Mechanically Enhanced Detoxification of Chemical Warfare Agent Simulants by a Two-Dimensional Piezoresponsive Metal-Organic Framework.

Chemical warfare agents (CWAs) refer to toxic chemical substances used in warfare. Recently, CWAs have been a critical threat for public safety due to their high toxicity. Metal-organic frameworks have exhibited great potential in protecting against CWAs due to their high crystallinity, stable structure, large specific surface area, high porosity, and adjustable structure. However, the metal clusters of most reported MOFs might be highly consumed when applied in CWA hydrolysis. Herein, we fabricated a two-dimensional piezoresponsive UiO-66-F4 and subjected it to CWA simulant dimethyl-4-nitrophenyl phosphate (DMNP) detoxification under sonic conditions. The results show that sonication can effectively enhance the removal performance under optimal conditions; the reaction rate constant k was upgraded 45% by sonication. Moreover, the first-principle calculation revealed that the band gap could be further widened with the application of mechanical stress, which was beneficial for the generation of 1O2, thus further upgrading the detoxification performance toward DMNP. This work demonstrated that mechanical vibration could be introduced to CWA protection, but promising applications are rarely reported.

Stereoselective alkyl C-glycosylation of glycosyl esters via anomeric C-O bond homolysis: efficient access to C-glycosyl amino acids and C-glycosyl peptides.

C-Glycosyl peptides possess excellent metabolic stability and therapeutic properties and thus play critical roles in biological studies as well as drug discoveries. However, the limited accessibility of C-glycosyl amino acids has significantly hindered the broader research of their structural features and mode of action. Herein, for the first time we disclose a novel visible-light-driven radical conjugate addition of 1,4-dihydropyridine (DHP)-derived glycosyl esters with dehydroalanine derivatives, generating C-glycosyl amino acids and C-glycosyl peptides in good yields with excellent stereoselectivities. Redox-active glycosyl esters, as readily accessible and bench-stable radical precursors, could be easily converted to glycosyl radicals via anomeric C(sp3)-O bond homolysis under mild conditions. Importantly, the generality and practicality of this transformation were fully demonstrated in >40 examples including 2-dexosugars, oligosaccharides, oligopeptides, and complex drug molecules. Given its mild reaction conditions, robust sugar scope, and high anomeric control and diastereoselectivity, the method presented herein could find widespread utility in the preparation of C(sp3)-linked sugar-based peptidomimetics.

Porphyrin-Moiety-Functionalized Metal-Organic Layers Exhibiting Catalytic Capabilities for Detoxifying Nerve Agent and Blister Agent Simulants.

The development of very efficient bifunctional catalysts for the simultaneous detoxification of two kinds of the deadliest chemical warfare agents (CWAs), nerve agent and blister agent, is highly desirable. In this study, two porphyrin-based ligands [tetrakis(4-carboxyphenyl) porphyrin (TCPP) and protoporphyrin IX (PPIX)] are introduced into 2D Zr-1,3,5-tris(4-carboxyphenyl)benzene (BTB) metal-organic layers (MOLs), composed of six-connected Zr6 nodes and the tritopic carboxylate ligand BTB, by a solvent-assisted ligand incorporation method. The loads of TCPP and PPIX are 6.4 and 10.9 wt %, respectively. The detoxification of simulants of the nerve agent and the blister agent was conducted to investigate the catalytic activity of porphyrin-moiety-functionalized MOLs. The reaction half-life of optimal TCPP-functionalized MOL catalyzing the hydrolysis of a nerve agent simulant is only 2.8 min, meanwhile, the half-life of the selective catalytic oxidation of a blister agent simulant is only 1.2 min under LED illumination. More importantly, such a degradation half-life is only about 4 min under natural sunlight (∼60 mW/cm2). To our knowledge, TCPP-functionalized MOL is by far the most efficient catalyst for blister agent simulant degradation under solar light. Therefore, 2D ultrathin MOLs on demand appear to be a promising and efficient material platform for the development of bifunctional catalysts for CWA protection.

Harvesting mechanical energy for hydrogen generation by piezoelectric metal-organic frameworks.

