Bismuth Oxyhalides Research Articles

Thin Films of Bismuth Oxyhalides (BiOX, X = Cl, Br, I) Deposited by Thermal Evaporation for the Decontamination of Water and Air by Photocatalysis

Thin films of BiOCl, BiOBr, and BiOI (BiOX) were deposited by thermal evaporation for their potential application in the decontamination of water and air through their photocatalytic activity, which was compared among the three. The BiOX thin films were subjected to characterization through X-ray diffraction, high-resolution transmission electron microscopy, and scanning electron microscopy. Additionally, the optical properties were determined from the diffuse reflectance spectrum obtained with a spectrophotometer. To assess the efficacy of the semiconductor films in water decontamination, the evolution of rhodamine B discoloration and its mineralization was monitored by measuring total organic carbon. The decontaminating activity in the air was evaluated in a gas reactor, measuring the conversion of NOx-type gases. The results demonstrated that the thin films of the three oxides exhibited decontaminating photocatalytic activity in both water and air. However, notable distinctions were observed in the photocatalytic activities of the three bismuth oxyhalides in water, while in air, they exhibited similarities. In aqueous environments, the mineralization percentages exhibited notable variation after 96 h, with the BiOBr film displaying a value of 9.2%/mg and the BiOCl film a value of 3.9%/mg. In contrast, the NO conversion rate in the air was approximately 0.6%/mg for the three oxyhalide films.

Electronic, optical, phonon, and thermodynamic properties of bismuth oxyhalides for photocatalysis application using density functional theory

Bismuth oxyhalide (BiOX) represents a class of layered materials distinguished by unique physicochemical and optical characteristics. This study delivers an extensive investigation into the properties of BiOX crystals, employing first-principles calculations to analyze the electronic band structure, projected density of states (PDOS), Raman and infrared (IR) spectra, dielectric functions, alongside phonon and thermodynamic properties. The computed electronic band gaps BiOI, BiOBr, BiOCl, and BiOF crystals were determined to be 2.19 eV, 3.05 eV, 3.29 eV, and 3.43 eV, respectively. Furthermore, an analysis of the PDOS for each BiOX type indicates that the valence band maximum (VBM) primarily comprises dominant O 2p and halide X np states, while the conduction band minimum (CBM) predominantly features Bi 6p states. In addition, significant absorption edges for BiOI, BiOBr, BiOCl, and BiOF crystals, oriented along the [100] axis, were observed at wavelengths of 540 nm, 449 nm, 367 nm, and 320 nm, respectively. The Raman spectral analysis revealed a noticeable shift correlating with the increasing number of halogen atoms, with intensity enhancements observed at elevated temperatures. Phonon dispersion studies corroborated the geometric stability of the optimized structures of BiOX crystals. Thermodynamic evaluations suggested that BiOX materials exhibit qualities characteristic of hard materials at higher temperatures while displaying softer material attributes at lower temperatures. In summary, this research substantially enriches the current understanding of bismuth oxyhalides by detailing their structural, electronic, optical, phonon, and thermodynamic properties. The findings presented in this study provide a foundational basis for future advancements in photocatalytic applications and material development.

Enhanced Synergistic performance of ZnO@BiOX (X=Cl, Br, I) heterojunction for photocatalytic degradation of emerging pollutants under visible light

In this work, we study the influence of the proportion and halogen type present in heterojunctions of zinc oxide and bismuth oxyhalides ZnO@BiOX (Where X=Cl-, Br-, I- and several binary combinations of them) on the photocatalytic activity in the degradation of rhodamine-B (Rh-B) under visible light, as well as in two important emergent contaminants resorcinol and sulfadiazine. The materials were synthesized by a solvothermal process at 130 °C, starting from ZnO nanoparticles and BiOX precursors (Bi+ and X=Cl-, Br-, I- ions). It was found that the best combination of halogens was 75 % Br- and 25 % Cl- (ZnO@BiOBrCl bromine-chlorine ratio 3:1) forming a Z-type heterojunction with a time constant of τ = 5.6067 min (κ = τ-1 = 0.1784 min−1) in the degradation of Rh-B (C0 = 30 ppm, VRxn = 250 mL). The same composite degraded totally resorcinol in 250 min, and 85.2 % of sulfadiazine in 150 min.

