Degradation of acetaminophen with ferrous/copperoxide activate persulfate: Synergism of iron and copper.

To enhance the advanced oxidation process based on persulfate, CuO was introduced into the Fe2+/PS system to achieve a synergistic effect between Fe and Cu. Results showed that Fe2+ was able to adsorb onto the CuO surface to form Fe(II) and further reduced Cu(II) into Cu(I), which can further release into the solution to participate in oxidation reactions. In this case, SO4·- can be generated via Fe2+ and Cu+ reactions with PS and ·OH from Cu+ reaction with dissolved oxygen (DO). The degradation efficiency of APAP was studied under the optimal condition (initial pH 6.5, PS = 0.8 g L-1, Fe2+ = 0.7 mM, CuO = 0.3 g L-1), and the results indicated that the Fe2+/CuO/PS system can achieve a higher degradation rate of APAP (92% within 90 min) rather than Fe2+/PS and CuO/PS system (79% and 10%). Quenching experiment was performed to verify the active radicals in the Fe2+/CuO/PS system. Sulfate and hydroxyl radicals were generated in the Fe2+/CuO/PS system. Besides, some critical factors, such as Fe2+ concentration, catalyst dosage, PS concentration, initial pH (buffers and nonbuffers), and dissolved oxygen were evaluated in bath experiments. Results indicated that dissolved oxygen was essential in the Fe2+/CuO/PS system. APAP degradation experiments were conducted in surface water, and the intermediates were detected via GC-MS. The results indicated that the Fe2+/CuO/PS system is effective in the treatment of APAP in natural waters.

Zhang Y ，Zhang Q ，Dong Z ，Wu L ，Hong J ... -  《-》

Comparison of radical and non-radical activated persulfate systems for the degradation of imidacloprid in water.

The study focuses on degradation efficiency of non-radical activation and radical activation systems of persulfate (PS) to degrade imidacloprid (IMI) by using sodium persulfate (SPS) as PS source. Copper oxide (CuO)-SPS and CuO/biochar (BC)-SPS were selected as PS non-radical activation systems, and pyrite (PyR)-SPS was selected as PS radical activation system. The degradation by CuO-SPS, CuO/BC-SPS and PyR-SPS systems was investigated from acidic to basic conditions (pH 3.0-11.0). Highest degradation by CuO-SPS and CuO/BC-SPS systems was achieved over pH 11.0. In contrast, highest degradation by PyR-SPS system was achieved over pH 3.0, however, PyR-SPS system was also found effective up to pH 9.0. It was found that degradation was more efficient in PS radical activation system, indicating that IMI could be oxidized by radicals rather than by activated PS. Electron paramagnetic resonance (EPR) analysis was carried out to investigate the generation of sulfate (SO4-) and hydroxyl (OH) radicals, which indicated the presence of SO4- and OH in CuO-SPS, CuO/BC and PyR-SPS systems. However, free radical quenching analysis indicated that radicals were main reactive oxygen species for degradation. The lower degradation in PS non-radical activation systems was probably resulted from radicals existed as minor reactive oxygen species. The findings indicated that non-radical oxidation systems showed low reality for degradation and good degradation could be achieved by radical oxidation system. The degradation was also carried out in real waters to investigate the potential applicability of applied systems, which supported PyR-SPS system for effective degradation.

Hayat W ，Zhang Y ，Hussain I ，Huang S ，Du X ... -  《-》

Cu(II)-enhanced degradation of acid orange 7 by Fe(II)-activated persulfate with hydroxylamine over a wide pH range.

