Dehydration Condensation Reaction Research Articles

On-line cure monitoring of phenol formaldehyde resin using embedded fiber Bragg grating sensor

On-line cure monitoring techniques have shown advantages for identifying the stages of curing and can lead to smart curing process of resin system and its composites. In this study, an on-line measuring technique with fiber Bragg grating (FBG) sensors was used to gain clear understanding of the curing stages of phenolic resin, as well as to determine its chemical shrinkage level. The FBG sensors were embedded in phenolic resin and worked under temperature raising and isothermal conditions. Through the interface between FBG sensor and resin, curing shrinkage strain was transferred to the grating, changing the central wavelength of FBG and producing strain. The feasibility of FBG sensors for monitoring chemical shrinkage during curing was verified by employing epoxy and benzoxazine resins that exhibits low chemical shrinkage. For cure monitoring of phenolic resin, the results show that the strain signal can be corresponded to various responses, such as solvent volatilization, hydroxylation and dehydration condensation reactions during temperature raising curing process. Through these strain characteristics, the curing state of phenolic resin can be obtained, which degree of cure ranges from 0.05 to 0.9. In isothermal curing process of phenolic resin, an exponential correlation between chemical shrinkage induced compressive strain and degree of cure of resin was identified, indicating that the real-time compressive strain is proportional to the degree of cure of phenolic resin. By evaluating real-time curing shrinkage levels, the estimation of curing degree of phenolic resin can be achieved utilizing exponential correlation of curing degree and curing shrinkage level.

Fabrication of hierarchical superhydrophobic structures by silane enriched with nanomaterials for enhancing permeability and freeze-thaw resistance

In this paper, the method of dehydration condensation reaction was used to establish a superhydrophobic cement mortar surface with the contact angle of 159.3° and the slide angle of 6.1° by using organosilane and inorganic nanomaterials. The nanoparticles built roughness and the silane provided low surface energy, which in combination achieved self-cleaning, waterproof and durability improvement. The superhydrophobic coating with good penetration depth is able to show superhydrophobicity after simply brushing and curing at room temperature for 24 hours and maintain hydrophobicity after surface abrasion. A variety of liquid droplets can roll freely from the surface of superhydrophobic cement mortar and carry contaminants rolling down to show self-cleaning performance. In terms of durability, the coating appears good adhesion to the surface of cement mortar, which retained its hydrophobic property after tape-peeling tests and outdoor simulation tests. In addition, compared with ordinary cement mortar, the superhydrophobic cement mortar demonstrates excellent waterproof ability and freeze-thaw resistance through low water absorption and slow quality reduction after multiple freeze-thaw cycles. These key characteristics provide advantages for concrete protection applications in harsh environments.

Cage-like octa(aminopropyl) silsesquioxane functionalized Ti3C2Tx for selective adsorption of Pb (II) ions by synergistic effect of coordination and oxidation

Transition metal carbides or nitride (MXene) have attracted wide attention due to their unique properties and promising applications in batteries, sensors, and catalysis. Due to its good hydrophilicity and abundant groups, it is also favored in environmental remediation. In this work, a cage-like octa(aminopropyl) silsesquioxane (POSS-NH2) was chosen as the modifier to decorate the Ti3C2Tx and an amino-rich lamellar material, Ti3C2Tx/POSS-NH2, was prepared successfully via a dehydration condensation reaction. Ti3C2Tx/POSS-NH2 shows excellent adsorption capability toward Pb (II) ions within a wide pH range with an optimal adsorption capacity of 552.31 mg·g–1 at the pH value of 6. Even at strong acidic conditions (pH=2), the value is still as high as 283.65 mg·g–1. The Ti3C2Tx/POSS-NH2 also shows preferential selectivity for lead ions in lead-containing wastewaters containing Cu (II), Zn (II), Fe (II) and Mg (II) ions. The kinetics, isotherm, and thermodynamic analyses were also studied. It is found that the adsorption process is an endothermic one and complies with the Langmuir isothermal adsorption model. The experimental data of Pb (II） ions adsorption by Ti3C2Tx/POSS-NH2 can be well simulated with the pseudo-second-order kinetic model. XPS and FTIR results showed that the Pb (II) ions were captured by a synergistic effect of coordination of -NH2 on the Ti3C2Tx/POSS-NH2 surface and the oxidation of oxygenated moieties in the layered structure of Ti3C2Tx. The excellent properties of Ti3C2Tx/POSS-NH2 allow it to occupy an important position in the treatment of lead-containing wastewater.

