In Situ Electrochemical Synthesis of Squamous-like Cu2S Induced by Sulfate-Reducing Bacteria as a Fenton-like Catalyst in Wastewater Treatment: Catalytic Performance and Mechanism.

In this paper, a novel method was proposed for the synthesis of Cu2S on copper mesh via electrolysis in SRB culture medium. It was found that following electrolysis in SRB medium, squamous-like Cu2S arrays were obtained on the copper mesh, and the Cu2S loading contents varied with the electrolyzing parameters. The resultant Cu2S on copper mesh in SRB (CSCM-SRB) with the highest catalytic MB degradation properties was produced by electrolysis at 3.75 mA/cm2 for 900 s. The optimized MB-degrading conditions were determined to be 1.2 cm2/mL CSCM-SRB with 0.05 M H2O2 at 35 °C when pH = 6, under which the degradation of MB reached over 99% after 120 min of reaction. Disinfecting properties was also proven by antibacterial tests, revealing that an almost 100% antibacterial rate against E. coli was obtained after 8 min. The organic compounds produced by SRB adsorbed on CSCM-SRB strongly promoted the degradation of MB. Furthermore, possible Fenton-like mechanisms of CSCM-SRB were proposed, illustrating that ·O2-, ·OH, and 1O2 acted as the main functional species during Fenton-like reactions, leading to effective MB degradation and high antibacterial properties. Finally, a simple device for wastewater treatment was designed, providing possible applications in real environments.

Effect of yeast extract on microbiologically influenced corrosion of X70 pipeline steel by Desulfovibrio bizertensis SY-1.

Microbiologically influenced corrosion (MIC) is a complicated process that happens ubiquitously and quietly in many fields. As a useful nutritional ingredient in microbial culture media, yeast extract (YE) is a routinely added in the MIC field. However, how the YE participated in MIC is not fully clarified. In the present work, the effect of YE on the growth of sulfate reducing prokaryotes (SRP) Desulfovibrio bizertensis SY-1 and corrosion behavior of X70 pipeline steel were studied. It was found that the weight loss of steel coupons in sterile media was doubled when YE was removed from culture media. However, in the SRP assays without YE the number of planktonic cells decreased, but the attachment of bacteria on steel surfaces was enhanced significantly. Besides, the corrosion rate of steel in SRP assays increased fourfold after removing YE from culture media. MIC was not determined for assays with planktonic SRP but only for biofilm assays. The results confirm the effect of YE on D. bizertensis SY-1 growth and also the inhibitory role of YE on MIC.

Sulfur vacancy-enhanced In2S3-x hollow microtubes for photocatalytic Cr (VI) and tetracycline removal.

Morphological regulation and defect engineering are efficient methods for photocatalytic technology by improving photon absorption and electron dissociation. Herein, In2S3-x hollow microtubes with S-vacancies (MIS) were fabricated via a simple solvothermal reaction using In-based metal-organic frameworks (In-MOFs) as a precursor. Experimental results demonstrate that the hollow structure and optimal S-vacancies can jointly accelerate the photocatalytic reaction, attributed to a larger specific surface area, more active sites, and faster electron transfer efficiency. The champion MIS(2) displayed significantly better photocatalytic activity for Cr(VI) reduction and tetracycline (TC) degradation. The Cr(VI) reduction rate by MIS(2) is 3.67 and 2.82 times higher than those of optimal In2S3 template-free (HIS(2)) and MIS(1) with poor S-vacancies, respectively. The removal efficiency of TC by MIS(2) is 1.37 and 1.15 times higher than those of HIS(2) and MIS(1). Further integration of MIS(2) with aerogel simplifies the recovery process significantly.

Ultrasound assisted electrodeposition of photocatalytic antibacterial MoS2-Zn coatings controlled by sodium dodecyl sulfate.

