Efficient and sustainable design of pyridyl-bis-thiourea pincer ligand-immobilised Merrifield polymer precursor for arsenic ions adsorption

Abstract

ABSTRACT An improved yield of a composite named Merrifield-pyridoyl-bis-thiourea derivative (MR-PyBTU) was effectively synthesised from the Merrifield Polymer Precursor (MR) and utilised for the adsorption of arsenic trioxide (As3+) ions from wastewater samples containing 1.5 mg/L of As3+ ions. The structure of the (PVAm-MMB) composite was confirmed using various analytical techniques, ensuring successful functionalization. Key experimental conditions namely pH, equilibrium time, starting concentration of As3+ ions, composite dosage, temperature, and choice of eluting agents were systematically optimised. At an ambient temperature, a pH value of 4.5, with 20 minutes of agitation, and an initial concentration of 250 mg/L As3+ ions, the composite demonstrated its highest sorption efficiency at a capacity of 50 mg/g. Equilibrium isotherm analyses indicated that the experimental data aligned more closely with the Langmuir model compared to the Freundlich model. Remarkably, the Langmuir model’s predicted uptake capability of 51.282 mg/g closely matched the actual observed values. Kinetic analyses supported by the pseudo-first-order model accurately described the sorption process, yielding a theoretical sorption capability of 49.113 mg/g. Thermodynamic assessments suggested that the sorption process is exothermic, spontaneous, and more favourable at lower temperatures. Efficient desorption of As3+ ions from the saturated composite was attained with 0.025 M NaOH, reaching approximately 98% efficiency. This composite’s ability to remove As3+ ions from wastewater aligns with Food and Agriculture Organization (WHO) and World Health Organization (FAO) guidelines, ensuring its safe discharge into marine environments after a single treatment cycle. Additionally, the compound 4-amino-N2, N6-bis((3-chloro-1,4-dioxo-1,4-dihydronaphthalen-2-yl) carbamothioyl) pyridine-2,6-dicarboxamide (PyBTU) exhibited potent antioxidant and antibacterial properties against Gram-negative bacteria, Gram-positive bacteria, Escherichia coli, and Bacillus subtilis.