Photothermal-Enhanced S-Scheme Heterojunction of Hollow Core-Shell FeNi2 S4 @ZnIn2 S4 toward Photocatalytic Hydrogen Evolution.

Herein, guided by the results of density functional theory prediction, the study rationally designs a hollow core-shell FeNi2 S4 @ZnIn2 S4 (FNS@ZIS) Step-scheme (S-scheme) heterojunction for photocatalytic H2 evolution with photothermal-assisted. The hollow FNS spheres offered substrate for coating the ZIS nanosheets, which can inhibit ZIS nanosheets from agglomerating into pellet, enrich the active site, increase specific surfaces, and raise the light absorption. Notably, due to its excellent photothermal properties, FNS core generated heat unceasingly inside under visible-light irradiation and effectively prevent the heat loss of the reaction system, which increased the local temperature of photocatalysts and thus accelerated the charge migration. In addition, the S-scheme heterojunction construction via in situ growth has a tight interface, which can facilitate the separation and transfer of carriers and achieve high redox potential. Owning to the distinctive construction, the hollow core-shell FNS@ZIS S-scheme heterojunction show extraordinary stability and photocatalytic H2 evolution rate with 7.7 mmol h-1  g-1 , which is ≈15.2-fold than pristine ZIS. Based on the double evidence of theoretical predictions and experimental confirmations, the photothermal effect and electron transfer mechanism of this innovative material are investigated in depth by the following infrared thermography technology and deep DFT calculations.

Oxygen defect-mediated NiCo2O4 nanosheets as the electrode for pseudocapacitors with improved rate capability.

Transition metal oxide-based supercapacitors have attracted much attention due to their high theoretical specific capacitances. However, due to an insufficient utilization ratio and poor intrinsic conductivity of active materials, the rate performance of these electrodes is usually low. Herein, oxygen defect-mediated NiCo2O4 nanosheets with enhanced electrical conductivity (1.9 S m-1vs. 0.2 S m-1 of original NiCo2O4 NSs) are fabricated using a post NaBH4 reduction strategy (denoted as r-NiCo2O4 NSs). The derived r-NiCo2O4 materials have sheet-like morphology, increased oxygen defects and low valence metal species, and an unprecedented rate capability comparable to that of carbon-based electrode materials, with a satisfactory capacitance of 1812 F g-1 and 91.5% retention at 20 A g-1. The general strategy can be extended to other transition metal oxides to construct enhanced conductivity electrodes for related energy storage and conversion devices.

Charge-orbital synergistic engineering of TM@Ti3C2O1-xBx for highly selective CO2 electrochemical reduction.

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti3C2-MXene-based single TM atom electrocatalysts with a doped boron (B) atom (TM@Ti3C2O2-xBx, TM is V, Cr, Mn, Fe, Co or Ni, x = 0.11) are proposed for achieving a high performance catalytic CO2 reduction reaction (CO2RR). The results reveal that the doped B atom involves in the adsorption reaction of CO2 molecules and CO intermediates in the CO2RR. The TM-to-C and B-to-C π-back bonding contribute to the activation of the CO2 molecules and CO intermediates in the CO2RR. Enough electrons from the single TM atom and B atom occupied orbitals can be injected into the CO2 molecules and *CO intermediates through direct bonding interactions, which effectively alleviates the difficulty of the first hydrogenation reaction step and further helps CO reduction towards CH4. The calculated values of ΔG for the first hydrogenation reaction and the formation of *CHO on Ti3C2O2-xBx are significantly smaller than those of other single-atom catalysts (SACs). Fe@Ti3C2O2-xBx is found to have the highest electrocatalytic activity with a limiting potential of ∼0.40 V and exhibits a high selectivity for obtaining CH4 through the CO2RR compared with the hydrogen evolution reaction. This work is expected to open a research path for engineering the charge-orbital state of the innate atoms of a substrate based on mechanistic insights, which guides the rational design of highly selective MXene-based CO2RR electrocatalysts.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis.

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Facile synthesis of core-shell Co-MOF with hierarchical porosity for enhanced electrochemical detection of furaltadone in aquaculture water.

