Surface Hydroxyl and Oxygen Vacancies Engineering in ZnSnAl LDH: Synergistic Promotion of Photocatalytic Oxidation of Aromatic VOCs.

Photocatalytic oxidation has gained great interest in environmental remediation, but it is still limited by its low efficiency and catalytic deactivation in the degradation of aromatic VOCs. In this study, we concurrently regulated the surface hydroxyl and oxygen vacancies by introducing Al into ZnSn layered double hydroxide (LDH). The presence of distorted Al species induced local charge redistribution, leading to the remarkable formation of oxygen vacancies. These oxygen vacancies subsequently increased the amount of surface hydroxyl and elongated its bond length. The synergistic effects of surface hydroxyl and oxygen vacancies greatly enhanced reactant adsorption-activation and facilitated charge transfer to generate •OH, •O2-, and 1O2, resulting in highly efficient oxidation and ring-opening of various aromatic VOCs. Compared with commercial TiO2, the optimized ZnSnAl-50 catalyst exhibited about 2-fold activity for the toluene and styrene degradation and 10-fold activity for the chlorobenzene degradation. Moreover, ZnSnAl-50 demonstrated exceptional stability in the photocatalytic oxidation of toluene under a wide humidity range of 0-75%. This work marvelously improves the photocatalytic efficiency, stability, and adaptability through a novel strategy of surface hydroxyl and oxygen vacancies engineering.

Solvent-free synthesis of foam board-like CoSe2 alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation.

Singlet oxygen (1O2) is a highly effective reactive species in selectively oxidizing organic pollutants. However, it is still challenging to rationally design robust catalysts for the selective generation of 1O2. Herein, the coordination and engineering architecture of the foam board-like CoSe2 alloy were facilely constructed through a green solvent-free method and displayed almost 100% 1O2 production selectivity. The CoSe2 alloy showed excellent catalytic ability for the efficient and fast removal of organic pollutants via peroxymonosulfate (PMS) activation compared with previously reported cobalt-based catalysts. The CoSe2/PMS system exhibited strong resistance for a broad pH range (3.0-11.0) and various coexisting inorganic ions owing to the advantage of the strong bonding of Co-Se in CoSe2 alloy. Mechanism studies revealed that 1O2 was the only reactive oxygen species in the CoSe2/PMS system. Theoretical calculations demonstrated that Co was the dominant adsorption site for PMS in CoSe2, and the production pathway of 1O2 was PMS* â†’ *OH → *O → 1O2. In addition, it was proved that *OH and *O served as the rate-determining steps for the formation of 1O2 by PMS activation on CoSe2 alloy. These findings provide a rational strategy for preparing a series of low-cost transition metal-based alloy catalysts for PMS activation to achieve high-efficiency 1O2 production in the elimination of organic pollutants.

Understanding Bridging Sites and Accelerating Quantum Efficiency for Photocatalytic CO2 Reduction.

We report a novel double-shelled nanoboxes photocatalyst architecture with tailored interfaces that accelerate quantum efficiency for photocatalytic CO2 reduction reaction (CO2RR) via Mo-S bridging bonds sites in Sv-In2S3@2H-MoTe2. The X-ray absorption near-edge structure shows that the formation of Sv-In2S3@2H-MoTe2 adjusts the coordination environment via interface engineering and forms Mo-S polarized sites at the interface. The interfacial dynamics and catalytic behavior are clearly revealed by ultrafast femtosecond transient absorption, time-resolved, and in situ diffuse reflectance-Infrared Fourier transform spectroscopy. A tunable electronic structure through steric interaction of Mo-S bridging bonds induces a 1.7-fold enhancement in Sv-In2S3@2H-MoTe2(5) photogenerated carrier concentration relative to pristine Sv-In2S3. Benefiting from lower carrier transport activation energy, an internal quantum efficiency of 94.01% at 380 nm was used for photocatalytic CO2RR. This study proposes a new strategy to design photocatalyst through bridging sites to adjust the selectivity of photocatalytic CO2RR.

Metal(loid)s in organic-matter-polluted urban rivers in China: Spatial pattern, ecological risk and reciprocal interactions with aquatic microbiome.

