Comparative study of polystyrene/chemically modified wheat straw composite for green packaging application

The recalcitrant nature of native wheat straw (WS) biomass results from cellulose, lignin, hemicellulose and some amount of protein embedded together in a composite structure causing poor adhesion to a polymer matrix composite. Adequate pre-treatment can curtail the recalcitrance structure of WS and enhance the susceptible cellulose area to synthesize a green composite. This paper examined the effect of various chemical pre-treatment procedures in improving surface morphology of wheat straw. Moreover, polystyrene (PS), PS (60 wt%)/native WS (40 wt%), PS (60 wt%)/NaOH-treated WS (40 wt%), PS (60 wt%)/HCl-treated WS (40 wt%), and PS (60 wt%)/H2SO4-treated WS (40 wt%) composite films were prepared using solution casting method. The changes in crystalline structure, hydrophobicity, water vapor migration rate, and thermal and mechanical stabilities of synthesized bio-composites were examined. From the results it can be concluded that the alkali-treated WS is highly compatible with the PS and can be used to synthesize a biodegradable composite film for various industrial green packaging applications.     

Polybenzimidazole/poly(tetrafluoro ethylene) composite membranes for high temperature proton exchange membrane fuel cells

A porous poly(tetrafluoro ethylene) (PTFE) thin film (thickness 16 ± 2 μm) is used as a supporting material for polybenzimidazole (PBI) to prepare the PBI/PTFE composite membrane (thickness 38 ± 2 μm). The perfluorosulfonic acid resin (Nafion) is used as a coupling agent at the interface between PTFE and PBI to improve the bonding between PBI and PTFE. The composite membrane, after doping with phosphoric acid, is used to prepare membrane electrode assemblies (MEAs). A 450 h continuous fuel cell life test at 160 °C with a fixed current density i = 200 mA cm⁻² and a 20 cycles cell on/off test, in which the fuel cell is operated at 160 °C with i = 200 mA cm⁻² for 12 h and then switched off at room temperature in an ambient environment for 12 h per cycle, are performed. Both tests show good fuel cell performances.     

Crystallization of P Type Amorphous Silicon (a-Si: H) by AIC Method: Effect of Aluminum Thickness

In this work, we will study the crystallization of P type hydrogenated amorphous silicon (a-Si:H) by Aluminum Induced Crystallization technique (CIA) by varying the thickness of the aluminum films. We have deposited a 100 nm thickness of p-type a-Si:H layer on Corning glass substrates using PECVD technique. An aluminum layer with thickness ranging from 10 to 400 nm was thermally evaporated on the a-Si:H surface. The thermal annealing was performed in a conventional furnace at temperature of 550 °C for 4 h in flowing N2 ambient. The study of the crystallization of the Al/a-Si:H/Glass structure according the aluminum thickness was carried out by using Raman spectroscopy, X-rays diffraction and Hall Effect measurements. Raman results reveal the presence of the peaks between 510 and 520 cm−1, which are close to the peak of crystallized Si (about 521 cm−1) proving the crystallization of all samples. The XRD measurements show the presence of the characteristic peaks of the crystalline silicon, thus the a-Si: H (p) layer was effectively crystallized by the AIC method in a short time. Through Hall measurements we found an improvement in electrical properties and an increase in dopant concentration (+ 5.3 1014 to + 2.9 1017 cm2).     

Ring-opening polymerization of cyclic esters in the presence of choline/SnOct2 catalytic system

Low-molecular weight poly(ε-caprolactone), polylactides, and copolymers of ε-caprolactone and lactide were synthesized by ring-opening polymerization of cyclic monomers with choline (CHOL) as a initiator and SnOct₂ as a catalyst. Polymerization was conducted in bulk (120–160 °C) with high yield. Effects of temperature, reaction time, and CHOL dosage on the polymerization process were examined. Structure of products was characterized by means of MALDI-TOF, IR, and NMR.     

