Identifying the Role of Surface Hydroxyl on FeOCl in Bridging Electron Transfer toward Efficient Persulfate Activation.

FeOCl is a highly effective candidate material for advanced oxidation process (AOP) catalysts, but there remain enormous uncertainties about the essence of its outstanding activity. Herein, we clearly elucidate the mechanism involved in the FeOCl-catalyzed perdisulfate (PDS) activation, and the role of surface hydroxyls in bridging the electron transfer between Fe sites and PDS onto the FeOCl/H2O interface is highlighted. ATR-FTIR and Raman analyses reveal that phosphate could suppress the activity of FeOCl via substituting its surface hydroxyls, demonstrating the essential role of hydroxyl in PDS activation. By the use of X-ray absorption fine structure and density functional theory calculations, we found that the polar surface of FeOCl experienced prominent hydrolyzation, which enriched abundant electrons within the microarea around the Fe site, leading to a stronger attraction between FeOCl and PDS. As a result, PDS adsorption onto the FeOCl/H2O interface was obviously enhanced, the bond length of O-O in adsorbed PDS was lengthened, and the electron transfer from Fe atoms to O-O was also promoted. This work proposed a new strategy for PDS-based AOP development and a hint of building efficient heterogeneous AOP catalysts via regulating the hydroxylation of active sites.

Developing a QSPR Model of Organic Carbon Normalized Sorption Coefficients of Perfluorinated and Polyfluoroalkyl Substances.

Perfluorinated and polyfluoroalkyl substances (PFASs) are known for their long-distance migration, bioaccumulation, and toxicity. The transport of PFASs in the environment has been a source of increasing concerned. The organic carbon normalized sorption coefficient (Koc) is an important parameter from which to understand the distribution behavior of organic matter between solid and liquid phases. Currently, the theoretical prediction research on log Koc of PFASs is extremely limited. The existing models have limitations such as restricted application fields and unsatisfactory prediction results for some substances. In this study, a quantitative structure-property relationship (QSPR) model was established to predict the log Koc of PFASs, and the potential mechanism affecting the distribution of PFASs between two phases from the perspective of molecular structure was analyzed. The developed model had sufficient goodness of fit and robustness, satisfying the model application requirements. The molecular weight (MW) related to the hydrophobicity of the compound; lowest unoccupied molecular orbital energy (ELUMO) and maximum average local ionization energy on the molecular surface (ALIEmax), both related to electrostatic properties; and the dipole moment (µ), related to the polarity of the compound; are the key structural variables that affect the distribution behavior of PFASs. This study carried out a standardized modeling process, and the model dataset covered a comprehensive variety of PFASs. The model can be used to predict the log Koc of conventional and emerging PFASs effectively, filling the data gap of the log Koc of uncommon PFASs. The explanation of the mechanism of the model has proven to be of great value for understanding the distribution behavior and migration trends of PFASs between sediment/soil and water, and for estimating the potential environmental risks generated by PFASs.

Spatial and Temporal Variation of Drought Based on Satellite Derived Vegetation Condition Index in Nepal from 1982⁻2015.

Identification of drought is essential for many environmental and agricultural applications. To further understand drought, this study presented spatial and temporal variations of drought based on satellite derived Vegetation Condition Index (VCI) on annual (Jan⁻Dec), seasonal monsoon (Jun⁻Nov) and pre-monsoon (Mar⁻May) scales from 1982⁻2015 in Nepal. The Vegetation Condition Index (VCI) obtained from NOAA, AVHRR (National Oceanic and Atmospheric Administration, Advanced Very High Resolution Radiometer) and climate data from meteorological stations were used. VCI was used to grade the drought, and the Mann⁻Kendall test and linear trend analysis were conducted to examine drought trends and the Pearson correlation between VCI and climatic factors (i.e., temperature and precipitation) was also acquired. The results identified that severe drought was identified in 1982, 1984, 1985 and 2000 on all time scales. However, VCI has increased at the rate of 1.14 yr-1 (p = 0.04), 1.31 yr-1 (p = 0.03) and 0.77 yr-1 (p = 0.77) on the annual, seasonal monsoon and pre-monsoon scales, respectively. These increased VCIs indicated decreases in drought. However, spatially, increased trends of drought were also found in some regions in Nepal. For instance, northern areas mainly in the Trans-Himalayan regions identified severe drought. The foothills and the lowlands of Terai (southern Nepal) experienced normal VCI, i.e., no drought. Similarly, the Anomaly Vegetation Condition Index (AVCI) was mostly negative before 2000 which indicated deficient soil moisture. The exceedance probability analysis results on the annual time scale showed that there was a 20% chance of occurring severe drought (VCI ≤ 35%) and a 35% chance of occurring normal drought (35% ≤ VCI ≤ 50%) in Nepal. Drought was also linked with climates in which temperature on the annual and seasonal monsoon scales was significant and positively correlated with VCI. Drought occurrence and trends in Nepal need to be further studied for comprehensive information and understanding.

