No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Inhibitive effect of sepiolite-supported MgAl-LDH on chloride-induced corrosion of steel in simulated concrete pore solution
... For instance, the utilization of zeolite or SiO 2 as a substrate for the vertical synthesis of LDHs on their surface can effectively enhance both the surface area and Cl − binding capacity of LDH. The core has the potential to enhance the mechanical properties and optimize the porosity of the cement, attributed to the seeding effect and pozzolanic activity [22,29,30]. Another effective approach is to modify the LDH surface with nanoparticles. ...
Calcined layered double hydroxides (CLDH) and nano-SiO2 are commonly added to cement-based materials to enhance their resistance against chloride ions (Cl−) and mechanical performance, respectively. In this work, the CLDH and nano-SiO2 were combined to synthesize SiO2@CLDH, aiming for a synergistic effect between the two materials. The deposition of nano-SiO2 on the CLDH substrate enhanced the utilization of nano-SiO2 by promoting their dispersion in the cement pastes. Interestingly, the alkaline pore solution could induce a phase-
transformation of SiO2@CLDH, leading to the formation of a hydrated calcium silicate (C-S-H) layer on the rehydrated LDH surface (i.e., C-S-H@LDH). The C-S-H layer could enhance the surface adsorption for Cl−; effectively hinder the displacement of interlayer Cl− by SO42− and also improve the carbonization resistance of C-S-H@LDH. However, the amount of nano-SiO2 loading on the CLDH surface exhibits a ‘trade-off’ effect. Excessive nano-SiO2 loading leads to an overabundance of nascent C-S-H gel, which envelops the CLDH and hinders the
rehydration of CLDH. Moreover, the nascent C-S-H gel layer could act as the cross-linker between rehydrated LDH and cement pastes, thereby increasing the compressive strength of cement. In general, the incorporation of SiO2@CLDHs into cement could significantly increase the hydration degree, the compressive strength, adsorption of Cl−, and optimize the pore size of cement pastes. This study highlighted that when investigating the effects of doping materials on cement performance, it is crucial to recognize that cement may concurrently influence the physicochemical properties of the doping materials.
... Open-circuit potential curves of rebar as a function of chloride concentration in simulated concrete pore solutions with/without LDHstype inhibitors. [38,[58][59][60]: ...
In this study, the corrosion performance of carbon steel samples in 0.5 M sulfuric acid by the addition of novel inhibitors, 200 ppm of (25% and 50%) titanium dioxide nanoparticles in benzalkonium chloride, was thoroughly investigated. Gravimetric measurements, cyclic and linear potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and hydrogen collection by water displacement evaluated inhibition performance. Analogously, TiO2/ILB (50%), TiO2/ILB (75%), and ILB inhibitors enhanced corrosion protection with over 80% inhibition efficiency in electrochemical tests. In addition, weight loss and hydrogen collection measurements reached comparable results. According to potentiodynamic polarization curves, inhibitors exhibited dual behavior, but cathodic protection was more predominant. Scanning electron microscopy (SEM) was employed to examine the surface morphology before and after immersion using corrosion tests. The correlation between electronic properties and inhibition efficiencies of tilted inhibitors was determined by simple linear regression. Electronic properties were calculated for neutral and protonated forms using a polarizable continuum model by the DFT method at the B3LYP/6-311+G (d, p) level of theory. The active adsorbed sites of HM1-HM3 on the metal surface were determined by analyzing their corresponding electrostatic surface potentials (ESP). Furthermore, molecular dynamics simulations were performed to illustrate the most conceivable adsorption configuration between the inhibitors and metal surfaces.
In this article, a novel type of [email protected] Linde type A [email protected] layered double hydroxides ([email protected] Mg-Al LDHs) was fabricated via in situ co-deposition method for efficient corrosion protection of carbon steel. The corrosion inhibition effect of fabricated [email protected] Mg-Al LDH on steel was decided by a comparative experiment in saturated Ca(OH)2 solution. The batch experiment on the equilibrium isotherms of chloride binding in the solution clearly demonstrated that compared to pure Mg-Al LDHs, the [email protected] LDHs exhibited an higher chloride binding capacity due to the highly dispersed LDHs with large surface area on the zeolite-LTA support. In addition, a better corrosion inhibition capacity of [email protected] LDHs was proved by the measurements of open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP) and optical microscopy (OM). Some nitrate ions on the steel surface detected by X-ray photoelectron spectroscopy (XPS) confirmed the dual effects of aggressive chloride removal and simultaneously released NO3⁻, which were responsible for the ultimate inhibition effect of [email protected] LDHs.
The search for new alternatives to replace chromate-based coatings is a matter of great importance. Since their official ban due to the raised concerns of hexavalent chromium to the human health and the environment, significant efforts have been devoted to finding a more suitable alternative for the corrosion protection of aluminum alloys. However, the task has been quite challenging since the potential replacement needs to fulfill several requirements both in terms of cost and exceptional corrosion performance. Layered double hydroxides (LDHs) have generated a lot of interest in the past few years. They have been proposed as prospective candidates to replace chromate based protective systems. The particular structure of LDH nanocontainers allows them to intercalate a number of corrosion inhibitors and release them on demand under the action of corrosion relevant triggers. Moreover, their flexible use as pigments in paints or as a pre-treatment directly as conversion layers makes their implementation even more convenient. This review presents a critical view to the studies performed till today on LDHs for corrosion protection of aluminum alloys.
