Mesoporous amorphous non-noble metals as versatile substrates for high loading and uniform dispersion of Pt-group single atoms.

Atomically dispersed Pt-group metals are promising as nanocatalysts because of their unique geometric structures and ultrahigh atomic utilization. However, loading isolated Pt-group metals in single-atom alloys (SAAs) with distinctive bimetallic sites is challenging. In this study, we present amorphous mesoporous Ni boride (Ni-B) as an ideal substrate to uniformly disperse Pt atoms with tunable loadings (1.7 to 12.2 wt %). The effect of the morphology, composition, and crystal phase of the Ni-B host on the growth and dispersion of Pt atoms is discussed. The resulting amorphous Pt-Ni-B mesoporous nanospheres exhibit superior electrocatalytic H2 evolution performance in acidic media. This strategy holds the potential to synthesize a diverse library of mesoporous amorphous Pt-group SAAs, by leveraging functional amorphous nanostructured 3d transition-metal borides as substrates, thereby proposing a comprehensive strategy to control atomically dispersed Pt-group metals.

Water-Resistance-Based S-Scheme Heterojunction for Deep Mineralization of Toluene.

Deep mineralization of low concentration toluene (C7 H8 ) is one of the most significant but challenging reactions in photocatalysis. It is generally assumed that hydroxyl radicals (⋅OH) as the main reactive species contribute to the enhanced photoactivity, however, it remains ambiguous at this stage. Herein, a S-scheme ZnSn(OH)6 -based heterojunction with AlOOH as water resistant surface layer is in situ designed for tuning the free radical species and achieving deep mineralization of C7 H8 . By employing a combination of in situ DRIFTS and materials characterization techniques, we discover that the dominant intermediates such as benzaldehyde and benzoic acid instead of toxic phenols are formed under the action of holes (h+ ) and superoxide radicals (⋅O2 - ). These dominant intermediates turn out to greatly decrease the ring-opening reaction barrier. This study offers new possibilities for rationally tailoring the active species and thus directionally producing dominant intermediates via designing water resistant surface layer.

Surface Hydrogen Bond-Induced Oxygen Vacancies of TiO2 for Two-Electron Molecular Oxygen Activation and Efficient NO Oxidation.

Defect engineering can provide a feasible approach to achieving ambient molecular oxygen activation. However, conventional surface defects (e.g., oxygen vacancies, OVs), featured with the coordinatively unsaturated metal sites, often favor the reduction of O2 to •O2- rather than O22- via two-electron transfer, hindering the efficient pollutant removal with high electron utilization. Herein, we demonstrate that this bottleneck can be well discharged by modulating the electronic structure of OVs via phosphorization. As a proof of concept, TiO2 nanoparticles are adopted as a model material for NaH2PO2 (HP) modification, in which HP induces the formation of OVs via weakening the Ti-O bonds through the hydrogen bond interactions. Additionally, the formed Ti-O-P covalent bond refines the electronic structure of OVs, which enables rapid electron transfer for two-electron molecular oxygen activation. As exemplified by NO oxidation, HP-modified TiO2 with abundant OVs achieved complete NO removal with high selectivity for benign nitrate, superior to that of pristine TiO2. This study highlights a promising approach to regulate the O2 activation via an electronic structure modulation and provides fresh insights into the rational design of a photocatalyst for environmental remediation.

Microwave assisted synthesis of PQ-GDY@NH2-UIO-66(Zr) for improved photocatalytic removal of NOx under visible light.

