Insight into the photocatalytic reduction of hexavalent chromium using photodeposited metal nanoparticle-TiO2 photocatalysis.

Hexavalent chromium (Cr(VI)) is carcinogenic to organisms. It is widely used in several industries. In this work, we investigated the Cr(VI) photocatalytic reaction with a scavenger on Pt and Cu-TiO2 photocatalysts. Metal-deposited TiO2 was successfully synthesized by a photodeposition method. TEM-EDX, XRD, and UV-DR were analyzed to study the changes in morphology, crystallinity, and the electronic properties of photocatalysts. The rate of charge recombination during reduction and photoluminescence (PL) spectroscopy was used to examine the catalysts in depth. Cu-TiO2 demonstrates the highest photocatalytic activity for 63.74% of Cr(VI) removal. To understand the photoreduction of Cr(VI), the fate transformation of Cr species during the adsorption and reaction was investigated using in situ XANES. The results demonstrated that the Cr(III) was noticeably main component adsorbed over the catalyst, particularly in Cu-TiO2. The presence of humic acid can boost the Cr(VI) removal efficiency and enhanced the Cr(VI) reduction to Cr(III). We believe that the extensive research on Cr(VI) photoreduction on metal-TiO2 heterojunction will provide a comprehensive understanding of catalytic behaviors, paving the way for rationally designed novel Cr reduction catalysts.

Photocatalytic reactor design and its application in real wastewater treatment using TiO2 coated on the stainless-steel mesh.

The application of wastewater treatment using TiO2 coated on the stainless-steel mesh is promising for disintegrating organic pollutants in wastewater. This research successfully coated TiO2 particles on stainless-steel mesh for the photocatalyst process by using the dip-coating method. This method was selected due to its simplicity and low cost, as well as its extensive application prospects in wastewater treatment. The photocatalytic oxidation of real wastewater treatment was developed and designed for a photo-reactor in terms of flow rate (varied on 2.0-4.0 L/min) and light distance (varied on 5.0-15.0 cm), whereas the preparation of the material process was investigated in terms of TiO2 catalyst dosage (varied on 1.0-3.0 g) and layers of coating (varied on 1 to 3 layers). Experiments were employed to degrade organic wastewater from methylene blue (MB) for a prelim experiment and real wastewater effluent testing for the application. The optimized TiO2 dosage was 2.0 g with 2 layers of coating coated on the stainless-steel mesh. The designed photo-reactor was optimized with a flow rate of 2.0 L/min and a light distance of 10.0 cm to treat the organic pollutants in raw domestic wastewater effluent on photocatalytic activity. MB successfully degraded about 96% in 3 h under UV-C irradiation after adsorption equilibrium was completed (3 h), whereas the efficiency of BOD removal was 89% under UV-C irradiation in 4 h. Therefore, TiO2 (2.0 g) coated on stainless-steel mesh with 2 layers of the coating prepared by dip-coating is a potentially effective alternative for real wastewater treatment.

Photocatalytic performance of electrospun CNT/TiO2 nanofibers in a simulated air purifier under visible light irradiation.

The photocatalytic treatment of gaseous benzene under visible light irradiation was developed using electrospun carbon nanotube/titanium dioxide (CNT/TiO2) nanofibers as visible light active photocatalysts. The CNT/TiO2 nanofibers were fabricated by electrospinning CNT/poly(vinyl pyrrolidone) (PVP) solution followed by the removal of PVP by calcination at 450 °C. The molar ratio of CNT/TiO2 was fixed at 0.05:1 by weight, and the quantity of CNT/TiO2 loaded in PVP solution varied between 30 and 60 % wt. CNT/TiO2 nanofibers have high specific surface area (116 m2/g), significantly higher than that of TiO2 nanofibers (44 m2/g). The photocatalytic performance of the CNT/TiO2 nanofibers was investigated by decolorization of 1 × 10-5 M methylene blue (MB) dye (in water solution) and degradation of 100 ppm gaseous benzene under visible light irradiation. The 50-CNT/TiO2 nanofibers (calcined CNT/TiO2 nanofibers fabricated from a spinning solution of 50 % wt CNT/TiO2 based on PVP) had higher MB degradation efficiency (58 %) than did other CNT/TiO2 nanofibers and pristine TiO2 nanofibers (15 %) under visible light irradiation. The photocatalytic degradation of gaseous benzene under visible light irradiation on filters made of 50-CNT/TiO2 nanofibers was carried out in a simulated air purifier system. Similar to MB results, the degradation efficiency of gaseous benzene by 50-CNT/TiO2 nanofibers (52 %) was higher than by other CNT/TiO2 nanofibers and pristine TiO2 nanofibers (18 %). The synergistic effects of the larger surface area and lower band gap energy of CNT/TiO2 nanofibers were presented as strong adsorption ability and greater visible light adsorption. The CNT/TiO2 nanofiber prepared in this study has potential for use in air purifiers to improve air treatment efficiency with less energy.