Facile synthesis and enhanced photocatalytic activity of a novel FeVO4/Bi4O5Br2 heterojunction photocatalyst through step-scheme charge transfer mechanism

Construction of a step-scheme (S-scheme) heterojunction photocatalyst is currently under investigation as it is known to facilitate a decrease in the e–/h+ recombination rate and preserves a strong redox ability. This research work has reported on the use of microwave irradiation combined with the wet impregnation synthesis of FeVO4/Bi4O5Br2 heterojunctions at different weight percentages (%wt) of FeVO4 (0.5%, 1%, 3% and 5%wt). The visible-light-driven photocatalytic activities for the photoreduction of Cr(VI), and the decontamination of certain organic pollutants (bisphenol A; BPA, rhodamine B; RhB, and tetracycline hydrochloride; TC) were also investigated. Ethylene glycol that was used as a reaction medium in the microwave synthesis process played a key role in the formation control of a flower-like structure of bismuth-rich Bi4O5Br2. Among the heterojunction photocatalysts, FeVO4/Bi4O5Br2 with 1%wt of FeVO4 markedly maximized the photocatalytic activity. Specifically, 95% of Cr(VI) was reduced by a reduction rate that was 6.0 times higher than that of Bi4O5Br2. Similarly, this photocatalyst was able to degrade 90%, 97%, and 88% of BPA, RhB, and TC at degradation rates that were 2.0, 1.2, and 1.6 times higher than Bi4O5Br2, respectively. Trapping experiments indicated that •O2− and h+ were the main active species responsible for the organic pollutant degradation, while •OH played a minor role in this process. These outcomes were confirmed with the use of the nitrotetrazolium blue transformation method and the terephthalic acid photoluminescence probing technique. Enhancement in the photo-activity of 1%wt-FeVO4/Bi4O5Br2 was attributed to the extended visible-light absorption range as well as the efficient generation, separation, and migration of photo-generated charge carriers through the S-scheme charge transfer mechanism which was supported by the results from the trapping experiments, XPS and UV–vis DRS analyses, Ag and PbO2 photo-deposition experiments, and electrochemical studies, along with the consideration of the reduction potentials of reactive oxygen species

Double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary heterojunction photocatalyst for simultaneous photocatalytic removal of hexavalent chromium and rhodamine B

Hypothesis Fabrication of the heterojunction photocatalyst with appropriate band potentials as a promising method of inhibiting electron-hole pair recombination leading to enhanced photocatalytic properties. Experiments Herein, BiOBr, Bi4O5Br2, and binary BiOBr/Bi4O5Br2 composite were selectively synthesized by employing a one-step microwave irradiation method. Then, double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary composites with different weight percentages (%wt) of FeVO4 were fabricated and their photocatalytic applications were studied. The photodegradation of organic compounds (rhodamine B (RhB), methylene blue (MB) and salicylic acid (SA)), along with the photoreduction of hexavalent chromium (Cr(VI)) were investigated. Findings Comparing with the single and binary photocatalysts, and a commercial TiO2, the 1 %wt-FeVO4/Bi4O5Br2/BiOBr photocatalyst demonstrated superior visible-light-driven photocatalytic performance. In a Cr(VI)/RhB combined system, Cr(VI) photoreduction was further improved and coexisting RhB molecules were simultaneously degraded. Removal of Cr(VI) and RhB were maximized by adjusting both pH values and catalyst dosages. Based on UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical investigations, active-species trapping, nitrotetrazolium blue transformation, and silver photo-deposition experiments, a double Z-scheme charge transfer mechanism with an RhB-sensitized effect was proposed. This special mechanism has led to significant enhancement in charge segregation and migration, along with higher redox properties of the ternary composite, which were responsible for the excellent photocatalytic activity

Bismuth-rich oxyhalide (Bi7O9I3?Bi4O5Br2) solid-solution photocatalysts for the degradation of phenolic compounds under visible light

