Energy-splitting from persistent luminescence nanoparticles with trivalent Cr ions for ratiometric temperature sensing.

MgGa2O4 (MGO) with the spinel structure exhibits abundance defects and could achieve the modulation of emission by ion doping as persistent luminescence nanoparticles (PLNPs). Here, we introduced Cr3+ ions into MGO to achieve near-infrared (NIR) emission, and Pr3+ ions to tune the lattice environment for enhanced NIR emission. The optimal composite, MgGa2O4: 0.005Cr3+, 0.003Pr3+ (MGCP), achieved enhanced NIR emission at 709 nm under 222 nm excitation. The concentration quenching was observed due to electric dipole-quadrupole interaction at high Cr3+ and Pr3+ content. The afterglow mechanism was revealed, while the energy-splitting occurs from trivalent Cr3+ ions at 650 and 709 nm, thanks to the complex lattice environment. We observed that the emission at 709 nm decreased, while the satellite signal at 650 nm increased first and then decreased intensity with increasing temperature, due to the intervalence charge transfer for Cr3+ ions at 303-528 K. Ratiometric temperature sensing was therefore realized with superb linearity, high absolute sensitivity at 303 K for 4.18%, and accuracy at 528 K for 2.62 K, confirming with the luminescence intensity ratio at 709 and 650 nm under excitation at 222 nm. Thus, we provide a method with energy-splitting emission of Cr3+ ions to design temperature sensing.

Construction of hierarchical NCMTs@MoO2/FeNi3 tubular heterostructures for enhanced performance in catalysis and protein adsorption.

A new type of hybrid material (NCMTs@MoO2/FeNi3) with a multi-layer heterostructure was designed and fabricated via a one-step pyrolysis process using FeOOH/NiMoO4@PDA as the precursor. FeOOH/NiMoO4@PDA was prepared by the solvothermal method, followed by the nickel-ion etching method coupled with the polymerization of dopamine (DA). The as-obtained material was made of nitrogen-doped carbon nanotubes embedded with FeNi3 and MoO2 nanoparticles (NPs). Notably, the FeNi3 NPs exhibited significantly improved performance in the reduction of 4-nitrophenol (4-NP) and adsorption of histidine-rich protein as well as provided appropriate magnetism resources. The MoO2 NPs imparted a metallic nature with excellent conductivity, and the N-doped mesoporous carbon microtubes also improved conductivity and facilitated mass transfer, thus leading to enhanced performance in catalysis. Benefiting from the 1D hierarchical porous structure and compositional features, the NCMTs@MoO2/FeNi3 composites exhibited excellent performance in 4-NP reduction and protein adsorption via specific metal affinity between the polyhistidine groups of proteins and the FeNi3 NPs. The result presented here indicates that the strategy of combining tailored components, heterostructuring, and carbon integration is a promising way to obtain high-performance composites for other energy-related applications.

Carbon dots with enhanced red emission for ratiometric sensing and encryption applications.

The excitation-dependent emission properties of carbon dots (Cdots) are extensively reported, but their red emission is often weak, limiting their wider application. Here we introduce ethidium bromide, as a functional precursor with red emission, to enhance the red emission for Cdots, with comparable intensity at a broad wavelength range to multi-emission Cdots (M-Cdots). We found that Cdots prepared with ethidium bromide/ethylenediamine exhibited strong blue and red emission at 440 and 615 nm, with optimal excitation at 360 and 470 nm as M-Cdots, respectively, but the Cdots from single ethidium bromide (EB-Cdots) possessed weak red emission. M-Cdots exhibited a broad absorption band at 478 nm, but a band blue-shifted to 425 nm was observed for EB-Cdots, while no absorption was observed at 478-425 nm for the Cdots prepared with citric acid and ethylenediamine. Thus, we proposed that C=O and C=N formed a π-conjugation structure as the absorption band at 478 nm for the red emission of M-Cdots, as also confirmed with the excitation at 470 nm. Moreover, the π-conjugation structure is fragile and sensitive to harsh conditions, so red emission was difficult to observe for the Cdots prepared with citric acid/ethylenediamine or single ethidium bromide. M-Cdots possess two centers for blue and red emission with different structures. The dual emission was therefore used for ratiometric sensing with dichromate (Cr2O72-) and formaldehyde (HCHO) as the targets using the intensity ratio of the emissions at 615 and 440 nm. Due to the comparable intensity at a broad wavelength range, we designed encryption codes with five excitations at 360, 400, 420, 450, and 470 nm as the inputs, and the emission colors were used for information decoding. Thus, we determined why red emission was difficult to realize for Cdots, and our results could motivate the design of red-emission Cdots for extensive applications.

