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Ceramic materials based on silicon oxycarbide (SiOC) and reduced graphene oxide (rGO) were produced by polymer pyrolysis and evaluated in terms of phase development and porosity. Carbonaceous phase, initially prepared from graphite oxide, was incorporated into silicone dihydroxy terminated in different amounts (0, 5, 15 and 25 wt%) and submitted to pyrolysis at 1500 °C to obtain SiOC/rGO ceramics. Higher ceramic yields and more thermally stable materials were obtained after rGO addition, whose results were associated to the chemical interaction degree between rGO and polymer structure. Cgraphite and SiC phases were generated in rGO-containing ceramics and a mixture of α- and β-SiC was achieved from 15 wt% rGO, enhancing their crystallinity with increasing of rGO content. Porosity features were influenced by the carbonaceous phase amount and different rGO-polymer interaction degrees. SiOC/rGO ceramics demonstrated desirable structural characteristics for future investigations in electrical and/or electrochemical applications.

In the present paper, a new analytical preconcentration/speciation method for antimony species determination in bottled mineral water samples using the SiO2/Al2O3/SnO2 adsorbent was developed. The method is based on selective adsorption of Sb(III) ions by SiO2/Al2O3/SnO2 under a wide pH range (2.5–7.5). Total antimony was determined with previous sample treatment using 0.1% (w/v) l -cysteine and the concentration of Sb(V) species was determined by the difference between total and Sb(III). The proposed method provided an analytical curve ranging from 0.50 to 5.00 μg L−1 (r = 0.999), limit of detection (LD) of 0.17 µg L−1 and preconcentration factor (PF) of 136-fold. The method exhibited tolerance to different metal ions and the accuracy was attested from addition and recovery tests (95.2–106.0%) in bottled mineral water samples using 2.0% (w/v) l -cysteine, as well as by analysis of certified material. Only Sb(III) species were determined in mineral water (0.54–1.04 μg L−1).

This work deals on the preparation of silicon oxycarbide (SiOC) and silicon boron oxycarbide (SiBOC) ceramics from pyrolysis involving alkoxysilanes with different organic groups. Boron content, organic substituent and annealing time were evaluated on crystallization and composition of resulting ceramics. B-free precursors composed of methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES) and vinyltrimethoxysilane (VTMS) were obtained by the sol-gel method, whilst B-containing precursors were prepared by adding to each alkoxysilane a proper amount of boric acid resulting in B/Si atomic ratios of 0.1 and 0.5. Precursors were pyrolyzed at 1500 °C for 1 and 3 h to produce respective SiOC and SiBOC ceramics. X-ray diffraction (XRD) patterns revealed enhanced SiC phase crystallization for PTES-derived ceramics, followed by those containing vinyl and methyl groups, which was also confirmed by X-ray photoelectron spectroscopy (XPS) from percentages of Si-C and Si-O bonds. Csp2 and Csp3 amounts varied among ceramics, indicating direct influence of organic substituent on conductive carbon phase development. Boron addition induced the growth of SiC crystallites, having more evident effect in matrices with higher proportions of amorphous fraction and lower residual carbon amounts. Organic group nature, boron content and annealing time played an important role for production and evolution of SiC and C phases into ceramics.

A flow-injection preconcentration system using detection by the thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS) is proposed. Cd2+ are adsorbed on avocado seed activated carbon (ASAC) packed into a cylindrical mini-column and eluted using HCl solutions for the detection system. A 25–1 fractional factorial and Doehlert matrix design were employed to determine the optimum conditions for cadmium preconcentration (pH 7.68, buffer concentration (Tris/Tris-HCl) of 0.023 mol L-1, eluent concentration (HCl) of 2.0 mol L-1, the adsorbent mass of 100.0 mg and preconcentration flow rate of 4.8 mL min-1). The preconcentration method presents linearity within the range of 0.41-15.00 µg L-1, limits of quantification and detection of 0.41 and 0.12 µg L-1, respectively, preconcentration factor of 10.7, consumption of index of 0.93 mL and sample throughput of 26 h-1. The precision assessed as the relative standard deviation (RSD) were found to be 0.48, 0.90 and 2.30% for inter-day precision (n = 2), and 0.30, 0.44 and 2.48% for intra-day precision (n = 6) for respective cadmium concentration of 0.50, 5.00 and 15.00 µg L-1. The proposed method was applied satisfactorily in samples of cigarette (62.84 ± 11.28 µg kg-1), human hair (69.61 ± 2.38 µg kg-1) and water samples [lake (0.65 ± 0.01 µg L-1), tap and mineral].

Made available in DSpace on 2020-12-12T01:36:23Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 In the current study, the synthesis of hematite (α-Fe2O3) at different temperatures (750 and 900 °C), and reduced graphene oxide (rGO), obtained from an adaptation to the Hummers’s method, was evaluated. These materials were characterized by X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, among others. The deposition of samples on the conductive surface of tin-doped indium oxide coated glass substrate, was performed by the Layer-by-Layer technique. The films were prepared with 1- and 4-bilayers α-Fe2O3, using a cationic polyelectrolyte diallyldimethylammonium chloride (PDDA) or rGO. It was observed that the rGO/α-Fe2O3 films presented higher photocurrent and less resistivity when compared to the PDDA/α-Fe2O3 films. The largest photocurrent was obtained with the 4-bilayers rGO/α-Fe2O3 at 900 °C film, with 2.15 µA cm−2. In addition, a kinetic study for photoelectrocatalytic decolorization of the methylene blue dye under visible light was performed. The electrode that showed the greatest photoelectroactivity was the 4-bilayers rGO/α-Fe2O3 at 900 °C film, resulting in kobs = 11.90 × 10−3 min−1 and about 78% decolorization after 120 min. Departamento de Química Universidade Estadual de Londrina Instituto de Química Universidade de São Paulo Colégio Técnico Industrial Faculdade de Engenharia Universidade Estadual Paulista (UNESP) Departamento de Física Universidade Estadual de Londrina Colégio Técnico Industrial Faculdade de Engenharia Universidade Estadual Paulista (UNESP)

The present paper describes the synthesis, characterization, and evaluation of two cross-linked molecularly imprinted poly(methacrylic acid) and polyvinylimidazole towards selective extraction of imazethapyr in aqueous medium. Characterization of materials was performed by FT-IR, TGA, SEM, TEM, elemental analysis and nitrogen adsorption/desorption measurements. Based on relative selectivity coefficients (k′), the molecularly imprinted polyvinylimidazole showed higher selectivity towards imazethapyr and some similar structurally compounds belonging to imidalizones families, imazapic and imazapyr, when compared with poly(methacrylic acid). The kinetics and isotherms of sorption as well as the thermodynamic parameters were then obtained by using the polyvinylimidazole. It was observed that the pseudo-first and second-order models provided the best fit for imazethapyr sorption. Regarding the sorption isotherm, the dual-site Langmuir–Freundlich model presented the best fit for the experimental data, thereby suggesting the existence of sorption sites with different affinities. The maximum sorption capacities obtained for the imprinted and non-imprinted polymers were found to be 27.1 and 24.4 mg g−1, respectively. According to the obtained thermodynamic parameters, ΔG (0.96 kJ mol−1), ΔH (−22.81 kJ mol−1) and ΔS (−79.73 J mol−1 K−1), it might be suggested that the sorption process is not too much favorable, exothermic and provides increase of order at the solid-solution interface. In this case, the low temperature is favorable for the sorption of imazethapyr, typical of physisorption, which match with low sorption activation energy (20.25 kJ mol−1) determined from Arrhenius equation. The molecularly imprinted polyvinylimidazole exhibited higher sorption capacity when compared with previously reported commercial sorbents for imazethapyr.

