Hydrolytic Condensation Research Articles

Polyurethane composites based on silsesquioxane derivatives of different structures

A series of siloxane–silsesquioxane resins with Q8 structures, as network nodes containing reactive Si–H groups in the siloxane backbone, connecting silsesquioxane moieties, were prepared in a hydrolytic condensation process and successfully functionalized by hydrosilylation of allyl alcohol. The proposed material being an alternative to the well-defined silsesquioxanes has been characterized and used for preparation of a series of polyurethane (PU)-based composites by simple reaction of 3-hydroxypropyl groups of siloxane–silsesquioxane resin with 1,6-diisocyanatohexane and subsequently with 1,6-hexanediol to get polyurethane composite. A series of composites based on PU and octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane were prepared in the same manner to investigate the influence of the filler amount (1, 3 or 5%) and its structure on thermal properties of the obtained materials.

Copper-loaded nanocellulose sponge as a sustainable catalyst for regioselective hydroboration of alkynes

It is desirable for catalyst supports to be biodegradable, easily-modifiable, and possessing high surface area. In this work, thiolated nanocellulose sponge was prepared from hydrolytic silane condensation of cellulose nanofibrils (CNF) and used as a green support to immobilize copper cations via in situ CuII to CuI reduction and complexation. The sponge featured high porosity (90.5%) and low density (29.4 mg/cm3) with regular morphology. The sponge easily recovered 94% of its original shape in water after experiencing 80% deformation under stress of 95 kPa. When used in catalyzing hydroboration of alkynes, excellent conversion and up to 99% regioselectivity were achieved with the copper-loaded sponge. The sponge-supported catalysts worked well in the absence of additional ligands, had a broad substrate scope, and retained 93% of their activity after six catalytic cycles. This simple and scalable strategy offers an efficient route for immobilizing metal catalysts on porous supports.

The Effects of Leaching Process to the TiO2 Synthesis from Bangka Ilmenite

Ilmenite mineral is a naturally occurring iron titanate (FeTiO3) and is abundant in nature. The separation of components into TiO2 and Fe2O3 must be expand. The purpose of this research is to synthesis TiO2 nanoparticles from the filtrate of Bangka ilmenite leaching process. Leaching of ilmenite was done with H2SO4 and HCl at various concentrations. The formation of TiO2 crystal determined by hydrolysis conditions and condensation reaction. TiO2 synthesized from the filtrate of sulfuric acid leaching that produced from TiO2 anatase phase when hydrolyzed in an aquaregia solvent and low concentrations of HCl (0.1M). Hydrolysis conditions at higher concentrations of HCl (1M) was produced TiO2 anatase-rutile phase. The synthesis of TiO2 from the filtrate of hydrochloric acid leaching was produced anatase phase. While the condition under the alcoholic solvent (2-propanol: H2O (v/v) = 9: 1) anatase phase crystallites grow in the temperature range up to 550 °C, above this temperature, TiO2 transform into rutile phase.

Durable and fluorine-free superhydrophobic coatings from palygorskite-rich spent bleaching earth

Abstract With the increasing consumption of vegetable oils, value-added recycling of spent bleaching earth (SBE) is of wide concern. Here, we report a simple and sustainable method for converting SBE containing palygorskite (PAL) to hybrid carbon materials (PAL/C) with a nanorod-like structure, which can then be used as building blocks for the preparation of durable and fluorine-free superhydrophobic coatings. The PAL/C composites were prepared by calcination of the SBE containing PAL in air. Then, the homogeneous suspensions in ethanol were prepared by hydrolytic condensation of n-hexadecyltrimethoxysilane onto the PAL/C nanorods. Superhydrophobic coatings can be readily prepared by spray-coating the suspensions onto substrates. The PAL/C composites and the superhydrophobic coatings were characterized using a variety of analytical techniques including scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Superhydrophobicity of the coatings depends upon their surface topography, which can be precisely regulated by the calcination temperature of SBE and the concentration of the PAL/C composites in the suspensions. The superhydrophobic coatings show high water contact angle and extremely low sliding angle of 1.2°. The superhydrophobic coatings also feature high mechanical, thermal and chemical durability. This is because the PAL/C nanorods are closely linked and encapsulated together by polysiloxane (POS) among them, forming a highly crosslinked network. We believe that this study will shed light on the value-added recycling of SBE and cost-effective preparation of bioinspired antiwetting coatings.