Pyrazinoquinoxaline-based graphdiyne (PQ-GDY) contains a fixed number of sp-sp2 hybridized carbon atoms and pyrazine-like sp2 hybridized N atoms. In this paper, NH2-UIO-66(Zr) on PQ-GDY substrate was successfully constructed with the help of microwave-assisted heating. PQ-GDY surface acts as a microwave antenna under microwave irradiation to rapidly absorb microwave energy and form hot spots (hot spot effect), which facilitates the formation of well-dispersed NH2-UIO-66(Zr) with good crystallinity. Transient absorption spectra show that high hole transport property of PQ-GDY can accelerate the migration of photogenerated holes from NH2-UIO-66(Zr) to PQ-GDY and greatly reduce the recombination rate of photogenerated electrons and holes due to the strong interaction between PQ-GDY and NH2-UIO-66(Zr). Under visible light (λ ≥ 420 nm), PQ-GDY@NH2-UIO-66(Zr) shows high photocatalytic stability and high NOx removal rate up to 74%, which is 44% higher than that of primitive NH2-UIO-66(Zr). At the same time, it inhibits the formation of toxic by-products (NO2) and limits its concentration to a low level.

Modulating the Active Hydrogen Adsorption on Fe─N Interface for Boosted Electrocatalytic Nitrate Reduction with Ultra-Long Stability.

The electrocatalytic reduction of nitrate (NO3 - ) to nitrogen (N2 ) is an environmentally friendly approach for efficient N-cycle management (toward a nitrogen-neutral cycle). However, poor catalyst durability and the competitive hydrogen evolution reaction significantly impede its practical application. Interface-chemistry engineering, utilizing the close relationship between the catalyst surface/interface microenvironment and electron/proton transfer process, has facilitated the development of catalysts with high intrinsic activity and physicochemical durability. This study reports the synthesis of a nitrogen-doped carbon-coated rice-like iron nitride (RL-Fe2 N@NC) electrocatalyst with excellent electrocatalytic nitrate-reduction reaction activity (high N2 selectivity (≈96%) and NO3 - conversion (≈86%)). According to detailed mechanistic investigations by in situ tests and theoretical calculations, the strong hydrogenation ability of iron nitride and enhanced nitrate enrichment of the system synergistically contribute to the rapid hydrogenation of nitrogen-containing species, increasing the intrinsic activity of the catalyst and reducing the occurrence of the competing hydrogen-evolution side reaction. Moreover, RL-Fe2 N@NC shows excellent stability, retaining good NO3 - -to-N2 electrocatalysis activity for more than 40 cycles (one cycle per day). This paper could guide the interfacial design of Fe-based composite nanostructures for electrocatalytic nitrate reduction, facilitating a shift toward nitrogen neutrality.

Hydroxyl Radical-Mediated Efficient Photoelectrocatalytic NO Oxidation with Simultaneous Nitrate Storage Using A Flow Photoanode Reactor.

The selective conversion of dilute NO pollutant into low-toxic product and simultaneous storage of metabolic nitrogen for crop plants remains a great challenge from the perspective of waste management and sustainable chemistry. This study demonstrates that this bottleneck can be well tackled by refining the reactive oxygen species (ROS) on Ni-modified NH2 -UiO-66(Zr) (Ni@NU) using nickel foam (NF) as a three-dimensional (3D) substrate through a flow photoanode reactor via the gas-phase photoelectrocatalysis. By rationally refining the ROS to ⋅OH, Ni@NU/NF can rapidly eliminate 82 % of NO without releasing remarkable NO2 under a low bias voltage (0.3 V) and visible light irradiation. The abundant mesoporous pores on Ni@NU/NF are conducive to the diffusion and storage of the formed nitrate, which enables the progressive conversion NO into nitrate with selectivity over 99 % for long-term use. Through calculation, 90 % of NO could be recovered as the nitrate species, indicating that this state-of-the-art strategy can capture, enrich and recycle the pollutant N source from the atmosphere. This study offers a new perspective of NO pollutant treatment and sustainable nitrogen exploitation, which may possess great potential to the development of highly efficient air purification systems for industrial and indoor NOx control.

Activation of chloride by oxygen vacancies-enriched TiO2 photoanode for efficient photoelectrochemical treatment of persistent organic pollutants and simultaneous H2 generation.

