Understanding and Tuning the Intrinsic Hydrophobicity of Rare-Earth Oxides: A DFT+U Study

Ceria-Catalyzed Hydrolytic Cleavage of Sulfonamides

Nanoceria is a promising nanomaterial for the catalytic hydrolysis of a wide variety of substances. In this study, it was experimentally demonstrated for the first time that CeO2 nanostructures show extraordinary reactivity toward sulfonamide drugs (sulfadimethoxine, sulfamerazine, and sulfapyridine) in aqueous solution without any illumination, activation, or pH adjustment. Hydrolytic cleavage of various bonds, including S-N, C-N, and C-S, was proposed as the main reaction mechanism and was indicated by the formation of various reaction products, namely, sulfanilic acid, sulfanilamide, and aniline, which were identified by HPLC-DAD, LC-MS/MS, and NMR spectroscopy. The kinetics and efficiency of the ceria-catalyzed hydrolytic cleavage were dependent on the structure of the sulfonamide molecule and physicochemical properties of Nanoceria prepared by three different precipitation methods. However, in general, all three ceria samples were able to cleave SA drugs tested, proving the robust and unique surface reactivity toward these compounds inherent to cerium dioxide. The demonstrated reactivity of CeO2 to molecules containing sulfonamide or even sulfonyl (and similar) functional groups may be significant for both heterogeneous catalysis and environmentally important degradation reactions.

Origin of the Hydrophobic Behaviour of Hydrophilic CeO2

The nature of the hydrophobicity found in rare-earth oxides is intriguing. The CeO2 (100) surface, despite its strongly hydrophilic nature, exhibits hydrophobic behaviour when immersed in water. In order to understand this puzzling and counter-intuitive effect we performed a detailed analysis of the confined water structure and dynamics. We report here an ab-initio molecular dynamics simulation (AIMD) study which demonstrates that the first adsorbed water layer, in immediate contact with the hydroxylated CeO2 surface, generates a hydrophobic interface with respect to the rest of the liquid water. The hydrophobicity is manifested in several ways: a considerable diffusion enhancement of the confined liquid water as compared with bulk water at the same thermodynamic condition, a weak adhesion energy and few H-bonds above the hydrophobic water layer, which may also sustain a water droplet. These findings introduce a new concept in water/rare-earth oxide interfaces: hydrophobicity mediated by specific water patterns on a hydrophilic surface.

The apparent surface free energy of rare earth oxides is governed by hydrocarbon adsorption

The surface free energy of rare earth oxides (REOs) has been debated during the last decade, with some reporting REOs to be intrinsically hydrophilic and others reporting hydrophobic. Here, we investigate the wettability and surface chemistry of pristine and smooth REO surfaces, conclusively showing that hydrophobicity stems from wettability transition due to volatile organic compound adsorption. We show that, for indoor ambient atmospheres and well-controlled saturated hydrocarbon atmospheres, the apparent advancing and receding contact angles of water increase with exposure time. We examined the surfaces comprehensively with multiple surface analysis techniques to confirm hydrocarbon adsorption and correlate it to wettability transition mechanisms. We demonstrate that both physisorption and chemisorption occur on the surface, with chemisorbed hydrocarbons promoting further physisorption due to their high affinity with similar hydrocarbon molecules. This study offers a better understanding of the intrinsic wettability of REOs and provides design guidelines for REO-based durable hydrophobic coatings.

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REOs are intrinsically hydrophilic but become hydrophobic as they adsorb hydrocarbons

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Our results demonstrate that both physisorption and chemisorption occur on the surface

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The adsorption of hydrocarbons was confirmed by multiple surface chemistry analysis

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Our work offers a better fundamental understanding of the intrinsic wettability of REO

Adsorption of Carbon Dioxide on Mono-Layer Thick Oxidized Samarium Films on Ni(100)

Studies of adsorption of CO2 on nanoscopic surfaces are relevant for technological applications in heterogeneous catalysis as well as for sorption of this important greenhouse gas. Presently, adsorption of carbon dioxide on pure and oxidized thin samarium layers near mono-layer thickness on Ni(100) has been investigated by photoelectron spectroscopy and temperature programmed desorption. It is observed that very little CO2 adsorb on the metallic sample for exposures in the vacuum regime at room temperature. For the oxidized sample, a large enhancement in CO2 adsorption is observed in the desorption measurements. Indications of carbonate formation on the surface were found by C 1s and O 1s XPS. After annealing of the oxidized samples to 900 K very little CO2 was found to adsorb. Differences in desorption spectra before and after annealing of the oxidized samples are correlated with changes in XPS intensities, and with changes in sample work function which determines the energy difference between molecular orbitals and substrate Fermi level, and thus the probability of charge transfer between adsorbed molecule and substrate.

