Preparation of highly efficient self-healing anticorrosion epoxy coating by integration of benzotriazole corrosion inhibitor loaded 2D-COF

A Multifunctional Coating with Active Corrosion Protection Through a Synergistic pH- and Thermal-Responsive Mechanism

This article aims to develop CeO2 nanocontainer-constructed coating with a synergistic self-healing and protective nature through a simple mechanical blending technique to manage metal corrosion. The proposed coating exhibits excellent corrosion resistance, which is primarily attributed to the combination of thermal-driven healing and active corrosion inhibition. Paraffin wax and 2-polybenzothiazole-loaded CeO2 nanotubes (CeO2-MBT) are directly doped into epoxy coating to perform such a multifunctional role. CeO2 nanocontainers and encapsulated corrosion inhibitor MBT can be released by pH triggers to achieve instant corrosion inhibition upon the surface of metal substrate. In addition, any physical defects in the coating are responsively repaired by heating incorporated paraffin wax to regain structural integrity and consequent barrier function. Corrosion protection efficiency remains sufficient even after ten cycles of damage and healing. Such a multiple-functional coating strategy provides an alternative pathway toward efficient and sustainable performance to tackle corrosion-related challenges of metal components in both short-term and long-term services.

Highly sensitive and selective determination of uranyl ions based on Ag/Ag2O-COF composite SERS substrate

Uranium is an essential nuclear material in civilian and military areas; however, its extensive application raises concerns about the potential safety issues in the fields of environmental protection and nuclear industry. In this study, we developed an Ag/Ag2O-COF (covalent-organic framework) composite SERS substrate to detect uranyl ions (UO22+) in environmental aqueous solutions. Herein, the strong SERS effect of uranyl adsorbed in Ag/Ag2O composite and the high adsorption efficiency of COF TpPa-1 were combined to realize the trace detection of uranyl ions. This method displayed a linear range of 10-8 mol L-1 to 10-6 mol L-1 with the detection limit of 8.9 × 10-10 mol L-1 for uranyl ions. Furthermore, common metal cations and oxo-ions hardly affected the SERS detection of uranyl, which is helpful for the trace analysis of uranyl in natural water samples. Although the proposed strategy is deployed for uranyl detection, the reusable and high-efficiency system may be expanded to trace detection of other substance with Raman activity.

When covalent organic frameworks meet zeolites: Enhancing rhodamine B removal through the synergy in the emerging organic-inorganic nanoadsorbents

The development of new porous materials has attracted intense attention as adsorbents for removing pollutants from wastewater. However, pure inorganic and organic porous materials confront various problems in purifying the wastewater. In this work, we integrated a covalent organic framework (TpPa-1) with an inorganic zeolite (TS-1) for the first time via a solvothermal method to fabricate new-type nanoadsorbents. The covalent organic framework/zeolite (TpPa-1/TS-1) nanoadsorbents combined the merits of the zeolite and COF components and possessed efficient adsorptive removal of organic contaminants from solution. Structural morphology and chemical composition characterization by powder X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis demonstrated the successful preparation of TpPa-1/TS-1 composite nanoadsorbents. The resultant composite adsorbent TpPa-1/TS-1 removed rhodamine B at 1.7 and 2.6 times the efficiency of TpPa-1 and TS-1, respectively. Additional investigation revealed that the Freundlich adsorption isotherm and the pseudo-second-order kinetic model could be employed to represent the adsorption process more appropriately. Thermodynamic calculation analysis showed that the adsorption process proceeded spontaneously and exothermically. Besides, the effects of pH, absorbent mass and ionic strength on the adsorption performance were systematically investigated. The prepared composite adsorbent showed a slight decrease in removal efficiency after eight cycles of repeated use, and real water environment experiments also showed the high stability of the adsorbent. The enhanced performance can be attributed to electrostatic interaction, acid-base interaction, hydrogen bonding and π-π interactions.

