Enhanced photocatalytic activity of nano-silica/copper plasmon by aminofunctional silane for dye pollutant degradation.

The synthesis of silica gel nanostructures and loading it with copper specie via a hydrothermal process were performed. The sample is treated with an amino-functional reagent 3-aminopropyl triethoxysilane (APTES). The products were characterized by X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), TGA/DSC measurements, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the nanostructures were studied for degradation of methylene blue dye (as a classic dye contaminant) in aqueous solution utilizing visible light source. The results displayed that the sample treated with APTES is much more effective in photocatalytic degradation of methylene blue. This modified catalyst could eliminate methylene blue dye (50 mL, 18 µg mL-1) within 60 min under visible light. The degradation efficiency was increased by shortening the degradation time to 30 min in the alkaline medium. The pseudo-first-order model well describes the kinetics of the reaction.

Hollow fiber liquid-phase microextraction based on the use of a rotating extraction cell: A green approach for trace determination of rhodamine 6G and methylene blue dyes.

In this work, a novel mode of hollow fiber liquid-phase microextraction (HF-LPME) technique namely rotating extraction cell solvent bar microextraction (REC-SBME) was introduced. The proposed method was applied for the preconcentration of methylene blue (MB) and rhodamine 6G (RG) in some real samples, including soft drink, lipstick, environmental water, and wastewater samples. In the extraction setup, two pieces of hollow fibers were fixed on a mechanical support and immersed in a rotating extraction cell containing the sample solution during the extraction process. The rotation of the extraction cell by using an electric motor led to an enhancement in the mass transfer of the dyes from the sample solution into the organic acceptor phase. In the developed procedure, the UV-Vis spectrophotometry and HPLC-UV/Vis were employed as detection methods for the analysis of the acceptor phase and the obtained results were compared. Optimization of the extraction factors affecting the method, including organic solvent type, sample solution pH, extraction time, rotational rate, the volume of sample and acceptor solutions, salt addition, and temperature was performed in order to obtain the best preconcentration factor. Linear dynamic range obtained by HPLC-UV/Vis and spectrophotometry was observed in the ranges of 2.5-1200 ng mL-1 for RG and 1.6-600 ng mL-1 for MB with R2 more than 0.9971. Also, relative standard deviation (RSD) values (n = 3) less than 3.8% were obtained. The good conformity of the obtained results makes UV-Vis spectrophotometric method an ideal tool for routine analysis of trace dyes in the complex matrices after REC-SBME.

Solvent stir bar microextraction technique with three-hollow fiber configuration for trace determination of nitrite in river water samples.

In this work, trace determination of nitrite in river water samples was studied using solvent stir bar microextraction system with three-hollow fiber configuration (3HF-SSBME) as a preconcentration step prior to UV-Vis spectrophotometry. The obtained results showed that the increase in the number of solvent bars can improve the extraction performance by increasing the contact area between acceptor and sample solutions. The extraction process relies on the well-known oxidation-reduction reaction of nitrite with iodide excess in acidic donor phase to form triiodide, and then its extraction into organic acceptor phase using a cationic surfactant. Various extraction parameters affecting the method were optimized and examined in detail. Detection limit of 1.6 µg L-1 and preconcentration factor of 282 can be attained after an extraction time of 8 min under the optimum conditions of this technique. The proposed method showed a linear response up to 1000 µg L-1 (r2 = 0.996) with relative standard deviation values less than 4.0%. The accuracy of the developed method was assessed using the Griess technique. Finally, the proposed method was successfully employed for quantification of nitrite in river water samples (Ghezelozan, Zanjan, Iran).

A four-hollow fibers geometry of revolving solvent bar microextraction setup for the enrichment of trace ammonia.