Metal-organic frameworks (MOFs) exhibited huge application potential in electrochemical analysis field, how to facilely and effectively boost the electrochemical sensing activity of MOFs materials still face enormous challenges. In this work, core-shell Co-MOF (Co-TCA@ZIF-67) polyhedrons with hierarchical porosity was easily synthesized via simple chemical etching reaction by selecting thiocyanuric acid as the etching reagent. Benefiting from the introduction of mesopores and thiocyanuric acid/Co2+ complex on the surface of ZIF-67 frameworks, the property and functions of the pristine ZIF-67 was seriously tailored. Compared with the pristine ZIF-67, the as-resulted Co-TCA@ZIF-67 nanoparticles displayed greatly enhanced physical adsorption capacity and electrochemical reduction activity toward the antibiotic drug furaltadone. As a result, a novel furaltadone electrochemical sensor with high sensitivity was fabricated. The linear detection range was from 50 nM to 5 µM with sensitivity of 110.40 µA-1 µM-1 cm-2 and detection limit of 12 nM. This work demonstrated chemical etching strategy is truly a facile and effective way to modify the electrochemical sensing performance of MOFs-based materials, and we believed the chemically etched MOFs materials will play a stronger role in terms of food safety and environmental conservation.

Tailoring Advanced N-Defective and S-Doped g-C3 N4 for Photocatalytic H2 Evolution.

Although challenges remain, synergistic adjusting various microstructures and photo/electrochemical parameters of graphitic carbon nitride (g-C3 N4 ) in photocatalytic hydrogen evolution reaction (HER) are the keys to alleviating the energy crisis and environmental pollution. In this work, a novel nitrogen-defective and sulfur-doped g-C3 N4 (S-g-C3 N4 -D) is designed elaborately. Subsequent physical and chemical characterization proved that the developed S-g-C3 N4 -D not only displays well-defined 2D lamellar morphology with a large porosity and a high specific surface area but also has an efficient light utilization and carriers-separation and transfer. Moreover, the calculated optimal Gibbs free energy of adsorbed hydrogen (ΔGH* ) for S-g-C3 N4 -D at the S active sites is close to zero (≈0.24 eV) on the basis of first-principle density functional theory (DFT). Accordingly, the developed S-g-C3 N4 -D catalyst shows a high H2 evolution rate of 5651.5 µmol g-1  h-1 . Both DFT calculations and experimental results reveal that a memorable defective g-C3 N4 /S-doped g-C3 N4 step-scheme heterojunction is constructed between S-doped domains and N-defective domains in the structural configuration of S-g-C3 N4 -D. This work exhibits a significant guidance for the design and fabrication of high-efficiency photocatalysts.

Correction: Additive-mediated intercalation and surface modification of MXenes.

Correction for 'Additive-mediated intercalation and surface modification of MXenes' by Jing Zou et al., Chem. Soc. Rev., 2022, DOI: 10.1039/d0cs01487g.

Additive-mediated intercalation and surface modification of MXenes.

2D carbides and nitrides of transition metals, also known as MXenes, are an emerging class of 2D nanomaterials that have shown excellent performances and broad application prospects in the fields of energy storage, catalysis, sensing, electromagnetic shielding, electronics and photonics, and life sciences. This unusual diversity of applications is due to their superior hydrophilicity and conductivity, high carrier concentration, ultra-high volumetric capacitance, rich surface chemistry, and large specific surface area. However, it is difficult to make MXenes with the desired surface functional groups that deliver high reactivity and high stability, because most MXenes are extracted from ceramics (MAX phase) by an etching process, where a large number of metal atoms are inevitably exposed on the surface, with other anions and cations embedded uncontrollably. The exposed metal atoms and implanted ions are thermodynamically unstable and readily react with trace oxygen or oxygen-containing groups to form the corresponding metal oxides or degrade chemically, resulting in a sharp decline in activity and loss of excellent physicochemical properties. The addition of certain synergistic additives during the intercalation and chemical modification of surface functional groups under non-hazardous conditions can result in stable and efficient MXene-based materials with exceptional optical, electrical, and magnetic properties. This review discusses several such methods, mainly additive-mediated intercalation and chemical modification of the surface functional groups of MXene-based materials, followed by their potential applications. Finally, perspectives are given to discuss the future challenges and promising opportunities of this exciting field.

Shedding light on the energy applications of emerging 2D hybrid organic-inorganic halide perovskites.

Unique performance of the hybrid organic-inorganic halide perovskites (HOIPs) has attracted great attention because of their continuous exploration and breakthrough in a multitude of energy-related applications. However, the instability and lead-induced toxicity that arise in bulk perovskites are the two major challenges that impede their future commercialization process. To find a solution, a series of two-dimensional HOIPs (2D HOIPs) are investigated to prolong the device lifetime with highly efficient photoelectric conversion and energy storage. Herein, the recent advances of 2D HOIPs and their structural derivatives for the energy realms are summarized and discussed. The basic understanding of crystal structures, physicochemical properties, and growth mechanisms is presented. In addition, the current challenges and future directions to provide a roadmap for the development of next generation 2D HOIPs are prospected.

