Optimization of the metakaolin geopolymer preparation for maximized ammonium adsorption capacity

Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH₄ ⁺) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH₄ ⁺ adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH₄ ⁺ removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.     

Functional Peptide Monolayers at Interfaces

Amphiphilic peptides can be designed to form ordered supramolecular structures at hydrophilic-hydrophobic interfaces. These systems rely on the ability of peptides to fold into certain secondary structures at interfaces. This review focuses on the design of amphiphilic β-sheet peptide assemblies in monolayers at interfaces, and their relevance to inducing mineralization and interactions with specific ions. In addition, the review discusses recent studies demonstrating the applicability of designed amphiphilic β-sheet peptides to detection of specific small molecules and to elucidating intermolecular interactions relevant to drug delivery and enzyme catalysis systems.     

Preparation of dual‐layer acetylated methyl cellulose hollow fiber membranes via co‐extrusion using thermally induced phase separation and non‐solvent induced phase separation methods

Dual‐layer acetylated methyl cellulose (AMC) hollow fiber membranes were prepared by coupling the thermally induced phase separation (TIPS) and non‐solvent induced phase separation (NIPS) methods through a co‐extrusion process. The TIPS layer was optimized by investigating the effects of coagulant composition on morphology and tensile strength. The solvent in the aqueous coagulation bath caused both delayed liquid–liquid demixing and decreased polymer concentration at the membrane surface, leading to porous structure. The addition of an additive (triethylene glycol, (TEG)) to the NIPS solution resolved the adhesion instability problem of the TIPS and NIPS layers, which occurred due to the different phase separation rates. The dual‐layer AMC membrane showed good mechanical strength and performance. Comparison of the fouling resistance of the AMC membranes with dual‐layer polyvinylidene fluoride (PVDF) hollow fiber membranes fabricated with the same method revealed less fouling of the AMC than the PVDF hollow fiber membrane. This study demonstrated that a dual‐layer AMC membrane with good mechanical strength, performance, and fouling resistance can be successfully fabricated by a one‐step process of TIPS and NIPS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42715.     

Impact compaction on a subgrade layer overlying deep deposit

Recent expansions of urban communities around the world have forced geotechnical engineers to deal with weak deep deposit for the construction of highways and roads. The current practice in estimating the level of field compaction is based on the results of a laboratory test, known as ‘Proctor’, where wide discrepancies are found between the laboratory-predicted and the field measurements. Impact compaction is a widespread soil-improvement technique that has been used with proven effectiveness. The technique is environmentally friendly, simple to apply and relatively inexpensive. This study presents a numerical model, which was developed to simulate the case of a dry thin subgrade layer overlying a deep deposit and subjected to impact compaction. The model is capable of measuring the total energy applied to the surface of the subgrade layer and its two components; namely the portion dissipated into the lower deposit and the portion remaining in the subgrade layer causing its compaction. A design guideline is presented.     

Effects of pigmentation on siloxane–polyurethane coatings and their performance as fouling-release marine coatings

Siloxane–polyurethane paints were formulated and characterized for coating properties and performance as fouling-release (FR) marine coatings. Paints were formulated at 20 and 30 pigment volume concentrations with titanium dioxide, and aminopropyl-terminated poly(dimethylsiloxane) (APT-PDMS) loadings were varied from 0 to 30% based on binder mass. The coatings were characterized for water contact angle, surface energy (SE), gloss, and pseudobarnacle (PB) adhesion. The assessment of the FR performance compared with polyurethane (PU) and silicone standards through the use of laboratory biological assays was also performed. Biofilm retention and adhesion were conducted with the marine bacterium Cellulophaga lytica, and the microalgae diatom Navicula incerta. Live adult barnacle reattachment using Amphibalanus amphitrite was also performed. The pigmented coatings were found to have properties and FR performance similar to those prepared without pigment. However, a higher loading of PDMS was required, in some cases, to obtain the same properties as coatings prepared without pigment. These coatings rely on a self-stratification mechanism to bring the PDMS to the coating surface. The slight reduction in water contact angle (WCA) and increase in pseudobarnacle release force with pigmentation suggests that pigmentation slowed or interfered with the self-stratification mechanism. However, increasing the PDMS loading is an apparent method for overcoming this issue, allowing for coatings having similar properties as those of clear coatings and FR performance similar to those of silicone standard coatings.     

