Enhanced phosphate removal from practical wastewater via in situ assembled dimension-engineered MOF@carbon heterostructures

Abstract

Developing metal–organic framework-incorporated carbon heterostructure (MOF@C) adsorbents with advanced phosphate removal capability is of remarkable significance in satisfying the increasingly stringent wastewater discharge criteria. Nevertheless, the tailored synthesis of MOF@C architectures and related structure-performance modulation remains elusive to date. Herein, we report on the dimensional engineering of MOF@C to prepare ZIF8@single-walled carbon nanotube (SCNT) and ZIF8@reduced graphene oxide (rGO) heterostructures with satisfactory phosphate removal efficiency. The maximum phosphate adsorption capacity of ZIF8@rGO is 491.2 mg g−1, with the largest partition coefficient value of 1900 mg g−1 μM−1 and an initial concentration of 2 mg L−1 under a neutral condition; thus, the prepared heterostructures evidently surpass state-of-the-art adsorbents. The high adsorption capacity is attributable to the two-dimensional graphene support, which provides a more effective surface area for ZIF8 anchoring than that of one-dimensional CNT. Furthermore, phosphate removal on these dimension-engineered MOF@C is examined as a function of pH, system temperature, and coexisting anions. The underlying mechanism is further elucidated via X-ray photoelectron spectroscopy/X-ray diffraction analysis and density functional theoretical simulation; enhanced phosphate removal by ZIF8@rGO is mainly attributable to the ligand exchange between the phosphates and the adsorbent. Our findings can aid the design of multifunctional MOF@C adsorbents for efficient phosphate removal from contaminated waterbodies.