https://ir.vidyasagar.ac.in/jspui/handle/123456789/1083 2026-04-26T06:39:21Z 2026-04-26T06:39:21Z Samanta, Anindita https://ir.vidyasagar.ac.in/jspui/handle/123456789/6273 2021-10-28T09:47:55Z 2021-10-04T00:00:00Z

Title: Preparation and characterization of some Binary II-VI Nanocrystalline Compounds Authors: Samanta, Anindita Abstract: i Nanotechnology is an emergent technique for developing our global life in versatile arena such as engineering, electronics and communication, power generation, disease detection and treatment etc. Nanoparticles exhibit potentiality for application in multi-functional nano- devices that are helpful in optoelectronics, spintronics, chemical and biosensors, drug delivery, catalysis, etc. Zinc Oxide (II-VI metal oxide semiconductor) and its modified nanocrystalline compounds have generated a growing interest among researchers due to the ease in tuning the electrical, optical, multiferroic properties of the compounds suited to the needs of the specific devices. ZnO is an n-type direct wide band gap (3.37 eV) semiconductor with high exciton binding energy of 60 meV, high electron mobility, high redox potential, stable chemical composition and have strong luminescence at room temperature. It reveals a strong excitonic emission peak in UV region mainly due to the recombination of free excitons. Attracting luminescent property of ZnO, positions it as a promising candidate for various optoelectronic devices. ZnO has promising applications in chemical sensor, low voltage phosphor material, varistor, solar cells and photocatalysis etc. Dilute magnetic semiconductor (DMS), wherein both the semiconducting and magnetic properties coexist, are in high demand in the electronic industry. Application capability of diluted magnetic semiconductors in spintronic and multiferroic devices has drawn an intense interest of recent researchers. Multiferroicity in DMS is one of the necessary requirements for spintronic device application. The doping of transition metal ions (Mn, Co, Ni, V and Fe) in ZnO matrix develops room temperature ferromagnetism (RTFM) in addition to the change in band gap and other associated properties and is a strong member in the DMS category of materials. Ferromagnetic properties in some non-magnetic element like magnesium (Mg) and lithium (Li) doped ZnO also have been observed. Although, ferromagnetism in transition metal modified ZnO is forecasted in the year 2000, reports on the magnetoelectric (ME) coupling and multiferroicity of these compounds are very few. ii The degree of magnetization in these DMS compounds depends on the particle size and shape of the nanoparticles which vary according to the growth technique. TM doped ZnO nanostructures can be synthesized using various growth techniques, such as co-precipitation, sol-gel, hydrothermal, microemulsion , pyrosol and electrochemical method. The chemical precipitation and sol-gel method result in the synthesis of the ZnO based DMS nanoparticles with controlled sizes (10-30 nm) and shapes and are inexpensive and easy compared to other classical methods of synthesis. Further, the effluents of textile industries with major amounts of non-fixed dyes, azo dyes and inorganic salts are a major source of environment pollution. Destruction of industrial pollutants through photocatalytic degradation is considered to be a trendy method. Nanoscale wide band gap semiconductors are attracting worldwide attention for their enhanced photocatalytic degradation properties. Suitably doped ZnO nanostructures have a bright prospect as a fruitful photocatalyst for the degradation of organic pollutants and furthering sustainable ecology. Mg 2+ doping in ZnO matrix is expected to accomplish such enhanced photocatalytic activities. Addition of rare earth elements in some compounds results in better optical and photocatalytic effects. Recently, it has also been conveyed that optically active rare earth Nd 3+ ion doped ZnO nanoparticles perform as interesting photocatalyst for the purification of pollutant water. The main focus of this research exertion is to establish doped ZnO nanoparticles as potential candidate for optoelectronic devices and striking DMS material for spintronic and multiferroic applications. We thus inspired to study the optical, electrical, magnetic and magnetoelectric coupling properties of ZnO nanoparticles synthesized through simple and inexpensive chemical precipitation and sol-gel technique using hydroxyoxalate type materials. Also the other important objective has been to study the prospect of modified ZnO as an enriched photocatalyst for degradation of aqua pollutants. In the present work, pure and doped ZnO nanoparticles have been synthesized successfully through the chemical precipitation and sol-gel technique. Ni, Co, Fe, Mg and Nd doped ZnO nanoparticles were characterized