Condensation Of Hydroxyl Groups Research Articles

Controllable interlayer hydroxyl condensation of MWW zeolite and its alkylation performance of benzene with ethylene

MWW zeolite holds great promise in the petrochemical industry. However, achieving precise control over its dimension and interlayer hydroxyl condensation remains challenging when using a single, low-toxicity, readily available template. In this study, the rational and targeted hydrothermal synthesis of two-dimensional (2D) MCM-22(P) and three-dimensional (3D) MCM-49 using low-toxic piperidine is realized. The synergistic effect of the organic template and inorganic ions plays a crucial role in the precise synthesis of 2D and 3D MWW zeolite. In contrast to the traditional hexamethyleneimine template, piperidine introduces a distinct characteristic whereby disordered MWW layers coexist with the synthesized products. Specifically, the higher concentration of Na+ species directs more Al species to locate in the T1 site, promoting the condensation of interlayer hydroxyl and leading to the formation of 3D MWW zeolite. In contrast, a system with abundant PI can suppress the condensation of interlayer hydroxyl, resulting in the formation of 2D MWW zeolite. H-MCM-49 synthesized exhibits higher ethylene conversion and ethylbenzene selectivity than H-MCM-22 in the liquid alkylation of benzene and ethylene.

Advances in the green and controllable synthesis of MWW zeolite.

MWW zeolite is one of the commercialized zeolites that shows great promise in heterogeneous catalysis and other interdisciplinary application fields due to its coexisting multi-channel system. The green and controllable synthesis of MWW zeolite is conducive to its more efficient and broader application. Many researchers focus on precisely controlling the dimension, interlayer hydroxyl condensation, and aluminum siting, as well as obtaining MWW with low-toxicity, readily available organic structure directing agents (OSDAs) or without OSDAs. This review summarizes recent advancements in the synthesis and application of MWW zeolite, with a particular emphasis on selecting different OSDAs, controlling the interlayer condensation degree and adjusting aluminum distribution. Future research directions and development trends of MWW zeolite are also forecasted.

Preparation of Hydrophobic Octadecylphosphonic Acid-Coated Magnetite Nanoparticles for the Demulsification of n-Hexane-in-Water Nanoemulsions.

To design more environmentally friendly, economical, and efficient demulsifiers for oily wastewater treatment, hydrophobic octadecylphosphonic acid (ODPA)-modified Fe3O4 nanoparticles (referred to as Fe3O4@ODPA) were prepared by condensation of hydroxyl groups between ODPA and Fe3O4 nanoparticles using the co-precipitation method. The prepared magnetite nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric/differential thermogravimetric (TG/DTG) analysis. The water contact angles (θW) of Fe3O4@ODPA nanoparticles were more than 120°, indicating hydrophobic nature, and the diameter of the obtained spherical-shaped magnetite nanoparticles was 12-15 nm. The ODPA coating amount (AO) (coating weight per gram Fe3O4) and specific surface area (SO) of Fe3O4@ODPA were 0.124-0.144 g·g-1 and 78.65-91.01 m2·g-1, respectively. To evaluate the demulsification ability, stability, and reusability, the magnetite nanoparticles were used to demulsify an n-hexane-in-water nanoemulsion. The effects of the magnetite nanoparticle dosage (CS), pH value of nanoemulsion, and NaCl or CaCl2 electrolytes on the demulsification efficiency (RO) were investigated. The RO of Fe3O4@ODPA samples was found to be higher than that of bare Fe3O4 samples (S0, ST, and SN) under all CS values. With the increase in CS, the RO of Fe3O4@ODPA samples initially increased and then approached equilibrium value at Cs = 80.0 g·L-1. A maximum RO of ~93% was achieved at CS = 100.0 g·L-1 for the Fe3O4@ODPA sample S2. The pH and two electrolytes had a minor effect on RO. The Fe3O4@ODPA nanoparticles maintained high RO even after being reused for demulsification 11 times. This indicates that the hydrophobic Fe3O4@ODPA samples can be used as an effective magnetite demulsifer for oil-in-water nanoemulsions.

Synthesis and Characterization of Novel Phenolic Resin/Siloxane Aerogels via Ambient Pressure Drying

Novel phenolic resin/silicone aerogels (PR-Si) were prepared through a facile sol-gel polymerization and ambient pressure drying process without solvent exchange. Without the addition of an additional catalyst, the hydroxyl condensation reaction between the siloxane oligomer and the phenolic resin resulted in the silicon being incorporated into the PR. The obtained aerogels exhibited high compressive strength (0.84–21.11 MPa) and low thermal conductivities [0.046–0.077 W/(m·K)]. The introduction of a Si–O network structure in the PR effectively improved the mechanical properties and thermal stability of aerogels. It is clear from the TGA plot that the mass loss temperature of the PR-Si aerogel was increased by 73 and 79 °C for the weight loss temperatures of 5 and 10% compared to cured pure PR.