Black-odorous urban rivers can serve as reservoirs for heavy metals and other pollutants, in which sewage-derived labile organic matter triggering the water blackening and odorization largely determine the fate and ecological impact of the heavy metals. Nonetheless, information on the pollution and ecological risk of heavy metals and their reciprocal impact on microbiome in organic matter-polluted urban rivers remain unknown. In this study, sediment samples were collected and analyzed from 173 typical black-odorous urban rivers in 74 cities across China, providing a comprehensive nationwide assessment of heavy metal contamination. The results revealed substantial contamination levels of 6 heavy metals (i.e., Cu, Zn, Pb, Cr, Cd, and Li), with average concentrations ranging from 1.85 to 6.90 times higher than their respective background values in soil. Notably, the southern, eastern, and central regions of China exhibited particularly elevated contamination levels. In comparison to oligotrophic and eutrophic waters, the black-odorous urban rivers triggered by organic matter exhibited significantly higher proportions of the unstable form of these heavy metals, indicating elevated ecological risks. Further analyses suggested the critical roles of organic matter in shaping the form and bioavailability of heavy metals through fueling microbial processes. In addition, most heavy metals had significantly higher but varied impact on the prokaryotic populations relative to eukaryotes.

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation.

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO2/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O2 and H2O. The resulting reactive oxygen species, including O2 -, O2 2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd0 ⇆ Pd2+, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

Electrochemical generation of hydrogen peroxide from a zinc gallium oxide anode with dual active sites.

Electrochemical water oxidation enables the conversion of H2O to H2O2. It holds distinct advantages to the O2 reduction reaction, which is restricted by the inefficient mass transfer and limited solubility of O2 in aqueous media. Nonetheless, most reported anodes suffer from high overpotentials (usually >1000 mV) and low selectivity. Electrolysis at high overpotentials often causes serious decomposition of peroxides and leads to declined selectivity. Herein, we report a ZnGa2O4 anode with dual active sites to improve the selectivity and resist the decomposition of peroxides. Its faradaic efficiency reaches 82% at 2.3 V versus RHE for H2O2 generation through both direct (via OH-) and indirect (via HCO3-) pathways. The percarbonate is the critical species generated through the conversion of bicarbonate at Ga-Ga dual sites. The peroxy bond is stable on the surface of the ZnGa2O4 anode, significantly improving faradaic efficiency.

Low-valent copper on molybdenum triggers molecular oxygen activation to selectively generate singlet oxygen for advanced oxidation processes.

Singlet oxygen (1O2), which is difficult to generate, plays an important role in chemosynthesis, biomedicine and environment. Molecular oxygen (O2) is a green oxidant to produce 1O2 cost-effectively. However, O2 activation is difficult due to its spin-forbidden nature. Moreover, the main products of O2 activation are basically hydrogen peroxide (H2O2) and hydroxyl radical (•OH), but rarely 1O2. Herein, we innovatively realize the selective generation of 1O2 via O2 activation by a facile molybdenum (Mo)/Cu2+ system. In this system, Mo firstly reduces Cu2+ in solution to low-valence Cu0/Cu+ on its surface. Cu0/Cu+ activates O2 to generate superoxide radical (O2•-). Importantly, O2•- can be captured immediately and oxidized to 1O2 by surface-bound Mo6+ rather than reduced to H2O2. As a result, the Mo/Cu2+ system can selectively produce 1O2. Under air and O2 conditions, the degradation efficiency of ibuprofen by Mo/Cu2+ system is 67.2 % and 76.6 %, respectively. The degradation efficiencies of bisphenol A, rhodamine B and furfuryl alcohol are 77.1 %, 87.7 % and 91.1 %, respectively. The dosages of Mo and Cu2+ are 0.4 g/L and 3 mM, respectively, and the reaction time is 2 h. Interestingly, the activity of Mo decreased by only 4.2 % after 4 cycles. Therefore, this study provides a green pathway to selectively generate 1O2 for advanced oxidation processes.

Construction of a Novel Cascade Electrolysis-Heterocatalysis System by Using Zeolite-Encaged Ultrasmall Palladium Catalysts for H2 O2 Generation.