Mechanochemically synthesized flower-like bismuth oxyhalides: An electrochemical platform for diclofenac detection

The emerging drug diclofenac (DICF) has been found to penetrates aquatic systems at alarming concentrations and poses serious and irreversible ecotoxicological threats around the world. In this work, we present the solid-state mechanochemical synthesis of 3D flower-like bismuth oxyhalides (BiOX, where X = Cl, Br, and I) as electrode materials for electrochemical detection of DICF. The characteristics of the flower-like BiOX are systematically investigated using spectroscopic and microscopic techniques. The BiOI-modified glassy carbon electrode (GCE) exhibits superior electrochemical performance for DICF detection compared to the pristine GCE, BiOCl/GCE, and BiOBr/GCE. The 3D flower-like architecture of BiOI facilitates favorable electrocatalytic activities due to its abundant electroactive sites, good conductivity, large surface area, and fast ion diffusion. Notably, the BiOI/GCE displays wide linear ranges (0.5–11.3 & 11.3−76), a low limit of detection (0.11 μM), high sensitivity (1.33 μA μM–1 cm–2), excellent repeatability (2.91 %), good reproducibility (2.88 %), and anti-interfering ability (<±5 %). To validate the practicality of the fabricated BiOI/GCE, the quantitative detection of DICF in human urine and river water is demonstrated and achieves acceptable recovery values. This study introduces an innovative approach to design and produce electrode materials with distinct properties, enabling enhanced electrocatalysis for various electrochemical sensing applications.

Carboxylated cellulose-derived carbon mediated flower-like bismuth oxyhalides for efficient Cr(VI) reduction under visible light

Exquisitely tailoring the morphologies of photocatalysts could achieve high activities. In this study, the morphological transformation of bismuth oxyhalide (BiOX, X = Br, I and Cl) from disordered lamellae to regular flowers was facilely achieved via the use of carboxylated cellulose-derived carbon (CDC). The sphere-like structure and abundant surface functional groups of CDC induce the formation of such flower-like morphologies of BiOX/CDC, and this morphology results in a pronounced increase in surface area (e.g., the surface area of BiOBr increases from 3 to 106 m2 g−1) and porosity. Combined with the good light absorption and conductivity of CDC, the flower-like BiOX/CDC exhibited impressive photocatalytic activity under visible light. Regarding the probing Cr(VI) reduction reaction, the representative BiOBr/CDC is capable of reducing 98% of Cr(VI) within 30 min of visible-light illumination, which is markedly greater than those of pure BiOBr (6%) and CDC (16%). Likewise, BiOI/CDC and BiOCl/CDC also have decent photocatalytic Cr(VI) reduction capacities (89% for BiOI/CDC and 69% for BiOCl/CDC) under visible light in comparison with pristine BiOI (13%) and BiOCl (1.5%). This work furnishes a novel and facile approach to tune photocatalyst morphologies and sheds light on the great potential of biomass-derived carbon, which may enlighten the judicious design of photocatalysts with high efficiency.

Photoelectric properties of the semiconductor Bi2YbO4Cl with broad spectral response

Bi2YbO4Cl with a fluorite layer structure belongs to the family of the bismuth rare-earth oxyhalides Bi2REO4X (X=Cl, Br, I). However, the synthesis and photoelectric properties of Bi2YbO4Cl have almost not been reported. In this work, Bi2YbO4Cl was synthesized using the solid-state method and the solvothermal method. Yb3+ ions show a strong characteristic absorption peak at 980 nm, which was measured by ultraviolet–visible–near-infrared absorption spectra. The transient photoconductivity of Bi2YbO4Cl was obtained by time-resolved terahertz spectroscopy system under 400 and 800 nm laser excitations, respectively. The frequency-dependent transient photoconductivity analysis reveals the Drude-Smith behavior in Bi2YbO4Cl. Under photoexcitation, the hot charge carriers with a long relaxation lifetime and a carrier mobility of 48 cm2/(V·s) are obtained. The synthesis of Bi2YbO4Cl is of great significance for the development of novel photocatalytic and photoharvesting materials with broad spectral response.