A three-dimensional network modifier (dimethyldiethoxysilane) makes ZrO2-SiO2 aerogel with excellent thermal insulation performance and high-temperature stability

Dimethyl-diethoxysilane-modified ZrO2-SiO2 aerogels (DDS/ZSAs) have been prepared by using diethoxydimethylsilane as a co-precursor in the sol-gel process. Dimethyldiethoxysilane acts as a modifier for the three-dimensional structure and composition of aerogels. The pore volume increased from 1.65 cm3/g to 3.21 cm3/g, and the thermal conductivity decreased from 0.03013 Wm−1K−1 to 0.02332 Wm−1K−1 at room temperature. The number of hydroxyl groups on the aerogel surface is effectively reduced, and the particle growth caused by hydroxyl condensation was inhibited during firing. The increase in the number of Si-O-Zr bonds inhibited the growth of t-ZrO2, the phase transition temperature of the aerogel was significantly improved, and the crystallinity and crystal plane types were significantly reduced. Therefore, the porous microstructure of the modified aerogel remains good at 1000 °C. After heat treatment at 1000 °C, it still has a high specific surface area (259.6 m2/g), a high pore volume (1.51 cm3/g), and a low thermal conductivity (0.04206 Wm−1K−1). The thermal insulation performance and temperature resistance of ZrO2-SiO2 aerogels were double improved. In addition, DDS/ZSAs have high hydrophobicity and can be used in harsh wet and high-temperature environments. The research work is instructive for the design of superthermal insulation materials with high thermal stability and low thermal conductivity.

Surface hydroxyl modification for silicate-stabilized low-melting glassy tellurite adhesive enabling low resistance of silver conductive paste

With the booming development of new electronic devices, the demand of high-end silver conductive paste has been sharply increased. In this study, we achieve low sheet resistance silver paste by using silicate stabilized glassy tellurite adhesive with hydrophobic surface through effective surface modification. We developed a wet milling process and employed lauryl gallate to remove surface hydroxyl content of micro-scale silicate-containing tellurite low-melting glasses. This surface modification can effectively prevent agglomeration caused by hydroxyl condensation, meanwhile eliminate defects of sintered silver layer. The introduction of silicate to tellurite glassy adhesive is used to improve water and alkaline resistance and corrode wafer surface to enhance its contact with silver. A sintered silver layer with low sheet resistance of 35.6 mΩ/□ was obtained, despite only 1–3 μm size silver particles are used and sintered at relatively low temperature around 500 °C. This research provides a practical path-forward of improving overall performance of metal conductive pastes from a new angle of innovating glassy adhesive.

Synthesis of Novel Ionic Porous Organic Polymers and Its Application in Hydroxyl Condensation Reaction

Synthesis of Novel Ionic Porous Organic Polymers and Its Application in Hydroxyl Condensation Reaction

Study on the Hydrophobic Modification of MTES/NH3 Vapor Surface Treatment for SiO2 Broadband Anti-Reflection Coating.

In this article, ammonia and methyltriethoxysilane (MTES) were chosen as vapor phase modifiers for the base-catalyzed SiO2 film. The surface of the film became more dense because of the hydroxyl condensation under the catalyst of ammonia, while the introduction of methyl groups by MTES of vapor treatment hindered the condensation to avoid over-change in film thickness. The hydrophobic of film was improved while the surface roughness of the film increased after treatment. The treated double-layer broadband anti-reflection (AR) coating retains high optical properties with the transmittance of 99.61%, 98.85%, and 99.16% at 355 nm, 532 nm, and 1064 nm, respectively. After exposing to the high humidity condition for 30 days, the broadband AR coating after treatment shows good optical durability, and the transmittance at 355 nm only drops by 0.12%. This vapor surface treatment can find potential application in high-power laser systems and solar cells.

