RESUMO
Effects of ball milling (BM) on the structure and physicochemical properties of three types of citrus fibers were investigated. With the extension of the grinding time, the particle size of citrus fibers significantly decreased. Fourier transform infrared spectroscopy (FTIR) showed that the three citrus fibers had similar chemical groups, and more -OH and phenolic acid groups were exposed after BM, and pectin and lignin were not degraded. Scanning electron microscope (SEM) results showed that the appearance of particles changed from spherical to fragmented, irregular shapes. The water holding capacity (WHC), oil holding capacity (OHC), and water swelling capacity (WSC) of citrus fibers LM, JK, and FS reached the maximum value after BM of 2 h (increasing by 18.5%), 4 h (increasing by 46.1%), and 10 h (increasing by 38.3%), respectively. After 10 h BM, citrus fibers FS and JK had the highest adsorption capacity of cholesterol and sodium cholate, increasing by 48.3% and 48.6%, respectively. This indicates that BM transforms the spatial structure of citrus fibers and improves their physicochemical properties.
RESUMO
Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg0) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Sex/Activated carbon (Sex/AC) was synthesized and applied to remove Hg0 in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Sex/AC reached 17.98 mg/g Hg0 adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg0 removal above 85% at the NO and SO2 conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Sex/AC. Chemical adsorption plays a dominant role in Hg0 removal: Selenium anchored on the surface of AC would capture Hg0 in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg0 released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg0 to HgO. This work provided a novel and highly efficient carbon-based sorbent -Sex/AC to capture the mercury in coal combustion flue gas. Graphical abstract Selenium-modified porous activated carbon and the interface functional group promotes the synergistic effect of physical adsorption and chemical adsorption to promote the adsorption capacity of Hg0.