Fabrication of branched-TiO2 microrods on the FTO glass for photocatalytic reduction of Cr(VI) under visible-light irradiation

Flower-like Bi2S3-In2S3 heterojunction for efficient solar light induced photoreduction of Cr(VI)

To develop Bi₂S₃-based heterojunction for efficient solar light induced photoreduction of Cr(VI), flower-like Bi₂S₃-In₂S₃ composites consisted of nanorods were prepared via a microwave-assisted hydrothermal route. In contrast with pure Bi₂S₃, Bi₂S₃-In₂S₃ composites exhibited the enhanced photoreduction activity while the decreased adsorption capacity for Cr(VI) removal. The best removal efficiency of 70 mg L^-1 Cr(VI) solution (99.86%) was achieved by the optimal 3-Bi₂S₃-In₂S₃ with a Bi/In molar ratio of 4:1 within 140 min. It's ascribed to the narrow band gap for strengthened visible-light response, the tight interface between Bi₂S₃ and In₂S₃ for rapid transfer and separation of charge carriers, and the enough S vacancies for highly-efficient active sites of adsorption-photoreduction. However, the long-term photo-corrosion resulted in the slightly inferior reusability of 3-Bi₂S₃-In₂S₃ under solar light irradiation after five cycles.

Simultaneous Adsorption and Reduction of Cr(VI) to Cr(III) in Aqueous Solution Using Nitrogen-Rich Aminal Linked Porous Organic Polymers

Two novel nitrogen-rich aminal linked porous organic polymers, NRAPOP-O and NRAPOP-S, have been prepared using a single step-one pot Schiff-base condensation reaction of 9,10-bis-(4,6-diamino-S-triazin-2-yl)benzene and 2-furaldehyde or 2-thiophenecarboxaldehyde, respectively. The two polymers show excellent thermal and physiochemical stabilities and possess high porosity with Brunauer–Emmett–Teller (BET) surface areas of 692 and 803 m2 g−1 for NRAPOP-O and NRAPOP-S, respectively. Because of such porosity, attractive chemical and physical properties, and the availability of redox-active sites and physical environment, the NRAPOPs were able to effectively remove Cr(VI) from solution, reduce it to Cr(III), and simultaneously release it into the solution. The efficiency of the adsorption process was assessed under various influencing factors such as pH, contact time, polymer dosage, and initial concentration of Cr(VI). At the optimum conditions, 100% removal of Cr(VI) was achieved, with simultaneous reduction and release of Cr(III) by NRAPOP-O with 80% efficiency. Moreover, the polymers can be easily regenerated by the addition of reducing agents such as hydrazine without significant loss in the detoxication of Cr(VI).

Cr (VI) reduction by photocatalyic process: Nb2O5 an alternative catalyst

In this study, Nb₂O₅ catalyst was applied in the photocatalytic process for the Chromium reduction. Cr (VI) is a compound classified as highly toxic and often found in industrial tannery effluents. The techniques used for the photocatalytic material characterization were: X-ray diffraction, Specific surface area (B.E.T method), photo-acoustic spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Dispersive Energy Spectrometry (EDS). A comparison between Nb₂O₅ and TiO₂ (widely used in photocatalytic reactions) indicated that Nb₂O₅ has 20% more Cr (VI) reduction than TiO₂. Tests carried out with Nb₂O₅ calcined at 500 °C and with non-calcined Nb₂O₅ showed that the heat treatment did not favor the reaction. Parameters such as pH, radiation intensity, initial concentration of Cr (VI) and amount of catalyst were studied. The results indicated that the acid (pH 2), emitted radiation intensity (250 W), initial concentration Cr (VI) at 10 mg L^-1 and 1.5 g L^-1 Nb₂O₅ non-calcined are the process optimal conditions. In addition, the reuse tests for Nb₂O₅ in consecutive cycles four, were realized. Photostability was maintained at approximately 90% for all cycles when Nb₂O₅ calcined was used. On the other hand, when using Nb₂O₅ non-calcined reduced by 21% during the four tests. This behavior is possibly due to the greater adsorption capacity of the non-calcined material. Making the Nb₂O₅ catalyst attractive for considering larger scale tests.

TiO2@lipophilic Porphyrin Composites: New Insights into Tuning the Photoreduction of Cr(VI) to Cr(III) in Aqueous Phase

Metal-free and Cu(II)-lipophilic porphyrins [H2Pp and Cu(II)Pp] loaded on titanium dioxide in the anatase phase (TiO2) were prepared and used as a heterogeneous catalyst for the photoreduction of Cr(VI) to Cr(III) in aqueous suspensions under UV–Vis light irradiation. TiO2 impregnated with copper(II) porphyrin [TiO2@Cu(II)Pp] was the most effective in photocatalyst reduction of toxic chromate Cr(VI) to non-toxic chromium Cr(III). We further evaluated an experimental design with the scope of fast optimization of the process conditions related to the use of TiO2 or TiO2-porphyrin based photocatalysts. A full factorial design as a chemometric tool was successfully employed for screening the affecting factors involved in photoconversion catalysis, with the modification of TiO2 both with porphyrin H2Pp and Cu(II)Pp. The studied experimental factors were the catalyst amount, the concentration of Cr(VI) ions, and the pH of the medium. The performed multivariate approach was successfully used for fast fitting and better evaluation of significant factors affecting the experimental responses, with the advantage of reducing the number of available experiments. Thus, the stability of the optimized TiO2 embedded Cu(II)Pp was investigated, confirming the high reproducibility and suitability for environmental purposes.