Development and Application of a ReaxFF Reactive Force Field for Cerium Oxide/Water Interfaces

Ceria (CeO₂) is a well-known catalytic oxide with many environmental, energy production, and industrial applications, most of them involving water as a reactant, byproduct, solvent, or simple spectator. In this work, we parameterized a Ce/O/H ReaxFF for the study of ceria and ceria/water interfaces. The parameters were fitted to an ab initio training set obtained at the DFT/PBE0 level, including the structures, cohesive energies, and elastic properties of the crystalline phases Ce, CeO₂, and Ce₂O₃; the O-defective structures and energies of vacancy formation on CeO₂ bulk and CeO₂ (111) surface, as well as the absorption and reaction energies of H₂ and H₂O molecules on CeO₂ (111). The new potential reproduced reasonably well all the fitted properties as well as the relative stabilities of the different ceria surfaces, the oxygen vacancies formation, and the energies and structures of associative and dissociative water molecules on them. Molecular dynamics simulations of the liquid water on the CeO₂ (111) and CeO₂ (100) surfaces were carried out to study the coverage and the mechanism of water dissociation. After equilibration, on average, 35% of surface sites of CeO₂ (111) are hydroxylated whereas 15% of them are saturated with molecular water associatively adsorbed. As for the CeO₂ (100) surface, we observed that water preferentially dissociates covering 90% of the available surface sites in excellent agreement with recent experimental findings.

Environmentally friendly, durable and transparent anti-fouling coatings applicable onto various substrates

Anti-fouling coatings are of great interest because of their unique wettability and self-cleaning property, but their widespread applications are seriously hindered by low stability, heavy usage of fluorinated compounds and low transparency, etc. Here, we report a new kind of smooth anti-fouling coatings based on methyltrimethoxysilane. The coatings were fabricated by preparing a stock solution via hydrolytic condensation of methyltrimethoxysilane in isopropanol, followed by wiping the glass slide with the non-woven fabric that sucked the stock solution. The transparent anti-fouling coatings have excellent anti-fouling properties against various fluids such as water, n-hexadecane, diiodomethane, daily encountered liquids (e.g., milk, coffee, red wine, soy sauce and cooking oil), mark seals, artificial fingerprint liquids and paints (both water-based and oil-based), etc. The fluids can easily roll off from the 4-30° titled coatings. Furthermore, the coatings have good mechanical (200 cycles of friction, scratching and bending), chemical (saline, acidic and basic solutions) and thermal stability (boiling and 300 °C heating) regarding the easy sliding behavior of the probing liquids. In addition, the anti-fouling coatings are applicable onto various substrates via the same procedure. The smooth anti-fouling coatings have huge potential applications, owing to the excellent anti-fouling properties, high stability as well as the non-fluorinated and simple preparation method.

Effects of cerium and tungsten substitution on antiviral and antibacterial properties of lanthanum molybdate

Powders of cerium (Ce)-substituted and tungsten (W)-substituted La₂Mo₂O₉ (LMO) were prepared using polymerizable complex method. Their antiviral and antibacterial performances were then evaluated using bacteriophage Qβ, bacteriophage Φ6, Escherichia coli, and Staphylococcus aureus. The obtained powders, which were almost single-phase, exhibited both antiviral and antibacterial properties. Effects of dissolved ions on their antiviral activity against bacteriophage Qβ were remarkable. A certain contribution of direct contact to the powder surface was also inferred along with the dissolved ion effect for antiviral activity against bacteriophage Φ6. Dissolved ion effects and pH values suggest that both Mo and W are in the form of polyacids. Antiviral activity against bacteriophage Φ6 was improved by substituting Ce for La in LMO. Similarly to LMO, Ce-substituted LMO exhibited hydrophobicity. Inactivation of alkaline phosphatase enzyme proteins was inferred as one mechanism of the antiviral and antibacterial activities of the obtained powders.

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Ce and W were partially substituted in La₂Mo₂O₉ (LMO).