Amphiphilic heterojunctions with atomically dispersed copper–alkynyl active units for highly efficient CO2 photoreduction

The efficiency of CO2 photoreduction is limited by slow charge kinetics and the mass transfer of hydrophobic CO2 and H2O over the photocatalyst. Herein, we present a copper–alkynyl bond coordination polymer (CA-CP) with atomically-dispersed copper–alkynyl units (ADCAUs). By incorporating hydrophobic CA-CP with hydrophilic iodine vacancy-rich bismuth oxyhalides (IV-BX), we construct amphiphilic heterojunction photocatalysts (CA-CP/IV-BX) for visible-light-driven CO2 photoreduction. CA-CP/IV-BX achieves excellent stability, 100 % CO selectivity and a CO-evolution rate of 157.6 μmol g−1 h−1 coupled with O2 releasing. Experimental and theoretical calculations elucidate that the ADCAUs favor adsorption and activation of CO2, and have high CO selectivity. Moreover, the amphiphilic janus structure not only ensures the spatial synergy effect of CO2 reduction and H2O oxidation, but also promotes charge separation and proton feeding, boosting CO2 photoreduction activity. This work develops Cu–alkynyl coordination polymer photocatalysts with ADCAUs and provides insights into hydrophobic–hydrophilic biphasic photocatalysts for synergistic CO2 reduction and H2O oxidation.

Constructing In-Plane Energy Funnel in Bismuth Oxyhalide to Achieve Spatial Carrier Accumulation

Constructing In-Plane Energy Funnel in Bismuth Oxyhalide to Achieve Spatial Carrier Accumulation

Self-hybridization structures of BiOBr0.5Cl0.5: An ultra-high capacity anode material for half/full potassium-ion batteries

Potassium-ion batteries (PIBs) are gaining attention among emerging technologies for their cost-effectiveness and the abundance of resources they utilize. Within this context, bismuth oxyhalides (BiOX) have emerged as exceptional candidates for anode materials in PIBs due to their unique structural and superior electrochemical properties. However, challenges such as structural instability and low electronic conductivity remain to be addressed. In this study, a flower-like BiOBr0.5Cl0.5/rGO composite anode material was synthesized, demonstrating outstanding K+ storage performance. The self-hybridized structure enhances ion adsorption and diffusion, which in turn improves charge and discharge efficiency as well as long-term stability. In situ X-ray diffraction (XRD) tests confirmed the gradual release and alloying potassium storage mechanism of Bi metal, which occurs through the intermediate KxBiOBr0.5Cl0.5 phase within the BiOBr0.5Cl0.5 anode. This composite exhibited a high specific capacity of 246.4 mAh/g at 50 A/g and maintained excellent capacity retention after 2400 cycles at 5 A/g. Additionally, in full battery tests, it showed good rate performance and long cycle life, maintaining a discharge specific capacity of 119.6 mAh/g at a high current density of 10 A/g. Comprehensive characterizations revealed insights into the structural, electrochemical, and kinetic properties, advancing high-performance PIBs.

Crystal facet/interface anchored Janus activity of BiOBr in driving photocatalytic water splitting

