Effect of B. subtilis in simulated acid red soil on the corrosion behavior of X80 pipeline steel.

The eastern section of China's West-east gas transmission project is laid in acidic red soil. NRB are widespread in soils and play an important role in metal corrosion. In this article, the corrosion failure behavior and mechanism of X80 pipeline steel under the action of NRB in simulated acidic soil were studied. It was found that the biofilm of B. subtilis had significant inhibitory on the overall corrosion of X80 steel. Electrochemical results prove that the corrosion rate of the sterile group after 14 days of immersion was about 4.5 times that of the bacterial group. However, the biofilm promotes the formation of local corrosion pits. Confocal laser scanning microscopy images indicate that that the corrosion pit depth of the bacterial group (46.1 µm) was three times that of the bacterial-free group (15.7 µm) after 14 days. The pH of the acidic environment was slightly improved by B. subtilis. XPS results proved that B. subtilis complicates the corrosion products of X80 steel through its nitrate reduction ability and metabolism.

A Bifunctional BiOBr/ZIF-8/ZnO Photocatalyst with Rich Oxygen Vacancy for Enhanced Wastewater Treatment and H2O2 Generation.

Photocatalytic technology is considered an ideal approach for clean energy conversion and environmental pollution applications. In this work, a bifunctional BiOBr/ZIF-8/ZnO photocatalyst was proposed for removing phenols in wastewater and generating hydrogen peroxide. Insights from scanning electron microscopy measurements revealed the well-dispersion of ZIF-8/ZnO was on the BiOBr layer, which could effectively prevent agglomeration of ZIF-8 and facilitate the separation of carriers. In addition, the optimal H2O2 yield of the BiOBr/ZIF-8/ZnO sample could reach 116 mmol·L-1·g-1 within 2 h, much higher than that of pure BiOBr (with the value of 82 mmol·L-1·g-1). The optimal BiOBr/ZIF-8/ZnO sample could also remove 90% of the phenol or bisphenol A in 2 h, and its kinetic constants were 3.8 times and 2.3 times that of pure BiOBr, respectively. Based on the analysis of the various experimental characterizations, the photocatalytic mechanism of the S-scheme BiOBr/ZIF-8/ZnO composite for the degradation of phenolic pollutants and generation of H2O2 was proposed. The formation of the heterojunction and the oxygen vacancy work together to significantly improve its photocatalytic efficiency. In addition, the BiOBr/ZIF-8/ZnO catalyst has a certain impact on the degradation of phenol in actual wastewater, providing a way to effectively remove refractory pollutants and generate H2O2 in actual water.

Extracellular electron transfer routes in microbiologically influenced corrosion of X80 steel by Bacillus licheniformis.

Bacillus licheniformis can take up electrons from X80 steel for nitrate reduction and accelerate corrosion. In this work, the routes B. licheniformis adopts for extracellular electron transfer (EET) were revealed using electrochemical tests, fluorescence staining, high performance liquid chromatography (HPLC) and weight loss tests, and their kinetics were also analyzed in detail. The results showed that B. licheniformis can take up electrons from steel surface via three routes: direct electron transfer by cytochromes, direct electron transfer by flavin-bound cytochromes and mediated electron transfer by diffusible flavin. B. licheniformis itself can only secrete traces of riboflavin which are mainly bound to the surface cytochromes assisting electron transfer. Adding flavins can increase the bound content, and with the binding sites of cytochrome becoming saturated the rest of flavins will mediate electron transfer through diffusion even more efficiently than the bound.

Hydroxyl regulating effect on surface structure of BiOBr photocatalyst toward high-efficiency degradation performance.

Herein, photocatalytic degradation of levofloxacin hydrochloride (LVF) by a simple surface hydroxyl strategy on BiOBr photocatalyst was studied under simulated visible light irradiation. Interestingly, the BiOBr contained abundant hydroxyl groups following its modification with glucose, which enhanced the photocatalytic degradation of levofloxacin hydrochloride (LVF). The degradation efficiency of LVF over the optimized composite of BiOBr-5 could reach 91.67% in 20 min, which was much higher than that of pristine BiOBr (59.26%). Following, the biotoxicity of antibiotics to Escherichia coli DH5a could be eliminated after LVF photocatalytic degradation. This strategy proposed in this work can provide new ideas for tuning the surface structures of photocatalysts via specific functional groups for the highly efficient degradation and efficient removal of antibiotics in wastewater.