Synthesis and characterization of silver-rich coatings loaded with functionalized clay nanoparticles

A synthetic exfoliated nanoclay smectite type, Laponite® S482, was incorporated as a functionalized load in a silica hybrid matrix synthesized by the sol–gel route. The previous functionalization was carried out through a “grafting” reaction with (3-glycidoxypropyl)trimethoxysilane (GPTMS) assisted by ultrasonic dispersion. The precursor sols were synthesized by acid-catalyzed hydrolytic condensation between tetraethoxysilane (TEOS) and functionalized GPTMS, a silver ions source was added in order to obtain a coating material with controlled silver releasing properties. Coatings were obtained by “dip-coating” on different substrates. Structural characterization of the coatings was conducted by SAXS and SEM-EDS, the results revealed a complex silica matrix with intercalated nanoclays, an organic fraction and a homogeneous content of Ag+. The electrochemical characterization was realized by EIS tests on stainless steel coated substrates AISI 316L type; the results showed good barriers properties and a high integrity of the coatings loaded with nanoclay. The evolution of the release of Ag+ ions was studied by XRF, through exposing the coatings to a leaching process at steady state and determining the residual content of Ag within the coat at different immersion times. It was found that the addition of 1.5 wt. % of clay, in respect to condensed silica, decreased the initial diffusion rate of Ag+ ions at near the half part, allowing its potential use in the development of antibacterial coatings with longer terms of life.

Effects of modification of palygorskite on superamphiphobicity and microstructure of palygorskite@fluorinated polysiloxane superamphiphobic coatings

Abstract Palygorskite (PAL) is a promising natural clay mineral for the preparation of bionic super anti-wetting coatings, a new application field of PAL. Here, the effects of modification of PAL on superamphiphobicity and microstructure of the PAL@fluorinated polysiloxane (PAL@fluoroPOS) superamphiphobic coatings were systematically studied. First, PAL was modified via acid activation, solid-state grinding and heat activation. Then, the PAL@fluoroPOS coatings were prepared by hydrolytic condensation of 1H,1H,2H,2H-perfluorodecyltriethoxysilane and tetraethoxysilane onto the modified PAL, followed by spay-coating onto substrates. It was found that the microstructure of the coatings is controllable by acid activation and solid-state grinding. Acid activation with HCl at moderate conditions (2 M HCl, 15 °C) and grinding for a proper time (10 min) are helpful to improve superamphiphobicity of the coatings by forming smaller protrusions and micropores on the surface of the coatings. On the contrary, heat activation results in decline of the superamphiphobicity, especially at high temperature. The achieved coatings show excellent superamphiphobicity, and are mechanically robust and thermally stable, which can withstand intensive water jetting at 100 kPa for 20 min and 350 °C for 1 h. Moreover, the coatings can be applied onto various substrates like aluminum foil, PTFE plate, wood plate and polyester textile. We believe that the findings will promote the development of novel clay-based super anti-wetting coatings.

Effect of Ammonium Salts on the Hydrothermal Synthesis of TiO₂ Nanocubes for Dye-Sensitized Solar Cells.

TiO2 nanocubes were synthesized via hydrolysis condensation of titanium tetra-isopropoxide (TTIP) in aqueous media, followed by hydrothermal treatment with ammonium salts. Various ammonium salts with different alkyl chain such as ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH) and tetrabutylammonium hydroxide (TBAH) were investigated. The crystalline phase, shape, and morphology of TiO2 nanocubes were studied by XRD, TEM, and SEM analysis. These TiO2 nanocubes were pure anatase phase and tended to assemble with well-ordered and close-packed domains. Both alkyl chain length of ammonium salts and hydrothermal duration affected the TiO2 nanocube formation process. The ammonium salts with longer alkyl chain formed TiO2 nanocubes in shorter hydrothermal time and offered the smallest particle size. The above TiO2 nanocubes were applied as photoanode materials in N719 anchored dye-sensitized solar cells and one of the cells exhibited the maximum power conversion efficiency of 7.85%.

