Enhanced Photocatalytic Degradation of Methyl Orange Dye under the Daylight Irradiation over CN-TiO₂ Modified with OMS-2

Enhanced degradation of 2,6-dimethylphenol by photocatalytic systems using TiO2 assisted with H2O2 and Fe(III)

In this study, several photocatalytic degradation systems were investigated using 2,6-dimethylphenol (2,6-DMP) as a model compound. Highly reactive species are formed in four systems, Fe(III), TiO₂, TiO₂/H₂O₂ and TiO₂/Fe(III) where complete degradation of 2,6-DMP was achieved under UV radiation. Photodegradation of the 2,6-DMP has been described by pseudo-first order kinetic model in the presence of TiO₂. In UV/TiO₂-H₂O₂ system, the addition of H₂O₂ in the TiO₂ suspension improves the degradation rate of 2,6-DMP from 70% to 100% for a H₂O₂ concentration of 10^-2 M in 3 h. In homogeneous system, HO^• and Fe²⁺ can be generated by the irradiation of Fe(III) solution. The speciation of Fe(III) obtained from Visual MINTEQ soft showed the formation of several species and Fe(OH)²⁺ were the most predominant and active species in a pH range of 2.5-3.5. At a low concentration of TiO₂ (30 mg L^-1), an important positive effect due to the iron addition has been shown in TiO₂/Fe(III) system, the entrance of metallic ions at different concentrations enhanced the photocatalytic activity of TiO₂. A degradation percentage of 90% was achieved in the UV/TiO₂-Fe(III) system under optimal conditions against 57% in UV/TiO₂ system. Strong synergistic effect was observed in the UV/TiO₂-H₂O₂ binary system. On the basis of literature, a pathway for 2,6-DMP degradation was proposed. The mechanism of degradation of the 2,6-DMP did not involve only HO^• radicals, an interaction of Fe(III) in the excited state with 2,6-DMP occurred giving rise to the formation of 2,6-dimethylphenoxyl radical.

Starch, cellulose, pectin, gum, alginate, chitin and chitosan derived (nano)materials for sustainable water treatment: A review

Natural biopolymers, polymeric organic molecules produced by living organisms and/or renewable resources, are considered greener, sustainable, and eco-friendly materials. Natural polysaccharides comprising cellulose, chitin/chitosan, starch, gum, alginate, and pectin are sustainable materials owing to their outstanding structural features, abundant availability, and nontoxicity, ease of modification, biocompatibility, and promissing potentials. Plentiful polysaccharides have been utilized for making assorted (nano)catalysts in recent years; fabrication of polysaccharides-supported metal/metal oxide (nano)materials is one of the effective strategies in nanotechnology. Water is one of the world's foremost environmental stress concerns. Nanomaterial-adorned polysaccharides-based entities have functioned as novel and more efficient (nano)catalysts or sorbents in eliminating an array of aqueous pollutants and contaminants, including ionic metals and organic/inorganic pollutants from wastewater. This review encompasses recent advancements, trends and challenges for natural biopolymers assembled from renewable resources for exploitation in the production of starch, cellulose, pectin, gum, alginate, chitin and chitosan-derived (nano)materials.

Preparation and Photocatalytic Properties of N-Doped Graphene/TiO2Composites

N-doped graphene (NG)/TiO2composites were prepared by a two-step hydrothermal method using HF as the surface etchant and urea as the nitrogen source. The morphology, structure, and bonding conditions of the NG/TiO2composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and photoluminescence (PL) spectroscopy. The effects of NG on the lifetime of photogenerated electron-hole pairs, adsorption capacity, and photocatalytic activity of the composite photocatalysts were also investigated. The photocatalytic activity was evaluated under ultraviolet light and sunlight irradiation. The recovery testing was completed under ultraviolet light irradiation. The results show that TiO2was uniformly loaded on the NG surface by chemical bonding. The introduction of NG effectively inhibited the recombination of photogenerated electron-hole pairs and improved both the adsorption capacity and photocatalytic activity of the composites. The 7 wt % NG/TiO2showed the best adsorption capacity of methyl orange (MO). The best photocatalytic activity occurred for 5 wt % NG/TiO2composites, and after four recovery tests, the photocatalytic degradation of MO under 60 min ultraviolet light irradiation exceeded 90%.

