Self-catalysis synthesis of Co3O4@SiO2-Ag nanocapsules under near-neutral condition as excellent performance catalyst
Introduction
In recent decades, SiO2 nanocapsules loaded with metal/metal oxides have been widely concerned and developed rapidly [1], [2], [3]. Compared with pure solid particles, hollow nanocapsules given materials higher specific surface area and surface energy, which could better demonstrate the size superiority of nanomaterials. For the preparation of nanocapsules, current research trend is still predominantly coating method, the target of nanoparticles dispersed in the hydrophilic sol micelle, to enhance the compatibility with silica, finally the metal/metal oxide nanoparticles parcel in successive silica shell [4], [5], [6]. However, this method had some disadvantages: the preparation steps were complicated; the metal/metal oxide nanoparticles were easy aggregation, deactivation and poisoning, with short service life and low cycle performance. In contrast, nanoparticles generated in situ were obviously superior. This method referred to the introduction of precursors to prepare nanoparticles into the substrate of the composite, and then the active nanoparticles were formed in the central position of the composite by calcination or other methods. The advantages of the composite were that the active nanoparticles have high dispersibility, uniform size and high stability [6], [7], [8] (Fig. 1).
Our present work was based on hydrothermal synthesis template and silicon source autocatalytic hydrolysis condensation reaction to construct a continuous Si–O–Si network. Bromoacetate was selected as the precursor of organometallic salt, at the same time, the protonated amine group [9] was formed as the catalytic site for self-catalytic reaction, accordingly to introduce the metal oxide into Si–O–Si network in situ. Ag was introduced through the characteristic reaction with bromine ions. Finally, the organic parts in the shell and the hard template at the core were removed by high-temperature calcining, and the hollow silica nanocapsules loaded with metal/metal oxide were synthesized. And shown good performance in the catalytic degradation test of organic dyes.
Section snippets
Preparation of Co3O4@SiO2-Ag nanocapsules
0.500 g PVP was dissolved in 35 mL ethanol, then added 0.400 g C nanosphere template, 0.260 g CTAB, 0.400 mL APTES and 0.400 mL TEOS. Dissolving 0.300 g CoBA2 in 10 mL water and 35 mL ethanol, then dropped into the system. After centrifuge and drying, CoBA2@SiO2/C core shell intermediate powder. The prepared CoBA2@SiO2/C powder was soaked in AgNO3 saturated solution, the CoBA2@SiO2/C-AgBr was obtained. And then the powder was calcined at 700 °C in 1 °C/min of heating rate. Finally, Co3O4@SiO2
Results and discussion
First, the coordination of carboxylates successfully introduced Co2+ into the silicon source, and then the protonated amine group formed by APTES in the aqueous solution would attack this position, providing an autocatalytic site for the formation of the Si–O–Si network [10]. Based on the above reaction, CTAB was selected as pore-forming agent to initiate the formation of mesopores on the nanocapsule shell layer. PVP was selected as dispersant to control the particle size of CoBA2@SiO2. Based
Conclusion
A novel nanocapsule has shown excellent catalytic performance in terms of degradation of organic dyes. The loading of Ag and Co3O4 nanoparticles increased the reaction sites and significantly enhanced the catalytic performance of the materials. We expect that this approach can be used to design various silica-based nanocapsules with controllable properties, such as optical, magnetic and electrical.
Credit author statement
Yu Chen, Tieyu Cui and Fang Cui did the conceptualization, data curation and formal analysis for study. Zhenhui Li, Qinghai Ma, Jiajia Zhang and Zhiyi Chai sort out the resources and software. Qinghai Ma did the supervision and validation. Yu Chen did writing - original draft, Jiajia Zhang and Xulin Xu did writing - review & editing. All authors read and approved the final manuscript.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
We gratefully acknowledge the financial support from the National Nature Science Foundation of China (No. 51873049 and 51673055).
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