Synthesis of highly hydrophobic rutile titania-silica nanocomposites by an improved hydrolysis co-precipitation method

Highly hydrophobic rutile titania-silica nanocomposites were synthesized by an improved hydrolysis co-precipitation method using low-cost sodium metasilicate and titanium oxysulfate (TiOSO₄) as precursors, followed sequentially by calcination at 800 °C and modification with trimethylchlorosilane (TMCS). It was found that the resulting TiO₂-SiO₂ nanocomposites had a Ti/Si molar ratio of 5:1 and exhibited single-phase rutile with a specific surface area of 269 m² g⁻¹. The addition of acetylacetone (AcAc) during the hydrolysis co-precipitation process played a key role in the growth of well-ordered TiO₂-SiO₂ crystallites since the hydrolysis rate of TiOSO₄ might be retarded due to the complexation of AcAc to the Ti atoms in TiOSO₄. The TMCS-modified TiO₂-SiO₂ nanocomposites exhibited a high root-mean-square (RMS) roughness of 22 nm and good hydrophobicity with a static contact angle of 143.7°, highlighting its potential application as a filler in exterior wall coatings.     

Modeling and simulation of mass transfer in near-critical extraction using a hollow fiber membrane contactor

In this study is presented a general methodology to predict the performance of a continuous near-critical fluid extraction process to remove compounds from aqueous solutions using a hollow fiber membrane contactor. The stabilization of the gas-liquid interface in the membrane porosity and a high surface area to contact both phases represent some of the advantages that hollow fiber contactors offer over conventional contactor devices for the extraction of compounds from liquid feeds.A mathematical model has been developed integrating a resistances-in-series mass transfer system that takes into account boundary layers, membrane porosity and thermodynamic considerations with mass balances of the membrane contactor. Simulation algorithms were easily implemented with low calculation requirements.The system studied in this work is a membrane based extractor of ethanol and acetone from aqueous solutions using near-critical CO₂. Predictions of extraction percentages obtained by simulations have been compared to the experimental values reported by Bothun et al. [2003a. Compressed solvents for the extraction of fermentation products within a hollow fiber membrane contactor. Journal of Supercritical Fluids 25, 119-134]. Simulations of extraction percentage of ethanol and acetone show an average difference of 36.3% and 6.75% with the experimental data, respectively. More accurate predictions of the extraction of acetone could be explained by a better estimation of the transport properties in the aqueous phase that controls the extraction of this solute.When the model was validated, the effect of the configuration and the operating parameters was studied and local mass transfer resistances were evaluated. The proposed approach allows the evaluation of the relevance of membrane hydrophobicity for extraction in solutions under different thermodynamic conditions. This original methodology based on well-known phenomenological equations represents a general approach which could be applied in other processes using membrane contactors with different configurations.     

有机硅接枝三聚氰胺树脂的合成与表面性能

以三聚氰胺和多聚甲醛为原料、羟基封端聚二甲基硅氧烷（PDMS-OH）为改性剂，制得一系列改性三聚氰胺树脂（MF-PDMS）。研究了反应介质、PDMS-OH用量对MF-PDMS树脂性能的影响，以及与树脂固化后的MF-PDMS材料性能的关系。采用红外光谱（FT-IR）、固体核磁共振氢谱（1H NMR）、X射线光电子能谱（XPS）、扫描电镜-能谱（SEM-EDS）表征了MF-PDMS材料的结构、表面化学组成，采用接触角测定仪、浸泡法分别测试了材料的接触角、吸水性，采用热重（TG）测试了对材料的热稳定性。结果表明：在二甲基乙酰胺（DMAc）反应介质中，PDMS-OH与三聚氰胺、甲醛可一步合成MF-PDMS树脂，接枝共聚的PDMS-OH可高效的提高MF-PDMS材料的疏水性能和热稳定性，当PDMS-OH的摩尔分数为1.0%（以三聚氰胺物质的量计）时材料的水接触角为91.81°、表面自由能降至28.1 mN/m、吸水质量分数降至2.83%、400 ℃时的残留率为58.03%、700 ℃时的残留率为16.60%。     

