Sumanta Jana

Fabrication of SnO2/α-Fe2O3, SnO2/α-Fe2O3–PB Heterostructure Thin Films: Enhanced Photodegradation and Peroxide Sensing

We report the synthesis of SnO2/α-Fe2O3 heterostructure thin films by employing two-step processes: galvanic and chemical deposition. Fe2O3 is a narrow band gap semiconductor and has short hole diffusion length. Therefore, the photogenerated electrons and holes are not easy to separate in Fe2O3. Combining Fe2O3 to SnO2, a wide-energy-gap semiconductor having suitable valence band and conduction band position is a promising candidate for the photo catalysts. The chemical modification of this heterostructure was achieved by electro-active Prussian blue (PB) molecule. The photocatalytic activities of SnO2, α-Fe2O3, SnO2/α-Fe2O3, and SnO2/α-Fe2O3-PB thin films were investigated for organic dye degradation. It was observed that the coupled and combined modified systems showed better reactivity compared to individual single-component materials. The electrocatalytic activity of the synthesized thin films has also been studied where hydrogen peroxide (H2O2) was taken as a model compound. Amperometric study also reveals that the couple and combined modified thin films are more effective at sensing hydrogen peroxide (H2O2) than single-component materials.

Precursor-driven selective synthesis of hexagonal chalcocite (Cu2S) nanocrystals: structural, optical, electrical and photocatalytic properties

The reaction of CuCl2·2H2O with the methyl ester of 3,5-dimethyl pyrazole-1-dithioic acid (mdpa) yields a blackish brown complex of composition, [Cu(mdpa)2][CuCl2]. The complex formed a well-defined crystal and is characterized by single-crystal X-ray diffraction, thermogravimetry (TG), and spectroscopic studies. The molecule possesses a distorted tetrahedral configuration with a CuN2S2 chromophore with +1 oxidation state of copper. The TG study reveals that the molecule is a suitable precursor for copper sulfide nanoparticles. The low temperature thermal decomposition of the single-source precursor produces hexagonal chalcocite (Cu2S) nanostructures in ethylene diamine and ethylene glycol. A selective synthesis of copper-rich high chalcocite was obtained using the new precursor. The size and morphology of the synthesized Cu2S nanoparticles are guided by the precursor and likely to be less dependent on the solvent used in the experiment. The nanoparticles were characterized by X-ray diffraction, scanning electronic microscope, and UV-Vis spectroscopic studies. The optical band gap of the as-synthesized Cu2S nanoparticles is measured to be 1.80–2.40 eV. The Cu2S nanoparticles are found to be good catalysts in UV photo catalytic decomposition (90%) of Congo red (CR) dye following first-order reaction kinetics, and the reusability study of the Cu2S catalyst also shows excellent catalytic performance (80%).

Photocatalytic degradation of organic dye on porous iron sulfide film surface

Thin films of nanocrystalline and porous FeS(2) with marcasite phase have been deposited from a greenish-blue iron nitroprusside precursor film, which readily gives FeS(2) on reacting with an aqueous solution of sodium sulfide. High resolution X-ray diffraction (HRXRD) pattern indicated the formation of polycrystalline and orthorhombic (marcasite) phase of FeS(2), whereas the field emission scanning electron microscopy (FESEM) showed the morphology of the films to be consisted of grains of average 25 nm diameter with unevenly distributed numerous pores. Optical characterization (UV-Vis and photoluminescence) revealed significant amount of blueshift in the band gap energy of the deposited material, which is attributed to the strong quantum confinement effect exerted by the FeS(2) nanocrystals. The deposited FeS(2) films showed good photocatalytic activity toward the degradation of Rose Bengal dye and could be found efficient for wastewater treatment.

