Size-controlled growth of ZnSe nanocrystals for high-performance photocatalytic H2O2 production in pure water.

Semiconductor photocatalysis is deemed as a novel and promising process that can produce H2O2 from earth-abundant water and gaseous dioxygen using sunlight as the energy supply. The searching of novel catalysts for photocatalytic H2O2 production has received increasing attention in the last few years. Herein, size-controlled growth of ZnSe nanocrystals was realized via a solvothermal method by varying the amount of Se and KBH4. The performance of the as-obtained ZnSe nanocrystals towards photocatalytic H2O2 production depends on the mean size of the synthesized nanocrystals. Under O2-bubbling, the optimal ZnSe sample presented an excellent H2O2 production efficiency (8.596 mmol g-1 h-1), and the apparent quantum efficiency for H2O2 production reaches as high as 2.84% at λ = 420 nm. Under air-bubbling, the accumulation of H2O2 was as high as 1.758 mmol L-1 after 3 h irradiation at the ZnSe dosage of 0.4 g L-1. The photocatalytic H2O2 production performance is far superior to the most investigated semiconductors such as TiO2, g-C3N4, and ZnS.

Effects of Additives on Electrochromic Properties of Nanocrystalline Tungsten Oxide Films Prepared by Complexation-Assisted Sol-Gel Method.

To improve the electrochromic (EC) properties of sol-gel-derived WO3 films, a series of organic small molecules, such as dopamine (DA), catechol, tyramine, phenol and 2-phenylethylamine, were added into peroxotungstic acid precursor sols as structure-directing additives, and five modified WO3 films were prepared by a simple and low-cost complexation-assisted sol-gel method. The effects of the above additives on the EC properties of the modified WO3 films have been studied in detail. Compared with the pure WO3 polycrystalline film, all the modified films combine the advantages of nanocrystalline and amorphous phases and show higher EC properties attributed to the unique nanocrystal-embedded amorphous structure. The results indicate that different additives with different numbers and types of functional groups (hydroxyl and amino groups) can change the microstructure, morphology, and thus electrochemical and EC properties of the films in various degrees. The additives, in order of their strong interactions with the sols, are DA, catechol, tyramine, phenol and 2-phenylethylamine, primarily depending on the number of hydroxyl groups. Of all the additives, DA with both catechol hydroxyl and amino groups shows the most positive effect; that is, the WO3 film modified with DA exhibits the best EC properties in terms of contrast, switching speed, stability, and coloration efficiency.

Oxygen-powered flower-like FeMo6@CeO2 self-cascade nanozymes: a turn-on enhancement fluorescence sensor.

Enzyme cascade reactions in organisms have sparked tremendous interest for their coupled catalysis-facilitated efficient biochemical reactions. However, multi-enzyme cascade nanozymes remain largely unused. In the work, flower-like porous ceria-based integrated enzymes (INAzyme), FeMo6@CeO2 (FMC-n), were readily prepared using an efficient thermally induced process. Owing to a larger specific surface area and excellent adsorption, the flower-like matrix (CeO2) can serve as not only an effective sorbent for the conversion of dissolved oxygen in solution but also an excellent support for self-cascade reactions with FeMo6. Based on the electron transfer through Fe and Ce cycles, FMC-n INAzyme exhibits intrinsic oxidase-, peroxidase- and Fenton-like activities. Moreover, by assessing the Vo mobility and F-Vo relative content of FMC-2 and FC-66, we found that the contribution of enhanced accessibility through the specific surface area (SSA) to the activity of the INAzyme is significantly higher than the active sites. Finally, a fluorescence turn-on enhancement sensing platform based on self-cascade FMC-n for the detection of Cys was established, culminating in a LOD of as low as 0.014 µM in the range of 1-100 µM.

An Unprecedented FeMo6 @Ce-Uio-66 Nanocomposite with Cascade Enzyme-Mimic Activity as Colorimetric Sensing Platform.

Introducing the idea of integrated design and cascade activity into nanozyme, the novel integrated nanozymes (INAzymes), FeMo6 @Ce-Uio-66 (FC-66(n)), were designed and synthesized by encapsulating iron-based polyoxometalates (FeMo6 ) into the ceria-based metal-organic framework (Ce-Uio-66). Due to the oxygen-driven reversible Ce3+ /Ce4+ couple sites, the "Fenton-like" effect by iron centers, the "nanoscale proximity" effects by nanocages, and their synergistic effects, FC-66(n) as INAzymes exhibit elegant cascade enzyme-mimic activities (oxidase-, peroxidase-, and Fenton-like activity), which realizes INAzyme activities based on polyoxometalates based metal-organic framework (POMOFs). By employing dopamine (DA) detection as a model reaction, a high-efficient fluorescent "turning-on-enhanced" platform under near neutral conditions was established.