Multi-level Reactive Oxygen Species Amplifier to Enhance Photo-/Chemo-Dynamic/Ca2+ Overload Synergistic Therapy.

Reactive oxygen species (ROS)-involved photodynamic therapy (PDT) and chemodynamic therapy (CDT) hold great promise for tumor treatment. However, hypoxia, insufficient H2O2, and overexpressed glutathione (GSH) in the tumor microenvironment (TME) hinder ROS generation significantly. Herein, we reported CaO2@Cu-TCPP/CUR with O2/H2O2/Ca2+ self-supply and GSH depletion for enhanced PDT/CDT and Ca2+ overload synergistic therapy. CaO2 nanospheres were first prepared and used as templates for guiding the coordination between the carboxyl of tetra-(4-carboxyphenyl)porphine (TCPP) and Cu2+ ions as hollow CaO2@Cu-TCPP, which facilitated GSH-activated TCPP-based PDT and Cu+-mediated CDT. The hollow structure was then loaded with curcumin (CUR) to form CaO2@Cu-TCPP/CUR composites. Cu-TCPP prevented degradation of CaO2, while Cu2+ ions reacted with GSH to deplete GSH, produce Cu+ ions, and release TCPP, CaO2, and CUR. CaO2 reacted with H2O to generate O2, H2O2, and Ca2+ to achieve O2/H2O2/Ca2+ self-supply for TCPP-based PDT, Cu+-mediated CDT, and CUR-enhanced Ca2+ overload therapy. Thus, this multilevel ROS amplifier enhances synergistic therapy with fewer side effects and drug resistance.

Fe3O4 nanoparticles entrapped in the inner surfaces of N-doped carbon microtubes with enhanced biomimetic activity.

Tubular structured composites have attracted great interest in catalysis research owing to their void-confinement effects. In this work, we synthesized a pair of hollow N-doped carbon microtubes (NCMTs) with Fe3O4 nanoparticles (NPs) encapsulated inside NCMTs (Fe3O4@NCMTs) and supported outside NCMTs (NCMTs@Fe3O4) while keeping other structural features the same. The impact of structural effects on the catalytic activities was investigated by comparing a pair of hollow-structured nanocomposites. It was found that the Fe3O4@NCMTs possessed a higher peroxidase-like activity when compared with NCMTs@Fe3O4, demonstrating structural superiority of Fe3O4@NCMTs. Based on the excellent peroxidase-like catalytic activity and stability of Fe3O4@NCMTs, an ultra-sensitive colorimetric method was developed for the detection of H2O2 and GSH with detection limits of 0.15 µM and 0.49 µM, respectively, which has potential application value in biological sciences and biotechnology.

Interfacing Ag2S Nanoparticles and MoS2 Nanosheets on Polypyrrole Nanotubes with Enhanced Catalytic Performance.

