Controlled hydrogenation into defective interlayer bismuth oxychloride via vacancy engineering

The practical feasibility of bismuth oxyhalide semiconductors with controlled surface defects in photocatalytic degradation of toluene in air

The photocatalytic degradation (PCD) of toluene (as model aromatic volatile organic compound (VOC)) is studied using two-dimensional semiconductors (bismuth oxyhalides (BiOX (X = Cl and Br)) synthesized with surface defects (BiOX-R (R = reduction)) through a solvothermal-induced reduction process. The PCD efficiency of BiOCl-R against 5 ppm toluene (20 % relative humidity (RH)) is 98.6 % under ultraviolet light irradiation with the quantum yield and clean air delivery rate of 1.04E-03 molecules photon-1 and 3 L/h, respectively. A combined evaluation of catalyst properties, experimental data, and density functional theory simulations consistently indicates that the formation of surface defects should promote the adsorption and activation of toluene, molecular oxygen (O2), and water (H2O) molecules. Meanwhile, the geometric and electronic structure of defective BiOX favorably generates superoxide anion (O2-) and hydroxyl (OH) radicals through electron (e-)-assisted O2 activation and hole (h+)-mediated H2O oxidation, respectively. Notably, the BiOCl-R surface becomes more advantageous to reduce the reaction energy barrier in the ring-opening processes of intermediate forms like benzaldehyde and benzoic acid. Overall, the results of this study offer practical guidelines for the design of advanced photocatalysts with controlled surface defects for the efficient PCD of aromatic VOCs in air.

A surface reconstruction route for increasingly improved photocatalytic H2O2 production using Sr2Bi3Ta2O11Cl

Photocatalytic hydrogen peroxide (H2O2) generation is attractive for the chemical industry and energy production. However, photocatalysts generally deteriorate significantly during use to limit their application. Here we present highly active Sr2Bi3Ta2O11Cl single-crystal nanoplates for conversion of O2 to H2O2 using ambient air with a production rate of ∼3 mmol h-1 g-1 (maximum 17.5% photon conversion). Importantly, Sr2Bi3Ta2O11Cl is not only stable during 30 days of H2O2 production but also gets consistently activated to increase the H2O2 yield by >244%, unlike any other catalyst for H2O2 production. Multi-pronged characterization confirms that the synergistic increase in activity originates from in situ surface reconstruction by oxygen-deficient vacancy associate formation that improves (i) surface oxygen adsorption, (ii) sunlight harvesting, and (iii) charge-transfer from the low-valent metal atoms surrounding oxygen vacancies to reactants. The study establishes the prospects of rational defect engineering for realizing non-degrading photocatalysts for realistic H2O2 production.

High-Performance Photocatalytic Reduction of Nitrogen to Ammonia Driven by Oxygen Vacancy and Ferroelectric Polarization Field of SrBi4 Ti4 O15 Nanosheets

Photo-responsive semiconductors can facilitate nitrogen activation and ammonia production, but the high recombination rate of photogenerated carriers represents a significant barrier. Ferroelectric photocatalysts show great promise in overcoming this challenge. Herein, by adopting a low-temperature hydrothermal procedure with varying concentrations of glyoxal as the reducing agent, oxygen vacancies (Vo) are effectively produced on the surface of ferroelectric SrBi₄ Ti₄ O₁₅ (SBTO) nanosheets, which leads to a considerable increase in photocatalytic activity toward nitrogen fixation under simulated solar light with an ammonia production rate of 53.41 µmol g^-1 h^-1 , without the need of sacrificial agents or photosensitizers. This is ascribed to oxygen vacancies that markedly enhance the self-polarization and internal electric field of ferroelectric SBTO, and hence, facilitate the separation of photogenerated charge carriers and light trapping as well as N₂ adsorption and activation, as compared to pristine SBTO. Consistent results are obtained in theoretical studies. Results from this study highlight the significance of surface oxygen vacancies in enhancing the performance of photocatalytic nitrogen fixation by ferroelectric catalysts.

Construction of Hexagonal Prism-like Defective BiOCL Hierarchitecture for Photocatalytic Degradation of Tetracycline Hydrochloride

Oxygen vacancy manipulation and hierarchical morphology construction in oxygen-containing semiconductors have been demonstrated to be effective strategies for developing high efficiency photocatalysts. In most studies of bismuth-based photocatalysts, hierarchical morphology and crystal defects are achieved separately, so the catalysts are not able to benefit from both features. Herein, using boiling ethylene glycol as the treatment solution, we developed an etching-recrystallization method for the fabrication of 3D hierarchical defective BiOCl at ambient pressure. The target hierarchical 3D-BiOCl is composed of self-assembled BiOCl nanosheets, which exhibit a hexagonal prism-like morphology on a micron scale, while simultaneously containing numerous oxygen vacancies within the crystal structure. Consequently, the target catalyst was endowed with a higher specific surface area, greater light harvesting capability, as well as more efficient separation and transfer of photo-excited charges than pristine BiOCl. As a result, 3D-BiOCl presented an impressive photocatalytic activity for the degradation of tetracycline hydrochloride in both visible light and natural white light emitting diode (LED) irradiation. Moreover, an extraordinary recycling property was demonstrated for the target photocatalyst thanks to its hierarchical structure. This study outlines a simple and energy-efficient approach for producing high-performance hierarchically defective BiOCl, which may also open up new possibilities for the morphological and crystal structural defect regulation of other Bi-based photocatalysts.

Bismuth telluride functionalized bismuth oxychloride used for enhancing antibacterial activity and wound healing efficacy with sunlight irradiation

Bacterial infection can lead to chronic non-healing wounds and serious tissue damage. The wound healing process could be accelerated through bacterial inactivation using some semiconductor nanomaterials with the irradiation of light. Herein, we develop sunlight triggered bismuth telluride-bismuth oxychloride heterostructure nanosheets as antibacterial agents for promoting wound healing, in which bismuth telluride can effectively narrow the bandgap of bismuth oxychloride, resulting in more sunlight absorption and higher antibacterial activity. In fact, the bandgap of bismuth oxychloride has been narrowed from 3.25 eV to 2.37 eV as proved by ultraviolet-visible diffuse reflectance spectroscopy. With simulated sunlight irradiation, bismuth telluride-bismuth oxychloride nanosheets could effectively produce reactive oxygen species and inhibit the growth of both Gram-positive and Gram-negative bacteria. In vivo experiments further confirmed the excellent wound healing capability of bismuth telluride-bismuth oxychloride nanosheets. This work may provide a facile strategy for designing sunlight triggered bacterial inactivation agents.

Broadband dielectric spectroscopy for monitoring temperature-dependent chloride ion motion in BiOCl plates

The dielectric properties and electrical conduction mechanism of bismuth oxychloride (BiOCl) plates synthesized using chloramine-T as the chloride ion source were investigated. Thermally-activated structure rebuilding was monitored using broadband dielectric spectroscopy, which showed that the onset temperature of this process was 283 K. This rebuilding was related to the introduction of free chloride ions into [Bi2O2]2+ layers and their growth, which increased the intensity of the (101) diffraction peak. The electrical conductivity and dielectric permittivity were related to the movement of chloride ions between plates (in the low-frequency region), the interplanar motion of Cl- ions at higher frequencies, vibrations of these ions, and charge carrier hopping at frequencies above 10 kHz. The influence of the free chloride ion concentration on the electrical conductivity was also described. Structure rebuilding was associated with a lower concentration of free chloride ions, which significantly decreased the conductivity. According to the analysis, the BiOCl plate conductivity was related to the movement of Cl- ions, not electrons.