Removal of p-nitrophenol by double-modified nanoscale zero-valent iron with biochar and sulfide: Key factors and mechanisms

Abstract

In this study, the mechanisms and key factors of p-nitrophenol (PNP) removal by biochar (BC) and sulfide double-modified nanoscale zero-valent iron (nZVI) were systematically investigated. The results showed that the residence time of the hydrothermal carbonization of waste bamboo chopsticks was the key factor affecting the removal of PNP by nZVI/BC. The biochar derived from waste bamboo chopsticks prepared at a hydrothermal temperature of 240 °C for 1 h was the most suitable nZVI loading material. The hydrophobicity of the biochar had a greater impact on S-nZVI/BC. Biochar effectively alleviated the agglomeration of nZVI and formed a miniature galvanic cell with nZVI to promote its corrosion. The effective reducing agents in the S-nZVI/BC system were Fe0, Fe2+, S2−, and S22−, and the system had stronger reducibility then nZVI. The reaction rate of S-nZVI/BC for PNP removal was 2.6 times higher than that of nZVI. In addition, the double modification of nZNI reduced the energy barrier of the PNP removal reaction and alleviated the surface passivation of nZVI. The apparent activation energy of the reaction under anaerobic conditions after sulfidation treatment was reduced by 23.7 %, while the PNP removal efficiency increased by 8 % under aerobic conditions. Density Function Theory (DFT) calculations revealed that PNP was more easily adsorbed and participated in the reaction on the surface of the sulfide shell layer than oxidized shell layer. This work confirms that biochar loading and surface sulfidation can enhance the reactivity and stability of nZVI.