Nano-photosensitizers with gallic acid-involved Fe-O-Cu "electronic storage station" bridging ligand-to-metal charge transfer for efficient catalytic theranostics.

NH2-MIL-88B (Fe) (MOF) is a promising photocatalytic material for antitumor therapy because of its distinctive electronic structure. However, inadequate separation of photo-generated electrons and slow reaction rate in low/high-valence iron (Fe) cycles limit their clinical application. In the present study, "electronic storage station" as a ligand-to-metal charge transfer bridge bond was constructed to inhibit recombination of electron/hole under 650 nm laser irradiation. Cupric (Cu) ions and gallic acid (GA) were self-assembled into a MOF (denoted as CGMOF) to create an FeO(GA)Cu bridge bond. GA, characterized by robust electron delocalization and abundant electron-donating groups, significantly enhances electron transfer efficiency for photodynamic therapy (PDT). CGMOF can respond to endogenous glutathione and release cuprous ions, accelerating the iron ion/ferrous ion cycles for chemodynamic therapy (CDT). The released Fe species can serve as T2-weighted magnetic resonance imaging contrast. Extended X-ray absorption fine structure spectra confirmed the presence of GA-containing FeOCu bonds in CGMOF. Furthermore, a series of photo-electrochemical tests confirmed that the formation of FeO(GA)Cu bond prominently elevated the redox capacity and increased the carrier density of CGMOF by 2.74-fold compared to that of MOF. In addition, cinnamaldehyde was grafted onto CGMOF for tumor-responsive hydrogen peroxide self-supply. Concurrently, hyaluronic acid was surface-modified to achieve the targeted delivery of nano-photosensitizers. In summary, this study presents an innovative approach for engineering Fe-based metal-organic frameworks for synergetic PDT/CDT applications.

Interplay between Intermediate Anionic and Cationic Species and the Reflection to Voltage Hysteresis of Oxygen-Redox Battery Electrodes: A Holistic Picture.

Ligand-to-metal charge transfer (LMCT) is conceived as a universal theory to account for voltage hysteresis in oxygen-redox battery electrodes. However, the influence of oxygen anionic species on mediating LMCT and its reflection to voltage hysteresis remain poorly understood. Herein, we demonstrate a close interplay between the chemical states of oxidized oxygen species, the cationic species, and the kinetics of LMCT and forcefully identify their influence on the magnitude of voltage hysteresis. Combining electrochemical/spectroscopic evidence and first-principles calculations, we clarify two distinct kinds of dynamic LMCT processes─that is, the formation of trapped molecular O2 accompanied by the reduction of Ni4+/Ni3+ to Ni2+ (fast LMCT) during relaxation in Li-rich cation-disordered rock-salt (DRX) Li1.3Ni0.27Ta0.43O2 with extremely large voltage hysteresis, the formation of O-O dimers, and the partial reduction of Mn4+ to Mn3+ (slow LMCT) in DRX-Li1.3Mn0.4Ta0.3O2 with medium hysteresis. We further validate the maintenance of both cationic (Mn4+) and anionic (O-•) species during relaxation in Na2Mn3O7, reconciling its nonhysteretic behavior to the absence of LMCT. This study highlights the critical role of intermediate anionic species in mediating LMCT and provides a causal explanation of various voltage hysteresis signatures of oxygen-redox materials.

Photoinduced Ligand-to-Metal Charge Transfer in Base-Metal Catalysis.

The absorption of light by photosensitizers has been shown to offer novel reactive pathways through electronic excited state intermediates, complementing ground state mechanisms. Such strategies have been applied in both photocatalysis and photoredox catalysis, driven by generating reactive intermediates from their long-lived excited states. One developing area is photoinduced ligand-to-metal charge transfer (LMCT) catalysis, in which coordination of a ligand to a metal center and subsequent excitation with light results in the formation of a reactive radical and a reduced metal center. This mini review concerns the foundations and recent developments in ligand-to-metal charge transfer in transition metal catalysis focusing on the organic transformations made possible through this mechanism.

Ultrathin layer TAFC on BiVO4 with ligand-to-metal charge transfer enhances built-in electric field for boosting photoelectrochemical water oxidation.

