Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing.

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 µM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

On-Demand Assembly of Nanocrystals into a Superstructure Library in Co(OH)2 Single-Walled Nanotubes.

The hierarchical self-assembly of colloidal particles facilitates the bottom-up manufacturing of metamaterials with synergistically integrated functionalities. Here, we define a modular assembly methodology that enables multinary co-assembly of nanoparticles in one-dimensional confined space. A series of isotropic and anisotropic nanocrystals such as plasmonic, metallic, visible, and near-infrared responsive nanoparticles as well as transition-metal phosphides can be selectively assembled within the single-walled Co(OH)2 nanotubes to achieve various increasingly sophisticated assembly systems, including unary, binary, ternary, and quaternary superstructures. Moreover, the selective assembly of distinct functional nanoparticles produces different integrated functional superstructures. This generalizable methodology provides predictable pathways to complex architectures with structural programming and customization that are otherwise inaccessible.

Spongelike Bimetallic Selenides Derived from Prussian Blue Analogue on Layered Ni(II)-Based MOF for High-Efficiency Supercapacitors.

Recently, employing metal-organic frameworks (MOFs) as precursors to prepare various metal oxides, sulfides, and selenides has drawn enormous attention in the field of energy storage. In this paper, the nanosheets of an organophosphate-based Ni-MOF were successfully synthesized and employed as the template to prepare the Prussian blue analogue (PBA) nanoslices and nanoparticles on the nanosheet (PBA/Ni-MOF-NS-x h, x h stands for the reaction time.) by an in situ etching method. After selenization by the solvothermal method, the PBA nanoslices and nanoparticles were transformed into spongelike bimetallic selenides (labeled as PBA/Ni-MOF-NS-x h-Se) decorated with some nanoparticles. All of the characterization results including PXRD, SEM, TEM, EDS, XPS, and BET demonstrated the successful transformation. Impressively, the as-synthesized PBA/Ni-MOF-NS-12 h-Se exhibited a high specific capacitance of 1897.90 F g-1 at a current density of 1 A g-1 and a superior capacitance retention rate of 73.32% as the current density increased to 20 A g-1. In addition, the asymmetric supercapacitor device, PBA/Ni-MOF-NS-12 h-Se//AC, delivered a high energy density of 30.69 W h kg-1 at 0.85 kW kg-1 and extraordinary cycling stability with an 83.00% capacitance retention rate over 5000 cycles.

Ultrathin Carbon Nitride Nanosheets Exfoliated and In Situ Modified with a Nickel Bis(Chelate) Complex for Boosting Photocatalytic Performances.

Exfoliation and interfacial modification of two-dimensional (2D) polymeric carbon nitride (CN) are considerably vital for applications in photo/electrocatalysis fields. Here, a grinding-ultrasonic route was designed to construct nickel bis(chelate) complex (Ni(abt)2, abt = 2-aminobenzenethiolate)-modified CN ultrathin nanosheets. Under the assistance of the shear force derived from the grinding process, Ni(abt)2 was implanted into the interlamination of bulk CN, resulting in the formation of ultrathin CN (UCN) nanosheets. Simultaneously, Ni(abt)2 molecules were anchored on the surfaces of as-formed UCN nanosheets due to the π-π stacking interaction. Interestingly, compared with single Ni(abt)2 and UCN, the as-obtained Ni(abt)2/UCN nanosheets exhibited excellent photocatalytic hydrogen evolution capability. A molecule-semiconductor internal electron transmission mechanism was suggested for explaining the separation and transfer of electron-hole pairs. Density functional theory (DFT) calculations demonstrated that the interface-induced electron redistribution tuned the electron density and hydrogen adsorption of the active centers, thus enhancing the photocatalytic performance of the hybrid catalyst. In addition, the as-obtained Ni(abt)2/UCN nanosheets could also catalyze the reduction of nitroaromatics in the presence of NaBH4. It was found that under the simulated sunlight irradiation, the conversion efficiency of nitroaromatic compounds to amino aromatic ones was up to 97.3%, far higher than that under the condition without light irradiation (51.7%), suggesting that the photocatalytic-produced hydrogen took part in the reduction of nitroaromatic compounds.

Electronic Modulation of Metal-Organic Frameworks Caused by Atomically Dispersed Ru for Efficient Hydrogen Evolution.