Protective and Flame-Retardant Bifunctional Epoxy-Based Nanocomposite Coating by Intercomponent Synergy between Modified CaAl-LDH and rGO

Extensive utilization in various settings poses extra requirements of coatings beyond just anticorrosion properties. Herein, 8-hydroxyquinoline (8-HQ) intercalated CaAl-based layered double hydroxide (CaAl-8HQ-LDH) was loaded on reduced GO (rGO) through a one-pot hydrothermal reaction, which was employed as the nanofiller endowing the epoxy (EP/CaAl-8HQ LDH@rGO) with excellent flame-retardancy while ensuring efficient protection for mild steel. Results of electrochemical impedance spectroscopy (EIS) demonstrated the durability of the EP/CaAl-8HQ LDH@rGO-coated specimen, with the impedance at the lowest frequency (|Z|0.01Hz) maintained as 1.84 × 1010 Ω cm2 after 120 days of immersion in a 3.5 wt % NaCl solution. Even for the scratched EP/CaAl-8HQ LDH@rGO system, only a slight decline in |Z|0.01Hz was observed during 180 h of exposure to the NaCl solution, indicating a self-healing feature supported by salt spray tests. UL-94 burning tests revealed the V-0 rating for EP/CaAl-8HQ LDH@rGO with improved thermostability. Strong physical barrier from two-dimensional rGO and the release of 8-HQ from LDH interlayers accounted for the anticorrosive and self-healing properties. However, O2-concentration dilution and charring-layer promotion governed the flame-retardant behavior of the nanocomposite coating. The intercomponent synergy of nanofillers achieved in this work may provide a useful reference for designing multifunctional coatings.

Advanced materials for smart protective coatings: Unleashing the potential of metal/covalent organic frameworks, 2D nanomaterials and carbonaceous structures

The detrimental impact of corrosion on metallic materials remains a pressing concern across industries. Recently, intelligent anti-corrosive coatings for safeguarding metal infrastructures have garnered significant interest. These coatings are equipped with micro/nano carriers that store corrosion inhibitors and release them when triggered by external stimuli. These advanced coatings have the capability to elevate the electrochemical impedance values of steel by 2-3 orders of magnitude compared to the blank coating. However, achieving intelligent, durable, and reliable anti-corrosive coatings requires careful consideration in the design of these micro/nano carriers. This review paper primarily focuses on investigating the corrosion inhibition mechanism of various nano/micro carriers/barriers and identifying the challenges associated with using them for achieving desired properties in anti-corrosive coatings. Furthermore, the fundamental aspects required for nano/micro carriers, including compatibility with the coating matrix, high specific surface area, stability in different environments, stimuli-responsive behavior, and facile synthesis were investigated. To achieve this aim, we explored the properties of micro/nanocarriers based on oxide nanoparticles, carbonaceous and two-dimensional (2D) nanomaterials. Finally, we reviewed recent literature on the application of state-of the art nanocarriers based on metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs). We believe that the outcomes of this review paper offer valuable insights for researchers in selecting appropriate materials that can effectively enhance the corrosion resistance of coatings.

A High-Performance Anti-Corrosive Epoxy Coating Based on Ultra-Thin Hydroxyapatite Nanosheets with pH-Responsive Functions

The changes in the working environment have necessitated greater requirements in terms of the long-term anti-corrosion ability of metal anti-corrosion coatings, and the emergence of intelligent coatings has met this demand. A nanocontainer with a hydrophobic inner cavity and hydrophilic outer cavity called β-cyclodextrin (β-CD) was grafted onto the surface of hydroxyapatite (HAp) with a silane coupling agent, encapsulating benzotriazole (BTA) and embedded in epoxy resin to improve the coating anticorrosion performance. The excellent corrosion resistance of the coating in immersion and scratch experiments was derived from the inert protective layer formed by the reaction of the rapidly released corrosion inhibitor with the corrosion products on the metal surface. After 30 days of immersion experiment, the coating could still maintain the low-frequency impedance value of 6.28 × 107 Ω cm2. In this work, the enhancement of the physical barrier function of HAp nanoparticle and the pH-response function conferred by β-cyclodextrin provided the coating with good passive and active acting abilities in corrosive environments, respectively.

Pre-oxidation coupled with charged covalent organic framework membranes for highly efficient removal of organic chloramines precursors in algae-containing water treatment

