Sustainable synthesis of CQD-modified ZIF-8 from sago hampas for improved methylene blue dye removal

Abstract

High levels of synthetic dyes like methylene blue (MB) in aquatic ecosystems threaten both environmental stability and human health. This research investigates MB adsorption using a composite material known as Carbon Quantum Dots/Zeolitic Imidazole Framework-8 (CQDs/ZIF-8). The composite was made via hydrothermal synthesis from sago waste and then modified with impregnation. To understand its properties, the composite was analyzed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Ultraviolet-Visible Spectroscopy (UV-Vis). The composite adsorbed MB was observed by changing factors such as initial dye concentration, amount of adsorbent, solution pH, and contact time. Various models were used to analyze the data including linear and non-linear isotherm models (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich) and kinetic models (Pseudo-First-Order, Pseudo-Second-Order, Elovich). Model accuracy was analyzed using the coefficient of determination and error analysis. The best removal rates were 88.60% at pH 10, 91.56% at 5 ppm MB concentration, 93.20% after 80 min, and 82.64% with 30 mg of adsorbent. The non-linear Freundlich isotherm and pseudo-second-order kinetic model fit the data best, with a very high correlation (R2 = 0.9993). Non-linear models are better suited for predicting how adsorption works compared to linear ones.