Generation of active Co(III) and peroxodiphosphate by synergistic electrocatalytic system with phosphate and the mediator cobalt(II) and its degradation performance.

The promising synergistic electrocatalytic system of phosphate (PO43-) with the mediator cobalt(II) (for short E-Co(II)-PO43-) was employed to degrade cationic dye methylene blue (MB). The exploration in the electrocatalytic process revealed that the main intermediate active oxidation products were Co(III), accompanied with hydroxyl radicals and peroxodiphosphates (P2O84-). Their synergistic electrocatalytic degradation rate to MB and total organic carbon (TOC) was up to 100 and 60% in 40 min, respectively, which was 5 times and 2.6 times that in a direct electrocatalytic system, correspondingly. The degradation process of the E-Co(II)-PO43- system on MB started with the bond being broken at the N-C junction of the MB molecule and intermediate active oxidation substances being generated, such as phenothiazine, 2-amino-5-(N-methylformamide) benzene sulfonic acid and N1,N1-dimethyl-1,4 diaminobenzene. Then, the intermediates were degraded into aniline, phenol and benzene sulfonic acid, and eventually decomposed into inorganic substances like CO2 and water. The electrocatalytic degradation mechanism of E-Co(II)-PO43- system on MB was the combination of indirect oxidation of the intermediate oxidants like Co(III), P2O84- and the hydroxyl radical with direct electrocatalysis on the platinum titanium electrode, where the electrocatalytic oxidation of Co(III) was dominant.

Fabrication of Bifunctional Chitosan-Based Flocculants: Characterization, Assessment of Flocculation, and Sterilization Performance.

In this study, a series of chitosan-based quaternary ammonium graft flocculants, namely chitosan-graft-poly(acrylamide and methacryloyl ethyl trimethyl ammonium chloride) [CTS-g-P(AM-DMC)], was successfully synthesized by plasma initiation, and the as-prepared [CTS-g-P(AM-DMC)] had both flocculation and sterilization functions. Various characterization techniques were used to study the structure and physicochemical properties of the chitosan-based flocculants. ¹H nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), and thermogravimetric analysis/differential scanning calorimetry (TG/DSC) confirmed the successful synthesis of CTS-g-P(AM-DMC). Scanning electron microscopy (SEM) analysis exhibited that CTS-g-P(AM-DMC) contained a smooth convex and porous structure with an enormous surface area. CTS-g-P(AM-DMC) was then used to flocculate the simulated wastewater of the kaolin suspension and the Salmonella suspension. Besides external factors, such as the dosage of flocculant and pH, the effect of the internal factor graft ratio was also evaluated. The experimental results showed that CTS-g-P(AM-DMC) also revealed a strong sterilization effect, aside from the excellent flocculation effect. Moreover, the sterilization mechanism was investigated through a series of conductivity measurements and the analysis of fluorescence-based cell live/dead tests. The results indicated that CTS-g-P(AM-DMC) destroyed the cell membrane of Salmonella through its grafted quaternary ammonium salt, thereby exhibiting sterilization property.

Enhanced Treatment Properties of Iron Oxide Amended Sands Coupled with Polyelectrolyte to Humic Acid.

To improve the removal efficiency of micropollutant humic acid at low temperature, microflocculation filtration experiments were conducted with homemade iron oxide amended sands (IOAS), cationic polyelectrolyte (CPE) and polyaluminium chloride (PACl). Fractal properties of flocs structures and IOAS surface and their effects on the removal efficiency of humic acid were investigated. Results showed that IOAS had a porous surface with fractal dimensions (D) (D = 1.744) and a strong adsorption capacity for humic acid. The flocs produced by PACl were small in size, loosely packed with a higher D, and therefore settled slowly. By contrast, the formed flocs by adding CPE with only 1~5% of PACl had strong and open structures with a high effective density, rapid settling velocity and a lower D. Compared with PACl flocs, the larger size CPE flocs and PACl+CPE flocs deposited and packed up on IOAS, creating smaller pores and resulting in a lower D and higher filtration capacity.