Influence of marine Shewanella putrefaciens and mediated calcium deposition on Q235 carbon steel corrosion.

The microbiologically influenced corrosion inhibition (MICI) of Q235 carbon steel by Shewanella putrefaciens and mediated calcium deposition were investigated by regulating microbial mineralization. In a calcium-rich medium, S. putrefaciens rapidly created a protective calcium carbonate layer on the steel surface, which blocked Cl- diffusion. Without calcium, the biofilm and rust layer mitigated pitting corrosion but did not prevent Cl- penetration. Potentiodynamic polarization results indicated that the current densities (icorr values) of the corrosion produced in the S. putrefaciens-inoculated media with and without calcium were 0.4 µA/cm2 and 0.6 µA/cm2, respectively. Similarly, compared with those under sterile conditions, the corrosion inhibition rates were 92.2% and 87.4% higher, respectively. Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) confirmed that the MICI was caused by the combination of microbial aerobic respiration and the deposited layers. Even under nonbiological conditions, S. putrefaciens-induced calcium carbonate deposition inhibited corrosion.

Investigating Different Local Polyurethane Coatings Degradation Effects and Corrosion Behaivors by Talaromyces funiculosus via Wire Beam Electrodes.

The degradation effect of mold on the coating in a hot and humid environment is one of the important factors that cause layer failure. Combined with the wire beam electrode (WBE) and the traditional surface analysis technique, the local biodegradation of the coatings and the corrosion behaviors of metal substrates can be characterized accurately by a WBE. Herein, a WBE was used to study the degradation impact of Talaromyces funiculosus (T. funiculosus) isolated from a tropical rainforest environment on the corrosion of polyurethane (PU) coating. After immersion for 14 days, the local current density distribution of the WBE surface can reach ~10-3 A/cm2 in the fungal liquid mediums but maintains ~10-7 A/cm2 in sterile liquid mediums. The |Z|0.01Hz value of the high current densities area (#85 electrode) was 1.06 × 109 Ω cm2 in a fungal liquid medium after 14 days of immersion. After being attacked by T. funiculosus, the degradation of the PU was more severe, and there were wrinkles, cracks, blisters, and even micro-holes distributed randomly on the surface of electrodes. This resulted from the self-corrosion caused by the T. funiculosus degradation of the coating; the corrosion caused by the electric coupling effect of the coating was introduced. Energy dispersive spectroscopy (EDS) and Raman spectra results showed that the corrosion products were flakey and globular, which consisted of γ-FeOOH, γ-Fe2O3, and α-FeOOH.

Insight into Degrading Effects of Two Fungi on Polyurethane Coating Failure in a Simulated Atmospheric Environment.

Two different fungi, Talaromyces funiculosus (T. funiculosus) and Phanerochaete chrysosporium (P. chrysosporium), were collected from the Xishuangbanna atmospheric corrosion site and incubated on a polyurethane (PU) coating at 30 °C for two weeks under 95% relative humidity (RH). The biodegrading effects of these fungi on the coating failure were investigated from aspects of metabolism and electrochemistry. The results showed that T. funiculosus contributed more to the degradation of the PU coating failure than P. chrysosporium, and two factors played dominant roles. First, the weight of the T. funiculosus mycelium was nearly 3 times more than that of P. chrysosporium, indicating there was more substrate mycelium of T. funiculosus deep into the coatings to get more nutrition in atmospheric during colonization. Second, T. funiculosus secreted carboxylic acids, such as citric, propanoic, succinic, and tartaric acids, and accelerated the hydrolysis of the ester and urethane bonds in the PU coatings. As a result, the mycelium of T. funiculosus readily penetrated the interface of the coating and substrate resulting in a rapid proliferation. Thus, the |Z|0.01Hz value of the coating decreased to 5.1 × 104 Ω·cm2 after 14 days of colonization by T. funiculosus while the value remained at 7.2 × 107 Ω·cm2 after colonization by P. chrysosporium. These insights suggest that the biodegradation process in simulated atmospheric environments would provide theoretical guidance and directions for the design of antifungal PU coatings.

Matrine@chitosan-D-proline nanocapsules as antifouling agents with antibacterial properties and biofilm dispersibility in the marine environment.

Antifoulants are the most vital substances in antifouling coatings to prevent marine organisms from colonizing the undersea substrate surfaces. In addition to antibacterial performance, inhibition of biofilm formation is an important criterion for antifouling coatings. In this study, we synthesized pH-responsive matrine@chitosan-D-proline (Mat@CS-Pro) nanocapsules of about 280 nm with antibacterial properties and biofilm dispersibility. The prepared Mat@CS-Pro nanocapsules exhibited high-level antibacterial properties, reaching about 93, 88, and 96% for E. coli, S. aureus, and P. aeruginosa, respectively. Such nanocapsules can cause irreversible damage to bacteria and cause them to lose their intact cell structures. Moreover, Mat@CS-Pro nanocapsules also possessed outstanding dispersal biofilm performances, in which the biofilm thickness of E. coli, S. aureus, and P. aeruginosa was decreased by 33, 74, and 42%, respectively, after 3 days of incubation. Besides, the Mat@CS-Pro nanocapsules had remarkable pH-responsive properties. As the environmental pH became acidic, the nanocapsules swelled to about 475 nm and the released concentration could reach 28.5 ppm after immersion for 10 h but maintained a low releasing rate in pH 8 conditions.