Effect of graphene film on laser textured alumina surface characteristics

Laser gas assisted texturing of alumina surface is considered and the effects of graphene film on the properties of the textured surface are examined. Since laser texturing under the high pressure nitrogen gas jet environments results in formation of aluminum nitride compounds, free energy of the textured surface reduces considerably. The mismatch between the surface free energies of the graphene film and the laser textured surface makes it difficult to transfer the graphene film on the textured surface without rippling and edge defects. A graphene oxide film is formed at the textured surface prior to transferring of the graphene film. The characteristics of the laser textured and the graphene transferred surfaces are assessed using the analytical tools including electron and atomic force microscopes, Raman spectroscopy, X-ray diffraction, and UV visible absorbance spectroscopy. Surface hydrophobicity of the graphene transferred and laser textured surfaces is determined incorporating the water droplet contact angle measurement technique. Friction coefficient of the graphene transferred and laser textured surfaces are measured using the scratch tester. It is found that laser texturing results in hydrophobic characteristics because of the micro/nano size pillars formed at the surface and reduced surface energy due to aluminum nitride compounds. Transferring of the graphene film on to the laser textured surface reduces both the water droplet contact angle and the contact angle hysteresis. The presence of the graphene film reduces the friction coefficient and it does not alter notably the absorption characteristics of the laser textured surface.     

Facile synthesis of hydrophobic,thermally stable,and insulative organically modified silica aerogels using co-precursor method

Silica aerogels have low density and high specific surface area, but there are restrictions regarding their durability and commercialization owing to their fragile nature and the strong moisture absorbing behavior of the siloxane network. To overcome these restrictions, this study evaluated hybrid organically modified silica (ORMOSIL) aerogels by employing 3-(trimethoxysilylpropyl) methacrylate (TMSPM) in tetraethyl orthosilicate (TEOS) through a two-step sol-gel co-precursor method. The methacrylate organic groups were incorporated into the silica networks via reactions between the Si-OH moieties in silica aerogels, resulting in ORMOSIL aerogels. The properties of the ORMOSIL aerogels were strongly affected by the amount of TMSPM co-precursor. The highest concentration of TMSPM (30 wt%) resulted in ORMOSIL aerogels with improved characteristics when compared with the pristine TEOS-based silica aerogels, such as hardness (0.15 GPa), Young's modulus (1.26 GPa), low thermal conductivity (0.038 W/m K), high water contact angle (140°), and high thermal stability (350 °C).     

Influence of coal particles on froth stability and flotation performance

Solid particles have significant effect on flotation froth. In this research, the effects of coal particles of different size and hydrophobicity on froth stability and flotation performance were studied. The froth stability was measured in both the froth formation and froth decay processes by maximum froth height, froth half-life time and water recovery. The results show that fine particles of moderate hydrophobicity contributed most to maximum froth height in the froth formation process and were most favorable for flotation. Fine hydrophilic particles stabilized the froth in the froth formation process but the froth half-life time was very short due to the high water solid ratio. High hydrophobic particles of both fine and coarse size fractions greatly increased the froth half-life time in the froth decay process. But the froths were very rigid and the maximum froth heights were very low. The presence of fine hydrophobic particles was very unfavorable for the recovery of coarse particles.     