Photoelectrochemical (PEC) activation of chloride ions (Cl-) to degrade persistent organic pollutants (POPs) is a promising strategy for the treatment of industrial saline organic wastewater. However, the wide application of this technology is greatly restricted due to the general photoanode activation of Cl- with poor capability, the propensity to produce toxic by-products chlorates, and the narrow pH range. Herein, oxygen vacancies-enriched titanium dioxide (Ov-TiO2) photoanode is explored to strongly activate Cl- to drive the deep mineralization of POPs wastewater in a wide pH range (2-12) with simultaneous production of H2. More importantly, nearly no toxic by-product of chlorates was produced during such PEC-Cl system. The degradation efficiency of 4-CP and H2 generation rate by Ov-TiO2 were 99.9% within 60 min and 198.2 µmol h-1 cm-2, respectively, which are far superior to that on the TiO2 (33.1% within 60 min, 27.5 µmol h-1 cm-2) working electrode. DFT calculation and capture experiments revealed that Ov-TiO2 with abundant oxygen vacancies is conducive to the activation of Cl- to produce more reactive chlorine species, evidenced by its high production of free chlorine (48.7 mg L-1 vs 7.5 mg L-1 of TiO2). The as-designed PEC-Cl system in this work is expected to realize the purification of industrial saline organic wastewater coupling with green energy H2 evolution.

Singlet Oxygen and Mobile Hydroxyl Radicals Co-operating on Gas-Solid Catalytic Reaction Interfaces for Deeply Oxidizing NOx.

Learning from the important role of porphyrin-based chromophores in natural photosynthesis, a bionic photocatalytic system based on tetrakis (4-carboxyphenyl) porphyrin-coupled TiO2 was designed for photo-induced treating low-concentration NOx indoor gas (550 parts per billion), achieving a high NO removal rate of 91% and a long stability under visible-light (λ ≥ 420 nm) irradiation. Besides the great contribution of the conventional •O2- reactive species, a synergic effect between a singlet oxygen (1O2) and mobile hydroxyl radicals (•OHf) was first illustrated for removing NOx indoor gas (1O2 + 2NO → 2NO2, NO2 + •OHf → HNO3), inhibiting the production of the byproducts of NO2. This work is helpful for understanding the surface mechanism of photocatalytic NOx oxidation and provides a new perspective for the development of highly efficient air purification systems.

Dual-emitting metal-organic frameworks for ratiometric fluorescence detection of fluoride and Al3+ in sequence.

Fluoride (F-) and Al3+ are two common ions existing in drinking water and natural water bodies. Excessive intake of F- can lead to serious health issues such as fluorosis and bone diseases while accumulated consumption of Al3+ may cause neurotoxicity-based diseases. Developing a fast, reliable, and sensitive sensor for visually detecting both F- and Al3+ is of great significance. In the present work, a ratiometric fluorescence sensor was constructed by incorporating rhodamine B (RhB) in situ into a zirconium-based metal-organic framework, UiO-66-NH2. The obtained nanocomposite UiO-66-NH2@RhB exhibited similar octahedral structure to UiO-66-NH2 with high BET surface area, and showed two emission peaks at 450 nm and 585 nm. The blue fluorescence from UiO-66-NH2 was enhanced by the addition of F- while subsequent Al3+ addition diminished the increased fluorescence intensity, and the red emission from RhB as the reference remained unchangeable to improve the detection precision. Under optimal conditions, detection of limits as low as 1.55 µM for F- and 0.54 µM for Al3+ in aqueous solution were achieved with good selectivity. High recoveries in drinking water samples were also acquired, showing potential applications of this ratiometric fluorescence sensor for practical evaluation of F- and Al3+.

Self-Suspended Photothermal Microreactor for Water Desalination and Integrated Volatile Organic Compound Removal.

