Facile synthesis and synergistic mechanism of CoFe2O4@three-dimensional graphene aerogels towards peroxymonosulfate activation for highly efficient degradation of recalcitrant organic pollutants.

Magnetic CoFe2O4 is a promising heterogeneous catalyst with great separation and catalytic performance on peroxymonosulfate (PMS) activation. However, for extremely recalcitrant organic pollutants (e.g. Benzotriazole (BTA)), CoFe2O4/PMS system exhibits much low catalytic performance and high metal ion leaching. As such, CoFe2O4 supported on three-dimensional graphene aerogels (CoFe2O4@3DG) was synthesized via facile hydrothermal method. It turns out that 3DG as supporter significantly enhances specific surface area, redox activity and electron transfer of composite. The degradation rate constant in the CoFe2O4@3DG/PMS system (0.0203 min-1) is 15 times higher than that in the CoFe2O4/PMS system (0.0013 min-1). It results from synergistic activation of PMS by CoFe2O4 and 3DG to generate multiple reactive oxygen species (•OH, SO4-•, O2-• and 1O2). Particularly, high graphitization structure and low oxygen groups content of 3DG facilitate PMS adsorption on its surface and electron transfer from BTA to PMS. Ultimately, BTA is degraded into CO2, NH3 and intermediates through benzene and triazole ring-opening reactions. Moreover, CoFe2O4@3DG/PMS system displays good stability and recyclability. Therefore, this study provides a new way to improve CoFe2O4 activity for extremely recalcitrant organic pollutants degradation and new insights into synergistic activation of PMS by CoFe2O4 and 3DG, which further advances cobalt-based catalysts in heterogeneous catalysis.

Future changes in Yuan River ecohydrology: Individual and cumulative impacts of climates change and cascade hydropower development on runoff and aquatic habitat quality.

The eco-hydrological system in southwestern China is undergoing great changes in recent decades owing to climate change and extensive cascading hydropower exploitation. With a growing recognition that multiple drivers often interact in complex and nonadditive ways, the purpose of this study is to predict the potential future changes in streamflow and fish habitat quality in the Yuan River and quantify the individual and cumulative effect of cascade damming and climate change. The bias corrected and spatial downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Model (GCM) projections are employed to drive the Soil and Water Assessment Tool (SWAT) hydrological model and to simulate and predict runoff responses under diverse scenarios. Physical habitat simulation model is established to quantify the relationship between river hydrology and fish habitat, and the relative change rate is used to assess the individual and combined effects of cascade damming and climate change. Mean annual temperature, precipitation and runoff in 2015-2100 show an increasing trend compared with that in 1951-2010, with a particularly pronounced difference between dry and wet years. The ecological habitat quality is improved under cascade hydropower development since that ecological requirement has been incorporated in the reservoir operation policy. As for middle reach, the runoff change from January to August is determined mainly by damming, and climate change influence becomes more pronounced in dry seasons from September to December. Cascade development has an effect on runoff of lower reach only in dry seasons due to the limited regulation capacity of reservoirs, and climate changes have an effect on runoff in wet seasons. Climate changes have a less significant effect on fish habitat quality in middle reach than damming, but a more significant effect in lower reach. In addition, the effect of climate changes on fish habitat quality in lower reach is high in dry seasons but low in flood seasons.

Thermally activated persulfate oxidation of NAPL chlorinated organic compounds: effect of soil composition on oxidant demand in different soil-persulfate systems.

This study investigates the interaction of persulfate with soil components and chlorinated volatile organic compounds (CVOCs), using thermally activated persulfate oxidation in three soil types: high sand content; high clay content; and paddy field soil. The effect of soil composition on the available oxidant demand and CVOC removal rate was evaluated. Results suggest that the treatment efficiency of CVOCs in soil can be ranked as follows: cis-1,2-dichloroethene > trichloroethylene > 1,2-dichloroethane > 1,1,1-trichloroethane. The reactions of soil components with persulfate, shown by the reduction in soil phase natural organics and mineral content, occurred in parallel with persulfate oxidation of CVOCs. Natural oxidant demand from the reaction of soil components with persulfate exerted a large relative contribution to the total oxidant demand. The main influencing factor in oxidant demand in paddy-soil-persulfate systems was natural organics, rather than mineral content as seen with sand and clay soil types exposed to the persulfate system. The competition between CVOCs and soil components for oxidation by persulfate indicates that soil composition exhibits a considerable influence on the available oxidant demand and CVOC removal efficiency. Therefore, soil composition of natural organics and mineral content is a critical factor in estimating the oxidation efficiency of in-situ remediation systems.