Photoactive and Intrinsically Fuel Sensing Metal-Organic Framework Motors for Tailoring Collective Behaviors of Active-Passive Colloids.

Microorganisms display nonequilibrium predator-prey behaviors, such as chasing-escaping and schooling via chemotactic interactions. Even though artificial systems have revealed such biomimetic behaviors, switching between them by control over chemotactic interactions is rare. Here, a spindle-like iron-based metal-organic framework (MOF) colloidal motor which self-propels in glucose and H2 O2 , triggered by UV light is reported. These motors display intrinsic UV light-triggered fuel-dependent chemotactic interactions, which are used to tailor the collective dynamics of active-passive colloidal mixtures. In particular, the mixtures of active MOF motors with passive colloids exhibit distinctive "chasing-escaping" or "schooling" behaviors, depending on glucose or hydrogen peroxide being used as the fuel. The transition in the collective behaviors is attributed to an alteration in the sign of ionic diffusiophoretic interactions, resulting from a change in the ionic clouds produced. This study offers a new strategy on tuning the communication between active and passive colloids, which holds substantial potentials for fundamental research in active matter and practical applications in cargo delivery, chemical sensing, and particle segregation.

Inorganic-Organic Hybrid Copolymeric Colloids as Multicolor Emission, Fuel-Free, UV- and Visible-Light-Actuated Micropumps.

Light-actuated micromachines are of enormous interest due to their ability to harvest light for triggering catalytic reactions to acquire free energy for mechanical work. This work presents an inorganic-organic hybrid copolymeric poly(cyclotriphosphazene-co-barbituric acid) colloid, which displays multiwavelength excited emission and catalytic activities, exploiting the unique structural, chemical, and optical features of inorganic heterocyclic ring hexachlorocyclotriphosphazene and organic co-monomer barbituric acid. Specifically, this work reveals particle-resolved unusual multicolor emission under excitation with the same or different wavelengths of light using fluorescence microscopy. The result is rationalized by density functional theory studies. In this work, the authors find that emission is coincident with fluorometric measurements, and the photocatalytic properties are anticipated from the overall band structure. This work also demonstrates the use of these colloids as micropumps, which can be remotely activated by UV, blue, and green lights under fuel-free conditions, and ascribe the behavior to ionic diffusiophoresis arising from light-triggered generation of H+ and other charged species. This work offers a new class of polymeric colloids with multiple-wavelength excited emission and catalytic activities, which is expected to open new opportunities in the design of fuel-free, photo-actuated micromachines and active systems.

Development of novel K0.8Ni0.4Ti1.6O4 nano bamboo leaves, microstructural characterization, double absorption, and photocatalytic removal of organic pollutant.

Novel K0.8Ni0.4Ti1.6O4 (KNTO) nano bamboo leaves were prepared for the first time under a simple hydrothermal method with 3 M KOH at 320 °C over 80 min. Highly pure KNTO possessing layered structure was determined by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). Double absorption feature of KNTO semiconductor was revealed at band energies of 1.88 and 2.08 eV by the UV-vis diffuse reflectance spectra and confirmed by the photoluminescence (PL) spectra. The photocatalytic activity was explored by the photodegradation of MB organic dye. KNTO not only exhibits strong adsorptive ability on methylene blue (MB) in dark environment, but also possesses good photodegradation capability of 94% degradation in 60 min. Degradation mechanism revealed that the photogenerated holes play an essential role in the MB degradation process, which is confirmed by trapping experiments. The recycling experiments demonstrated very high recycling ability and durability of KNTO nano bamboo leaves, suggesting KNTO is a potential candidate for high efficiency organic pollutant removal in the wastewater treatment.

Synergetic Effects of Pd0 Metal Nanoparticles and Pd2+ Ions on Enhanced Photocatalytic Activity of ZnWO4 Nanorods for Nitric Oxide Removal.

