Surfaces

The invasive presence of nanoplastics in various ecosystems makes them a significant environmental problem nowadays. One of the main production mechanisms of nanoplastics is mechanical wear. The combination of friction, abrasion, and shear forces can indeed lead to the progressive fragmentation of polymeric materials. The high surface area–volume ratio of the resulting nanoparticles not only alters the physicochemical properties of the polymers but also leads to increased interaction with biological systems, which raises questions about the persistence of nanoplastics in the environment and their potential toxicity. Despite the growing body of research on microplastics, studies specifically addressing the formation, characterization, and impact of wear-induced nanoplastics remain limited. This article describes current research on the formation mechanisms of nanoplastics generated by mechanical wear, highlighting the tribological processes underlying their release. Advanced characterization techniques used to identify the morphology and composition of these particles are also mentioned. The techniques include atomic force microscopy (AFM), scanning electron microscopy (SEM), and, to some extent, Raman spectroscopy. In the case of AFM, an example of application to the extrusion of nanoplastics from polystyrene surfaces subjected to repeated nanoscratching is also provided. Full article

Environmental humidity is a determining factor in the degradation of concrete structures, particularly in the corrosion process of reinforcement bars. This study analyzed four concrete mixtures with different mucilage contents replacing mixing water: 0, 5, 10, and 15%. Two sets of specimens were fabricated and subjected to a 420-day test period under two different working conditions: natural environmental conditions and high-humidity conditions. Open-circuit potential parameters were analyzed to compare the behavior of the mixtures and determine the corrosion rate. It was observed that under environmental conditions, the mixtures with 0% and 15% mucilage exhibited higher corrosion rates, with values of 0.046 and 0.049 mm/year, respectively, compared to the mixtures with low mucilage additions of 5% and 10%, which showed values of 0.041 and 0.038 mm/year, respectively. The corrosion rates of the mixtures under high-humidity conditions were 0.010 for M0, 0.009 for M1 and M2, and 0.014 for M3. The results indicate that mixtures with 5% and 10% mucilage show better corrosion protection, suggesting that this approach could be a sustainable, low-cost solution to enhance the durability of concrete structures, particularly in coastal areas with high humidity levels. It is concluded that adding nopal mucilage in low concentrations as a substitute for mixing water in concrete formulations not only modifies the properties of concrete, but also reduces the corrosion rate of reinforcement steel under high-humidity conditions, thereby extending the service life of constructions. Full article

Platinum exhibits essential characteristics for enhancing electrochemical processes, but the use of electrodes made entirely of Pt is not cost-effective. A more affordable alternative is electrodepositing Pt black on accessible metallic surfaces, such as brass, to ensure that the electrodes are both resistant to corrosive environments and possess catalytic capabilities. Pourbaix and kinetic analyses were performed to establish the optimal potential and current conditions for electrodepositing Pt black on brass utilizing a Pb-free Pt solution. The Pourbaix analysis indicated that Pt electrodeposition is achieved from the PtCl₆⁻ ionic species and occurs before hydrogen evolution. Kinetic studies further revealed that Pt black nanoscale deposition on a brass surface requires mechanical surface treatment and electrochemical polishing, followed by metallic Pt electrodeposition under potentiostatic control at −295 mV vs. SCE. Subsequent Pt black deposition was achieved under galvanostatic control at −500 A cm⁻². Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed the formation of nanostructures of metallic Pt and Pt black on brass, with the latter presenting a larger surface area to enhance the active sites for catalysis in electrochemical processes. Full article