In situ generation of hydrogen peroxide (H2 O2 ) has attracted extensive attention, especially in water treatment. However, traditional anthraquinones can only produce high-concentration H2 O2 and its transportation and storage are not convenient and dangerous. Herein, an in situ and on-demand strategy to produce H2 O2 by using a cascade water electrolysis together with a heterocatalysis system is provided. Beginning with water, H2, and O2 can be generated via electrolysis and then react with each other to produce H2 O2 immediately on efficient zeolite-encaged ultrasmall Pd catalysts. Significantly, the H2 O2 generation rate in the optimized cascade system reaches up to 0.85 mol L-1 h-1 gPd -1 , overcoming most of the state-of-the-art catalysts in previous literature. The confinement effect of zeolites is not only beneficial to the formation of highly dispersed metal species, promoting the H2 O2 generation, but also inhibits the H2 O2 decomposition, enhancing the production yield of H2 O2 . In addition, the effect of electrolytes, sizes of Pd species, as well as zeolite acidity are also systematically studied. This work provides a new avenue for H2 O2 generation via a highly efficient cascade electrolysis-heterocatalysis system by using zeolite-supported metal catalysts. The high catalytic efficiency and green process for H2 O2 generation make it very promising for further practical applications.

Spontaneous Formation of Low Valence Copper on Red Phosphorus to Effectively Activate Molecular Oxygen for Advanced Oxidation Process.

Efficient spontaneous molecular oxygen (O2) activation is an important technology in advanced oxidation processes. Its activation under ambient conditions without using solar energy or electricity is a very interesting topic. Low valence copper (LVC) exhibits theoretical ultrahigh activity toward O2. However, LVC is difficult to prepare and suffers from poor stability. Here, we first report a novel method for the fabrication of LVC material (P-Cu) via the spontaneous reaction of red phosphorus (P) and Cu2+. Red P, a material with excellent electron donating ability and can directly reduce Cu2+ in solution to LVC via forming Cu-P bonds. With the aid of the Cu-P bond, LVC maintains an electron-rich state and can rapidly activate O2 to produce ·OH. By using air, the ·OH yield reaches a high value of 423 µmol g-1 h-1, which is higher than traditional photocatalytic and Fenton-like systems. Moreover, the property of P-Cu is superior to that of classical nano-zero-valent copper. This work first reports the concept of spontaneous formation of LVC and develops a novel avenue for efficient O2 activation under ambient conditions.

Atomically Dispersed Au-Assisted C-C Coupling on Red Phosphorus for CO2 Photoreduction to C2H6.

Single-atom catalysts have exhibited great potential in the photocatalytic conversion of CO2 to C2 products, but generation of gaseous multi-carbon hydrocarbon products is still challenging. Previously, supports of a single atom consist of multiple elements, making C-C coupling difficult because the coordination environment of single-atom sites is diversified and difficult to control. Here, we steer C-C coupling by implanting an Au single atom on the red phosphorus (Au1/RP), support with uniform structure composed of a single element, lower electronegativity, and better ability to absorb CO2. The electron-rich phosphorus atoms near the Au single atoms can function as active sites for CO2 activation. The Au single atom can effectively reduce the energy barrier of C-C coupling, boosting the reaction kinetics of the formation of C2H6. Notably, the C2H6 selectivity and turnover frequency of Au1/RP reach 96% and 7.39 h-1 without a sacrificial agent, respectively, which almost represents the best photocatalyst for C2 chemical synthesis to date. This research will provide new ideas for the design of high-efficiency photocatalysts for CO2 conversion to C2 products.

Carbon Nitride Photocatalysts with Integrated Oxidation and Reduction Atomic Active Centers for Improved CO2 Conversion.

Single-atom active-site catalysts have attracted significant attention in the field of photocatalytic CO2 conversion. However, designing active sites for CO2 reduction and H2 O oxidation simultaneously on a photocatalyst and combining the corresponding half-reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single-atom active-site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn1 Co1 /CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H2 O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO2 activation by increasing the bond length and bond angle of CO2 molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn1 Co1 /CN exhibited a CO production rate of 47 µmol g-1 h-1 , which is significantly higher than that of the corresponding single-metal active-site photocatalyst.

High-efficiency photoreduction of CO2 in a low vacuum.

Photoreduction of CO2 into CO, CH4 or hydrocarbons is attractive, due to environmental compatibility and economic feasibility. Optimizing the reaction engineering of CO2 reduction is an effective and general strategy that should be given special consideration. In this article, the photocatalytic CO2 reduction performances are originally investigated in a low vacuum in both dilute (10%) and pure CO2. We discover that the CH4 yield increased above one hundred times as the vacuum degree increased from barometric pressure to -80 kPa in dilute CO2. It also reveals long-term stability and good cycling performance in a low vacuum. The enhanced CO2 photoreduction performance in a low vacuum comes from better accumulation of photogenerated electrons, less intense Brownian movement of gas molecules in the environment and hindrance of the active site-blocking of gas molecules in the environment. Improved photocatalytic CO2 reduction in a low vacuum is further verified by Pt-TiO2 catalysts. This research presents a general route for producing clean fuels by photocatalytic CO2 reduction in a more effective way.

