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Photocatalytic reduction of CO2with H2O is thought as an environment friendly approach for sustainable development. It is highly desirable but remains challenging to develop photocatalyst with metal-free site for CO2reduction. Here, we fabricated a heterostructure by integrating azine-based COF with ZnIn2S4, where the azine unit in COF acts as metal-free sites for CO2adsorption and reduction. The as-formed interfused heterointerface in the heterostructure ensures the effective electron transfer from ZnIn2S4across the interface to the COF, resulting in a spatial separation of redox sites for CO2reduction and water oxidation. The hybrid catalyst exhibits remarkably enhanced photocatalytic activity for CO2reduction to CO, which is 8 and 6 times than the COF and ZnIn2S4, respectively, and is even comparable with some metal-catalyzed CO2reduction systems. This study provides a new paradigm to mimic natural photosynthesis by using metal-free site for CO2reduction.

Electrochemical CO2reduction (CO2RR) is a promising technology to mitigate the greenhouse effect and convert CO2to value-added chemicals. Yet, achieving high catalytic activity, selectivity, and stability for target products is still a big challenge. Herein, interstitially Sn-doped Bi (Snx-Bi, xis the atomic ratio of Sn to Bi, x= 1/2, 1/16, 1/24 or 1/40) nanowire bundles (NBs) are prepared by reducing Sn-doped Bi2S3. Notably, Sn1/24-Bi NBs exhibit ultrahigh formate selectivity over a broad potential window of 1400 mV (Faradaic efficiency over 90% from −0.5 to −1.9 V vs.reversible hydrogen electrode (RHE)) with an industry-compatible current density of −319 mA cm−2at −1.9 V vs.RHE. Moreover, superior long-term stability for more than 84 h at ∼−200 mA cm−2is realized. Experimental results and density functional theory (DFT) calculations reveal that interstitially doped Sn optimizes the adsorption affinity of *OCHO intermediate and reduces the electron transfer energy barrier of bismuth catalyst, resulting in the remarkable CO2RR performance. This study provides valuable inspiration for the design of doped electrocatalysts with enhanced catalytic activity, selectivity, and durability for electrochemical CO2-to-formate conversion.

Covalent organic frameworks (COFs) represent a burgeoning category of highly tunable crystalline porous materials, which have garnered significant attention as promising platforms for designing novel photo- and electrocatalysts. Single-site catalysis holds paramount importance in revealing the catalytic reaction mechanism and enhancing catalytic performance because of the maximum utilization of metal atoms and presence of a definite active center. Given the distinct advantages of single-site catalysts, such as single metal ions, single atoms, single active sites, and metal clusters, and COFs materials, there is a current surge of interest in using COFs materials as support materials to anchor highly dispersed single-sites. Consequently, the design and preparation of COF-based single-site catalysts have emerged as a prominent research topic in the fields of photo- and electrocatalysis, to address the pressing environmental and energy issues. This review provides an overview of the development of COF-based single-site photo- and electrocatalysts. Advanced applications of COF-based single-site photo- and electrocatalysts are comprehensively summarized and reviewed. Additionally, the review addresses the challenges faced by COF-based single-site photo- and electrocatalysts and discusses their future development trends. We aim to provide new insights into the application of COF-based single-site materials in photo- and electrocatalysis and further promote the development of catalytic science.

Orienting electron transport to suppress charge recombination is attractive for efficient photocatalysis but remains challenging. Herein, we demonstrate the synthesis of crystalline linear conjugated polyimides viathe condensation of carboxylic anhydrides and amine monomers for the photocatalytic reduction of CO2. Oriented electron transport was achieved using crystalline polyimides integrated with electronic push-pull units. Directional intramolecular electron transfer is driven by the dipole effects of the adjacent building units. The sulfone-based polyimide exhibited excellent photocatalytic performance for CO2reduction. Our work provides a new example photoreduction of CO2and a strategy for developing efficient photocatalysts with oriented electron transport.

Weld penetration recognition is of great significance to improve welding quality and automation level. Weld pool images can be used as the input of convolutional neural networks (CNNs) to recognize the weld penetration state, but it is difficult to design and train an efficient CNN model from scratch for real-time recognition. In the study, a flexible visual sensing welding system was developed to construct a gas tungsten arc welding (GTAW) pool image dataset. Pretrained on the ImageNet dataset, the MobileNetV2-based transfer learning model was used to fit the custom dataset and recognize weld penetration states, including lack of fusion, lack of penetration, desirable penetration, and excessive penetration. Compared with the MobileNetV2 trained from scratch and the ResNet based on transfer learning, the results show that the proposed method improves model development efficiency on small datasets, while greatly reducing the memory occupied on industrial equipment. The recognition accuracy on the validation set achieved 99.88%, and the recognition time of a single image was about 65 ms. The model was visualized by gradient-weighted class activation mapping (Grad-CAM), showing key areas the model depends on to recognize the weld penetration state. Finally, the GTAW penetration monitoring system was designed for online evaluation.

