Copper-surface-mediated synthesis of acetylenic carbon-rich nanofibers for active metal-free photocathodes

Two-Dimensional Silver-Isocyanide Frameworks

Metal-organic frameworks (MOFs) have been widely studied due to their versatile applications and easily tunable structures. However, heteroatom-metal coordination dominates the MOFs community, and the rational synthesis of carbon-metal coordination-based MOFs remains a significant challenge. Herein, two-dimensional (2D) MOFs based on silver-carbon linkages are synthesized through the coordination between silver(I) salt and isocyanide-based monomers at ambient condition. The as-synthesized 2D MOFs possess well-defined crystalline structures and a staggered AB stacking mode. Most interestingly, these 2D MOFs, without π-π stacking between layers, exhibit narrow band gaps down to 1.42 eV. As electrochemical catalysts for converting CO2 to CO, such 2D MOFs demonstrate Faradaic efficiency over 92 %. Surprisingly, the CO2 reduction catalyzed by these MOFs indicates favorable adsorption of CO2 and *COOH on the active carbon sites of the isocyanide groups rather than on silver sites. This is attributed to the critical σ donor role of isocyanides and the corresponding ligand-to-metal charge-transfer effect. This work not only paves the way toward a new family of MOFs based on metal-isocyanide coordination but also offers a rare platform for understanding the electrocatalysis processes on strongly polarized carbon species.

3D Z-scheme conjugated polymer/Cu2O for organic photoelectrochemical transistor bioassay

Organic photoelectrochemical transistor (OPECT) is an emerging technology studying photo-electric-biological recognition events. Here, this work reports the three-dimensional (3D) Z-scheme poly (1,4-diethynylbenzene) (pDEB)@Cu2O heterojunction as a high-efficacy photogating module and its application for OPECT bioassay. Specifically, 3D Z-scheme pDEB@Cu2O heterojunction enabled fast charge transport and ion diffusion in the system, achieving remarkable amplification capability with a current gain as high as ca. 9.6 × 103. By linking with GOx-labeled sandwich immunorecognition, the impact of GOx-generated H2O2 on the OPECT made possible the sensitive bioassay. Exemplified by carcinoembryonic antigen (CEA) as the model target, the OPECT device achieved a linear detection range spanning from 100 fg/mL to 100 ng/mL and coupled with a detection limit as low as 72 fg/mL. This work provided a generic and extensible platform for the designation of novel bioassay systems.

Copper-Surface-Mediated Synthesis of sp2 Carbon-Conjugated Covalent Organic Framework Photocathodes for Photoelectrochemical Hydrogen Evolution

Sp2-carbon (sp2-c) covalent organic frameworks (COFs), featuring distinctive π-conjugated network structures, facilitate the migration of photo-generated carriers, rendering them exceptionally appealing for applications in photoelectrochemical water splitting. However, owing to the powdery nature of COFs, leaving anchor the sp2-c COFs powder tightly onto a conductive substrate challenging. Here, we propose a method for preparing photoactive substance-conductive substrate integrated photocathodes through copper surface-mediated knoevenagel polycondensation (Cu-SMKP), this approach results in a uniform and stable sp2-c COF film, directly grown on commercial copper foam (COFTh-Cu). The COFTh-Cu demonstrates a high H2-evolution photocurrent density of 56 μA cm-2 at 0.3 V vs. RHE, sustaining stability for 12 h. The as-prepared COFTh-Cu represents a 4.5-fold increase in current density compared to traditional spin-coating methods and outperforms most COF photocathodes without cocatalysts. This innovative copper surface-mediated approach for preparing photocathodes opens up a crucial pathway towards the realization of highly active COF photocathodes.

Periodic Single-Metal Site Catalysts: Creating Homogeneous and Ordered Atomic-Precision Structures

Heterogeneous single-metal-site catalysts (SMSCs), often referred to as single-atom catalysts (SACs), demonstrate promising catalytic activity, selectivity, and stability across a wide spectrum of reactions due to their rationally designed microenvironments encompassing coordination geometry, binding ligands, and electronic configurations. However, the inherent disorderliness of SMSCs at both atomic scale and nanoscale poses challenges in deciphering working principles and establishing the correlations between microenvironments and the catalytic performances of SMSCs. The rearrangement of randomly dispersed single metals into homogeneous and atomic-precisely structured periodic single-metal site catalysts (PSMSCs) not only simplifies the chaos in SMSCs systems but also unveils new opportunities for manipulating catalytic performance and gaining profound insights into reaction mechanisms. Moreover, the synergistic effects of adjacent single metals and the integration effects of periodic single-metal arrangement further broaden the industrial application scope of SMSCs. This perspective offers a comprehensive overview of recent advancements and outlines prospective avenues for research in the design and characterizations of PSMSCs, while also acknowledging the formidable challenges encountered and the promising prospects that lie ahead.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Biopolymer-supramolecular polymer hybrids for photocatalytic hydrogen production

Solar generation of H2 is a promising strategy for dense energy storage. Supramolecular polymers composed of chromophore amphiphile monomers containing perylene monoimide (PMI) have been reported as crystalline light-harvesting assemblies for aqueous H2-evolving catalysts. Gelation of these supramolecular polymers with multivalent ions creates hydrogels with high diffusivity but insufficient mechanical stability and catalyst retention for reusability. We report here on using sodium alginate (SA) biopolymer to both induce supramolecular polymerization of PMI and co-immobilize them with catalysts in a robust hydrogel with high diffusivity that can also be 3D-printed. Faster mass transfer was achieved by controlling the material macrostructure by reducing gel diameter and microstructure by reducing biopolymer loading. Optimized gels produce H2 at rates rivaling solution-based PMI and generate H2 for up to 6 days. The PMI assemblies in the SA matrix create a percolation network capable of bulk-electron transfer under illumination. These PMI-SA materials were then 3D-printed on conductive substrates to create 3D hydrogel photoelectrodes with optimized porosity. The design of these versatile hybrid materials was bioinspired by the soft matter environment of natural photosynthetic systems and opens the opportunity to carry out light-to-fuel conversion within soft matter with arbitrary shapes and particular local environments.