In this work, for the first time, a revolving solvent bar microextraction (RSBME) system was introduced as an efficient alternative method to conventional SBME. The setup proposed for RSBME provides a stable and repeatable method to increase the preconcentration factor. In order to provide the maximum extraction capacity of the organic acceptor phase, four-hollow fibers were applied. In this setup, an electrical motor driving rotator was employed as mechanical support for the hollow fibers and also to stir the donor phase during extraction time. The applicability of this technique was assessed by preconcentration-determination of ammonia in the environmental water samples. The effective factors on the RSBME efficiency were examined and optimized. Under the optimized RSBME conditions, ammonia was quantified by microcell UV-Vis spectrophotometry, with extensive linearity ranging from 15 to 1000 µg L-1 (R2 = 0.9972), and RSD values less than 3.5%. A preconcentration of 372-fold with the detection limit of 4.5 µg L-1 was achieved. The green character of this technique was evaluated based on the analytical Eco-Scale tool and compared with a reference method. The setup proposed can be applied for the simultaneous extraction of acidic and basic compounds from biological and environmental samples in the near future.

Trace Determination of Iron in Real Waters and Fruit Juice Samples Using Rapid Method: Optimized Dispersive Liquid-Liquid Microextraction with Synthesized Nontoxic Chelating Agent.

The purpose of this research was to optimize a new method for preconcentration and determination of trace iron concentrations in aqueous solutions. For this purpose, a newly synthesized ligand, 3-(3-hydroxy-2-methyl-4-oxopyridin-1(4H)-yl) benzoic acid (3-OH-3-MOPBA), was used in the dispersive liquid-liquid microextraction (DLLME) method coupled with UV-vis spectroscopy. The experiments considering input variables of extractant volume, disperser volume, salt concentration, and pH were designed with the aid of central composite design (CCD). The results were analyzed using response surface methodology (RSM). The limit of detection (LOD) was found to be 4.0 µg L-1 under the optimized conditions. A calibration curve with a good linearity (R2 = 0.9986) was obtained over the concentration range of 15-800 µg L-1. The relative standard deviations (RSD) were found to be around 2.1% (n = 7). The main advantages of the developed method are simple application, environment friendly, short time, and low cost which makes this method to be applied routinely for measuring iron in various water samples.

Optimization of a methodology for determination of iron concentration in aqueous samples using a newly synthesized chelating agent in dispersive liquid-liquid microextraction.

The aim of this study was to establish a new dispersive liquid-liquid microextraction (DLLME) technique for the determination of iron concentration in aqueous solutions and fruit juices based on the reaction between iron and 3-hydroxy-1-(3-hydroxyphenyl)-2-methylpyridin-4(1H)-one (3-OH-PMPO) as a chelating agent. A central composite design (CCD) was applied to optimize the effects of independent parameters (pH, volume of disperser solvent and extractant solvent and chelating agent concentration) on extraction efficiency. Under the optimized conditions, the analytical curve is linear in a concentration range of 10-750 µgL-1 with a detection limit of 5 µgL-1. The relative standard deviation (RSD) for ten repeated determinations of iron concentrations at 40 and 200 µgL-1 was calculated to be 4.2% and 1.2%, respectively. Relative recovery of iron in several water samples was investigated and the average was obtained in the range of 91-108%.

Selective determination of caffeine in foods with 3D-graphene based ultrasound-assisted magnetic solid phase extraction.

An efficient method was applied for extraction of caffeine in food samples. Three-dimensional graphene-Fe3O4 (3D-G-Fe3O4) nanoparticles was successfully synthesized and used as adsorbent in magnetic solid phase extraction (MSPE) step. The properties of synthesized adsorbent were characterized by fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. The influence of main parameters of extraction procedure such as ultrasound parameter, amount of nanoparticles, pH, salt concentration and desorption condition were investigated and optimized. Under the optimized experimental conditions, the figure of merit results showed excellent linear dynamic range (LDR) of 0.5-500 µg mL-1, with determination coefficient (R2) higher than 0.996 and limit of detection (LOD) of 0.1 µg mL-1. Intra- and inter-day relative standard deviations (RSDs) were less than 5.9 and 7.1%, respectively. The method was successfully applied for determination of caffeine in different food samples.

Ultrasonically assisted removal of Congo Red, Phloxine B and Fast green FCF in ternary mixture using novel nanocomposite following their simultaneous analysis by derivative spectrophotometry.

