Immersion In Aqueous Solution Research Articles

Photoelectrochemistry of Redox-Active Self-Assembled Monolayers Formed on n-Si/Au Nanoparticle Photoelectrodes.

Controlling the chemistry of the electrode-solution interface is critically important for applications in sensing, energy storage, corrosion prevention, molecular electronics, and surface patterning. While numerous methods of chemically modifying electrodes exist, self-assembled monolayers (SAMs) containing redox-active moieties are particularly important because they are easy to prepare, have well-defined interfaces, and can exhibit textbook photoelectrochemistry. Here, we investigate the photoelectrochemistry of redox-active SAMs on semiconductor/metal interfaces, where the SAM is attached to the metal site instead of the semiconductor. n-Si/Au photoelectrodes were fabricated using a benchtop electrodeposition procedure and subsequently modified by immersion in aqueous solutions of (ferrocenyl)hexanethiol and mercaptohexanol. We explored the relevant preparation conditions, finding that after optimization, we were able to obtain canonical cyclic voltammetry for a surface-bound redox molecule that could be turned on and off using light. We then characterized the optimized electrodes under varying illumination intensities, finding that the heterogeneous electron transfer kinetics improved under higher illumination intensities. These results lay the foundation for future studies of semiconductor/metal/molecule interfaces relevant to sensing and electrocatalysis.

Solvent-Responsive Nonporous Adaptive Crystals Derived from Pyridinium Hydrochloride and the Application in Iodine Adsorption.

Nonporous adaptive crystals (NACs) are crystalline nonporous materials that can undergo a structural adaptive phase transformation to accommodate specific guest via porous cavity or lattice voids. Most of the NACs are based on pillararenes because of their flexible backbone and intrinsic porous structure. Here a readily prepared organic hydrochloride of 4-(4-(diphenylamino)phenyl)pyridin-1-ium chloride (TPAPyH), exhibiting the solvent dimension-dependent adaptive crystallinity is reported. Wherein it forms a nonporous α crystal in a solvent with larger dimensions, while forming two porous β and γ crystals capable of accommodating solvent molecules in solvent with small size. Furthermore, the thermal-induced single-crystal-to-single-crystal (SCSC) transition from the β to α phase can be initiated. Upon exposure to iodine vapor or immersion in aqueous solution, the nonporous α phase transforms to porous β phase by adsorbing iodine molecules. Owing to the formation of trihalide anion I2Cl- within the crystal cavity, TPAPyH exhibits remarkable performance in iodine storage, with a high uptaking capacity of 1.27 g g-1 and elevated iodine desorption temperature of up to 110 and 82°C following the first and second adsorption stage. The unexpected adaptivity of TPAPyH inspires the design of NACs for selective adsorption and separation of volatile compound from organic small molecules.

Facile Bond Exchanging Strategy for Engineering Wet Adhesion and Antioxidant/Antibacterial Thin Layer over a Dynamic Hydrogel via the Carbon Dots Derived from Tannic Acid/ε-Polylysine.

Adhesive hydrogels, playing an essential role in stretchable electronics, soft robotics, tissue engineering, and so forth, upon functioning often need to adhere to various substrates in wet conditions and simultaneously exhibit antibacterial/antioxidant properties while possessing the intrinsic stretchability and elasticity of the hydrogel network intact. Therefore, simple approaches to conveniently access adhesive hydrogels with multifunctional surfaces are being pursued. Herein, a facile strategy has been proposed to construct multifunctional adhesive hydrogels via surface engineering of a multifunctional carbon dot (CD)-decorated polymeric thin layer by dynamic bond exchange. By this strategy, a double cross-linked network hydrogel of polyacrylamide (PAM) and oxidized dextran (ODA) was engineered with a unique dense layer over the Schiff base hydrogel matrix by aqueous solution immersion of PA-120, versatile CDs derived from tannic acid (TA) and ε-polylysine (PL). Without any additional agents, the PA-120 CDs with residual polyphenolic/catechol and amine moieties were incorporated into the surface structure of the hydrogel network by the combined action of the Schiff base and hydrogen bonds to form a dense surface layer that can exhibit high wet adhesive performance via the amine-polyphenol/catechol pair. The armor-like dense architecture also endowed hydrogels with considerably enhanced tensile/compression properties and excellent antioxidant/antibacterial abilities. Besides, the single-sided modified Janus hydrogel and completely surface-modified hydrogel can be flexibly developed through this approach. This strategy will provide new insights into the preparation and application of surface-modified hydrogels featuring multiple functions and tunable interfacial properties.

