J. Theerthagiri

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.

Synthesis and characterization of a CuS–WO3 composite photocatalyst for enhanced visible light photocatalytic activity

WO3 nanorods and flower-like CuS were synthesized by a hydrothermal process. The visible light driven CuS–WO3 photocatalyst was prepared by adding different weight ratios (10–40%) of CuS on WO3 by a wet impregnation method. The synthesized photocatalysts were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Field emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDAX) and UV-vis diffuse reflectance (DRS) spectroscopy. The photocatalytic performance of synthesized photocatalysts was evaluated for the photodegradation of methylene blue (MB) under visible light irradiation. The 10% CuS–WO3 photocatalyst showed higher photocatalytic degradation activity than others which could be due to the increased absorption of light in the visible region and also a lower recombination of charge carriers. Further, the photoelectrochemical measurements carried out for 10% CuS–WO3 revealed the faster migration of photo-induced charge-carriers. A possible reaction mechanism for the enhancement of photocatalytic activity of CuS–WO3 has been proposed.

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.

Cu2S-incorporated ZnS nanocomposites for photocatalytic hydrogen evolution

Sodium Lauryl Sulphate (SLS) surfactant and propylene diamine (PD), assisted wet chemical synthesis was used to make ZnS–Cu2S nanoflakes wherein the added copper(II) transforms into copper(I) sulphide and is found to be deposited on the surface of ZnS. With a variation of copper concentration from 0 to 5% there is a morphological transformation from ZnS nanorods eventually to ZnS–Cu2S nanoflakes through a transition morphology of nanocactus leaves. During the addition of copper there is an incorporation of Cu2S into the ZnS phase (100) as is clearly evidenced by various characterization methods. Visible light photocatalytic hydrogen production activities using these nanoflakes of ZnS–Cu2S are reported with good results. The influence of Cu2S shifts the band gap of ZnS from the UV to the visible region, reducing the need for an expensive co-catalyst like platinum for photolysis of water. Though hydrogen production is not as high as that depicted by other earlier works the material that we have created is a relatively cheap, simple two component heterostructure with no expensive third component. It is also free from toxic materials such as CdS. However, our results are better than for most other copper loaded ZnS systems in the literature. Furthermore, the morphological evolution to nanoflakes from nanorods, the concentration and dispersion of Cu2S over ZnS and the interface between Cu2S and ZnS semiconductors play a vital role in hydrogen production. 5% Cu2S on ZnS seems to be the optimum concentration for maximum evolution of hydrogen.

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.

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.

Recent Advances in Metal Chalcogenides (MX; X = S, Se) Nanostructures for Electrochemical Supercapacitor Applications: A Brief Review

Supercapacitors (SCs) have received a great deal of attention and play an important role for future self-powered devices, mainly owing to their higher power density. Among all types of electrical energy storage devices, electrochemical supercapacitors are considered to be the most promising because of their superior performance characteristics, including short charging time, high power density, safety, easy fabrication procedures, and long operational life. An SC consists of two foremost components, namely electrode materials, and electrolyte. The selection of appropriate electrode materials with rational nanostructured designs has resulted in improved electrochemical properties for high performance and has reduced the cost of SCs. In this review, we mainly spotlight the non-metallic oxide, especially metal chalcogenides (MX; X = S, Se) based nanostructured electrode materials for electrochemical SCs. Different non-metallic oxide materials are highlighted in various categories, such as transition metal sulfides and selenides materials. Finally, the designing strategy and future improvements on metal chalcogenide materials for the application of electrochemical SCs are also discussed.