New breakthrough in rapid degradation of lignin derivative compounds · A novel high stable and reusable green organic photocatalyst

The pulp and paper sectors are thriving yet pose significant environmental threats to water bodies, mainly due to the substantial release of pollutants. Lignin-derived compounds are among the most problematic of these contaminants. To address this issue, we present our initial results on utilizing organic semiconductor photocatalysis under visible light for treating lignin-derived compounds. Our investigation has been centered around creating a green and cost-effective organic semiconductor photocatalyst. This catalyst is designed using a structure of bagasse cellulose spheres to support PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c']dithiophene-4,8-dione))]: MeIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-cyclopentane-1,3-dione[c]-1-methyl-thiophe))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene)). This photocatalyst demonstrates remarkable efficiency, achieving over 91 % degradation of lignin-derived compounds. The superior photocatalytic performance is attributed to three main factors: (1) The ability of PM6 to broaden MeIC's absorption range from 300 to 800 nm, allowing for effective utilization of visible light; (2) the synergistic interaction between PM6 and MeIC, which ensures compatible energy levels and a vast, evenly spread surface area, promoting charge mobility and extensive donor/acceptor interfaces. This synergy significantly enhances the generation and transport of carriers, resulting in a high production of free radicals that accelerate the decomposition of organic materials; (3) The deployment of PM6:MeIC on biomass-based carriers increases the interaction surface with the organic substances. Notably, PM6: MeIC showcases outstanding durability, with its degradation efficiency remaining between 84 % and 91 % across 100 cycles. This study presents a promising approach for designing advanced photocatalysts aimed at degrading common pollutants in papermaking wastewater.

Donor-Acceptor Conjugated Acetylenic Polymers for High-Performance Bifunctional Photoelectrodes

Due to the drastic required thermodynamical requirements, a photoelectrode material that can function as both a photocathode and a photoanode remains elusive. In this work, we demonstrate for the first time that, under simulated solar light and without co-catalysts, donor-acceptor conjugated acetylenic polymers (CAPs) exhibit both impressive oxygen evolution (OER) and hydrogen evolution (HER) photocurrents in alkaline and neutral medium, respectively. In particular, poly(2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine) (pTET) provides a benchmark OER photocurrent density of ~200 μA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) at pH 13 and a remarkable HER photocurrent density of ~190 μA cm-2 at 0.3 V vs. RHE at pH 6.8. By combining theoretical investigations and electrochemical-operando Resonance Raman spectroscopy, we show that the OER proceeds with two different mechanisms, with the electron-depleted triple bonds acting as single-site OER in combination with the C4-C5 atoms of the phenyl rings as dual sites. The HER, instead, occurs via an electron transfer from the tri-acetylenic linkages to the triazine rings, which act as the HER active sites. This work represents a novel application of organic-based materials and contributes to the development of high-performance photoelectrochemical catalysts for the solar fuels' generation.

Lithiophilic Hydrogen-Substituted Graphdiyne Aerogels with Ionically Conductive Channels for High-Performance Lithium Metal Batteries

Lithium (Li) metal stands as a promising anode in advancing high-energy-density batteries. However, intrinsic issues associated with metallic Li, especially the dendritic growth, have hindered its practical application. Herein, we focus on molecular combined structural design to develop dendrite-free anodes. Specifically, using hydrogen-substituted graphdiyne (HGDY) aerogel hosts, we successfully fabricated a promising Li composite anode (Li@HGDY). The HGDY aerogel's lithiophilic nature and hierarchical pores drive molten Li infusion and reduce local current density within the three-dimensional HGDY host. The unique molecular structure of HGDY provides favorable bulk pathways for lithium-ion transport. By simultaneous regulation of electron and ion transport within the HGDY host, uniform lithium stripping/platting is fulfilled. Li@HGDY symmetric cells exhibit a low overpotential and stable cycling. The Li@HGDY||lithium iron phosphate full cell retained 98.1% capacity after 170 cycles at 0.4 C. This study sheds new light on designing high-capacity and long-lasting lithium metal anodes.

The Emergence of High-Performance Conjugated Polymer/Inorganic Semiconductor Hybrid Photoelectrodes for Solar-Driven Photoelectrochemical Water Splitting

Solar-driven photoelectrochemical (PEC) energy conversion holds great potential in converting solar energy into storable and transportable chemicals or fuels, providing a viable route toward a carbon-neutral society. Conjugated polymers are rapidly emerging as a new class of materials for PEC water splitting. They exhibit many intriguing properties including tunable electronic structures through molecular engineering, excellent light harvesting capability with high absorption coefficients, and facile fabrication of large-area thin films via solution processing. Recent advances have indicated that integrating rationally designed conjugated polymers with inorganic semiconductors is a promising strategy for fabricating efficient and stable hybrid photoelectrodes for high-efficiency PEC water splitting. This review introduces the history of developing conjugated polymers for PEC water splitting. Notable examples of utilizing conjugated polymers to broaden the light absorption range, improve stability, and enhance the charge separation efficiency of hybrid photoelectrodes are highlighted. Furthermore, key challenges and future research opportunities for further improvements are also presented. This review provides an up-to-date overview of fabricating stable and high-efficiency PEC devices by integrating conjugated polymers with state-of-the-art semiconductors and would have significant implications for the broad solar-to-chemical energy conversion research.