The interactions between chiral analytes and chitosan-based chiral stationary phases during enantioseparation.

The goal of the present study was to disclose the interactions between chitosan-type chiral selectors (CSs) and chiral analytes during enantioseparation. Hence, six chitosan 3,6-bis(phenylcarbamate)-2-(cyclohexylmethylurea)s were synthesized and characterized. These chitosan derivatives were employed as CSs with which the corresponding coated-type chiral stationary phases (CSPs) were prepared. According to the nature and position of the substituents on the phenyl group, the CSs and CSPs were divided into three sets. The counterparts of the three sets were 3,5-diMe versus 3,5-diCl, 4-Me versus 4-Cl and 3-Me versus 3-Cl. The enantioseparation capability of the CSPs was evaluated with high-performance liquid chromatography. The CSPs demonstrated a good enantioseparation capability to the tested chiral analytes. In enantioselectivity, the CSs with 3,5-diCl and with 4-Me roughly were better than the counterparts with 3,5-diMe and with 4-Cl respectively. The CS with 3-Me enantiomerically recognized more analytes than the one with 3-Cl, but showed lower separation factors in more enantioseparations. The acidity of the amide hydrogen in the phenylcarbamates was investigated with density functional theory calculations and 1H NMR measurements. The trend of the acidity variation with different substituents on the phenyl group was confirmed by the retention factors of acetone on the CSPs. Compared the retention factors of analytes on every set of the counterparts, the formation of hydrogen bond (HB) in enantioseparation could be outlined as follows: when the CSs interacted with chiral analytes without reactive hydrogen but with lone paired electrons, the carbamate N‒Hs in the CSs were HB donors and the analytes were HB acceptors; if the CSs interacted with analytes with a reactive hydrogen, the role of the CSs in HB formation was related to the acidity of the reactive hydrogen; the patterns of HB formation between the CSs and analytes were also impacted by compositions of mobile phases, in addition to the nature, number and position of substituents on the phenyl group. Based on the discussion, chiral recognition mechanism could be understood in more detail. Besides, the strategy to improve enantioseparation capability of a CSP by introducing a substituent onto phenyl group was clarified and further comprehended.

Atomic-Scale Superlubricity in Ti2CO2@MoS2 Layered Heterojunctions Interface: A First Principles Calculation Study.

The two dimensional (2D)-layered transition-metal carbides and nitrides (MXene) have been proved to be an excellent solid lubricant owing to their high mechanical strength, low shearing strength, and self-lubricating properties. However, the interfacial friction behavior between Ti n+1C n (n = 1, 2) MXene and its heterogeneous system is not thoroughly exploited yet. Here, four types of van der Waals structures (Ti2CO2@Ti2CO2, Ti3C2O2@Ti3C2O2 MoS2@MoS2, and Ti2CO2@MoS2) have been investigated by density functional theory (DFT) calculations. The results exhibit that Ti2CO2@MoS2 possesses the lowest sliding energy barrier around 0.015 eV/oxygen(O) atom compared with the other three constructed models. Therefore, this work mainly focuses on the inner relation of Ti2CO2@MoS2 interlayer friction behaviors and its attributing factors, including normal force and charge density. The DFT analysis shows that the roughness of the potential energy corrugated plane is positively correlated with normal force and predicted the ultralow friction coefficient (µ) at 0.09 when sliding along the minimum energy potential route. Moreover, friction coefficient fluctuates at the normal force less than 10 nN determined by the combined effect of interfacial charge interlock and redistribution. This work reveals the intrinsic connection between the friction and charge interaction at heterogeneous interfaces.

Integrated prodrug micelles with two-photon bioimaging and pH-triggered drug delivery for cancer theranostics.