This work provides insight into the fabrication of ZnAl layered double hydroxides (LDHs) intercalated with organic phthalates (PTL) and their corrosion protection of steel reinforced concrete. The structure, composition and morphology of the LDH products prepared by various methods were systematically characterized to find out the relationship of preparation-structure-properties. The ZnAl-LDH-PTL prepared by co-precipitation method presented the best performance of corrosion protection due to its good crystallinity. The corrosion protection mechanism of LDH for steel in concrete system was also discussed.
We present here a simple method for the synthesis of core-shell SiO2@LDH (LDH: layered double hydroxide) particles using an in situ co-precipitation method without any pretreatment. The LDH composition, the overall particle size and morphology can be tuned giving new opportunities for the development of novel sorbents and catalyst systems.
This work investigated the passivation and chloride-induced corrosion of carbon steel exposed to an extract solution (PCSA) of ordinary Portland cement (OPC) blended with calcium sulfoaluminate (CSA) cement. As evaluated by EIS and XPS measurements, carbon steel gained inferior passivity by forming a thinner and less protective passive film in PCSA solution compared with that in the pure OPC solution. However, after chloride attack, comparable corrosion resistance was confirmed for steel exposed to both solutions. Furthermore, enhanced pitting corrosion resistance was identified for steel after 30 d of immersion in PCSA solution, which was mainly attributed to the formation of an Al-rich layer on the steel surface as well as the reduced chloride concentration in solution by the unreacted aluminum phase.
As a supplementary cementitious material, red mud (RM) has a great potential for producing low-carbon con-
crete. However, it may induce alkali-aggregate reaction owing to its high alkalinity, so acids have been widely used for neutralization. Moreover, as an organic corrosion inhibitor for metals used in acid and neutral envi-
ronments, phytic acid (PA) is not suitable for direct application in reinforced concrete. Accordingly, a novel low- carbon and corrosion-resistant concrete was designed with both RM and PA. Due to the generation of a bilayer PA-related protective film on the steel surface, a synergistic inhibition mechanism of RM and PA was proposed.
The effect of anionic charge of MgAl-LDHs on the corrosion behaviors of reinforcing steel induced by chloride was carefully explored in this study through electrochemical methods and DFT simulations. The results show that the binding energies (E B) was more negative as anionic charge increased. Therefore, the chloride exchange rate (δ) of LDHs-PO 4 3− was much smaller than that of LDHs-H 2 PO 4 − and LDHs-PO 3 F 2− , leading to the worst anti-corrosion efficiency of LDHs-PO 4 3−. Moreover, CaF 2 could be formed in the LDHs-PO 3 F 2− specimen, which improved the compactness of protective layer on the steel surface, resulting in that LDHs-PO 3 F 2− had a higher anti-corrosion efficiency than LDHs-H 2 PO 4 − .
Post-combustion carbon dioxide capture using inexpensive and highly efficient materials is a powerful tool for lowering industrial CO2 emissions. Herein, by impregnating acid-modified sepiolite with pentaethylenehexamine (PEHA), a series of adsorbents were delivered. For the comprehensive study of the adsorbents, the textural properties, saturation adsorption experiment, breakthrough adsorption experiment, kinetic models, reaction mechanism, economic evaluation, cyclic and thermal stability were measured. The results exhibited that the optimal H-P-0.9 adsorbent demonstrated a adsorption capacity of 2.47 mmol/g at 50 °C with good regeneration. Considering application to capture CO2 in flue gas, breakthrough adsorption experiments were studied, a higher adsorption capacity of 2.94 mmol/g at 50 °C (with 5% H2O) appeared in contrast to other sepiolite sorbents. The main factors of CO2 capture process were chemisorption and physisorption by Avrami model. Furthermore, appropriate moisture promoted the CO2 capture performance of the adsorbent. In addition, the result of in-situ DRIFTs revealed the capture process follows the anion cation mechanism, CO2 was finally converted to carbamate. The economic evaluation showed that the adsorbent capture 1 t CO2 at a low price of 2.0×10⁵ $. These results proved that the sepiolite-based adsorbent may be a potential material for CO2 capture with low price and excellent adsorption capacity.
This study investigated the chloride-induced depassivation and corrosion of mild steel in the magnesium potassium phosphate cement (MKPC) pore solutions at different magnesia-to-phosphate (M/P) ratios via several electrochemical methods and surface characterizations. Results showed that although the pH of MKPC is much lower than that of PC, the corrosion resistance of mild steel is significantly higher, with critical chloride values in MKPC being several orders higher than that in PC. Chloride-induced corrosion resistance increases with increasing M/P ratios. Whilst both pH and HPO4²⁻/PO4³⁻ ions influence the formation of corrosion products, the pH plays a dominant role in the corrosion resistance.
The influence of phytate ions (IP6) on the corrosion resistance of carbon steel with and without passive films in simulated concrete pore solutions with chloride ions was investigated using various electrochemical measurements and surface characterization techniques. The results show that IP 6 can effectively improve the corrosion resistance of the bare carbon steel. However, IP 6 is confirmed to be detrimental to the naturally formed passive films, thus decreasing the corrosion resistance of the pre-passivated carbon steel. Moreover, owing to the syn-ergistic degradation effects of IP 6 and chloride ions, the more pronounced pitting corrosion is highlighted for the pre-passivated carbon steel.
