Pulakesh Bera

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 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.

Facile synthesis of nickel oxide thin films from PVP encapsulated nickel sulfide thin films: an efficient material for electrochemical sensing of glucose, hydrogen peroxide and photodegradation of dye

Nickel oxide thin films were grown on ITO (indium tin oxide) substrates by two-step processes: (i) electrodeposition of polymer encapsulated nickel sulfide (PVP-NiS) thin films and (ii) thermal air oxidation of the as-deposited PVP-NiS thin films at 350 °C. A drastic morphological change occurred due to the phase transformation. The cyclic voltammetry study shows that the ITO/NiO electrode facilitates the oxidation of glucose along with an excellent reactivity towards its sensing. The CV study also reveals that the material is effective as an electrode material for the reduction of hydrogen peroxide (H2O2). The amperometric study shows that the electrode has an ultrasensitive current response (1013.76 μA mM−1) with a detection limit of 4.6 μM (signal to noise ratio (S/N) = 3) for glucose and a sensitivity of 82.73 μA mM−1 with a detection limit of 5.2 μM was observed for H2O2. In addition, excellent selectivity and stability have been observed for both cases. The sensor was tested in a wide range concentration of glucose and peroxide and a linear response was observed. Low detection limit, high sensitivity as well as ease of fabrication are some of the advantages of the proposed ITO/NiO sensor. The material also shows a high photocatalytic activity toward dye degradation. The morphological advantage, i.e. spherical porous nanograins, allows a more efficient transport of the reactant molecules to the active interfaces and results in a strong photocatalytic activity to degrade methyl orange (MO) dye.

Copper(II) and cobalt(II) complexes of 5-methyl pyrazole-3-carboxylic acid: synthesis, X-ray crystallography, thermal analysis and in vitro antimicrobial activity

Abstract The coordination behavior of 5-methylpyrazole-3-carboxylic acid (Hmpca) has been demonstrated by the solid state isolation and characterization of [Cu(mpca)2(H2O)]·3H2O (1) [Cu(mpca)2]·H2O (2) and [Co(mpca)2(H2O)2] (3). The new compounds are characterized by X-ray crystallography, thermogravimetric analysis and DFT study. The redox properties of the complexes are examined by cyclic voltammetric analysis. The antibacterial and antifungal activities of the compounds against eight bacteria (Escherichia coli, Enterococcus faecalis, Bacillus subtilis, Klebsiella pneumoniae, Proteus vulgaris, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi) and two fungi (Aspergillus flavus and Candida albicans) are screened using modified agar well diffusion method. The metal complexes demonstrate better inhibition on all bacteria and fungi than the ligand. The high lipophilicity of the complexes accounts for good inhibitory action toward microbes. Among the reported complexes, 3 emerges as an excellent antifungal agent and a better antibiotic than standard fluconazole. The structure and activity relationship indicate that complexes having sufficient Jahn–Teller distortion with high logP values, cross the cell membrane of the microbes creating intercellular damage. Graphical Abstract