Photocatalytic activity of new nanostructures of an Ag(i) metal–organic framework (Ag-MOF) for the efficient degradation of MCPA and 2,4-D herbicides under sunlight irradiation

Abstract

A new Ag(I) metal–organic framework (Ag-MOF) [Ag(p-OH-C₆H₄COOH)₂(NO₃)]_n [Ag(PHBA)₂(NO₃)]_n, (1) (PHBA: C₈H₆O₄{p-hydroxybenzoic acid}) was synthesized using two different methods; the laying method (single crystal) and sonochemical irradiation (nanostructures). Scanning electron microscopy (SEM), powder XRD, and FT-IR spectroscopy were used to characterize the materials. The impacts of various parameters, including the ultrasonic (US) power, reaction time, reactant concentration, and temperature requirements to reach a controlled synthesis were extensively investigated. Compound 1-5 (obtained via sonochemical irradiation) showed an excellent catalytic activity towards simultaneous photodegradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) and 2,4-dichlorophenoxyacetic acid (2,4-D) in an aqueous solution under sunlight irradiation. The response surface methodology (RSM) for the modelization and optimization of the photodegradation of the MCPA/2,4-D mixture was utilized. The maximum photodegradation efficiencies for 2,4-D and MCPA (96.0 and 98.0% respectively) were observed under optimal conditions of C₀ = 4.5 mg L⁻¹, catalyst dose = 0.4 g L⁻¹, pH = 5.5 and irradiation time = 20 min. The determined quantum yield of Ag-MOF was 3.21 × 10⁻⁵ molecules per photon with excellent reusability in terms of the degradation efficiency (e.g., 97% for the first cycle and 86% for the fifth). Ag-MOF is suggested for the efficient treatment of organic pollutants in wastewater systems.