Presence Of Visible Irradiation Research Articles

Synthesis, characterization and photodegradation activity of graphitic C3N4-SrTiO3 nanocomposites

Porous graphitic nitride (gC3N4) by template free simple condensation and SrTiO3 nanocubes by sol-gel method were synthesized. Composites containing Different percentages of pGCN were prepared (x% pGCN-ST where x = 5, 10, 30, 50 & 70%). The as synthesized composites were characterized by various instrumental techniques such as X-Ray diffractometer, Fourier transform infrared spectrophotometer, BET surface area analyzer, UV Visible diffuse reflectance spectrophotometer, X-Ray photoelectron spectrophotometer, SEM with Energy dispersive X-ray analyzer (SEM/EDAX) and elemental mapping, Transmission electron microscope, Photoluminescence spectrophotometer and Electrochemical impedance. The composite catalysts were evaluated for their photocatalytic degradation of reactive blue 198 (RB 198), reactive black 5 (RB 5) and reactive yellow 145 (RY 145) in the presence of visible irradiation. Among the different composites 50% pGCN-ST catalyst showed remarkable decolourization of all the three dyes under different irradiation (UV, visible and solar). Kinetics studies were revealed that the photodecolourization reaction followed pseudo first order. TOC and COD studies confirmed that the dyes were mineralized significantly. A possible mechanism for photocatalytic degradation was also proposed in this study.

Enhanced photocatalytic activity of Fe3O4-WO3-APTES for azo dye removal from aqueous solutions in the presence of visible irradiation

ABSTRACTDevelopment of highly active photocatalysts for treatment of dye-laden wastewaters is vital. The photocatalytic removal of azo dye Reactive Black 5 was investigated by Fe3O4-WO3-3-aminopropyltriethoxysilane (APTES) nanoparticles in the presence of visible light. The Fe3O4-WO3-APTES nanoparticles were synthesized via a facile coprecipitation method. The photocatalyst was characterized by XRD, FT-IR, SEM, EDX, VSM, UV–Vis, and pHPZC techniques. The effects of some operational parameters such as solution pH, nanophotocatalyst dosage, initial RB5 concentration, H2O2 concentration, different purging gases, and type of organic compounds on the removal efficiency were studied by the Fe3O4-WO3-APTES nanoparticles as a photocatalyst. Maximum phtocatalytic activity was obtained at pH 3. The photocatalytic removal of RB5 increased with increasing H2O2 concentration up to 5 mM. The removal efficiency declined in the presence of different purging gases and all types of organic compounds. First-order rate constant (kobs) decreased from 0.027 to 0.0022 min−1 and electrical energy per order (EEo) increased from 21.33 to 261.82 (kWh/m3) with increasing RB5 concentration from 10 to 100 mg/L, respectively. The efficiency of LED/Fe3O4-WO3-APTES process for RB5 removal was approximately 89.9%, which was more effective than the LED/Fe3O4-WO3 process (60.72%). Also, photocatalytic activity decreased after five successive cycles.

Visible light photocatalytic activities of template free porous graphitic carbon nitride—BiOBr composite catalysts towards the mineralization of reactive dyes

Template free porous g-C3N4 (pGCN) and flower like bismuth oxybromide catalysts were synthesized by poly condensation and precipitation methods respectively. Various weight percentages of porous GCN-BiOBr composite catalysts (x% pGCN-BiOBr where x=5, 10, 30, 50 & 70wt% of pGCN) were synthesized by impregnation method. All the synthesized catalysts were characterized by X-Ray diffractometer, Fourier transform infrared spectrophotometer, BET surface area analyzer, UV Visible diffuse reflectance spectrophotometer, X-Ray photoelectron spectrophotometer, SEM with Energy dispersive X-ray analyzer (SEM/EDAX) and elemental mapping, Transmission electron microscope, Photoluminescence spectrophotometer and Electrochemical impedance. Photocatalytic degradation of all the synthesized catalysts were tested towards the harmful reactive dyes such as reactive blue 198 (RB 198), reactive black 5 (RB 5) and reactive yellow 145 (RY 145) in presence of visible irradiation. Among the catalysts 30% pGCN-BiOBr resulted in the highest photocatalytic activity towards the degradation of all the three dyes in presence of UV, visible and solar irradiations. Kinetics studies on the photocatalytic mineralization of dyes indicated that it followed pseudo first order. HPLC, TOC and COD studies confirm that the dyes are mineralized into CO2, water and mineral salts.

Modification of TiO2 to enhance photocatalytic degradation of organics in aqueous solutions

Heterogeneous photocatalysis, an advanced oxidation process (AOP), has shown to be efficient for the degradation of refractory organics in aqueous solutions into simple compounds. Two issues that arise with the use of unmodified TiO2 are the fast recombination of electron/hole pairs and the lower effectiveness in the presence of visible irradiation. This study aims to develop a photocatalyst by doping transition metals, especially noble metals such as Ag, onto the original TiO2. The combination of photocatalysts is a method to improve the photocatalytic activity for the degradation of organic compounds in wastewater. In this study, first Ag-doped TiO2 is prepared and then, a composite of Fe2O3/TiO2 is synthesized in different mass ratios. A series of experiments is conducted for the treatment of two azo dyes, Congo Red (CR) and Methyl Orange (MO), by photocatalysis under the UV–vis irradiation. The degradation of organic materials is measured in terms of total organic carbon (TOC). Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) along with the Brunauer, Emmet, and Teller (BET) method have been utilized to illustrate the characteristics of the prepared powder photocatalysts. X-ray diffraction (XRD) was used to identify crystallinity and phase conversion of the photocatalyst. Results show that silver doped TiO2 increases the degradation of MO (12.2%) and CR (14.5%) compared to that of the bare TiO2. The degradation efficiency of MO and CR increases by applying composite photocatalyst of Fe2O3/TiO2 in the range of 28.9 and 25.1%, respectively, compared to that of the bare TiO2.

Photochemical Degradation of Azo Dyes in the Presence of Hydrogen Peroxide and Hematite under Visible Light Irradiation: Surface Complex Forming and Reaction Mechanism

The photochemical degradation mechanisms of an azo dye Direct Red 4BS and Methyl Orange on hematite in the presence of H2O2 were investigated. The decolorization of azo dyes was attributed to the forming surface complex between specific bond of the dyes and hematite, which facilitate the electron transfer from hematite to azo bond. No mineralization of azo dyes occurred in the presence of visible irradiation, only chromogenic group destroyed in the photo-chemical reaction process. Surface complex between azo dyes and hematite will be destroyed under alkaline solution which suggested the active site or the formed surface complex had been destroyed by OH–. Chemical adsorption of the azo dyes on hematite was critical factor which affect the decolorization efficiency of the photoreaction.