The present study demonstrates the development of a voltammetric sensor based on graphite/restricted access molecularly imprinted poly(methacrylic acid)/SiO2 composite for folic acid determination in pharmaceutical formulation. The insertion of hybrid molecularly imprinted polymer with restricted access (RAM-MIP) into the graphite paste provided enhance in the cathodic peak current for FA. As the electric conductivity of RAM-MIP is very poor, the optimum content was found to be very low (3%, w/w) in the composite. Under optimized conditions (0.1 mol L−1 Britton-Robinson buffer and pH 4.5) using square wave voltammetry (frequency of 150 Hz, pulse amplitude of 90 mV and potential increment of 7 mV) a limit of detection of 0.72 μg L−1 (1.63 nmol L−1) and a linear range from 5.0 to 100.0 μg L−1 (0.01 to 0.23 μmol L−1) were obtained. The method precision was assessed in terms of inter-day (n = 6) and intra-day precision (two consecutive days), whose relative standard deviations (RSD%) ranged from 3.56 to 5.01%. The developed method was applied for FA determination in pharmaceutical samples whose accuracy was attested by means of addition and recovery assays (97.7–105.0%) as well as by high performance liquid chromatography (HPLC) as a reference technique, thus indicating that RAM-MIP sensor might be successfully applied for quality control in the real samples.

The present study describes the development of a solid phase preconcentration method for cobalt determination at trace levels using cross-linked poly(vinylpyridine-co-protoporphyrin) as a highly efficient adsorbent and a hyphenated flow injection-FAAS system. The influence of molar amount of protoporphyrin and 4-vinylpyridine in the copolymer was studied aiming at obtaining the optimum synthesis condition in terms of adsorption capacity and swelling effect. The polymers were characterized by FT-IR, SEM, nitrogen adsorption/desorption, and swelling analyses. The method is based on cobalt preconcentration at pH 9.0 in 0.01 mol L−1 Tris/Tris-HCl buffer through the cylindrical mini-column packed with 50 mg of adsorbent at a flow rate of 7.4 mL min−1, whilst the elution was carried out by using 2.0 mol L−1 HNO3. Using the best synthesis conditions, the solid phase preconcentration method using poly(vinylpyridine-co-protoporphyrin) named poly(4VP-PP) (5.00 mmol of 4-vinylpyridine and 0.10 mmol of protoporphyrin) provided a linear range from 4.60–200.0 μg L−1, the limit of detection of 1.38 μg L−1, preconcentration factor of 38, consumption of index of 0.53 mL and analytical frequency of 22 h−1. Using the poly(4VP-PP), the method showed high selectivity for cobalt determination in the presence of concomitant ions, when compared to poly(4VP), thereby indicanting the great importance of protoporphyrin on the selective analytical performance of the method. The poly(4VP-PP) was successfully applied for the preconcentration of cobalt from different kind of samples without matrix interference, including dark chocolate powder, black tea, infusion of black tea, and water samples (mineral, tap, and lake waters), with high recovery results (91–104%). The feasibility of the method was also attested by analysis of certified reference material of marine sediment (MESS-3).

In the present study a newly designed hybrid polymer based on poly(methacrylic acid)/SiO2/Al2O3 synthesized by combination of random free-radical polymerization followed by sol–gel process was evaluated for imazethapyr herbicide adsorption from aqueous medium. The adsorbent material has been characterized by FT-IR, SEM, TGA and X-ray diffraction. The adsorption kinetic properties were obtained by application of kinetic models (pseudo-first order, pseudo-second order and intraparticle diffusion). Although the fit models to experimental data were similar each others, the pseudo-second provided a slight best fit for herbicide adsorption onto hybrid polymer. From binding isotherm adsorption, the dual-site Langmuir-Freundlich model showed the best fit and maximum adsorption capacity of 4.50 mg g− 1. Thermodynamic parameters seem to indicate that adsorption of herbicide by hybrid material is exothermic, with decreasing in the disorder of the system and spontaneous. From the magnitude of ΔH (− 24.68 kJ mol− 1) and the activation energy (12.21 kJ mol− 1), it can be infer that adsorption of imazethapyr by hybrid polymer if of physical nature. From the achieved results, the poly(methacrylic acid)/SiO2/Al2O3 material showed good adsorptive characteristic for imazethapyr and this strategy open a convenient approach for preparation of new hybrid adsorbent materials in the field of separation science.

This paper describes the development of an electrochemical sensor highly selective to Pb 2 + ions based on drop-coated glassy carbon electrode (GCE) with a suspension of ion imprinted polymer (IIP) loaded with 1-(2-pyridylazo)-2-naphthol (PAN) (IIP-PAN) and multi-walled carbon nanotubes (MWCNT). The polymer has been characterized by SEM and TGA. The electrochemical method is based on open-circuit preconcentration of Pb 2 + onto modified electrode in 0.05 mol L − 1 Tris-HCl buffer solution at pH 6.0 during 20 min. The reduction of Pb 2 + was than performed on closed circuit at − 1.2 V during 60 s in a 0.05 mol L − 1 HCl solution, followed by subsequent differential pulse anodic stripping voltammetric determination in the range from − 0.8 to − 0.3 V. Electrode modified provided a better analytical response than those modified with its respective non imprinted polymer (NIP), IIP without PAN and MWCNT alone, which clearly demonstrates the synergic effect of recognition sites of IIP-PAN and MWCNT. Competitive adsorption studies for the binary Pb 2 + /Cu 2 + , Pb 2 + /Cd 2 + , Pb 2 + /Ni 2 + , Pb 2 + /Ni 2 + , Pb 2 + /Zn 2 + mixtures revealed the respective relative selective coefficients ( k ′) 301, 13.3, 9.5, 63.0 and 133.3, thus indicating that IIP-PAN is much more selective than NIP. Presence of potential interfering metal ions was also studied and the proposed electrode proved to be very tolerable. Limits of detection (LOD) and quantification (LOQ) were found to be 0.16 μg L − 1 and 0.50 μg L − 1 , respectively. The inter-day method precision was found to be 1.72 and 1.86% (relative standard deviation) and the intra-day precision was found to be 1.68 and 2.53% for 5.0 and 10.0 μg L − 1 of Pb 2 + , respectively. The developed sensor was effectively applied to water samples and synthetic urine with satisfactory recovery values from 95 to 103%. The accuracy of method was checked by analysis of standard reference material 1643e Trace Elements in Water NIST.