Rust triggers rapid reduction of Cr6+ by red phosphorus: The importance of electronic transfer medium of Fe3.

Red phosphorus (P) is one of the metalloid materials, with five external electrons, it should be an excellent electron donor. However, the activity of red P to reduce Cr6+ is limited. Due to electrostatic repulsion, it is difficult for the electrons on the red P to transfer to the chromate anion (Cr6+). Interestingly, we found that Fe3+ derived from rust, waste iron or Fe3+ reagents can be used as the electron transport medium to solve the electron transport obstacles between red P and Cr6+. As a result, the reduction of Cr6+ by red P/rust system takes only 20 min, which is far lower than the 140 min of red P. The reduction rate of Cr6+ in the red P/rust system is about 12.3 times that of red P. The reaction mechanism is that red P is not easy to access chromate anions but can easily adsorb Fe3+. The adsorbed Fe3+ will be reduced to Fe2+ by red P, and the regenerated Fe2+ will diffuse into the solution to rapidly reduce Cr6+. Therefore, this work provides an alternative waste iron reuse pathway and also sheds light on the important role of electron medium in reduction reaction.

Hydrogen Peroxide Production from Water Oxidation on a CuWO4 Anode in Oxygen-Deficient Conditions for Water Decontamination.

Hydrogen peroxide, an environmentally benign oxidant, is an effective chemical agent for water purification. On-site production of H2O2 is considered economical because it avoids the cost of storage and transportation. Traditional generation of H2O2 from oxygen reduction, as a heterogeneous electrochemical reaction, suffers from mass transfer problems because of the limited solubility and low diffusion rate of oxygen in water. These limitations can be overcome if H2O2 is formed by water oxidation. Herein, conversion of water to hydrogen peroxide was achieved efficiently on a CuWO4 anode. This water oxidation strategy can generate H2O2 at a rate of ∼11.8 µmol min-1 cm-2 at 3.0 V versus reversible hydrogen electrode. Importantly, this on-site H2O2 production shows high efficiency in water purification in O2-deficient conditions. This water oxidation anode offers a feasible way to provide a green purification agent with only water as the final byproduct, avoiding toxic intermediates and residues during the production and application.

Efficient inactivation of intracellular bacteria in dormant amoeba spores by FeP.

Waterborne pathogens and related diseases are a severe public health threat worldwide. Recent studies suggest that microbial interactions among infectious agents can significantly disrupt the disinfection processes, and current disinfection methods cannot inactivate intracellular pathogens effectively, posing an emerging threat to the safety of drinking water. This study developed a novel strategy, the FeP/persulfate (PS) system, to effectively inactivate intracellular bacteria within the amoeba spore. We found that the sulfate radical (SO4•-) produced by the FeP/PS system can be quickly converted into hydroxyl radicals (•OH), and •OH can penetrate the amoeba spores and inactivate the bacteria hidden inside amoeba spores. Therefore, this study proposes a novel technique to overcome the protective effects of microbial interactions and provides a new direction to inactivate intracellular pathogens efficiently.

Photocatalytic degradation of ibuprofen on S-doped BiOBr.

Doping heterogeneous atoms into BiOX is recognized as an effective method to improve its photocatalytic activity. Here, S-doped BiOBr (S-BiOBr) was synthesized via a solvothermal method in the absence of water, which is supposed to substitute O as S2- in the lattice. This material is firstly used for the visible-light-driven degradation of ibuprofen, a model anti-inflammatory drug. The degradation efficiency of S-BiOBr is much higher than that of pure BiOBr. The degradation kinetic constant for S-BiOBr (2.48 × 10-2 min-1) is about 3 times as high as that of pure BiOBr (0.83 × 10-2 min-1). It is found that S-doping tunes the band structure of BiOBr, leading to a narrower band gap and thus higher utilization efficiency of visible light. The degradation of ibuprofen on S-BiOBr can be attributed to the generation of H2O2 and OH radicals. OH radical plays a synergistic role along with holes in the photocatalytic degradation process, which is supposed to be better than the reported single hole- or superoxide-dominant reaction. This work reveals a previously unrecognized and more efficient method for the degradation of organic contaminants on BiOBr.

