Ultra–selective and sustainable extraction of trace Cr(VI) from real waters using a thermally regenerable MOF composite of pDMAEMA-DUT-5

Abstract

Trace amount of Cr(VI) in water still threatens human health and ecology. Several reported amine-based adsorbents can remove trace Cr(VI) in acidic solutions of pH 2–5, but perform badly at neutral and alkaline conditions, which is insufficient for treating natural waters. Also, the chemical eluate leads to secondary pollution. Here, the amine-rich thermo-responsive poly(dimethylaminoethyl methacrylate) (pDMAEMA) was selected based on its high pK_a value and introduced into MOFs to produce pDMAEMA-DUT-5 for effective removal of trace Cr(VI) from natural waters. The composite with a polymer loading of 23.4 wt% achieved the highest adsorption capacity of 182.2 mg g⁻¹ under an optimized condition, that is, at pH 3 and 25 °C. Besides, this material effectively reduced trace Cr(VI) content in natural waters from 100 to 1 μg L⁻¹ by one filtration in a column. Its high selectivity was verified and further confirmed by the strong adsorption energy of Cr(VI) and −N(CH₃)₂. Furthermore, the composite could be fully regenerated in 45 °C water within 10 min, concentrating Cr(VI) for 270 folds in one adsorption–desorption cycle and maintaining over 99 % performance after five cycles. It demonstrated excellent removal efficiency, high selectivity, and thermal regeneration stability. This work presents a simple strategy to design highly selective and reusable ion adsorbents for effective and sustainable removal or recovery of toxic and precious ions, while its thermal regeneration function largely simplifies further treatments.