Synthesis and Kinetic Studies on Dimer Fatty Acid/Polyethylene Glycol Polyester

Dimer fatty acid polyethylene glycol polyester, a new kind of non-ionic polymeric surfactant, was synthesized by using dimer fatty acid and polyethylene glycol (400) as materials in this paper. The optimum reaction conditions of esterification were as follows: the molar ratio of dimer fatty acid (DFA)/PEG (400) is 1 / 1.20, the preferable catalyst is stannous chloride and the amount is 0.3% (w/w) of the mass of DFA, reaction temperature is 200°C, reaction time is 6 h. The conversion ratio of polyesterification can reach 98.11%. A new kinetic model of polyesterification reaction catalyzed with stannous chloride was presented. The Genetic Algorithms and Runge–Kutta were used to estimate the parameters of the kinetic model. The results of experiments and computer operations indicated that the reaction order is 0.998 to the carboxyl and 1 order to the hydroxyl. The activation energy obtained from Arrhenius plot is 97.18 kJ mol⁻¹, and the pre-exponential frequency factor is lnA = 21.39 kg² mol⁻² min⁻¹ at temperature range of 160 ∼ 190°C.     

Economical and Ecological Biotreatment/Half Bleaching of Cotton-Containing Knit Fabrics on Industrial Scale

ABSTRACT

Bio-scouring/half bleaching of cotton-containing knit fabrics was carried out on an industrial scale. A comparison between the traditional hot-alkaline scouring/half bleaching and the enzymatic scouring/half bleaching from product quality, economic as well as environment perspectives were made. The results detailed in this case study indicate that (1) the loss in fabric weight as well as the improvement in degree of whiteness are governed by the treatment method (i.e., hot-alkaline scouring/half bleaching > bio-scouring/half bleaching; (2) bio-scouring/half bleaching technique gives rise to better bleaching fabric softness, higher strength retention along with greater depth of shades; (3) the extent of improvement in fabric wettability follows the descending order: hot-alkaline scouring/half bleaching = bio-scouring/half bleaching > > untreated; and (4) the saving in materials and energy costs, the improvement in fabric properties as well as the reduction in pollutants concentrations (i.e., better wastewater quality are determined by the pretreatment technique and follow the descending order: bio-scouring/half bleaching > alkaline-scouring/half bleaching.     

Radiation modification of functional properties in PVC/mica electrical insulations

Summary The effects of γ-irradiation on poly(vinyl chloride) blended with fillers (plasticizer, lead stabilizer and mica) are presented. Mechanical and electrical investigations were carried out on samples that received doses of maximum 160 kGy. The results on tensile strength, volume resistivity and loss factor prove that poly(vinyl chloride) may be used as electrical insulator after short γ-exposure. Because mica plays a role of absorbent for hydrochloric acid formed by PVC degradation, favorable properties are obtained for dose up to 120 kGy. The volume resistivity decreases constantly while tan δ remains unchanged for a large frequency range (10²–10⁵ cps). Mica content of 14% induces a decrease in unirradiated PVC of one order of magnitude. After irradiation at 160 kGy volume resistivity increases of about five times relative to 40 kGy irradiated samples. At 150 kGy tensile strength decreases only with 10%, and elongation at break presents a light modification in the selected dose range. The largest differences between the maximum current values obtained for applied doses are presented by PVC with the highest concentration of mica (14%). At 40 kGy, when the degradation becomes relevant, the dipoles are not efficiently trapped by mica and the current does not attend a steady state for a long period (more than half an hour). For higher doses the steady-state current is reached after only 1–3 minutes, due to crosslinking. Some considerations concerning the consequences of high energy exposure of poly(vinyl chloride) on electrical behaviour are presented.     