In this study, we report a green, one-step synthesis of fluorescent carbon quantum dots (PET-FCQDs) derived from polyethylene terephthalate (PET) waste using an environmentally friendly pyrolytic method. The PET-FCQDs were systematically characterized using techniques such as UV-Vis spectroscopy, fluorescence spectroscopy, ATR-FTIR, TGA, and fluorescence microscope, confirming their nanoscale size (2–50 nm), rich functional groups and thermal stability. Thermal stability and dynamics evaluated by the Coats–Redfern method showed endothermic reactions with an activation energy of 88.84–125.05 kJ/mol. Density functional theory studies showed a binding energy, highest occupied molecular orbital, lowest unoccupied molecular orbital, and energy gap of −675.39, −5.23, −5.07, and 0.17 eV, respectively. The as-synthesized PET-FCQDs demonstrated excellent optical properties with quantum yield ($\Phi$) of 49.6% and were applied as a dual-mode fluorescent sensing probe for the detection of Pd²⁺, ciprofloxacin (CIP), and fluoxetine (FLX) in aqueous systems via fluorescence quenching and enhancement mechanisms. For Pd²⁺, the fluorescence emission intensity at 470 nm was quenched proportionally to the increasing concentration, while CIP and FLX induced fluorescence enhancement. The Stern–Volmer analysis confirmed strong interaction between the analytes and PET-FCQDs, distinguishing dynamic quenching for Pd²⁺ and static interactions for CIP and FLX. The method exhibited linear detection ranges of 1–10 mg/L for Pd²⁺, 50–150 µg/L for CIP, and 100–400 ng/L for FLX, with corresponding limits of detection (LOD) of 1.26 mg/L, 3.3 µg/L, and 134 ng/L, respectively. Recovery studies in spiked tap water and river water samples demonstrated the practical applicability of PET-FCQDs, although matrix effects were observed, particularly for FLX. This work not only highlights a sustainable route for PET waste upcycling but also demonstrates the potential of PET-FCQDs as cost-effective, sensitive, and versatile fluorescent probes for environmental monitoring of heavy metal ions and pharmaceutical pollutants. Further optimization of the sensing platform could enhance its selectivity and performance in real-world applications. Full article

Polypyrrole (PPy) is cationic in its conducting form, requiring a charge-balancing counterion, or dopant. The release of bioactive dopants, driven by the reduction of PPy films, offers a route to controlled drug delivery. Thiol-terminated long chain poly (ethylene glycol) (PEG) reacts with a dodecylbenzene sulfonate (DBSA)-doped PPy, forming a dense overlayer and partially liberating DBSA via the chemical reduction of the film. The resulting PEG brush acts as a barrier to dopant diffusion from the film, but proteins have been shown to disrupt this layer, releasing the DBSA. The mechanism by which this disruption occurs has not been thoroughly investigated. In this study, dopant release from PEG-PPy composites was examined via systematic exposure to a variety of chemical stimuli, including macromolecules such as poly (ethylene imine), polyethylene glycol, and poloxamers, as well as small-molecular-weight alcohols, carboxylic acids, and amines. Dopant release was quantified by quartz crystal microbalance. Poly (ethylene imine) efficiently released DBSA, while anionic and uncharged macromolecules did not. All classes of small molecules triggered dopant release, with longer homologues magnifying the response. The mechanisms of dopant removal are dependent on the functional groups of the stimulating agent and include ion exchange and nucleophilic reduction of the polycationic backbone. Tosylate, salicylate, and penicillin dopants showed release behaviors similar to DBSA, demonstrating the generality of the PEG barrier. Full article

The realization of novel electronic devices based on 2D materials, i.e., field-effect transistors, has recently stimulated a renewed interest regarding ultrathin fluoride epitaxial films. Thanks to their chemical and dielectric properties, ionic fluorides could have the potential to be used as insulators in many applications that require high processing control down to the nanoscale. Here we provide a review of some of the principal results that have been achieved in the past decades regarding the controlled growth of epitaxial fluorides on different types of materials relevant for electronics. The aim is to provide a concise summary of the growth modes, crystallinity, film morphologies, and chemical interactions of different types of fluorides on different type of substrates, highlighting the possibilities of applications and the future perspectives. Full article

Green diesel is a high-quality biofuel obtained through the transformation of triglycerides into linear alkanes. In order to obtain green diesel, this study investigates the impact of impregnation pH on the surface species of NiMo/Al₂O₃ catalysts in the hydroprocessing of soybean oil. NiMo catalysts supported on Al₂O₃ were synthesized at different pH values (pH = 7 and 9). In the oxide state, solids were characterized by UV-Vis diffuse reflectance, Raman, and FT-IR spectroscopies, and, in the sulfide state, they were characterized by HR-TEM. The results show that the pH of impregnation significantly determines the surface species formed. An impregnation at pH = 7 favors the formation of Ni²⁺_(Oh) and Ni²⁺_(Oh-dis) interacting with non-crystalline molybdenum trioxide, while the formation of Ni²⁺/Al₂O₃, Ni_2+(Oh-dis), and MoO₃ species is favored at pH = 9. These surface species play a fundamental role in the hydrogenolysis and deoxygenation steps. Catalyst impregnated at pH = 7 shows higher activity due to the formation of shorter MoS₂ slabs. This study emphasized the importance of controlling impregnation conditions for optimizing catalyst performance. Full article

