Tandem Integration of Biological and Electrochemical Catalysis for Efficient Polyester Upcycling under Ambient Conditions.

Excessive production of waste polyethylene terephthalate (PET) poses an ecological challenge, which necessitates developing technologies to extract the values from end-of-life PET. Upcycling has proven effective in addressing the low profitability of current recycling strategies, yet existing upcycling technologies operate under energy-intensive conditions. Here we report a cascade strategy to steer the transformation of PET waste into glycolate in an overall yield of 92.6% under ambient conditions. The cascade approach involves setting up a robust hydrolase with 95.6% PET depolymerization into ethylene glycol (EG) monomer within 12 h, followed by an electrochemical process initiated by a CO-tolerant Pd/Ni(OH)2 catalyst to convert the EG intermediate into glycolate with high Faradaic efficiency of 97.5%. Techno-economic analysis and life cycle assessment indicate that, compared with the widely adopted electrochemical technology that heavily relies on alkaline pretreatment for PET depolymerization, our designed enzymatic-electrochemical approach offers a cost-effective and low-carbon pathway to upgrade PET.

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides.

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02 mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

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.

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.

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.

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.

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 Brown Mesoporous TiO2-x /MCF Composite with an Extremely High Quantum Yield of Solar Energy Photocatalysis for H2 Evolution.

A brown mesoporous TiO2-x /MCF composite with a high fluorine dopant concentration (8.01 at%) is synthesized by a vacuum activation method. It exhibits an excellent solar absorption and a record-breaking quantum yield (Φ = 46%) and a high photon-hydrogen energy conversion efficiency (η = 34%,) for solar photocatalytic H2 production, which are all higher than that of the black hydrogen-doped TiO2 (Φ = 35%, η = 24%). The MCFs serve to improve the adsorption of F atoms onto the TiO2 /MCF composite surface, which after the formation of oxygen vacancies by vacuum activation, facilitate the abundant substitution of these vacancies with F atoms. The decrease of recombination sites induced by high-concentration F doping and the synergistic effect between lattice Ti(3+)-F and surface Ti(3+)-F are responsible for the enhanced lifetime of electrons, the observed excellent absorption of solar light, and the photocatalytic production of H2 for these catalysts. The as-prepared F-doped composite is an ideal solar light-driven photocatalyst with great potential for applications ranging from the remediation of environmental pollution to the harnessing of solar energy for H2 production.

Chiral Carbonaceous Nanotubes Modified with Titania Nanocrystals: Plasmon-Free and Recyclable SERS Sensitivity.

Chiral carbonaceous nanotubes (CNT) were successfully used in plasmon-free surface-enhanced Raman scattering (SERS) for the first time. Further modification of TiO2 nanocrystals on the chiral CNTs successfully realized the recycling of SERS substrate as chiral CNT/TiO2 hybrids. The high SERS sensitivity of methylene blue (MB) over the chiral CNT/TiO2 hybrids is ascribed to the laser-driven birefringence induced by the helical structure, which provides much more opportunities for the occurrence of Raman scattering. The TiO2 nanocrystals highly dispersed on the surface and inside the hollow cavity of chiral CNTs can completely degrade the MB under the solar light irradiation, leading to the self-cleaning of SERS substrate. The present research opens a new way for the application of chiral inorganic materials in plasmon-free SERS detection.

Mesoporous TiO2 nanocrystals grown in situ on graphene aerogels for high photocatalysis and lithium-ion batteries.

TiO2/graphene composites have been well studied as a solar light photocatalysts and electrode materials for lithium-ion batteries (LIBs). Recent reports have shown that ultralight 3D-graphene aerogels (GAs) can better adsorb organic pollutants and can provide multidimensional electron transport pathways, implying a significant potential application for photocatalysis and LIBs. Here, we report a simple one-step hydrothermal method toward in situ growth of ultradispersed mesoporous TiO2 nanocrystals with (001) facets on GAs. This method uses glucose as the dispersant and linker owing to its hierarchically porous structure and a high surface area. The TiO2/GAs reported here exhibit a highly recyclable photocatalytic activity for methyl orange pollutant and a high specific capacity in LIBs. The strong interaction between TiO2 and GAs, the facet characteristics, the high electrical conductivity, and the three-dimensional hierarchically porous structure of these composites results in highly active photocatalysis, a high rate capability, and stable cycling.

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.

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.

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.

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.

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.

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.

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.

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.