Improving water resistance and mechanical properties of starch-based films by incorporating microcrystalline cellulose in a dynamic network structure

The widespread use of starch-based films is hindered by inadequate tensile strength and high water sensitivity. To address these limitations, a novel starch film with a dynamic network structure was produced via the dehydration-condensation reaction of N, N′-methylene diacrylamide (MBA) and microcrystalline cellulose (MCC). The improvement in mechanical properties was enhanced by the incorporation of MCC, which was achieved through intermolecular hydrogen bonding and chemical crosslinking. To verify the interactions among MCC, MBA, and starch, x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and x-ray diffraction (XRD) were conducted. The results established the predicted interactions. The dynamic network structure of the film reduced the water absorption capacity (WAC) of starch and MCC hydroxyl groups, as confirmed by differential scanning calorimeter (DSC) and dynamic mechanical thermal analysis (DMTA). These analyses showed a restriction in the mobility of starch chains, resulting in a higher glass transition temperature (Tg) of 69.26 °C. The modified starch films exhibited excellent potential for packaging applications, demonstrating a higher contact angle (CA) of 89.63°, the lowest WAC of 4.73 g/g, and the lowest water vapor transmission rate (WVTR) of 13.13 g/m2/d, along with improved mechanical properties and identical light transmittance compared to pure starch films.

High-performance pyramid-SiNWs biosensor for NH3 gas detection

NH3 is widely existed in the environment and is closely associated with various health issues. Additionally, detecting the small amounts of NH3 exhaled by patients with liver and kidney diseases offers potential opportunities for painless early disease diagnosis. Therefore, there is an urgent need for a convenient, rapid, and highly sensitive real-time NH3 monitoring method. This work presents a high-performance NH3 sensor based on olfactory receptor-derived peptides (ORPs) on a pyramid silicon nanowires (SiNWs) structure substrate. First, we successfully fabricated the pyramid-SiNWs structure on a silicon substrate using a chemical etching method. Subsequently, by dehydrative condensation reaction between the amino groups on APTES and the carboxyl groups of ORPs, ORPs were successfully immobilized onto the pyramid-SiNWs structure. This methodology allows the ORPs sensor on the pyramid-SiNWs substrate to detect NH3 as low as 1 ppb, which was the reported lowest limit of detection, with a higher response rate compared to ORPs sensors on flat SiNWs substrates. The sensors also exhibit good sensitivity and stability for NH3 gas detection. The results show the feasibility and potential applications of ORPs-pyramid-SiNWs structure sensors, in the fields of food safety, disease monitoring, and environmental protection, etc.

