Integrating of metal-organic framework UiO-66-NH2 and cellulose nanofibers mat for high-performance adsorption of dye rose bengal

UiO-66-NH₂ is an efficient material for removing pollutants from wastewater due to its high specific surface area, high porosity and water stability. However, recycling them from wastewater is difficult. In this study, the cellulose nanofibers mat deacetylated from cellulose acetate nanofibers were used to combine with UiO-66-NH₂ by the method of in-situ growth to remove the toxic dye, rose bengal. Compared to previous work, the prepared composite could not only provide ease of separation of UiO-66-NH₂ from the water after adsorption but also demonstrate better adsorption capacity (683 mg∙g^‒1 (T = 25 °C, pH = 3)) than that of the simple UiO-66-NH₂ (309.6 mg∙g^‒1 (T = 25 °C, pH = 3)). Through the analysis of adsorption kinetics and isotherms, the adsorption for rose bengal is mainly suitable for the pseudo-second-order kinetic model and Freundlich model. Furthermore, the relevant research revealed that the main adsorption mechanism of the composite was electrostatic interaction, hydrogen bonding and π–π interaction. Overall, the approach depicts an efficient model for integrating metal-organic frameworks on cellulose nanofibers to improve metal-organic framework recovery performance with potentially broad applications.     

Low-temperature selective catalytic reduction of NO with NH based on MnO-CeO/ACFN

MnO_x-CeO_x/ACFN were prepared by the impregnation method and used as catalyst for selective catalytic reduction of NO with NH₃ at 80°C–150°C. The catalyst was characterized by N₂-BET, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The fraction of the mesopore and the oxygen functional groups on the surface of activated carbon fiber (ACF) increased after the treatment with nitric acid, which was favorable to improve the catalytic activities of MnO_x-CeO_x/ACFN. The experimental results show that the conversion of NO is nearly 100% in the range 100°C–150°C under the optimal preparation conditions of MnO_x-CeO_x/ACFN. In addition, the effects of a series of performance parameters, including initial NH₃ concentration, NO concentration and O₂ concentration, on the conversion of NO were studied.     

Mechanism of methanol decomposition on the Pd/WC(0001) surface unveiled by first-principles calculations

In this study, the decomposition of methanol into the CO and H species on the Pd/tungsten carbide (WC)(0001) surface is systematically investigated using periodic density functional theory (DFT) calculations. The possible reaction pathways and intermediates are determined. The results reveal that saturated molecules, i.e., methanol and formaldehyde, adsorb weakly on the Pd/ WC(0001) surface. Both CO and H prefer three-fold sites, with adsorption energies of −1.51 and −2.67 eV, respectively. On the other hand, CH₃O stably binds at three-fold and bridge sites, with an adsorption energy of −2.58 eV. However, most of the other intermediates tend to adsorb to the surface with the carbon and oxygen atoms in their sp³ and hydroxyl-like configurations, respectively. Hence, the C atom of CH₂OH preferentially attaches to the top sites, CHOH and CH₂O adsorb at the bridge sites, while COH and CHO occupy the three-fold sites. The DFT calculations indicate that the rupture of the initial C–H bond promotes the decomposition of CH₃OH and CH₂OH, whereas in the case of CHOH, O–H bond scission is favored over the C–H bond rupture. Thus, the most probable methanol decomposition pathway on the Pd/WC(0001) surface is CH₃OH → CH₂OH → trans-CHOH → CHO → CO. The present study demonstrates that the synergistic effect of WC (as carrier) and Pd (as catalyst) alters the CH₃OH decomposition pathway and reduces the noble metal utilization.     

