Kationska izmenjava v strukturah kovinsko-organskih materialov za zajemanje plinov

Lisac, Tjaša (author), Mazaj, Matjaž (mentor), Golobič, Amalija (comentor)

Eden izmed večjih okoljskih problemov je naraščanje emisij ogljikovega dioksida kot posledica zgorevanja fosilnih goriv. Poleg uporabe obnovljivih virov energije imajo vedno pomembnejšo vlogo tehnologije za zajemanje in shranjevanje CO2 (ang. Carbon Capture and Storage – CCS). Kovinsko-organski porozni materiali (ang. Metal-Organic Frameworks – MOFs) so se v zadnjih letih izkazali kot učinkoviti materiali za zajem CO2 na osnovi fizisorpcije. V magistrskem delu sem z modifikacijo že znanih struktur nameravala izboljšati adsorpcijske kapacitete izbranih MOF-materialov za CO2. Na Zn-1,4-benzendikarboksilatu sem preučila posintezno kationsko izmenjavo s kationi alkalijskih kovin. V zeolitno imidazolatna ogrodja materialov ZIF-4, ZIF-7 in ZIF-8 pa sem z delno vgradnjo litijevih kationov na mesta ogrodnih cinkovih kationov poskušala vpeljati praznine. Pri tem sem povečevala delež litijevih kationov glede na cinkove. Karakterizacijo dobljenih produktov sem izvedla z rentgensko praškovno difrakcijo, termogravimetrično analizo, dušikovo fizisorpcijsko analizo in meritvami adsorpcijskih kapacitet za vezavo CO2. Primerno velike kristale sem okarakterizirala z rentgensko strukturno analizo. Meritve N2 adsorpcijskih izoterm kažejo, da se specifična površina Zn-1,4-benzenkarboksilata pri kationski izmenjavi s kalijevimi ioni poveča za 22 % glede na osnovni material. Enak trend je opazen pri adsorpciji CO2. Med zeolitno imidazolatnimi materiali največjo spremembo v adsorpcijski kapaciteti CO2 opazimo pri ZIF-7. Modifikaciji z največjim deležem litijevih kationov glede na cinkove katione se adsorpcijska kapaciteta poveča za 70 % glede na osnovni material. Modifikacije ZIF-4 večjih sprememb specifičnih površin in adsorpcijskih kapacitet CO2 ne kažejo. Pri modifikaciji ZIF-8 z največjim deležem litijevih kationov opazimo povečanje specifične površine za 64 % glede na osnovni material, vendar se adsorpcijska kapaciteta CO2 poveča le za 10 %. Učinkovitejšo adsorpcijo preprečuje hidrofobnost ogrodja.

• Language: Slovenian
• Keywords: zajem ogljikovega dioksida, kovinsko-organski porozni materiali, posintezna kationska izmenjava, izomorfna substitucija, adsorpcija
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2020
• PID: 20.500.12556/RUL-118619
• COBISS.SI-ID: 27038979
• Publication date in RUL: 28.08.2020

Secondary language

• Language: English
• Title: Cationic exchange in metal-organic framework materials for gas capture

Abstract

The escalating levels of carbon dioxide as a result of fossil fuels combustion is one of the greatest environmental concerns. Therefore carbon capture and storage technologies will play a vital role beside the use of renewable sources of energy. In the last few years, metal-organic frameworks have emerged as promising materials for CO2 capture on the basis of physisorption. In my master's degree thesis I tried to improve the adsorption capacities of selected materials by modifying already known structures for CO2 capture. On Zn-1,4-benzenecarboxylate postsynthetic cationic exchange with alkali metal cations was performed. I also studied representatives of zeolitic imidazolate frameworks ZIF-4, ZIF-7 and ZIF-8. I performed substitution of zinc cations with lithium cations to make some additional vacancies within the framework, wherein I was increasing the amount of lithium cations according to zinc cations. The characterization of products was performed by X-ray powder difraction, thermogravimetric analysis, N2 physisorption analysis and measurements of CO2 adsorption capacities. Crystals of an appropriate size were characterized by single-crystal XRD. Measurements of N2 adsorption isotherms show that the specific surface area of Zn-1,4-benzenecarboxylate exchanged with potassium cations increases for 22 % relative to the parent material. The same trend is observed for CO2 adsorption. Among zeolitic imidazolate frameworks the largest change in CO2 adsorption capacity is observed for ZIF-7. Modification with the highest proportion of lithium cations according to zinc cations have the largest gain in adsorption, achieving 70 % improvement relative to the parent material. There are no major changes in specific area and CO2 adsorption capacities for ZIF-4 modifications. ZIF-8 modification with the highest amount of lithium cations shows the increasing in specific surface area for 64 % relative to the parent material, however CO2 adsorption capacity increases only for 10 %. The more efficient adsorption is inhibited by the framework hydrophobicity.

• Keywords: carbon dioxide capture, metal-organic frameworks, postsynthetic cationic exchange, isomorphic substitution, adsorption