(Invited) Bonding Strength of Cu-Cu Hybrid Bonding for 3D Integration Process

Introduction Cu-Cu hybrid bonding is a significant technology in the manufacture of 3D stacked semiconductor devices and is indispensable for the integration of 3D heterogeneous stacked packages.1 A process is used to thin the bonded semiconductor during 3D stacking integration, but delamination can occur when the bonding strength of the bonded interface is insufficient.Therefore, the bonding strength is a key factor in the 3D stacked integration process, and mechanisms for improving the strength have been thoroughly investigated. Cu-Cu hybrid bonding strength During Cu-Cu hybrid bonding, the bonding strength between bonded wafers, which is a crucial factor, is complicated to describe because of the various materials contained in the bonding interface. Because the bonding interface includes not only Cu/Cu and dielectric/dielectric films, but also Cu/dielectrics as a result of the misalignment of Cu pads, the strength of the Cu-Cu hybrid bond needs to comprehensively account for these interfaces. We investigated the relationship between the bonding strength and amount of misalignment using patterned Si substrates that were bonded after intentionally being aligned with an offset and thermally annealed.Although the bonding strength before annealing was confirmed to decrease lineally depending on the amount of misalignment, the wafers showed a different behavior after annealing in the region where the amount of misalignment was low. Simulation calculations elucidated the behavior of the overall bonding strength. When a Cu pad with a large recess contacted the opposing Cu pad, an uneven amount of pressure was generated between their contact surfaces because of the thermal expansion produced by the annealing. An area with very low pressure was also found between the surfaces, and extremely little or no diffusion occurred in this area.2 This phenomenon was not observed in a case where the amount of recess was small in both the experiments and simulation calculations, which showed linear relationships dependent on the misalignment after annealing.This study determined the misalignment dependence of the bonding strength after annealing considering the recess of the Cu pad, and an integrated model of the comprehensive bonding strength that included three interfaces involved in the Cu-Cu hybrid bonding could be presented. Improvement of bonding strength between dielectric films We are also continuing to study ways to improve the bonding strength of the interface between the dielectrics films that exist in the interfaces of a Cu-Cu hybrid bond. Elucidating the mechanism of strength generation would offer a guideline to improve the bonding strength.The dielectric films are bonded using a dehydration condensation reaction on the plasma-activated surface by thermal annealing. This bonding process has been widely studied from the perspective of the amount of surface Si-OH by considering the activation method and condition, type of dielectrics, and flatness of the surface. Because few investigations have considered factors other than the bonding interfaces, we focused on the influence of the H2O contained in the dielectric film to be bonded and investigated the relationship between the amount of H2O in the film and the bonding strength.The deposition conditions of the dielectric films produced using Plasma Enhanced Chemical Vapor Deposition (PE-CVD) were varied to prepare five types of films that contained various amounts of H2O. After CMP treatment of each film, the surface roughness and amount of Si-OH were measured, and it was confirmed that there was no significant difference. When the bonding strength was obtained by bonding using these films and plotted against the amount of H2O, it was found that the bonding strength was dependent on the amount of H2O. In addition, after being bonded and annealed, it was confirmed that the expansion of the dielectric film depended on the amount of H2O, as seen in cross-sectional STEM images of the interface.An investigation of the mechanism for this phenomenon suggested that the bonding strength was increased by filling the gap in the bonding interface through the expansion of the film. This study suggested that filling up the gap in the interface would be one approach for improving the bonding strength.These results offer a deep understanding of the mechanism for the bonding strength of Cu-Cu hybrid bonds and will contribute to the development of 3D stacking technology in the future.

A novel phosphorus-nitrogen-based hyperbranched polysiloxane for improving the fire safety of PA6 with suppressed melt droplets and good mechanical properties

The combustible defects of polyamide 6 (PA6), especially the flammable melt-dripping behavior, have greatly limited its application in some particular fields. In this work, a halogen-free hyperbranched polysiloxane (PBDSi) containing DOPO and Schiff base was designed via Michael's addition reaction and dehydration-condensation reaction. Results showed that the char yield (Yc) of PBDSi attained 37.9 wt%, confirming the satisfactory charring behavior of PBDSi for preparing flame-retardant PA6. Just by adding 3 wt% of PBDSi, the serious melt droplets of PA6 were suppressed effectively. The prepared PA6/PBDSi-3 with 5 wt% of PBDSi could achieve the highest value of limited oxygen index (LOI) of 27.2 %, while that of PA6 is 21.0 %. Meanwhile, PA6/PBDSi-3 obtained an apparent reduction in the peak heat release rate (PHRR) value of 31.1 % compared with pure PA6. The cooperated effect of DOPO, Schiff base, and polysiloxane that contributed to generating a silicon-phosphorous-rich char layer and releasing incombustible volatiles that were determined to be the essential factor for the improved fire safety of PA6/PBDSi were explored intensively. Inspiringly, PA6/PBDSi composites exhibited a slight mechanical loss concerning PA6, overcoming the great challenge of developing additive flame-retardant materials to balance mechanical properties and fire safety.