In this study dependency of simultaneous adsorption of Congo Red (CR), Phloxine B (BP) and Fast green FCF (FG) onto CuS/ZnS nanocomposites loaded on activated carbon (CuS/ZnS-NCs-AC) to pH, adsorbent mass, sonication time and initial dyes concentration were modeled and optimized, while CuS/ZnS-NCs-AC was identified by XRD, FESEM and EDS analysis. CR, PB and FG concentration determination were undertaken by first and second order derivative spectrophotometry in ternary mixture. According to central composite design (CCD) based on desirability function (DF), the best experimental conditions was set as pH 6.0, 0.02g CuS/ZnS-NCs-AC, 5min sonication time, 15mgL-1 for PB and 10mgL-1 for other dyes. Conduction of experiments to above conditions lead to highest dyes removal efficiency of 99.72, 98.8 and 98.17 for CR, PB and FG, respectively. The adsorption data efficiently fitted by Langmuir isotherm model, while the order of maximum adsorption capacity (Qmax) for PB (128.21mgg-1)>CR (88.57mgg-1)>FG (73.40mgg-1) is related to their different structure and charges. Kinetics of process was efficiently explained according to pseudo-second-order kinetic in cooperation of Weber and Morris based on intraparticle diffusion.

The choice of ultrasound assisted extraction coupled with spectrophotometric for rapid determination of gallic acid in water samples: Central composite design for optimization of process variables.

A sensitive procedure namely ultrasound-assisted (UA) coupled dispersive nano solid-phase microextraction spectrophotometry (DNSPME-UV-Vis) was designed for preconcentration and subsequent determination of gallic acid (GA) from water samples, while the detailed of composition and morphology and also purity and structure of this new sorbent was identified by techniques like field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Energy-dispersive X-ray spectroscopy (EDX) techniques. Among conventional parameters viz. pH, amount of sorbent, sonication time and volume of elution solvent based on Response Surface Methodology (RSM) and central composite design according to statistics based contour the best operational conditions was set at pH of 2.0; 1.5mg sorbent, 4.0min sonication and 150µL ethanol. Under these pre-qualified conditions the method has linear response over wide concentration range of 15-6000ngmL-1 with a correlation coefficient of 0.9996. The good figure of merits like acceptable LOD (S/N=3) and LOQ (S/N=10) with numerical value of 2.923 and 9.744ngmL-1, respectively and relative recovery between 95.54 and 100.02% show the applicability and efficiency of this method for real samples analysis with RSDs below 6.0%. Finally the method with good performance were used for monitoring under study analyte in various real samples like tap, river and mineral waters.

A new microplatform based on titanium dioxide nanofibers/graphene oxide nanosheets nanocomposite modified screen printed carbon electrode for electrochemical determination of adenine in the presence of guanine.

The current techniques for determining adenine have several shortcomings such as high cost, high time consumption, tedious pretreatment steps and the requirements for highly skilled personnel often restrict their use in routine analytical practice. This paper describes the development and utilization of a new nanocomposite consisting of titanium dioxide nanofibers (TNFs) and graphene oxide nanosheets (GONs) for screen printed carbon electrode (SPCE) modification. The synthesized GONs and TNFs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The modified electrode (TNFs/GONs/SPCE) was used for electrochemical characterization of adenine. The TNFs/GONs/SPCE exhibited an increase in peak current and the electron transfer kinetics and decrease in the overpotential for the oxidation reaction of adenine. Using differential pulse voltammetry (DPV), the prepared sensor showed good sensitivity for determining adenine in two ranges from 0.1-1 and 1-10 µM, with a detection limit (DL) of 1.71 nM. Electrochemical studies suggested that the TNFs/GONs/SPCE provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of adenine, which was indicated by the improvement of anodic peak current and a decrease in anodic peak potential. The amount of adenine in pBudCE4.1 plasmid was determined via the proposed sensor and the result was in good compatibility with the sequence data of pBudCE4.1 plasmid.

Photocatalytic activity of TiO2 nanoparticles synthesized in presence of ammonium hexafluorosilicate.

A series of silicon incorporated TiO2 with anatase crystalline phase were prepared via sol-gel using ammonium hexafluorosilicate (AHFS). The synthesized products were characterized using X-ray diffraction, FTIR, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectrophotometry (DRS), energy dispersive X-ray analysis (EDX) and BET surface area measurement. Presence of Si-O-Ti bonds is revealed based on the XPS results. The products were tested for their activity as photocatalysts for degradation of congo red as a prob molecule. The 20% AHFS incorporation displayed the highest photocatalytic activity. This adequate amount of AHFS was beneficial for transferring photogenerated electron and reducing the recombination of electron-holes.

