Photocatalytic Degradation of Glyphosate in Water by N‐Doped SnO2/TiO2 Thin‐Film‐Coated Glass Fibers

Photocatalytic degradation of glyphosate contaminated in water was investigated. The N‐doped SnO₂/TiO₂ films were prepared via sol–gel method, and coated on glass fibers by dipping method. The effects of nitrogen doping on coating morphology, physical properties and glyphosate degradation rates were experimentally determined. Main variable was the concentration of nitrogen doping in range 0–40 mol%. Nitrogen doping results in shifting the absorption wavelengths and narrowing the band gap energy those lead to enhancement of photocatalytic performance. The near optimal 20N/SnO₂/TiO₂ composite thin film exhibited about two‐ and four‐folds of glyphosate degradation rates compared to the undoped SnO₂/TiO₂ and TiO₂ films when photocatalytic treatment were performed under UV and solar irradiations, respectively, due to its narrowest band gap energy (optical absorption wavelength shifting to visible light region) and smallest crystallite size influenced by N‐doping.     

Ultrathin Metal–Organic Framework Nanosheets with Ultrahigh Loading of Single Pt Atoms for Efficient Visible‐Light‐Driven Photocatalytic H2 Evolution

A surfactant‐stabilized coordination strategy is used to make two‐dimensional (2D) single‐atom catalysts (SACs) with an ultrahigh Pt loading of 12.0 wt %, by assembly of pre‐formed single Pt atom coordinated porphyrin precursors into free‐standing metal–organic framework (MOF) nanosheets with an ultrathin thickness of 2.4±0.9 nm. This is the first example of 2D MOF‐based SACs. Remarkably, the 2D SACs exhibit a record‐high photocatalytic H₂ evolution rate of 11 320 μmol g^?1 h^?1 via water splitting under visible light irradiation (λ>420 nm) compared with those of reported MOF‐based photocatalysts. Moreover, the MOF nanosheets can be readily drop‐casted onto solid substrates, forming thin films while still retaining their photocatalytic activity, which is highly desirable for practical solar H₂ production.     

Microwave‐Hydrothermal Preparation and Visible‐Light Photoactivity of Plasmonic Photocatalyst Ag‐TiO2 Nanocomposite Hollow Spheres

Visible‐light‐driven plasmonic photocatalyst Ag‐TiO₂ nanocomposite hollow spheres are prepared by a template‐free chemically‐induced self‐transformation strategy under microwave‐hydrothermal conditions, followed by a photochemical reduction process under xenon lamp irradiation. The prepared samples are characterized by using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N₂ adsorption‐desorption isotherms, X‐ray photoelectron spectroscopy, UV/Vis and Raman spectroscopy. Production of ?OH radicals on the surface of visible‐light illuminated TiO₂ was detected by using a photoluminescence method with terephthalic acid as the probe molecule. The photocatalytic activity of as‐prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under visible‐light irradiation. The results show that the surface plasmon absorption band of the silver nanoparticles supported on the TiO₂ hollow spheres was red shifted, and a strong surface enhanced Raman scattering effect for the Ag‐TiO₂ nanocomposite sample was observed. The prepared nanocomposite hollow spheres exhibits a highly visible‐light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of pure TiO₂ and commercial Degussa P25 (P25) powders. Especially, the as‐prepared Ag‐TiO₂ nanocomposite hollow spheres at the nominal atomic ratio of silver to titanium ( R ) of 2 showed the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2.     

Photocatalytic Nanocomposite Films Fabricated by Layer‐by‐Layer Self‐assembly of TiO2 Nanoparticles and Lignosulfonates

Photocatalytic multilayer nanocomposite films composed of anatase TiO₂ nanoparticles and lignosulfonates (LS) were fabricated on quartz slides by the layer‐by‐layer (LBL) self‐assembly technique. X‐ray photoelectron spectroscopy (XPS), UV‐vis spectroscopy and atomic force microscopy (AFM) were used to characterize the TiO₂/LS multilayer nanocomposite films. Moreover, the photocatalytic properties (decomposition of methyl orange and bacteria) of multilayer nanocomposite films were investigated. XPS results indicated that the intensities of titanium and sulfur peaks increased with the LBL deposition process. A linear increase in absorbance at 280 nm was found by UV‐Vis spectroscopy, suggesting that stepwise multilayer growth occurs on the substrate and this deposition process is highly reproducible. AFM images showed that quartz slide was completely covered by TiO₂ nanoparticles when a 10‐bilayer multilayer film was formed. The decomposition efficiency of methyl orange by TiO₂/LS multilayer films under the same UV irradiation time increased linearly with the number of TiO₂ layers, and the results of decomposition of bacteria under UV irradiation showed that TiO₂/LS multilayer nanocomposite films exhibited excellent decomposition activity of bacteria (Escherichia coil).     

