Preparation and piezoelectric catalytic performance of HT-Bi2MoO6 microspheres for dye degradation

Ag-modified g-C3N4 with enhanced activity for the photocatalytic reduction of hexavalent chromium in the presence of EDTA under ultraviolet irradiation

The photocatalytic reduction of Cr6+ to Cr3+ in an aqueous solution, using 3 wt% Ag/g-C3N4 in the presence of ethylenediaminetetraacetic acid (EDTA), has been investigated here. The photocatalytic reduction of Cr6+ with pure g-C3N4 was very low. The addition of Ag and EDTA can significantly improve the photocatalytic reduction of Cr6+ using g-C3N4. In the presence of EDTA, the efficiency with Ag/g-C3N4 was better than those with Au/g-C3N4 and Cu/g-C3N4. With EDTA, the reduction rate constant increased from 0.0005 for pure g-C3N4 to 0.12 min-1 for 3 wt% Ag/g-C3N4. By increasing the concentration of EDTA from 0 to 500 mg L-1, the reduction efficiency of Cr6+ increased extremely, and the rate constant raised from 0.008 to 0.12 min-1. The optimal EDTA concentration was 500 mg L-1 for the photocatalyst Ag/g-C3N4. The Ag-EDTA complex may be reduced to metallic silver by the conduction band electrons of g-C3N4. The electron-hole recombination was significantly suppressed by the electron trapping of Ag. EDTA may act in by the formation of Cr3+-complex and the separation of Cr3+ from the g-C3N4 surface and by the valence band hole scavenger of g-C3N4. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL) were used to characterize g-C3N4 and Ag/g-C3N4 nanoparticles. A possible mechanism for photocatalytic Cr6+ reduction has also been demonstrated.

Efficient removal of 3,6-dichlorocarbazole with Fe0-activated peroxymonosulfate: performance, intermediates and mechanism

Nowadays, polyhalogenated carbazoles (PHCZs) are a major pollutant that has recently sparked widespread concern. In this work, peroxymonosulfate (PMS) was activated by zero valent iron (Fe⁰) to remove 3,6-dichlorocarbazole (3,6-CCZ). First, the key parameters influencing 3,6-CCZ degradation (PMS dosage, Fe⁰ dosage, initial pH, temperature and co-existing ions) were determined. Under the determined optimum conditions, the removal rate of 3,6-CCZ reached 100% within 1.5 h. Sulfate radicals (SO₄·^-), hydroxyl radicals (OH·), and singlet oxygen (¹O₂) generated in the reaction were directly identified with 0.1 M 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) by in-situ electron paramagnetic resonance (EPR) and indirectly identified by radical quenching experiments. The main reactive oxygen species (ROS) were different from most reported hydroxyl radicals (OH·) and sulfate radicals (SO₄·^-). In this study, it was found that OH· and ¹O₂ play a major role. Then, fresh and reacted Fe⁰ were characterized by XRD, SEM, and XPS. Iron corrosion products such as Fe₂O₃, Fe₃O₄, and FeOOH were generated. Finally, 3,6-CCZ degradation intermediates were identified by GC-MS and its degradation pathway was speculated. The intermediate pathway confirmed the combined action of (OH·) and (¹O₂) in 3,6-CCZ removal. This study provides new insight into the activation mechanism of Fe⁰-activated PMS and the removal mechanism of 3,6-CCZ.Highlights Fe⁰ is a long-lasting and efficient catalyst of PMS for the degradation of 3,6-CCZ.The key parameters influencing 3,6-CCZ degradation were determined.The degradation pathways of 3,6-CCZ were inferred.OH· and ¹O₂ were the main ROS in Fe⁰-activated PMS system.

Intrinsically morphological effect of perovskite BaTiO3 boosting piezocatalytic uranium extraction efficiency and mechanism investigation

Developing a convenient, efficient and eco-friendly approach for the recovery of U(VI) ion is a key measure to solve the environmental problems arising from the utilization of nuclear energy. Herein, the high efficiency of uranium extraction is realized by the piezo property of perovskite BaTiO₃, revealing the intrinsically morphological engineering effect on the piezocatalytic performance. Especially, BaTiO₃ nanowires (BTO NWs) exhibit not only an excellent piezocatalytic activity with U(VI) extraction rate of 96.8% in a UO₂(NO₃)₂ aqueous solution compared to 71.3% of BaTiO₃ nanoparticles (BTO NPs), but also a promising piezocatalyst for U extraction in a real U-mining wastewater with various pH ranges. Piezo response force microscopy and finite elemental simulation show that the piezo response of BTO NWs is much higher than BTO NPs. Additionally, some factors (pH, various ions, different powers) are explored on piezocatalytic efficiency for U(VI) extraction. The results from electron spin resonance and the charge/radical capture experiments confirm that the active species (e^-, •O^2-, •OH) stemmed from the piezo induction of BTO NWs and BTO NPs in the piezocatalytic U(VI) reduction process. The present work reveals the structure-performance correlation during piezocatalysis and highlights the crucial role of piezocatalysis in dealing with environmental problems.