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These powders inactivated E. coli, S. aureus, bacteriophage Qβ, and bacteriophage Φ6.

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Inactivation of alkaline phosphatase enzyme proteins on these materials was confirmed.

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Antiviral activity against bacteriophage Φ6 of LMO was improved by substituting Ce.

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Hydrophobicity and UV shielding performance were also confirmed for this material.

Atomic Layer Deposition onto Thermoplastic Polymeric Nanofibrous Aerogel Templates for Tailored Surface Properties

Poly(vinyl alcohol-co-ethylene) (EVOH) nanofibrous aerogel (NFA) templates were fabricated through vacuum freeze-drying from EVOH nanofibrous suspensions. Aluminum oxide (Al₂O₃) layers were deposited onto highly porous templates to form organic-inorganic hybrid aerogels by the atomic layer deposition (ALD) technique. Chemical and physical measurements showed that mechanical properties were improved through ALD. In addition, the surface chemistry of ALD modified aerogels showed a fascinating cyclic change based on the number of ALD deposition cycles. A transition from hydrophilicity to hydrophobicity was observed after a few cycles of ALD coating; however, additional deposition cycles changed the wettability characteristics back to hydrophilicity. This hydrophilic-hydrophobic-hydrophilic variation is shown to be governed by a combination of geometrical and chemical surface properties. Furthermore, the deposited Al₂O₃ could substantially improve aerogels strength and reduce permanent deformation after cyclic compression. The Young's modulus of aerogels increased from 5.54 to 33.27 kPa, and the maximum stress at 80% strain went up from 31.13 to 176.11 kPa, after 100 cycles of trimethyl-aluminum (TMA)/water ALD. Thermogravimetric analysis (TGA) results confirm that ALD can effectively improve the heat resistance characteristics of polymeric aerogel. The onset temperature and the residual mass increased with increasing numbers of ALD cycles. During pyrolysis, the nanofiber cores were decomposed, and the brittle pure Al₂O₃ self-supporting nanotube aerogels with the continuous hollow nanotubular network were formed. A coating of continuous thickness Al₂O₃ layer on individual nanofiber was achieved after 100 ALD cycles. In additional to mechanical strength and physical property changes, the ALD modified aerogel also shows a superhydrophobic and oleophilic surface chemistry, which could potentially be used to remove oils/organic solvents from water. The resultant aerogels exhibit excellent absorption capacity (31-73 g/g) for various liquids, and the material could be reused after distillation or squeezing. A successful scale-up of such materials could provide some insights into the design and development of thermoplastic polymeric NFAs with substantial industrial applications.

Facet-Dependent Adsorption and Fractionation of Natural Organic Matter on Crystalline Metal Oxide Nanoparticles

Natural organic matter (NOM) and crystalline metal oxide nanoparticles are both prevalent in natural aquatic environments, and their interactions have important environmental and biogeochemical implications. Here, we show that these interactions are significantly affected by an intrinsic property of metal oxide nanocrystals, the exposed facets. Both anatase (TiO₂) and hematite (α-Fe₂O₃) nanocrystals, representing common engineered and naturally occurring metal oxides, exhibited apparent facet-dependent adsorption of humic acid and fulvic acid. This facet-dependent binding was primarily driven by surface complexation between the NOM carboxyl groups and surficial metal atoms. Thus, the adsorption affinity of different-faceted nanocrystals was determined by the atomic arrangements of crystal facets that controlled the activity of metal atoms and, consequently, the ligand exchange and binding configuration of the carboxyl groups in the first hydration shell of nanocrystals. Distinct facet-dependent fractionation patterns were observed during adsorption of NOM components, particularly the low-molecular-weight and photorefractory constituents. The molecular fractionation of NOM between water and metal oxide nanoparticles was dictated by the combined effects of facet-dependent metal complexation, hydrophobic interaction, and steric hindrance and may significantly influence the NOM-driven processes occurring both in aqueous phases and at water-nanoparticle interfaces.

