Electrospun PVA/Co3O4 Nanofibers: A Sustainable Catalyst for Peroxymonosulfate-Mediated Degradation of Tetracycline

Abstract

This study develops a poly-(vinyl alcohol) (PVA) nanofiber incorporated with cobalt oxide (Co₃O₄) for catalytic degradation of antibiotics using peroxymonosulfate (PMS) to generate sulfate radical (SO₄ ^•-) (E° = 2.5-3.1 V vs NHE). These radicals efficiently degrade tetracycline through selective oxidation, offering advantages over conventional hydroxyl radical-based processes. The nanofiber fabrication involved electrospinning of PVA (8% w/v) containing cobalt oxide suspension (5 g L^-1) and citric acid (15% w/w polymer). Thermal cross-linking at 160 °C for 2 h enhanced the material's aqueous stability and mechanical properties. Scanning electron microscopy revealed uniform fibers (627-645 nm diameter), while X-ray diffraction, thermal analyses, and spectroscopy confirmed increased crystallinity in PVA/Co₃O₄ composites. Optimization studies through factorial design identified pH and PMS concentration as key parameters, achieving 60% tetracycline degradation within 60 min. The successful integration of Co₃O₄ into biodegradable PVA nanofibers presents a sustainable, cost-effective approach for water treatment applications, particularly targeting emerging pharmaceutical contaminants.

1

Images obtained by scanning electron microscopy (SEM) of electrospun nonwovens of PVA (A) and PVA/Co₃O₄ (B) at 15,000× magnification, with the average fiber diameter represented in the histogram, respectively (C,D).

2

Fourier-transform infrared (FTIR) spectra using the ATR module of nonwoven fabrics of poly­(vinyl alcohol) (PVA) and PVA/Co₃O₄, both reticulated with citric acid.

3

X-ray diffractograms (XRD) for PVA and PVA/Co₃O₄ electrospun nonwovens, both reticulated with citric acid.

4

(a) Thermogravimetric analysis (TGA) curves and (b) derivative thermogravimetric analysis (DTG) curves of poly­(vinyl alcohol) nonwovens (PVA), and poly­(vinyl alcohol) incorporated with a 10% (v/v) cobalt oxide suspension nonwovens (PVA/Co₃O₄).

5

Differential scanning calorimetry (DSC) analysis of poly­(vinyl alcohol) nonwoven (PVA) and poly­(vinyl alcohol) incorporated with cobalt oxide nonwoven material (PVA/Co₃O₄).

6

Stress–strain curves for PVA and PVA/Co₃O₄ nonwoven fabrics.

7

Graph of (final pHinitial pH) versus initial pH for the determination of pH_pzc (point of zero charge): (a) for PVA and (b) for PVA/Co₃O₄.

8

Degradation of TC versus treatment time for: (−■−) PVA/Co₃O₄ in the presence of PMS and (−▲−) without PMS; (−●−) just PMS, and (−▼−) PVA in the presence of PMS. Conditions:16.8 mg L^–1 TC solution, pH 6, [PMS] = 1.1 mmol L^–1, under constant stirring.

9

Pareto chart relating the significance of the variables pH and PMS concentration in the % degradation of tetracycline using nonwoven poly­(vinyl alcohol) incorporated with cobalt oxide (PVA/Co₃O₄). Conditions: 16.8 mg L^–1 TC solution, under constant stirring.

10

Influence of scavengers on the degradation of tetracycline hydrochloride by the PVA/Co₃O₄ + PMS system using sodium azide (SA), methyl alcohol (MeOH), and tert-butyl alcohol (TBA) in the proportion of 50 × [PMS] = 5.6 × 10^–2 mol L^–1. Conditions: 16.8 mg L^–1 TC solution, pH 9, [PMS] = 0.567 mmol L^–1, under constant stirring.

11

A proposed mechanism for the system containing the electrospun PVA/Co₃O₄ nanomaterial activating PMS to generate reactive species via radical (^•OH and SO₄ ^•–) and nonradical (¹O₂) pathways for tetracycline (TC) degradation.

12

Reusability analysis of the PVA/Co₃O₄ nanomaterial showing TC degradation efficiency over five consecutive degradation cycles. Conditions: 16.8 mg L^–1 TC solution, pH 9, [PMS] = 0.567 mmol L^–1, under constant stirring.