Designing excellent electrocatalysts for the hydrogen evolution reaction (HER) is extremely significant in producing clean and sustainable hydrogen fuel. Herein, a rational strategy is developed to fabricate a promising electrocatalyst by introducing atomically dispersed Ru into a cobalt-based metal-organic framework (MOF), Co-BPDC (Co(bpdc)(H2 O)2 , BPDC: 4,4'-Biphenyldicarboxylic acid). The obtained CoRu-BPDC nanosheet arrays exhibit remarkable HER performance with an overpotential of 37 mV at a current density of 10 mA cm-2 in alkaline media, which is superior to most of the MOF-based electrocatalysts and comparable to the commercial Pt/C. Synchrotron radiation-based X-ray absorption fine structure (XAFS) spectroscopy studies verify that the isolated Ru atoms are dispersed in Co-BPDC nanosheets with the formation of five-coordinated Ru-O5 species. XAFS spectroscopy combined with density functional theory (DFT) calculations unravels that atomically dispersed Ru can modulate the electronic structure of the as-obtained Co-BPDC, contributing to the optimization of binding strength for H* and the enhancement of HER performance. This work opens a new avenue to rationally design highly-active single-atom modified MOF-based HER electrocatalysts via modulating electronic structures of MOF.

Phase Segregation in Cu0.5 Ni0.5 Alloy Boosting Urea-Assisted Hydrogen Production in Alkaline Media.

Coupling urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is promising for energy-efficient hydrogen production. However, developing cheap and highly active bifunctional electrocatalysts for overall urea electrolysis remains challenging. In this work, a metastable Cu0.5 Ni0.5 alloy is synthesized by a one-step electrodeposition method. It only requires the potentials of 1.33 and -28 mV to obtain the current density of ±10 mA cm-2 for UOR and HER, respectively. The metastable alloy is considered to be the main reason causing the above excellent performances. In the alkaline medium, the as-prepared Cu0.5 Ni0.5 alloy exhibits good stability for HER; and conversely, NiOOH species can be rapidly formed during the UOR due to the phase segregation of Cu0.5 Ni0.5 alloy. In particular, for the energy-saving hydrogen generation system coupled with HER and UOR, only 1.38 V of voltage is needed at 10 mA cm-2 ; and at 100 mA cm-2 , the voltage decreases by ≈305 mV compared with that of the routine water electrolysis system (HER || OER). Compared with some catalysts reported recently, the Cu0.5 Ni0.5 catalyst owns superior electrocatalytic activity and durability. Furthermore, this work provides a simple, mild, and rapid method for designing highly active bifunctional electrocatalysts toward urea-supporting overall water splitting.

Atomically precise Ni6(SC2H4Ph)12 nanoclusters on graphitic carbon nitride nanosheets for boosting photocatalytic hydrogen evolution.

Much effort has been devoted to improving the photocatalytic capacity of graphitic carbon nitride (g-C3N4). In this paper, we reported the successful synthesis of a hybrid photocatalyst with superb photocatalytic hydrogen production activity through decorating atomically precise Ni6(SC2H4Ph)12 nanoclusters on g-C3N4 nanosheets (labeled as Ni6/g-C3N4) at room temperature. Zeta potential experiments demonstrated that the electrostatic interaction between Ni6 and g-C3N4 led to the formation of Ni6/g-C3N4. The photocatalytic measurements revealed that the 5 %-Ni6/g-C3N4 prepared with the original mass ratio of m(Ni6)/m(g-C3N4) = 1/20 exhibited the strongest hydrogen production activity. In the system with triethanolamine (TEOA) as the sacrifice agent, the visible-light hydrogen production rate reached up to 5.87 mmol h-1 g-1, approximately 290 times higher than that of pure g-C3N4 (0.02 mmol h-1 g-1). Density functional theory (DFT) calculations testified that the above significant enhancement of photocatalytic hydrogen evolution of the hybrid photocatalyst arose from the photogenerated electrons transfer from Ni6 to g-C3N4.

Enhanced Mechanical Stability and Proton Conductivity Performance from the Dense Mn(II)-Metal-Organic Framework to Porous Mn(II)-Fe(III)-Metal-Organic Framework.

