A new carboxyethyltin functionalized sandwich-type tungstoarsenate: Synthesis, catalytic activity and corrosion inhibition behavior for carbon steel

Enhanced Corrosion Resistance of Carbon Steel in Hydrochloric Acid Solution by Polyoxometalate-Estertin Derivatives

The development of acid-resistant and efficient corrosion inhibitors is of great significance for metal protection in many industrial processes. In this work, eight cases of sandwich-type polyoxometalate (POM)-based inorganic-organic hybrids, namely, carboxyethyltin and transition metal (TM) cofunctionalized tungstoantimonates and tungstobismuthates, formulated as Na _x K_10-x [(SnR)₂(TM(H₂O)₃)₂(B-β-SbW₉O₃₃)₂]·mH₂O and Na _y K_10-y [(SnR)₂(TM(H₂O)₃)₂(B-β-BiW₉O₃₃)₂]·nH₂O (abbreviated as SbW₉-TM-SnR and BiW₉-TM-SnR; TM = Mn, Co, Ni, and Zn; m = 18, 24, 24, and 22; n = 30, 25, 20, and 21; SnR = Sn(CH₂CH₂COO)) are first used as green corrosion inhibitors for 20^# carbon steel in 0.5-2.0 M HCl solutions. Weight loss and electrochemical experiments prove that the corrosion inhibition efficiency is all above 81% for these POM-based corrosion inhibitors at 150 mg L^-1, and SbW₉-Mn-SnR shows the highest efficiency of 96.9% at 150 mg L^-1 after immersion in a 0.5 M HCl solution for 10 h. Scanning electron microscopy-energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses show that these POM-based inhibitors form films on the carbon steel and the adsorption mechanism obeys the Langmuir adsorption model. The thermodynamic activation parameters were calculated, proving the occurrence of both chemical and physical adsorptions. The film-forming mechanism was also analyzed. This work provides guidance for synthesizing new lacunary POM-based materials to protect metals from corrosion in HCl pickling.

Cubic Liquid Crystals of Polyoxometalate-Based Ionic Liquids

Thermotropic ionic liquid crystals of polyoxometalate (POM)-based ionic liquids (POM-based ILs), which are formed by a POM, K₇PW₁₁O₃₉, and cationic surfactants, tetra-n-alkylammonium bromide ((C_nH_2n+1)₄N⁺Br^-, n = 6 and 7), are first proposed. As a model system, the cubic phase structure of a POM-based IL, {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉, was determined to form in a wide range of temperatures, exhibiting good thermostability, excellent mechanical strength, and high viscosity. Furthermore, the lyotropic ionic liquid crystals formed by {(C₇H₁₅)₄N⁺}₇PW₁₁O₃₉ in solvents such as chloroform or toluene still maintained a cubic structure. These cubic ionic liquid crystals (CILCs) were used as anticorrosion coatings both in acidic and neutral environments. The electrochemical measurements of Cu and Fe surfaces coated by CILCs showed an excellent ability of anticorrosion, indicating that the metals can be perfectly protected by the CILC coatings with high resistance and low capacitance. We assume that the CILCs may serve as barriers to stop oxygen diffusing to metals and interrupt the electron tunnels between the metal surfaces and the electrolyte solutions. Such environmentally friendly CILCs of POMs-based ILs are convenient for coating and removal, being vital to versatile industrial and academic applications.