The impact of H-ZSM-5 catalyst on the mechanism of fuel-N conversion during glutamic acid pyrolysis

During the pyrolysis of biomass, Fuel-bound Nitrogen (Fuel-N) is converted into N-containing compounds present in bio-oil and biochar. These compounds are easily oxidized into NOx during subsequent utilization, causing ecological damage. Catalytic fast pyrolysis has emerged as a promising method for denitrogenation in recent years, but the underlying catalyst mechanism still needs to be determined. This study analyzed the impact of catalyst H-ZSM-5 on the mechanism of Fuel-N conversion during the pyrolysis of glutamic acid, a model compound for nitrogenous biomass, through experimental studies and theoretical calculations. According to literature data, the pyrolysis of glutamic acid predominantly yielded the N-containing products pyrrole, glutarimide, and pyrrolidone. The H-ZSM-5 catalyst showed optimum denitrification at 600 ℃, resulting in a 49.62% reduction in the proportion of N-containing compounds. In the catalytic pyrolysis products, the generation of toluene and naphthalene increased. In-situ DRIFTS experiments were consistent with the results of Py-GC-MS experiments, with catalytic pyrolysis promoting deaminations and decarboxylations, decreased imines and nitriles, and increased aromatic hydrocarbons. Additionally, the energy barrier changes of each pyrolysis pathway were calculated based on Density Functional Theory (DFT). The results showed that the H-ZSM-5 catalyst primarily promoted the deamination reaction, followed by the decarboxylation and dehydration condensation reactions, while inhibiting the dehydrogenation reaction. Moreover, the energy barrier for unsaturated hydrocarbon addition reactions was reduced, facilitating the formation of aromatic compounds. The acid sites inside the H-ZSM-5 catalyst weakly interacted with the reactants, making it easier to detach the amino group during catalytic pyrolysis. This study provides a reference for the denitrification of bio-oil and biochar. Subsequent work can realize the regulation of nitrogen conversion by changing the acidity and concentration of catalyst acid sites.

Effect of the Chemical Properties of Silane Coupling Agents on Interfacial Bonding Strength with Thermoplastics in the Resizing of Recycled Carbon Fibers

Upcycling recycled carbon fibers recovered from waste carbon composites can reduce the price of carbon fibers while improving disposal-related environmental problems. This study assessed and characterized recycled carbon fibers subjected to sizing treatment using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (APS) chemically coordinated with polyamide 6 (PA6) and polypropylene (PP) resins. Sizing treatment with 1 wt.% APS for 10 s yielded O=C-O on the surface of the carbon fiber, and the -SiOH in the APS underwent a dehydration–condensation reaction that converted O=C-O (lactone groups) into bonds of C-O (hydroxyl groups) and C=O (carbonyl groups). The effects of C-O and C=O on the interfacial bonding force increased to a maximum, resulting in an oxygen-to-carbon ratio (O/C) of 0.26. The polar/surface energy ratio showed the highest value of 32.29% at 10 s, and the interfacial bonding force showed the maximum value of 32 MPa at 10 s, which is about 15% better than that of commercial carbon fiber (PA6-based condition). In 10 s resizing treatments with 0.5 wt.% 3-methacryloxypropyltrimethoxysilane (MPS), C-O, C=O, and O=C-O underwent a dehydration–condensation reaction with -SiOH, which broke the bonds between carbon and oxygen and introduced a methacrylate group (H2C=C(CH3)CO2H), resulting in a significant increase in C-O and C=O, with an O/C of 0.51. The polar/surface free energy ratio was about 38% at 10 s, with the interfacial bonding force increasing to 27% compared to commercial carbon fiber (PP-based conditions). MPS exhibited a superior interfacial shear strength improvement, two times higher than that of APS, with excellent coordination with PP resin and commercial carbon fiber, although the interfacial bonding strength of the PP resin was significantly lower.

