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Single-atom site catalysts (SACs) have made great achievements due to their nearly 100% atomic utilization and uniform active sites. Regulating the surrounding environment of active sites, including electron structure and coordination environment via atom-level interface regulation, to design and construct an advanced SACs is of great significance for boosting electrocatalytic reactions. In this review, we systemically summarized the fundamental understandings and intrinsic mechanisms of SACs for electrocatalytic applications based on the interface site regulations. We elaborated the several different regulation strategies of SACs to demonstrate their ascendancy in electrocatalytic applications. Firstly, the interfacial electronic interaction was presented to reveal the electron transfer behavior of active sites. Secondly, the different coordination structures of metal active center coordinated with two or three non-metal elements were also summarized. In addition, other atom-level interfaces of SACs, including metal atom–atom interface, metal atom-X-atom interface (X: non-metal element), metal atom-particle interface, were highlighted and the corresponding promoting effect towards electrocatalysis was disclosed. Finally, we outlooked the limitations, perspectives and challenges of SACs based on atomic interface regulation.

Summary In the history of synthesis, people applied heat, electricity, and other means to expand the synthesis field, thus promoting the construction of the magnificent material world. However, with the time passing, beyond the synthetic methods used in a laboratory, are there other solutions? The arising concept of single-atom catalysts (SACs) expands synthesis to the atomic scale. Through the fine-tuned and atom-level methods, people can obtain a catalytic scheme completely different from homogeneous catalysis, ultimately realizing the high-efficient, economical, and precise catalysis of synthesis. In this review, we focus on the latest development of synthesis involving SACs in the past 10 years. By discussing the reaction mechanism and combining the advantages of SACs, the structure-activity relationship is clarified, and the catalytic nature and general uses of SACs in the synthesis are summarized. Finally, we propose the opportunities, challenges, and development directions of SACs in organic synthesis in the next step.

Single-atom site catalysts (SACs) and two-dimensional materials (2DM) have gradually become two hot topics in catalysis over the past decades. Their combination with each other can further endow the derived SACs with extraordinary properties such as high loading, identical active sites, uniform coordination environment, distinctive metal-support interaction, and enhanced catalytic activities. In this review, we highlight the recent development in this specific research topic according to the types of substrates and focus on their applications in energy conversion field. Additionally, we also make a brief introduction to the synthesis and characterization methods for SACs supported on 2DM (SACs/2DM). Finally, the challenges and perspectives are summarized based on the current development status. It is believed that this work will make contributions to the rational design and fabrication of novel SACs/2DM, promoting their practical energy applications in the future.

Hyperspectral image (HSI) has been an important valuable information source for many remote sensing applications due to its rich spectral information. However, limited by existing imaging system, the spatial resolution of HSI greatly limits its practical applications. In this paper, in order to deal with the challenge of feature extraction and super-resolution of HSI, a progressive split-merge super-resolution (PSMSR) framework is proposed to overcome the inherent resolution limitations, which apply a multi-level split strategy from the task level, spectral level and feature level. Within this framework, a gradient-guided group-attention network (GGAN) is designed to extract the spatial-spectral features and reconstruct realistic texture, where group attention block (GAB) aims to increase the distinguishing ability of spectral channels, and gradient information is fully fused in the reconstruction process to promote sharp edges and realistic texture. Compared with current state-of-the-art CNN-based SR methods, the proposed method achieves significant improvement in six evaluation metrics and visual quality on multiple and diverse scenes, and it obtains a higher classification accuracy in classification experiment and gets better SR results on real data, which proves that our method can effectively improve the spatial resolution while preserving the spectral correlation. In addition, a series of ablation experiments prove the effectiveness of each component of our method.

