Piezocatalytic Degradation Research Articles

Piezocatalytic degradation of methylene blue, tetrabromobisphenol A and tetracycline hydrochloride using Bi4Ti3O12 with different morphologies

In this paper, we report the piezocatalytic application of morphologically different Bi4Ti3O12 nanostructures for piezocatalytic degradation of various environmental pollutants. Three types of Bi4Ti3O12 nanostructures with different morphologies, i.e. nanosheet-assembled hierarchical microrods, microplates, and nanoflake-assembled hierarchical microspheres, have been synthesized via a hydrothermal route and a molten salt route. Three typical environmental pollutants — methylene blue (MB), tetrabromobisphenol A (TBBPA) and tetracycline hydrochloride (TC) — were separately used the target pollutant to evaluate the piezocatalytic degradation performances of the as-synthesized Bi4Ti3O12 nanostructures under ultrasonic vibration. It is demonstrated that all the Bi4Ti3O12 samples exhibit a pronounced piezocatalytic degradation of these pollutants. The highest piezocatalytic degradation performance is observed for the Bi4Ti3O12 microplates. Further, the effects of pH, initial pollutant concentration, catalyst dosage and various anions on the piezocatalytic degradation of MB over the Bi4Ti3O12 microplates were investigated. A possible piezocatalytic mechanism of Bi4Ti3O12 was proposed and analyzed.

Stimulated piezotronical decontamination using Cu2MgSnS4 modified BaTiO3

Water resources are drastically decreasing due to the aquatic pollutants involved with the rapid growth of microbial colonies. Mitigation of contaminants and corresponding actions is necessary to impede severe health risks and fulfill clean water demand. Piezocatalysis appears as a potential advanced oxidation technique based on vibrational energy harvesting mechanism and conversion with piezo materials’ assistance. Owing to the effectiveness of piezocatalysis, we synthesized the Cu2MgSnS4 modified BaTiO3 (CMTS@BTO) displayed remarkable piezocatalytic degradation against organic contaminants and microbes. CMTS@BTO revealed more than 90% disinfection in heterotrophic conditions while also degraded 88–98% of organic dyes using ultrasound vibrations. Our findings have a significant contribution to water remediation and indicate potential use in other biological applications.

A new strategy for large-scale synthesis of Na0.5Bi0.5TiO3 nanowires and their application in piezocatalytic degradation.

Developing new techniques that can synthesize one-dimensional piezoelectric materials on a large scale is of great significance for boosting piezocatalytic applications. In this work, we proposed a high-efficiency template hydrothermal method for large-scale synthesis of piezoelectric Na0.5Bi0.5TiO3 (NBT) nanowires. By ion-exchange with Bi3+, Na2Ti3O7 template nanowires can be easily and entirely transformed to NBT. The piezocatalytic activity of the NBT nanowires was thoroughly investigated with respect to their capability to degrade typical organic pollutants, including Rhodamine B, methylene blue, methyl orange, tetracycline hydrochloride, phenol, and bisphenol A. The NBT nanowires exhibited the highest efficiency in piezocatalytic degradation of Rhodamine B, which was completely decomposed within 80 min (rate constant ∼0.0575 min−1). The electron spin resonance spin-trapping technique and active species capture experiments were employed to characterize free radicals. The present work is advantageous for the high yield of NBT nanowires and the excellent piezocatalytic performance. The reported template hydrothermal method can potentially be extended to the synthesis of other perovskite nanowires.

Efficiently harvesting the ultrasonic vibration energy of two-dimensional graphitic carbon nitride for piezocatalytic degradation of dichlorophenols

The ultrasound-induced piezoelectric field drives electrons and holes to migrate in opposite directions towards the surface of 2D g-C3N4, leading to the formation of active species, which further degrade dichlorophenols into small molecules.

BaTiO3 nanocubes/cuboids with selectively deposited Ag nanoparticles: Efficient piezocatalytic degradation and mechanism

The selective deposition of noble metals on catalysts is an attractive modification method for improving catalytic efficiency. However, it is sometimes hard to achieve when facet energies of nano-catalysts show negligible differences. Here, we reported a piezoelectrochemical method which can realize the selective deposition of Ag nanoparticles on the positively polar end of {001}-enclosed BaTiO3 (BTO) nanocubes/cuboids. Furthermore, BTO nanocubes/cuboids with selectively-deposited Ag nanoparticles show approximately 2 times higher piezocatalytic activity than those with randomly-loaded Ag nanoparticles, and much higher than pure BTO nanocubes/cuboids. The piezocatalytic mechanism revealed that the Ag nanoparticles deposited on positively polar end act as “fast lanes” for electrons to transfer to catalysts/solution interfaces, while those loaded on negatively polar end serve as holes trappers hindering ∙OH formation and pollutant degradation. This work confirms an efficient way to improve piezocatalytic performance and provides an insightful discussion of piezocatalytic mechanism.

