Search Results (42)

To elucidate the effects of TiO₂ nanoparticles on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coatings formed on 6061 aluminum alloy, MAO coatings were prepared in a silicate-based electrolyte with varying TiO₂ nanoparticle concentrations. The coating structure and properties were evaluated using a coating thickness gauge, surface profilometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and an electrochemical workstation. The results show that, with increasing TiO₂ content, both coating thickness and surface roughness gradually increase, while the surface porosity first decreases and then increases. An appropriate amount of TiO₂ effectively lowers the surface porosity and enhances coating compactness. The T₁ condition exhibited the least precipitation of corrosion products during immersion tests and thus the best corrosion resistance. Compared to the untreated 6061 aluminum alloy substrate, the optimized coating demonstrated a reduction in corrosion current density (J_corr) by more than one order of magnitude, reaching 1.127 × 10⁻⁶ A·cm⁻², while its polarization resistance (R_p) increased by over one order of magnitude, attaining 3.558 × 10⁴ Ω·cm². Furthermore, relative to the TiO₂-free T₀ coating, the J_corr of the optimized coating was further reduced by approximately 2.5 times, with its R_p enhanced by about 2.3 times. XRD analysis indicated that the MAO coatings primarily consist of α-Al₂O₃ and γ- Al₂O₃. This study provides theoretical and experimental support for the application of TiO₂ nanoparticles in MAO processes. Full article

Background/Objectives: In this study, three antimicrobial peptides (1–3) were conjugated onto bare aluminum nanoparticles (NP) to produce peptide-conjugated nanoparticles (NP1–NP3) in order to evaluate their biological effects. Methods: The peptide-functionalized Al₂O₃ nanoparticles were characterized and subsequently analyzed for their antimicrobial activity against selected bacterial strains. The findings were compared with those of bare Al₂O₃ nanoparticles and free antimicrobial peptides. Through this comparison, the enhanced impact of combining nanoparticles with peptides in addressing antimicrobial resistance was demonstrated. Additionally, biofilm inhibition, microbial cell viability inhibition, DNA cleavage, antioxidant, and amylolytic activity assays were performed to comprehensively evaluate the biological functionality of the synthesized nanoparticles. Results: Although all tested samples exhibited significant antimicrobial activity, peptide-conjugated nanoparticles NP1, NP2, and NP3 provided superior activity with an MIC value of 16 mg/L. The highest biofilm inhibition activities were observed for NP2 as 53% and 70% against S. aureus and P. aeruginosa, respectively. Additionally, NP1–NP3 inhibited microbial cell viability by 100% at a concentration of 6.25 mg/L and free peptide 3 displayed E. coli inhibition as 100% at a concentration of 12.5 mg/L. Furthermore, we evaluated the biological potential of antimicrobial peptide-functionalized Al₂O₃ nanoparticles through antibiofilm, antioxidant, antidiabetic activities, and DNA cleavage assays. Peptide-conjugated nanoparticles NP1, NP2, and NP3 exhibited the highest antioxidant activities as 43.70%, 45.22%, and 59.57%, respectively. Except for NP3, the compounds were observed to act as α-amylase enzyme activators. NP and NP1–NP3 completely degraded the supercoiled circular form into small pieces. Conclusions: Our findings suggest that peptide–aluminum nanoparticle conjugation may be a promising formulation for enhancing biological activity. Further in vitro and in vivo tests may help clarify the therapeutic potential of this novel nanoformulation. Full article

Titanium alloys are widely employed in structural and electrochemical applications owing to their excellent mechanical properties and inherent corrosion resistance. However, their stability in harsh acidic environments, such as those encountered in energy storage systems, remains a critical issue. In this study, composite ceramic coatings were synthesized on a Ti6Al4V alloy using plasma electrolytic oxidation (PEO) in silicate-, phosphate-, and sulfate-based electrolytes, with and without the addition of α-alumina nanoparticles. The resulting coatings were comprehensively characterized to assess their surface morphology, chemical and phase compositions, and corrosion performance. Thus, the corrosion current density decreased from 9.7 × 10⁴ for bare Ti6Al4V to 143 nA/cm² for the coating fabricated in phosphate electrolyte with alumina nanoparticles, while the corrosion potential shifted anodically from –0.68 to +0.49 V vs. silver chloride electrode in 5 M H₂SO₄. Among the tested electrolytes, coatings produced in the phosphate-based electrolyte with Al₂O₃ showed the highest polarization resistance (113 kΩ·cm²), outperforming those fabricated in silicate- (71.6 kΩ·cm²) and sulfate-based (89.0 kΩ·cm²) systems. The composite coatings exhibited a multiphase structure with reduced surface porosity and the incorporation of crystalline oxide phases. Notably, titania–alumina nanoparticle composites demonstrated significantly enhanced corrosion resistance. These findings confirm that PEO-derived composite coatings provide an effective surface engineering strategy for enhancing the stability of the Ti6Al4V alloy in aggressive acidic environments relevant to advanced electrochemical systems. Full article

