An inexpensive, rapid, safe, and recycling-favoring method for the fabrication of core/shell PVP/CdS composite fibers from a gas–solid reaction between H2S vapor and electrospun PVP/CdCl2

Organic/inorganic composite fibers are materials that have shown possible applications in diverse areas. A well-known technique for incorporating metal sulfides into polymer fibers is a gas–solid reaction between a polymer/(metal salt) material and H2S gas. Since the methods available in literature to perform this gas–solid reaction are not well described as well as for the concern of the toxicity of the H2S gas, the design of a safer but economical and effective method for the reaction involving this neurotoxic reactant is indispensable. Thus, to meet the above, in this paper a low-cost, rapid, safer, and recycling-favoring method is fully described to prepare PVP/CdS composite fibers by means of a gas–solid reaction between PVP/CdCl2 and H2S vapor. For this, the PVP/CdCl2 composite fibers were first produced by the electrospinning technique, followed by the exposure to H2S vapor inside a sealed chamber to rapidly form the CdS compound in the original composite fibers. The H2S vapor was produced from a supersaturated H2S solution, which resulted from the reaction between a Na2S solution already contained in said chamber and an HCl solution injected later; therefore, this reaction was done without having to open the reaction chamber. After the production of the PVP/CdS products, the remaining H2S is neutralized with a NaOH solution injected into the chamber to produce Na2S again, which is capable of being reused in subsequent sulfidation reactions, and thus preventing environmental contamination. The entire process resulted in PVP/CdS composite material having a core/shell type structure, in which the PVP fibers were coated with ~29 nm size CdS nanoparticles formed by nanocrystals of about 12.8 nm and preferentially ordered in the hexagonal crystalline structure, as deduced from X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements; the Fourier transform infrared measurements revealed the existence of chemical interactions between the CdS nanoparticles and the carbonyl groups of PVP. The whole process described above could be applied to incorporate other metal sulfides into different types of polymer fibers.