Utilizing the localized surface piezoelectricity of centrosymmetric Sr1-xFexTiO3 (x≤0.2) ceramics for piezocatalytic dye degradation

Centrosymmetric Sr1-xFexTiO3 (x = 0, 0.01, 0.05, 0.1, 0.2) ceramics were synthesized using solid-state reaction method. XRD confirmed the perovskite SrTiO3 phase in all samples and indicated the conversion of cubic to pseudocubic crystal symmetry with increase in Fe substitution. Raman spectroscopy showed first and second order Raman scattering modes in all samples and a new Raman mode in 691–701 cm-1 in Fe substituted samples. The irregular morphology of grains in Sr1-xFexTiO3 (x≤0.1) was interestingly transformed into rhombicuboctahedron morphology in x = 0.2 sample. All samples showed significant piezocatalytic degradation of methylene blue (MB) dye. The piezocatalytic dye degradation was increased with increase in Fe substitution. The best piezocatalytic dye degradation rate of 0.00448 min-1 was achieved in x = 0.2 sample. The localized surface piezoelectricity along with some other sono-induced phenomena might be responsible for piezocatalytic activity. The sample with x = 0.2 also showed promising MB dye degradation under visible light (k = 0.00364 min-1).

Harvesting the Vibration Energy with BaTiO3@Graphene for the Piezocatalytic Degradation of Methylene Blue

Piezocatalysis is a newly advanced oxidation process (AOP) which can be triggered by mechanical force to generate electric field, and then drives free charge carriers to participate redox reactions. In this work, reduced graphene oxide (rGO) is integrated with the widely used barium titanate (BTO) to regulate the surface free charges of composites. The piezocatalytic activity of integrated composite (BTO@rGO) is strongly related with the mass ratio of BTO and rGO. Driven by ultrasonic force, BTO@rGO can completely decompose methylene blue (MB) within 120 min when the mass ratio of BTO to rGO is 2:1, showing the best activity comparing with samples of other mass ratios (10:1, 5:1, and 1:1). The introduction of graphene facilitates the interface charge transfer to BTO, which is proved by peak shift information of Raman and X-ray photoelectron spectroscopy (XPS). The generated hydroxyl radical (.OH) is the active species participating in MB oxidation. This work not only gives a clear understanding of interface electron transfer mechanism but also sheds light on the construction of well-performed piezocatalysts.

Effective promoting piezocatalytic property of zinc oxide for degradation of organic pollutants and insight into piezocatalytic mechanism

The piezoelectric zinc oxides with different morphology (ZnO nanoparticles and nanorods, hereafter abbreviated as ZnO NPs and NRs) are successfully synthesized using facile, green and harmless solid-state chemistry method at room temperature. The piezocatalytic activity of zinc oxide towards methylene blue (MB) of organic pollutants degradation has been explored under ultrasonic vibration. The ZnO NRs exhibit effectively enhanced piezocatalytic performance towards degradation dye compared with the ZnO NPs. In particular, the piezocatalytic decolorization ratio of MB solution is up to ~38% in ZnO NRs under 120 min, ~ 99% under 5.5 h and show good recycling utilization characteristics, indicating great potential for dye wastewater decolorization treatment. The main oxidizing hydroxyl radical (OH) and superoxide radicals (O2−) of the piezocatalytic reactions are confirmed and the production of piezocatalytic degradation process induced polarization electric charges. Moreover, we investigate the relationship between morphology and piezoelectric potential based on the finite element method for ZnO NPs and NRs, which further clarify the enhanced piezocatalytic activity and insight into piezocatalytic mechanism. This work offers a novel strategy towards wastewater decontamination applications and further understanding the relationship between piezocatalysis, morphology, and piezocatalytic mechanism in piezoelectric materials.

Novel MoS2/C nanosheets as excellent piezocatalyst for degradation of imidacloprid with ultralow dosage

MoS2/C ultrathin nanosheets were synthesized via hydrothermal method by adding soft template of hexadecyl trimethyl ammonium bromide (CTAB) and employed as the piezocatalyst for the degradation of imidacloprid (IMD). Compared with pure MoS2, MoS2/C nanosheets shows excellent piezocatalytic degradation rate of 96% in 15 min with ultralow dosage (30 mg·L−1). The removal efficiency of total organic carbon (TOC) also remains over 80% after ten cycles. The improved piezocatalytic performance is attributed to the large surface area with more edges and unsaturated S atoms of MoS2/C ultrathin nanosheets, which is vital for the mass transfer of the reactants and products and facilitate piezoelectric effect.

