Synthesis of Hollow Nanotubes of Zn₂SiO₄ or SiO₂: Mechanistic Understanding and Uranium Adsorption Behavior

Abstract

We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.

ZnO-SiO2 and Zn2SiO4 Synthesis Utilizing Oil Palm Leaves for Degradation of Methylene Blue Dye in Aqueous Solution

“…The product of Zn2SiO4, in the current approach, is explained by the interface reaction between Zn 2+ and O 2-with silica shell at high temperatures [11,22]. Other studies mentioned that the formation of Zn2SiO4 from ZnO and SiO2 started 700 °C and clearly identified at 800 °C [23].…”

“…In addition, use of zinc acetate and TEOS to form the sol-gel followed by thermal treatment at 800 -1000 °C was also evaluated [14]. Recently, heating ZnO-SiO2 composite (synthesized from ZnO and TEOS using the wet-chemical synthetic method) at 900 °C under open-air revealed the formation of Zn2SiO4 nanorods [15].…”

Growth and Removal Behavior of Magnesium Oxide Microspheres towards Methyl Orange and Methylene Blue in Aqueous Solution

“…7C [42][43]. Obviously, the MgO in aqueous solution absorbs a proton from water to form MgOH2 + based on pH [44][45]. This difference in the adsorption ability for each dye under the similar investigated conditions is related to the surface charge on the MgO [22].…”

Fabrication and Adsorption Behavior of Magnesium Silicate Hydrate Nanoparticles towards Methylene Blue

“…However, most special attentions has been paid to the enhancement of adsorption capacity by increasing surface area and optimizing pore size, such as mesoporous [ 6 ], hierarchical [ 7 ], nanosized [ 8 ], sandwich-like [ 9 ], nanotubes [ 10 ], and yolk-shell magnesium silicate [ 11 ]. Besides the pore structure, the surface properties also play crucial roles in enhancing the adsorption capacity [ 12 , 13 , 14 , 15 , 16 ]. For example, Ferrero [ 17 ] considered that the adsorption mechanism of magnesium silicate was concerned with both of the electrostatic attraction and the ion-exchange for methylene blue.…”