Order-Disorder Engineering of Carbon Nitride for Photocatalytic H2O2 Generation Coupled with Pollutant Removal.

Highly crystalline carbon nitride (CCN), benefiting from the reduced structural imperfections, enables improved electron-hole separation. Yet, the crystalline phase with insufficient inherent defects suffers from a poor performance toward the reaction intermediate adsorption with respect to the amorphous phase. Herein, a crystalline-amorphous carbon nitride (CACN) with an isotype structure was constructed via a two-step adjacent calcination strategy. Through specific oxygen etching and crystallization, the formation of a built-in electric field at the interface could drive charge transfer and separation, thus promoting photoredox reaction. As expected, the optimized CACN exhibited a H2O2 generation efficiency as high as 2.15 mM gcat-1 h-1, paired with a promoted pollutant degradation efficiency, which outperform its crystalline (CCN) and amorphous [amorphous carbon nitride (ACN)] counterparts. The detailed electron/hole transportation via a built-in electronic field and free radical formation based on the enhanced adsorption of oxygen were considered, and the synchronous reaction pathway was carried out. This work paves a novel pathway for the synthesis of carbon nitride with an isotype structure from the perspective of interfacial engineering.

Development of a multi-needle fiberoptic Raman spectroscopy technique for simultaneous multi-site deep tissue Raman measurements in the brain.

We report on the development of a multi-needle fiberoptic Raman spectroscopy (MNF-RS) technique for simultaneous multi-site deep Raman measurements in brain tissue. The multi-needle fiberoptic Raman probe is designed and fabricated using a number of 100 µm core diameter, aluminum-coated fibers under a coaxial laser excitation and Raman collection scheme, enabling simultaneous collection of deep tissue Raman spectra from a number of tissue sites. We have also developed a Raman retrieval algorithm based on the transformation matrix of each individual needle fiber probe projected to different pixels of a charge-coupled device (CCD) for recovering the tissue Raman spectra collected by each needle fiber probe, allowing simultaneous multi-channel detection by a single Raman spectrometer. High-quality tissue Raman spectra of different tissue types (e.g., muscle, fat, gray matter, and white matter in porcine brain) can be acquired in both the fingerprint (900-1800 cm-1) and high-wavenumber (2800-3300 cm-1) regions within sub-second times using the MNF-RS technique. We also demonstrate that by advancing the multi-needle fiberoptic Raman probe into deep porcine brain, tissue Raman spectra can be acquired simultaneously from different brain regions (e.g., cortex, thalamus, midbrain, and cerebellum). The significant biochemical differences across different brain tissues can also be distinguished, suggesting the promising potential of the MNF-RS technique for label-free neuroscience study at the molecular level.

Recent advances on solar-driven valorization of polyethylene terephthalate plastics into value-added chemicals.

The random disposal and immature recycling of post-consumer polyethylene terephthalate (PET) packages lead to a severe threaten to the ecological system owing to slow natural degradation kinetics of PET plastic, and meanwhile cause a waste of carbon resources stored in PET plastics. Many methods have been developed to recycle PET plastics, such as mechanical recycling, which induces a reduced quality relative to the virgin PET. In recent years, the photocatalytic conversion of PET plastic wastes into chemicals has received considerable attention due to their unique advantages, including mild conditions, less energy consumption, and simple operation. In this review, we have summarized the latest achievements in photoreforming of PET plastics into value-added chemicals. Primarily, we described the mechanism for bond cleavage during PET photoreforming, the emerging pretreatment methodologies for PET plastics, and the advantages of photocatalytic PET plastics conversion. Then, we introduced electro-/bio-assisted photocatalysis technologies for PET disposal and commented their strengths and limitations. Finally, we put forward the challenges and potential advances in the domain of photocatalytic PET plastics conversion.

Symmetry or asymmetry: which one is the platform of nitrogen vacancies for alkaline hydrogen evolution.