Steam generation and photocatalytic degradation of organic pollutants based on solar light are regarded as two important strategies for addressing the water scarcity issues. The water evaporation efficiency was greatly inhibited by the high cost, low stability, and low efficiencies of solar light absorption and photothermal conversion of photothermal materials. Moreover, volatile organic compounds (VOCs) are easily volatilized and enriched in as-distilled water during the photothermal process. Inspired by the structure of biomass materials in nature, a bifunctional solar light-driven steam generation and VOC removal microreactor was explored by coating commercial TiO2 (P25) powders on a carbonized biomass waste Flammulina. With the 3D aligned porous carbon architectures, this microreactor exhibited both a high water evaporation rate (37.0 kg m-2 h-1) and a high energy conversion efficiency (91.2%) under simulated sunlight irradiation (light intensity = 25.5 kW m-2). A high VOC removal rate (80.9% in 40 min) was also achieved during the steam generation process via choosing phenol as the probe pollutant molecules. The nature-inspired designing concept and bifunctional microreactor in this study may open up a new strategy for producing clean distilled water from seawater with an efficient removal of VOCs.

MOFs Conferred with Transient Metal Centers for Enhanced Photocatalytic Activity.

Highly effective photocatalysts for the hydrogen-evolution reaction were developed by conferring the linkers of NH2 -MIL-125(Ti), a metal-organic framework (MOF) constructed from TiOx clusters and 2-aminoterephthalic acid (linkers), with active copper centers. This design enables effective transfer of electrons from the linkers to the transient Cu2+ /Cu+ centers, leading to 7000-fold and 27-fold increase of carrier density and lifetime of photogenerated charges, respectively, as well as high-rate production of H2 under visible-light irradiation. This work provides a novel design of a photocatalyst for hydrogen evolution using non-noble Cu2+ /Cu+ as co-catalysts.

Gas-Phase Photoelectrocatalytic Oxidation of NO via TiO2 Nanorod Array/FTO Photoanodes.

Most photoelectrocatalytic (PEC) reactions are performed in the liquid phase for convenient electron transfer in an electrolyte solution. Herein, a novel PEC reactor involving a tandem combination of TiO2 nanorod array/fluorine-doped tin oxide (TiO2-NR/FTO) working electrodes and an electrochemical auxiliary cell was constructed to drive the highly efficient PEC oxidation of indoor gas (NOx). With the aid of a low bias voltage (0.3 V), the as-formed PEC reactor exhibited an 80% removal rate for oxidizing NO (500 ppb) under light irradiation, which is much higher than that of the traditional photocatalytic (PC) process. Upon being irradiated by light, the photogenerated electrons are quickly separated from the holes and transferred to the counter electrode (Pt) owing to the applied bias voltage, leaving photogenerated holes in the TiO2-NR/FTO electrode for oxidizing NO molecules. Moreover, both dry and humid NO could be effectively removed by the tandem TiO2-NR/FTO-based gas-phase PEC reactor, indicating that the NO molecules could also be directly oxidized by photogenerated holes in addition to hydroxyl radicals. The presence of trace amounts of water could promote the PEC oxidation of NO owing to the formation of hydroxyl radicals induced by reactions between the water and holes, which could further oxidize NO. This PEC reactor offers an energy-saving, environmentally friendly, and efficient route to treat air polluted with low concentrations of gases (NOx and SOx).

Strong Hollow Spherical La2NiO4 Photocatalytic Microreactor for Round-the-Clock Environmental Remediation.

This work reports a moderate round-the-clock route to treating organic pollutants by utilizing a La2NiO4 hollow-sphere microreactor. A glycerol-assisted solvothermal route followed by an annealing process was applied for fabricating the catalyst. Both the physicochemical properties and the catalytic performance of the as-obtained microreactor for treating pollutants were discussed. The microreactor exhibited a strong ability to degrade phenol and anionic dyes in the absence of light irradiation, owing to its high surface area and positively charged surface. With the aid of visible-light irradiation, the degradation rate of the organic pollutants could be further accelerated due to the light multireflection in a hollow structure, which enhances the utilization of light. The present work indicates that the hollow-sphere La2NiO4 microreactor is effectively energy saving for environmental remediation.