Iron oxychloride (FeOCl): an efficient Fenton-like catalyst for producing hydroxyl radicals in degradation of organic contaminants.

An iron oxychloride (FeOCl) catalyst was developed for oxidative degradation of persistent organic compounds in aqueous solutions. Exceptionally high activity for the production of hydroxyl radical (OH·) by H2O2 decomposition was achieved, being 2-4 orders of magnitudes greater than that over other Fe-based heterogeneous catalysts. The relationship of catalyst structure and performance has been established by using multitechniques, such as XRD, HRTEM, and EPR. The unique structural configuration of iron atoms and the reducible electronic properties of FeOCl are responsible for the excellent activity. This study paves the way toward the rational design of relevant catalysts for applications, such as wastewater treatment, soil remediation, and other emerging environmental problems.

Low-temperature degradation of toluene over Ag-MnOx-ACF composite catalyst.

Volatile organic compounds (VOCs) have caused a serious threat to the atmosphere and human health. Therefore, it is of great significance to exploit effective catalytic materials for the safe and effective catalytic elimination of VOCs. Herein, Ag-MnOx-ACF composite catalysts were constructed via a two-step impregnation strategy and used for catalytic toluene degradation. A remarkable low-temperature catalytic activity (T100 = 50℃), excellent stability, as well as CO2 selectivity (80%) were achieved over the Ag-MnOx-ACF catalyst. A series of characterizations indicated that the unique manganese defects structure of birnessite phase manganese oxide played an essential role for toluene oxidation, which was conducive to generating surface adsorbed oxygen. The higher ratio of Mn3+/Mn4+, abundant surface adsorbed oxygen and highly dispersed Ag species were determined to significantly facilitate toluene degradation. The mechanism of efficient degradation of toluene at low temperature was proposed. O3 and H2O molecules were activated via surface hydroxyl and Mn defects on Ag-MnOx-ACF to produce sufficient •OH, enhancing the degradation performance of toluene. We provide a new idea for the catalytic oxidation of benzene VOCs at low even room temperatures.

Optimized H2-evolving dye-sensitized LaFeO3 photocathodes prepared via the layer-by-layer assembly of dyes and catalysts.

A molecular dye and a molecular catalyst were loaded onto the surface of a mesoporous LaFeO3 (LFO) film via layer-by-layer assembly relying on the coordination of phosphates and Zr4+. After assembling six layers of the dye and four layers of the catalyst, the (NiP-4 + PQA-6)@LFO photocathode exhibited a significant photocurrent for light-driven H2 generation.

Anchoring ultrasmall Pd nanoparticles by bipyridine functional covalent organic frameworks for semihydrogenation of acetylene.