Hollow POM@MOF-derived Porous NiMo6 @Co3 O4 for Biothiol Colorimetric Detection.

Developing highly active and sensitive peroxidase mimics for L -cysteine (L -Cys) colorimetric detection is very important for biotechnology and medical diagnosis. Herein, polyoxometalate-doped porous Co3 O4 composite (NiMo6 @Co3 O4 ) was designed and prepared for the first time. Compared with pure and commercial Co3 O4 , NiMo6 @Co3 O4 (n) composites exhibit the enhanced peroxidase-mimicking activities and stabilities due to the strong synergistic effect between porous Co3 O4 and multi-electron NiMo6 clusters. Moreover, the peroxidase-mimicking activities of NiMo6 @Co3 O4 (n) composites are heavily dependent on the doping mass of NiMo6 , and the optimized NiMo6 @Co3 O4 (2) exhibits the superlative peroxidase-mimicking activity. More importantly, a sensitive L -Cys colorimetric detection is developed with the sensitivity of 0.023 µM-1 and the detection limit at least 0.018 µM in the linear range of 1-20 µM, which is by far the best enzyme-mimetic performances, to the best our knowledge.

Seeded Growth of Au@CuxO Core-Shell Mesoporous Nanospheres and Their Photocatalytic Properties.

We report a facile synthesis of Au@CuxO core-shell mesoporous nanospheres with tunable size in the aqueous phase via seeded growth. The success of the current work relies on the use of a halide-free copper (Cu) precursor and n-oleyl-1,3-propanediamine as a capping agent to facilitate the formation of a copperish oxide shell with a mesoporous structure and the presence of mixed oxidation states of Cu. By varying the amount of spherical Au seeds while keeping other parameters unchanged, their diameters could be readily tuned without noticeable change in morphology. As compared with commercial Cu2O, the as-prepared Au@CuxO core-shell mesoporous nanospheres exhibit the higher adsorption ability, enhanced activity, and excellent stability toward photocatalytic degradation of methyl orange (MO) under visible light irradiation, indicating their potential applications in water treatment.

Iron reduction and diopside-based glass ceramic preparation based on mineral carbonation of steel slag.

In this article, a new process for treating steel slag and CO2 simultaneously and preparing calcium carbonate, metallic iron, and glass ceramics without wastewater or gas production is proposed. The reduction of iron and preparation of diopside glass ceramics are studied in this paper, and the results show that the carbon thermal reduction product of the original slag does not reach its melting point, and the slag and iron are well separated in the samples containing the leached steel slag and added silica. Part of the parent glass is converted into a glass ceramic after heat treatment, and the crystalline phases of samples are melilite, diopside, and partial melilite, and diopside and anorthite, respectively. The crystallization activation energy of the best sample in this article is E = 660.664 kJ/mol. The Avrami indices calculated at different heating rates are all less than 3, which indicates that the crystallization mode of the glass involves surface crystallization. This finding is consistent with the results for the prepared glass ceramics.

Effects of Polyoxometalates on the Hydroxylation of N-Heterocyclic Ligands.

Four polyoxometalate (POM)-based Cu complexes with the hydroxylated pyridine analogue 3-(2-hydroxylpyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl (btpo), H3{[Cu2(btpo)2](PW12O40)}·2H2O (1), H3{[Cu2(btpo)2](PMo12O40)}·2H2O (2), H2{[Cu2(btpo)2](SiW12O40)·SO4 (3), and H4{[Cu4(btpo)4](SiW12O40)}·8H2O (4), were synthesized hydrothermally under acid conditions. Single-crystal X-ray structural analysis reveals that 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl was hydroxylated into btpo in compounds 1-4, again providing structural evidence for the Gillard mechanism, in which H2O as a weak nucleophile can attack the α-C atom of N-heterocyclic molecules at a lower pH value (ca. 1.0) with the help of POMs.

Polyelectrolyte-functionalized reduced graphene oxide wrapped helical POMOF nanocomposites for bioenzyme-free colorimetric biosensing.

