Poly(vinyl alcohol) electrospun nanofibrous membrane modified with spirolactam–rhodamine derivatives for visible detection and removal of metal ions

Abstract

Poly(vinyl alcohol) electrospun nanofibrous (PVANF) membranes that could sensitively detect and adsorb metal ions were modified with spirolactam–rhodamineine derivatives (PVANF–SRD) membranes and sulfo-spirolactam–rhodamine derivatives (PVANF–SSRD) membranes. Surface chemistry and morphology during functionalization of PVANF membranes were monitored using Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). These two membranes could display real-time sensing by the naked eye based on ring-opening reaction of spirolactam–rhodamine derivatives induced by corresponding metals. PVANF–SRD and PVANF–SSRD membranes exhibited high selectivity and sensitivity toward Fe³⁺/Cr³⁺ and Hg²⁺, respectively. In terms of PVANF–SSRD membranes, adsorption capacity for Hg²⁺ in contaminated water was studied. Freundlich isotherm could better describe the interactions than Langmuir: K_f = 7.0175 mg g⁻¹ (r² = 0.9996) for Hg²⁺. The regenerability of these two membranes was investigated via Na₄EDTA solution treatment, and results demonstrated good sustainability in detection and adsorption efficiency.