Hossein Dehghani

Electrocatalytic oxidation and voltammetric determination of levodopa in the presence of carbidopa at the surface of a nanostructure based electrochemical sensor.

In the present paper, the use of a carbon paste electrode modified by meso-tetrakis(3-methylphenyl) cobalt porphyrin (CP) and TiO(2) nanoparticles for the determination of levodopa (LD) and carbidopa (CD) was described. Initially, cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. Next, the mediated oxidation of LD at the modified electrode was described. At the optimum pH of 7.0, the oxidation of LD occurs at a potential about 150 mV less positive than that of an unmodified carbon paste electrode. Based on differential pulse voltammetry (DPV), the oxidation of LD exhibited a dynamic range between 0.1 and 100.0 μM and a detection limit (3σ) of 69 ± 2 nM. DPV was used for simultaneous determination of LD and CD at the modified electrode, and quantitation of LD and CD in some real samples (such as tablets of Parkin-C Fort and Madopar, water, urine, and human blood serum) by the standard addition method.

Synthesis of 1:2 molecular complexes between free base meso-tetraarylporphyrins and sulfur trioxide

The interaction of meso-tetraarylporphyrins, H2T(4-X)PP, with sulfur trioxide pyridine complex (SO3.py) in chloroform only produced 1:2 molecular complexes, [H2T(4-X)PP(SO3)2]. UV-vis, 1H NMR, and FT-IR spectra, as well as elemental analysis, suggested pseudo tetrahedrally distorted porphyrin core structures with σ-bonding from two pyrrolenine nitrogen donors to the d orbital of sulfur in two SO3s and the occurrence of two hydrogen bonds between two pyrrolic NH and oxygens of sulfur trioxides from above and below the mean plane of the porphyrins.

Ca-doped CuS/graphene sheet nanocomposite as a highly catalytic counter electrode for improving quantum dot-sensitized solar cell performance

Copper sulfide (CuS) is one of the most important counter electrodes (CEs) in high-efficiency, quantum dot-sensitized solar cells (QDSSCs). In this work, we investigated the effect of Mg, Ca, Sr and Ba ion incorporation into the CuS layer on the photovoltaic performance of quantum dot-sensitized solar cells. Metal ion-doped CuS was deposited by the successive ionic layer adsorption and reaction (SILAR) method on the FTO substrate. As a result, the quantum dot photoanode with the optimized Ca-doped CuS CE exhibited power conversion efficiency (PCE) of 2.33%, which is much higher than bare CuS CE (PCE 1.68%), Ba-doped CuS (1.81%), Mg-doped CuS (1.82%) and Sr-doped CuS (1.67%). A sandwiched structural Ca-doped CuS/graphen sheet (Ca-doped CuS/GS) electrode was prepared by repeating electrophoretic deposition (EPD) of graphene sheets and deposition of Ca-doped CuS nanoparticles. When a Ca-doped CuS/graphene sheet (Ca-doped CuS/GS) was used as a CE, the QDSSC exhibited higher power conversion efficiency (2.73%) compared to cells with Ca-doped CuS (2.33%) and bare-CuS (1.68%) cathodes. A full description of reasons for efficiency enhancement are discussed in this paper by using diverse electrochemical and spectral analyses.

Effects of triphenyl phosphate as an inexpensive additive on the photovoltaic performance of dye-sensitized nanocrystalline TiO2 solar cells

The effect mechanism of triphenyl phosphate (TPP) is studied as an effective and inexpensive additive in the electrolyte of dye-sensitized solar cells (DSSCs) performance. The N719- and TPA-sensitized devices with a modified electrolyte show high efficiencies of 7.04% and 2.73% under 100 mW cm−2 light illumination, respectively. The enhancement in Voc arises from increasing electron density in the conduction band (CB) of TiO2 that leads to a shift in the Fermi level (EF) and thereby a suppression in electron recombination occurs. Electrochemical and spectroscopic data exhibit slower electron recombination and indicates that TPP forms a charge transfer complex with iodine in the electrolyte. This complexation decreases the concentration of free triiodide and limits the electron recombination so that it improves Jsc. Furthermore, the results reveal that TPP is a suitable inexpensive alternative for 4-tert-butylpyridine (TBP) additive in the DSSCs. We replaced TBP with TPP in DSSC based on TPA dye and observed an 73% increase in η compared to the blank electrolyte (without additive). Also, we investigate the effects of substituents in the phosphate additive structure on the photovoltaic properties by comparing our findings with previous work and found that the aliphatic phosphate additives exhibit a better performance compared to aromatic phosphate additives in the DSSCs.

