Anup Mondal

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%).

A novel amperometric biosensor for hydrogen peroxide and glucose based on cuprous sulfide nanoplates

A facile, greener and template free route has been developed to produce cuprous sulfide (Cu2S) nanoplates (NPs) with average diameters of 70-150 nm, via one step solvothermal decomposition of a single-source precursor (SSP) Cu(ACDC)2 [ACDC = 2-aminocyclopentene-1-dithiocarboxylate] in the presence of ethylenediamine (EN) and triethylenetetramine (TETA) as structure orienting agents. The precursor complex and nanomaterials were thoroughly characterized by several common techniques and measurements, which give the composition and characteristics of the materials. Amperometric biosensors for hydrogen peroxide (H2O2) and glucose have been constructed by immobilizing the synthesized Cu2S NPs in glutaraldehyde on a glassy carbon (GC) electrode using a direct drop-coating method. The proposed sensor has displayed faster response, high and reproducible sensitivity (64.27 μA mM-1) with linear range of 10 μM to 3.75 mM, towards the electrochemical biosensing of H2O2 at -0.35 V (vs. Ag/AgCl). The sensor also showed high and reproducible sensitivity (61.67 μA mM-1) towards glucose determination with linear range of 10 μM to 3.1 mM. The anti-inference ability of electroactive molecules and favorable stability are some of the advantages of the proposed sensor. Finally, using the sensor we have determined the glucose concentration in a human blood serum sample. The results strongly demonstrate the usefulness of Cu2S NPs for biosensor design and other biological applications.

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.

Electrochemically synthesized microcrystalline tin sulphide thin films: high dielectric stability with lower relaxation time and efficient photochemical and photoelectrochemical properties

A detailed study has been carried out on the structural, dielectric and impedance properties of polycrystalline p-type SnS thin films grown on transparent conducting oxide (TCO) coated glass substrates from an aqueous solution of tartaric acid, SnSO4 and Na2S2O3 by a modified electrochemical technique. The as-deposited films were found to be smooth, almost pinhole free and well adherent to the bottom substrate. X-ray diffraction studies revealed the formation of polycrystalline SnS films with an orthorhombic phase. Field emission scanning electron microscopy and atomic force microscopy revealed a moderately compact surface morphology with evenly distributed almost spherical grains. Optical measurements showed direct band gap energy of 1.5 eV. Detailed electrical (dc and ac) analyses showed the p-type nature of the deposited films with unique dielectric behavior. The band-gap energy, resistivity, dielectric constant and relaxation time make this material and ideal absorber layer, which is also reflected in the efficient photochemical and photoelectrochemical behavior.

α-Fe2O3 nanospheres: facile synthesis and highly efficient photo-degradation of organic dyes and surface activation by nano-Pt for enhanced methanol sensing

We report a simplified electrochemical route to synthesize thin films of nanosphere α-Fe2O3 from a suitable electrolytic solution. X-ray diffraction studies revealed the formation of pure hematite phase (hexagonal structure) α-Fe2O3 films. Field emission scanning electron microscopy revealed a highly compact surface morphology with evenly distributed almost spherical grains. Raman, electron paramagnetic resonance and Fourier transform infrared spectroscopic analyses confirmed the presence of α phase Fe2O3 (hematite). Optical analysis revealed a band gap energy of 2.15 eV; this is most suitable for visible light driven photocatalysis towards the degradation of Indigo Carmine (IC) and Rhodamine B (Rh B) dyes, which are widely used in the textile industry and were taken as model organic compounds. About 90% photodegradation was achieved at rates of 0.0188 min−1 for IC and 0.0133 min−1 for Rh B. The synthesized films were used as modified electrodes, and their catalytic activity towards methanol oxidation was investigated. A comparison was also made between Pt modified FTO/Fe2O3 and unmodified FTO/Fe2O3 electrodes towards dye degradation and methanol oxidation, and it was found that the Pt modified FTO/Fe2O3 electrode yielded superior results.

Facile electrochemical deposition of Cu7Te4 thin films with visible-light driven photocatalytic activity and thermoelectric performance

We report a facile strategy to fabricate thin films of Cu7Te4 via a two-electrode galvanic method and demonstrate its application as a recyclable photocatalyst with visible-light-driven photocatalytic activity and photostability. The organic dyes Methylene Blue (MB), and Rose Bengal (RB) and Cr(VI) as a toxic metal ion were chosen to explore the photocatalytic performance. MB was completely degraded (97%) under visible light irradiation in 60 min while RB was degraded up to 92% within 90 min irradiation. Furthermore, the Cu7Te4 thin film also showed superior photoactivity to reduce toxic Cr(VI) to Cr(III). The effective removal of Cr(VI) up to 99.8% at pH 2 was observed in 30 min. The related photocatalytic mechanism is discussed based on the active species trapping experiments. In addition, the Cu7Te4 thin film shows improved thermoelectric performance at room temperature, which may be attributed to the lower value of thermal conductivity obtained in the present case.

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.

Galvanic deposition of nanocrystalline ZnO thin films from a ZnO–Zn(OH)2 mixed phase precursor on p-Si substrate

A galvanic technique for the deposition of ZnO thin films is reported. The depositions were carried out on p-type single-crystal silicon substrates at room temperature, from a solution of ZnSO(4), where the Zn rod acted as a sacrificing anode and p-Si was the cathode. The deposition of ZnO by this method is pH sensitive, and a pH between 4 and 5 is found to be optimum for film deposition. This deposition technique is simple, inexpensive and can be carried out at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies revealed the nanocrystalline structure of the films. The resistivity of the annealed ZnO films was determined by the Van der Pauw measurement technique.