Ca-Al LDH hybrid self-healing microcapsules were fabricated with tung oil as core and ethyl cellulose (EC) as wall via solvent evaporation method. The self-healing and chlorine adsorption properties of hybrid microcapsules in cement-based materials were investigated. The corrosion resistance performance of microcapsules in simulated chlorine-contaminated concrete pore solution (SCPS) was characterized by electrochemical probe technique. First-principles based on density functional theory was applied to study the hybrid mechanism of Ca-Al LDH on self-healing microcapsules. The results demonstrate that the nano-layered Ca-Al LDH within the hybrid wall provided additional nucleation sites for cement hydration. The chlorine adsorption capacity of cement paste doped with 3 wt % and 6 wt % microcapsules was 14.7% and 26.7% higher than that of pure cement paste in SCPS, respectively. Hybrid microcapsules improved the anticorrosion of steel bars in SCPS by coupling effect of self-healing and chlorine resistance. The formation of Ca-Al [email protected] hybrid materials is an exothermic process with perfect binding stability. The chlorine adsorption property of microcapsules was improved by the interface charge redistribution of Ca-Al [email protected] hybrid materials.
Chloride-induced corrosion of carbon steel could be inhibited by molybdate (MO), while the MO/chloride ratio plays a vital role. This ratio has been reduced in constant chloride concentration using acetate (AC) as an organic corrosion inhibitor. Results showed that the MO-AC mixture, regardless of the concentration, possessed remarkable inhibition capability at the low concentration of MO. Electrochemical evaluations and surface analyses demonstrated the excellent behaviour of MO-AC, which promoted the formation of Fe2(MoO4)3, resulting in enhancing the properties of the passive-adsorbed layers. Based on the XPS results, more MO contributed to the formation of Fe2O3 in MO-AC as the Mo⁶⁺/Mo⁴⁺ ratio decreased and the value of Fe³⁺/Fe⁰ increased. Also, the low MO concentration assisted AC adsorption.
Sepiolite (Sep) and palygorskite (Pal) are naturally available one-dimensional (1D) clay minerals. Their special pore structures, affluent surface groups, high specific surface area and better ion-exchange capacity make them feasible for the construction of functional antimicrobial nanocomposite and hybrid materials. The silanol groups at the external surface of these 1D clay minerals and their surface electrical charge play crucial roles in the interactions with various antimicrobial agents, and the presence of structural cavities (tunnels and channels) allows small molecules to be immobilized inside them. The main functions gifted by Sep and Pal to the formed nanomaterials include improvement of dispersion behavior of loading agents, targeting release of the active compounds in a sustained manner, and enhancement of material stability. In addition, the characters of non-toxicity, biocompatibility, and eco-friendliness make the 1D clay minerals and their derived composites widely used in fields involving human health. In this review, various antimicrobial nanocomposite and hybrid materials developed through incorporation of Sep and Pal with myriad antimicrobial agents such as metal and metal oxide nanoparticles, metal ions, antibiotics, essential oils, surfactants, and biopolymers with improved physicochemical properties as well as enhanced antimicrobial activities were discussed. These antimicrobial nanocomposite and hybrid materials could be applicable in various fields such as food packaging, wound dressing, and feed additives for animal health, and will become promising innovative antimicrobial nano-materials to inhibit pathogenic bacteria.
Rebar corrosion is one of the most important phenomena affecting durability of reinforced concrete structures. Corrosion inhibitors are considered an effective preventative technique to delay the onset of corrosion and/reduce the corrosion rare. Substances can be both organic and inorganic in nature. Besides the well-known effectiveness of nitrite-based inhibitor, new organic and inorganic substances have been investigated as alternative to face safety and environmental issues related to sodium or potassium nitrites. From the ‘90s, a wide number of organic substances were studied, including amines, alkanolamines, carboxylates and mixtures of esters. The present literature review is focused on the effectiveness of the most commonly used inhibitors as nitrites and amines. The use of nitrates, new organic and green compounds, i.e., natural substances typically extracted from plants, are investigated as potential corrosion inhibitors.
By means of a comparative experiment, the inhibitive effect of a novel SiO2@MgAl-layered double hydroxide(SiO2@LDH) intercalated with NO2⁻ core-shell nanocomposite, which was fabricated by an in-situ coprecipitation method, on steel has been investigated in Cl⁻ contaminated saturated Ca(OH)2 solution. The results show that compared with SiO2 and NO2⁻ intercalated LDH, the Cl⁻ uptake capacity and inhibitive effect of SiO2@ LDH intercalated with NO2⁻ are greatly improved. The enhanced capacity of Cl⁻ uptake by the reaction production of SiO2 and Ca(OH)2, and the highly dispersed LDH and simultaneously released inhibitive NO2⁻ mainly contribute to the excellent inhibitive effect of nanocomposite.
