Magnetic CuO@Fe₃O₄ nanocomposite as a highly active heterogeneous catalyst of persulfate for 2,4-dichlorophenol degradation in aqueous solution

Abstract

A new magnetic CuO@Fe 3 O 4 nanocomposite was fabricated through an impregnation method and then characterized through X-ray diffraction, high-resolution transmission electron microscopy, nitrogen adsorption-desorption, and energy dispersive X-ray spectroscopy. The effects of initial solution pH, catalyst addition, reaction temperature, target contaminant, and persulfate (PS) concentration on 2,4-dichlorophenol (2,4-DCP) degradation in the activated PS system with the composite was evaluated. Results showed that the composite can degrade 96.9% of 2,4-DCP after 180 min under the following reaction conditions: PS, 10 mM; CuO@Fe 3 O 4 , 0.624 g L À1 ; 2,4-DCP, 100 mg L À1 ; pH, 6.8 AE 0.3; and temperature, 30 C. Quenching tests of different scavengers revealed that SO 4 c À and cOH are responsible for 2,4-DCP degradation. The pseudo-first-order kinetic model was then established to describe 2,4-DCP mineralization.The composite also exhibited stable catalytic performance after using for three cycles, thereby indicating the promising application of the catalyst for remediation of water contaminated with 2,4-DCP.Comparative experiments were carried out on PS, CuO@Fe 3 O 4 , and PS/CuO@Fe 3 O 4 systems to determine the effects of the synthesized CuO@Fe 3 O 4 composites on PS activation for 2,4-DCP degradation. These experiments were conducted in the same reactor and controlled under the same operating conditions. The results are shown in Fig. 2(a). Without PS, 2,4-DCP can stably exist in the presence of the catalysts for 180 min. In the control group with PS only, about 4% of 2,4-DCP was removed from the solution over the same time period. Accordingly, the addition of 0.624 g L À1 CuO@Fe 3 O 4 composite to PS solution resulted in rapid and pronounced degradation of 2,4-DCP, with 96.9% removal during the 180 min reaction time, compared with the addition of the CuO@Fe 3 O 4 composites and PS only. Comparatively, 0.928 g L À1 Fe 3 O 4 (0.004 mM Fe(II)) equal to 0.624 g L À1 CuO@Fe 3 O 4 (0.002 mM Fe(II) + 0.002 mM Cu(II)) removed 8.1% 2,4-DCP in the existence of PS. It agrees with previous reports. 37 These data indicate that sulfate free radicals can be efficiently produced by combining activated PS with the CuO@Fe 3 O 4 composite to oxidize 2,4-DCP. The effect Fig. 1 Characterization of catalysts. (a) XRD pattern. (b) Magnetization curves measured at room temperature for the synthesized CuO@Fe 3 O 4 composites before (solid line) and after three reaction cycles (dash line). (c) Nitrogen absorption/desorption isotherms and pore size distribution curve (the inset pattern). (d) EDX spectra and component molar ratio of the composites. (e) HRTEM images. 57062 | RSC Adv., 2015, 5, 57058-57066 This journal is

One-step preparation and application of magnetic sludge-derived biochar on acid orange 7 removal via both adsorption and persulfate based oxidation

“…TBA is well known as efficient OHc scavenger but not sensitive with SO 4 c À because of high reaction rate constants with OHc (3.8-7.6 Â 10 8 M À1 s À1 ) and lower ones with SO 4 c À (4.0-9.1 Â 10 5 M À1 s À1 ). 4 Fig. 7a showed quenching results of TBA.…”

“…Sulfate radicals and hydroxyl radicals were reported as the main oxidative radicals in most system employed PS as oxidant. 3,4,45 Two radical scavengers (MeOH and TBA) were employed in the scavenger experiments under pH 5.22. TBA is well known as efficient OHc scavenger but not sensitive with SO 4 c À because of high reaction rate constants with OHc (3.8-7.6 Â 10 8 M À1 s À1 ) and lower ones with SO 4 c À (4.0-9.1 Â 10 5 M À1 s À1 ).…”

“…Further decrease of rate constant from 0.0179 to 0.012 min À1 was observed when TBA concentration increased from 18.5 mM to 370.0 mM, suggesting that OHc contributed to AO7 removal. Owing to the high reaction rate constants with both of SO 4 c À (1.2-2.8 Â 10 9 M À1 s À1 ) and OHc (1.6-7.7 Â 10 7 M À1 s À1 ), 4 MeOH was employed to quench both of SO 4 c À and OHc (Fig. 7b).…”

“…1,2 PS alone showed low efficiency on organic pollutant removal under ambient conditions. 3,4 Appropriate activation methods should be used to produce more activated sulfate radicals (SO 4 c À , E 0 ¼ 2.5-3.1 V) 2 and hydroxyl radicals (OHc, E 0 ¼ 1.9-2.7 V). 5 Methods such as thermal-, 6 ultraviolet (UV) light- 7 and microwave- 8 activation needed high energy consumption, and baseactivated systems only showed high efficiency under alkaline conditions.…”

Degradation kinetics and mechanism of pentoxifylline by ultraviolet activated peroxydisulfate

“…The pH of the PTX solution was adjusted to 3, 5.2 or 10.5 by sulfuric acid or sodium hydroxide, respectively. 19 Inorganic salt (sodium chloride, sodium nitrate or sodium carbonate) were added in one portion to 200 mL of solution 0.2 mM PTX using appropriate equivalents of 1, 10 or 100 mM. Processes were carried out at room temperature (24 AE 3 C).…”