The Cu-BTC (Copper -1,3,5-benzene tricarboxylate) is one of the representative metal organic frameworks (MOFs) that has shown outstanding performance for carbon dioxide (CO2) adsorption. However, its conventional synthesis duration is relatively long, and the process requires the addition of bulk amounts of organic solvents. Herein, an enhanced solvent-free synthesis strategy was demonstrated in this work for the Cu-BTC synthesis. For this enhanced method, Cu-BTC was synthesized in 3 hours by mechanically grinding the mixture of copper (Cu) metal precursor and BTC organic linker without using solvent. The as-synthesized Cu-BTC samples were analyzed using various characterization techniques to examine and confirm their properties. The thermal stability result revealed that the self-synthesized Cu-BTC could sustain high temperature up to 290 ℃. Among the samples synthesized at different mole ratios, the Cu-BTC sample with the Cu to BTC mole ratio of 1.5:1 showed the highest BET surface area and the most significant pore volume of 1044 m 2 g -1 and 0.62 cm 3 g -1 , respectively. Its CO2 adsorption capacity was comparable with those fabricated using the solvent-based method, i.e., 1.7 mmol g -1 at 30 ℃ and 1 bar. The results also showed that the synthesized Cu-BTC exhibited regenerative ability up to five adsorption-desorption cycles.

MIL-101(Cr), a subclass of metal–organic frameworks (MOFs), is a promising adsorbent for carbon dioxide (CO2) removal due to its large pore volume and high surface area. Solvent-free synthesis of MIL-101(Cr) was employed in this work to offer a green alternative to the current approach of synthesizing MIL-101(Cr) using a hazardous solvent. Characterization techniques including XRD, SEM, and FTIR were employed to confirm the formation of pure MIL-101(Cr) synthesized using a solvent-free method. The thermogravimetric analysis revealed that MIL-101(Cr) shows high thermal stability up to 350 °C. Among the materials synthesized, MIL-101(Cr) at the molar ratio of chromium precursor to terephthalic organic acid of 1:1 possesses the highest surface area and greatest pore volume. Its BET surface area and total pore volume are 1110 m2/g and 0.5 cm3/g, respectively. Correspondingly, its CO2 adsorption capacity at room temperature is the highest (18.8 mmol/g), suggesting it is a superior adsorbent for CO2 removal. The textural properties significantly affect the CO2 adsorption capacity, in which large pore volume and high surface area are favorable for the adsorption mechanism.

UiO-66(Ce) metal-organic framework (MOF) has been a promising material for broad applications, including gas adsorption, photocatalysis, water treatment and reaction catalysis. For its usual preparation, a large amount of solvent is required and added during its fabrication process. This solvent is harmful to the environment most of the time. It is neither recyclable nor reusable, indicating the difficulty in waste disposal after MOF fabrication and the challenges for its scaling-up production. Given this, a solvent-free way of synthesizing the UiO-66 MOF to develop its sustainable synthesis was reported here. The MOF can be obtained by mechanically grinding the cerium (IV) ammonium nitrate (CAN) and terephthalic acid (BDC) using mortar and pestle without the addition of any solvent. Then the mixture was transferred into an autoclave and heated at 100 °C for one day. In this work, UiO-66(Ce) MOF samples with varying Ce to BDC molar ratios were successfully fabricated using the solvent-free method, supported by the XRD, SEM, EDX and FT-IR analysis results. By looking at their XRD patterns, two characteristic peaks for UiO-66(Ce) MOF were observed at 8.4° and 9.1°. The SEM images revealed the spherical crystalline morphology of UiO-66 MOF. At the same time, the EDX analysis result found the elemental composition of UiO-66 MOF was coherent with the reactants used, suggesting the excellent purity of MOF product formed in this work. As verified by the thermal stability test, the UiO-66 MOF produced here is thermally stable up to 250 °C in the air atmosphere.

Background: The use of membrane technology has developed rapidly since the proposal of the Robeson upper bound. Nevertheless, the researchers proposed various methods and techniques to enhance the permeability and selectivity to achieve a breakthrough of the upper bound. Method: Metal-organic framework (MOF) and covalent organic framework (COF) were the recentlyinterest- arising materials enhancing gas separation performance. In this study, recent advances in MOF and COF were comprehensively discussed in terms of the materials, properties and synthesis method. Later, the MOF and COF nanocomposite mixed matrix membrane development was discussed to evaluate the recent improvement of these membranes used in the O2/N2 gas separation performance. This work intends to overview the recent progress and development of the metal-organic framework, covalent organic frameworks and the used nanocomposite membrane in O2/N2 gas separation. Result: This topic review was carried out from a thorough literature review of metal-organic frameworks, covalent organic frameworks and the used nanocomposite membrane in O2/N2 gas separation. Additionally, the recent achievement of the O2/N2 gas separation by nanocomposite membrane in term of permeability and selectivity are also discussed. Conclusion: Findings from this study suggested that MOF and COF-based nanocomposite membranes could be used in either the O2/N2 and N2/O2 gas separation process with the possibility of being involved in the gas production sector.

Global warming issue due to the excessive carbon dioxide gas emission have raised strong interest in capturing or reducing the CO2 from flue gas or atmosphere. Physisorption-based CO2 capture applying the metal organic framework (MOF) provides a promising alternative for capturing CO2 due to the simplicity, low operating cost, and low energy requirement of the adsorption approach combined with the high CO2 adsorption capacity MOF material. In this study, a series of Chromium based MIL MOF with a variety molar ratio of chromium metal to 1,4-Benzene Dicarboxylate (BDC) organic linker were prepared via the solvent-free method (mechanochemical) to develop a clean and efficient way of synthesising MOF samples as promising CO2 adsorbents. The XRD results and FTIR spectra have confirmed the successful fabrication of MIL-101(Cr) MOF using the solvent-free method. The SEM images illustrated fine growth of irregular shaped coarse particles for Cr MOF with equal mole ratio of Cr to BDC. The MIL-101(Cr) samples were also tested on their CO2 adsorption capacity to understand the influence of molar ratio of the starting materials on the CO2 adsorption capacity. It was found that the MIL-101(Cr)1 led to the formation of a product with the highest CO2 uptake capacity of 18.78 mmol/g. In contrast, the EDS analysis result revealed that all the samples synthesised in this work were well incorporated with the Chromium element. It is therefore suggested that the molar ratio of Cr to BDC plays a critical role in determining the CO2 gas adsorption capacity.