Photocatalytic Dehalogenation of Aromatic Halides on Ta2O5-Supported Pt–Pd Bimetallic Alloy Nanoparticles Activated by Visible Light

Redox-neutral electrochemical decontamination of hypersaline wastewater with high technology readiness level

Industrial hypersaline wastewaters contain diverse pollutants that harm the environment. Recovering clean water, alkali and acid from these wastewaters can promote circular economy and environmental protection. However, current electrochemical and advanced oxidation processes, which rely on hydroxyl radicals to degrade organic compounds, are inefficient and energy intensive. Here we report a flow-through redox-neutral electrochemical reactor (FRER) that effectively removes organic contaminants from hypersaline wastewaters via the chlorination-dehalogenation-hydroxylation route involving radical-radical cross-coupling. Bench-scale experiments demonstrate that the FRER achieves over 75% removal of total organic carbon across various compounds, and it maintains decontamination performance for over 360 h and continuously treats real hypersaline wastewaters for two months without corrosion. Integrating the FRER with electrodialysis reduces operating costs by 63.3% and CO2 emissions by 82.6% when compared with traditional multi-effect evaporation-crystallization techniques, placing our system at technology readiness levels of 7-8. The desalinated water, high-purity NaOH (>95%) and acid produced offset industrial production activities and thus support global sustainable development objectives.

Bimetallic Nanoalloy Catalysts for Green Energy Production: Advances in Synthesis Routes and Characterization Techniques

Bimetallic Nanoalloy catalysts have diverse uses in clean energy, sensing, catalysis, biomedicine, and energy storage, with some supported and unsupported catalysts. Conventional synthetic methods for producing bimetallic alloy nanoparticles often produce unalloyed and bulky particles that do not exhibit desired characteristics. Alloys, when prepared with advanced nanoscale methods, give higher surface area, activity, and selectivity than individual metals due to changes in their electronic properties and reduced size. This review demonstrates the synthesis methods and principles to produce and characterize highly dispersed, well-alloyed bimetallic nanoalloy particles in relatively simple, effective, and generalized approaches and the overall existence of conventional synthetic methods with modifications to prepare bimetallic alloy catalysts. The basic concepts and mechanistic understanding are represented with purposely selected examples. Herein, the enthralling properties with widespread applications of nanoalloy catalysts in heterogeneous catalysis are also presented, especially for Hydrogen Evolution Reaction (HER), Oxidation Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and alcohol oxidation with a particular focus on Pt and Pd-based bimetallic nanoalloys and their numerous fields of applications. The high entropy alloy is described as a complicated subject with an emphasis on laser-based green synthesis of nanoparticles and, in conclusion, the forecasts and contemporary challenges for the controlled synthesis of nanoalloys are addressed.

Adducing Knowledge Capabilities of Instrumental Techniques Through the Exploration of Heterostructures' Modification Methods

The ongoing evolution of technology has facilitated the global research community to rapidly escalate the constant development of novel advancements in science. At the forefront of such achievements in the field of photocatalysis is the utilisation, and in oftentimes, the adaptation of modern instrumentation to understand photo-physical properties of complex heterostructures. For example, coupling in-situ X-ray Raman scattering spectroscopy for real-time degradation of catalytic materials.

A 2D bimetallic Ni-Co hydroxide monolayer cocatalyst for boosting photocatalytic H2 evolution

Here, we report two-dimensional (2D) Ni-Co hydroxide monolayers (NiCo-HMs) as a highly active cocatalyst for enhancing the photocatalytic H₂ evolution of 2D g-C₃N₄ nanosheets. The NiCo-HMs can expand the interface of electron migration, promote the separation of photogenerated carriers, provide synergistic Co-Ni active sites, and optimize atomic hydrogen adsorption to improve the kinetics of the catalytic reaction. The resulting 2D/2D NiCo-HMs/g-C₃N₄ heterojunction displays a high photocatalytic H₂ evolution of 3.58 mmol g^-1 h^-1.