Novel Carboxylation Method for Polyetheretherketone (PEEK) Surface Modification Using Friedel–Crafts Acylation

Recently, polyetheretherketone (PEEK) has shown promising dental applications. Surface treatment is essential for dental applications owing to its poor surface energy and wettability; however, no consensus on an effective treatment method has been achieved. In this study, we attempted to carboxylate PEEK sample surfaces via Friedel–Crafts acylation using succinic anhydride and AlBr3. The possibility of further chemical modifications using carboxyl groups was examined. The samples were subjected to dehydration–condensation reactions with 1H,1H-pentadecafluorooctylamine and N,N’-dicyclohexylcarbodiimide. Furthermore, the sample’s surface properties at each reaction stage were evaluated. An absorption band in the 3300–3500 cm−1 wavenumber region was observed. Additionally, peak suggestive of COOH was observed in the sample spectra. Secondary modification diminished the absorption band in 3300–3500 cm−1 and a clear F1s signal was observed. Thus, Friedel–Crafts acylation with succinic anhydride produced carboxyl groups on the PEEK sample surfaces. Further chemical modification of the carboxyl groups by dehydration-condensation reactions is also possible. Thus, a series of reactions can be employed to impart desired chemical structures to PEEK surfaces.

Study on a nano-porous gold/polyamidoamine (NPG/PAMAM)-based electrochemical aptamer biosensor for the detection of ochratoxin a in the red wine

In this study, a novel electrochemical aptamer sensor for detecting ochratoxin A (OTA) was constructed. First, a gold-copper alloy film was prepared via electrochemical deposition, and copper was selectively dissolved in constant potential mode for obtaining the nano-porous gold modified screen-printed carbon electrodes (NPG/SPCE). Then, 2-mercaptoethylamine was dropped on the NPG/SPCE surface and Au-S covalent bonds were formed for immobilizing the metal. Glutaraldehyde as cross-linking agent was added, which resulted in immobilization and attachment of PAMAM to the 2-mercaptoethylamine through the dehydration condensation reaction. During the preparation process, the nano-porous gold and PAMAM-modified layers were characterized by SEM, XRD, and IR spectroscopy, respectively. The characterization results showed that the nano-porous gold and PAMAM composite films were successfully modified. Finally, the OTA aptamer was cross-linked with PAMAM by glutaraldehyde to complete construction of the Apt/PAMAM/NPG/SPCE sensor. The electrochemical performance of this sensor was tested in ochratoxin A solutions with the DPV method. The results showed that the sensor’s reproducibility, stability, and specificity were good. The spiked recoveries in red wine ranged from 99.65%∼101.6%, with a linear range of 0.5 ng/mL∼20 ng/mL and a minimum detection limit of 0.141 ng/mL. Thus, the novel biosensor may provide a promising tool for the trace detection of OTA.

High-loading of organosilane-grafted carbon dots in high-performance luminescent solar concentrators with ultrahigh transparency

Carbon dots (CDs) generally suffer from aggregation-induced fluorescence quenching effect in solid-state, which significantly limits their application in photoelectric devices. Due to this effect, it is a great challenge to achieve high-transparency and high-performance luminescent solar concentrators (LSCs) based on CDs. Here, the synthesis of organosilane-grafted carbon dots (Si-CDs) is rationally designed by hydrothermal method using anhydrous citric acid, ethanolamine and KH-792 as the reaction precursors. The obtained Si-CDs can be uniformly dispersed in the polyvinyl alcohol (PVA) matrix through the dehydration condensation reaction and hydrogen bonding between the silicon hydroxyl group of Si-CDs and the hydroxyl group of PVA. Based on this property, Si-CDs/PVA thin-film LSCs (5 ×5 ×0.2 cm3) with ultrahigh CD loading (25 wt%) and high transparency can be fabricated, exhibiting excellent absorption in the UV spectral region and about 90 % transmission in the visible range. Furthermore, the power conversion efficiency (PCE) of the LSCs can reach 2.09 % under a standard solar light and shows excellent stability even over 12 weeks. This synthetic design is expected to be beneficial for future development of CD synthesis and paves the way for the development of CDs-based photoelectric devices.