The tubular architecture with multiple components can bring synergistic effects to improve the enzyme-like activity of molybdenum-based nanomaterials. Here, a facile polypyrrole (PPy)-protected hydrothermal sulfidation process was implemented to engineer MoS2/Ag2S heterointerfaces encapsulated in one-dimensional (1D) PPy nanotubes with MoO3@Ag nanorods as the self-sacrificing precursor. Notably, the sulfidation treatment led to the generation of MoS2 nanosheets (NSs) and Ag2S nanoparticles (NPs) and the creation of a tubular structure with a "kill three birds with one stone" role. The Ag2S/MoS2@PPy nanotubes showed the synergistic combined effects of Ag2S NPs, MoS2 NSs, and the 1D tube-like nanostructure. Based on the synergistic effects from these multiple components and the tubular structure, Ag2S/MoS2@PPy nanocomposites were used as a colorimetric sensing platform for detecting H2O2. Moreover, the reduction of 4-nitrophenol (4-NP) revealed excellent catalytic activity in the presence of NaBH4 and Ag2S/MoS2@PPy nanocomposites. This work highlights the effects of MoS2/Ag2S heterointerfaces and the hierarchical tubular structure in catalysis, thereby providing a new avenue for reducing 4-NP and the enzyme-like catalytic field.

Co, Fe Dual-Doped MoS2 Nanosheets on Polypyrrole Microtubes as Effective Peroxidase Mimics for Glutathione Sensing.

Heteroatom doping is considered an effective way to enhance the catalytic activity of MoS2 nanosheets (NSs). In the paper, dual-metal doping was proposed to incorporate Fe and Co into hierarchical MoS2 ultrathin NSs, which grew directly on polypyrrole microtubes (Fe, Co-MoS2@PPy), for the enhanced enzyme-like catalytic reaction. The particular hollow tubular structure realized effective electron transfer. The doped Fe and Co tuned the electronic architecture of the MoS2 NSs to enhance the enzyme-like catalytic activity. The abundant exposed void spaces facilitated ion diffusion/penetration between the PPy interlayer and Fe-Co doped MoS2 shell, leading to heterostructured synergistic effects. Therefore, the synthesized Fe and Co-MoS2@PPy composites showed remarkable catalytic activity. The high catalytic efficiency of Fe and Co-MoS2@PPy was confirmed with the reaction of tetramethylbenzidine (TMB) and H2O2 for visible detection. The blue color disappeared after adding glutathione (GSH). Thus, this procedure was used as a convenient way to detect GSH with a detection limit of 0.76 µM. The dual-metal-doped strategy was confirmed to improve the performance of MoS2 nanocomposites and could be used as a promising matrix for other applications, such as electrochemical energy conversion, medical diagnosis, and others.

"Three-in-One" Nanozyme Composite for Augmented Cascade Catalytic Tumor Therapy.

Cascade catalytic reaction exhibits simple procedure and high efficiency, such as that from the orderly assembly of different enzymes in biological systems. Mimicking of the natural cascade procedure becomes critical, but the orderly assembly of different enzymes is still challenging. Herein, single Au-Pt nanozyme is reported with "three-in-one" functions to initiate cascade conversions for O2 supply as mimic catalase, H2 O2 production with its glucose oxidase-like property, and • OH generation as mimic peroxidase for chemodynamic therapy (CDT). Thus, the complex assembly and cross-talk among the different enzymes are avoided. To this end, metastable Cu2 O NPs, as scaffolds, are used to anchor ultrasmall Au-Pt nanozyme, while metal-organic framework (MOF) is used to encapsulate the nanozyme for tumor microenvironment response and shielding protein adsorption. Pluronic F127 is then modified on the surface to improve hydrophilicity and biocompatibility of the composite. The endogenous acidity and glutathione in tumor degrade MOF to expose nanozyme for cascade catalytic CDT. The high photothermal conversion ability also enhances the CDT, while Cu2+ ions consume GSH to further improve CDT efficiency as augmented cascade catalytic tumor therapy. Thus, a new paradigm is provided with drug-free single nanozyme for improving tumor therapeutic efficacy and minimizing side effects.

General Approach to Construct C-C Single Bond-Linked Covalent Organic Frameworks.