Piezocatalysis, the process of directly converting mechanical energy into chemical energy, has emerged as a promising alternative strategy for green H2 production. Nevertheless, conventional inorganic piezoelectric materials suffer from limited structural tailorability and small surface area, which greatly impedes their mechanically driven catalytic efficiency. Herein, we design and fabricate a novel UiO-66(Zr)-F4 metal-organic framework (MOF) nanosheet for piezocatalytic water splitting, with the highest H2 evolution rate reaching 178.5 µmol g-1 within 5 h under ultrasonic vibration excitation (110 W, 40 kHz), far exceeding that of the original UiO-66 host. A reduced bandgap from 2.78 to 2.43 eV is achieved after introducing a fluorinated ligand. Piezoresponse force microscopy measurements demonstrate a much stronger piezoelectric response for UiO-66(Zr)-F4, which may result from the polarity of the introduced fluorinated ligand. This work highlights the potential of MOF-based porous piezoelectric nanomaterials in harvesting mechanical energy to drive chemical reactions such as water splitting.

Metal-organic framework-derived magnetic carbon for efficient decontamination of organic pollutants via periodate activation: Surface atomic structure and mechanistic considerations.

Practical implementation of periodate-based advanced oxidation processes for environmental remediation largely relies on the development of cost-effective and high-performance activators. Surface atomic engineering toward these activators is desirable but it remains challenging to realize improved activation properties. Here, a surface atomic engineering strategy used to obtain a novel hybrid activator, namely cobalt-coordinated nitrogen-doped graphitic carbon nanosheet-enwrapped cobalt nanoparticles (denoted as Co@NC-rGO), from a sandwich-architectured metal-organic framework/graphene oxide composite is reported. This activator exhibits prominent periodate activation properties toward pollutant degradation, surpassing previously reported transition-metal-based activators. Importantly, the activator shows good stability, magnetic reusability, and the potential for application in a complex water matrix. Density functional theory modeling implies that the strong activation capability of Co@NC-rGO is related to its surface atomic structure for which the embedded cobalt nanoparticles with abundant interfacial Co-N coordinations display modified electronic configurations on the active centers and benefit periodate adsorption. Quenching experiments and electrochemical measurements showed that the system could oxidize organics through a dominant nonradical pathway. Additionally, a lower concentration of cobalt leaching was observed for the Co@NC-rGO/periodate system than for its Co@NC-rGO/persulfate counterpart. Our work provides a pathway toward engineering surface atomic structures in hybrid activators for efficient periodate activation.

Regulation of electronic structures of MOF-derived carbon via ligand adjustment for enhanced Fenton-like reactions.

Peroxymonosulfate (PMS)-based Fenton-like reactions are widely used for wastewater remediation. Metal-free carbonaceous activators can avoid the secondary pollution caused by metal leaching but often suffer from insufficient activity due to limited active centers and mass transfer barriers. Here, we prepared a series of heteroatom (N, S, F)-doped, highly porous carbonaceous materials (UC-X, X = N, S, F) by pyrolyzing UiO-66 precursors assembled by various organic ligands. Density functional theory calculations showed that the heteroatoms modulated the electronic structures of the carbon plane. UC-X exhibited significantly enhanced PMS activation capability compared with the undoped counterpart, in the efficiency order of UC-N > UC-S > UC-F > UC. UC-N (calcined at 1000°C) showed the best PMS activation, exceeding that of commonly used carbocatalysts. The prominent performance of UC-N originated from its unique porous structure and homogeneously dispersed graphitic N moieties. Trapping experiments and electron spin resonance showed a nonradical degradation pathway in the UC-N/PMS system, through which organics were oxidized by donating electrons to UC-N/PMS* metastable complexes. This work not only reports a universal way to access high-performance, metal-free PMS activators but also provides insight into the underlying mechanism of the carbon-activated PMS process.

Cobalt-Enhanced Mass Transfer and Catalytic Production of Sulfate Radicals in MOF-Derived CeO2 • Co3 O4 Nanoflowers for Efficient Degradation of Antibiotics.

