Plant-Powered Nanocatalyst Destroys Ciprofloxacin Antibiotic in Water with Sunlight

Ciprofloxacin, one of the world’s most widely prescribed fluoroquinolone antibiotics, has become a stubborn fixture of the global water cycle. Detected in surface waters, groundwater and even drinking water supplies at concentrations ranging from nanograms to micrograms per liter, the compound is chemically stable, poorly biodegradable and largely excreted unmetabolized by patients. Conventional wastewater treatment plants, designed to strip out organic matter and nutrients, are largely powerless against it. The consequences are not abstract: trace-level antibiotics are sufficient to select for resistant bacteria, disrupt aquatic microbial communities and inflict genotoxic damage on organisms downstream. Now, a research team led by scientists affiliated with Birjand University of Medical Sciences in Iran reports a plant-based route to a magnetic photocatalyst that can completely eliminate the drug from water under simulated sunlight, offering a greener answer to one of environmental chemistry’s most persistent problems.

The new material, described in the Journal of the Saudi Chemical Society, is a nanocomposite that marries two semiconductors with complementary talents: magnesium iron sulfide (MgFe2S4), a magnetic spinel sulfide with a narrow band gap, and cobalt bismuth oxyiodide (CoBiO2I), a layered bismuth-based semiconductor that absorbs visible light strongly. Individually, each material falls short. MgFe2S4 nanoparticles tend to aggregate, burying their active sites, and their photogenerated electrons and holes recombine too quickly to do much useful chemistry. CoBiO2I, meanwhile, suffers from photocorrosion, limited surface area and no magnetism at all, making it awkward to recover from treated water. Fused into a single heterostructure, the two phases overcome each other’s weaknesses, and the resulting core-shell architecture can be pulled out of solution with a simple external magnet.

What sets the study apart is not just the heterojunction but how it was made. Rather than relying on conventional hydrothermal or solvothermal chemistry, which typically demands energy-intensive conditions and toxic reducing agents such as hydrazine or sodium borohydride, the team turned to an extract of Capsella bursa-pastoris, common shepherd’s purse, collected in South Khorasan Province, Iran. Dried plant powder was extracted with methanol at room temperature over three days, yielding a dark-brown solid rich in flavonoids, tannins, alkaloids and amino acids. These phytochemicals act as biological mediators, reducing metal ions, capping growing nanoparticles and preventing the aggregation that plagues chemically synthesized counterparts. Although methanol extraction and high-temperature calcination at 700 degrees Celsius were still required, the researchers argue the route remains substantially more sustainable than conventional synthesis, and they identify replacing methanol with aqueous extraction and lowering the calcination temperature as priorities for future work.

Characterization confirmed the design worked as intended. X-ray diffraction revealed sharp spinel peaks for MgFe2S4 coexisting with new reflections from CoBiO2I, with no impurity phases, and a Scherrer-analysis crystallite size of roughly 13 nanometers. Infrared spectroscopy showed Mg-S and Fe-S bonds alongside Bi-O-I vibrations, with shifts in the hydroxyl bands hinting at hydrogen bonding across the interface. Field-emission scanning and transmission electron microscopy captured the striking morphology: roughly spherical magnetic cores wrapped in feather-like, interconnected CoBiO2I nanosheets forming a core-shell heterojunction. Energy-dispersive X-ray mapping showed all elements uniformly distributed, with the surface-dominated bismuth signal and weak magnesium and sulfur signals independently confirming the encapsulation of the magnetic core. Vibrating-sample magnetometry recorded saturation magnetization of 27.83 emu per gram for the composite, down from 68.05 for the bare spinel but more than enough for magnetic separation.

Optical measurements explained why the composite outperforms its parents. Diffuse reflectance spectroscopy gave band gaps of about 1.35 electronvolts for MgFe2S4 and 2.39 electronvolts for the composite, a slight blue shift the authors attribute to the formation of an S-scheme heterojunction. In this arrangement, Fermi-level equilibration between the two semiconductors bends their bands and creates an internal electric field that drives low-energy electrons in MgFe2S4 to recombine with low-energy holes in CoBiO2I, while preserving the high-energy electrons and holes that actually drive redox reactions. Photoluminescence spectroscopy provided the corroborating evidence: the composite’s emission intensity was markedly quenched relative to pure MgFe2S4, indicating sharply suppressed radiative recombination. A conductive carbonaceous residue derived from coke powder used during sulfidation appears to act as an electron shuttle, further extending the lifetime of photogenerated carriers.