A Noble‐Metal‐Free Nickel(II) Polypyridyl Catalyst for Visible‐Light‐Driven Hydrogen Production from Water

The complex [Ni(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) is an active catalyst for visible‐light‐driven H₂ production from water when employed with [Ir(dfppy)₂(Hdcbpy)] [dfppy=2‐(3,4‐difluorophenyl)pyridine, Hdcbpy=4‐carboxy‐2,2′‐bipyridine‐4′‐carboxylate] as the photosensitizer and triethanolamine as the sacrificial electron donor. The highest turnover number of 520 with respect to the nickel(II) catalyst is obtained in a 8:2 acetonitrile/water solution at pH 9. The H₂‐evolution system is more stable after the addition of an extra free bpy ligand, owing to faster catalyst regeneration. The photocatalytic results demonstrate that the nickel(II) polypyridyl catalyst can act as a more effective catalyst than the commonly utilized [Co(bpy)₃]²⁺. This study may offer a new paradigm for constructing simple and noble‐metal‐free catalysts for photocatalytic hydrogen production.     

Development of Hybrid BiOClxBr1−x‐Embedded Alumina Films and Their Application as Highly Efficient Visible‐Light‐Driven Photocatalytic Reactors

A highly stable 75 wt % BiOCl_xBr_1?x‐loaded alumina composite film has been developed for the fabrication of glass‐based photoreactors. A very simple approach has been adopted that does not involve the use of a special instrument and can be applied to all types of substrates irrespective to their size and shape. The structure and morphology of the films were well characterized by XRD, SEM, TEM, N₂‐sorption, IR, Raman, and UV/Vis diffuse reflectance spectroscopy. BiOCl_xBr_1?x microspheres (1–3 μm) with closely packed thin nanoplates (width ≈10 nm) were integrated within alumina to develop a hybrid film. The photocatalytic capacity of the films was evaluated for the decomposition of Rhodamine B (RhB) and naphthalene under visible‐light irradiation. The composite films showed a remarkable photocatalytic activity and stability and have been reused for several cycles without any deterioration of their original activity.     

Solvent‐Free One‐Step Photochemical Hydroxylation of Benzene Derivatives by the Singlet Excited State of 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone Acting as a Super Oxidant

Photoinduced hydroxylation of neat deaerated benzene to phenol occurred under visible‐light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), which acts as a super photooxidant in the presence of water. Photocatalytic solvent‐free hydroxylation of benzene derivatives with electron‐withdrawing substituents such as benzonitrile, nitrobenzene, and trifluoromethylbenzene used as neat solvents has been achieved for the first time by using DDQ as a super photooxidant to yield the corresponding phenol derivatives and 2,3‐dichloro‐5,6‐dicyanohydroquinone (DDQH₂) in the presence of water under deaerated conditions. In the presence of dioxygen and tert‐butyl nitrite, the photocatalytic hydroxylation of neat benzene occurred with DDQ as a photocatalyst to produce phenol. The photocatalytic reactions are initiated by oxidation of benzene derivatives with the singlet and triplet excited states of DDQ to form the corresponding radical cations, which associate with benzene derivatives to produce the dimer radical cations, which were detected by the femto‐ and nanosecond laser flash photolysis measurements to clarify the photocatalytic reaction mechanisms. Radical cations of benzene derivatives react with water to yield the OH‐adduct radicals. On the other hand, DDQ ^{. ?} produced by the photoinduced electron transfer from benzene derivatives reacts with the OH‐adduct radicals to yield the corresponding phenol derivatives and DDQH₂. DDQ is recovered by the reaction of DDQH₂ with tert‐butyl nitrite when DDQ acts as a photocatalyst for the hydroxylation of benzene derivatives by dioxygen.     