Photocatalytic MoS2 with visible light response is considered as a promising bactericidal material owing to its non-toxicity and high antibacterial efficiency. However, photocatalysts always exist as powder, so it is difficult to settle photocatalysts on the metal surface, which limits their application in aqueous environments. To solve this problem, ultrasound and sodium dodecyl sulfate (SDS) were introduced into the co-deposition process of MoS2 and zinc matrix, so that novel MoS2-Zn coatings were obtained. In this process, ultrasound and SDS strongly promoted the dispersion and adsorption of MoS2 on the co-depositing surfaces. Then MoS2 were proved to be composited into the Zn matrix with effective structures, and the addition of SDS effectively increased the loading content of MoS2 in the MoS2-Zn coatings. Besides, the antibacterial performance of the MoS2-Zn coatings was evaluated with three typical fouling bacteria E.coli, S.aureus and B.wiedmannii. The MoS2-Zn coating showed high and broad-spectrum antibacterial properties with over 98 % inhibition rate against these three bacteria. Furthermore, it is proved that the MoS2-Zn coatings generated superoxide (·O2-) and hydroxyl radicals (·OH) under visible light, which played the dominant and subordinate roles in the antibacterial process, respectively. The MoS2-Zn coatings also showed high antibacterial stability after four "light-dark" cycles. According to the results of the attached bacteria, the MoS2-Zn coatings were considered to effectively repel the living pelagic bacteria instead of killing the attached ones, which was highly environmentally friendly. The obtained MoS2-Zn coatings were considered promising in biofilm inhibiting and marine antifouling fields.

Comprehensive Review on the Use of Biocides in Microbiologically Influenced Corrosion.

A microbiologically influenced corrosion (MIC) causes huge economic losses and serious environmental damage every year. The prevention and control measures for MIC mainly include physical, chemical, and biological methods. Among them, biocide application is the most cost-effective method. Although various biocides have their own advantages in preventing and treating MIC, most biocides have the problem of polluting the environment and increasing microorganism resistance. Therefore, it has stimulated the exploration of continuously developing new environmentally friendly and efficient biocides. In this review, the application advantages and research progress of various biocides used to prevent and control MIC are discussed. Also, this review provides a resource for the research and rational use of biocides regarding MIC mitigation and prevention.

Regulating N Species in N-Doped Carbon Electro-Catalysts for High-Efficiency Synthesis of Hydrogen Peroxide in Simulated Seawater.

Electrochemical oxygen reduction reaction (ORR) is an attractive and alternative route for the on-site production of hydrogen peroxide (H2 O2 ). The electrochemical synthesis of H2 O2 in neutral electrolyte is in early studying stage and promising in ocean-energy application. Herein, N-doped carbon materials (N-Cx ) with different N types are prepared through the pyrolysis of zeolitic imidazolate frameworks. The N-Cx catalysts, especially N-C800 , exhibit an attracting 2e- ORR catalytic activity, corresponding to a high H2 O2 selectivity (≈95%) and preferable stability in 0.5 m NaCl solution. Additionally, the N-C800 possesses an attractive H2 O2 production amount up to 631.2 mmol g-1  h-1 and high Faraday efficiency (79.8%) in H-type cell. The remarkable 2e- ORR electrocatalytic performance of N-Cx catalysts is associated with the N species and N content in the materials. Density functional theory calculations suggest carbon atoms adjacent to graphitic N are the main catalytic sites and exhibit a smaller activation energy, which are more responsible than those in pyridinic N and pyrrolic N doped carbon materials. Furthermore, the N-C800 catalyst demonstrates an effective antibacterial performance for marine bacteria in simulated seawater. This work provides a new insight for electro-generation of H2 O2 in neutral electrolyte and triggers a great promise in ocean-energy application.

An ecofriendly coaxial antibacterial and anticorrosion nanofiber pullulan-ethyl cellulose embedded with carvacrol coating for protection against marine corrosion.

