Ultrasonic-assisted adsorption of methylene blue using shrimp shells as a low-cost adsorbent: Evaluation on the adsorption isotherm, kinetics, and thermodynamics

Abstract

Methylene blue is a synthetic dye that widely used in various industries. However, its presence in wastewater negatively affects the environment, human health, and aquatic life. Adsorption is recognized as an effective and economical method for removing methylene blue from wastewater. Calcium-based adsorbents such as shrimp shell waste can be used for this purpose. Furthermore, the adsorption process can be intensified using ultrasonic waves. This study aimed to prepare, characterize, and apply shrimp shell-based adsorbents for ultrasonic-assisted methylene blue adsorption. Adsorbents were prepared using three different methods (coded by A1, A2, and A3) to study their effects on the characteristics and performance of methylene blue adsorption. The adsorption process was also performed by varying the solution pH, adsorbent mass, adsorption time, adsorption temperature, and initial methylene blue concentration. The results indicated that the preparation method significantly influenced the characteristics of each adsorbent, as validated by Scanning Electron Microscope-Energy Dispersive X-Ray Spectroscopy, Fourier Transform InfraRed, Particle Size Analyzer, and Surface Area Analyzer. Under optimal conditions, A2 and A3 exhibited the highest methylene blue removal rates, reaching 99.771 % and 99,820 %, respectively. The adsorption isotherm study shows that methylene blue adsorption onto A1 follows the Freundlich model, whereas onto A2 and A3 followed the Langmuir model. The adsorption kinetics study revealed that the experimental data for all three adsorbents conformed well to the Pseudo-Second Order model, with R² values ranging from 0.99998 to 1.0000. Finally, the thermodynamic assessment demonstrated that ultrasonic-assisted MB adsorption with the three adsorbents was spontaneous, with ΔG° values of -1,542, -10,669, and -10,680 kJ/mol, ΔS° values of 62.845, 150.900, and 162.260 kJ/mol.K, and ΔH° values of 17,347, 35,088, and 38,339 kJ/mol for A1, A2, and A3, respectively.