Thiophosphoryltriamide encapsulated into magnetic MCM-41-NH2 as a novel magnetically recoverable mesoporous adsorbent for Hg2+ removal in wastewater: Crystal structure and molecular calculations

Abstract

Water contaminants using heavy metal ions particularly Hg²⁺, due to harmful effects on human health and aquatic ecosystem, are challenging global environmental impact. Hence, the objective of this work is the synthesis of a new absorbent thiophosphoric triamide (PS) decorated on magnetic amine-functionalized mesoporous silica (MCM-41-NH₂) for Hg²⁺ removal. First, HgCl₂[P(S)(C₆H₁₁NH)₃]₂ (C) was synthesized by reaction of mercuric chloride and the thiophosphoric triamide ligand (PS). A distorted tetrahedral geometry surrounding the Hg²⁺ ion was revealed for the obtained complex. Nano-cubic structures of complex and its corresponding ligand (PS´ and Ć) were prepared with size between 60 and 80 nm at chloroform solvent as well. According to the strong interaction of PS to coordination with mercury (II), a newly thiophosphoryl functionalized magnetic mesoporous silica adsorbent, named Fe₃O₄@MCM-41-NH₂/PS, was synthesized with narrow pore size distribution, high specific surface area, and total pore volume, respectively, 7.726 nm, 93.353 m²/g, and 0.137 cm³/g. Initial concentration of Hg²⁺, adsorbent dosage, pH, temperature, and interfering ions were studied to eliminate Hg²⁺ from aqueous solution. Moreover, the material exhibited excellent recyclability owing to its magnetic properties, facilitating easy separation and reuse. The adsorption behavior of Hg²⁺ onto Fe₃O₄@MCM-41-NH₂/PS was best described by the Langmuir isotherm and pseudo-second-order kinetic models and the maximum adsorption capacity was determined to be 161.29 mg g⁻¹ at pH 8 and the temperature of 25 °C. Further, Monte Carlo simulations exhibited the decisive role of S, O, and NH groups for the elevated adsorption of mercury ions on Fe₃O₄@MCM-41-NH₂/PS in the presence of water.