Gas-Phase Photoelectrocatalysis for Breaking Down Nitric Oxide.

Photoelectrocatalysis (PEC) produces high-efficiency electron-hole separation by applying a bias voltage between semiconductor-based electrodes to achieve high photocatalytic reaction rates. However, using PEC to treat polluted gas in a gas-phase reaction is difficult because of the lack of a conductive medium. Herein, we report an efficient PEC system to oxidize NO gas by using parallel photoactive composites (TiO2 nanoribbons-carbon nanotubes) coated on stainless-steel mesh as photoanodes in a gas-phase chamber and Pt foil as the working electrode in a liquid-phase auxiliary cell. Carbon nanotubes (CNTs) were utilized as conductive scaffolds to enhance the interaction between TiO2 and stainless-steel skeletons for accelerated photogenerated electron transfer. Such a PEC system exhibited super-high performance for the treatment of indoor NO gas (550 ppb) with high selectivity for nitrate under UV-light irradiation owing to the conductive, intertwined network structure of the photoanode, fast photocarrier separation, and longer photogenerated hole lifetime. The photogenerated holes were proven to be the most important active sites for directly driving PEC oxidation of indoor NO gas, even in the absence of water vapor. This work created an efficient PEC air-purification filter for treating indoor polluted air under ambient conditions.

A chloroplast structured photocatalyst enabled by microwave synthesis.

Photosynthesis occurs through the synergistic effects of the non-ncontinuously distributed components in the chloroplast. Inspired by nature, we mimic chloroplast and develop a generic approach to synthesize non-continuously distributed semiconductors threaded by carbon nanotubes. In the synthesis, carbon nanotubes serve as microwave antennas to produce local super-hot dots on the surface, which might induce and accelerate various organic/inorganic semiconductors assembly. With the unique nanoscale designed bionic architecture, a chloroplast structured photocatalyst with 3-dimentional dual electron transfer pathways facilitate enhanced photocatalytic performance. The as-synthesized carbon nanotubes-titanium oxide achieves a record-breaking efficiency of 86% for nitric oxide treatment under ultraviolet light irradiation. As a general strategy, a wide variety of carbon nanotubes threaded chloroplast structured nanomaterials can be synthesized and these nanomaterials could find applications in energy chemistry, environmental science and human health.

Copper Phosphide-Enhanced Lower Charge Trapping Occurrence in Graphitic-C3N4 for Efficient Noble-Metal-Free Photocatalytic H2 Evolution.

Graphitic carbon nitride (g-C3N4) fundamental photophysical processes exhibit a high frequency of charge trapping due to physicochemical defects. In this study, a copper phosphide (Cu3P) and g-C3N4 hybrid was synthesized via a facile phosphorization method. Cu3P, as an electron acceptor, efficiently captures the photogenerated electrons and drastically improved the charge separation rate to cause a significantly enhanced photocatalytic performance. Moreover, the robust and intimate chemical interactions between Cu3P and g-C3N4 offers a rectified charge-transfer channel that can lead to a higher H2 evolution rate (HRE, 277.2 µmol h-1 g-1) for this hybrid that is up to 370 times greater than that achieved from using bare g-C3N4 (HRE, 0.75 µmol h-1 g-1) with a quantum efficiency of 3.74% under visible light irradiation (λ = 420 nm). To better determine the photophysical characteristics of the Cu3P-induced charge antitrapping behavior, ultrafast time-resolved spectroscopy measurements were used to investigate the charge carriers' dynamics from femtosecond to nanosecond time domains. The experimental results clearly revealed that Cu3P can effectively enhance charge transfer and suppress photoelectron-hole recombination.

Efficient Photocatalytic Fuel Cell via Simultaneous Visible-Photoelectrocatalytic Degradation and Electricity Generation on a Porous Coral-like WO3/W Photoelectrode.

