Comparison of Co-amoxiclav Removal from Aqueous Solutions Using <i>Spirulina</i> platensis Microalgae and Manganese Molybdate-Modified <i>Spirulina</i> Biochar

Abstract

Background: The release of antibiotics into aquatic environments, particularly co-amoxiclav, poses a serious threat to ecosystem integrity and human health. Therefore, developing efficient bio-based adsorbents to remove these persistent compounds is critically important. Objectives: The primary objective of this study was to compare the removal of co-amoxiclav from aqueous solutions using Spirulina platensis microalgae and manganese molybdate-modified Spirulina biochar. Methods: In this study, three adsorbents were evaluated: live Spirulina platensis, biochar derived from Spirulina, and biochar modified with MnMoO4 nanostructures. The modified biochar was synthesized by the controlled precipitation of MnMoO4 onto the biochar surface. The adsorbents were characterized using Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM). Batch adsorption experiments (n = 90) were conducted under varying pH values (3 - 11), contact times (10 - 240 min), and initial co-amoxiclav concentrations (5 - 100 mg/L). Residual co-amoxiclav concentrations were determined using UV-visible (UV-vis) spectrophotometry. Results: BET analysis showed that the modification increased the biochar’s specific surface area (185.4 m2/g), pore volume (0.238 cm3/g), and average pore diameter (5.14 nm). FTIR and XRD confirmed the formation of stable metal–oxygen bonds and the crystalline MnMoO4 phase. FE-SEM images revealed increased surface roughness and the formation of rod-like and flower-like nanoparticle morphologies. At approximately neutral pH, the highest removal efficiencies were observed: 84% for MnMoO4-modified biochar, 76% for raw biochar, and 64% for live Spirulina. The time-dependent decrease in co-amoxiclav concentration indicated a multistep uptake mechanism involving surface adsorption, electrostatic interactions, metal complexation, and π–π interactions. Conclusions: MnMoO4-modified Spirulina biochar can be considered an efficient, stable, and promising adsorbent for advanced treatment of pharmaceutical wastewater containing co-amoxiclav.