Degradation of 4-Chlorophenol in Aqueous Solution by Sono-Electro-Fenton Process

Abstract

Electro-Fenton (EF) and ultrasound radiation (US) have been of interest for the removal of chlorinated compounds from water. This study evaluates the effects of different parameters on sono-electro-Fenton (SEF) for degradation of 4-chlorophenol (4-CP) in an aqueous solution. This study uses pulsing US waves along with Pd-catalyzed EF to degrade contaminants in water while maintaining temperature. The usage of pulsing US waves along with Pd catalyzed EF to remove contaminants while maintaining temperature has not been reported previously. SEF ability to degrade 4-CP was compared with the performance of each process (EF and sonolysis) alone. Initial pH, current density, background electrolyte, Fe 2+ concentration, Pd/Al2O3 catalyst concentration, US waves, and sonifier amplitude were optimized in a two electrode (Ti/mixed metal oxide or Ti/MMO) batch system. The degradation of 4-CP increased from 1.85% by US to 83% by EF to nearly >99.9% by coupled SEF. With US radiation under 70% amplitude and 1:10 ON/OFF ratio, the removal rate of 4-CP increased to 98% compared to 62% under EF alone within the first 120 min in the presence of 80 mg L -1 Fe 2+ , 16.94 mA cm ─2 of current density, 1 g L -1 Pd/Al2O3 catalyst (10 mg Pd), and initial pH of 3. However, the degradation rate decreased after 120 min of treatment, and complete 4-CP removal was observed after 300 minutes. The sonolysis impacted the 4-CP removal under coupled SEF, mostly due to the contribution of mass transfer (micromixing), while radical formation was found to be absent under the conditions tested (20kHz). The pulsed US was found to increase the temperature by only 8.7 o C, which was found not to impact the 4-CP volatilization or degradation. These results imply that low-level US frequency through pulses is a practical and efficient approach to support electro-Fenton reaction, improving reaction rates without the need for electrolyte cooling.

Recent advances in electro-Fenton process and its emerging applications

“…Accelerated destruction of 4,6-dinitrol-o-cresol and 2,4-dichlorophenoxyacetic acid was achieved by sono-EF compared to EF, whereas no improvement was observed for the degradation dye azobenzene (Oturan et al, 2008). Enhanced degradation of 4-chlorophenol was reported for sono-EF, achieving >99.9% removal compared to 83% and 1.85% obtained with EF and sonolysis alone (Nazari et al, 2018).…”

Fenton Reagent for Organic Compound Removal in Wastewater

“…There is room for modification in the Fenton process, which includes, but is not limited to the utilization of ultrasound (Sono-Fenton process -SF) [8,[11][12][13][14], anodic oxidation (Electro-Fenton Process -EF) [15][16][17][18], using UV light and adding ferric or ferrous oxalate ions (Photo-Fenton process -PF) [19][20][21][22][23], utilizing both ultrasound and ultraviolet light (Sono-Photo-Fenton process -SPF) [24][25][26], utilizing both ultrasound and anodic oxidation (Sono-Electro-Fenton process -SEF) [27], and utilizing a combination of electrochemical and photochemical properties of UV radiation (Photo-Electro-Fenton process -PEF) [2]. Other notable modifications have been developed, such as Solar-Photo-Electro-Fenton process (SPEF) [28], Peroxi Coagulation (PC), Photo-Peroxi Coagulation (PPC), Photo-Electro Catalysis (PEC), Ferred Fenton process, and Electrochemical Peroxidation (ECP) [29].…”

Immobilized palladium-catalyzed electro-Fenton's degradation of chlorobenzene in groundwater

“…However, in-situ groundwater remediation requires high stability electrodes because it could be applied in-situ for a few years (Doering et al, 2001;Chen, 2004;Brillas et al, 2009;Yuan et al, 2013a;Rajic et al, 2015). Electrochemically-induced transformation can occur via direct or indirect oxidation and/or reduction mechanisms (Liang et al, 2007;Yuan et al, 2007;Rajic et al, 2015;Rajic et al, 2016a;Nazari et al, 2018). Indirect oxidation and reduction processes use electrolysis products for contaminant transformation.…”

“…Ti-based mixed metal oxide or Ti/MMO). Examples of indirect electrochemical transformations of contaminants include reduction of chlorinated solvents through hydrodechlorination, which is supported by Pd catalyst and H 2 produced at the cathode (Rajic et al, 2015;Rajic et al, 2016b) and electrochemically-induced oxidation via Fenton's reaction (Kavitha and Palanivelu, 2004;Liang et al, 2007;Yuan et al, 2012;Yuan et al, 2013a;Wood et al, 2017;Nazari et al, 2018).…”

“…Pd-catalyzed EF system supports H 2 O 2 generation through a reaction between O 2 and H 2 produced at the anode and cathode, respectively (Eq. (2)) (Yuan et al, 2011;Yuan et al, 2013a;Nazari et al, 2018). H 2 O 2 then, in the presence of a Fe 2+ ion, generates hydroxyl radicals ( • OH) (Eq.…”