Oriented valorization of cellulose and xylan into anhydrosugars by using low-temperature pyrolysis

Fast pyrolysis is a promising method to convert cellulose and hemicellulose into anhydrosugars, but the current method is energy intensive and provides poor yield and selectivity for anhydrosugars. The possibility of using mineral acid pretreatment to achieve oriented pyrolysis of cellulose and xylan at low temperature was explored in this study. The pyrolysis behaviors and mechanism of cellulose and xylan were investigated by pyrolysis–gas chromatography/mass spectrometry and in-situ diffuse reflectance infrared Fourier transform spectroscopy combined with two-dimensional perturbation correlation infrared spectroscopy. The results showed that H2SO4-impregnation and HCl-demineralization achieved the oriented pyrolysis of cellulose and xylan into anhydrosugars at 300 °C. The highest yields of levoglucosan and levoglucosenone (33.3 and 9.7%) were obtained from pyrolysis of 0.1%H2SO4-impregnated cellulose at 300 °C, while those of xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose (19.4 and 8.4%) were produced from pyrolysis of HCl-demineralized xylan at 300 °C. It is inferred that H2SO4 could promote the condensation of hydroxyls at C6 and C1 positions and the cleavage of glycosidic bonds to form levoglucosan. And AAEMs could inhibit the intra-molecular dehydration of C3 hydroxyl and C2 hydrogen atom of levoglucosan to form levoglucosenone. The demineralization of xylan could promote the cleavage of glycosidic bonds and dehydration reactions to form xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose. These findings provide a simple method to achieve oriented pyrolysis of cellulose and xylan at low temperature.

The interaction of water with organophosphonic acid surface modified titania: An in-depth in-situ DRIFT study

Organophosphonic acid surface modification is performed to alter the surface properties of titania or other ceramics. By changing the modification conditions the physicochemical properties of the surface can be controlled. While these changes have been studied on the macroscale for different functional groups, showing differences in sorption behavior and application, their local impact on the surface OH-groups and resulting interaction with water is still unclear. Hence, we report an in-depth in-situ IR investigation supported by quantum chemical calculations and focused on the states of adsorbed water and the surface OH-groups of organophosphonic acid modified P25. Infrared spectra are recorded from fully saturated to fully dehydrated state by systematic desorption in vacuum and in function of temperature. Interesting differences in water desorption/interaction behavior for propylphosphonic acid modified titania are revealed, in which not only the number of grafted groups but also their distribution influences (the strength of) the interaction with water. Furthermore, when modifying with phenylphosphonic acid, additional water interactions in between the aromatic rings, could be observed. Finally, an interesting difference in thermal behavior of surface hydroxyl condensation could be observed for the modified surfaces. In contrast to pristine P25, they still feature surface hydroxyl groups at 250 °C.

Surface acoustic wave ammonia sensor based on SiO2–SnO2 composite film operated at room temperature

Sensitive thin film layers of SnO2, SiO2 and SiO2–SnO2 were deposited on a surface acoustic wave resonator using sol-gel method and spin coating techniques. Their ammonia-sensing performance operated at room temperature was characterized and their sensing mechanisms were comprehensively studied. When exposed to ammonia, the sensors made of SnO2 and SiO2–SnO2 films exhibit positive frequency shifts, whereas the SiO2 film sensors exhibit a negative frequency shift. The positive frequency shift is related to the dehydration and condensation of hydroxyl groups, which makes the films stiffer and lighter. The negative frequency shift is mainly caused by the increase of mass loading due to the adsorption of ammonia. The gas sensor based on SiO2–SnO2 film shows a positive frequency shift of 631 Hz when it is exposed to ammonia with a low concentration of 3 ppm, and it also shows good repeatability and stability, as well as a good selectivity to ammonia compared with gases of C6H14, C2H5OH, C3H6O, CO, H2, NO2, and CH4.

Thermal decomposition of aluminum carboxylates based precursor for alumina fibers

The thermal decomposition process of alumina precursor fibers plays an important role in the preparation of high-performance alumina fibers. In this study, alumina precursor fibers were prepared by sol–gel method, using aluminum carboxylate system. The evolution of the precursor fiber composition and microstructure during the thermal decomposition process was systematically investigated. The thermogravimetric-mass spectroscopy and thermogravimetric-differential scanning calorimetry curves indicated that decomposition process of precursor fibers mainly consisted of five stages, which occurred at 100, 150, 200, 370, and 580 °C, respectively. The chemical structure of fibers was characterized by fourier transform infrared spectroscopy and elemental analysis, which verified the removal of C and N elements from the precursor fibers and the formation of Al–O–Al skeleton structure during the decomposition process. These results demonstrated that the five stages correspond to the removal of free water molecules, dehydration and condensation of hydroxyl groups, decomposition of some carboxylates, complete decomposition of nitrate acid radical as well as formic acid radicals, and total decomposition of acetic acid radicals. Furthermore, the thermal decomposition kinetics of alumina precursor fibers was investigated by Kissinger and Flynn–Wall–Ozawa (FWO) methods. The activation energies (Ea) for the five stages were calculated by Kissinger method, and the results were proved to be relatively accurate by the FWO method.

