Green synthesis of metal-organic framework MIL-101(Cr) – An assessment by quantitative green chemistry metrics

Abstract

MIL-101(Cr) is a metal–organic framework with high surface area and porosity synthesized for environmental applications, even though conventional synthesis uses toxic chemicals such as N, N-dimethylformamide (DMF) or hydrofluoric acid (HF). Therefore, we present a green evaluation of a novel synthesis that avoids adding any toxic modulator and uses waste polyethylene terephthalate (PET) as a source of the organic linker terephthalic acid (H2BDC). As a result of this strategy, MIL-101(Cr)-PET had a similar crystalline structure to conventional synthesized MIL-101(Cr)-BDC. Nitrogen gas adsorption measurements were applied to analyze textural properties; MIL-101(Cr)-PET presents a lower BET surface area (1852 m2/g) than MIL-101(Cr)-BDC (3431 m2/g). However, MIL-101(Cr)-PET exhibited similar toluene adsorption performance (42 mmol/g) than MIL-101(Cr)-BDC (40 mmol/g). A green assessment of MIL-101(Cr)-BDC synthesis using DOZN™ green chemistry evaluator revealed that the major impacts are in the Green Chemistry Principles of Prevention, Less Hazardous Chemical Synthesis, Safer Solvents and Auxiliaries, and Inherently Safer Chemistry for Accident Prevention due to the use of DMF in the activation process. Based on the environmental score, a reduction of 50 % in impacts on the 12 Green Chemistry Principles was achieved when PET was used as a source of H2BDC in addition to the elimination of nitric acid as a modulator and the use of non-toxic solvents. The outcomes of this study show that the greener synthesis of MIL-101(Cr) has the potential to become a competitive material for toluene adsorption at diluted concentrations for indoor air quality applications.