An efficient novel linker for Cu-MOF Design: Remediation of Congo Red (CR) and Tropaeolin OO (TOO) as organic pollutants

Abstract

The widespread discharge of synthetic dyes into aquatic environments poses a serious threat to ecosystems, water quality, and public health. In this study, a copper-based metal–organic framework (Cu-MOF) was synthesized via a solvothermal method using an unconventional organic linker, 1,2,4-benzene-tricarboxylic anhydride (BTC). An unconventional 1,2,4-BTC linker was chosen for its adjacent carboxyl groups. This configuration enables intramolecular hydrogen bonding, which stabilizes the framework and provides additional sites for pollutant capture. The linker's identity was first confirmed by NMR. The resulting Cu-MOF was systematically characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDX), and X-ray Photoelectron Spectroscopy (XPS). These analyses confirmed the formation of a highly crystalline and porous structure, while Brunauer–Emmett–Teller (BET) measurements indicated a low N2-accessible surface area with macropores and interparticle holes. Thermogravimetric Analysis (TGA) confirmed strong thermal stability. The Cu-MOF's negative surface charge electrostatically attracted anionic dyes, enabling high removal rates of 89% for Congo Red (CR) and 85% for Tropaeolin OO. Adsorption followed pseudo-second-order kinetics, and the Temkin isotherm model indicated binding occurred on a heterogeneous surface through indirect interactions. Thermodynamic evaluations confirmed that the adsorption process was both spontaneous and endothermic. Reusability tests demonstrated that the Cu-MOF retained over 60% of its initial efficiency after five regeneration cycles, highlighting its durability. The Cu-MOF is an effective, durable, and reusable material for sustainably removing hazardous azo dyes from wastewater.