Organic–inorganic hybrid hydrophobic Mg(OH)2−xFx–MTES coating with ultraviolet durability and high visible transmittance

Hollow rod-like Mg(OH)2−xFx sol was synthesized by a solvothermal method, and then organic–inorganic hybrid Mg(OH)2−xFx–MTES copolymer sol was obtained by a hydroxyl condensation reaction between Mg(OH)2−xFx and MTES hydrolysate. The copolymer sols were deposited on glass substrates by a dip-coating method. The results showed that the average transmittance of the coating reached 99.13% in the visible wavelength range of 400–800 nm, and the water contact angle of the coating reached 133.3°. After the coatings were irradiated by ultraviolet light for 1200 h, the transmittance and the water contact angle of the coatings were hardly affected, the coatings exhibited excellent hydrophobicity and ultraviolet durability. At the same time, the mechanical properties of the coating are greatly enhanced by the formation of Si–O–Mg bond and the coatings have the advantage of durability in harsh environments.

Influence of graphene oxide on ‘in situ’ preparation of nanocomposites with polyvinyl butyral

In this work, polyvinyl butyral (PVB) nanocomposites reinforced with 0.5 to 2.5 wt% of graphene oxide (GO) were synthesized via „in situ‟ polymerization. PVB was obtained by condensation of hydroxyl groups of polyvinyl alcohol (PVA) with butyraldehyde (BU) Thermogravimetric analyzes (TGA) showed the increase in the thermal conductivity of the nanocomposites compared to PVB. FTIR results showed the conversion of PVA to PVB, but no changes in the spectrum were observed for nanocomposites. Nuclear magnetic resonance spectroscopy (1H NMR) shows a change in the degree of acetalization of PVB with the presence of the nanoparticles. When the increase in the concentration of GO, a decrease in the degree of acetalization of PVB is observed. The differential scanning calorimetry (DSC), show a decrease in Tg values, probably caused by the change of degree of acetalization. The results of the Raman spectroscopy analysis show upshift in the G band up to 20 cm-1, associated with the presence of van der Walls interaction between the GO and PVB and the mechanical compression phenomena of the GO nanoparticles are compressed in the „bulk‟ of polymer. Thus, it was observed that the „in situ‟ polymerization process contributed to the formation of a colloid between GO and water used as solvent in the synthesis. The formation of this colloid helped to improve the interfacial interaction between GO and PVB. However, the presence of GO also contributed to change the degree of acetalization of PVB, as it decreased the condensation of some hydroxyl groups of the precursor PVA degree of acetalization. Keywords: polyvinyl butyral, graphene oxide, nanocomposites.

Improvement of Thermal Stability of ZrO<sub>2</sub>-SiO<sub>2</sub> Aerogel Modified by Ca(II) Cations

Ca (II) modified ZrO2-SiO2 aerogel (CaZSA) with excellent thermal stability at 1000 °C was prepared by aging the ZrO2-SiO2 wet gel in calcium nitrate (Ca (NO3)2) ethanol solution followed with alcohol supercritical fluid drying method. The reaction between surface hydroxyl groups on the aerogel and Ca (II) ions played an important role in reducing the high temperature activity and inhibiting the particle growth caused by the condensation of hydroxyl groups of aerogel. Moreover, tiny secondary-phase particles, Ca (II) ions, introduced along grain boundaries serve as the pinning particles to inhibit the crystallization of ZrO2-SiO2 aerogel (ZSA). Thus the high-temperature stability of ZSA was significantly improved by surface modification with Ca (II). The specific surface area of CaZSA still maintained 223 m2·g-1 after 1000 °C calcination, which was 52.7% higher than that of ZSA at the same treatment condition.

Hydrothermal Stability of Molecular Sieves SBA-15 Research

Hydrothermal Stability of Molecular Sieves SBA-15 was studied. It was characterized by N2 adsorption, X-ray diffraction and FT-IR analysis. The results indicated that water, heat and alkaline environments are acidic center caused some of the molecular sieve SBA-15, the influence of the structure of the SBA- 15 mesoporous molecular sieves have some damage, led to the decrease of the pore diameter, specific surface area. This is because the thermal stability of mesoporous molecular sieve is closely related to the silicon hydroxyl condensation. Due to the contraction of silicon hydroxyl, generated the Si-O-Si unit structure, causes the d100. Moderate Si-OH condensation can increase the stability of mesoporous structure, and excessive Si-fuelled by condensation of Ozzie and Harriet channel by Si-O keys tensile force, spacing gradually reduced resulting in progressive collapse of mesoporous structure.

