Rare Earth Elements Doped Semiconductors: from Fundamentals to their Exploitation in Sustanaible Water Treatments
Department of Chemistry, Università di Torino, via P. Giuria 5- 10125 Torino (ITALY)
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Recently, several groups started to investigate the role of rare earth elements (RE = La, Ce, Pr, Er and Yb) as dopant of different oxides. Among semiconductor nanomaterials, we chose ZnO thanks to several interesting properties and broad applications. We synthesized via hydrothermal or precipitation processes and characterized different photocatalysts based on ZnO doped with a low amount of RE (1% molar); then, the photocatalytic performance of pristine and rare earth elements doped zinc oxide was tested toward the abatement of a model pollutant in MilliQ water and wastewater matrices. ZnO doped with Ce, Er and particularly with Yb exhibited photoactivity higher than bare zinc oxide and the benchmark TiO2 P25, especially in wastewater matrix.
Aiming at identifying the best operating conditions that couples the highest degradation efficiency with the lowest environmental loading, the results of an experimental design face centered model were combined to life cycle assessment (LCA). The concentration of photocatalyst, type of REE used as dopant, its precursor and dopant concentration in the photocatalyst constituted the set of explanatory variables. Cumulative energy demand and Global Warming Potentials were used as indicators in LCA.
The best performing materials and optimized experimental conditions were then exploited to the abatement of some refractory pollutants. Furthermore, we combined the use of REE doped ZnO with enzymes aimed to further increase activity, and evaluated for their ability to remove a mixture of organic pollutants. These materials were tested in their free form as well as supported on poly(styrene-co-maleic anhydride) (SMA) nanofiber mats fabricated though the process of electrospinning. In free form they showed a good removal efficacy of all the contaminants even in a mixed matrix environment which mimics a real scenario.
By combining enzymes attached to the SMA nanofibres and oxides nanoparticles into the polymer nanofibres, a synergic effect was observed and it was particularly marked when using Ce-doped ZnO in wastewater matrix. Supporting these materials on nanofiber mats did not compromise on the effectiveness of the materials.
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