Constructing Janus junctions is expected to provide a novel perspective for analyzing the intrinsic photocatalytic activity of bismuth oxyhalide. Herein, Janus-typed BiOBr(010)/BiOBr(001) homojunction with efficiently photocatalytic H2 evolution has been achieved by a hydrothermal synthesis. The experimental results show that the designed Janus-typed junction can effectively elevate the carrier lifetime, significantly enhance the photocurrent, and prominently reduce the overpotential. The potential difference (0.34 eV) between (010) facet and (001) facet can drive the carrier transport at the interface for Janus junctions. Theoretical calculations indicate that the designed Janus junction has a stable mechanical structure, providing certain support for the long lifetime of the photocatalyst in the photocatalytic process. The carrier distributions in the Janus junction exhibit the typical characteristic distribution. Interestingly, the photo-generated electrons are only localized in BiOBr(001) component, which embodies significantly a role of n-type semiconductor. This essentially activates HER activity (32 µmol/h g−1) of Janus junction. The holes preferentially localize in the BiOBr(010) component of Janus junction. This component undertaking p-type role reduces the free energy of the rate determining step (from OH* to O*) in the oxygen evolution process (0.88 eV). The Janus junction intensively suppresses the carrier recombination probability at the high symmetry point (reciprocal space) in BiOBr. Ab initio molecular dynamics calculations show that the adsorbed water is easy to decompose on the surface of Janus junction. The obtained results of the photocatalytic water splitting further confirm that the designed BiOBr(010)/BiOBr(001) has Janus characteristics, which are consistent with theoretical calculations and tracer tracing results. The diffusion characteristics of hydrogen also evidence that the interaction of the internal electric field in the Janus junction can drive the HER performance. Additionally, these results offer us a unique angle of view to regulate the charge carrier dynamics by the highly oriented facet coupling for the layered semiconductor.

Solid Solution Behavior of High Performance BiOBrxI1-X Photoanodes Probed Using Solid-State NMR, XRD and Optical Spectroscopy

Bismuth oxyhalides (BIOX) are a family of solution-synthesizable 2D layered semiconductors constituted of earth-abundant elements namely bismuth, oxygen and the halogens. BIOX based thin films and heterojunctions are the subject of immense scientific interest due to their impressive performance in photocatalytic and photoelectrochemical devices. Solid solutions of Br/I bismuth oxyhalides exhibit continuously tunable absorption and emission spectra similar to that observed in mixed halide MAPbClxBryI3-x-y perovskites and mixed anion III-V GaAsxP1-x semiconductors. The excited state decay showed two components for all the mixed halide BiOX semiconductors with a dominant short-lived component in the nanosecond range and a weaker longer-lived component of ~100 ns. The average photoluminescence (PL) lifetime varied from 5.4 ns in bare BiOI to 1.49 ns in bare BiOBr with intermediate compositions exhibiting monotonically increasing average PL lifetimes with increasing iodine content. Using a combination of characterization techniques such as solid-state nuclear magnetic resonance (ssNMR), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and optical spectroscopy, we demonstrate the formation of atomic level solid solutions in Br/I bismuth oxyhalides. Through refinement of the lattice parameters using powder XRD and complementary atomic-level 209Bi SSNMR spectroscopy, we found that Vegard's law was obeyed by the BIOBrxI1-x solid solutions. By varying the Br:I ratio, it is also possible to tune the electronic band gap as well as the energy levels corresponding to the conduction band minimum (ECB, min) and the valence band maximum (EVB, max), thus allowing control over the thermodynamic driving force available to drive chemical reactions using photogenerated or electrically injected charge carriers. Suppression of the longitudinal optical phonon in solid solutions of Br/I bismuth oxyhalides is suggestive of lower phonon scattering of charge carriers and improved electronic transport. A synergistic enhancement of more than 1 order of magnitude in the photoelectrochemical water-splitting performance was obtained for the optimized solid solution (BiOBr0.67I0.33) under AM 1.5G 1 sun illumination. Our results pave the way for a one pot synthesis protocol to form BiOX thin films, powders and colloidal suspensions with deterministic control over the stoichiometry.

Synergistic vacancy defects and the surface hydrophobic-to-superhydrophilic wetting engineering in W/S co-doped BiOI for enhanced photocatalytic hydrogen evolution

