Graphene-modified TiO2 nanotube arrays as an adsorbent in micro-solid phase extraction for determination of carbamate pesticides in water samples

Graphene is a good adsorbent for organic pollutants, especially for compounds containing benzene rings. When used in TiO₂ nanotube arrays for micro-solid phase extraction (μ-SPE), the combination of graphene’s strong adsorptive properties with its good separation capabilities results in excellent sample preconcentration performance. In the present study, graphene-modified TiO₂ nanotube arrays were prepared by electrodeposition using a cyclic voltammetric reduction method. Four carbamate pesticides, including metolcarb, carbaryl, isoprocarb, and diethofencarb, were used as model analytes to validate the enrichment properties of the prepared adsorbent in μ-SPE. Factors affecting the enrichment efficiency of the μ-SPE procedure were optimized and included sample pH, elution solvents, salting-out effect, adsorption time and desorption time. Under optimal conditions, graphene-modified TiO₂ nanotube arrays exhibited excellent enrichment efficiency for carbamate pesticides. The detection limits of these carbamate pesticides ranged from 2.27 to 3.26 μg L⁻¹. The proposed method was validated using four environmental water samples, and yields of pesticides recovered from spiked test samples of the four analytes were in the range of 83.9–108.8%. These results indicate that graphene-modified TiO₂ nanotube arrays exhibit good adsorption to the target pollutants, and the method described in this work could be used as a faster and easier alternative procedure for routine analysis of carbamate pesticides in real water samples.     

Structure and properties of the regenerated cellulose membranes prepared from cellulose carbamate in NaOH/ZnO aqueous solution

Regenerated cellulose (RC) membranes were prepared from cellulose carbamate—NaOH/ZnO aqueous solutions by coagulating with H₂SO₄ solution. Structure, morphology and properties of the membranes were investigated by using scanning electron micrograph (SEM), X-ray diffraction, Fourier transform infrared spectroscopy, flow rate method, and tensile testing. The results from SEM and water permeability revealed that the pore size and water permeability of the membranes in wet state changed drastically as a function of the concentration of H₂SO₄ and coagulation temperature, whereas they hardly changed with the coagulation time. RC membranes coagulated with the relatively dilute H₂SO₄ solution at relatively low temperature exhibited better mechanical properties. This work provided a promising way to prepare cellulose membranes with different pore sizes and good physical properties.     

Sulfation of Hydroxyethyl Cellulose by N(SO3Na)3 and the Anticoagulant Activity of Sulfated Hydroxyethyl Cellulose

Hydroxyethyl cellulose sulfate (HECS) was synthesized by sulfation of hydroxyethyl cellulose with N(SO₃Na)₃, which was manufactured by reaction of sodium bisulfite and sodium nitrite. Barium sulfate nephelometry and light scattering method were used to determine degrees of substitution (DSs) and molecular weights (M_ws), respectively. Sulfate products with DS values from 0.26 to 1.88 and M_w in the range of 12.1–54.8 kDa were obtained at temperatures from 30°C to 80°C. Furthermore, the anticoagulant activity of HECS with different DSs, concentrations, and M_ws was studied. Clotting assays revealed that the introduction of sulfate groups into hydroxyethyl cellulose could improve its anticoagulant activity.     

Synthesis of Novel Cellulose Carbamates Possessing Terminal Amino Groups and Their Bioactivity

Cellulose phenyl carbonates are an excellent platform to synthesize a broad variety of soluble and functional cellulose carbamates. In this study, the synthesis of cellulose carbamates with terminal amino groups, namely ω‐aminoethylcellulose‐ and ω‐aminoethyl‐p‐aminobenzyl‐cellulose carbamate, is discussed. The products are well soluble and their structures can be clearly described by NMR spectroscopy. The cellulose carbamates exhibit a bactericide and fungicide activity in vitro. The ω‐aminoethylcellulose carbamate possesses a strong activity against Candida albicans and Staphylococcus aureus (IC₅₀ of 0.02 mg mL^?1 and 0.05 mg mL^?1). The antimicrobial activity and cytotoxicity can be improved by p‐amino‐benzylamine (ABA) as an additional substituent. The mixed cellulose carbamate exhibits a high biocompatibility (LC₅₀ of 3.18 mg mL^?1) and forms films on cotton and PES, which exhibit a strong activity against S. aureus and Klebsiella pneumoniae.

