A B S T R A C TElectrochemical reduction treatment was found to be a promising method for dechlorination of Trichloroacetic acid (TCAA), and acceleration of electron transfer or enhancement of the concentration of atomic H* significantly improve the electrochemical dechlorination process. Bimetallic Pd-based catalysts have the unique property of simultaneously catalyzing the production of atomic H* and reducing target pollutants. Herein, a bimetallic Pd-In electrocatalyst with atomic ratio of 1:1 was evenly deposited on an Al 2 O 3 substrate, and the bimetallic Pd-In structure was confirmed via X-ray photoelectron spectroscopy (XPS). Electrochemical removal of trichloroacetic acid (TCAA) by the PdIn/Al 2 O 3 catalyst was performed in a three-dimensional reactor. 94% of TCAA with the initial concentration of 500 mg L À1 could be degraded within 30 min under a relatively low current density (0.9 mA cm À2 ). In contrast to the presence of refractory intermediates (dichloroacetic acid (DCAA)) found in the Pd/Al 2 O 3 system, TCAA could be thoroughly reduced to monochloroacetic acid (MCAA) using Pd-In/ Al 2 O 3 catalysts. According to scavenger experiments, an electron transfer process and atomic H* formation function both existed in the TCAA reduction process, and the enhanced indirect atomic H* reduction process (confirmed by ESR signals) played a chief role in the TCAA removal. Moreover, the synergistic effects of Pd and In were proven to be able to enhance both direct electron transfer and indirect atomic H* formation, indicating a promising prospect for bimetallic electrochemical reduction treatment.
In this work, the electroreductive removal of bromate by a Pd 1 −In 4 /Al 2 O 3 catalyst in a three-dimensional electrochemical reactor was investigated. A total of 96.4% of bromate could be efficiently reduced and completely converted into bromide within 30 min under optimized conditions. On the basis of the characterization results and kinetics analysis, a synergistic effect of Pd and In was observed, and Pd 1 −In 4 /Al 2 O 3 had the highest reaction rate constant of 0.1275 min −1 (vs 0.0413, 0.0328, and 0.0253 min −1 for In/Al 2 O 3 , Pd/Al 2 O 3 , and Al 2 O 3 ). The results of electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the bromate removal process, while the direct reduction played a more important role. Moreover, the introduction of In could increase the zeta potential of Pd 1 −In 4 /Al 2 O 3 , facilitating bromate adsorption and its subsequent reduction on the catalyst. Finally, a reaction mechanism for bromate reduction by Pd 1 −In 4 /Al 2 O 3 was proposed based on all the experimental results. ■ INTRODUCTIONBromate is an oxyhalide disinfection byproduct frequently detected in drinking water from ozonation of bromidecontaining source waters.1 Because of its carcinogenic and genotoxic properties, the World Health Organization (WHO) has promulgated a 10 μg/L standard for bromate in drinking water.2 To meet this strict limitation, numerous treatment methods have been explored, including filtration, chemical reduction, biodegradation, activated carbon techniques, and photocatalysis.3−8 Among these technologies, liquid phase catalytic hydrogenation has proven to be an efficient and clean method to eliminate bromate. 9,10 Wang et al. reported the hydrogenation reduction of bromate using a core−shell-structured catalyst with encapsulated Pd nanoparticles.11 However, the catalytic hydrogenation needs an external supply of H 2 , while the storage and transportation of H 2 may be a hidden danger. Alternatively, the electrochemical reduction of bromate is found to be a promising approach due to its low maintenance requirements and efficient minimization of toxic chemicals and secondary pollution.12−14 Kishimoto and Matsuda reported an efficient electrochemical method to reduce bromate to bromide using a two-compartment electrolytic flow cell with activated carbon felt as electrodes. 15 The results showed that bromate contamination can be removed within a few minutes, but this process required acidic conditions. Zhao et al. studied the effectiveness of a boron-doped diamond electrode in bromate removal by electrochemical reduction, and nearly 90% of bromate could be removed with the bias potential of −1.0 V within 2 h.14 However, the application of these cathodes for water treatment would be limited due to the low A/V ratio (ratio of the electrode area and solution volume). Hence, it is necessary to design a new electrochemical reactor and electrode with high efficiency. Recently, a three-dimensional el...
According to the statistics of 160 typical fire and explosion accidents in oil storage areas at home and abroad nearly 50 years, 122 of them occurred the secondary accidents in the emergency responses. Based on 122 accident cases, 21 causal factors leading to secondary accidents are summarized. In order to quantify the influencing degree of these causal factors on the accident consequences, a multiple linear regression model was established between them. In the modeling process, these factors are decomposed into the criterion layer, variable layer, and bottom layer. The improved analytic hierarchy process (IAHP) was used to establish the relationship between the bottom factors and variable factors, and the regression analysis method was used to establish the relational model between variable layer and criterion layer. For 122 cases of the secondary accidents, this study took the year as a statistical dimension, and obtained 40 groups of sample data. The first 34 groups of sample data were used to build the causal factors model, and the last 6 groups of sample data were tested the generalization ability of the model by using the established regression model combined with grey prediction model. The results show that the prediction ability of the established model was better than that of the grey prediction model alone. Moreover, the relative contribution and change trend of the causal factors were evaluated using the mutation progression method, and corresponding preventive countermeasures were proposed. It was found that human professional skills, knowledge and literacy, environmental issues, and firefighting facilities are the main influencing factors that lead to the secondary accidents. These three kinds of factors show a gradual improvement trend, and the existing prevention measures should be maintained and further improved. The problem of inherent objects or equipment factors has not been effectively improved and has a worsening trend, which is the focus of prevention in the future, and the prevention and control efforts need to be moderately increased. The research results have important guiding significance for understanding the quantitative influences of causal factors on the accident consequences, improving emergency response capabilities, reducing accident losses, and avoiding secondary accidents.
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