Bismuth oxyhalide (BiOI) has been used for photoelectrochemical catalysis in the field of catalytic hydrogen evolution, but it in a single-phase form has hardly been reported for photocatalytic hydrogen evolution reaction (PHER). Herein, we designed a W/S co-doped BiOI-based superhydrophilic catalyst with oxygen vacancy-rich defects and heterovalent valence states for efficient PHER under visible light. The W/S doping in BiOI not only adjusts the energy band structure and expands the visible light response range, but also transforms its hydrophobicity into superhydrophilicity, with which the gas bubble amount can be reduced and PHER activity enhanced. The introduction of sulfur regulates the content of oxygen vacancies which enhance the active surface sites for capturing water molecules and activating the H-O-H bond. The added tungsten exists in different valence states of W6+ and W5+ which is beneficial for electron hopping and PHER activity. The W/S-BiOI-3 with the suitable W/S doping content exhibits the highest visible-light PHER rate of 9.46 mmol·g−1·h−1, with an apparent quantum efficiency (AQE) of 9.7 % at 420 nm. W/S-BiOI-3 shows excellent PHER activity, stability, and durability, which provides a feasible scheme for other bismuth-based halogen oxides to be used in PHER.

Precise structure-tailoring of multicomponent nanocatalysts enabled by continuous flow-controlled flash nanoprecipitation technique

Nanostructured catalysts with diverse compositions offer an exciting prospect for various catalytic applications. The precise control of nanostructures allows to tune the physicochemical properties of nanocatalysts and improve their performance. However, most preparative methods rely on conventional batch systems, which require tedious procedures and cause low productivity. Herein, we reported a novel engineered flash nanoprecipitation (FNP) technique to synthesize well-structured nanocatalysts in a continuous-flow procedure with intelligent operation and high productivity, in which a series of multicomponent bismuth oxyhalides (BiOClxBr1-x) were demonstrated as the model catalysts. This method was established on the uninterrupted continuous synthesis of BiOClxBr1-x with precisely controlled microstructure by simply altering the flow rate ratio of precursor fluids in the reactor. The computational fluid dynamics (CFD) simulation showed that the automized flow setup could achieve the accurate control over the intensified fluid mixing. Significantly, a volcano relationship between the halogen compositions and catalytic activities toward photodegradation of tetracycline (TC) was observed, which indicated that the structural changes enabled band structure-dependent regulation. The FNP-processed BiOCl0.75Br0.25 possessed a balanced redox ability and light absorption, thus located at the peak of volcano with a five-fold enhancement of intrinsic photocatalytic activity. Overall, this work provides a promising prospect of continuous-flow technique in the engineered manufacturing of the advanced nanomaterials, offering fine-tuning of the nanostructures of materials with low cost and high productivity.

Elucidating Structural Disorder in Ultra-Thin Bi-Rich Bismuth Oxyhalide Photocatalysts.

Advancing the field of photocatalysis requires the elucidation of structural properties that underpin the photocatalytic properties of promising materials. The focus of the present study is layered, Bi-rich bismuth oxyhalides, which are widely studied for photocatalytic applications yet poorly structurally understood, due to high levels of disorder, nano-sized domains, and the large number of structurally similar compounds. By connecting insights from multiple scattering techniques, utilizing electron-, X-ray- and neutron probes, the crystal phase of the synthesized materials is allocated as layered Bi24O31X10 (X = Cl, Br), albeit with significant deviation from the reported 3Dcrystalline model. The materials comprise anisotropic platelet-shaped crystalline domains, exhibiting significant in-plane ordering in two dimensionsbut disorder and an ultra-thin morphology in the layer stacking direction. Increased synthesis pH tailored larger, more ordered crystalline domains, leading to longer excited state lifetimes determined via femtosecond transient absorption spectroscopy (fs-TAS). Although this likely contributes to improved photocatalytic properties, assessed via the photooxidation of benzylamine, increasing the overall surface area facilitated the most significant improvement in photocatalytic performance. This study, therefore, enabled both phase allocation and a nuanced discussion of the structure-property relationship for complicated, ultra-thin photocatalysts.

