Adsorption characteristics and mechanism of norfloxacin in water by γ-Fe2O3@BC

Abstract

Using waste pomelo peel as raw material, pomelo peel-based biochar (BC) was prepared by pyrolysis at 400 °C, and the pomelo peel-based biochar was prepared by loading γ-Fe2O3 onto the surface of the pomelo peel-based biochar by unlimited oxygen chemical precipitation. The results showed that the pomelo peel biochar loaded with γ-Fe2O3 had higher specific surface area and larger pore volume. The load of γ-Fe2O3 gives γ-Fe2O3@BC excellent magnetic separation ability, and its magnetic saturation intensity is as high as 30.60 emu/g. BC and γ-Fe2O3@BC were applied to remove norfloxacin (NOR) from a water body. It was found that the adsorption of NOR by both of them followed the pseudo-second-order kinetic model. The adsorption isotherm mainly conforms to the Sips model, and the adsorption process of NOR is a spontaneous endothermic reaction. The pH and ionic strength have a great influence on the adsorption of NOR by BC and γ-Fe2O3@BC, and they play a role mainly by influencing the morphology of NOR in water. The adsorption mechanism showed that cation exchange and hydrogen bonding were the main forces for BC to adsorb NOR. Moreover, the γ-Fe2O3 particles enhanced the hydrophobicity of the pomelo peel-based biochar, making the hydrophobicity become the main force for the adsorption of NOR by the γ-Fe2O3@BC. The adsorption–desorption experiment showed that after four cycles of recycling, the adsorption capacity of γ-Fe2O3@BC for NOR was still up to 61.43% of the initial adsorption capacity, and it had a good recycling property.

A review of the adsorption method for norfloxacin reduction from aqueous media

“…Niu, Liu [102] obtained an opposite result as increase in temperature from 25 ℃ to 45 ℃, improved the adsorption capacity from 746 mg/g to 798 mg/g. Similar observations have also been obtained by several studies [ 103 , 104 ]. This disparity in Q max value with respect to the change in temperature is hinged on the reaction temperature type.…”

“…When the pKa is less than 6.22, NRFX exists as NRFX + (cationic form). It exists as NRFX ± (zwitterionic form) when the pKa is between 6.22 and 8.51, and as NRFX − (anionic form) when the pKa is greater than 8.51 [104] .…”

“…This could be attributed to the fact that biochar and activated carbon are characterized by irregular lamellar structure, which enhances its heterogeneous surface to promote multilayer adsorption of NRFX [3,114,141]. Aside Langmuir and Freundlich isotherm, a few other equilibrium models which effectively described NRFX adsorption include Redlich-Peterson [ 16 , 80 , 108 , 183 ], Sips [ 5 , 14 , 104 ], Dubinin-Astakhov [ 91 , 111 ], Koble-Corrigan [ 102 , 120 ], Polanyi-Manes [157] , and Temkin [134] .…”

“…In most of the studies, it can be seen that the presence of these other species led to a reduction in the absorption of NRFX. But some of them increased the removal impact [ 9 , 104 , 159 ], while others had no effect [ 139 , 165 ]. In the adsorption of NRFX using pomelo peel-based biochar and γ-Fe 2 O 3 -loaded biochar (γ-Fe 2 O 3 /BC) [104] , it was discovered that the presence of Na + reduced the adsorption of NRFX by the biochar adsorbent, and the reduction was stronger as the concentration of the Na + increases (from 0.02 to 0.10 mol/L).…”

“…But some of them increased the removal impact [ 9 , 104 , 159 ], while others had no effect [ 139 , 165 ]. In the adsorption of NRFX using pomelo peel-based biochar and γ-Fe 2 O 3 -loaded biochar (γ-Fe 2 O 3 /BC) [104] , it was discovered that the presence of Na + reduced the adsorption of NRFX by the biochar adsorbent, and the reduction was stronger as the concentration of the Na + increases (from 0.02 to 0.10 mol/L). This is due to the fact that Na + may engage in cation exchange and rival NRFX for active binding sites on the biochar surface.…”