Enhanced piezocatalytic and piezo-photocatalytic dye degradation via S-scheme mechanism with photodeposited nickel oxide nanoparticles on PbBiO2Br nanosheets

The fabrication of an S-scheme heterojunction demonstrates as an efficient strategy for achieving efficient charge separation and enhancing catalytic activity of piezocatalysts. In this study, a new S-scheme heterojunction was fabricated on the PbBiO2Br surface through the photo-deposition of NiO nanoparticles. It was then employed in the piezoelectric catalytic degradation of Rhodamine B (RhB). The results demonstrate that the NiO/PbBiO2Br composite exhibits efficient performance in piezocatalytic RhB degradation. The optimal sample is the NiO/PbBiO2Br synthesized after 2 h of irradiation, achieving a RhB degradation rate of 3.11 h-1, which is 12.4 times higher than that of pure PbBiO2Br. Simultaneous exposure to visible light and ultrasound further increases in the RhB degradation rate, reaching 4.60 h-1, highlighting the synergistic effect of light and piezoelectricity in the NiO/PbBiO2Br composite. A comprehensive exploration of the charge migration mechanism at the NiO/PbBiO2Br heterojunction was undertaken through electrochemical analyses, theoretical calculations, and in-situ X-ray photoelectron spectroscopy analysis. The outcomes reveal that p-type semiconductor NiO and n-type semiconductor PbBiO2Br possess matching band structures, establishing an S-scheme heterojunction structure at their interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and accumulate on the conduction band of PbBiO2Br and valence band of NiO, respectively, thereby achieving effective spatial separation of charge carriers. The catalyst's synergistic photo-piezoelectric catalysis effect can be ascribed to its role in promoting the generation and separation of charge carriers under both light irradiation and the piezoelectric field. The results of this investigation offer valuable insights into the development and production of catalytic materials that exhibit outstanding performance through the synergy of piezocatalysis and photocatalysis.

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.

Effect of Sr and Ti substitutions on optical and photocatalytic properties of Bi1-x Sr x Fe1-x Ti x O3 nanomaterials

The potential use of down-sized BFO-xSTO systems (x ≤ 25%) as highly efficient photoanodes for photocatalytic water splitting is investigated. BFO-xSTO is prepared by a solid-state method and subsequently deposited by spray coating. The compounds possess rhombohedral symmetry for x ≤ 15% and phase coexistence for x > 15%, as demonstrated by Raman spectroscopy and transmission electron microscopy. Our findings revealed a drastic grain size decrease with increasing STO content, namely 260 nm for BFO to 50 nm for BFO with 25% STO. Moreover, BFO-xSTO, x > 10% exhibited high optical absorption (> 80%) in the full spectrum and interestingly a very promising band alignment with water redox potentials. Moreover, the photochemical measurements revealed a photocurrent density of ∼0.17 μA cm-2 achieved for x = 15% at 0 bias. Using DFT calculations, the substitution effects on the electronic, optical, and photocatalytic performances of the BFO system were investigated and quantified. Surprisingly, a high hydrogen yield (∼191 μmol g-1) was achieved by BFO-12.5%STO compared to 1 μmol g-1 and 57 μmol g-1 for BFO and STO, respectively. This result highlights the beneficial effects of both the downsizing and substitution of BFO on the photocatalytic water splitting and hydrogen production performances of Bi1-x Sr x Fe1-x Ti x O3 systems.

Bandgap-engineered ferroelectric single-crystalline NBT-BT based nanocomposites with excellent visible light-ultrasound catalytic performance

Bandgap engineered ferroelectrics exhibit encouraging multi-energy catalytic performance by coupling the piezoelectricity and photoexcitation, which shows immense potential for environmental remediation and fuel production. However, it is challenging to prepare nano single-crystalline ferroelectric piezo-photoelectric with strong visible light absorption ability. Here, Ni mediated NBT-BT(NBT-BNT) single-crystalline nanocubes around 100 nm with considerable visible light absorption were synthesized by a high-temperature hydrothermal method. The mechanism of Ni2+ on the formation of NBT-BT nanocubes was proposed. The catalytic efficiency of NBT-BNT nanocubes is enhanced by decorating carbon quantum dots (CQDs). The RhB can be degraded within 8 min and the hydrogen production rate reaches up to ∼350 μmol g-1h-1 under visible light-ultrasonic condition. Moreover, under the simulated sunlight-ultrasound condition, RhB can be degraded within merely 3 min and a high H2 production rate of ∼747 μmol g-1h-1 is achieved. This work presents a paradigm for preparing ferroelectric single-crystalline nanocatalysts for multi-energy catalytic application.

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.

Sol-Gel Synthesis of Ce4-x Sr1+x Fe5-x Zn x O14+δ [0 ≤ x ≤ 0.45] Superparamagnetic Oxide Systems and Its Magnetic, Dielectric, and Drug Delivery Properties

