US-12617808-B1 - Silica hollow sphere with a MOF composite layer and method for preparing the same

US12617808B1US 12617808 B1US12617808 B1US 12617808B1US-12617808-B1

Abstract

The present invention relates to the technical field of surface modification of silica, and more particularly to silica hollow sphere with a MOF composite layer and method for preparing the same. The silica hollow sphere comprises: a hollow spherical structure made of silica, an amino-silane layer covalently grafted onto the surface of the core layer, a ZIF-8 crystal layer grown in situ with amino groups serving as nucleation sites, and thiol groups distributed on the outer surface of the MOF crystals. The purpose of the present invention is to provide silica hollow sphere with a MOF composite layer and method for preparing the same. The silica hollow sphere with the composite layer exhibits good compatibility and stability in an LCP matrix, while maintaining low dielectric loss, thereby effectively improving the performance of high-frequency FPCs.

Inventors

Minyu Zeng
Xiquan Chen
Feng Qin

Assignees

DONGGUAN LONGZEE ELECTRONIC TECHNOLOGY CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20251016
Priority Date: 20250526

Claims (3)

1 . A method for preparing a silica hollow sphere with a MOF composite layer, comprising the steps of: S 100 : pretreating a silica hollow spheres to activate surface hydroxyl groups and obtain a hollow spherical structure made of silica, having an average particle size of 200-800 nm, a wall thickness of 20-50 nm, and a specific surface area of ≥350 m2/g; S 200 : aminofunctionalizing the activated silica hollow spheres using a 3-8 wt % y-aminopropyltriethoxysilane solution at pH 4-6, 60-80° C. for 4-8 hours to obtain an amino-silane layer with an amino group density of 2.5-3.2 groups per nm 2 and a layer thickness of 1-3 nm; S 300 : growing a ZIF-8 crystal layer in situ, with the amino groups serving as nucleation sites, in a methanol solution containing 0.05-0.2 M zinc nitrate and 0.3-0.6 M 2-methylimidazole at 30-40° C. for 8-24 hours to obtain a ZIF-8 crystal layer having a thickness of 50-150 nm, a crystal size of 20-50 nm, and a pore size of 3.3-3.5{acute over (Å)}; S 400 : reacting the product obtained in step S 300 with a 0.3-0.8 M thioacetamide solution at 50-70° C. for 2-6 hours to perform surface thiolation modification, producing a thiol-modified product with a sulfur content of 0.5-2 wt %.
2 . A silica hollow sphere with a MOF composite layer prepared by the method of claim 1 , wherein the following structural relationship is satisfied: N SH N NH 2 = a , 0.3 ≤ a ≤ 0.6 Where: N SH represents the thiol group density, N NH2 represents the amino group density.
3 . The silica hollow sphere with a MOF composite layer according to claim 2 , wherein a cavity volume of the core layer accounts for ≥40% of the total volume of the core layer, and the hydroxyl group density of surface hydroxyl groups in the silica hollow spheres after pretreatment activation is 4.8-5.2 groups per nm 2 ; the silane molecules of the amino-silane layer are oriented upright, with a molecular tilt angle of ≤15° as measured by ellipsometry; the thiol groups are located at the edge positions of the MOF crystals.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The application claims priority to Chinese patent application No. 202510678943.8, filed on May 26, 2025, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present invention relates to the technical field of surface modification of silica, and more particularly to silica hollow sphere with an MOF composite layer and method for preparing the same. BACKGROUND Currently, liquid crystal polymer (LCP) composites in high-frequency flexible printed circuits (FPCs) face several critical issues, including poor dielectric properties before and after humid-heat aging, low adhesion strength with copper foil, high coating technique requirements, and insufficient technical data for substrate-integrated waveguide (SIW) design. Silica hollow spheres have attracted increasing attention in recent years due to their excellent physicochemical properties and broad application prospects. They have demonstrated good performance in fields such as catalysis, drug delivery, and adsorption materials. Research has shown that they can be applied in high-frequency FPC structures to enhance performance. However, prior silica hollow spheres still exhibit certain limitations in practical applications, mainly due to the singularity and insufficient functionalization of their surface properties. Conventional silica hollow spheres typically possess only hydroxyl groups on their surfaces, lacking other functional groups. This results in single-functionality, poor interfacial stability, and insufficient molecular selectivity in the LCP matrix, thereby adversely affecting the performance of high-frequency FPCs. SUMMARY To overcome the drawbacks and deficiencies of the prior arts, the purpose of the present invention is to provide silica hollow sphere with a MOF composite layer and method for preparing the same. The silica hollow sphere with the composite layer exhibits good compatibility and stability in an LCP matrix, while maintaining low dielectric loss, thereby effectively improving the performance of high-frequency FPCs. The present invention is achieved by the following technical solutions: In a first aspect, the present invention discloses silica hollow sphere with a MOF composite layer, comprising: Core layer: a hollow spherical structure made of silica, having an average particle size of 200-800 nm, a wall thickness of 20-50 nm, and a specific surface area of ≥350 m2/g;Bridging layer: an amino-silane layer covalently grafted onto the surface of the core layer, with an amino group density of 2.5-3.2 groups per nm2, a layer thickness of 1-3 nm;MOF crystal layer: a ZIF-8 crystal layer grown in situ with the amino groups serving as nucleation sites, having a thickness of 50-150 nm, a crystal size of 20-50 nm, and a pore size of 3.3-3.5 Å;Functionalized surface layer: thiol groups distributed on the outer surface of the MOF crystals, wherein the sulfur content is 0.5-2 wt %, and the following structural relationship is satisfied: NSHNNH2=a,0.3≤a≤0.6where: NSH represents the thiol group density, NNH2 represents the amino group density. In combination with the first aspect, furthermore, the cavity volume of the core layer accounts for ≥40%, and the hydroxyl group density is 4.8-5.2 groups per nm2; the silane molecules of the amino-silane layer are oriented upright, with a molecular tilt angle of ≤15° as measured by ellipsometry;the thiol groups are located at the edge positions of the MOF crystals. In a second aspect, the present invention discloses method for preparing the silica hollow sphere, comprising the steps of: S100: pretreating the silica hollow spheres to activate surface hydroxyl groups;S200: aminofunctionalizing the activated silica hollow spheres using a γ-aminopropyltriethoxysilane solution to obtain aminofunctionalized silica;S300: growing a ZIF-8 crystal layer in situ, with the amino groups serving as nucleation sites, in a methanol solution containing zinc salt and 2-methylimidazole;S400: reacting the product obtained in step S300 with a thioacetamide solution to perform surface thiolation modification. In combination with the second aspect, furthermore, in step S200, the concentration of the γ-aminopropyltriethoxysilane solution is 3-8 wt %, the reaction pH value is 4-6, the reaction temperature is 60-80° C., and the reaction time is 4-8 hours. In combination with the second aspect, furthermore, in step S300, the zinc salt is zinc nitrate, the zinc ion concentration is 0.05-0.2 M, the concentration of 2-methylimidazole is 0.3-0.6 M, the reaction temperature is 30-40° C., and the reaction time is 8-24 hours. In combination with the second aspect, furthermore, in step S400, the concentration of the thioacetamide solution is 0.3-0.8 M, the reaction temperature is 50-70° C., the reaction time is 2-6 hours, and the obtained product has a sulfur content of 0.5-2 wt %. In a third aspect, the present invention discloses method for predicting the dielectric l