A novel hybrid ion imprinted polymer (HIIP) is proposed aiming at the development of an online micro-solid phase preconcentration system of Cd2 + coupled to TS-FF-AAS. To evaluate the selective and adsorptive performance of HIIP towards Cd2 +, hybrid non-imprinted polymer (HNIP), organic ion imprinted polymer (OIIP), and the inorganic ion imprinted polymer (IIIP) were synthesized and compared with each other. Adsorption capacity of HIIP was 53% higher than HNIP, and dual-site Langmuir–Freundlich isotherm model showed the best fit for data of both polymers. The preconcentration system coupled to TS-FF-AAS was performed by loading 10.0 mL of Cd2 + solution at pH 7.5 through 80.0 mg of HIIP packed into a micro-column with posterior online elution using 1.0 mol L− 1 HCl/ethanol 1:1 (v/v) mixture. The developed method was highly tolerant for other metal ions Zn2 +, Pb2 +, Cu2 +, Co2 +, Fe2 +, and Hg2 + at analyte:interferent (1:50, m/m) ratio and Ca2 + and Mg2 + at 1:500 (m/m) ratio. Analytical curve ranging from 0.5 to 7.0 μg L− 1, limit of detection of 30 ng L− 1 and preconcentration factor of 14-fold were obtained. Intra-day and inter-day (3 days) experiment precision (n = 10) was, respectively, 3.9 and 0.6% (relative standard deviation, RSD), and 4.4 and 2.4% for concentrations of 0.7 and 6.5 μg L− 1. Sensitivity of method (Abs L μg− 1) was about 3.3, 2.2 and 1.9-fold higher when compared to preconcentration method using HNIP, OIIP and IIIP, respectively, thus clearly showing that hybrid polymer and imprinting process enhance Cd2 + adsorption. Addition and recovery experiments ranging from 94 to 106% in mineral, lake water and tap water, urine and cigarette samples attested the feasibility of method for analysis of matrices containing different components. Moreover, the accuracy of method was checked from analysis of certified reference material (DOLT-4, fish liver), being the obtained value of 23.9 ± 0.6 mg kg− 1 (n = 3) statistically equal to the certified value of 24.3 ± 0.8 mg kg− 1, by applying Student t-test at 95% confidence level.

In the present study, a new ion-selective imprinted polymer based on poly(methacrylic acid) loaded with 1-(2-pyridylazo)-2-naphthol (PAN) (IIP/PAN) has been synthesized, characterized and evaluated as a solid adsorbent for the preconcentration of Pb2+ with on-line determination by Flame Atomic Absorption Spectrometry (FAAS). For comparative study, a blank polymer (NIP) and IIP (imprinted polymer) without PAN were synthesized. The polymers were characterized by FT-IR and textural data through nitrogen adsorption/desorption measurements. Selectivity studies were performed by comparing the competitive adsorption of Pb2+ with Cu2+, Cd2+, Ni2+, Co2+ and Zn2+ on IIPs and NIP, yielding relative selectivity coefficients (k′) higher for IIP/PAN than for IIP and NIP, which confirms the effect of PAN on the improvement of selective performance of IIP. Adsorption kinetic studies showed that the equilibrium adsorption of Pb2+ was reached at 100 min for the three polymers and its data were well described by pseudo-second-order and Elovich models. The maximum adsorption capacities (MAC) were found to be 41.4 mg g−1 for IIP/PAN, 34.2 mg g−1 for IIP and 30.1 mg g−1 for NIP. The proposed on-line preconcentration method was based on loading 20.0 mL of Pb(II) solution (pH 5.70 buffered with 0.048 mol L−1 acetate buffer) through 30 mg of IIP/PAN packed into a minicolumn at 4.0 mL min−1 flow rate with further elution using 1.0 mol L−1 HCl solution. The limits of detection (LOD) and quantification (LOQ) were found to be 0.52 and 1.79 μg L−1, respectively, and linearity was from 1.75 to 200.0 μg L−1 (r = 0.989). The precision of the method assessed in terms of repeatability was found to be 4.1 and 1.9% for 10.0 and 150.0 μg L−1 Pb(II) solutions, respectively. The developed method was successfully applied to different kinds of samples (water, synthetic seawater, serum physiological solution, chocolate powder and Gingko biloba) and its accuracy was assessed by means of recovery tests and analysis of a certified reference material (MESS-3, marine sediment).

In the present study, new sorbents for solid-phase extraction (SPE) based on poly(methacrylic acid-trimethylolpropane trimethacrylate) (PMA-TRIM) and poly(vinylimidazole-TRIM) (PV-TRIM) for simultaneous extraction of tebuthiuron (TBT), hexazinone (HEX), diuron (DIU) and ametryn (AME) and posterior determination by HPLC-DAD were developed. The method was based on the preconcentration of 50.0 mL of water at pH 6.0 through 200 mg of each sorbent packed into a cartridge with further elution by 3.0 mL of methanol. The analytical curves were linear for the herbicides in the range 1.0–150.0 μg L−1 with limits of detection (LOD) of 0.40, 0.31, 0.12, 0.34 μg L−1 for TBT, HEX, DIU and AME, respectively, when using PMA-TRIM as the sorbent and 0.14, 0.44, 0.17 and 0.39 μg L−1, respectively, when using PV-TRIM. The precision in terms of repeatability assessed as RSD (relative standard deviation, n = 10) for the multiresidue analysis ranged from 1.23% to 1.91% and 0.97% to 1.79% for respective concentrations of 10.0 and 100 μg L−1 using the PV-TRIM polymer and 2.13% to 3.31% and 1.43% to 2.91% using PMA-TRIM. As observed, better analytical performance was achieved using PV-TRIM as the sorbent. The obtained analytical performance from the polymers, mainly PV-TRIM in terms of LOD and preconcentration factor (PF) was much higher compared to commercial sorbents octadecyl-C18-silica (C18) and Amberlite® XAD4 poly(styrene-divinylbenzene) (DVB). Moreover, exceptional reusability was achieved (>161 recycles) without loss of adsorption capacity. To assess the accuracy of the preconcentration method, analyses of surface waters (well and river water), collected from an area near the cultivation of sugar cane, were carried out. From the recovery test ranging from 96% to 101%, it was concluded that the solid-phase extraction prior to HPLC-DAD analysis is appropriate and it is an alternative for multiresidue analysis in natural water.

The development of a novel molecularly imprinted solid-phase extraction (MISPE) method for simultaneous preconcentration of imazapyr (IMP), imazapic (IMZ) and imazethapyr (IMT) with determination by HPLC-PAD (High performance liquid chromatography – photodiode-array detector) is proposed. The polymer synthesis was performed using imazethapyr as template molecule and 1-vinylimidazole as functional monomer. The method is based on preconcentration of 100.0 mL of sample through 200.0 mg of molecularly imprinted poly(vinylimidazole-TRIM) (MIP-1VN) at pH 4.0, followed by elution with 2.0 mL of MeOH:CH2Cl2:HAc (34:62:4, v/v). The range of analytical curve (0.29–200.0, 0.21–200.0 and 0.15–200.0 µg L−1), limits of detection (0.09, 0.06 and 0.04 µg L−1) and preconcentration factors (92, 96 and 98) determined for the herbicides, IMP, IMZ and IMT, respectively, were greatly superior when compared with those ones obtained with commercial adsorbents. The analytical method was successfully applied to spiked surface water and rice samples with good results of recovery values (86–107%).

