Enhanced photocatalytic activity of Bi24O31Br10 microsheets constructing heterojunction with AgI for Hg0 removal

Self-assembled micro and nano rod-shaped porphyrin@Bi12O17Cl2 composite as an efficient photocatalyst for degradation of organic contaminants

Bi12O17Cl2 is a potential photocatalyst in practical applications due to its excellent photostability, visible light activity, and competitive bandgap energy. However, the fast recombination of photogenerated charge carriers makes it impractical for pollution mitigation. Recently, aggregated porphyrins have emerged as photosensitizers in light-dependent applications such as photocatalysis. Although Bi12O17Cl2 and porphyrin can function as separate photocatalysts, their photocatalytic properties in terms of visible light adsorption, charge separation and transport, can be improved when they are combined to form heterostructure. In this study, rod-shaped aggregated 5,10,15, 20-Tetrakis (4-carboxyphenyl) porphyrin was synthesized by CTAB-assisted, self-assembly strategy and Bi12O17Cl2 by a facile microwave method. The porphyrin and Bi12O17Cl2 were combined to generate a series of x%Porphyrin@Bi12O17Cl2 having 0.02% wt., 0.1% wt., 0.4% wt., 1% wt. and 10% wt. as compositions of porphyrin. The materials' photocatalytic degradation efficiency was tested on Rhodamine B dye as a representative pollutant. The best and worst performances were reported for 1%Porphyrin@Bi12O17Cl2 and 10%Porphyrin@Bi12O17Cl2, respectively, which are 3.1 and 0.5 times increases in efficiency compared to pure Bi12O17Cl2. From the radical trapping experiment, electrons and superoxide were the dominant reactive species in the degradation process. The enhanced photocatalytic capability of the materials was attributed to the photosensitizing property of porphyrin and the heterojunction formation, which promotes the separation of photogenerated charge carriers. A plausible step-scheme (S-scheme) was proposed for the photocatalytic degradation mechanism. The S-scheme provided the high redox potential of the photogenerated charge carriers. The findings herein offer a new option for improving the photocatalytic performance of Bi12O17Cl2 for environmental applications through the photosensitization strategy.

Study on Photochemical Properties of a Sr-SnS2/CaIn2S4 Heterostructure to Improve Cr(VI) Removal

Compound semiconductor photocatalysis technology is considered to be a promising treatment for solving water problems efficiently. The point of designing high-efficiency catalysts is to optimize the band gap structure and facilitate the separation of charge carriers by establishing new electron migration pathways. Recently, 3D porous CaIn2S4 was found to have good photocatalytic ability. However, the quick recombination and agglomeration of carriers still limit its application. Herein, we prepared a heterostructure by introducing 2D Sr-doped SnS2 to 3D CaIn2S4 by a hydrothermal synthesis method. The optimal dosage of Sr-SnS2 is 3%, and the photocatalytic Cr(VI) removal efficiency of 3% Sr-SnS2/CaIn2S4 (SSCS-3) is 5.82 and 10.83 times those of pure CaIn2S4 and SnS2, respectively. According to the results of characterization tests and calculation verification, we inferred that the enhanced photocatalytic removal of Cr(VI) is due to the introduction of Sr-SnS2 that can promote the rapid transfer of photogenerated electrons to the surface of CaIn2S4, and the heterostructure formed between 2D Sr-SnS2 and 3D CaIn2S4 can also provide abundant reaction sites. The promotion of carrier separation is mainly due to the formation of a built-in electric field of the Sr-SnS2/CaIn2S4 heterostructure. This work provides new ideas and technologies for the treatment of Cr(VI) in wastewater.

Visible-light-driven AgI/Bi4O5I2 S-scheme heterojunction for efficient tetracycline hydrochloride removal: Mechanism and degradation pathway

The existence of excessive tetracycline hydrochloride (TCH) in the ecological environment has seriously threatened human health, so there is an urgent need to develop a high-performance photocatalyst that can efficiently and greenly remove TCH. Currently, most photocatalysts have the problems of fast recombination of photogenerated charge carriers and low degradation efficiency. Herein, S-scheme AgI/Bi₄O₅I₂ (AB) heterojunctions was constructed for TCH removal. Compared with the single component, the apparent kinetic constant of the 0.7AB is 5.6 and 10.2 time as high as the AgI and Bi₄O₅I₂, and the photocatalytic activity only decreases by 3.0% after four recycle runs. In addition, to verify the potential practical application of the fabricated AgI/Bi₄O₅I₂ nanocomposite, the photocatalytic degradation of TCH was performed under different conditions by regulating the dosage of photocatalyst, the TCH concentration, pH, and the existence of various anions. Systematical characterizations are conducted to investigate the intrinsic physical and chemical properties of the constructed AgI/Bi₄O₅I₂ composites. Based on the synergetic characterizations by in situ X-ray photoelectron spectroscopy, band edge measurements, as well as reactive oxygen species (ROS) detections, the S-scheme photocatalytic mechanism is proved. This work provides a valuable reference for developing efficient and stable S-scheme AgI/Bi₄O₅I₂ photocatalyst for TCH removal.

