Ultrasonic Pretreated Sludge Derived Stable Magnetic Active Carbon for Cr(VI) Removal from Wastewater

A stable magnetic carbon was synthesized using activated sludge as the carbon precursor. The ultrasonic pretreatment was used to destroy the cells in the activated sludge and to release the soluble carbon source, which was responsible for the improved stability of the synthesized magnetic carbon. 800 W was demonstrated as the optimized ultrasonication power for the pretreatment of activated sludge. Then, the carbonization parameters, such as pyrolysis temperature, heating rate, and dwell time were optimized as 800 °C, 10 °C/min, and 60 min, respectively. To be more specific, this activated sludge derived magnetic carbon can reduce almost all the hexavalent chromium (Cr­(VI)) (2.0 mg/L) in 10 min and has a maximum capacity as high as 203 mg/g. The iron release rate of the synthesized activated sludge derived magnetic carbon was decreased, which improved the electron utilization of zerovalent iron (ZVI). This composite was demonstrated to have a good stability and recyclability as well. Finally, the Cr­(VI) removal mechanisms were clarified under the acidic and the natural conditions

Significantly Accelerated Hydroxyl Radical Generation by Fe(III)–Oxalate Photochemistry in Aerosol Droplets

Fe(III)–oxalate complexes are ubiquitous in atmospheric environments, which can release reactive oxygen species (ROS) such as H2O2, O•2–, and OH• under light irradiation. Although Fe(III)–oxalate photochemistry has been investigated extensively, the understanding of its involvement in authentic atmospheric environments such as aerosol droplets is far from enough, since the current available knowledge has mainly been obtained in bulk-phase studies. Here, we find that the production of OH• by Fe(III)–oxalate in aerosol microdroplets is about 10-fold greater than that of its bulk-phase counterpart. In addition, in the presence of Fe(III)–oxalate complexes, the rate of photo-oxidation from SO2 to sulfate in microdroplets was about 19-fold faster than that in the bulk phase. The availability of efficient reactants and mass transfer due to droplet effects made dominant contributions to the accelerated OH• and SO42– formation. This work highlights the necessary consideration of droplet effects in atmospheric laboratory studies and model simulations