This paper reports the synthesis of novel nanocomposite based on multi-walled carbon nanotubes (MWCNT) covalently bonded by molecularly imprinted poly(methacrylic acid-hemin) (MIP-MWCNT) using tert-butylhydroquinone (TBHQ) as template molecule and its use in the construction of electrochemical sensor. Chemical, physical and morphological structure of nanocomposite was characterized by FT-IR, TGA, SEM, TEM and textural analysis. The electrochemical sensor highly selective to TBHQ was prepared by drop-casting a suspension of nanocomposite on the surface of a glassy carbon electrode. From cyclic voltammetry, it was observed that the electrochemical sensor modified with MIP-MWCNT exhibited great recognition performance, higher analytical response and catalytic properties towards the TBHQ when compared to NIP-MWCNT (nanocomposite polymerized without adding TBHQ), MIP-MWCNT without hemin and MIP-hemin without MWCNT. Such results demonstrated the synergic effect of imprinting influence, MWCNT and hemin in improving the performance of electrochemical sensor. From chronoamperometric measures, the electrochemical sensor modified with MIP-MWCNT could recognize TBHQ selectively in the presence of electroactives and structurally similar compounds. Under optimized conditions by pulse differential voltammetry (pulse amplitude of 100 mV, pulse time of 25 ms and scan rate of 10 mV s−1) and measures in 0.15 mol L−1 H2SO4, the proposed method successfully enabled the simultaneous determination of TBHQ and butylated hydroxyanisole (BHA), yielding limits of detection of 0.85 and 0.50 μmol L−1, respectively. The feasibility of the method was checked by simultaneous determination of TBHQ and BHA in soybean oil, margarine, mayonnaise and biodiesel, whose results were statistically equal to those achieved by high performance liquid chromatography (HPLC).

This study deals with the preparation of ceramic materials based on silicon oxycarbide (SiOC), by pyrolysis of polymeric precursors consisting of poly(methylsiloxane) (PMS) and divinylbenzene (DVB), with or without activated charcoal (AC) as additional carbon source. The precursors were obtained by hydrosilylation reaction catalyzed by Pt(0)-complex at 80:20 and 20:80 (PMS:DVB) molar ratios, containing or not 3 wt.% AC. SiOC-based materials were obtained by pyrolysis at 1000 and 1500 °C, under argon atmosphere, and characterized by FT-IR, Raman, 29Si MAS NMR, XRD, elemental analysis, SEM and HRTEM techniques. The presence of AC in PMS-rich ceramic produced carbon long nanowires, and possibly SiC nanowires. The increase of the temperature induced the phase segregation, with the predominance of SiO2 and/or SiC phases, besides having influence on the crystallization of β-SiC and organization of segregated carbon phase (Cfree), with the formation of multiwall carbon nanotubes (MWCNT). The ceramics containing AC were tested as a new electrochemical sensing platform for the detection of acetaminophen by cyclic voltammetry. Higher peak current and lower over potential for acetaminophen, as compared with glassy carbon electrode, were observed by using the ceramic obtained at 1500 °C containing MWCNT as electrodic material, which clearly indicates the great electrocatalytic effect of material.

This study describes the simultaneous formation of graphitic carbon nanostructures in combination with nanowires and crystallites based on silicon carbide (SiC) on porous Co-modified silicon oxycarbide (SiCO) ceramics derived from polymeric precursors. Polyethylene (PE)-containing polymers with and without cobalt acetate, Co(Ac)2, were prepared by hydrosylilation reaction between 2,4,6,8-tetramethylcyclotetrasiloxane and divinylbenzene followed by pyrolysis at 1000 and 1500 °C to obtain the corresponding porous ceramic materials. The presence of Co(Ac)2 promoted the formation of conducting and semiconducting phases of graphitic carbon and SiC and this tendency was intensified by the simultaneous presence of PE and Co(Ac)2 at 1500 °C. The production of SiC nanowires seems to be originated from their crystallites initially formed into matrix. However, their pronounced development was dependent on reductive atmosphere mainly generated by PE degradation. The presented approach and selected starting materials showed to be desirable to obtain SiCO-based ceramics with potential for new electrical applications.

In the present study a hybrid molecularly imprinted poly(methacrylic acid-trimethylolpropane trimethacrylate)-silica (MIP) was synthesized and modified with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) with posterior opening of epoxy ring to provide hydrophilic properties of material in the extraction of folic acid from aqueous medium. The chemical and structural aggregates of hybrid material were characterized by means of Fourier Transform Infrared (FT-IR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Thermogravimetric analysis (TGA) and textural data. Selectivity data of MIP were compared to non-imprinted polymer (NIP) through competitive sorption studies in the presence of caffeine, paracetamol or 4-aminobenzamide yielding relative selectivity coefficients (k′) higher than one unit, thus confirming the selective character of MIP even in the presence of structurally smaller compounds than the folic acid. The lower hydrophobic sorption by bovine serum albumin (BSA) in the MIP as compared to unmodified MIP proves the hydrophilicity of polymer surface by using GPTMS with opening ring. Under acid medium(pH 1.5) the sorption of folic acid onto MIP from batch experiments was higher than the one achieved for NIP. Equilibrium sorption of folic acid was reached at 120 min for MIP, NIP and MIP without GPTMS and kinetic sorption data were well described by pseudo-second-order, Elovich and intraparticle diffusion models. Thus, these results indicate the existence of different binding energy sites in the polymers and a complex mechanism consisting of both surface sorption and intraparticle transport of folic acid within the pores of polymers.

A new hybrid molecularly imprinted polymer (MIP) combined with restricted access (RAM) has been synthesized based on random free-radical polymerization and a sol–gel process. From competitive adsorption studies by using the RAM-MIP and RAM-NIP with folic acid and structurally similar molecules (caffeine, 4-aminobenzamide or paracetamol), relative selectivity coefficients (k) higher than one unit were achieved, indicating good recognition selectivity for folic acid. The percentage of BSA protein exclusion was higher for the RAM-MIP (55.3 ± 2.0) as compared to the MIP (35.9 ± 2.5%). The solid phase extraction (SPE) procedure was performed by loading the acid extract from milk powder samples previously submitted to saponification and acidification with 10% trichloroacetic acid (TCA) until pH 1.5, through 100 mg of RAM-MIP packed into SPE cartridge. The elution step was carried out by using a mixture of acetonitrile : 0.266 mol L−1 acetate buffer at pH 5.7 (15 : 85, v/v), the same composition of the mobile phase of HPLC. The intra-day precision (n = 10) of the procedure assessed as relative standard deviation (RSD) was 4.7 and 4.1% for the respective concentrations of 20.0 and 150.0 μg L−1. The applicability of the method was attested by analysis of different brands of milk powder samples fortified with folic acid, as well as by high recovery percentages 95.0–108.4% obtained upon addition and recovery tests. The cleanup process accomplished by RAM-MIP was so efficient that very few remaining matrix components were detected in the eluate by high performance liquid chromatography.