Acetylene hydrogenation is a well-accepted solution to reduce by-products in the ethylene production process, while one of the key technical difficulties lies in developing a catalyst that can provide highly dispersed active sites. In this work, a highly crystalline layered covalent organic framework (COF) material (TbBpy) with excellent thermal stability was synthesized and firstly applied as support for ultrasmall Pd nanoparticles to catalyze acetylene hydrogenation. 100% of C2H2 conversion and 88.2% of C2H4 selectivity can be obtained at 120 °C with the space velocity of 70 000 h-1. The reaction mechanism was elucidated by applying a series of characterization techniques and theoretical calculation. The results indicate that the coordination between Pd and N atom in the bipyridine functional groups of COFs successfully increased the dispersibility and stability of Pd particles, and the introduction of COFs not only improved the adsorption of acetylene and H2 onto catalyst surface, but enhanced the electron transfer process, which can be responsible for the high selectivity and activity of catalyst. This work, for the first time, reported the excellent performance of Pd@TbBpy as a catalyst for acetylene hydrogenation and will facilitate the development and application of COFs materials in the area of petrochemicals.

Catalytic degradation of benzene at room temperature over FeN4O2 sites embedded in porous carbon.

Benzene and its aromatic derivatives are typical volatile organic compounds for indoor and outdoor air pollution, harmful to human health and the environment. It has been considered extremely difficult to break down benzene rings at ambient conditions without external energy input, due to the extraordinary stability of the aromatic structure. Here, we show one such solution that can thoroughly degrade benzene to basically water and carbon dioxide at 25 °C in air using atomically dispersed Fe in N-doped porous carbon, with almost 100% benzene conversion. Further experimental studies combined with molecular simulations reveal the mechanism of this catalytic reaction. Hydroxyl radicals (·OH) evolved on the atomically dispersed FeN4O2 catalytic centers were found responsible for initiating and completing the oxidation of benzene. This work provides a new chemistry to degrade aromatics at ambient conditions and also a pathway to generate active ·OH oxidant for generic remediation of organic pollutants.

Spatiotemporal variations in damages to cropland from agrometeorological disasters in mainland China during 1978-2018.

Drought, flood, hail, low temperature, and frost (LTF) are the main agrometeorological disasters (AMDs) in China; however, comprehensive and quantitative studies on cropland damage induced by AMDs across the whole country in terms of long-term trends are still lacking and urgently needed. Based on historical statistical data from yearbooks and bulletins, the overall characteristics of cropland damage by AMDs during 1978-2018 were analyzed using a pre-whitening procedure and a Mann-Kendall trend test at yearly and provincial scales in China. The results showed that drought was the most severe, with an average covered area of 22.2 million ha and an affected area of 11.2 million ha every year during 1978-2018, followed by flood, hail, and LTF. A decreasing trend was observed in covered area and affected area by drought, flood, and hail, while only LTF showed an increasing trend. On provincial scale, more than 70% of the covered area by AMDs was induced by drought and flood in most provincial districts. In all provincial districts of northern China, more than 50% of the covered area was induced by drought. In most provincial districts of southern China, more than 40% of the covered area was induced by flood. Hail disasters were prominent in Xinjiang, with significant increasing trends among all parameters. Compared with the other three AMDs, LTF covered and affected the smallest cropland area, but significant increasing trends were observed in the northwest and middle parts of China. The results of this study systematically display the characteristics of damage to cropland by four main AMDs, which are critical and necessary for disaster risk reduction and adaptive strategy development.

In situ phytoremediation of polycyclic aromatic hydrocarbon-contaminated agricultural greenhouse soil using celery.

Although celery has been established as an effective plant in the remediation of organic pollutant-contaminated soil, few studies have investigated the associated biological processes in rhizosphere and the effect of celery on agricultural field remediation in situ. In this study, a polycyclic aromatic hydrocarbon (PAH)-contaminated agricultural greenhouse was used as the experimental site, and three celery species (Apium graveolens L., Oenanthe javanica (Blume) DC., Libanotis seseloides (Fisch. & C.A. Mey. ex Turcz.) Turcz.) were applied for in situ remediation. After 90 days, the PAH dissipation rate of the L. seseloides treatment was highest (50.21%), and most of the PAHs were limited to its roots (translocation factor 0.516). This suggested that L. seseloides is a potential species for phytoremediation coupled with agro-production. The culturable microbial population and invertase activity results strongly supported that O. javanica is suitable for the establishment of exogenous bacteria-celery co-remediation techniques. Pearson's correlation analysis showed that the polyphenol oxidase (PPO) activity was highly significantly positively correlated with the PAH dissipation rate (r = 0.984, P < 0.01), and we suggest that PPO can be used as a microecological index during PAH remediation.