In this study, the pozzolanic activity of low-grade natural sepiolite was enhanced by calcination for further utilizing as a supplementary cementitious material. Sampled sepiolite was calcinated at 400, 600, 700, 800, 900, and 1000 °C, and the calcinated sepiolite were characterized and respectively blending with pastes for examining their rheological and hydration behaviors. It was found the pozzolanic activity of sepiolite was maybe mainly determined by the active Si phase content, and 800-SP showed the highest pozzolanic activity. The rheological behaviors of fresh paste blended with sepiolite calcinated at different temperatures shows obviously different. In early curing stage, the addition of sepiolite obviously accelerated the cement hydration. But in later curing stage, comparing with U-SP, the calcinated sepiolite showed hindering effect on cement hydration, and this effect was obviously regular with the increasing calcinated temperature. Additionally, by comparing with all pastes blended with sepiolite, which blended with 800-SP showed the highest compressive strength values.
Corrosion performance of the reinforcement was dramatically affected by chemical compositions of pore solution in alkali-activated fly ash. In this study, the electrochemical behavior and surface properties of reinforcement were characterized in chloride-contaminated simulated alkali-activated fly ash pore (SAFP) solution. The results indicated that due to the high alkalinity and formation of zeolite-like adsorption layer (about 20 nm), the reinforcement was still in passive state and exhibited high corrosion resistance in chloride-contaminated SAFP solution. However, the protective effect of passivation film (consisted of mainly FeOOH outer film and FeO inner film) and corrosion resistance of the reinforcement were reduced by chlorides. Further, the chloride threshold in SAFP solution was 10 times larger than simulated cement pore solution, due to the competitive adsorption between OH − /silicates and chlorides.
The novel type of [email protected] Linde type A [email protected] layered double hydroxides ([email protected] LDH) was synthesized by in-situ co-precipitation method. The kinetic, thermodynamic and equilibrium studies on the chloride adsorption of the as-fabricated [email protected] LDH were performed by a comparative experiment in simulated concrete pore solution. The morphology and microstructure of as-fabricated [email protected] LDH were observed by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrum (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) technique. The results show that the [email protected] LDH [email protected] structure can effectively adsorb the chloride ions from the simulated concrete pore solution, and its chloride adsorption capacity is obviously higher relative to pure MgAl LDH powder. The initial pH value, additional SO4²⁻ and adsorbent dosage exert a remarkable influence on the chloride adsorption capacity. Furthermore, the adsorption process can be described by the Langmuir model and Pseudo-second-order kinetic. The negative values of Gibbs free energy (ΔG⁰) and standard enthalpy change (ΔH⁰) confirm the adsorption process spontaneous and exothermic in nature. In addition, the excellent chloride adsorption capacity of [email protected] LDH is attributed to the anion exchange of highly dispersed LDH with large surface area on the zeolite-LTA support.
It is essential to develop a class of EP composite with improved fire retardance, mechanical strength and thermal resistance performances for some practical applications, such as in aeronautic and automobile fields. Due to the highly tunable structure of layered double hydroxides (LDHs), transition metals Ni²⁺ and Fe³⁺ were selected as the cation components considering their excellent catalytic charring ability. To overcome the easy agglomeration of LDH during polymer process, sepiolite nanofiber (SEP) was used as a carrier for LDH and thus a novel low-cost one-dimensional flame retardant [email protected] was successfully synthesized via facile self-assembly. With the addition of 2.3 wt% [email protected] alone, EP composite owns a V-1 rating in UL-94 test, an LOI value of 31.1%, 21% reduction of peak heat release rate and decreased 16.0% total smoke production. Additionally, the total carbon monoxide production has been decreased by 25.3%. Combining the analyses of the char residue and thermogravimetric infrared spectrometry (TG-FTIR) of EP/[email protected] systems, the flame-retardant mechanism has been drawn as follows: a) physical solidified char residue by sepiolite nanofibers; b) reinforced char residue thanks to the catalytic charring effect of both Ni/Fe alloy catalyst (originated from partially reduced oxide metals) and Brønsted acid sites in sepiolite. Moreover, the tensile strength and glass transition temperature of EP composite have been enhanced simultaneously. In a nutshell, it is an economically effective channel targeting to improve the comprehensive properties of EP through loading Ni–Fe LDH assisted by sepiolite nanofibers.
This study presents the influence of binary admixture of sepiolite and fly ash on the performance of modified cement mortar including hydration heat, mechanical strength, carbonation resistance, chloride diffusion and the interaction between various binders. The experimental results showed that single incorporation of sepiolite can to some extent increase the strength of mortar, while it was even significant if a binary sepiolite-fly ash composite system was adopted. When the sepiolite content was 15%, the carbonation resistance of the modified mortar can be improved and its carbonation depth was decreased by 37.8%. It took place for chloride resistance of the corresponding modified mortar as well. Meanwhile, using binary admixture of sepiolite and fly ash, it can effectively shorten the induction period of cement hydration and reduce the cumulative hydration heat release of the modified system.