Rational Design of Conjugated Acetylenic Polymers Enables a Two-Electron Water Oxidation Pathway for Enhanced Photosynthetic Hydrogen Peroxide Generation

Herein, the design of conjugated acetylenic polymers (CAPs) featuring diverse spatial arrangements and intramolecular spacers of diacetylene moieties (─C≡C─C≡C─) for photocatalytic hydrogen peroxide (H2 O2 ) production from water and O2 , without the need for sacrificial agents, is presented. It is shown that the linear configuration of diacetylene moieties within conjugated acetylenic polymers (CAPs) induces a pronounced polarization of electron distribution, which imparts enhanced charge-carrier mobility when compared to CAPs' networks featuring cross-linked arrangements. Moreover, optimizing the intramolecular spacer between diacetylene moieties within the linear structure leads to the exceptional modulation of the band structures, specifically resulting in a downshifted valence band (VB) and rendering the two-electron water oxidation pathway thermodynamically feasible for H2 O2 production. Consequently, the optimized CAPs with a linear configuration (LCAP-2), featuring spatially separated reduction centers (benzene rings) and oxidation centers (diacetylene moieties), exhibit a remarkable H2 O2 yield rate of 920.1 µmol g-1 h-1 , superior than that of the linear LCAP-1 (593.2 µmol g-1 h-1 ) and the cross-linked CCAP (433.4 µmol g-1 h-1 ). The apparent quantum efficiency (AQE) and solar-to-chemical energy conversion (SCC) efficiency of LCAP-2 are calculated to be 9.1% (λ = 420 nm) and 0.59%, respectively, surpassing the performance of most previously reported conjugated polymers.

Galvanic-Replacement-Assisted Synthesis of Nanostructured Silver-Surface for SERS Characterization of Two-Dimensional Polymers

Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful technology in trace analysis. However, the wide applications of SERS in practice are limited by the expensive substrate materials and the complicated preparation processes. Here we report a simple and economical galvanic-replacement-assisted synthesis route to prepare Ag nanoparticles on Cu(0) foil (nanoAg@Cu), which can be directly used as SERS substrate. The fabrication process is fast (ca. 10 min) and easily scaled up to centimeters or even larger. In addition, the morphology of the nanoAg@Cu (with Ag particles size from 30 nm to 160 nm) can be adjusted by various additives (e.g., amino-containing ligands). Finally, we show that the as-prepared nanoAg@Cu can be used for SERS characterization of two-dimensional polymers, and ca. 298 times relative enhancement of Raman intensity is achieved. This work offers a simple and economical strategy for the scalable fabrication of silver-based SERS substrate in thin film analysis.

The effect of morphology and crystal structure on the photocatalytic and photoelectrochemical performances of WO3

A template-based solvothermal method was successfully developed for the controlled synthesis of two-dimensional (2D) monoclinic WO3 nanoplate/nanosheet arrays and three-dimensional (3D) hexagonal WO3 nanosphere/nanocage structures with single crystal petals. The structure-directing agents played an important role in controlling the morphology and phase of WO3 samples. The results showed that the WO3 nanospheres exhibited the highest visible light absorption capacity and a photocurrent density of 0.37 mA cm-2 at 1.23 V vs. RHE under simulated sunlight. Moreover, the photocatalytic dye results displayed 83.2% methylene blue degradation and 87.9% rhodamine B degradation within 120 min under visible light irradiation. The high performance of the WO3 nanospheres, resulted from the hierarchical structure, increased surface area and enhanced light absorption, which improved the photogenerated charge carrier transfer and separation capability.

Synthesis of sp2 Carbon-Conjugated Covalent Organic Framework Thin-Films via Copper-Surface-Mediated Knoevenagel Polycondensation

sp2 carbon-conjugated covalent organic framework (sp2 c-COF) featured with high π-conjugation, high chemical stabilities, and designable chemical structures, are thus promising for applications including adsorption and separation, optoelectronic devices, and catalysis. For the most of these applications, large-area and continuous films are required. However, due to the needs of harsh conditions in the formation of CC bonds, classical interfacial methodologies are challenged in the synthesis of sp2 c-COFs films. Herein, a novel and robust interfacial method namely copper-surface-mediated Knoevenagel polycondensation (Cu-SMKP), is shown for scalable synthesis of sp2 c-COF films on various Cu substrates. Using this approach, large-area and continuous sp2 c-COF films could be prepared on various complicated Cu surfaces with thickness from tens to hundreds of nanometers. The resultant sp2 c-COF films on Cu substrate could be used directly as functional electrode for extraction of uranium from spiked seawater, which gives an exceptionally uptake capacity of 2475 mg g-1 . These results delineate significant synthetic advances in sp2 c-COF films and implemented them as functional electrodes for uranyl capture.

Engineering of Graphdiyne-Based Functional Coatings for the Protection of Arbitrary Shapes of Copper Substrates

Copper-based materials are very important for many application fields from marine industry to energy management and electronic devices. For most of these applications, the copper objects require long-term contact to a wet and salty environment, which leads to serious corrosion of copper. In this work, we report a thin graphdiyne layer directly grown on arbitrary shapes of copper objects at mild conditions, which could function as a protective coating for the copper substrates in artificial seawater with corrosion inhibition efficiency of ∼99.75%. To further improve the protective performance of the coating, the graphdiyne layer is fluorinated and followed by infusion with a fluorine-containing lubricant (i.e., perfluoropolyether). As a result, a slippery surface is obtained, which shows enhanced corrosion inhibition efficiency of ∼99.99% as well as excellent antibiofouling properties against microorganisms, such as protein and algae. Finally, the coatings are successfully applied in the protection of a commercial copper radiator from long-term attack of artificial seawater without disturbing its thermal conductivity. These results demonstrate the great potential of graphdiyne-based functional coatings for the protection of copper devices in aggressive environments.