As one of the most promising fluorescent nanomaterials, carbon dots (CDs) have been extensively studied for their fluorescent properties in solution. However, research on the synthesis of multicolor solid-state fluorescence (SSF) CDs (from blue to red) is rarely reported. Herein, we used o-phenylenediamine, m-phenylenediamine and p-phenylenediamine with dithiosalicylic acid (DTSA) in the solvothermal reaction using acetic acid as a solvent to obtain aggregation-induced emissive (AIE) CDs of red (620 nm), green (520 nm), and blue (478 nm), respectively. XPS spectra and TEM image show that with the red-shift of luminescence, the particle size and content of C = O of the CDs gradually increases. Finally, based on the non-matrix solid-state multicolor luminescence characteristics of CDs, the application of white light LED devices is realized. Besides, based on the fat-soluble properties of CDs, fingerprint detection applications are realized.

Proton-exchange membrane fuel cells (PEMFCs) are a promising new energy-conversion technology due to their safe and environmentally friendly characteristics in a wide range of operating conditions. However, catalysis of the acidic oxygen reduction reaction (ORR) at the cathode is the main obstacle. In this regard, platinum-free single-atomic-site catalysts (SACs) with designable active sites are a potential solution. Unlike catalysts for the ORR in alkaline media that have been widely explored, there is still a gap between the performance of SACs and Pt-based catalysts in acidic media. In this review, we introduce the latest progress of SACs in acidic ORR. SACs consist of metal centers and substrates. We conclude controllable synthetic strategies for SACs from single-atomic sites and substrate design, discuss the relationship between the structure of single-atom sites and acidic ORR performance of SACs at the atomic level, and propose challenges and perspectives of SACs in acidic ORR.

Summary Atomically dispersed Fe–N–C catalyst has shown great performance in the CO2-to-CO conversion, yet the high CO selectivity is achieved only within a rather narrow potential range, which cannot well meet the requirements for the following CO dimerization or hydrogenation. Here, we developed a hydrogen-pyrolysis etching strategy to precisely manipulate the uncoordinated N dopants in the Fe–N–C catalyst. This strategy could preferentially eliminate pyridinic and pyrrolic N atoms while leaving graphitic N. The resulting catalyst gave a CO faradaic efficiency (FECO) above 90% over a broad window from −0.3 to −0.8 V (versus RHE) (in particular, FECO > 97% at −0.6 V). In situ ATR-SEIRAS and first-principle calculations further revealed that this strategy can not only suppress the parasitic H2 generation but also promote CO2 activation and protonation with the assistance of co-adsorbed H2O on the “atomic interface” of “FeN4/graphitic N.”

Tin phosphide (Sn4P3) that identified as a potential anode for sodium ion batteries (SIBs) based on its high theoretical specific capacity mostly confronts with the huge challenges in rapid capacity decay, severe volume evolution and weak diffusion kinetics upon cycling. It is of great theoretical and practical significance to develop the multilevel structured metal phosphide anode in high performance SIBs systems. Herein, we construct a nanochain-like architecture built from hollow yolk-shell Sn4P3@C nanospheres (Sn4P3@CNF) by electrospinning method and phosphorization treatment, in which all hollow Sn4P3 nanospheres are uniformly chained to one dimensional (1D) carbon nanofibers, forming a necklace-like hybrid conductive construction. The synergistic effect between hollow Sn4P3 nanospheres and nanochain architecture not only offers unblocked transfer channels for Na+ and accelerates the long-distance electronic transmission, but also guarantees excellent electrode kinetics and accommodates volume expansion. The Sn4P3@CNF electrode delivers a highly reversible discharge capacity of 297.6 mAh g−1 at 1 A g−1 after 1750 cycles, 250.6 mAh g−1 at 2 A g−1 after 4700 cycles, as well as ultrastable cycling durability up to 14000 cycles with a capacity of 157.8 mAh g−1 even at a high rate of 5 A g−1. These results demonstrate the greatest cyclability reported so far on Sn4P3-based anodes for SIBs. Meanwhile, the consecutive CV measurement further confirms a capacitive electrochemical redox behavior of Sn4P3@CNF upon cycling. More interestingly, the Sn4P3@CNF electrode displays the superior cycling stability and rate capability in sodium ion full cells as combined with a high-voltage Na3V2(PO4)3 cathode, where the full cell delivers an initial discharge capacity of 286.4 mAh g−1 and maintains a 67.2% capacity retention after 160 cycles at 1 A g−1, making it a great potential for practical application in SIBs systems.