Hypothesis: The development of solid-solution photocatalysts with tunable bandgaps and band struc- tures, which are significant factors that influence their photocatalytic properties, is crucial. Experiments: We fabricated a series of novel bismuth-rich Bi7O9I3–Bi4O5Br2 solid-solution photocatalysts with controlled I:Br molar ratios (denoted as B-IxBr1-x, x = 0.2, 0.3, 0.4, or 0.6) via a rapid, facile, and energy- efficient microwave-heating route. The photodegradations under visible-light irradiation of the phenolic compounds (4-nitrophenol (4NP), 3-nitrophenol (3NP), and bisphenol A (BPA)), and the simultaneous photodegradation of BPA and rhodamine B (RhB) in a coexisting BPA ? RhB system were investigated. Findings: The B-I0.3Br0.7 solid solution provided the highest photocatalytic activity toward 4NP degrada- tion, with degradation rates 32 and 4 times higher than those of Bi7O9I3 and Bi4O5Br2, respectively. The photodegradation efficiency of the studied phenolic compounds followed the order BPA (97.5%) > 4NP (72.8%) > 3NP (27.5%). The RhB-sensitization mechanism significantly enhanced the photodegradation efficiency of BPA. Electrochemical measurements demonstrated the efficient separation and migration of charge carriers in the B-I0.3Br0.7 solid solution, which enhanced the photocatalytic activity. The B- I0.3Br0.7 solid solution effectively activated molecular oxygen to produce ?O2 ?, which subsequently pro- duced other reactive species, including H2O2 and ?OH, as revealed by reactive-species trapping, nitroblue tetrazolium transformation, and o-tolidine oxidation experiments

Photocatalytic activity of CuInS2 nanoparticles synthesized via a simple and rapid microwave heating process

In this research, visible–light photocatalytic activities of CuInS2 nanoparticles for degradation of three organic dyes (rhodamine B; RhB, methylene blue; MB, and methyl orange; MO) were investigated. The CuInS2 nanoparticles were synthesized by a simple and rapid microwave heating process using sodium sulfide as a sulfur source and then characterized by x–ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) techniques. The synthesized CuInS2 nanoparticles exhibited excellent photocatalytic degradation activity to the cationic dyes (RhB and MB) when compared with that of anionic dye (MO). Zeta potential of the CuInS2 photocatalyst was measured to elucidate the adsorption ability toward dye molecules. A possible photocatalytic degradation mechanism was proposed based on active species quenching experiments and Mott–Schottky analysis

Enhanced visible-light photocatalytic activity of FeVO4/Bi2WO6 heterojunction via Z-scheme charge-transfer mechanism

The design and construction of a Z-scheme heterojunction, aiming to strengthen its redox ability for photocatalytic applications, is challenging. In this study, a series of x mol%-FeVO4/Bi2WO6 heterostructures were fabricated. FeVO4 content was tuned for enhanced organic pollutants photodegradation. The 2.5 mol%-FeVO4/Bi2WO6 photocatalyst exhibited superior photodegradation efficiency with high recyclability and stability for bisphenol A and methylene blue, which was 3.3 and 2.6 times faster than that of Bi2WO6, respectively. Moreover, the fabricated photocatalyst showed remarkable selectivity toward methylene blue as compared to that toward brilliant green and methyl orange. The photo-efficacy was enhanced owing to the close interfacial contact between Bi2WO6 and FeVO4 nanoparticles, resulting in a Z-scheme FeVO4/Bi2WO6 heterojunction, which enabled efficient charge transfer imparting strong reducing ability to the electrons for the reduction of O2 to •O2−, and subsequent production of H2O2 and •OH. This work highlights a potential photocatalyst for photodegradation of environmental pollutants

Direct Z-scheme FeVO4/BiOCl heterojunction as a highly efficient visible-light-driven photocatalyst for photocatalytic dye degradation and Cr(VI) reduction

In this work, potential applications of a direct Z-scheme FeVO4/BiOCl heterojunction for photocatalytic degradation of organic dyes (methylene blue, MB and rhodamine B, RhB) and reduction of hexavalent chromium (Cr(VI)) ion under visible light irradiation were reported. Firstly, FeVO4 and BiOCl were synthesized by using a microwave heating method. Then, the FeVO4/BiOCl nanocomposites with different weight percentages of FeVO4 (1, 3, 6.25, 12.5 and 25%wt) were fabricated by a method of modified wet impregnation. The photocatalytic degradation activities of the nanocomposites were investigated in parallel with pure BiOCl and FeVO4. Among the as-prepared nanocomposites, the FeVO4/BiOCl nanocomposite with 6.25%wt of FeVO4 exhibited the highest photocatalytic dye degradation efficiency; 99.8% of RhB was degraded after being irradiated for 360 min, while 87.2% of MB was degraded. Similarly, this nanocomposite photocatalytically reduced 97.8% of Cr(VI) at a pH value of 3. The superior photocatalytic activity can be ascribed to the effective visible light absorption of the FeVO4/BiOCl heterojunction and the suppression of the recombination process of photogenerated electron–hole pairs. Additionally, the improved charge migration and separation efficiencies between FeVO4 and BiOCl through the direct Z-scheme charge transfer pathway are involved, as evidenced by the trapping experiments, and the UV–visible diffuse reflectance (UV–vis DRS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy analyses. Photocatalytic mechanisms of the direct Z-scheme FeVO4/BiOCl heterojunction for the photodegradation of RhB and photoreduction of Cr(VI) have been proposed and discussed in greater detail