Dual-functional Z-scheme CdSe/Se/BiOBr photocatalyst: Generation of hydrogen peroxide and efficient degradation of ciprofloxacin.

The major challenges of clean energy and environmental pollution have resulted in the development of photocatalysis technologies for energy conversion and the degradation of refractory pollutants. Herein, a novel CdSe/Se/BiOBr hydrangea-like photocatalyst was used to produce hydrogen peroxide (H2O2) and degrade ciprofloxacin (CIP). The Z-scheme heterojunction structure of the photocatalyst and the doping of selenium (Se) led to the efficient separation of electron-hole pairs and charge transfer. The optimized sample of 2 wt% CdSe/Se/BiOBr produced 142.15 mg·L-1 rate of H2O2, which was much higher than that produced by pure BiOBr (89.4 mg·L-1) or CdSe/Se (10.9 mg·L-1). Additionally, almost 100 % of CIP was degraded within 30 min, with a first order rate constant of nearly 5.35 times that of pure BiOBr and 81.44 times that of pure CdSe/Se. The excellent removal efficiency of CIP from natural water matrices confirmed that the composites are promising for the removal of contaminants from natural waterways. Based on trapping experiments, electron spin resonance spectra (ESR) spectroscopy, and density functional theory (DFT) calculations, the photocatalytic mechanisms of H2O2 and CIP degradation by the Z-scheme CdSe/Se/BiOBr composites were proposed. Overall, the dual-functional CdSe/Se/BiOBr composite could potentially be applied for photocatalytic production of H2O2 and treatment of organic pollutants in water.

Characteristic and Mechanistic Investigation of Stress-Assisted Microbiologically Influenced Corrosion of X80 Steel in Near-Neutral Solutions.

The behavior and mechanisms of the stress-assisted microbiologically influenced corrosion (MIC) of X80 pipeline steel induced by sulfate-reducing bacteria (SRB) were investigated using focused ion beam-scanning electron microscopy (FIB). Electrochemical results show that SRB and stress have a synergistic effect on the corrosion of X80 steel. SRB accelerated the transformation of Fe3O4 into iron-sulfur compounds and may have caused the film breakage of X80 steel products. The obtained FIB results provide direct evidence that SRB promotes the corrosion of X80 steel.

Influence of NaCl concentration on microbiologically influenced corrosion of carbon steel by halophilic archaeon Natronorubrum tibetense.

The influence of NaCl concentration on microbiologically influenced corrosion (MIC) of Q235 carbon steel by the halophilic archaeon Natronorubrum tibetense was investigated by immersion tests and electrochemical measurements. An increase in NaCl concentration from 0 g/mL to 0.1 g/mL promoted the anodic dissolution of carbon steel and accelerated its corrosion, but MIC did not occur. A further increase in NaCl concentration to 0.2 g/mL led to MIC in inoculated medium, and the occurrence of the MIC resulted in further aggravation of carbon steel corrosion. Once the NaCl concentration reached 0.3 g/mL, the high concentration of chloride ions greatly interfered with the adsorption of dissolved oxygen and the attachment of N. tibetense cells to the surface of carbon steel, thus reducing the corrosion rate of carbon steel and inhibiting the MIC.

Study of biofilm-influenced corrosion on X80 pipeline steel by a nitrate-reducing bacterium, Bacillus cereus, in artificial Beijing soil.