Gold Ultralow Loading on Nickel Foam for Nitrogen Electrochemical Reduction

Gold electroless deposition on nickel foam offers several advantages over traditional electrodeposition techniques. One of the main advantages is that it can produce uniform thickness coatings on complex shapes and geometries, such as porous and three-dimensional substrates like nickel foam. The resulting gold-nickel foam composite has high surface area and good electrical conductivity, making it suitable for various electrochemical applications, including catalysis, sensing, and energy storage.In this work we focused on the development of synthetic strategies to grow and optimize the surface coverage of gold on nickel foam and the evaluation of its suitability for the electrochemical reduction of nitrogen for ammonia synthesis.The gold electroless deposition on Ni Foam has been obtained by immersion in aqueous solution containing KAuCl4 and HCl, with or without stirring and addition of a surfactant agent (Isopropyl Alcohol). Depositions were performed by varying the immersion time from 30 seconds to 30 minutes. Scanning electron microscopy (SEM) has been employed to compare different deposition conditions and to optimize the morphology of the nanofilms, allowing higher catalytic activity. The electrochemical performance of the gold deposited on nickel foam was evaluated in a standard two compartments electrochemical cell using a Pt wire as counter electrode (CE), a saturated calomel electrode (SCE, saturated KCl) as reference and 0.1 M Na2SO4 solution as electrolyte. Electrochemical active surface area (EASA) and linear sweep voltammetry (LSV) have been adopted to evaluate the active area and the overpotential toward hydrogen evolution reaction (HER). Chronoamperometry experiments were carried out at various potentials to evaluate the performance of the catalyst for the electroreduction of nitrogen and ammonia synthesis.The amount of ammonia produced was measured by the indophenol blue method.The maximum NH3 yield of 2.8x10-11 mol s-1 cm-2 was achieved at -0.045 V vs RHE. The maximum faradaic efficiency of 5.8% was achieved at more positive potential (0.015 V vs RHE) due to the HER.The results show that the gold on nickel foam exhibits excellent electrochemical stability and high conductivity.This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under grant agreement No 101006941. This project started on the 1st of November 2020 with a duration of 42 months.

Multifunctional coating on magnesium alloy: Superhydrophobic, self-healing, anti-corrosion and wear-resistant

Superhydrophobic coating (SHC) was fabricated on magnesium (Mg) alloy by sequential surface etching, in-situ growth of MgAl-layered double hydroxides (LDHs), and modification of octadecyl-trimethoxy-silane (OTMS). The so-fabricated SHC possessed high contact angle above 150° and low sliding angle below 10° by using the probe droplet of aqueous solution of HCl (pH = 2), NaOH (pH = 13), NaCl (3.5 wt.%) or others such as milk, cola, and tea. The lubricant behavior as well as wear resistance was enhanced by such a SHC as compared with the bare Mg alloy. Moreover, corrosion of Mg alloy was greatly slowed by such a SHC which maintained long-term hydrophobic property after corrosion immersion in aqueous solution of NaCl for 6 weeks. The scratch on the SHC could be self-healed by immersing into water due to the hydrolytic polycondensation of silane and corrosion decomposition of LDHs within 8 days.

Antibiotic quantitative fluorescence chemical sensor based on Zn-MOF aggregation-induced emission characteristics