by structural, optical, electrical, magnetic and ME characterization. All the prepared materials crystallize with hexagonal wurtzite structure. Average crystallite size of the fabricated nanopowders remained in the range of 15-30 nm. The nanocrystalline nature and self-organization of the nanoparticles have been confirmed through SAED study. Chemical bonding and composite elements of the samples was detected through FTIR and EDX characterization. The variations of band gap in case of doped ZnO were deliberated according to the Moss-Burstein band filling effect, which is generally observed in n-type semiconductors. The intense fluorescence emission at 367 nm has been discussed through exciton recombination corresponding to near band edge emission. The visible emission bands have been assigned to the defect states likes oxygen vacancies and zinc interstitials. The tuned optical properties of doped ZnO make it suitable for application in photonic and optoelectronic devices. All these materials have low dielectric loss. Ferroelectric loops observed in these compounds can be explained through the interaction of dipoles in the non centro-symmetric structure. The origin of observed ferromagnetism in doped ZnO nanocompounds at low temperature is correlated to the relevant mechanisms referred in the literature based on bound magnetic polarons (BMP), oxygen vacancies and zinc interstitials. The variation of room temperature ME voltage coefficient as function of magnetic field has been studied to investigate the interplay between charge carriers and spin ordering. The TM doped ZnO nanoparticles exhibit a strong ME coupling coefficient which facilitates their application in multiferroic devices. It has been shown through various characterizations that the doped ZnO nanocompounds are superior for various photonic, spintronic, magnetoelectric and multiferroic devices (tunnel magneto- resistance, magnetic sensor, multiple state memory devices). Photocatalytic reactions are processed through OH • and O 2 • radicals created on the surface of Mg and Nd modified ZnO nanoparticles. Photocatalytic activity enhances with higher doping concentration due to separation efficiency of the electron–hole pairs and modifications of physical and chemical properties. Both band gap energy and crystallite size are monitoring factors of photocatalytic performance. The observed superior photocatalytic properties in the Mg and Nd doped ZnO nanoparticles make them promising candidates for efficient sunlight-assisted photocatalytic effect, self-cleaning and photovoltaic applications. The prepared Mg and Nd doped ZnO nanoparticles are found to have sunlight assisted photcatalytic degradation property with a rate constant far higher to that of other II-VI semiconductor based compositions and have the capability to effectively and promptly clean the waste water from its dye based contaminants.

2021-10-04T00:00:00Z Rana, Chandan https://ir.vidyasagar.ac.in/jspui/handle/123456789/6271 2021-09-30T10:13:46Z 2021-08-17T00:00:00Z

Title: Growth and characterization of SnS nanostructured materials and Its applications Authors: Rana, Chandan Abstract: Semiconducting materials are promising materials in different field of nanoscience and technology. Tin Sulfide (SnS) is a significant and functional material in the semiconductor engineering. Considering the importance and various applications of SnS nanocrystals the work is mainly planned to grow SnS nanocrystals in a simple and cost effective way. The research works cover the growth, characterization and applications of SnS nanocrystals. The grown nanomaterials are applied in ethanol Gas Sensor, Si based Heterojunction Solar Cells and natural Dye Sensitized Solar Cells. The grown nanomaterials are also used to investigate the molecular interaction with protein. The SnS nanoparticles are grown with the variation of growth conditions as well as growth process to apply the materials in device fabrication. The effects of various growth conditions such as growth time, growth temperature, doped as well as bio synthesis on the growth of SnS nanocrystals have been investigated. The grown samples have been characterized structurally through X- ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and selected area diffraction (SEAD). The elemental compositions of the grown samples were analyzed through EDAX analysis. The optical properties of the grown materials have been investigated through UV-VIS absorption spectroscopy and photoluminescence (PL) spectroscopy. The optical band gap of samples has been calculated from optical absorption spectra. We have successfully synthesized SnS nanoparticles in a simple cost effective chemical reduction method by varying growth time i.e 3 hours to 14 hours. The grown samples have been ultra-sonicated in ethanol. The dispersed