Coaxial electrospun coatings with antibacterial and anticorrosion properties have a marked potential to protect against corrosion in marine environments. Ethyl cellulose is a promising biopolymer for corrosion caused by microorganisms owing to its high mechanical strength, nontoxicity, and biodegradability. In this study, a coaxial electrospun coating loaded with antibacterial carvacrol (CV) in the core and anticorrosion pullulan (Pu) and ethyl cellulose (EC) as a shell layer was successfully fabricated. The formation of core-shell structure was confirmed using transmission electron microscopy. Pu-EC@CV coaxial nanofiber had small diameters, uniform distribution, smooth surface, strong hydrophobicity, and no fractures. Electrochemical impedance spectroscopy was used to analyze corrosion of the electrospun coating surface in a medium containing bacterial solution. The results indicated significant corrosion resistance of the coating surface. In addition, the antibacterial activity and mechanism of coaxial electrospun were studied. The Pu-EC@CV nanofiber coating exhibited excellent antibacterial properties by effectively increasing the permeability of cell membranes and killing bacteria, as determined by plate counts, scanning electron microscopy, cell membrane permeability, and the activity of alkaline phosphatase. In summary, the coaxial electrospun pullulan-ethyl cellulose embedded with CV coating can be used as antibacterial and anticorrosion materials and may have potential applications in the field of marine corrosion.

Peroxidase-like phosphate hydrate nanosheets bio-synthesized by a marine Shewanella algae strain for highly sensitive dopamine detection.

The sensitive and rapid detection of dopamine (DA) is of great significance for early diagnosis of related diseases. Current detection strategies of DA are time-consuming, expensive and inaccurate, while biosynthetic nanomaterials were considered highly stable and environment friendly, which were promising on colorimetric sensing. Thus, in this study, novel zinc phosphate hydrate nanosheets (SA@ZnPNS) biosynthesized by Shewanella algae were designed for the detection of DA. SA@ZnPNS showed high peroxidase-like activity which catalyzed the oxidation reaction of 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. Results showed that the catalytic reaction of SA@ZnPNS followed Michaelis-Menton kinetics, and catalytic process conformed to ping-pong mechanism with chief active species of hydroxyl radicals. The colorimetric detection of DA in human serum samples was performed based on SA@ZnPNS peroxidase-like activity. The linear range of DA detection was 0.1-40 µM, and the detection limit was 0.083 µM. This study provided a simple and practical method for the detection of DA and expanded the application of biosynthesized nanoparticles to biosensing fields.

N-Doped Carbon/CeO2 Composite as a Biomimetic Catalyst for Antibacterial Application.

Exploring new and high efficiency mimic enzymes is a vital and novel strategy for antibacterial application. Haloperoxidase-like enzymes have attracted wide attention thanks to their amazing catalytic property for hypohalous acid generation from hydrogen peroxide and halides. However, few materials have displayed halogenating catalytic performance until now. Herein, we synthesized N-doped C/CeO2 (N-C/CeO2) composite materials by a combination of the liquid and solid-state method. N-C/CeO2 can possess haloperoxidase-like catalytic activity by catalyzing the bromination of organic signaling compounds (phenol red) with H2O2 at a wide range of temperatures (20 °C to 55 °C), with a solution color changing from yellow to blue. Meanwhile, it exhibits high catalytic stability/recyclability in the catalytic reaction. The synthesized N-C/CeO2 composite can effectively catalyze the oxidation of Br- with H2O2 to produce HBrO without the presence of phenol red. The produced HBrO can resist typical marine bacteria like Pseudomonas aeruginosa. This study provides an efficient biomimetic haloperoxidase and a novel sustainable method for antibacterial application.

Experimental and Theoretical Studies toward Superior Anti-corrosive Nanocomposite Coatings of Aminosilane Wrapped Layer-by-Layer Graphene Oxide@MXene/Waterborne Epoxy.

Herein, layer-by-layer MXene/graphene oxide nanosheets wrapped with 3-aminopropyltriethoxy silane (abbreviated as F-GO@MXene) are proposed as an anti-corrosion promoter for waterborne epoxies. The GO@MXene nanohybrid is synthesized by a solvothermal reaction to produce a multi-layered 2D structure without defects. Then, the GO@MXene is modified by silane wrapping under a reflux reaction, in order to achieve chemical stability and to create active sites on the nanohybrid surface for reaction with the polymer matrix of the coating. The organic coating modified with 0.1 wt % F-GO@MXene has revealed superior corrosion protection efficiency than the organic coatings modified with either F-GO or F-MXene nanosheets. The impedance modulus at low frequency for the pure epoxy, epoxy/F-MXene, epoxy/F-GO, and epoxy/F-GO@MXene coatings is 4.17 × 105, 5.5 × 108, 4.46 × 108, and 1.14 × 1010 Ω·cm2 after 30 days of immersion in the corrosive media, respectively. The remarkable anti-corrosion property is assigned to the intense effect of the nanohybrid on the barrier performance, surface roughness, and adhesion strength of the epoxy coating. The complemental analysis based on first-principles density functional theory reveals that the adhesion strength related to the silane functional groups in its complexes follows the order F-GO@MXene > F-MXene > F-GO. The enhanced stabilization predicted on the GO@MXene nanohybrid ultimately stems from the combined role of the electrostatic and van der Waals forces, suggesting an increase in the penetration path of the corrosive media.