Endocytic uptake and lysosomal localization are suggested to be the key mechanisms underlying the toxicity of metal oxide nanoparticles (MONPs), with dissolution in the acidic milieu driving the response. In this study, we aimed to investigate if MONPs of varying solubility are similarly sequestered intracellularly, including in lysosomes and the role of the acidic lysosomal milieu on toxicity induced by copper oxide (CuO) nanoparticles (NPs), nickel oxide (NiO) NPs, aluminum oxide (Al₂O₃) NPs, and titanium dioxide (TiO₂) NPs of varying solubility in FE1 lung epithelial cells. Mitsui-7 multi-walled carbon nanotubes (MWCNTs) served as contrasts against particles. Enhanced darkfield hyperspectral imaging (EDF-HSI) with fluorescence microscopy was used to determine their potential association with lysosomes. The v-ATPase inhibitor Bafilomycin A1 (BaFA1) was used to assess the role of lysosomal acidification on toxicity. The results showed co-localization of all MONPs with lysosomes, with insoluble TiO₂ NPs showing the greatest co-localization. However, only acute toxicity induced by soluble CuO NPs was affected by the presence of BaFA1, showing a 14% improvement in relative survival. In addition, all MONPs were found to be associated with large actin aggregates; however, treatment with insoluble TiO₂ NPs, but not soluble CuO NPs, impaired the organization of F-actin and α-tubulin. These results indicate that MONPs are sequestered similarly intracellularly; however, the nature or magnitude of their toxicity is not similarly impacted by it. Future studies involving a broader variety of NPs are needed to fully understand the role of differential sequestration of NPs on cellular toxicity. Full article

The adsorption and reaction of nitric oxide (NO) molecules on the surface of the model-supported metal/oxide system, consisting of Ni nanoparticles deposited on α-Al₂O₃ (0001) in ultra-high vacuum, have been studied using in situ surface-sensitive techniques and density functional theory (DFT) calculations. As a combination of X-ray and Auger electron spectroscopy (XPS, AES), Fourier-transform infrared (FTIR) spectroscopy, and temperature-programmed desorption (TPD) techniques reveals, there is a threshold of Ni particle mean size (<d>) of c.a. 2 nm, differentiating the electron state of adsorbed NO molecules and their reaction. The main feature of Ni particles normally not exceeding 2 nm is that the NO adsorbs in the form of (NO)₂ dimers, whereas, for larger particles, the NO molecules adsorb in the form of monomers, usually characteristic for the bulk Ni substrate. This difference is demonstrated to be the main reason for the different reaction of NO molecules on the surface of Ni/alumina. The striking feature is that, in the case of ultra-small Ni particles (<d> ≤ 2 nm), the nitrous oxide (N₂O) molecules are formed upon heating as a result of the NO self-reduction mechanism, which are otherwise not formed in the case of larger Ni particles. According to DFT results, this is due to the significant synergistic impact of NO co-adsorption on the neighboring NO dissociation reaction over ultra-small Ni particles, mediated by the metal/oxide perimeter interface. The observed molecular conversion effects offer an opportunity to tune the catalytic selectivity of this and related metal/oxide systems via varying the supported metal particle size. Full article

Batch heterogeneous catalytic ozonation experiments were performed using commercial and synthesized nanoparticles as catalysts in aqueous ozone. The transferred ozone dose (TOD) ranged from 0 to 150 μM, and nanoparticles were added in concentrations between 0 and 1.5 g L⁻¹, with all experiments conducted at 20 °C and a total volume of 240 mL. A Ce-doped TiO₂ catalyst (1% molar ratio of Ce/Ti) was synthesized via the sol–gel method. Response surface methodology (RSM) was applied to identify the most significant factors affecting the removal of selected pharmaceuticals, with TOD emerging as the most critical variable. Higher TOD resulted in greater removal efficiencies. Furthermore, it was found that the commercially available metal oxides α-Al₂O₃, Mn₂O₃, TiO₂, and CeO₂, as well as the synthesized CeTiO_x, did not increase the catalytic activity of ozone during the degradation of ibuprofen (IBF) and para-chlorobenzoic acid (pCBA). Carbamazepine (CBZ) and diclofenac (DCF) are compounds susceptible to ozone oxidation, thus their complete degradation at 150 μM transferred ozone dose was attained. The limited catalytic effect was attributed to the rapid consumption of ozone within the first minute of reaction, as well as the saturation of catalyst active sites by water molecules, which inhibited effective ozone adsorption and subsequent hydroxyl radical generation (^●OH). Full article

