Synthesis and characterization of Black Au nanoparticles deposited over g-C3N4 nanosheets: enhanced photocatalytic degradation of methylene blue.

Black AuNPs, prepared by a facile seeding growth method under ambient conditions, displayed efficient broadband absorption of the incident light over the entire visible and near-infrared regions of the solar spectrum. The spherical black AuNPs with the size of 2-4 nm were deposited over mesoporous g-C3N4 nanosheets. Novel black AuNPs/g-C3N4 plasmonic photocatalysts were used to remove methylene blue (MB) dye from an aqueous solution. The degradation efficiency for the optimal coupling of 1.3 wt.% black AuNPs with g-C3N4 (1.2 g) was found to be 85% within 60 min under visible light irradiation. The calculated kinetic constant was 0.0186 min-1 which was 6.4 and 2.9 times greater than those for g-C3N4 and AuNPs/g-C3N4 nanocomposite, respectively. The excellent potential in photocatalysis was attributed to the synergistic interactions of the g-C3N4 conduction band and the localized surface plasmon resonance effect of black AuNPs. These properties were responsible for the generation of high-energy electrons, a negative shift in the Fermi level of black AuNPs, and the migration of charge carriers. This work studied a new insight into black gold nanoparticles via the design of a visible-light-driven photocatalyst and provided a perspective on valuable photo-related applications such as water treatment.

A new diosgenin sensor based on molecularly imprinted polymer of para aminobenzoic acid selected by computer-aided design.

A novel electropolymerized molecularly imprinted polymer (MIP) film, based on diosgenin on a glassy carbon electrode (GCE), has been synthesized. Based on density functional theory (DFT), para-aminobenzoic acid (pABA), which is a green substance, was selected from five functional monomers by Gaussian software for MIP production, to be the suitable monomer. The MIP's synthesis conditions were optimized, and the imprinting effect was confirmed by comparing the electrochemical reaction of MIP, with that of non-imprinted polymer (NIP). The calibration curve of diosgenin on MIP/GCE was obtained with a linear range of 0.003 to 0.13 mM. The limit of detection (LOD) and limit of quantification (LOQ) were determined to be 8.95 × 10-4 mM and 2.98 × 10-3 mM, respectively. This method exhibited good stability, high sensitivity, and high selectivity for diosgenin. The developed method is the first method reported to be used for the electroanalysis of diosgenin, and it has been successfully applied to the analysis of diosgenin in Trigonella foenum graecum seed extract.

Determination of nickel in water, food, and biological samples by electrothermal atomic absorption spectrometry after preconcentration on modified carbon nanotubes.

A new and sensitive SPE method using modified carbon nanotubes for extraction and preconcentration, and electrothermal atomic absorption spectrometric determination of nickel (Ni) in real samples at ng/L levels was investigated. First, multiwalled carbon nanotubes were oxidized with concentrated HNO3, then modified with 2-(5-bormo-2-pyridylazo)-5-diethylaminophenol reagent. The adsorption was achieved quantitatively on a modified carbon nanotubes column in a pH range of 6.5 to 8.5; the adsorbed Ni(II) ions were then desorbed by passing 5.0 mL of 1 M HNO3. The effects of analytical parameters, including pH of the solution, eluent type and volume, sample volume, flow rate of the eluent, and matrix ions, were investigated for optimization of the presented procedure. The enrichment factor was 180, and the LOD for Ni was 4.9 ng/L. The method was applied to the determination of Ni in water, food, and biological samples, and reproducible results were obtained.

Ultrasound-assisted emulsification microextraction based on solidification floating organic drop trace amounts of manganese prior to graphite furnace atomic absorption spectrometry determination.

