Remarkably enhanced catalytic performance in CoOx/Bi4Ti3O12 heterostructures for methyl orange degradation via piezocatalysis and piezo-photocatalysis.

A novel heterojunction composite of CoOx/Bi4Ti3O12 was synthesized through a combination of molten salt and photodeposition methods. The optimal sample exhibited superior performance in the piezocatalytic degradation of methyl orange (MO) dye with a degradation rate of 1.09 h-1, which was 2.4 times higher than that of pristine Bi4Ti3O12. Various characterizations were conducted to reveal the fundamental nature accountable for the outstanding piezocatalytic performance of CoOx/Bi4Ti3O12. The investigation of the band structure indicated that the CoOx/Bi4Ti3O12 composite formed a type-I p-n heterojunction structure, with CoOx acting as a hole trapper to effectively separate and transfer piezogenerated carriers. Significantly, the MO degradation rate of the best CoOx/Bi4Ti3O12 sample further increased to 2.96 h-1 under combined ultrasonic vibration and simulated sunlight. The synergy between piezocatalysis and photocatalysis can be ascribed to the following factors. The photoexcitation process ensures the sufficient generation of charge carriers in the CoOx/Bi4Ti3O12, while the piezoelectric field within Bi4Ti3O12 promotes the separation of electron-hole pairs in the bulk phase. Furthermore, the heterojunction structure between Bi4Ti3O12 and CoOx significantly facilitates the surface separation of charge carriers. This increased involvement of free electrons and holes in the reaction leads to a remarkable enhancement in catalytic MO degradation. This work contributes to the understanding of the coupling mechanism between the piezoelectric effect and photocatalysis, and also provides a promising strategy for the development of efficient catalysts for wastewater treatment.

In Situ Fabrication of an S-Scheme NaNbO3/Bi2O2CO3 Heterojunction for Enhanced Performance in Photocatalytic Nitrogen Fixation.

In this study, NaNbO3 microcubes were introduced during the preparation of Bi2O2CO3 nanosheets to construct a series of NaNbO3/Bi2O2CO3 heterojunctions with varying NaNbO3 content. Their photoactivities for N2 fixation were examined and compared. Results demonstrated that 7.5% NaNbO3/Bi2O2CO3 had the highest photoactivity. The NH3 production rate under simulated solar light is 453.1 µmol L-1 g-1 h-1, representing 2.0 and 3.8-fold increases compared to those of Bi2O2CO3 and NaNbO3, respectively. A comprehensive investigation encompassing the physical and chemical properties of the NaNbO3/Bi2O2CO3 photocatalyst was conducted. Bi2O2CO3 nanosheets were discovered to be distributed on the NaNbO3 microcubes surface. The addition of NaNbO3 exhibited nearly no effect on the photoabsorption performance and specific surface area of the Bi2O2CO3. However, the tight contact between NaNbO3 and Bi2O2CO3 and their appropriate band positions led to the formation of a heterojunction structure between them. The electron drift occurring in the interface region induces the creation of an internal electric field and energy band bending. This facilitates the transfer of photogenerated electrons and holes through an S-scheme mechanism, achieving efficient separation without compromising the redox performance. As a result, the NaNbO3/Bi2O2CO3 composite exhibits exceptional performance in the photocatalytic nitrogen fixation reaction. This study expands the application of S-scheme photocatalysts in the field of N2 reduction and provides insights into the preparation of efficient S-scheme photocatalysts.

One-step fabrication of Cu-doped Bi2MoO6 microflower for enhancing performance in photocatalytic nitrogen fixation.