Microbiologically influenced corrosion inhibition mechanisms in corrosion protection: A review.

Microbial activities can change the properties of biofilm/metal interfaces to accelerate or decelerate the corrosion of metals in a given environment. Microbiologically influenced corrosion inhibition (MICI) is the inhibition of corrosion that is directly or indirectly induced by microbial action. Compared with conventional methods for protection from corrosion, MICI is environmentally friendly and an emerging approach for the prevention and treatment of (bio)corrosion. However, due to the diversity of microorganisms and the fact that their metabolic processes are greatly complicated by environmental factors, MICI is still facing challenges for practical application. This review provides a comprehensive overview of the mechanisms of MICI under different conditions and their advantages and disadvantages for potential applications in corrosion protection.

Facile synthesis of BTA@NiCo2O4 hollow structure for excellent microwave absorption and anticorrosion performance.

A three-dimensional hollow NiCo2O4 structure was successfully prepared with a precipitation-hydrothermal method. A balance between magnetic and dielectric losses was achieved by using a hollow NiCo2O4 structure loaded with benzotriazole (BTA), and thus the performance of electromagnetic waves was attenuated. The minimum reflection loss value of BTA@NiCo2O4 at 16.01 GHz was -35.39 dB when the absorber thickness was 2 mm, at which the absorption bandwidth for an RL of less than -10 dB is as high as 4.64 GHz. The absorption mechanism was characterized by the synergy among interfacial polarization, multiple reflection, and dipole polarization enhancement between NiCo2O4 and BTA. Interestingly, the epoxy/BTA@NiCo2O4 coating not only exhibited an outstanding microwave absorption (MA) performance but also has excellent anticorrosion and self-healing properties, as shown by the results of electrochemical impedance spectroscopy and confocal laser scanning microscopy. This work would be very helpful to the development of novel coatings with excellent MA performance and anticorrosion and self-healing properties.

Self-Healing Coatings Containing Core-Shell Nanofibers with pH-Responsive Performance.

The micro-nanofibers prepared by the electrospinning technique can be used as a good container for loading healing agents. The core-shell electrospun nanofibers with polyacrylonitrile as the outer shell and tannic acid (TA) and tung oil as the core healing agents were synthesized by a coaxial electrospinning method and exhibited pH-sensitive ability. The nanofibers as additives were added to an epoxy resin coating as a self-healing coating. The morphological stability of the electrospun nanofibers were observed by a scanning electron microscope and a transmission electron microscope. Fourier transform infrared spectroscopy and fluorescence microscopy reveal that the successful synthesis and uniform distribution of core-shell fibers. The mechanical properties test revealed that the tensile properties of the coating could be improved by adding nanofibers. The infrared mapping test, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy, which were carried out on the scratched part of the coating, proved the release of the healing agent in the damaged part. TA forms a protective film on the exposed metal surface through molecular adsorption under acidic conditions. Meanwhile, the curing of tung oil can effectively compensate into the microcracks to form a TA protective film, which could improve the self-healing performance. As the tung oil dries and solidifies in the alkaline solution, the cross-linking effect of the molecules is combined to form a tight film and strength the self-healing ability. TA as an acidic healing agent and tung oil as an alkaline healing agent played the role of pH-sensitive products in healing the cracked coating. The self-healing rates of coating immersing in 3.5 wt % acidic NaCl solution and alkaline solution were 81.6 and 71.2%, respectively. The composite coating shows a great pH-sensitive self-healing ability to heal the cracked coating.

Narrow pH response multilayer films with controlled release of ibuprofen on magnesium alloy.

An intelligent narrow pH-triggered multilayer film was prepared on magnesium alloys, aiming to solve the implant infections during the implantation period and improve the corrosion resistance of magnesium alloys. The encapsulation of ibuprofen by chitosan (IBU@CS) makes the release of IBU sensitive to narrow pH (pH 6.8-7.4). Positive charged IBU@CS was assembled with heparin (Hep) to fabricate (Hep/IBU@CS)10 film on AZ31 alloys using layer-by-layer method. The microstructure, composition and anticorrosion properties of the film were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and electrochemical experiments. Cellular activity was studied by MTT cell viability assay. The results showed that the Hep/IBU@CS multilayer films improved the corrosion resistance of magnesium alloys. The in vitro test demonstrated that the release of IBU in the film presented narrow pH sensitivity. The films showed no obvious signs of cytotoxicity conformed by the MTT assay and presented antibacterial properties. These preliminary results demonstrate the potential use of the Hep/IBU@CS multilayer films on magnesium-based implants.

Antifouling and antibacterial behaviors of capsaicin-based pH responsive smart coatings in marine environments.