Striking a balance between the stability and activity of metal nanoparticles (NPs) is crucial in designing efficient heterogeneous catalysts. This challenge requires supporters with highly tunable behaviour enabling metal active sites with appropriate electronic properties. Herein, we demonstrate a newly synthesized pyridine-functionalized covalent organic framework (COF) rendering Pt NPs with enhanced stability and electronic density. Periodic channels with pendant pyridine groups can efficiently stabilize Pt NPs as active sites. Local charge transfer from the COF to Pt was confirmed by experimental and theoretical methods. The increased electron density on Pt promotes the rate-limiting cleavage of the O–H band in H2O, resulting in enhanced catalytic activity for the hydrolysis of ammonia borane (AB) for H2production compared to other non-pyridine-functionalized COF-based catalysts. The mechanistic insights into the local charge transfer advance the applicability of COFs for heterogeneous catalysis.

Yolk–shell composites offer a promising platform for integrating cores into hollow shells to create unique structures and properties. However, the concomitant functionality and tunability of yolk–shell nanocomposites is still a great challenge but highly desirable. Herein, we demonstrate a rational design for the fabrication of yolk–shell-structured covalent organic framework (COF)@metal–organic framework (MOF) (YS-COF@MOF) nanocomposites with COF as the external shell and MOF as the inner yolk. Series of the YS-COF@MOF composites with different MOF cores and COF shells were readily synthesized via a template-free solvothermal method. Control experiments showed that the formation of the hollow cavity between the core and the shell originated from the amorphous-to-crystalline transformation and the simultaneous shrinkage of the shell under the pyrrolidine-catalyzed conditions. The resultant YS-COF@MOF merges the inherent structure tunability and functionality of both COFs and MOFs. The functions of YS-COF@MOF can be regulated and optimized by judicious selections of metal ions and organic building blocks. Representative YS-TpPa@UiO-66-(COOH)2with spatially distributed acidic and basic sites exhibited synergistically enhanced catalytic activity in one-pot deacetalization–Knoevenagel cascade reactions.

Magnetic arc blow during the welding of submersible pressure hulls can severely impact the weld quality. Real-time estimation of the arc posture by the teaching-replay welding robot is a crucial and challenging step for further correction of the magnetic blow. This paper proposes a lightweight deep learning model capable of real-time estimation of the welding arc posture. The model takes arc images as input and outputs the angle of arc magnetic blow end-to-end. Specifically, to enable the model to learn the prior knowledge of human perception of arc magnetic blow angles, a training strategy utilizing keypoint detection as an auxiliary task has been proposed. This approach enhances the estimation accuracy of the model without incurring additional inference costs. Additionally, an efficient multi-scale attention (EMA) mechanism was integrated into the angle prediction branch to facilitate the learning of long-range feature dependencies. To confirm the effectiveness of the model, an arc magnetic blow image dataset was constructed for training and testing. The experimental results show that the model achieves a cumulative score (CS3) of 98.47 % and a mean absolute error (MAE) of 0.9985° during testing. The model achieves an inference speed of 70.49 FPS on an Intel® Core™ i7-8750H CPU, which satisfies the criteria for real-time monitoring.

The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability. In this study, we demonstrate an efficient catalytic system formed by integrating Co single sites, which act as the active sites, in covalent triazine frameworks (CTFs), which act as the photoabsorber, for the photocatalytic production of syngas from CO2in aqueous solution. The enhanced light absorption of the CTFs, which contain intramolecular heterojunctions, in conjunction with 0.8 mmol L−1of the Co complex enables excellent syngas production with a yield of 3303 μmol g−1(CO:H2= 1.4:1) in 10 h, which is about three times greater than that achieved using CTF without a heterojunction. In the photocatalytic reaction, the coordinated single Co centers accept the photogenerated electrons from the CTF, and serve as active sites for CO2conversion through an adsorption-activation-reaction mechanism. Theoretical calculations further reveal that the intramolecular heterojunctions highly promote photogenerated charge separation, thus boosting photocatalytic syngas production. This work reveals the promising potential of CTFs for single-metal-site-based photocatalysis.

This work reported an unpresented rare-earth-ion bearing metal–organic framework (MOF) Y10(C8H4O4)6(CO3)3(OH)12built of inorganic slabs as structural units. Eu3+has been introduced into the lattice of Y10(C8H4O4)6(CO3)3(OH)12to make it optically active. Systematical structural analysis combined with single crystal X-ray diffraction demonstrates Eu3+was incorporated into the lattice of Y10(C8H4O4)6(CO3)3(OH)12endowing the MOF with promising optical activity. Even though there was a trace amount of Eu3+< 1%, this compound displayed excellent luminescent activity with quantum efficiency reaching up to 69%, benefiting from the inorganic circumstance of Y3+/Eu3+in layered structure. The concentration-dependent electronic transition character of Eu3+is systematically studied, according to Judd–Ofelt theory normally applicable in inorganic compounds. The phase analysis and optical spectroscopy study result reveal that the local crystallographic circumstance of the rare-earth metal ion basically remained inactive after the replacement of Y3+by Eu3+. Benefiting from this rigid structure, such Eu3+-substituted Y10(C8H4O4)6(CO3)3(OH)12powder exhibits good luminescence probing ability toward Fe3+ion, displaying a limit detection concentration of Fe3+down to 12.7 μM in aqueous solution. The findings here confirm Eu3+is not only an environmental probing ion but could also serve an ideal indicator for investigating the structure change and properties of luminescent MOFs for diverse applications.