Antibiotics discharge has been a critical issue as the abuse in clinical disease treatment and aquaculture industry. Advanced oxidation process (AOPs) is regarded as a promising approach to degrade organic pollutants from wastewater, however, the catalysts for AOPs always present low activities, and uncontrollable porosities, thus hindering their further wider applications. In this work, an aliovalent-substitution strategy is employed in metal-organic framework (MOF) precursors assembly, aiming to introduce Co(II/III) into Ce-O clusters which could modify the structure of the clusters, then change the crystallization, enlarge the surface area, and regulate the morphology. The introduction of Co(II/III) also enlarges the pore size for mass transfer and enriches the active sites for the production of sulfate radicals (SO4• - ) in MOF-derived catalysts, leading to excellent performance in antibiotics removal. Significantly, the CeO2 •Co3 O4 nanoflowers could efficiently enhance the generation of sulfate radical SO4• - and promote the norfloxacin removal efficiency to 99% within 20 min. The CeO2 •Co3 O4 nanoflowers also present remarkable universality toward various antibiotics and organic pollutants. The aliovalent-substitution strategy is anticipated to find wide use in the exploration of high-performance MOF-derived catalysts for various applications.

Ce-based heterogeneous catalysts by partial thermal decomposition of Ce-MOFs in activation of peroxymonosulfate for the removal of organic pollutants under visible light.

Metal-organic framework (MOF) derivatives have drawn considerable attention for applications in various fields. In this work, spindle-shaped Ce-TCPPs were assembled by a rapid microwave-assisted hydrothermal method. After thermal treatment at low temperature under a N2 atmosphere, the Ce-TCPPs were partially pyrolyzed and converted to a novel CeO2/N-doped carbon/Ce-TCPP nanocomposite. Compared to completely decomposed materials, these partially decomposed heterogeneous catalysts exhibited significantly higher photocatalytic activation ability toward PMS for the removal of organic pollutants (e.g., rhodamine B, methylene blue, methyl orange, tetracycline and oxytetracycline). For the optimized sample thermal treated at 450 °C, a 100 mL RhB solution (10 mg/L) can be removed within 20 min with the assistance of PMS under visible light. The significantly enhanced activity can be attributed to the effective spatial separation of photogenerated electrons and holes in the formed Z-scheme CeO2/N-doped carbon/Ce-TCPP system. This work may provide useful guidance for the design and fabrication of MOF-derived photocatalytic systems for environmental remediation.

Atomically Dispersed Cobalt Sites on Graphene as Efficient Periodate Activators for Selective Organic Pollutant Degradation.

Pollutant degradation via periodate (IO4-)-based advanced oxidation processes (AOPs) provides an economical, energy-efficient way for sustainable pollution control. Although single-atomic metal activation (SMA) can be exploited to optimize the pollution degradation process and understand the associated mechanisms governing IO4--based AOPs, studies on this topic are rare. Herein, we demonstrated the first instance of using SMA for IO4- analysis by employing atomically dispersed Co active sites supported by N-doped graphene (N-rGO-CoSA) activators. N-rGO-CoSA efficiently activated IO4- for organic pollutant degradation over a wide pH range without producing radical species. The IO4- species underwent stoichiometric decomposition to generate the iodate (IO3-) species. Whereas Co2+ and Co3O4 could not drive IO4- activation; the Co-N coordination sites exhibited high activation efficiency. The conductive graphene matrix reduced the contaminants/electron transport distance/resistance for these oxidation reactions and boosted the activation capacity by working in conjunction with metal centers. The N-rGO-CoSA/IO4- system exhibited a substrate-dependent reactivity that was not caused by iodyl (IO3·) radicals. Electrochemical experiments demonstrated that the N-rGO-CoSA/IO4- system decomposed organic pollutants via electron-transfer-mediated nonradical processes, where N-rGO-CoSA/periodate* metastable complexes were the predominant oxidants, thereby opening a new avenue for designing efficient IO4- activators for the selective oxidation of organic pollutants.

Enhanced Piezocatalytic Activity of Sr0.5Ba0.5Nb2O6 Nanostructures by Engineering Surface Oxygen Vacancies and Self-Generated Heterojunctions.