Antifouling biocides releasing restricts the longevity of antifouling coatings. Compared with the anchoring state, the releasing behavior of agents is much faster on the voyage, while the biofouling process is tougher. In this work, a series of capsaicin-based pH-triggered polyethylene glycol/capsaicin@chitosan (PEG/CAP@CS), polyvinyl alcohol (PVA)/CAP@CS and alginate (ALG)/CAP@CS multilayer films are prepared with controlling antimicrobial properties in marine environments. There are 23.70, 23.35 and 22.06 ppb CAP releasing from (PVA/CAP@CS)20, (PEG/CAP@CS)20 and (ALG/CAP@CS)20 films after immersing in pH 4 solutions for 60 days, while only 13.07, 12.95 and 11.55 ppb CAP have been found in alkaline solutions after immersing for the same time, respectively. All these three types of films exhibit extraordinary pH responsive properties. They can control the CAP release at a low level in alkaline solutions, and make the CAP release fast in acid solutions. Moreover, the antibacterial properties against P.aeruginosa are outstanding about 95.84%, 95.0% and 96.91% for (PVA/CAP@CS)20, (PEG/CAP@CS)20 and (ALG/CAP@CS)20 films, respectively. The bacteriostasis of (ALG/CAP@CS)20 film keeps 92.73% after 60 days in alkaline solution, which means it is steadily controlled in the marine environment. Although with similar antibacterial properties to those of (PEG/CAP@CS)20 film, (PVA/CAP@CS)20 film displays the maximum decrease with about 92% in acid solution after 60 days. The ALG/CAP@CS film with the best-controlled release performance and long-term antibacterial properties provides novel guidance for developing new antifouling coatings application in the marine environment.

Fabrication of Cu2O-Ag nanocomposites with enhanced durability and bactericidal activity.

Hybrid Cuprous oxide-silver (Cu2O-Ag) have attracted tremendous attention due to their various applications in photocatalysis, surface enhanced Raman scattering (SERS), and optical features. Here we expanded the application to exhibit excellent chemical stability and synergistic bactericidal. We prepared Cu2O-Ag heterostructure through thermally decomposing Ag-acetate to deposit Ag nanoparticles (Ag NPs) onto Cu2O surface. Cu2O-Ag heterostructure bears exceptional stability while exposing to oxygen, water, and light, owing to the physical coating of Ag NPs and transferring the electrons and holes inside the Cu2O to the surface through a Schottky barrier to prevent photocorrosion. The deposition of Ag NPs also improved the intensity and time of oxidative stress reaction of Cu2O, proved by reactive oxygen species (ROS) examination. Ag NPs distributed on the surface of Cu2O particles formed a large of ion release channel, resulting in excellent sustained release of copper ions. Density functional theory (DFT) calculations were used to investigate the mechanism of photocatalysis and ROS generation. The constructed Cu2O-Ag heterostructure exhibit highly long-term sterilization activity against Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) which were maintained around 70% and 80% and were increased by 40% and 50% compared with free Cu2O after being immersed in phosphate buffer saline (PBS) solutions within 14 days.

Zinc oxide/vanadium pentoxide heterostructures with enhanced day-night antibacterial activities.

Low photocatalytic efficiency of visible light and fast recombination of photo-generated carriers are two challenges facing the applications of photocatalyst sterilant zinc oxide (ZnO). Meanwhile, both light and dark photocatalytic activities are important. It is of great theoretical and practical significance to construct a day-night photocatalytic antibacterial material, which is beneficial to the effective use of energy and to tackle the limitation of using photocatalytic bacteriostat. ZnO nanoflowers decorated vanadium pentoxide (V2O5) nanowires heterojunction (ZVH) was firstly fabricated using a facile water-bathing method. The designed ZVH structure efficiently produced abundant reactive oxygen species (ROS) in both light and darkness. It yielded 99.8% and 99.0% of antibacterial rate against S. aureus due to oxidative stress induced by ROS in light and darkness, respectively. The generation of ROS played a major role in the antibacterial activities against S. aureus under both light and dark conditions. The prepared ZVH with improved antibacterial properties provides an alternative for day-night antibacterial agents.

Long-term antibacterial stable reduced graphene oxide nanocomposites loaded with cuprous oxide nanoparticles.

Stable reduced graphene oxide-cuprous oxide (rGO-Cu2O) nanocomposites with long-term antibacterial activities were prepared by reducing copper sulfate supported on GO using ascorbic acid as reducing agent in the presence of polyethylene glycol (PEG) and sodium hydroxide at room temperature. The rGO provided a protective barrier for Cu2O, preventing Cu2O from reacting with external solution to leach copper ions too quickly. Meanwhile, the rGO also promoted the separation of photoexcited charge carriers of Cu2O nanoparticles to enhance the oxidative stress reactive and protected Cu2O from falling apart in the phosphate buffered solution (PBS) solution to prolong the generation time of reactive oxygen species (ROS). More importantly, the large specific surface area of rGO improved the dispersibility of Cu2O by electrostatic interaction. The synergistic effect of sustained release of copper ions, elevated ROS production ability and uniform dispersion of rGO-Cu2O nanocomposites resulted in the excellent antibacterial activities of rGO-Cu2O nanocomposites against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) which were maintained around 70% and 65% and were increased by 40% and 35% compared with free Cu2O after immersing 30 days in PBS solutions.