Synthesis of N-Unprotected Diaryl Ketimines and Alkyl Ketimines from Ketones and Ammonia Using Porous Solid Acids with Analysis of Their Adsorption Behavior

Abstract The most atom-efficient synthetic method for N-unprotected ketimines (N-H ketimines) from ketones is the dehydration condensation reaction with ammonia (NH3). However, until now, few synthetic methods for N-H ketimines with high versatility have been known. In this study, we examined various solid acids and found that N-H diaryl ketimines with various functional groups on the aryl groups could be synthesized in high yields from diaryl ketones and NH3 under solvent-free conditions using silica-alumina (SiO2-Al2O3) or proton-exchanged Y-type zeolite (H-Y). Solid-state 13C and 15N NMR measurements indicated that the N-H ketimine formed in the pores of acidic zeolite was coordinated to NH4+ species on the pore surface. By quantum chemical calculations we also discussed the reason why the dehydration-condensation reaction between ketone and NH3, which is an endothermic reaction in a vacuum, was biased toward the product side in the actual experiment. In addition, this synthetic method can be applied to synthesize N-H alkyl ketimines with α-acidic hydrogens, which are less stable and more sensitive to hydrolysis and oligomerization than diaryl ketimines.

N–N Bond Formation by a Small-Ring Phosphine Catalyst via the PIII/PV Cycle: Mechanistic Study and Guidelines to Obtain a Good Catalyst

The mechanism of the N–N cross-coupling of nitroarene and aniline catalyzed by 1,2,2,3,4,4-hexamethylphosphetane oxide (1PO) as well as the prediction of a better catalyst was theoretically investigated using DFT and DLPNO-CCSD(T) calculations. An active species 1P is generated through deoxygenation of 1PO by diphenylsilane. Then, 1P extracts one oxygen atom from nitroarene to produce nitrosoarene. In this deoxygenation step, the [3 + 1] cheletropic addition is a rate-determining step with the ΔG0≠ and ΔG0 values of 28.8 and −7.3 kcal/mol, respectively. Next, nitrosoarene exclusively undergoes a dehydrative condensation reaction with aniline to form an azo-cation intermediate, which is the origin of the high selectivity in this cross-coupling reaction. In this step, 2,4,6-trimethylbenzoic acid plays an essential role to significantly reduce the ΔG0≠ value from 41.1 to 14.8 kcal/mol. Subsequently, 1P reacts with the azo cation to form a stable hydrazinylphosphonium species through the nucleophilic attack of the phosphorus atom to the cationic nitrogen atom. The phosphonium center preferably accepts a hydroxyl group from water to ensure the formation of hydrazine in the subsequent step. In the [3 + 1] cheletropic addition step, the highest occupied molecular orbital (HOMO) of 1P plays an important role. The small-ring scaffold of 1P raises the HOMO energy compared to acyclic phosphorus compounds to achieve high activity of 1P. Substitution of a dimethylamino group for the methyl group in 1P was theoretically predicted to improve the activity by further increasing the HOMO energy.

Multiscale analysis of silane coupling agent modified rubber-fiber concrete interfaces

This study employs PVA fibers to improve the performance of rubber concrete and silane coupling agent to change the incompatibility between rubber and cement in order to weaken the issue of a weak interfacial transition zone between rubber and cement foundation (KH570). The results showed that 1.5% content of KH570 modified 15% content of rubber-1.5% content of PVA fiber with the best effect. KH570 was identified using XRD, FTIR, and SEM characteristics. It was discovered that KH570 experienced a dehydration condensation reaction with free or adsorbed water in the cement, which helped to maintain the integrity between the cement matrix and the rubber. It strengthened the bond between the cement, the rubber, and the PVA fibers and enhanced the cement's capacity to encapsulate the rubber. Finally, molecular dynamics simulations reveal that cement and rubber are connected by Si-O-Si and molecules appear to be cross-distributed, increasing interfacial compatibility and reducing interfacial effects. It can be clearly observed in the interfacial bonding mechanism that KH570 is mainly a C-S-H matrix with parallel or perpendicular connections at the tail end.