A new pyrazolyl dithioate function in the precursor for the shape controlled growth of CdS nanocrystals: optical and photocatalytic activities

The dithiocarbazate functionalized 3,5-dimethyl pyrazole ligands and their cadmium(II) complexes e.g., [Cd(mdpa)2Cl2] (where mdpa is the methyl ester of 3,5-dimethyl pyrazole-1-dithioic acid) and [Cd(bdpa)2Cl2] (where bdpa is the benzyl ester of 3,5-dimethyl pyrazole-1-dithioic acid) have been synthesized. The complexes are used as single-source precursors (SPs) for the synthesis of spherical and rod-like CdS nanocrystals in a solvothermal process without using any external surfactants. In situ generated thiols (CH3SH in the case of the mdpa complex and PhCH2SH in the case of the bdpa complex) in thermolysis of the SP govern the growth of nanocrystals. The spherical and rod shaped CdS nanocrystals are produced in the presence of CH3SH and PhCH2SH, respectively. A possible growth mechanism of nanocrystals based on the preferential thiol bonding to the nucleus is discussed. The nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The UV-Vis spectroscopic studies of CdS nanocrystals show the quantum confinement effect with a band gap of 2.2 eV to 2.6 eV, and the narrow intense PL emissions of the samples are red-shifted (λmax = 570 nm) due to trap-related electron–hole recombination. The CdS nanocrystals are successfully applied in the photodegradation of rose bengal (RB) and methylene blue (MB) dyes under visible light.

Single-source mediated facile electrosynthesis of p-Cu2S thin films on TCO (SnO2:F) with enhanced photocatalytic activities

Electrosynthesis of p-Cu2S thin films on a fluorine-doped tin oxide coated transparent conducting TCO (SnO2:F) glass substrate is carried out by chronoamperometry and cyclic voltammetry (CV) using an ethanolic solution of a single-source precursor (SP), [Cu(mdpa)2][CuCl2] (where mdpa is 3,5-dimethyl pyrazole-1-dithioic acid). The appropriate potential at which the formation of stoichiometric p-Cu2S thin films occurs was found to be −0.48 V. The mechanism of the selective deposition of the p-Cu2S phase can be described by the electroreduction of Cu–N/S bonds in the coordination sphere following the dissociation of a precursor complex into Cu+ and mdpa. The free ligand mdpa is reduced to sulfide ion producing volatile organics in the electrochemical process. The quality deposition of thin films depends on the optimization of the SP concentration. An X-ray diffraction study reveals the high chalcosite phase of copper sulfide with preferential orientation along the (110) plane. The I–V characteristic of the as deposited Cu2S/TCO thin film shows a non-ohmic behavior suggesting the formation of a p–n heterojunction diode. The p-Cu2S/TCO thin films are found to be excellent photocatalysts for the photo-degradation of Congo Red (CR) under visible light irradiation. It has also been shown that the photocatalytic activity of the deposited thin films increased many fold with the addition of a catalytic amount of hydrogen peroxide in the photo-degradation of Rose Bengal (RB) dye under visible light irradiation. A possible mechanism for the improved photoactivity of p-Cu2S/TCO is proposed and involves the electron scavenging property of H2O2 followed by OH− radical formation, significantly accelerating the photodegradation of RB dye.

Photo-induced exciton generation in polyvinylpyrrolidone encapsulated Ag2S core-shells: Electrochemical deposition, regular shape and high order of particle size distribution

Visible light induced frequency switching behavior, exhibited by the electrochemically deposited thin films of polyvinylpyrrolidone (PVP) encapsulated Ag2S nanosphere (core-shell) is shown here. A low frequency (∼40 Hz) pulse was found to be generated upon illumination with 1 Sun due to excitonic transition, which also showed good switching behavior with the “on” and “off” state of the light. Capping of the semiconductor surface by a polymer like PVP reduces the surface states and thus lowers the built in barrier height and the width of depletion region. So, the number of photo generated but non recombining electron-hole pairs (excitons) increases, which put their signature in some unique physical properties like increase in photoluminescence (PL) intensity, light induced frequency switching behavior due to free exciton generation, etc. Here, the depositions were carried out on indium tin oxide coated glass substrates from an aqueous solution of AgNO3, thioacetamide, and PVP. The films were structurally c...