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Electrochemically activating peroxydisulfate (PDS) can eliminate organic pollution using electron as activator without the involvement of byproducts. Notwithstanding, the process suffered from long hydraulic retention time, and the activation regime remained unclear. Herein, using Pd/Al2O3 catalyst as particle electrode for initiating PDS oxidation in the cathodic cell can degrade various organic pollutants with varying the kinetic constants from 0.0256 min−1 to 0.0645 min−1, which were at least 5-fold higher than that in previous studies. The reactive oxygen species were determined to be SO4•–/•OH. These radicals were readily formed from the single-electron reduction of PDS by electro-induced atomic hydrogen (indirect reduction mechanism), while direct two-electron transfer from electro-generated H2 to PDS consumed its oxidation capacity without yielding radical due to the higher energy barrier. Revealing the mechanism of electrochemically unleashing the oxidative power of PDS into SO4•– can rationalize the design of scalable electrode for PDS-based water purification.

The high cost associated with the disposal of iron sludge in Fe2+ activated oxidation systems significantly limits their widespread use. In this study, we constructed a trace iron-based peroxydisulfate (PDS) oxidation system (Pd-EFP) using Pd/Al2O3 as the particle electrode and externally added PDS as an oxidant. At an initial solution pH of 3.0 and a current density of 3.33 mA/cm2, with the addition of 10 mM PDS, 50 mg Pd/Al2O3, and 2 mg/L Fe ions, 80.12% of 180 µM benzoic acid (BA) was degraded within 120 min. The Pd/Al2O3 catalyst provided sufficiently large surface area for atomic H* production from the adsorption of electrogenerated H2 or H+ conversion via electro-induction on the Pd/Al2O3 surface, which subsequently accelerated the transformation from Fe3+ to Fe2+. Using this method, organics could be degraded by both SO4·- and ·OH via the Fe2+-activated PDS process. In the Pd-EFP process, the optimal dosage of Fe ions was determined to be 36 μM (2 mg/L). Correspondently, the optimal current density and PDS concentration in the Pd-EFP system were 3.33 mA/cm2 and 20 mM, respectively. Furthermore, degradation of BA was efficiently promoted by the N2 atmosphere, which could steer the reaction on the surface of Pd/Al2O3 in the right direction toward Fe3+ reduction by atomic H*, by dispelling accumulated H2 above the reaction liquid and suppressing oxygen reduction. Finally, the Pd/Al2O3 catalyst was found to be durable in the Pd-EFP system according to reusability experiments and X-ray diffraction patterns of the fresh and used Pd/Al2O3 catalyst. This research provides an environmentally benign system for recycling Fe3+ in Fe2+/PDS processes and for suppressing iron sludge production. Post-print / Final draft

Organo Arizona SAz-2 Ca-montmorillonite was prepared with different surfactant (DDTMA and HDTMA) loadings through direct ion exchange. The structural properties of the prepared organoclays were characterized by XRD and BET instruments. Batch experiments were carried out on the adsorption of bisphenol A (BPA) under different experimental conditions of pH and temperature to determine the optimum adsorption conditions. The hydrophobic phase and positively charged surface created by the loaded surfactant molecules are responsible for the adsorption of BPA. The adsorption of BPA onto organoclays is well described by pseudo-second order kinetic model and the Langmuir isotherm. The maximum adsorption capacity of the organoclays for BPA obtained from a Langmuir isotherm was 151.52 mg/g at 297 K. This value is among the highest values for BPA adsorption compared with other adsorbents. In addition, the adsorption process was spontaneous and exothermic based on the adsorption thermodynamics study. The organoclays intercalated with longer chain surfactant molecules possessed a greater adsorption capacity for BPA even under alkaline conditions. This process provides a pathway for the removal of BPA from contaminated waters.