Efficient hydrothermal deoxygenation of methyl palmitate to diesel-like hydrocarbons on carbon encapsulated Ni–Sn intermetallic compounds with methanol as hydrogen donor

Porous carbon-encapsulated Ni and Ni–Sn intermetallic compound catalysts were prepared by the one-pot extended Stöber method followed by carbonization and tested for in-situ hydrothermal deoxygenation of methyl palmitate with methanol as the hydrogen donor. During the catalyst preparation, Sn doping reduces the size of carbon spheres, and the formation of Ni–Sn intermetallic compounds restrain the graphitization, contributing to larger pore volume and pore diameter. Consequently, a more facile mass transfer occurs in carbon-encapsulated Ni–Sn intermetallic compound catalysts than in carbon-encapsulated Ni catalysts. During the in-situ hydrothermal deoxygenation, the synergism between Ni and Sn favors palmitic acid hydrogenation to a highly reactive hexadecanal that easily either decarbonylate to n-pentadecane or is hydrogenated to hexadecanol. At high reaction temperature, hexadecanol undergoes dehydrogenation–decarbonylation, generating n-pentadecane. Also, the C–C bond hydrolysis and methanation are suppressed on Ni–Sn intermetallic compounds, favorable for increasing the carbon yield and reducing the H₂ consumption. The n-pentadecane and n-hexadecane yields reached 88.1% and 92.8% on carbon-encapsulated Ni₃Sn₂ intermetallic compound at 330 °C. After washing and H₂ reduction, the carbon-encapsulated Ni₃Sn₂ intermetallic compound remains stable during three recycling cycles. This is ascribed to the carbon confinement that effectively suppresses the sintering and loss of metal particles under harsh hydrothermal conditions.     

Selective hydrogenation of acetylene over Pd/CeO2

Five hundred ppm Pd/CeO₂ catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction. Pd/CeO₂ catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction. Excellent ethylene selectivity of ~100% was obtained in the whole reaction temperature range of 50°C–200°C for samples calcined at temperatures of 600°C and 800°C. This could be ascribed to the formation of Pd_xCe_1−xO_2−y or Pd-O-Ce surface species based on the X-ray diffraction and X-ray photoelectron spectroscopy results, indicating the strong interaction between palladium and ceria.     

A density functional theory study of methane activation on MgO supported Ni9M1 cluster: role of M on C–H activation

Methane activation is a pivotal step in the application of natural gas converting into high-value added chemicals via methane steam/dry reforming reactions. Ni element was found to be the most widely used catalyst. In present work, methane activation on MgO supported Ni–M (M = Fe, Co, Cu, Pd, Pt) cluster was explored through detailed density functional theory calculations, compared to pure Ni cluster. CH₄ adsorption on Cu promoted Ni cluster requires overcoming an energy of 0.07 eV, indicating that it is slightly endothermic and unfavored to occur, while the adsorption energies of other promoters M (M = Fe, Co, Pd and Pt) are all higher than that of pure Ni cluster. The role of M on the first C–H bond cleavage of CH₄ was investigated. Doping elements of the same period in Ni cluster, such as Fe, Co and Cu, for C–H bond activation follows the trend of the decrease of metal atom radius. As a result, Ni–Fe shows the best ability for C–H bond cleavage. In addition, doping the elements of the same family, like Pd and Pt, for CH₄ activation is according to the increase of metal atom radius. Consequently, C–H bond activation demands a lower energy barrier on Ni–Pt cluster. To illustrate the adsorptive dissociation behaviors of CH₄ at different Ni–M clusters, the Mulliken atomic charge was analyzed. In general, the electron gain of CH₄ binding at different Ni–M clusters follows the sequence of Ni–Cu (–0.02 e) < Ni (–0.04 e) < Ni–Pd (–0.08 e) < Ni–Pt (–0.09 e) < Ni–Co (–0.10 e) < Ni–Fe (–0.12 e), and the binding strength between catalysts and CH ₄ raises with the CH₄ electron gain increasing. This work provides insights into understanding the role of promoter metal M on thermal-catalytic activation of CH₄ over Ni/MgO catalysts, and is useful to interpret the reaction at an atomic scale.     