Postsynthetic modification (PSM) of the metal-organic framework (MOF) has been demonstrated to be an effective strategy to enhance performance. In this particular work, the anion framework Mn-MOF {[Mn3O(H2O)3(HTC)]2-} (HTC6- = (5'-(3,5-dicarboxyphenyl)-[1,1':3',1″-terphenyl]-3,3″,5,5″-tetracarboxylate] was obtained, and NH2(CH3)2+ ions were filled within the pores to balance the charge. In order to release the internal pores of Mn-MOF, the trivalent Fe(III) was introduced instead of Mn(II) nodes, resulting in the porous Mn1-xFex-MOF, and the NH2(CH3)2+ ions were simultaneously deported from the pores. The content of Fe(III) in Mn1-xFex-MOF was highly dependent on the concentration of Fe(III) solution, and the maximum could be up to Mn0.05Fe0.95-MOF with a BET surface area of 1209.457 m2 g-1. Compared to the amorphization of dense Mn-MOF at 0.8 GPa in a diamond anvil cell, the mechanical stability of porous Mn0.05Fe0.95-MOF has been dramatically enhanced, and the framework integrity could be maintained up to 16.5 GPa. The proton conductivity for the Mn1-xFex-MOF series was also investigated, where Mn0.93Fe0.07-MOF showed the best performance of 1.47 × 10-2 S cm-1 under 70 °C and 98% RH due to the onset of reversed charge from the anionic framework to cationic framework and the formation of the most compact hydrogen bonding net. This work has not only provided an example for the PSM strategy but also illustrated that the versatile functionalities of MOF materials were mainly ascribed to the tunable porosity.

Ultrathin 2D Eu3+@Zn-MOF Nanosheets: A Functional Nanoplatform for Highly Selective, Sensitive, and Visualized Detection of Organochlorine Pesticides in a Water Environment.

Facile and rapid detection of residual organic pesticides on the fruits and vegetables has recently drawn increased attention in the food safety field. Herein, a surfactant-assisted solvothermal route with subsequent post-modification was designed for the preparation of Eu3+-functionated Zn-BDC ultrathin nanosheets (labeled as Eu3+@Zn-MOF-NS, BDC: 1,4-benzenedicarboxylate) with the thickness of 5 nm. The as-obtained Eu3+@Zn-MOF-NS could be homogeneously dispersed in aqueous systems to form a highly-stable collosol. Under the UV excitation of 325 nm, the as-obtained Eu3+@Zn-MOF-NS displayed red photoluminescence emission of Eu3+ ions, which could be notably quenched by an organochlorine pesticide, 2,6-dichloro-4-nitroaniline (DCNA), without interferences from ions, organic small molecules, and other pesticides. The detection limit and Ksv were 0.17 µM (35 ppb) and 3.2 × 105 M-1 in the water system, respectively. Moreover, the present 2D Eu3+@Zn-MOF sensor was also employed for the detection of DCNA in Chaohu Lake water and tap water and in apple, cabbage, and pakchoi samples with the relative standard deviation (RSD) ranging from 4.74 to 9.77%. Further investigations revealed that the competitive absorption between DCNA and the as-obtained Eu3+@Zn-MOF-NS resulted in the fluorescence quenching of the probe.

Ce-Doped Ni-S nanosheets on Ni foam supported NiMoO4 micropillars: fast electrodeposition, improved electrocatalytic activity and ultralong durability for the oxygen evolution reaction in various electrolytes.

Developing active, durable, and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is drawing increased interest. Here, a mild hydrothermal-electrodeposition two-step route is designed for the preparation of Ce-doped Ni-S@NiMoO4 micropillar composites on nickel foam (CeNiS@NiMoO4/NF). The as-constructed CeNiS@NiMoO4/NF electrode shows an ultralow overpotential, fast kinetics, superb intrinsic activity and excellent long-term stability for the OER. In 1 M KOH solution, 187 mV overpotential is required to deliver a current density of 10 mA cm-2 with a Tafel slope of 35.28 mV dec-1, and in a saline-alkaline solution of 1 M KOH and 0.5 M NaCl, only 260 mV overpotential is needed to reach 100 mA cm-2, demonstrating its excellent OER performance. The above outstanding electrocatalytic activity is attributed to the influence of CeNiS nanosheets on the surface microstructure of NiMoO4 micropillars, which not only improves the conductivity of the catalyst, but also increases the surface area, as well as accelerates the escape of gases produced. Compared with other non-precious metal OER electrocatalysts, the as-prepared CeNiS@NiMoO4/NF presents stronger or close electrocatalytic activity and better durability, which provides a new electrocatalyst selection in practical applications.