Photoinduced charge property of Ag‐TiO2 films and its relationships with photocatalytic activity under visible illumination

In this article, TiO₂ films were synthesized by traditional spin coating method. To improve their photocatalytic activities, we deposited silver on these films by photodeposition. These films also were characterized by several testing techniques, such as X‐ray diffraction, ultraviolet–visible diffuse reflection spectrum, XPS, Raman spectroscopy (Raman), surface photovoltage spectroscopy, and SEM. The activity of different films was evaluated for degrading rhodamine B solution under visible illumination. The effects of AgNO₃ solution concentration on photoinduced charge property and photocatalytic activity were investigated. The results show that the Ag‐TiO₂ film immersed in 10^?3 mol·L^?1 AgNO₃ solution exhibits higher activity, which is in good agreement with the characterization results. The weaker the surface photovoltage spectroscopy signal, the higher the photocatalytic activity. Moreover, the activity of some films is higher than that of international Degussa P‐25 TiO₂ under visible illumination. Copyright © 2012 John Wiley & Sons, Ltd.     

Interfacial Self‐Assembly of Closely Packed Nanoparticle Arrays of Silica@Multiporphyrin Hybrids as Light‐Sensitizers for Dye Degradation and Viologen Photochromism

Light‐sensitizer functionalized organic–inorganic hybrid materials have attracted much attention owing to their potential applications in the fields of optoelectronics, heterogeneous catalysis, sensors, and nanotechnology. Here, an interfacial self‐assembly of zero‐dimensional (0D) silica@multiporphyrin array nanohybrids and their 3D Langmuir–Blodgett (LB) films is reported. Photoactive tetrapyridylporphyrin (TPyP) was first assembled on the silica nanoparticles’ surfaces via silane, substitution, and coordination reactions to produce nanoSiO₂@(Pd‐TPyP)_n hybrids. Then, the Cd²⁺‐nanoSiO₂@(Pd‐TPyP)_n monolayers and LB films were constructed on the CdCl₂ subphase surface. These monolayers and LB films displayed stronger stability, as well as more uniform and closely packed nanoparticle arrays compared with those prepared on the pure water surface, owing to the formation of strong network‐like Pd‐ and Cd‐TPyP coordination units, which significantly enhanced the nanoparticles’ interaction. Further, compared with that of the 0D nanoSiO₂@(Pd‐TPyP)_n hybrids, the degradation efficiency was nearly 20 times higher when the hybrids’ LB films were used as light‐sensitizers for the photocatalytic degradation of RhB. Finally, flexible photochromic devices were constructed by using the LB films sandwiched between two electrodes, which displayed a reversible photoinduced redox reaction of viologen together with a color change process. Because TPyP was strongly immobilized on the nanoparticles’ surfaces and the particles were connected through the Py‐Pd²⁺‐Py and Py‐Cd²⁺‐Py coordination units with the 3D network‐like architecture, the present nanohybrids and LB films had good stability and reusability.     

Efficient Noble‐Metal‐Free γ‐Fe2O3@NiO Core–Shell Nanostructured Photocatalysts for Water Oxidation

Flowerlike noble‐metal‐free γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures have been fabricated and examined as a catalyst in the photocatalytic oxidation of water with [Ru(bpy)₃](ClO₄)₂ as a photosensitizer and Na₂S₂O₈ as a sacrificial electron acceptor. An apparent TOF of 0.29 μmols^?1 m^?2 and oxygen yield of 51 % were obtained with γ‐Fe₂O₃@NiO. The γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures could be easily separated from the reaction solution whilst maintaining excellent water‐oxidation activity in the fourth and fifth runs. The surface conditions of γ‐Fe₂O₃@NiO also remained unchanged after the photocatalytic reaction, as confirmed by X‐ray photoelectron spectroscopy (XPS).     

BiVO4‐TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method

Composite photocatalyst films have been fabricated by depositing BiVO₄ upon TiO₂ via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP‐OES), XPS, photoluminescence and Mott–Schottky analyses. SILAR processing was found to deposit monoclinic‐scheelite BiVO₄ nanoparticles onto the surface, giving successive improvements in the films′ visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO₄ conduction band and valence band lying cathodically shifted from those of TiO₂. The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo‐first‐order rate constant of 0.004 min^?1. As a reference material, the same SILAR modification has been made to an inactive wide‐band‐gap ZrO₂ film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO₄–ZrO₂ system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self‐sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst′s conduction band.     