Thermal,Electrical and Physical Properties of Glasses Based on Basaltic Rocks

Six glass compositions based on basaltic rocks and some industrial wastes, Batches were melted in an electric furnace at temperature 1400 °C for 2 h and then casted into rods and discs shapes. Many important techniques were used in the present study including X- ray fluorescence, thermal expansion, dielectric properties, indentation micro hardness, bending strength, density and chemical durability, The expansion coefficient in the temperature range 25–300 °C lies in the range between 48.78 to 59.76 × 10−7 /°C and the temperatures of Tg started at 668.79 °C and ranging between 668.79–632.34 °C and Ts started at 737 °C and lies in the range and 737–711.6 °C respectively. The lower expansion glasses have higher transition and softening temperatures and vice versa. Bending strength and Vickers micro hardness show a gradual decrease from 118 to 56 MPa and 6120–4020 MPa respectively with increasing cement dust content. In the same time the density increases from 2.79 to 2.96 g/cm3 by increasing cement dust content.     

Silicon Carbide Ceramic Particulate Reinforced AA2024 Alloy Composite - Part I: Evaluation of Mechanical and Sliding Tribology Performance

In this research work, a master batch (comprising of AA2024 alloy, Silicon Nitride (Si3N4) and Graphite particulates) was reinforced by Silicon-Carbide (SiC) ceramic particulates (0–6 wt.-%; at steps of 2%; i.e. four composites samples viz. ASC-0; ASC-2; ASC-4; ASC-6) with the aim of enhancing mechanical and sliding tribology performance. The semi-automatic stir-casting fabrication process was followed as per standard industrial practice in-order-to fabricate the sample plates of the said alloy composites as per design. Thereafter, the sample specimens were prepared via wire EDM cutting followed by polishing over emery paper; as per ASTM standard dimensions and various physical (density and void content), mechanical (tensile strength, flexural strength, impact strength, hardness etc.), sliding tribology performance (steady state sliding wear; ASTM G-99; Pin-on-Disc tribo-meter), thermal (thermal conductivity, Thermo-Gravimetric Analysis (TGA)); thermo-mechanical (Dynamic Mechanical Analysis (DMA)), fracture-analysis, X-ray diffraction (XRD) etc. characterisation were performed and discussed. In Part-1: Physical, mechanical and sliding tribology performances were discussed. The Taguchi design of experiment technique was employed for designing of experimental runs having input controlling parameters like sliding velocity (0.654–2.616 m/s), sliding distance (784.8–3139.2 m), normal load (5–50 N), reinforcement content (0–6 wt.-%) and environment temperature (20–50 °C). The worn surface morphology studies were performed to understand prevalent wear mechanism using Field Emission Scanning Electron Microscope (FESEM) along with Energy-dispersive X-ray spectroscopy (EDS) that reveals elemental composition and its dispersion on the surface. In Part-2: evaluation of characterizations like thermal, thermo-mechanical, fracture-analysis, X-ray diffraction (XRD) etc. were discussed in correlation with mechanical and sliding wear performance. In Part-3: the entire performance data are analysed using hybrid AHP-TOPSIS technique (an MCDM technique; computationally simple and easy to understand) in-order-to rank the composites formulations.     

Impact of Exogenous Silicate Amendments on Nitrogen Metabolism in Wheat Seedlings Subjected to Arsenate Stress

We intended to investigate the response of arsenate on nitrogen metabolism in wheat seedlings and aimed to assess the efficacy of silicon amendments in modulating the metabolic disturbances caused by arsenate stress. The nitrogen metabolism of wheat cultivated in different levels of arsenate with or without silicate in a medium supplemented with modified Hoagland’s solution for 21 days was studied. Experimental design was completely randomized with different arsenate concentrations (0, 25, 50 and 100 μM) with or without 5 mM silicate. Arsenate treatment decreased growth along with decline in nitrate (NO3−) uptake and accumulation. Activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) as well as glutamate synthase (GOGAT) were lowered in the test seedlings. Decline in nitrite (NO2−) and amino acid contents were also evident along with an enhancement in the accumulation of toxic ammonia. Silicate supplementation under arsenate stress however, improved growth, repaired the arsenate-induced effects leading to an enhancement in nitrate (NO3−) uptake and consequently improved nitrite (NO2−) and amino acid contents as well. The total and soluble nitrogen contents were enhanced along with enhancements in activities of enzymes associated with nitrate metabolism while ammonia accumulation was lowered. Results therefore, imply the involvement of exogenous silicon amendments in relieving the metabolic alterations in nitrogen metabolism caused by arsenate stress that enabled wheat seedlings to adapt under arsenate excess and eventually promoted plant growth.     