Fabrication of Mechanically Strong Honeycombs with Aerogel Cores

Honeycomb aerogel composites were fabricated by reinforcing selected regions of a native aerogel matrix using photopolymerization. First, alcogels were synthesized by hydrolysis–condensation of a siloxane, and by adding a multifunctional acrylic monomer and a visible-light initiator to the gelation solution. Alcogels were then placed on a programmable translation stage and exposed to a laser. Polymerization and mechanical reinforcement were induced in the exposed regions. After exposure alcogels were dried supercritically. Thermal conductivity and out-of-plane modulus of the resulting honeycombs could be varied between values typical of native aerogels (11 mW/mK and 0.75 MPa) and those of uniformly polymerized composites (65.8 mW/mK and 36.26 MPa) by varying the translation stage speed between 2 and 3 mm/s. The results were interpreted using a rule-of-mixtures model. The mechanical properties of the composites were also investigated using finite element analysis.

Superamphiphobic Coatings with Low Sliding Angles from Attapulgite/Carbon Composites

AbstractPreparation of superamphiphobic coatings with low sliding angles (SAs) for liquids of low surface tension is challenging. Here, a simple and sustainable approach for preparation of superamphiphobic coatings with low SAs from attapulgite/carbon (APT/C) composites is reported. The coatings are prepared by hydrolytic condensation of 1H,1H,2H,2H‐perfluorodecyltriethoxysilane and tetraethoxysilane with the APT/C composites followed by spray‐coating onto substrates. The APT/C composites are prepared by pyrolysis of spent bleaching earth containing APT. The influences of pyrolysis temperature of spent bleaching earth and the APT/C concentration on superamphiphobicity and surface morphology of the coatings are studied. Carbon nanoparticles are formed on the APT nanorods in the pyrolysis process. The APT/C nanorods are wrapped and linked together by a layer of fluorinated polysiloxane (fluoroPOS). The coatings exhibit excellent superamphiphobicity with high contact angles (CAs) and low SAs even for n‐decane (CAn‐decane = 154.2°, SAn‐decane = 11.3°). This is because the new three‐tier micro‐/nano‐/nanostructure is constructed by the combination of APT nanorods, carbon nanoparticles, and fluoroPOS. Also, the superamphiphobic coatings show very good chemical and thermal stability. It is believed that this study will shed light on preparation of superamphiphobic coatings with low SAs via a simple, cost‐effective, and sustainable approach.

Preparation of Nano Spherical α-Fe2O3 Supported on 12-Tungstosilicic Acid Using Two Different Methods: A Novel Catalyst

In this research, spherical α-Fe2O3 nanoparticles (NPs) were supported on the surface of 12-tungstosilicic acid (12-TSA.7H2O) as a catalyst support, using two different Forced Hydrolysis and Reflux Condensation (FHRC) and Solid-State Dispersion (SSD) methods. α-Fe2O3 and 12-TSA.7H2O were synthesized due to previous reports. All products were characterized by using FT-IR, SEM, EDX, elemental map, XRD and BET surface area. The results indicated that the supported catalyst (α-Fe2O3/12-TSA.7H2O) successfully was prepared and no change was found on the chemical structures of 12-TSA.7H2O and α-Fe2O3. By using XRD analysis average sizes of spherical α-Fe2O3 NPs supported by SSD and FHRC methods were measured 50.5 and 70.82 nm, respectively. The catalyst presented in this study can be applied in the different areas such as nano photocatalytic reactions.