In the present work, commercial nano-carbon black (CB) particles were functionalized with 3-mercaptopropyltrimethoxysilane (3-MPTMS) through a silanization reaction to improve their adsorption capacity towards Pb(II) ions and hence extend their application as an alternative and low-cost nanocarbonaceous material in the field of separation science. The material was characterized by FT-IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, as well as by thermogravimetric analysis and textural data. After the characterization of the material (3-MPTMS/CB) a FIA-FAAS preconcentration method for Pb(II) ions was developed, which in turn was performed by loading 20.0 mL of a 200 μg L−1 Pb(II) solution at pH 4.76 (buffered with 0.0358 mol L−1 acetate buffer) through 100 mg of 3-MPTMS/CB packed into a mini-column at a flow rate of 4.0 mL min−1. The optimized conditions of the proposed method have been achieved through a 25-1 fractional factorial and Doehlert matrix design. The improvements in the adsorption capacity of CB towards Pb(II) after chemical modification with 3-MPTMS were noticed by comparing the sensitivity of the analytical curve built with CB and 3-MPTMS/CB. Very satisfactory figures of merit including a limit of detection (LOD) of 1.33 μg L−1, limit of quantification (LOQ) of 4.45 μg L−1, preconcentration factor of 28.0, consumptive index of 0.714 mL, preconcentration efficiency of 5.6 min−1 and sample throughput of 12 h−1 were obtained. The precision of the method was assessed as relative standard deviation (RSD) (%) for 10 measures of 10.0 and 160.0 μg L−1 Pb(II) solutions yielding values of 3.0 and 2.3%, respectively. The preconcentration method was successfully applied to the Pb(II) ion determination in different kinds of water and Ginkgo biloba samples with satisfactory recovery values (91–108%). In addition, the accuracy of the proposed method was also checked by analysis of a certified marine sediment reference material (MESS-3).

The present paper describes the development of a new electroanalytical method for prostate cancer biomarker (sarcosine) by coupling molecularly imprinted solid-phase extraction (MISPE) with electrochemical determination at a MWCNT/Nafion®/Ni(OH)2-modified screen-printed electrode using a flow injection analysis (FIA) system. The synthesized MIP prepared by using dual functional monomers 2-acrylamido-2-methyl-1-propanesulfonic acid and 4-vinylpyridine was characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and nitrogen adsorption/desorption measurements. The optimized pH for adsorption of sarcosine was 5.0 and the elution was completed with MeOH:HAc (90:10, v/v), whilst the electrochemical determination was performed in FIA system using a sample volume of 121.0 μL, 0.05 mol L−1 NaOH carrier solution, a flow rate of 2.0 mL min−1 and applied potential of 0.7 V vs Ag/AgCl. The proposed method provided enrichment factor of 50.6-fold, linear analytical curve from 3.2 to 25.0 μmol L−1 (R2 = 0.995), and limit of detection of 0.96 μmol L−1. The precision was evaluated in terms of intra (n = 6) and interday (n = 2) for concentrations of 10.0, 15.0, and 20.0 μmol L−1, giving rise to low percentages of relative standard deviations (RSD %), ranging from 2.2 to 4.3%. A highly improved response for sarcosine using MIP when compared to NIP (non-imprinted polymer) was obtained. The method also exhibited higher selectivity toward sarcosine compared to glycine, alanine, proline, and urea. Analysis of synthetic urine samples yielded recoveries in the range of 95.0–108.0%, thereby indicating the absence of matrix effect and the feasibility of the method for sarcosine determination.

This study describes the influence of carbon black (Cblack) on structural evolution and porosity of silicon oxycarbide (SiOC)-based ceramics obtained from pyrolysis of silicone-derived polymeric precursors. Initially, polymeric precursors were synthesized by hydrosilylation reaction between poly(methylhydrosiloxane) (PHMS) and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (D4Vi), with different Cblack contents (0, 1, 3, 5 and 10 wt%), followed by pyrolysis under argon at 1000 and 1500 °C, to give rise to the respective SiOC/Cblack ceramic composites. FTIR-ATR, TG, XRD, N2 gas physisorption at 77 K were used to characterize the carbonaceous phase, preceramic polymers and resulting ceramics. Cblack incorporation, together with the pyrolysis temperature, generated more porous ceramic materials and intensified the semiconducting SiC phase formation, maintaining the presence of conducting Cgraphitic structures embedded into SiOC matrices. Results concerning structural and textural features were associated to the different distributions of Cblack into polymeric precursors. Moreover, the availability of residual carbon to react with degradation products during pyrolysis and produce SiC and Cgraphitic crystalline phases was reported. Cblack immobilization into preceramic Si-containing polymers plays an important role to produce SiOC/Cblack ceramic composites with predominance of electroactive phases. The presence of Cblack also contributed to higher porosities on resulting composites, which are suitable features for electrochemical investigations in polymer-derived ceramic matrices.

The present paper describes a new restricted access material-ion imprinted polymer for on-line preconcentration of Cd2+ from natural water samples, and simultaneous clean-up of humic acid. Cadmium-imprinted poly(allylthiourea) was synthesized and modified with 2-hydroxyethyl methacrylate (IIP-HEMA) to obtain the restricted access ability. The on-line flow injection system coupled to FAAS (FIA-FAAS) was based on percolation of 20.0 mL of the sample (pH 8.70 and in presence of organic matter) through a mini-column (100.0 mg of IIP-HEMA) at 7.5 mL min−1 flow rate. The elution step was performed using 2.0 mol L−1 HNO3 at 5.0 mL min−1 flow rate. The method provided linearity in the range 0.56–50.00 μg L−1 and limit of detection of 0.17 μg L−1. The preconcentration factor was found to be 37-fold, consumption index of 0.54 mL, preconcentration efficiency of 13.10 min−1 and sample throughput of 21 h−1. The precision of the method was evaluated in terms of intra-day and inter-day repeatability and the relative standard deviation percentage (%RSD) obtained by two-level concentration (2.50 and 40.00 μg L−1) in the presence and absence of humic acid were

A SiO2/Al2O3/Sb2O5 mixed oxide was synthesized via a sol-gel method and applied to the on-line preconcentration of Ni(II) with determination by flame atomic absorption spectrometry. The mixed oxide was characterized by infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray fluorescence, thermogravimetric analysis, and the specific surface area. Analysis was performed by percolating 20.0 mL of sample at pH 7.1 through 100 mg of SiO2/Al2O3/Sb2O5 packed into a mini-column at 9.5 mL min−1. Under the optimum conditions, a preconcentration factor of 77.5-fold, linear dynamic range from 5.0 to 270.0 µg L−1, and limits of detection and quantification of 0.48 and 1.61 µg L−1 were obtained. The effects of several concomitant ions were evaluated and no interferences were observed. The method was employed for the analysis of water with good recoveries (92.9–100.6%) and the accuracy was verified by using a marine sediment certified reference material (MESS-3).

In the present study a new cross-linked copolymer poly(methacrylic acid–trimethylolpropane trimethacrylate) (named PMA) and poly(vinylimidazole–trimethylolpropane trimethacrylate) (named PVI) was synthesized through precipitation polymerization and applied to the adsorption of tebuthiuron. Adsorbent materials were characterized by using FT-IR, SEM, TGA, textural data, and elemental analysis. Kinetic study showed that the tebuthiuron adsorption was very quick and the equilibrium time was achieved at 20 min for both polymers. Experimental kinetic data for both polymers were very well described by the second-order kinetic model, thus indicating that tebuthiuron adsorption involves chemical adsorption in different binding sites, which could control the reaction rate. Adsorption equilibrium data were better fitted to the dual-site Langmuir–Freundlich model, which recognizes the existence of two kinds of adsorption sites on the polymer surface ascribed to the presence of carboxyl and carbonyl groups from PMA and imidazole ring and carbonyl group from PVI. The maximum adsorption capacities of PMA and PVI were found to be 186.76 and 213.89 mg g− 1, respectively, which are much higher than other adsorbents.

