Search

Magnetic core–shell Fe3O4@SiO2 nanoparticles were synthesized by sol–gel method. Based on the characterization and experimental results, the adsorbent was found to have an average particle size of approximately 120 nm, a pore size range of 2–5 nm and superparamagnetic properties. It exhibited electrostatic and hydrogen bonding interactions during adsorption of methyl orange (MO). The adsorption of MO on the magnetic Fe3O4@SiO2 nanoparticles exhibited pseudo-second-order kinetics, the adsorption process is a spontaneous endothermic adsorption process, which conforms to the Langmuir adsorption isotherm model. he maximum amount of MO was adsorbed at pH = 2, T = 45 °C and t = 30 min, and the highest adsorption capacity was 182.503 mg/g; The unit adsorption capacity of the Fe3O4@SiO2 nanoparticles still reached 83% of the original capacity after 5 cycles, so the material was reusable and met the requirements of environmental protection. This study reveals the great potential of magnetic mesoporous nanoparticles for removal of dyes from wastewater. [ABSTRACT FROM AUTHOR]

• Building a complete gas-gap heat switch model that covers the entire switching process. • Integrating activated carbon's adsorption characteristics into the theoretical model. • Designing the 4He gas-gap heat switch based on the model and testing its performance to validate the model. • Applying the gas-gap heat switch to a 4He sub-Kelvin sorption cooler and achieving a temperature of 773 mK. Gas-gap heat switches (GGHSs) are significant components in sub-Kelvin sorption coolers (SKSCs). To develop an effective GGHS for SKSCs, a complete GGHS theoretical model is proposed by integrating the adsorption characteristics of activated carbon and the principle of GGHSs. This model establishes a relationship between the temperature of activated carbon and the corresponding thermal conductance of GGHSs. Based on this model, a 4He GGHS was designed, which consists of two cylindrical copper blocks separated by a 0.2 mm gas gap and a surface area of 9.896 cm2. The device was charged with 100 kPa of 4He at 297 K. Near the base temperature of the GM cryocooler of 3 K, an ON thermal resistance of 20 K/W and an OFF thermal resistance of 21,650 K/W with 1 mW applied to the hot end were obtained, achieving a switching ratio of 1082.5. The experimental results were analyzed and compared with the theoretical data, and proved to be in good agreement. Finally, the GGHS was integrated with a SKSC, achieving an ultimate temperature of 773 mK. [ABSTRACT FROM AUTHOR]