Dual Functional Conjugated Acetylenic Polymers: High-Efficacy Modulation for Organic Photoelectrochemical Transistors and Structural Evolution for Bioelectronic Detection

Conjugated acetylenic polymers (CAPs) have emerged as a unique class of metal-free semiconductors with tunable electrical and optical properties yet their full potential remains largely unexplored. Organic bioelectronics is envisioned to create more opportunities for innovative biomedical applications. Herein, we report a poly(1,4-diethynylbenzene) (pDEB)/NiO gated enhancement-mode poly(ethylene dioxythiophene)-poly(styrene sulfonate) organic photoelectrochemical transistor (OPECT) and its structural evolution toward bioelectronic detection. pDEB was synthesized via copper-mediated Glaser polycondensation of DEB monomers on the NiO/FTO substrate, and the as-synthesized pDEB/NiO/FTO can efficiently modulate the enhancement-mode device with a high current gain. Linking with a sandwich immunoassay, the labeled alkaline phosphatase can catalyze sodium thiophosphate to generate H₂S, which will react with the diacetylene group in pDEB through the Michael addition reaction, resulting in an altered molecular structure and thus the transistor response. Exemplified by HIgG as the model target, the developed biosensor achieves highly sensitive detection with a linear range of 70 fg mL^-1-10 ng mL^-1 and a low detection limit of 28.5 fg mL^-1. This work features the dual functional CAP-gated OPECT, providing not only a novel gating module but also a structurally new rationale for bioelectronic detection.

Redox-Active Azulene-based 2D Conjugated Covalent Organic Framework for Organic Memristors

As a conjugated and unsymmetric building block composed of an electron-poor seven-membered sp² carbon ring and an electron-rich five-membered carbon ring, azulene and its derivatives have been recognized as one of the most promising building blocks for novel electronic devices due to its intrinsic redox activity. By using 1,3,5-tris(4-aminophenyl)-benzene and azulene-1,3-dicarbaldehyde as the starting materials, an azulene(Azu)-based 2D conjugated covalent organic framework, COF-Azu, is prepared through liquid-liquid interface polymerization strategy for the first time. The as-fabricated Al/COF-Azu/indium tin oxide (ITO) memristor shows typical non-volatile resistive switching performance due to the electric filed induced intramolecular charge transfer effect. Associated with the unique memristive performance, a simple convolutional neural network is built for image recognition. After 8 epochs of training, image recognition accuracy of 80 % for a neutral network trained on a larger data set is achieved.

Ultra-Fast Preparation of Large-Area Graphdiyne-Based Membranes via Alkynylated Surface-Modification for Nanofiltration

Graphdiynes (GDYs), two-dimensional graphene-like carbon systems, are considered as potential advanced membrane material due to their unique physicochemical features. Nevertheless, the scale-up of integrated GDY membranes is technologically challenging, and most studies remain at the theoretical stage. Herein, we report a simple and efficient alkynylated surface-mediated strategy to prepare hydrogen-substituted graphdiyne (HsGDY) membranes on commercial alumina tubes. Surface alkynylation initiates an accelerated surface-confined coupling reaction in the presence of a copper catalyst and facilitates the nanoscale epitaxial lateral growth of HsGDY. A continuous and ultra-thin HsGDY membrane (∼100 nm) can be produced within 15 min. The resulting membranes exhibit outstanding molecular sieving together with excellent water permeances (ca. 1100 L m^-2  h^-1 MPa^-1 ), and show a long-term durability in cross-flow nanofiltration, owing to the superhydrophilic surface and hydrophobic pore walls.

Hydrogen-substituted graphdiyne encapsulated cuprous oxide photocathode for efficient and stable photoelectrochemical water reduction

Photoelectrochemical (PEC) water splitting is an appealing approach for “green” hydrogen generation. The natural p-type semiconductor of Cu₂O is one of the most promising photocathode candidates for direct hydrogen generation. However, the Cu₂O-based photocathodes still suffer severe self-photo-corrosion and fast surface electron-hole recombination issues. Herein, we propose a facile in-situ encapsulation strategy to protect Cu₂O with hydrogen-substituted graphdiyne (HsGDY) and promote water reduction performance. The HsGDY encapsulated Cu₂O nanowires (HsGDY@Cu₂O NWs) photocathode demonstrates a high photocurrent density of −12.88 mA cm⁻² at 0 V versus the reversible hydrogen electrode under 1 sun illumination, approaching to the theoretical value of Cu₂O. The HsGDY@Cu₂O NWs photocathode as well as presents excellent stability and contributes an impressive hydrogen generation rate of 218.2 ± 11.3 μmol h⁻¹cm⁻², which value has been further magnified to 861.1 ± 24.8 μmol h⁻¹cm⁻² under illumination of concentrated solar light. The in-situ encapsulation strategy opens an avenue for rational design photocathodes for efficient and stable PEC water reduction.

Cu2O-based photocathodes for photoelectrochemical water reduction suffer severe self-photo-corrosion issue. Here the authors report an in-situ encapsulation strategy with hydrogen-substituted graphdiyne to protect Cu2O for water reduction with a photocurrent density of −12.88 mA cm-2.

Polymer Photoelectrodes for Solar Fuel Production: Progress and Challenges

Converting solar energy to fuels has attracted substantial interest over the past decades because it has the potential to sustainably meet the increasing global energy demand. However, achieving this potential requires significant technological advances. Polymer photoelectrodes are composed of earth-abundant elements, e.g. carbon, nitrogen, oxygen, hydrogen, which promise to be more economically sustainable than their inorganic counterparts. Furthermore, the electronic structure of polymer photoelectrodes can be more easily tuned to fit the solar spectrum than inorganic counterparts, promising a feasible practical application. As a fast-moving area, in particular, over the past ten years, we have witnessed an explosion of reports on polymer materials, including photoelectrodes, cocatalysts, device architectures, and fundamental understanding experimentally and theoretically, all of which have been detailed in this review. Furthermore, the prospects of this field are discussed to highlight the future development of polymer photoelectrodes.