The biofilm of Bacillus cereus on the surface of X80 pipeline steel was investigated from forming to shedding. Based on the observed biofilm morphology and pit analysis, it was found that B. cereus biofilm could stimulate X80 pipeline steel pitting corrosion, which was attributed to the nitrate reduction of bacteria beneath the biofilm. Electrochemical measurements and general corrosion rate results showed that B. cereus biofilm can better accelerate X80 pipeline steel corrosion compared to sterile solutions. Interestingly, the results also showed that thick biofilms had a slight tendency to inhibit the general corrosion process compared with its formation and exfoliation, which was confirmed by scanning Kelvin probe. The corrosion rate of X80 pipeline steel in artificial Beijing soil is closely related to the state of the biofilm, and nitrate reducing bacteria accelerates the occurrence of pits. The corresponding corrosion mechanisms are proposed.

Microbiologically influenced corrosion of X80 pipeline steel by nitrate reducing bacteria in artificial Beijing soil.

In this work, we investigated microbiologically influenced corrosion (MIC) of X80 pipeline steel caused by nitrate-reducing bacteria Brevibacterium frigoritolerans (B. frigoritolerans) in an artificial Beijing soil using electrochemical measurements and surface analyses under aerobic conditions. The B. frigoritolerans was isolated from the surrounding soil of the X80 pipeline steel specimen in Beijing using culturing and molecular biology techniques. Confocal laser scanning microscopy images showed that the largest pit depth after 14 days due to B. frigoritolerans was approximately 7.16 µm. Electrochemical tests showed that the B. frigoritolerans could change the stability of the corrosion products on the 7th day. Inhomogeneous biofilm and the conductivity of Fe2O3 accelerated the corrosion process. The presence of NH4+ on the surface of the X80 pipeline steel revealed that the B. frigoritolerans acted as a biological cathode to promote the cathodic reaction.

Microbiologically influenced corrosion of 304 stainless steel by nitrate reducing Bacillus cereus in simulated Beijing soil solution.

In this work, microbiologically influenced corrosion (MIC) of 304 stainless steel (SS) caused by Bacillus cereus was investigated by electrochemical measurements and surface analyses in simulated Beijing soil solution under aerobic condition. The nitrate-reducing bacterium (NRB), B. cereus, was isolated from Beijing soil and identified using 16S rDNA. Confocal laser scanning microscopy (CLSM) images showed that the largest pit depths on 304 SS with and without B. cereus after 14 days of incubation were 7.17 and 4.59 µm, respectively, indicating that pitting corrosion was accelerated by B. cereus. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS) results revealed that B. cereus and its metabolic products were detrimental to the integrity of the passive film on 304 SS. The electrochemical results showed that B. cereus significantly reduced the corrosion resistance of 304 SS and accelerated the anodic dissolution reaction, thereby speeding up the corrosion process.

Effect of Dissolved Oxygen Concentration on the Microbiologically Influenced Corrosion of Q235 Carbon Steel by Halophilic Archaeon Natronorubrum tibetense.

The influence of dissolved oxygen concentration (DOC) on the microbiologically influenced corrosion (MIC) of Q235 carbon steel in the culture medium of halophilic archaeon Natronorubrum tibetense was investigated. The increase of DOC from 0.0 to 3.0 ppm was found to strengthen the oxygen concentration cell by promoting cathodic reaction. Meanwhile, the increased DOC also promoted archaeal cell growth, which could consume more metallic iron as energy source and aggravated the localized corrosion. When the DOC further increased to 5.0 ppm, the uniform corrosion was dominant as the biofilms became uniformly presented on the steel surface. Combined with the stronger inhibition effect of oxygen diffusion by the increased biofilm coverage, the MIC of carbon steel in the 5.0 ppm medium was weaker than that in the 3.0 ppm medium. From weight loss and electrochemical tests, the results all demonstrated that the carbon steel in the 3.0 ppm medium had the largest corrosion rate.

Effect of alternating current and Bacillus cereus on the stress corrosion behavior and mechanism of X80 steel in a Beijing soil solution.

The effects of alternating current (AC) and Bacillus cereus (B. cereus) on the stress corrosion behavior and mechanism of X80 pipeline steel were investigated in a Beijing soil solution in this study. Both AC and B. cereus can promote the generation of pits in X80 steel. B. cereus is a type of nitrate-reducing bacteria and hence nitrate reduction occurs at the bottom of the corrosion product film or the biofilm. Meanwhile, the anode accelerates the dissolution of X80 steel and generates some pits in the local working area. The synergistic effect of AC and nitrate- reducing bacteria (NRB) promotes X80 steel corrosion and increases its susceptibility to stress corrosion cracking (SCC).