Systematic study of H2 production from catalytic photoreforming of cellulose over Pt catalysts supported on TiO2

Hydrogen (H₂) production from photocatalytic reforming of cellulose is a promising way for sustainable H₂ to be generated. Herein, we report a systematic study of the photocatalytic reforming of cellulose over Pt/m-TiO₂ (i.e. mixed TiO₂, 80% of anatase and 20% of rutile) catalysts in water. The optimum operation condition was established by studying the effect of Pt loading, catalyst concentration, cellulose concentration and reaction temperature on the gas production rate of H₂ (r_H2) and CO₂ (r_CO2), suggesting an optimum operation condition at 40 ℃ with 1.0 g·L^-1 of cellulose and 0.75 g·L^-1 of 0.16-Pt/m-TiO₂ catalyst (with 0.16 wt% Pt loadting) to achieve a relatively sound photocatalytic performance with rH₂ = 9.95 μmol·h^-1. It is also shown that although the photoreforming of cellulose was operated at a relatively mild condition (i.e. with an UV-A lamp irradiation at 40 ℃ in the aqueous system), a low loading of Pt at ~0.16 wt% on m-TiO₂ could promote the H₂ production effectively. Additionally, by comparing the reaction order expressed from both r_H2 (a₁) and rCO₂ (a₂) with respect to cellulose and water, the possible mechanism of H₂ production was proposed.     

Adhesion of microorganisms to polymer membranes: a photobactericidal effect of surface treatment with TiO2

The adhesion of Escherichia coli, Pseudomonas putida and Acinetobacter calcoaceticus cells to Microdyn-Nadir ultrafiltration membranes of various chemical nature: PS100 (polysulfone), P005 (polyethersulfone), C100 (regenerated cellulose) was studied. It was shown that an adhesiveness of the microorganisms to the membranes essentially depends on hydrophobic/hydrophilic properties of both the cells and membranes. In particular, it was found that the adhesion of relatively hydrophilic E. coli to membrane surfaces is essentially lower comparing with the adhesion of more hydrophobic P. putida, or A. calcoaceticus cells. In a turn the microorganisms attachment to more hydrophobic polyethersulfone and polysulfone membranes is higher than to hydrophilic cellulose one. It was shown that the volume fluxes of membranes with adhesive microorganisms dropped while samples were kept in contact with natural surface water due to increasing of cell number on membrane surface. In attempts to reduce membrane biofouling, TiO₂ particles were deposited on membrane surface with following ultraviolet (UV) irradiation at 365 nm. It was shown that due to photobactericidal effect the fluxes of surface modified membranes were 1.7–2.3 times higher comparing with those for control membrane samples (without TiO₂ deposition and UV treatment).     

Crystal-to-crystal transformation from the triclinic to the cubic crystal system by partial desolvation

Diffusion reaction of the labile building block Mg(acacCN)₂ (acacCN= 3-cyanoacetylacetonate) with silver salts leads to a series of solvated Mg/Ag bimetallic coordination polymers with composition [Mg(acacCN)₃Ag]·solvent. Despite their common stoichiometry, the topology of these polymers depends on the solvent of crystallization. The two-dimensional coordination compound [Mg(acacCN)₃Ag]·4CHCl₃ in space group P\bar{\mathrm{1}} is obtained as platelet-shaped crystals from a mixture of methanol and chloroform. When kept in the reaction mixture, these thin plates within one week convert to isometric tetrahedral crystals of the 3D network [Mg(acacCN)₃Ag]·2CHCl₃ in the cubic space group P2₁3. The transformation reaction proceeds via dissolution and recrystallization. The co-crystallized solvent molecules play an important role for stabilizing the target structure: They subtend Cl···Cl contacts and interact via non-classical C–H···O hydrogen bonds with the coordination framework. In the new cubic coordination network, both Mg(II) and Ag(I) adopt octahedral coordination, with unprecedented face-sharing by bridging O atoms of three acetylacetonato moieties. Prolonged standing of [Mg(acacCN)₃Ag]·2CHCl₃ in the reaction medium leads to further degradation, under formation of [Ag(acacCN)].     