Synthesis and performance evaluation of a novel biodegradable dispersant for offshore cementing

We developed a novel biodegradable oil-well dispersant, gelatin grafted acetone formaldehyde sulphonates (GAFS). This dispersant was prepared based on the chemical modification of naturally biodegradable products: gelatin. GAFS was synthesized through aldehyde ketone addition, hydroxyl condensation and Mannich amine methylation reaction. Functional groups and molecular structure of GAFS were characterized by FTIR (Fourier Transform Infrared Spectroscopy) and NMR (Nuclear Magnetic Resonance). Lab tests were conducted to determine the biodegradation rate, rheological properties, thickening time, compressive strength and dispersing property of GAFS in Class-G cement slurry. It is found that GAFS exhibits no retarding by-effect on oil well cement and can be considered biodegradable based on the biodegradation test results. The measured adsorption capacity and zeta potential of GAFS in Class-G well cement slurry show that: GAFS can be adsorbed greatly onto the surface of cement particles, resulting in strong electrostatic repulsion between cement particles and consequently generating an excellent dispersion performance.

The effect of structural properties of natural silica precursors in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100 °C

The low-temperature synthesis of zeolite ZSM-5 below 100°C is gaining new attention. This is due to the fact that such synthesis may simultaneously implement the introduction of mesopores into crystalline microporous zeolite structure. Herein, we report the use of natural silica precursors from rice husks in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100°C and their structural properties which govern the course of crystallization. Rice husks are agricultural wastes with high silica content, which should be exploited to give a positive impact, i.e. highly value-added materials. In this study, the amorphous silica from rice husks was extracted using sequential base-acid treatment. The extracted silica was similarly reactive as Ludox HS-40, even with the reduced amounts of the organic structure-directing agent (OSDA). The product was highly crystalline ZSM-5 with spherical morphology composed of small crystallites, enabling the presence of intercrystallite mesopores. The subjection of extracted silica into the calcination at 550°C for 6h, prior to the low-temperature synthesis, altered the silica structure via hydroxyl condensation. The distinct structural properties affected the occurring crystallization in which the resulted products were ZSM-5–disordered-mesoporous silica composites. The possible mechanisms of these two different results may involve the dual roles of tetrapropylammonium ion (TPA+) as zeolite OSDA and non-templating structure directing agent. These insights were based on the spectroscopic (FTIR, Raman, 29Si and 27Al MAS NMR spectroscopy), microscopic (TEM and HRTEM) and physicochemical characterizations (XRD and N2 adsorption-desorption isotherm).

Improvement of thermal stability of ZrO2–SiO2 aerogels by an inorganic–organic synergetic surface modification

The thermal stability of ZrO2–SiO2 aerogels was significantly improved by inorganic–organic synergetic surface modifications: inorganic ions [Fe(III)] surface modification and hexamethyldisilazane gas phase modification. The replacement of Hs from surface hydroxyl groups on the aerogel by Fe(III) ions and silyl groups played a critical role in isolating the hydrous particles of ZrO2–SiO2 aerogels. So the particle growth caused by the condensation of hydroxyl groups upon firing was inhibited. Meanwhile, the decomposition of the silyl groups upon heat treatment produced SiO2 particles, which could serve as pining particle to inhibit the crystallization of ZrO2. Hence, the porous microstructure of the modified aerogels was still well preserved up to 1000 °C, with a high specific surface area of 203.5 m2/g, and a considerable pore volume of 0.721 cc/g. These characteristics of the modified aerogels suggest that it has great potential on ultrahigh-temperature applications in the fields of thermal insulation, catalysis, and catalyst support, etc.

Effects of Composition and Structure of Mg/Al Oxides on Their Activity and Selectivity for the Condensation of Methyl Ketones

The effects of chemical composition and pretreatment on Mg–Al hydrotalcites and alumina-supported MgO were evaluated for the gas-phase, self-condensation reaction of C3–C5 biomass-derived methyl ketones. We show that the selectivity toward the acyclic dimer enone and the cyclic enone trimer can be tuned by controlling the temperature of hydrotalcite calcination. Methyl ketone cyclization is promoted by Lewis acidic sites present on the hydrotalcite catalysts. XRD and thermal decomposition analysis reveal that the formation of periclase MgO starts above 623 K accompanied by complete disappearance of the hydrotalcite structure and is accompanied by an increase in hydroxyl condensation as the formation of well-crystallized periclase. 27Al MQMAS and 25Mg MAS NMR show that at progressively higher temperatures, Al3+ cations diffuses out of the octahedral brucite layers and incorporate into the tetrahedral and octahedral sites of the MgO matrix thereby creating defects to compensate the excess positive charge ge...