Enhanced removal of amoxicillin from synthetic wastewater using surface-modified carbon nanotubes: Synthesis, characterization, and process optimization

Amoxicillin (AMX), a widely used β-lactam antibiotic, is a persistent water contaminant that is only partially removed by conventional wastewater treatment processes. This study investigates acid-functionalized carbon nanotubes (FNPs) as adsorbents for AMX removal from synthetic pharmaceutical wastewater. Carbon nanotubes (CNTs) were synthesized on potassium hydroxide-activated powdered activated carbon via chemical vapor deposition and subsequently functionalized with a sulfuric and nitric acid mixture (3:1 v/v) to introduce oxygen-containing surface groups. Characterization by FTIR, XRD, SEM, and TGA confirmed successful CNTs synthesis, graphitic crystallinity, enrichment with oxygenated surface groups, and adequate thermal stability. The effects of solution pH, temperature, adsorbent dosage, contact time, and stirring speed were systematically evaluated, and response surface methodology (RSM) was applied to optimize operating conditions. Adsorption capacity increased with temperature and decreased with increasing pH, while stirring speed had minimal influence. A maximum adsorption capacity of 357.14 mg/g was achieved at 500 ppm AMX under optimized conditions of pH 2, 50°C, 6 h, and 1.5 g/L adsorbent dosage; and 250 mg/g was obtained at 100 ppm under pH 2, 50°C, and 5 h. Pseudo-second-order kinetics (R² = 0.9929) and the Langmuir isotherm provided the best fit to experimental data, and thermodynamic analysis confirmed endothermic and spontaneous adsorption consistent with chemisorption. Sodium hydroxide was identified as the most effective desorption agent; moderate capacity retention with a progressive decline was observed over two adsorption–desorption cycles, indicating the need for further regeneration protocol optimization.

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