Porous TiO₂ Fibres Loaded with Plasmonic Au Nanoparticles for Water Treatment

Facing the global shortage of clean water, photocatalytic degradation is one of the greenest technologies to decompose the organic pollutants in wastewater. Over the past decades, TiO₂ has been the most popular photocatalytic material. Upon light irradiation, it generates highly reactive free radicals that can inactivate the microorganisms and mineralize the organic matter. However, there are factors limiting overall photocatalytic efficiency, mainly, the narrow visible-light photoresponse due to wide band gap, and the limited quantum yield due to the rapid recombination of charge carriers. More importantly, although TiO₂ nanopowder demonstrates high photocatalytic reactivity, it is difficult to be removed and recycled from water suspension, therefore, not suitable for applying in large-scale water treatment.<br/>To address the identified issues, we developed highly porous TiO2 fibers coupled with plasmonic Au nanoparticles (NPs). We synthesized TiO₂ fibers by electrospinning from solution containing TiO₂ precursor and calcining the precursor fibres at high temperature. Cu ions were doped into TiO₂ lattice to reduce the bandgap from 3.22 eV to 2.89 eV, thus extending the photosensitive light wavelength from 385 to 430 nm. We are the first to engineer the porous structure by combining the previously reported strategies for producing mesoporous TiO2 fibers, e.g., use surfactant and control the crystallization, with a sacrificial polymer template method, in which the thermal decomposition of polymer particles creates homogenously distributed macropores. New science has been overserved in the synergetic effects of these two strategies in manipulating the porous structure of ceramic fibres.<br/>The porous TiO₂ fiber is an ideal host for anchoring noble metal NPs to form Schottky heterojunctions. In our study, we create plasmonic Au NPs/TiO₂ fibres that show doubled photocatalytic efficiency in the photodegradation of two types of organic dyes, methyl blue and methyl orange, compared to bare TiO₂ fiber. We focus on understanding the localized surface plasmon resonance of Au NPs in enhancing the photocatalytic activities of TiO₂ fiber in terms of the overlapping of absorption band and the enhanced localized light intensity. Furthermore, our Au NPs/TiO₂ fibres could also be easily filtered out from water and reused for at least six times without losing the efficiency, therefore, showing great potential for degradation of organic pollutants in large-scale water treatment.