Gln-Lys isopeptide bond and boroxine synergy to develop strong, anti-mildew and low-cost soy protein adhesives

The development of renewable soy protein (SP) adhesives has aroused growing interest in the wood industry. This research aims to develop a low-cost, sustainable, and high-performance SP adhesive without a petrochemical crosslinker. The hard skin barrier benefits from the dense cross-linked layer of cuticle cells constructed by the peptide bonds between membrane proteins and the dehydration condensation reaction between adjacent hydroxyl groups of polysaccharides. Inspired by the above skin mechanism, a biomimetic strategy of commercially available transglutaminase (TGase) was applied, which constructed Gln-Lys isopeptide bonds within the SP chains. The covalent boroxine structure formed by dehydration of the hydroxyl groups of boronic acid engineered a dense and robust network like skin barrier, converting the SP into a strong, water-resistant, anti-mildew, and flame-retardant adhesive. The resultant adhesive showed outstanding wet shear strength of 1.55 MPa, about 138.5% greater than the pure SP adhesive, and the residual rate increased from 86.19% to 95.99%. The small content of TGase achieved satisfactory performances and low-cost SP adhesive, establishing its usefulness as a crosslinker to replace the petroleum-based modifiers. Notably, the boronic acid mounted on the SP chains by TGase protected proteins from microbial consumption, thus extending the anti-mildew shelf-life of the liquid adhesives from 2 to 15 days. Moreover, the dense and rigid structure containing Gln-Lys isopeptide bonds and boroxine network effectively improved the flame resistance of the cured adhesives, which reduced the peak heat release rate (PHRR) from 95.1 to 84.2 W/g. Therefore, this simple bionic strategy achieved the goal of formulating green, low-cost, high-performance, and multifunctional SP-based adhesives.

Investigation of the hydrophobicity and microstructure of fly ash-slag geopolymer modified by polydimethylsiloxane

The replacement of geopolymer for Portland cement exhibits the potential for reducing the CO2 footprint and saving natural resources during the production of building materials. However, geopolymer is a class of inorganic cementitious material, easy to suffer water intrusion with aggressive ions, such as chloride and sulphate, resulting in the destruction of structural integrity. In this study, hydroxyl-terminated polydimethylsiloxane (PDMS) was used as an additive to improve the hydrophobicity of fly ash-slag geopolymer. The microstructure was characterized using mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the contact angle (CA) of the geopolymers increased from 57.32° to 127.64°, and the water absorption decreased from 6.96% to 1.61% as a function of the dosages of PDMS, contributing to the hydrophobic nature of the geopolymers. On the other hand, the addition of PDMS led to the formation of a less compact pore structure of geopolymers, accompanied by a transformation from internal gel pores into capillary pores and macropores. The pore enlargement will have adverse effects on the compressive strength of the geopolymers, but it can still meet the requirements for daily work. According to the analysis of microscopic test results, PDMS and N-A-S-H gel were likely to undergo dehydration condensation reaction in a strong alkaline environment, they were connected in the form of covalent bonds, so that the geopolymers have hydrophobicity.

Elucidation of exhaust gas recirculation deposit formation mechanism based on chemical analysis of components

