Core Surface Modification Research Articles

Surface modification of core–shell structured ZIF-67@Cobalt coordination compound to improve the fire safety of biomass aerogel insulation materials

Biomass materials are considered to be excellent candidates to replace petroleum-based materials, but inherent flammability limits their applications. In this work, biomass aerogel (BA) was prepared by freeze-drying method from sodium alginate (SA) and polyvinyl alcohol (PVA). To improve fire safety of BAs, a core–shell structured ZIF-67@Cobalt coordination compound was successfully synthesized, which was surface functionalized by 3,5-diamino-1,2,4-triazole and 9,10-dihydro-9-oxo-10-phospho-diphenyl-10-oxide (DOPO), named as DOPO-NH2-ZIF-67. The addition of DOPO-NH2-ZIF-67 (2 wt%) outstandingly improved fire safety of BA, in contrast to neat BA, peak heat release rate, peak smoke production rate, and total smoke production were reduced by 66.6%, 85.10%, and 72.76%, respectively. Furthermore, the incorporation of ZIF-67 and its derivatives has no adverse effect on the thermal insulation performance of BA composites and significantly improved their compressive strength from 0.27 MPa to 1.76 MPa. Preparation of core–shell structured ZIFs rich in active groups furnishes a conceivable way to synthesize an effective flame retardant, and a prospective method for the fabrication of aerogel insulation materials with green and economical additive-free technology is proposed.

Microwave absorption enhancement of e-Fe3O4@C microspheres by core surface modification

Abstract Magnetic particles can be combined with carbon materials to prepare core-shell microwave absorbers and the proper core/shell weight ratio yields the optimal absorption effects. However, few studies have focused on the influence of core surface modification on the microwave absorption performance. In this work, e-Fe3O4@C composite microspheres are synthesized by surface etching of core Fe3O4 microspheres in HCl followed by polymerization/carbonization. Core surface modification improves the microwave absorption capability of the e-Fe3O4@C microsphere films. The minimal reflection loss (RLmin) is −54.38 dB at 12.4 GHz for a film thickness of 2.6 mm and the maximum effective bandwidth is extended to 4.1 GHz (3 mm). Etching of the Fe3O4 core surface increases the interfacial contact area consequently enhancing interface polarization and defects created by surface etching produce additional dipole polarization to further increase the dielectric loss. The underlying mechanism is investigated and described. The results reveal a novel and effective strategy to enhance the properties of core-shell microwave absorption materials.

Multi-step synthesis of core–shell magnetic nanoparticles bearing acid-chelating functional moieties

Two synthetic approaches have been investigated for the surface modification of core–shell-shaped silica-coated magnetic nanoparticles with acid functions. A step procedure based on covalent attachment with diethylmalonate reagent and subsequent hydrolysis of the ester functions proved to be more efficient and versatile for the incorporation of such functionality than the one-pot method. The changes in surface morphology and chemical functionality were examined by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, zeta potential analysis, and transmission electron microscopy. The acid-functionalized Fe3O4@SiO2 nanomaterial exhibited high adsorption affinity for the cationic dye methylene blue and, as such, is potentially of interest for wastewater treatment as an effective adsorbent for cationic dyes.

Drag reduction in reservoir rock surface: Hydrophobic modification by SiO2 nanofluids

Based on the adsorption behavior of modified silica nanoparticles in the sandstone core surface, the hydrophobic surface was constructed, which consists of micro-nanoscale hierarchical structure. This modified core surface presents a property of drag reduction and meets the challenge of high injection pressure and low injection rate in low or ultra-low permeability reservoir. The modification effects on the surface of silica nanoparticles and reservoir cores, mainly concerning hydrophobicity and fine structure, were determined by measurements of contact angle and scanning electron microscopy. Experimental results indicate that after successful modification, the contact angle of silica nanoparticles varies from 19.5° to 141.7°, exhibiting remarkable hydrophobic properties. These modified hydrophobic silica nanoparticles display a good adsorption behavior at the core surface to form micro-nanobinary structure. As for the wettability of these modified core surfaces, a reversal has happened from hydrophilic into hydrophobic and its contact angle increases from 59.1° to 105.9°. The core displacement experiments show that the relative permeability for water has significantly increased by an average of 40.3% via core surface modification, with the effects of reducing injection pressure and improving injection performance of water flooding. Meanwhile, the mechanisms of drag reduction and improving water injection operation induced from the modified core surface were uncovered. The present study will establish a fundamental understanding on the drag reduction at the core surface modified by nanofluids and its applications in more industries.

Surface modification of core–shell nanowire with protein adsorption

Silver and ferrite nanotubes were obtained in nanoporous alumina templates (AAO) of 200 nm diameter by wetting chemical deposition followed by thermal crystallization. Iron filling in the nanotubes was fabricated by DC electrodeposition. Step by step fabrication in AAO was followed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The core–shell nanowires were removed from the templates and verified by TEM and energy dispersive spectroscopy (EDS) techniques. Metallic (Ag) surfaces of nanowires were functionalized with alkenothiols terminated by methyl groups. Ferrite nanotubes were functionalized to –NH 2 groups on the surface. In addition, these groups were bonded to protein–trypsin in two ways: covalently bonded to amine groups by glutaraldehyde and noncovalent absorption to alkenothiols. All the modifications were observed by infra-red spectroscopy (IR).

Characterization and Synthesis of Silica-Coated Silver Nanoparticles by Sol-Gel Method with Controlling of Adding Ammonical Silver Nitrate Amount

In this study, silica-coated silver nanoparticles (SSNPs) with a core–shell structure are successfully fabricated using a simple sol-gel method without using primer, surfactant or surface modification of core. To investigate the influence of ammonical silver nitrate (AgNO3) on the synthesis of SSNPs, the amount of an aqueous solution of AgNO3 was varied in the range from 3 to 12 mL. It was found that the thickness of silver shell could be formed in the range of ∼20 to ∼60 nm, and the UV–vis optical absorption measurement revealed a pronounced red-shift of the surface plasmon resonance (SPR) band from 442 to 516 nm.

Novel Method to Fabricate SiO2/Ag Composite Spheres and Their Catalytic, Surface-Enhanced Raman Scattering Properties

This paper presents a novel method for the fabrication of SiO2/Ag composite spheres with the aid of the reducing and stabilizing function of polyvinylpyrrolidone (PVP). In this approach, [Ag(NH3)2]+ ions were first adsorbed on the surfaces of silica spheres via electrostatic attraction between the silanol groups and ions; these [Ag(NH3)2]+ ions adsorbed on silica spheres were then reduced and protected by PVP to obtain SiO2/Ag composite spheres. Neither additional reducing agent nor core surface modification was needed; the particle size and the coverage degree of silver nanoparticles on the silica spheres could be easily tuned by altering the concentration of the precursor-[Ag(NH3)2]+ ions. UV−visible spectrometer analysis showed these composite spheres had very good catalytic property; Raman spectrometer measurement showed that these composite spheres exhibited excellent surface-enhanced Raman scattering (SERS) performance.