The activation of persulfate by Fe(II) coupled with hydroxylamine (the HA/Fe(II)/PS system) was highly effective for the degradation of refractory organic contaminants under acidic pH conditions. However, owing to the precipitation of ferric hydroxide and/or the slow reduction from Fe(III) to Fe(II), the HA/Fe(II)/PS system was invalid under neutral and alkaline pH conditions. In this study, it was observed that the degradation of acid orange 7 (AO7) was strongly enhanced over the wide pH range of 2-9 when trace Cu(II) (0.5-5 μM) was spiked into the HA/Fe(II)/PS system. It was evident that Cu(I) was generated via the reduction of Cu(II) by HA in the bimetallic system at both pH 3 and pH 8, and the steady concentration of Fe(II) in the bimetallic system was much higher than that in the HA/Fe(II)/PS system due to the rapid reaction between Fe(III) and Cu(I). Quenching experiments using tert-butyl alcohol, methanol and sodium bromide as the scavengers and electron spin resonance experiments confirmed that the primary reactive species responsible for AO7 degradation were sulfate radical at both pH 3 and pH 8, rather than hydroxyl radical and Cu(III). Nevertheless, sulfate radical was mainly produced by Fe(II)-activated PS at pH 3, while both Cu(I) and Fe(II) made important contributions to the generation of sulfate radical at pH 8. The bimetallic system was also highly effective in degrading other organic contaminants, such as phenol, diclofenac, reactive red 2 and orange G. This study might provide a promising idea based on Fe(II)-activated PS for degrading organic contaminants over a wide pH range.

Liu X ，Yuan B ，Zou J ，Wu L ，Dai L ，Ma H ，Li K ，Ma J ... -  《-》

An efficient CuO-γFe2O3 composite activates persulfate for organic pollutants removal: Performance, advantages and mechanism.

CuO-γFe2O3 was fabricated as a novel and effective persulfate (PS) catalyst to remove bio-refractory organic pollutants. Characterization results showed that CuO-γFe2O3 possessed a relatively large surface area among transition metal oxides which provided favorable adsorption and activation sites for PS to degrade pollutants. There was an obvious synergy between CuO and γFe2O3 in the composite, which played 84.7% role in Acid orange 7 (AO7) removal. Under the optimal conditions (CuO-γFe2O3 dosage = 0.6 g L-1, PS dosage = 0.8 g L-1, unadjusted solution pH), almost complete AO7 was rapidly eliminated in 5 min. Moreover, the wide workable pH range (2-13), good stability (0.82 mg L-1 Cu leached, almost no Fe leached) and reusability (4 times) were the significant virtues of CuO-γFe2O3 for wastewater treatment. Besides, the reaction mechanism mainly based on the interaction among Cu(II/III) and Fe(II/III) species for sulfate radical (SO4-) generation was emphatically elucidated by the analyses of radicals, PS utilization, TOC removal and metal chemical states. Finally, CuO-γFe2O3+PS system displayed desirable removal of multiple organic pollutants with different molecular structures. In light of the prominent advantages of CuO-γFe2O3+PS, this work extended activated PS process in treating refractory organic wastewater.

Xian G ，Niu L ，Zhang G ，Zhou N ，Long Z ，Zhi R ... -  《-》

Pyrite enables persulfate activation for efficient atrazine degradation.

Persulfate (PS) is widely used for environmental remediation, but its organic contaminant removal performance strongly depends on its activation. In this study, we demonstrate that pyrite (FeS2) can more effectively activate PS than the commonly used FeSO4 for atrazine degradation. When 3.0 mM of PS and 4.2 mM of iron salts were used, the atrazine degradation efficiency of FeS2/PS was 1.4 times that of FeSO4/PS, while the amount of consumed PS in case of FeS2 was only 53% of that by FeSO4. The better PS activation performance of FeS2 could be attributed to its slow and sustainable release of dissolved Fe(II), inhibiting the quenching reaction between •SO4-/•OH and Fe(II) ions, and thus producing more reactive oxygen species for the atrazine degradation. More importantly, the surface bound Fe(II) of FeS2 could activate molecular oxygen to generate superoxide radical (•O2-), which could further promote the effective decomposition of PS by accelerating the Fe(III)/Fe(II) redox cycle. This study unravels the roles of dissolved Fe(II) and surface bound Fe(II) on the persulfate activation, and provides a promising heterogeneous persulfate activator for pollutant control and environmental remediation.

Wang X ，Wang Y ，Chen N ，Shi Y ，Zhang L ... -  《-》