Hierarchically porous FeNi3@FeNi layered double hydroxide nanostructures: one-step fast electrodeposition and highly efficient electrocatalytic performances for overall water splitting.

FeNi-layered double hydroxide (LDH) is thought to be an excellent electrocatalyst for oxygen evolution reaction (OER) but it always shows extremely poor electrocatalytic activity toward hydrogen evolution reaction (HER) in alkaline media. Hence, it is significant to improve its HER activity to make it a bifunctional electrocatalyst for the decomposition of water. Here, a simple galvanostatic electrodeposition method was designed for the successful construction of the bifunctional FeNi3@FeNi LDH electrocatalyst. The as-prepared catalyst displayed excellent electrocatalytic activity for HER/OER in 1.0 M KOH. To drive the current density of 10 mA cm-2 for HER/OER, an overpotential of 106/199 mV was needed, respectively. In a two-electrode system with the FeNi3@FeNi LDH/NF as the anode and the cathode simultaneously, the overpotential hardly changed after continuously working for 168 h at 10 mA cm-2. Compared with other FeNi-based catalysts, the present catalyst possessed close or better electrocatalytic activity.

Highly water-stable Cd-MOF/Tb3+ ultrathin fluorescence nanosheets for ultrasensitive and selective detection of Cefixime.

Two-dimensional Cd-MOF/Tb3+ (Cd-MOF = [Cd (µ-2,3-pdc) (H2O)3]n (2,3-pdc = 2,3-pyridine dicarboxylic acid)) fluorescent nanosheets with the thickness of 1.4 nm were successfully synthesized by a simple solution route with subsequent ultrasonic exfoliation at room temperature. It was found that as-obtained Cd-MOF/Tb3+ ultrathin nanosheets could be homogeneously dispersed in aqueous system to form a sol with excellent stability. Also, the fluorescence intensity of nanosheets remarkably increased to almost 12 times higher than that of Cd-MOF/Tb3+ microsheets before exfoliation. Further investigations uncovered that the above strong fluorescence of Cd-MOF/Tb3+ nanosheets could be highly sensitively quenched by Cefixime antibiotic in aqueous solution without interference from other antibiotics, amino acids and pesticides. Hence, the as-obtained ultrathin Cd-MOF/Tb3+ nanosheets could be prepared as a highly selective and sensitive fluorescence probe for the detection of Cefixime in aqueous system. Compared with the bulk Cd-MOF/Tb3+ sensor, the Cd-MOF/Tb3+ ultrathin nanosheets sensor exhibited a far lower detection limit down to 26.7 nM for CFX. Also, the as-obtained nanosheets sensor presented satisfactory recovery ranging from 98.07% to 103.01% and acceptable repeatability (RSD < 6.29%, n = 6) for the detection of CFX in domestic water. Furthermore, the sensing mechanism studies revealed that the high selection of the present fluorescent probe for detection of CFX should be attributed to the cooperation of the photoinduced electron transfer and the inner filter effect.

Fe-Doped Co-Mo-S microtube: a highly efficient bifunctional electrocatalyst for overall water splitting in alkaline solution.

Fe-Doped Co-Mo-S microtubes were successfully synthesized through a multistep synthetic route, employing MoO3 microrods as the sacrificial template, Co(NO3)2·6H2O and Fe(SO4)2·7H2O as the metal sources, 2-methylimidazole (2-MI) as the ligand and thioacetamide (TAA) as the S2- ion source. The as-prepared products were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), (high-resolution) transmission electron microscopy (TEM/HRTEM) and HAADF-STEM-EDS elemental mapping. Experiments showed that the as-obtained Fe-doped Co-Mo-S microtube catalyst demanded overpotentials of ∼105 and 268 mV to afford the current density of -10 mA cm-2 for hydrogen evolution reaction (HER) and 10 mA cm-2 for oxygen evolution reaction (OER) with a durability of 60 h in 1.0 M KOH solution, respectively. In a two-electrode water-splitting device, the as-prepared Fe-doped Co-Mo-S microtubes acted as both anode and cathode simultaneously. To deliver a current density of 10 mA cm-2, a cell voltage of 1.605 V was required in 1.0 M KOH solution. After continuously catalyzing the overall water splitting for 60 h, the overpotential hardly changed, implying remarkable long-term stability. Obviously, the present Fe-doped Co-Mo-S microtubes have potential applications as bifunctional catalysts for electrochemical water splitting.