The synthesis of Al-ZnO nanoparticles (NPs) was achieved using a green synthesis approach, utilizing leaf extract from Anisomeles indica (L.) in a straightforward co-precipitation method. The goal of this study was to investigate the production of Al-ZnO nanoparticles through the reduction and capping method utilizing Anisomeles indica (L.) leaf extract. The powder X-ray diffraction, UV spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy with EDAX analysis were used to analyze the nanoparticles. X-ray diffraction analysis confirmed the presence of spherical structures with an average grain size of 40 nm in diameter, while UV–visible spectroscopy revealed a prominent absorption peak at 360 nm. FTIR spectra demonstrated the presence of stretching vibrations associated with O-H, N-H, C=C, C-N, and C=O as well as C-Cl groups indicating their involvement in the reduction and stabilization of nanoparticles. SEM image revealed the presence of spongy, spherical, porous agglomerated nanoparticles, confirming the chemical composition of Al-ZnO nanoparticles through the use of the EDAX technique. Al-ZnO nanoparticles showed increased bactericidal activity against both Gram-positive and Gram-negative bacteria. The antioxidant property of the green synthesized Al-ZnO nanoparticles was confirmed by DPPH radical scavenging with an IC₅₀ value of 23.52 indicating excellent antioxidant capability. Green synthesized Al-ZnO nanoparticles were shown in in vivo studies on HeLa cell lines to be effective for cancer treatment. Additionally, α-amylase inhibition assay and α-glucosidase inhibition assay demonstrated their potent anti-diabetic activities. Moving forward, the current methodology suggests that the presence of phenolic groups, flavonoids, and amines in Al-ZnO nanoparticles synthesized with Anisomeles indica (L.) extract exhibit significant promise for eliciting biological responses, including antioxidant and anti-diabetic effects, in the realms of biomedical and pharmaceutical applications. Full article

A series of nanocrystalline iron oxide samples (M1–M5) which differ from each other in average crystallite size (from 26 to 37 nm) was studied. The raw material was nanocrystalline iron with an average crystallite size equal to 21 nm promoted with hardly reducible oxides: Al₂O₃, CaO, K₂O (in total, max. 10 wt%). Nanocrystalline iron was subjected to oxidation with water vapor to achieve different oxidation degrees (α = 0.16–1.00). Metallic iron remaining in the samples after the oxidizing step was removed by etching. Magnetic resonance spectra of all samples were obtained at room temperature. All resonance lines were asymmetric and intense. These spectra were fitted by Lorentzian and Gaussian functions. All spectral parameters depend on the preparation method of the nanoparticles. We suppose that the Lorentz fit gives us a spectrum from larger agglomerated sizes whereas the Gaussian fit comes from much smaller magnetic centers. For the nanocrystalline samples with the largest size of iron oxide nanocrystallites, the highest value of total integrated intensity was obtained, indicating that at smaller sizes, they are more mobile in reorientation processes resulting in more settings of anti-parallel magnetic moments. The magnetic anisotropy should also increase with the increase in size of nanocrystallites. Full article

A new type of multiphase nanoparticle-reinforced TiAl matrix composites ((Ti₂AlC + Al₂O₃)_p/TiAl composites) was successfully prepared by vacuum hot-pressing sintering using Ti powder and Al powder, which were ball-milled with different contents of stearic acid (CH₃(CH₂)₁₆COOH). The component, microstructure, reaction mechanism, and mechanical properties were studied. The results indicated that the composites prepared by adding stearic acid as a process control agent during the ball-milling process not only contained γ-TiAl and α₂-Ti₃Al phases but also Ti₂AlC and Al₂O₃ phases. The results of SEM and TEM showed that the composites were composed of equiaxed TiAl and Ti₃Al grains, and the Ti₂AlC and Al₂O₃ particles were mainly distributed along the TiAl grain boundary in chain form, which can effectively reduce the TiAl grain size. Through the room-temperature compression test, the maximum compression stress was significantly improved in those composites that added the stearic acid, due to the reinforcement particles. The maximum compression stress was 1590 MPa with a 24.3% fracture strain. In addition, the generated crack deflection and Ti₂AlC and Al₂O₃ particles could also enhance the toughness of the TiAl alloy. (Ti₂AlC + Al₂O₃)_p/TiAl composites generated by adding stearic acid played a key role in improving the mechanical properties of the TiAl matrix. Full article