Doping and novel metallic nanoparticles loading on the photocatalyst are two effective means to enhance its photocatalytic activity. In our study, Pd0/Pd2+-co-modified ZnWO4 nanorods were fabricated by a two-step hydrothermal process and room-temperature reduction method. The performance of the as-prepared samples was evaluated through the photocatalytic nitric oxide (NOx) removal under simulated solar and visible-light irradiation. Pd0/Pd2+-co-modified ZnWO4 nanorods present a significantly enhanced photocatalytic activity for NOx removal compared with Pd0-loaded or Pd2+-doped ZnWO4 under simulated sunlight irradiation owing to a narrower band gap of Pd2+ doping compared with that of pure ZnWO4. The role of Pd0 nanoparticles is to act as an electron reservoir to restrain the recombination of e-/h+ pairs. According to the trapping measurements, the photoinduced holes and electrons play critical roles during the photocatalytic process. In addition, electron spin resonance (ESR) results further confirm that •O2- and •OH radicals are present and assist in the photocatalysis under simulated solar light irradiation. Stability test demonstrated that 1.5% Pd0/0.5% Pd2+-co-modified ZnWO4 nanorods as photocatalyst have high photocatalytic stability in NOx removal. This work proved that Pd0/Pd2+-co-modified ZnWO4 nanorods can be considered as an efficient photocatalyst for NOx removal.

Novel Single-Crystal Hollandite K1.46Fe0.8Ti7.2O16 Microrods: Synthesis, Double Absorption, and Magnetism.

Novel multifeatured hollandite K1.46Fe0.8Ti7.2O16 (KFTO) was synthesized by a simple hydrothermal method. Magnetic KFTO microrods were well controlled to long rectangular rods with pyramid-shaped tops. A KFTO growth mechanism was proposed on the basis of examining phase and morphology of the samples acquired at different reaction times. The KFTO morphology was confirmed by the calculated surface energies. The UV-vis diffuse reflectance spectra of KFTO microrods showed double absorption with band gaps of 2.01 and 2.16 eV, which was further confirmed by photoluminescence. First-principles studies revealed that the double absorption and magnetic properties originate from the d-d transitions of Fe3+ under the crystal field. The magnetic property could be applied in ferromagnetic semiconductor devices and the double absorption could be applied in visible-light harvesting. This work highlights the multifunctional KFTO microrods with low cost and environmental friendliness.

Novel magnetic properties of CoTe nanorods and diversified CoTe2 nanostructures obtained at different NaOH concentrations.

CoTe and CoTe2 nanorods with average diameter of 100 nm were synthesized by a simple hydrothermal process, and different CoTe2 nanostructures were obtained by changing the NaOH concentration. CoTe nanorods exhibit weak ferromagnetism while CoTe2 nanorods present paramagnetic behavior. Different magnetic behaviors occur in the other CoTe2 nanostructures due to Na+ entrance into CoTe2 crystals. A first-principles study on Na-doped CoTe2 confirms the magnetic characteristics.

LaCoO3/SBA-15 as a high surface area catalyst to activate peroxymonosulfate for degrading atrazine in water.

An efficient perovskite-based heterogeneous catalyst is highly desired to activate peroxymonosulfate (PMS) for removing organic pollutants in water. A high surface area PMS-activator was fabricated by loading LaCoO3 on SBA-15 to degrade atrazine (ATR) in water. The LaCoO3/SBA-15 depicted better textural properties and higher catalytic activity than LaCoO3. In 6.0 min, atrazine (ATZ) degradation in the selected LaCoO3/SBA-15/PMS system, LaCoO3, adsorption by LaCoO3/SBA-15, sole PMS processes reached approximately 100%, 55.15%, 12.80%, and 16.65 % respectively. Furthermore, 0.04 mg L-1 Co was leached from LaCoO3/SBA-15 during PMS activation by LaCoO3/SBA-15. The LaCoO3/SBA-15 showed stable catalytic activity after reuse. The use of radical scavengers and electron paramagnetic resonance spectroscopy (EPR) demonstrated that ROS such as 1O2, O2•-, •OH, and SO4•- were generated by PMS activated by LaCoO3/SBA-15 owing to redox reactions [Co2+/Co3+, and O2-/O2]. EPR, XPS, ATR-FTIR, EIS, LSV, and chronoamperometric measurements were used to explain the catalytic mechanism for PMS activation. Excellent atrazine degradation was due to high surface area, porous nature, diffusion-friendly structure, and ROS. Our investigation proposes that perovskites with different A and B metals and modified perovskites can be loaded on high surface area materials to activate PMS into ROS.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts.