Antibiotic residues in water and food can aggravate the development of antibiotic-resistant bacteria. As a result, that is critical to creating a practical approach for detecting leftover antibiotics in a timely and sensitive manner. This research utilize the water instability of MOFs, and uses the zinc-based metal–organic framework of tetra (4-carboxyphenyl) ethylene (Zn-TCPE) as the sensing unit to create a new fluorescence sensing platform based on multiple colorimetric responses for ultra-fast and sensitive detection of tobramycin. Due to poor water stability, Zn-TCPE with aggregation-induced emission (AIE) would break into untidy pieces following immersion in aqueous solution. More importantly, the fluorescence of the Zn-TCPE aqueous solution was dimmed because the crystal framework of the Zn-TCPE was destroyed by the coordination of water molecules, causing the AIE-active organic linkers (H4TCPE) to undergo non-radiative emission motion, implying underlying mechanism research in the fluorescence “turn-off-on” mode. Because hydrophilic functional groups such as amino and hydroxyl can coordinate with metal ions, the Zn-TCPE aqueous solution showed great sensitivity for the response of amino, hydroxyl, and ether groups. The coordinated coordination of amino, hydroxyl, and ether groups with Zn2+ explains the reaction mechanism, culminating in the full destruction of Zn-TCPE. With the crystal structure collapse of Zn-TCPE, the AIE organic linkers are freed and then reassemble to form emissive aggregates with increased fluorescence. Because aminoglycoside (AG) antibiotics have hydrophilic functional groups such as amino, hydroxyl, and ether groups, they are employed as a molecular model for study. Interestingly, the Zn-TCPE probe has a strong selectivity for distinguishing AG antibiotics sulfate from other antibiotics.

Preparation of Mechanically Anisotropic Polysaccharide Composite Films Using Roll-Press Techniques.

Natural polysaccharides are biocompatible and biodegradable; therefore, they can be used as feedstock for biodegradable structural materials and biomaterials. In this study, anisotropic polysaccharide composite films consisting of chondroitin sulfate C (CS) and chitosan (CHI) were fabricated from their polyion complex (PIC) gels by roll-press techniques. The obtained films (CS/CHI films) were thin and transparent, similar to the composite films prepared by hot-press techniques. The roll-press conditions were optimized, and it was observed that the molecular weight of CHI did not significantly affect the formability of the films, whereas the roll temperature and rolling speed were important. The tensile tests of the roll-pressed films revealed that the mechanical strength of the films in the mechanical direction (MD) was approximately 5 times higher than that in the transverse direction (TD), indicating that the roll-press techniques imparted mechanical anisotropy to the films. Additionally, the films shrank in the MD and expanded in the TD after immersion in aqueous solutions, followed by drying. Such anisotropic shrinking and expanding properties indicate that these films can be used as shape-memory materials.

Improvement in long-term stability of field effect transistor biosensor in aqueous environments using a combination of silane and reduced graphene oxide coating

A field-effect transistor (FET) biosensor that can directly detect target molecules is a promising diagnostic tool for healthcare and medical applications. However, the immersion of FET sensors in aqueous physiological environments for the long-term stability might damage the insulating layer of silicon dioxide, resulting in the degradation of the sensor response reproducibility. In this study, to improve the durability of the sensor response for long-term immersion in aqueous solution, we examined the effectiveness of reduced graphene oxide (rGO) coating on the gate insulator of FET sensors. The rGO coating was applied to the gate surface of the FET biosensor modified with an amino-terminated self-assembled monolayer by two steps: deposition of graphene oxide (GO) dispersion onto the monolayer-modified surface and subsequent thermal reduction of GO. The transconductance of both GO-coated and rGO-coated FETs remained unchanged after incubation under physiological conditions, suggesting that graphene prevents cations in the electrolytes from invading the gate insulator of the FET. Furthermore, functionalizing the rGO-coated FET surface enabled specific detection of target molecule.

Nano-MIL-88A(Fe) Enabled Clear Cellulose Films with Excellent UV-Shielding Performance and Robust Environment Resistance

While tremendous efforts have been dedicated to developing cellulose-based ultraviolet (UV)-blocking films, challenges still remain in simultaneously achieving high transparency, low haze and excellent UV shielding properties via simple and green strategy. Here, we present a facile and eco-friendly route to fabricate flexible, biodegradable and clear UV-shielding nano-MIL-88A(Fe)@carboxymethylated cellulose films (M(Fe)CCFs) via in situ synthesis of nano-MIL-88A(Fe) in carboxymethylated cellulose hydrogel followed by natural drying. The carboxymethylated cellulose film has high transmittance (93.2%) and low haze (1.8%). The introduction of nano-MIL-88A(Fe) endowed M(Fe)CCFs superior UV-shielding ability, while retaining high transmittance (81.5–85.3%) and low haze (2.5–4.9%). Moreover, M(Fe)CCFs showed stable UV blocking performance under UV irradiation, high temperature, acidic or alkaline conditions. Quite encouragingly, the UV-shielding ability of M(Fe)CCFs did not deteriorate, even after 30 days of immersion in aqueous solution, providing films with a long-term use capacity. Thus, M(Fe)CCFs show high potential in the UV protection field. Overall, these UV-blocking films with outstanding performances are a promising candidate to replace conventional film materials made from synthetic polymers in fields such as packaging and flexible electronics.

XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air

Changes in the surface chemical state of a nearly equiatomic nickel–titanium (NiTi) alloy caused by immersion in aqueous solutions of HNO3 and H2SO4 as well as subsequent heating in air at 723 K were analyzed using X‐ray photoelectron spectroscopy (XPS). An XPS analysis using angle‐resolved technique and a mathematical deconvolution technique revealed that a passive layer formed in an ambient atmosphere contained TiO2 as a major state and Ni(OH)2 and NiO as minor states. The Ni(OH)2 on the alloy remained in the region even when heated in air at 723 K. Therefore, the resulting layer became a Ti‐oxide layer with Ni segregated region at the surface, which was NiO formed via dehydration of Ni(OH)2. However, immersion in an aqueous solution of HNO3 or H2SO4 enables Ni(OH)2 state to dissolve in the passive layer of a NiTi alloy; thereby, the Ni segregated region rarely appeared in the oxide layer by heating. The Ni segregated region at the surface becomes an obstacle for the inward diffusion of oxygen; thus, the annihilation of such a segregated region results in an increase in the thickness of the oxide layer.

Study on the Influence of Different Aqueous Solutions on the Mechanical Properties and Microstructure of Limestone

Abstract Uniaxial and triaxial compression tests were carried out on limestone samples immersed in distilled water and pH = 2 solution for 80 days to investigate the influences of aqueous solutions on the mechanical properties of limestone. Scanning electron microscopy and image recognition techniques were employed to analyze the morphology of limestone before and after immersion in aqueous solutions. The test results show that the peak stress and elastic modulus of the limestone specimens were reduced while the Poisson’s ratios were increased after 80 days of soaking. A series of chemical reactions take place between water and rock samples during the process of soaking. Energy-dispersive spectrometer analysis results showed that the content of calcium in the surface of the sample decreases after soaking, while the contents of aluminum, magnesium, and silicon are increased. From the image analysis results, it is demonstrated that the number and area of microscopic pores of the sample after immersion increased. The physical-chemical actions between the aqueous solutions and the samples lead to the deterioration of the mechanical properties of the rock.

Characterization of black coating on Fe360 steel obtained with immersion in aqueous solutions

Blackening process of steel is widely used in many industrial applications to create a protective layer against corrosion, environmental attack and to improve the aesthetic features. This study is focused on obtaining a black coating on a low carbon steel surface employing three different solution. In particular, two solution based on sodium nitrate and sodium hydroxide were used at boiling point, while the third based on selenous acid at ambient temperature. The samples were immersed for 5, 15 and 30 min in the boiling solutions, while for cold solution it was chosen 1 min of immersion time. The morphology of the protective layer were studied with stereo-microscope in order to evaluate the color, and Scanning Electron Microscope (SEM) to identify any defects in the surface, X-ray diffraction (XRD) was used to evaluate the composition of the protective layer. The corrosion resistance was measured performing potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The layer obtained with 15 min immersion time for the two boiling solutions is dense and adherent as shown by SEM analysis. For the other immersion times the layer was not uniform with porosities. Cold solution lead to a not homogenous layer reducing corrosion resistance.

Unexpected Superhydrophobicity on a Wide Range of Substrates via a One-step Immersion in Aqueous Solution without Hydrophobic Agent

Superhydrophobic surfaces were unexpectedly constructed by immersing a variety of substrates (aluminum sheet, melamine sponge, cotton fabric, and wood) into an aqueous solution containing tea polyphenols and metal ions (Fe2+, Ag+, Ce3+) and the potential applications in corrosion resistance for superhydrophobic aluminum, water absorption resistance for superhydrophobic wood, oil/water separation for superhydrophobic sponge and self-cleaning for superhydrophobic fabric were investigated.

