Photocatalytic degradation of ammonium dinitramide over novel S-scheme g-C3N4/BiOBr heterostructure nanosheets

Rational design of Bi2Sn2O7/Bi5O7I S-scheme heterojunction for visible photocatalytic oxidation of emerging pollutants

The construction of an S-scheme heterostructure is considered as a promising strategy for enhancing photocatalytic performance. Herein, a three-dimensional Bi5O7I (BOI) microsphere decorated with Bi2Sn2O7 (BSO) nanoparticles was prepared for the first time via a simple ultrasonic-assisted electrostatic self-assembly strategy and used for the degradation of 2,4-dinitrophenylhydrazine. 3 wt% Bi2Sn2O7/Bi5O7I has the highest degradation activity (93.7 %), with an apparent rate constant of 0.0848 min-1, which is 2.55 times that of the original Bi5O7I (0.0333 min-1). Moreover, the optimal binary heterojunction photocatalyst has good reusability and universal applicability. The results of cyclic voltammetry tests clarify that the optimal photocatalyst can provide more surface reactive sites. The results of radical trapping experiments and electron spin resonance indicate that holes (h+) and superoxide radicals are the main active radicals in the degradation process of 2,4-dinitrophenylhydrazine. Photoelectrochemical and photoluminescence confirm that 3 wt% Bi2Sn2O7/Bi5O7I composites exhibit the highest separation rate of photogenerated carriers. Finally, based on the results of experimental studies and theoretical calculations, the S-scheme charge transfer path on Bi2Sn2O7/Bi5O7I composite is determined. This work provides a new perspective on how to design high-performance S-scheme bismuth oxyhalide-based heterojunction photocatalysts for solar energy conversion.

Interface engineering of 0D/2D Cu2O/BiOBr Z-scheme heterojunction for efficient degradation of sulfamethoxazole: Mechanism, degradation pathway, and DFT calculation

Constructed heterojunction has been considered an efficient strategy to enhance the migration and transfer of photoinduced charge carriers. Herein, a Z-scheme Cu2O/BiOBr heterojunction with 0D/2D structure was fabricated by microwave hydrothermal method. It was found that the optimal composites photocatalyst showed excellent activity for sulfamethoxazole (SMZ) illumination, and the removal rate reached 90.7%, which was higher than pristine Cu2O (53.0%) and BiOBr (60.0%). Subsequently, the operational parameters such as catalyst dosage, concentrations of pollutants, and pH of solution were investigated. According to the ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRs), Mott-Schottky curve, and density functional theory (DFT) analysis, the Z-scheme degradation mechanism of Cu2O/BiOBr heterostructure was proposed. Among them, the interface structure of 0-dimensions/2-dimensions (0D/2D) can significantly increase the number of heterojunctions in the composite catalyst, and Z-scheme heterostructures can accelerate the generation and migration of photoinduced charge carriers, which has a facilitation effect on improving the decomposition activity of the photocatalyst. Moreover, three possible pathways for SMZ degradation were inferred. This study provides a promising strategy for constructing novel heterojunctions with high photocatalytic performance.

Improved visible light triggered photocatalytic activities of BiOCl photocatalysts via a synergistic effect of doping and heterojunction engineering

To manipulate the photocatalytic activities of BiOCl photocatalysts, doping and heterojunction engineering are simultaneously adopted. Herein, the photocatalysts Sm3+-doped BiOCl and BiOCl:Sm3+@yg-C3N4 were designed, in which their phase structure, morphology, optical properties and photocatalytic activities were systematically discussed. Excited at 408 nm, red emissions are seen from Sm3+-doped BiOCl microplates and their intensities were impacted by doping content, reaching the maximum value when the Sm3+ content was 1 mol% and the involved concentration mechanism was dominated by quadrupole-quadrupole interaction. Through analyzing the degradation of TC, the visible light triggered photocatalytic behaviors of the resultant compounds were studied. Compared with BiOCl microplates, an improved TC removal ability was seen in Sm3+-doped BiOCl microplates and the products with a Sm3+ content of 0.5 mol% show the best performance. Moreover, through constructing the heterojunction with g-C3N4, the TC removal capacity was further enhanced and the BiOCl:Sm3+@60%g-C3N4 exhibits the optimal photocatalytic activity, which was also much better than that of the commercial SnO2 and TiO2. Accordingly, the ˙O2-, h+ and ˙OH active species were proven to contribute to the involved visible light driven photocatalytic mechanism. Furthermore, the separation and recombination of photogenerated carries via the Z-scheme transfer process in the designed heterojunction composites, led to splendid photocatalytic properties. Additionally, it was verified that the TC solution treated with synthesized compounds was nontoxic toward plant growth. Our findings may propose an available route to regulate the photocatalytic performance of the visible light driven photocatalysts.