C-C single bond-linked covalent organic frameworks (CSBL-COFs) are extremely needed because of their excellent stabilities and potential applications in harsh conditions. However, strategies to generate CSBL-COFs are limited to the acetylenic self-homocoupling Glaser-Hay reaction or post-synthetic reduction of vinylene-based COFs. Exploring new strategies to expand the realm of CSBL-COFs is urgently needed but extremely challenging. To address the synthetic challenges, we for the first time developed a general approach via the reaction between aromatic aldehydes and active methyl group-involving monomers with enhanced acidity, which realized the successful construction of a series of CSBL-COFs. As expected, the obtained CSBL-COFs exhibited outstanding chemical stability, which can stabilize in 6 M NaOH, 3 M HCl, boiling water, and 100 mg/mL NaBH4 for at least 3 days. It is important to mention that CSBL-COFs possess a large amount of ionic sites distributed throughout the networks; gentle shaking allowed our COFs to easily self-disperse as nanoparticles and suspend in water for at least 12 h without reprecipitating. As far as we know, such self-dispersed COFs with high water dispersity are rare to date, and few examples are mainly limited to the guanidinium- and pseudorotaxane-based COFs. Our work thus developed a family of self-dispersed COFs for potential applications in different sorts of fields. Our contribution would thus pave a new avenue for constructing a broader class of CSBL-COFs for their wide applications in various fields.

Organic Electrochemical Transistor Based on Hydrophobic Polymer Tuned by Ionic Gels.

Hydrophobic conjugated polymers have poor ionic transport property, so hydrophilic side chains are often grafted for their application as organic electrochemical transistors (OECTs). However, this modification lowers their charge transport ability. Here, an ionic gel interfacial layer is applied to improve the ionic transport while retaining the charge transport ability of the polymers. By using the ionic gels comprising gel matrix and ionic liquids as the interfacial layers, the hydrophobic polymer achieves the OECT feature with high transconductance, low threshold voltage, high current on/off ratio, short switching time, and high operational stability. The working mechanism is also revealed. Moreover, the OECT performance can be tuned by varying the types and ratios of ionic gels. With the proposed ionic gel strategy, OECTs can be effectively realized with hydrophobic conjugated polymers.

Reactive Template-Engaged Synthesis of NiSx/MoS2 Nanosheets Decorated on Hollow and Porous Carbon Microtubes with Optimal Electronic Modulation toward High-Performance Enzyme-like Performance.

As a promising cost-effective nanozyme, MoS2 nanosheets (NSs) have been considered as a good candidate for the enzyme-like catalysis. However, their catalytic activity is still restricted by the insufficient active sites and poor conductivity, and thus, the comprehensive performances are still unsatisfactory. To address these issues, herein, we design and fabricate an intelligent tubular nanostructure of hierarchical hollow nanotubes, which are assembled by NiSx/MoS2 NSs encapsulated into N-doped carbon microtubes (NiSx/MoS2@NCMTs). The N-doped carbon microtubes (NCMTs) serve as a conductive skeleton, integrating with NiSx/MoS2 NSs and ensuring their well-distribution, thereby maximally exposing more active sites. Additionally, the tube-like structure is favorable for increasing the mass transfusion to ensure their excellent catalytic performance. Profiting from their component and structural advantages, the obtained NiSx/MoS2@NCMTs exhibit a surprisingly enhanced enzyme-like activity. Based on these, a facile colorimetric sensing platform to detect H2O2 and GSH has been developed. This proposed approach can be expected to synthesize a series of tubular heterostructured MoS2-based composites, which will be widely applied in catalysis, energy storage, disease diagnosis, etc.

Formation of SiO2@C-Ni magnetic nanotubes with excellent performance in 4-nitrophenol reduction.

A facile and rational strategy for immobilizing nickel nanoparticles (Ni NPs) on silica nanotubes (SiO2@C-Ni) was developed via the Stöber method, nickel ion mediated dopamine polymerization and carbonization treatment, coupled with removal of the template of one-dimensional (1D) MnO2 nanowires (NWs). The as-prepared SiO2@C-Ni nanotubes show vast interior space with a large specific surface area and an open channel, which offer a spacious transport channel for molecular diffusion and electron transfer. Consequently, SiO2@C-Ni nanotubes exhibited outstanding catalytic efficiency and excellent stability for 4-nitrophenol (4-NP) reduction. Their superior catalytic activity could be ascribed to the high coverage of Ni NPs and the tubular structure of the obtained SiO2@C-Ni, by which the silica nanotubes enhanced the accessibility of the active sites and increased the mass transfer. This facile and controllable strategy may introduce a new avenue for designing metal NP-supported composites with high dispersion for diverse applications.