Photocatalytic fuel cells (PFCs) have proven to be effective for generating electricity and degrading pollutants with a goal to resolve environmental and energy problems. However, the degradation of persistent organic pollutants (POPs), such as perfluorooctanoic acid (PFOA), remains challenging. In the present work, a porous coral-like WO3/W (PCW) photoelectrode with a well-designed energy band structure was used for the photoelectrocatalytic degradation of POPs and the simultaneous generation of electricity. The as-constructed bionic porous coral-like nanostructure greatly improved the light-harvesting capacity of the PCW photoelectrode. A maximum photocurrent density (0.31 mA/cm2) under visible light (λ > 420 nm) irradiation and a high incident photon conversion efficiency (IPCE) value (5.72% at 420 nm) were achieved. Because of the unique porous coral-like structure, the suitable energy band position, and the strong oxidation ability, this PCW photoelectrode-based PFC system exhibited a strong ability for simultaneous photoelectrocatalytic degradation of PFOA and electricity generation under visible-light irradiation, with a power output of 0.0013 mV/cm2 using PFOA as the fuel. This work provides a promising way to construct a reliable PFC using highly toxic POPs to generate electricity.

A flexible CdS nanorods-carbon nanotubes/stainless steel mesh photoanode for boosted photoelectrocatalytic hydrogen evolution.

An innovative flexible reticular photoanode (CdS-nanorods/CNTs coated on stainless iron mesh) was designed for efficiently driving photoelectrocatalytic (PEC) hydrogen (H2) evolution under visible-light irradiation. Such CdS-NRs/CNTs-based flexible photoanodes exhibited a record-breaking H2 evolution rate (728 mmol h-1 g-1) among the reported CdS-based photoanodes under visible-light irradiation owing to the photoelectron transport channels (CNTs) and high separation efficiency of electrons and holes.

Photoelectrocatalytic reduction of CO2 to methanol over a photosystem II-enhanced Cu foam/Si-nanowire system.

A solar-light double illumination photoelectrocatalytic cell (SLDIPEC) was fabricated for autonomous CO2 reduction and O2 evolution with the aid of photosystem II (PS-II, an efficient light-driven water-oxidized enzyme from nature) and utilized in a photoanode solution. The proposed SLPEC system was composed of Cu foam as the photoanode and p-Si nanowires (Si-NW) as the photocathode. Under solar irradiation, it exhibited a super-photoelectrocatalytic performance for CO2 conversion to methanol, with a high evolution rate (41.94mmol/hr), owing to fast electron transfer from PS-II to Cu foam. Electrons were subsequently trapped by Si-NW through an external circuit via bias voltage (0.5V), and a suitable conduction band potential of Si (-0.6eV) allowed CO2 to be easily reduced to CH3OH at the photocathode. The constructed Z-scheme between Cu foam and Si-NW can allow the SLDIPEC system to reduce CO2 (8.03mmol/hr) in the absence of bias voltage. This approach makes full use of the energy band mismatch of the photoanode and photocathode to design a highly efficient device for solving environmental issues and producing clean energy.

Porous CuO nanotubes/graphene with sandwich architecture as high-performance anodes for lithium-ion batteries.

Constructing a porous conductive framework represents a promising strategy for designing high-performance anodes for Li-ion batteries. Here, porous CuO nanotubes/graphene with hierarchical architectures were fabricated by simple annealing of copper nanowires/graphene hybrids synthesized by a microwave-assisted process. In these nanoarchitectures, the embedded porous CuO nanotubes can prevent restacking of the graphene sheets, whereas graphene can increase the electrical conductivity of CuO. Moreover, these two components constitute a sandwich-like interlaced framework that favors ion diffusion, as well as promoting better electron transport. As a result, the as-prepared nanohybrid exhibits a high specific capacity of 725 mA h g-1 and a capacity retention of ∼81% after 250 cycles, as well as outstanding rate performance in comparison to those of bare CuO or a CuO-CNT (carbon nanotubes) hybrid.