To reveal the mechanism of charge transfer between interfaces of BiVO4-based heterogeneous materials in photoelectrochemical water splitting system, the cocatalyst was grown in situ using tannic acid (TA) as a ligand and Fe and Co ions as metal centers (TAFC), and then uniformly and ultra-thinly coated on BiVO4 to form photoanodes. The results show that the BiVO4/TAFC achieves a superior photocurrent density (4.97 mA cm-2 at 1.23 VRHE). The charge separation and charge injection efficiencies were also significantly higher, 82.0 % and 78.9 %, respectively. From XPS, UPS, KPFM, and density functional theory calculations, Ligand-to-metal charge transfer (LMCT) acts as an electron transport highway in TAFC ultrathin layer to promote the concentration of electrons towards metal center, leading to an increase in the work function, which enhances the built-in electric field and further improves the charge transport. This study demonstrated that the LMCT pathway on TA-metal complexes enhances the built-in electric field in BiVO4/TAFC to promote charge transport and thus enhance water oxidation, providing a new understanding of the performance improvement mechanism for the surface-modified composite photoanodes.

Metal-Loaded Synthetic Melanin via Oxidative Polymerization of Neurotransmitter Norepinephrine Exhibiting High Photothermal Conversion.

Polydopamine (PDA)-derived melanin-like materials exhibit significant photothermal conversion owing to their broad-spectrum light absorption. However, their low near-infrared (NIR) absorption and inadequate hydrophilicity compromise their utilization of solar energy. Herein, we developed metal-loaded poly(norepinephrine) nanoparticles (PNE NPs) by predoping metal ions (Fe3+, Mn3+, Co2+, Ca2+, Ga3+, and Mg2+) with norepinephrine, a neuron-derived biomimetic molecule, to address the limitations of PDA. The chelation between catechol and metal ions induces a ligand-to-metal charge transfer (LMCT) through the formation of donor-acceptor pairs, modulating the light absorption behavior and reducing the band gap. Under 1 sun illumination, the Fe-loaded PNE coated wood evaporator achieved a high seawater evaporation rate and efficiency of 1.75 kg m-2 h-1 and 92.4%, respectively, owing to the superior hydrophilicity and photothermal performance of PNE. Therefore, this study offers a comprehensive exploration of the role of metal ions in enhancing the photothermal properties of synthetic melanins.

Photochemically Inert Broad-Spectrum Sunscreen by Metal-Phenolic Network Coatings of Titanium Oxide Nanoparticles.

Titanium dioxide (TiO2) nanoparticles are extensively used as a sunscreen filter due to their long-active ultraviolet (UV)-blocking performance. However, their practical use is being challenged by high photochemical activities and limited absorption spectrum. Current solutions include the coating of TiO2 with synthetic polymers and formulating a sunscreen product with additional organic UV filters. Unfortunately, these approaches are no longer considered effective because of recent environmental and public health issues. Herein, TiO2-metal-phenolic network hybrid nanoparticles (TiO2-MPN NPs) are developed as the sole active ingredient for sunscreen products through photochemical suppression and absorption spectrum widening. The MPNs are generated by the complexation of tannic acid with multivalent metal ions, forming a robust coating shell. The TiO2-MPN hybridization extends the absorption region to the high-energy-visible (HEV) light range via a new ligand-to-metal charge transfer photoexcitation pathway, boosting both the sun protection factor and ultraviolet-A protection factor about 4-fold. The TiO2-MPN NPs suppressed the photoinduced reactive oxygen species by 99.9% for 6 h under simulated solar irradiation. Accordingly, they substantially alleviated UV- and HEV-induced cytotoxicity of fibroblasts. This work outlines a new tactic for the eco-friendly and biocompatible design of sunscreen agents by selectively inhibiting the photocatalytic activities of semiconductor nanoparticles while broadening their optical spectrum.

Fe-MOF-based fluorescent sensor with on/off capabilities for the highly sensitive detection of tert-butylhydroquinone in edible oils.