Cobalt and chlorine co-doped Bi5O7I catalysts for LED-induced photocatalytic or PMS-activation antibiotics degradation

Multifunctional semiconductor catalysts can meet the urgent needs for the removal of antibiotic pollutants in water. Bifunctional catalysts, cobalt and chlorine co-doped Bi5O7I (signed as Co-BIC) catalysts, were purposefully designed through a two-step aqueous strategy. The preformed Bi5O7I precursor provided one-dimensional structure and Bi-rich character for the construction of Co-BIC catalysts. Co and Cl co-doping in Bi5O7I crystals can form a doping energy level and improve the internal electric field, which led to enlarged visible-light absorption and charge separation efficiency during the photocatalytic reaction process. These advantages made Co-BIC crystals exhibit good photocatalytic activities for the removal of antibiotic levofloxacin (LEV), ciprofloxacin (CIP) and tetracycline (TC) under visible LED (100 W) light irradiation. The degradation efficiency of LEV, CIP and TC over the typical Co-BIC-60 catalyst can reach more than 80 % under 60 min of LED irradiation. In the system of Co-BIC activated peroxymonosulfate (PMS), ∼ 90 % of LEV, CIP and TC degraded within 20 min over 20 mg of Co-BIC-60 catalyst. The mechanism of photocatalytic degradation and PMS oxidation degradation over Co-BIC catalysts was proposed on band structures of Co-BIC catalysts and the active species in the capture experiments. This work could provide new ideas for the preparation of bismuth oxyhalide catalysts coupled with transition metal elements.

Influence of Composition and Structure on the Optoelectronic Properties of Photocatalytic Bi4NbO8Cl-Bi2GdO4Cl Intergrowths.

Mixed metal oxyhalides are an exciting class of photocatalysts, capable of the sustainable generation of fuels and remediation of pollutants with solar energy. Bismuth oxyhalides of the types Bi4MO8X (M = Nb and Ta; X = Cl and Br) and Bi2AO4X (A = most lanthanides; X = Cl, Br, and I) have an electronic structure that imparts photostability, as their valence band maxima (VBM) are composed of O 2p orbitals rather than X np orbitals that typify many other bismuth oxyhalides. Here, flux-based synthesis of intergrowth Bi4NbO8Cl-Bi2GdO4Cl is reported, testing the hypothesis that both intergrowth stoichiometry and M identity serve as levers toward tunable optoelectronic properties. X-ray scattering and atomically resolved electron microscopy verify intergrowth formation. Facile manipulation of the Bi4NbO8Cl-to-Bi2GdO4Cl ratio is achieved with the specific ratio influencing both the crystal and electronic structures of the intergrowths. This compositional flexibility and crystal structure engineering can be leveraged for photocatalytic applications, with comparisons to the previously reported Bi4TaO8Cl-Bi2GdO4Cl intergrowth revealing how subtle structural and compositional features can impact photocatalytic materials.

First-principles quantum computational study to investigate radiation energy-dependent effect on optoelectronic properties of bismuth oxyhalides BiOX (X= I, Br)

Metal oxyhalides are potential candidates for fundamental and technological interest in pharmaceutical, biological, optical, photoluminance, sensing, energy, and photocatalyst applications. In this study, using first-principles density functional quantum computational approach, we investigate the electronic and optical properties of two members of bismuth oxyhalides, BiOX (X = I, Br). The study is mainly aimed to characterize and examine the light radiation energy-dependent optical properties of the compounds by using mBJ desnty functional with the full potential linearized augmented plane wave method. The oxyhalides show indirect bandgap semiconductor nature having bandgaps of 2.2 eV for BiOI and 3.5 eV for BiOBr. Besides, these are p-type materials owing to a large hole-like carrier density of states in the valence bands close to the Fermi level. The energy bands show considerable dispersion of particles. The increasing reflectivity at high light energy shows the potential of the materials as good reflectors in shielding screens or glasses to avoid damage from the ultraviolet radiation.

Mo-modified BiOI0.5Cl0.5 composites preparation for antibiotic removal

Photocatalytic technology has the advantages of high efficiency, mild reaction conditions, low cost, and minimal secondary contamination in antibiotic degradation. Bismuth oxyhalides(BiOX) has garnered considerable attention and application as a photocatalyst, due to its suitable band gap and light capture capability. In this study, we successfully synthesized the BiOI0.5Cl0.5 (BCI) material through hydrothermal treatment. Furthermore, Molybdenum (Mo) atoms were diffused into the composite to form Mo-doped Mo@BiOI0.5Cl0.5. Various techniques were employed to characterize the structures, chemical compositions, and morphologies of the obtained materials.The photocatalytic performance of the obtained materials was investigated, revealing that MBCI-3 exhibited superior performance in the photocatalytic degradation of contaminants. Over a span of 20 min, 100% of rhodamine B and 86.0% of tetracycline were successfully removed from water. The enhancement in photocatalytic performance can be attributed to the alteration in the band gap of the BCI complex, leading to improved light absorption, while the incorporation of Mo atoms expedites electron transfer. Finally, the role of h+ and O2•- radicals in photocatalytic degradation was verified through radical trapping experiments.

