In the pursuit of multifunctional coatings, the controlled growth of materials on stationary platforms holds paramount importance for achieving superior corrosion protection and optimal photocatalytic performance. This study introduces a cutting-edge approach, intertwining bifunctional metal-organic frameworks (MOFs) seamlessly into defective MgO layers produced by the anodic oxidation of AZ31 alloy. Key metallic oxides of Zn, Sn, and V take center stage as metallic sources for MOF formation, complemented by the organic prowess of L-Tryptophan as an α-amino acid linker. Leveraging the electronic structure of metallic oxides reacting with tryptophan molecules, controlled morphologies with distinct characteristics are induced on the defective surface of the MgO layer, enabling the precise modulation of surface defects. The hybrid composite demonstrates an adaptive microstructure in diverse aqueous environments, offering dual functionality with electrochemical stability and visible light photocatalytic activity for crystal violet degradation. Among the samples, the SnOF complex exhibited remarkable electrochemical stability with a low corrosion current density of 7.50 × 10⁻¹⁰ A·cm⁻², along with a 94.56 % degradation efficiency after 90 min under visible light exposure. The VOF complex, under similar visible light conditions, demonstrated exceptional performance with a higher degradation efficiency of 97.79 % and excellent electrochemical stability characterized by a corrosion current density of 3.26 × 10⁻⁹ A·cm⁻². Additionally, Density Functional Theory (DFT) computations shed light on the basic bonding patterns between MOFs and inorganic components, providing electronic understanding of their electrochemical and photocatalytic activities.

This study explores the potential of LDH flakes decorated with metallic oxide nanoparticles to function as both anti-corrosion barriers against chloride anions and heterogeneous photocatalysts for tetracycline degradation under visible light. The process involves modifying the primarily MgO-based inorganic porous film by growing a MgFe LDH film, followed by the individual and dual incorporation of SnO₂ and WO₃ nanoparticles. The dual incorporation of these nanoparticles into the LDH matrix leads to synergistic interactions, effectively sealing pre-existing defects within LDH flakes and facilitating the in-situ formation of catalytic sites through oxidation and the induction of surface oxygen vacancy defects, which synergistically contribute to the enhancement of both electrochemical and photocatalytic activities. The enhanced electrochemical stability is reflected in a significant reduction in corrosion current density by 4 orders of magnitude compared to unmodified porous film. Additionally, the decorated film demonstrates sustained photocatalytic functionality, achieving significant degradation (95.5%) of tetracycline within two hours. This study presents a novel approach, highlighting the dual effectiveness of LDHs decorated by dual metal oxides as an anti-corrosive agent and photocatalyst, with promising implications for environmental remediation and wastewater purification.

Meeting the demands of complex and advanced applications requires the development of high-performance hybrid materials with unique properties. However, the integration of polymeric frameworks with MgO/WO₃ composite layers faces challenges due to the lack of understanding of the formation mechanism and the challenge of determining the impact of self-assembled architecture on anticorrosive properties. In this study, we aimed to enhance the corrosion resistance of the MgO layer produced by plasma electrolysis (PE) of AZ31 Mg alloy by incorporating WO₃ with partially phosphorated poly(vinyl alcohol) (PPVA). Two types of porous MgO layers were produced using the PE process with an alkaline-phosphate electrolyte, one with and one without WO₃ nanoparticles, which were subsequently immersed in an aqueous solution of PPVA. Incorporating PPVA into the WO₃-MgO layer resulted in hybrids being deposited in a fragmented manner, creating a ``laminar reef-like structure'' that sealed most of the structural defects in the layer. The PPVA-sealed WO₃-based coating exhibited superior corrosion resistance compared to the other samples. Computational analyses were employed to explore the mechanism underlying the formation of PPVA/WO₃ hybrids on the MgO layer. These findings suggest that PPVA-WO₃-MgO hybrid coatings can potentially improve corrosion resistance in various fields.

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability. In this work, a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide (LDH) films using novel metal-organic frameworks (MOFs). Initially, Mg-Al LDH nanocontainers, grown on a magnesium oxide layer produced through plasma electrolytic oxidation (PEO) of AZ31 Mg alloy substrate, were intercalated with cobalt via an oxidation route, providing the metallic coordination center for the MOF formation. In the subsequent step, a pioneering technique is introduced, utilizing tryptophan as the organic linker for the first time at a pH of 10. The self-assembly of cobalt- tryptophan complex, driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites, facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH’s film. The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.% NaCl solution, surpassing the performance of PEO and pure LDH coatings. This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF, effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate. The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

The hybridization of metal-organic framework (MOF) with inorganic layers would lead to the discovery of novel hybrid materials that can provide a compelling strategy for enhancing its photocatalytic and electrochemical response. In the present study, a highly efficient multifunctional hybrid material was developed by exploiting the defective layer formed on AZ31 Mg alloy through plasma electrolytic oxidation (PEO) as a nucleation and growth site for Co-MOF. The concentrations of the organic linker 2-Methylimidazole (2, MIm) and cobalt nitrate as a source of Co²⁺ ions were varied to control the growth of the obtained Co-MOF. Lower concentrations of the 2, MIm ligand favored the formation of leaf-like MOF structures through an anisotropic, two-dimensional growth, while higher concentrations led to rapid, isotropic nucleation and the creation of polyhedral Co-MOF structures. The sample characterized by polyhedral Co-MOF structures exhibited superior electrochemical stability, with the lowest corrosion current density (3.11 ​× ​10⁻⁹ A/cm²) and the highest top layer resistance (2.34 ​× ​10⁶ ​Ω ​cm²), and demonstrated outstanding photocatalytic efficiency, achieving a remarkable 99.98 ​% degradation of methylene blue, an organic pollutant, in model wastewater. To assess the active adsorption sites of the Co-MOF, density functional theory (DFT) was utilized. This study explores the changes in morphologies of the coatings of Co-MOF with the change of solution concentration to form coatings with enhanced properties on the metallic substrate, which could establish the groundwork for the development of next-generation multifunctional frameworks with diverse applications.