In the present study, an ultrasound-assisted emulsification microextraction based on solidification floating organic drop method is described for preconcentration of trace amounts of Mn (II). 2-(5-Bromo-2-pyridylazo)-5 diethylaminophenol was added to a solution of Mn(+2) at ph = 10.0. After this, 1-undecanol was added to the solution as an extraction solvent, and solution was stirred. Several factors influencing the microextraction efficiency, such as pH, the amount of chelating agent, nature and volume of extraction solvent, the volume of sample solution, stirring rate, and extraction time were investigated and optimized. Then sample vial was cooled by inserting into an ice bath, and the solidified was transferred into a suitable vial for immediate melting. Finally the sample was injected into a graphite furnace atomic absorption spectrometry. Under the optimum condition the linear dynamic range was 0.50-10.0 ng mL(-1) with a correlation coefficient of 0.9926, and the detection limit of 0.3 ng mL(-1) was obtained. The enrichment factor was 160. The proposed method was successfully applied for separation and determination of manganese in sea, rain, tap, and river water samples.

Multiwalled carbon nanotube modified with 1-(2-pyridylazo)-2-naphthol for stripping voltammetric determination of Pb(II).

The present work is focused on the modification of multiwalled carbon nanotubes with a ligand, 1-(2-pyridylazo)-2-naphthol (PAN), and its potential application for the development of a new, simple and selective modified glassy carbon electrode for stripping voltammetric determination of Pb(II). The electrochemical method is based on closed circuit accumulation of lead ions onto a PAN-modified multiwalled carbon nanotube electrode from 0.1 mol L(-1) oxalate buffer solution (pH = 3.0) during 150 s at the potential of -0.9 V, following by differential pulse anodic stripping voltammetric determination in the range -0.9 to -0.35 V. The analytical curve for Pb(II) ions covers a linear range varying from 0.8 up to 220.4 microg L(-1). The limit of detection was found to be 0.1 microg L(-1), while the relative standard deviation (RSD) at 50.0 microg L(-1) was 1.8% (n = 5). Many of the coexisting ions had little or no effect on the determination of lead(II). The results suggest that the proposed method can be applied as a simple and efficient alternative technique for the determination of lead ions which has good accuracy in real samples such as natural waters and standard alloys. In addition, this method demonstrates the powerful application of carbon nanotubes in the field of mercury-free electrodes in voltammetric stripping analysis.

Cathodic adsorptive stripping voltammetric determination of trace amounts of uranium (VI) based on its complex with Chromazorul-S.

An adsorptive stripping voltammetric procedure for trace determination of uranium (U; VI) at a hanging mercury drop electrode is described. The complex of U(VI) with Chromazorul-S was adsorbed and accumulated from an ammonia buffer solution of pH 8.8, including 2.4 x 10(-5) M Chromazorul-S at the potential -0.2 V for 120 s. After that, the cathodic voltammograms were recorded by potential sweep from -0.2 to -0.9 V in the differential pulse mode. The relationship between the cathodic peak currents versus U(VI) concentrations was linear over the range of 0.7-340 ng/mL. The detection limit was 0.1 ng/mL, and the relative standard deviations (7 determinations) at 10, 100, and 300 ng/mL U(VI) were 2.1, 1.6, and 1.1%, respectively. The validity of this method was estimated by determination of spiked U(VI) in natural water and soil samples. The results were successful.

Simultaneous determination of nickel and copper by H-point standard addition method-first-order derivative spectrophotometry in plant samples after separation and preconcentration on modified natural clinoptilolite as a new sorbent.

For the simultaneous determination of nickel(ll) and copper(ll) in plant samples, a rapid and accurate method was developed. In this method, solid-phase extraction (SPE) and first-order derivative spectrophotometry (FDS) are combined, and the result is coupled with the H-point standard addition method (HPSAM). Compared with normal spectrophotometry, derivative spectrophotometry offers the advantages of increased selectivity and sensitivity. As there is no need for carrying out any pretreatment of the sample, the spectrophotometry method is easy, but because of a high detection limit, it is not so practical. In order to decrease the detection limit, it is suggested to combine spectrophotometry with a preconcentration method such as SPE. In the present work, after separation and preconcentration of Ni(ll) and Cu(ll) on modified clinoptilolite zeolite that is loaded with 2-[1-(2-hydroxy-5-sulforphenyl)-3-phenyl-5-formaza-no]-benzoic acid monosodium salt (zincon) as a selective chromogenic reagent, FDS-HPSAM, which is a simple and selective spectrophotometric method, has been applied for simultaneous determination of these ions. With optimum conditions, the detection limit in original solutions is 0.7 and 0.5 ng/mL, respectively, for nickel and copper. The linear concentration ranges in the proposed method for nickel and copper ions in original solutions are 1.1 to 3.0 x 10(3) and 0.9 to 2.0 x 10(3) ng/mL, respectively. The recommended procedure is applied to successful determination of Cu(ll) and Ni(ll) in standard and real samples.