In this work, a "turn off-on" fluorescent sensor was developed for highly sensitive determination of tert-butylhydroquinone (TBHQ) based on an Fe(III)-based metal-organic framework (Fe-MOF). An Fe-MOF with an octahedral structure was synthesized via a simple hydrothermal method using ferric chloride hexahydrate and 2-aminoterephthalic acid (NH2-BDC) as raw materials. The fluorescence of Fe-MOF is extremely weak owing to ligand-to-metal charge transfer (LMCT) and internal filtration effect (IFE). When the system contained TBHQ, the binding of TBHQ to Fe(III) inhibited the LMCT of the fluorescent ligand NH2-BDC to Fe(III), releasing the fluorescence of NH2-BDC and thus restoring the fluorescence. With this as the basis, a rapid, sensitive, and selective fluorescence sensor is developed for the detection of TBHQ. Under the optimal conditions, TBHQ showed good linearity with fluorescence intensity in the range of 0-1.5 × 102 µmol L-1 and a detection limit of 0.0030 µmol L-1 (S/N = 3). The selectivity, reproducibility, and stability of the developed Fe-MOF-based sensors are comprehensively studied. Finally, the practicality of the method is verified by examining the detection of TBHQ in soybean oil; the results are consistent with those obtained using conventional high-performance liquid chromatography.

Blocking Accretion Enables Dimension Reduction of Metal-Organic Framework for Photocatalytic Performance.

The evolution and formation process of two-dimensional metal-organic frameworks (MOFs) primarily arise from the anisotropic growth of crystals, leading to variations in photocatalytic performance. It is crucial to achieve a synergistic combination of anisotropic electron transfer direction and dimension reduction strategies. In this study, a novel approach that effectively blocks crystal growth accretion through the coordination of solvent molecules is presented, achieving the successful synthesis of impurity-free two-dimensional nanosheet Zn-PTC with exceptional hydrogen evolution reaction (HER) performance (15.4 mmol g-1  h-1 ). The structural and photophysical characterizations validate the successful prevention of crystal accretion, while establishing correlation between structural anisotropy and intrinsic charge transfer mode through transient spectroscopy. These findings unequivocally demonstrate that electron transfer along the [001] direction plays a pivotal role in the redox performance of nano-Zn-PTC. Subsequently, by coupling the photocatalytic performance and density functional theory (DFT) simulation calculations, the carrier diffusion kinetics is explored, revealing that effective dimension reduction along the ligand-to-metal charge transfer (LMCT) direction is the key to achieving superior photocatalytic performance.

Method for highly selective, ultrasensitive fluorimetric detection of Cu2+ and Al3+ by Schiff bases containing o-phenylenediamine and o-aminophenol.

Schiff base probes (1 and 2) made from o-phenylenediamine and o-aminophenol were appeared as highly selective fluorimetric chemosensor of Cu2+ and Al3+ ions respectively. Strong fluorescence emission of probe 1 at 415 nm (excitation at 350 nm) was instantly turned off on addition of Cu2+. Very weak fluorescence of probe 2 at 506 nm (excitation at 400 nm) was immediately turned on specifically by Al3+. Job's plot and ESI-MS results suggested 1:1 molar stoichiometric ratio of metal ion and probe in their respective complexes. Probe 1 and 2 had demonstrated very low detection limit (9.9 and 2.5 nM respectively). Binding of Cu2+ with probe 1 was found chemically reversible on addition of EDTA, while complexation between Al3+ and probe 2 was not reversible. On the basis of density functional theory (DFT) and spectroscopic results, probable mode of sensing of the metal ions by the probes were proposed. Quenching of the fluorescence of probe 1 by Cu2+ was attributed to the extensive transfer of charge from the probe molecule to paramagnetic copper ion. Whereas, in the Al3+-complex of probe 2, photo-induced electron transfer (PET) process from the imine nitrogen to salicylaldehyde moiety was restricted and thereby the weak emission intensity of probe 2 was enhanced significantly. Effective pH range of sensing the metal ions by probe 1 and 2 were 4 to 8 and 6 to 10 respectively. Probe 1 was also applied in the design of a logic gate for Cu2+ detection. Moreover, probe 1 and 2 was also used in water sample analysis for quantitative estimation of Cu2+ and Al3+ respectively.

Visible-Light-Driven Photocatalytic Dehydrogenation of Alcohols on TiO2 via Ligand-to-Metal Charge Transfer for Coproduction of H2 and Aldehydes.