The leaching concentrations of different metals in stainless steel pickling residue (SSPR) were determined and the toxic metals were treated using Na2S∙xH2O, FeSO4∙6H2O, and phosphoric acid. A modified European Community Bureau of Reference (BCR) sequential extraction was used to identify the speciation of the concerned metals. Results showed that SSPR contains a large amount of Ca (58.41%), Fe (29.44%), Cr (3.83%), Ni (2.94%), Mn (2.82%) and some of Al, Cu, Mg, Zn. Among them, Cr and Ni were the most toxic metals in SSPR, thus the raw SSPR falls into hazardous waste category due to the leaching amount of Cr. In addition, the leached Cr was identified as Cr6+ (MgCrO4) in the waste. BCR test revealed that risk assessment code (RAC) of Cr and Ni were 33.29% and 61.7%, indicating they posed “high” and “very high” risk to the environment, respectively. After fixing by Na2S∙xH2O and FeSO4∙6H2O, the leaching concentrations of Cr and Ni were less than 1.5 and 0.5 mg/L, respectively. After fixing by Na2S∙xH2O and FeSO4∙6H2O the treated SSPR can be safely reused as roadbed materials, concrete and cement aggregates. This study provides a useful implication in treatment and beneficial reuse of heavy metal-containing hazardous wastes.

Summary The concept of chemical bond polarity is well recognized; however, its tunability and corresponding effects on heterogeneous catalysis have never been discussed. Here, we report a method to control the polarity of the Cu-O bond in the heterogeneous Cu catalyst, and thus tune its activity for the hydroboration reaction. By synthetic procedure control, single-atomic-site Cu catalysts on ceria with more ionic Cu-O bonds (Cu1-O(I)/CeO2) and with more covalent Cu-O bonds (Cu1-O(C)/CeO2) can be obtained, respectively. The more ionic Cu-O bond makes Cu1-O(I)/CeO2 display a much higher activity than Cu1-O(C)/CeO2 in selective hydroboration of diverse alkynes with no additives, producing versatile vinylboronate compounds. The enhanced activity stems from the more ionic Cu-O bond facilitating the formation of key intermediate copper ethoxide species by dissociating ethanol molecules. These results may improve our understanding of the correlation between the nature of chemical bonds and catalytic properties and lead to better-performing heterogeneous catalysts.

The measurement signal from the inner flush-mounted electrostatic sensor includes both induced charge signal and transferred charge signal. The extraction of induced charge signal from the mixed signals is of great significance to the solid phase velocity measurement. In this paper, a method of extracting induced charge signal based on the waveform characteristic in time domain is proposed. In the calibration experiment of the belt-style electrostatic velocity measurement rig, the mean absolute percentage error and the mean relative standard deviation (1.30%/1.01%) are lower than the direct cross-correlation method (4.81%/5.71%) and the Empirical Mode Decomposition (EMD-based) method (2.55%/2.38%), moreover, the average signal-to-noise ratio (SNR) of the proposed method is the greatest. In the experiment of gas-solid two-phase flow rig, the average correlation coefficient and the mean relative standard deviation are 0.77 and 2.46%, which are better than the direct cross-correlation (0.48/2.87%) and the Discrete Wavelet Transform (DWT) (0.74/2.69%).

Summary As a new, emerging class in catalysis field, single-atomic-site catalysts (SASCs) have displayed outstanding activities, selectivities, and stabilities in a range of important catalytic reactions. The compositions and structures of SASCs have a great impact on catalytic performances; therefore, the central task is to rationally manipulate the structures with atomic-level precision, and thereupon to design different active sites to promote the overall performances. Here, we compare SASCs with clusters/nanoparticles in term of their catalytic behaviors, and systematically interpret the impacts of the microscopic structures of SASCs on catalytic performances. Subsequently, we summarize the reports on synergistic catalysis over diatomic, multiatomic sites, single-atom alloys, and atomic interfaces, and highlight the great significance of in situ characterization technologies for monitoring the active sites. Finally, we discuss the limitations, development trends, and future challenges of SASCs, and present an outlook on further constructing more sophisticated active sites for more complex catalytic reactions.