Influence of different viscosity grade cellulose-based polymers on the development of valsartan controlled release tablets

This work is based on formulating and optimizing controlled release (CR) valsartan (160 mg) tablets using different viscosity grades of the cellulosic polymer. The objective was to develop an effective once-daily drug delivery system of this cardiovascular agent. Central composite design was used for designing the formulations. Polymers used were Methocel® K4M, K15M and K100M. Compatibility of excipients with active was studied through FT-IR. Micromeritic properties were determined and formulations exhibiting appropriate flow characteristics were compressed. Swelling behavior and in vitro buoyancy effect were studied and response surface curves were constructed to optimize the formulation. Multi-point dissolution profiles of valsartan CR tablets at pH 1.2, 4.5 and 6.8 were obtained. Model-dependent and model-independent methods were performed including f2, stability test as per ICH guidelines and ANOVA. FT-IR studies revealed the compatibility of valsartan with all excipients. Formulation K4T9 (containing 25% K4M polymer) was selected to be the best optimized trial, based on physical properties and controlled release profile (23% at 4 h, 82% at 16 h and 100% at 24 h). Results of buoyancy and swelling behavior indicated that HPMC-K4M polymer exhibited excellent floating lag time and swelling indexes. In vitro drug release kinetics showed that formulation K4T9 displayed Korsmeyer–Peppas drug release pattern with r value > 0.99. The manufacturing process of K4T9 was also found to be reproducible with a shelf life period of 41 and 36 months at room temperature and accelerated conditions, respectively. Valsartan CR matrix-based formulation was successfully prepared with Methocel K4M retardant.     

Effect of dietary linoleic acid content on the distribution of triacylglycerol molecular species in rat adipose tissue

The present study examined the effect of varying dietary linoleate intake (0.01, 0.24, 2.4, 24, 80 or 160 g/kg diet) for 24 weeks on the distribution of triacylglycerol (TG) molecular species in rat epididymal adipose tissue. Adipose TG fractions were purified by thin-layer chromatography and separated into different molecular species by reversephase high-performance liquid chromatography. The identification of TG species was based on fatty acid composition, retention time and the theoretical carbon number. When the dietary 18∶2n−6 content was equal to or less than 24 g/kg, no significant amounts of n−6 fatty acids (mainly 18∶2n−6) were observed in adipose tissue TG despite the fact that the levels of 20∶4n−6 in liver phospholipids increased significantly. There were 12 major molecular species in adipose tissue when the dietary 18∶2n−6 content was less than 2.4 g/kg. When the diteary 18∶2n−6 content reached 24 g/kg, an additional six TG species containing one, two or three molecules of 18∶2n−6 were observed. The levels of TG molecules containign two or three 18∶2n−6 residues were further increased when the diet contained very large amounts of linoleic acid (160 g/kg). Conversely, those TG species containing only one 18∶2n−6 residue became less abundant. It is suggested that the accumulation of these linoleate-rich TG molecular species in adipose tissue, particularly di- and trilinoleoyl containing TG, is the result of an adequate or an excessive intake of linoleic acid.     

