Active Carbon Fibers Grown with Manganese Dioxide Nanowires for Highly-Efficient Adsorption of Organic Pollutants from Acidic and Neutral Aqueous Solutions

Removal of organic pollutants from aqueous solution under acidic and neutral surroundings is of great significance, especially for industrial water purification in which the organic compounds were involved in acidic water, such as dyes in printing wastewater. The design of efficient adsorbents which can continuously give highly-efficient adsorption performance towards organic pollutants in low-pH value aqueous solutions is a great challenge. Here, we report a concept that combines conventional materials with chemically-stable nanomaterials to address this issue. In our investigation, activated carbon fibers (ACFs) were grown with dense manganese dioxide (MnO₂) nanowires, which were found to possess good adsorbing properties to organic pollutants in both acidic and neutral aqueous solutions. The adsorbents were prepared via a facile hydrothermal route based on the in situ redox reaction of potassium permanganate on ACFs without using any other oxidant or reductant additions. The ACFs not only serve as a sacrificial reductant, but also used as a substrate for MnO₂ nanowires growth. In adsorbing measurements, methyl orange was employed as organic pollutant probe. The effect of pH value, kinetics adsorption process under a pH value of 3, and isothermal models were investigated. The adsorption behavior well fits with typical Freundlich adsorption model. Furthermore, the adsorption capacity can be retained higher than 90% after five adsorption cycles. Our findings can be promising for developing a large variety of efficient and stable adsorbents by combining conventional materials with nanostructures for water purification applications.