Composite films of metal doped CoS/carbon allotropes; efficient electrocatalyst counter electrodes for high performance quantum dot-sensitized solar cells.

This study reports the enhanced catalytic ability of metal ions-doped CoS and CoS/carbon allotrope counter electrodes (CEs) (synthesized using a successive ionic layer adsorption and reaction (SILAR) method) to improve the power conversion efficiency (η) in quantum dot-sensitized solar cells (QDSSCs). Firstly, doping effects of different metal ions (Mg2+, Ca2+, Sr2+ and Ba2+) in the CoS CE on the QDSSCs performance have been investigated. Overall, among the different metal doped CoS CEs, the best energy conversion efficiency of 2.19%, achieved for Sr, is the highest reported for QDSSCs constructed with metal doped CoS. A sandwich structural Sr- and Ba-CoS/carbon allotrope (graphene sheet (GS), graphene oxide (GO) and carbon nanotube (CNT)) composite CEs have been prepared by repeating electrophoretic deposition (EPD) of carbon materials and deposition of CoS nanoparticles. Dramatic enhancements of η have been observed with the Sr- and Ba-CoS/GO CEs based QDSSCs (∼76% and ∼41%, respectively), which is higher than that of the bare CoS CE. Because of the large specific surface area and superior electrical conductivity of GS, GO and CNT and the high electrocatalytic activity of CoS, these CEs show an improvement in the photocurrent density in the cells, as revealed from electrochemical and spectral data.

Fabrication and study of optical and electrochemical properties of CdS nanoparticles and the GO–CdS nanocomposite

CdS nanoparticles (NPs) have been successfully synthesized using the cadmium(II)–salophen complex and anhydrous sodium thiosulfate (Na2S2O3) as a sulfur source in dimethyl sulfoxide (DMSO) via a thermal deposition approach. The average size of the CdS NPs is 3.7 nm. The graphene oxide (GO)–CdS nanocomposite was successfully prepared via a facile process. The as-prepared nanocomposite possesses excellent optical and electrochemical properties. The structure, morphology, optical and electrochemical properties of the CdS NPs and the GO–CdS nanocomposite were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (Pl) spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). UV-Vis spectra show that compared to CdS NPs, the absorption edge of the GO–CdS nanocomposite is red shifted slightly and the absorption intensity is decreased. Photoluminescence spectra of CdS NPs consist of an emission peak which is centered at around 510 nm, when excited at 325 nm. It is noteworthy that the blue luminescence intensity of the GO–CdS nanocomposite is lower than that of pure CdS NPs. The electrochemical observation of samples suggests that the CdS nanoparticles integrate with GO sheets and thereby facilitate the electron transfer. Furthermore, the possible growth mechanism of CdS nanoparticles is presented.

Spectrophotometric studies of the thermodynamics of sitting-atop complexation between free base meso-tetraarylporphyrins and titanium(IV) chloride.

Titanium(IV) chloride reacts with free base meso-tetraarylporphyrin and its ortho, meta and para-substituted derivatives (H(2)T(X)PP; X: OCH(3), CH(3) and Cl) for formation of sitting-atop (SAT) complexes, [TiCl(4)(H(2)T(X)PP)]. The computer fitting of the variation of the absorbance versus mole ratio by KINFIT program was used for calculation of the formation constants of these complexes in chloroform. Thermodynamic parameters, DeltaG degrees , DeltaH degrees , DeltaS degrees , have been determined and the influence of the temperature and the substituted aryl groups (electronic and steric effects) in the free base porphyrins on the stability of the SAT complexes was studied.

