Coordination-Enhanced Synthesis for Hollow Mesoporous Silica Nanoreactors

Abstract

Recent progress has put the spotlight on functional nanoparticles encapsulated inside hollow silica nanospheres as so-called catalytic nanoreactors for various reactions. However, the synthetic methods used so far vary from one nanoparticle system to another, not providing access to the synthesis of a large variety of such materials. Here, we report an alternative, namely, a coordination-enhanced synthesis leading to a single system, which can directly produce a vast number of different hollow mesoporous silica nanoreactors with metal or metal-oxide nanoparticles inside their cavities (M@HMSNs or MxOy@HMSNs, where M stands for the chosen metal). We have successfully used the method with more than 21 different metals (Ru, Pd, Pt, Au, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, In, Sn, Ba, La, Ce, and Eu). Specifically, a triple ligand is used to coordinate the various metal ions to form a negatively charged complex three-dimensional (3-D) network, which further combines by electrostatic attraction with a positively charged/neutral diblock copolymer, to obtain metal-ion-bound micelles. After silica deposition, calcination, and (if required) reduction, the corresponding M@HMSNs, MxOy@HMSNs or even their bianalogues are obtained by simply varying the metal ions in the recipe. As an illustration, we show that Pd@HMSNs display greatly enhanced catalytic hydrodechlorination activity and excellent stability due to their unique structures. Hence, the design concept is very flexible and can be extended to even include multicomponent catalytic nanoparticles, which likely extends the range of applications almost beyond imagination.