Charge Coupling Enhanced Photocatalytic Activity of BaTiO3/MoO3 Heterostructures

Mechanistic insights into chemical bonded BaTiO3/MoS2 dual piezoelectric heterojunction for Robust Piezo-Photocatalytic performance

To solve the limited active sites, high carrier recombination rate, and the photo-corrosion issues of layered MoS2, a novel chemically bonded BaTiO3/MoS2 (BM-x, x  = 2, 5, 10, and 20) dual piezoelectric heterojunction was synthesized. Density functional theory (DFT) calculations combined with experimental characterizations revealed that chemical bonds are formed between the 3d orbitals of Ti in BaTiO3 and the 3p orbitals of S in MoS2. These strong interactions enable BaTiO3 to be firmly anchored on the surface of 2D MoS2 sheets and thus enhance the structural stability of the catalyst. Furthermore, the intimate interfacial contact facilitates electron transfer from BaTiO3 to MoS2, while the formed type-II heterostructure induces a built-in electric field that significantly improves the generation and separation of photogenerated charge carriers. Under the synergistic effect of ultrasonic vibration and light irradiation, the valence band maximum (VBM) and conduction band minimum (CBM) of the two phases become tilted, resulting in a significant increase in the planar potential difference between them and therefore enhancing the built-in electric field. Thus, the BM-10 sample achieves a high degradation rate and an excellent Cr(VI) removal efficiency. These findings provide new insights into the structural regulation and the optimization of catalytic activity for MoS2-based piezoelectric photocatalysts.

S-scheme heterojunction of MoO3 nanobelts and MoS2 nanoflowers for photocatalytic degradation

This project presents the fabrication of an efficient heterojunction photocatalyst through combining 3D MoS2 nanoflowers with 2D MoO3 nanobelts, both having highly prominent photocatalytic features. The prepared MoS2@MoO3 heterojunction exhibited superior photocatalytic activity towards the degradation of Azo dye under visible light irradiation and attained about 96% degradation within four hours. Such a high photocatalytic activity might be associated with the high BET surface area, and especially with the S-scheme mechanism that occurs between p-type MoS2 and p-type MoO3, probably due to the fact that this offers effectively separated and transitioned photogenerated electron-hole pairs, while the recombination rate is reduced. The addition of MoO3 increased the bandgap of MoS2 and consequently enhanced the photoinduced electron transfer rate and prolonged the lifetime of the charge carriers. In a word, the generation of hole and •O2- radicals in the whole process of degradation, which have been proved by scavenger tests and Mott-Schottky analysis, proved the MoS2@MoO3 p-p heterojunction to be photocatalytically active. This work underlines the successful application of bandgap and morphological engineering in the design of photocatalysts and points out the 3D/2D MoS2@MoO3 heterojunction structure as the basis for further development of transition metal chalcogenide (TMC)/transition metal oxide (TMO) photocatalysts with a view to tackling important environmental problems by means of sustainable technologies.

The role of BaTiO3 nanoparticles as photocatalysts in the synthesis and characterization of novel fruit dyes is investigated

