BiOCl Decorated NaNbO3 Nanocubes: A Novel p-n Heterojunction Photocatalyst With Improved Activity for Ofloxacin Degradation

Photocatalysis Meets Piezoelectricity in a Type-I Oxygen Vacancy-Rich BaTiO3/BiOBr Heterojunction: Mechanism Insights from Characterizations to DFT Calculations

It is a challenging task to design a piezoelectric photocatalyst with excellent performance under mechanical agitation instead of ultrasonic irradiation. Integrating vacancy defects into a heterojunction seems to be an effective strategy for synergistically increasing its piezo-photocatalytic performance. For this goal, a two-step hydrothermal method was adopted to architect a type-I oxygen-vacancy-rich BaTiO3/BiOBr heterojunction to surge the degradation of Rhodamine B (RhB) under the combined action of simulated sunlight irradiation and mechanical agitation. Various instrumental techniques demonstrated the formation of a BaTiO3/BiOBr heterojunction with high crystallinity. The existence of surface oxygen vacancies was confirmed by XPS and EPR tests. PFM results manifested that this heterojunction had excellent piezoelectric properties, with a piezoelectric response value of 30.31 pm V-1. Comparative experiments indicated that RhB degradation efficiency under piezo-photocatalysis over this heterojunction largely exceeded the total sum of those under piezocatalysis and photocatalysis. h+, ·O2-, and 1O2 were the dominant reactive species for RhB degradation. The improved separation efficiency of photogenerated charges was verified by electrochemical measurements. DFT calculations indicated that the polarization of BaTiO3 could affect the electronic band structure of BiOBr. This work will provide comprehensive insights into piezo-photocatalytic mechanism at a microcosmic level and help to develop new-styled piezoelectric photocatalysts.

Morphological and elemental tuning of BiOCl/BiVO4 heterostructure for uric acid electrochemical sensor and antibiotic photocatalytic degradation

Deep eutectic solvents (DES) consisting of EG-(ChCl: C₂H₆O₂) and TU-(ChCl: CH₄N₂S) assisted synthesized BiOCl/BiVO₄ heterostructured catalyst studied for electrochemical uric acid (UA) sensor and tetracycline photocatalytic degradation. The chemical composition of the BiOCl/BiVO₄ catalyst was analyzed by X-ray photoelectron spectroscopy (XPS). UV-vis spectroscopy reveals increased absorption of visible light till the near-infrared region, which results in a narrowing of band gap energy from 2.3 eV to 2.2 eV for BiOCl/BiVO₄-TU. Morphology of catalyst analyzed using field-emission scanning electron microscope (FE-SEM) and Transmission electron microscope (TEM) technique. Time-Resolved photoluminescence (TRPL) confirms an increased lifetime of e^-/h⁺ pair after heterostructure formation. The catalyst-modified glassy carbon electrode shows selectivity toward the detection of uric acid (UA). The limit of detection (LOD) is estimated to be 0.04688 μM for UA; also, interference and stability of catalyst were studied. Photocatalytic activity of the synthesized catalyst was investigated by degrading tetracycline (TC) antibiotic pollutants, and their intermediate product was analyzed by ion trap mass spectrometry (MS).

Type II Heterojunction Formed between {010} or {012} Facets Dominated Bismuth Vanadium Oxide and Carbon Nitride to Enhance the Photocatalytic Degradation of Tetracycline

Both type II and Z schemes can explain the charge transfer behavior of the heterojunction structure well, but the type of heterojunction structure formed between bismuth vanadium oxide and carbon nitride still has not been clarified. Herein, we rationally prepared bismuth vanadium oxide with {010} and {012} facets predominantly and carbon nitride as a decoration to construct a core-shell structure with bismuth vanadium oxide wrapped in carbon nitride to ensure the same photocatalytic reaction interface. Through energy band establishment and radical species investigation, both {010} and {012} facets dominated bismuth vanadium oxide/carbon nitride composites exhibit the type II heterojunction structures rather than the Z-scheme heterojunctions. Furthermore, to investigate the effect of type II heterojunction, the photocatalytic tetracycline degradations were performed, finding that {010} facets dominated bismuth vanadium oxide/carbon nitride composite demonstrated the higher degradation efficiency than that of {012} facets, due to the higher conduction band energy. Additionally, through the free radical trapping experiments and intermediate detection of degradation products, the superoxide radical was proven to be the main active radical to decompose the tetracycline molecules. Therein, the tetracycline molecules were degraded to water and carbon dioxide by dihydroxylation-demethylation-ring opening reactions. This work investigates the effect of crystal planes on heterojunction types through two different exposed crystal planes of bismuth vanadate oxide, which can provide some basic research and theoretical support for the progressive and controlled synthesis of photocatalysts with heterojunction structures.

