A new strategy for PET depolymerization: Application of bimetallic MOF-74 as a selective catalyst.

Large-volume production of poly(ethylene terephthalate) (PET), especially in the form of bottles and food packaging containers, causes problems with polymer waste management. Waste PET could be recycled thermally, mechanically or chemically and the last method allows to obtain individual monomers, but most often it is carried out in the presence of homogeneous catalysts, that are difficult to separate and reuse. In view of this, this work reports for the first time, application of bimetallic MOF-74 - as heterogeneous catalyst - for depolymerization of PET with high monomer (bishydroxyethyl terephthalate, BHET) recovery. The effect of type and amount of second metal in the MOF-74 (Mg/M) was systematically investigated. The results showed increased activity of MOF-74 (Mg/M) containing Co2+, Zn2+ and Mn2+ as a second metal, while the opposite correlation was observed for Cu2+ and Ni2+. It was found that the highest catalytic activity was demonstrated by the introduction of Mg-Mn into MOF-74 with ratio molar 1:1, which resulted in complete depolymerization of PET and 91.8% BHET yield within 4 h. Furthermore, the obtained catalyst showed good stability in 5 reaction cycles and allowed to achieve high-purity BHET, which was confirmed by HPLC analysis. The as-prepared MOF-74 (Mg/Mn) was easy to separate from the post-reaction mixture, clean and reuse in the next depolymerization reaction.

Design and Synthesis of NTU-9/C3N4 Photocatalysts: Effects of NTU-9 Content and Composite Preparation Method.

Hybrid materials based on graphitic carbon nitride (g-C3N4) and NTU-9 metal-organic frameworks (MOF) were designed and prepared via solvothermal synthesis and calcination in air. The as-prepared photocatalysts were subsequently characterized using Brunauer-Emmett-Teller (BET) analysis, UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) emission spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The obtained NTU-9/C3N4 composites showed a greatly improved photocatalytic performance for the degradation of toluene in the gas phase under LED visible-light irradiation (λmax = 415 nm). The physicochemical properties and photocatalytic activities of the obtained NTU-9/C3N4 materials were tuned by varying the NTU-9 content (5-15 wt%) and preparation method of the composite materials. For composites prepared by calcination, the photocatalytic activity increased with decreasing NTU-9 content as a result of the formation of TiO2 from the MOFs. The best photocatalytic performance (65% of toluene was photodegraded after 60 min) was achieved by the NTU-9/C3N4 sample prepared via the solvothermal method and containing 15 wt% MOF, which can be attributed to the appropriate amount and stable combination of composite components, efficient charge separation, and enhanced visible-light absorption ability. The photocatalytic mechanisms of the prepared hybrid materials depending on the preparation method are also discussed.

Photocatalytic hydrogen evolution from glycerol-water mixture under visible light over zinc indium sulfide (ZnIn2S4) nanosheets grown on bismuth oxychloride (BiOCl) microplates.

ZnIn2S4 (ZIS) is one of the widely studied photocatalyst for photocatalytic hydrogen evolution applications due to its prominent visible light response and strong reduction ability. However, its photocatalytic glycerol reforming performance for hydrogen evolution has never been reported. Herein, the visible light driven BiOCl@ZnIn2S4 (BiOCl@ZIS) composite was synthesized by growth of ZIS nanosheets on a template-like hydrothermally pre-prepared wide-band-gap BiOCl microplates using simple oil-bath method to be used for the first time for photocatalytic glycerol reforming for photocatalytic hydrogen evolution (PHE) under visible light irradiation (λ > 420 nm). The optimum amount of BiOCl microplates in the composite was found 4 wt% (4% BiOCl@ZIS) in the presence of in-situ 1 wt% Pt deposition. Then, the in-situ Pt photodeposition optimization studies over 4% BiOCl@ZIS composite showed the highest PHE rate of 674 µmol g-1h-1 with the ultra-low platinum amount (0.0625 wt%). The possible mechanisms behind this improvement can be ascribed to the formation of Bi2S3 low-band-gap semiconductor during BiOCl@ZIS composite synthesis resulting in Z-scheme charge transfer mechanism between ZIS and Bi2S3 upon visible light irradiation. This work expresses not only the photocatalytic glycerol reforming over ZIS photocatalyst but also a solid proof of the contribution of wide-band-gap BiOCl photocatalysts to enhancement of ZIS PHE performance under visible light.

Morphology control through the synthesis of metal-organic frameworks.

Designable morphology and predictable properties are the most challenging goals in material engineering. Features such as shape, size, porosity, agglomeration ratio significantly affect the final properties of metal-organic frameworks (MOFs) and can be regulated throughout synthesis parameters but require a deep understanding of the mechanisms of MOFs formation. Herein, we systematically summarize the effects of the individual synthesis factors, such as pH of reaction mixture, including acidic or basic character of modulators, temperature, solvents types, surfactants type and content and ionic liquids on the morphology of growing MOFs. We identified main mechanisms of MOFs' growth leading to different morphology of final particles and next systematically discuss the effect of miscellaneous parameters on MOFs morphology based on the main mechanisms related to the nucleation, growth and formation of final MOFs structure, including coordination modulation, protonation/deprotonation acting and modulation by surfactants or capping agents. The effect of microwaves and ultrasound employment during synthesis is also considered due to their affecting especially nucleation and particles growing steps during MOFs formation.

Fabrication of Durable Ordered Ta2O5 Nanotube Arrays Decorated with Bi2S3 Quantum Dots.

One of the most important challenges in the fabrication of ordered tantalum pentaoxide (Ta2O5) nanotube arrays (NTs) via the electrochemical method is the formation of nanotubes that adhere well to the Ta substrate. In this paper, we propose a new protocol that allows tight-fitting Ta2O5 nanotubes to be obtained through the anodic oxidation of tantalum foil. Moreover, to enhance their activity in the photocatalytic reaction, in this study, they have been decorated by nontoxic bismuth sulfide (Bi2S3) quantum dots (QDs) via a simple successive ionic layer adsorption and reaction (SILAR) method. Transmission electron microscopy (TEM) analysis revealed that quantum dots with a size in the range of 6-11 nm were located both inside and on the external surfaces of the Ta2O5 NTs. The effect of the anodization time and annealing conditions, as well as the effect of cycle numbers in the SILAR method, on the surface properties and photoactivity of Ta2O5 nanotubes and Bi2S3/Ta2O5 composites have been investigated. The Ta2O5 nanotubes decorated with Bi2S3 QDs exhibit high photocatalytic activity in the toluene degradation reaction, i.e., 99% of toluene (C0 = 200 ppm) was degraded after 5 min of UV-Vis irradiation. Therefore, the proposed anodic oxidation of tantalum (Ta) foil followed by SILAR decorating allows a photocatalytic surface, ready to use for pollutant degradation in the gas phase, to be obtained.