In the present work, the photocatalytic activity against the natural dye extracted from the novel fruits has been studied by the BaTiO3 nanoparticles (NPs) under a ultra-violet (UV) light source. The large concentrations of an essential phenolic agent present in this phytochemical extract superimposed with cloths fibers make strong stain and degrade into another form of toxic, which is excluded from the many textiles industries as the colorful waste waters without recycling and removal of that dye pigments have been investigated using both photodegradation and photoluminescence techniques. The entitled nanoparticles (NPs) were prepared using the soft chemical root-modified solvothermal synthesis combo method and exposure to heat treatment such that the annealing process has been done for different temperatures ranging from 100°C to 250°C. As for as concern the characterization, as a start, structural and morphology studies have been reported here that highly crystalline oriented peaks data using powder x-ray diffraction techniques (PXRD) as well as the surface morphology including the size, shape, and mass distribution using the field emission scanning electron microscopy (FESEM) techniques, which purely belong to rutile tetragonal structure of the crystal system and circular and noncircular flakes like rough surface morphology materials respectively. The lattice dissociation constant 'ε' value of the BaTiO3 NPs has determined to be ~2.71 × 10-3 using the Williamson-Hall (W-H plot) analysis of crystallographic data. In the UV visible spectroscopy findings, since the extreme quantum confinement of BaTiO3 nanoflakes/nanodisc, the optical energy bandgap has been estimated to be a range of 1.98 to 2.67 eV (~2.48 eV) found from the Tauc plot analysis, which contributes to the significantly owing to the enhanced photocatalytic efficiency with excellent performance along exciton formation, superoxide ions, and hydroxyl free radicals generations under UV-vis light irradiation resulting in efficient degradation of typical novel fruit organic dye. Photoluminescence spectra observed at room temperature and low temperature have been observed for the BaTiO3 nanoflakes, which exhibit the blue emission due to the crystalline defects such as the appearance of Ba vacancies leads to the conceivable beginning of p-type conductivity and the origination of free exciton emission reveals the direct bandgap transition nature of nanoflakes. RESEARCH HIGHLIGHTS: According to our findings, 89.71% of the natural syzygium cumin is degraded by photocatalysis reaction. As a plausible mechanism for the destruction of natural dyes under solar light, photocatalytic destruction has been proposed. The reaction between these reactive free radical species leads to high efficiency photodegradation with a short decay time. In addition to water treatment and environmental cleaning applications, the excellent performance of this photocatalyst makes it a promising candidate for other applications. Hence, the synthesized BaTiO3 nanoflakes showcase a highly significant advancement towards the development of a textiles dye recycling method.

Sc-Modified C3N4 Nanotubes for High-Capacity Hydrogen Storage: A Theoretical Prediction

Utilizing hydrogen as a viable substitute for fossil fuels requires the exploration of hydrogen storage materials with high capacity, high quality, and effective reversibility at room temperature. In this study, the stability and capacity for hydrogen storage in the Sc-modified C3N4 nanotube are thoroughly examined through the application of density functional theory (DFT). Our finding indicates that a strong coupling between the Sc-3d orbitals and N-2p orbitals stabilizes the Sc-modified C3N4 nanotube at a high temperature (500 K), and the high migration barrier (5.10 eV) between adjacent Sc atoms prevents the creation of metal clusters. Particularly, it has been found that each Sc-modified C3N4 nanotube is capable of adsorbing up to nine H2 molecules, and the gravimetric hydrogen storage density is calculated to be 7.29 wt%. It reveals an average adsorption energy of -0.20 eV, with an estimated average desorption temperature of 258 K. This shows that a Sc-modified C3N4 nanotube can store hydrogen at low temperatures and harness it at room temperature, which will reduce energy consumption and protect the system from high desorption temperatures. Moreover, charge donation and reverse transfer from the Sc-3d orbital to the H-1s orbital suggest the presence of the Kubas effect between the Sc-modified C3N4 nanotube and H2 molecules. We draw the conclusion that a Sc-modified C3N4 nanotube exhibits exceptional potential as a stable and efficient hydrogen storage substrate.

Nanoparticulate Perovskites for Photocatalytic Water Reduction

SrTiO₃ and BaTiO₃ nanoparticles (NPs) were activated using H₂O₂ or aqueous HNO₃, and pristine and activated NPs were functionalized with a 2,2'-bipyridine phosphonic acid anchoring ligand (1), followed by reaction with RuCl₃^.3H₂O and bpy, RhCl₃^.3H₂O and bpy, or RuCl₃^.3H₂O. The surface-bound metal complex functionalized NPs were used for the photogeneration of H₂ from water, and their activity was compared to related systems using TiO₂ NPs. The role of pH during surface complexation was found to be important. The NPs were characterized using Fourier transform infrared (FTIR) and solid-state absorption spectroscopies, thermogravimetric analysis mass spectrometry (TGA-MS), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), and the dihydrogen generation was analyzed using gas chromatography-mass spectrometry (GC-MS). Our findings indicate that extensively functionalized SrTiO₃ or BaTiO₃ NPs may perform better than TiO₂ NPs for water reduction.