Comparative study of atrazine degradation by magnetic clay activated persulfate and H2O2.

To effectively remove the endocrine disrupting chemicals (EDCs) in water, Fe3O4 was loaded on the surface of modified sepiolite clay by the method of co-precipitation to catalyze potassium persulfate (K2S2O8) and hydrogen peroxide (H2O2) respectively to generate SO4˙- and ·OH for atrazine (ATZ) removal. The magnetic clay catalyst was characterized by XRD, SEM, N2 adsorption-desorption and isoelectric point. The degradation efficiency of ATZ in the two systems was systematically compared in terms of initial pH, oxidant dosage and oxidant utilization rate. The results revealed that, after 90 minutes, systems with K2S2O8 and H2O2 can remove 65.7% and 57.8% of the ATZ under the given conditions (30 °C, catalyst load: 1 g L-1, initial pH: 5, [ATZ]0: 10 mg L-1, [H2O2]0: 46 mmol L-1, [PDS]0: 46 mmol L-1). The magnetic clay catalyst still maintained good catalytic activity and stability during the four consecutive runs. Based on the quenching experiments, it was demonstrated that the dominant radical species in the two systems were SO4˙-/·OH and ·OH, respectively. However, the degradation efficiency of the two systems presented different responses toward the condition variations; the system with K2S2O8 was relatively more sensitive to solution pH, the oxidant efficiency was generally higher than that of the H2O2 system (except 184 mmol L-1).

Atrazine degradation using Fe3O4-sepiolite catalyzed persulfate: Reactivity, mechanism and stability.

In this study, with sepiolite as a support, a novel magnetic Fe3O4-sepiolite composite was fabricated by coprecipitation method. The characterization results reveal that the sepiolite support could anchor Fe3O4 nanoparticles with good dispersion. The composite was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. 71.6% of ATZ and 20.9% of solution TOC could be removed after 60 min with 92 mmol/L of PS ([ATZ]0 = 10 mmol/L). Due to the good adsorption capacity of Fe3O4-sepiolite composite toward ATZ, the degradation was considered to be facilitated by an adsorption process, since the adsorbed ATZ can be more easily transported to the active sites and be degraded in situ. Operation factors, including PS dose and solution pH, were investigated and found to be influential for the ATZ removal. The Fe3O4-sepiolite composite maintained its catalytic activity and structural stability with negligible Fe leaching during the recycling batch experiments. The intermediate products were further identified and the possible transformation pathway was then proposed based on the results. The findings of this research promote the application of Fe3O4-sepiolite composite as efficient and recyclable heterogeneous catalyst for organic degradation, and provide insights into the development of alternative catalysts with good adsorptive properties.

Effective removal by coagulation of contaminants in concentrated leachate from municipal solid waste incineration power plants.

Municipal solid waste (MSW) incineration is widely used in China. Concentrated leachate, containing high concentrations of pollutants, is an important type of secondary pollution produced in MSW incineration power plants and requires proper treatment. In this study, various coagulants were used to treat concentrated leachate from a nanofiltration (NF) membrane that treated leachate from an MSW incineration plant. The optimal coagulation condition was determined in this study. Under the optimal condition, removals of chemical oxygen demand, light absorbing substances (at 254 nm), total nitrogen, color and turbidity were 68.42%, 69.01%, 44.14%, 92.31% and 87.44%, respectively. Much of the refractory organic matter with relatively high molecular weight, aromaticity and humification degree was removed, and effluent had a lower molecular weight than raw NF concentrated leachate. Study also found that some parts of high molecular weight compounds from NF CL were removed by coagulation process, but the change of distribution of molecular weight was not outstanding. The NF concentrated leachate, both before and after coagulation, contained a large amount of chloride. Hence, a follow-up study should be conducted to find an effective additional processing that can remove organic matter using the high concentration of chloride in the NF concentrated leachate coagulation effluent. This study provides a theoretical basis for the treatment of concentrated leachate from MSW incineration power plants.