Synthesis and antimicrobial activities of acrylamide polymers containing quaternary ammonium salts on bacteria and phytopathogenic fungi

Three series of acrylamide monomers/polymers containing quaternary ammonium salts (QASs), i.e., acrylamide QAS monomers (QDs), homopolymers of QDs (PQDs) and copolymers of QDs with acrylate monomer (PQDCs), were synthesized and employed in antimicrobial tests against both bacteria (Escherichia coli (E. coli) and Staphylococcus albus (S. albus)) and phytopathogenic fungi (Rhizoctonia solani (R. solani) and Fusarium oxysporum f. sp. cubense race 4 (Foc4)). The antibacterial activity of the QASs was evaluated by determining the minimum inhibitory concentration (MIC) against E. coli and S. albus by the TTC coloration method, and the antifungal activity was measured by mycelia growth inhibition as well as MIC and the minimum fungicidal concentration (MFC) values. The results indicated that PQD homopolymers and PQDC copolymers showed far better antimicrobial activities than QD monomers. PQDC copolymers by incorporating hydrophobic acrylate units into the main chain of polyacrylamide backbone displayed even better antimicrobial activities, depending on QAS structure and hydrophobic content. Moreover, polymers with benzyl group attached to nitrogen atom showed better inhibitory effect on bacteria and phytopathogenic fungi. The results could assist understanding and development of future design of antimicrobial polymers as potential fungicide agents to control plant disease.     

Predicting Partitioning in Aqueous Two-Phase Systems and the Effects of Temperature Changes

Abstract

The use of aqueous two-phase extraction can be attractive for some separations, but the choice of such systems is frequently done in an empirical manner. Predictive models are needed for optimal design, but previous ones appear to have limitations. In addition, these systems have usually been used previously at temperatures around 25°C; however, it is possible that better separations may be achieved at other temperatures. An equation is developed here which can predict partitioning for a wide range of solutes. The effect of temperature on partitioning has been determined, and this can also be predicted by using the equation. Thus, this model may prove quite useful in designing and optimizing extractive separations.

     

Frontal Polymerization Synthesis of Monolithic Macroporous Polymers

A frontal polymerization method is used to produce highly porous polymer monoliths. The method is an approach to polymer synthesis that exploits the heat produced by the reaction itself. This heat triggers polymerization of neighboring monomer molecules, leading to a self‐sustaining hot front, which propagates along the reacting vessel. Dissolved or microencapsulated foaming agents are decomposed only at the fronts, synchronizing the polymerization and the foaming. The ultimate pore structures appear to depend on the polymerization‐front velocity and temperature. The resultant materials are porous, exhibiting tunable pore volume and a multimodal pore size distribution. No organic solvents or high‐pressure equipment are used in the process, and no solvent residues are left in the resulting materials. Specifically, this route allows for the synthesis of large‐scale samples with the additional advantages of high velocity, low energy cost, and the avoidance of multiple process steps. Substitution of hydrophilic acrylamide, N‐isopropylacrylamide, with hydrophobic styrene and methyl methacrylate also leads to porous monolithic materials, suggesting that frontal polymerization represents a powerful and facile method for an exothermic polymerization reaction and the creation of porous polymers.     

Two step sol-gel processing of TEOS based hydrophobic silica aerogels using trimethylethoxysilane as a co-precursor

The experimental results on the surface modification of tetraethoxysilane (TEOS) based silica aerogels using trimethylethoxysilane (TMES) as a co-precursor by two step sol-gel process are reported. The molar ratio of MeOH/TEOS was fixed at 17 and TMES/TEOS ratio was varied from 0.38 to 1.14. The concentration and quantity of acidic water (oxalic acid) added in the first step and base water (ammonium hydroxide) in the second step were also varied. The best quality superhydrophobic aerogels could be obtained with only distilled water (without any acid catalyst) in the first stage and the basic water in the second step of the sol-gel process. The molar ratio of TEOS: TMES: MeOH: distilled water: basic water was optimized at 1:0.86:17:4.9:4.9, respectively. The surface modification has been confirmed from the Fourier transform infrared spectroscopy measurements while the hydrophobicity was quantified in terms of the contact angle measurements. The TMES/TEOS based aerogel powder could be used to transport micro-liters of water in the form of water marbles. The aerogels have been characterized by the bulk density, porosity, thermal conductivity, contact angle measurements and the transmission electron microscopy (TEM).