Hierarchically porous monoliths based on low-valence transition metal (Cu, Co, Mn) oxides: gelation and phase separation

Abstract

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.

Identifying and Engineering Active Sites at the Surface of Porous Single-Crystalline Oxide Monoliths to Enhance Catalytic Activity and Stability

“…High specific areas are advantageous to the promotion of Pt loading weight and the atomic dispersion of Pt under higher loading weight. 32 In future we will focus on other parent single crystals with proper lattice parameters to grow porous single crystals with higher specific surface areas using the lattice reconstruction strategy. We further calculate the defect formation .…”

Macroporosity Control by Phase Separation in Sol-Gel Derived Monoliths and Microspheres

“…The role of the metal–salt counter ion was found to be very important. Lu et al [ 92 ] addressed this issue and were able to obtain homogeneous gelation for three kinds of low-valence metal–salts. They studied factors such as the concentration of the polymer (Cu-system), the Mw (Co-system), and the amount of HCl (Mn-system), regarding the 3D interconnected macroporosity of the resulting monoliths.…”

Preparation of hierarchically porous spinel CoMn2O4 monoliths via sol–gel process accompanied by phase separation

“…Recently, we have developed a modified epoxide-mediated method to afford the homogeneous gelation of divalent metal cations. 8 The metal bromides are mixed with ECH in a polar aprotic solvent, DMF, to produce brominated metal alkoxides, via an incomplete ring-opening reaction between metal bromides and ECH (Eq. 3).…”

“…To the best of our knowledge, the HPM of CoMn 2 O 4 has not been prepared yet. Recently, we have reported a new route to prepare metal oxide monolithic gels from divalent metal salts, that is, MnBr 2 , CoBr 2 , and CuBr 2 , and corresponding metal oxide HPMs by the dual‐polymer strategy 8 . For the sake of verifying whether this strategy can also be extended to the synthesis of complex metal oxides and investigating the details of the roles of each polymer, we have prepared the macroporous gels starting from cobalt(II) and manganese(II) salt solutions, which can be converted to the HPMs based on the spinel CoMn 2 O 4 .…”

“…The sol-gel process accompanied by phase separation has proven its feasibility and versatility in the preparation of hierarchically porous monoliths (denoted as "HPMs" hereafter) with three-dimensionally (3D) interconnected macropores and open nano-sized pores (referred to nanopores), based on various kinds of materials such as silica/organic-hybrid silica, [1][2][3] metal oxides, [4][5][6][7][8] metal phosphates, [9][10][11][12][13][14] and metalorganic framework. 15 The 3D interconnected macropores ranged from hundreds of nanometers to tens of micrometers are obtained by inducing phase separation in the course of gelation, and solidifying the temporal phase-separating structure as illustrated in Scheme 1.…”