The combination of LDHs nanocontainer and organic inhibitor demonstrates a great prospect in the field of corrosion protection. Whereas the traditional ion exchange method has a low efficiency owing to the small space and the firm force between the LDHs laminates. A high-efficiency approach of intercalating organic inhibitor into the LDHs is delivered in this work. The MgAl-LDHs loaded with 5-aminoindazole (AIA) were synthesized by separating the layered structures of hydrotalcites into single-layer nanosheets and then restructuring the exfoliated nanosheets with organic inhibitor. The as-synthesized LDHs-AIA⁻ displayed a controlled release behavior and excellent anti-corrosion performance on the copper in 3.5 wt% NaCl solution, which were characterized by UV–vis spectra and electrochemical tests. Furthermore, a series of structure and morphology tests involving SEM, TEM, XRD, FTIR, XPS and TGA were also used for further analysis the LDHs. And the analysis of corrosion products and the anti-corrosion mechanism were carried out by SEM, XRD tests. The theoretical calculations concerning the adsorption of corrosion inhibitors on the copper surface were also investigated. It can be concluded that the inhibitor-loaded LDHs have the ability to adjustably release the corrosion inhibitor in corrosive medium, thereafter the corrosion inhibitor can adsorb onto the active sites of copper surface to prevent corrosion.
The surface basicity and hydrophilic character of Mg and Al or Fe-based layered double hydroxides were assessed through thermal programmed desorption (TPD) of CO2 and H2O in terms of CO2 and water retention capacity (CRC and WRC), respectively. LDH calcination up to 450 °C produced slightly irreversible and detrimental effects on both properties, much less pronounced for Fe-based samples. These properties turned out to be completely revived after calcination below 200 °C. Iron-based LDH showed higher hydrophilic character but lower surface basicity than MgAl-2. Both CRC and WRC increased simultaneously with increasing PNLCO beyond a certain level. Water and CO2 adsorb via competitive interactions with weak to medium adsorption sites, but favor mutually their retention on strong basic sites. These results allow predicting LDH behavior in the adsorption of acidic gases and potential large-scale CO2 capture in humid conditions without previous dehydration.
The corrosion behavior of two types of stirrups, a plain steel bar and a ribbed steel bar, were studied in this work. The results demonstrated that a better passive state was achieved on B500, which was due to a relatively higher concentration of Fe²⁺ oxides at the first 2 nm depths of the film, even though B500 film had relatively less FeOx contents, because Fe²⁺ oxides had a better protective property than Fe³⁺ oxides. Furthermore, the slightly lower donor density of B500 film in the M-S analysis results presented the much less point defect in the film, showing an increase in the anti-corrosion property of passive film. These contributed to a higher chloride threshold value of B500, 4 times higher than that of S275. Therefore, compared with S275, B500 stirrups could be more suitable for the application in the severe service environment.
Layered Double Hydroxides (LDHs) are well-known nanomaterials for the construction of self-healing corrosion protective composite coatings with controlled release ability of the active corrosion inhibitors. In this paper, the LDH surface has been modified with SiO2 nanoparticles through a sol-gel method, and then its active corrosion inhibition behaviors in the saline solution and sol-gel film were investigated by polarization, electrochemical impedance spectroscopy (EIS) and salt spray tests. XRD, TGA, and FE-SEM tests were conducted to characterize the constructed LDH particles. The results demonstrated that the LDH(Mo)SS sample provided superior active inhibition efficiency in the solution and coating phases due to the controlled release ability of the LDH particles intercalated with MoO4²⁻ anions as well as the barrier properties of this sample.
This paper aims to examine the corrosion protection of reinforcing steel in concrete due to carbonation alone and the coupled action of chloride penetration and carbonation by MgAl-NO2 layered double hydroxides (LDHs), which was synthesized by calcination rehydration method. The results reveal that MgAl-NO2 LDHs have a better inhibition effect on the steel corrosion by carbonation alone than the coupled action of chloride penetration and carbonation. The inhibition mechanism for carbonation alone is mainly attributed to the alkalinity increase and NO2- release. The Cl- uptake additionally contributes to the corrosion inhibition for the coupled action of chloride penetration and carbonation.
In recent years, layered double hydroxides (LDHs) derived metal oxides as highly efficient catalysts for selective catalytic reduction of NOx with NH3 (NH3-SCR) have attracted great attention. The high dispersibility and interchangeability of cations within the brucite-like layers make LDHs an indispensable branch of catalytic materials. With the increasingly stringent and ultra-low emission regulations, there is an urgent need for highly efficient and stable low-medium temperature denitration catalysts in markets. In this contribution, we have critically summarized the recent research progress in the LDHs derived NH3-SCR catalysts, including their ability for NOx removal, N2 selectivity, active temperature window, stability and resistance to poisoning. The advantages and defects of various types of LDHs-derived catalysts are comparatively summarized, and the corresponding modification strategies are discussed. In addition, considering the importance of the catalyst's resistance to poisoning in practical applications, we discuss the poisoning mechanism of each component in flue gases, and provide the corresponding strategies to improve the poisoning resistance of catalysts. Finally, from the perspective of practical applications and operation cost, the regeneration measures of catalysts after poisoning is also discussed. We hope that this work can give timely technical guidance and valuable insights for the applications of LDHs materials in the field of NOx control.
This work studied the passivation of carbon steel bar in cement pastes prepared with and without nano-silica by using electrochemical measurements and surface characterization methods. The results showed that the passivation of steel bar in cement paste was dominated by the chemistry of the pore solution and the evolution over time, which are closely associated with the hydration process of the cement. The addition of nano-silica influenced the alkalinity of the pore solution in cement paste and modified the pore structure of the cement paste, which resulted in a different passivation process and a thicker passive film with a higher proportion of Fe2+ oxides. The intrinsic corrosion resistance of the steel bars in concrete prepared with nano-silica was expected to be enhanced.
