ADVANCED OXIDATION/REDUCTION TECHNOLOGIES: AN PERSPECTIVE FROM IBEROAMERICAN COUNTRIES Removal of emerging pollutant dibutylhydroxytoluene from water with CNT/TiO 2 catalysts in a visible LED photoreactor María Patricia de la Flor 1 & Rafael Camarillo 1 & Fabiola Martínez 1 & Carlos Jiménez 1 & Rafael Quiles 1 & Jesusa Rincón 1 Received: 29 May 2020 /Accepted: 4 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract For the photocatalytic degradation of antioxidant 2,6-di-tert-butyl-hydroxytoluene (BHT), several TiO 2 -based composites have been prepared in MWCNT from titanium isopropoxide and ethanol via supercritical CO 2 synthesis followed by calcination at 400 °C. TEM and XRD showed uniform coverage of CNT by 10 nm TiO 2 particles in the anatase form, and spectral analyses revealed the formation of CNT/TiO 2 structure. Further, synthesized material displayed significant visible light absorption and absorption edge shifted to longer wavelengths. Once the material was characterized, the effect of adsorption and photochemical degradation of BHT was investigated in the wavelength range from 400 to 700 nm, in batch mode, by monitoring the concentrations of BHT as a function of time. CNT/TiO 2 composites were more efficient than commercial TiO 2 P25 in the photodegradation of the antioxidant. In particular, CNT 50 /TiO 2 50 , a composite with 50% by weight of CNT, was the best catalyst, stable, and completely degrading BHT within 30 min of exposure to visible light. The role played by different reactive oxidative species (h + , OH · , 1 O 2 , and O ∙− 2 ) in the photocatalytic reaction was also studied by using appropriate radical scavengers that inhibited the corresponding active species. Superoxide radical was found the main oxidizing agent. Keywords BHT . CNT/TiO 2 . Enhanced photocatalysis . Visible light degradation . Emergent pollutants . Water treatment Introduction Water is responsible of life as we know it, and for this reason, water pollution is an important problem to solve. Because of this, regulations have been put into place to limit the presence of pollutants in natural water sources and different technolo- gies proposed to remove them from wastewater (Camarillo and Rincón 2011; Camarillo et al. 2009; Rincón et al. 1993). Nevertheless, a large number of microcontaminants such as those of the watch list in Decision 2015/495/EU are not cov- ered by legal regulations and little is known about their removal, particularly regarding realistic concentrations in aqueous environments (Barbosa et al. 2016). BHT (2,6-di-tert-butyl-hydroxytoluene) is one of the sub- stances included in the abovementioned watch list. It is a syn- thetic phenolic antioxidant (E-321) widely used in the food and cosmetic industries as antioxidant and/or UV filter in sunscreen creams. Because of this widespread use, its presence in natural waters is frequent, at concentrations ranging from 10 to 2000 ng/ L (Jurado et al. 2019; Rodil et al. 2010), that may entail a signif- icant risk for the aquatic environment due to its potential toxico- logical effects (Nieva-Echevarría et al. 2015). Accordingly, its elimination from the effluents of municipal and industrial waste- water treatment plants should be studied (Barbosa et al. 2016). Similarly to other pollutants, the presence of BHT in water streams may be reduced by heterogeneous photocatalysis (Kudlek 2018; Orozco-Hernández et al. 2019; Garg et al. 2019). Until now TiO 2 has been the catalyst more widely used due to its high photocatalytic activity, chemical stability, nontoxicity, eco-friendliness, and low cost (Nguyen et al. 2020). A major drawback is that its high band gap (~ 3.2 eV) makes it primarily active for UV light, which corresponds to only 4% of the incident solar energy (Gomes et al. 2019). Responsible Editor: Vítor Pais Vilar Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-020-11126-y) contains supplementary material, which is available to authorized users. * Jesusa Rincón jesusa.rincon@uclm.es 1 Department of Chemical Engineering, Faculty of Environmental Sciences and Biochemistry, University of Castilla-La Mancha, Avda. Carlos III, s/n, 45071 Toledo, Spain Environmental Science and Pollution Research https://doi.org/10.1007/s11356-020-11126-y