Layered KTO/BiOCl nanostructures for the efficient visible light photocatalytic degradation of harmful dyes

Novel KTO/BiOCl nanostructured photocatalysts with various weight proportions were synthesized using a simple hydrothermal process. The as-prepared nanostructured composite catalysts were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis diffused reflectance spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy with high resolution, X-ray photoelectron spectroscopy, and photoluminescence (PL). The photocatalytic activity of prepared catalysts was examined using Rhodamine B (RhB) and Congo Red (CR) as the aimed pollutants. BiOCl nanoparticles were distributed uniformly on the surface of the K₂Ti₄O₉ nanobelts. The optical properties showed that the layered titanate with BiOCl nanostructured photocatalyst displayed improved photoresponsivity due to the narrowed bandgap. The PL results showed that the greater inhibition of the electron-hole recombination process and KTO/BiOCl with a mass proportion of 20% revealed the most favorable photocatalytic behavior. The rate constant of RhB and CR degradation was five times as high as that of the bare BiOCl and titanate. The superior photocatalytic performance was attributed to the advancement of heterojunction between the KTO nanobelt and BiOCl. The KTO/BiOCl nanostructure is a promising visible, active photocatalyst, and the photocatalytic mechanism is discussed using the possible band structures of BiOCl and KTO.

Role of p-n junction initiated mixed-dimensional 0D/2D, 1D/2D, and 2D/2D BiOX (X = Cl, Br, and I)/TiO2 nanocomposite interfaces for environmental remediation applications: A review

Nowadays, we are critically facing various environmental issues. Among these, water contamination is the foremost issue, which worsens our health and living organisms in the water. Thus, it is necessary to provide an avenue to minimize the toxic matter through the development of facile technique and harmless photocatalyst. In this review, we intended to uncover the findings associated with various 0D, 1D, and 2D nanostructures featured photocatalysts for advancements in interfacial characteristics and toxic matter degradation. In this context, we evaluated the promising mixed-dimensional 0D/2D, 1D/2D, and 2D/2D bismuth oxyhalides BiOX (X = Cl, Br, and I) integrated TiO₂ nanostructure interfaces. Tunable mixed-dimensional interfaces highlighted with higher surface area, more heterojunctions, variation in the conduction and valence band potential, narrowed band gap, and built-in electric field formation between BiOX and TiO₂, which exhibits remarkable toxic dye, heavy metals, and antibiotics degradation. Further, this review further examines insights into the charge carrier generation, separation, and shortened charge transfer path at reduced recombination. Considering the advantages of type-II, S-scheme, and Z-scheme charge transfer mechanisms in the BiOX/TiO₂, we heightened the combination of various reactive species generation. In a word, the concept of mixed-dimensional BiOX/TiO₂ heterojunction interface endows toxic matter adsorption and decomposition into useful products. Challenges and future perspectives are also provided.

Self-Assembled Interwoven Nanohierarchitectures of NaNbO3 and NaNb1-x Ta x O3 (0.05 ≤ x ≤ 0.20): Synthesis, Structural Characterization, Photocatalytic Applications, and Dielectric Properties