Corrosion behavior of X80 pipeline steel in the presence of Brevibacterium halotolerans in Beijing soil.

In this study, the corrosion behavior of X80 pipeline steel in the presence of Brevibacterium halotolerans (B. halotolerans) was investigated by surface analysis and electrochemical measurements. Results show that B. halotolerans can attach to the surface of X80 steel, and the entire surface is covered with B. halotolerans. The corrosion products induced by B. halotolerans were FeOOH, Fe2O3 and FeSO4. X80 steel corrosion was accelerated in the presence of B. halotolerans and was susceptible to pitting corrosion. The formation of pitting corrosion could be due that the B. halotolerans oxidization of elemental iron in X80 steel to either obtain electrons from the reduction of nitrate in the underlying biofilm or in the damaged corrosion product film.

Incorporation of reduced graphene oxide into faceted flower-like {001} TiO2 for enhanced photocatalytic activity.

Anatase TiO2 with {001} facets is much more active than that with {101} facets, which has been verified via experiments and theoretical calculations. Graphene has garnered much attention since it was initially synthesized, due to its unique properties. In this study, reduced graphene oxide (RGO)/{001} faceted TiO2 composites were fabricated via a solvothermal method. The composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrophotometry, photoluminescence and Raman analysis. The results revealed that the graphene oxide was reduced during the preparation process of the {001} faceted TiO2, and combined with the surface of {001} TiO2. The photocatalytic activities of the composites were evaluated through the degradation of basic violet, under both white light (λ > 390 nm) and visible light (λ = 420 nm) irradiation. The results indicated that the photocatalytic activities of the {001} faceted TiO2 were significantly improved following the incorporation of RGO, particularly under visible light irradiation. Theoretical calculations showed that the band structure of the {001} faceted TiO2 was modified via graphene hybridization, where the separation of photoinduced electron-hole pairs was promoted; thus, the photocatalytic activity was enhanced.

One-Pot Hydrothermal Synthesis of SnO2/BiOBr Heterojunction Photocatalysts for the Efficient Degradation of Organic Pollutants Under Visible Light.

The establishment of p-n heterojunction between semiconductors is an effective means to improve the performance of semiconductor photocatalysts. For the first time, we synthesize SnO2/BiOBr heterojunction photocatalysts using a one-step hydrothermal method. Systematic material characterizations suggest that the photocatalysts consist of irregular BiOBr nanosheets with the length about 200 nm and width about 150 nm, and SnO2 nanoparticles are anchored uniformly onto the nanosheets. Most importantly, electrochemical characterizations including transient photocurrent profiles and electrochemical impedance spectra suggest that SnO2/BiOBr heterojunctions are created, which facilitates the charge separation and transfer efficiency of photogenerated charge carriers. As such, SnO2/BiOBr photocatalysts exhibit remarkable photocatalytic activities in terms of degrading a series of organic pollutants. Radical trapping experiments and electron spin resonance spectra suggest that superoxide radicals (•O2-) and hydroxyl radicals (•OH) are primary medium species running through the photocatalytic degradation process and enhanced photocatalytic performance.

Electrochemical and Stress Corrosion Mechanism of Submarine Pipeline in Simulated Seawater in Presence of Different Alternating Current Densities.

In this study, electrochemical measurements, immersion tests, and slow strain rate tensile (SSRT) tests were applied to investigate the electrochemical and stress corrosion cracking (SCC) behavior of X70 steel in simulated seawater with the interference of different alternating current (AC) densities. The results indicate that AC significantly strengthens the cathodic reaction, especially the oxygen reduction reaction. Simultaneously, hydrogen evolution reaction occurs when the limiting diffusion current density of oxygen reaches, and thus, icorr sharply increases with the increase in AC density. Additionally, when AC is imposed, the X70 steel exhibits higher SCC susceptibility in the simulated seawater, and the susceptibility increases with the increasing AC density. The SCC mechanism is controlled by both anodic dissolution (AD) and hydrogen embrittlement (HE) with the interference of AC.

