Removal Of Organic Molecules Research Articles

Construction of heterogeneous structures of MIL-101(Fe)/Ce/g-C3N4 nanocomposites for enhanced photocatalytic activity under visible light

A heterostructured MIL-101(Fe)/Ce/g-C3N4 (MCCN) composite was designed and synthesized by solvothermal method. The composite was characterized by XRD, SEM, EDS, FT-IR, BET, XPS, UV–Vis DRS, PL and EIS. The MCCN photocatalyst exhibits superior photocatalytic performance for the degradation of rhodamine B (RhB) and methylene blue (MB), and the efficiencies are found to be 90.36% and 88.17%, respectively. The kinetic constants k of MCCN-3 against RhB and MB dyes are 0.04094 min−1 and 0.03319 min−1, respectively, under visible light for 75 ​min irradiation. The improved degradation efficiency of MCCN attributed to the enhanced light absorption and the transport channels of electron-hole pairs by forming a heterojunction between MIL-101(Fe) and Ce/g-C3N4 with a favourable band position. Moreover, the possible mechanism of photocatalytic degradation of dyes was proposed though free radical trapping experiments. This work provides an effective way for constructing novel visible-light-driven photocatalyst in the removal of organic molecules from waste water.

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

New Porous Heterostructures Based on Organo-Modified Graphene Oxide for CO2 Capture.

In this work, we report on a facile and rapid synthetic procedure to create highly porous heterostructures with tailored properties through the silylation of organically modified graphene oxide. Three silica precursors with various structural characteristics (comprising alkyl or phenyl groups) were employed to create high-yield silica networks as pillars between the organo-modified graphene oxide layers. The removal of organic molecules through the thermal decomposition generates porous heterostructures with very high surface areas (≥ 500 m2/g), which are very attractive for potential use in diverse applications such as catalysis, adsorption and as fillers in polymer nanocomposites. The final hybrid products were characterized by X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scanning electron microscopy and porosity measurements. As proof of principle, the porous heterostructure with the maximum surface area was chosen for investigating its CO2 adsorption properties.

Rhodamine B degradation by nanosized zeolitic imidazolate framework-8 (ZIF-8).

Adsorption and photodegradation of rhodamine B by ZIF-8 nanocrystals were studied using spectroscopic techniques coupled with density functional theory (DFT) cluster calculations. A fast adsorption rate was observed in the dark, but upon exposure to visible light or UV irradiation the adsorption rate noticeably increased. Although several studies previously reported this phenomenon involving bulk ZIF-8 powder, this is the first mechanistic study to our knowledge that demonstrates adsorption and degradation of rhodamine B by nanosized ZIF-8 under various light conditions. The combined study of N2 sorption pore analysis and surface-sensitive X-ray photoelectron spectroscopy (XPS) confirmed the surface adsorption was mainly due to the open metal sites and surface groups of nanoporous ZIF-8. The fluorescence studies suggested ZIF-8 nanocrystals were able to generate hydroxyl radicals in water but only under UV illumination. The work presented here provides an insight into understanding nanoscale metal–organic frameworks (MOFs) in the removal of organic molecules from wastewater.

Permeability of uncharged organic molecules in reverse osmosis desalination membranes

Reverse osmosis (RO) membranes are primarily designed for removal of salts i.e. for desalination of brackish and seawater, but they have also found applications in removal of organic molecules. While it is clear that steric exclusion is the dominant removal mechanism, the fundamental explanation for how and why the separation occurs remains elusive. Until recently there was no strong microscopic evidences elucidating the structure of the active polyamide layers of RO membranes, and thus they have been conceived as “black boxes”; or as an array of straight capillaries with a distribution of radii; or as polymers with a small amount of polymer free domains. The knowledge of diffusion and sorption coefficients is a prerequisite for understanding the intrinsic permeability of any organic solute in any polymer. At the same time, it is technically challenging to accurately measure these two fundamental parameters in very thin (20–300 nm) water-swollen active layers. In this work we have measured partition and diffusion coefficients and RO permeabilities of ten organic solutes in water-swollen active layers of two types of RO membranes, low (SWC4+) and high flux (XLE). We deduced from our results and recent microscopic studies that the solute flux of organic molecules in polyamide layer of RO membranes occurs in two domains, dense polymer (the key barrier layer) and the water filled domains.

