High surface area mesoporous titanium-zirconium oxide nanofibrous web: a heavy metal ion adsorbent

A mixed titanium-zirconium (Ti : Zr = 2 : 1 atomic ratio) oxide non-woven nanofibrous web was prepared by using an electrospinning technique followed by thermal treatment. A hydrocarbon surfactant was incorporated into the electrospinning solution and was pyrolysed during heating. The surfactant acted as a structure-directing agent to create intra-fibre pores, and significantly increased the surface area of the fibres, thereby maximising the number of sites for further surface modification as well as heavy metal ion adsorption. The high surface area (248 m(2) g(-1)) titanium-zirconium oxide nanofibre surface was functionalised via a phosphonic acid coupling reaction to give different functional groups for attracting metal ions (i.e., phosphonate and amine groups). The cadmium adsorption capacity of the phosphonate-functionalised nanofibres was up to 10 times higher than that of the non-modified or amine-functionalised nanofibres. In addition, the cadmium adsorption on the phosphonate-functionalised nanofibres was less dependent on the pH of analyte solutions than the metal oxide nanofibres where the surface charge changed in varied pH environments. The size of the nanofibrous web can be easily scaled for making a large web convenient for handling and recovery after use, compared with high surface area heavy metal ion adsorbents that are nanometre or micrometre in size.