Regioisomer-Directed Self-Assembly of Alternating Copolymers for Highly Enhanced Photocatalytic H2 Evolution

Porphyrin-based photocatalytic materials have received great attention, and the effect of the substituents, central ions, and aggregated structure on the catalysis performance has been studied up to now. Herein, we report the effect of porphyrin isomerism on their aggregated structures as well as the photocatalytic activity. Two trans- and cis-porphyrin-based alternating copolymers with the same compositions (P1 and P2) are successfully synthesized. It is found that P1 self-assembles into propeller-like nanoparticles and P2 into multilayer hollow nanospheres. Furthermore, the hydrogen production rate of P1 (5533 μmol g^-1 h^-1) is 30 times higher than that of P2 (173 μmol g^-1 h^-1). Mechanism studies reveal that the high photocatalytic properties of P1 originate from the more ordered arrangement of porphyrins than P2, which facilitates the mobility and separation of photoinduced carriers. We believe the covalent and noncovalent polymer self-assembly process as well as the isomerism effect as disclosed here will shed new light on the design of high performance photocatalysts.

Hierarchical Nanocapsules of Cu-Doped MoS2@H-Substituted Graphdiyne for Magnesium Storage

Hierarchical nanocomposites, which integrate electroactive materials into carbonaceous species, are significant in addressing the structural stability and electrical conductivity of electrode materials in post-lithium-ion batteries. Herein, a hierarchical nanocapsule that encapsulates Cu-doped MoS₂ (Cu-MoS₂) nanopetals with inner added skeletons in an organic-carbon-rich nanotube of hydrogen-substituted graphdiyne (HsGDY) has been developed for rechargeable magnesium batteries (RMB). Notably, both the incorporation of Cu in MoS₂ and the generation of the inner added nanoboxes are developed from a dual-template of Cu-cysteine@HsGDY hybrid nanowire; the synthesis involves two morphology/composition evolutions by CuS@HsGDY intermediates both taking place sequentially in one continuous process. These Cu-doped MoS₂ nanopetals with stress-release skeletons provide abundant active sites for Mg²⁺ storage. The microporous HsGDY enveloped with an extended π-conjugation system offers more effective electron and ion transfer channels. These advantages work together to make this nanocapsule an effective cathode material for RMB with a large reversible capacity and superior rate and cycling performance.

2D graphdiyne: an emerging carbon material

As a new member of carbon allotropes, graphdiyne (GDY) has the characteristics of being one-atom-thick with two-dimensional layers comprising sp and sp² hybridized carbon atoms, and represents a trend in the development of carbon materials. Its unique chemical and electronic structures give GDY many unique and fascinating properties such as rich chemical bonds, highly conjugated and super-large π structures, infinitely distributed pores and high inhomogeneity of charge distribution. GDY has entered a period of rapid development, especially with the significant emergence of fundamental research and applied research achievements over the past five years. As one of the frontiers of chemistry and materials science, graphdiyne was listed in the Top 10 research areas in the 2020 Research Frontiers report and was jointly released in the Top 10 in the world by Clarivate and the Chinese Academy of Sciences. The research results have shown the great potential of GDY in the applications of energy, catalysis, environmental science, electronic devices, detectors, biomedicine and therapy, etc. Scientists are eager to explore and fully reveal the new properties, discover new scientific concepts and phenomena, discover the new conversion modes and mechanisms of GDY in photoelectricity, energy, and catalysis, etc., and build the important scientific value of new conversion devices. This review covers research on the foundation and application of GDY, such as the controlled preparation of new methods of GDY and GDY-based materials, studies on new mechanisms and properties in chemistry and physics, and the foundation and applications in energy, catalysis, photoelectric and devices.

Homogeneous Photoelectrochemical Aptasensors for Tetracycline Based on Sulfur-Doped g-C3N4/n-GaN Heterostructures Formed through Self-Assembly

The complex synthesis of photoelectric materials and the difficulty of fixing the identification elements on the photoelectrode are long-standing problems in the field of photoelectrochemical (PEC) biosensing. In this work, a simple PEC aptasensor construction strategy based on a sulfur-doped g-C₃N₄ (SCN)/n-GaN heterostructure photoelectrode was proposed. The SCN/n-GaN heterostructure can be formed through self-assembly in solution since SCN can be uniformly dispersed in solution. In addition, as a dual-function mediate, an aptamer can be fixed on an SCN substrate automatically because of the good adsorption performance of SCN. Therefore, tedious steps of PEC electrode preparation and the fixing of recognition elements were both avoided. Compared with the traditional ones, the construction difficulty and time cost of the prepared PEC aptasensors are greatly reduced. The simplified experimental process improves the stability and reproducibility of the aptasensor. Finally, tetracycline (TET) was used as a model target to verify the sensing performance of the proposed PEC strategy. TET can consume the photogenerated holes of the SCN/n-GaN heterostructure, promote carrier migration, and result in the change in the photocurrent. The linear relationship between the change in the photocurrent intensity and the TET concentration can be used to detect TET. The aptasensor has a linear range of 0.10-10.0 nmol L^-1 and the detection limit is 0.030 nmol L^-1 (3S/N). The aptasensor was applied to the detection of TET in milk samples with satisfactory results.

N-confused porphyrin-based conjugated microporous polymers

Metal porphyrins, which possess metal-N coordination centers, are important building blocks for the construction of porous organic materials with catalytic performance. However, most of the previous work has focused on controlling the metal elements instead of the metal-N coordinations. Here, Pt(II) N-confused porphyrin and Pt(II) porphyrin based conjugated microporous polymers were synthesized by Yamamoto coupling reaction. The structural and property differences of Pt-N₃C and Pt-N₄ were studied. Calculations demonstrate that the Pt-N₃C-based porous polymer exhibits broader photoabsorption and narrower bandgap than conventional Pt-N₄-based porous polymers.

