UV-Induced Synthesis of Hybrid HMDSO/SiO2 Thin Films with Compositional Gradients for High-Performance Atomic Oxygen Resistance.

A flexible, dense, defect-free, highly adhesive, and highly dissociation energy-rich protective coating is essential to enhance the atomic oxygen (AO) resistance of polymeric materials in a low Earth orbit (LEO). In this work, a dense, defect-free hybrid HMDSO/SiO2 thin film coating with compositional gradients on the surface of polyimide was synthesized using vacuum-ultraviolet (VUV) irradiation. The effects of VUV irradiation on the morphology, optical transmittance, and chemical components of plasma-polymerized HMDSO (pp-HMDSO) thin-film coatings deposited on the polyimide surface were investigated in depth. There were no defects such as cracks and holes in the surface morphology of pp-HMDSO films after VUV irradiation, but the surface roughness increased slightly, and the corresponding optical transmittance decreased slightly. The chemical components of pp-HMDSO films were changed in the depth direction starting from the top of the surface, forming hybrid HMDSO/SiO2 thin films with compositional gradients. The component gradient HMDSO/SiO2 composite coating further enhanced the atomic oxygen resistance of the polyimide due to the surface layer of the UV-modified coating enriched with high dissociation energy SiOx material. Therefore, this work provides a facile UV-induced synthesis method to prepare dense, defect-free, and highly dissociation energy-rich protective gradient coatings, which are promising not only for excellent AO protection in LEO but also for potential application in water-oxygen barrier films.

Low-grade sepiolite with low loading of Na/La salts for simultaneous removal of ammonia and phosphate from wastewater.

Efficient treatment of wastewater is of paramount importance for protecting the ecosystem. In this work, we prepared a low-grade sepiolite with low Na/La salt loadings (Na/La-Sep) and employed it for the simultaneous removal of ammonia (N) and phosphate (P) species in the wastewater. The key factors influencing the nutrient removal efficiency of Na/La-Sep, such as the concentration of the La/Na salt solution, the co-existing ion type, and surface zero charges, were investigated. Na/La-Sep exhibits excellent N and P adsorption capability and reduced the N and P concentrations in the spiked and real-world wastewaters to below the allowable N and P discharge limits. Due to the extraordinarily low cost of low-grade sepiolite and the low loading of Na/La salts, Na/La-Sep has a substantially lower cost when compared to other reported clay mineral adsorbents. Furthermore, the N and P removal mechanisms by Na/La-Sep were unraveled by combining the kinetic studies, the molecular dynamics (MD) simulation, and the electron density difference. The present findings might shed light on a new way to develop cost-efficient and high-efficiency adsorbents for alleviating eutrophication and deepen the understanding of N and P removal at a molecular level.