Conventional nitrogen vacancies with a symmetric coordination of metal cations (i.e., M1-Nv-M1) play a crucial role in tuning the local environment of the metal sites in metal nitrides and improving their electrochemical activity in the hydrogen evolution reaction (HER). However, the symmetric Nv sites, which feature a uniform charge distribution on adjacent metal sites, suffer from sluggish water dissociation kinetics and a poor capability for hydrogen desorption. Here, we fabricated Cr-doped and Nv-rich Co4N nanorods grown on a Ni foam (Cr-Co4N-Nv/NF) with asymmetric Cr-Nv-Co sites to effectively catalyze hydrogen evolution under alkaline conditions, with a low overpotential of 33 mV at a current density of 10 mA cm-2 and a small Tafel slope of 37 mV dec-1. The experimental characterizations and theoretical simulations collectively reveal that the construction of asymmetric Cr-Nv-Co sites gives rise to the upshift of the d-band center, thus promoting water adsorption and activation. Moreover, asymmetric Nv sites allow a balance between hydrogen adsorption and desorption, which avoids the limited desorption process over the symmetric Co-Nv-Co sites.

Electrochemical Production of Glycolate Fuelled By Polyethylene Terephthalate Plastics with Improved Techno-Economics.

Electrochemical valorization of polyethylene terephthalate (PET) waste streams into commodity chemicals offers a potentially sustainable route for creating a circular plastic economy. However, PET wastes upcycling into valuable C2 product remains a huge challenge by the lack of an electrocatalyst that can steer the oxidation economically and selectively. Here, it is reported a catalyst comprising Pt nanoparticles hybridized with γ-NiOOH nanosheets supported on Ni foam (Pt/γ-NiOOH/NF) that favors electrochemical transformation of real-word PET hydrolysate into glycolate with high Faradaic efficiency (> 90%) and selectivity (> 90%) across wide reactant (ethylene glycol, EG) concentration ranges under a marginal applied voltage of 0.55 V, which can be paired with cathodic hydrogen production. Computational studies combined with experimental characterizations elucidate that the Pt/γ-NiOOH interface with substantial charge accumulation gives rise to an optimized adsorption energy of EG and a decreased energy barrier of potential determining step. A techno-economic analysis demonstrates that, with the nearly same amount of resource investment, the electroreforming strategy towards glycolate production can raise revenue by up to 2.2 times relative to conventional chemical process. This work may thus serve as a framework for PET wastes valorization process with net-zero carbon footprint and high economic viability.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion.

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO2 reduction, N2 reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.

Spin state engineering of spinel oxides by integration of Cr doping and a p-n junction for water oxidation.

Spinel Co3O4 has emerged as a promising electrocatalyst towards alkaline water oxidation, but its activity is restricted by the undesirable electronic configuration of the octahedral Co3+ site. Herein, we simultaneously manipulate Cr doping and p-n junction engineering on Co3O4 nanorods, which contributes to the formation of Co2+ and Ni3+ octahedral sites with optimal eg fillings, thus achieving a superior OER performance.

Emerging Cocatalysts on g-C3 N4 for Photocatalytic Hydrogen Evolution.

Over the past few decades, graphitic carbon nitride (g-C3 N4 ) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g-C3 N4 severely inhibits the further large-scale application of g-C3 N4 . In this case, the utilization of cocatalysts is a novel frontline in the g-C3 N4 -based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high-performance cocatalysts based on g-C3 N4 toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.

Metal Substitution Steering Electron Correlations in Pyrochlore Ruthenates for Efficient Acidic Water Oxidation.