Porous organic polymers for light-driven organic transformations

As a new generation of porous materials, porous organic polymers (POPs), have recently emerged as a powerful platform of heterogeneous photocatalysis. POPs are constructed using extensive organic synthesis methodologies, with various functional organic units being connected via high-energy covalent bonds. This review systematically presents the recent advances in POPs for visible-light driven organic transformations. Herein, we firstly summarize the common construction strategies for POP-based photocatalysts based on two major approaches: pre-design and post-modification; secondly, we categorize and summarize the synthesis methods and organic reaction types for constructing various types of POPs. We then classify and introduce the specific reactions of current light-driven POP-mediated organic transformations. Finally, we outline the current state of development and the problems faced in light-driven organic transformations by POPs, and we present some perspectives to motivate the reader to explore solutions to these problems and confront the present challenges in the development process.

Cascaded Nanozyme System with High Reaction Selectivity by Substrate Screening and Channeling in a Microfluidic Device

Surpassing natural enzymes in cost, stability and mass production, nanozymes have attracted wide attention in fields from disease diagnosis to tumor therapy. However, nanozymes intrinsically have low reaction selectivity, which significantly restricts their applications. A general method is reported to address this challenge by following a biomimetic operation principle of substrates channeling and screening. Two oxidase- and peroxidase-like nanozymes (i.e., emerging N-doped carbon nanocages and Prussian blue nanoparticles), were cascaded as a proof of concept to improve the reaction selectivity in transforming the substrate into the targeted product by more than 2000 times. The cascaded nanozymes were also adopted to a spatially confined microfluidic device, leading to more than 100-fold enhancement of the reaction efficiency due to signal amplification.

Cu nanowires modified with carbon-rich conjugated framework PTEB for stabilizing lithium metal anodes

Lithium metal anodes provide a direction for the development of high-energy-density lithium-ion batteries. To overcome lithium dendritic growth and low Coulombic efficiency in lithium plating/stripping processes, the design of a three-dimensional (3D) host structure is a feasible solution. Herein, copper nanowires in situ-coated with a carbon-rich conjugated framework, poly(1,3,5-triethynylbenzene), and grown on copper foam were constructed as a 3D lithium host, and shown to effectively yield a low nucleation overpotential, smooth lithium deposition, and improved cycling stability. This well-designed 3D host structure achieved a high Coulombic efficiency of over 99% for 150 cycles and showed reversible lithium plating/stripping stability for over 800 h at 2 mA cm^-2. This work has highlighted the benefits of using an interface modification strategy, and provided a feasible route for 3D host structure design in the development of lithium metal anodes.

2D Graphdiyne: A Rising Star on the Horizon of Energy Conversion

Two-dimensional (2D) graphdiyne (GDY), a rapidly rising star on the horizon of carbon materials, is a new carbon allotrope featuring sp- and sp² -cohybridized carbon atoms and 2D one-atom-thick network. Since the first successful synthesis of GDY by Professor Li's group in 2010, GDY has attached great interests from both scientific and industrial viewpoints based on its unique structure and physicochemical properties, which provides a fertile ground for applications in various fields including electrocatalysis, energy conversion, energy storage and optoelectronic devices. In this work, various potential properties of the GDY-based electrocatalysts and their recent advances in energy conversion are reviewed, including atomic catalysts, heterogeneous catalysts, and metal-free catalysts. The critical role of GDY in improving catalytic activity and stability is analyzed. The perspectives of the challenges and opportunities faced by GDY-based materials for energy conversion are also outlined.

Designing All Graphdiyne Materials as Graphene Derivatives: Topologically Driven Modulation of Electronic Properties

Designing new 2D systems with tunable properties is an important subject for science and technology. Starting from graphene, we developed an algorithm to systematically generate 2D carbon crystals belonging to the family of graphdiynes (GDYs) and having different structures and sp/sp² carbon ratios. We analyze how structural and topological effects can tune the relative stability and the electronic behavior, to propose a rationale for the development of new systems with tailored properties. A total of 26 structures have been generated, including the already known polymorphs such as α-, β-, and γ-GDY. Periodic density functional theory calculations have been employed to optimize the 2D crystal structures and to compute the total energy, the band structure, and the density of states. Relative energies with respect to graphene have been found to increase when the values of the carbon sp/sp² ratio increase, following however different trends based on the peculiar topologies present in the crystals. These topologies also influence the band structure, giving rise to semiconductors with a finite band gap, zero-gap semiconductors displaying Dirac cones, or metallic systems. The different trends allow identifying some topological effects as possible guidelines in the design of new 2D carbon materials beyond graphene.

Visible Light-Regulated Heterogeneous Catalytic PET-RAFT by High Crystallinity Covalent Organic Framework

Covalent organic frameworks (COFs) are a class of promising photocatalysts for conversing light energy into chemical energy. Based on the tunable building blocks, COFs can be well-designed as photocatalyst for mediating reversible addition-fragmentation chain-transfer (RAFT) polymerization. Herein, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2″-bipyridine-5,5″-diamine (Bpy) are chosen to construct imine-based TFPPy-Bpy-COFs for catalyzing RAFT polymerization of methacrylates under white light irradiation. The well-defined polymers with precise molecular weight and narrow molecular weight distribution are obtained. The switch on/off light experiments suggest excellent temporal control toward RAFT polymerization system and the chain-extension reaction indicates high chain-end fidelity of macro-initiators. Mechanism study clarifies that the electron transfer between excited state of TFPPy-Bpy-COFs and RAFT agent can form living radicals to mediate polymerization. This methodology provides a novel platform for reversible-deactivation radical polymerization using COFs as heterogeneous catalysts.