Nanodrug carriers with fluorescence radiation are widely used in cancer diagnosis and therapy due to their real-time imaging, less side effect, better drug utilization as well as the good bioimaging ability. However, traditional nanocarriers still suffer from unexpectable drug leakage, unsatisfactory tumor-targeted drug delivery and shallow imaging depth, which limit their further application in cancer theranostics. In this study, an integrated nanoplatform is constructed by polymeric prodrug micelles with two-photon and aggregation-induced emission bioimaging, charge reversal and drug delivery triggered by acidic pH. The prodrug micelles can be self-assembled by the TP-PEI (DA/DOX)-PEG prodrug polymer, which consists of the two-photon fluorophore (TP), dimethylmaleic anhydride (DA) grafted polyethyleneimine (PEI) and polyethylene glycol (PEG). The PEG segment, DOX and DA are bridged to polymer by acid cleavable bonds, which provides the micelles a 'stealth' property and a satisfactory stability during blood circulation, while the outside PEG segment is abandoned along with the DA protection in the tumor acidic microenvironment, thus leading to charge reversal-mediated accelerated endocytosis and tumor-targeted drug delivery. The great antitumor efficacy and reduced side effect of these pH-sensitive prodrug micelles are confirmed by antitumor assays in vitro and in vivo. Meanwhile, these micelles exhibited great deep-tissue two-photon bioimaging ability up to 150 µm in depth. The great antitumor efficacy, reduced side effect and deep two-photon tissue imaging make the TP-PEI (DA/DOX)-PEG prodrug micelles would be an efficient strategy for theranostic nanoplatform in cancer treatment.

Single-Metal Atoms Supported on MBenes for Robust Electrochemical Hydrogen Evolution.

Two-dimensional (2D) photo- and electrocatalysts play a key role in hydrogen production through water splitting, and much efforts have been undertaken to seek a low-cost and efficient alternative candidate to noble-metal Pt. Herein, the method of introducing several different transition-metal atoms to tune the catalytic properties of 2D MBene is proposed. Density functional theory calculations reveal that the H-O bonding strength can be weakened by charge transfer between the oxygen atom and the introduced single-metal atom. The weakening of the bond greatly improves the MBene catalytic activity of hydrogen evolution reaction. Interestingly, the Gibbs free energy (|ΔGH|) of W2B2O2 decreases from |-0.67| to 0.013 eV by embedding a V adatom. This work should initiate 2D material MBene applications in green catalysis and energy sectors.

Two-photon AIE luminogen labeled multifunctional polymeric micelles for theranostics.

Intelligent polymeric micelles with fluorescence imaging feature have been emerged as promising tools for theranostics. However, conventional fluorescent dyes are limited by short wavelength excitation, interference of tissue autofluorescence, limited imaging depth and quenched emission in aggregation state. Methods: We synthesized a novel mPEG-SS-Poly (AEMA-co-TBIS) (mPEATss) copolymer to develop multifunctional polymeric micelles with great AIE feature for cancer therapy and AIE active two-photon bioimaging. The stimuli-responsive behavior and AIE active two-photon cell and tissue imaging as well as in vitro and in vivo antitumor ability of DOX-loaded mPEATss were studied. Results: mPEATss micelles showed excellent AIE active two-photon cell imaging ability and deep tissue imaging ability. Antitumor drug DOX could be encapsulated to form a drug-loaded micellar system with a small diameter of 65 nm. The disassembly and charge-conversion of mPEATss micelles could be triggered by acidic environment, resulting in accelerated drug release and great antitumor efficacy. In vivo, ex vivo imaging and in vivo pharmacokinetic study demonstrated that mPEATss micelles could efficiently accumulate in tumor sites, which ensured ideal anticancer effect. Conclusions: This pH and redox dual responsive and AIE active two-photon imaging polymeric micelles would be a promising candidate for theranostics.

Synergistic additive-mediated CVD growth and chemical modification of 2D materials.

Research on 2D materials has recently become one of the hottest topics that has attracted broad interdisciplinary attention. 2D materials offer fascinating platforms for fundamental science and technological explorations at the nanometer scale and molecular level, and exhibit diverse potential applications for future advanced nano-photonics and electronics. The chemical vapor deposition (CVD) technique has shown great promise for producing high-quality 2D materials with superior electro-optical performance. However, it is difficult to synthesize continuous single-crystal 2D materials with large domain sizes and good uniformity due to the low vapor pressure of their precursors. It has been observed that the addition of selected synergistic additives to the CVD process under mild conditions can result in uniformly large-area and highly crystalline monolayer 2D materials with exceptional optical/electrical properties. Moreover, the 2D material-based devices chemically modified by synergistic additives can achieve superior performances compared to those previously reported. In this review, we compare several typical synergistic additive-mediated CVD growth processes of 2D materials, as well as their superior properties, and provide some perspectives and challenges for the future of this emerging research field.

Waste-wood-derived biochar cathode and its application in electro-Fenton for sulfathiazole treatment at alkaline pH with pyrophosphate electrolyte.