Durable flame retardant and antibacterial finishing on cotton fabrics with cyclotriphosphazene/polydopamine/silver nanoparticles hybrid coatings

Durable flame retardant and antibacterial hybrid coatings were developed for cotton fabrics via simultaneous polymerization of dopamine and hydrolytic condensation of N3P3[NH(CH2)3Si(OC2H5)3]6. Silver nanoparticles were also introduced to the coatings by in situ reaction of AgNO3 with catechol moieties on polydopamine (PDA) in the absence of any external reducing agents. Energy dispersive spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were employed to study the morphology and constitution of the coatings. Thermal stability and combustion behaviors were characterized with thermogravimetric analysis (TGA) and vertical flammability tests. Considerable flame retardancy was obtained for the modified cotton fabrics, which also exhibited decent antibacterial activities (99.99%) against Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli. The modification was durable with largely intact flame retardancy and antimicrobial properties after 30 washing cycles.

Structure and properties of epoxy-siloxane-silica nanocomposite coatings for corrosion protection

HypothesisThe fraction of the silica/siloxane phase is a crucial parameter, which determines the structure and thus the properties of epoxy-siloxane-silica hybrid coatings. A careful adjustment of the colloidal precursor formulation allows tuning the nanostructure towards a highly condensed and cross-linked hybrid nanocomposite, suitable as an efficient anticorrosive coating. ExperimentsNovel epoxy-siloxane-silica hybrids have been prepared through the curing reaction of poly(bisphenol A-co-epichlorohydrin) (DGEBA) with diethyltriamine (DETA) and (3-glycidoxypropyl)methyltriethoxysilane (GPTMS), followed by hydrolytic condensation of tetraethoxysilane (TEOS) and GPTMS. At a constant proportion of the organic phase, the effects of the varying molar proportions of siloxane (GPTMS) and silica (TEOS) on the film properties have been investigated. FindingsA detailed structural analysis suggests for intermediate TEOS to GPTMS ratios a structure of highly condensed silica-siloxane domains covalently bonded to the embedding epoxy phase. The homogeneous distribution of the quasi-spherical sub-nonmetric silica-siloxane nodes is in agreement with low surface roughness (<5 nm), observed by atomic force microscopy. This dense nanostructure results in high thermal stability (>300 °C), strong adhesion to steel substrate and excellent barrier property in saline solution, with corrosion resistance in the GΩ cm2 range.

Organic-inorganic hybrid electrochromic materials, polysilsesquioxanes containing triarylamine, changing color from colorless to blue

Four kinds of soluble monomers, containing triarylamine (TAA) group with reactive siloxane group, were synthesized under mild conditions via the reaction between 3-(triethoxysilyl)propyl isocyanate (TEOSPIC) and four TAA derivatives, respectively. Then the corresponding colorless organic-inorganic hybrid materials (PSSOs) were derived from the hydrolytic condensation of the monomers. PSSOs revealed good solubility in polar solvents on account of the effect of propeller-like TAA unit as well as the auxo-action effect of the flexible chain within the monomers. The structural characteristics of these PSSOs were identified by 1H NMR, 29Si NMR, FT-IR spectroscopies and X-ray diffraction (XRD). The morphology, dynamic changes of the transmittance and current before and after electro-oxidizing reaction were studied, and didn’t show significant change suggesting good stability of the PSSOs. Meanwhile, these PSSOs performed high contrast of optical transmittance change up to 84% with the highest coloration efficiency to 241 cm2·C−1. Furthermore, electrofluorescent properties of PSSOs were investigated with high-contrast.

Preparation of Silica-Alumina Nanoparticles via Blast-Furnace Slag Dissolution in Low-Concentration Acetic Acid for Carbonation

Blast-furnace slag (BFS) has been used as a feedstock for CO2 sequestration by indirect mineral carbonation to produce calcium carbonate precipitates and solid residues. The most-abundant elements in these residues, Si and Al, are usually considered to be impurities that need to be removed in acid-dissolution processes involving BFS. The co-production of value-added materials from these residues is an attractive option for strengthening the economic competitiveness of mineral carbonation methods. In view of this, we separated the Si and Al, as their hydrated forms, during the dissolution of BFS in acetic acid prior to carbonation. During the sol-gel processing of Si-Al nanoparticles, a catalyst is usually required during the hydrolysis and subsequent condensation processes. In this study, only condensation occurs because the low-concentrations of acetic acid used facilitate in-situ hydrolysis during the dissolution process. Aging was carried out not only to structurally arrange the Si and Al but also to oxidize the marginal Fe(II) to reddish Fe(III). Silica-alumina nanoparticles (78% Si and 22% Al) were prepared by a simple sol-gel route at ambient pressure. These nanoparticles were amorphous and below 20 nm in size. Fourier-transform infrared (FT-IR) studies reveal that the nanoparticles consist of Si–O–Si and Si–O–Al bonds. 27Al nuclear magnetic resonance (NMR) spectroscopy reveals a significant resonance corresponding to tetra-coordinated Al inside the particle framework.

