New SiO2–NiO Aerogel Sorbents for Desulfurization by π-Complexation: Influence of Molar Ratio of Si/Ni
SiO2–NiO aerogels with different molar ratios of Si/Ni (n(Si/Ni)) were prepared by a sol–gel method and atmospheric pressure drying technology. The morphology and structure of SiO2–NiO aerogels were characterized by XRD, BET, XRF, and SEM methods. The equilibrium adsorption performance of thiophene or benzothiophene on the SiO2–NiO aerogels were studied at three different adsorption temperatures (298, 313, 333 K). The adsorption equilibrium data of thiophene on SiO2–NiO aerogels were more in line with the Temkin model at the lower temperature, while they were well fitted with both Langmuir and Temkin isotherms at the higher temperature. The maximum saturation adsorption capacities obtained by the Langmuir isotherms at different temperature decreased in the order qm(298 K) > qm(313 K) ≈ qm(333 K). The maximum saturation adsorption capacities of thiophene or benzothiophene on SiO2–NiO aerogels with different n(Si/Ni) values at 298 K decreased in the order SiO2–NiO-23 > SiO2–NiO-74 > SiO2–NiO-6. The maximum saturation adsorption capacities of thiophene and benzothiophene on SiO2–NiO-23 aerogels are 6.4564 and 2.1316 mgS/g, respectively. Both the amount of adsorption active sites and the textural structure of aerogels could significantly affect the adsorption performance. The higher the nickel content, specific surface area, pore volume, and larger pore size of the aerogel, the larger the adsorption capacity. The absolute value of adsorption heat of thiophene on SiO2–NiO aerogels increased gradually with the increase of n(Si/Ni) (the reduction of the Ni content).
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