R.A. Senthil

Photocatalytic and photoelectrochemical studies of visible-light active α-Fe2O3–g-C3N4 nanocomposites

Nanocrystalline hematite iron oxide (α-Fe2O3) and graphitic carbon nitride (g-C3N4) were prepared and used as precursors to synthesise α-Fe2O3–g-C3N4 composite photocatalysts of various compositions by a wet impregnation method. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV-vis diffuse reflection spectroscopy (DRS) and photoluminescence spectroscopy (PL). The efficiency of the photocatalysts was evaluated by photoelectrochemical measurements and photodegradation of direct red 81 (DR81) as a target textile pollutant under visible light irradiation. The α-Fe2O3–g-C3N4 composites exhibited remarkably improved visible-light induced photocatalytic activity. The composite photocatalysts with optimal α-Fe2O3 content with the highest photocatalytic activity was found to be 2%-α-Fe2O3–g-C3N4. The synergistic enhancement in the photocatalytic degradation of composite photocatalysts might be due to an increase in the visible-light absorption efficiency and rapid photoinduced charge separation. A possible photocatalytic mechanism has been proposed for the photocatalytic activity of α-Fe2O3–g-C3N4 composite photocatalysts.

One-step electrochemical deposition of Ni1−xMoxS ternary sulfides as an efficient counter electrode for dye-sensitized solar cells

Ternary sulfides of Ni1−xMoxS films with various compositions (x = 0, 0.05, 0.1, and 0.2) were fabricated on a fluorine doped tin oxide (FTO) glass substrate by a simple one-step electrochemical deposition method. The electrochemically deposited ternary sulfides were utilized as a low-cost and highly efficient platinum free counter electrode (CE) for dye-sensitized solar cells (DSSCs). The structure, surface morphology and elemental composition of the electrochemically deposited ternary sulfides were examined by using X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDS). A phthaloylchitosan (PhCh) based polymer electrolyte was used as an electrolyte for DSSCs. Cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization studies revealed that the Ni0.95Mo0.05S CE exhibited lower charge-transfer resistance at the CE/electrolyte interface and higher electrocatalytic activity towards the regeneration of I− from I3− relative to other compositions. The Ni0.95Mo0.05S ternary sulfide offers a positive synergistic effect for the electrochemical catalytic activity towards the reduction of I3−, which may be due to an increase in active catalytic sites and low-charge transfer resistance and achieved a high power conversion efficiency of 7.15% with a Voc of 0.65 V, a Jsc of 17.21 mA cm−2, and a FF of 0.64 with a PhCh-based polymer electrolyte, which is comparable to that of the conventional Pt CE (7.20%). The present investigation demonstrates that the electrochemically deposited Ni0.95Mo0.05S ternary sulfide is a promising candidate as a low-cost and highly efficient CE in DSSCs.

Electrochemical deposition of carbon materials incorporated nickel sulfide composite as counter electrode for dye-sensitized solar cells

The various carbon-based materials incorporated nickel sulfide (NiS) composites have been electrochemically deposited on fluorine-doped tin oxide (FTO) glass substrate. The structure, surface morphology, and elemental composition of the electrodeposited NiS composite materials were characterized by XRD, HR-SEM, and EDS. The electrochemically deposited various NiS composites such as NiS/AB (acetylene black), NiS/VC (Vulcan carbon), and NiS/MWCNT (multi walled carbon nanotubes) have been served as an efficient, low-cost counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Electrochemical impedance spectroscopy and cyclic voltammetry of NiS/AB CE composite materials exhibits a good conductivity and superior electrocatalytic performance over other various carbon incorporated materials. The positive synergistic effects, which increase the active catalytic sites and improved interfacial charge transfer, may be accountable for the superior electrocatalytic performance of NiS/AB composite materials The fabricated DSSC with NiS/AB CE reached a power conversion efficiency of 6.75%, which is equivalent with platinum electrode (7.20%). These results validate that the electrochemically deposited NiS/AB composite film is an auspicious alternative for low-cost and high efficient DSSCs.

High performance dye-sensitized solar cell based on 2-mercaptobenzimidazole doped poly(vinylidinefluoride-co-hexafluoropropylene) based polymer electrolyte

ABSTRACT In this work, the influence of 2-mercaptobenzimidazole (2-MCBI) on poly(vinylidinefluoride-co-hexafluoropropylene)/KI/I2 (PVDF-HFP/KI/I2) polymer electrolytes were studied. The pure and different weight percentage ratios (20, 30, 40 and 50%) of 2-MCBI doped PVDF-HFP/KI/I2 electrolytes were prepared by a solution casting technique. The as-prepared polymer electrolyte films were characterized using various techniques such as Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffractometer (XRD), alternating current (AC)-impedance analysis. The addition of 2-MCBI with pure PVDF-HFP/KI/I2 was found to increase the ionic conductivity of electrolyte. Among the various additions, 30 wt% 2-MCBI doped PVDF-HFP/KI/I2 showed the highest room temperature ionic conductivity values than the others. The dye-sensitized solar cell (DSSC) fabricated using this optimized polymer electrolyte achieved a high power conversion efficiency of 4.40% than the pure PVDF-HFP/KI/I2 (1.74%) at similar experimental conditions. Thus, the 2-MCBI doped polymer electrolyte has proven to be an effective substitute to the liquid electrolyte in DSSCs.