Rational design of CdS/BiOCl S-scheme heterojunction for effective boosting piezocatalytic H2 evolution and pollutants degradation performances

Piezocatalysis as an emerging technology is broadly applied in hydrogen evolution and organic pollutants degradation aspects. However, the dissatisfactory piezocatalytic activity is a severe bottleneck for its practical applications. In this work, CdS/BiOCl S-scheme heterojunction piezocatalysts were constructed and explored the performances of piezocatalytic hydrogen (H₂) evolution and organic pollutants degradation (methylene orange, rhodamine B and tetracycline hydrochloride) under strain by ultrasonic vibration. Interestingly, CdS/BiOCl presents a volcano-type relationship between catalytic activity and CdS contents, namely firstly increases and then decreases with the increase of CdS content. Optimal 20 % CdS/BiOCl endows superior piezocatalytic H₂ generation rate of 1048.2 μmol g^-1h^-1 in methanol solution, which is 2.3 and 3.4 times higher than that of pure BiOCl and CdS, respectively. This value is also much higher than the recently reported Bi-based and most of other typical piezocatalysts. Meanwhile, 5 % CdS/BiOCl delivers the highest reaction kinetics rate constant and degradation rate toward various pollutants compared with other catalysts, which also exceeds that of the previously numerous results. Improved catalytic capacity of CdS/BiOCl is mainly ascribed to the construction of S-scheme heterojunction for enhancing the redox capacity as well as inducing more effective charge carriers separation and transfer. Moreover, S-scheme charge transfer mechanism is demonstrated via electron paramagnetic resonance and Quasi-In-situ X-ray photoelectron spectroscopy measurements. Eventually, a novel piezocatalytic mechanism of CdS/BiOCl S-scheme heterojunction has been proposed. This research develops a novel pathway for designing highly efficient piezocatalysts and provides a deeper understanding in construction of Bi-based S-scheme heterojunction catalysts for energy conservation and wastewater disposal applications.

The Ovs surface defecting of an S-scheme g-C3N4/H2Ti3O7 nanoheterostructures with accelerated spatial charge transfer

Semiconductor photocatalysis was a rising star in the sustainable transformation of solar energy for environmental problems governance. Herein, an S-scheme g-C₃N₄/H₂Ti₃O₇ heterostructure was constructed and applied to tetracycline hydrochloride (TCH) destruction. The g-C₃N₄/H₂Ti₃O₇ composite has a superior photocatalytic property to degrade TCH in contrast with bare g-C₃N₄ and H₂Ti₃O₇. The 20% g-C₃N₄/H₂Ti₃O₇ (CNHTO20) composite exhibited the optimum photocatalytic performance, and the degradation efficiency of 20 mg/L TCH reached 87.37% within 3 h (K = 0.572 min^-1). The affluent active sites of the g-C₃N₄ nanosheet and effective interfacial charge separation of the S-scheme pathway facilitated the excellent performance. Moreover, the ample oxygen vacancies (Ovs) act as the electron mediator, not only reducing the band gap energy by producing the formation of defect levels, but also broadening the photo response range and promoting the interfacial charge transfer. The coordination complexes formed between TCH molecules and Ti (IV) ions in CNHTO20 composites induce strong visible light absorption through ligand-metal charge transfer (LMCT). The Ti⁴⁺/Ti³⁺ metal cycle in CNHTO20 was conducive to the separation of the photogenerated electron-hole pairs on the heterojunction interface as well. The ESR characterization and trapping experiments certified that the dominant substances were OH, O₂^- and h⁺. The AQY calculated by the COD removal rate was 0.16%. Conclusively, the S-scheme heterojunction between H₂Ti₃O₇ and g-C₃N₄ enabled the CNHTO photocatalyst with high redox ability and boosted photocatalytic performance accordingly. This study may shed some enlightenment on the construction of heterojunctions and the realistic treatment of wastewater.

