Antimony enrichment in aquatic environments is of great concern to international community. High-temperature geothermal waters usually contain excessive Sb, which are apt to contaminate the groundwaters or surface waters used as drinking waters in and around a hydrothermal area. However, Sb removal from geothermal water is rarely documented and the effect of high temperature on Sb removal has not received much attention. In this study, batch sorption experiments were conducted to investigate Sb removal from water by a hydroxyl-intercalated, mechanochemically synthesized Mg-Fe-LDH (i.e. Mg-Fe-OH-LDH) capable of avoiding secondary pollutions commonly related to other Mg-Fe-LDH intercalated by undesirable anions, such as Cl − and NO 3 − . The sorption capacities of Mg-Fe-OH-LDH for Sb(III) and Sb(V) were up to 48.7 and 30.0 mg/g, respectively. Notably, Mg-Fe-OH-LDH performed even better in removing aqueous Sb(V) at higher temperatures, superior to sorption of Sb by iron oxides that is generally exothermic and tends to be inhibited by increasing reaction temperature. The removal of Sb(V) existing as Sb(OH) 6 − by Mg-Fe-OH-LDH was attributable to its exchange with interlayer hydroxyl, and therefore could be impaired to some degree by coexisting anions with stronger electronegativity or smaller ionic radii . In contrast, anion exchange didn't contribute so much to Sb(III) sorption, because the main Sb(III) species at pH < 10 is neutral Sb(OH) 3 . XPS analyses confirmed that inner-sphere complexation between sorbed Sb(III) and Fe on Mg-Fe-OH-LDH layers was formed, which was hardly affected by competitive anions. Mg-Fe-OH-LDH is promising to be practically applied in removing both Sb(III) and Sb(V) from contaminated natural waters, wastewaters, or geothermal waters potentially acting as a pollution source .
In this study, the Mg-Fe-LDH@biochar composite was firstly fabricated and applied for effectively activation peroxymonosulfate (PMS) for aqueous doxycycline (DOX) degradation. The physiochemical properties of the as-synthesized composite were thoroughly characterized. In the developed Mg-Fe-LDH@biochar/PMS system, the catalytic DOX degradations were evaluated under different conditions. Under the optimal condition (0.75 g/L catalyst loading, 0.75 g/L PMS dosage, pH = 7.0), about 88.76% DOX (35 mg/L) was removed within 120 mins. The results of quenching test and electron paramagnetic resonance (EPR) illustrated that the •OH, SO 4 • - and •O 2 – radicals all contributed to the DOX degradation in the Mg-Fe-LDH@biochar/PMS system, whereas the 1 O 2 -based non-radical degradation played the dominant role in DOX removal. The developed system was almost not adversely affected by the high-strength anions and exhibited high DOX decomposition rates in a wide pH range from 3.0 to 9.0, indicating the great potential in the practical application. The satisfactory reusability of the composite catalyst was demonstrated in the recycling test, with the DOX removal efficiency slightly declined from 90.08 to 84.42% after five runs. Based on the generation of reactive oxidative species and the transformation intermediates identified by HPLC-MS, the possible degradation pathways and reaction mechanism of DOX degradation in Mg-Fe-LDH@biochar/PMS system were proposed.
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