Dependence on fossil fuels for energy purposes leads to the global energy crises due to the nonrenewable nature and high CO₂ production for environmental pollution. Therefore, new ways of nanocatalysis for environmental remediation and sustainable energy resources are being explored. Herein, we report a facile surfactant free, low temperature, and environmentally benign hydrothermal route for development of pure and (5, 10, 15, and 20 mol %) Ta-doped horizontally and vertically interwoven NaNbO₃ nanohierarchitecture photocatalysts. To the best of our knowledge, such a type of hierarchical structure of NaNbO₃ has never been reported before, and changes in the microstructure of these nanoarchitectures on Ta-doping has also been examined for the first time. As-synthesized nanostructures were characterized by different techniques including X-ray diffraction analysis, electron microscopic studies, X-ray photoelectron spectroscopic studies, etc. Ta-doping considerably affects the microstructure of the nanohierarchitectures of NaNbO₃, which was analyzed by FESEM analysis. The UV-visible diffused reflectance spectroscopy study shows considerable change in the band gap of as-synthesized nanostructures and was found to be ranging from 2.8 to 3.5 eV in pure and different mole % Ta-doped NaNbO₃. With an increase in dopant concentration, the surface area increases and was equal to 5.8, 6.8, 7.0, 9.2, and 9.7 m²/g for pure and 5, 10, 15, and 20 mol % Ta-doped NaNbO₃, respectively. Photocatalytic activity toward the degradation of methylene blue dye and H₂ evolution reaction shows the highest activity (89% dye removal and 21.4 mmol g^-1 catalyst H₂ evolution) for the 10 mol % NaNbO₃ nanostructure which was attributed to a change in the conduction band maximum of the material. At 100 °C and 500 kHz, the dielectric constants of pure and 5, 10, 15, and 20 mol % Ta-doped NaNbO₃ were found to be 111, 510, 491, 488, and 187, respectively. The current study provides the rational insight into the design of nanohierarchitectures and how microstructure affects different properties of the material upon doping.

NaNbO3 Nanorods: Photopiezocatalysts for Elevated Bacterial Disinfection and Wastewater Treatment

In the present work, ferroelectric sodium niobate (NaNbO₃) nanorods are formulated to attain photopiezocatalysis for water pollutant degradation and bacterial disinfection. NaNbO₃ nanorods, integrating the advantages of photocatalysis (generation of free charge carriers) and piezocatalysis (separation of these charge carriers), possess synergistic effects, which results in a higher catalytic activity than photocatalysis and piezocatalysis alone. Active species that are involved in the catalytic process are found to be ^•O₂ ^- < OH^• < h⁺, indicating the significance of piezocatalysis and photocatalysis. The degradation efficiency of sodium niobate (NaNbO₃) nanorods for Rhodamine B in the presence of both sunlight and ultrasonic vibration is 98.9% within 60 min (k = 7.6 × 10^-2 min^-1). The piezo potential generated by NaNbO₃ nanorods was reported to be 16 V. The antibacterial activity of the produced sample was found to be effective against Escherichia coli. With inhibitory zones of 23 mm, sodium niobate has a greater antibacterial activity.

A visible light driven 3D hierarchical CoTiO3/BiOBr direct Z-scheme heterostructure with enhanced photocatalytic degradation performance

The CoTiO3/BiOBr (CTBB) composite displays excellent photocatalytic activity because of the unique nanostructure induced efficient charge separation and transportation in interface of CoTiO3 and BiOBr.

Fabrication of one dimensional hierarchical WO3/BiOI heterojunctions with enhanced visible light activity for degradation of pollutants

One-dimensional (1D) hierarchical WO₃/BiOI p–n (WB) heterojunctions with different mass percentages of WO₃ were fabricated through a precipitation process. Various analytical techniques were employed to characterize the resulting WB composites, and their photocatalytic properties were measured by the degradation of rhodamine B (RhB) and methylene blue (MB) under irradiation of visible light. The WB heterojunctions showed largely enhanced photocatalytic performance as compared to the pure photocatalysts. Notably, the degradation rate constant of RhB by WB-10 was 3.3 and 33.6 times higher than those of pure BiOI and WO₃, respectively. The enhanced activity could be attributed to the hierarchical p–n heterostructures, which can supply more reaction sites and effectively promote the separation of photogenerated charge carriers, as confirmed by PL and photocurrent. Trapping experiments implied that holes (h⁺) and superoxide anion radicals (˙O₂⁻) were the dominant active species for organic pollutants decomposition on the WB composites. This work may benefit the construction of hierarchical heterostructures with high photocatalytic efficiency.

One-dimensional (1D) hierarchical WO₃/BiOI p–n (WB) heterojunctions with different mass percentages of WO₃ were fabricated through a precipitation process.