Nonwetting Behavior of Al-Co Quasicrystalline Approximants Owing to Their Unique Electronic Structures

Good wetting is generally observed for liquid metals on metallic substrates, while poor wetting usually occurs for metals on insulating oxides. In this work, we report unexpected large contact angles for lead on two metallic approximants to decagonal quasicrystals, namely, Al₅Co₂ and Al₁₃Co₄. Intrinsic surface wettability is predicted from first principles, using a thermodynamic model based on the Young equation, and validated by the good agreement with experimental measurements performed under ultra-high vacuum by scanning electron microscopy. The atomistic details of the atomic and electronic structures at the Pb-substrate interface, and the comparison with Pb(111)/Al(111), underline the influence of the specific electronic structures of quasicrystalline approximants on wetting. Our work suggests a possible correlation of the contact angles with the density of states at the Fermi energy and paves the way for a better fundamental understanding of wettability on intermetallic substrates, which has potential consequences in several applications such as supported catalysts, protective coatings, or crystal growth.

The water/ceria(111) interface: Computational overview and new structures

Thin film structures of water on the CeO₂(111) surface for coverages between 0.5 and 2.0 water monolayers have been optimized and analyzed using density functional theory (optPBE-vdW functional). We present a new 1.0 ML structure that is both the lowest in energy published and features a hydrogen-bond network extending the surface in one-dimension, contrary to what has been found in the literature, and contrary to what has been expected due to the large bulk ceria cell dimension. The adsorption energies for the monolayer and multilayered water structures agree well with experimental temperature programmed desorption results from the literature, and we discuss the stability window of CeO₂(111) surfaces covered with 0.5-2.0 ML of water.

Quasi-degenerate states and their dynamics in oxygen deficient reducible metal oxides

The physical and chemical properties of oxides are defined by the presence of oxygen vacancies. Experimentally, non-defective structures are almost impossible to achieve due to synthetic constraints. Therefore, it is crucial to account for vacancies when evaluating the characteristics of these materials. The electronic structure of oxygen-depleted oxides deeply differs from that of the native forms, in particular, of reducible metal oxides, where excess electrons can localize in various distinct positions. In this perspective, we present recent developments from our group describing the complexity of these defective materials that highlight the need for an accurate description of (i) intrinsic vacancies in polar terminations, (ii) multiple geometries and complex electronic structures with several states attainable at typical working conditions, and (iii) the associated dynamics for both vacancy diffusion and the coexistence of more than one electronic structure. All these aspects widen our current understanding of defects in oxides and need to be adequately introduced in emerging high-throughput screening methodologies.

Preparation of hydrophobic La2Mo2O9 ceramics with antibacterial and antiviral properties

After powder of La₂Mo₂O₉ (LMO) was prepared using complex polymerization, dense sintered bodies (96% relative density) of LMO were obtained from the powder through pressureless sintering in a synthesized air atmosphere. The water contact angle of the LMO ceramics increased gradually during storage in ambient air. It reached 93.6 ± 3.0° in 624 h. Results of XPS analysis and ozone treatment suggest that organic substances in ambient air adsorbed onto the LMO surface during storage. Measurements of antibacterial (Escherichia coli and Staphylococcus aureus) and antiviral (bacteriophage Qβ and bacteriophage Φ6) activities of LMO revealed that their survival rates decreased more than 99.9% within 6 h. Based on results obtained using dissolved ion contact method and from comparison of the antibacterial and antiviral activities with La₂O₃ and MoO₃, one can infer that the synergistic effect of La₂O₃ and MoO₃ plays an important role in the high antibacterial and antiviral activity of LMO.

The Impact of CeO2 Loading on the Activity and Stability of PdO/γ-AlOOH/γ-Al2O3 Monolith Catalysts for CH4 Oxidation

This study reports on the activity and stability of PdO/γ-AlOOH/γ-Al2O3 monolith catalysts, promoted with varying amounts of CeO2, for CH4 oxidation. Although the beneficial effects of CeO2 have been reported for powdered catalysts, this study used a cordierite (2MgO.2Al2O3.5SiO2) mini-monolith (400 cells per square inch, 1 cm diameter × 2.5 cm length; ~52 cells), washcoated with a suspension of γ-Al2O3 combined with boehmite (γ-AlOOH), followed by sequential deposition of Ce and Pd (0.5 wt.%) by wetness impregnation. The monolith catalysts’ CH4 oxidation activity and stability were assessed in the presence of CO, CO2, H2O and SO2 at low temperature (≤550 °C), relevant to emission control from lean-burn natural gas vehicles (NGVs). The CeO2 loading (0 to 4 wt.%) did not significantly impact the adhesion and thermal stability of the washcoat, but CeO2 reduced the inhibition of CH4 oxidation by H2O and SO2. The catalyst activity, measured by temperature-programmed methane oxidation (TPO) in a dry feed gas with 0.07 vol.% CH4, showed that adding CeO2 to the γ-AlOOH/γ-Al2O3 washcoat suppressed the activity of the catalysts; whereas, CeO2 improved the catalyst activity when H2O (2 and 5 vol.%) was present in the feed gas. Moreover, adding CeO2 decreased catalyst deactivation that occurred in the presence of 10 vol.% H2O and 5 ppmv SO2 at 500 °C, measured over a 25 h time-on-stream (TOS) period. The highest catalyst activity and stability for CH4 oxidation in the presence of H2O was obtained by adding 2 wt.% CeO2 to the washcoat.

