ABSTRACT
This study focuses on the adsorption process of L-cysteine (Cys), a sulfur-containing amino acid, onto monolayers of gold nanoparticles (AuNPs) prepared through distinct protocols on mica substrates. Two types of AuNPs were prepared using two different methods: the first employed a physical approach, which combined the Inert Gas Condensation (IGC) technique with the magnetron sputtering method, while the second utilized a chemical method involving the reduction of tetrachloroauric acid with trisodium citrate (TC). The characterization of AuNPs was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM), of up to 5 ± 1.3 nm for bare AuNPs obtained through vacuum techniques, and up to 12 ± 5 nm for negatively charged, citrate-stabilized TCAuNPs(-). The application of spectroscopic techniques based on the surface-enhanced effects allows for describing the adsorption process in both micro- and nanoscale systems: Cys/bare AuNPs and Cys/ TCAuNPs(-). The commonly used surface-enhanced Raman spectroscopy (SERS) technique provided insights into adsorption behaviours at the microscale level. In the case of TCAuNPs(-), an interaction involving the lone electron pair of sulfur (S) atom and metal surface, while on the bare AuNPs, S is adsorbed on the surface, but the cleavage of the SH group is not discernible. Nanoscale analysis was complemented using AFM combined with the surface-enhanced infrared absorption spectroscopy (AFM-SEIRA) technique. AFM-SEIRA map indicated the formation of hot spot which were predominantly located between aggregated TCAuNPs(-) and on specific NPs surfaces (area between NPs and gold-coated tip). Results from the SERS and AFM-SEIRA techniques were in good agreement, underscoring the comprehensive understanding achieved through the chosen experimental approach regarding the Cys interactions with layers of AuNPs.
ABSTRACT
The work presents a comprehensive vibrational analysis of the process of adsorption of threonine (Thr) onto an Fe surface with deposited Cu nanoparticles (NPs) (of about 4-5 nm in size) in a corrosive environment. The application of surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRA) provides the opportunity for detailed description of adsorption geometry of amino acid onto a metal surface. The combination of conventional infrared spectroscopy (IR) with atomic force microscopy (AFM) resulted in a nano-SEIRA technique which made it possible to provide a precise description of adsorbate binding to the metal surface. The studies presented confirmed that there is a very good correlation between the spectra recorded by the SERS, SEIRA, and nano-SEIRA techniques. Threonine significantly influenced the process of corrosion of the investigated surface due to the existing strong interaction between the protonated amine and carboxylate groups and the CuNPs deposited onto the Fe surface. In addition, the application of two polarization modulations (s and p) in nano-SEIRA allows subtle changes to be observed in the molecule geometry upon adsorption, with the carboxylate group of Thr being almost horizontally oriented onto the metal surface; whereas the amine group that contains nitrogen is oriented perpendicular to this surface.
ABSTRACT
The effect of CO2 partial pressure on the corrosion inhibition efficiency of gum arabic (GA) on the N80 carbon steel pipeline in a CO2-water saline environment was studied by using gravimetric and electrochemical measurements at different CO2 partial pressures (e.g., PCO2 = 1, 20 and 40 bar) and temperatures (e.g., 25 and 60 °C). The results showed that the inhibitor efficiency increased with an increase in inhibitor concentration and CO2 partial pressure. The corrosion inhibition efficiency was found to be 84.53% and 75.41% after 24 and 168 h of immersion at PCO2 = 40 bar, respectively. The surface was further evaluated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS) measurements. The SEM-EDS and GIXRD measurements reveal that the surface of the metal was found to be strongly affected by the presence of the inhibitor and CO2 partial pressure. In the presence of GA, the protective layer on the metal surface becomes more compact with increasing the CO2 partial pressure. The XPS measurements provided direct evidence of the adsorption of GA molecules on the carbon steel surface and corroborated the gravimetric results.
ABSTRACT
Bimetallic Co-Pt nanorods exhibit an enhanced capacity for the production of gas from liquid-phase chemicals. Based on the systematic structural and magnetic characterization we discuss potential applications of these hybrid nanostructures for localized fuel generation in microdevices. Experimental proof of the feasibility for controlling the rate of catalytic reaction via external magnetic stimuli is shown. This unique functionality makes these hybrids promising candidates for optimizing the energy conversion rate in microfluidics fuel cells.
