Synthetization and characteraization of porous materials for cooling and gas storage application

• Main Author: Teng, Guang Way
• Other Authors: Anutosh Chakraborty
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/78674
• Institution: Nanyang Technological University

Modern civilization had led to many environmental damages over the decades. The extensive burning and depletion of limited fossil fuels have led to the needs of a reliable replacement fuel. The globe’s CO2 emission have risen sharply. Conventional cooling techniques(refrigeration system) involving the use of refrigerants also poses environmental issue if not properly disposed. One such method that may solve the above environmental problems is the use of an Adsorption System using a suitable adsorbent to store Gases(CO2, CH4) and Water. MOF-74 were suggested as potential adsorbent as they have high BET surface area, high water stability(especially for Nickel and Cobalt based MOF-74) and suggested to have mild condition/low-pressure optimal adsorption/desorption property. The objective of this project is to perform synthesis and characterization of various MOF-74. The project then proceed to perform characterization to evaluate these MOF-74 as adsorbent materials. In the project, we first synthesize Zn-MOF-74, Ni-MOF-74 and Co-MOF-74 by modifying the synthesis protocol. In the synthesis, ethanol was used as the primarily solvent for incubation, and DMF which was commonly used in the conventional synthesis of MOF-74 was avoided. During purification, acetone was used for washing of samples instead of methanol which were used conventionally. The project then proceed to synthesize Ni-MOF-74 and Co-MOF-74 with the use of a 1:1:1 DMF/Ethanol/Water mixture as solvent following the conventional approach closely. We then proceed to perform characterization of the 5 synthesized, employing, Brunauer–Emmett–Teller (BET) analysis (base on N2 adsorption isotherm), Scanning Electron Microscope (SEM) analysis, Thermal Gravimetric Analysis (TGA) analysis and Differential scanning calorimetry (DSC) analysis. 2 of the samples, namely Ni-MOF-74 (modified protocols) and Zn-MOF-74 (modified protocols) were characterized with N2 adsorption isotherm to calculate BET area, pore volume and pore size. These samples were later used to obtain CO2 adsorption isotherm. The Ni-MOF-74 and Zn-MOF-74 synthesized with modified protocol only has a BET surface area of 63.552m^2/g and 70.458m^2/g from N2 adsorption. The morphology structure observed in SEM images are extremely different from MOF-74 of similar metal base that were synthesized by other research. TGA study finds that the synthesized Co-MOF-74, Ni-MOF-74 and Zn-MOF-74, with modified protocol are still thermally stable up to about 500°C, 350°C, 550°C respectively. DSC of modified protocol samples analysis shows that Zn-MOF-74 and Co-MOF-74 is not able to produce a valid water adsorption phase curve observed in a well synthesized MOF. Ni-MOF-74 synthesized with modified protocol is the only sample that produce the sample that resemble the adsorption curve to a certain extent. SEM images shows that Co-MOF-74 and Ni-MOF-74 synthesized by conventional synthesis methodology has morphology pattern that resemble the samples from literature reviews sample, up to a certain extent. TGA study showed that these samples are also thermally stable up to about 450 °C and 300 °C respectively. During the study, it was also noted that the samples showed steeper wt% drop during heating at lower temperature. This suggest that the samples synthesized with conventional method may have greater adsorption/desorption rate at lower temperature resulting in high water mass loss during low temperature heating. DSC of conventional protocol samples analysis shows. Co-MOF-74 synthesized conventionally has higher water adsorption enthalpy than both Ni-MOF-74 synthesized (conventional and modified protocol). Zn-MOF-74 appears to be most thermally stable, collapsing at 550°C. The Co-MOF-74 synthesized in this project is also outstandingly thermally stable up to 450°C to 500°C for conventional protocol and modified protocol respectively. Ni-MOF-74 are also decently thermally stable, collapsing at 300 °C and 350 °C for conventional protocol and modified protocol respectively. In additional to literature claim that Co-MOF-74 have outstanding water stability, Co-MOF-74 synthesized in our experiment conventionally also has high water adsorption enthalpy (approximated) than Ni-MOF-74 through DSC analysis and thermal stability. Co-MOF-74 synthesized conventionally is thus, worthy of continuous investigation as it consistently outperforms the other samples the project has synthesized.