A hydrostable mesoporous γ-Al2O3 membrane modified with Si–C–H organic-inorganic hybrid derived from polycarbosilane

Greener solvents for the processing of preceramic polycarbosilane: application in the preparation of B4C/SiC composites

The innovation introduced in this study consists of replacing toluene with safer solvents such as cyclopentane or diethyl ether in the processing of a preceramic polycarbosilane (allylhydridopolycarbosilane, AHPCS) and assessing its impact on the functionalisation of B4C powders to produce B4C/SiC composites. Fourier-transform infrared (FT-IR) with ATR and nuclear magnetic resonance (NMR) spectroscopy revealed no major modification in the polymer structure. SEC/MALS analysis showed a slight change in the number-average molar mass of the polymer regardless of the functionalisation solvent used in correlation with a slight decrease in the polymer ceramic yield due to oligomer loss. The thermal behaviour of the preceramic polymer investigated via mass spectrometry remained unaffected by the solvent change. The search for polymer residues after distillation highlighted the recyclability of both the functionalisation solvent and the polymer, despite a slight increase in the molar mass of the polymer. Finally, the sinterability of B4C/AHPCS samples was studied with the preparation of B4C/SiC composites via a polymer-derived ceramic (PDC) route and spark plasma sintering (SPS). The effect of the solvent on the microstructure and relative density of the specimens (>92%) is negligible. The specimens retain a fine and homogeneous phase distribution despite process modification. The results highlight the approach developed to use greener solvents for the chemical synthesis of functionalised ceramics and represent a step towards the generalisation of more environmentally friendly processes.

An Overview of Photocatalytic Membrane Degradation Development

Environmental pollution has become a worldwide issue. Rapid industrial and agricultural practices have increased organic contaminants in water supplies. Hence, many strategies have been developed to address this concern. In order to supply clean water for various applications, high-performance treatment technology is required to effectively remove organic and inorganic contaminants. Utilizing photocatalytic membrane reactors (PMRs) has shown promise as a viable alternative process in the water and wastewater industry due to its efficiency, low cost, simplicity, and low environmental impact. PMRs are commonly categorized into two main categories: those with the photocatalyst suspended in solution and those with the photocatalyst immobilized in/on a membrane. Herein, the working and fouling mechanisms in PMRs membranes are investigated; the interplay of fouling and photocatalytic activity and the development of fouling prevention strategies are elucidated; and the significance of photocatalysis in membrane fouling mechanisms such as pore plugging and cake layering is thoroughly explored.

Mercapto-functionalized ordered mesoporous silica-modified PVDF membrane for efficiently scavenging Cd2+ from water

In this study, (3-mercaptopropyl) triethoxysilane (MPTMS)-modified ordered mesoporous silica (OMS) materials were prepared using a post-grifting method, with MPTMS as the organic functionalized reagent. The OMS materials were analyzed by FT-IR spectra, N₂ sorption, and small angle X-ray scattering to evaluate their potential for scavenging Cd²⁺ from water. Moreover, a (3-mercaptopropyl) triethoxysilane-functionalized ordered mesoporous silica modified polyvinylidene fluoride (MPTMS-OMS/PVDF) membrane was synthesized using the solvent phase inversion method to remediate wastewater containing heavy metal ions. The MPTMS-OMS was characterized by a maximum specific surface area of 422 m²/g, high surface hydrophilicity, and high pure water flux. The MPTMS-OMS/PVDF exhibited a dynamic adsorption capacity for Cd²⁺ in water. At an MPTMS-OMS content of 5 wt%, the Cd²⁺ removal efficiency was 90%, whereas the pure PVDF showed no Cd²⁺ adsorption capacity. These results highlight the potential of the MPTMS-OMS/PVDF membrane to eliminate Cd²⁺ during the decontamination of aqueous streams containing low-concentrations of contaminants.

Reversible Redox Property of Co(III) in Amorphous Co-doped SiO2/γ-Al2O3 Layered Composites

This paper reports on a unique reversible reducing and oxidizing (redox) property of Co(III) in Co-doped amorphous SiO₂/γ-Al₂O₃ composites. The Fenton reaction during the H₂O₂-catalyzed sol–gel synthesis utilized in this study lead to the partial formation of Co(III) in addition to Co(II) within the composites. High-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyses for the composite powder sample with a composition of Al:Si:Co = 85:10:5 showed the amorphous state of the Co-doped SiO₂ that modified γ-Al₂O₃ nanocrystalline surfaces. In situ X-ray absorption fine structure (XAFS) spectroscopic analysis suggested reversible redox reactions of Co species in the composite powder sample during heat-treatment under H₂ at 500 °C followed by subsequent cooling to RT under Ar. Further analyses by in situ IR spectroscopy combined with cyclic temperature programmed reduction/desorption (TPR/TPD) measurements and X-ray photoelectron spectroscopic (XPS) analysis revealed that the alternating Co(III)/(II) redox reactions were associated with OH formation (hydrogenation)-deformation (dehydrogenation) of the amorphous aluminosilicate matrix formed in situ at the SiO₂/γ-Al₂O₃ hetero interface, and the redox reactions were governed by the H₂ partial pressure at 250–500 °C. As a result, a supported mesoporous γ-Al₂O₃/Co-doped amorphous SiO₂/mesoporous γ-Al₂O₃ three-layered composite membrane exhibited an H₂-triggered chemical valve property: mesopores under H₂ flow (open) and micropores under He flow (closure) at 300–500 °C.

Hydrogen Selective SiCH Inorganic-Organic Hybrid/γ-Al2O3 Composite Membranes

Solar hydrogen production via the photoelectrochemical water-splitting reaction is attractive as one of the environmental-friendly approaches for producing H₂. Since the reaction simultaneously generates H₂ and O₂, this method requires immediate H₂ recovery from the syngas including O₂ under high-humidity conditions around 50 °C. In this study, a supported mesoporous γ-Al₂O₃ membrane was modified with allyl-hydrido-polycarbosilane as a preceramic polymer and subsequently heat-treated in Ar to deliver a ternary SiCH organic–inorganic hybrid/γ-Al₂O₃ composite membrane. Relations between the polymer/hybrid conversion temperature, hydrophobicity, and H₂ affinity of the polymer-derived SiCH hybrids were studied to functionalize the composite membranes as H₂-selective under saturated water vapor partial pressure at 50 °C. As a result, the composite membranes synthesized at temperatures as low as 300–500 °C showed a H₂ permeance of 1.0–4.3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with a H₂/N₂ selectivity of 6.0–11.3 under a mixed H₂-N₂ (2:1) feed gas flow. Further modification by the 120 °C-melt impregnation of low molecular weight polycarbosilane successfully improved the H₂-permselectivity of the 500 °C-synthesized composite membrane by maintaining the H₂ permeance combined with improved H₂/N₂ selectivity as 3.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with 36. These results revealed a great potential of the polymer-derived SiCH hybrids as novel hydrophobic membranes for purification of solar hydrogen.