In recent decades, NO3- contamination in groundwater system has posed severe concern to human health and environment due to the massive use of fertilizers and discharge of untreated industrial wastewater. Nano-sized bimetallic catalysts supported by hematite (Cu-Pd-hematite) have been known as promising and appealing remediation approach for the effective NO3- reduction with accelerated reaction kinetics and high selectivity towards eco-friendly N2. However, no relevant research has been reported for the environmental implementation of the bimetallic catalytic technology to the contaminated groundwater and soil remediation with various oxyanions, resulting in an incomplete removal and unsuitable product formation. In this study, we examined the competitive inhibition of groundwater oxyanions (ClO4-, PO43-, SO42-, BrO3-, SO32-, HCO3-, CO32-, and Cl-) during the catalytic NO3- reduction by nano-sized Cu-Pd-hematite catalyst potentially applicable for contaminated groundwater conditions. The catalytic NO3- reduction kinetics was significantly affected in the order of HCO3-&lt;ClO4-&lt;CO32-&lt;SO42-&lt;Cl-&lt;PO43-&lt;BrO3-&lt;SO32- at their high concentrations (100 mg/L), while others played a competitive inhibitor role at the higher level. The novel findings suggest that the inhibitory effect of Cl-, PO43-, BrO3- and SO32- on the catalytic NO3- reduction needs to be seriously considered for its proper application to catalytic nitrate remediation of anion enriched groundwater to avoid the slow reaction kinetics and weak denitrification. The results highlight that the product selectivity during the catalytic NO3- reduction was sensitively influenced by the variations of oxyanion concentrations. The selectivity towards N2 during the NO3- reduction decreased significantly as HCO3-, CO32-, and ClO4- concentrations increased. However, it increased as SO32-, SO42- and PO43- concentrations increased. The nano-sized Cu-Pd-hematite catalyst showed remarkable continuous NO3- reduction with good selectivity towards N2 and NH4+ in the presence of the oxyanions, and the formation of NO2- can only be observed with CO32- at 500 mg/L. The primary reaction mechanism of competitive inhibition by the oxyanions for the catalytic NO3- reduction was the suppression of catalytic active Cu sites and the alteration of product formation by different levels of the Hads species on the active Pd surface.

Effect of different groundwater oxyanions on the catalytic nitrate reduction and end-product selectivity

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.