Modification of commercial Y zeolites by alkaline-treatment for improved performance in the isomerization of glucose to fructose

Study on phosphate removal from aqueous solutions using magnesium-ammonium- and zirconium-modified zeolites: equilibrium, kinetic, and fixed-bed column study

Eutrophication is an environmental issue which occurs when the environment becomes enriched with nutrients. Phosphorus (P) is a key nutrient limiting the phytoplankton and algal growth in many aquatic environments. Therefore, P removal could be a promising technique to control the eutrophication. Herein, a natural zeolite (NZ) was modified by two practical techniques, including zirconium (ZrMZ) and magnesium-ammonium modification (MNZ), and employed for phosphate removal. Batch, equilibrium, and column experiments were conducted to determine various adsorption parameters. Equilibrium data were fitted to two different isotherms and Freundlich isotherm provided the best fit which confirms multi-layer adsorption of phosphate ions on the adsorbents. The kinetic experiments demonstrated that the adsorption process is fast with more than 80% of phosphate adsorbed in the first 4 h, and a subsequent equilibrium was established after 16 h. The kinetic data were well described by pseudo-second-order model, suggesting that chemisorption is the mechanism of sorption. Intraparticle diffusion showed a rate-limiting step for phosphate adsorption on all the adsorbents, especially MNZ and ZrMZ. The fixed-bed column study showed that the phosphate concentration in the outlet (C) of ZrMZ column did not reach the initial concentration (C₀) after passing 250 bed volume (BV), while it reached C₀ after 100 BV when the MNZ was employed. Given the considerable improvement were seen, the results of this study suggest that surface of zeolite can be modified with zirconium (and in a less extent magnesium-ammonium) to enhance adsorption of phosphate from many eutrophic lakes.

Enhanced Catalytic Activity of Modified ZSM-5 Towards Glucose Isomerization to Fructose

The present study focuses on generating mesopores within H-ZSM-5 (H-Z) zeolite via desilication and dealumination to incorporate Lewis acidic metal, such as Sn, into the framework (Sn₄ ZS₁₈₀ A₁₅ ) to catalyse glucose isomerisation. Sn₄ ZS₁₈₀ A₁₅ possesses enhanced surface area (457 m²  g^-1 ), mesopore volume (0.585 cm³  g^-1 ) and a high weak-medium to strong acidic sites ratio, compared to parent H-Z (395 m²  g^-1 ; 0.174 cm³  g^-1 ). DRS-UV-Vis and XPS results corroborate Sn incorporation into the framework of Sn₄ ZS₁₈₀ A₁₅ , based on the absorbance peak around 200-220 nm and peaks appearing at 495.8 and 487.4 eV, respectively. Sn₄ ZS₁₈₀ A₁₅ exhibits higher catalytic activity towards glucose isomerisation in ethanol-water at 110 °C, yielding 44.2 % fructose with 80.0 % selectivity. Conversely, the parent H-Z afforded negligible glucose conversion with a fructose yield of <1 % under identical conditions. Moreover, Sn-incorporated on dealuminated (Sn₄ ZS₀ A₁₅ ) and desilicated (Sn₄ ZS₁₈₀ A₀ ) catalysts give a low yield of fructose (7-10 %), signifying the requirement of the desilication-dealumination process before incorporating Sn into the framework.

Effects of monosaccharide composition on quantitative analysis of total sugar content by phenol-sulfuric acid method

Phenol-sulfuric acid method is one of the most common methods applied to the analysis of total sugar content during polysaccharides study. However, it was found that the results obtained from the phenol-sulfuric acid method was generally lower than the real total sugar content, especially when acidic monosaccharides were contained in the polysaccharides samples. Therefore, the present study focused to unveil the proposed problem. Based on the optimization of colorimetric conditions, such as optimal wave length of absorption, linearity range, color reaction time and temperature, it indicated that the phenol-sulfuric acid method was a convenient and accurate way for the total sugar content analysis. In addition, the color-rendering capabilities of 10 common monosaccharides were systematically analyzed to obtain a relative correction factor for each monosaccharide relative to glucose, which was proved to be the main reason for the deviation in the detection of total sugar content. Moreover, the key points during the application of phenol-sulfuric acid method were suggested. This study provides a scientific theoretical basis and a reliable experimental research method for the accurate determination of total sugar content by the phenol-sulfuric acid method, and which will also promote the application of this convenient method in the polysaccharides study.

Alkali-Treated Alumina and Zirconia Powders Decorated with Hydroxyapatite for Prospective Biomedical Applications

The alumina and zirconia surfaces were pretreated with chemical etching using alkaline mixtures of ammonia, hydrogen peroxide and sodium hydroxide, and followed with application of the powder layer of Ca-deficient hydroxyapatite (CDH). The influence of etching bath conditions time and concentration on surface development, chemical composition and morphology of medicinal ceramic powders were studied. The following analyses were performed: morphology (scanning electron microscopy), phase composition (X-ray diffraction analysis), changes in binding interactions and chemical composition (FT-Infrared and Energy dispersive spectroscopies). Both types of etchants did not expose the original phase composition changes or newly created phases for both types of ceramics. Subsequent decoration of the surface with hydroxyapatite revealed differences in the morphological appearance of the layer on both ceramic surfaces. The treated zirconia surface accepted CDH as a flowing layer on the surface, while the alumina was decorated with individual CDH aggregates. The goal of this study was to focus further on the ceramic fillers for polymer-ceramic composites used as a biomaterial in dental prosthetics.