Removal of excess polymer from a suspension containing hybrids of thermoresponsive polymer and carbon nanotubes using aggregation phenomenon

Hybrids of organic molecules and single-walled carbon nanotubes (SWNTs) are attractive candidates for nanobiodevices. The removal of organic molecules after dispersing the SWNTs in organic media is a significant step in the preparation of these hybrid suspensions. We investigated the aggregation phenomenon in hybrids of poly(N-isopropylacrylamide) (PNIPAAm) and SWNTs. Our results indicate that the hybrids efficiently precipitated when a buffer or salt solution was added to the suspension at 25 °C. 4 mM tris(hydroxymethyl)aminomethane hydrochloride (Tris–HCl) buffer was sufficient to precipitate the hybrids. Then, by repeated centrifugations and replacements of solvents, excess PNIPAAm molecules were efficiently removed from the suspension. Results of UV–vis spectroscopy and atomic force microscopy (AFM) suggest that the PNIPAAm–SWNT hybrids retained their hybridized structures even after the treatment process. However, the aggregation phenomenon was not observed at 4 °C.

Synthesis, structure and magnetic properties of (Fe1−xNix)3C nanoparticles

Ni doped Fe3C ((Fe1−xNix)3C) Nanoparticles (NPs) were prepared via a sol-gel method. The structure, morphology and magnetic properties of the materials are researched. Analysis results show that the crystallite size and magnetic parameters of the materials are affected by the Ni-dopant. Furthermore, it is also well investigated of the water purification for the mesoporosity, magnetic, high specific surface area and facile magnetic separation of the materials. The current synthetic approach is versatile and simple, and thus shows great promise for the large scale synthesis of Fe3C based NPs that are useful for water treatment such as the removal of organic molecules.

Multifunctional Polymer/Porous Boron Nitride Nanosheet Membranes for Superior Trapping Emulsified Oils and Organic Molecules

Effective oil/water separation and removal of organic molecules from water are of worldwide importance for water source protection. Multifunctional sorbent materials with excellent sorption capacity, stability, and recyclability properties need to be developed. Here, flexible and multifunctional polymer/porous boron nitride nanosheets (BNNSs) membranes with high water permeability, exhibiting high effectiveness and stability in the purification of simulated wastewater tainted with either oil/water emulsion or organic molecules, are reported. Remarkably, the flexible nature of these porous membranes enables simplicity of operation for water remediation processing and ease of post‐processing collection. The composite membrane also displays a remarkably high permeability of 8 × 104 L μm m−2 h−1 bar−1, roughly three orders of magnitude higher than pure polymer, and excellent filter efficiencies for the pharmaceuticals ciprofloxacin, chlortetracycline, and carbamazepine (up to 14.2 L g−1 of BNNSs in the composite membrane for a concentration of 10 mg L−1 ciprofloxacin) and the dye methylene blue (up to 9.3 L g−1 of BNNSs in the composite membrane at a concentration of 30 mg L−1). Exhausted membranes can be readily rejuvenated by simple washing with retention of their high‐performance characteristics. The results demonstrate the potential efficacy and practicality of these membranes for water cleaning.

Selective binding and removal of organic molecules in a flexible polymeric material with stretchable metallosalen chains

A dynamic porous coordination network with a hydrophobic channel was assembled from stretchable 1D metallosalen polymer, which has the ability to recognize and, particularly, separate aromatic hydrocarbons from aliphatic mixtures with high selectivity.

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B ® and Nanofil 784 ®, and a sodium MMT (Cloisite Na ®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis–gas–mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B ® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784 ® compatibilizer has been conversely found. As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B ®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784 ®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes –OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.