The increasing demand for sustainable materials in the coatings industry is driving the replacement of synthetic components with bio-based alternatives. In this study, Tagua powder, derived from the seeds of Phytelephas macrocarpa, was incorporated as a filler in a waterborne acrylic-based coating to evaluate its effects on abrasion and protective properties. Two different particle size ranges (40–63 µm and ≤40 µm) and concentrations (1 wt% and 3 wt%) were tested. Morphological analyses confirmed a homogeneous dispersion of the filler within the coating matrix, with larger particles inducing surface roughness. The results demonstrated that the addition of Tagua powder significantly improved abrasion resistance, with the coating containing 3 wt% of larger particles (40–63 µm), reducing mass loss by 24.5% after 1000 Taber abrasion cycles compared to the reference coating. However, due to its lignocellulosic nature, the filler increased water uptake, leading to a decrease in barrier properties. Coatings with 3 wt% filler exhibited a reduction in electrochemical impedance modulus by approximately one order of magnitude after 670 h of immersion in a 3.5 wt% NaCl solution, indicating lower corrosion protection. Despite this, the performance in filiform corrosion resistance remained comparable to the reference, suggesting that Tagua powder does not critically affect adhesion properties. These findings highlight the potential of Tagua powder as a functional bio-based filler, offering enhanced mechanical durability while requiring a strategic coating design, such as a multilayer system, to mitigate moisture sensitivity. This study provides valuable insights into the development of environmentally friendly coatings with improved wear resistance. Full article

The metal injection molding (MIM) manufacturing process has made relevant advances for applications in components with complex geometries, small dimensions, and high production volumes. New technologies such as hot isostatic pressing (HIP), uniform polymer extraction, and sintering with reduced temperature variations improve metallurgical and mechanical properties. However, there are still knowledge gaps in understanding these technologies and the behavior of catalytic low-alloy steels obtained by the MIM process and cyclic applications. This study aims to analyze the behavior of Catamold 100Cr6 steel subjected to quenching and tempering heat treatment in different microhardness ranges and the effect of compressive stresses on the samples obtained by polishing using ceramic microchips. The samples were characterized using optical microscopy, scanning electron microscopy, an EDS microprobe, and X-ray diffraction and subjected to elastic return cycling and an experimental device developed to apply a 19° bending angle. The findings show a significant increase in fatigue life due to the compressive stresses (up to—430 MPa) generated by the reduction in retained austenite and surface plastic microdeformation, indicating the effectiveness of 100Cr6 Catamold steel in cyclic applications. Full article

Piping system failures in process industries pose significant financial, environmental, and social risks, with inadequate design and corrosion being major contributors. This review synthesizes the academic and normative literature on pipeline design and anticorrosive protection strategies, providing a comprehensive examination of pipeline layout determination, material selection, and methods for mitigating corrosion. A particular focus is placed on organic coating as a pivotal strategy for corrosion reduction, with in-depth insights into their selection and evaluation criteria. By highlighting best practices and advancements in design and protection strategies, this review aims to enhance the overall integrity and safety of piping systems. The findings are intended to support industry professionals in implementing more effective measures to prevent pipeline failures and improve system reliability, while also presenting recent advances and current demands. Full article

For the first time, the adsorption of hydrogen on the (110) surface of the A15 Ti₃Sb compound with a cubic structure (Cr₃Si type; space group $Pm\overline{3}n$) for the accumulation of hydrogen H was calculated using the density functional theory method (DFT SGGA-PBE). Taking into account the relaxation of the Ti₃Sb–H system, the equilibrium positions of hydrogen on the Ti₃Sb (110) surface were determined depending on the supercell size. Hydrogen adsorption on the Ti₃Sb (110) surface of supercells is preferable in pit sites. All DFT calculations of the Ti₃Sb–H system were performed on relaxed and optimized supercells (2 × 1 × 1, 3 × 3 × 3, and 5 × 5 × 5). Relaxation of the supercell reduced the calculated adsorption energy compared with the non-relaxed supercell. The calculated band structure and curves of local and partial densities of states of Ti₃Sb–H were used to explain the interaction of hydrogen with the Ti₃Sb (110) surface. The activation energy of H diffusion along the coordinates tetrahedral interstitial site → tetrahedral interstitial site (TIS–TIS) and tetrahedral interstitial site → octahedral interstitial site (TIS–OIS), along with the diffusion coefficient of H in the cubic lattice of Ti₃Sb, were calculated. Full article

We report the formation of multi-walled carbon nanotubes (MWCNTs) through the interaction of an atmospheric-pressure plasma jet, generated via a capillary discharge, with a graphite surface. The structural properties of MWCNTs on the graphite anodes demonstrated a clear dependence on discharge power. Utilizing scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy, we observed a progression toward the disordering and interconnection of the nanotubes alongside the emergence of graphitized clusters with increasing discharge energy. The formation of relatively defect-free MWCNTs at minimal discharge energy presents an opportunity for their synthesis with low energy consumption of 4.7 kJ/cm². The suggested energy-efficient, rapid, and straightforward technique for tailoring MWCNT formation significantly reduces the reliance on complex and expensive instrumentation, presenting a promising pathway for effective surface modification. Full article