Synergy of MoO2 with Pt as Unilateral Dual Cocatalyst for Improving Photocatalytic Hydrogen Evolution over g-C3 N4

Pt is usually used as cocatalyst for g-C₃ N₄ to produce H₂ by photocatalytic splitting of water. However, the photocatalytic performance is still limited by the fast recombination of photo-generated electrons and holes, as well as the poor absorption of visible light. In this work, MoO₂ /g-C₃ N₄ composites were prepared, in which MoO₂ synergetic with Pt photo-deposited during H₂ evolution reaction worked as unilateral dual cocatalyst to improve the photocatalytic activity. Within 4 hours of irradiation, the hydrogen production rate of MoO₂ -Pt dual cocatalyst modified g-C₃ N₄ reached 3804.89 μmol/g/h, which was 120.18 times of that of pure g-C₃ N₄ (GCN, 31.66 μmol/g/h), 10.98 times of that of MoO₂ modified g-C₃ N₄ (346.39 μmol/g/h), and 9.18 times of that of Pt modified g-C₃ N₄ (413.64 μmol/g/h). Characterization results demonstrate that the deficient MoO₂ not only promoted visible light absorption of g-C₃ N₄ , but also worked as a "electron pool" to capture and transfer electrons to Pt.

Recent Advances in Ferroelectric Materials-Based Photoelectrochemical Reaction

Inorganic perovskite ferroelectric-based nanomaterials as sustainable new energy materials, due to their intrinsic ferroelectricity and environmental compatibility, are intended to play a crucial role in photoelectrochemical field as major functional materials. Because of versatile physical properties and excellent optoelectronic properties, ferroelectric-based nanomaterials attract much attention in the field of photocatalysis, photoelectrochemical water splitting and photovoltaic. The aim of this review is to cover the recent advances by stating the different kinds of ferroelectrics separately in the photoelectrochemical field as well as discussing how ferroelectric polarization will impact functioning of photo-induced carrier separation and transportation in the interface of the compounded semiconductors. In addition, the future prospects of ferroelectric-based nanomaterials are also discussed.

Novel Z-scheme binary zinc tungsten oxide/nickel ferrite nanohybrids for photocatalytic reduction of chromium (Cr (VI)), photoelectrochemical water splitting and degradation of toxic organic pollutants

A simple hydrothermal approach was demonstrated for synthesizing a coupled NiFe₂O₄-ZnWO₄ nanocomposite, wherein one-dimensional ZnWO₄ nanorods were inserted into two-dimensional NiFe₂O₄ nanoplates. Herein, we evaluated the photocatalytic removal of Cr(VI), and degradation of tetracycline (TC) and methylene blue (MB) by the nanocomposite, as well as its ability to split water. The ZnWO₄ nanorods enriched the synergistic interactions, upgraded the solar light fascination proficiency, and demonstrated outstanding detachment and migration of the photogenerated charges, as confirmed by a transient photocurrent study and electrochemical impedance spectroscopy measurements. Compared to pristine NiFe₂O₄ and ZnWO_4, the NiFe₂O₄-ZnWO₄ nanocomposite exhibited a higher Cr(VI) reduction (93.5%) and removal of TC (97.9%) and MB (99.6%). Radical trapping results suggested that hydroxyl and superoxide species are dominant reactive species, thereby facilitating the Z-scheme mechanism. Furthermore, a probable photocatalytic mechanism was projected based on the experimental results. The photoelectrochemical analysis confirmed that NiFe₂O₄-ZnWO₄ exhibited minor charge-transfer resistance and large photocurrents. We propose a novel and efficient approach for designing a coupled heterostructured nanocomposites with a significant solar light ability for ecological conservation and water splitting.