Flexible ligand-Gd dye-encapsulated dual-emission metal-organic framework.

Multiple emission metal-organic frameworks (MOFs) are superior materials for ratiometric fluorescence sensing and visible detection applications. The guest-encapsulation strategy is a simple method for the integration of the open structure of MOFs and the abundant choice of emissive guests. Herein, we reveal the factors that affect the performance of host-guest multi-emission MOFs based on the choice of ligands, metal nodes, and guest dyes. The size of organic dyes is often larger than 1 nm, which is incompatible with the small pores of traditional MOFs. Therefore, we selected a flexible ligand, i.e., 1,3,5-tris(5-methoxy-1,3-benzene dicarboxylic acid)benzene (L), to enlarge the pore size of the MOF to 18 Å. Energy transfer may occur from the ligand and guest dye to the metal nodes; thus, we selected the Gd3+ ion because of its high excited state level. L and Gd3+ ions were used to form the Gd-L MOF with the pore size of 18 Å, as revealed by the single crystal result. Rhodamine B (RhB), as the guest dye with the size of 15.9 × 11.8 × 5.6 Å3, was encapsulated in Gd-L MOF, which was denoted as RhB@MOF. The matched size between RhB and the MOF pore and the breathing effect of the flexible MOF effectively prevented the leakage of RhB. Accordingly, dual emission was observed at 360 nm and 583 nm under the excitation of 290 nm from RhB@MOF. Alternatively, Cu2+ quenched the emission at 360 nm due to the electron transfer process, while Fe3+ interacted with both L and RhB, and thus quenched the two emissions simultaneously. However, other metal ions showed little effect on the two emissions. Consequently, the differentiation between Cu2+ and Fe3+ as well as them from other metal ions was realized with the dual-emission MOF. Thus, the guest-encapsulation strategy is simple and flexible ligands are efficient to encapsulate molecular dyes for dual-emission MOFs to improve their sensing performance, while flexible ligands are powerful to enhance the capacity and extend the applications of MOFs.

Highly active CoNi nanoparticles confined in N-doped carbon microtubes for efficient catalytic performance.

Engineering a tube-like architecture with bimetallic nanoparticles (NPs) has been considered an effective strategy for enhancing catalytic performance. Herein, we report a simple method for preparing one-dimensional (1D) carbon-based tubular composites incorporated with bimetallic active CoNi alloy NPs. CoNi alloy NPs were produced from the co-reduction of Co and Ni ions existing within a zeolitic imidazolate framework (ZIF)-based precursor and polydopamine (PDA) layer after N2-protected thermal treatment. Moreover, the coated PDA outer layer was preserved for constructing a tubular structure, which eventually resulted in a composite of N-doped carbon microtubes (NCMTs) and CoNi NPs (CoNi@NCMTs). The resultant CoNi@NCMTs exhibited excellent catalytic activity for reducing 4-nitrophenol to 4-aminophenol. The synergy between the N-doped carbon microtubes and the well-dispersed bimetallic CoNi NPs provided outstanding catalytic performance, constructing inexpensive transition metal nanocatalysts. Moreover, the catalytic activity of the CoNi@NCMTs was well conserved even after five consecutive cyclic reactions. Importantly, hierarchical MoO3@CoNi-LDH can be a good precursor to obtain tube-like structured CoNi-LDH, CoNi-LDH@SiO2 and CoNi-LDH@NiMoO4 composites.

Hierarchical microtubes constructed using Fe-doped MoS2 nanosheets for biosensing applications.