Bi5O7I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi5O7I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi5O7I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi5O7I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi5O7I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi5O7I were also developed to further boost the efficiency of Bi5O7I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi5O7I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

Controlled Fabrication of K2Ti8O17 Nanowires for Highly Efficient and Ultrafast Adsorption toward Methylene Blue.

Advanced adsorbents need high adsorption rate and superior adsorption capability to clean up organic methylene blue (MB) from wastewater. We prepared K2Ti8O17 nanowires grown along the [0 1 0] direction with a one-step hydrothermal method. The K2Ti8O17 nanowires with tens of nanometers in diameter and tens of micrometers in length were achieved with smooth surfaces and twisted wire-like morphology. The K2Ti8O17 nanowires exhibit high uptake capacity of ∼208.8 mg·g-1 in the MB removal under equilibrium pH = 7. The adsorption equilibrium of MB onto the K2Ti8O17 adsorbent is achieved with a 97% removal rate of MB within only ∼21 min, which is the shortest adsorption time among the recently reported inorganic adsorbents toward MB. The adsorption process has a good agreement with the well-known pseudo-second-order kinetic model (k2 = 0.2) and the Langmuir isotherm model. Fourier transform infrared measurements suggest that the adsorption can be assigned to the hydrogen bonding and electrostatic attraction between MB and K2Ti8O17. This ultrafast removal ability is due to the larger (0 2 0) interplanar spacing and zigzag surface structure of the nanowires, which provide abundant active adsorption sites. Thermodynamic parameters reflect the spontaneous, exothermic, and feasible uptake of MB. Besides, K2Ti8O17 nanowires enjoy high adsorptive ability for chromium(VI) ions and photocatalytic removal toward NO. This work highlights the great significance of K2Ti8O17 nanowires as a low-cost promising material used for the adsorptive elimination of organic contaminations in fast water purification on a large scale.

Novel Au/La-Bi5O7I Microspheres with Efficient Visible-Light Photocatalytic Activity for NO Removal: Synergistic Effect of Au Nanoparticles, La Doping, and Oxygen Vacancy.

Sphere-like Bi5O7I (BOI) doped with La (L-BOI) samples were prepared by a solvothermal method followed by calcination at 450 °C for 2 h. Au nanoparticles were loaded on 6% La-doped Bi5O7I (2%A-6%L-BOI) microspheres by a room-temperature chemical reduction method. The UV-vis absorption spectra show that the L-BOI and 2%A-6%L-BOI samples have a strong visible-light absorption in comparison with the pure BOI. The electron paramagnetic resonance results indicate that the number of oxygen vacancies in L-BOI samples is increased with an increasing amount of the La dopant. The band structure of the prepared photocatalysts is investigated by confirming the positions of the valence band (VB) measured by XPS-VB and the Fermi level computed by density functional theory, respectively. NO is selected as a target gaseous pollutant to confirm the influence of La doping and the plasmonic effect of Au nanoparticles on the photocatalytic activity of BOI microspheres. The 2%A-6%L-BOI sample exhibits an enhanced photocatalytic performance compared to BOI, L-BOI, and A-BOI photocatalysts under visible-light irradiation. Interestingly, the 2%A-6%L-BOI sample also can reduce the amount of intermediate NO2 during the NO removal process. The enhanced photocatalytic efficiency of the 2%A-6%L-BOI photocatalyst is profited from the synergy of La-ion doping, oxygen vacancy, and the surface plasmon resonance effect of Au nanoparticles. Based on the results of trapping experiments and electron spin resonance spectroscopy tests, h+, e-, and •O2- were involved in the NO oxidative removal.