For the sake of effective colorimetric sensing-pattern, a sensitive colorimetric sensor was conceived based on polyoxometalates based metal-organic frameworks (POMOFs) and polydiallyldimethylammonium chloride functionalized reduced graphene oxide (PDDA-rGO) for the first time, in which PDDA as a "glue" molecule turns rGO nanosheets into general platforms for bonding POMOFs nanoparticles. Herein, a new POMOF compound with fascinating helices-on-helices feature, [Ni4(Trz)6(H2O)2][SiW12O40].4H2O (Trz = 1,2,4-triazole) (abbreviated as Ni4SiW12), was synthesized and characterized, then PDDA-rGO sheet as dispersive and conductive material was successfully introduced to Ni4SiW12 fabricating new PDDA-rGO/Ni4SiW12-n nanocomposites, (abbreviated as PMPG-n). The resulting PMPG-n nanocomposites as peroxidase mimetic show excellent catalytic activities under extreme condition (pH value 2.5), attributed to the nature and synergies from POMs, MOFs and PDDA-rGOs. Note that the peroxidase-like activity of PMPG-1 (the mass ratio of Ni4SiW12 to PDDA-rGO is 1:1) exhibits higher sensitivity (1-60 µM), faster response (10 min) and the lowest limit of detection (2.07 µM) among all reported materials to citric acid (CA) to date. This work opens up new application prospects in colorimetric sensing system for food quality control and safety, biotechnology and clinical diagnosis.

Assembly of 12-Tungstovanadate-Templated Nanocage and Nanocomposites with Single-Walled Carbon Nanotubes as Anodes in Lithium-Ion Batteries.

A new 12-tungstovanadate-templated 3D nanocage framework, Ag10(µ4-ttz)4(H2O)4(VW12O40) (VW12@MOCF), was designed based on a "molecular library", hydrothermally synthesized, structurally characterized, and explored as anode material for lithium-ion batteries (LIBs). Combination of the structural superiority of VW12@MOCF with the good electrical conductivity of the single-walled carbon nanotubes (SWNTs) renders the VW12@MOCF/SWNT-2 nanocomposite reasonable electrochemical performance and stability as anode materials of LIBs. The successful cooperative fabrication of nanocages and polyoxometalate (POMs) must initiate extensive research interests.

Heightened Integration of POM-based Metal-Organic Frameworks with Functionalized Single-Walled Carbon Nanotubes for Superior Energy Storage.

To increase the conductivity of polyoxometalate-based metal-organic frameworks (POMOFs) and promote their applications in the field of energy storage, herein, a simple approach was employed to improve their overall electrochemical performances by introducing a functionalized single-walled carbon nanotubes (SWNT-COOH). A new POMOF compound, [Cu18 (trz)12 Cl3 (H2 O)2 ][PW12 O40 ] (CuPW), was successfully synthesized, then the size-matched functionalized SWNT-COOH was introduced to fabricate CuPW/SWNT-COOH composite (PMNT-COOH) by employing a simple sonication-driven periodic functionalization strategy. When the PMNT-COOH nanocomposite was used as the anode material for Lithium-ion batteries (LIBs), PMNT-COOH(3) (CuPWNC:SWNT-COOH=3:1) showed superior behavior of energy storage, a high reversible capacity of 885 mA h g-1 up to a cycle life of 170 cycles. The electrochemical results indicate that the uniform packing of SWNT-COOH provided a favored contact between the electrolyte and the electrode, resulting in enhanced specific capacity during lithium insertion/extraction process. This fabrication of PMNT-COOH nanocomposite opens new avenues for the design and synthesis of new generation electrode materials for LIBs.

The Indirect Mineral Carbonation of Electric Arc Furnace Slag Under Microwave Irradiation.

The indirect mineral carbonation of industrial residues is one of the potential technologies for CO2 sequestration. In this paper, the leaching and carbonation of electric arc furnace (EAF) slag under microwave irradiation was investigated. The experimental results show that the main reactive calcium-containing phase in the EAF slag carbonation process is calcium silicate, and the final leaching ratio of larger particles is lower than that of smaller particles due to the silica layer produced on the surface of the calcium silicate. The Drozdov equation with a self-impeding coefficient can describe EAF slag leaching kinetics under microwave irradiation. The explosive homogeneous nucleation phenomenon under microwave irradiation contributes to the thinning and narrowing of crystals. Microwave irradiation can inhibit the crystaltype transformation of vaterite.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs.

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag3(FKZ)2(H2O)2][H3SiW12O40] (AgFKZSiW12) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW12@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW12 clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW12@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW12 (2 min). Moreover, the AgFKZSiW12@PPy-based colorimetric biosensing platform towards H2O2 and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 µM and 2.7 µM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.