A new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) prepared via a double-imprinting process was developed for the recognition and preconcentration of Pb(2+) from water samples. The sorbent was characterized by FT-IR, SEM, TGA and textural data. The maximum dynamic sorption capacity of Pb(2+) was 42.04 mg Pb(2+) g(-1) of the double-imprinted polymer. The sorption kinetics data were described by a pseudo-second-order model. The double-imprinted polymer exhibited a higher sorption efficiency of Pb(2+) than the blank polymer (non-imprinted polymer). The preconcentration procedure involved the loading of a Pb(2+) solution at pH 7.25 through 40.0 mg of the double-imprinted polymer packed in a mini-column at 5.0 mL min(-1). The selective efficiency of proposed method for the Pb(2+) preconcentration was assured by competitive sorption using different proportions of Pb(2+)/cations and Pb(2+)/anions. An analytical curve was obtained in the range 0.0-300.0 μg L(-1) (r=0.999) and a limit of detection of 2.46 μg L(-1) was obtained. The preconcentration factor was found to be 21, the consumptive index 0.95 mL and the concentration efficiency 5.25 min(-1). The preconcentration method was successfully applied to the Pb(2+) ions determination in different kinds of water samples with high recovery values (91.3-108.9%).

An on-line preconcentration system was coupled to flame atomic absorption spectrometry (FAAS) for the determination of copper(II) in water using poly(acrylamide-co-ethylene glycol dimethacrylate) synthesized via a hierarchical double-imprinting process. The on-line preconcentration procedure was based on loading the sample into a minicolumn packed with the synthesized material, followed by elution with 1.8 mol L−1 HNO3. To achieve the highest performance, the method was optimized by 25-1 fractional and 22 full factorial designs. Under the optimum conditions, the following analytical parameters were obtained: detection limit of 0.48 µ gL−1, quantification limit of 1.61 µgL−1, preconcentration factor of 31.0, consumption index of 0.58 mL, preconcentration efficiency of 8.63 min−1, and sample throughput of 15 h−1. The precision of the method was evaluated as the relative standard deviation (n=10) of 10.0 and 150.0 µgL−1 copper(II), yielding values of 3.27% and 1.97%, respectively. The analytical efficacy of ...

A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate) using a double-imprinting approach for the Cu2+ selective separation from aqueous medium was prepared. In the imprinting process, both Cu2+ ions and surfactant micelles (cetyltrimethylammonium bromide – CTAB) were employed as templates. The hierarchically imprinted organic polymer named (IIP-CTAB), single-imprinted (IIP-no CTAB) and non-imprinted (NIP-CTAB and NIP-no CTAB) polymers were characterized by SEM, FTIR, TG, elemental analysis and textural data from BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda). Compared to these materials, IIP-CTAB showed higher selectivity, specific surface area and adsorption capacity toward Cu2+ ions. Good selectivity for Cu2+ was obtained for the Cu2+/Cd2+, Cu2+/Zn2+ and Cu2+/Co2+ systems when IIP-CTAB was compared to the single-imprinted (IIP-no CTAB) and non double-imprinted polymer (NIP-CTAB), thereby confirming the improvement in the polymer selectivity due to double-imprinting effect. For adsorption kinetic data, the best fit was provided with the pseudo-second-order model for the four materials, thereby indicating the chemical nature of the Cu2+ adsorption process. Cu2+ adsorption under equilibrium was found to follow dual-site Langmuir–Freundlich model isotherm, thus suggesting the existence of adsorption sites with low and high binding energy on the adsorbent surface. From column experiments 600 adsorption–desorption cycles using 1.8 mol L−1 HNO3 as eluent confirmed the great recoverability of adsorbent. The synthesis approach here investigated has been found to be very attractive for the designing of organic ion imprinted polymer and can be expanded to the other polymers to improve performance of ion imprinted polymers in the field of solid phase extraction.

The present paper describes the feasibility of on-line preconcentration of nickel ions from aqueous medium on Ni(II)-imprinted cross-linked poly(methacrylic acid) (IIP) synthesised through a double-imprinting method and their subsequent determination by FAAS. The proposed method consisted in loading the sample (20.0 mL, pH 7.25) through a mini-column packed with 50 mg of the IIP for 2 min. The elution step was performed with 1.0 mol L−1 HNO3 at a flow rate of 7.0 mL min−1. The following parameters were obtained: quantification limit (QL) – 3.74 µg L−1, preconcentration factor (PF) – 36, consumption index (CI) – 0.55 mL, concentration efficiency (CE) – 18 min−1, and sample throughput – 25 h−1. The precision of the procedure assessed in terms of repeatability for ten determinations was 5.6% and 2.5% for respective concentrations of 5.0 and 110.0 µg L−1. Moreover, the analytical curve was obtained in the range of 5.0–180.0 µg L−1 (r = 0.9973), and a 1.64-fold increase in the method sensitivity was observed w...

A new Nb 2 O 5 /ZnO mixed oxide dispersed in a silica matrix (i.e., SiO 2 /Nb 2 O 5 /ZnO) was synthesized via sol–gel method and used as an adsorbent of cobalt ions (Co 2+ ). The material presented a high surface area (323 m 2 g −1 ) and the maximum adsorption capacity was found to be 0.518 mg g −1 , determined from the non-linear Langmuir–Freundlich isotherm model. The material was used as a chelating agent free-solid phase extractor (CAF-SPE) in an on-line preconcentration procedure, based on the adsorption of Co 2+ ions (16.0 mL, pH 7.4) at a high flow rate (8.0 mL min −1 ) onto a mini-column packed with the adsorbent (200 mg). The analyte was then eluted with 1.0 mol L −1 HCl and transported toward the FAAS detector. Linear calibration range was obtained from 0.96 up to 150.0 μg L −1 , with a limit of detection of 0.28 μg L −1 . The precision of method, estimated as relative standard deviation of ten replicate measurements of 30 and 150 μg L −1 analyte solutions, was found to be 4.6% and 3.1%, respectively. The reliability of method was verified through the analysis of water and food samples and the accuracy was confirmed by using a certified reference material.

The main purpose of this research was to synthesize crosslinked poly(4-vinylpyridine-ethylene glycol dimethacrylate) and evaluate its feasibility for highly sensitive and selective determination of Cd in water samples by using flow injection flame atomic absorption spectrometry. The crosslinked polymer, prepared by bulk polymerization, was characterized by FTIR spectrometry and scanning electron microscopy. The flow injection solid-phase method was based on preconcentration of 20.0 mL of sample through 100 mg of the polymer packed into a minicolumn at pH 8.25 using a flow rate of 6.0 mL/min, followed by elution with 1.0 M HNO3. The sample solution parameters influencing the preconcentration behavior of Cd ions, such as pH, buffer concentration, and flow rate, were simultaneously studied and optimized using a Doehlert matrix. Values of 0.10 μg/L, 2.0–210 μg/L, 32.3, 18/h, 9.7/min, and 0.62 mL were obtained for LOD, linear range, preconcentration factor, sample throughput, concentration efficiency, and consumption index, respectively. The effect of the presence of the inorganic cations Pb(II), U(IV), Co(II), Hg(II), Cu(II), As(III), Mg(II), Sb(III), Ni(II), Th(IV), Ba(II), and Ca(II) on the method was studied, and the preconcentration of Cd was observed to have no interference. The accuracy of the method was assessed by analysis of natural water samples using addition and recovery tests and inductively coupled plasma/MS as a reference technique, as well as by analysis of a standard reference material of trace elements in water.