The structural design of multiple functional components could enhance the synergistic catalytic performance of MoS2-based composites in enzyme-like catalysis. Herein, one-dimensional (1D) Fe-MoS2 microtubes were designed to prepare tubular Fe-doped MoS2 composites with MoO3 microrods as self-sacrificing precursors. Remarkably, the results indicated that the generated ammonia released from the sulfidation process led to the dissolution of MoO3 cores and the generation of a tubular structure. The Fe-MoS2 composites integrated the synergistic effects of Fe-doped MoS2 nanosheets (NSs) and the 1D tubular structure. Thus, a higher catalytic activity was observed in peroxidase-like catalysis than in other components, such as MoO3@FeOOH, FeOOH and MoS2 NSs. The peroxidase-like mechanism originated from the generation of the ˙OH radical. The Fe-MoS2 microtube-based colorimetric assay was used to detect H2O2 with a detection limit (LOD) of 0.51 µM in a linear range from 1.25 to 50 µM. The colorimetric method was simple, selective, and sensitive for glutathione (GSH) detection in the range of 0.25-125 µM with a detection limit (LOD) of 0.12 µM. Thus, we provide a facile synthetic strategy for simultaneously integrating electronic modulation and structural design to develop an efficient MoS2-based functional catalyst.

Coupled nickel-cobalt nanoparticles/N,P,S-co-doped carbon hybrid nanocages with high performance for catalysis and protein adsorption.

Carbon-supported bimetallic NiCo nanoparticles (NPs) have emerged as attractive catalysts and adsorbents for the reduction of 4-nitrophenol (4-NP) and separation of histidine-rich (His-rich) protein recently due to their low cost, high catalytic activity and good affinity for His-rich protein. In this study, new strongly coupled nickel-cobalt alloy/N,P,S co-doped carbon (NPSC) nanocages are rationally designed via chemical etching of the ZIF-67 dodecahedron with Ni2+ under sonication at room temperature, followed by poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) coating and subsequent carbonization treatment in a nitrogen atmosphere. When evaluated as a catalyst for 4-NP or an adsorbent for His-rich protein, the as-prepared NiCo@NPSC nanocages obtained at 700 °C show better performance than those obtained at other temperatures (500 and 900 °C). This improved catalytic effect is attributed to the controllable size and fine distribution of the NiCo NPs together with the effective contact between the catalysts and the N,P,S co-doped carbon matrix, leading to a superior catalytic effect on the reduction of 4-NP and the adsorption of His-rich protein. This catalyst design principle can be easily extended to other catalysis research fields.

Mixed-Ligand Metal-Organic Frameworks for All-in-One Theranostics with Controlled Drug Delivery and Enhanced Photodynamic Therapy.

Mixed-ligand metal-organic frameworks (MOFs) multiply the properties and improve the versatility of conventional MOFs for theranostic applications. A tumor targeting and tumoral microenvironment-responsive system is significant for specific and efficient cancer theranostics. Herein, we report a kind of versatile mixed-porphyrin ligand MOF as a multifunctional matrix for multimodality-imaging-guided synergistic therapy. Tetrakis(4-carboxyphenyl)porphyrin (TCPP) shows the properties of fluorescence (FL) and photodynamic therapy (PDT), while Mn-TCPP owns magically the properties of T1-weighted magnetic resonance (MR) imaging and photothermal conversion for photothermal imaging and photothermal therapy (PTT). Because of the same coordination capacity and mode of TCPP and Mn-TCPP to Zr4+ ions, MOFs with adjustable ligand ratios were easily prepared. The mixed-ligand MOFs exhibited a high drug loading capacity for 10-hydroxycamptothecin (HCPT, 65%). After modification with hyaluronic acid (HA) through a disulfide bond (-S-S-), the MOF-S-S-HA composites possess enhanced PDT and tumor-targeted redox-responsive drug release properties due to the -S-S- bond. Thus, excellent fluorescence, MR, and photothermal trimodality imaging, redox-responsive drug release, and enhanced PDT/PTT are integrated together in the mixed-ligand MOFs as "all-in-one" theranostic agents.

Rational design of dual-ligand Eu-MOF for ratiometric fluorescence sensing Cu2+ ions in human serum to diagnose Wilson's disease.

