The metals in question are among the most frequently detected pollutants in industrial wastewater. Lead and copper ions originate from mining, electroplating, battery manufacturing, and metallurgical processing, and even at trace concentrations they can trigger neurological, renal, and cardiovascular disorders in humans while accumulating in aquatic food chains. Conventional remediation techniques such as chemical precipitation, ion exchange, coagulation–flocculation, and activated carbon adsorption all carry drawbacks, including high operational costs, the generation of contaminated sludge, and poor performance at low metal concentrations. Membrane-based separation has emerged as an appealing alternative because of its operational simplicity, compact footprint, and potential for continuous treatment, but the performance of any membrane depends heavily on how it is made.

That is where the Brazilian team’s choice of fabrication method becomes significant. Most nanofiber membranes described in the literature are produced by electrospinning, a technique that draws fibers from a polymer solution using high voltage. Electrospinning produces excellent fibers but suffers from low production rates and high energy consumption, which have limited its industrial adoption. The researchers instead used solution blow spinning, or SBS, a technique that replaces the electric field with a stream of compressed air. In SBS, the polymer solution is fed through a concentric nozzle while pressurized air simultaneously stretches the emerging jet into fine fibers, which are collected on a rotating drum. The method requires no high-voltage equipment, offers higher throughput, and still yields highly porous micro- and nanofibrous mats, making it an attractive route to membranes that could one day be manufactured at scale.

To give the inherently hydrophobic PVDF an affinity for metal ions, the team dispersed montmorillonite clay into the polymer solution at loadings ranging from 3 to 30 percent by weight relative to the polymer. Montmorillonite is a layered silicate with a high specific surface area and a substantial cation exchange capacity. Its negatively charged interlayer spaces and surface hydroxyl groups attract divalent metal cations such as Pb²⁺ and Cu²⁺ through electrostatic interactions and ion exchange, effectively turning the clay particles scattered through the fibrous network into a dense population of active adsorption sites. The researchers fabricated two families of membranes: pristine PVDF nanofiber mats and PVDF–clay composites, keeping the solution volume constant at five milliliters for every production run so that thickness differences could be attributed to the clay content itself.

Scanning electron microscopy confirmed that the process worked as intended. The membranes displayed uniform, smooth, cylindrical fibers with only occasional bead-like imperfections, a sign that the spinning parameters—30 percent polymer concentration, a solution flow rate of 76 microliters per hour, air pressure of 140 kilopascals, a working distance of 21 centimeters, and a collector speed of 80 revolutions per minute—were well chosen. X-ray diffraction revealed the characteristic crystalline phases of PVDF alongside clay-derived peaks corresponding to quartz and aluminum oxide, confirming that the filler was genuinely incorporated into the fibers. At the highest loading of 30 percent, however, clay agglomerates began to appear, producing structural defects, thinner and more fragile films, and, above that threshold, outright clogging and failure of fiber formation.

Before testing adsorption, the team determined the point of zero charge of the membranes, the pH at which the surface carries equal numbers of positive and negative charges. This value came out at 6.9 in pure water and 6.4 in a water–ethanol mixture, and the adsorption experiments were conducted near these values to minimize interference from the liquid medium. Batch tests, in which membrane pieces of roughly 50 milligrams were stirred with 20 milliliters of metal solution at 5 milligrams per liter, showed a familiar pattern: rapid uptake in the first hours as abundant adsorption sites were available, followed by a gradual slowdown as those sites filled. Adsorption was consistently higher in the water–ethanol mixture, which the authors attribute to ethanol acting like a surfactant, lowering the surface tension of water and helping the solution wet the hydrophobic polymer and penetrate the spaces between fibers to reach buried clay sites.

The kinetic and equilibrium analysis told a coherent mechanistic story. A pseudo-first-order model fit the data poorly, with correlation coefficients as low as 0.674, whereas the pseudo-second-order model tracked the experiments closely in both media, indicating that the rate-limiting step involves chemical interaction—chemisorption—between the metal ions and functional sites on the clay surface. Equilibrium data were best described by the Langmuir isotherm, which assumes monolayer adsorption on a finite number of identical sites, and the calculated maximum adsorption capacities matched the experimental values well. The dimensionless separation factor derived from the Langmuir constant was below one in every test, confirming that adsorption of both metals is thermodynamically favorable. Still, the Langmuir constants were low, between 0.044 and 0.298, and more than half of the dissolved metal remained in solution at equilibrium in the static tests—a limitation the researchers trace directly to the hydrophobic PVDF matrix, which impedes ion access to clay sites in stagnant water.

The picture changed dramatically when the membranes were operated as filters. In dead-end filtration experiments, in which the metal solution was forced through a 12.5 square centimeter membrane area under roughly one bar of pressure from a vacuum pump, removal efficiencies soared above 90 percent, with the membrane containing 10 percent clay achieving 92 percent copper removal in aqueous medium. The lead removal performance matched that of comparable electrospun membranes reported in the literature, but with the advantage of a faster, cheaper production process. Even pure PVDF removed a meaningful fraction of the metals, demonstrating that the porous fibrous architecture itself contributes to capture. The combined mechanism—physical retention by the dense fiber network working in tandem with adsorption at clay sites under pressure-driven flow—proved far more effective than batch adsorption alone, because the applied pressure overcomes the wetting resistance that limits ion penetration in static conditions.

Intriguingly, more clay was not always better. At 30 percent loading, filtration performance deteriorated: aggregates identified by energy-dispersive X-ray analysis acted as bypass routes that let water, and the metals it carried, slip through without contacting adsorbent sites, while the weakened mechanical properties of the highly loaded membranes allowed pores to widen under pressure. The study also revealed a classic trade-off between selectivity and permeability, with thicker, less permeable membranes delivering the highest selectivity. The authors are candid about the work’s limits: no regeneration or reuse studies were performed, long-term stability remains untested, and performance in multicomponent, real-world wastewater has yet to be assessed. Future work, they note, should address membrane reuse, metal leaching, permeability–selectivity trade-offs, and continuous-flow operation. Even so, the message is clear: solution blow spinning can rapidly produce PVDF–clay nanofiber membranes that excel as filtration materials, and with moderate clay loadings of around 10 percent, they offer a promising, scalable route to stripping toxic lead and copper from contaminated water.

Subject of Research: PVDF–montmorillonite clay nanofibrous membranes produced by solution blow spinning for the removal of lead and copper ions from contaminated water

Article Title: Removal of Pb and Cu metals by PVDF/clay membranes obtained through solution blow spinning technique

Article References: da Cruz Dias, G., Zadorosny, L., Sanches, A. O., dos Santos, M. C., & Malmonge, L. F. (2026). Removal of Pb and Cu metals by PVDF/clay membranes obtained through solution blow spinning technique. Journal of Materials Science: Polymers, 1(1), Article 18. https://doi.org/10.1007/s44493-026-00020-7

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00020-7

Keywords: solution blow spinning, PVDF, montmorillonite clay, nanofibrous membranes, heavy metal removal, lead, copper, water treatment, adsorption kinetics, Langmuir isotherm, membrane filtration, wastewater remediation