Synthesis of Efficient Ni0.9X0.1Se2 (X=Cd, Co, Sn and Zn) Based Ternary Selenides for Dye-Sensitized Solar Cells

A low-cost platinum (Pt) free electrocatalyst of NiSe2 and Ni0.9X0.1Se2 (X=Cd, Co, Sn and Zn) have been developed by hydrothermal reduction route and utilized as counter electrode (CE) in dye-sensitized solar cells (DSSCs). The purity, phase formation and morphology of the sample were characterized by X-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy. The electrocatalytic activity of the synthesized selenides for the reduction of I3- to I- was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. The Ni0.9Zn0.1Se2 CE exhibited lower internal resistance and higher electrocatalytic activity than the other ternary metal selenides and this may be due to an increase in the electrocatalytic active sites on the surface of Ni0.9Zn0.1Se2. As a result, the DSSC fabricated with Ni0.9Sn0.1Se2 CE achieved a high power conversion efficiency of 4.20% under an illumination of 100 mW/cm2, which is comparable to that of DSSC with Pt CE (6.11%). These results demonstrate the potential application of Ni0.9Zn0.1Se2 as an alternative CE to replace expensive Pt in DSSCs. This study can be further extended for the development of new metal selenides based CE electrocatalysts with high activity for the DSSCs.

A sensitive electrochemical detection of hydroquinone using newly synthesized α-Fe2O3-graphene oxide nanocomposite as an electrode material

This article presents the effect of hematite phase iron oxide (α-Fe2O3) on the electrocatalytic activity of graphene oxide (GO) for electrochemical detection of hydroquinone in aqueous solution. The different weight percentage (wt%) (1, 2 and 3%) of α-Fe2O3 added GO nanocomposites were synthesized by wet-impregnation method. The cyclic voltammetry studies using 2% α-Fe2O3-GO modified glassy carbon electrodes was found to exhibit an excellent electrocatalytic activity than α-Fe2O3 and GO electrodes that may be due to the synergistic effect of α-Fe2O3nanoparicles and GO sheet. In addition, the modified electrode exhibited a good reproducibility as well as long-term stability. Hence, the 2% α-Fe2O3-GO can be a promising catalytic material for electrochemical sensor applications.

Synthesis, Characterization and Optical Properties of CdxZn1-xS Nanocrystals

Nanocrystalline Cd1-XZnXS (X=0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) were synthesized by simple wet chemical method via co-precipitation. The formation, phase purity and crystalline size were ascertained by X-ray diffraction (XRD). The shape and surface morphology of the synthesized samples were characterized by scanning electron microscopy (SEM). The optical properties of the Cd1-XZnXS samples were investigated using UV-vis absorption spectroscopy and photoluminescence spectroscopy (PL) studies. The optical properties of the sample was dramatically changed by varying the composition of Cd1-XZnXS system, which may be due to the synergic effect originated by combining CdS and ZnS. The obtained optical behaviors suggest that the material can be suitable for the photocatalytic degradation of organic pollutants. The prsent investigation demontrated that the synthetic approach developed in this is highly reproducible and can be readily scaled up for potential industrial production.

A Comparative Study on the Role of Precursors of Graphitic Carbon Nitrides for the Photocatalytic Degradation of Direct Red 81

The graphitic carbon nitride (g-C3N4) materials have been synthesized from nitrogen rich precursors such as urea and thiourea by directly heating at 520 °C for 2 h. The as-synthesized carbon nitride samples were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) and particle size analysis. The photoelectrochemical measurements were performed using several on-off cycles under visible-light irradiation. The x-ray diffraction peak is broader which indicates the fine powder nature of the synthesized materials. The estimated crystallite size of carbon nitrides synthesized from urea (U-CN) and thiourea (T-CN) are 4.0 and 4.4 nm respectively. The particle size of U-CN and T-CN were analysed by particle size analyser and were found to be 57.3 and 273.3 nm respectively. The photocatalytic activity for the degradation of the textile dye namely, direct red-81 (DR81) using these carbon nitrides were carried out under visible light irradiation. In the present investigation, a comparison study on the carbon nitrides synthesized from cheap precursors such as urea and thiourea for the degradation of DR81 has been carried out. The results inferred that U-CN exhibited higher photocatalytic activity than T-CN. The photoelectrochemical studies confirmed that the (e--h+) charge carrier separation is more efficient in U-CN than that of T-CN and therefore showed high photocatalytic degradation. Further, the smaller particle size of U-CN is also responsible for the observed degradation trend.

Hematite Fe2O3 Nanoparticles Incorporated Polyvinyl Alcohol Based Polymer Electrolytes for Dye-Sensitized Solar Cells

Influence of hematite iron oxide nanoparticles (α-Fe2O3 NPs) on ionic conductivity of polyvinyl alcohol/KI/I2 (PVA/KI/I2) polymer electrolytes was investigated in this work. The pure and different weight percentage (wt %) ratios (2, 3, 4 and 5 % with respect to PVA) of α-Fe2O3 NPs incorporated PVA/KI/I2 polymer electrolyte films were prepared by solution casting method using DMSO as solvent. The prepared polymer electrolyte films were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometer (XRD) and alternating current (AC)-impedance analysis. The AC-impedance studies revealed a significant increase in the ionic conductivity of α-Fe2O3 NPs incorporated PVA/KI/I2 polymer electrolytes than compared to pure PVA/KI/I2. This incorporated polymer electrolytes reduces the crystallinity of the polymer and enhance the mobility of I-/I3- redox couple, thereby increasing the ionic conductivity of polymer electrolytes. The highest ionic conductivity of 1.167 × 10-4 Scm-1 was observed for 4 wt % of α-Fe2O3 NPs incorporated PVA/KI/I2 polymer electrolyte. Also, the dye sensitized solar cell (DSSC) fabricated with this electrolyte showed an enhanced power conversion efficiency of 3.62 % than that of pure PVA/KI/I2 electrolyte (1.51 %). Thus, the synthesized α-Fe2O3 NPs added polymer electrolyte can be serve as a suitable material for dye sensitized solar cell application studies.