Parameter Optimization of Rotary Ultrasonic Machining on Quartz Glass Using Response Surface Methodology (RSM)

In the current research, rotary ultrasonic machining was used to drill holes in quartz material. The effect of different RUM parameters namely tool feed rate, tool rotational speed and ultrasonic power on material removal rate and surface roughness has been studied experimentally. The response surface methodology with central composite design has been used to design the experiments. From the desirability approach, the optimum setting of the rotary ultrasonic machining parameters was found to be the tool rotational speed of 4968 rpm, feed rate of 0.55 mm/min, and ultrasonic power of 80% for achieving the maximum MRR of 0.2135 mm3/s and minimum SR of 0.3685 μm. Microstructure analysis of the machined surface was performed by using scanning electron microscopy in order to study the mechanisms of material removal under the different settings of RUM parameters. It was observed that at very low feed (0.08 mm/min) and high rpm (5681) the material is predominantly removed by plastic deformation whereas at high feed (0.92 mm/min) and low rpm (2318) the material is removed by brittle fracture.     

Synthesis of physically cross-linked gum Arabic-based polymer hydrogels with enhanced mechanical,load bearing and shape memory behavior

The TiO2 dispersed physically cross-linked polymer hydrogels were synthesized through a single step free radical addition polymerization mechanism based on acrylic acid and gum Arabic (GA) as polymer constituents, and ferric ions (Fe3+) as physical cross-linker. The effect of TiO2 powder was investigated on thermal and mechanical properties of the hydrogels by dispersion of 0.01, 0.02 and 0.03 g of TiO2 in hydrogels. The prepared hydrogels were successfully characterized through FTIR, XRD, SEM and thermogravimetric analysis (TGA). For the mechanical properties, dynamic mechanical analysis and universal testing machine (UTM) were used. The DMA results showed that the storage modulus was increased with the TiO2, while UTM results showed that 0.02 g of TiO2 powder significantly enhanced the fracture stress, elastic modulus, toughness and stretchability by 4514%, 4328%, 4124% and 20%, respectively, compared to the virgin hydrogels. Cole–Cole plot confirmed the homogeneity and viscoelastic behavior of the system, while manual load bearing and shape memory test showed that the hydrogels bear a load of 2.5 kg for a long time and it is recovered within 10 s to its original state. The materials can be applied for the synthesis of artificial body parts in the field of bio-engineering. The use of un-modified GA for the synthesis of hydrogels will open a new window for the researchers working in this field.     

H2 adsorption and H/D exchange on Au/TS-1 and Au/S-1 catalysts

We report a combined quantum-mechanics/molecular-mechanics (QM/MM) analysis of H₂ dissociation and hydrogen–deuterium (H/D) exchange on four potential active sites inside the TS-1 pores: (1) Au₃/T6–Ti-non-defect, (2) Au₃/T6–Si-non-defect, (3) Au₃/T6–Ti-defect, and (4) Au₃/T6–Si-defect. We provide full kinetic and thermodynamic data calculated at standard conditions (298.15 K, 1 atm) for Eley–Rideal mechanisms on these sites. The H/D exchange on Au₃/TS-1 occurs in two steps: (1) first H₂ dissociation on Au₃/TS-1 to form H–Au₃–H species and (2) D₂ (or second H₂) attack on these H–Au₃–H species to form HD. The energetics of the first H₂ dissociation step is site-sensitive (with respect to Au sites), while that of the D₂ (or second H₂) addition step is not site-sensitive. We found that two different mechanisms for the second step are both kinetically and thermodynamically favorable. The most favorable mechanism (ΔE _act ~ 28 kcal/mol) involves an attack of D₂ on both the H atoms in the H–Au₃–H intermediate, and two HD molecules are formed simultaneously. The first H₂ dissociation step is almost thermoneutral and the D₂ (or second H₂) addition step is somewhat exothermic. A comparison of the pure QM and QM/MM calculations on Au₃/TS-1 suggests that the formation of the H–Au₃–H species inside the TS-1 pores becomes thermodynamically more favorable due to the long-range interactions. The activation energies for the first H₂ dissociation step (19–24 kcal/mol) are lower than those for the D₂ (or second H₂) addition step (28–31 kcal/mol). Therefore, the increase in the HD formation rate with temperature is likely to be stronger than the increase in the H–Au₃–H formation rate. On the basis of the calculated activation energies and the reaction thermochemistry, we predict a viable Eley–Rideal H/D exchange pathway that may operate at or above 573 K. We also found potential H/D exchange channels on bare TS-1 (without Au₃) where gas-phase D₂ (or second H₂) attacks the Ti–OH or Si–OH groups (of defect sites) and exchanges one of the D atoms to form HD and Ti–OD or Si–OD groups.     

