Onion peel derived carbon nanoparticles incorporated polysulfone membranes: enhanced dye removal from water†

Abstract

The ongoing discharge of hazardous dyes from industrial processes has intensified global water pollution, posing serious threats to aquatic ecosystems and human health. Addressing this challenge, our study explores the potential of bio-based carbon nanomaterials (CNM), synthesized from onion peel biowaste and designated as ON11, as effective agents in dye removal. These CNMs were incorporated into a mixed matrix membrane (MMM), using polysulfone (PSU) as the membrane substrate, to enhance dye adsorption. The CNM synthesis was achieved through a simple, eco-friendly process. We examined their impact on adsorption efficiency by introducing ON11 nanoparticles at varying concentrations into the PSU membrane (ON11@PSU). This CNM-embedded membrane structure offers a solution to challenges associated with the large-scale application of nanomaterials, particularly by minimizing leaching into water and improving durability. The ON11 and ON11@PSU membranes were characterized using various techniques, including SEM, Raman spectroscopy, XRD, optical profilometer, and FTIR, to confirm their behavior, morphology, and structural integrity. The surface area of ON11 was 423.26 m² g⁻¹, with BJH average pore diameter of 4.5 nm and BET pore volume of 0.26 cm³ g⁻¹. ON11 nanoparticles were adsorptive in nature, and their utility in membrane adsorption is explored. The influence of parameters, including contact time, dye concentration, membrane thickness, pH, and adsorbent dosage, was systematically evaluated to optimize the dye adsorption efficiency of the ON11@PSU membrane pad. It was observed that the thickness of the 60 μm membrane (S_a = 2.170 μm and S_q = 2.75 μm) showed higher removal efficiency for all the selected dyes than the other thicknesses at the native pH itself. The MMM demonstrated its effectiveness as an adsorbent membrane, achieving maximum removal efficiencies of approximately 98% for MG dye, 92% for RhB dye, and 67% for MB dye. The negative zeta potential of adsorptive membranes enabled the electrostatic attraction of positively charged dyes, enhancing adsorption capacity. The findings contribute to developing sustainable and effective membrane utility as adsorbents, opening avenues for the effective use of agricultural waste products in environmental remediation applications.