Complex coacervation using proteins and polysaccharides enables efficient microencapsulation with high thermal stability, facilitating continuous core component release and yielding coacervates with superior properties for diverse applications. This study investigates the use of casein and pectin for microencapsulating Ocimum basilicum L. essential oil (EO) and phenolic extract (PE). Microencapsulation yield and efficiency were 85.3% and 89.8% for EO microcapsules (EO-MC) and 53.1% and 70.0% for PE microcapsules (PE-MC). Optical microscopy revealed spherical microcapsules; EO-MC had smooth surfaces, while PE-MC had porous surfaces. Thermal analysis showed stability, with both types exhibiting two stages of weight loss. XRD analysis indicated increased crystallinity in EO-MC and high crystallinity in PE-MC due to phenolic interactions. FTIR spectroscopy confirmed molecular interactions, including hydrogen bonding between phenolic compounds and the biopolymer matrix and amide bonds between the carboxyl groups of pectin and the amino groups of casein, ensuring the successful encapsulation of the bioactive compounds. These findings highlight the potential of casein and pectin for microencapsulating extracts, particularly EOs, for food industry applications. Full article

Soil contamination by petroleum derivatives is a growing environmental issue that affects ecosystems and human health, since the hydrocarbons present in them are persistent and toxic, compromising soil quality and biodiversity. This study investigated the potential of a biosurfactant from Candida bombicola URM 3718, to be applied to remove oils from contaminated soils. After isolation, its main surface-active characteristics were evaluated. The biomolecule was then characterized by NMR and FTIR spectroscopy analyses, and its ability to remove motor oil adsorbed on soils with different particle sizes and its genotoxicity profile were determined. Tests to determine surfactant activities revealed a reduction in water surface tension to 30 mN/m with a critical micelle concentration (CMC) of 0.03 g/L. The surfactant was shown to have a glycolipid nature. The removal of burned engine oil sorbed on various kinds of soil was investigated in both static and kinetic assays using the biosurfactant at different concentrations, namely, ½ CMC (0.015 g/L), CMC (0.03 g/L), and 2 × CMC (0.06 g/L). In the static tests, the maximum removal percentage was 65.32% for burned engine oil adsorbed on sandy soil, 59.04% on silty soil, and 57.42% on clayey soil, while in the kinetic tests, this parameter reached 98.60%, 93.22%, and 92.55% for sandy, silty, and clayey soils, respectively. The genotoxicity profile evaluated in Allium cepa roots did not reveal necrosis or the occurrence of micronuclei in the plant root cap cells, demonstrating that the biomolecule thus produced is not toxic. Such findings, when taken together, indicate that the C. bombicola URM 3718 biosurfactant was effective in removing oils and could, therefore, be used as an alternative agent for remediating hydrocarbon-polluted soil. Full article

Calcium carbonate scaling causes significant damage and financial losses to various industries, particularly in deep-water oil exploration. It is affected by factors like pressure, temperature, pH, solution chemistry, and surface finish. Surface finish is critical, as it interacts with the fluid and serves as a substrate for the anchoring of calcium carbonate crystals. However, many studies investigate this phenomenon under conditions that differ from those encountered in deep-water oil exploration. Tests are commonly performed under atmospheric pressure and lacking fluid flow or CO₂ influence, which limits their relevance to industrial conditions. This study aims to evaluate the influence of surface finish on the formation of calcium carbonate scaling under conditions that more closely resemble actual operating environments. 304 stainless steel was selected to replicate industrial conditions, owing to its chemical stability and common use in industrial settings. The tests were conducted in a plant with high-pressure capabilities, operating under continuous flow conditions with CO₂ injection. Controlled surfaces were prepared through metallographic polishing, machining, sandblasting, and laser texturing techniques. Surface characterization was performed using a 3D optical profilometer and scratch testing to measure the average adhesion force. The polymorphs formed were characterized by Raman spectroscopy. Fractal dimension analysis was applied to quantify the complexity of the analyzed surfaces. The results indicate that surfaces with higher fractal dimensions exhibit greater scaling mass and higher adhesion force. The main polymorph observed was calcite. Additionally, it was noted that the texture orientation relative to the flow affects scaling, with higher scaling values observed on surfaces oriented perpendicular to the flow. These findings are crucial for optimizing material selection and surface treatments in deep-water oil exploration, enhancing operational efficiency and reducing costs. Full article

