Wenlian William Lee

Synthesis of bismuth oxyiodides and their composites: characterization, photocatalytic activity, and degradation mechanisms

Bismuth oxyiodides have been prepared using controlled hydrothermal methods. The products are characterized by SEM-EDS, XRD, XPS, FTIR, PL, EPR, and DRS. It is illustrated that BiOI, Bi4O5I2, Bi7O9I3, Bi5O7I, and BiOxIy/BiOpIq composites can be selectively synthesized through a facile solution-based hydrothermal method. UV-Vis spectra display the bismuth oxyiodide materials as indirect semiconductors with an optical bandgap of 1.86–3.316 eV. The photocatalytic efficiency of the powder suspension is evaluated by measuring the Crystal Violet (CV) concentration. This is the first study to demonstrate the superior activities of BiOI, Bi4O5I2, Bi7O9I3, Bi5O7I, and BiOxIy/BiOpIq composites as promising visible-light-responsive photocatalysts. The quenching effects of various scavengers and EPR indicate that the reactive O2˙− plays a major role and ˙OH and h+ play a minor role. The Bi7O9I3/Bi5O7I composite shows the highest photocatalytic activity reaching a maximum rate constant of 0.2225 h−1, which is 6 times higher than that of BiOI and Bi7O9I3 and 4 times higher than that of Bi5O7I.

Mechanistic pathways differences between P25-TiO2 and Pt-TiO2 mediated CV photodegradation

The Crystal Violet (CV) dye represented one of the major triphenylmethane dyes used in textile-processing and some other industrial processes. Various metals doped titanium dioxide (TiO(2)) photocatalysts have been studied intensively for the photodegradation of dye in wastewater treatment. In order to understand the mechanistic detail of the metal dosage on the activities enhancement of the TiO(2) based photocatalyst, this study investigated the CV photodegradation reactions under UV light irradiation using a Pt modified TiO(2) photocatalyst. The results showed that Pt-TiO(2) with 5.8% (W/W) Pt dosage yielded optimum photocatalytic activity. Also the effect of pH value on the CV degradation was well assessed for their product distributions. The degradation products and intermediates were separated and characterized by HPLC-ESI-MS and GC-MS techniques. The results indicated that both the N-de-methylation reaction and the oxidative cleavage reaction of conjugated chromophore structure occurred, but with significantly different intermediates distribution implying that Pt doped TiO(2) facilitate different degradation pathways compared to the P25-TiO(2) system.

Novel synthesis of bismuth oxyiodide/graphitic carbon nitride nanocomposites with enhanced visible-light photocatalytic activity

The first systematic synthetic study of bismuth oxyiodide/graphitic carbon nitride (BiOxIy/g-C3N4) nanocomposite preparation using a controlled hydrothermal method is reported. The structure and morphology of BiOxIy/g-C3N4 photocatalysts are characterized by XRD, TEM, FT-IR, HR-XPS, FE-SEM-EDS, UV-vis-DRS and BET. The photodegradation activities are evaluated against the decolorization of crystal violet (CV) in aqueous solution under visible light illumination. In particular, the catalytic performance illustrates the best reaction rate constant, being 0.170 h−1 using Bi7O9I3/Bi5O7I/g-C3N4 composite as the photocatalyst; which is 5, 4, and 1.5 times higher than the reaction rate constant of BiOI, g-C3N4, and Bi7O9I3/Bi5O7I, as photocatalysts, respectively. From the quenching effects of different scavengers, the EPR results demonstrate that the reactive O2˙− plays the major role and h+ and ˙OH play minor roles in the CV degradation. The probable photodegradation mechanisms are proposed and discussed in this research. This work is useful for the synthesis of BiOxIy/g-C3N4 and the photocatalytic degradation of the CV for future applications in environmental pollution and control.

A novel heterojunction photocatalyst, Bi2SiO5/g-C3N4: synthesis, characterization, photocatalytic activity, and mechanism

A new type of heterojunction photocatalyst, Bi2SiO5/g-C3N4, was prepared using a controlled hydrothermal method. The structure and morphology of the Bi2SiO5/g-C3N4 photocatalyst were characterized by XRD, HR-TEM, FE-SEM-EDS, HR-XPS, FT-IR, PL, BET, EPR, and UV-Vis-DRS. The obtained Bi2SiO5/g-C3N4 photocatalyst exhibits enhanced photocatalytic activity on the decolorization of crystal violet (CV) under visible-light irradiation. In particular, the catalytic performance illustrates the best reaction rate constant of 0.1257 h−1 using Bi2SiO5/g-C3N4 as the photocatalyst, which is 5 and 3 times higher than the reaction rate constants of Bi2SiO5 and g-C3N4 as photocatalysts, respectively. This study shows that Bi2SiO5/g-C3N4 can be used to suppress the recombination of photoinduced electron–hole pairs and contribute to the enhanced photocatalytic efficiency of semiconductors in the visible light-driven catalysis. The quenching effects of different scavengers, and EPR results demonstrate that the reactive O2˙− plays the major role and ˙OH, h+ and 1O2 play minor roles in CV degradation. The probable photodegradation mechanisms are proposed and discussed.

Synthesis of a SrFeO3−x/g-C3N4 heterojunction with improved visible-light photocatalytic activities in chloramphenicol and crystal violet degradation

Some solid magnetic photocatalysts containing ferrites are convenient for being separated from reaction solutions by a magnet. This study reports the use of the SrFeO3−x/g-C3N4 photocatalyst heterojunction for the photocatalytic degradation chloramphenicol (CAP) and crystal violet (CV) under visible irradiation. Herein, the novel heterojunction of SrFeO3−x/g-C3N4 is fabricated by sintering SrFeO3−x with g-C3N4. This is the first report of a systematic synthetic study on the preparation and characterization of SrFeO3−x/g-C3N4 photocatalyst using a sintering method. The photocatalytic activities are evaluated by degrading CAP and CV in aqueous solution induced by visible light. The intermediates formed in the degradation of CAP are separated and identified by HPLC-ESI-MS technique. The quenching effects of different scavengers and EPR display that the reactive O2˙− and ˙OH radicals play the major roles and h+ plays a minor role in the CAP degradation. The possible degradation pathways are proposed and discussed in this research. The study is useful to the synthesis of SrFeO3−x/g-C3N4 and the degradation of CAP and CV for future applications concerning environmental pollution and control.