This study enhances the photocatalytic N2 immobilization performance of Bi2MoO6 through Cu doping. Cu-doped Bi2MoO6 was synthesized via a simple solvothermal method. Various characterizations were implemented to examine the influence of Cu doping on the properties of Bi2MoO6. Results indicated that the doped Cu element had a valence state of + 2 and substituted the position of Bi3+. Cu doping exerted minimal effect on the morphology of Bi2MoO6 but largely influenced the energy band structure. The band gap was slightly narrowed, and the conduction band was raised, such that Cu-doped Bi2MoO6 could generate more electrons with stronger reducibility. Moreover, importantly, Cu doping reduced work function and improved charge separation efficiency, which was considered the major cause of enhanced photoactivity. In addition, the Cu-Bi2MoO6 catalyst exhibited higher capability in the adsorption and activation of N2. Under the combined effects of the aforementioned changes, Cu-Bi2MoO6 demonstrated considerably higher photocatalytic efficiency than Bi2MoO6. The optimized NH3 generation rate reached 302 µmol/L g-1h-1 and 157 µmol/L g-1h-1 under simulated solar light and visible light, respectively, both achieving about 2.2 times higher than that of Bi2MoO6. This work provides a successful example of improving photocatalytic N2 fixation, and it may show some light on the design and preparation of heteroatom-doped semiconductor photocatalysts for N2-to-NH3 conversion.

Preparation of NaNbO3 microcube with abundant oxygen vacancies and its high photocatalytic N2 fixation activity in the help of Pt nanoparticles.

In this study, the photocatalytic N2 immobilization performance of NaNbO3 is enhanced via oxygen vacancy introduction and Pt loading. The designed Pt-loaded NaNbO3 with rich oxygen defects (Pt/O-NaNbO3) is synthesized by combining ion-exchange and photodeposition methods. Characterization result indicates that the O-NaNbO3 has hollow microcube morphology and higher surface area than NaNbO3. The introduced oxygen defects greatly affect the energy band structure. The band gap is slightly narrowed and the conduction band is raised, allowing O-NaNbO3 to generate electrons with strong reducibility. Moreover, the oxygen defects reduced the work function of NaNbO3, leading to increased charge separation in the bulk phase. The loaded Pt nanoparticles can further increase the surface charge separation via the formed Schottky barriers between Pt and O-NaNbO3, which was thought to be the primary cause of the increased photocatalytic activity. Additionally, the oxygen vacancies and metal Pt also contribute to the adsorption and activation of N2. Under the combined effect of the above changes, Pt/O-NaNbO3 presents much higher photoactivity than NaNbO3. The optimized NH3 production rate reaches 293.3 µmol/L g-1h-1 under simulated solar light, which is approximately 2.2 and 20.2 times higher than that of O-NaNbO3 and NaNbO3, respectively. This research offers a successful illustration of how to improve photocatalytic N2 fixation and may shed some light on how to design and construct efficient photocatalysts by combining several techniques.

Novel Bi2WO6/ZnSnO3 heterojunction for the ultrasonic-vibration-driven piezocatalytic degradation of RhB.

This study designed and prepared a new piezoelectric catalytic nanomaterial, Bi2WO6/ZnSnO3, and applied it in piezocatalytic water purification. Results indicated that the composite had superior piezocatalytic efficiency and stability in rhodamine B (RhB) degradation under ultrasonic vibration. The Bi2WO6/ZnSnO3 sample with 10% Bi2WO6 had the optimum activity with a degradation rate of 2.15 h-1, which was 7.4 and 11.3 times that of ZnSnO3 and Bi2WO6, respectively. Various characterizations were conducted to study the morphology, structure, and piezoelectric properties of the Bi2WO6/ZnSnO3 composites and reveal the reasons for their improved piezocatalytic performance. Results showed that ZnSnO3 cubes were dispersed throughout the surface of Bi2WO6 nanosheets, which enhanced the specific surface area and facilitated the piezocatalytic reaction. Additionally, type-II heterojunction structures formed at the contact interface of Bi2WO6 and ZnSnO3, driving the migration of piezoelectric-induced electrons and holes. Accordingly, the separation efficiency of charge carriers improved, and the piezoelectric catalytic activity was significantly enhanced. This study may provide a potential composite catalyst and a promising idea for the design of highly efficient piezoelectric catalyst.

A novel NiO/BaTiO3 heterojunction for piezocatalytic water purification under ultrasonic vibration.