Vapor‐Surface Sol‐Gel Deposition of Titania Alternated with Protein Adsorption for Assembly of Electroactive,Enzyme‐Active Films

Combining vapor‐surface sol‐gel deposition of titania with alternate adsorption of oppositely charged iron heme proteins provided ultrathin {TiO₂/protein}_n films with reversible voltammetry extended to 15 TiO₂/protein bilayers, more than twice that of more conventional polyion‐protein or nanoparticle‐protein films made by alternate layer‐by‐layer adsorption. Catalytic activity toward O₂, H₂O₂, and NO was also improved significantly compared to the conventionally fabricated films. The method involves vaporization of titanium butoxide into thin films of water, forming porous TiO₂ sol‐gel layers. Myoglobin (Mb), hemoglobin (Hb), and horseradish peroxidase (HRP) were assembled by adsorption alternated with the vapor‐deposited TiO₂ layers. Improved electrochemical and catalytic performance may be related to better film permeability leading to better mass transport within the films, as suggested by studies with soluble voltammetric probes, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical and electrocatalytic activity of the films can be controlled by tailoring the amount of water with which the metal alkoxide precursor vapor reacts and the number of bilayers deposited in the assembly.     

Strong‐Base‐Assisted Synthesis of a Crystalline Covalent Triazine Framework with High Hydrophilicity via Benzylamine Monomer for Photocatalytic Water Splitting

Methods to synthesize crystalline covalent triazine frameworks (CTFs) are limited and little attention has been paid to development of hydrophilic CTFs and photocatalytic overall water splitting. A route to synthesize crystalline and hydrophilic CTF‐HUST‐A1 with a benzylamine‐functionalized monomer is presented. The base reagent used plays an important role in the enhancement of crystallinity and hydrophilicity. CTF‐HUST‐A1 exhibits good crystallinity, excellent hydrophilicity, and excellent photocatalytic activity in sacrificial photocatalytic hydrogen evolution (hydrogen evolution rate up to 9200 μmol g^?1 h^?1). Photocatalytic overall water splitting is achieved by depositing dual co‐catalysts in CTF‐HUST‐A1, with H₂ evolution and O₂ evolution rates of 25.4 μmol g^?1 h^?1 and 12.9 μmol g^?1 h^?1 in pure water without using sacrificial agent.     

Rare‐Earth Single Erbium Atoms for Enhanced Photocatalytic CO2 Reduction

The solar‐driven photocatalytic reduction of CO₂ (CO₂RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO₂ emissions. However, low catalytic efficiency and poor selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO₂RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er₁/CN‐NT) with a tunable dispersion density of single atoms. Er₁/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO₂RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO₂RR.     

Highly Luminescent and Water‐Soluble Two‐Dimensional Supramolecular Organic Framework: All‐Organic Photosensitizer Template for Visible‐Light‐Driven Hydrogen Evolution from Water

A highly fluorescent (Φ_F=0.60) and water‐soluble two‐dimensional (2D) honeycomb‐shaped supramolecular organic framework (SOF) was successfully synthesized in pure aqueous solution via self‐assembly of novel cyanostilbene‐functionalized trilateral guest molecules and cucurbit[8]uril hosts. The size of this fluorescent 2D SOF was >500 nm in diameter, 1.7 nm in thickness, and 3.9 nm in the honeycomb pore diameter. This 2D SOF holds potential as a new all‐organic photosensitizer template for photocatalytic H₂ evolution from pure water.     

Noble‐Metal‐Free Janus‐like Structures by Cation Exchange for Z‐Scheme Photocatalytic Water Splitting under Broadband Light Irradiation

Z‐scheme water splitting is a promising approach based on high‐performance photocatalysis by harvesting broadband solar energy. Its efficiency depends on the well‐defined interfaces between two semiconductors for the charge kinetics and their exposed surfaces for chemical reactions. Herein, we report a facile cation‐exchange approach to obtain compounds with both properties without the need for noble metals by forming Janus‐like structures consisting of γ‐MnS and Cu₇S₄ with high‐quality interfaces. The Janus‐like γ‐MnS/Cu₇S₄ structures displayed dramatically enhanced photocatalytic hydrogen production rates of up to 718 μmol g⁻¹ h⁻¹ under full‐spectrum irradiation. Upon further integration with an MnO_x oxygen‐evolution cocatalyst, overall water splitting was accomplished with the Janus structures. This work provides insight into the surface and interface design of hybrid photocatalysts, and offers a noble‐metal‐free approach to broadband photocatalytic hydrogen production.     

