Green Synthesis of MnO₂ Nanoparticles on Eggshell Membrane for Rapid Tetracycline Decontamination

Abstract

Leveraging the abundant reticular proteins and reducing functional groups in eggshell membrane (ESM), we have developed a single‑step, green route to synthesize manganese dioxide (MnO₂) nanoparticles from potassium permanganate. In this process, ESM simultaneously serves as a template and reductant, eliminating harsh conditions, complex post‑treatments, and the need for centrifugation or filtration. The resulting MnO₂ NPs/ESM composite exhibits uniform nanoparticle coverage and a loading of 2.88 % MnO₂. When applied to tetracycline hydrochloride (TCH) decontamination, 72.27 % of 50 mg L⁻¹ TCH is removed in 20 min, and the removal efficiency reaches 83.10 % after 60 min under buffered conditions (pH 3.0). Kinetic analysis confirms a pseudo‑second‑order degradation pathway, underscoring the practical potential of this nano‑material for wastewater remediation.

Background

Pharmaceuticals and personal care products (PPCPs), especially antibiotics such as tetracyclines, persist in aquatic environments, posing ecological and health risks. Conventional treatment methods struggle to fully degrade these compounds. MnO₂ nanoparticles have emerged as promising oxidants due to their high surface area, tunable structure, and eco‑friendly nature. However, typical MnO₂‑based decontamination processes require complex separation steps, limiting scalability.

Eggshell membrane, a protein‑rich by‑product, offers unique binding sites for metal ions and has been successfully employed as a biotemplate for noble metal and metal‑oxide nanoparticles. Its fibrous network and abundant –OH, –NH₂, and –SH groups provide both a scaffold and a reducing environment.

Materials and Methods

Reagents and Apparatus

All chemicals were analytical grade. Deionized water (18.2 MΩ cm⁻¹) was used throughout. ESM was extracted from fresh eggshells, washed, and dried at room temperature. Potassium permanganate (KMnO₄, 1 mmol L⁻¹) served as the Mn source.

Synthesis of MnO₂ NPs/ESM

Five‑milligram ESM slices were immersed in 20 mL KMnO₄ solution and stirred at room temperature for 35 min. The color change from purple to light brown, along with a gradual pH rise, confirmed MnO₂ formation. After rinsing with water, the membranes were dried and stored for further use.

TCH Decontamination Procedure

In a 15 mL solution of 50 mg L⁻¹ TCH (PBS, pH 3.0), 20 ESM slices were added and stirred for 60 min. UV–vis spectra were recorded at 358 nm to quantify residual TCH. Removal efficiency was calculated as R = (1 – C/C₀) × 100 %.

Results and Discussion

Characterization of MnO₂ NPs/ESM

SEM images reveal a multilayered fibrous network uniformly coated with ~5 nm spherical nanoparticles. TEM confirms the particle size and a lattice spacing of 2.5 Å, matching the (400) plane of α‑MnO₂. XPS shows Mn²⁺ oxidation state with characteristic Mn 2p and O 1s peaks. Thermogravimetric analysis indicates a 2.88 % MnO₂ loading. The composite’s easy recovery by simple membrane removal highlights its operational advantage.

TCH Decontamination Performance

Under buffered conditions (pH 3.0), the composite achieved 72.27 % removal in 20 min and 83.10 % after 60 min. Without buffer, removal was 78.37 % at 60 min, with a faster initial rate but slower overall progress due to pH rise during degradation. The process follows a pseudo‑second‑order kinetic model, indicating surface‑mediated oxidative degradation.

Comparison with Commercial MnO₂

Compared to commercial MnO₂ powder, MnO₂ NPs/ESM delivered 15–20 % higher removal efficiency under identical conditions, while avoiding the need for centrifugation or filtration.

Conclusions

We demonstrate a facile, green synthesis of MnO₂ nanoparticles on eggshell membrane that achieves efficient tetracycline decontamination with rapid, straightforward recovery. This approach offers a scalable, low‑cost solution for PPCP removal from wastewater.