Organic chloramines in water would pose both chemical and microbiological risks. It is essential to remove the precursors of organic chloramine (amino acids and decomposed peptides/proteins) to limit its formation in disinfection. In our work, nanofiltration was chosen to remove organic chloramines precursors. To solve the "trade-off" effect and low rejection of small molecules in algae organic matter, we synthesized a thin film composite (TFC) nanofiltration (NF) membrane with a crumpled polyamide (PA) layer via interfacial polymerization on polyacrylonitrile (PAN) composite support loaded with covalent organic framework (COF) nanoparticles (TpPa-SO₃H). The obtained NF membrane (PA-TpPa-SO₃H/PAN) increased the permeance from 10.2 to 28.2 L m^-2 h^-1 bar^-1 and the amino acid rejection from 24% to 69% compared to the control NF membrane. The addition of TpPa-SO₃H nanoparticles decreased the thickness of PA layers, increased the hydrophilicity of the membrane, and increased the transition energy barrier for amino acids transferring through the membrane, which was identified by scanning electron microscope, contact angle test, and density functional theory computations, respectively. Finally, pre-oxidation coupled with PA-TpPa-SO₃H/PAN membrane nanofiltration on the limitation of organic chloramines formation was evaluated. We found that the combined application of KMnO₄ pre-oxidation and PA-TpPa-SO₃H/PAN membranes nanofiltration in algae-containing water treatment could minimize the formation of organic chloramines in subsequent chlorination and maintain a high flux during filtration. Our work provides an effective way for algae-containing water treatment and organic chloramines control.

Improved Interfacial Interactions of Dip Coatings by In Situ Introducing Silica to Enhance Corrosion Resistance and Metal Bonding Strength

Corrosion is an irreversible phenomenon in nature that has been a major source of metal degradation. We herein provide a unique approach for embedding nanoparticles into epoxy resins via hydrogen bonding adsorption of in situ hydrophilic silica. Based on this adsorption action, a super-anticorrosive epoxy-based Teflon (MEP-PTFE) coating for usage on metals such as aluminum alloys was developed utilizing one-step dip coating, with promising engineering and public applications. It should be noted that the binding strength between the resultant MEP-PTFE coating and the substrate was 13.5 N. This coating had an impedance modulus of over 8 × 10⁹ Ω·cm² at 0.01 Hz and an impressive corrosion inhibition efficiency of 99.999%. The anticorrosion barrier from the diffusion control to the charge transfer control was revealed for the future good design of resin matrix coatings with excellent corrosion resistance.

Influence of Rust Inhibitors on the Microstructure of a Steel Passive Film in Chloride Concrete

To compare the corrosion inhibition behaviors of rust inhibitors with different mechanisms on steel bars, the rust resistance effect of sodium molybdate (Na2MoO4), sodium chromate (Na2CrO4), benzotriazole (BTA), N-N dimethyl ethanolamine, sodium molybdate (Na2MoO4) + benzotriazole (BTA), and sodium chromate (Na2CrO4) + benzotriazole (BTA) on steel bars in a simulated chloride concrete pore solution was studied. The rust resistance effects of different types of rust inhibitors were assessed by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The effects of different types of rust inhibitors on the film formation characteristics of a passive film on a steel bar surface were expounded. The results show that: When sodium molybdate (Na2MoO4) and benzotriazole (BTA) acted together, the impedance value and the capacitive reactance arc radius were the largest, and the density of the passive film and the inhibition efficiency were the highest. The composition of the passive film was primarily composed of iron compounds, and it also contained oxide and adsorption films that were formed on the steel bar surface by the rust inhibitors. The rust resistance effect was proportional to the compactness of the passive film.

Effect of covalent organic framework modified graphene oxide on anticorrosion and self-healing properties of epoxy resin coatings

Graphene oxide (GO) can enhance the corrosion resistance of epoxy coating, but there are problems such as poor filler dispersion and mechanical damage that will reduce the coating corrosion resistance. To resolve these problems, here, we used a facile and green liquid-phase synthetic strategy to grow covalent organic framework (COF) on GO sheets with 1,3,5-Triformylphloroglucinol and p-phenylenediamine as monomers for the COF synthesis. The COF could not only improve the compatibility of GO with epoxy coating, but also act as a nanocontainer for loading corrosion inhibitors. Electrochemical impedance spectroscopy showed that the low-frequency impedance of GO/COF-2% coating immersed in 3.5 wt% NaCl solution for 60 days was 8.58 × 10⁸ Ω cm². This was one order of magnitude higher than that of GO-2%, showing excellent corrosion resistance. Then, corrosion inhibitor of benzotriazole (BTA) was loaded into GO/COF, where the adsorption and release of BTA was controlled by environmental pH values. Results proved that the GO/COF@BTA-2% reinforced epoxy coating had superior corrosion resistance as well as self-healing ability because of the good compatibility, greater crosslinking density and controllable release of BTA.