An evaluation was made of the use of MgAl-LDH with incorporated nitroprusside as an adsorbent to remove inorganic arsenic (As(III) and As(V)) and organic arsenic (DMA) from aqueous matrices. The material was synthesized by the co-precipitation method at constant pH and was characterized by Raman spectroscopy, infrared spectroscopy, thermogravimetry, X-ray diffraction, and high-resolution transmission electron microscopy, before and after use in the adsorption process. The effects on adsorption of contact time, initial metalloid concentration, and pH were investigated. For an initial concentration of 10 mg L⁻¹ and pH 2.00, the MgAl-LDH with incorporated nitroprusside was only able to adsorb the DMA and As(V) species, with removal percentages of 25.10 and 103.8%, respectively. At pH 6.02 and 12.00, only the inorganic species were adsorbed, with removal percentages of 22.93% and 60.07%, respectively, for As(III), and 89.81% and 71.64%, respectively, for As(V). Application of the Langmuir and Freundlich isotherm models indicated that the adsorption mechanism depended on the pH of the medium and the arsenic species. The results showed that the use of MgAl-LDH with incorporated nitroprusside has potential for the development of techniques for the speciation of arsenic species.
Circumferential non-uniform corrosion of steel bars usually occurs in chloride contaminated RC structures and often lead to premature concrete cover cracking. This paper presents a numerical model developed to investigate the time-dependent process of non-uniform corrosion for steel bars at different locations in concrete. The model also considers the effects of longitudinal cracking on the chloride and oxygen diffusion. Corrosion is triggered around a steel bar once the chloride content reaches the chloride threshold at that point, which is determined based on chloride penetration. Thereafter, time-dependent corrosion rate around the circumferential surface of a steel bar is obtained through electrochemical theory, which make it possible to describe a cross-sectional corrosion profile showing the timeline of damage. A case study is developed to demonstrate the analysis procedure of the proposed time-dependent non-uniform corrosion model and to present the differences in the corrosion process between the side-located rebar and corner-located rebar. Then, the derived model can be partially verified with experimental results. In this research, the simulation results with the verified model indicates that the corrosion of side-located rebar at the top and bottom areas are more severe based on the effects of corrosion-induced cracking which allows more chloride penetration and oxygen diffusion. Also, the conducted parametric study shows that the time it takes to obtain the same critical corrosion angle increases with the increase of concrete cover thickness and steel bar diameter, but the safe time decreases with the increase of chloride penetration and oxygen diffusion coefficient.
The common practice of using inhibition efficiency (η%) to determine the standard Gibbs energy of adsorption (ΔG adso ) for a corrosion inhibitor in acidic solution is evaluated. It is demonstrated that the typical assumption that η% is a good proxy for fractional surface coverage (θ) is not necessarily valid. Consequently, the accuracy of the ΔG adso value obtained from such data is doubtful. Moreover, it is argued that even a more direct measurement of θ may still not allow one to extract an accurate estimate of ΔG adso .
Mechanochemical activation was used to prepare Mg(Li)Al-layered double hydroxides (LDH) with molar ratios of cations Mg/Al = 2 and 4 and Li/Al = 0.5. The influence of cationic composition and nature of interlayer anions (CO 3²⁻ , OH ⁻ ) on the structural properties of LDH and the properties of oxide phases formed by LDH calcination was investigated by XRD and SEM. Textural properties (nitrogen adsorption–desorption isotherms at 77.4 K) and acid-base properties (CO 2 double isotherm method, TPD-CO 2 , aldol condensation of furfural with acetone reaction) were studied in detail for mixed oxides. It was shown that mixed oxides based on the LDH that were prepared by mechanochemical route have high specific surface area and porosity. An increase in the Mg/Al ratio, the introduction of Li, and the use of LDH with OH- counterions made it possible not only to increase the total basicity of mixed oxides but also to vary the fraction of basic sites with a different strength.
Mg-Al layered double hydroxides intercalated with nitrite ions was prepared by three different methods: calcined-rehydration (R-LDH), hydrothermal (H-LDH) and coprecipitation (C-LDH) method. The products were characterized and the results indicated that C-LDH had the highest intercalated rate of anions. The ion substitution test also verified C-LDH exhibited the largest adsorption capacity of chloridion. The inhibition efficiency and corrosion current density of C-LDH from electrochemical test both had the better performance than R-LDH and H-LDH over immersion time. Therefore, C-LDH could had the best anticorrosion in a long period and its mechanism of corrosion protection was also discussed.
This paper presents an experimental study on the rheological behaviour and mechanical strength of cement pastes and mortars prepared with high-calcium sepiolite (HCSP). HCSP was used to replace 0.0%, 2.5%, 5.0%, 7.5%, 10.0%, and 15.0% of cement. The rheological behaviour of fresh specimens was investigated along with the yield stress and plastic viscosity, which were approximated using the Bingham plastic model. Tests were also conducted to investigate the compressive strength, flexural strength, and drying shrinkage of hardened specimens. The results showed that the addition of HCSP has an adverse effect on the rheological behaviour of fresh specimens. The compressive strength and flexural strength are highest for specimens with an HCSP content of 7.5% but this is somewhat negated by the high drying shrinkage values. In contrast, the drying shrinkage values are lowest for specimens with the highest HCSP content (15.0%). It can be concluded that HCSP is a potential cement replacement material, but it is necessary to improve the workability of the fresh specimens and reduce drying shrinkage of the hardened specimens before this mineral can be used in the production of structural concrete.