Ni-doped MoS2 embedded in natural wood containing porous cellulose for piezo-catalytic degradation of tetracycline

Wood is a natural material with low cost and easy recovery, which porous, layered, excellent structure and mechanical properties make it possible to apply in wastewater treatment. We have successfully grown MoS₂ on natural wood containing porous cellulose and introduced the high conductivity circuit path provided by Ni nanoparticles to construct a new piezoelectric three-dimensional wood block for the efficient degradation of tetracycline. Ni/MoS₂/Wood exhibited excellent piezo-catalytic degradation performance, and the degradation rate of tetracycline reached 95.96 % (k = 0.0411 min^-1) under ultrasonic vibration. After 5 cycles, the degradation rate still reached 90.20 %. In addition, Ni/MoS₂/Wood was used as the reactor filler to degrade tetracycline through piezoelectric response triggered by hydrodynamic force, and the degradation rate reached 90.27 % after 60 min. Further, the mechanism and the possible degradation pathways of tetracycline degradation were proposed. This low-cost, recyclable and stable three-dimensional wood block piezoelectric material provides a new idea for the practical application of wastewater treatment.

In-situ-reduced synthesis of cyano group modified g-C3N4/CaCO3 composite with highly enhanced photocatalytic activity for nicotine elimination

Graphite carbon nitride has many excellent properties as a two-dimensional semiconductor material so that it has a wide application prospect in the field of photocatalysis. However, the traditional problems such as high recombination rate of photogenerated carriers limit its application. In this work, we introduce nitrogen deficiency into g-C₃N₄ to solve this problem a simple and safe in-situ reduction method. g-C₃N₄/CaCO₃ was obtained by a simple and safe one-step calcination method with industrial-grade micron particles CaCO₃. Cyano group modification was in-situ reduced during the thermal polymerization process, which would change the internal electronic structure of g-C₃N₄. The successful combination of g-C₃N₄ and CaCO₃ and the introduction of cyanide have been proved by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The formation of the cyano group, an electron-absorbing group, promotes the effective separation of photogenic electron hole pairs and inhibits the recombination of photogenic carriers. These advantages result in the generation of more •O₂^- and ¹O₂ in the catalytic system, which increases the photocatalytic efficiency of nicotine degradation by ten times. Furthermore, the degradation process of nicotine has been studied in this work to provide a basis for the degradation of nicotine organic pollutants in the air.

Outlook on bismuth-based photocatalysts for environmental applications: A specific emphasis on Z-scheme mechanisms

Semiconductor photocatalysis is thought to be a viable solution for addressing the growing problem of environmental pollution. Bismuth (Bi) metal oxides can function as a direct plasmonic photocatalyst or cocatalyst to accelerate the photogenerated charge separation and thus improve their photocatalytic activity. Hence, Bi-based photocatalysts have received a lot of attention due to their extensive environmental applications, including pollutant remediation and energy concepts. Massive efforts have been undertaken in the recent decade to find superior Bi-metal oxides (Bi₂XO_6, X = MO, W, or Cr) and to uncover the corresponding photocatalytic reaction mechanism for the degradation of organic contaminants in water. Herein, the unique crystalline and electronic properties and main synthesis methods, as well as the major Bi-Based direct Z-scheme photocatalysts, are timely discussed and summarized in their usage in water treatment. Besides, the impact of Bi₂XO₆ in energy storage devices and solar energy conversion is reviewed as an energy application. Finally, the future development and challenges of Z-scheme-based Bi₂XO₆ photocatalysts are briefly explored, summarized, and forecasted.