Precise incorporation of transition metals into organolead oxyhalide crystalline materials for photocatalysis

Organolead halide crystalline materials are an emerging class of high-performance photocatalysts. However, limited studies have been performed to tune their photoactive properties by precise introduction of transition metals. Herein, we report the successful incorporation of four different transition metal centers (Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺) into a lead oxyhalide crystalline matrix via isoreticular synthesis. Importantly, the precise control of the incoming transition metal positions has been achieved by its octahedral coordination with three organic ligands. Among them, the Zn²⁺-incorporated material exhibits the highest catalytic activity and recyclable activity in benzylamine oxidation under UV light, which is probably ascribed to the long carrier lifetime and efficient carrier transfer.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm^-2 with a small Tafel slope of 56.23 mV dec^-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

Selective Photoinduced Reduction of Nitroarenes to N-Arylhydroxylamines

We report the selective photoinduced reduction of nitroarenes to N-arylhydroxylamines. The present methodology facilitates this transformation in the absence of catalyst or additives and uses only light and methylhydrazine. This noncatalytic photoinduced transformation proceeds with a broad scope, excellent functional-group tolerance, and high yields. The potential of this protocol reflects on the selective and straightforward conversion of two general antibiotics, azomycin and chloramphenicol, to the bioactive hydroxylamine species.

Biocatalytic Carbon-Hydrogen and Carbon-Fluorine Bond Cleavage through Hydroxylation Promoted by a Histidyl-Ligated Heme Enzyme

LmbB2 is a peroxygenase-like enzyme that hydroxylates L-tyrosine to L-3,4-dihydroxyphenylalanine (DOPA) in the presence of hydrogen peroxide. However, its heme cofactor is ligated by a proximal histidine, not cysteine. We show that LmbB2 can oxidize L-tyrosine analogs with ring-deactivated substituents such as 3-nitro-, fluoro-, chloro-, iodo-L-tyrosine. We also found that the 4-hydroxyl group of the substrate is essential for reacting with the heme-based oxidant and activating the aromatic C-H bond. The most interesting observation of this study was obtained with 3-fluoro-L-tyrosine as a substrate and mechanistic probe. The LmbB2-mediated catalytic reaction yielded two hydroxylated products with comparable populations, i.e., oxidative C-H bond cleavage at C5 to generate 3-fluoro-5-hydroxyl-L-tyrosine and oxygenation at C3 concomitant with a carbon-fluorine bond cleavage to yield DOPA and fluoride. An iron protein-mediated hydroxylation on both C-H and C-F bonds with multiple turnovers is unprecedented. Thus, this finding reveals a significant potential of biocatalysis in C-H/C-X bond (X = halogen) cleavage. Further ¹⁸O-labeling results suggest that the source of oxygen for hydroxylation is a peroxide, and that a commonly expected oxidation by a high-valent iron intermediate followed by hydrolysis is not supported for the C-F bond cleavage. Instead, the C-F bond cleavage is proposed to be initiated by a nucleophilic aromatic substitution mediated by the iron-hydroperoxo species. Based on the experimental results, two mechanisms are proposed to explain how LmbB2 hydroxylates the substrate and cleaves C-H/C-F bond. This study broadens the understanding of heme enzyme catalysis and sheds light on enzymatic applications in medicinal and environmental fields.

Ta2O5/rGO Nanocomposite Modified Electrodes for Detection of Tryptophan through Electrochemical Route

l-tryptophan is one of the eight kinds of essential amino acids for sustainable human life activity. It is common to detect the concentration of tryptophan in human serum for diagnosing and preventing brain related diseases. Herein, in this study, GCE (glassy carbon electrode) modified by Ta₂O₅-reduced graphene oxide (-rGO) composite (Ta₂O₅-rGO-GCE) is synthesized by the hydrothermal synthesis-calcination methods, which is used for detecting the concentration of tryptophan in human serum under the as-obtained optimal detection conditions. As a result, the obtained Ta₂O₅-rGO-GCE shows larger electrochemical activity area than other bare GCE and rGO-GCE due to the synergistic effect of Ta₂O₅ NPs and rGO. Meanwhile, Ta₂O₅-rGO-GCE shows an excellent response to tryptophan during the oxidation process in 0.1 M phosphate buffer solution (pH = 6). Moreover, three wide linear detection range (1.0-8.0 μM, 8.0-80 μM and 80-800 μM) and a low limit of detection (LOD) of 0.84 μM (S/N = 3) in the detection of tryptophan are also presented, showing the larger linear ranges and lower detection limit by employing Ta₂O₅-rGO-GCE. Finally, the as-proposed Ta₂O₅-rGO-GCE with satisfactory recoveries (101~106%) is successfully realized for the detection of tryptophan in human serum. The synthesis of Ta₂O₅-rGO-GCE in this article could provide a slight view for the synthesis of other electrochemical catalytic systems in detection of trace substance in human serum.