Bismuth oxyhalide as efficient photocatalyst for water, air treatment and bacteria inactivation under UV and visible light

Fifteen bismuth oxyhalides were synthetized, including BiOX, BiOX/BixOyXz, heterostructures and BiOXxY1−x (X, Y = Cl, Br, I) solid solutions. The photocatalytic activity and intermediates formation of as-prepared bismuth-based semiconductors (BBS) were compared with the benchmark TiO2 P25 photocatalyst for NOx air purification, phenol decomposition, and E.Coli bacteria inactivation. TiO2 P25 possessed the highest photocatalytic oxidation rate of phenol (K = 0.003 min−1) and NO degradation efficiency (η = 38 %) when exposed to UV light, but also the lowest performance under visible light on both photocatalytic process (K = 0.0007 min−1 and η = 14 %). Under visible light, BiOI/Bi4O5I2 or solid solutions (BiOI0.5Cl0.5 and BiOI0.5Br0.5) enhanced the photocatalyic for phenol degradation (K = 0.01–0.026 min−1) and NO (35–37 %). BBS samples generated more NO2 during NOx oxidation, but less typical intermediates (benzoquinone, hydroquinone and catechol) during phenol decomposition were detected. BiOCl0.5I0.5 and BiOBr0.5I0.5 composites exhibited the most outstanding antibacterial performance under both irradiation conditions resulting in E. coli 102-3 cfu/mL after 60 min irradiation. The differences can be mainly linked to a different ROS-mediated mechanism of TiO2 and BBS. The BBS photocatalytic results is closely related to the balance between effective light absorption and adequate redox potentials.

Pillar[5]arene functionalized Au NPs and BiOX (Cl/Br/I) heterojunction constructed the enhanced photo-electrochemical sensor for ultrasensitive detection of serotonin

The functional photoelectric materials based on bismuth oxyhalides (BiOX, X = Cl, Br and I) have been widely used in the field of photo-electrochemistry (PEC) due to their excellent physical, chemical and optical properties. Herein, a series of BiOX nanoflowers conjugated water-soluble pillar[5]arenes functionalized Au (Au@WP5/BiOX) modified PEC sensor are constructed and investigated for the PEC detection of serotonin. Upon exploring the physical properties, such as size, visible light absorption capacity, band gap and impedance, of the three BiOX materials, it is discovered that BiOBr is more effective in detecting 5-HT due to its high redox ability, moderate band gap (∼2.03 eV), and low impedance. BiOBr can provide a high and stable starting photocurrent compared to the other two bismuth oxyhalides. When used in acidic or neutral environments, 5-HT with a positive charge can undergo electrostatic adsorption and host-guest complexation behavior with WP5, which has a negative charge. By using WP5, the recognition ability of the material to 5-HT molecules can be enhanced, and the adsorption of 5-HT molecules on Au@WP5/BiOBr can be accelerated. The local surface plasmon resonance effect (LSPR) of gold nanoparticles (Au NPs) can accelerate the electrochemical reaction rate and charge transfer rate, which ultimately leads to the amplification of the photocurrent signal. As a result, the 5-HT detection sensor based on Au@WP5/BiOBr has a wide detection range from 0.01 to 100 μM and a low detection limit of 3 nM (S/N = 3) compared to other sensors, including Au@WP5/BiOCl and Au@WP5/BiOI. The proposed PEC sensor also exhibits good stability and selectivity, making it a promising strategy for detecting biological small molecules using pillar[5]arene functionalized PEC active materials.