## 1 Introduction  
In recent years, layered double hydroxide (LDH) has been widely used in the field of corrosion protection due to its unique layered structure, anion-accommodating capacity, and anion exchange characteristic [1]. Based on the attractive anion-accommodating capacity of LDH, a wide range of various inhibitors has been intercalated in its gallery. Upon contact with corrosive medium, the loaded inhibitor anions would participate in the anion exchange reaction between them and the aggressive anions in the environment such as Cl\({}^{-}\) and SO\({}_{4}\)\({}^{-}\)[2]. As a result, the aggressive anions were adsorbed into the gallery of LDH, and the inhibitor anions were released out into the environment, presenting a dual function including reducing the concentration of aggressive chlorides and releasing corrosion inhibitors in this case. The released inhibitor is able to prevent the corrosion of initiation, propagation, and development [3]. On one hand, the self-healing property can be attributed to the enhanced physical barrier effect by filling pores with corrosion products after initiation of corrosion. On the other hand, it is of great significance that the release of inhibitor anions in the defect sites is able to inhibit the development of corrosion by passivation, complexing, and precipitation [4]. One significant application of LDH in the field of anticorrosion is the incorporation of LDH powders as fillers in the organic coatings applied on metal substrates. LDH in coatings is able to absorb chlorides through an anion exchange reaction, resulting in the decrease in the chloride concentration and the release of corrosion inhibitors in the system. In addition, the intercalated chlorides in the gallery were able to further prevent the permeation of chlorides by acting as a concentration gradient wall as shown in Figure 1.  
In the published literature, many researchers focused on the modification of LDH using inhibitors, and enhanced corrosion protection effect was obtained. For example, [PERSON] et al. prepared nitrite-intercalated MgAl-LDH and added it into the epoxy coating, and the localized electrochemical impedance spectroscopy (LEIS) test results indicated that the coatings containing LDH-NO2 presented the most significant corrosion resistance upon the presence of scratches in comparison with the blank coating and the coating with LDH-CO3 [5]. [PERSON] et al. reported the application of MgAl-LDH-PO4\({}^{3-}\) in a silane primer top-coated by epoxy-polyamide on mild steel. The electrochemical results verified its active corrosion protection ability due to the release of PO4\({}^{3-}\)[6]. [PERSON] et al. synthesized nitrate and molybden intercalated ZnAl-LDH, and the controlled release of NO2\({}^{-}\) and MoO4\({}^{2-}\) resulted in a relatively long-term corrosion effect [7]. In addition, an environmentally friendly corrosion inhibitor aspartic acid (ASP) was used to modify MgAl-LDH films on Mg alloys by a one-step hydrothermal method by [PERSON] et al. It can be seen that the MgAl-LDH-ASP coating presented an excellent self-healing ability due to the synergistic effect between ASP and the laminate structure of LDH [8]. [PERSON] et al. prepared MgAl-LDH loaded with 5-aminoidazole (AIA), which displayed a controllable release behavior and excellent anticorrosion performance on copper in a 3.5 wt.% NaCl solution [9]. It can be concluded that most of the reported literature paid lots of attention to the modification of LDH with inhibitors, and the inhibitor releasing behavior was studied systematically, while the corresponding chloride adsorption behavior and capacity lack systematic investigation. It should be noted that the inhibitor loading content was closely related with the chloride adsorption capability based on the anion exchange mechanism. Therefore, the optimization of the chloride adsorption capacity before modification would play a positive role in improving the inhibitor loading amount.