Photocatalytic solid-phase degradation of polyethylene with fluoride-doped titania under low consumption ultraviolet radiation

Photodegradation of plastic in solid-phase requires the polymer to be composited with an efficient photocatalyst. We report herein the successful synthesis and characterization of fluoride-doped-TiO₂ and its applicability, for the first time, on solid-phase photodegradation of polyethylene films. Nearly half weight loss of polyethylene, containing only 2% of the photocatalyst, is eliminated after three weeks of ultraviolet A radiation using a low consumption light emitting diode lamp, defeating previously reported data. The half-life time of the plastic was around 3 weeks, highlighting the viability of this process for real applications. Results were compared to raw PE and PE composite with well-known TiO₂, resulting in, respectively, 0 and 26% of weight loss. The degradation process was monitored by optical microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared and X-ray photoelectron spectroscopy, which revealed the formation of plastic cracks, loss of polyethylene crystallinity and thus stability, the oxidation of C-H bonds and the oxidized state of the surface compounds during photodegradation. The obtained results open a path for the future production of cleaner and self-photodegradable plastics, where the photocatalyst would be introduced in all the manufactured plastics, making possible the quicker photodegradation of the plastics that end up on the environment and the plastics reaching wastewater treatment plants.

In-situ constructed 2D/2D ZnIn2S4/Bi4Ti3O12 S-scheme heterojunction for degradation of tetracycline: Performance and mechanism insights

Semiconductor materials dominated photocatalytic technology is one of the most efficient approaches to degrade organic pollutants. However, the limited light absorption range and rapid recombination of photogenerated carriers greatly restrict the application of photocatalysts. Rational design of photocatalysts to achieve high catalytic activity and stability is of great importance. Herein, ZnIn₂S₄/Bi₄Ti₃O₁₂ S-scheme heterojunction is synthesized by growing the ZnIn₂S₄ nanosheets on the sheet-like Bi₄Ti₃O₁₂ surface via a low-temperature solvothermal method. The TC removal efficiency of optimized heterojunction reaches 82.1% within 60 min under visible light, and the rate constant is nearly 6.8 times than that of pristine ZnIn₂S₄. The favorable photocatalytic performance of heterojunction is attributed to the tight contact interface and efficient separation of photogenerated carriers. Besides, the difference in work function between ZnIn₂S₄ and Bi₄Ti₃O₁₂ leads to band bending and the establishment of built-in electric field on the contact interface of heterojunction, which facilitates the migration and separation of photogenerated carriers. Furthermore, the cycling test demonstrates the attractive stability of heterojunction. The possible TC photodegradation pathways and toxicity assessment of the intermediates are also analyzed. In conclusion, this work provides an effective strategy to prepare S-scheme heterojunction photocatalysts with favorable photocatalytic activity, which can enhance wastewater purification efficiency.

Fabrication of 2D/2D BiOBr/g-C3N4 with efficient photocatalytic activity and clarification of its mechanism

Precise regulation of photoexcited charge carriers for separation and transportation is a core requirement for practical application in the photocatalysis field. Herein, a 2D/2D BiOBr/g-C₃N₄ heterojunction is prepared by a self-assembly method and exhibits enhanced and stable activity for photocatalytic degradation of bisphenol A (BPA) and norfloxacin (NFA) under visible light. Compared to pure g-C₃N₄, the kinetic constants of BPA and NFA degradation over BiOBr/g-C₃N₄ are enhanced by about 14.74 and 4.01 times, respectively. The separation and transportation mechanism for the photoexcited charge carriers is clarified by electron paramagnetic resonance (EPR), in situ X-ray photoelectron spectroscopy (in situ XPS), and theoretical calculations. The results show that BiOBr/g-C₃N₄ exhibits the feature of a relative p-n junction, in which the charges photoexcited on BiOBr/g-C₃N₄ with high redox potentials can be kept and spatially separated. Moreover, the built-in electric field with the direction of g-C₃N₄ → BiOBr and the opportune band curvature provide the driving force for charge separation and transportation. Additionally, BPA and NFA degradation intermediates are also detected by liquid chromatography-mass spectrometry. It is of great significance to fabricate efficient photocatalysts for environmental purification and other targeted reactions.