Photocatalytic reduction of CO2into energy-rich carbon compounds has attracted increasing attention. However, it is still a challenge to selectively and effectively convert CO2to a desirable reaction product. Herein, we report a design of a synergistic photocatalyst for selective reduction of CO2to CO by using a covalent organic framework bearing single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated CO2reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g–1of CO in a 5 h reaction with a 96% selectivity over H2evolution. More importantly, when the CO2partial pressure was reduced to 0.1 atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in which the TpBpy not only serves as a host for CO2molecules and Ni catalytic sites but also facilitates the activation of CO2and inhibits the competitive H2evolution.

Seeking efficient visible-light-driven photocatalysts for water splitting to produce H2has attracted much attention. Chemical doping is an effective strategy to enhance photocatalytic performance. Herein, we reported phosphorus-doped covalent triazine-based frameworks (CTFs) for photocatalytic H2evolution. Phosphorus-doped CTFs were fabricated by a facile thermal treatment using easily available red phosphorus as the external phosphorus species. The introduction of phosphorus atoms into the frameworks modified the optical and electronic property of CTFs, thus promoting the generation, separation, and migration of photoinduced electron–hole pairs. Consequently, the photocatalytic H2-production efficiency of phosphorus-doped CTFs was greatly improved, which was 4.5, 3.9, and 1.8 times as high as that of undoped CTFs and phosphorus-doped g-C3N4calcined from melamine and urea, respectively.

Materials with different Au–Pd ratios bimetallic alloy nanoparticles (NPs) supported on MgAl–LDH (Au–Pd/LDH) were prepared by an impregnation–reduction method and developed as photocatalysts for the selective oxidation of benzyl alcohol to benzaldehyde under visible light irradiation. A typical sample (Au9–Pd1/LDH) showed efficient photocatalytic activity with 91.1% conversion and 99% selectivity. The conversion was greatly increased from 3.6% for Au/LDH and 1.5% for Pd/LDH, respectively. Moreover, it was four times higher than that for Au9–Pd1/TiO2. The ESR spectrum demonstrated that the main reactive species were superoxide radicals (O2−) generated by the transfer of hot electrons from the Au–Pd alloy NPs to the surface adsorbed molecular oxygen. The formation of hot electrons was attributed to localized surface plasmon resonance (LSPR) of the alloy NPs. Based on XPS analysis, a synergistic electron effect in the Au–Pd alloy was observed due to the transfer of electrons from Pd to Au atoms. This effect enhances the adsorption ability of Pd atoms to oxygen molecules and facilitates the formation of O2−. The results from CO2-TPD and in situFT-IR analyses indicated that benzyl alcohol could be efficiently activated at the surface base sites on the LDH viasurface coordination to form a metal-alkoxide intermediate. Here, the intermediate could be more easily oxidized by O2−to form benzaldehyde. Finally, a possible mechanism based on the cooperation effect between the alloy NPs and the surface basic sites on the LDH was proposed to illustrate the photocatalytic process.

Two click-based porous organic polymers (CPP-1 and CPP-2) are readily synthesized through a click reaction. Using CPP-1 and CPP-2 as supports, palladium nanoparticles (NPs) with uniform and dual distributions were prepared through H2and NaBH4reduction routes, respectively. Ultrafine palladium NPs are effectively immobilized in the interior cavities of polymers. The coordination of 1,2,3-triazolyl to palladium and the confinement effect of polymers on palladium NPs are verified by solid-state 13C NMR and IR spectra, XPS analyses, EDX mapping, and computational calculation. The steric and electronic properties of polymers have a considerable influence on the interaction between polymers and palladium NPs, as well as the catalytic performances of NPs. The ultrafine palladium NPs with uniform distribution exhibit superior stability and recyclability over palladium NPs with dual distributions and palladium on charcoal in the hydrogenation of nitroarenes, and no obvious agglomeration and loss of catalytic activity were observed after recycling several times. The excellent performances mainly result from synergetic effects between palladium NPs and polymers.

A series of ten acylhydrazine‐ and acylhydrazone‐type ligands were designed and synthesized. Their electronic and steric properties were easily modified and tuned by varying the substituents in the vicinity of the acylhydrazine and acylhydrazone units. The effect of ligands on the catalytic activity of Ullmann reactions was assessed by using a combination of these ligands with CuI. The catalytic system is very efficient for the C–N coupling reaction of azoles with aryl and heteroaryl bromides.

The donor–acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor–acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron–hole pairs that could be separated by donor–acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O2to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor–acceptor pairs in the COF and their interactions to the reactants and intermediates.

The applied catalytic system can be recycled at least four times.

The used PYIM ligand is prepared in a three‐step synthesis.

Benzoic acid N′‐phenylhydrazide displays the best activity among ten ligands tested in the title Ullmann reaction of bromoacetophenone (I) with imidazole.