Synthesis and characterization of bimetallic TiO2/CNT/Pd-Cu for efficient remediation of endocrine disruptors under solar light

Abstract

Metal and bimetal doped TiO2 supported on CNT hybrids were successfully synthesized in supercritical CO2 medium and evaluated for their solar light photocatalytic efficiency to degrade the endocrine disruptors clothianidin (CLT), estrone (E1) and estradiol (E2). Metallic dopants analyzed were Pd and Cu at metal concentrations of 2% by weight. The morphological analysis of the hybrids showed metal-doped TiO2 nanoparticles of around 10 nm over CNT. All of them exhibited highly crystalline anatase phase and shifted the absorption edge through the visible region. Band gap reduction was more pronounced for bimetallic Pd, Cu codoped TiO2 (TiO2/CNT/Pd-Cu) than with monometal-doped samples (TiO2/CNT/Pd and TiO2/CNT/Cu). Bimetalic codoping also led to an enhancement in the charge transfer process (Rct=1.4 ohms and Rs=19.4 ohms for TiO2/CNT/Pd-Cu vs. Rct=13.0 ohms and Rs=38.5 ohms for TiO2/CNT) and photodegradation of target endocrine disruptors. At the vanishing times of these pollutants by treatment with TiO2/CNT/Pd-Cu, the removals achieved with the metal-doped catalyst least active (TiO2/CNT/Cu) were 80% (clothianidin), 84% (estrone) and 82% (estradiol), far higher than those observed with commercial P25 (53% for clothianidin, 56% for estrone and 54% for estradiol). The improved performance of bimetallic TiO2/CNT/Pd-Cu over its monometallic references was explained on the basis of a combination of factors mainly related to its band gap structure, easier availability of charge carriers and plasmonic effects. Furthermore, this catalyst showed a highly stable photocatalytic performance. Thus, neither background species present in a real WWTP effluent, nor four successive uses of the catalyst significantly affected to the removal efficiency of pollutants.