Copper levels in body fluids provide an important reference for the diagnosis of Wilson's disease, which associated with blood abnormalities, kidney and cardiovascular disease, and neuropathy. Metal-organic frameworks (MOF) can easily realize dual-emission from single excitation as ratiometric fluorescence sensing and visible detection platform with the intensity ratio of two emissions for simple, rapid, sensitive, and specific analysis of biological samples. Here, we rationally designed a dual-emission Eu-MOF with dual-ligand strategy, denoted as Eu-DATA/BDC. While terephthalic acid (H2BDC) was selected to sensitize Eu3+ ions for the antenna effect emission, 2,5-diaminoterephthalic acid (H2DATA) maintained its own emission and was used to identify Cu2+ ions. Thus, dual-emission from Eu-DATA/BDC and specific recognition of Cu2+ ions were realized for ratiometric sensing of Cu2+ ions. A wide linear concentration range (1-40 µM), low detection limit (0.15 µM), and fast response (less than 10 s) were realized. The color change also achieved the visible detection by naked eye. Copper levels were tested with human serum samples and compared to the ICP-OES results, confirmed the potential of Eu-DATA/BDC probe in the diagnosis of Wilson's disease. The response mechanism to Cu2+ ions was proposed as electron transfer between host and guest for fluorescence quenching. Thus, dual-ligand is a simple and efficient strategy to prepared dual-emission Eu-MOF for the ratiometric sensing and visible detection.

Design and Multiple Applications of Mixed-Ligand Metal-Organic Frameworks with Dual Emission.

Herein, we revealed the factors that affect the emission in mixed-ligand metal-organic frameworks (MOFs) with the combination of terephthalic acid (BDC), 2-aminoterephthalic acid (BDC-NH2), and 2,5-dihydroxylterephthalic acid [BDC-(OH)2] as models. The -NH2 and -(OH)2 groups change the π-conjugation and luminescence behaviors than BDC, so the ligands show different optical behaviors. The Zn2+ ion with a 3d10 full electronic structure shows little effect on the emission of the ligand and is selected as the metal node. We found that the emission of BDC is weak and incompatible to that of BDC-NH2, so only the emission of BDC-NH2 was observed in the BDC/BDC-NH2-MOF. Crosstalk occurs between the emissions from BDC and BDC-(OH)2 for the single emission from BDC/BDC-(OH)2-MOFs, even different ratios are selected. The MOFs prepared with BDC-NH2 and BDC-(OH)2 show dual emission at 450 and 550 nm, while the relative intensity was easily tuned with the ligand ratio and excitation wavelength. Thus, abundant optical behaviors and extensive applications were realized, including but not limited to (1) dual emission from single MOFs, (2) tunable color from blue to yellow with the excitation from 290 to 370 nm for information encryption and decryption, (3) white emission obtained under an excitation of 330 nm, and (4) response of -NH2 groups to HCHO and Fe3+ ions for ratiometric fluorescence sensing and visual detection. This work revealed the factors that affect the emission in mixed-ligand MOFs, studied their optical behaviors, and realized different applications with single MOFs.

Facile strategy for the synthesis of silver nanoparticles on magnetic Fe3O4@C core-shell nanocomposites and their application in catalytic reduction.

The integration of noble metal nanoparticles (NPs) on magnetic hollow structures is of particular importance for high catalytic activity, while the magnetic property is useful for the recovery of the composites. Herein, we prepared Ag NP decorated Fe3O4@C hollow magnetic microtubes by a facile and controllable approach. To this end, tannic acid-ferric ion (TA-Fe) first polymerized in situ on the MoO3@FeOOH microrods and served as a reducing/stabilizing agent to integrate Ag NPs with high coverage. Moreover, no extra reductant was required owing to the reducibility of TA for the formation of FeOOH@TA-Fe/Ag microtubes. After thermal treatment under an N2 atmosphere, hollow Fe3O4@C-Ag microtubes are obtained with a high surface area and excellent magnetism. Remarkable catalytic activity was achieved towards the reduction of 4-nitrophenol (4-NP) owing to the high coverage of Ag NPs on the tube-like structure, while the composite was easily collected with an external magnet. The integration of Ag NPs and the magnetic hollow structure provides a great platform for designing hybrid catalysts with high efficiency and recoverability.