A Highly Efficient Nanostructured Sorbent of Sulfuric Acid from Ecofriendly Electrospun Poly(vinyl alcohol) Mats

Abstract

Concentrated sulfuric acid is widely used in industrial processes all around the world. Its handling can generate spills with an enormous risk for the operator and the environment. Usually, alkalis are used to remedy this type of spillage, releasing a large amount of heat during the reaction. Absorbent pads are a solution to this problem. Here we present a new and light nanostructured material with extraordinary sorption capacity for concentrated sulfuric acid (98 wt %). The total acid uptake achieved is greater than 1200 wt %, sorbing 12.6 times its own weight of 98 wt % H 2 SO 4 , in just 5 min. It was obtained by applying a green process to a biodegradable polymer (poly(vinyl alcohol), PVA). First, an aqueous solution of PVA was electrospun to get a nanofibrous mat. Then, the mat was heat-treated by two sequential steps below 200 °C (900 min at 155 °C and 420 min at 195 °C). We show that both thermal steps are necessary to maximize acid sorption and that when one of them is not performed, the obtained sorption capacity is much lower (about 400 wt %, sorbing only 4 times its own weight). This phenomenon is explained in terms of transformations of polymeric structures caused by the proposed heat treatment. The sorption mechanism begins with the chemical addition of sulfuric acid to the polymer's surface unsaturations, followed by an increase in surface energy and additional absorption of acid into the material. This study opens up new possibilities for the development of sorbents from environmentally friendly materials and processes.

Ultramicroporous Carbon Nanofibrous Mats for Hydrogen Storage

“…However, when the treatment with dilute acid was performed after HT (PVAmat-HT-acid), the char decreased up to (24 ± 2)% (see Figure A). The enhanced thermal stability and the improved carbonaceous residue obtained are a consequence of carbon double bonds generated during the multistage heat treatment. , The decrease of char residue in the PVAmat-HT-acid material compared to that of PVAmat-HT is probably a consequence of sulfation reactions in which the sulfuric acid reacts with the CC double bonds present in the polymeric structure of the material (PVAmat-HT). In this reaction, the sulfate group (−OSO 3 H) is added to the polymeric chain, decreasing the number of instaurations .…”

“…PVA carbon nanofibrous mats were prepared by electrospinning of a 12% aqueous solution of PVA (Elvanol T25, Dupont, USA, MW = 125.000 g/mol) following the methodology reported by Vergara-Rubio et al The as-spun PVA (PVAmat) was exposed to a multistage temperature program below 195 °C to partially dehydrate and transform the original PVA chemical structure into one of the polyene type (PVAmat-HT). The performed heat treatment details can be found in ref .…”

“…PVA carbon nanofibrous mats were prepared by electrospinning of a 12% aqueous solution of PVA (Elvanol T25, Dupont, USA, MW = 125.000 g/mol) following the methodology reported by Vergara-Rubio et al The as-spun PVA (PVAmat) was exposed to a multistage temperature program below 195 °C to partially dehydrate and transform the original PVA chemical structure into one of the polyene type (PVAmat-HT). The performed heat treatment details can be found in ref . After that heat treatment, two different strategies were followed, direct pyrolysis of the sample in a tube furnace at 800 °C under an argon atmosphere (PVAmat-HT-Pyro) or application of a previous treatment with dilute sulfuric acid (25 wt %) and then pyrolysis under the same conditions as before (PVAmat-HT-acid-Pyro).…”

“…22−24 Recently, our group proposed a slow and stepped heat treatment that allowed the transformation of PVA electrospun mats into a new and more stable structure of the polyene type, capable of withstanding highly concentrated sulfuric acid exposure. 25 However, as far as we know, no reports in the literature propose the use of sulfuric acid to treat PVA nanofibers prior to its pyrolysis with the aim of modifying the obtained carbons' textural properties. Moreover, there are no reports where CNFMs obtained by pyrolysis of PVA nanofibers are used for hydrogen storage using either sulfuric acid as an activator or only heat treatments.…”

Active Neutralizing Mats for Corrosive Chemical Storage

“…The temperature can abruptly increase, causing the evaporation of acidic or alkaline fumes. Another strategy is the use of sorbents to decrease the release of heat and minimize water consumption [ 3 , 4 ]. There are several commercial mats indicated for chemical storage cabinets; nevertheless, these products are prevalently focused solely on absorption, rather than on their neutralization.…”