Fibrous Phase Red Phosphorene as a New Photocatalyst for Carbon Dioxide Reduction and Hydrogen Evolution.

2D photocatalysts are one of the hottest issues in energy and material science. In the field of photocatalysis, a 2D material with an appropriate bandgap of 1.3 to 2.0 eV is desirable. Herein, a new kind of fibrous phase red phosphorene with a bandgap between 1.43 to 1.54 eV is obtained. This is much better than black phosphorus because the bandgap of black P depends of its layer number. The black P needs to be as thin as 1-2 layers for suitable band diagram, which is difficult to control. The fibrous red phosphorene is first used for photocatalytic CO2 reduction, and its activity is superior to the majority of mainstream photocatalysts and reaches a record-high value among phosphorus. Besides, its activity in hydrogen evolution is higher than most of the phosphorus photocatalysts. The intralayer charge transfer is much easier than interlayer transfer. The mobility of electron and hole along the phosphorene plane is about 20 times higher than that perpendicular to different layers. The activity sites is at region between the two P[21] chains. These regions are easy to be exposed for fibrous phase phosphorene, making it to exhibit high activity.

A High-Efficiency Hematite Photoanode with Enhanced Bonding Energy Around Fe Atoms.

Hematite nanoarrays are important photoanode materials. However, they suffer from serious problems of charge transfer and surface states; in particular, the surface states hinder the increase in photocurrent. A previous strategy to suppress the surface state is the deposition of an Fe-free metal oxide overlayer. Herein, from the viewpoint of atomic bonding energy, it is found that the strength of bonding around Fe atoms in the hematite is the key to suppressing the surface states. By treating the surface of hematite with Se and NaBH4 , the Fe2 O3 transforms to a double-layer nanostructure. In the outer layer, the Fe-O bonding is reinforced and the Fe-Se bonding is even stronger. Therefore, the surface states are inhibited and the increase in the photocurrent density becomes much faster. Besides, the treatment constructs a nanoscale p-n junction to promote the charge transfer. Improvements are achieved in onset potential (0.25 V shift) and in photocurrent density (5.8 times). This work pinpoints the key to suppressing the surface states and preparing a high-efficiency hematite nanoarray, and deepens our understanding of hematite photoanodes.

Conversion of Biomasses and Copper into Catalysts for Photocatalytic CO2 Reduction.

The rapid increase of CO2 in the atmosphere has caused serious environmental problems. Burning of biomass wastes increases the content of CO2 in the environment. Herein, we propose a new strategy to convert biomass into photocatalysts for artificial CO2 reduction. Using a hydrothermal method, carbohydrates from biomass can be converted into hydrothermal carbonaceous carbon (HTCC). The HTCC consists of plenty of sp2-hybridized structures, which are capable of absorbing solar light for photocatalytic CO2 reduction. Furthermore, with the addition of Cu cocatalysts, higher activity can be obtained for CO2 reduction. The activity of Cu-HTCC is 32 and 1.7 times higher than that of commercial TiO2 and pure HTCC, respectively. This method provides a new strategy of trash to treasure, which converts biomass waste into photocatalysts for CO2 reduction.

Visible-light photocatalysis and charge carrier dynamics of elemental crystalline red phosphorus.

Elemental red phosphorus (red P) is a new class of photocatalysts with a desirable bandgap of ∼1.7 eV and has a strong visible-light response. Here, we show that the efficiency of red P is limited by severe electron trapping at deep traps that are intrinsic to the different crystal facets of the red P. To overcome this, we synthesized the red P/RGO (reduced graphene oxide) composite in a one-step ampoule chemical vapor deposition synthesis that formed a conducive interface between the red P photocatalyst and the RGO acceptor for efficient interfacial charge transport. As substantiated through photoelectrochemical characterization and ultrafast (femtoseconds) transient absorption spectroscopy, the interfacing with RGO provided a rapid pathway for the photocharges in red P to be interfacially separated, thereby circumventing the slower the charge trapping process. As a result, up to a sevenfold increase in the photocatalytic hydrogen production rate (apparent quantum yield = 3.1% at 650 nm) was obtained for the red P/RGO relative to the pristine red P.