Under a 500-watt xenon lamp with a visible-light cutoff, the composite delivered headline results. After optimizing pH, catalyst loading and reaction time, the team achieved complete, 100 percent degradation of ciprofloxacin within 200 minutes at pH 9 with 1 gram per liter of catalyst and an initial drug concentration of 20 milligrams per liter. That represents roughly a 35 percent improvement over the bare magnetic spinel, which managed only 65.29 percent under comparable conditions, while pure CoBiO2I peaked at about 71 percent. Degradation followed pseudo-first-order kinetics, with a rate constant of 0.0349 per minute at the optimized concentration, nearly ten times the 0.0036 per minute measured for MgFe2S4 alone. At lower pollutant concentrations of 5 milligrams per liter, the rate constant rose to 0.0654 per minute, reflecting the concentration dependence typical of surface-mediated photocatalysis.

Importantly, the team did not equate the disappearance of the drug’s UV-Vis absorption peak with true detoxification. Direct chemical oxygen demand and total organic carbon measurements, taken with a Shimadzu TOC-L analyzer and Hach colorimetric method, showed 79.03 percent COD removal and 54.23 percent TOC removal for the composite, compared with 41.91 and 31.81 percent for MgFe2S4. The gap between degradation and mineralization confirms the formation of intermediate organic compounds, a well-known feature of fluoroquinolone oxidation pathways, and the authors stress that TOC remains the gold-standard metric for judging whether antibiotic treatment genuinely destroys the pollutant rather than merely fragmenting it.

Radical scavenging experiments mapped the reaction mechanism. Adding isopropyl alcohol to trap hydroxyl radicals cut degradation to 53.47 percent, while EDTA, which captures photogenerated holes, reduced it to 61.37 percent, identifying hydroxyl radicals and holes as the dominant reactive species. Chloroform, a superoxide scavenger, lowered efficiency to 87.86 percent and potassium persulfate, an electron scavenger, barely dented it at 98.96 percent, marking electrons and superoxide as minor players. Mott-Schottky analysis placed the conduction band of MgFe2S4 at about minus 0.79 volts versus normal hydrogen electrode, negative enough to reduce oxygen to superoxide, while the valence band of CoBiO2I at 2.64 volts is positive enough to oxidize hydroxide into hydroxyl radicals, exactly the band alignment the S-scheme model predicts.

Practical durability rounded out the case. Across ten consecutive photocatalytic cycles, with the catalyst magnetically recovered, washed and reused each time, the composite retained 87.25 percent of its initial degradation efficiency, a loss the authors attribute to site blockage by by-products, gradual fouling and the wear of repeated washing. Replicate experiments showed a relative percent difference of just 0.30 percent, well within accepted precision thresholds. The authors acknowledge open questions, including whether near-neutral pH, more representative of real wastewater than the optimal alkaline pH 9, can deliver acceptable performance, and they note that direct verification of the S-scheme mechanism through high-resolution interfacial imaging and valence-band XPS was beyond their instrumental reach. They also flag the need to assess long-term metal leaching and the ecotoxicity of degradation intermediates before scale-up. Even so, the combination of complete degradation, strong mineralization, magnetic recyclability and a synthesis route that swaps hydrazine for shepherd’s purse marks the MgFe2S4/CoBiO2I heterojunction as one of the more compelling entries in the crowded field of visible-light photocatalysts for pharmaceutical pollution.

Subject of Research: Plant-extract-mediated synthesis of a magnetic MgFe2S4/CoBiO2I heterojunction photocatalyst for degrading the antibiotic ciprofloxacin in water

Article Title: Phytochemical-mediated design of magnetic MgFe2S4/CoBiO2I heterojunction for enhanced photocatalytic degradation of ciprofloxacin

Article References: Azqandi, M., Nasseh, N., Esmaeli-Nasrabadi, F., Kargar, M., Ahmadzadeh, S., Dolatabadi, M., & Jahanshahi, R. (2026). Phytochemical-mediated design of magnetic MgFe2S4/CoBiO2I heterojunction for enhanced photocatalytic degradation of ciprofloxacin. Journal of Saudi Chemical Society, 30(5), Article 68. https://doi.org/10.1007/s44442-026-00118-1

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00118-1

Keywords: photocatalysis, ciprofloxacin, MgFe2S4/CoBiO2I heterojunction, green synthesis, Capsella bursa-pastoris, antibiotic pollution, water treatment, magnetic recovery, S-scheme mechanism, visible light, mineralization, nanocomposite