Lanthanum and zirconium co-doped ZnO nanocomposites: synthesis, characterization and study of photocatalytic activity.

Nanocomposits of zinc oxide co-doped with lanthanum and zirconium were prepared using the modified sol-gel method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), and BET surface area measurement. For comparison, the La and Zr mono doped ZnO have also been prepared under the same conditions. The XRD results revealed that all the materials showed a hexagonal wurtzite crystal structure. It was found that the particle size of La-Zr-doped ZnO is much smaller as compared to that of pure ZnO. The effect of operational parameters such as, doping concentration, catalyst loading, pH and initial concentration of methylene blue on the extent of degradation was investigated. The photocatalytic activity of the undoped ZnO, mono-doped and La-Zr-ZnO photocatalysts was evaluated by the photocatalytic degradation of methylene blue in aqueous solution. The presence of lanthanium and/or zirconium causes a red shift in the absorption band of ZnO. The results show that the photocatalytic activity of the La-Zr-ZnO photocatalyst is much higher than that of undoped and mono-doped ZnO, resulting from the La and Zr synergistic effect. The co-operation of the lanthanum and zirconium ion leads to the narrowing of the band gap and greatly improves the photocatalytic activity. The photocatalyst co-doped with lanthanum and zirconium 4 mol% shows the best photoactivity and photodecomposition efficiencies were improved by 92% under UV-Vis irradiation at the end of 30 min, compared with the pure and mono doped samples.

Ionic liquid-based dispersive liquid-liquid microextraction for the determination of formaldehyde in wastewaters and detergents.

Spectrophotometry in combination with ionic liquid-based dispersive liquid-liquid microextraction (DLLME) was applied for the extraction and determination of formaldehyde in real samples. The method is based on the reaction of formaldehyde with methyl acetoacetate in the presence of ammonia. The variation in the absorbance of the reaction product was measured at 375 nm. An appropriate mixture of ethanol (disperser solvent) and ionic liquid, 1-hexyl-3-methylimidazoliumhexafluoro-phosphate [C(6)MIM][PF(6)] (extraction solvent) was rapidly injected into a water sample containing formaldehyde. After extraction, sedimented phase was analyzed by spectrophotometry. Under the optimum conditions, the calibration graph was linear in the range of 0.1-20 ng mL(-1) with the detection limit of 0.02 ng mL(-1) and limit of quantification of 0.08 ng mL(-1) for formaldehyde. The relative standard deviation (RSD%, n = 5) for the extraction and determination of 0.8 ng mL(-1) of formaldehyde in the aqueous samples was 2.5%. The results showed that DLLME is a very simple, rapid, sensitive, and efficient analytical method for the determination of trace amounts of formaldehyde in wastewaters and detergents, and suitable results were obtained.

MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac.

This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH)2 nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF6) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 µM, with a detection limit of 0.04 µM. Electrochemical studies suggested that the MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current.

A Fast Response Membrane Sensor based on Ethyl 1, 2, 3, 4-tetrahydro-6-methyl-4-phenyl-2-thioxopyrimidine-5-carboxylate for Detection of Lanthanum (III) Ions at Wide Concentration Range.

A PVC membrane La (III) ion-selective electrode has been constructed using ethyl1,2,3,4-tetrahydro-6-methyl-4-phenyl-2-thioxopyrimidine-5-carboxylate (ETMPTC) as a neutral ionophore. This electrode responds to La (III) ion with a sensitivity of 19.9 ± 0.3 mV/decade over the range 9.3 × 10-8 to 1.0 × 10-1 M at pH 3.0-10.0. The limit of detection was 1.7 × 10-8 M. It has a response time of < 11s and can be used for at least 3 months without any divergence in potentials. The proposed electrode shows fairly good discrimination of La (III) ion from several cations. The effect of organic solvents on electrode response was examined. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. The isothermal temperature coefficient of this electrode amounted to 0.00013 V/ °C. This sensor not only was used as an indicator electrode in potentiometric titration of lanthanum ion against EDTA but also was used to determination of La3+ concentration in the presence of certain interfering ions.