Mechanistic Modeling of pH-Dependent Adsorption of Methylene Blue on Thermally Stabilized Electrospun Polyvinyl Alcohol Membranes Containing Clinoptilolite

Abstract Synthetic dyes such as methylene blue are persistent pollutants in textile effluents, posing environmental and health risks due to their toxicity and low biodegradability. In this work, electrospun polyvinyl alcohol membranes containing natural clinoptilolite (0, 1, 3, and 5 wt%) were thermally stabilized and applied for methylene blue adsorption. Multi-technique characterization (scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and mechanical testing) confirmed the successful incorporation of clinoptilolite and its effects on membrane structure, composition, and physicochemical properties. Adsorption studies showed that the membrane containing 5 wt% clinoptilolite achieved the highest removal efficiency (32.39%). Equilibrium data were well described by the Langmuir model (r 2 = 0.88–0.97), yielding maximum adsorption capacities of 5.22, 3.36, and 6.08 mg·g − 1 at pH 4, 7, and 9, respectively. Electrostatic attraction was the dominant mechanism at pH 9, supported by the membrane point of zero charge (pH 6.35) and dye speciation data. The mechanistic kinetic model proposed by Ferro Orozco successfully described pH-dependent adsorption (r 2 = 0.95–0.99), with the highest adsorption rate constant at pH 4 (54.60 mM − 1 ·h − 1 ) and maximum site density at pH 9 (0.019 mmol·g − 1 ). Model-based simulations evaluated the effects of adsorbent dose and contact time, revealing a nonlinear decrease in the time required to reach the discharge threshold with increasing dose. By integrating mechanistic modeling with this hybrid membrane system, this study provided predictive insight and supported the assessment of operational conditions for membrane-based wastewater treatment.