A novel CuInS2/m-BiVO4 p-n heterojunction photocatalyst with enhanced visible-light photocatalytic activity

Novel CuInS2/m-BiVO4 composites with different mass ratios (CuInS2 to m-BiVO4 = 1:3, 1:1, and 3:1) were synthesized and their potential visible-light photocatalytic applications for photodegradation of some organic dyes (methylene blue, rhodamine B, and methyl orange) and inactivation of bacteria (Pseudomonas aeruginosa) were investigated. CuInS2/m-BiVO4 with a mass ratio of 1:3 exhibited better photocatalytic degradation of methylene blue and antibacterial activity than those of either pure CuInS2 or m-BiVO4. Moreover, this composite photocatalyst showed different photocatalytic selectivity in terms of the organic dye degradation. Salicylic acid was also used to test the photocatalytic activity of this composite to clarify the dye sensitization effect. The photoelectrochemical (PEC) properties of the CuInS2/m-BiVO4 photoelectrode, evaluated by linear sweep voltammetry (LSV) measurement, revealed that the composite photoelectrode exhibited higher current density and onset potential in comparison with the m-BiVO4 photoelectrode. In addition, the electrochemical impedance spectroscopy (EIS) measurement also proved a faster rate of charge transfer at the electrode/electrolyte interface. The enhancement of photocatalytic and PEC activities of the CuInS2/m-BiVO4 composite was revealed not only that the CuInS2/m-BiVO4 composite extended light absorption in the visible light region, but also that the formation of a p-n heterojunction could promote photogenerated charges as well as facilitate effective charge separation and transportation between the CuInS2 and m-BiVO4 contact interface

Synthesis of BiVO4 photocatalyst via cyclic microwave irradiation method

Visible light-active BiVO4 photocatalyst was successfully synthesized through a cyclic microwave irradiation method without further calcination process. The synthesized powder was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The BiVO4 powder revealed an excellent photocatalytic degradation of methylene blue under visible light irradiation. The degraded methylene blue was monitored by both UV-Vis spectrophotometer and absorbance in RGB channels. Similar decolorization percentage as well as pseudo first-order rate constant were achieved with high accuracy and sensitivity. The light absorption in RGB channels is an alternative simple and cartable way requiring lower amount of sample for detecting the dye degradation photocatalytic activity

Synthesis of NiO nanostructures by sonocatalyzed microwave irradiation technique and their acetone sensing properties

Nickel oxide (NiO) nanostructures were synthesized by sonocatalyzed microwave irradiation technique, followed by calcination process. Electron microscopic images of NiO powder calcined at 500 °C revealed coexistence of nanorods and spherical nanoparticles. The NiO powders calcined at 600 and 700 °C composed of spherical nanoparticles, where a larger particle size was observed for the powder calcined at 700 °C. The acetone sensor response of the fabricated NiO sensors revealed that shape and size of the NiO particles affected the response. The response increased with increasing acetone gas concentration, which reached a maximum value at the operating temperature of 325 °C

Novel FeVO4/Bi7O9I3 nanocomposite with enhanced photocatalytic dye degradation and photoelectrochemical properties

Novel FeVO4/Bi7O9I3 nanocomposites with different weight percentages (3, 6.25, 12.5, and 25%wt) of FeVO4 were successfully synthesized by cyclic microwave irradiation, followed by wet impregnation. The applications for photocatalytic dye degradation and photoelectrochemical (PEC) were investigated. The 6.25%wt-FeVO4/Bi7O9I3 nanocomposite exhibited excellent photocatalytic degradation of methylene blue, rhodamine B, and methyl orange with decolorization efficiencies of 81.3%, 98.9%, and 94.9% within 360 min, respectively. Moreover, this nanocomposite possessed excellent reusability and stability during the photocatalytic degradation process. PEC performance in water oxidation of the 6.25%wt-FeVO4/Bi7O9I3 photoanode was evaluated by linear sweep voltammetry (LSV) measurement. Enhanced PEC performance with photocurrent density of 0.029 mA cm−2 at 1.23 V (vs. RHE) was observed under visible-light irradiation, which was ca. 3.7 times higher than that of the pure Bi7O9I3. Based on the optical characterization, energy band positions, and active species trapping experiments, a possible photocatalytic mechanism of the FeVO4/Bi7O9I3 heterojunction was discussed. The enhancement in the photocatalytic and the PEC performance ascribed to synergistic effects of visible-light absorption and a favorable “type II heterojunction” structure of the FeVO4/Bi7O9I3 nanocomposite. These were the main effects that promoted the photogenerated electrons and holes transfer across the contact interface between FeVO4 and Bi7O9I3, as well as suppressed the recombination of photogenerated electron-hole pairs and facilitated charge separation and transportation