The Mechanism of Anticorrosion Performance and Mechanical Property Differences between Seawater Sea-Sand and Freshwater River-Sand Ultra-High-Performance Polymer Cement Mortar (UHPC).

There are abundant sea-sand resources on the earth. Traditional sea-sand concrete faced various problems relating to insufficient anticorrosion ability. In this paper, artificial seawater, sea sand, industrial waste, steel fiber, and polycarboxylate superplasticizer were used to prepare ultra-high-performance polymer cement mortar (SSUHPC). At the same time, freshwater river-sand ultra-high-performance polymer cement mortar (FRUHPC) with the same mixing ratio was prepared for comparative study. The compressive strength of SSUHPC reached 162.1 MPa, while the that of FRUHPC reached 173.3 MPa, which was slightly higher. Meanwhile, SSUHPC showed excellent anticorrosion characteristics in terms of carbonization, frost resistance and chloride resistance, and especially for sulfate resistance. The composition of SSUHPC was separated into three parts: mortar, pore and steel fiber, and the performance difference mechanisms of SSUHPC and FRUHPC were investigated by X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The hydration degree of mortar in SSUHPC was higher, with higher content of CSH and CH, and its better optimized gel pore characteristics gave SSUHPC better corrosion resistance. The mechanical properties of SSUHPC were slightly poor due to the uneven dispersion of steel fibers and air pores, with an- air pore porosity of 1.52% (above 200 µm) that was twice that of FRUHPC (0.6%). In this paper, the mechanics and anticorrosion performance of ultra-high-performance polymer cement mortar prepared with seawater sea sand were comprehensively evaluated, and the mechanism of performance difference between SSUHPC and FRUHPC was revealed, conducive to the targeted improvement of sea sand concrete.

Rationally Structured Triboelectric Nanogenerator Arrays for Harvesting Water-Current Energy and Self-Powered Sensing.

Water-current energy is an enormous and widely distributed clean energy in nature, with different scales from large ocean flow to small local turbulence. However, few effective technologies have been proposed to make use of different forms of water currents as a power source. Here, high-performance paired triboelectric nanogenerators (P-TENGs) capable of integrating massively into a thin flexible layer as a structured triboelectric surface (STS) are demonstrated for harvesting water-current energy. Novel gas packet exchange structure and rigid-flexible coupling deformation mechanism are introduced to ensure that the device can work very effectively even in deep water under high water pressure. The rationally designed TENG array in the STS enables highly efficient power take-off from the flow. Typically, the STS demonstrates a high-frequency output up to 57 Hz, largely superior to current TENG devices, and the power density is improved by over 100 times for triboelectric devices harvesting current energy. The flexible STS is capable of attaching to various surfaces or applying independently for self-powered sensing and underwater power supply, showing great potential for water-current energy utilization. Moreover, the work also initiates universal strategies to fabricate high-frequency devices under large environment pressure, which may profoundly enrich the design of TENGs.

Novel MOF-Based Photocatalyst AgBr/AgCl@ZIF-8 with Enhanced Photocatalytic Degradation and Antibacterial Properties.

A novel visible light-driven AgBr/AgCl@ZIF-8 catalyst was synthesized by a simple and rapid method. The composition and structure of the photocatalyst were characterized by XRD, SEM, UV-DRS, and XPS. It could be observed that the 2-methylimidazole zinc salt (ZIF-8) exhibited the rhombic dodecahedron morphology with the AgCl and AgBr particles evenly distributed around it. The composite photocatalyst AgBr/AgCl@ZIF-8 showed good photocatalytic degradation and antibacterial properties. The degradation rate of RhB solution was 98%, with 60 min of irradiation of visible light, and almost all P. aeruginosaudomonas aeruginosa (P. aeruginosa), Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli) were inactivated under the irradiation of 90 min. In addition, the prepared catalyst had excellent stability and reusability. Based on the free radical capture experiment, ·O2- and h+ were believed to be the main active substances, and possible photocatalytic degradation and sterilization mechanisms of AgBr/AgCl@ZIF-8 were proposed.