Doping of Nb5+ Species at the Au-TiO2 Interface for Plasmonic Photocatalysis Enhancement

Au nanoparticles loaded on semiconductor TiO₂ absorb visible light due to their surface plasmon resonance (SPR) and inject the photogenerated hot electrons (e_hot^-) into the conduction band of TiO₂. The separated charges promote oxidation and reduction reactions. The step that determines the rate of the plasmonic photocatalysis on the Au/TiO₂ system is the e_hot^- injection through the Schottky barrier created at the Au-TiO₂ interface. In the present work, niobium (Nb⁵⁺) oxide species were doped at the Au-TiO₂ interface by loading Nb⁵⁺ onto the TiO₂ surface followed by deposition of Au particles (2 wt % of TiO₂). Visible light irradiation of the Au/Nb⁵⁺/TiO₂ catalysts promotes aerobic oxidation of alcohols with much higher efficiency than that of undoped Au/TiO₂. Lewis acidity of the Nb⁵⁺ species located at the interface cancels the negative charges of Au and creates a barrier with a narrower depletion layer, promoting tunneling e_hot^- injection. Efficiency of the e_hot^- injection depends on the amount of Nb⁵⁺ doped. Loading small amounts of Nb⁵⁺ (∼0.1 wt % of TiO₂) creates mononuclear NbO₄ species and shows large activity enhancement. In contrast, loading larger amounts of Nb⁵⁺ creates aggregated polynuclear Nb₂O₅ species. They decrease the electron density of Au particles and weaken their SPR absorption. This suppresses the e_hot^- generation on the Au particles and decreases the activity of plasmonic photocatalysis.

Bimetallic PtAu Alloy Nanoparticles-Integrated g-C3N4 Hybrid as an Efficient Photocatalyst for Water-to-Hydrogen Conversion

Herein, we report the synthesis of metal (Pt and Au) and metal alloy (PtAu) nanoparticles (NPs)-integrated graphitic carbon nitride (g-C₃N₄) hybrids using a facile solvothermal route for water-splitting application. The metal and metal alloy NPs with varying percentages of Pt and Au are found to be in the size range of 3-5 nm and uniformly distributed on the g-C₃N₄ sheets. The metal and metal alloy NPs act as cocatalyst for g-C₃N₄ to enhance the photocatalytic activity for hydrogen (H₂) generation through higher light absorption and efficient charge separation. The alloy composition plays an important role to maximize the photoactivity, with an optimized PtAu/g-C₃N₄ sample delivered 1009 μmol g^-1 h^-1 of H₂. The visible light assisted photocatalytic H₂ evolution is further investigated with the optimized PtAu alloy NPs-integrated g-C₃N₄. This study presents a robust, stable, and easily synthesizable PtAu/g-C₃N₄ hybrid material as a promising photocatalyst for H₂ generation through water splitting.

Photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin by Pd modified g-C3N4 photocatalysts under UV-vis irradiation: Efficacy, kinetics and mechanism

Polychlorinated dibenzo-p-dioxins (PCDDs), as a group of notorious anthropogenic environmental toxicants, are arguably ubiquitous in nature. In this study, we investigated the photocatalytic reductive dechlorination of 2-chlorodibenzo-p-dioxin (2-CDD) over Pd/g-C₃N₄ catalysts under UV-vis irradiation. The g-C₃N₄ and a series of Pd/g-C₃N₄ catalysts were prepared by thermal polymerization and mechanical mixing-illumination method and characterized by XRD, TEM, BET, SEM and UV-vis DRS analyses. Among all the samples, the Pd/g-C₃N₄ (5 wt%) yielded the optimal dechlorination activity with a total 2-CDD conversion of 54% within 4 h, and 76% of those converted 2-CDD were evolved to dibenzo-p-dioxin (DD). The kinetics of dechlorination could be described as pseudo-first-order decay model (R² > 0.84). Corresponding rate constants (k) increased from 0.052 to 0.17 h^-1 with Pd contents up to 5 wt% and decreased to 0.13 h^-1 with a 10 wt% of Pd. The enhanced activities originated from the surface plasmonic resonance (SPR) effect of Pd nanoparticles and the formation of Schottky barrier between Pd and g-C₃N₄, which extend the spectrum responsive range and suppress the charge recombination of g-C₃N₄. This is the first report on the photocatalytic reductive removal of PCDDs and may provide a new approach for PCDDs pollution control.

Superstructure Ta2O5 mesocrystals derived from (NH4)2Ta2O3F6 mesocrystals with efficient photocatalytic activity

Superstructured mesocrystalline Ta₂O₅ nanosheets were successfully prepared from mesocrystalline (NH₄)₂Ta₂O₃F₆ nanorods by the annealing method.