     

High‐performance liquid chromatographic enantioseparation of fluorinated cyclic β3‐amino acid derivatives on polysaccharide‐based chiral stationary phases. Comparison with nonfluorinated counterparts

The stereoisomers of five fluorinated cyclic β³‐amino acid derivatives and their nonfluorinated counterparts were separated on chiral stationary phases containing as chiral selectors cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate), cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate), amylose tris‐(3,5‐dimethylphenyl carbamate) or amylose tris‐(5‐chloro‐2‐methylphenyl carbamate). The enantioseparations were carried out in normal‐phase mode with n‐hexane/alcohol/alkylamine mobile phases in the temperature range 5–40 °C. The effects of the mobile phase composition, the nature and concentration of the alcohol and alkylamine additives, the structures of the analytes and temperature on the separations were investigated. Thermodynamic parameters were calculated from plots of ln α vs. 1/T. The Δ(ΔH°) values ranged between ?5.0 and +1.6 kJ/mol, while Δ(ΔS°) varied between ?12.6 and +5.7 J/mol/K. The enantioseparation was enthalpically controlled, the retention factor and the separation factor decreasing with increasing temperature, but entropically controlled separation was also observed. The elution sequence was determined for all of the investigated analytes. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of sulfuric and phosphoric acid pretreatments on enzymatic hydrolysis of corn stover

The pretreatment of corn stover with H₂SO₄ and H₃PO₄ was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H₂SO₄ pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H₃PO₄. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose removal than to delignification.     

Polymer-solvent effects in cellulose urethane and methyl cellulose urethane solutions

The polymer-solvent interaction was studied for two similar cellulose derivatives in the semi-dilute concentration range by static and dynamic light scattering. The trisubstituted 3-chlorophenyl carbamate (3Cl-CTC) and a mixed trisubstituted derivative with methyl groups (degree of methyl substituents: DS _Me = 1.6–1.7)combined with the abovementioned 3-chlorophenyl carbamate groups filling the still open positions at the cellulose backbone were synthesized, fractionated and characterized according to standard methods. Different kinds of associations, entangled clusters with a rod-like shape on one side and entanglement networks on the other side, exist in semi-dilute dioxane solutions caused by different polymer-solvent interactions. These quite different associations lead to either a liquid crystalline or a gel-like state upon increase of concentration.     

Equilibrium solubility of carbon dioxide in 2(methylamino)ethanol

In this paper the equilibrium solubility of carbon dioxide in 1.0 M, 2.0 M and 4.0 M 2(methylamino)ethanol (MAE) is measured at 303, 313 and 333 K, and at CO₂ partial pressures ranging from 1 to 100 kPa using stirred cell reactor. The Kent-Eisenberg model was used to predict the solubility of carbon dioxide in MAE solutions. The equilibrium constant representing hydrolysis of carbamate ion is correlated with temperature, CO₂ partial pressure and amine concentration by non-linear regression, using experimental results of carbamate ion concentrations. The model predicted results showed good agreement with the experimental solubility results. The solubility profile of CO₂ in MAE showed better performance when compared with other commercial amines.     

High‐performance liquid chromatographic enantioseparation of amino alcohol analogues possessing 1,2,3,4‐tetrahydroisoquinoline skeleton on polysaccharide‐based chiral stationary phases

The stereoisomers of 1,2,3,4‐tetrahydroisoquinoline amino alcohol analogues and derivatives thereof were separated in normal‐phase mode on chiral stationary phases based on preprepared silica coated with cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate) or cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate). On all the investigated chiral columns, the retention and the enantioseparation were influenced by the nature and the concentrations of the mobile phase components and additives, and also the temperature. Experiments were performed in the temperature range 10–50°C. Thermodynamic parameters were calculated from plots of lnα vs 1/T. On these polysaccharide‐based chiral columns, both enthalpy‐driven separations and entropy‐controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. The sequence of elution of the stereoisomers was determined in all cases. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of the components of the PdCl2/Fe/I2/Py catalytic system on nitrobenzene carbonylation to ethyl N-phenylcarbamate

The PdCl₂/Fe/I₂/Py catalytic system (Py-pyridine), reported to be highly active in the reaction of nitrobenzene carbonylation to ethyl phenylcarbamate was studied. The present paper describes the role of catalyst components and its effect on the activity and selectivity of the catalyst. The increase in the amount of PdCl₂ in the system while retaining a constant level of the other catalyst components, results in the increase of both carbamate and aniline yields. The increase in the amount of iron while retaining the other components constant, initially causes an increase in the carbamate yield; however, at Fe: Pd ratios higher than 36, the carbamate yield remains constant. The change in the amount of iron has no effect on the amount of aniline formed in the system. An increase in the amount of iodine in the system while retaining the other components constant, results in a decrease in carbamate yield and a considerable increase in the aniline yield of the reaction products.     

Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol

Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H₂SO₄, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H₂SO₄. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H₂SO₄ and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2wt% H₂SO₄ at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.     

The effect of N2O4 on the crystalline structure of cellulose

Depending on reaction conditions, the system cellulose–N₂O₄ may give two different unstable crystalline compounds, one being an ester (cellulose trinitrite), the second, an adduct of cellulose and HNO₃ (the Knecht compound). For these compounds, mechanisms of the formation of the crystalline phase as a result of topochemical reaction and self-organization are discussed. The different characteristics of structural transformations of the fiber under nitrosation and nitration are noted. The existence of polymorphic forms of the Knecht compound is suggested. These labile nitrogen-containing compounds make possible the regeneration of cellulose in its various modifications (cellulose I, II, IV, or amorphous cellulose) from the cellulose–N₂O₄ system. The formation of unstable compounds and their ability to crystallize in the reaction medium allows the passage from amorphous cellulose to its crystalline modifications II or IV under mild conditions. The causes of decrystallization of cellulose by N₂O₄ are established. © 1993 John Wiley & Sons, Inc.     

Preparation and Antibacterial Function of Quaternary Ammonium Salts Grafted Cellulose Fiber Initiated by Fe2 +-H2O2 Redox

The surface contact disinfecting technique is a newly developed method for water sterilization. In this paper, the grafted quaternary ammonium salts (QAS) antibacterial fibers were prepared and designed to apply for the surface contact disinfecting process in water treatment. The antibacterial fibers were directly prepared by grafting methacryloxylethyl benzyl dimethyl ammonium chloride (DMAE-BC) onto cellulose fiber using thiocarbonate-H₂O₂ redox system. All kinds of factors in the grafting reactions, such as reaction time, reaction temperature, monomer concentration, initiator concentration, which influence the percentage of grafting, were studied and optimized. The modified cellulose fibers were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope(SEM). The effects of the percentage of grafting of the grafted cellulose fibers on bactericidal activity were also studied. The spread plate method was used to characterize the bactericidal activity. The disinfection process was further investigated by directly observing the morphology of the bacterial cells adsorbed on the antibacterial fibers with SEM and measuring extracelluar total protein concentration in suspension. The poly(DMAE-BC)-grafted cellulose ?ber was found to exhibit particularly high activity against E.coli.     

Characterization of Highly Porous Materials from Cellulose Carbamate

Highly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X-ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm³ were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m²/g and total pore volumes of up to 18 cm³/g.     

Regioselective sulfation of trimethylsilyl cellulose using different SO3-complexes

Trimethylsilyl cellulose (DS_Si = 2.9) dissolved in dry tetrahydrofurane was reacted with SO₃-complexes of N,N-dimethylformamide, triethylamine, pyridine and ethyldiisopropylamine. Under the given reaction conditions, i.e. 25 °C, 24 h, 2.2 mol equivalent SO₃-complex, the SO₃ attacks the trimethylsilyl ether groups followed by the formation of sodium sulfate cellulose under sodium hydroxide work-up conditions. The regioselectivity of the sulfation is controlled by the complex partner of SO₃. Cellulose sulfates with preferred O-6 sulfation were obtained using SO₃-N,N-dimethylformamide. In case of SO₃-triethylamine, cellulose-2-sulfates could be prepared with good regioselectivity. Small residual amounts of silicon in the cellulose sulfates (0.1–0.2% w/w) can be quantified using inductively coupled plasma-optical emission spectroscopy (ICP-OES), and can be decreased up to 80% by heating (70 °C, 24 h) the polymers in vacuum.     

Effect of structural and physico-chemical features of cellulosic substrates on the efficiency of enzymatic hydrolysis

Effects of major physicochemical and structural parameters of cellulose on the rate and degree of its enzymatic hydrolysis were tested with cellulosic materials from various sources. Some different pretreatments were: mechanical (milling), physical (X-ray irradiation), and chemical (cadoxen, H₃PO₄, H₂SO₄, NaOH, Fe²+/H₂O₂). The average size of cellulose particles and its degree of polymerization had little effect on the efficiency of enzymatic hydrolysis. For samples of pure cellulose (cotton linter, microcrystalline cellulose, α-cellulose), increase in the specific surface area accessible to protein molecules and decrease in the crystallinity index accelerated the enzymatic hydrolysis (the correlation coefficients were 0.89 and 0.92, respectively). In the case of lignocellulose (bagasse), a quantitative linear relationship only between specific surface area and reactivity was observed.     

