Acid-salt-modified natural zeolite as a highly efficient adsorbent for pharmaceuticals from contaminated water

Acetaminophen (ACT), commonly known as paracetamol, is a widely used nonprescription analgesic and antipyretic. However, its extensive presence in aquatic resources poses a significant threat to aquatic organisms because of its toxic characteristics. In this study, the removal of ACT using acid-salt modified Philippines natural zeolite (ASMPNZ) was investigated. ASMPNZ was chemically modified with nitric acid and sodium chloride. The morphological structure and functional groups of ASMPNZ were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The central composite design (CCD) of the response surface methodology (RSM) was used to determine the optimum values of parameters. The optimum conditions, 0.40 g of ASMPNZ, 60 min of reaction time, and pH 2, achieved a maximum removal efficiency of 94.3 % of ACT removal. These optimum values of parameters were validated by conducting an actual experiment, and the result showed that the removal efficiency (93.9 %) is within the 95 % confidence interval. The Langmuir isotherm model suggests that ACT adsorption onto ASMPNZ follows monolayer coverage on a homogenous surface. Kinetic studies revealed that the pseudo-second order model provided the best fit, indicating chemisorption as the prevalent adsorption mechanism. This study demonstrates that ASMPNZ is an efficient adsorbent for the removal of ACT-contaminated water and offers a promising solution for mitigating pharmaceutical pollution in aquatic environments. Unlike prior studies that rely on single-step zeolite modification, we investigate a low-cost Philippine natural zeolite sequentially modified by acid and salt and, via RSM-guided optimization with experimental validation, achieve high ACT removal (94 % at 0.40 g, 60 min, pH 2; qmax = 237.5 mg/g) while elucidating a Langmuir monolayer, pseudo-second-order chemisorption mechanism.