Piezocatalysis provides a promising strategy for directly converting weak mechanical energy into chemical energy. In this work, we report a simple one-step hydrogen reduction route for the simultaneous generation of surface defects and heterojunctions in Sr0.5Ba0.5Nb2O6 nanorods fabricated by a molten salt synthesis method. The as-fabricated Sr0.5Ba0.5Nb2O6/Sr2Nb2O7 nanocomposites with controllable oxygen vacancies exhibited excellent piezocatalytic activity under ultrasonic vibration, with an about 7 times enhancement of the rate constant (k = 0.0395 min-1) for rhodamine B degradation and an about 10 times enhancement of the water-splitting efficiency for hydrogen generation (109.4 µmol g-1 h-1) for the optimized sample (H2 annealed at 500 °C) compared to pristine Sr0.5Ba0.5Nb2O6 nanorods. This work demonstrates the essential role of a well-modulated oxygen vacancy concentration in the piezocatalytic activity and provides an inspiring guide for designing self-generated heterojunction piezocatalysts.

Piezocatalytic Effect Induced Hydrogen Production from Water over Non-noble Metal Ni Deposited Ultralong GaN Nanowires.

Piezoelectric material-based catalysis that relies on an external stress-induced piezopotential has been demonstrated to be an effective strategy toward various chemical reactions. In this work, non-noble metal Ni-decorated ultralong monocrystal GaN nanowires (NWs) were prepared through a chemical vapor deposition (CVD) technique, followed by a photodeposition method. The piezocatalytic activity of the GaN NWs was enhanced by ∼9 times after depositing the Ni cocatalyst, generating hydrogen gas of ∼88.3 µmol·g-1·h-1 under ultrasonic vibration (110 W and 40 kHz), which is comparable to that of Pt-loaded GaN NWs. Moreover, Ni/GaN NWs with smaller diameters (∼100 nm) demonstrated superior piezocatalytic efficiency, which can be attributed to the large piezoelectric potential evidenced by both finite-element analysis and piezoresponse force microscopy measurements. These results demonstrate the promising application potential of non-noble metal loaded GaN nanostructures in hydrogen generation driven by weak mechanical energy from the surrounding environment.

Enhanced and environment-friendly chemical looping gasification of crop straw using red mud as a sinter-resistant oxygen carrier.

Syngas production from biomass gasification is a promising technology, which is widely used in the chemical industry. Crop straw and red mud are typical agricultural and industrial wastes, respectively, which are cheap and widespread; however, they cause serious environmental pollution due to the open burning of straw and the toxicity and alkalinity of red mud. In the present work, we converted crop straw into syngas by chemical looping gasification using red mud as a sinter-resistant oxygen carrier. The reactivity of red mud, the syngas yields, and the air pollutant emissions under different conditions were systematically investigated through a thermo-gravimetric analyzer and mass spectrometer. Compared with pure Fe2O3, red mud can promote the syngas yields from crop straw gasification owing to the presence of inert Al2O3 and SiO2. Red mud can effectively reduce the emission of air pollutants owing to the presence of alkaline components such as CaO and Na2O. As the Fe2O3/fuel mass ratio increases, the syngas yield increases and the air pollutant emissions simultaneously reduce; whereas the syngas yield and the air pollutant emissions decrease with increasing heating rate. After calcination at high temperature, the structure of red mud remains stable with slight agglomeration, and can be easily regenerated. Therefore, the promising results provide a breakthrough for efficient utilization and disposal of both crop straw and red mud.

Cu2O nanoparticles anchored on carbon for the efficient removal of propofol from operating room wastewater via peroxymonosulfate activation: efficiency, mechanism, and pathway.

Anesthetic drug wastage has increasingly become the main resource of operating room sewage, which poses a great risk to the safety of humans and other organisms. Propofol is the most widely used anesthetic drug in the world, and also occupies the largest proportion of the total anesthetic wastage in the operating room. In this work, a 2D Cu2O anchored carbon catalyst (Cu2O@NC) was prepared by the assembly-pyrolysis process and successfully applied to peroxymonosulfate (PMS) activation. We took propofol as a typical example and investigated the removal activity through heterostructure-enhanced advanced oxidation processes (AOPs). Through the degradation process, propofol can be removed from 20 ppm to ultralow levels within 5 min using the PMS/Cu2O@NC system. The degradation pathway of propofol was deduced through quantum chemical calculation and LC/GC-MS results. The final products were verified as CO2 and H2O. Moreover, sulfate radicals (SO4˙-) proved to be the dominant reactive oxidation species by radical scavenger experiments and ESR results. In addition, it has great universality for various pharmaceuticals such as tetracycline (TC), amoxicillin (AMX), cephalexin (CPX), and norfloxacin (NFX). Our work provided the possibility to treat operation room sewage in a rapid, high-efficiency, and feasible way.

