Development of a visible-light-active-NiTiO3 coating for the efficient removal of the persistent herbicide 2,6-dichlorobenzamide (BAM) from drinking water.

In the present research work, the photocatalytic evaluation of NiTiO3 nanoparticles immobilized on glass plates by the spin-coating procedure was carried out in the degradation of the recalcitrant herbicide 2,6-dichlorobenzamide (BAM). The concentrations of Ni employed to synthesize NiTiO3 nanoparticles were 1 wt% (1TESNi) and 2 wt% (2TESNi). The stability of coatings was evaluated by several washings and thermal treatments, which were verified by UV-vis analyses. The morphology of the coatings was studied by scanning electron microscopy (SEM-EDS). The coatings displayed thickness values of 1.35 and 2.56 µm for TiO2 and 1TESNi, respectively. The crystalline phases of the coatings were analyzed by X-ray diffraction (XRD), confirming the presence of NiTiO3 and other phases related to TiO2. The bandgap of 1TESNi, compared with the bare TiO2, was reduced from 2.96 to 2.40 eV as a consequence of Ni addition. The TiO2, 1TESNi and 2TESNi coatings were evaluated in the photodegradation of BAM using visible-light for 240 min. The highest effectiveness was displayed by the 1TESNi coating, obtaining degradation of 92.56% after 240 min. Also, the photocatalytic efficiency of the 1TESNi coating was only reduced 1.99% after 3 reuse cycles in the BAM degradation. The scavenger tests revealed that the main oxidizing species involved in the reaction were the •OH- and •O2- radicals. The 1TESNi coating showed the highest photocatalytic efficiency because of its absorption in the visible-light region, valuable surface area and electronic charge separation. Thus, these advantageous features guarantee that NiTiO3 coatings are an efficient method for degrading recalcitrant herbicides from drinking water using a practical way to recover and reuse photocatalysts.

Efficient solar removal of acetaminophen contaminant from water using flexible graphene composites functionalized with Ni@TiO2:W nanoparticles.

This work presents the morphological, structural and photocatalytic properties of flexible graphene composites decorated with Ni@TiO2:W nanoparticles (TiNiW NPs) with an average size of 27 ± 2 nm. The TiNiW NPs were immobilized on the surface of a flexible graphene composite using a PVA-based slurry-paste (FG/TiNiW composite). The SEM study showed that the TiNiW NPs remained exposed on the surface of the FG/TiNiW composite, which benefited its photocatalytic activity. The photocatalytic performance for the degradation of acetaminophen (ACT) was evaluated using both the TiNiW powders and the FG/TiNiW composite, obtaining maximum degradation efficiencies of 100 and 86%, respectively, after 3 h under natural solar irradiation. The degradation of ACT was caused mainly by the reactive oxygen species such as OH radicals and h+, which was confirmed by scavenger experiments. Photoluminescence, XPS and absorbance experiments revealed that oxygen vacancy defects were created by i) doping the TiNiW NPs with W and by ii) introducing graphene into the composites. These defects enhanced the absorbance of light in the range of 400-800 nm, which in turn, promoted the photocatalytic degradation of ACT. Moreover, the reuse experiments confirmed that both the TiNiW NPs and FG/TiNiW composite were very stable for the degradation of ACT, since degradation efficiencies >82% were obtained after 4 reuse cycles for both photocatalysts. The experimental findings of this work demonstrate that the flexible TiO2/graphene composites are a feasible option for the removal of pharmaceutical contaminants from water using natural solar irradiation.