Kinetic study on the liquefaction of bagasse in polyhydric alcohols based on the cell wall component of the liquefied residue

Natural lignocellulose differs from the synthetic polymer due to the mineral matter which has a great influence on its degradation. To better understand lignocelluloses liquefaction, the bagasse was liquefied in alcoholic solvent [polyethylene glycol (PEG 400)/glycerol] catalyzed by sulfuric acid at 140–180 °C under atmospheric pressure. The amount of major components (cellulose, hemicellulose, lignin and ash) in the liquefied residue was used as a measurement of the extent of liquefaction. The results showed that hemicellulose is the most reactive component to liquefaction among other major cell wall components, followed by the lignin and cellulose. The content of the ash increased slowly with the reaction time under all reaction temperatures due to the re-condensation or re-precipitation of liquefied components. Based on the experimental results, the reaction kinetics for bagasse liquefaction was modeled and the activation energies, frequency factors and reaction orders for cellulose and lignin were calculated in a conventional manner. The activation energies for the liquefaction of lignin, cellulose and bagasse were 30.51 kJ mol−1, 72.83 kJ mol−1, and 67.09 kJ mol−1, respectively. The results of the enthalpy indicated the liquefaction of biomass is a highly endothermic reaction process. A better understanding to the liquefaction kinetics of biomass could be conducted based on the cell wall component of the liquefied residue.     

Thermo-mechanical properties of high density polyethylene with zinc oxide as a filler

This study investigates the microstructural, thermal, and mechanical behavior of high density polyethylene (HDPE)-based composites prepared using compression molding technique. HDPE was mixed with either micro-size zinc oxide (bulk ZnO) or zinc oxide nanoparticles (nano-ZnO) as fillers’ contents at 0, 10, 20, 30, and 40 wt%. The structural, morphological, and thermal properties of the composites were identified using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), and thermal gravimetric analysis (TGA). The results showed good dispersion and interaction mechanisms between HDPE and the fillers at low weight percentage. The thermal stability of HDPE was enhanced by adding both bulk and nano-ZnO, especially for higher filler loading. Tensile tests at different speeds and Vickers microhardness tests conducted at different indentation loads (0.25–5 N) at t = 60 s were performed to realize how the mechanical properties of the composites were influenced. The values of stiffness, ultimate tensile strength, and yield stress increased by increasing the filler loading to 20 wt% of either bulk ZnO or nano-ZnO. The values of ultimate tensile strain and ductility were deteriorated by increasing the filler loading. Nano-ZnO, at 20 wt% content in composite, showed higher mechanical properties than bulk composite, so it has been recommended for a better tensile performance at higher strain rates. Vickers microhardness measurements showed that the tested samples exhibited reverse indentation size effect (RISE) behavior. The obtained results were analyzed using Meyer’s law which was a preferred approach for analysis of HDPE/ZnO composite.     

Simultaneous MS-IR Studies of Surface Formate Reactivity Under Methanol Synthesis Conditions on Cu/SiO<Subscript>2</Subscript>

