Facile fabrication of hybrid titanium(IV) isopropoxide/pozzolan nanosheets (TnS-Pz) of high photocatalytic activity: characterization and application for Cr(VI) reduction in an aqueous solution

This paper presents the synthesis of a hybrid material through the use of natural pozzolan and titanium(IV) isopropoxide using the sol-gel method and its application in the photocatalytic hexavalent chromium reduction. The characterization data indicated a mesoporous material possessing a surface area of 271.7 m² g^-1. The morphology studies (SEM and TEM) showed nanosheet hybrid structures. The analysis of DRUV, FTIR, XRD, and Mössbauer spectroscopy provides a different electronic structure of the synthetized material when compared with the originals, proving the hybridization process between pozzolan and titanium(IV) isopropoxide. The photocatalytic reduction of Cr(VI) to Cr(III) using the hybrid material showed a better performance than conventional photocatalysts (precursor and TiO₂-P25). Operational conditions such as chromium initial concentration (0.02-0.20 mM), solution pH (3-6), and type of scavenger (citric or tartaric acid) were evaluated in order to determine the best experimental conditions for the Cr(VI) photoreduction. At their optimum (catalyst load of 15 mg L^-1, tartaric acid as scavenger, [scavenger]₀/[Cr(VI)]₀ M ratio = 3:1, pH 3, and 25 °C), the total photoreduction of 0.20 mM Cr(VI) was achieved in 180 min. The novel hybrid materials synthesized from pozzolan and titanium(IV) isopropoxide showed to be a potential catalyst for the Cr(VI) reduction in aqueous solution. Graphical abstract.

Toxicity of enzymatically decolored textile dyes solution by horseradish peroxidase

The oxidative systems including enzymatic systems have been widely studied as an alternative for textile effluents treatment. However, studies have shown that some oxidative processes can produce degradation products with higher toxicity than the untreated dye. In this work, enzymatic dye decolorization was evaluated by horseradish peroxidase enzyme (HRP) and the toxicity of discoloration products was evaluate against Daphnia magna, Euglena gracilis algae, and Vibrio fischeri. Dye decolorization kinetics data were evaluated and the pseudo-second-order model showed the best-fitting to the experimental data. In addition, it was observed an increased acute and chronic toxicity associated with the decolorization efficiency. The Reactive Blue 19 and Reactive Black dye showed the highest toxicity against D. Magna (16 toxicity factor) and V. Fischeri (32 toxicity factor) after enzymatic decolorization. For the chronic toxicity against D. Magna, Reactive Red was the only dye with no fertility inhibition. In relation to toxicity tests with E. gracilis algae, it was not observed photosynthetic inhibition for all dyes. This study verified the viability of the enzyme horseradish peroxidase in the textile dyes decolorization and the importance to evaluate the decolorization products.