Preparation of antireflection coatings with novel cationic–nonionic PU‐SiO2 core–shell particle dispersions

ABSTRACTA novel polyurethane (PU)‐SiO2 core–shell particle dispersion was prepared by an acid‐catalyzed sol–gel process using cationic–nonionic PU particle as template. Results of average sizes, polydispersity index, and transmission electron microscope indicated that tetramethylorthosilicate were first diffused to the surface of PU particles, then occurring hydrolysis–condensation reaction to form core–shell particles. Antireflection coating formulation was prepared by as‐prepared core–shell particle dispersion and SiO2 sol binder. After dip‐coating in the formulation, antireflection coating was formed on glass surface by calcination. Scanning electron microscopy images showed that pores had been formed inside coating after removing PU template particles, and the coating surface could be almost fully closed. In addition, ultraviolet–visible spectrophotometer analysis showed that the maximum transmittance of antireflection glasses can be as high as 98.6% at 548 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45762.

Butylated caffeic acid: An efficient novel antioxidant

A novel antioxidant, butylated caffeic acid (BCA) was rationally designed by adding a tert-butyl group to caffeic acid, which was synthesized at a high yield (36.2%) from 2-methoxy-4-methylphenol by a four-step reaction including Friedel-Crafts alkylation, bromine oxidation, ether bond hydrolysis and Knoevenagel condensation. Its antioxidant capacity was much stronger than common commercial antioxidant tert-butyl hydroquinone (TBHQ) and its mother compound, caffeic acid, in both rancimat and deep frying tests. When investigated via the DPPH method, the antioxidant capacity of BCA was almost equal to TBHQ, but lower than caffeic acid. BCA could be a potentially strong antioxidant, especially for food processing at high temperatures such as deep frying and baking.

Epoxy-silica/clay nanocomposite for silver-based antibacterial thin coatings: Synthesis and structural characterization

Development of new functional coatings in the field of health care, as antibacterial applications, deals with a straight control of the diffusive properties that rules the releasing of the active component. In this work, the development of a silver-rich nanocomposite thin coating, loaded with organically modified clay nanoparticles, is presented. The synthesis process included an environment-friendly silanization process of clay nanoparticles (Laponite® S482) with (3-glycidoxypropyl)trimethoxysilane (GPTMS) and the further hydrolytic condensation with tetraethoxysilane (TEOS). Silanization process and the obtained coatings were analysed by Fourier transformed infrared spectroscopy, UV–visible spectroscopy, X-ray diffraction, thermogravimetric curves and scanning electron microscopy. The silanization process of clay nanoparticles with the organically reactive alkyl alkoxysilane, allowed to stabilize and exfoliate the clay nanosheets within a hybrid organic-inorganic sol-gel material. Ring opening of grafted epoxy groups carried to an increasing of the basal spacing, of intercalated clay nanosheets, from 1.3 to 1.8nm. Moreover, incorporation of organically modified clay nanosheets introduced a significant stabilization on the development of silver nanoparticles inside the structure of the nanocomposite coating, retaining the silver inside the coating material and restricting the growing of silver nanoparticles on the surface of the coating. Antibacterial behaviour, against E. coli cultures, performed through agar diffusion tests, provided promising results that allow assuming that the studied nanocomposite coating serves as a reservoir of ionic silver, permitting the antibacterial effect.

