Raman Observation of the “Volcano Curve” in the Formation of Carbonized Metal–Organic Frameworks

Abstract

The carbonization of various types of metal–organic frameworks (MOFs) was carried out under N2 gas flow and high temperature. The formation of carbonized MOFs (CMOFs) was monitored by Raman spectroscopy. In addition to the well-known D and G bands in Raman spectra, the salient G′ band feature was observed only in Mn-, Fe-, Co-, and Ni-containing CMOFs. On the other hand, CMOFs containing other metals (Al, Cr, V, Cu, and Zr) do not show the G′ band. Furthermore, the G′ band was also observed when we mixed the nitrate salts of Mn­(II), Fe­(III), and Co­(II) with Al-containing MOFs using the same treatment conditions as in the formation of CMOFs. The G′ band is known to be related to the stacking order of graphitic layers. The presence of the Raman G′ band in CMOFs can be ascribed to the catalytic activity of Mn, Fe, Co, and Ni. The trend of the G′ band to G band intensity ratio resembles the “volcano curve” in the description of the behavior of catalytic activities of transition metals. The G′ bands in Mn-, Fe-, Co-, and Ni-containing CMOFs were well-fitted with two-component peaks which indicates that these CMOFs have well-stacked graphitic structures.

Impact of hydrofluoric acid treatment on the composition, electrical conductivity, and structure of carbonized metal–organic frameworks

“…Our previous study of CMOFs has indicated that the metal content in CMOFs does not have strong binding interactions with the carbon frameworks as indicated by the trends of the G' band to G band intensity ratio I G ′ / I G , which is an index for the degree of graphitization and stacking order of the graphene layers. [ 26 ] In this work, instead of using the I G ′ / I G trend, the same conclusion is confirmed again by the small fluctuation of the I D / I G ratios before and after HF treatment (Table 2). The defect amount in carbon products does not change significantly with or without metal ions embedded in the carbon frameworks.…”

“…The carbonization of MOFs has attracted special attention, because MOFs have been demonstrated as promising sources to synthesize porous carbon materials. [ 16–24 ] Several types of MOFs have been employed as the source materials to prepare porous carbons by direct pyrolysis of MOF‐5, [ 16–18 ] various kinds of Al‐containing MOFs, [ 24–26 ] isoreticular metal‐organic framework, [ 10 ] zeolitic imidazolate frameworks (ZIFs), [ 20–23 ] and porous aromatic frameworks [ 27 ] at high temperature. The carbonized MOFs (CMOFs) show high surface area and porosity, distinctive structures and morphologies, and robust electrochemical, [ 16–24 ] gas storage, [ 19,20,28 ] and catalysis [ 20,29–31 ] performances.…”

“…Recently, we have found that in order to produce high‐quality graphitic structured carbons, only MOFs containing certain types of metal ions can deliver the result. [ 26 ]…”

Multidimension‐Controllable Synthesis of MOF‐Derived Co@N‐Doped Carbon Composite with Magnetic‐Dielectric Synergy toward Strong Microwave Absorption

“…The D band (1350 cm −1 ) indicates the local defects and the disordered carbon induced by extensive oxidation, whereas the G band (1589 cm −1 ) originates from first‐order scattering of E 2g mode observed for sp 2 carbon domains, indicating the existence of crystalline graphitic carbon. [ 12 ] Due to the nitrogen introduced CNT, the ratios between the intensity of D and G bands (I D /I G ) of Co@NCNT‐c, Co@NCNT‐d, and Co@NCNT‐o are 0.81, 0.71, and 0.70, respectively, revealing the increased degree of graphitization compared to Co@NC‐f (0.86) and Co@NC‐s (0.88) composites. It is noted that the A 2 band around 1480 cm −1 appeared in all the specimens, suggesting the presence of amorphous carbon structures.…”

Self-transforming ultrathin α-Co(OH)2 nanosheet arrays from metal-organic framework modified graphene oxide with sandwichlike structure for efficient electrocatalytic oxygen evolution

“…Raman spectra were employed to interpret the composite graphitization degree. The peaks at 1,590 cm −1 (G band) and 1,360 cm −1 (D band) are allocated to the sp 2 -bonded carbon atoms vibration and the defect-induced vibration, respectively [32,33]. Compared to Co(OH)2-GNS, the peaks of Co(OH)2 at G band and D band are non-existent, indicating the GO was introduced successfully in Co(OH)2-GNS.…”