Immobilization of heavy metals in ceramsite prepared using contaminated soils: Effectiveness and potential mechanisms.

Heavy metal contaminated soils pose a serious threat to the environment, and preparing ceramsite using contaminated soils was proposed as an effective method to address this threat in this study. Specifically, two typical soils (i.e., contaminated clay and sandy soil) were mixed with different ratios and calcined at temperature 1000-1200 °C to prepare ceramsite. Special attentions were paid to evaluating the immobilization of heavy metals in ceramsite and identifying the corresponding immobilization mechanisms. Using the leachability of heavy metals from ceramsite as evaluation criteria, the optimum mixing ratio of clay/sandy soil and sintering temperature were determined as 0.6:0.4 and 1200 °C. Moreover, based on the spectroscopic characterizations and thermodynamic calculation, high sintering temperature well facilitated the liquid phases formation, promoting the reactions between heavy metals and aluminosilicates and the valence state conversion of heavy metals. Accordingly, heavy metals were well immobilized in ceramsite by forming thermodynamically stable minerals, being encapsulated in solid matrix, and transforming to valence states with low mobility. The leaching conditions including pH and temperature had minimal effect on the immobilization of heavy metals in ceramsite. In summary, ceramsite prepared by contaminated soils was environmentally friendly and had good potential in engineering application as building materials.

Enhanced arsenic removal by reusable hexagonal CeO2/Fe2O3 nanosheets with exposed (0001) facet.

Arsenite in wastewater has caused increasing concern because of high toxicity and mobility. Iron oxides are widely available and regarded as effective adsorbents for arsenic. However, conventional iron oxides usually are only effective for arsenate (As(V)) adsorption by complexation, but not for As(III) adsorption because of their poor catalytic oxidation activities, which greatly limits arsenic removal efficiency. In this study, a uniform hexagonal FeCe bimetal oxide nanosheets (Fe0.21Ce0.29O) enclosed by high active (0001) planes was synthesized by a solvothermal method to improve the catalytic activity of Fe2O3. The experimental results showed that adsorption capacity of Fe0.21Ce0.29O reached 61.1 mg/g for arsenic and 70 % of that at equilibrium was achieved in <10 min. Based on characterization analyses and density functional theory simulation, the new insight in oxidation and complexation mechanism of arsenic was proposed. Firstly, As(III) was adsorbed to adsorbent surface by forming stable structure of Ce-O-As or Fe-O-As, and then converted into As(V) by dissolved oxygen under the catalysis of (0001) planes densely distributed on Fe2O3 and CeO2 surfaces. The formed As(V) species were bound on Fe0.21Ce0.29O surface by forming bidentate and monodentate surface complexes. Finally, the safety of As-containing solution treated with Fe0.21Ce0.29O was well proved by the zebrafish embryo developmental toxicity tests.

Facile synthesis of CoFe2O4@BC activated peroxymonosulfate for p-nitrochlorobenzene degradation: Matrix effect and toxicity evaluation.

p-Nitrochlorobenzene (p-NCB) is widely used in industry and poses a potential threat to the public health due to its persistence, carcinogenicity and mutagenicity. Herein, magnetic catalyst CoFe2O4@Biochar (CoFe2O4@BC) was synthesized by a facile sol-gel method, efficiently activating peroxymonosulfate (PMS) to degrade p-NCB. The synergistic effect of Fe and Co in well-dispersed CoFe2O4 and the electron transfer promote the production of reactive oxygen species (ROS) (OH, SO4- and O2-), efficiently removing p-NCB enriched by CoFe2O4@BC. Under optimum conditions, the CoFe2O4@BC/PMS system could remove 89% of p-NCB from water, and the degradation efficiency could reach 80% in soil. Toxic chlorinated intermediates appeared during the degradation process and thus efficient dechlorination process can lower the toxicity of the reaction solution, which was also proved by the oxygen uptake inhibition experiment as well as zebrafish toxicity experiments. Furthermore, p-NCB degradation efficiency could be inhibited by Cl-, HCO3-, HPO42- and humic acid (HA) through quenching effect or occupation of CoFe2O4@BC surface active sites while HPO42- could also improve the efficiency by directly activating PMS. The CoFe2O4@BC/PMS system can be efficiently applied in the remediation of p-NCB pollution in water and soil.

Insights into the mechanism of redox pairs and oxygen vacancies of Fe2O3@CoFe2O4 hybrids for efficient refractory organic pollutants degradation.

The core-shell Fe2O3@CoFe2O4 hybrids microspheres with abundant oxygen vacancies were synthesized through in-situ ion exchange-calcination method and employed to induce peroxymonosulfate (PMS) to eliminate organic pollutants. The superior catalytic activity and stability of Fe2O3@CoFe2O4 were attributed to the synergistic effects of M2+/M3+ (M denotes Co or Fe) redox cycles. SO4·-, ·OH, O2·- and 1O2 were proved to be the main reactive oxygen species (ROS) involved in the phenol degradation process through quenching experiments and EPR measurements, while the surface-bound SO4·- played a dominant role. Trace metal ions leached during the reaction enhanced the PMS activation, and the oxygen vacancies electron transfer process played a critical role in the formation of O2·-/1O2 and the cycle of M2+/M3+ redox pairs. The formation of ROS and function of 1O2 were also revealed from bulk reaction and interface reaction. This study highlighted the simultaneous evolution of PMS reduction and oxidation to generate ROS, which provided an insight into the efficient catalytic degradation of persistent organic pollutants (POPs).