For the first time, a biomass-derived porous carbon cathode (WDC) was fabricated via a facile one-step pyrolysis of recovered wood-waste without any post-treatment. The WDC along with pyrophosphate (PP) as electrolyte were used in electro-Fenton (EF) at pH 8 for sulfathiazole (STZ) treatment. The H2O2 accumulation capacity of WDC was optimized via the following parameters: pyrolysis temperature, applied current and electrolyte. Results showed that the WDC cathode prepared at 900 °C achieved the highest H2O2 accumulation (13.80 mg L-1 in 3 h) due to its larger electroactive surface area (28.81 cm2). Interestingly, it was found that PP decreased the decomposition rate of H2O2 in solution as compared to conventional electrolyte, which resulted in higher H2O2 accumulation. PP allowed operating EF at pH of 8 due to the formation of Fe2+-PP complexes in solution. Moreover, Fe2+-PP was able to activate oxygen to produce OH. In this way, the degradation of STZ took place through four main pathways: 1) via OH from the Fe2+-PP complex, 2) via OH from EF reactions, 3) via surface OH at the boron doped diamond electrode (BDD) and 4) via SO4- from BDD activation. Finally, microtox tests revealed that some toxic intermediates were generated during WDC/BDD/PP EF treatment, but they were removed at the end of the process.

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes.

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 Å and lateral dimensions of about 30 µm × 50 µm were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

Systematic Bandgap Engineering of Graphene Quantum Dots and Applications for Photocatalytic Water Splitting and CO2 Reduction.

Graphene quantum dots (GQDs), which is the latest addition to the nanocarbon material family, promise a wide spectrum of applications. Herein, we demonstrate two different functionalization strategies to systematically tailor the bandgap structures of GQDs whereby making them snugly suitable for particular applications. Furthermore, the functionalized GQDs with a narrow bandgap and intramolecular Z-scheme structure are employed as the efficient photocatalysts for water splitting and carbon dioxide reduction under visible light. The underlying mechanisms of our observations are studied and discussed.

Fabry-Perot Cavity-Enhanced Optical Absorption in Ultrasensitive Tunable Photodiodes Based on Hybrid 2D Materials.

Monolayer two-dimensional (2D) transition metal dichalcogenides (TMDs) show interesting optical and electrical properties because of their direct bandgap. However, the low absorption of atomically thin TMDs limits their applications. Here, we report enhanced absorption and optoelectronic properties of monolayer molybdenum disulfide (MoS2) by using an asymmetric Fabry-Perot cavity. The cavity is based on a hybrid structure of MoS2/ hexagonal boron nitride (BN)/Au/SiO2 realized through layer-by-layer vertical stacking. Photoluminescence (PL) intensity of monolayer MoS2 is enhanced over 2 orders of magnitude. Theoretical calculations show that the strong absorption of MoS2 comes from photonic localization on the top of the microcavity at optimal BN spacer thickness. The n/n+ MoS2 homojunction photodiode incorporating this asymmetric Fabry-Perot cavity exhibits excellent current rectifying behavior with an ideality factor of 1 and an ultrasensitive and gate-tunable external photo gain and specific detectivity. Our work offers an effective method to achieve uniform enhanced light absorption by monolayer TMDs, which has promising applications for highly sensitive optoelectronic devices.

Use of Single-Layer g-C3N4/Ag Hybrids for Surface-Enhanced Raman Scattering (SERS).

Surface-enhanced Raman scattering (SERS) substrates with high activity and stability are desirable for SERS sensing. Here, we report a new single atomic layer graphitic-C3N4 (S-g-C3N4) and Ag nanoparticles (NPs) hybrid as high-performance SERS substrates. The SERS mechanism of the highly stable S-g-C3N4/Ag substrates was systematically investigated by a combination of experiments and theoretical calculations. From the results of XPS and Raman spectroscopies, it was found that there was a strong interaction between S-g-C3N4 and Ag NPs, which facilitates the uniform distribution of Ag NPs over the edges and surfaces of S-g-C3N4 nanosheets, and induces a charge transfer from S-g-C3N4 to the oxidizing agent through the silver surface, ultimately protecting Ag NPs from oxidation. Based on the theoretical calculations, we found that the net surface charge of the Ag atoms on the S-g-C3N4/Ag substrates was positive and the Ag NPs presented high dispersibility, suggesting that the Ag atoms on the S-g-C3N4/Ag substrates were not likely to be oxidized, thereby ensuring the high stability of the S-g-C3N4/Ag substrate. An understanding of the stability mechanism in this system can be helpful for developing other effective SERS substrates with long-term stability.