Preparation and characterization of activated carbon from pumpkin peel using zinc chloride and investigation of its efficiency in the removal of ciprofloxacin from aqueous solutions

Due to global industrialization, population growth, and the expansion of economic activities, the demand for clean water has significantly increased (Das, 2025). As water use and demand rise, the availability of clean water is decreasing due to pollution and other factors (Boretti et al., 2019). Pollution in aquatic ecosystems is increasingly driven by intense human activities, including the chemical, textile, metallurgical, and mining industries, agricultural practices, and the widespread use of non-biodegradable materials, industrial colors, cosmetics, pharmaceuticals, and pesticides (Al-Buriahi et al., 2022; Pascariu et al., 2020; Pltonykova et al., 2020). The growing production and consumption of such pollutants have further degraded water quality. Once introduced into the ecosystem, these pollutants can cause enzymatic, hormonal, and genetic disruptions in humans (Malakootian et al., 2021). Antibiotics are extensively used in human medicine and veterinary applications to combat bacterial infections, and more recently, they have been employed in cancer therapies (Nguyen et al., 2022; Chandrasekaran et al., 2020). Furthermore, it is predicted that 50% to 90% of antibiotics administered to humans and animals are excreted via feces and urine into the sewage system without undergoing metabolic transformation in the body (Abolghasemi et al., 2025). However, when not effectively degraded or removed from wastewater, they pose a significant ecological threat, with residues infiltrating groundwater, surface water, and even drinking water sources (Igwegbe et al., 2021). Ciprofloxacin (CIP) is a widely used fluoroquinolone antibiotic prescribed for the treatment of various infections (Zhang et al., 2017; Rehman et al., 2019; Thai et al., 2023). It enters aquatic environments through hospital effluents, animal farm runoff, domestic wastewater, and pharmaceutical manufacturing discharges. Approximately 50% of administered CIP is excreted unmetabolized by humans (Peñafiel et al., 2021). Therefore, its effective removal from wastewater is critical to mitigating its adverse effects on ecosystems and human health (Carabineiro et al., 2011; Igwegbe et al., 2021). Among the available treatment technologies, adsorption stands out as a simple, ecologically sustainable, and economical approach for wastewater purification (Rashid et al., 2021). In this context, commercial activated carbon is commonly used as an adsorbent for the removal of pharmaceutical residues (Silva et al., 2018). The use of agricultural and industrial wastes as precursors for activated carbon production offers significant economic and environmental advantages (Costa et al., 2021). Although activated carbon is widely applied in industrial wastewater treatment, its recovery from aqueous media is often challenging and may result in secondary pollution. Issues such as filter clogging further hinder its large-scale applications (Moosavi et al., 2020). Magnetic separation technology presents a promising alternative to overcome these limitations. Magnetic activated carbon can be efficiently separated from aqueous solutions under an external magnetic field, facilitating adsorbent recovery and reducing operational complications (Jiang et al., 2021). A review of the literature indicates that magnetic activated carbon has considerable potential, particularly in the treatment of hospital and pharmaceutical industry effluents. The reusability of the material due to its magnetic properties enhances the overall cost-effectiveness of the system. These advantages render the method a viable alternative to conventional water treatment techniques (Li et al., 2024). In the Sakarya region, pumpkin (Cucurbita spp.) is commonly cultivated and traditionally used in desserts. However, its peels are typically discarded as waste. The production of activated carbon from such plant-based waste offers a dual benefit-effective waste management and pharmaceutical pollutant removal from water. In this study, pumpkin peels were converted into activated carbon (PPAC) using zinc chloride for the first time. Subsequently, magnetic properties were imparted to the material to produce magnetic activated carbon (PPMAC), which was then employed for the removal of ciprofloxacin (CIP) from aqueous medium. The synthesized PPAC and PPMAC were characterized using BET surface area analysis, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD). Characterization results revealed that the surface areas of PPAC and PPMAC were found to be 946.4 m²/g and 798.0 m²/g, respectively. It can be said that the surface areas of the produced activated carbons are large. According to the literature, typical activated carbons exhibit surface areas ranging between 500–1500 m²/g (Gupta, 2009). Such surface areas enhance adsorption efficiency, especially for removing pharmaceuticals and heavy metals from aqueous solutions. Moreover, elemental analysis confirmed the presence of carbon (C) in both PPAC and PPMAC, along with Fe and Co in PPMAC. Batch adsorption studies were utilized to evaluate the performance of PPMAC in CIP removal. CIP concentrations in aqueous solutions were determined using UV-Vis spectrophotometry. Effective parameters such as solution pH (3.0–10.0), contact time (60–1440 min), initial CIP concentration (10–150 mg/L), and PPMAC dosage (25–100 mg) were systematically varied. The adsorption efficiency was found to be pH-dependent, with optimal performance under neutral to mildly basic conditions. CIP removal increased with prolonged contact time, reaching maximum efficiency at 1440 min. Higher initial CIP concentrations led to greater adsorption of CIP per gram of PPMAC, and percent removal efficiency positively correlated with the PPMAC dosage. Adsorption kinetics of CIP onto PPMAC agreed with a pseudo-second-order model, suggesting that chemisorption was the dominant process. Among the adsorption isotherms tested, the Langmuir model exhibited a better fit, suggesting monolayer adsorption on a homogeneous surface. The maximum CIP adsorption capacity (qmax) of PPMAC calculated from the Langmuir model was 69.9 mg/g. In conclusion, the conversion of pumpkin peel-based waste into magnetic activated carbon provides a sustainable and cost-effective solution for wastewater treatment. The PPMAC derived from pumpkin peels with the magnetic properties easily separated from aqueous resulting strong potential for the removal of ciprofloxacin from waters. Its high adsorption capacity and ease of separation make it a promising alternative to conventional adsorbents in environmental remediation applications.