This study reports reactive adsorptive dechlorination of hydrocarbon oil over TiO 2 -based metal oxides at the temperatures of 20–150 °C. TiO 2 and a series of TiO 2 -CeO 2 were prepared by precipitation method and characterized by N 2 adsorption, XRD, FT-IR, pyridine-IR, NH 3 -TPD and CO 2 -TPD. The characterization results showed that both the acidity and basicity of the adsorbent had a significant impact on its dechlorination capacity. TiO 2 -U precipitated by urea exhibited higher dechlorination capacity than TiO 2 -A precipitated by ammonia due to the higher surface area, more acid and base amounts of the former. Among various Ti (1− x ) Ce x O 2 (x=0.1, 0.3, 0.5, 0.7, 0.9, 1) oxides, Ti 0.7 Ce 0.3 O 2 and Ti 0.3 Ce 0.7 O 2 bimetallic oxides showed higher dechlorination capacity than TiO 2 -U, and the chlorine removal over Ti 0.7 Ce 0.3 O 2 reached 82.8% after adsorption at 150 °C for 3 h. Mixing 5 wt% of alkali earth metal oxide into Ti 0.7 Ce 0.3 O 2 mechanically enhanced its dechlorination capacity, and the chlorine removal over Ti 0.7 Ce 0.3 O 2 -BaO reached as high as 92.1%. The chlorine removal increased with increasing the adsorption temperature. Ion chromatography and GC-MS analysis revealed that organochlorine compound was converted into Cl − and its corresponding alcohol over the adsorbent at 150 °C. Finally, the mechanism of reactive adsorption dechlorination was proposed.
Microplastics (MPs) and polychlorinated biphenyls (PCBs) generally coexist in the environment, posing risks to public health and the environment. This study investigated the effect of different MPs on the microbial anaerobic reductive dechlorination of Aroclor 1260, a commercial PCB mixture. MP exposure inhibited microbial reductive dechlorination of PCBs, with inhibition rates of 39.43%, 23.97%, and 17.53% by polyethylene (PE), polypropylene (PP), and polystyrene (PS), respectively. The dechlorination rate decreased from 1.63 μM Cl − d −1 to 0.99–1.34 μM Cl − d −1 after MP amendment. Chlorine removal in the meta-position of PCBs was primarily inhibited by MPs, with no changes in the final PCB dechlorination metabolites. The microbial community compositions in MP biofilms were not significantly different ( P > 0.05) from those in suspension culture, although possessing greater Dehalococcoides abundance (0.52–0.81% in MP biofilms; 0.03–0.12% in suspension culture). The co-occurrence network analysis revealed that the presence of MPs attenuated microbial synergistic interactions in the dechlorinating culture systems, which may contribute to the inhibitory effect on microbial PCB dechlorination. These findings are important for comprehensively understanding microbial dechlorination behavior and the environmental fate of PCBs in environments with co-existing PCBs and MPs and for guiding the application of in situ PCB bioremediation.
Ce-Ti-Zr mixed oxide catalysts prepared by sol-gel method were used in catalytic combustion of CH 2 Cl 2 . The characterization reveals that the incorporation of Ce and Zr into TiO 2 anatase or Ti and Zr into CeO 2 fluorite promotes hydroxyl groups, Lewis acidity and surface oxygen through the formation of Ti-O-Zr, Ti-O-Ce and Ce-O-Zr species. Ce-Ti-Zr catalysts show high activity for CH 2 Cl 2 oxidation with the rate of 5.66 × 10 −3 –6.45 × 10 −3 μmol s −1 m −2 at 250 °C and high stability for 50 h. The substitution of surface oxygen for Cl maintains the availability of Ti-OH and thus promotes Cl removal as HCl, which is verified by a great increase in the stable activity of physically closely contacted mixture of separated CeO 2 and TiO 2 or Ti 9 Zr 1 particles. In situ FT-IR shows that CH 2 Cl 2 interacts with Ti-OH to form -O-CH 2 -O-, which is quickly rearranged into formate. Finally, formate is oxidized with surface oxygen into CO or CO 2 .
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