An FTIR Spectroscopic Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines

Herein, the reaction between CO₂ and piperidine, as well as commercially available functionalised piperidine derivatives, for example, those with methyl‐, hydroxyl‐ and hydroxyalkyl substituents, has been investigated. The chemical reactions between CO₂ and the functionalised piperidines were followed in situ by using attenuated total reflectance (ATR) FTIR spectroscopy. The effect of structural variations on CO₂ absorption was assessed in relation to the ionic reaction products identifiable by IR spectroscopy, that is, carbamate versus bicarbonate absorbance, CO₂ absorption capacity and the mass‐transfer coefficient at zero loading. On absorption of CO₂, the formation of the carbamate derivatives of the 3‐ and 4‐hydroxyl‐, 3‐ and 4‐hydroxymethyl‐, and 4‐hydroxyethyl‐substituted piperidines were found to be kinetically less favourable than the carbamate derivatives of piperidine and the 3‐ and 4‐methyl‐substituted piperidines. As the CO₂ loading of piperidine and the 3‐ and 4‐methyl‐ and hydroxyalkyl‐substituted piperidines exceeded 0.5 moles of CO₂ per mole of amine, the hydrolysis of the carbamate derivative of these amines was observed in the IR spectra collected. From the subset of amines analysed, the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines were found to favour bicarbonate formation in the reaction with CO₂. Based on IR spectral data, the ability of these amines to form the carbamate derivatives was also established. Computational calculations at the B3LYP/6‐31+G** and MP2/6‐31+G** levels of theory were also performed to investigate the electronic/steric effects of the substituents on the reactivity (CO₂ capture performance) of different amines, as well as their carbamate structures. The theoretical results obtained for the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines suggest that a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area of the nitrogen atom play a role in destabilising the carbamate derivative and increasing its susceptibility to hydrolysis. A theoretical investigation into the structure of the carbamate derivatives of these amines revealed shorter N? C bond lengths and a less‐delocalised electron distribution in the carboxylate moiety.     

Trapping of carbamic acid species with (trimethylsilyl)diazomethane

Methoxycarbonylation of a variety of amines into the corresponding methyl carbamates was accomplished by allowing them to react with (trimethylsilyl)diazomethane TMSCHN₂ under bubbling of CO₂. The reaction was performed at room temperature for a period of ca. 2 h in benzene-MeOH (4/1 v/v), which was the solvent of choice. In this mixed solvent, undesirable bicarbonate is formed in equilibrium along with carbamate anion. Owing to the irreversibility in the esterification step by TMSCHN₂, however, the yield of methyl carbamate can reach very high.     

HTO/Cellulose Aerogel for Rapid and Highly Selective Li+ Recovery from Seawater

To achieve rapid and highly efficient recovery of Li⁺ from seawater, a series of H₂TiO₃/cellulose aerogels (HTO/CA) with a porous network were prepared by a simple and effective method. The as-prepared HTO/CA were characterized and their Li⁺ adsorption performance was evaluated. The obtained results revealed that the maximum capacity of HTO/CA to adsorb Li⁺ was 28.58 ± 0.71 mg g⁻¹. The dynamic k₂ value indicated that the Li⁺ adsorption rate of HTO/CA was nearly five times that of HTO powder. Furthermore, the aerogel retained extremely high Li⁺ selectivity compared with Mg²⁺, Ca²⁺, K⁺, and Na⁺. After regeneration for five cycles, the HTO/CA retained a Li⁺ adsorption capacity of 22.95 mg g⁻¹. Moreover, the HTO/CA showed an excellent adsorption efficiency of 69.93% ± 0.04% and high selectivity to Li⁺ in actual seawater. These findings confirm its potential as an adsorbent for recovering Li⁺ from seawater.     

Influence of UV pretreatment on the abies wood catalytic delignification in the medium “acetic acid–hydrogen peroxide–TiO2”

Some regularities of abies-wood oxidative delignification by acetic acid–hydrogen peroxide mixture under the action of suspended TiO₂ catalyst and UV pretreatment of wood pulp were studied. The combined action of TiO₂ catalyst and of UV-pretreatment of abies-wood allow to produce at optimal conditions of the delignification process the chemically pure cellulose containing no residual lignin. The major characteristics of cellulose product obtained from abies-wood correspond to the characteristics of microcrystalline cellulose.