Synthesis, Self-Assembly, Transformation, and Functionalization of Nanoscale Artificial Allophane Spherules for Catalytic Applications

Abstract

Mesoporous materials with large surface area and chemical inertness are of great importance, and currently prevailing synthetic approaches involve usages of micelles as pore-directing agents to create such mesopores. In this work, allophanes, which are hollow aluminosilicate spherules of 3.5–5.5 nm in size, have been synthesized and assembled simultaneously for the first time in a controlled manner to generate mesoporous spherical allophane assemblages (MSAAs) with diameters of 445 ± 40 nm, specific surface area as high as 1032 m2/g, pore volume 1.104 mL/g at P/P 0 = 0.975, and average mesopore size at 3.4 nm. Furthermore, the thus-prepared MSAA could be doped with transition metal ions to create a series of isomorphous derivatives; they could also be converted to aluminum-based hierarchical assemblages of layered double hydroxide easily. Different from the conventional channel-like mesopores, the new mesoporosity attained in MSAA is easily accessible because their mesopores are generated from the interparticle spaces of spherical building units of hollow spherules. Therefore, the mesoporous MSAA provides an excellent platform for construction of integrated nanocatalysts. Highly dispersed noble metal nanoclusters such as Pt, Au, and Pd could be deposited on the surface or in the interior mesopores of the MSAA. Excellent activity and stability of MSAA-based catalysts for Suzuki couplings and electrochemical sensing of H2O2 have been demonstrated using Pd/MSAA and Au/MSAA nanocomposites, respectively.

Overall structure of Au12Ag60(S-c-C6H11)31Br9(Dppp)6: achieving a stronger assembly of icosahedral M13units

“…The signal at m / z 5050.03 Da belongs to [Au 12 Ag 60 (S- c -C 6 H 11 ) 31 Br 8 (Dppp) 5 (CH 3 CN)] 3+ , which is generated by the loss of one Br atom and one Dppp ligand from the parent species, [Au 12 Ag 60 (S-c-C 6 H11) 31 Br 9 (Dppp) 6 ] 2+ . 51 The isotope pattern is consistent with the calculated one ( m / z = 5049.94 Da, the inset of Fig. 4B).…”

Architectural Designs and Synthetic Strategies of Advanced Nanocatalysts

“…The resultant TCSA/Pd exhibited excellent activity and recyclability for Suzuki–Miyaura coupling reactions. In another study, mesoporous spherical allophane assemblages (MSAA), with an overall diameter of 445 ± 40 nm, are comprised of numerous hollow aluminosilicate spherules in the size range of 3.5–5.5 nm . Afterward, the MSAA can serve as a high‐surface‐area support for introducing Pt, Au, and Pd NPs on their external surfaces or in their interior mesopores.…”

Hierarchy Concepts in Design and Synthesis of Nanocatalysts

“…Displayed in Figure 3, for example, a stepwise solution synthesis of Matryoshka type of MOFs is displayed, where the box‐within‐a‐box architecture is realized from alternate heteroepitaxial growth of two important MOF materials, ZIF‐8 (Zn 2+ +imidazolate) and ZIF‐67 (Co 2+ +imidazolate), which are topologically isomorphic [28] . On the other hand, low density bubbles‐within‐a‐bubble or bubbles‐within‐a‐sphere hierarchical assemblages of metal silicates can be obtained through one‐pot chemical transformative synthesis [29,30] …”

“…are effective methods to obtain a conceivable end product. The latter ( bottom‐up ) approach is even more powerful and versatile, in which the overall solid product can be constructed from smaller building units and multiple synthetic or assembling processes can be applied in order to deliver a targeted catalyst system [28,29,30,8] . Such processes include self‐templating, [38,42,48] soft‐templating, [49,50] oriented attachment, [51] layer‐by‐layer assembly/coating, [52,28,53] homoepitaxy and heteroepitaxy, [28,54] confined transformation, [55,56,57] and even conventional low‐cost metal impregnation, [58] including anchorage of organometallics etc.…”