Enhanced reduction of p-nitrophenol by zerovalent iron modified with carbon quantum dots

The pollution of aromatic nitro compounds in water is a critical issue, and the reduction of p-nitrophenol (p-NP) by the combination of catalyst/reductant has been a hot topic in recent years. The methods reported previously bore several defects, such as high cost for material synthesis and secondary pollution to the environment. Herein, this study employed the non-toxic and inexpensive materials, carbon quantum dots (C-dots) as the catalyst and zerovalent iron (ZVI) as the reductant, to prepare the ZVI modified with C-dots (C-dots@ZVI) for p-NP removal in water under anaerobic condition. The results showed that the removal rate of p-NP, the capacity, and the selectivity of ZVI towards p-NP removal were greatly improved, due to the involvement of C-dots. The rate constant of p-NP removal by C-dots@ZVI was 1192.7 folds of that by ZVI. The capacity of p-NP removal by C-dots@ZVI at 24.0 h was 24.8 orders of magnitude higher than that of ZVI. At the end of 2.0 h reaction with p-NP, the utilization ratio and electron efficiency of C-dots@ZVI were increased by 3.7 times and 2.9 times, respectively, compared to those of ZVI. The enhancing effect of C-dots on p-NP sequestration by ZVI should be mainly associated with the promoted hydrophobicity of ZVI surface, the facilitated electron transfer, and the accelerated corrosion of ZVI. As an innovative catalyst/reductant system for p-NP reduction, C-dots@ZVI is effective, facile, low-cost, and environmental-friendly.