Condensation Heat-Transfer Performance of Thermally Stable Superhydrophobic Cerium-Oxide Surfaces

We introduce a thin (<200 nm) superhydrophobic cerium-oxide surface formed by a one-step wet chemical process to enhance the condensation heat-transfer performance with improved thermal stability compared to silane-treated surfaces. The developed cerium-oxide surface showed a superhydrophobic characteristic with a low (<5°) contact angle hysteresis because of the unique surface morphology and hydrophobicity of cerium oxide. The surface was successfully incorporated to popular engineering materials including copper, aluminum, and steel. Thermal stability of the surfaces was investigated by exposing them to hot (∼100 °C) steam conditions for 12 h. The introduced ceria surfaces could maintain active dropwise condensation after the thermal stability test, whereas silane-treated surfaces completely lost their hydrophobicity. The heat-transfer coefficient was calculated using the thermal network model incorporating the droplet size distribution and morphology obtained from the microscopic measurement. The analysis shows that the suggested cerium-oxide surfaces can provide approximately 2 times and 5 times higher heat-transfer coefficient before and after the thermal stability test, respectively, mainly because of the decrease in the thermal conduction resistance across droplets. The results indicate that the introduced nanostructured cerium-oxide surface is a promising condenser coating to enhance the droplet mobility and the resulting condensation heat-transfer performance for various thermal and environmental applications, especially those being exposed to hot steam conditions.

Atomic-scale computational design of hydrophobic RE surface-doped Al2O3 and TiO2

Intrinsically hydrophobic rare-earth oxides (REOs) have emerged as a robust class of ceramics for a variety of applications. Recently, the hydrophobicity of REOs has been observed experimentally and subsequently scrutinized using electronic structure density functional theory (DFT) calculations. In this work, we applied the DFT method to analyze the possibility of tuning the wettability of commonly used hydrophilic Al₂O₃ and TiO₂ by surface doping with Ce. The calculations indicate that Ce can preferentially segregate to the surface of Al₂O₃ and TiO₂ and form a Ce-rich oxide layer, which is stable under a wide range of oxygen chemical potentials. A remarkable increase in the water contact angle is predicted for Ce-doped Al₂O₃(0001), whereas the water contact angle calculated for Ce-doped TiO₂(110) remains unchanged, regardless of the Ce concentration. The wetting properties of Ce-doped Al₂O₃ are governed by two factors: (1) the unique electronic structure of the rare-earth metal promotes hydrogen bond formation between H₂O and surface oxygen; (2) significant relaxation of the surface Ce and O atoms hampers direct interaction between H₂O and Al cations, preventing dissociative water adsorption. These results provide a valuable opportunity for Al₂O₃ surface modification, in terms of achieving hydrophobicity.

Formation of Water Layers on Graphene Surfaces

Although graphitic materials were thought to be hydrophobic, recent experimental results based on contact angle measurements show that the hydrophobicity of graphitic surfaces stems from airborne contamination of hydrocarbons. This leads us to question whether a pristine graphitic surface is indeed hydrophobic. To investigate the water wettability of graphitic surfaces, we use molecular dynamics simulations of water molecules on the surface of a single graphene layer at room temperature. The results indicate that a water droplet spreads over the entire surface and that a double-layer structure of water molecules forms on the surface, which means that wetting of graphitic surfaces is possible, but only by two layers of water molecules. No further water layers can cohere to the double-layer structure, but the formation of three-dimensional clusters of liquid water is confirmed. The surface of the double-layer structure acts as a hydrophobic surface. Such peculiar behavior of water molecules can be reasonably explained by the formation of hydrogen bonds: The hydrogen bonds of the interfacial water molecules form between the first two layers and also within each layer. This hydrogen-bond network is confined within the double layer, which means that no "dangling hydrogen bonds" appear on the surface of the double-layer structure. This formation of hydrogen bonds stabilizes the double-layer structure and makes its surface hydrophobic. Thus, the numerical simulations indicate that a graphene surface is perfectly wettable on the atomic scale and becomes hydrophobic once it is covered by this double layer of water molecules.

