Introduction
The increasing presence of pharmaceutical contaminants, particularly antibiotics such as ciprofloxacin (CIP) and sulfamethoxazole (SMX), in aquatic environments has raised serious environmental and public health concerns. Conventional wastewater treatment systems are often ineffective at completely removing these persistent compounds, leading to antibiotic resistance and ecological toxicity. In this context, adsorption using biochar derived from waste biomass has emerged as a sustainable and cost-effective remediation strategy. This study focuses on a comparative evaluation of CO₂-activated biochars produced from leather tannery waste (ABT) and Sargassum brown macroalgae (ABS) for the efficient removal of CIP and SMX from water, emphasizing their physicochemical properties, adsorption performance, and reusability.
Physicochemical Characteristics of ABT and ABS Biochars
Detailed material characterization revealed significant differences between the two biochars. N₂ physisorption analysis showed that ABS possesses a remarkably higher Langmuir surface area and a hierarchical micro–mesoporous structure, facilitating enhanced mass transfer. In contrast, ABT exhibited a lower surface area with predominantly microporous characteristics. CHNS elemental analysis and FTIR spectroscopy confirmed the presence of nitrogen-, oxygen-, and sulfur-containing functional groups on both materials, which play a critical role in enhancing surface polarity, chemical reactivity, and affinity toward antibiotic molecules.
Adsorption Isotherm Behavior and Capacity Comparison
Adsorption equilibrium data for both CIP and SMX fitted well with the Langmuir isotherm model, indicating monolayer adsorption on homogeneous active sites. ABS demonstrated significantly higher maximum adsorption capacities for both antibiotics compared to ABT, highlighting the advantage of its higher surface area and pore accessibility. The superior performance of ABS suggests that pore structure and surface chemistry synergistically influence antibiotic uptake, making macroalgae-derived biochar a more efficient adsorbent for aqueous pharmaceutical pollutants.
Adsorption Kinetics and Mechanistic Insights
Kinetic studies revealed that the adsorption of CIP and SMX onto both biochars followed a pseudo-second-order model with excellent correlation coefficients, suggesting that chemisorption is the rate-limiting step. ABS showed faster adsorption rates than ABT, attributed to its mesoporous structure, which reduces diffusion resistance and allows rapid access to active sites. The adsorption mechanism is governed by a combination of electrostatic attraction, hydrogen bonding, ฯ–ฯ interactions, and pore-filling effects.
Effect of pH and Surface Charge Interactions
The adsorption performance of both biochars was strongly influenced by solution pH, which affects antibiotic speciation and surface charge characteristics. The point of zero charge (pHPZC) differed between ABT and ABS, leading to distinct electrostatic interaction regimes. Below or above the pHPZC, electrostatic attraction or repulsion between the biochar surface and antibiotic molecules significantly altered removal efficiency. Non-electrostatic interactions, such as hydrophobic and ฯ–ฯ interactions, also contributed to adsorption across a wide pH range.
Reusability, Stability, and Environmental Implications
Reusability tests over eight adsorption–desorption cycles demonstrated that ABS maintained more than 75% removal efficiency for both antibiotics, whereas ABT showed a gradual decline. This superior stability underscores the structural robustness and regeneration potential of ABS. Overall, the findings highlight the promise of Sargassum-derived CO₂-activated biochar as a sustainable, high-performance adsorbent for antibiotic-contaminated water, offering a value-added pathway for marine biomass waste utilization in environmental remediation.
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Hashtags:
#AntibioticRemoval, #BiocharAdsorption, #Ciprofloxacin, #Sulfamethoxazole, #WaterTreatment, #EnvironmentalRemediation, #SustainableMaterials, #WasteDerivedBiochar, #LeatherTanneryWaste, #SargassumAlgae, #CO2Activation, #AdsorptionIsotherms, #AdsorptionKinetics, #EmergingContaminants, #PharmaceuticalPollution, #CircularEconomy, #GreenTechnology, #WastewaterTreatment, #EnvironmentalEngineering, #CleanWater
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