Highly efficient AgBr/h-MoO3 with charge separation tuning for photocatalytic degradation of trimethoprim: Mechanism insight and toxicity assessment

A highly solar active AgBr/h-MoO₃ composite was constructed by a facile precipitation method, and the charge separation tuning was achieved by photoreduction of AgBr. The photoreduced Ag⁰ on AgBr/h-MoO₃ acted as charge transfer bridge to form Z-scheme heterostructure, while the high degree of Ag reduction converted the material into type-II heterostructure. The synthesized optimal material promoted charge separation and visible light activity due to the incorporation of highly solar active AgBr, which showed ca. 2 times activity on trimethoprim (TMP) degradation than h-MoO₃. The contribution of reactive species on TMP degradation followed the order of O₂^- >¹O₂ > h⁺, which agree well with the proposed charge separation mechanism. The photocatalytic degradation mechanism of TMP was proposed based on the radical quenching, intermediate analysis and DFT calculation. The toxicity analysis based on QSAR calculation showed that part of the degradation intermediates are more toxic than TMP, thus sufficient mineralization are required to eliminate the potential risks of treated water. Moreover, the material showed high stability and activity after four reusing cycles, and it is applicable to treat contaminants in various water matrix. This work is expected to provide new insight into the charge separation tuning mechanism for the AgX based heterojunction, and rational design of highly efficient photocatalysts for organic contaminants degradation by solar irradiation.

A critical review on strategies for improving efficiency of BaTiO3-based photocatalysts for wastewater treatment

Barium titanate (BaTiO₃) photocatalysts with perovskite structures are promising candidates for the effective removal of hazardous organic pollutants from water/wastewater owing to several advantages, including low cost, non-toxicity, high stability, environmental friendliness, favorable band positions, high oxygen vacancies, multiple crystal phases, rapid migration of charge carriers at the surface, band bending, spontaneous polarization, and easy tailoring of the sizes and morphologies. However, this high dielectric/ferroelectric material is only active in UV light (band gap: 3.2 eV), which reduces the photocatalytic degradation performance. To make barium titanate more suitable for photocatalysis, the surfaces of the powders can be modified to broaden the absorption band. In this paper, various strategies for improving photocatalysis of barium titanate for removing organic pollutants (mostly dyes and drugs) from water/wastewater are critically reviewed. They include modifying the sizes and morphologies of the particles by varying the reaction times and synthesis temperatures, doping with metals/non-metals, loading with noble metal NPs (Ag and Au), and fabrication of heterojunction photocatalysts (conventional type II and Z-scheme). The current challenges and possible future directions of BaTiO₃-based materials are also discussed. This comprehensive review is expected to advance the design of highly efficient BaTiO₃-based materials for photocatalytic applications in water/wastewater treatment.

Highly enhanced H2 evolution of MoO3/g-C3N4 hybrid composites based on a direct Z-scheme photocatalytic system

A direct Z-scheme MoO₃/g-C₃N₄ heterojunction with appropriate oxygen vacancies is successfully fabricated via an in situ method of a one-pot pyrolysis strategy.

α-FeOOH-MoO3 Nanorod for Effective Photo-Fenton Degradation of Dyes and Antibiotics at a Wide Range of pH

It's highly significant to develop a novel catalyst, which can be active at a wide range of pH, for an effective photo-Fenton reaction. In this work, α-FeOOH-MoO₃ nanorod was prepared by a one-step hydrothermal method and applied in photo-Fenton degradation of organic pollutants. Benefit from the electron migration mechanism of Z-scheme and excellent photoelectric performance, the catalyst exhibited superior photo-Fenton activity in degradation of organic pollutants. In addition, the catalyst holds good stability after 5 recycles. These results demonstrated that this catalyst has wide application prospect in organic wastewater treatment.