Metal–Organic Frameworks with Incorporated Carbon Nanotubes: Improving Carbon Dioxide and Methane Storage Capacities by Lithium Doping

Abstract

Reduction of the anthropogenic emission of CO 2 is currently a top priority because CO 2 emission is closely associated with climate change. Carbon capture and storage (CCS) [1] and the development of renewable and clean energy sources are two approaches for the reduction of CO 2 emission. One of the most promising alternative fuels is CH 4 , which is the major component of natural gas. The efficient storage of CH 4 is still one of the main challenges for its widespread application. Accordingly, the development of more efficient approaches for CO 2 capture and CH 4 storage is critically important.Recently, metal-organic frameworks (MOFs, e.g., MOF-210 and NU-100) [2] have shown great potential for gas storage because of their high specific surface area (SSA) and functionalized pore walls. However, most MOF materials still show relatively low CO 2 and CH 4 uptakes. To enhance CO 2 and CH 4 adsorption, it is imperative to develop new materials, such as covalent organic frameworks (COFs), [3] or to modify MOFs by using postsynthetic approaches. [2b, 4] Herein, we focus on the latter strategy. One of the modification approaches is incorporation of carbon nanotubes (CNTs) into MOFs in order to achieve enhanced composite performance, because of the unusual mechanical and hydrophobicity properties of CNTs.[5] Another approach is doping MOFs or COFs with electropositive metals.Recent studies indicate that the surface carboxylate functional groups of a substrate could act as nucleation sites to form MOFs by heterogeneous nucleation and crystal growth.[6] Both experimental and theoretical investigations indicate that the H 2 adsorption capacities of MOFs can be enhanced significantly by doping alkali-metal ions, in particular Li + ions, to the frameworks, owing to the strong affinity of Li + ions towards H 2 molecules. [3d, 7] Similarly, Lan et al. also showed theoretically that doping of COFs with Li + ions can significantly enhance the CH 4 uptake of COFs.[8] Most recently, the multiscale simulations performed by Lan et al. indicate that Li is the best surface modifier of COFs for CO 2 capture among a series of metals (Li, Na, K, Be, Mg Ca, Sc and Ti).[9] Furthermore, their simulations show that the excess CO 2 uptakes of the lithium-doped COFs can be enhanced by four to eight times compared to the undoped COFs at 298 K and 1 bar. [9] Motivated by these experimental and theoretical results, we synthesized hybrid MOF materials by using the two modification techniques outlined above, that is, 1) incorporation of CNTs into [Cu 3 (C 9 sites that become available for interaction with other molecules after removal of H 2 O in from Cu 2+ carbonyl complexes, and can also be easily rehydrated without change of the crystalline nature of the material after exposure to air [11] (see Figure S1 in the Supporting Information). Although the btc ligand can not act as an electron receptor for the electron transfer from the naphthalenide radical anion, [7c] the rehydration of the Cu 2+ sites in the framework makes the electron trans...

In situ synthesis of zeolitic imidazolate frameworks/carbon nanotube composites with enhanced CO2 adsorption

“…22 Later on, Chen and co-workers confined MOF-5 into the hollow space of MWCNTs; the material displayed structure stability in atmospheric humidity for more than 3 days, and provided effective protection against the decomposition of sensitive MOF-5. 27 Incorporation of 0.034 wt% MWCNTs into HKUST-1 has been reported by Xiang et 23 Similarly, Anbia et al had incorporated 10 wt% MWCNTs into MIL-101 to synthesize a hybrid composite; a significant enhancement in the CO 2 adsorption capacity at 298 K and thermal stability was observed in the composite material. 24 The increment in the CO 2 adsorption capacity of MWCNT@MIL-101 is attributed to the increase of the micropore volume of MIL-101 by MWCNT incorporation.…”

Adsorption characterization and CO2 breakthrough of MWCNT/Mg-MOF-74 and MWCNT/MIL-100(Fe) composites

“…Furthermore, the thermal stability along with the adsorption uptake was improved by adding CNT to MIL-101-68 (Al) [32]. Incorporating CNT and lithium ions with MOF Cu 3 (btc) 2 resulted in improving the CO 2 capacity by about 305% compared with those of the base adsorbent (Cu 3 (btc) 2 ) [33]. In addition, the adsorption capacity of CO 2 at high pressure and room temperature (10 bars and 298 K) was improved by adding MWCNT to MIL101 [34].…”

CO2 Capture on Metal-Organic Framework and Graphene Oxide Composite Using a High-Pressure Static Adsorption Apparatus

“…However, the large void space in MOFs is not completely utilized for gas storage because of weak interactions between the walls of MOFs and usually small gas molecules. [8] In order to utilize effectively the MOF pore space, other materials with ordinary structure like microporous [9] and layered [10], [11] can be incorporated as composite components. Bandosz group are well experienced in synthesis of MOF-5/GO and HKUST-1/GO composites as well as their application for either acidic (NO 2 [12], H 2 S [13]) or basic (NH 3 [14], [15]) gases adsorption.…”