The development of new rechargeable metal-ion (Na+, K+ or Al3+) batteries (MIBs) with high performance would break the global monopoly on lithium-ion batteries (LIBs). However, because of the larger ionic sizes of Na+, K+ and Al3+ in comparison to Li+, the requirement of electrode materials with suitable tunnels for these metal ions insertion/extraction is more stringent. Over years, a large number of electrodes materials are studied and optimized for a specific type of MIB, yet a universal suitable candidate that can be applied for all of them still remains scarce. Here we report a solvothermal method coupled with the sulfidation strategy to engineer novel multi-layer architecture of FeS2@C hybrids which is constructed from building blocks of ultrathin nanoflakes, favoring fast electrochemical energy storage. Electrochemical measurements show that the multi-layer structured FeS2@C hybrids enables reversible sodium-, potassium- and aluminum-ion storage process with high specific capacities, excellent rate capability and outstanding cycling stability. We hope that this research will inspire new ideas for developing various electrode materials for high-performance MIBs.

The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are critical processes for many energy conversion technologies, where efficient catalyst plays a key role in these reactions. Here we report a novel in situ strategy to embed Co9S8 nanoparticles (NPs) into nitrogen and sulfur codoped hollow porous carbon (Co9S8@N-S-HPC). In this strategy, the ZIF-8 surface is firstly decorated by cobalt thiourea, and then coated with a shell of polymeric resorcinol-formaldehyde, followed by a high temperature pyrolysis treatment. The resulting Co9S8@N-S-HPC shows comparable catalytic activity for ORR compared with commercial 20 wt% Pt/C catalyst and superior long-term stability under alkaline conditions. Simultaneously, Co9S8@N-S-HPC also exhibits an excellent HER activity with low onset overpotential of 68 mV, a small Tafel slope of 78 mV per decade and a long-term durability in alkaline medium. First-principles calculations reveal that Co9S8 particle can anchor in N-S-HPC via a Co-S bond and enhance the binding of Co9S8 and N-S-HPC. The N-S-HPC can affect the electronic structure of supported Co9S8 strongly. The combined experimental and theoretical investigation show the outstanding ORR and HER performances of Co9S8@N-S-HPC are attributed to its unique nanostructure and synergistic interactions between Co9S8 NPs and N-S-HPC.

This article presents an original study on the feasibility of reuse fly ash (FA) solidified/stabilized stainless steel pickling residue (SSPR). SSPR was characterized using different leaching procedure and solidified/stabilized using aluminum potassium sulfate dodecahydrate (KAl(SO4)2.12H2O) amended fly ash. A modified four-step Community Bureau of Reference (BCR) sequential leaching test and risk assessment code (RAC) was employed to evaluate the potential hazards of metals in SSPR. Results show that SSPR mainly consists of sulfates and heavy metals. The major elements are Ca and Fe, with the total amount of 191,600 and 122,400 mg/kg. Cr is the most notable metal with a total amount of 22,500 mg/kg. Its concentrations in HJ/T 299 and HJ/T 300 extracts are 28.6 and 285 mg/L respectively. Another metal that is of some concern is Ni, its concentration in HJ/T 300 extract is 229 mg/L and total content in the residues is 10,690 mg/kg. The RAC of four list heavy metals are: Ni (61.36%) > Zn (43.48%) > Cr (20.64%) > Cu (19.83%). Therefore, SSPR has a higher potential to be hazardous to the environment. After treatment by 10% of KAl(SO4)2.12H2O with 40% of FA2 (10KA40FA2), the concentration of Cr is 7.9 mg/L in HJ/T 299 extract and 12.68 mg/L in HJ/T 300 extract. While these two values for Ni is 0 and 14.34 mg/L. The RAC of the metals after treatment by 10KA40FA2 followed the order of Ni (20.38%) > Zn (10.59%) > Cu (8.54%) > Cr (7.71%). The unconfined compression strength (UCS) tests showed that the 7-d UCS of the 10KA40FA2 remolded sample achieved 3556.2 kPa which was much higher than that of raw SSPR remolded sample of 1746.7 kPa.