Porous extreme low κ (EL κ) dielectrics using a PECVD porogen approach

The introduction of new dielectrics into silicon chip interconnection technology, to improve the electrical performance of ultra large-scale integration (ULSI), is marked by continuous revisions to meet the International Technology Roadmap for Semiconductors (ITRS) projection. Amorphous a-SiOC:H ( κ = 2.9 ) deposited by plasma-enhanced chemical vapor deposition (PECVD) from linear precursors is now in scale up towards production. Using other precursors like cyclic siloxanes, κ value is reduced to 2.5 at least. The main way to reduce the dielectric constant is to introduce porosity into the film. In this work, a two-step porogen approach is followed to perform extreme low (EL) κ ( κ < 2.5 ) deposition. Firstly, a dual-phase thin film is deposited by PECVD using two advanced precursors: decamethylcyclopentasiloxane (D5) to create a a-SiOC:H matrix and a sacrificial organic precursor. Within the matrix, the organic precursor generates organic inclusions. In a second step, the organic phase is removed by a suitable curing to induce porosity. Various types of organic precursors are investigated and thin films are then characterized. Incorporation and removal of organic molecules from a-SiOC:H material are closely studied using infrared spectroscopy. Using cyclohexene oxide as organic precursor (porogen), κ value of the porous dielectric is measured at 2.2. Nitrogen adsorption isotherms measurements prove the cured material porosity. This work clearly demonstrates the ability of achieving an EL κ with a PECVD porogen approach using D5 as matrix precursor and new organic precursors as porogen.

Quantum Size Effect Silicon Structures via Molecularly Self-Assembled Hybrid Templates

AbstractA novel approach for the synthesis of advanced functional inorganic materials with atomic-scale control over the size of periodic features on the sub-30 nm scale is presented. The key innovative aspect of this technique is the direct, bottom-up formation of a two-dimensional periodic array of spatially separated nanostructures in a self-organized thin-film porous template. This thin-film template is fabricated via biologically inspired hierarchical self-assembly of organic surfactant molecules in the presence of inorganic charged silicate species. The removal of organic molecules from such an organic/inorganic hybrid system creates a periodic array of pore channels of ∼3-30 nm diameter inside the thin-film silica template. This porous template is employed as a shadow mask to directly grow various functional nanostructures inside the confined environment of the periodic pore arrays. In the present study, silicon nanostructures were grown inside the templates by both chemical and physical (sputtering) vapor deposition. The quantum size effect was clearly pronounced in the room temperature photoluminescence spectra of the samples prepared by sputtering from a Si target, which makes the approach highly promising for the fabrication of nanoscale optoelectronic devices.

A new way to obtain acid or bifunctional catalysts. II. Straightforward calcination of as-synthesized [Ga,A1]-ZSM-5 zeolites obtained from alkali-free media

The acid or bifunctional behavior of catalysts obtained by the straightforward calcination (530–800°C) of as-synthesized [GaA1]-ZSM-5 zeolite, obtained from alkali-free media, was determined using propane, cyclohexane and cyclohexene transformations ( T = 530°C, p = 1 atm) as reaction models. Solids were characterized by XRD, FTIR, N 2 adsorption, 27A1 and 71Ga MAS NMR and chemical analysis. The catalyst acidities were evaluated using n-heptane cracking and m-xylene isomerization as reaction models. Results show that calcination temperatures (T c)between 530 and 550°C, causes only the removal of organic molecules used for the synthesis of the zeolite, leading then to pure acidic catalysts. At 700 ⩽ T c ⩽ 800°C, simultaneously with the removal of those organic molecules, a significant chemical change of the zeolite framework composition take place (degalliation and dealumination). The presence of extraframework gallium species (EFGS), led to acid gallium promoted bifunctional catalysts with catalytic properties for propane and naphthenes aromatization almost identical to those for gallium promoted zeolites obtained by conventional methods (ion exchange and/or impregnation).