Comparative study of the adsorption performance of NH2-functionalized metal organic frameworks with activated carbon composites for the treatment of phenolic wastewaters

Abstract

To better understand the role of the —NH2 group in adsorption process of phenolic wastewaters, NH2-functionalized MIL-53(Al) composites with activated carbon (NH2-M(Al)@(B)AC) were prepared. The results showed that the NH2 group could increase the mesopore volume for composites, which promotes mass transfer and full utilization of active sites, because hierarchical mesopore structure makes the adsorbent easier to enter the internal adsorption sites. Furthermore, the introduction of the NH2 group can improve the adsorption capacity, decrease the activation energy, and enhance the interaction between the adsorbent and p-nitrophenol, demonstrating that the NH2 group plays a crucial role in the adsorption of p-nitrophenol. The density functional theory calculation results show that the H-bond interaction between the —NH2 group in the adsorbent and the NO2 in the p-nitrophenol (adsorption energy of –35.5 kJ·mol−1), and base-acid interaction between the primary —NH2 group in the adsorbent and the acidic OH group in the p-nitrophenol (adsorption energy of –27.3 kJ·mol−1) are predominant mechanisms for adsorption in terms of the NH2-functionalized adsorbent. Both NH2-functionalized M(Al)@AC and M(Al)@BAC composites exhibited higher p-nitrophenol adsorption capacity than corresponding nonfunctionalized composites. Among the composites, the NH2-M(Al)@BAC had the highest p-nitrophenol adsorption capacity of 474 mg·g−1.