Overoxidized polypyrrole doped with 4,5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene disulfonic acid as a selective and regenerable film for the stripping detection of copper(II).

A conducting polymer modified electrode based on the incorporation of 4,5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene disulfonic acid, SPADNS, as an anionic complexing ligand into polypyrrole film during electropolymerization was prepared. The electroanalysis of copper(II) in this modified electrode was achieved by medium exchange and differential pulse voltammetry. Copper ions were accumulated from ammonia buffer on the electrode surface by the formation of a chemical complex at open circuit. The resulting electrode with complexed Cu(2+) was then transferred to an acetate buffer and subjected to anodic stripping voltammetry. The analytical performance was evaluated and, finally, linear calibration graphs were obtained in the concentration range of 2 - 250 ng ml(-1) for Cu(II). The detection limit was found to be 1.1 ng ml(-1) and RSD was obtained at 3.1 and 1.9% for two different concentrations. Many coexisting metal ions had little or no effect on the determination of copper. The developed method was applied to Cu(II) determination in natural water and human hair samples. Also, the rapid and convenient regeneration of electrode allows the use of a single modified electrode in multiple analyses.

Stripping voltammetric determination of silver(I) at carbon paste electrode modified with 3-amino-2-mercapto quinazolin-4(3H)-one.

A differential pulse anodic stripping voltammetric method was developed for the determination of Ag(I) at a 3-amino-2-mercapto quinazolin-4(3H)-one modified carbon paste electrode. The analysis procedure consisted of an open circuit accumulation step in stirred sample solution for 12min. This was followed by medium exchange to a clean solution where the accumulated Ag(I) was reduced for 15s in -0.6V. Subsequently an anodic potential scan was effected from -0.2 to +0.2V to obtain the voltammetric peak. The detection limit of silver(I) was 0.4microg L(-1) and R.S.D. for 10, 100 and 200microg L(-1) silver(I) were 2.4, 1.8 and 1.3%, respectively. The calibration curve was linear for 0.9-300microg L(-1) silver(I). Many coexisting ions had little or no effect on the determination of silver(I). The procedure was applied to determination of silver(I) in X-ray photographic films and natural waters. In X-ray photographic film samples, the results have compared to those obtained by atomic absorption spectroscopy.

Voltammetric determination of Cu(II) in natural waters and human hair at a meso-2,3-dimercaptosuccinic acid self-assembled gold electrode.

An electrochemical sensor for the detection of copper(II) ions is described using a meso-2,3-dimercaptosuccinic acid (DMSA) self-assembled gold electrode. First in ammonia buffer pH 8, copper(II) ions complex with self-assembled monolayer (SAM) via the free carboxyl groups on immobilized meso-2,3-dimercaptosuccinic acid (accumulation step). Then, the medium is exchanged to acetate buffer pH 4.6 and the complexed Cu(II) ions are reduced in negative potential of -0.3V (reduction step). Following this, reduced coppers are oxidized and detected by differential pulse (DP) voltammetric scans from -0.3 to +0.7V (stripping step). The effective parameters in sensor response were examined. The detection limit of copper(II) was 1.29mugL(-1) and R.S.D. for 200mugL(-1) was 1.06%. The calibration curve was linear for 3-225mugL(-1) copper(II). The procedure was applied for determination of Cu(II) to natural waters and human hairs. The accuracy and precision of results were comparable to those obtained by flame atomic absorption spectroscopy (FAAS).