Nanoporous materials such as Mobil composite material number 41 (MCM-41) are attractive for applications such as catalysis, adsorption, supports, and carriers. Green synthesis of MCM-41 is particularly appealing because the chemical reagents are useful and valuable. We report on the eco-friendly synthesis of MCM-41 nanoporous materials via multi-cycle approach by re-using the non-reacted reagents in supernatant as mother liquor after separating the solid product. This approach was achieved via minimal requirement of chemical compensation where additional fresh reactants were added into the mother liquor followed by pH adjustment after each cycle of synthesis. The solid product of each successive batch was collected and characterized while the non-reacted reagents in supernatant can be recovered and re-used to produce subsequent cycle of MCM-41. The multi-cycle synthesis is demonstrated up to three times in this research. This approach suggests a low cost and eco-friendly synthesis of nanoporous material since less waste is discarded after the product has been collected, and in addition, product yield can be maintained at the high level.
The unique three-dimensional pore structure of KCC-1 has attracted significant attention and has proven to be different compared to other conventional mesoporous silica such as the MCM-41 family, SBA-15, or even MSN nanoparticles. In this research, we carefully examine the morphology of KCC-1 to define more appropriate nomenclature. We also propose a formation mechanism of KCC-1 based on our experimental evidence. Herein, the KCC-1 morphology was interpreted mainly on the basis of compiling all observation and information taken from SEM and TEM images. Further analysis on TEM images was carried out. The gray value intensity profile was derived from TEM images in order to determine the specific pattern of this unique morphology that is found to be clearly different from that of other types of porous spherical-like morphologies. On the basis of these results, the KCC-1 morphology would be more appropriately reclassified as bicontinuous concentric lamellar morphology. Some physical characteristics such as the origin of emulsion, electrical conductivity, and the local structure of water molecules in the KCC-1 emulsion were disclosed to reveal the formation mechanism of KCC-1. The origin of the KCC-1 emulsion was characterized by the observation of the Tyndall effect, conductometry to determine the critical micelle concentration, and Raman spectroscopy. In addition, the morphological evolution study during KCC-1 synthesis completes the portrait of the formation of mesoporous silica KCC-1.
Lubricant oils take significant part in current health and environmental considerations since they are an integral and indispensable component of modern technology. Antioxidants are probably the most important additives used in oils because oxidative deterioration plays a major role in oil degradation. Zeolite nanoparticles (NPs) have been proven as another option as green antioxidants in oil formulation. The anti-oxidative behavior of zeolite NPs is obvious; however, the phenomenon is still under investigation. Herein, a study of the effect of extra-framework cations stabilized on Linde Type L (LTL) zeolite NPs (ca. 20 nm) on inhibition of oxidation in palm oil-based lubricant oil is reported. Hydrophilic LTL zeolites with a Si/Al ratio of 3.2 containing four different inorganic cations (Li(+), Na(+), K(+), Ca(2+)) were applied. The oxidation of the lubricant oil was followed by visual observation, colorimetry, fourier transform infrared (FTIR) spectroscopy, (1)H NMR spectroscopy, total acid number (TAN), and rheology analyses. The effect of extra-framework cations to slow down the rate of oil oxidation and to control the viscosity of oil is demonstrated. The degradation rate of the lubricant oil samples is decreased considerably as the polarizability of cation is increased with the presence of zeolite NPs. More importantly, the microporous zeolite NPs have a great influence in halting the steps that lead to the polymerization of the oils and thus increasing the lifetime of oils.
Mesoporous silica nanoparticles (MSNs) were synthesized with variable microwave power in the range of 100-450 W, and the resulting enhancement of MSN crystal growth was evaluated for the adsorption and release of ibuprofen. X-ray diffraction (XRD) revealed that the MSN prepared under the highest microwave power (MSN450) produced the most crystallized and prominent mesoporous structure. Enhancement of the crystal growth improved the hexagonal order and range of silica, which led to greater surface area, pore width and pore volume. MSN450 exhibited higher ibuprofen adsorption (98.3 mg/g), followed by MSN300(81.3 mg/g) and MSN100(74.1 mg/g), confirming that more crystallized MSN demonstrated higher adsorptivity toward ibuprofen. Significantly, MSN450 also contained more hydroxyl groups that provided more adsorption sites. In addition, MSN450 exhibited comparable ibuprofen adsorption with conventionally synthesized MSN, indicating the potential of microwave treatment in the synthesis of related porous materials. In vitro drug release was also investigated with simulated biological fluids and the kinetics was studied under different pH conditions. MSN450 showed the slowest release rate of ibuprofen, followed by MSN300 and MSN100. This was due to the wide pore diameter and longer range of silica order of the MSN450. Ibuprofen release from MSN450 at pH 5 and 7 was found to obey a zero-order kinetic model, while release at pH 2 followed the Kosmeyer-Peppas model.
The efficiency of zeolite X nanocrystals (FAU-type framework structure) containing different extra-framework cations (Li(+), Na(+), K(+), and Ca(2+)) in slowing the thermal oxidation of palm oil is reported. The oxidation study of palm oil is conducted in the presence of zeolite nanocrystals (0.5 wt %) at 150 °C. Several characterization techniques such as visual analysis, colorimetry, rheometry, total acid number (TAN), FT-IR spectroscopy, (1)H NMR spectroscopy, and Karl Fischer analyses are applied to follow the oxidative evolution of the oil. It was found that zeolite nanocrystals decelerate the oxidation of palm oil through stabilization of hydroperoxides, which are the primary oxidation product, and concurrently via adsorption of the secondary oxidation products (alcohols, aldehydes, ketones, carboxylic acids, and esters). In addition to the experimental results, periodic density functional theory (DFT) calculations are performed to elucidate further the oxidation process of the palm oil in the presence of zeolite nanocrystals. The DFT calculations show that the metal complexes formed with peroxides are more stable than the complexes with alkenes with the same ions. The peroxides captured in the zeolite X nanocrystals consequently decelerate further oxidation toward formation of acids. Unlike the monovalent alkali metal cations in the zeolite X nanocrystals (K(+), Na(+), and Li(+)), Ca(2+) reduced the acidity of the oil by neutralizing the acidic carboxylate compounds to COO(-)(Ca(2+))1/2 species.
Biogas consisting of carbon dioxide/methane (CO2/CH4) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO2 can decrease the calorific value and generate greenhouse gas. Hence, separating CO2 from CH4 is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO2/CH4 separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO2/CH4 separation. The highest performance in terms of CO2 permeance and CO2/CH4 selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO2 permeance in the range of 2.0 × 10- 7-7.0 × 10- 6 mol m- 2 s- 1 Pa- 1 with CO2/CH4 selectivity ranging from 3 to 300. Current trends directed toward improving CO2/CH4 selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO2/CH4 selectivity. The modifications via ionic liquid and silane methods more influenced the CO2/CH4 selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.