RESUMO
Surface corrosion involves a series of redox reactions that are catalyzed by the presence of ions. On infrastructure surfaces and in complex and natural environments, iron surfaces readily undergo redox reactions, impacting chemical processes. In this study, the effect of how cations influence the formation of the mineral scale on iron surfaces and its connection to surface corrosion was investigated in CaCl2(aq) and NaCl(aq) electrolytes. Polarized modulated-infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to measure the oxidation and formation of carbonates at the air/electrolyte/iron interface, which confirmed that the iron surface oxidized faster in CaCl2(aq) than in NaCl(aq). PM-IRRAS, attenuated total reflectance-Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy show that after the adsorption of atmospheric O2 and CO2, calcium carbonate (CaCO3) in the form of calcite and aragonite was produced on iron in the presence of CaCl2(aq), whereas siderite (FeCO3) was produced on the surface of iron in the presence of NaCl(aq). However, in either solution without gradual O2 and CO2 exposure, a heterogeneous mixture of lepidocrocite (γ-FeOOH) and an iron hydroxy carbonate (Fex(OH)yCO3) was grown on the iron surface. In situ liquid AFM was used to measure the surface roughness in CaCl2(aq) and NaCl(aq), as an estimation of the corrosion rate. In CaCl2(aq), Fe was found to corrode faster than Fe in NaCl(aq) due to more ions at equimolar concentrations. Surface physical changes, as measured by ex situ AFM, confirmed the presence of a heterogeneous mixture of γ-FeOOH and an Fex(OH)yCO3 in the submerged region. This indicates that the cation does not affect the type of mineral grown on the Fe surface in the region completely submerged in the electrolyte. These results suggest that the cations play a unique role in the initial stages of corrosion at the interface region, influencing the uptake of atmospheric CO2 and mineral nucleation. The knowledge gained from these interfacial reactions are important for understanding the connection between surface corrosion, mineral grown, and CO2 capture for sequestration.
RESUMO
Reactions on iron oxide surfaces are prevalent in various chemical processes from heterogeneous catalysts to minerals. Nitrogen (N2) is known to dissociate on iron surfaces, a precursor for ammonia production in the Haber-Bosch process, where the dissociation of N2 is the limiting step in the reaction under equilibrium conditions. However, little is known about N2 adsorption on other iron-based materials, such as iron oxide surfaces that are ubiquitous in soils, steel pipelines, and other industrial materials. An atomistic description is reported for the binding of N2 on the Fe3O4(001) surface using first principles calculations with ambient pressure X-ray photoelectron spectroscopy. Two primary adsorption sites are experimentally identified from N2 dissociation on Fe3O4(001). The electronic signatures associated with the valence band region unambiguously show how the electronic structure of magnetite transforms near ambient pressures due to the binding of atomic nitrogen to different surface sites. Overall, the experimental and theoretical results of our study bridge the gap between ultra-high vacuum studies and reaction conditions to provide insight into other nitrogen-based chemistry on iron oxide surfaces that impact the agriculture and energy industries.
RESUMO
A simple two-step, shaking-assisted polydopamine (PDA) coating technique was used to impart polypropylene (PP) mesh with antimicrobial properties. In this modified method, a relatively large concentration of dopamine (20 mg ml-1) was first used to create a stable PDA primer layer, while the second step utilized a significantly lower concentration of dopamine (2 mg ml-1) to promote the formation and deposition of large aggregates of PDA nanoparticles. Gentle shaking (70 rpm) was employed to increase the deposition of PDA nanoparticle aggregates and the formation of a thicker PDA coating with nano-scaled surface roughness (RMS = 110 nm and Ra = 82 nm). Cyclic voltammetry experiment confirmed that the PDA coating remained redox active, despite extensive oxidative cross-linking. When the PDA-coated mesh was hydrated in phosphate saline buffer (pH 7.4), it was activated to generate 200 µM hydrogen peroxide (H2O2) for over 48 h. The sustained release of low doses of H2O2 was antibacterial against both gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria. PDA coating achieved 100% reduction (LRV ~3.15) when incubated against E. coli and 98.9% reduction (LRV ~1.97) against S. epi in 24 h.