The coverages and surface lifetimes of copper-bound formates on Cu/SiO₂ catalysts, and the steady-state rates of reverse water-gas shift and methanol synthesis have been measured simultaneously by mass (MS) and infrared (IR) spectroscopies under a variety of elevated pressure conditions at temperatures between 140 and 160 °C. DCOO lifetimes under steady state catalytic conditions in CO₂:D₂ atmospheres were measured by ¹²C–¹³C isotope transients (SSITKA). The values range from 220 s at 160 °C to 660 s at 140 °C. The catalytic rates of both reverse water gas shift (RWGS) and methanol synthesis are ~100-fold slower than this formate removal rate back to CO₂ + 1/2 H₂, and thus they do not significantly influence the formate lifetime or coverage at steady state. The formate coverage is instead determined by formate’s rapid production/decomposition equilibrium with gas phase CO₂ + H₂. The results are consistent with formate being an intermediate in methanol synthesis, but with the rate-controlling step being after formate production (for example, its further hydrogenation to methoxy). A 2–3 fold shorter life time (faster decomposition rate) was observed for formate under reactions conditions, with both D₂ and CO₂ present, than in pure Ar or D₂ + Ar alone. This effect, due in part to the effects of the coadsorbates produced under reaction conditions, illustrates the importance of using in situ techniques in the study of catalytic mechanisms. The carbon which appears in the methanol product spends a longer time on the surface than the formate species, 1.8 times as long at 140 °C. The additional delay on the surface is attributed in part to readsorption of methanol on the catalyst, thus obscuring the mechanistic link between formate and methanol.     

Pd-Decorated CNT-Promoted Pd-Ga2O3 Catalyst for Hydrogenation of CO2 to Methanol

Abstract  

A type of Pd-decorated CNT-promoted Pd-Ga catalysts was developed. The catalyst displayed excellent performance for CO₂ hydrogenation to methanol. Under the reaction conditions of 5.0 MPa and 523 K, the observed specific reaction rate of CO₂ hydrogenation reached 2.23 μmol s⁻¹ (m²-Pd)⁻¹, which was 1.39 times that (1.60 μmol s⁻¹ (m²-Pd)⁻¹) of the non-promoted Pd-Ga host. The addition of a small amount of the Pd-decorated CNTs to the Pd-Ga host catalyst did not cause a marked change in the E _a of the CO₂ hydrogenation reaction. The function of the CNT-promoter was mainly in increasing the molar percentage of the catalytically active Pd⁰-species in the total Pd-amount at the surface of the functioning catalyst, and in improving the capability of the catalyst to adsorb and activate H₂ (one of the reactants). Compared to the “Herringbone-type” CNTs, the “Parallel-type” CNTs possess less active surface (with less dangling bonds), and thus, lower capacity for adsorbing H₂, resulting in the rather limited promoter effect.     

Molecularly imprinted poly(4,4′-methylenedianiline) for selective electrochemical detection of dibenzothiophene

Self-cross linked poly(4,4′-diaminodiphenylmethane) was prepared by an oxidative polymerization. Also a molecular imprinted polymer was prepared by employing 4,4′-diaminodiphenylmethane as the functional monomer, ammonium persulfate and dibenzothiophene as the oxidizing agent and template, respectively. It is suggested that the π–π stacking effect between 4,4′-methylenedianiline and dibenzothiophene induced the compact imprinted polymer and the formation of more imprinted sites. Field emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and FTIR spectroscopy were used for the characterization of the synthesized polymers. The removal of template molecules leads to the preparation of molecularly imprinted polymer (MIP), which was subsequently used as an electrode material for the preparation of an electrochemical sensor for the detection of dibenzothiophene. Electrochemical behavior of dibenzothiophene on the sensors' construction based upon the application of imprinted (MIP) and non-imprinted (NIP) polymers was investigated in 0.1 mol L−1 of LiClO4 (as the supporting electrolyte), by means of cyclic voltammetry. The obtained cyclic voltammograms of the MIP electrode showed one irreversible anodic peak at ~ 1.5 V. This peak was attributed to the electrochemical oxidation of dibenzothiophene to dibenzothiophene sulfoxide. The current variation acquired through the developed imprinted sensors as a function of dibenzothiophene concentration was linear in the concentration range of 60–150 mg L−1. The corresponding limit of detection was calculated as 11 mg L−1. The imprinted sensor showed a significantly improved sensitivity towards the investigated analyte rather than that observed using a non-imprinted polymer.