Exploring the Role of Adsorption and Surface State on the Hydrophobicity of Rare Earth Oxides

Rare earth oxides (REOs) are attracting attention for use as cost-effective, high-performance dropwise condensers because of their favorable thermal properties and robust nature. However, to engineer a suitable surface for industrial applications, the mechanism governing wetting must be first fully elucidated. Recent studies exploring the water-wetting state of REOs have suggested that these oxides are intrinsically hydrophobic owing to the unique electronic structure of the lanthanide series. These claims have been countered with evidence that they are inherently hydrophilic and that adsorption of contaminants from the environment is responsible for the apparent hydrophobic nature of these surfaces. Here, using X-ray photoelectron spectroscopy and dynamic water contact angle measurements, we provide further evidence to show that REOs are intrinsically hydrophilic, with ceria demonstrating advancing water contact angles of ≈6° in a clean surface state and similar surface energies to two transition metal oxides (≳72 mJ/m²). Using two model volatile species, it is shown that an adsorption mechanism is responsible for the apparent hydrophobic property observed in REOs as well as in transition metal oxides and silica. This is correlated with the screening of the polar surface energy contribution of the underlying oxide with apparent surface energies reduced to <40 mJ/m² for the case of nonane adsorption. Moreover, we show that the degree of surface hydroxylation plays an important role in the observed contact angle hysteresis with the receding contact angle of ceria increasing from ∼10° to 45° following thermal annealing in an inert atmosphere. Our findings suggest that high atomic number metal oxides capable of strongly adsorbing volatile species may represent a viable paradigm toward realizing robust surface coating for industrial condensers if certain challenges can be overcome.

A modified Wenzel model for water wetting on van der Waals layered materials with topographic surfaces

A modified Wenzel model is proposed for describing the wetting behavior of van der Waals layered materials with topographic surfaces, based on the measured linear relationship between water wetting and surface roughness for high quality Bi₂Se₃ thin films, synthesized using molecular beam epitaxy (MBE) in the optimized temperature window of 180-200 °C. The water contact angles are found to have apparent dependence on the nanoscale surface morphology, enabling film wettability as a new tool to quickly characterize the quality of atomically thin films. The water contact angle of the ideal Bi₂Se₃ surface is inferred to be ∼98.4°, indicating its intrinsic hydrophobic nature; however, the edge of the terrace on its surface is extremely hydrophilic, leading to easy hydrophobic/hydrophilic transitions. The atomistic mechanism is further revealed by first principles calculations. The regulated wettability is of great importance for electronic applications of Bi₂Se₃ and other two-dimensional materials with distinctive electronic structures.

Buckling failure of square ice-nanotube arrays constrained in graphene nanocapillaries

Graphene confinement provides a new physical and mechanical environment with ultrahigh van der Waals pressure, resulting in new quasi-two-dimensional phases of few-layer ice. Polymorphic transition can occur in bilayer constrained water/ice system. Here, we perform a comprehensive study of the phase transition of AA-stacked bilayer water constrained within a graphene nanocapillary. The compression-limit and superheating-limit (phase) diagrams are obtained, based on the extensive molecular-dynamics simulations at numerous thermodynamic states. Liquid-to-solid, solid-to-solid, and solid-to-liquid-to-solid phase transitions are observed in the compression and superheating of bilayer water. Interestingly, there is a temperature threshold (∼275 K) in the compression-limit diagram, which indicates that the first-order and continuous-like phase transitions of bilayer water depend on the temperature. Two obviously different physical processes, compression and superheating, display similar structural evolution; that is, square ice-nanotube arrays (BL-VHDI) will bend first and then transform into bilayer triangular AA stacking ice (BL-AAI). The superheating limit of BL-VHDI exhibits local maxima, while that of BL-AAI increases monotonically. More importantly, from a mechanics point of view, we propose a novel mechanism of the transformation from BL-VHDI to BL-AAI, both for the compression and superheating limits. This structural transformation can be regarded as the "buckling failure" of the square-ice-nanotube columns, which is dominated by the lateral pressure.