Preparation of Silver‐Modified Nickel Foams by Galvanic Displacement and Their Use as Cathodes for the Reductive Dechlorination of Herbicides

Abstract

International audienceNew 3D electrodes are prepared and tested in reductive herbicide dechlorination as the first step of an environmental remediation process. Commercial nickel foams are modified through the spontaneous deposition of silver nanoparticles. Some of the solutions of Ag+ ions employed in the galvanic displacement reactions contain complexing agents, such as thiosulfate or thiocyanate, and a capping agent, polyvinylpyrrolidone (PVP), which influences the morphology and growth kinetics of the silver deposits. Modified foams are used as cathodes for the reductive dechlorination of Alachlor(TM), a common chloroacetanilide herbicide, in a series of tests that confirm the catalytic activity of silver. Electrodes prepared in a thiosulfate solution containing PVP allow extensive reduction of Alachlor(TM) to give deschloroalachlor as the only dechlorinated product

Reductive dehalogenation of a chloroacetanilide herbicide in a flow electrochemical cell fitted with Ag‐modified Ni foams

“…The activity of Ag‐modified Ni foams for the dechlorination of Alachlor™ (Scheme ) in a two‐compartment cell has been shown in our previous study …”

“…The deposition of Ag nanoparticles on Ni foam was described elsewhere . Before its use in spontaneous deposition or in electrolysis experiments, the Ni foam was successively washed with acetone, dichloromethane, dried in a nitrogen stream and then washed again with water or 0.5 mol L ‐1 HNO 3 in an ultrasonic bath.…”

“…We recently reported an original method to prepare Ni foams modified with Ag nanoparticles by galvanic displacement and their use for reductive dechlorination of chloroacetanilide herbicides . To go further into the environmental application and test the possibility to achieve a combined process involving an electrochemical pre‐treatment followed by a biological process, we used Ag‐modified Ni foams in a flow electrochemical cell in different electrolytic media for dechlorination of Alachlor™. We will see that these new electrolytic conditions, easily adaptable to large‐scale processes, allow quasi‐total dechlorination of Alachlor™.…”

Electrocatalysts Prepared by Galvanic Replacement

“…In this case, however, a thicker shell of M noble is formed and the latter also enters the core of the catalyst, resulting in a M noble -M mixed core (evidence of that is presented in [102] and discussed in the next section). If the galvanic replacement step does not proceed to the completion of a full noble metal shell (as is the case of either slow or uneven processes) and there is no further catalyst treatment, then the surface of the material contains both M noble and M sites and can usually only be employed as a cathode under alkaline conditions (otherwise M will be leached); this is the case of catalytic layers produced on bulk Cu, Ni, and Fe alloy substrates and used as cathodes in aqueous media by Musiani and co-workers [129,132,134,137,138] and Trasatti and co-workers [139,140]. However, if the starting material is made of nanoparticles of M then, choosing the appropriate preparation conditions (e.g., concentration of M noble ions, complexing agents, time of reaction) or/and catalyst post-treatment (e.g., acid pepsis) a variety of interesting nanoparticle structures can be obtained (including hollow M noble or M noble -M nanoparticles), as reviewed in [54].…”

“…In more detail, they proposed the use of Rh(Ni) catalytic layers on Ni foams as a cathode for efficient nitrate removal by its reduction [134] and the use of Rh(Cu) layers on Cu porous electrodeposits as sensing cathodes for nitrate and nitrite detection [138]. They have also introduced Ag(Ni) cathodes for the reductive dechlorination of pesticide pollutants [137].…”