Abstract
The catalytic effect of copper in Devarda’s Al-Cu-Zn alloy (Dev. alloy) and sole metallic copper, copper salts and copper oxides in the coaction of NaBH4 within the hydrodehalogenation (HDH) of polybrominated phenols, such as the herbicide Bromoxynil in alkaline aqueous solution has been investigated. Namely, the hydrodebromination (HDB) activity of Dev. alloy/NaOH system has been compared to heterogeneous Cu-based catalysts using NaBH4 as a reductant. Differences in the solid-state structures of used Cu-based heterogeneous catalysts after the mentioned HDB process have been studied using the powder XRD and SEM techniques. It was found that some of the used copper-based catalysts are reusable and reasonably effective even at room temperature. Efficiency of the most promising copper-based reduction systems (Dev. alloy/NaOH and Cu-based catalysts/NaBH4) have been successfully tested within the HDB of industrially important brominated flame retardant tetrabromobisphenol A (TBBPA). Dev. alloy/NaOH and Cu-based catalyst generated in-situ within the CuSO4/NaBH4 produced were recognized as the most active HDB agents for complete debromination of both BRX and TBBPA.
Highlights
Copper and its salts exhibit broad catalytic activity mainly due to the accessible and reasonable stability of Cu(0), Cu(I) and Cu(II) oxidation states [1,2,3,4,5]
Bromoxynil (BRX) is a brominated hydroxybenzonitrile-based selective contact foliage herbicide used to control a variety of broadleaf weeds
In the past several years, bromoxynil has been applied in increasing quantities as a possible replacement for atrazine, which has been banned in many countries [10]
Summary
Copper and its salts exhibit broad catalytic activity mainly due to the accessible and reasonable stability of Cu(0), Cu(I) and Cu(II) oxidation states [1,2,3,4,5] They are effective catalysts for both Carom–H bonds transformations [1,2] and Carom–halogen cleavage reactions [3,4]. It was published that photochemical H-atom abstraction from the OH group of BRX results in the formation of unstable phenoxy radical, which can undergo self-reaction resulting in the formation of brominated dibenzo-p-dioxins [21]. These brominated compounds are considered as the most dangerous persistent organic pollutants (POP) [22]. Our primary objectives were to; (1) test the reaction conditions (minimal excess of reagents) necessary for the complete Cu-mediated HDB of BRX in alkaline aqueous solution, including the possibility of used/spent Cu-catalyst recycling, (2) compare effect of metallic copper, different copper alloys and copper compounds on the HDB efficiency of BRX, and (3) apply and compare studied reaction conditions for the possible HDB of TBBPA
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