Exploring the advanced oxygen evolution reaction (OER) electrocatalysts is highly desirable toward sustainable energy conversion and storage, yet improved efficiency in acidic media is largely hindered by its sluggish reaction kinetics. Herein, we rationally manipulate the electronic states of the strongly electron correlated pyrochlore ruthenate Y2Ru2O7 alternative through partial A-site substitution of Sr2+ for Y3+, efficiently improving its intrinsic OER activity. The optimized Y1.7Sr0.3Ru2O7 candidate observes a highly intrinsic mass activity of 1018 A gRu-1 at an overpotential of 300 mV with excellent durability in 0.5 M H2SO4 electrolyte. Combining synchrotron-radiation X-ray spectroscopic investigations with theoretical simulations, we reveal that the electron correlations in the Ru 4d band are weakened through coordinatively geometric regulation and charge redistribution by the exotic Sr2+ cation, enabling the delocalization of Ru 4d electrons via an insulator-to-metal transition. The induced Ru-O covalency promotion and band alignment rearrangement decreases the charge transfer energy to accelerate interfacial charge transfer kinetics. Meanwhile, the chemical affinity of oxygen intermediates is also rationalized to weaken the metal-oxygen binding strength, thus lowering the energy barrier of the overall reaction. This work offers fresh insights into designing advanced solid-state electrocatalysts and underlines the versatility of electronic structure manipulation in tuning catalytic activity.

A Ternary Dumbbell Structure with Spatially Separated Catalytic Sites for Photocatalytic Overall Water Splitting.

Solar-driven overall water splitting based on metal sulfide semiconductor photocatalysts remains as a challenge owing to the strong charge recombination and deficient catalytic active sites. Additionally, significant inhibition of back reactions, especially the oxidation of sulfide ions during the photocatalytic water oxidation catalysis, is an arduous task that requires an efficient photogenerated hole transfer dynamics. Here, a ternary dumbbell-shaped catalyst based on RuO2/CdS/MoS2 with spatially separated catalytic sites is developed to achieve simultaneous production of hydrogen and oxygen under simulated solar-light without any sacrificial agents. Particularly, MoS2 nanosheets anchored on the two ends of CdS nanowires are identified as a reduction cocatalyst to accelerate hydrogen evolution, while RuO2 nanoparticles as an oxidation cocatalyst are deposited onto the sidewalls of CdS nanowires to facilitate oxygen evolution kinetics. The density functional theory simulations and ultrafast spectroscopic results reveal that photogenerated electrons and holes directionally migrate to MoS2 and RuO2 catalytic sites, respectively, thus achieving efficient charge carrier separation. The design of ternary dumbbell structure guarantees metal sulfides against photocorrosion and thus extends their range in solar water splitting.

Lattice oxygen activation enabled by high-valence metal sites for enhanced water oxidation.

Anodic oxygen evolution reaction (OER) is recognized as kinetic bottleneck in water electrolysis. Transition metal sites with high valence states can accelerate the reaction kinetics to offer highly intrinsic activity, but suffer from thermodynamic formation barrier. Here, we show subtle engineering of highly oxidized Ni4+ species in surface reconstructed (oxy)hydroxides on multicomponent FeCoCrNi alloy film through interatomically electronic interplay. Our spectroscopic investigations with theoretical studies uncover that Fe component enables the formation of Ni4+ species, which is energetically favored by the multistep evolution of Ni2+→Ni3+→Ni4+. The dynamically constructed Ni4+ species drives holes into oxygen ligands to facilitate intramolecular oxygen coupling, triggering lattice oxygen activation to form Fe-Ni dual-sites as ultimate catalytic center with highly intrinsic activity. As a result, the surface reconstructed FeCoCrNi OER catalyst delivers outstanding mass activity and turnover frequency of 3601 A gmetal-1 and 0.483 s-1 at an overpotential of 300 mV in alkaline electrolyte, respectively.

Computational Design of Transition Metal Single-Atom Electrocatalysts on PtS2 for Efficient Nitrogen Reduction.

Electrocatalytic nitrogen reduction is promising to serve as a sustainable and environmentally friendly strategy to achieve ammonia production. Single-atom catalysts (SACs) hold great promise to convert N2 into NH3 because of the unique molecular catalysis property and ultrahigh atomic utilization ratio. Here, we demonstrate a universal computational design principle to assess the N2 reduction reaction (NRR) performance of SACs anchored on a monolayer PtS2 substrate (SACs-PtS2). Our density functional theory simulations unveil that the barriers of the NRR limiting potential step on different SAC centers are observed to be linearly correlated to the integral of unoccupied d states (UDSs) of SACs. As a result, the Ru SAC-PtS2 catalyst with the largest number of UDSs exhibits a much lower barrier of the limiting step than those of other SACs-PtS2 catalysts and the Ru(0001) benchmark. Our work bridges the apparent NRR activity and intrinsic electronic structure of SAC centers and offers effective guidance to screen and design efficient SACs for the electrochemical NRR process.