In this work, we use finite element simulations to investigate the influence of cooling water temperature on the axial growth rate of the large single crystal diamond with the convex shape catalyst under high pressure and high temperature (HPHT) conditions. The simulation results show that adjusting the axial cooling water temperature can change the axial temperature gradient and the convection velocity in the catalyst, which lead to the different axial growth rate of the diamond crystal. The different axial growth rates lead to the change of crystal morphology. Simulation results are confirmed by our synthesis experiments. Morphology and structural properties of the synthesized diamonds are characterized by optical microscope and Raman spectrum. This result not only provides a theoretical explanation for the regulation mechanism of cooling water on the axial growth rate of diamond, more importantly, adjusting the axial cooling water can further improve the morphology of the synthetic diamond, which is of great guiding significance in the commercial production of diamond.

Summary The electrochemical direct synthesis of hydrogen peroxide (H2O2) is significant but still challenging because of the lack of highly selective and active catalysts. Here, we report the synthesis of hollow nanospheres constructed by atomically dispersing platinum in amorphous CuSx support (h-Pt1-CuSx) with a high concentration of single atomic Pt sites (24.8 at%), and this catalyst can consistently reduce O2 into H2O2 with selectivity of 92%–96% over a wide potential range of 0.05–0.7 V versus RHE in HClO4 electrolyte. Scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy confirmed the atomically isolated form of Pt with a low valance of +0.75. An electrochemical device that can synthesize H2O2 directly from H2 and O2 is fabricated with H2O2 productivity as high as 546 ± 30 mol kgcat−1 h−1. The well-defined and high-concentration single atomic Pt sites result in ultrahigh productivity of H2O2.

Platinum (Pt)-based catalysts have been unanimously considered the most efficient catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). Unfortunately, the exorbitant cost of Pt hampers the widespread adoption and development of PEMFCs. Scientists have devoted tremendous efforts to achieving higher catalytic activity with less Pt usage by constructing delicate nanostructures. Substituting Pt with cheaper metals may be a feasible solution but suffers from a relatively low intrinsic activity. Recently, single-atom catalysts (SACs), which possess the highest metal utilization and excellent activity because of the minimum size of metal and unique coordination structure, are developing rapidly and have been regarded as a potential alternative to Pt-based materials. Here, we review the development of conventional Pt- and nonprecious-metal-based ORR catalysts and summarize recent achievement in SACs for the ORR. A brief perspective on the remaining challenges and future directions of SACs is also presented.

In this work, we investigate the effect of cavity size on the change of the physical fields of diamond synthetic cavity and the mechanism of large cavity to improve the growth rate of the large single crystal diamond under high pressure and high temperature (HPHT) conditions. Finite element method (FEM) is used to simulate the temperature and convection field of the Φ15 and Φ10 cavity assemblies. Temperature simulation results indicate that the increase of cavity size leads to the increase of axial and radial temperature difference of catalyst. Convection simulation results show that the convection velocity and strength of the catalyst increases significantly with the increase of the cavity size. The increase of temperature difference and convection velocity and strength lead to the acceleration of crystal growth. The simulation results were perfectly validated by the synthetic experiments. This work not only elucidates the mechanism of large cavity to improve the growth rate, but also provides a theoretical reference for the application of the large-size cavity in the diamond synthetic industry.