Topological defect-containing Fe/N co-doped mesoporous carbon nanosheets as novel electrocatalysts for the oxygen reduction reaction and Zn-air batteries

Developing effective electrocatalysts for the oxygen reduction reaction is of great significance for clean and renewable energy technologies, such as metal-air batteries and fuel cells. Defect engineering is the central focus of this field because the overall catalytic performance crucially depends on highly active defects. For the ORR, topological defects have been proven to have a positive effect. However, because preparation and characterization of such defects are difficult, a basic understanding of the relationship between topological defects and catalytic performance remains elusive. In this study, topological defect-containing Fe/N co-doped mesoporous carbon nanosheets were synthesized using azulene-based sandwich-like polymer nanosheets as the precursor. As electrocatalysts, such porous carbon nanosheets exhibited promising ORR activity, methanol tolerance ability, and stability with a half-wave potential of 841 mV under alkaline conditions, which is superior to those of most of the reported porous carbons. As the air cathode for Zn-air batteries, the catalyst exhibited a peak power density of 153 mW cm^-2 and a specific capacity of 628 mA h g^-1,which were higher than those of a Pt/C-based Zn-air battery. Density functional theory calculation further proved the positive effect of topological defects on the oxygen reduction activity. These results indicate that bottom-up topological defect engineering could be a new and promising strategy for developing high-performance electrocatalysts.

Thiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2‐b]thiophene) (pDET) to poly(2,6‐diethynylbenzo[1,2‐b:4,5‐b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2‐b:2′,3′‐d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm⁻² and 120 μA cm⁻² (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron‐enriched C_β of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution.

Ether-linked porphyrin covalent organic framework with broadband optical switch

It is still a challenge to design and synthesize novel switchable optical materials with ultrafast nonlinear optical (NLO) response in a broad spectral range. These materials have exhibited great application potential in many high-technology fields such as biological imaging, chemical sensors, optical data storage, laser protection, and controllable intelligent and optoelectronic devices. By using porphyrins with highly delocalized 18 π-electron conjugated system as functional building blocks, the first ether-linked porphyrin covalent organic framework materials (COF-Pors) with highly ordered lattice structure have been successfully synthesized. In contrast to the starting porphyrins that only exhibit reverse saturable absorption (RSA) response at 532 nm, the as-prepared COF-Pors shows large NLO effect in a broad range from visible to near infrared. Upon laser illumination, COF-Pors exhibits typical saturable absorption (SA) effect at lower incident laser energy, and RSA response at higher pulse energy.

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The first ether-linked porphyrin covalent organic framework (COF-Pors) was synthesized.

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COF-Pors exhibits reversible intensity-dependent SA to RSA transition in DMF dispersions.

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COF-Pors shows an NLO switching effect in a broad range from visible to near infrared.

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COF-Pors exhibits SA at lower pulse energy and RSA at higher pulse energy.

A Terpyridine-Fe2+-Based Coordination Polymer Film for On-Chip Micro-Supercapacitor with AC Line-Filtering Performance

The preparation of redox-active, ultrathin polymer films as the electrode materials represents a major challenge for miniaturized flexible electronics. Herein, we demonstrated a liquid–liquid interfacial polymerization approach to a coordination polymer films with ultrathin thickness from tri(terpyridine)-based building block and iron atoms. The as-synthesized polymer films exhibit flexible properties, good redox-active and narrow bandgap. After directly transferred to silicon wafers, the on-chip micro-supercapacitors of TpPB-Fe-MSC achieved the high specific capacitances of 1.25 mF cm⁻² at 50 mV s⁻¹ and volumetric energy density of 5.8 mWh cm⁻³, which are superior to most of semiconductive polymer-based micro-supercapacitor (MSC) devices. In addition, as-fabricated on-chip MSCs exhibit typical alternating current (AC) line-filtering performance (−71.3° at 120 Hz) and a short resistance–capacitance (RC) time (0.06 ms) with the electrolytes of PVA/LiCl. This study provides a simple interfacial approach to redox-active polymer films for microsized energy storage devices.

B/N-Enriched Semi-Conductive Polymer Film for Micro-Supercapacitors with AC Line-Filtering Performance

Microsupercapacitors (MSCs) have drawn great attention for use as miniaturized electrochemical energy storage devices in portable, wearable, as well as implantable electronics. Many materials have been developed as electrodes for MSCs. However, the thin-film fabrication for most of these materials involves multistep operations, including filtration, spray coating, and sputtering. Most importantly, these methods present challenges for the preparation of thin films at the atomic or molecular scale. Therefore, the understanding of performance of ultrathin-film-based MSCs remains challenge. Herein, a B/N-enriched polymer film is successfully prepared using the photoassisted interfacial approach. The as-synthesized polymer film exhibits typical semiconductive characteristics and can be easily scaled up to a large area of up to tens of square centimeters. This ultrathin polymer film can be directly transferred to silicon wafers to fabricate MSC through laser scribing. The prepared MSC exhibits specific volumetric capacitance as high as 20.9 F cm^-3, corresponding to volumetric energy density of 2.9 mWh cm^-3 (at 0.1 V s^-1). Moreover, the volumetric power density can reach 1461 W cm^-3, surpassing most existing semiconductive polymer film-based MSC devices. In addition, the prepared MSC exhibits typical AC line-filtering ability (-67° at 120 Hz). This study offers a facile interfacial approach to preparing semiconductive polymer films with aromatic moieties for microsized energy storage devices.

Copolymerization of urea and murexide for efficient photocatalytic hydrogen evolution and tetracycline degradation

A g-C₃N₄ based material modified with murexide has been prepared and used for photocatalytic hydrogen production and degradation of tetracycline.

