Key Takeaways & Executive Findings
- •• • Under optimized conditions (50 mmol·L−1 Na2SO4, 1.67 mA·cm−2, pH 2), sulfathiazole removal reached 95.7% with 76.7% TOC removal, demonstrating near-complete degradation and significant mineralization, critical for reducing antibiotic resistance in wastewater effluents. • • The BiVO4/TiO2 heterostructure exhibited a bandgap of 2.12 eV and a valence band edge at 2.775 V vs. RHE, enabling efficient generation of ·OH, 1O2, and SO4−· radicals under visible light, which is essential for oxidizing recalcitrant sulfonamide structures. • • Removal efficiencies varied from 52.0% (sulfaguanidine) to 95.7% (sulfathiazole), indicating that molecular structure—particularly electron-donating groups like guanidine—affects degradation kinetics, guiding targeted design of treatment processes. • • The system maintained high stability and catalytic efficiency across acidic and alkaline conditions, suggesting operational robustness for real-world wastewater treatment, where pH fluctuations are common.
Abstract
The photoelectrocatalytic degradation of seven sulfonamide antibiotics—sulfathiazole (STZ), sulfadiazine (SDZ), sulfisoxazole (SIA), sulfamethoxazole (SMZ), sulfapyridine (SPD), sulfadimidine (SMT), and sulfaguanidine (SG)—was investigated using a bismuth vanadate-loaded titanium dioxide array (BiVO4/TiO2) as the anode under visible light irradiation. Systematic evaluation of BiVO4 loading, solution pH, current density, electrolyte type, and electrolyte concentration revealed optimal conditions of 50 mmol·L−1 Na2SO4, a current density of 1.67 mA·cm−2, and pH 2. Under these conditions, STZ removal and total organic carbon (TOC) removal reached 95.7% and 76.7%, respectively. Removal efficiencies for SDZ, SIA, SMZ, SPD, SMT, and SG were 94.9%, 80.9%, 79.1%, 57.7%, 52.3%, and 52.0%, with TOC removal ranging from 50% to 76.7%. Quenching experiments and electron paramagnetic resonance (EPR) identified hydroxyl radicals (·OH), singlet oxygen (1O2), and sulfate radicals (SO4−·) as dominant reactive species. The BiVO4/TiO2 composite exhibited a valence band edge at EVB = 2.775 V vs. RHE, enabling oxidation of H2O, OH−, and SO4^2− to generate these radicals. The heterostructure narrowed the bandgap to 2.12 eV and enhanced visible light response, facilitating efficient charge separation and transfer. Degradation pathways involved oxidation of aniline moieties to nitro groups, followed by hydroxylation and cleavage of S–N, N–C, or S–C bonds, ultimately mineralizing to CO2, H2O, SO4^2−, and NO3−. The system demonstrated high stability and catalytic efficiency across acidic and alkaline conditions, offering a promising approach for antibiotic removal from environmental waters.
1. Introduction
Conventional water treatment technologies, including adsorption and biological degradation, often fail to completely remove sulfonamide antibiotics, leading to their persistence in aquatic environments and the proliferation of antibiotic resistance. Advanced oxidation processes (AOPs) such as photocatalysis offer potential, but pristine TiO2 suffers from wide bandgap (3.2 eV) limiting visible light utilization, while BiVO4 exhibits rapid charge carrier recombination, reducing quantum efficiency. These limitations have hindered practical application of photocatalytic degradation for antibiotic-laden wastewater.
This study addresses these bottlenecks by constructing a BiVO4/TiO2 heterojunction array anode, which synergistically combines the visible-light absorption of BiVO4 (bandgap ~2.4 eV) with the electron-transport properties of TiO2. The intimate interfacial contact facilitates charge separation, as evidenced by a narrowed bandgap of 2.12 eV and a positive valence band edge (2.775 V vs. RHE), enabling generation of highly oxidizing radicals. The photoelectrocatalytic system achieves high removal efficiencies (up to 95.7%) and mineralization (up to 76.7%) under mild conditions (low current density, neutral pH), demonstrating a robust and energy-efficient approach for sulfonamide degradation.
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HE Yuling, LI Na, ZHAO Rusong, NIU Hongyun, CAI Yaqi (2026). Photoelectrocatalytic Degradation of Sulfonamide Antibiotics Using BiVO4/TiO2 Array Anode. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025030404
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Frequently Asked Questions
What is the long-term operational stability of the BiVO4/TiO2 anode under continuous flow conditions, and how does it withstand fouling or deactivation?
The study reports high stability and catalytic efficiency across acidic and alkaline conditions, but long-term continuous operation data are not provided. The system's robustness suggests potential for repeated use, but fouling from organic intermediates or inorganic precipitates could reduce performance over extended periods. Further studies are needed to assess longevity and regeneration protocols.
How does the energy consumption of this photoelectrocatalytic system compare to conventional AOPs like UV/H2O2 or ozonation for sulfonamide removal?
The system operates at a low current density of 1.67 mA·cm−2, which implies relatively low electrical energy input. However, a direct comparison of electrical energy per order (EE/O) or total cost with UV/H2O2 or ozonation is not provided. The visible light activation reduces energy demand compared to UV-based processes, but the need for electrolyte (Na2SO4) and pH adjustment adds chemical costs. A techno-economic analysis is required for definitive comparison.
What are the degradation intermediates and their potential toxicity? Are the final products completely mineralized or are there persistent byproducts?
The study identified that aniline moieties are oxidized to nitro groups, followed by hydroxylation and cleavage of S–N, N–C, or S–C bonds, ultimately mineralizing to CO2, H2O, SO4^2−, and NO3−. TOC removal ranged from 50% to 76.7%, indicating incomplete mineralization for some compounds. The residual organic intermediates may pose toxicity risks, but specific intermediate identification and toxicity assays were not reported. Further analysis is needed to ensure complete detoxification.
How scalable is this electrode fabrication process for industrial-scale wastewater treatment? What are the costs and challenges in producing large-area BiVO4/TiO2 arrays?
The fabrication involves loading BiVO4 onto TiO2 arrays, likely via solvothermal or electrodeposition methods, which can be scaled using roll-to-roll or large-area coating techniques. However, uniformity and adhesion over large areas are challenging. The cost of bismuth and vanadium precursors, as well as the need for conductive substrates, may be significant. The study does not provide cost estimates, but the low current density and visible light operation could offset energy costs. Pilot-scale studies are necessary to evaluate economic feasibility.
What is the effect of real water matrices (e.g., natural organic matter, chloride ions) on the degradation efficiency and radical generation?
The study used a simple Na2SO4 electrolyte and controlled pH. Real wastewater contains various ions and organic matter that can scavenge radicals or compete for active sites. For instance, chloride ions can react with ·OH to form less reactive chlorine radicals, while NOM can absorb UV/visible light and quench radicals. The system's performance in complex matrices is unknown. Future studies should test with real wastewater to evaluate practical applicability.
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