Antioxidant Effects of Berry Phenolics Incorporated in Oil-in-Water Emulsions with Continuous Phase β-Lactoglobulin

The purpose of this study was to evaluate the effects of berry phenolics, in this case, black currant (Ribes nigrum) anthocyanins and raspberry (Rubus idaeus) ellagitannins, in the presence of continuous phase β-lactoglobulin (β-Lg), on the oxidative stability of Brij 35-stabilized corn oil-in-water emulsions. The extent of lipid oxidation in emulsions was measured by determining the formation of lipid hydroperoxides and hexanal, and extent of protein oxidation by monitoring the loss of tryptophan and cysteine residues in the continuous phase β-Lg. Berry phenolics at concentration levels of 20 and 50 μM were able to prevent lipid oxidation with and without β-Lg in the aqueous phase. The results show that a combination of β-Lg and berry phenolics was more efficient in inhibiting hexanal formation than either component alone. Synergistic effects on antioxidant activity toward hexanal were observed only at the 20 μM levels of berry phenolics in combination with continuous phase β-Lg. The berry phenolics were also able to inhibit the oxidation of tryptophan and cysteine residues of β-Lg. The results show that the amino acid residues were oxidized prior to the propagation of lipid oxidation. This suggests that these amino acids were able to inhibit fatty acid scission. The information gained from this study would be useful in protecting emulsion-based food products from oxidative deterioration.     

Structure and digestibility of tissues in normal and brown midrib pearl millet (Pennisetum glaucum)

The tissues in leaf blades, midribs, sheaths and stems of normal (N), 5848, and two brown midrib (bmr) mutants, 5753 and 5778, of pearl millet (Pennisetum glaucum (L) R Br) were examined for structural characteristics related to digestibility. The anatomies of the various plant parts were not substantially different between N and bmr plants. The more rigid, lignified tissues such as vascular bundles in all plant parts and the rind of stems were not digested after incubation for 7 days in N or bmr plants, indicating that modifications in these tissues were not sufficient to affect biodegradation. Modifications in the digestible tissues resulted in faster and more extensive degradation in bmr plants, and these changes appear to be the most significant in relation to biodegradation. The parenchyma of midveins and stems, which occupies c 70 and 60% of the cross-sectional area of these respective parts, were the sites where modification in phenolics resulted in the greatest improvement in digestibility.     

Hydration of dibarium silicate I. Stoicheiometry of hydration

Dibarium silicate, Ba₂SiO₄, was hydrated in two ways: in paste form at 25° using a water/solid weight ratio of 0.7:1, and in a polyethylene bottle rotated on a wheel at 5°, 25° and 50°, using a water/solid weight ratio of 9.0:1. When Ba₂SiO₄ is hydrated in paste form, the stoicheiometry of the reaction at 25° is the same as in bottle-hydration at 50°: 2BaO.SiO₂+2.2H₂O = 1.2BaO.SiO₂.1.4H₂O+0.8Ba(OH)₂. The stoicheiometry of bottle-hydration at 5° and 25° is represented by the equation: 2BaO.SiO₂+2.2H₂O = BaO.SiO.1.2H₂O+Ba(OH)₂. Barium silicate hydrate, 1.2BaO.SiO₂.1.4H₂O, is well crystallised and has a specific surface area of ? 3m²/g. The crystals are plate-like and have a tendency to form clusters. The low-baria hydrate, BaO.SiO₂.1.2H₂O, is poorly crystallised and consists of thin platelets. It has a specific surface area of ? 35m²/g. The thermal dehydration of fully hydrated barium silicate and of the barium silicate hydrates was investigated by thermogravimetric and differential thermal analysis techniques. The similarities and differences between the barium silicate hydrates obtained in the hydration of barium silicate and the calcium silicate hydrates obtained in the hydration of β-dicalcium silicate and Ca₃SiO₅ are discussed. A mechanism of hydration of barium silicate is proposed which involves solution, precipitation and crystallisation steps.