For the tribological properties of nanoparticle-modified PTFE, a more comprehensive study has been conducted, but there is still some room for research on tribology behavior, tribofilm formation and structure evolution of polytetrafluoroethylene (PTFE) filled with α-Al₂O₃ and SiO₂ nanoparticles during sliding against steel counterparts under different loads. At the same time, it establishes the linkage and mechanism between the maintenance of mechanical strength and the tribological application of polymers in service and provides corresponding scientific data and theoretical guidance for the long-lasting application of polymer lubrication materials. It is found that both composites exhibit good wear resistance across the pressure of 1 MPa to 10 MPa, with the α-Al₂O₃/PTFE composite demonstrating better performance stability compared to the SiO₂/PTFE composite. The high wear resistance is attributed to the formation of tribofilms at the friction interface. For the α-Al₂O₃/PTFE, an island-like tribofilm is formed with a thickness ranging from 100 to 200 nm, while the tribofilm of the SiO₂/PTFE composite is thinner, measuring approximately 50 to 100 nm, and manifests a striped pattern. The chemical composition, both at the surface and subsurface levels, as well as the morphology of the tribofilms, were studied using FTIR spectrometry, X-ray photoelectron spectroscopy (XPS), and FIB-TEM. It is found that the difference in thickness and microstructure of the tribofilms for the two composites is mainly due to the tribochemistry of the nanoparticles. The α-Al₂O₃ nanoparticle plays a “cohesion” role during the formation of the tribofilm, which facilitates the formation of a thicker, more uniform, and stronger adhered tribofilm on the metallic counterpart, making it more robust against higher shear stress. Full article

The oxidation of β-NiAl at high temperatures leads to the preferential formation of metastable alumina, such as θ-Al₂O₃, which exhibits a significantly faster growth rate compared to stable α-Al₂O₃. However, our recent research has shown that through the use of the surface-dispersing nanoparticles (NPs) of metal oxides with a hexagonal closed pack (hcp), such as α-Al₂O₃, the thermal growth of α-Al₂O₃ can be facilitated. The present study employed laser additive manufacturing (LAM) to develop an integrated α-Al₂O₃ NPs surface-seeded two-phase intermetallic alloy comprising brittle β-NiAl and tougher γ’-Ni₃Al, which demonstrated better comprehensive mechanical properties. It was found that seeding the α-Al₂O₃ NPs promoted the early stage growth of α-Al₂O₃ on both β and γ’ phases during oxidation in air at 1000 °C. This led to a decrease in the oxidation rate but an enhancement in adhesion of the formed alumina scale in comparison to the naked β/γ’ two-phase alloy. The reasons for this result were interpreted. Full article

In order to study the application of nanofluids for enhancing heat transfer in the field of liquid-cooled data centers, a mathematical and physical model of liquid-cooled servers was established in this paper. FC–40 was used as the server cooling liquid base, and simulation studies were conducted on the flow and heat transfer of five types of nanofluid: Cu–FC40, CuO–FC40, Al–FC40, Al₂O₃–FC40, and TiO₂–FC40. The results showed that using Al–FC40 nanofluids as the cooling medium had the best heat transfer effect. Under the same operating conditions, the average Nusselt number Nu and friction resistance coefficient f of five types of nanofluid were analyzed, and the heat transfer state of Al–FC40 nanofluid had the smallest f. Further analysis was conducted on the influence of ‘nanoparticle volume fraction’ α and ‘server inlet flow rate’ u on fluid flow and heat transfer. Our research found that an increase in α and the acceleration of u can effectively reduce the surface temperature of server components. As u increases, Nu gradually increases and f generally decreases, but the amplitude of the increase and decrease becomes smoother. Full article

Enhanced oil recovery using nanoparticles is a promising method. However, when injected into a reservoir, nanoparticles can block pores and cause permeability damage. Therefore, enhancing their performance to lower the permeability damage effect is crucial. This study investigated the effect of pH alteration through carbon dioxide (CO₂) injection on the permeability damage of limestone caused by an aluminum oxide (α-Al₂O₃) nanofluid. The methodology involved nanofluid alternating CO₂ core flooding experiments by using nanofluids with a pH of 4.5 and 2.8. After core flooding, the permeability damage was calculated as a percentage of the reduction in the original permeability. The results revealed that the permeability damage in the case of nanofluid alternating CO₂ injection was 23.23%. In the nanofluid with a pH of 4.5 injection case, the permeability damage was 47.53%. In the 2.8 pH nanofluid injection case, the permeability damage was 31.01%. The retention of nanoparticles was confirmed through scanning electron microscopy and energy dispersive X-ray analysis. Permeability damage could be attributed to the large nanoparticles’ agglomeration size, roughness of pore surfaces, and nanoparticle sedimentation. The results of the study revealed that altering pH through the α-Al₂O₃ nanofluid alternating CO₂ injection can effectively reduce the permeability damage of limestone. Full article