[email protected] ([email protected]) composites were designed and prepared based on the assembly of layered double hydroxides (LDH) on acidified sepiolites (Sep) for the simultaneous photocatalytic degradation of methyl orange (MO) and methylene blue (MB). The structure, morphology, texture, optical properties, and photocatalytic performance of the prepared [email protected] were studied in detail. Among the [email protected] composites, Sep4@LDH (4.0 g Sep) exhibited the highest photocatalytic activity under visible-light irradiation, which could be attributed to its large surface area, high crystallinity, and plentiful active sites on its surface. The photodegradation of the dyes followed a pseudo first-order kinetic model (Langmuir-Hinshelwood model), indicating that the copious and homogeneous active sites on the surface of the composites contributed to the high photocatalytic activity. The photodegradation mechanism was studied by examining the active species (•OH, h⁺, and •O2⁻ anions) using appropriate scavengers. It was found that •OH radicals played a critical role in the photocatalytic process of MO and MB, where the generation of •OH radicals occurred on the electron/hole (e⁻/h⁺) pairs on the surface of the [email protected] composites. © 2018 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences
This work reports the modification of ordinary Portland cement with ultrafine ground granulated blast furnace slag (GGBS) as a mineral admixture and calcium nitrate as a chemical admixture and examines how mechanical and corrosion properties are improved by this modification. Ultrafine GGBS with average particle size of 4–6 μM was introduced as a replacement mineral admixture (10%) to ordinary Portland cement while calcium nitrate was introduced as a chemical admixture at 2% amount of cementitious material, in the preparation of concrete. X-ray diffraction studies on powdered concrete showed that the amount of silica in the concrete increases with the introduction of GGBS. Calcium hydroxide was converted to calcium silicates. Ultrafine GGBS reduced the workability and water absorption and increased the compressive strength of the concrete (18%) and the bond strength of the steel rebar (45%). Adding calcium nitrate further reduced water absorption of the concrete but improved workability, compressive strength (32%) and bond strength (131%). The pH of the concrete powdered solution became more alkaline with the replacement of ultrafine GGBS and addition of calcium nitrate. Free chloride content dropped by 39% and 65%, respectively, with the introduction of GGBS and nitrate. Corrosion behaviour of the concrete specimens were studied using measurement of open circuit potentials, linear polarization resistance and Tafel polarization in an accelerated corrosion medium of 3.5% NaCl and 1 M sulphuric acid. Corrosion potential and current of the control specimens decreased with time for 40 days after which an increase was observed. Ultrafine GGBS shifted the corrosion potential in the cathodic direction, indicating retardation of the cathodic reaction (ex. oxygen reduction). Calcium nitrate, on the other hand, shifted the corrosion potential anodically by promoting the formation of a passive film of iron(III) hydroxide on the steel surface. Corrosion currents in GGBS and nitrate-modified concrete decreased by 200-fold compared to the control specimen on the first day, and by 480-fold on the 50th day (150-times smaller than the specimen modified with GGBS alone). Finally, scanning electron microscopy images of the corroded rebar at the end of 50th day indicate that pitting and intergranular corrosion occurs, with its extent reduced significantly by the introduction of admixtures. These results demonstrate that ultrafine GGBS and calcium nitrate as admixtures enhance the mechanical properties of concrete and reduce the corrosion of rebar.
The corrosion inhibition mechanism of mild steel in acidic solution and in the presence of two cationic gemini surfactants have been studied. These are two surfactants having 12-carbon hydrophobic tails: one with a tetramethylene spacer and the other one with the same spacer containing two hydroxyl groups. EIS and polarization and electrochemical noise measurements revealed superior corrosion inhibition of hydroxyl functional surfactant compared with its counterpart with no hydroxyl group. Surface analysis including AFM, and SEM confirmed less corrosion attacks on the sample exposed to hydroxyl functional surfactant solution. Quantum chemical parameters revealed a good correlation with electrochemical results.
The effect of citrate ions on the passive film stability on carbon steel, at pH 13, was evaluated. The study involved cyclic voltammograms, potentiodynamic polarization curves, micro-Raman spectroscopy and weight-loss tests. No beneficial effects on delaying or inhibiting pitting were observed in the presence of citrate ions. Organic compounds with carboxylate groups are promising corrosion inhibitors. However, the incorporation of citrate ions is clearly harmful to carbon steel in alkaline solutions and accelerates the corrosion process. Citrate ions adsorption is not observed on passive steel. Instead, citrate ions can unexpectedly dissolve the passive layer facilitating the corrosion process.
