Triphenylamine functionalized metal-organic framework NH2-MIL-101 (Fe) for efficient removal of roxarsone from wastewater

Roxarsone (3-nitro-4-hydroxyphenylarsenic acid, ROX) is easily converted into highly toxic inorganic arsenic compounds, therefore, the development of highly efficient adsorbents for the removal of ROX from wastewater is necessary but remains challenging. In this study, NH 2 -MIL-101 (Fe) was synthesised and modified with TPA-CHO (4-(N, N-diphenylamine) benzaldehyde) to obtain TPA-MIL-101(Fe) with triphenylamine functionalised groups. The modified TPA-MIL-101(Fe) exhibits the very high adsorption capacity (728.2 mg g −1 ) and fast adsorption equilibrium (2 h). The TPA-MIL-101(Fe) showed excellent selectivity, and the adsorption efficiency hardly decreased in the presence of competing ions (Cl − , NO 3 − , SO 4 2− ). The TPA-MIL-101(Fe) showed good adsorption performance for ROX at pH 3–13, with the best performance at pH = 9. In addition, TPA-MIL-101(Fe) was able to remove trace amounts of ROX from actual water samples (<5 mg L −1 ) with an efficiency of 99.46 %, and the remaining ROX content meets the international drinking water standards of the World Health Organization (29 μg L −1 ). The mechanism studies have shown that the Fe-O-As coordination and the π-π stacking interaction between TPA-MIL-101(Fe) and ROX greatly enhance its adsorption performance. In conclusion, this work provides a promising material for effective removal of ROX from the environmental water.