A novel Zn(II)-based metal-organic framework as a high selective and sensitive sensor for fluorescent detections of aromatic nitrophenols and antibiotic metronidazole.

A novel fluorescent Zn(II)-based metal-organic framework (Zn-MOF), [Zn2(oba)4(4,4'-bpy)2]n, was successfully synthesized through a simple solvothermal route at 130 °C for 48 h, employing Zn(NO3)2·6H2O, 4,4'-Oxybis(benzoic acid) (oba) and 4,4'-Bipyridine (4,4'-bpy) as the initial reactants, dimethylacetamide (DMA) as the reaction medium. The as-obtained Zn-MOF was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric analysis (TGA) and elemental analysis. The fluorescence tests showed that the as-obtained Zn-MOF emit a strong violet light centered at 445 nm under the excitation of 323 nm UV light. Intriguingly, the above strong violet emission could be highly selectively quenched by aromatic nitrophenols or antibiotic metronidazole (MET) in aqueous systems with fairly low detection limits. Other substituted phenols and antibiotics, as well as some cations, anions, amino acids and small organic molecules hardly affected the violet emission of the as-obtained Zn-MOF, indicating that this novel Zn-MOF could be prepared as a selective fluorescent probe for detections of aromatic nitrophenols and MET antibiotic in water solutions.

Cobalt-Based MOF-on-MOF Two-Dimensional Heterojunction Nanostructures for Enhanced Oxygen Evolution Reaction Electrocatalytic Activity.

Two-dimensional (2D) Co-based MOF-on-MOF heterojunction nanostructures with improved electrocatalytic activity were successfully constructed via a mild two-step solution route, employing Co2+ ions as the center atoms, and 1,4-benzenedicarboxylate (BDC) and 4,4'-biphenyldicarboxylate (BPDC) as ligands. The as-obtained heterojunction nanostructures were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) technologies. Electrochemical measurements showed that as-prepared Co-BPDC/Co-BDC heterojunction nanostructures presented markedly enhanced OER electrocatalytic activity, compared with single Co-BPDC, Co-BDC, and/or their physical mixture. Also, the Co-BPDC/Co-BDC-3 heterojunction prepared after treatment for 3 h exhibited the strongest catalytic activity. To reach the current density jgeo = 10 mA cm-2, the Co-BPDC/Co-BDC-3 heterojunction-modified glassy carbon electrode required an overpotential of 335 mV in 1 M KOH, which was reduced by 57 and 93 mV, compared to the electrodes modified by Co-BDC and Co-BPDC, respectively. Simultaneously, the heterojunction catalyst also displayed better long-term stability. The improvement of the above performances should be attributed to the increased structure stability, BET surface area, ECSA, and electron transfer ability of the heterojunction.

Chlorine-doped α-Co(OH)2 hollow nano-dodecahedrons prepared by a ZIF-67 self-sacrificing template route and enhanced OER catalytic activity.

Hollow α-Co(OH)2 and Cl-doped α-Co(OH)2 nano-dodecahedrons were successfully synthesized via a ZIF-67-assisted template route in the absence/presence of NaCl. The reactions were carried out in a Teflon-lined stainless-steel autoclave at 40 °C for 4 h, employing dodecahedral ZIF-67 and hexamethylenetetramine (HMT) as the reactants. The as-obtained hollow nano-dodecahedrons were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray photoelectron energy, EDS mapping and N2 sorption-desorption technologies. Electrochemical measurements showed that both α-Co(OH)2 and Cl-doped α-Co(OH)2 hollow nano-dodecahedrons displayed excellent catalytic activities for the oxygen evolution reaction (OER) and Cl-doped α-Co(OH)2 hollow ones possessed stronger electrocatalytic performances. To deliver a current density of 10 mA cm-2, Cl-doped α-Co(OH)2 hollow nano-dodecahedrons required a low overpotential of 298 mV, which is smaller than most reported α-Co(OH)2 catalysts. Also, the as-obtained hollow catalyst still had excellent OER cycling stability and durability. After 1000 CV cycles, the overpotential merely slightly increased. Continuously catalyzing at the current density of 10 mA cm-2 for 40 h, the voltage only increased ∼2.5%.

NH2-MIL-53(Al) nanocrystals: a fluorescent probe for the fast detection of aromatic nitro-compounds and ions in aqueous systems.