Synergistic photocatalytic effect of BiOBr-BiOI heterojunctions due to appropriate layer stacking

The increasing interest in acquiring efficient visible-light active photocatalytic materials has led to the formation of heterojunctions with different combinations of semiconductors. Despite the fact that increasingly more complex structures are proposed, there are still many unclear factors affecting their performance and limiting their prompt implementation. In this work, we used the spray pyrolysis technique to deposit individual visible light-active BiOBr and BiOI films and formed the heterojunctions BiOBr-BiOI and BiOI-BiOBr to determine the effect of the stacking order of semiconductors. These materials were widely characterized; their structural, optical, (photo)electrochemical, and photocatalytic properties were evaluated, revealing that the configuration BiOI-BiOBr boosted the photocatalytic indigo carmine dye removal under simulated sunlight irradiation, but the opposite layout quenched it. The high efficiency is attributed to a better use of the incident radiation and the effective migration of the photogenerated carriers. BiOBr - with a wider band gap and a less negative conduction band with respect to BiOI - provides its good attributes to the heterostructure, such as high stability and low recombination rates, when it is at the surface. We demonstrated that in thin-film heterostructures, the order in which the layers are stacked becomes decisive for the photocatalytic performance and that the energy band gap and the relative band positions of both semiconductors are the principal features that govern the photocatalytic mechanism. These findings provide a key to designing more efficient photocatalysts without several unsuccessful trials.

A 2D/1D heterojunction nanocomposite built from polymeric carbon nitride and MIL-88A(Fe) derived α-Fe2O3 for enhanced photocatalytic degradation of rhodamine B

2D/1D heterojunction α-Fe2O3/C3N4 photocatalysts containing α-Fe2O3 microrods and polymeric carbon nitride flakes are synthesised through the calcination of Fe-based metal-organic frameworks and boost the visible light photocatalytic degradation of rhodamine B.

A review on hierarchical Bi2MoO6 nanostructures for photocatalysis applications

This overview provides comprehensive understanding and development trends of hierarchical Bi2MoO6 nanostructures as photocatalysts for efficient photocatalysis applications.

In situ composite of Co-MOF on a Ti-based material for visible light multiphase catalysis: synthesis and the photocatalytic degradation mechanism

A Co-MOF/Ti-based Z-type heterojunction prepared by an in situ growth method exhibits good photocatalytic activity for tetracycline.

Enhancement of redox capacity derived from O-doping of g-C3N4/WO3 nanosheets for the photocatalytic degradation of tetracycline under different dissolved oxygen concentration

Element doping is an essential method for adjusting band structure, light absorbance and charge transfer, and separation of semiconductors. Besides this, whether the photocatalyst can function in an oxygen-deficient environment is also important. Herein, a novel Z-scheme heterojunction photocatalyst O-doped g-C₃N₄/WO₃ (OCN/W) was fabricated and used for the photocatalytic degradation of tetracycline (TC) at different dissolved oxygen concentrations. The introduction of O atoms into g-C₃N₄via hydrothermal treatment manipulates the band structure of the material by increasing the conduction band potential, thus producing more ˙O₂^-. The TC removal rate of OCN/W-2.0 is 89.8% within 60 min under visible light irradiation, which is 1.77 times higher than that of porous g-C₃N₄ nanosheets (PCN). Furthermore, the photocatalytic performance of OCN/W-2.0 also reaches 75% even under oxygen-deficient conditions. The effects of different anions and humic acid in the reaction system can be neglected. The enhanced performance can be attributed to the improved charge separation and the outstanding optical properties of the Z-scheme heterojunction. A possible mechanism was postulated, in which ˙O₂^- and h⁺ are the main reactive species in TC degradation. The OCN/W-2.0 shows a stable structure and outstanding reusability. This work provides insight into antibiotics removal under different dissolved oxygen conditions and the design of photocatalysts for practical applications.

Photodeposition of CoOx nanoparticles on BiFeO3 nanodisk for efficiently piezocatalytic degradation of rhodamine B by utilizing ultrasonic vibration energy

Piezoelectric materials have received much attention due to their great potential in environmental remediation by utilizing vibrational energy. In this paper, a novel piezoelectric catalyst, CoOx nanoparticles anchored BiFeO3 nanodisk composite, was intentionally synthesized via a photodeposition method and applied in piezocatalytic degradation of rhodamine B (RhB) under ultrasonic vibration. The as-synthesized CoOx/BiFeO3 composite presents high piezocatalytic efficiency and stability. The RhB degradation rate is determined to be 1.29 h-1, which is 2.38 folds higher than that of pure BiFeO3. Via optimizing the reaction conditions, the piezocatalytic degradation rate of the CoOx/BiFeO3 can be further increased to 3.20 h-1. A thorough characterization was implemented to investigate the structure, piezoelectric property, and charge separation efficiency of the CoOx/BiFeO3 to reveal the nature behind the high piezocatalytic activity. It is found that the CoOx nanoparticles are tightly adhered and uniformly dispersed on the surface of the BiFeO3 nanodisks. Strong interaction between CoOx and BiFeO3 triggers the formation of a heterojunction structure, which further induces the migration of the piezoinduced holes on the BiFeO3 to CoOx nanoparticles. The recombination of electron-hole pairs is retarded, thereby increasing the piezocatalytic performance greatly. This work may offer a new paradigm for the design of high-efficiency piezoelectric catalysts.

