ABSTRACT
Formaldehyde adsorption on intrinsic La2O3 surface, four-fold coordinated oxygen vacancy (VO4c), six-fold coordinated oxygen vacancy (VO6c), and iridium-doped La2O3(001) surface was studied by the first-principles method. The results show that formaldehyde adsorption on the Ir-doped La2O3(001) surface with VO6c is the strongest because of the directional movement of electrons caused by the interaction of the Ir-5d orbitals and internal oxygen vacancy, wherein the adsorption energy is 3.23 eV. This model showed a significant increase in adsorption energy, indicating that Ir doping improves the formaldehyde adsorption capacity of the La2O3(001) surface. The energy band analysis shows that iridium doping introduces impurity energy levels into the intrinsic La2O3 energy band, which enhances the interaction between the La2O3(001) surface and formaldehyde molecules. Density of state analysis indicated that the adsorption of formaldehyde molecules on the La2O3(001) surface is mainly due to the interaction between the O-2p, C-2p orbitals of formaldehyde and the Ir-5d orbital of iridium atoms. Furthermore, the existence of VO4c and VO6c defects has no effect on the position and shape of the valence and conduction bands. The effects of oxygen vacancy and iridium doping on the optical properties mainly appeared in the low-energy infrared and visible regions, making the O-2p, C-2p orbitals of formaldehyde and the Ir-5d, O-2p orbitals of the La2O3(001) surface become hybridized near the Fermi level and the electronic transition from the valence band to conduction band more likely to occur. The La2O3 material can be used as an ideal photocatalytic material for formaldehyde degradation.
ABSTRACT
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.
ABSTRACT
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.