NH2-MIL-53(Al) nanocrystals were successfully fabricated by an improved solvothermal route at 120 °C for 24 h without the addition of any surfactants or capping agents, employing AlCl3·6H2O and 2-amino terephthalic acid (NH2-BDC) as the initial reactants, and N,N-dimethylformamide (DMF) and water with a volume ratio of 5/25 as the mixed solvent. The as-obtained product was characterized by XRD, FESEM and FTIR. Under the excitation of 380 nm UV light, the as-obtained NH2-MIL-53(Al) nanocrystals displayed strong fluorescence emission. It was found that some aromatic nitro-compounds (ANCs) or ions in aqueous systems could strongly quench the above fluorescence, indicating that the as-obtained NH2-MIL-53(Al) nanocrystals could be made into a fluorescent probe for the detection of ANCs and ions in aqueous systems. Simultaneously, the mechanism to cause fluorescence quenching was discussed.

Simple vapor-solid-reaction route for porous Cu2O nanorods with good HER catalytic activity.

In this work, a simple vapor-solid reaction route was designed for the preparation of porous Cu2O nanorods with good HER catalytic performance, employing Cu(OH)2 nanorods as the precursor and ethylene glycol as the reductant. The reaction was carried out under an Ar atmosphere in the temperature range of 200-280 °C for 2 h. The final product was characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), (high-resolution) transmission electron microscopy (TEM/HRTEM), X-ray photoelectron spectroscopy (XPS), HAADF-STEM-EDS mapping and nitrogen adsorption-desorption isotherms. It was found that pure Cu2O was always obtained in the temperature range of 200-280 °C and well retained the outline of the precursor. Nevertheless, electrochemical experiments showed that porous Cu2O nanorods prepared at 200 °C (labeled as Cu2O-200) exhibited much stronger HER catalytic activity than those obtained at higher temperatures, which were labeled as Cu2O-220, Cu2O-240, Cu2O-260 and Cu2O-280, respectively. In an alkaline solution of 1.0 M KOH, Cu2O-200 presented a low overpotential of ∼184 mV, a small Tafel slope of 106 mV dec-1, and a high durability over 20 h at a current density of 10 mA cm-2. The above good performances were attributed to the high surface area and high-speed electronic transmission networks of Cu2O-200, which provided fast transportation and short diffusion path for the electrolyte and evolved H2 bubbles.

A titanium-based photo-Fenton bifunctional catalyst of mp-MXene/TiO2-x nanodots for dramatic enhancement of catalytic efficiency in advanced oxidation processes.

mp-MXene/TiO2-x nanodots (NDs) structurally composed of microporous MXene monolayers embedded with Ti3+-doped TiO2 nanodots were developed for the first time. The drastically enhanced catalytic efficiency (as much as 13 times higher than that of P25) in degrading dye molecules over mp-MXene/TiO2-x NDs is due to a synergistic effect of the pseudo-Fenton reaction and photocatalysis.

Fluorescent Zn-PDC/Tb3+ Coordination Polymer Nanostructure: A Candidate for Highly Selective Detections of Cefixime Antibiotic and Acetone in Aqueous System.

Tb3+-doped zinc-based coordination polymer nanospindle bundles (Zn-PDC/Tb3+, or [Zn(2,5-PDC)(H2O)2]·H2O/Tb3+) were synthesized by a simple solution precipitation route at room temperature, employing Zn(NO3)2, Tb(NO3)3, and 2,5-Na2PDC as the initial reactants, and a mixture of water and ethanol with the volume ratio of 10:10 as the solvent. The as-obtained nanostructures presented strong fluorescent emission under the excitation of 298 nm light, which was attributed to the characteristic emission of the Tb3+ ion. It was found that the above-mentioned strong fluorescence of the nanostructures could be selectively quenched by cefixime (CFX) in aqueous solution. The other common antibiotics hardly interfered. Thus, as-obtained Zn-PDC/Tb3+ nanostructures could be prepared as a highly sensitive fluorescence probe for selective detection of CFX in an aqueous system. The corresponding detection limit reached 72 ppb. The theoretic calculation and UV-vis absorption experiments confirmed that the fluorescence quenching of Zn-PDC/Tb3+ nanostructures toward CFX should be attributed to the electron transfer and the fluorescence inner filter effect between the fluorescent matter and the analyte. In addition, the strong fluorescence of the nanostructures could also be selectively quenched by acetone in the water system.