Extracellular Polymeric Substances and Biocorrosion/Biofouling: Recent Advances and Future Perspectives.

Microbial cells secrete extracellular polymeric substances (EPS) to adhere to material surfaces, if they get in contact with solid materials such as metals. After phase equilibrium, microorganisms can adhere firmly to the metal surfaces causing metal dissolution and corrosion. Attachment and adhesion of microorganisms via EPS increase the possibility and the rate of metal corrosion. Many components of EPS are electrochemical and redox active, making them closely related to metal corrosion. Functional groups in EPS have specific adsorption ability, causing them to play a key role in biocorrosion. This review emphasizes EPS properties related to metal corrosion and protection and the underlying microbially influenced corrosion (MIC) mechanisms. Future perspectives regarding a comprehensive study of MIC mechanisms and green methodologies for corrosion protection are provided.

Corrosion of an AZ31B Magnesium Alloy by Sulfate-Reducing Prokaryotes in a Mudflat Environment.

To study the abnormal failure of magnesium anodes for buried pipelines in marine engineering in the unique environment of mudflats, a strain of a sulfate-reducing prokaryote (SRP) was isolated from pipe-laying soil, and identified as Desulfovibrio sp. HQM3. Weight-loss test, electrochemical measurements, SEM, EDS, XRD, and CLSM techniques were used to study the effect of corrosion on the AZ31B magnesium alloy. Under the influence of SRP, the magnesium alloy corroded severely at rates up to 1.31 mm/year in the mudflat environment. SRP accelerated corrosion by 0.3mm/year. Pitting occurred on the samples in both abiotic and biotic systems. The pitting depth reached 163.47 µm in the biotic system after 14 days. The main composition of a petal-like corrosion product was Mg(OH)2. The results show that a mudflat environment can lead to an accelerated corrosion of magnesium alloys.

Sulphate Corrosion Mechanism of Ultra-High-Performance Concrete (UHPC) Prepared with Seawater and Sea Sand.

The lack of river sand is becoming increasingly serious. In this study, we consider how to use sea sand to prepare innovative construction and building materials with excellent mechanical and durability properties. Sulphate corrosion causes expansion, cracking and spalling of concrete, resulting in the reduction or even loss of concrete strength and cementation force. In this paper, artificial seawater, sea sand, industrial waste, steel fiber and polycarboxylate superplasticizer were used to prepare ultra-high-performance polymer cement mortar (SSUHPC), and the sulphate corrosion mechanism was investigated. The strength and cementation force of mortar on the SSUHPC surface decreased and flaked off with the development of sulphate erosion, and the steel fiber rusted and fell off. A 3D model was established based on X-ray computed tomography (X-CT), and the results showed that SSUHPC maintained excellent internal structural characteristics despite severe sulphate erosion on the surface. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were adopted to investigate the sulphate corrosion mechanism of SSUHPC. We found a transition zone within 1-5 mm of the surface of SSUHPC. The Vickers hardness of mortar in this area was increased by 5~15%, and the porosity was reduced to 3.8489%. Obvious structural damage did not occur in this area, but a high content of gypsum appeared. UHPC prepared with seawater sea sand was found to have better sulphate resistance than that prepared with freshwater river sand, which supports the development and utilization of sea sand in concrete.

Effects of Inorganic Metabolites of Sulphate-Reducing Bacteria on the Corrosion of AZ31B and AZ63B Magnesium Alloy in 3.5 wt.% NaCl Solution.