In this paper, we discuss options for the synthesis of granular free-binder ZSM-5 zeolites using synthetic aluminosilicates prepared by sol-gel technology with organic and inorganic silicon sources. It has been shown that the properties of the amorphous aluminosilicate used to prepare the initial granules influence the crystallization conditions, as well as the morphology and size of the crystals formed from granular ZSM-5 zeolite. The granular free-binder Pt/ZSM-5 with a developed secondary porous structure showed higher activity in the hydrocracking of hexadecane than the granular binder Pt/ZSM-5. At a reaction temperature of 220 °C, the conversion of n-hexadecane in the granular free-binder sample was 59.1%. At the same time, the selectivity for hexadecane isomers was 15.7%. Full article

Environmental pollution from organic dyes such as malachite green and rhodamine B poses significant threats to ecosystems and human health due to their toxic properties. The rapid detection of these contaminants with high sensitivity and selectivity is crucial and can be effectively achieved using nonlinear optical methods. In this study, we combine the Simplified Bond Hyperpolarizability Model (SBHM) and molecular docking (MD) simulations to investigate the Second-Harmonic Generation (SHG) intensity of organic dyes on a silicon (Si(001)) substrate for nanoscale pollutant detection. Our simulations show good agreement with rotational anisotropy (RA) SHG intensity experimental data across all polarization angles, with a total error estimate of 3%. We find for the first time that the SBHM not only identifies the different organic pollutant dyes on the surface, as in conventional SHG detection, but can also determine their relative orientation and different concentrations on the surface. Meanwhile, MD simulations reveal that rhodamine B shows a strong adsorption affinity of $-10.4\mathrm{kcal}/\mathrm{mol}$ to a single-layer graphene oxide (GO) substrate, primarily through $\pi$-$\pi$ stacking interactions (36 instances) and by adopting a perpendicular molecular orientation. These characteristics significantly enhance SHG sensitivity. A nonlinear susceptibility analysis reveals good agreement between the SBHM and group theory. The susceptibility tensors confirm that the dominant contributions to the SHG signal arise from both the molecular structure and the surface interactions. This underscores the potential of GO-coated silicon substrates for detecting trace levels of organic pollutants with interaction distances ranging from $3.75\AA$ to $5.81\AA$. This approach offers valuable applications in environmental monitoring, combining the sensitivity of SHG with the adsorption properties of GO for nanoscale detection. Full article

In this research work, the influence of the electrolyte hydrodynamic conditions on the corrosion mechanism of the high-strength low-alloy (HSLA) X100 steel used in the petroleum transportation pipelines was analyzed. A Rotary Cylinder Electrode (RCE) was used to simulate the hydrodynamic conditions (1000 and 5000 rpm). Mechanical, microstructural and elemental characterization tests were performed on X100 steel, and the electrochemical impedance spectroscopy (EIS) technique was used to analyze the corrosion mechanism, while the morphology of the corrosion process on the corroded surfaces was obtained by scanning electronic microscopy (SEM). It was found that the increasing rotation rate (υ rot) generates a fully developed flow regime where the system was dominated by a mass transfer process and increases the kinetics of chemical and electrochemical reactions so there is an increase in the corrosion rate (CR). On the other hand, the adsorption of corrosion product films that limits the charge transfer process depended on the magnitude of the shear stress that can generate wear and roughness, as well as a greater number of anodic sites, leaving the metal exposure to the corrosive medium. Full article

Aluminum–copper alloys are commonly used in the aerospace industry due to their low density and high strength. Pitting corrosion is the major problem of Al-Cu alloys due to the presence of largely separated electrochemical potential difference phases. Microstructure refinement and phase homogenization of the alloys are believed to be the factors that contribute to decreasing the galvanic coupling between phases, hence decreasing the pitting tendency. In this work, we investigate whether microstructure refinement is the only factor that contributes to pitting or whether some other factors are involved in the pitting tendency. The investigation was conducted on two frequently used aerospace aluminum–copper alloys, Al-2024 T3 and Al-2014 T6. The surface refinement was conducted by laser surface melting, and microstructure characterization was conducted by scanning electron microscopy with an energy-dispersive X-ray analysis. Phase identification before and after the laser surface melting was conducted by X-ray diffraction, while pitting tendency was measured by a polarization test in 1 molar sodium chloride solution. These experimental results revealed that the enrichment of copper in the α-matrix phase was the major contributing factor in pitting as compared to the largely believed microstructural phase refinement. Full article