TiO2 coating types influencing the role of water vapor on the photocatalytic oxidation of methyl ethyl ketone in the gas phase

Four TiO₂-based materials, named A, B, C and D, are used to investigate the influence of water vapor on the gas–solid adsorption and heterogeneous photocatalytic oxidation of gaseous methyl ethyl ketone (MEK). Two of the photocatalysts (A and B) are constituted of powdered TiO₂ deposited onto two different supports (ordinary glass and non-woven cellulose fibers). The other ones (C and D) are composed of a thin film of TiO₂ coated on glass substrates. The effect of water vapor on MEK initial conversion rates is studied for the four photocatalytic materials using the Langmuir–Hinshelwood model at the initial time. On the concentrations range where the model hypotheses are verified, adsorption constants K and kinetics constants k are calculated for experiments under both dry and humid atmosphere. When the relative humidity is increased, the evolution of these constants shows that water vapor acts differently depending on the form of deposited TiO₂ (powder and film).     

Regioselective acylation of pyridoxine catalyzed by immobilized lipase in ionic liquid

The regioselective acylation of pyridoxine catalyzed by immobilized lipase (Candida Antarctica) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) has been investigated, and compared with that in acetonitrile (ACN). The acetylation of pyridoxine using acetic anhydride in [BMIM]PF₆ gave comparable conversion of pyridoxine to 5-monoacetyl pyridoxine with considerably higher regioselectivity (93%–95%) than that in ACN (70%–73%). Among the tested parameters, water activity (a_w) and temperature have profound effects on the reaction performances in either [BMIM]PF₆ or ACN. For the reaction in [BMIM]PF₆, higher temperature (50°C–55°C) and lower a_w (<0.01) are preferable conditions to obtain better conversion and regioselectivity. Mass transfer limitation and intrinsic kinetic from the ionic nature of ionic liquids (ILs) may account for a different rate-temperature profile and a lower velocity at lower temperature in [BMIM]PF₆-mediated reaction. Moreover, consecutive batch reactions for enzyme reuse also show that lipase exhibited a much higher thermal stability and better reusability in [BMIM]PF₆ than in ACN, which represents another advantage of ILs as an alternative to traditional solvents beyond green technology.     

Development of an in-situ H2 reduction and moderate oxidation method for 3,5-dimethylpyridine hydrogenation in trickle bed reactor

The Ru/C catalyst prepared by impregnation method was used for hydrogenation of 3,5-dimethylpyridine in a trickle bed reactor. Under the same reduction conditions (300 °C in H₂), the catalytic activity of the non-in-situ reduced Ru/C-n catalyst was higher than that of the in-situ reduced Ru/C-y catalyst. Therefore, an in-situ H₂ reduction and moderate oxidation method was developed to increase the catalyst activity. Moreover, the influence of oxidation temperature on the developed method was investigated. The catalysts were characterized by Brunauer–Emmett–Teller method, hydrogen temperature programmed reduction H₂-TPR, hydrogen temperature-programmed dispersion (H₂-TPD), X-ray diffraction, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, O₂ chemisorption and oxygen temperature-programmed dispersion (O₂-TPD) analyses. The results showed that there existed an optimal Ru/RuO_x ratio for the catalyst, and the highest 3,5-dimethylpyridine conversion was obtained for the Ru/C-i1 catalyst prepared by in-situ H₂ reduction and moderate oxidation (oxidized at 100 °C). Excessive oxidation (200 °C) resulted in a significant decrease in the Ru/RuO_x ratio of the in-situ H₂ reduction and moderate oxidized Ru/C-i2 catalyst, the interaction between RuO_x species and the support changed, and the hard-to-reduce RuO_x species was formed, leading to a significant decrease in catalyst activity. The developed in-situ H₂ reduction and moderate oxidation method eliminated the step of the non-in-situ reduction of catalyst outside the trickle bed reactor.     

Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography

Cellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose II) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose II, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70°C, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.     

Rapid homogeneous preparation of cellulose graft copolymer in BMIMCL under microwave irradiation

Acrylic acid(AA) was grafted onto cellulose in homogeneous media by using ammonium persulfate as an initiator in the presence of N,N′‐methylenebisacrylamide as a crosslinker under microwave (MW) irradiation. The powerful and highly efficient direct solvent, 1‐butyl‐3‐methylinidazolium chloride ionic liquid was used as the solvent for the dissolution of cellulose and the media for the homogeneous graft polymerization of AA onto cellulose. The use of MW resulted in a drastic reduction of reaction time: 3 min irradiation was sufficient, compared with 30 min to 5 h, as conventional heating was used. Investigation was conducted on the effect of reaction parameters, such as monomer concentration, crosslinker dosage, exposure temperature and exposure time. The structure of the graft copolymer was confirmed by IR spectrum, thermogravimetric analyzer, and scanning electron microscope. The results show that the MW irradiation method can increase the reaction rate. And the graft copolymer is also an effective metal ion adsorbent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Activation of Ground Blast-Furnace Slag by Alkali-Metal and Alkaline-Earth Hydroxides

The effects of pH, time, valence, and radius of the activator cation on the reaction products and microstructure of ground granulated iron blast-furnace slag were studied by thermogravimetry and derivative thermogravimetry, X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray microanalysis. Blast-furnace slag was activated by alkali-metal hydroxides of Li, Na, and K (12.34 pH 14.71) and alkaline-earth hydroxides of Ca, Sr, and Ba(12.47 pH 13.53) using a water/slag ratio of 0.4 and curing for 1 day to 26 months. Reactivity of the slag was more strongly dependent on pH than on time. The reaction products were mainly varieties of C─S─H, (C,M)₄AH₁₃, and minor amounts of Ca(OH)₂ and C₂ASH₈ (strätlingite). The nature of C─S─H was dependent on pH. A 1.2-nm peak appeared in X-ray diffractograms only when the activation pH was ⌣14.7. Water was present in the C─S─H in a way similar to water in tobermorite and synthetic C─S─H. Leached Ca from unreacted blast-furnace slag was present around the glass particles as an amorphous layer which crystallized into Ca(OH)₂ with time; Mg behaved similarly. The effect of the charge or ionic radius of the activator cation was insignificant.     

Novel Ag-AgBr decorated composite membrane for dye rejection and photodegradation under visible light

Photocatalytic membranes have received increasing attention due to their excellent separation and photodegradation of organic contaminants in wastewater. Herein, we bound Ag-AgBr nanoparticles onto a synthesized polyacrylonitrile-ethanolamine (PAN-ETA) membrane with the aid of a chitosan (CS)-TiO₂ layer via vacuum filtration and in-situ partial reduction. The introduction of the CS-TiO₂ layer improved surface hydrophilicity and provided attachment sites for the Ag-AgBr nanoparticles. The PAN-ETA/CS-TiO₂/Ag-AgBr photocatalytic membranes showed a relatively high water permeation flux (~ 47 L·m^–2·h^–1·bar^–1) and dyes rejection (methyl orange: 88.22%; congo red: 95%; methyl blue: 97.41%; rose bengal: 99.98%). Additionally, the composite membranes exhibited potential long-term stability for dye/salt separation (dye rejection: ~97%; salt rejection: ~6.5%). Moreover, the methylene blue and rhodamine B solutions (20 mL, 10 mg·L⁻¹) were degraded approximately 90.75% and 96.81% in batch mode via the synthesized photocatalytic membranes under visible light irradiation for 30 min. This study provides a feasible method for the combination of polymeric membranes and inorganic catalytic materials.     

