Convert waste to MOF: Nitro-MIL-53(Al) synthesized from waste acid leachate for highly efficient capture of p-nitrophenol

As inspired by the sustainable concept of "turning waste into materials", a feasible "killing three birds with one stone" strategy was proposed to design and synthesize Al-based MOF material from Al-rich acid leachate of natural kaolinite for capture of p-nitrophenol (PNP). The acid leachate neutralized with aluminum compound, as Al sources and reaction medium, was directly reacted with nitroterephthalic acid (NTPA) to form Al-MOF (named Nitro-MIL-53(Al)), so that the harmless disposal of acidic wastewater, the recovery of valuable metal, and the synthesis of new materials were achieved simultaneously. The porous Nitro-MIL-53(Al) adsorbent has superb adsorption capacity (173.01 mg/g) and removal efficiency (95.76 %, at 400 mg/L) towards PNP, and can be regenerated and reused more than 4 times. It still maintains higher adsorption capability of 117.76–153.21 mg/g for PNP in the waters containing different amounts of co-existing ions, respectively. The comprehensive analyses on structures and adsorption behaviors revealed that PNP was adsorbed onto Nitro-MIL-53(Al) by a chemisorption process, and π-π interaction, hydrogen bonds, and electrostatic attraction synergically contribute to the adsorption of PNP. This research provides a sustainable way to achieve simultaneously harmless disposal of waste liquid and development of new adsorption materials.