sample has been characterized structurally and optically. The crystallite size increases with increase of growth time. The band gap is maximum for 3h grown sample and decreases for samples grown for longer time. Photoluminescence spectra show possible defect states. Energy dispersive X-ray analysis shows that stoichiometry is well maintained for sample grown for 7h. SnS nanoparticles have been synthesized by simple wet chemical precipitation method using triethylamine (TEA) at room temperature. The grown samples were characterized by X-ray diffraction, Transmission electron microscopy (TEM), Field emission Scanning electron Microscopy (FESEM), Optical absorption spectra and PL. XRD image shows that the particles are orthorhombic structure. The TEM image shows that particles are chain-like shape and crystal size is about 20 nm. FESEM result also support the TEM result. AFM image shows that the surface roughness of the as prepared SnS nanocrystals is about 7.39 nm. Optical absorption study determines the band gap of the grown sample is about 1.76 eV. PL spectra of SnS shows an emission peak at 698.79 nm which is due to band to band transition. SnS nanocrystals were also synthesized by simple wet chemical precipitation method with the variation of growth temperature. The growth temperature was varied from 14 70 0 C. XRD results shows that the crystals are orthorhombic in phase. TEM images indicate that the grain sizes are almost spherical within the range 5 nm to 10 nm. A decrease in band gap is observed as particle size increase with increase of growth temperature. The temperature variation of p-type SnS nanocrystals indicates electrical conductivities were ranging from 0.020 to 0.037 Ohm 10 13 cm −3 to 1.54 × 10 14 cm −3 . -1 cm −1 and carrier concentrations were varying from 7.05 × SnS and SnS-Ag nanocomposite were synthesized by cost effective solvothermal technique. The as synthesized materials have been studied by structurally and optically through various tools and techniques. Structural characterization was investigated through by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Field Emission Scanning Electron Microscopy (FESEM). Elemental compositions were confirmed by 0 C to Electron Diffraction X-ray Analysis (EDAX). The Optical properties were characterized by UV-VIS absorption spectra, Photoluminescence spectra (PL) and Time Correlated Single Photon Counting (TCSPC). XRD results suggest that the samples are in orthorhombic structure in phase. The particle size has been estimated from TEM study. The calculated the band gap values were 2.04 eV and 1.80 eV of SnS and SnS-Ag nanocomposite respectively. A decrease in the band gap energy of SnS-Ag nanocomposite was observed compared to SnS. Pure SnS, Fe doped SnS and Mn doped SnS nanocrystals were prepared by simple chemical precipitation method. The structural and optical properties of the as prepared nanoparicles were studied. XRD results indicate the orthorhombic crystal phase of the as prepared samples. TEM results show that the crystal size increase with increase of doping and the grain size is greater for Mn doped SnS nanoparticles. A decrease in the band gap of Mn doped SnS was observed compared to pure as well as Fe doped SnS. SnS nanoparticles have been used to fabricate different types of devices in a cost effective way. The as grown time varying SnS NPs are deposited on glass for the fabrication of gas sensor. The sensing measurements were done at operating temperature ranging between 250 0 C and 300 °C for SnS based sensor. Here we have chosen three operating temperature i.e. 250 °C, 275 °C and 300 °C. The sensitivity in dry air conditions becomes maximum for 7 hours SnS sample at 300 °C. The percentage of sensitivity of 7 hours samples at 300°C was 61%. The gas sensing properties has been studied in dry air as well as humid conditions. The stability of the sensors has been also studied over 4 weeks and this indicates good stability. The SnS/Si as well as SnS:Ag/Si heterojunction solar cell has been fabricated. Open circuit voltage (V oc ), short circuit current (J sc ), fill factor (FF) as well as power conversion efficiency (η) were also calculated. The efficiency of SnS-Ag/Si heterojunction is greater than the SnS/Si heteojunction. The increase in conversion efficiency is due to the scattering effect from silver (Ag) nanoparticles. The as grown Fe doped and Mn doped SnS nanocrystals have been applied for fabrication of dye sensitized solar cell. Anthocyanin is a type of natural dye which was found in the various leaves of plants, flowers and fruits. These natural dyes are used as photo sensitizer in the fabricated dye sensitized solar cell. Acalypha Wilkesiana leaf extract was used as natural dye which can increase the power conversion efficiency of the fabricated solar cells. The performances