In this paper, we describe the synthesis of an ion imprinted polymer (IIP) by homogeneous polymerization and its use in solid-phase to extract and preconcentrate zinc ions. Under optimal conditions (pH 5.0, preconcentration flow rate of 12.0 mL min-1, and eluted with 1.0 mol L-1 HNO3) this procedure allows the determination of zinc with an enrichment factor of 10.2, and with limits of detection and quantification of 1.5 and 5.0 µg L-1, respectively. The accuracy of our results was confirmed by analysis of tap water and certified reference materials: NIST 1570a (Spinach leaves) and NIST 1515 (Apple leaves).

The main purpose of the present work is to synthesize and characterize a new sorbent material, which contains manganese oxide particles finely dispersed in a silica matrix, and evaluate its ability to improve the detectability of flame atomic absorption spectrometry (FAAS) for on-line determination of trace Cd(II) in aqueous and biological samples. The surface area, pore volume and micropore size of the sorbent were found to be 232 m2 g− 1, 0.0303 cm3 g− 1 and 1.7 nm, respectively. To accomplish the on-line sorbent preconcentration, 20.0 mL of a pH 9.0 Cd(II) solution at a flow rate of 10.0 mL min− 1 were preconcentrated onto 320 mg of the SiO2/MnOx material packed into a mini-column and then eluted with 1.0 mol L− 1 HNO3 toward the FAAS detector. The following analytical features were obtained: linear responses to Cd(II) ions in the range of 1.0–50.0 μg L− 1 (r = 0.9968), detection limit of 0.20 μg L− 1, preconcentration factor of 39.4, concentration efficiency of 19.7 min− 1, consumptive index of 0.51 mL, and analytical frequency of 20 h− 1. The dispersion of manganese oxide in the SiO2 matrix promoted a 2.15-fold improvement on detectability of Cd(II) ions in comparison with an analytical curve built with SiO2 as sorbent. The accuracy of the preconcentration method was verified through the analysis of natural water samples employing addition/recovery tests and GF AAS as reference technique, and analysis of certified reference materials — Lobster Hepatopancreas (TORT-2) and NIST SRM 1643e (“Trace elements in natural waters”).

A novel poly(methacrylic acid) material (IIP/CTAB) was prepared by a hierarchical double-imprinting process with Ni2+ ion and cationic surfactant—cetyltrimethylammonium bromide (CTAB) as templates, and it was employed to adsorb Ni2+ ions from aqueous medium. Other poly(methacrylic acid) materials— single-imprinted (IIP/no CTAB) and nonimprinted (NIP/no CTAB) were investigated in adsorption studies. All the synthesized polymers were characterized by FTIR, SEM, and nitrogen adsorption–desorption isotherm. The maximum Ni2+ adsorption capacities of IIP/CTAB and NIP/no CTAB were found to be 33.31 and 18.64 mg g–1, respectively, at pH 7.25. The relative selectivity coefficient (k′) values for Ni2+/Cu2+, Ni2+/Mn+, Ni2+/Co2+ and Ni2+/Pb2+ systems were higher than 1, thus confirming the significant improvement in the selectivity of the polymer. The kinetic data were described very well by the pseudo-second-order model, thereby confirming the chemical nature of the Ni2+ adsorption (chemisorption), whereas the dual-...

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol–gel process was evaluated as novel adsorbent for solid-phase extraction of Cd 2+ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted ( R 2 = 0.9982) to hybrid non-linear Langmuir–Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g −1 . The adsorption kinetics data also corroborated to the isotherm, where the Cd 2+ ions adsorption followed the pseudo-second-order kinetic ( R 2 = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min −1 flow rate. The on-line desorption of Cd 2+ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min −1 flow rate using 0.8 mol L −1 HNO 3 . Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g −1 . Analytical curve ranged from 0.0 up to 50.0 μg L −1 ( r = 0.997), limit of detection of 0.27 μg L −1 , preconcentration factor of 38.4, sample throughput of 30 h −1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd 2+ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.

The main goal of the present work was to evaluate the effect of protoporphyrin (PP) (as pendant group) incorporated into a poly(vinylpyridine) [poly(VPY)] polymer network on the sorption of Mn 2+ ions from an aqueous medium. The sorbent materials – poly(PP- co -VPY) and poly(VPY) – were characterized by SEM, FTIR, elemental analysis and nitrogen adsorption–desorption measurements (BET – Barrett–Joyner–Halenda and BJH – Brunauer–Emmett–Teller). It was observed that the pseudo-second-order kinetic model fitted the experimental data very well ( R 2 = 0.9967), confirming that the Mn 2+ sorption onto poly(PP- co -VPY) took place via chemical reactions (chemisorption). To describe the equilibrium between the Mn 2+ ions and sorbents and estimate the maximum sorption capacity, different models, including Langmuir, Freundlich, Dubinin–Radushkevich and dual-site non-linear Langmuir–Freundlich equations, were applied to the experimental data. The dual-site Langmuir–Freundlich model provided the best fit for poly(PP- co -VPY) and poly(VPY), yielding the maximum sorption capacity of 5.0 and 1.79 mg g −1 , respectively. These findings suggest the presence of homogeneous and heterogeneous binding sites able to sorb Mn 2+ ions. Binary solutions of Mn 2+ /Zn 2+ , Mn 2+ /Pb 2+ and Mn 2+ /Fe 3+ were submitted to competitive sorption in the polymers. The results obtained for these systems demonstrated 4.75, 18.24 and 388-fold increases in the rate of the Mn 2+ sorption onto poly(PP- co -VPY), when compared with poly(VPY). The protoporphyrin incorporation into poly(VPY) network appears to be an interesting approach to polymer synthesis by the homogeneous solution method focused on the preparation of solid-phase extraction columns.

In the present study, a novel synthesized adsorbent material based on 3-mercaptopropyltrimethoxysilane-functionalized multi-walled carbon nanotubes was used to increase the Pb2+ adsorption from aqueous solutions in a flow injection solid-phase extraction system coupled to flame atomic absorption spectrometry. Spectroscopic and microscopic techniques (Fourier transform infrared spectroscopy, energy dispersive spectroscopy, and scanning electron microscopy) were employed to confirm the chemical modification of the adsorbent surface. Preconcentration conditions (sample pH, flow rate, buffer solution, and eluent concentrations) were optimized using factorial and Doehlert matrix designs that made it possible to construct a linear graph in the 5.0- to 130.0-μg L−1 range (r = 0.9999) and estimate detection and quantification limits (1.7 and 5.7 μg L−1, respectively). The method precision was found to be 4.20 and 1.97 % for 5.0 and 100.0 μg L−1 Pb2+ solutions, respectively. When using the 3-mercaptopropyltrimethoxysilane-functionalized multi-walled carbon nanotubes, the sensitivity for the Pb2+ trace determination was improved to 95 % compared with the oxidized multi-walled carbon nanotubes, thus evidencing the significant enhancement of the adsorption capacity. The developed method was successfully applied to the analysis of Pb2+ species in different water samples and the PACS-2 marine sediment-certified reference material.

