Effect of polyacrylic acid (PAA) adsorption on stability of mixed alumina‐silica oxide suspension

Effects of Al3+ on the microstructure and bioflocculation of anoxic sludge

The aluminum ions generated from mining aluminum, electrolytic aluminum and the industrial production of aluminum-based coagulants (such as AlCl₃ and Al₂(SO₄)₃) enter sewage treatment plants and interact with activated sludges. An anaerobic/anoxic/oxic (A²O) process was used to reveal the effects of Al³⁺ on the pollutant removal efficiencies, bioflocculation and the microstructure of sludge. The results showed that a low concentration of Al³⁺ improved the pollutant removal efficiencies and increased the sludge particle size. However, a high concentration of Al³⁺ hindered microbial flocculation and reduced the pollutant removal efficiencies. With a 10 mg/L Al³⁺ addition, the chemical oxygen demand (COD), total nitrogen (TN) and NH₄⁺-N increased by 3%, 16% and 27%, and reached as high as 68%, 60% and 87%, respectively. At the same time, the dehydrogenase activity, flocculation ability (FA) and contact angle of the sludge reached their maximum levels at 41.3 mg/L/hr, 45% and 79.63°, respectively. The specific surface area of the sludge decreased to 7.084 m²/g and the sludge pore size distribution shifted to concentrate in the mesoporous range. Most of Al³⁺ was adsorbed on the surface of sludge, changing the physicochemical properties and physical structure of the sludge.

Uptake of silica particulate drug carriers in an intestine-on-a-chip: towards a better in vitro model of nanoparticulate carrier and mucus interactions

Micro and nano-particulate carriers have potential to increase bioavailability of oral drugs, but must first overcome the mucus barrier of the intestinal epithelium to facilitate absorption and entry to systemic circulation. We report on mucus-silica nanoparticulate carrier interactions in an in vitro intestine-on-a-chip (IOAC) microfluidic model. Caco-2 cells cultured within the IOAC model recapitulate the morphology of the human intestinal epithelium that is currently lacking in traditional static Transwell models. Fine control over the cell culture conditions produced a mucus layer, previously problematic to achieve without employing cell co-culture. The microdevice design also allowed for direct imaging of silica particulate carrier (40-700 nm) uptake through the mucus and cellular monolayer. PEGylated particulate carriers penetrated more readily through the mucus layer compared to non-PEGylated particulate carriers while larger particulate carriers tended to retard particulate carrier penetration through a dense mucus mesh. This was confirmed via imaging flow cytometry and UV-fluorescence spectroscopy. The IOAC also demonstrated the ability to mimic intestinal peristaltic fluidic conditions, which in turn affects the particulate carrier uptake. This in vitro IOAC model has potential to directly elucidate mucus interactions and uptake mechanisms for a range of drug carrier systems.

Aqueous hybrids of amino-functionalized nanosilica and acrylamide-based polymer for enhanced oil recovery

Amino-functionalized nanosilica (ANS) was prepared using nanosilica (NS) and 3-aminopropyltriethoxysilane (APTES) aiming to reinforce the interaction between nanoparticles and polymer molecules. The copolymer of acrylamide, 2-acrylamido-2-methyl-1-propane sulfonic acid (PM), and four ANS samples with different NS to APTES ratios were synthesized. A series of nanoparticle/polymer hybrid systems were fabricated by introducing NS or ANS suspension into PM aqueous solution. The rheological properties and surface activities of these hybrid systems were studied in comparison with PM. The results indicate that the salt-tolerance and heat-resistance properties of PM solution were improved by the introduction of ANS particles. Moreover, the structures of ANS samples have a significant effect on the effectiveness of the nanoparticles due to the fact that the amine group density on the ANS surface can affect the strength of intermolecular interaction between nanoparticles and polymer molecules. Additionally, the better ability of the ANS sample with proper amine group density showed in reducing the oil/water interfacial tension over NS and other ANS samples made it a more promising chemical for enhancing oil recovery. The results from core flooding tests show that the PM/ANS system has the greatest oil recovery factor (16.30%), while the values for PM/NS and PM are 10.84% and 6.00%, respectively.

The amino-functionalized nanosilica/polymer hybrid systems have better salt tolerance and EOR performance than unmodified nanosilica polymer hybrid systems.

Interfacial phenomena at a surface of individual and complex fumed nanooxides

Investigations of interfacial and temperature behaviors of nonpolar and polar adsorbates interacting with individual and complex fumed metal or metalloid oxides (FMO), initial and subjected to various treatments or chemical functionalization and compared to such porous adsorbents as silica gels, precipitated silica, mesoporous ordered silicas, filled polymeric composites, were analyzed. Complex nanooxides include core-shell nanoparticles, CSNP (50-200nm in size) with titania or alumina cores and silica or alumina shells in contrast to simple and smaller nanoparticles of individual FMO. CSNP could be destroyed under high-pressure cryogelation (HPCG) or mechanochemical activation (MCA). These treatments affect the structure of aggregates of nanoparticles and agglomerates of aggregates, resulting in their becoming more compacted. The analysis shows that complex FMO could be more sensitive to external actions than simple nanooxides such as fumed silica. Any treatment of 'soft' FMO affects the interfacial and temperature behaviors of polar and nonpolar adsorbates. Rearrangement of secondary particles and surface functionalization affects the freezing-melting point depression of adsorbates. For some adsorbates, open hysteresis loops became readily apparent in adsorption-desorption isotherms. Clustering of adsorbates bound in textural pores in aggregates of nanoparticles (i.e., voids between nanoparticles in secondary structures) causes reduced changes in enthalpy during phase transitions (freezing, fusion, evaporation). Freezing point depression and melting point elevation cause significant hysteresis freezing-melting effects for adsorbates bound to FMO in the textural pores. Relaxation phenomena for both low- and high-molecular weight adsorbates or filled polymeric composites are affected by the morphology of primary particles, structural organization of secondary particles of differently treated or functionalized FMO, content of adsorbates, co-adsorption order, and temperature.

Comparison of stability properties of poly(acrylic acid) adsorbed on the surface of silica, alumina and mixed silica-alumina nanoparticles — application of turbidimetry method

The influence of anionic poly(acrylic acid) — PAA addition on the stability of synthesized silica, alumina and mixed silica-alumina suspensions as a function of solution pH was studied. The turbidimetry method was used to monitor the changes of the examined systems stability over time. The calculated stability coefficients enabled estimation of polymer adsorption influence on stability of metal oxide suspension. It was shown that the alumina suspension without the polymer is the most unstable at the pH values 6 and 9, whereas the silica polymer was most unstable at pH 3. PAA with higher molecular weight (240 000) is a relatively effective stabilizer of all investigated adsorbents (except silica at pH 3). These properties of poly(acrylic acid) are highly desirable in many branches of industry (e.g. production of cosmetics, pharmaceuticals, paints) where polymers are widely used as effective stabilizers of colloidal suspensions.

Comparison of adsorption affinity of polyacrylic acid for surfaces of mixed silica-alumina

The influence of solution pH (in the range 3–9) on the adsorption of polyacrylic acid (PAA) on the mixed silica–alumina surface (SA-3: SiO₂ 97 %–Al₂O₃ 3 % and SA-96: SiO₂ 4 %–Al₂O₃ 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.