Chiing-Chang Chen

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.

Hydrothermal synthesis of bismuth oxybromide–bismuth oxyiodide composites with high visible light photocatalytic performance for the degradation of CV and phenol

This is the first report on a series of BiOpBrq/BiOmIn heterojunctions that were prepared using controlled hydrothermal methods. The compositions and morphologies of the BiOpBrq/BiOmIn could be controlled by adjusting some growth parameters, including reaction pH value, temperature, time, and KBr/KI molar ratio. The photocatalytic efficiency of the powder suspensions was evaluated by measuring crystal violet (CV) and phenol concentrations. Both the photocatalytic process and the photosensitized process were found to work concurrently. The quenching effects of various scavengers and EPR indicated that the reactive O2˙− played a major role and ˙OH and h+ played minor roles. The photocatalytic activity of the BiOpBrq/BiOmIn heterojunctons reached the maximum rate constant of 0.5285 (or 0.4713) h−1, 10 times higher than that of P25–TiO2, 14 times higher than that of BiOBr, and 6 times higher than that of BiOI.

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 series of BiOxIy/GO photocatalysts: synthesis, characterization, activity, and mechanism

A series of bismuth oxyiodide (BiOxIy)-grafted graphene oxide (GO) sheets with different GO contents were synthesized through a simple hydrothermal method. This is the first report where four composites of BiOI/GO, Bi4O5I2/GO, Bi7O9I3/GO, and Bi5O7I/GO have been characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The assembled BiOxIy/GO composites exhibited excellent photocatalytic activities in the degradation of crystal violet (CV) under visible light irradiation. The order of rate constants was as follows: Bi7O9I3/GO > Bi4O5I2/GO > Bi4O5I2 > Bi7O9I3 > Bi5O7I/GO > BiOI/GO > BiOI > Bi5O7I > GO. The photocatalytic activity of the Bi7O9I3/GO (or Bi4O5I2/GO) composite reached a maximum rate constant of 0.351 (or 0.322) h−1, which was 1.8 (or 1.7) times higher than that of Bi7O9I3 (or Bi4O5I2), 6–7 times higher than that of BiOI/GO, and 119–130 times higher than that of BiOI. The quenching effects of different scavengers and electron paramagnetic resonance demonstrated that the superoxide radical (O2˙−) played a major role and holes (h+) and hydroxyl radicals (˙OH) played a minor role as active species in the degradation of crystal violet (CV) and salicylic acid (SA). Possible photodegradation mechanisms are proposed and discussed in this research.

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.

Photolysis and photocatalytic decomposition of sulfamethazine antibiotics in an aqueous solution with TiO2

Photo-decomposition of sulfamethazine (SMT) involves photolytic and photo-catalytic reactions, which occur simultaneously. The relative contributions of these two reactions to the overall SMT photo-decompositions by TiO2 and the intermediates of SMT photo-decompositions were systematically examined with the effects of TiO2 loading, and the pH and the initial SMT concentrations in the solutions. The apparent rate constants of SMT photo-decomposition reactions, which were well described by the pseudo-first-order kinetic model, ranged from 0.24 to 1.61 h−1. The overall photo-decomposition efficiencies of 0.072 mM SMT were the highest at pH 5.5 with 0.5 g L−1 TiO2 due to the adsorption-induced photocatalytic decomposition of SMT on TiO2. However, the SMT photolysis occurred more rapidly at pH 10. Two reactive species of holes and hydroxyl radicals concurrently participated in the photocatalytic decomposition of SMT, and the latter dominated the oxidative reactions of SMT on TiO2. Eight intermediates of SMT photo-decomposition were determined using LC-MS. Their time-dependent distributions indicated that the photo-decomposition of SMT was triggered by hydroxylation on aniline and dimethylpyrimidinyl moieties, followed by the cleavage of the S–N bond of SMT. Our results illustrated that the intermediates with dimethylpyrimidinyl groups possess strong resistance to photo-decomposition and played a determinant role in the photo-decomposition of SMT.