Synthesizing BaTiO3 Nanostructures to Explore Morphological Influence, Kinetics, and Mechanism of Piezocatalytic Dye Degradation.

Piezocatalysts have attracted much attention due to their excellent degradation ability for organics. In this work, three types of BaTiO3 (BTO) nanostructures, including hydrothermally synthesized nanocubes (NCs), sol-gel calcined nanoparticles (NPs), and electrospun nanofibers (NFs), are prepared for catalyzing the dye degradation. Compared with the NCs and NPs, the NFs exhibit a higher piezocatalytic degradation performance due to the large specific surface area, fine crystal size, and easy deformation structure. Moreover, the kinetic factors, including initial dye concentration, ionic strength, ultrasonic power, and applied action, influencing the degradation performance of the BTO NFs are analyzed deeply. A high degradation rate constant of 0.0736 min-1 is achieved for rhodamine B, which is superior compared with the previous reports. The excellent stability of BTO NFs is demonstrated by the cycling tests, where a high degradation efficiency of 97.6% within 110 min is still obtained after the third cycle. Furthermore, the mechanism of piezocatalysis revealed that the hydroxyl and superoxide radicals are the main reactive species in the degradation process. This work is of importance for the development of high-performance piezocatalysts and highlights the potential of piezocatalysis for water remediation.

BaTiO3 Nanosheets and Caps Grown on TiO2 Nanorod Arrays as Thin-Film Catalysts for Piezocatalytic Applications.

Powder-form piezocatalysts suffer from poor recyclability and pose a potential threat of creating serious secondary pollution, which restrict their practical applications. Thin-film piezocatalysts, which not only exhibit good recyclability but also fully contact with solution, are believed to be one of the solutions to address these problems. In this work, the nanostructured BaTiO3 (BTO) thin films were fabricated by a facile hydrothermal method for their potential applications in piezocatalysis. The vertically standing BTO nanosheets grown on the top of TiO2 nanorod arrays exhibited superior piezocatalytic performance as well as piezo-electrochemical property. Given the different strain states between thin-film piezocatalyst and powder-form piezocatalyst, both the impact force of water and isostatic pressure are taken into consideration in finite element method (FEM) simulation. The FEM simulation shows that a stronger piezoelectric filed can be built in BTO nanosheets because of their easier deformation, and thus can lead to a higher piezocatalytic degradation efficiency. Our work presented here is expected to provide a potential route for the nanoengineering of thin-film piezocatalysts and clarify the catalytic mechanism for substrate-fixed piezocatalysts.

Exploring the piezocatalytic dye degradation capability of lithium niobate

The piezocatalysis dye degradation capability of LiNbO3 is reported for the first time. LiNbO3 was synthesized using a conventional solid-state reaction route. X-ray diffraction and Raman spectroscopy confirmed the formation of a single-phase of LiNbO3 in the as-synthesized material. Scanning electron microscope showed the micron-sized (0.2–2 μm) particles of LiNbO3 powder. The average pore diameter, the specific surface area, and total pore volume of LiNbO3 powder were measured to be 3.3 nm, 4.856 m2/g and 0.008 cc/g respectively. During piezocatalysis experiments using ultrasonicator, 0.1 g of LiNbO3 sample degraded ~99%, 93%, and 80% of methylene blue dye from the dye solution of 12 mg/L initial concentration during the first, second and third piezocatalysis cycle, respectively. The radical trapping experiments found the main active species behind the piezocatalysis dye degradation through LiNbO3 sample in this order: hydroxyl radical (OH) > superoxide radical (O2-) > holes (h+). LiNbO3 sample could be a promising candidate for the piezocatalytic degradation of organic dyes from the waste-water.

Piezo-potential induced molecular oxygen activation of defect-rich MoS2 ultrathin nanosheets for organic dye degradation in dark