Synergic removal of tetracycline using hydrophilic three-dimensional nitrogen-doped porous carbon embedded with copper oxide nanoparticles by coupling adsorption and photocatalytic oxidation processes.

Adsorption and photocatalytic oxidation are promising technologies for eliminating antibiotics (e.g. tetracycline) in aquatic environments. However, traditional powdery nanomaterials are limited by drawbacks of difficult separation and lack of synergistic function, which do not conform to the practical demand. Herein, we developed a simple one-step gelation-pyrolysis route to fabricate hydrophilic three-dimensional (3D) porous photocatalytic adsorbent, in which CuO nanoparticles are uniformly and firmly embedded in nitrogen-doped (N-doped) porous carbon frameworks. The obtained N-doped carbon/CuO bulky composites exhibited excellent ability to adsorb tetracycline hydrochloride (TC), which was subsequently photo-oxidized under visible light. Their hydrophilic nature favors the adsorption processes toward TC, with a maximum adsorption capacity reaching 25.03 mg∙g-1. In addition, >94.4% of TC molecules could be photo-degraded in 4 h with good cycling efficiency after three consecutive tests. Finally, a reaction scheme for removal process of TC was proposed. The obtained 3D porous N-doped carbon/CuO nanocomposites show great promise for efficient removal of antibiotics in aqueous solution by synergistically utilizing adsorption and photocatalytic oxidation processes.

Microwave-assisted hydrothermal assembly of 2D copper-porphyrin metal-organic frameworks for the removal of dyes and antibiotics from water.

Adsorption and photocatalysis are promising strategies to remove pollutants of dyes and antibiotics from wastewater. In this study, we demonstrate a rapid microwave-assisted hydrothermal route for the assembly of 2D copper-porphyrin Metal-Organic Frameworks (Cu-TCPP MOFs) within 1 h. The resulting 2D Cu-TCPP nanosheets with excellent crystallinity and a large surface area (342.72 m2/g) exhibited outstanding adsorption performance for typical dyes with adsorption capacities of about 185 mg/g for rhodamine B, 625 mg/g for methylene blue, and 290 mg/g for Congo red, respectively, as well as for representative antibiotics with adsorption capacities of about 130 mg/g for oxytocin, 150 mg/g for tetracycline, and 50 mg/g for norfloxacin, respectively. Meanwhile, the as-prepared 2D Cu-TCPP showed good photocatalytic degradation activity of pollutants after adsorption under irradiation by visible light, reaching removal efficiencies of 81.2 and 86.3% toward rhodamine B and norfloxacin, respectively. These results demonstrate the promising potential of 2D Cu-TCPP for use in the removal of contaminants from wastewater.

Coordination-Directed Assembly of Luminescent Semiconducting Oligomers and Weak Interaction-Induced Morphology Transformation.

Luminescent semiconducting oligomers (LSOs) have been one of the most popular molecular materials that can be applied in various fields because of their distinctive optical properties. The study of molecular packing and morphological change of oligomers is essential for the rational design of materials and regulation functions. Herein, we report two novel LSOs (OFBB and OFBT) with a slight difference in chemical structures but show a distinct difference in self-assembly behaviors in the coordination-driven process. OFBB forms spherical particles with Zn(II). Compared with OFBB, OFBT has an additional thiazole moiety, which forms spherical particles with Zn(II) and then transforms to a crystalline nanobelt in 2 h. The process and mechanism of the nanosphere and nanobelt formation were investigated in detail. The double S···N interaction between two benzothiazoles in adjacent oligomers played a significant contribution in this dynamic morphology transformation. In addition, the as-prepared two products showed excellent sensing toward nitrobenzene with good selectivity over other nitro-aromatic explosives.

Reaction-based chiroptical sensing of ClO- using circularly polarized luminescence via self-assembly organogel.

By covalent combination of a chiral amino acid, lipid, and achiral phenothiazine derivative, a reaction-based chiroptical probe, PTZ-D, was obtained. PTZ-D could self-assemble into a chiral organogel realizing the chirality transformation from a chiral amino acid to a self-assembled system and displaying unprecedented chiroptical monitoring of ClO- with switchable CPL signals.