Abstract:In this report, we describe new conditions for the formation of copper gels and aerogels via epoxide addition to CuBr 2 in dimethylformamide (DMF). These CuBr 2 -derived sols undergo a rapid gel transition and result in materials that have enhanced mechanical properties when compared with the gels derived from CuCl 2 . Additionally, upon air-annealing, they convert to nanoscopic CuO at temperatures much lower than the CuCl 2 analogues. Moreover, annealing under nitrogen results in copper species with reduced o… Show more
“…2). Thus, the solution pH is increased by the irreversible ring‐opening reaction, and the sol–gel transition is triggered. However, there are only a few reports on homogeneous gelation associated with divalent metal salts by this method 45‐47 . The most crucial reason is that the hydrolysis and polycondensation of divalent metal cations proceed rapidly resulting in undesired precipitation.…”
Section: Resultsmentioning
confidence: 99%
“…However, there are only a few reports on homogeneous gelation associated with divalent metal salts by this method. [45][46][47] The most crucial reason is that the hydrolysis and polycondensation of divalent metal cations proceed rapidly resulting in undesired precipitation. Recently, we have developed a modified epoxide-mediated method to afford the homogeneous gelation of divalent metal cations.…”
Cobalt manganite‐based hierarchically porous monoliths (HPMs) with three‐dimensionally (3D) interconnected macropores and open nanopores have been prepared via the sol–gel process accompanied by phase separation. The controlled hydrolysis and polycondensation of the brominated metal alkoxides, which are generated from an incomplete reaction between epichlorohydrin and MBr2 (M = Co and Mn) in N,N‐dimethylformamide (DMF), form a monolithic gel based on the two divalent metal cations. The dual‐polymer strategy using polyvinylpyrrolidone (PVP) and poly(ethylene oxide) (PEO) effectively induces the spinodal decomposition, where PVP and PEO are preferentially distributed to the gel phase and fluid phase, respectively, resulting in a porous gel characterized by the co‐continuous structure. The effects of DMF and PVP on the porous morphology derived from the phase separation have been systematically studied. Calcination of the as‐dried gels allows for the crystallization into the spinel phase yielding hierarchically porous CoMn2O4 monoliths, which have been examined in detail by the structural and compositional analyses.
“…2). Thus, the solution pH is increased by the irreversible ring‐opening reaction, and the sol–gel transition is triggered. However, there are only a few reports on homogeneous gelation associated with divalent metal salts by this method 45‐47 . The most crucial reason is that the hydrolysis and polycondensation of divalent metal cations proceed rapidly resulting in undesired precipitation.…”
Section: Resultsmentioning
confidence: 99%
“…However, there are only a few reports on homogeneous gelation associated with divalent metal salts by this method. [45][46][47] The most crucial reason is that the hydrolysis and polycondensation of divalent metal cations proceed rapidly resulting in undesired precipitation. Recently, we have developed a modified epoxide-mediated method to afford the homogeneous gelation of divalent metal cations.…”
Cobalt manganite‐based hierarchically porous monoliths (HPMs) with three‐dimensionally (3D) interconnected macropores and open nanopores have been prepared via the sol–gel process accompanied by phase separation. The controlled hydrolysis and polycondensation of the brominated metal alkoxides, which are generated from an incomplete reaction between epichlorohydrin and MBr2 (M = Co and Mn) in N,N‐dimethylformamide (DMF), form a monolithic gel based on the two divalent metal cations. The dual‐polymer strategy using polyvinylpyrrolidone (PVP) and poly(ethylene oxide) (PEO) effectively induces the spinodal decomposition, where PVP and PEO are preferentially distributed to the gel phase and fluid phase, respectively, resulting in a porous gel characterized by the co‐continuous structure. The effects of DMF and PVP on the porous morphology derived from the phase separation have been systematically studied. Calcination of the as‐dried gels allows for the crystallization into the spinel phase yielding hierarchically porous CoMn2O4 monoliths, which have been examined in detail by the structural and compositional analyses.
“…Moreover, Gash et al found that it was hard to prepare the metal oxide aerogels from M 2+ ions (M 2+ Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ) even by the epoxide-mediated sol-gel method, in which only precipitation was obtained (Gash et al, 2001b). Some divalent metal oxide aerogels have been prepared by the epoxide-mediated sol-gel method afterwards (Gash et al, 2004;Gao et al, 2007;Sick and Hope-Weeks, 2008;Wei et al, 2009;Baghi et al, 2013), but the preparation of HPMs still remained a challenge.…”
Section: Principle Of Sol-gel Process Accompanied By Phase Separationmentioning
The sol–gel process accompanied by phase separation is one of the methods to prepare hierarchically porous monoliths, hierarchically porous monolith, which is applicable not only to oxides but also to various materials compositions such as metal phosphates, organic-polymers/carbons, metal-organic frameworks. It is not until recently, however, that progress has been made in the preparation of low-valence metal oxide HPMs, such as those of magnesium, manganese, cobalt, nickel, etc. Due to the difficulty of divalent metal precursors to form homogeneous gels, different approaches from those established for trivalent and tetravalent counterparts have been attempted. This short review introduces the methods and trials in the preparation of metal oxide HPMs from divalent metal salts.
“…In the section on ‘gel formation’, we introduce a way to overcome the difficulty of homogeneous gelation for low-valence metal cations. The starting materials here refer back to the work reported by Hope-Weeks’ group, but the process and mechanism in our work are different [ 31 ]. In the section on ‘phase separation’, the effect of starting compositions on 3D interconnected macroporous structure of HP monoliths is discussed.…”
Hierarchically porous monoliths based on copper (Cu), cobalt (Co), and manganese (Mn) oxides with three-dimensionally (3D) interconnected macropores and open nanopores have been prepared using metal bromides as precursors via sol–gel process accompanied by phase separation. The difficulty of gelation for low-valence metal cation was overcome by introducing a highly electronegative Br atom nearby the metal atom to control the rates of hydrolysis and polycondensation. The 3D interconnected macropores were obtained using appropriate polymers to induce the phase separation. The domain sizes of macropores and skeletons can be controlled by reaction parameters such as concentration and/or average molecular weight of polymers, and the amount of hydrochloric acid. The crystalline metal oxide monoliths with their 3D interconnected macroporous structure preserved were obtained after the heat treatment in air.
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