Supramolecular Hydrogels with Tunable Swelling by Host Complexation with Cyclobis(paraquat-p-phenylene)

Controlling the swelling properties of hydrogels is of primary importance for many applications ranging from actuators and valves to tissue engineering and drug delivery. Herein, we report the use of cyclobis(paraquat-p-phenylene) (CBPQT4+,4X–) as a versatile host to fine-tune the swelling behavior of 1,5-dialkyloxynaphthalene guest containing poly(N,N-dimethylacrylamide) hydrogels (NaphtGelz) through supramolecular host–guest complexation. While the equilibrium swelling of NaphtGelz in water decreases with increasing amount of hydrophobic naphthalene groups, the opposite behavior is observed with superabsorbing behavior (up to 180 times their initial dry mass) upon immersion in aqueous solutions containing the macrocyclic CBPQT4+,4X– due to formation of tetracationic host–guest complexes. In this case, the swelling amplitude could be conveniently programmed either by variation of the naphthalene content of the hydrogels or by controlling the stoichiometry of the host–guest binding events. Furthermore, by modifying the nature of the counterions (X = Cl–, Br–, and I–) of the tetracationic CBPQT4+ macrocyclic host, the swelling of the hydrogels could be tuned in line with Pearson’s absolute hardness scale of X–. The swelling behavior of these supramolecular hydrogels could be successfully described by a theoretical model, taking into account the hydrophobic association of the naphthalene groups and their screening by host–guest complexation. Finally, addition of sodium dodecyl sulfate as a surfactant to the supramolecularly swollen hydrogels led to a large decrease in hydrogel size due to dissociation of the host–guest complexes and the formation of CBPQT4+,4DS– within the hydrogel.

Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media

We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.

Silicon Substrate Treated with Diluted NaOH Aqueous for Si/PEDOT: PSS Heterojunction Solar Cell with Performance Enhancement

Si/PEDOT: PSS solar cell is an important alternative for photovoltaic device due to its anticipated high theoretical efficiency and simple manufacturing process. In this study, processing silicon substrate with diluted NaOH aqueous solution was found to be an effective method for improving device performance, one that notably improves junction quality and light trapping ability. When immersed in diluted NaOH aqueous solution, the junction quality was improved according to the enlarged fill factor, reduced series resistance, and enhanced minor carrier lifetime. The diluted NaOH aqueous solution immersion etched the silicon surface and helped with the enhancement of light trapping ability, further improving the short-circuit current density. Although diluted NaOH aqueous solution immersion for bare silicon could improve the performance of devices, proper immersion time was needed. The influence of immersion time on device performances was investigated. The photovoltaic conversion efficiency easily increased from 10.01% to 12.05% when silicon substrate was immersed in diluted NaOH aqueous for 15 min. This study contributes to providing efficient and convenient methods for preparing high performance Si/PEDOT: PSS solar cells.

Biodegradable Polyanhydrides as Encapsulation Layers for Transient Electronics

AbstractBioresorbable electronic systems represent an emerging class of technology of interest due to their ability to dissolve, chemically degrade, disintegrate, and/or otherwise physically disappear harmlessly in biological environments, as the basis for temporary implants that avoid the need for secondary surgical extraction procedures. Polyanhydride‐based polymers can serve as hydrophobic encapsulation layers for such systems, as a subset of the broader field of transient electronics, where biodegradation eventually occurs by chain scission. Systematic experimental studies that involve immersion in phosphate‐buffered saline solution at various pH values and/or temperatures demonstrate that dissolution occurs through a surface erosion mechanism, with little swelling. The mechanical properties of this polymer are well suited for use in soft, flexible devices, where integration can occur through a mold‐based photopolymerization technique. Studies of the dependence of the polymer properties on monomer compositions and the rates of permeation on coating thicknesses reveal some of the underlying effects. Simple demonstrations illustrate the ability to sustain operation of underlying biodegradable electronic systems for durations between a few hours to a week during complete immersion in aqueous solutions that approximate physiological conditions. Systematic chemical, physical, and in vivo biological studies in animal models reveal no signs of toxicity or other adverse biological responses.