Quasi one-dimensional van der Waals gold selenide with strong interchain interaction and giant magnetoresistance.

The atomic structure of quasi one-dimensional (1D) van der Waals materials can be regarded as the stacking of atomic chains to form thin flakes or nanoribbons, which substantially differentiates them from typical two-dimensional (2D) layered materials and 1D nanotube/nanowire array. Here we present our studies on quasi 1D gold selenide (AuSe) that possesses highly anisotropic crystal structure, excellent electrical conductivity, giant magnetoresistance, and unusual reentrant metallic behavior. The low in-plane symmetry of AuSe gives rise to its high anisotropy of vibrational behavior. In contrast, quasi 1D AuSe exhibits high in-plane electrical conductivity along the directions of both atomic chains and perpendicular one, which can be understood as a result of strong interchain interaction. We found that AuSe exhibits a near quadratic nonsaturating giant magnetoresistance of 1841% with the magnetic field perpendicular to its in-plane. We also observe unusual reentrant metallic behavior, which is caused by the carrier mismatch in the multiband transport. Our works help to establish fundamental understandings on quasi 1D van der Waals semimetallic AuSe and identify it as a new candidate for exploring giant magnetoresistance and compensated semimetals.

Robust Photoelectrochemical Oxygen Evolution with N, Fe-CoS2 Nanorod Arrays.

Photoelectrochemical water splitting is a promising approach to enhance the efficiency of water splitting. However, it is still challenging to develop an efficient oxygen evolution reaction (OER) electrocatalyst that can be coupled with light due to inefficient light utilization. Here, we demonstrate that N, Fe-co-doped CoS2 (N, Fe-CoS2) nanorod arrays can act as a highly efficient photo-coupled electrochemical OER catalyst. In dark conditions, the N, Fe-doped CoS2 on self-supported stainless steel (SS) mesh shows a small OER overpotential (215 mV) at a current density of 10 mA cm-2, a reduced Tafel slope (43.2 mV dec-1), and negligible activity decay after 10 000 cycles. Upon visible-NIR light illumination, the N, Fe-doped anode exhibits superior photoelectrochemical performance because of the enhanced photoresponse, excellent light harvesting ability and promoted interfacial kinetics of charge separation. Our well-designed photoelectrochemical OER electrode can not only serve as a light absorption semiconductor but also the active catalytic sites for the OER reaction; the electrode composed of the single phase can efficiently avoid photocarrier recombination at the grain boundary. This study provides an insight into photoanode synthesis for photoelectrochemical OER and offers guidance on the future electrocatalyst design.

Phosphorus Incorporation into Co9 S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis.

The improvement of activity of electrocatalysts lies in the increment of the density of active sites or the enhancement of intrinsic activity of each active site. A common strategy to realize dual active sites is the use of bimetal compound catalysts, where each metal atom contributes one active site. In this work, a new concept is presented to realize dual active sites with tunable electron densities in monometal compound catalysts. Dual Co2+ tetrahedral (Co2+ (Td )) and Co3+ octahedral (Co3+ (Oh )) coordination active sites are developed and adjustable electron densities on the Co2+ (Td ) and Co3+ (Oh ) are further achieved by phosphorus incorporation (P-Co9 S8 ). The experimental results and density functional theory calculations show that the nonmetal P doping can systematically modulate charge density of Co2+ (Td ) and Co3+ (Oh ) in P-Co9 S8 and simultaneously improve the electrical conductivity of Co9 S8 , which substantially enhances oxygen evolution reaction performance of P-Co9 S8 .

Recent advances in three-dimensional graphene based materials for catalysis applications.