Thiophene-Bridged Donor-Acceptor sp2 -Carbon-Linked 2D Conjugated Polymers as Photocathodes for Water Reduction

Photoelectrochemical (PEC) water reduction, converting solar energy into environmentally friendly hydrogen fuel, requires delicate design and synthesis of semiconductors with appropriate bandgaps, suitable energy levels of the frontier orbitals, and high intrinsic charge mobility. In this work, the synthesis of a novel bithiophene-bridged donor-acceptor-based 2D sp2 -carbon-linked conjugated polymer (2D CCP) is demonstrated. The Knoevenagel polymerization between the electron-accepting building block 2,3,8,9,14,15-hexa(4-formylphenyl) diquinoxalino[2,3-a:2',3'-c]phenazine (HATN-6CHO) and the first electron-donating linker 2,2'-([2,2'-bithiophene]-5,5'-diyl)diacetonitrile (ThDAN) provides the 2D CCP-HATNThDAN (2D CCP-Th). Compared with the corresponding biphenyl-bridged 2D CCP-HATN-BDAN (2D CCP-BD), the bithiophene-based 2D CCP-Th exhibits a wide light-harvesting range (up to 674 nm), a optical energy gap (2.04 eV), and highest energy occupied molecular orbital-lowest unoccupied molecular orbital distributions for facilitated charge transfer, which make 2D CCP-Th a promising candidate for PEC water reduction. As a result, 2D CCP-Th presents a superb H2 -evolution photocurrent density up to ≈7.9 µA cm-2 at 0 V versus reversible hydrogen electrode, which is superior to the reported 2D covalent organic frameworks and most carbon nitride materials (0.09-6.0 µA cm-2 ). Density functional theory calculations identify the thiophene units and cyano substituents at the vinylene linkage as active sites for the evolution of H2 .

Nanocarbon-Enhanced 2D Photoelectrodes: A New Paradigm in Photoelectrochemical Water Splitting

Solar-driven photoelectrochemical (PEC) water splitting systems are highly promising for converting solar energy into clean and sustainable chemical energy. In such PEC systems, an integrated photoelectrode incorporates a light harvester for absorbing solar energy, an interlayer for transporting photogenerated charge carriers, and a co-catalyst for triggering redox reactions. Thus, understanding the correlations between the intrinsic structural properties and functions of the photoelectrodes is crucial. Here we critically examine various 2D layered photoanodes/photocathodes, including graphitic carbon nitrides, transition metal dichalcogenides, layered double hydroxides, layered bismuth oxyhalide nanosheets, and MXenes, combined with advanced nanocarbons (carbon dots, carbon nanotubes, graphene, and graphdiyne) as co-catalysts to assemble integrated photoelectrodes for oxygen evolution/hydrogen evolution reactions. The fundamental principles of PEC water splitting and physicochemical properties of photoelectrodes and the associated catalytic reactions are analyzed. Elaborate strategies for the assembly of 2D photoelectrodes with nanocarbons to enhance the PEC performances are introduced. The mechanisms of interplay of 2D photoelectrodes and nanocarbon co-catalysts are further discussed. The challenges and opportunities in the field are identified to guide future research for maximizing the conversion efficiency of PEC water splitting.

Conjugated Acetylenic Polymers Grafted Cuprous Oxide as an Efficient Z-Scheme Heterojunction for Photoelectrochemical Water Reduction

As attractive materials for photoeletrochemical hydrogen evolution reaction (PEC HER), conjugated polymers (e.g., conjugated acetylenic polymers [CAPs]) still show poor PEC HER performance due to the associated serious recombination of photogenerated electrons and holes. Herein, taking advantage of the in situ conversion of nanocopper into Cu₂ O on copper cellulose paper during catalyzing of the Glaser coupling reaction, a general strategy for the construction of a CAPs/Cu₂ O Z-scheme heterojunction for PEC water reduction is demonstrated. The as-fabricated poly(2,5-diethynylthieno[3,2-b]thiophene) (pDET)/Cu₂ O Z-scheme heterojunction exhibits a carrier separation efficiency of 16.1% at 0.3 V versus reversible hydrogen electrode (RHE), which is 6.7 and 1.4-times higher respectively than those for pDET and Cu₂ O under AM 1.5G irradiation (100 mW cm^-2 ) in the 0.1 m Na₂ SO₄ aqueous solution. Consequently, the photocurrent of the pDET/Cu₂ O Z-scheme heterojunction reaches ≈520 µA cm^-2 at 0.3 V versus RHE, which is much higher than pDET (≈80 µA cm^-2 ), Cu₂ O (≈100 µA cm^-2 ), and the state-of-the-art cocatalyst-free organic or organic-semiconductor-based heterojunctions/homojunctions photocathodes (1-370 µA cm^-2 ). This work advances the design of polymer-based Z-scheme heterojunctions and high-performance organic photoelectrodes.

Graphene-Like Covalent Organic Framework with a Wide Band Gap Synthesized On Surface via Stepwise Reactions

Developing graphene-like two-dimensional materials naturally possessing a band gap has sparked enormous interest. Thanks to the inherent wide band gap and high mobility in the 2D plane, covalent organic frameworks containing triazine rings (t-COFs) hold great promise in this regard, whilst the synthesis of single-layer t-COFs remains highly challenging. Herein, we present the fabrication of a well-defined graphene-like t-COF on Au(111). Instead of single/multiple-step single-type reactions commonly applied for on-surface synthesis, distinct stepwise on-surface reactions, including alkynyl cyclotrimerization, C-O bond cleavage, and C-H bond activation, are triggered on demand, leading to product evolution in a controlled step-by-step manner. Aside from the precise control in sophisticated on-surface synthesis, this work proposes a single-atomic-layer organic semiconductor with a wide band gap of 3.41 eV.