As a new concept, single-and odd-numbered layer of molybdenum disulfide (MoS2) is a piezocatalyst semiconductor. Herein, we report the created odd numbered layer of defect-rich MoS2 (DR-MoS2) with high sulfur (S) vacancy concentration (S/Mo ratio-0.83) which can strongly interact with adsorbed oxygen molecules for highly efficient generation of reactive oxygen species (ROS) in the piezocatalytic degradation process. DR-MoS2 presents far superior piezocatalytic activity for Eriochrome Black T dye degradation which is 2.14 and 18.12 times higher than that of defect-free MoS2 (DF-MoS2) and bulk MoS2. The abundant native S vacancies induced the enhanced carrier density (electron density) of DR-MoS2 is to be 4.6 × 1017 cm–3 and is roughly 15 times higher than that the 2.9 × 1016 cm–3 of DF-MoS2. The S vacancies induced the increased flat-band potential and the vast majority of charge density strengthens the electron transfer dynamics and increases the surface band bending, which drive the charge carrier separation efficiently along with piezopolarization. More importantly, Mo active sites created by S vacancy defects can facilitate the two-electron reduction of molecular oxygen activation by introducing Mo4+/Mo6+ redox couple. In addition, based on the experimental results, a tentative mechanism was proposed to explain the origin of the piezocatalytic enhancement in DR- MoS2.

Coupling effect of piezomaterial and DSA catalyst for degradation of metronidazole: Finding of induction electrocatalysis from remnant piezoelectric filed

Piezocatalysis is an emerging green advanced-oxidation technology for the degradation of toxic pollutants; however, piezomaterials are not generally excellent electrocatalysts. Herein, two complex piezocatalysts (SnO2/t-BaTiO3 and SnO2-Sb/t-BaTiO3) consisting of an electrocatalyst and piezomaterial, respectively, are designed to investigate the coupled effect of piezocatalytic and electrocatalytic processes on the degradation of pollutants. SnO2, especially SnO2-Sb, can considerably enhance the piezocatalytic degradation of the antibiotic metronidazole (MNZ). The piezocatalytic rate constants of SnO2/t-BaTiO3 and SnO2-Sb/t-BaTiO3 are 2.3 and 3.0 times that of t-BaTiO3, respectively. In the degradation process, SnO2 and SnO2-Sb are confirmed to act as dimensionally stable anode-like (DSA-like) catalysts because they can increase the response of the piezoelectrochemical anodic current and the generation of OH radicals as well as reduce the formation of 1O2. Significantly, the piezoelectric field can drive not only the free charges of t-BaTiO3 and its remnant piezoelectric field but also those of the loaded electrocatalyst SnO2 to participate in the degradation of MNZ. These results indicate that the coupling of an excellent electrocatalyst and piezomaterial is an effective method to promote piezocatalytic efficiency.

Few-layer transition metal dichalcogenides (MoS2, WS2, and WSe2) for water splitting and degradation of organic pollutants: Understanding the piezocatalytic effect

Piezoelectric materials have promising potential for converting mechanical energy into chemical energy (i.e. piezocatalysis) by coupling the piezotronic effect with electrochemical processes. Herein, piezocatalytic water splitting and degradation of organic pollutants have been realized in three few-layer transition metal dichalcogenides (TMDs) (namely MoS2, WS2, and WSe2). We showed that the H2 evolution rate reached 29.1, 15.4, and 11.3 μmol g−1 h−1 for MoS2, WS2, and WSe2 nanosheets respectively, under mechanical force provided by ultrasonic vibration. Moreover, their piezocatalytic activities can be further promoted by loading with heavy metal (e.g. Pt and Au) nanoparticles. In addition, all the samples exhibited good piezocatalytic degradation efficiency and reusability toward different organic pollutants (e.g. tetracycline and Rhodamine B). We also provided a systematic investigation on the piezoelectricity by piezoresponse force microscopy and piezoelectric stress coefficients (e11) by first-principle calculations of these three studied compounds, which are accordant with the piezocatalytic results. The present work clearly demonstrates a high correlation between piezoelectricity and mechanical vibration induced catalytic reactions in few-layer TMDs and may provide insight into the mechanisms of piezocatalytic effect.

High-piezocatalytic performance of eco-friendly (Bi1/2Na1/2)TiO3-based nanofibers by electrospinning

Piezocatalysis has been regarded as a great potential tool in water pollution treatment. In this report, eco-friendly piezoelectric 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO3 (BNBT) nanofibers were prepared by electrospinning and calcined at various temperatures. The piezocatalytic activities of the BNBT nanofibers were examined by the degradation of various dyes. It is indicated that the BNBT nanofibers calcined at 650 °C exhibit the optimum piezocatalytic performance and a degradation rate of 0.0518 min−1 is achieved for Acid Orange 7. The kinetic investigations reveal that the sorption of the dye molecules on the surfaces of the nanofibers can be suppressed by increasing the initial concentration or ionic strength of the dye solution, thus the piezocatalytic degradation efficiency is deteriorated. While the pH value of the reaction system plays an insignificant role in the piezocatalytic degradation process. Moreover, the electrospun BNBT nanofibers exhibit a good reusability and wide universality for the piezocatalytic degradation, which is important for the practical applications. This work provides an in-depth understanding of the piezocatalytic mechanisms in the degradation of the organic dyes and opens a new route for the development of high-performance and eco-friendly piezocatalysts.