This work designed and prepared a novel heterojunction composite NiO/BaTiO3 through a method of photodeposition and used it in piezocatalytic dye removal for the first time. Results of the piezocatalytic test indicated that the NiO/BaTiO3 composite presented superior efficiency and stability in the RhB degradation under the vibration of ultrasonic waves. The best NiO/BaTiO3 sample synthesized under light irradiation for 2 h displayed an RhB degradation rate of 2.41 h-1, which was 6.3 times faster than that of pure BaTiO3. By optimizing the piezocatalytic reaction conditions, the degradation rate constant of NiO/BaTiO3 can further reach 4.14 h-1 A variety of systematic characterizations were executed to determine the reason for the excellent piezocatalytic performance of NiO/BaTiO3. The band potentials of NiO and BaTiO3 are found to coincide, and at their contact interface, they may create a type-II p-n heterojunction structure. Driven by the potential difference and the built-in electric field, piezoelectrically enriched charge carriers can migrate between NiO and BaTiO3, resulting in improved efficiency in charge separation and an increase in the piezoelectric catalytic performance. This study may provide a potential composite catalyst and a promising idea for the design of highly efficient catalysts in the field of piezoelectric catalysis.

One-step preparation of MoOx/ZnS/ZnO composite and its excellent performance in piezocatalytic degradation of Rhodamine B under ultrasonic vibration.

This paper synthesized a new type of ternary piezoelectric catalyst MoOx/ZnS/ZnO (MZZ) by a one-step method. The catalytic degradation of Rhodamine B (RhB) solution (10 µg/g, pH = 7.0) shows that the composite catalyst has excellent piezoelectric catalytic activity under ultrasonic vibration (40 kHz). The piezoelectric degradation rate of the optimal sample reached 0.054 min-1, which was about 2.5 times that of pure ZnO. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) technologies were used to analyze the structure, morphology, and interface charge transfer properties of the MZZ piezocatalysts. The results showed that the composite catalyst may have a core-shell structure. ZnS is coated on the surface of ZnO, while MoOx adheres to the surface of ZnS. This structure endowed MZZ larger specific surface area than ZnO, which benefits the RhB adsorption. More importantly, the formed heterojunction structure between ZnS and ZnO promotes the separation of positive and negative charges induced by the piezoelectric effect. MoOx species may act as a charge trap to further promote more carriers to participate in the reaction. In addition, MoOx may also be beneficial in adsorbing dyes. Active species capture experiments show that superoxide radicals and holes are the main active species in piezoelectric catalytic reactions on MZZ catalysts.

Novel platinum-bismuth alloy loaded KTa0.5Nb0.5O3 composite photocatalyst for effective nitrogen-to-ammonium conversion.

A novel heterojunction composite BiPt/KTa0.5Nb0.5O3 (KTN) was designed and synthesized through a combination of hydrothermal and precipitation procedures. Bi and Pt contents were optimized. The best 1 %Bi-0.25 %Pt/KTN sample presented better photocatalytic performance in ammonia synthesis than KTN, 1 %Bi/KTN, and 0.25 %Pt/KTN. Under simulated sunlight, the NH3 generation rate of the best BiPt/KTN reached 6.3 times that of pure KTN. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) analysis revealed that BiPt alloy nanoparticles were formed and decorated on the surface of KTN nanocubes. The PtBi alloy provided an appropriate Schottky barrier with a height between those of Pt/KTN and Bi/KTN. The barrier can efficiently capture photogenerated charge carriers while also preventing their backflow and recombination. Thus, the PtBi/KTN presented the best capability in charge separation, thereby displaying the highest photocatalytic activity in the N2-to-NH3 reaction. Additionally, the loaded BiPt alloy also broadened the photoresponse of KTN to the visible light region via its surface plasmon resonance effect, which was another reason for the increased photoactivity. This study not only provided a potential photocatalyst for photocatalytic nitrogen fixation but also showed new ideas for the design of highly efficient catalysts via bimetal alloy modification.

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.

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.