Tao Zhang

Bio: Tao Zhang is an academic researcher from Harbin Institute of Technology. The author has contributed to research in topics: Heat pipe & Graphene. The author has an hindex of 31, co-authored 146 publications receiving 4252 citations. Previous affiliations of Tao Zhang include University of Nottingham & King Abdullah University of Science and Technology.

Production of Sulfate Radical from Peroxymonosulfate Induced by a Magnetically Separable CuFe2O4 Spinel in Water: Efficiency, Stability, and Mechanism

Abstract: A simple, nonhazardous, efficient and low energy-consuming process is desirable to generate powerful radicals from peroxymonosulfate (PMS) for recalcitrant pollutant removal. In this work, the production of radical species from PMS induced by a magnetic CuFe2O4 spinel was studied. Iopromide, a recalcitrant model pollutant, was used to investigate the efficiency of this process. CuFe2O4 showed higher activity and 30 times lower Cu2+ leaching (1.5 μg L–1 per 100 mg L–1) than a well-crystallized CuO at the same dosage. CuFe2O4 maintained its activity and crystallinity during repeated batch experiments. In comparison, the activity of CuO declined significantly, which was ascribed to the deterioration in its degree of crystallinity. The efficiency of the PMS/CuFe2O4 was highest at neutral pH and decreased at acidic and alkaline pHs. Sulfate radical was the primary radical species responsible for the iopromide degradation. On the basis of the stoichiometry of oxalate degradation in the PMS/CuFe2O4, the radical ...

Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation.

Abstract: Peroxydisulfate (PDS) is an appealing oxidant for contaminated groundwater and toxic industrial wastewaters. Activation of PDS is necessary for application because of its low reactivity. Present activation processes always generate sulfate radicals as actual oxidants which unselectively oxidize organics and halide anions reducing oxidation capacity of PDS and producing toxic halogenated products. Here we report that copper oxide (CuO) can efficiently activate PDS under mild conditions without producing sulfate radicals. The PDS/CuO coupled process is most efficient at neutral pH for decomposing a model compound, 2,4-dichlorophenol (2,4-DCP). In a continuous-flow reaction with an empty-bed contact time of 0.55 min, over 90% of 2,4-DCP (initially 20 μM) and 90% of adsorbable organic chlorine (AOCl) can be removed at the PDS/2,4-DCP molar ratio of 1 and 4, respectively. Based on kinetic study and surface characterization, PDS is proposed to be first activated by CuO through outer-sphere interaction, the rate-limiting step, followed by a rapid reaction with 2,4-DCP present in the solution. In the presence of ubiquitous chloride ions in groundwater/industrial wastewater, the PDS/CuO oxidation shows significant advantages over sulfate radical oxidation by achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly chlorinated degradation products. This work provides a new way of PDS activation for contaminant removal.

Surface hydroxyl groups of synthetic α-FeOOH in promoting OH generation from aqueous ozone: Property and activity relationship

Abstract: This work investigated the relationship between the property of the surface hydroxyl groups of hydroxylated synthetic α-FeOOH and their catalytic activity in promoting hydroxyl radical ( OH) generation from aqueous ozone. Nitrobenzene was used as an ozone-resistant probe to quantify OH generation. ATR-FTIR analysis reveals that sulfate and phosphate suppressed the catalytic activity of α-FeOOH through substituting its surface hydroxyl groups, which implies that the catalyst surface hydroxyl groups were active sites for promoting OH generation. Compared with other synthetic oxo-hydroxides such as β-FeOOH, γ-FeOOH and γ-AlOOH, α-FeOOH achieved a highest Rc value (i.e., 1.11 × 10−7, molar concentration ratio of OH to O3) in catalytic ozonation. No correlation could be established between the surface hydroxyl density and the OH-promoting activity of the oxo-hydroxides. In contrast, their catalytic activity was found to be reversely related to the IR stretching frequencies of surface hydroxyl groups. The results indicate that not all surface hydroxyl groups of the oxo-hydroxides possessed the same high catalytic activity, but the weak surface MeO–H bonds were favorable sites for promoting OH generation from aqueous ozone. The surface hydroxyl–ozone interaction was thus proposed for the catalyzed OH generation, which can explain why neutral surface hydroxyl species of α-FeOOH was more active than protonated or deprotonated species.

Trace Cupric Species Triggered Decomposition of Peroxymonosulfate and Degradation of Organic Pollutants: Cu(III) Being the Primary and Selective Intermediate Oxidant

Abstract: Activation of persulfates to degrade refractory organic pollutants is currently a hot topic of advanced oxidation. Developing simple and effective activation approaches is crucial for the practical application of persulfates. We report in this research that trace cupric species (Cu(II) in several μM) can efficiently trigger peroxymonosulfate (PMS) oxidation of various organic pollutants under slightly alkaline conditions. The intermediate oxidant dominating this process was investigated with electron paramagnetic resonance (EPR), chemical probing, and in situ Raman spectroscopy. Unlike conventional PMS activation, which generates sulfate radical, hydroxyl radical, or singlet oxygen as major oxidants, Cu(III) was confirmed to be the primary and selective intermediate oxidant during the Cu(II)/PMS oxidation. Hydroxyl radical is the secondary intermediate oxidant formed from the reaction of Cu(III) with OH-. Hybrid oxidation by the two oxidants imparts Cu(II)/PMS with high efficiency in the degradation of a series of pollutants. The results of this work suggest that, with no need of introducing complex catalysts, trace Cu(II) inherent in or artificially introduced to some water or wastewater can effectively trigger PMS oxidation of organic pollutants.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Abstract: Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Complex Hydrides for Hydrogen Storage

Abstract: Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks.

Abstract: Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.