Interfacial coupling effects on adsorptive and photocatalytic performances for photoresponsive graphene-wrapped SrTiO3@Ag under UV-visible light: experimental and DFT approach.

Understanding the graphene/semiconductor/metal interactions is crucial to design innovative photocatalytic materials with efficient photocatalytic activity for environmental cleanup applications. SrTiO3 on reduced graphene oxide (rGO) with various graphene contents was successfully synthesized in this study utilizing a simple hydrothermal method, followed by decorating the surface with Ag particles by using the photodeposition process. Under UV-visible light irradiation, the resulting composites were tested for their improved photocatalytic activity to decompose methylene blue (MB). The prepared photocatalysts were characterized by XRD, SEM, EDX, DLS, FT-IR, Raman spectroscopy, and DRS. First-principle density functional theory calculations (DFT) were also carried out by using the generalized gradient approximation (GGA) and PBE functional with the addition of on-site Coulomb correction (GGA + U). The obtained SrTiO3/rGO@Ag composites showed great improvement in the photocatalytic performances over pristine SrTiO3. For the degradation reaction of MB, SrTiO3/rGO20%@Ag4% composites yielded the best photocatalytic activity with efficacy reach 94%, which was also shown that it could be recycled up to four times with nearly unchanged photocatalytic activity.

Novel Fe2TiO5/reduced graphene oxide heterojunction photocatalyst with improved adsorption capacity and visible light photoactivity: experimental and DFT approach.

The design of high-efficiency materials is a major challenge for the degradation of organic pollutants. In this work, type II p-n heterojunction photocatalyst Fe2TiO5/rGO, with enhanced performance, was successfully prepared through simple process. The Fe2TiO5/rGO composites were prepared by hosting several amounts of reduced graphene oxide (rGO) into pseudobrookite nanocrystals (Fe2TiO5) which were priorly synthesized by a solid-state reaction. The morphology and the properties of the as-prepared composites were characterized through different techniques. The fixation of rGO sheets on Fe2TiO5 was proved using the X-ray diffraction analysis (XRD). The results of the scanning electron microscope (SEM) analysis showed a good mixing of rGO with Fe2TiO5. The X-ray fluorescence (XRF) confirmed the purity of the pristine Fe2TiO5. The dynamic light scattering (DLS) illustrated a strong tendency to aggregation. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) analysis was performed to characterize the electronic aspect as the gap and the Urbach energies. Finally, computational density functional theory (DFT) calculations were carried out to confirm the experimental results. The adsorptive and photoactivity of Fe2TiO5/rGO heterojunction photocatalysts were evaluated by methylene blue (MB) degradation under visible light irradiation. The highest MB degradation rate was achieved for Fe2TiO5/rGO10% photocatalyst with the highest value of the elimination rate.

Integration of photocatalysis and biological treatment for azo dye removal--application to AR183.

The feasibility of coupling photocatalysis with biological treatment to treat effluents containing azo dyes was examined in this work. With this aim, the degradation of Acid Red 183 was investigated. The very low biodegradability of AR183 was confirmed beforehand by measuring the biological oxygen demand (BOD5). Photocatalysis experiments were carried out in a closed-loop step photoreactor. The reactor walls were covered by TiO2 catalyst coated on non-woven paper, and the effluent flowed over the photocatalyst as a thin falling film. The removal of the dye was 82.7% after 4 h, and a quasi-complete decolorization (98.5%) was obtained for 10 h of irradiation (initial concentration 100 mg L(-1)). The decrease in concentration followed pseudo-first-order kinetics, with a constant k of 0.47 h(-1). Mineralization and oxidation yields were 80% and 75%, respectively, after 10 h of pretreatment. Therefore, even if target compound oxidation occurs (COD removal), indicating a modification to the chemical structure, the concomitant high mineralization was not in favour of subsequent microbial growth. The BOD5 measurement confirmed the non-biodegradability of the irradiated solution, which remained toxic since the EC50 decreased from 35 to 3 mg L(-1). The proposed integrated process appeared, therefore, to be not relevant for the treatment of AR183. However, this result should be confirmed for other azo dyes.