Lead-free sodium niobate nanowires with strong piezo-catalysis for dye wastewater degradation

Abstract In this work, the hydrothermally-synthesized sodium niobate nanowires were used to decompose Rhodamine B dye solution through the piezo-catalytic effect. With the sodium niobate catalyst, a high piezo-catalytic degradation ratio of ∼80% was achieved under the excitation of vibration for the Rhodamine B dye solution (∼5 mg/l). These active species in the catalytic process, hydroxyl radicals and superoxide radicals with the strong oxidation ability, were also observed, which confirmed the key role of piezoelectric effect for piezo-catalysis. The piezo-catalysis of sodium niobate nanowires provides a high-efficiency and reusable tool in application in depredating the dye wastewater.

The role of microstructure in piezocatalytic degradation of organic dye pollutants in wastewater

Piezoelectrically-induced catalytic effect, piezocatalysis, is considered with a great potential in addressing the environmental issues. In this work, BaTiO3 nanowires (BTO NWs) were prepared by combining the sol-gel-based electrospinning technique and post calcination process. Their microstructure characteristics, including crystal structure, crystalline size, surface area and dimension, were effectively adjusted by altering the calcination temperature, calcination time or precursor concentration. And the roles of these microstructure characteristics in the piezocatalytic activity were thoroughly investigated by degradation of methyl orange solution under ultrasonic vibration. Results indicated that the crystal structure and surface area play an important role in piezocatalytic activity of BTO NWs. Moreover, experimental results indicated that BTO NWs with smaller diameter or being composed of smaller size crystallites contributes to better piezocatalytic performance. Our present work gives a clear understanding of the role of microstructure in piezocatalysis and provides a way to develop high performance piezocatalysts.

Enhancement and mechanism of nano-BaTiO3 piezocatalytic degradation of tricyclazole by co-loading Pt and RuO2

It was found that dual electrocatalysts Pt and RuO2 could synergistically improve the piezo-degradation efficiency of nano t-BaTiO3 for pollutants.

(Invited) Piezocatalytic Degradation of Dye Molecules, Water Splitting, and Formation of Hydroxyl Radical through Piezoelectricity of MoS2 Nanoflowers

Two-dimensional (2D) materials such as MoS2, MoSe2, WS2, WSe2, etc, have received a greater amount of attention in a variety of applications including field-effect transistors, hydrogen production, nanogenerator and optoelectronic devices, and degradation of organic pollutants. Recently, the environmental issues including water and air pollution, and industrial and hazardous waste, are considerable and becoming a serious problem for many countries. The catalyst materials have provided a promising solution to suppress the environmental pollution from deteriorating. The high-performance catalysts are the prerequisites to meet the following aspect points such as eco-friendly processing, low investment costs, and remarkable catalytic activity. Therefore, many researchers have been engaged in developing highly efficient catalysts materials (i.e. photocatalysis) through a variety of technologies, including hybrid nanostructures, surface/interface engineering, and novel catalytic behavior. This work, we have demonstrated that the hydroxyl radicals (OH•) and hydrogen gas can be generated by the application of mechanical force to the edge sites of the MoS2 nanoflowers in a dark environment. The non-centrosymmetric structure of the single- and few-layered MoS2 nanoflowers were uniformly dispensed in the aqueous solution. A mechanical force was applied to the aqueous solution, and the hydroxyl radicals were generated from the MoS2 nanoflowers because a piezoelectric spontaneous polarization was created around the single- and odd number of layers. Based on the fluorescence (FL) spectra, the solution contained with the high concentration of highly oxidized free radicals, which was strongly dependent on the concentration of the MoS2 nanoflowers in the aqueous solution. The formation of the M- and S-vacancies sites on the single-layer MoS2 acted as the F-center defects, leading to the hydroxyl radicals being accommodated on the sites to decompose the organic dye molecules and prolong the radical’s lifetime up to 6 hours. More importantly, with applying the ultrasonic vibration to the MoS2 nanoflowers in the deionized water and ethanol solution, a remarkable hydrogen peak was observed by the gas chromatography mass spectrometry. Moreover, as increasing the concentration of the MoS2 nanoflowers in the solution, the intensity of the hydrogen generation was increased. This is the first work to demonstrate that the dye molecule can be instantly decomposed by the free radicals solution and produced the hydrogen gas using the piezoelectricity of single-layered MoS2 nanoflowers with the application of mechanical force in a dark environment.