The effects of various CeO2 additions on the electrochemical properties of lithium-sulfur batteries have been studied over synthesizing the sulfur-host matrix with unique surface appearance. It has been revealed that the appropriate additions of CeO2 (0.70–3.65 wt%) to the porous carbon were beneficial to enhance the cycle performance. The polar metal oxide CeO2 can chemically adsorb the sulfur species and promote redox reaction through catalysis properties. Meanwhile, the porous carbon can enhance the conductivity of cathode and form a favorable physical barrier to block the diffusion of polysulfide with abundant pore structures. As results, the CS-CeO2 composite (with 1.84 wt% CeO2) exhibits significantly improved electrochemical performance as a cathode material for Li-S batteries. The initial discharge capacity of assembled battery is as high as 1434.1 mAh g−1 at 0.05 C and the discharge capacity retains 873.6 mAh g−1 with a low decay rate of 0.077% per cycle after 200 cycles at 0.2 C. When the area sulfur content is as high as 4.53 mg cm−2, the CS-Ce2 cathode still retains a discharge capacity of 572.3 mAh g−1 at 1 C after 100 cycles.

Sodium ion batteries (SIBs) have achieved much attention and actively developed. Among possible anode materials of SIBs, nanosized metallic antimony is one of the most promising ones. However, the large volume changes of Sb and insufficient cyclability still remain a huge challenge for the large-scale applications. Herein, the effect of different Sb contents (named as C@Sb, C@Sb-L and C@Sb-H) on electrode performance, morphology, stability, and sodium storage mechanism has been systematically evaluated for the first time by a feasible electrospinning technique. As a result, the as-prepared C@Sb nanofibers exhibit excellent sodium storage performance with high-rate performance of 272.1 mAh g−1 at 20 A g−1, large reversible discharge capacity of 437.6 mAh g−1 after 300 cycles at 1 A g−1 and ultralong cycling life of 4000 cycles at 5 A g−1, such a cycling performance and high-rate capability for the C@Sb anode has rarely been reported. The significantly enhanced performance is ascribed to the synergetic effects between the well-dispersed ultrafine Sb nanoparticles and the N-rich 3D conductive carbon network structure. This homogeneously dispersed structure of ultrafine Sb nanoparticles encapsulated in the carbon network can dramatically improve the volume change and particle aggregation of Sb during ultralong charge/discharge process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sb anode. In addition, the full cell of Na3V2(PO4)3@C//C@Sb shows a high output potential of about 2.75 V and a discharge capacity of 264.3 mAh g−1 after 500 cycles at 1 A g−1. Those promising results should provide the basis for the potential large-scale application of Sb-based materials as high-performance anode for SIBs.

This article presents an original study on stabilization of heavy metals in SSPS using sodium sulfide hydrate. The speciation and pH dependent leaching of the target heavy metals (Cr, Cu, Ni and Zn) based on GB 5085.3 and GB 16889 in both raw SSPS and stabilized products were examined. Results indicated that Cr and Ni are the two main toxic elements in SSPS. The BCR sequential extraction indicated that 55.2% of Cr in raw SSPS exist as Fe-Mn oxides, while water soluble Cr which is mainly consists of Cr(VI) accounts for 3.50%. After stabilization, the residual fraction Cr reached to more than 60% and Cr(VI) was not detected. The leaching concentration of Ni meets the limit of reuse SSPS, meanwhile, the sum proportion of sulfides and residual Ni increased from 8.68% to a maximum value of 31.82%. pH dependent leaching tests expound that the leaching concentrations of Cr, Ni, Cu and Zn are significantly high at pH = 2. The leaching concentrations of Cu, Ni and Zn are extremely low when pH varied from 7 to 13. The best stabilization pH span is from 5.5 to 10 for SSPS. The XRD and SEM-EDS analysis showed that the major compounds in treated SSPS were bassanite and plaster of Paris (POP). Since the extreme conditions such as pH = 2 or pH = 13 are infrequently, the stabilized SSPS can be safely reused in roadbed materials, bricks and concrete aggregates based on China HJ/T 301.