Thermodynamic studies of sitting-atop (SAT) complexation of uranyl and free base meso -tetraarylporphyrins

The interaction of uranyl with meso-tetraphenylporphyrin and its para-substituted derivatives (H2t(4-X)pp, X : H, Br, Cl, CH(CH3)2, OCH3, CH3) in chloroform produced 1 : 1 sitting-atop (SAT) complexes ((uranyl)H2t(4-X)pp). Formation constants were calculated by computer fitting of complex absorbance versus mole ratio data to appropriate equations and found to decrease with temperature increase. Thermodynamic parameters, ΔG 0, ΔH 0 and ΔS 0 were obtained. The formation constants vary with changing of the substituent on the aryl rings of H2t(4-X)pp in the following order: (uranyl)H2t(4-OCH3)pp > (uranyl)H2t(4-CH3)pp > (uranyl)H2t(4-CH(CH3)2)pp > (uranyl)H2tpp > (uranyl)H2t(4-Br)pp > (uranyl)H2t(4-Cl)pp.

Thermodynamic studies of sitting-atop complexation between free base meso-tetraarylporphyrins and antimony(III) chloride in chloroform

Interaction of para, meta and ortho-substituted meso-tetraarylporphyrins, (H2t(X)pp, X: OMe, Me, H and Cl) with SbCl3 in chloroform solution afforded 1 : 1 sitting-atop (SAT) complexes ([(SbCl3)(H2t(X)pp)]). The formation constants were calculated by KINFIT and found to decrease with increasing temperature. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained. Formation constants of these complexes change with changing substituent (X) on the aryl rings of H2t(X)pp in the following order: (SbCl3)H2t(4-OMe)pp  > (SbCl3)H2t(4-Me)pp  > (SbCl3)H2tpp  > (SbCl3)H2t(4-Cl)pp  > (SbCl3)H2t(3-OMe)pp  > (SbCl3)H2t(3-Me)pp> (SbCl3)H2t(2-OMe)pp  > (SbCl3)H2t(2-Me)pp.

Pyridine derivatives; new efficient additives in bromide/tribromide electrolyte for dye sensitized solar cells

In this work, two new inexpensive pyridine derivatives, propyl isonicotinate (PIN) and isopropyl isonicotinate (IPIN), have been synthesized through a simple and low cost method and for the first time, they have been applied as effective additives in bromide/tribromide electrolyte in dye sensitized solar cells (DSSCs). Although the iodide/triiodide redox shuttle shows remarkable performance in DSSCs, but bromide/tribromide couple has a more positive redox potential in comparison to this couple. Therefore, it is good idea to design dyes whose HOMO and LUMO levels match with the redox potential of bromide/tribromide and the conduction band (CB) of TiO2, respectively. We have synthesized 3-(4-carbazole-9-yl-phenyl)-2-cyano-acrylic acid (TC301) and 2-cyano-3-(4-(3,6-di-tert-butyl-9H-carbazole-9-yl)phenyl) acrylic acid (TC302) as two carbazole dyes and applied them with modified electrolyte in DSSCs. The influence of PIN and IPIN additives in bromide/tribromide redox electrolyte on the DSSC performances is investigated. In comparison to electrolyte without additive, adding 0.5 M of these additives to the electrolyte solution leads to an increase in the open circuit voltage (Voc) and short current density (Jsc), consequently the energy conversion efficiency (η) improves. Electrochemical impedance spectroscopy show that the enhancement in Voc is due to increasing electron density in the CB of TiO2 so that a shift in the Fermi level (EF) occurs. It leads to a suppression in electron recombination that has beneficial effect on the Voc. Furthermore, cyclic voltammetry results reveal that PIN and IPIN has similar effect mechanisms to 4-tert-butylpyridine (TBP) additive in the DSSCs. Our findings show that TBP can be replaced with PIN and IPIN in the DSSCs.