Water-Induced Fused Silica Glass Surface Alterations Monitored Using Long-Period Fiber Gratings

Long-period gratings (LPGs) induced in optical fibers show exceptional refractive index (RI) sensitivity and thus they are often applied for label-free biosensing. However, during measurements at changing environmental conditions, the surface of the fiber made of fused silica is subjected to stresses that can cause alterations in its structure. The problem is particularly important when long-term or biosensing measurements are considered and when sensor surface may be exposed to subsequent drying and immersion in aqueous solutions. The aim of this paper was to investigate the influence of sequential drying in air and soaking in water of the fused silica fiber cladding surface on the optical response of LPGs. We demonstrated that transmission spectrum of LPG measured in water before and after drying in air differed significantly and further changed with subsequent drying steps indicating increase of the local RI. All these changes correspond to the alterations in the cladding surface, i.e., its fracturing and pores rearrangement, caused by the stress induced during drying and then immersing in water, as well as possible corrosion and formation of nanosized objects on the cladding surface. The effect can be additionally influenced by washing the samples in organic solvents. We confirmed that measurements done in a flow-cell system, where the sensor was kept wet during the sensing experiment may eliminate the water-induced fiber surface alteration effect and thus minimize the amount of false results. Described findings are highly important for biosensing applications of any optical-fiber-based devices.

Stabilization of T2 relaxation and magnetization transfer in cartilage explants by immersion in perfluorocarbon liquid.

Magnetic resonance imaging of ex vivo cartilage measures parameters such as T2 and magnetization transfer ratio (MTR), which reflect structural changes associated with osteoarthritis. Samples are often immersed in aqueous solutions to prevent dehydration and to to improve susceptibility matching. This study sought to determine the extent to which T2 and MTR changes are attributable to immersion alone and to identify immersion conditions to minimize this confounding factor. T2 and MTR were measured before and after immersion for up to 24 hours at 4°C. Bovine nasal and articular cartilage and human articular cartilage were studied. Experimental groups included undisturbed immersion in Fluorinert FC-770, a susceptibility-matched, hydrophobic liquid with minimal tissue penetration, and immersion in Fluorinert, Dulbecco's phosphate-buffered saline (DPBS), or saline, with removal from the magnet between scans. 19 F and 1 H-MRI were used to detect cartilage penetration by Fluorinert and swelling, respectively. Saline and DPBS immersion rapidly increased T2 , wet weight and cartilage volume and decreased MTR, suggesting increased water content for all cartilage types. Fluorinert-immersed samples exhibited minimal changes in T2 or MTR. No ingress of Fluorinert was detected after 2 weeks of continuous immersion at 4°C. Ex vivo quantitative MR studies of cartilage may be confounded by the effects of immersion in aqueous solution, which may be comparable to or larger than effects attributed to pathology. These effects may be mitigated by immersion in perfluorocarbon liquids such as Fluorinert FC-770.

Characterization of films fabricated on AZ31 magnesium alloy by heat treatment and immersion methods

Thin films were fabricated on the surface of AZ31 magnesium alloy by heat treatment and subsequent immersion in deionized water or a NaOH solution. In this study, dense films were synthesized during the initial stage of immersion by increasing the (OH)− concentration at the interface of the high-temperature substrate and the solution. The surface of the magnesium substrates was covered by dense films aligned with the surface during the initial stages of immersion. The surface features of these films were different from those of the films formed simply by immersion in aqueous solutions. The cross-sectional results showed that the films formed in a NaOH solution with heat treatment were denser than those grown by DI water immersion with heat treatment. The X-ray photoelectron spectroscopy results revealed that the films fabricated by immersing the heat-treated substrates were mostly composed of MgO and Mg(OH)2 in both the outer and inner layers. Potentiodynamic polarization measurements showed that the films formed by the immersion of heat-treated substrates showed passive regions, and hence could act as passive layers.The morphology and structure of the films were observed by field-emission scanning electron microscopy and transmission electron microscopy. The compositions of the films were investigated using scanning transmission electron microscopy-energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Potentiodynamic polarization measurements were conducted to investigate the corrosion behavior of the films.