Preparation, characterization, and evaluation of TiO2-ZrO2 nanofiltration membranes fired at different temperatures

A Brief Overview of the Microstructural Engineering of Inorganic-Organic Composite Membranes Derived from Organic Chelating Ligands

This review presents a concise conceptual overview of membranes derived from organic chelating ligands as studied in several works. The authors' approach is from the viewpoint of the classification of membranes by matrix composition. The first part presents composite matrix membranes as a key class of membranes and makes a case for the importance of organic chelating ligands in the formation of inorganic-organic composites. Organic chelating ligands, categorized into network-modifying and network-forming types, are explored in detail in the second part. Four key structural elements, of which organic chelating ligands (as organic modifiers) are one and which also include siloxane networks, transition-metal oxide networks and the polymerization/crosslinking of organic modifiers, form the building blocks of organic chelating ligand-derived inorganic-organic composites. Three and four parts explore microstructural engineering in membranes derived from network-modifying and network-forming ligands, respectively. The final part reviews robust carbon-ceramic composite membranes as important derivatives of inorganic-organic hybrid polymers for selective gas separation under hydrothermal conditions when the proper organic chelating ligand and crosslinking conditions are chosen. This review can serve as inspiration for taking advantage of the wide range of possibilities presented by organic chelating ligands.

Gas Permeation Characteristics of TiO2-ZrO2-Aromatic Organic Chelating Ligand (aOCL) Composite Membranes

Methyl gallate (MG) and ethyl ferulate (EF) with a benzene ring were separately used as aromatic organic chelating ligands (aOCLs) to prepare two versions of TiO₂-ZrO₂-aOCL composite sols via hydrolysis and polycondensation reactions with titanium(IV) isopropoxide (Ti(OC₃H₇)₄) and zirconium(IV) butoxide (Zr(OC₄H₉)₄). Thermogravimetric and FT-IR analysis of dry gels revealed that aromatic rings were present in the residual organic matter when the gel was fired under nitrogen at 300 °C. In X-ray diffraction (XRD) measurements, the TiO₂-ZrO₂ composite material prepared using these two aOCLs showed an amorphous structure with no crystalline peaks for TiO₂ and ZrO₂. In N₂ adsorption/desorption measurements at 77 K, the TiO₂-ZrO₂ samples using the aOCLs as a template appeared porous with a larger specific surface area than TiO₂-ZrO₂ without aOCL. TiO₂-ZrO₂-aOCL composite membranes were prepared by coating and firing TiO₂-ZrO₂-aOCL sol onto a SiO₂ intermediate layer using an α-alumina porous tube as a substrate. Compared with the TiO₂-ZrO₂ membrane, the TiO₂-ZrO₂-aOCL membranes had higher gas permselectivity. The TiO₂-ZrO₂-EF membrane showed a He permeance of 2.69 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ with permeance ratios of He/N₂ = 10.6 and He/CF₄ = 163, while the TiO₂-ZrO₂-MG membrane revealed a bit less He permeance at 8.56 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with greater permeance ratios of He/N₂ = 61.7 and He/CF₄ = 209 at 200 °C. A microporous TiO₂-ZrO₂ amorphous structure was obtained by introducing aOCL. The differences in the side chains of each aOCL could possibly account for the differences in the microporous structures of the resultant TiO₂-ZrO₂-aOCL membranes.

SiC mesoporous membranes for sulfuric acid decomposition at high temperatures in the iodine-sulfur process

Inorganic microporous materials have shown promise for the fabrication of membranes with chemical stability and resistance to high temperatures. Silicon-carbide (SiC) has been widely studied due to its outstanding mechanical stability under high temperatures and its resistance to corrosion and oxidation. This study is the first to prepare mesoporous SiC membranes for use in sulphuric acid decomposition to achieve thermochemical water splitting in the iodine–sulfur process. Single-gas permeation was carried out to confirm the stability of this mesoporous membrane under exposure to steam and H₂SO₄ vapor. Benefiting from the excellent chemical stability of the α-Al₂O₃ membrane support and the SiC particle layer, the SiC membrane exhibited stable gas permeance without significant degradation under H₂SO₄ vapor treatment at 600 °C. Additionally, with extraction, the membrane reactor exhibited an increased conversion from 25 to 41% for H₂SO₄ decomposition at 600 °C. The high performance combined with outstanding stability under acidic conditions suggests the developed SiC membrane is a promising candidate for H₂SO₄ decomposition in a catalytic membrane reactor.

In the present study, SiC particles derived mesoporous membrane was discovered and applied to membrane reactor for H₂SO₄ decomposition. The reaction equilibrium was moved the to the product side by membrane reactor with extraction at 600 °C.