Molten‐Salt‐Mediated Synthesis of an Atomic Nickel Co‐catalyst on TiO2 for Improved Photocatalytic H2 Evolution

Atomic co‐catalysts offer high potential to improve the photocatalytic performance, of which the preparation with earth‐abundant elements is challenging. Here, a new molten salt method (MSM) is designed to prepare atomic Ni co‐catalyst on widely studied TiO₂ nanoparticles. The liquid environment and space confinement effect of the molten salt leads to atomic dispersion of Ni ions on TiO₂, while the strong polarizing force provided by the molten salt promotes formation of strong Ni?O bonds. Interestingly, Ni atoms are found to facilitate the formation of oxygen vacancies (OV) on TiO₂ during the MSM process, which benefits the charge transfer and hydrogen evolution reaction. The synergy of atomic Ni co‐catalyst and OV results in 4‐time increase in H₂ evolution rate compared to that of the Ni co‐catalyst on TiO₂ prepared by an impregnation method. This work provides a new strategy of controlling atomic co‐catalyst together with defects for efficient photocatalytic water splitting.     

Boosting Visible‐Light‐Driven Photocatalytic Hydrogen Evolution with an Integrated Nickel Phosphide–Carbon Nitride System

Solar light harvesting by photocatalytic H₂ evolution from water could solve the problem of greenhouse gas emission from fossil fuels with alternative clean energy. However, the development of more efficient and robust catalytic systems remains a great challenge for the technological use on a large scale. Here we report the synthesis of a sol–gel prepared mesoporous graphitic carbon nitride (sg‐CN) combined with nickel phosphide (Ni₂P) which acts as a superior co‐catalyst for efficient photocatalytic H₂ evolution by visible light. This integrated system shows a much higher catalytic activity than the physical mixture of Ni₂P and sg‐CN or metallic nickel on sg‐CN under similar conditions. Time‐resolved photoluminescence and electron paramagnetic resonance (EPR) spectroscopic studies revealed that the enhanced carrier transfer at the Ni₂P–sg‐CN heterojunction is the prime source for improved activity.     

Stacking‐Layer‐Number Dependence of Water Adsorption in 3D Ordered Close‐Packed g‐C3N4 Nanosphere Arrays for Photocatalytic Hydrogen Evolution

Water adsorption capacity is a key factor to influence the photocatalytic H₂ evolution activity of polymeric g‐C₃N₄ . Herein, we report the synthesis of 3D ordered close‐packed g‐C₃N₄ nanosphere arrays (CNAs) that significantly enhance the water adsorption capacity. Through precisely controlling the average stacking‐layer number (ASLN) of the nanospheres in CNAs, we reveal an interesting stacking‐layer‐number dependence of water adsorption in the newly designed CNAs for accelerating the H₂ evolution reaction, which can be attributed to the differences in adsorption surface areas and adsorption sites endowed by the point‐defect cavities in sample CNAs.     

An Efficient,Visible‐Light‐Driven,Hydrogen Evolution Catalyst NiS/ZnxCd1−xS Nanocrystal Derived from a Metal–Organic Framework

Photocatalytic water splitting for hydrogen production using sustainable sunlight is a promising alternative to industrial hydrogen production. However, the scarcity of highly active, recyclable, inexpensive photocatalysts impedes the development of photocatalytic hydrogen evolution reaction (HER) schemes. Herein, a metal–organic framework (MOF)‐template strategy was developed to prepare non‐noble metal co‐catalyst/solid solution heterojunction NiS/Zn_xCd_1?xS with superior photocatalytic HER activity. By adjusting the doping metal concentration in MOFs, the chemical compositions and band gaps of the heterojunctions can be fine‐tuned, and the light absorption capacity and photocatalytic activity were further optimized. NiS/Zn_0.5Cd_0.5S exhibits an optimal HER rate of 16.78 mmol g^?1 h^?1 and high stability and recyclability under visible‐light irradiation (λ>420 nm). Detailed characterizations and in‐depth DFT calculations reveal the relationship between the heterojunction and photocatalytic activity and confirm the importance of NiS in accelerating the water dissociation kinetics, which is a crucial factor for photocatalytic HER.