In this work a solid phase on-line uranium ion preconcentration system coupled with spectrophotometry has been developed. The method is based on uranyl ion preconcentration at pH 3.75 onto multiwall carbon nanotubes treated with HNO3. After preconcentration, the uranyl ions are eluted with 0.32 mol L−1HCl followed by reaction with 3,6-bis[(2-arsonophenyl)-azo]-4,5-dihydroxy-2,7-naphthalendisulfonic acid 0.08%[w/v] (Arsenazo III), which had maximum monitored absorbance of 650 nm. Effects of the pertinent experimental parameters on the system were investigated by means of 26−2 fractional factorial design, while optimization was carried out using the Doehlert matrix. Under optimized conditions, detection and quantification limits were found to be 0.21 and 0.7 µg L−1, respectively. The analytical curve ranged from 5 to 150 µg L−1 (r = 0.998), while the relative standard deviations (RSD) were 3.27 and 2.56% for the respective uranium concentrations of 10 and 100 µg L−1 (n = 10). The features obtained for the o...

The mechanical properties of composites strongly depend on the type of filler-polymeric matrix interface. An interface characterized by a strong bond between the filler and the matrix generally results in better mechanical properties. In this work, polypropylene, PP, was used as polymeric matrix and silica short fibers, SF, which are amorphous biogenic silica, were employed as filler. In order to promote a better filler-matrix interfacial adhesion, these fibers were previously modified with vinyltrimethoxysilane. The composites were prepared by extrusion and injection molding processes and their mechanical properties were evaluated according to tensile testing, ASTM D 268, by means a fractional factorial design (2 5-1 ). The studied factors included fiber content in the matrix, fiber surface modification, injection flow and testing rate. The composite cryogenic fractured surfaces were investigated by field emission scanning electron microscopy, FESEM. The fiber modification promoted a better fiber-matrix interfacial adhesion, resulting in optimized mechanical properties in relation to the others. In this way, the fiber modification was the most important factor on the mechanical performance of the composites.

We describe the analytical performance of a hybrid material composed of SiO2, Al2O3 and TiO2. It was prepared by a sol–gel process and can act as an adsorbent in the continuous-flow enrichment of copper. A minicolumn was packed with the material, copper ions are adsorbed at pH 9.13, then eluted with 1.0 mol L−1 nitric acid, and determined by FAAS. The material was characterized by infrared spectroscopy, scanning electron and energy dispersive spectroscopy, energy dispersive X-ray fluorescence analysis, powder X-ray diffraction, and specific surface area analysis. No significant interference was observed for most ions in up to copper/interferent ratios of 1:100 and of 1:500 in case of Ca(II), Ba(II), and Mg(II). The breakthrough capacity is 1.4 mg g−1 under dynamic conditions. The limits of detection and of quantification are 0.50 and 1.4 μg L−1, respectively, and the calibration plot is linear in the range from 5.0 to 245.0 μg L−1 (r = 0.999). The relative standard deviation is 3.20 (for n = 7 and at a Cu(II) concentration of 10 μg L−1). The method was applied to the determination of trace copper ions in water, vegetable and alcohol fuel samples.

The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N'-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherms. The maximum sorption capacity of 4.59 mg g(-1) was estimated by the Langmuir-Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10 mL min(-1) followed by elution with 1.0 mol L(-1) nitric acid. By using 78 s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20 μg L(-1), preconcentration factor of 26, consumption index of 0.5 mL, concentration efficiency of 20 min(-1), and sample throughput of 39 h(-1). The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0 μg L(-1), respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver).

The present study describes the adsorption characteristic of Cd(II) onto Nb2O5/Al2O3 mixed oxide dispersed on silica matrix. The characterization of the adsorbent has been carried out by infrared spectroscopy (IR), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray fluorescence analysis (EDXRF) and specific surface area (SBET). From batch experiments, adsorption kinetic of Cd(II) was described by a pseudo-second-order kinetic model. The Langmuir linear isotherm fitted to the experimental adsorption isotherm very well, and the maximum adsorption capacity was found to be 17.88 mg g−1. Using the effective material, a method for Cd(II) preconcentration at trace level was developed. The method was based on on-line adsorption of Cd(II) onto SiO2/Al2O3/Nb2O5 at pH 8.64, in which the quantitative desorption occurs with 1.0 mol L−1 hydrochloric acid towards FAAS detector. The experimental parameters related to the system were studied by means of multivariate analysis, using 24 full factorial design and Doehlert matrix. The effect of SO42−, Cu2+, Zn2+ and Ni2+ foreign ions showed no interference at 1:100 analyte:interferent proportion. Under the most favorable experimental conditions, the preconcentration system provided a preconcentration factor of 18.4 times, consumption index of 1.08 mL, sample throughput of 14 h−1, concentration efficiency of 4.35 min−1, linear range from 5.0 up to 35.0 μg L−1 and limits of detection and quantification of 0.19 and 0.65 μg L−1 respectively. The feasibility of the proposed method for Cd(II) determination was assessed by analysis of water samples, cigarette sample and certified reference materials TORT-2 (Lobster hepatopancreas) and DOLT-4 (Dogfish liver).

A solid phase reactor based on molecularly imprinted poly(iron (III) protoporphyrin-methacrylic acid-ethylene glycol dimethacrylate) (MIP–MAA) has been synthesized by bulk method and applied as an selective material for the epinephrine determination in the presence of hydrogen peroxide. In order to prove the selective behaviour of MIP, two blank polymers named non-imprinted polymer (NIP1), non-imprinted polymer in the absence of hemin (NIP2) as well as a poly(iron (III) protoporphyrin-4-vynilpyridine-ethylene glycol dimethacrylate) (MIP–4VPy) were synthesized. The epinephrine-selective MIP–MAA reactor was used in a flow injection system, in which an epinephrine solution (120 μL) at pH 8.0 percolates in the presence of hydrogen peroxide (300 μmol L− 1) through MIP–MAA. The oxidation of epinephrine by hydrogen peroxide is increased by using MIP–MAA, being the product formed monitored by amperometry at 0.0 V vs. Ag/AgCl. The MIP–MAA showed better selective behaviour than NIP1, NIP2 and MIP–4VPy, demonstrating the effectiveness of molecular imprinting effect. Highly improved response was observed for epinephrine in detriment of similar substances (phenol, ascorbic acid, methyl- l -DOPA, p-aminophenol, catechol, l -DOPA and guaiacol). The method provided a calibration curve ranging from 10 to 500 μmol L− 1 and a limit of detection of 5.2 μmol L− 1. Kinetic data indicated a value of maximum rate Vmax (0.993 μA) and apparent Michaelis–Menten constant of Kmapp(725.6 μmol L− 1). The feasibility of biomimetic solid reactor was attested by its successful application for epinephrine determination in pharmaceutical formulation.