Developing visible-light-driven photocatalysts for the catalytic dehydrogenation of organics is of great significance for sustainable solar energy utilization. Here, we first report that aromatic alcohols could be efficiently split into H2 and aldehydes over TiO2 under visible-light irradiation through a ligand-to-metal charge transfer (LMCT) mechanism. A series of TiO2 catalysts with different surface contents of the hydroxyl group (-OH) have been synthesized by controlling the hydrothermal and calcination synthesis methods. An optimal H2 production rate of 18.6 µmol h-1 is obtained on TiO2 synthesized from the hydrothermal method with a high content of surface -OH. Experimental characterizations and comparison studies reveal that the surface -OH markedly influences the formation of LMCT complexes and thus changes the visible-light-driven photocatalytic performance. This work is anticipated to inspire further research endeavors in the design and fabrication of visible-light-driven photocatalyst systems based on the LMCT mechanism to realize the simultaneous synthesis of clean fuel and fine chemicals.

Microtubular cellulose-derived kapok fibre as a solid electron donor for boosting photocatalytic H2O2 production over C-doped g-C3N4 hybrid complexation.

Cellulose continues to play an important and emerging role in photocatalysis, and its favourable properties, such as electron-rich hydroxyl groups, could enhance the performance of photocatalytic reactions. For the first time, this study exploited the kapok fibre with microtubular structure (t-KF) as a solid electron donor to enhance the photocatalytic activity of C-doped g-C3N4 (CCN) via ligand-to-metal-charge-transfer (LMCT) to improve hydrogen peroxide (H2O2) production performance. As confirmed by various characterisation techniques, the hybrid complex consisting of CCN grafted on t-KF was successfully developed in the presence of succinic acid (SA) as a cross-linker via a simple hydrothermal approach. The complexation formation between CCN and t-KF results in the CCN-SA/t-KF sample displaying a higher photocatalytic activity than pristine g-C3N4 to produce H2O2 under visible light irradiation. The enhanced physicochemical and optoelectronic properties of CCN-SA/t-KF imply that the LMCT mechanism is crucial in improving photocatalytic activity. This study promotes utilising the unique t-KF material's properties to develop a low-cost and high-performance cellulose-based LMCT photocatalyst.

Tetracycline Removal through the Synergy of Catalysis and Photocatalysis by Novel NaYF4:Yb,Tm@TiO2-Acetylacetone Hybrid Core-Shell Structures.

Novel hybrid core-shell structures, in which up-converting (UC) NaYF4:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase TiO2-acetylacetonate (TiO2-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO2 conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF4:Yb,Tm@TiO2-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.

Self-Assembled Aza-BODIPY and Iron(III) Nanoparticles for Photothermal-Enhanced Chemodynamic Therapy in the NIR-II Window.

Despite its promising potential in cancer treatment, synergistic photothermal/chemodynamic therapy remains underdeveloped with regard to the utilization of metal-organic materials under second near-infrared (NIR-II) laser excitation. Herein, we report a three-dimensional network constructed via the metal coordination between catechol-functionalized aza-boron dipyrromethenes and iron ions (ABFe), which was further encapsulated by F127 to obtain ABFe nanoparticles (NPs) for combined photothermal/chemodynamic therapy. ABFe NPs exhibited intense absorption in the NIR-II range and negligible fluorescence. Upon 1064 nm laser irradiation, ABFe NPs showed high photothermal conversion efficiency (PCE = 55.0%) and excellent photothermal stability. The results of electron spin resonance spectra and o-phenylenediamine chromaticity spectrophotometry proved that ABFe NPs were capable of generating harmful reactive oxygen species from hydrogen peroxide for chemodynamic therapy, which was promoted by photothermal performance. Notably, in vitro and in vivo experiments demonstrated the great potential of ABFe NPs in photoacoustic imaging and photothermal-enhanced chemodynamic therapy under NIR-II laser irradiation. Therefore, the current work presents a prospective NIR-II excitation therapeutic nanomedicine for combination therapy, offering a novel strategy for simultaneously achieving extended NIR absorption of aza-BODIPY and enhanced chemodynamic therapy with metal-organic materials.

Carbon dots decorated magnetite nanocomposite obtained using yerba mate useful for remediation of textile wastewater through a photo-Fenton treatment: Ilex paraguariensis as a platform of environmental interest-part 2.