Synergistic Effect of Charge Separation and Multiple Reactive Oxygen Species Generation on Boosting Photocatalytic Degradation of Fluvastatin by ZnIn2S4/Bi2WO6 Z-Scheme Heterostructured Photocatalytst

The application of semiconductor photocatalysts with narrow band gaps is hindered by the rapid recombination of electron-hole pairs and limitation of multiple reactive oxygen species (ROS) synchronous generation. A n-n-type direct Z-scheme heterostructured photocatalyst was constructed based on the staggered band alignment of bismuth tungstate (Bi₂WO₆) and indium zinc sulfide (ZnIn₂S₄) to reveal the synergistic effect of charge separation and multiple ROS synchronous generation on boosting photocatalytic performance. Under irradiation, electrons in the conduction band (CB) of Bi₂WO₆ and holes in the valence band (VB) of ZnIn₂S₄ recombined at interface to prolong the lifetime of electrons in the CB of ZnIn₂S₄ and holes in the VB of Bi₂WO₆. Meanwhile, the multiple ROS synchronously generated to oxidize pollutant due to the strong redox ability of electrons of ZnIn₂S₄ and holes of Bi₂WO₆, which was determined by the CB potential of ZnIn₂S₄ and VB potential of Bi₂WO₆. The results provided valuable insights for the application of photocatalysts with a narrow band gap in the field of water pollution control.

Interference Effect of Experimental Parameters on the Mercury Removal Mechanism of Biomass Char under an Oxy-Fuel Atmosphere

In this paper, the effect of temperature, adsorption bed height, and initial mercury concentration under oxy-fuel combustion on mercury adsorption by 1% NH₄Cl-modified biomass char was studied. Modification enriched the pore structure of biomass char and increased the number of surface functional groups. Higher temperature would lead to the destruction of van der Waals and reduce the adsorption efficiency, while the change of adsorption bed height had no obvious effect. Adsorption thermodynamics shows that the mercury removal process is a spontaneous exothermic process. The increase of initial mercury concentration would increase the driving force of mercury diffusion to the surface and improve the adsorption capacity. Meanwhile, three kinetic models including the intraparticle diffusion model, pseudo-first-order model, and pseudo-second-order model were applied to explore the internal mechanism of mercury adsorption by biomass char. The results showed that the pseudo-first-order model and pseudo-second-order model could accurately describe the adsorption process, which meant that the progress of external mass transfer played an important role in the adsorption of mercury while chemical adsorption should not be ignored. The intraparticle diffusion model indicated that internal diffusion was not the only step to control the entire adsorption process and did not have an inhibition on mercury removal. Higher initial mercury concentration would promote the external mass transfer progress and chemical adsorption progress. In addition, higher temperature inhibited the external mass transfer, which was not conducive to the adsorption of mercury.

Bismuth-based photocatalyst for photocatalytic oxidation of flue gas mercury removal: A review

Photocatalytic oxidation method is a promising technology for solving flue gas mercury (Hg) pollution from industrial plants. Semiconductor photocatalysts have been widely applied in energy conversion and environmental remediation. However, key issues such as low light absorption capacity, wide energy band gap, and poor physicochemical stability severely limit the application of photocatalysts in practical industrial plants. In recent years, bismuth-based (Bi-based) photocatalysts, including bismuth oxide halide BiOX (X = Cl, Br or I), bismuth salt oxymetal BiVO₄, and BiOIO₃ etc., have increasingly aroused scientists' attention due to their peculiar crystalline geometric structures, tunable electronic structure and high photocatalytic performance. In present review, we firstly review the photocatalytic reaction mechanism and main photocatalytic oxidation mechanism of mercury. Secondly, the synthetic methods of Bi-based photocatalysts are summarized. Then, according to the mechanism of mercury removal, the experimental modifying approaches including heterojunction making, external atoms doping, defect creating, and crystal face regulating to promote the photocatalytic oxidation of mercury removal are summarized, as well as the determination of the band gap and electronic density of states (DOS) of Bi-based photocatalysts to elucidate the photocatalytic oxidation mechanism via density functional theory (DFT) calculation. Furthermore, constructing electronic transmission channels is an efficient way to improve the photocatalytic activity. Finally, challenges and perspectives of Bi-based photocatalyst for photocatalytic oxidation of mercury removal are presented. In addition, the excellent performance photocatalysts and efficient pollution removal equipment for mercury removal in industrial plants are still required in-depth study.