Over the past few decades, two-dimensional graphene based materials (2DGMs) have piqued the interest of scientists worldwide, and the exploration of their potential applications in catalysis, sensors, electronic devices and energy storage due to their extraordinary physical and chemical properties has rapidly progressed. As for these 2DGMs, there is a complementary need to assemble 2D building blocks hierarchically into more complicated and hierarchical three-dimensional graphene-based materials (3DGMs). Such a capability is vitally crucial in order to design sophisticated and multi-functional catalysts with tailorable properties. This comprehensive review describes some important recent advances with respect to 3DGMs, including their preparation methods, characterization and applications in catalysis, e.g., photocatalysis, electrocatalysis, organic catalysis, and CO oxidation. The importance of the relationship between the structure and catalytic performance, a topic which has become a central focus of research in order to develop high-performance catalytic systems, is discussed. Likely future developments and their associated challenges are proposed and discussed.

One-step large-scale highly active g-C3N4 nanosheets for efficient sunlight-driven photocatalytic hydrogen production.

The development of highly active, cost-effective, environmentally friendly and stable g-C3N4 based photocatalysts for H2 evolution is one of the most anticipated potential pathways for future hydrogen utilization. Herein, a facile gaseous bubble template approach was designed to prepare large-scale thin g-C3N4 nanosheets (g-C3N4 NSs) using melamine and ammonium sulphate as the bubble template. Through distinctive structural improvements for a large bandgap, excellent electron mobility, prolonged lifetime of the photogenerated charge carriers and a high specific surface area with highly accessible potential reaction sites, the as-synthesized g-C3N4 NSs demonstrated a high photocatalytic hydrogen evolution rate of 9871 µmol h-1 g-1 and efficient photocatalytic degradation of Rhodamine B (RhB) and phenol under simulated solar light irradiation.

Efficient Solar Light Harvesting CdS/Co9 S8 Hollow Cubes for Z-Scheme Photocatalytic Water Splitting.

Hollow structures with an efficient light harvesting and tunable interior component offer great advantages for constructing a Z-scheme system. Controlled design of hollow cobalt sulfide (Co9 S8 ) cubes embedded with cadmium sulfide quantum dots (QDs) is described, using hollow Co(OH)2 as the template and a one-pot hydrothermal strategy. The hollow CdS/Co9 S8 cubes utilize multiple reflections of light in the cubic structure to achieve enhanced photocatalytic activity. Importantly, the photoexcited charge carriers can be effectively separated by the construction of a redox-mediator-free Z-scheme system. The hydrogen evolution rate over hollow CdS/Co9 S8 is 134 and 9.1 times higher than that of pure hollow Co9 S8 and CdS QDs under simulated solar light irradiation, respectively. Moreover, this is the first report describing construction of a hollow Co9 S8 based Z-scheme system for photocatalytic water splitting, which gives full play to the advantages of light-harvesting and charges separation.

A robust and efficient catalyst of CdxZn1-xSe motivated by CoP for photocatalytic hydrogen evolution under sunlight irradiation.

CdxZn1-xSe/CoP composites have been well studied as effervescent photocatalysts for H2 evolution. These composites are highly efficient at 45.1 mmol h-1 g-1 and have a high quantum yield of 11.8% at ∼520 nm. The tunable energy band of CdxZn1-xSe facilitates photo-electrons transferring to CoP via chemical bonds between components. Advances in CdxZn1-xSe/CoP for photocatalytic H2 evolution provide a new strategy for future splitting of seawater.

Nitrogen-Doped Mesoporous Carbon-Encapsulated MoO2 Nanobelts as a High-Capacity and Stable Host for Lithium-Ion Storage.

N-doped mesoporous carbon-capped MoO2 nanobelts (designated as MoO2 @NC) were synthesized and applied to lithium-ion storage. Owing to the stable core-shell structural framework and conductive mesoporous carbon matrix, the as-prepared MoO2 @NC shows a high specific capacity of around 700 mA h g-1 at a current of 0.5 A g-1 , excellent cycling stability up to 100 cycles, and superior rate performance. The N-doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core-shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO2 @NC to be a suitable and promising material for lithium ion battery.