Two carbon dots (CD) with diameters of 4.9 ± 1.5 and 4.1 ± 1.2 nm were successfully synthesized through an acid ablation route with HNO3 or H2SO4, respectively, using Ilex paraguariensis as raw material. The CD were used to produce magnetite-containing nanocomposites through two different routes: hydrothermal and in situ. A thorough characterization of the particles by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) indicates that all nanomaterials have spherical-like morphology with a core-shell structure. The composition of this structure depends on the route used: with the hydrothermal route, the shell is composed of the CD, but with the in situ process, the CD act as nucleation centers, and so the iron oxide domains are in the shell. Regarding the photocatalytic mechanism for the degradation of methyl orange, the interaction between the CD and the magnetite plays an important role in the photo-Fenton reaction at pH 6.2, in which ligand-to-metal charge transfer processes (LTMCT) allow Fe2+ regeneration. All materials (100 ppm) showed catalytic activity in the elimination of methyl orange (8.5 ppm), achieving discoloration of up to 98% under visible irradiation over 400 nm in 7 h. This opens very interesting possibilities for the use of agro-industrial residues for sustainable synthesis of catalytic nanomaterials, and the role of the interaction of iron-based catalysts with organic matter in heterogeneous Fenton-based processes.

Effluent degradation followed hydrogen production using near-infrared sensitized nanocomposite of reduced nanographene oxide under visible light.

The purpose of this research work is to synthesize near-infrared dye-sensitized nanocomposites with core-shell nanostructures of titanium dioxide/reduced nanographene oxide (TiO2/r-NGO) to be an effective photocatalyst for effluent degradation followed hydrogen generation under visible light irradiation. The generation of hydrogen using photocatalysts has been intensely researched for the effective utilization of hydrogen in a controlled way. The mechanistic pathway for both hydrogen generation and effluent degradation utilizes the electrons generated through photoexcitation during dye sensitization. For this reason, the squaraine dyes were synthesized by the C-H-direct arylation method and made the nanocomposites with self-assembled core/shell nanocomposites (r-NGOT), where TiO2 serves as the core and r-NGO as the shell. Due to the lack of anchoring groups, VJ-Q was only adsorbed on the surface of r-NGOT through π-π stacking, which is confirmed by Fourier transformed-infrared spectroscopy, X-ray photoelectron spectroscopy, high resolution-transmission electron microscopy, and electron energy loss spectroscopy. The optical absorption spectra of VJ-Q/r-NGOT nanocomposites measured with diffuse reflectance UV/visible absorption spectroscopy covers the whole range of visible light wavelengths up to 800 nm. During the photocatalytic activity, VJ-Q/r-NGOT/Pt followed a ligand-to-metal-charge transfer (LMCT) type mechanism for the electron transfer to the core-shell nanostructure. This mechanistic pathway is utilized for the effluent dye degradation followed hydrogen generation through water splitting. The photocatalytic efficiency of the nanocomposite with adsorbed dye is superior to that of dye-TiO2 due to the large surface area provided by r-NGO and the prevention of dye aggregation. The work is significant due to the limited research works that are carried under dye-sensitized nanocomposites that have been utilized for both dye degradation and hydrogen generation.

Dual-Responsive Nanocomposites for Synergistic Antibacterial Therapies Facilitating Bacteria-Infected Wound Healing.

The rising dangers of bacterial infections have created an urgent need for the development of a new generation of antibacterial technologies and therapeutics. Antibacterial photodynamic therapy (PDT), considered as a noninvasive treatment with no drug resistance, has become a new promising photochemistry-involved treatment strategy. Titanium oxide (TiO2 ) is proved to be a very efficient PDT agent among the photosensitive materials, while the property of a large bandgap of TiO2 makes it only be excited by ultraviolet light, which is harmful to organisms. In this work, a novel ligand-to-metal charge transfer (LMCT) mediated TiO2 PDT strategy is proposed via the harmless near-infrared light irradiation. By choosing a mussel-inspired material, polydopamine (PDA) is involved in forming mesoporous TiO2 @PDA nanoparticles (mTiO2 @PDA NPs). The catechol groups of PDA can attach the TiO2 tightly even in colloidal environments, and can also form the LMCT bridge, exciting TiO2 to exert PDT function via 808 nm irradiation. Combining the sonodynamic therapy (SDT) of TiO2 and the photothermal therapy properties of PDA, this simple structure mTiO2 @PDA enables synergistic antibacterial applications with multiple functions under the dual excitation of NIR and ultrasound. This reliable all-in-one NPs can achieve great antibacterial effect and a rapid repair of infected wounds.

Tin perovskite solar cells with >1,300 h of operational stability in N2 through a synergistic chemical engineering approach.