Hexagonal mesoporous MgAl layered double hydroxide (LDH) was synthesized through a simple hydrothermal method and was employed without calcination as adsorbent in the removal of the direct anionic azo dye, Brilliant Yellow (BY). The adsorbent was characterized by XRD, FT-IR, SEM and BET surface area. Hexagonal platelets of MgAl LDH were fabricated with nanometric building blocks. Batch experiments were carried out for study effects of contact time, amount of adsorbent, solution pH and solution temperature on the removal efficiency of BY. The adsorption of BY onto the MgAl LDH was pH dependent and the highest value of adsorption capacity was observed at pH=6. The equilibrium adsorption data were obtained using the Langmuir, Freundlich and Temkin isotherms. The results indicated that the experimental adsorption data were fitted to Langmuir and Freundlich models. The maximum adsorption capacity of BY onto the MgAl LDH was found to be 115 mg/g. The kinetic data of adsorption were evaluated by pseudo-first order and pseudo-second order, which described well by pseudo-second order model. The negative values of ΔGo at all temperature indicated that the adsorption process was spontaneous. The values of ΔHo and ΔSo were calculated 19.3 kJ/mol and 80.5 J/mol. K, respectively. The positive value of ΔHo shows that the adsorption was endothermic, while positive ΔSo value reflects increased disorder at the solid–solution interface during the adsorption.
Carbon-nanoparticle-coated sepiolite hydrous-magnesium-silicate clay fibers are prepared by 220°C-autoclave hydrothermal carbonization of cellulose using 1.2-mol/L-hydrochloric-acid-pretreated sepiolite fibers. The deposited amorphous carbon nanoparticles (30–150 nm) nonuniformly and partially covering the sepiolite surface have surface functional groups (CH2, CH3, CC and CO), which enhance the organophilicity. Compared to a mixture of pristine sepiolite and hydrothermal carbon prepared without sepiolite, the carbon-coated sepiolite exhibits lower specific surface area but greater organic adsorption, due to the smaller pore size and particle size of the hydrothermal carbon coating compared to the hydrothermal carbon prepared without sepiolite. The acid pre-treatment decreases the sepiolite crystallinity and increases the deposited carbon content from 24.67 to 31.63 vol%, while increasing the specific surface area from 26.53 to 33.98 m²/g, increasing the fraction of phenol removed from 47.1% to 57.1%, and increasing the monolayer phenol adsorption capacity from 4.1 to 5.26 mg/g. Compared to the acid treated but uncoated sepiolite, the carbon coating decreases the density from 2.227 to 1.696 g/cm³ and decreases the specific surface area from 118 to 34 m²/g, but increases the fraction of phenol removed from 6.1% to 57.1%. The acid pre-treatment gives greater adsorption than the addition of acid to the hydrothermal process liquid.
A novel multifunctional inhibitor of MgAl-layered double hydroxides (LDHs) loaded with nitrite anions was synthesized via a calcination-rehydration in ambient atmosphere without inert gas protection. It was demonstrated that such LDHs loaded with inhibitor was able to efficiently control the corrosion of carbon steel in simulated carbonated concrete pore (SCCP) solution as well as in mortar. Based on the systematic measurements, a conceptual model was proposed to further understand the mechanism of multifunctional corrosion protection of MgAl-LDHs-NO2⁻ in steel reinforced concrete. Such unique multifunctional composite is markedly helpful to comprehensively control corrosion of steel in concrete.
Time-of-flight secondary ion mass spectroscopy (ToF SIMS) analysis was performed on 316L stainless steel polarized potentiodynamically up to different potentials in NaCl solution. The surface film thickness increased with the ending potential of the potentiodynamic polarization, when estimated by the oxygen ion depth profiles. The chloride ion intensities at the film/metal interface were correlated with the ending potentials during the potentiodynamic polarization and cumulative anodic charge densities that govern the pit initiation. The results and analysis support the passivity breakdown mechanisms considering the role of chloride ions at the metal/film interface, rather than at the film/solution interface.
This paper reports a new type of heterostructured materials based on the assembly of layered double hydroxides (LDH) to sepiolite fibrous clay. The assembly of Mg-Al and Zn-Al LDH has been explored following two procedures of synthesis: i) co-precipitation of the LDH in the presence of the clay; and ii) LDH reconstruction from the corresponding so-called “layered double oxide (LDO) phase” also in the presence of an aqueous dispersion of the clay. The resulting LDH/sepiolite nanoarchitectures were characterized by diverse physicochemical techniques (XRD, TG-DTA, FTIR, 29Si NMR, SEM and TEM), revealing the interaction of the generated LDH with sepiolite through the silanol groups at the external surface of the silicate. N2 adsorption–desorption isotherms evidence the effect of the sepiolite in providing a stable support for dispersing the LDH particles. The resulting materials show a relatively high external surface area and microporosity, with values depending on the sepiolite:LDH ratio in the final heterostructure. An interesting feature of these nanoarchitectures is related to the dual adsorption properties showing the possibility to simultaneously adsorb both cationic and anionic species. Moreover, the LDH can be transformed in the corresponding double metal-oxide by thermal treatment giving rise to nanoparticles that remain bonded onto the sepiolite fibers, which could be of interest in the preparation of highly disperse metal-oxide catalysts.
The aim of this study was to investigate how basic adsorption isotherms could be applied to predict removal efficiency or required adsorbent mass under given sets of initial conditions. The intrinsic parameters of the Langmuir and Freundlich adsorption isotherms were experimentally obtained and subsequently utilized to predict removal efficiencies for other sets of initial solute concentrations, solution volumes, and adsorbent masses, or to estimate the adsorbent mass required to remove solute at a desired removal efficiency. This was accomplished by combining the isotherms with mass balance of solutes between liquid solution and solid adsorbent phases.