Polymerization of surface-active monomers: 5. Syntheses and polymerizations of anionic surface-active monomers: sodium di(10-undecenyl)sulphosuccinate and sodium n-undecyl 10-undecenylsulphosuccinate

Novel, anionic surface-active monomers, sodium di(10-undecenyl)sulphosuccinate (DUSS) and sodium n-undecyl 10-undecenylsulphosuccinate (MUSS) were prepared. The monomers were soluble in both water and apolar organic solvents on heating. DUSS and MUSS in water exhibited Kraft points at about 39°C and 48°C, respectively. The critical micelle concentrations for aqueous solutions of DUSS and MUSS at 50°C were determined to be 2.4 × 10⁻⁵ and 1.2 × 10⁻⁵ mol l⁻¹, respectively. Polymerization of the monomers in darkness and under u.v. irradiation at 50°C were studied using three different solvents, namely water, n-hexane and dioxane, giving aqueous micelles (or vesicles), reversed micelles and isotropic solution, respectively. Only traces of polymers were formed for the polymerizations in darkness, while the polymerizations under u.v. irradiation gave polymers, except for the polymerization of MUSS in dioxane. The solvents used for the polymerization were observed to exert an effect on the solubility of the polymers of DUSS and only the polymer obtained from the polymerization in water was soluble in solvents such as water and N,N-dimethylformamide. Thus, the monomer aggregation, especially for the aqueous system, was found to affect the structure of the resulting polymers.     

Structural phase transition and high temperature phase structure of Friedels salt, 3CaO · Al2O3 · CaCl2 · 10H2O

Friedels salt, the chlorinated compound 3CaO · Al₂O₃ · CaCl₂ · 10H₂O (AFm phase), presents a structural phase transition at about 30°C from a monoclinic to a rhombohedral phase. It has been studied by X-ray powder diffraction and optical microscopy in transmitted light with crossed polarisers on single crystals prepared by hydrothermal synthesis. The high temperature phase was determined at 37°C from X-ray single crystal diffraction data. The compound crystallises in the space group R c with lattice parameters of a = 5.7358(6)Å and c = 46.849(9)Å (Z = 3 and D_x = 2.111 g/cm³). The refinement of 498 independent reflections with I > 2σ(I) led to a residual factor of 7.1%. The Friedels salt can be described as a layered structure with positively charged main layers of composition [Ca₂Al(OH)₆]⁺ and negatively charged layers of composition [Cl⁻,2H₂O]. The chloride anions are surrounded by 10 hydrogen atoms, of which six belong to hydroxyl groups and four to water molecules. The structural phase transition may be related to the size of the chloride anions, which are not adapted to the octahedral cavity formed by bonded water molecules.     

Acid hydrolysis behaviour of microbial cellulose II

A mutant strain of Acetobacter xylinum produces cellulose of anomalous band-like form (‘native band’), and this material has been found to be cellulose II, presumably having a folded-chain structure (according to recent work by Kuga et al.). In addition to the previous results of electron diffraction, X-ray analysis showed that this band material was composed of virtually pure cellulose II. We have studied the acid hydrolysis behaviour of this material to obtain additional evidence for the proposed structure. When hydrolysed with 1 N hydrochloric acid at 100°C, the degree of polymerization (DP) of the material decreased rapidly from 322 ( ) to 18.3 ( ). The latter value (levelling-off DP) corresponds to the observed width (10 nm) of strand-like constituents of the band material. The sample dissolved in and regenerated from 8.75% aqueous sodium hydroxide lost its original characteristic morphology and became irregular-shaped agglomerates. The leveling-off DP of this regenerated sample was 55.2 ( ), a typical value for common regenerated celluloses. These findings as a whole strongly suggest that the cellulose molecules in the native band are selectively cleaved at sharply folded parts by acid, producing fragments of the length of folding periodicity.