Continuous Single-Phase Synthesis of [Au25(Cys)18] Nanoclusters and their Photobactericidal Enhancement

Thiolate-gold nanoclusters have various applications. However, most of the synthesis methods require prolonged synthesis times from several hours to days. In the present study, we report a rapid synthesis method for [Au₂₅(Cys)₁₈] nanoclusters and their application for photobactericidal enhancement. For [Au₂₅(Cys)₁₈] synthesis, we employed a tube-in-tube membrane reactor using CO as a reducing agent at elevated temperatures. This approach allows continuous generation of high-quality [Au₂₅(Cys)₁₈] within 3 min. Photobactericidal tests against Staphylococcus aureus showed that crystal violet-treated polymer did not have photobactericidal activity, but addition of [Au₂₅(Cys)₁₈] in the treated polymer demonstrated a potent photobactericidal activity at a low white light flux, resulting in >4.29 log reduction in viable bacteria numbers. Steady-state and time-resolved photoluminescence spectroscopies demonstrated that after light irradiation, photoexcited electrons in crystal violet flowed to [Au₂₅(Cys)₁₈] in the silicone, suggesting that redox reaction from [Au₂₅(Cys)₁₈] enhanced the photobactericidal activity. Stability tests revealed that leaching of crystal violet and [Au₂₅(Cys)₁₈] from the treated silicone was negligible and cyclic testing showed that the silicone maintained a strong photobactericidal activity after repeated use.

Photobactericidal activity activated by thiolated gold nanoclusters at low flux levels of white light

The emergence of antibiotic resistant bacteria is a major threat to the practice of modern medicine. Photobactericidal agents have obtained significant attention as promising candidates to kill bacteria, and they have been extensively studied. However, to obtain photobactericidal activity, an intense white light source or UV-activation is usually required. Here we report a photobactericidal polymer containing crystal violet (CV) and thiolated gold nanocluster ([Au25(Cys)18]) activated at a low flux levels of white light. It was shown that the polymer encapsulated with CV do not have photobactericidal activity under white light illumination of an average 312 lux. However, encapsulation of [Au25(Cys)18] and CV into the polymer activates potent photobactericidal activity. The study of the photobactericidal mechanism shows that additional encapsulation of [Au25(Cys)18] into the CV treated polymer promotes redox reactions through generation of alternative electron transfer pathways, while it reduces photochemical reaction type-ІІ pathways resulting in promotion of hydrogen peroxide (H2O2) production.

Enhanced visible-light photocatalytic degradation of tetracycline by a novel hollow BiOCl@CeO2 heterostructured microspheres: Structural characterization and reaction mechanism

A high-efficiency hollow BiOCl@CeO₂ heterostructured microspheres with type-II staggered-gap type was successfully synthesized by precipitation-hydrothermal process loaded with BiOCl nanoparticles on CeO₂ microspheres. XRD, FT-IR, EDS, SEM, HRTEM and XPS results show that the prepared materials have good crystallization, morphology and retain hollow spherical structure of CeO₂. Batch experiments indicate that the photocatalytic performance of BiOCl@CeO₂ towards Tetracycline (TC) is superior to pure BiOCl or CeO₂ owing to the distinctive hollow structures and the formed heterostructure between BiOCl and CeO₂. Cyclic experiment exhibits that the optimal BiOCl@CeO₂ photocatalyst can still photodegrade more than 80% of TC in 120 min after 4 cycles. Additionally, the reactive oxidation species (ROS) trapping experiments reveal that the critical ROS include photogenerated holes (h⁺) and superoxide radical anions (O^2-). Finally, the possible degradation pathways of TC and enhanced photodegradation mechanism was systematically discussed. On this basis, the hollow BiOCl@CeO₂ heterostructured microspheres provide a new alternative with great potential in efficient visible-light-driven photodegradation of persistent organic pollutants.

Novel hierarchical Sn3O4/BiOX (X = Cl, Br, I) p–n heterostructures with enhanced photocatalytic activity under simulated solar light irradiation

Sn₃O₄/BiOX (X = Cl, Br, I), a series of p–n-heterojunction-based photocatalysts, were prepared by a combination of an ultrasonic-assisted precipitation–deposition method and hydrothermal method.