Study of the Structure, Electronic and Optical Properties of BiOI/Rutile-TiO2 Heterojunction by the First-Principle Calculation

Using the first-principle calculation that is based on the density functional theory (DFT), our group gains some insights of the structural, electronic and optical properties of two brand new types of BiOI/TiO2 heterojunctions: 1I-terminated BiOI {001} surface/TiO2 (1I-BiOI/TiO2) and BiO-terminated BiOI {001} surface/TiO2 (BiO-BiOI/TiO2). The calculation illustrates that BiOI/TiO2 heterojunction has excellent mechanical stability, and it shows that there is a great possibility for the BiOI/TiO2 heterojunction to be used in visible-light range, hence the photocatalytic ability can be enhanced dramatically. Especially, from the calculation, we discovered that there are two specific properties: the band-gap of 1I-BiOI/TiO2 heterojunction reduces to 0.28 eV, and the BiO-BiOI/TiO2 semiconductor material changes to n-type. The calculated band offset (BOs) for 1I-BiOI/TiO2 heterojunction indicates that the interfacial structure contributes a lot to a suitable band alignment which can disperse the photo-generated carriers into the opposite sides of the interface, so this could effectively weaken the electron-hole recombination. Meanwhile, the built-in potential around the interface accelerates the movement of the photo-generated electron-hole pairs. We believe this is the reason that the BiOI/TiO2 material shows perfect photocatalytic performance. This paper can provide theoretical support for the related research, especially the further research of the BiOI-based material.

Photocatalytic Degradation of 4-Nitrophenol by C, N-TiO2: Degradation Efficiency vs. Embryonic Toxicity of the Resulting Compounds

The photocatalytic activity of TiO₂ based photocatalysts can be improved by structural modification and elemental doping. In this study, through rational design, one type of carbon and nitrogen co-doped TiO₂ (C, N-TiO₂) photocatalyst with mesoporous structure was synthesized with improved photocatalytic activity in degrading 4-nitrophenol under simulated sunlight irradiation. The photocatalytic degradation efficiency of the C, N-TiO₂ was much higher than the anatase TiO₂ (A-TiO₂) based on absorbance and HPLC analyses. Moreover, using zebrafish embryos, we showed that the intermediate degradation compounds generated by photocatalytic degradation of 4-nitrophenol had higher toxicity than the parent compound. A repeated degradation process was necessary to render complete degradation and non-toxicity to the zebrafish embryos. Our results demonstrated the importance of evaluating the photocatalytic degradation efficiency in conjunction with the toxicity assessment of the degradation compounds.

Facile Synthesis of SrCO₃-Sr(OH)₂/PPy Nanocomposite with Enhanced Photocatalytic Activity under Visible Light

Pyrrole monomer was chemically polymerized onto SrCO₃-Sr(OH)₂ powders to obtain SrCO₃-Sr(OH)₂/polypyrrole nanocomposite to be used as a candidate for photocatalytic degradation of methylene blue dye (MB). The material was characterized by Fourier transform infrared (FTIR) spectroscopy, UV/Vis spectroscopy, and X-ray diffraction (XRD). It was observed from transmission electronic microscopy (TEM) analysis that the reported synthesis route allows the production of SrCO₃-Sr(OH)₂ nanoparticles with particle size below 100 nm which were embedded within a semiconducting polypyrrole matrix (PPy). The SrCO₃-Sr(OH)₂ and SrCO₃-Sr(OH)₂/PPy nanocomposites were tested in the photodegradation of MB dye under visible light irradiation. Also, the effects of MB dye initial concentration and the catalyst load on photodegradation efficiency were studied and discussed. Under the same conditions, the efficiency of photodegradation of MB employing the SrCO₃-Sr(OH)₂/PPy nanocomposite increases as compared with that obtained employing the SrCO₃-Sr(OH)₂ nanocomposite.