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn+2 oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH4), aimed at preventing the premature degradation of Sn-HPs. This strategy allows for obtaining efficiencies (PCE) above 10% with enhanced stability. The initial PCE remained unchanged upon 5 h in air (60% RH) at maximum-power-point (MPP). Remarkably, 96% of the initial PCE was kept after 1,300 h at MPP in N2. To the best of our knowledge, these are the highest reported values for Sn-based solar cells. Our findings demonstrate a beneficial synergistic effect when additives are incorporated, highlight the important role of iodide in the performance upon light soaking, and, ultimately, unveil the relevance of controlling the halide chemistry for future improvement of Sn-based perovskite devices.

Visible-Light Activation of a Dissolved Organic Matter-TiO2 Complex Mediated via Ligand-to-Metal Charge Transfer.

Given the widespread use of TiO2, its release into aquatic systems and complexation with dissolved organic matter (DOM) are highly possible, making it important to understand how such interactions affect photocatalytic activity under visible light. Here, we show that humic acid/TiO2 complexes (HA/TiO2) exhibit photoactivity (without significant electron-hole activation) under visible light through ligand-to-metal charge transfer (LMCT). The observed visible-light activities for pollutant removal and bacterial inactivation are primarily linked to the generation of H2O2via the conduction band. By systematically considering molecular-scale interactions between TiO2 and organic functional groups in HA, we find a key role of phenolic groups in visible-light absorption and H2O2 photogeneration. The photochemical formation of H2O2 in river waters spiked with TiO2 is notably elevated above naturally occurring H2O2 generated from background organic constituents due to LMCT contribution. Our findings suggest that H2O2 generation by HA/TiO2 is related to the quantity and functional group chemistry of DOM, which provides chemical insights into photocatalytic activity and potential ecotoxicity of TiO2 in environmental and engineered systems.

Photocatalytic reduction of Cr(VI) by Bi2.15WO6 complexed with polydopamine: Contribution of the ligand-to-metal charge transfer path.

Photocatalytic reduction of Cr(VI) in water environments attracts more attention; however, the mechanisms involved in this process have not been clearly elucidated yet. In this study, the photocatalytic reduction of Cr(VI) by polydopamine modified Bi2.15WO6 (PDA/BWO) under visible light was conducted. Kinetics results show that PDA apparently accelerates the reduction of Cr(VI). The quasi-first-order kinetic constant of Cr(VI) reduction by 5PDA/BWO is 70.0 times that of the original BWO, reaching 0.070 min-1. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman analyses confirm the formation of ligand-to-metal charge transfer (LMCT) complex [Bi(III)OC] between PDA and BWO. The formed Bi(III)OC complex enhances visible light response and narrows the bandgap of PDA/BWO. The photoelectrochemical and photoluminescent characterization further reveals that the formed Bi(III)OC complex inhibits the recombination of carriers, thus enhancing the photocatalytic reactivity of PDA/BWO. Electrons, are derived from three paths, including dye sensitization, LMCT and bandgap excitation, contribute to Cr(VI) reduction by PDA/BWO. This study provides new insights on the paths of Cr(VI) reduction by PDA/BWO under visible light.

A novel transformation pathway of p-arsanilic acid in water by colloid ferric hydroxide under UVA light.

Iron species that occur in natural surface water could affect the photochemical behavior of pollutants. Complexation between iron species and polycarboxylate or heavy metals has been widely reported, where the ligands could be oxidized via ligand-to-metal charge transfer (LMCT) by light inducement. Such complexation and photochemical reactions might also occur for low valance metal-containing organic compounds, which is worthy of investigation. This work studied the phototransformation of p-arsanilic acid (ASA), an organic arsenic compound that is widely used as a feed additive in the poultry industry, by colloidal ferric hydroxide (CFH) using black light lamps (λ = 365 nm) as the light source. The results revealed the contribution to ASA transformation at circumneutral conditions by CFH through an LMCT process, which is the same as that for As(III). The complexation between ASA and CFH was investigated using UV-vis spectroscopy. The estimated equilibrium constant for the CFH-ASA complex was log Kf271 = 4.22. The analysis of the photoproducts found the generation of both inorganic and organic arsenic. Our findings confirmed the similarities in the photochemical mechanisms of ASA and As(III) in the presence of CFH. The results help in further understanding the fate of organoarsenicals in the surface water environment.