This study seeks prevent and alleviate the failure of magnesium alloy anodes in pipelines, which we suspect is a problem related to SRB. The electrochemical corrosion behaviour of two kinds of magnesium alloys, AZ31B and AZ63B, in 3.5 wt.% NaCl solution with sulphide or phosphide-the two main inorganic metabolites of sulphate-reducing bacteria-were studied by electrochemical tests combined with other characterisation methods such as scanning electron microscopy and X-ray diffraction. The results show that the corrosion film formed by inorganic metabolites of SRB's initial stage of corrosion (1-3 d) can lead to the corrosion of magnesium alloys. However, the loose and porous corrosion product film cannot protect the substrate effectively. The inorganic metabolites in the solution can accelerate the corrosion of the surface of magnesium alloy after the corrosion products have fallen off. This study provides a theoretical basis for alleviating the premature failure of magnesium alloy anodes and for corrosion protection in the future.

Photogenerated cathodic protection properties of Ag/NiS/TiO2 nanocomposites.

TiO2 is a semiconductor material used in photoelectric conversion. In order to improve its light utilization rate, nickel sulfide and silver nanoparticles were synthesized on the surface of titanium dioxide nanowires by simple impregnation-deposition and photoreduction methods. A series of studies were conducted on the cathodic protection effect of Ag/NiS/TiO2 nanocomposites on 304 stainless steel, with additional analyses on the material's morphology, composition, and light absorption characteristics. The results indicate that when the number of nickel sulfide impregnation-deposition cycles is 6, and the silver nitrate photoreduction concentration is 0.1 M, the prepared Ag/NiS/TiO2 nanocomposites can provide the best cathodic protection for 304 stainless steel.

Inadequate dosing of THPS treatment increases microbially influenced corrosion of pipeline steel by inducing biofilm growth of Desulfovibrio hontreensis SY-21.

Biocides are often used to mitigate the microbially influenced corrosion (MIC) of construction materials in many fields. To study the effect of inadequate dosing of non-oxidizing biocide tetrakis (hydroxymethyl) phosphonium sulfate (THPS) on corrosion of pipeline steel caused by microorganisms, a novel marine isolate Desulfovibrio hontreensis SY-21 was selected as a test microorganism. Weight loss rate determination, morphological analyses, and corrosion product analyses combined with electrochemical measurements were performed to investigate the influence of THPS on the MIC of X70 pipeline steel. The responses of sessile and planktonic cells of D. hontreensis to THPS were also studied. Results showed that D. hontreensis cells could significantly promote steel corrosion and induce local corrosion pits. With a THPS addition within the tolerance range of D. hontreensis for the biocide, MIC of the steel was further promoted by 65%. The growth of planktonic cells was inhibited by the biocide, but the number of biofilm cells was significantly increased. This study revealed that THPS concentrations within a specific range increased the corrosive effect of the presence of D. hontreensis by promoting the growth of sessile cells and biofilm formation. Therefore, the use of the biocide in practical applications needs to be properly considered and managed.

Recent Progress of Electrochemical Production of Hydrogen Peroxide by Two-Electron Oxygen Reduction Reaction.

Shifting electrochemical oxygen reduction reaction (ORR) via two-electron pathway becomes increasingly crucial as an alternative/green method for hydrogen peroxide (H2 O2 ) generation. Here, the development of 2e- ORR catalysts in recent years is reviewed, in aspects of reaction mechanism exploration, types of high-performance catalysts, factors to influence catalytic performance, and potential applications of 2e- ORR. Based on the previous theoretical and experimental studies, the underlying 2e- ORR catalytic mechanism is firstly unveiled, in aspect of reaction pathway, thermodynamic free energy diagram, limiting potential, and volcano plots. Then, various types of efficient catalysts for producing H2 O2 via 2e- ORR pathway are summarized. Additionally, the catalytic active sites and factors to influence catalysts' performance, such as electronic structure, carbon defect, functional groups (O, N, B, S, F etc.), synergistic effect, and others (pH, pore structure, steric hindrance effect, etc.) are discussed. The H2 O2 electrogeneration via 2e- ORR also has various potential applications in wastewater treatment, disinfection, organics degradation, and energy storage. Finally, potential future directions and prospects in 2e- ORR catalysts for electrochemically producing H2 O2 are examined. These insights may help develop highly active/selective 2e- ORR catalysts and shape the potential application of this electrochemical H2 O2 producing method.