The Corrosion Behavior of AZ91D Magnesium Alloy in Simulated Haze Aqueous Solution.

The corrosion process of AZ91D magnesium alloy in simulated haze aqueous solution has been studied by electrochemical measurements, immersion tests and morphology characterization. Results show that AZ91D was corroded heavily in simulated haze aqueous solution due to the loose and breakable product film on the surface providing little corrosion barrier. The effect of different ions was investigated. It was found that both N O 3 − and N H 4 + played an important role in the corrosion process. N O 3 − helped to form passive film to protect the matrix, yet N H 4 + consumed OH−, resulting in the absence of Mg(OH)2 and serious corrosion. Meanwhile, S O 4 2 − and Cl− had influence on pitting corrosion. Magnesium aluminum oxide and MgAl2(SO4)4·22H2O instead of Mg(OH)2 were the dominate products, which is different from the former study. Corrosion rate changed with time, especially in the first 3 h. A two-stage corrosion mechanism is proposed after considering both the corrosion process and the influence of ions.

Corrosion effect of Bacillus cereus on X80 pipeline steel in a Beijing soil environment.

The corrosion of X80 pipeline steel in the presence of Bacillus cereus (B. cereus) was studied through electrochemical and surface analyses and live/dead staining. Scanning electron microscopy and live/dead straining results showed that a number of B. cereus adhered to the X80 steel. Electrochemical impedance spectroscopy showed that B. cereus could accelerate the corrosion of X80 steel. In addition, surface morphology observations indicated that B. cereus could accelerate pitting corrosion in X80 steel. The depth of the largest pits due to B. cereus was approximately 11.23µm. Many pits were found on the U-shaped bents and cracks formed under stress after 60days of immersion in the presence of B. cereus. These indicate that pitting corrosion can be accelerated by B. cereus. X-ray photoelectron spectroscopy results revealed that NH4+ existed on the surface of X80 steel. B. cereus is a type of nitrate-reducing bacteria and hence the corrosion mechanism of B. cereus may involve nitrate reduction on the X80 steel.

Mussel-inspired superhydrophobic surfaces with enhanced corrosion resistance and dual-action antibacterial properties.

In this study, a multilayer antibacterial film was assembled onto 316L stainless steel via mussel-inspired depositions of polydopamine (PDA) and silver (Ag) nanoparticles followed by post-modification with 1H, 1H, 2H, 2H-perfluorodecanethiol. The resulting surface exhibited excellent superhydrophobicity with hierarchical micro/nanostructures that were constructed by both PDA and Ag nanoparticles. The crystal structure and chemical composition of these surfaces were investigated using X-ray photoelectron spectroscopy (XPS) analysis. Potentiodynamic polarization measurements revealed that the corrosion resistance of the as-prepared surfaces were sequentially increased after each step of the fabrication process. Compared with the surface covered with only Ag nanoparticles, the superhydrophobic surfaces exhibited substantially enhanced antibacterial activity against the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, resulting from the synergistic antibacterial actions of the superhydrophobic surface and Ag nanoparticles. The superhydrophobic surface exhibited lower cytotoxicity, compared to the surface covered with Ag nanoparticles.

Failure Mechanisms of the Coating/Metal Interface in Waterborne Coatings: The Effect of Bonding.

Waterborne coating is the most popular type of coating, and improving its performance is a key point of research. Cathodic delamination is one of the major modes of failure for organic coatings. It refers to the weakening or loss of adhesion between the coating and substrate. Physical and chemical characteristics of coatings have been studied via scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurements, Fourier transform infrared spectroscopy (FTIR), and secondary ion mass spectrometry (SIMS). Early heterogeneous swelling at the metal-coating interface in non-defective coated metals was elucidated using frequency-dependent alternating-current scanning electrochemical microscopy. Two types of coatings (styrene-acrylic coating and terpolymer coating) were compared. The effects of thickness, surface roughness, and chemical bonding on cathodic delamination were investigated.