Comprehensive Study of Sol–Gel versus Hydrolysis–Condensation Methods To Prepare ZnO Films: Electron Transport Layers in Perovskite Solar Cells

Owing to the high charge mobility and low processing temperature, ZnO is regarded as an ideal candidate for electron transport layer (ETL) material in thin-film solar cells. For the film preparation, the presently dominated sol-gel (SG) and hydrolysis-condensation (HC) methods show great potential; however, the effect of these two methods on the performance of the resulting devices has not been investigated in the same frame. In this study, the ZnO films made through SG and HC methods were applied in perovskite solar cells (Pero-SCs), and the performances of corresponding devices were compared under parallel conditions. We found that the surface morphologies and the conductivities of the films prepared by SG and HC methods showed great differences. The HC-ZnO films with higher conductivity led to relatively higher device performance, and the best power conversion efficiencie (PCE) of 12.9% was obtained; meanwhile, for Pero-SCs based on SG-ZnO, the best PCE achieved was 10.9%. The better device performance of Pero-SCs based on HC-ZnO should be attributed to the better charge extraction and transportation ability of HC-ZnO film. Moreover, to further enhance the performance of Pero-SCs, a thin layer of pristine C60 was introduced between HC-ZnO and perovskite layers. By doing so, the quality of perovskite films was improved, and the PCE was elevated to 14.1%. The preparation of HC-ZnO film involves relatively lower-temperature (maximum 100 °C) processing; the films showed better charge extraction and transportation properties and can be a more promising ETL material in Pero-SCs.

Durable superamphiphobic coatings repelling both cool and hot liquids based on carbon nanotubes

Superamphiphobic coatings have wide potential applications in many fields, however, preparation of superamphiphobic coatings with low sliding angles and high durability is very challenging. Here, we report a facile spray-coating method for the preparation of durable superamphiphobic coatings repelling both cool and hot liquids from polyperfluoroalkylsilane-modified multiwalled carbon nanotubes (MWCNTs@fluoroPOS). The MWCNTs@fluoroPOS suspensions were preparation by hydrolytic condensation of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFDTES) and tetraethoxysilane (TEOS) on the surface of MWCNTs. The suspensions and the superamphiphobic coatings were characterized using a variety of analytical techniques such as scanning electron microscopy, transmitting electron microscopy and X-ray photoelectron spectroscopy. The effects of the diameter of MWCNTs, and the concentrations of MWCNTs, TEOS and PFDTES on wettability and microstructure of the coatings were also investigated. The coatings show high contact angles and low sliding angles for water and organic liquids of low surface tension such as n-hexadecane, toluene and n-decane. The coatings even exhibit excellent superamphiphobicity for hot water and hot organic liquids up to 80°C, which is seldom achieved according to the previous literatures. Moreover, the coatings feature high mechanical, chemical and environmental durability, and are applicable onto various substrates. The simple method, the high superamphiphobicity to both cool and hot liquids, and the excellent durability of the coatings have paved the way for their practical applications in various fields, e.g., anti-icing, anti-oil climbing and oil transportation, etc.

Transparent and durable superhydrophobic coatings for anti-bioadhesion

Although thousands of superhydrophobic coatings have been reported, transparent ones with high durability are rare. Here, transparent and durable superhydrophobic coatings were prepared by using multiwalled carbon nanotubes (MWCNTs) as the templates. The superhydrophobic coatings were prepared by spray-coating the homogeneous suspension of polysiloxane-modified MWCNTs (MWCNTs@POS) in toluene onto glass slides, calcination in air at 500°C to form the silica nanotubes (SNTs), and then chemical vapor deposition of polydimethylsiloxane at 200°C onto the surface of the SNTs coatings. The MWCNTs@POS suspension was prepared by hydrolytic condensation of hexadecyltrimethoxysilane and tetraethoxysilane on the surface of MWCNTs. The coatings showed excellent superhydrophobicity (water contact angle=166.6°, sliding angle=1°) and high transparency (83.1% at 600nm). In addition, the transparent superhydrophobic coatings featured high mechanical, chemical and thermal durability. The coatings retained the excellent superhydrophobicity after intensive water jetting at 100kPa for 60min, immersion in various corrosive liquids for 24h, or kept at 390°C for 1h. Moreover, the transparent and durable superhydrophobic coatings exhibited very good anti-bioadhesive properties.