mmol/g obtained after drying for 5 h. This study provides useful insights towards the development of materials such as Mg-Al LDHs for efficient CO2 adsorption and highlights the critical role of interlayer-bound water on the adsorption performance.

Tensile and compressive behavior of Na-, K-, Ca-Montmorillonite and temperature effects

Molecular dynamics (MD) method was applied to simulate the nano mechanical behavior of Na-, K-, Ca-montmorillonite (MMT) under uniaxial tension and compression, and to explore the effects of the loading direction and temperature. The relation between nano mechanical properties of Na-, K-, Ca-MMT and the hydration was investigated, a comparison was made considering the bulk modulus, shear modulus, elastic modulus and Poisson’s ratio. There are significant differences for the nano mechanical behavior of montmorillonite in different directions, the in-plane tensile and compressive elastic modulus and strength are greater than those in perpendicular to the crystal plane. The nano mechanical properties of Na-MMT have a negative relation with temperature. The nano mechanical properties were found to decrease with the increasing hydration for the montmorillonite. The stiffness coefficients are also influenced by the hydration and interlayer cations. The tensile strength of Ca-MMT is smallest among three types of montmorillonite. The bulk modulus, shear modulus, and Young’s modulus of polycrystal Na-, K-, Ca-MMT are also decreasing with the hydration water layers, while Poisson’s ratio remains unchanged with the increasing hydration. By observing the nano structure change, the tension failure is caused by a slip plane due to bond breaks and the compression failure caused by the local buckling of the crystal sheet in x- and y- direction, while in z- direction, the failure is due to the separation of the interlayer water molecules in tension and bond breaks to form a shear band in compression.

Theoretical Study on the Swelling Mechanism and Structural Stability of Ni3Al-LDH Based on Molecular Dynamics.

layered double hydroxide (LDH) as a kind of 2D layer material has a swelling phenomenon. Because swelling significantly affects the adsorption, catalysis, energy storage, and other application properties of LDHs, it is essential to study the interlayer spacing, structural stability, and ion diffusion after swelling. In this paper, a periodic computational model of Ni3Al-LDH is constructed, and the supramolecular structure, swelling law, stability, and anion diffusion properties of Ni3Al-LDH are investigated by molecular dynamics theory calculations. The results show that the interlayer water molecules of Ni3Al-LDH present a regular layered arrangement, combining with the interlayer anions by hydrogen bonds. As the number of water molecules increases, the hydrogen bond between the anion and the basal layer gradually weakens and disappears when the number of water molecules exceeds 32. The hydrogen bond between the anion and the water molecule gradually increases, reaching an extreme value when the number of water molecules is 16. The interlayer spacing of Ni3Al-LDH is not linear with the number of water molecules. The interlayer spacing increases slowly when the number of water molecules is more than 24. The maximum layer spacing is stable at around 19 Å. The interlayer spacing, binding energy, and hydration energy show an upper limit for swelling: the number of water molecules is 32. When the number of interlayer water molecules is 16, the water molecules' layer structure and LDH interlayer spacing are suitable for anions to obtain the maximum diffusion rate, 10.97 × 10-8 cm2·s-1.

Liquid Phase Exfoliation of Chemically Prelithiated Bilayered Vanadium Oxide in Aqueous Media for Li-Ion Batteries

Bilayered vanadium oxides are attractive for energy storage due to their high initial specific capacities, which could be stabilized by integrating the bilayers with conductive nanoflakes often produced in a form of aqueous dispersions. Therefore, exfoliation of the bilayered vanadium oxides in water with high yield is desirable. This work introduces the first aqueous exfoliation of chemically prelithiated bilayered vanadium oxide (i.e., δ-LixV2O5·nH2O or LVO) followed by vacuum filtration to produce a free-standing film, exhibiting a lamellar stacking of the bilayered vanadium oxide nanoflakes as evidenced by scanning electron microscopy. Due to the hydrated nature of bilayered vanadium oxides, the relationship between interlayer water content and the vacuum drying temperature (105 °C vs 200 °C) was studied using X-ray diffraction, thermogravimetric analysis, and Raman spectroscopy. It was found that vacuum drying the LVO nanoflakes at 200 °C enabled more efficient removal of crystallographic water than drying at 105 °C, and did not induce a phase transformation. Scanning transmission electron microscopy confirmed the layered structure of the samples, which was more well-ordered in the 200 °C case and had no clear boundaries between flakes at the atomic scale. Furthermore, electrochemical testing in nonaqueous Li-ion cells revealed that vacuum drying at 200 °C led to improvements in ion storage capacity and electrochemical stability. Improvements in electrochemical charge storage properties of the electrodes obtained via LVO exfoliation and free-standing film assembly in water dried at 200 °C reveal that conventional battery electrode drying protocols need to be revised as new electrochemically active materials are synthesized, such as hydrated layered oxides with expanded interlayer regions. The remaining capacity fading can be attributed to the structural LVO degradation, dissolution of vanadium oxide in electrolyte, and parasitic effects of the remaining interlayer water molecules. Our results establish an environmentally friendly and safe approach to obtain two-dimensional (2D) bilayered vanadium oxide nanoflakes and create a pathway to constructing novel 2D heterostructures for improved performance in energy storage applications.

A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

Janus composite membranes enable efficient solar-powered desalination and soil remediation

Solar-driven water evaporation offers a sustainable pathway for energy-efficient seawater desalination. However, its further practical performance is limited by salt accumulation during solar saline evaporation. Herein, a novel Janus composite membrane based on the assembly of hydrophilic vermiculite (VMT), multi-walled carbon nanotubes (MWCNTs), and hydrophobic polydimethylsiloxane (PDMS) is designed to function cooperatively for efficient solar absorption and long-term salt-rejection. The unique heterostructure endows the sandwich-like membrane with the capability of decoupling the steam generation process from the solar absorption surface to avoid the mutual interaction between the escaped steam and the incident light. Moreover, the tailorable hydrophilic/hydrophobic channels weaken the interaction between water molecules and layers, as well as reduce interlayer friction and water molecules viscosity to accelerate the flow rate. Benefiting from the above merits, the constructed vertical evaporator exhibits a high solar evaporation rate of 1.48 kg m−2 h−1 and an energy efficiency of 92% in saline water (3.5 wt% NaCl). Solar evaporation-induced soil remediation strategy on the basis of efficient removal of heavy metals and organic pollutants is further proposed, implying its potential applications in sustainable freshwater generation and environmental remediation.