ABSTRACT
(-)-Epigallocatechin gallate (EGCG) is a bioactive component of green tea that provides many health benefits. However, excessive intake of green tea may cause adverse effects of caffeine (CAF) since green tea (30-50 mg) has half the CAF content of coffee (80-100 mg). In this work, for enhancing the health benefits of green tea, natural rubber/hexagonal mesoporous silica (NR/HMS) nanocomposites with tunable textural properties were synthesized using different amine template sizes and applied as selective adsorbents to separate EGCG and CAF from green tea. The resulting adsorbents exhibited a wormhole-like silica framework, high specific surface area (528-578 m2 g-1), large pore volume (0.76-1.45 cm3 g-1), and hydrophobicity. The NR/HMS materials adsorbed EGCG more than CAF; the selectivity coefficient of EGCG adsorption was 3.6 times that of CAF adsorption. The EGCG adsorption capacity of the NR/HMS series was correlated with their pore size and surface hydrophobicity. Adsorption behavior was well described by a pseudo-second-order kinetic model, indicating that adsorption involved H-bonding interactions between the silanol groups of the mesoporous silica surfaces and the hydroxyl groups of EGCG and the carbonyl group of CAF. As for desorption, EGCG was more easily removed than CAF from the NR/HMS surface using an aqueous solution of ethanol. Moreover, the NR/HMS materials could be reused for EGCG adsorption at least three times. The results suggest the potential use of NR/HMS nanocomposites as selective adsorbents for the enrichment of EGCG in green tea. In addition, it could be applied as an adsorbent in the filter to reduce the CAF content in green tea by up to 81.92%.
Subject(s)
Caffeine , Nanocomposites , Tea , Rubber , Adsorption , Silicon DioxideABSTRACT
Glycerol is a byproduct from biodiesel production via conventional transesterification processes, representing approximately 10 wt% of the mass of biodiesel produced. Because of increasing biodiesel consumption, the volume of glycerol being produced has grown significantly, leading to a large surplus and, consequently, a dramatic drop in its market value. Thus, the valorization of glycerol into chemicals is a promising pathway toward sustainability in biodiesel industries. This study focused on upgrading biodiesel plant-derived glycerol into short-chain polyglycerols (PG), which are used as intermediates for producing emulsifiers in several consumer products, via catalytic etherification. To enhance environmental sustainability, solvent-free etherification of glycerol was performed over mixed oxides derived from magnesium-aluminum layered double hydroxides (MgAl LDH). For the first time, natural dolomite, a mixed calcium and magnesium carbonate (CaMg [CO3]2), was used as an Mg source in the preparation of MgAl LDH/CaCO3 nanocomposites via hydrothermal synthesis. The calcined MgAl LDH/CaCO3 nanocomposites were characterized by highly dispersed small crystallites of magnesium oxide. Their textural and acid-base properties were tuned by varying the Mg:Al molar ratio. The MgAl LDH/CaCO3 (an Mg:Al molar ratio of 1:1) calcined at 500 °C exhibited a superior catalytic performance to the MgAl LDH available commercially and the one synthesized by conventional co-precipitation. The nanocomposite catalyst displayed selectivity of >99% toward short-chain PG at 52.1 mol% glycerol conversion.