To comply with strict emission regulations, vehicles are equipped with exhaust gas recirculation (EGR) systems that control nitrogen oxide emissions by returning part of the exhaust gas to the intake air. However, since deposits form in the EGR piping and valves, leading to pipe clogging, valve sticking, and in the worst case, failure of these components, there is a need to clarify the mechanism of deposit formation to predict and reduce deposit accumulation. While most of the previous studies have focused on the powdery deposits that clog the EGR cooler, this study aims to elucidate the formation mechanism of both the lacquer-like hard deposits and wet soft deposits that cause EGR valve sticking by quantitative and molecular-level analyses. In these experiments, a portion of the exhaust gas from an actual diesel engine without soot removed by diesel particulate filter (DPF) was used. Deposits were continuously generated on a simulated EGR line with a downstream temperature gradient from the engine outlet, while measuring the inner wall temperature. The collected deposits were subjected to comprehensive chemical analysis. The analysis showed that 75 % of the solvent-soluble deposit components were polycyclic aromatic hydrocarbons (PAHs), which were the main component of the hard and soft deposits. Most of the PAHs in the hard deposits that formed at a high inner wall temperature were C17 or higher. The hard deposit with an inner wall temperature of 137 °C contained 0.016 mg/cm2 of 6-ring benzo[ghi]perylene and 0.26 × 10-3 mg/cm2 of 4-ring pyrene. On the other hand, the soft deposit is formed at an inner wall temperature of 80 °C, contained 0.022 mg/cm2 of pyrene, which is significantly more than in the hard deposit. This shows that PAHs in the exhaust gas condense when the gas temperature reaches their dew points, and that the deposits formed at higher inner wall temperatures contain more PAHs with higher boiling points. High-molecular weight aromatic compounds with oxygen and nitrogen functional groups were detected in the solvent-insoluble deposit components. These compounds were found to be derived from the polymerization of oxygenated and nitrogenated PAHs through dehydration condensation and cross-linking reactions.

Construction of diphenic acid molecular welded Ti3C2 with enlarged and stable interlayer spacing towards high rate alkali metal ions storage

Ti3C2-MXene has been generally studied in energy storage area because of adjustable surface chemistry, excellent electronic conductivity, and unique layered structure. However, the diffusion kinetic performance of alkali metal ions in Ti3C2 is restricted by the limited interlayer spacing. Enlarging interlayer spacing of Ti3C2 is beneficial to improve the ion diffusion rate. Here, a simple and effective diphenic acid (DHA) molecular welding strategy is reported to prepare DHA welded Ti3C2 (DHA-Ti3C2) by dehydration condensation reaction. The welded DHA molecule contributes the dual effects of pillar and strain on the layered structure of Ti3C2, which can improve ion diffusion kinetic performance and alleviate volume expansion during the alkali metal ions insertion/extraction process. The DHA-Ti3C2 exhibits high rate capability and long-term cycle stability because of the enlarged interlayer spacing and enhanced structure stability. The specific capacity of 444 mAh g−1 and 156 mAh g−1 at current density of 0.1 A g−1 can be reached after 200 cycles and 1700 cycles in Li+/Na+ batteries, respectively. This study offers a strategy to efficiently tuning the layered structure of two-dimensional (2D) materials for achieving the optimal alkali metal ions storage performance.

Self-Assembly of a U(VI)-Containing Polytungstate Tetramer with Lewis Acid-Base Catalytic Activity for a Dehydration Condensation Reaction.

A novel U(VI)-containing polytungstate (U-POW) tetramer, {K1.37Na26.63[K2(UO2)4Cl0.5(OH)5.5(γ-SiW10O36)4]}·ca66H2O (U4), was synthesized using the Keggin-type precursor [γ-SiW10O36]8- and UO2(NO3)2. U4 was further characterized by single-crystal X-ray diffraction, FT-IR, Raman spectroscopy, solid-state diffuse reflection spectroscopy, ICP-OES, ESI-MS, TGA, and PXRD. The central {K2(UO2)4Cl0.5(OH)5.5} chromophore was constructed dexterously from four uranyl, four halves of K ions, 5.5 bridging μ2-OH, and disordered Cl ions, and was further stabilized by four {γ-SiW10} moieties to construct the tetramer [K2(UO2)4Cl0.5(OH)5.5(γ-SiW10O36)4]28-. Notably, U4 could work as an effective bifunctional Lewis acid-base catalyst for the synthesis of pyrazoles via the condensation of hydrazines with 1,3-diketones under mild conditions, which is attributed to the synergetic effect of the Lewis acidity of U(VI) and the Lewis basicity of {γ-SiW10}.