Controlled hydrothermal synthesis of bismuth oxychloride/bismuth oxybromide/bismuth oxyiodide composites exhibiting visible-light photocatalytic degradation of 2-hydroxybenzoic acid and crystal violet

This paper presents an unprecedented systematic synthetic study of a controlled hydrothermal method for the preparation of bismuth oxychloride/bismuth oxybromide/bismuth oxyiodide ternary composites (BiOxCly/BiOmBrn/BiOpIq). The pH, temperature, and KCl:KBr:KI molar ratio for the reactions were adjusted to control the compositions and morphologies of BiOxCly/BiOmBrn/BiOpIq composites. Scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, Brunauer-Emmett-Teller specific surface areas, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy were applied to the products. The photocatalytic activities of dispersions were examined by monitoring the 2-hydroxybenzoic acid (HBA) and crystal violet concentrations. Various scavengers demonstrated quenching effects. O2- was crucial to HBA degradation, whereas h+ and OH played minor roles in HBA degradation. This text hypothesizes possible photodegradation mechanisms.

Composite photocatalyst, tetragonal lead bismuth oxyiodide/bismuth oxyiodide/graphitic carbon nitride: Synthesis, characterization, and photocatalytic activity

Semiconductor photocatalysts that are robust and galvanized by visible light have been increasingly sought after, with lead bismuth oxyhalide (PbBiO2X)-which constitutes a perovskite-like semiconductor-receiving vast attention recently. We noted, after a relevant literature survey, that tetragonal lead bismuth oxyiodide/bismuth oxyiodide/graphitic carbon nitride (t-PbBiO2I/Bi5O7I/g-C3N4)-supported crystal violet (CV) dye photocatalytic degradation under irradiation with visible light has yet to be reported. The current study provides the report of t-PbBiO2I/Bi5O7I/g-C3N4 composite isolation and characterization realized through field-emission scanning electron microscopy-energy-dispersive spectroscopy, X-ray diffraction, high-resolution X-ray photoelectron spectroscopy, transmission electron microscopy, photoluminescence spectroscopy, Brunauer-Emmett-Teller analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. Catalytic performance observation revealed that using t-PbBiO2I/Bi5O7I/g-C3N4 resulted in an optimal reaction rate constant of 0.3518u202fh-1, a derivation exceeding the derivations for the photocatalysts t-PbBiO2I, Bi5O7I, g-C3N4, and t-PbBiO2I/Bi5O7I by 15, 6.6, 13.1, and 1.4 times, respectively. As demonstrated by the quenching effects associated with diverse scavengers, the electron paramagnetic resonance results revealed reactive O2- to have a major role in the CV dye degradation. The paper proposes and also describes possible photodegradation mechanisms. The method that was realized in this study is valuable for PbBiO2I/Bi5O7I/g-C3N4 synthesis and CV dye photocatalytic degradation for future applications in environmental pollution regulation.

Bismuth oxyfluoride/bismuth oxyiodide nanocomposites enhance visible-light-driven photocatalytic activity

This is the first paper to report a series of bismuth oxyfluoride/bismuth oxyiodide (BiOpFq/BiOxIy) nanocomposites with different F/I molar ratios, pH values, and reaction temperatures that were synthesized through a template-free and controlled hydrothermal method. These nanocomposites were characterized through scanning electron microscope energy dispersive microscopy (SEM-EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and diffuse reflectance spectroscopy (DRS). Under visible-light irradiation, the BiOpFq/BiOxIy composites exhibited excellent photocatalytic activities in the degradation of crystal violet (CV) and 2-hydroxybenzoic acid (HBA). The order of rate constants was BiOF/BiOIu202f>u202fBiOIu202f≫u202fBiOF. The photocatalytic activity of BiOF/BiOI composites reached a maximum rate constant of 0.2305u202fh-1, 1.2 times higher than that of BiOI and 100 times higher than that of BiOF. Thus, the derived BiOF/BiOI is crucial for photocatalytic activity enhancement. After the removal of CV in the third cycle, no apparent deficits in photocatalytic activity were observed, and the observed deficit was 8.2% during the fifth run. Overall, the catalytic activity and stability observed for the proposed composites were determined to be adequate under visible-light irradiation. For various scavengers, the noted quenching effects demonstrated that reactive O2- has a notable role in the degradation of the applied CV.