Efficient gold capture from wastewater by NH2-MIL-125 and its application for photocatalysis: A turning waste into treasure approach

Based on the concept of turning waste into treasure, gold adsorption from wastewater by NH2-MIL-125 and its application for the construction of photocatalyst in VOCs elimination were studied. NH2-MIL-125 displayed exceptional adsorption capabilities toward Au(Ⅲ) ions (798.1 mg·g−1 at 298 K) with good selectivity and redox activity. The adsorption behaviors of gold were feasible, spontaneous as well as endothermic, and was well compatible with pseudo-second-order and Langmuir models. The amine group was mainly responsible for the gold ion adsorption via a coordination interaction, and the amine group reduced Au(Ⅲ) into the Au0 deposited on the NH2-MIL-125. The effects of foreign metal ions in gold-containing wastewater and pH on Au(Ⅲ) adsorption have been studied in detail. Furthermore, the used NH2-MIL-125 adsorbed with gold was further thermally transformed into Au@TiO2 photocatalyst. This method was demonstrated as more effective one in comparison to other methods to prepare Au@TiO2 photocatalyst for elimination of gaseous toluene originated from its strongest charge separation ability. Additionally, the degradation efficiency, mineralization, stability and photocatalytic mechanism were analyzed. This work verified the feasibility for the Au recovery by NH2-MIL-125 and its reuse for photocatalyst construction, and NH2-MIL-125 would be a potential candidate to realize resource regeneration and utilization.