Novel application of Ag/PbBiO2I nanocomposite in piezocatalytic degradation of rhodamine B via harvesting ultrasonic vibration energy

Ag/PbBiO2I nanocomposite was synthesized and firstly applied in piezocatalytic degradation of rhodamine B (RhB) under ultrasonic vibration. The two-dimensional structure endows PbBiO2I nanosheets piezoelectric property, so that it can drive the piezocatalytic reaction under ultrasonic vibration. The loading of Ag nanoparticles forms Schottky barriers between the Ag-PbBiO2I contact region, which improves the separation of charge carriers and subsequently increases the piezocatalytic efficiency. The RhB degradation rate of the optimal Ag/PbBiO2I sample is 0.0165 min-1, which reaches 6.8 times that of pure PbBiO2I. This work indicates that the PbBiO2I nanosheet shows promising potential in utilizing ultrasonic vibration energy.

KNbO3/ZnO heterojunction harvesting ultrasonic mechanical energy and solar energy to efficiently degrade methyl orange

In this paper, KNbO₃/ZnO nanocomposite was synthesized and used in piezo/photocatalytic degradation of methyl orange (MO) under simulated sunlight and ultrasonic vibration. Under simulated solar light, the optimal KNbO₃/ZnO sample presented a MO degradation rate of 0.047 min^-1, which is 2.47 times higher than that of ZnO. The promotion effect of KNbO₃ on ZnO was also observed in the piezoelectric catalytic reaction. In addition, the co-utilization of solar and mechanical energy can further increase the MO degradation rate. Piezoelectric property and photoresponse capability are the origins of the piezo/photo catalytic behavior of the KNbO₃/ZnO composite. Owing to the different band potentials of KNbO₃ and ZnO, the electric potential field at their interface can drive the second distribution of the photo/piezoinduced charge carriers and hence promote the photo/piezocatalytic activity. This phenomenon was verified by the analysis on transient photocurrent and piezocurrent response. Trapping experiments on reactive species were also conducted. Superoxide radicals, holes, and hydroxyl radicals were found to be the main reactive species during the photo/piezocatalytic reaction. Recycling test showed that the KNbO₃/ZnO composite exhibited good catalytic stability during six consecutive uses. Given its advantages of good catalytic activity and stability, the synthesized KNbO₃/ZnO nanocomposite material has great potential in the further use of solar and mechanical energy to develop new water purification technologies.

Cadmium sulfide modified zinc oxide heterojunction harvesting ultrasonic mechanical energy for efficient decomposition of dye wastewater

CdS/ZnO nano heterojunction was synthesized and applied in piezocatalytic degradation of rhodamine B (RhB) under ultrasonic vibration. The optimal CdS/ZnO composite with a CdS content of 35% presented the highest RhB degradation efficiency (98.8%) in 90 min. The degradation rate reached 4.02 h^-1, which was 5.6 and 2.8 times higher than that of CdS and ZnO, respectively. In addition, CdS/ZnO showed high stability in the piezocatalytic reaction. The as-prepared CdS/ZnO piezocatalysts were characterized by multiple techniques to reveal the nature behind the enhanced catalytic activity. Results indicated that CdS nanoparticles were tightly loaded onto the surface of ZnO. The piezoelectric properties of the CdS/ZnO composites were the origin of their piezocatalytic behavior. The suitable band potentials of CdS and ZnO triggered the formation of a heterojunction structure, thereby driving the second distribution of the piezo-induced charge carriers. Therefore, the separation efficiency of charge carriers and the piezocatalytic performance was greatly elevated. The high piezocatalytic activity and stability indicated that CdS/ZnO may have wide application potential in the piezocatalytic degradation of organic dyes by using ultrasonic vibration energy.

Fabrication of g-C3N4/Y-TiO2 Z-scheme heterojunction photocatalysts for enhanced photocatalytic activity

The g-C3N4/Y-TiO2 Z-scheme heterojunction photocatalysts for enhanced photocatalytic activity that use yttrium instead of noble metals was successfully manufactured.