A synergistic system of dielectric barrier discharge (DBD) combined with La/Ce-TiO2 was developed to investigate the decomposition performance of the environmentally persistent perfluorooctanoic acid (PFOA). The La/Ce-TiO2 was modified by sol–gel method and characterized by XRD, SEM, and energy dispersive X-ray. The effects of PFOA concentration, applied voltage, initial pH, liquid conductivity, and additives on the removal rate of PFOA were explored. The results showed that the La/Ce-TiO2 exhibited excellent catalytic effects on PFOA degradation in DBD system. When the applied voltage, PFOA concentration, pH value, and solution volume were 75 V, 100 mg/L, 3.63, and 1000 mL, respectively, the removal efficiency of PFOA was up to 97.5% by adding La4Ce1-TiO2 in DBD. The corresponding defluorination ratio, TOC removal, and decomposition yield were 62.2%, 57.3%, and 37 g/kWh, respectively. Furthermore, five main intermediates including CF3(CF2)6H, CF3(CF2)5COOH, CF3(CF2)5COH, CF3(CF2)4COOH, and CF3CF2CF3 were identified with LC–MS, and the degradation pathways of PFOA were proposed. The degradation mechanisms revealed that hydroxyl radicals play a significant role in the degradation of PFOA in the synergistic system.

Lanthanum (La) doped titanium dioxide (TiO2) introduced to the dielectric barrier discharge (DBD) system was successfully used to degrade 4-chlorophenol (4-CP). The photocatalytic materials were characterized by XRD, SEM, EDX and DRS techniques. The influence of the La doping ratio and pH on the degradation of 4-CP in the combined system of photocatalysis and plasma were investigated to evaluate the feasibility of the mixed degradation system. The 10 wt% La/TiO2 showed the highest percentage of 4-CP degradation (99.0%) and maximum rate constant (11.89 × 10−3 s−1). It was also found that the catalytic activity of 10La/TiO2 was higher than pure synthesized TiO2. Doped La effectively reduces the band gap, amends the surface and optimizes the crystal form of TiO2. Higher degradation efficiency of 4-CP was observed at higher pH values. The efficiency was 99.9% at pH 10.0 in this treatment system, while a decrease was observed at pH 2.0. Catechol, hydroquinone, benzoquinone and carboxylic acid were identified as the predominant aromatic intermediates for the degradation of 4-CP, and finally, transformed into CO2 and H2O.

•Moderate Al/Fe molar ratio and basicity improved (Al + Fe)b content in PAFC.•The purity of (Al + Fe)b separated by organic solvents was above 75%.•The micro-morphology of (Al + Fe)b showed a 3D network with rough surface.•The (Al + Fe)b outperformed PAFC and commercial PAC in turbidity and color removal.Taking blast furnace dust and aluminum dross as raw material, PAFC with high (Al + Fe)b content was prepared via optimizing Al/Fe molar ratio and basicity condition in this study. Separation, purification and characterization of (Al + Fe)b were further investigated. The results showed that the (Al + Fe)b content in PAFC peaked at 36.67% with Al/Fe = 7:3 and basicity(B)=1.8. The optimal conditions for purifying (Al + Fe)b by the organic solvents precipitation method were determined as follows: organic solvents (ethanol, propylene glycol and acetone mixed solution) volume ratio = 2:1:7. An organic mixed solution in measures of 50 mL, 100 mL and 50 mL was added into 10 mL of 0.3 M PAFC solution to extract (Al + Fe)c, (Al + Fe)b and (Al + Fe)a, respectively. The (Al + Fe)b content in the separated samples reached over 75% with the yield higher than 50% of the total PAFC. The infrared spectrum of the extracted (Al + Fe)b, PAFC, and commercial PAC showed that the content of hydroxyl bridge linked aluminum/iron in the extracted (Al + Fe)b sample was higher than those in PAC and PAFC. The transmission electron microscope images of the extracted (Al + Fe)b suggested a 3D network structure of the (Al + Fe)b with rough surfaces, which benefits adsorption and sweep of contaminants. Coagulation tests showed that the extracted (Al + Fe)b achieved better coagulation performance than PAFC and commercial PAC.

•Optimal parameters of PAFC synthesis from blast furnace dust were obtained.•Self-made PAFC outperformed commercial PAC in turbidity and color removal.•Coagulation mechanism of PAFC for turbidity and color removal were compared.The research focused on the synthesis and coagulation performance of polyaluminum ferric chloride (PAFC) coagulant in order to explore a comprehensive utilization for blast furnace dust. The optimal conditions for PAFC synthesis were: fifty grams of blast furnace dust reacted with 150 mL hydrochloric acid diluted solution for 3 h at 90 °C and 10 g of aluminum dross reacted with 150 mL hydrochloric acid diluted solution for 2.5 h under room temperature; In co-polymerization stage, the Al/Fe molar ratio = 7:3, basicity B = 1.8, polymerization temperature 60–70 °C, and reaction time (pre-polymerization time of aluminum + copolymerization time of aluminum and iron) 1.0 h + 3.0 h. The main results are as follows: (1) The coagulation tests indicated that self-made PAFC outperformed commercial PAC in turbidity and color removal. (2) Self-made PAFC and flocs generated in water treating process were measured by Scanning Electron Microscopy. Surface charge characteristics of PAFC were measured by Zetasizer 3000HS. Charge neutralization was a very important coagulation mechanism of PAFC in turbidity removal process. And there were other coagulation mechanisms besides charge neutralization such as bridge connection and sweep flocculation, playing significant roles in decolorization process.