In this work, we have successfully synthesized superparamagnetic nanocomposites, Ce_4-x Sr_1+x Fe_5-x Zn _x O_14+δ (0 ≤ x ≤ 0.45) (CSFZ) (TA1-TA4: x = 0, 0.15, 0.30, and 0.45) via the Nitrate-citrate sol-gel method. X-ray diffraction studies show the formation of single-phase nanocomposites (NCs) and the average crystallite size is found to be 18 nm. Energy-dispersive X-ray spectroscopy analysis supports the formation of the desired product with the expected composition. The scanning electron microscopy image shows that the prepared samples are in spherical shape and highly porous in nature. Most of the particle sizes present in the image are in the range of 5-20 nm. The optical studies show an intense peak at 583 nm corresponding to the instantaneous existence of both Fe²⁺ and Fe³⁺ intervalence electronic charge transition bands. X-ray photoelectron spectra analysis confirms the presence of elements with their preferred oxidation state. The superparamagnetic nature of the prepared sample was confirmed by vibrating sample magnetometer analysis. Synthesized materials show a low saturate magnetic moment ranging from 0.3400 to 0.1075 emu/g. The coercivity and retentivity value of the synthesized NC is zero. The NCs show high encapsulation efficiency toward ciprofloxacin hydrochloride because of their unique structure and release the loaded drug molecules in a sustained manner up to 10 h at pH 7.4. Such NCs have high potential for use as multifunctional material in various fields such as optical properties, conductivity studies, dielectric, sensor, and drug delivery properties.

The Future of Using Earth-Abundant Elements in Counter Electrodes for Dye-Sensitized Solar Cells

With limited global resources for many of the elements that are found in some of the most common renewable energy technologies, there is a growing need to use "Earth-abundant" elements as a long-term solution to growing energy demands. The dye-sensitized solar cell has the potential to produce low-cost renewable energy, with inexpensive production and most components using Earth-abundant elements. However, the most commonly used material for the cell counter electrode (CE) is platinum, an extremely expensive and rare element. A selection of the materials investigated as alternative CEs are discussed, including metal sulfides, oxides, carbides, and nitrides and carbon-based materials such as carbon nanotubes, graphene, and conductive polymers. As well as having the potential for lower cost, these materials can also produce more-efficient devices due to their high surface area and catalytic activity. Therefore, once issues such as stability have been studied in more detail and scale-up of production methods are considered, there is a very promising future for the replacement of Pt in DSSCs with lower-cost, Earth-abundant alternatives.

Hydrogen-treated BiFeO3 nanoparticles with enhanced photoelectrochemical performance

Compared with pristine BiFeO₃, hydrogen-treated BiFeO₃ nanoparticles exhibit higher photoelectrochemical performance.

Insights into the structure-photoreactivity relationships in well-defined perovskite ferroelectric KNbO3 nanowires

1D perovskite-type orthorhombic KNbO₃ nanowires display RhB photodegradation about two-fold as large as their monoclinic counterparts and a synergy between ferroelectric polarization and electronic structure in photoreactivity enhancement is uncovered.

Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this study, the geometric and electronic structure of perovskite ferroelectric KNbO₃ nanowires with respective orthorhombic and monoclinic polymorphs have been systematically addressed. By virtue of aberration-corrected scanning transmission electron microscopy, we directly visualize surface photocatalytic active sites, measure local atomic displacements at an accuracy of several picometers, and quantify ferroelectric polarization combined with first-principles calculations. The photoreactivity of the as-prepared KNbO₃ nanowires is assessed toward aqueous rhodamine B degradation under UV light. A synergy between the ferroelectric polarization and electronic structure in photoreactivity enhancement is uncovered, which accounts for the prominent reactivity order: orthorhombic > monoclinic. Additionally, by identifying new photocatalytic products, rhodamine B degradation pathways involving N-deethylation and conjugated structure cleavage are proposed. Our findings not only provide new insights into the structure–photoreactivity relationships in perovskite ferroelectric photocatalysts, but also have broad implications in perovskite-based water splitting and photovoltaics, among others.

Chemical protection of ZnO nanorods at ultralow pH To form a hierarchical BiFeO3/ZnO core-shell structure

ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.

Low frequency ultrasound (42 kHz) assisted degradation of Acid Blue 113 in the presence of visible light driven rare earth nanoclusters loaded TiO2 nanophotocatalysts

An attempt has been made to render the visible light driven photocatalytic activity to the TiO2 nanocatalysts by loading 1 wt% of rare earth (RE) nanoclusters (Gd(3+), Nd(3+) and Y(3+)) using a low frequency (42 kHz) producing commercial sonicator. The STEM-HAADF analysis confirms that the RE nanoclusters were residing at the surface of the TiO2. Transmission electron microscopic (TEM) and X-ray diffraction (XRD) analyses confirm that the loading of RE nanoclusters cannot make any significant changes in the crystal structure of TiO2. However, the optical properties of the resulted nanocatalysts were significantly modified and the nanocatalysts were employed to study the sonocatalytic, photocatalytic and sonophotocatalytic decolorization as well as mineralization of Acid Blue 113 (AB113). Among the experimented nanocatalysts maximum degradation of AB113 was achieved in the presence Y(3+)-TiO2 nanocatalysts. The decolorization of AB113 in the presence and absence of Y(3+) loaded TiO2 ensues the following order sonolysis<photocatalysis<sonocatalysis<sonophotocatalysis. The sonophotocatalytic decolorization of AB113 shows 1.4-fold (synergy index) enhanced rate when compared with the two corresponding individual advanced oxidation processes. The sonophotocatalytic mineralization shows that 65% of total organic carbon (TOC) can be removed from AB113 after the 5h of continuous irradiation however the mineralization cannot be able to show the synergetic effect.

BiFeO3/YSZ bilayer electrolyte for low temperature solid oxide fuel cell

Highly crystalline perovskite BiFeO₃ is obtained by a facile solution method. We have reported that the YSZ/BFO electrolyte with 17 μm/30 μm thickness, respectively, showed a maximum power density of 165 mW cm⁻² and open-circuit voltage of 0.75 V at 650 °C.