of the fabricated dye sensitized solar cell were studied through the current (I)-voltage (V) study. The open circuit voltage (V factor (FF) as well as power conversion efficiency (η) were also studied. oc ), Short circuit current (Jsc), Fill SnS nanoparticles were also synthesized by the extract of Gymnema Sylvestre leaves in aqueous medium through green synthesis. The leaves extract of Gymnema Sylvestre plant have been employed as an efficient capping agent for the synthesis of SnS NPs. Low cost natural dye sensitized solar cells (DSSCs) based on chemically grown as well as green synthesized SnS NPs were fabricated. Acalypha Wilkesiana leaf extract was used as the natural dyes as a photosensitizer. The fabricated dye sensitized solar cell has been characterized through J-V study. Comparative studies of the efficiencies of the fabricated solar cell have been investigated. The fill factor, open circuit voltage and short circuit current density of the fabricated dye sensitized solar cell were also estimated. Finally, the bimolecular interaction of bovine serum albumin (BSA) with SnS materials has been studied through different tools and techniques. The BSA-SnS NPs interaction, complexation formation and conformational changes of protein (BSA) with the SnS nanoparticles were investigated by microscopic as well as spectroscopic measurements. The quenching of fluorescence spectra under the association of SnS nanoparticles was used to study the molecular interaction of bovine serum albumin (BSA) with SnS nanocrystals. The interaction and the formation of SnS@BSA bioconjugate also investigated using optical spectroscopy measurements. A spontaneous binding process happened in between BSA and SnS nanocrystals which were confirmed by UV–VIS and fluorescence spectra. A little red shift in the optical absorption spectra of protein (BSA) was detected due to binding of protein (BSA) with SnS NPs. The SnS nanoparticles quench the fluorescence spectra of bovine serum albumin. The Stern–Volmer quenching constant, Hill coefficient (n), nature of binding as well as binding constant (K b ) of the BSA – SnS NPs conjugates were also calculated. The objective of my thesis is to synthesize good quality SnS nanocrystals by cost effective methods. We have synthesized different sizes of the nanocrystals by changing the growth conditions as well as growth technique. The nanostructured SnS have been applied in fabrication of devices as ethanol gas sensor, heterojunction solar cell with Si, dye sensitized solar cell using natural dye. Also the molecular interaction of SnS nanocrystals with bovine serum albumin (BSA) is studied. The thesis consists of eight chapters.

2021-08-17T00:00:00Z Ibrahim, Sk. https://ir.vidyasagar.ac.in/jspui/handle/123456789/6013 2021-05-06T09:00:57Z 2021-04-19T00:00:00Z

Title: Photocurrent Generation and Photocatalytic Activity of Some Solution Processable RGO and MoS2 Based Composite Materials Authors: Ibrahim, Sk. Abstract: The performance of different nano scale materials change when composite is formed by attaching with different 2 dimensional materials. In my thesis I have tried to synthesis different reduced graphene oxide (RGO) and molybdenum disulfide (MoS2) based composite materials by simple low cost, solution processable and easy to achieve soft chemical route. All the synthesized composite materials were well characterized structurally and optically. The solar light induced photo current generation and photocatalytic activities of these materials were studied in detail. Solution processable Reduced Graphene Oxide – Zinc Sulfide (RGO- ZnS) composite has been synthesized by a simple single-step one-pot solvothermal route and is reported in chapter 2. As- synthesized composite was characterized structurally and optically. The photo induced charge generation of RGO-ZnS in solid phase as well as in solution phase has been investigated under simulated solar light illumination. RGO-ZnS thin film photo detector shows an excellent photocurrent generation with a high degree of reproducibility. The photosensitivity (ratio of photo to dark current) of the detector varies linearly with the light intensity. A remarkable increase of photo- reduction efficiency of RGO-ZnS compare to controlled-ZnS or controlled- RGO towards the reduction of 4-Nitrophenol was observed. Chapter 3 reports the solvothermal synthesis of Reduced Graphene Oxide – Cadmium Sulfide (RGO-CdS) nanorod composite. The as synthesized composite was characterized structurally and optically by XRD, TEM, XPS, Raman, UV-Vis and PL spectroscopy. The photocurrent generation in large area thin-film photodetector devise is also reported. The photo catalytic activity of the composite was examined by the degradation of tetracycline (TC) antibiotic under solar light illumination. An enhanced photocatalytic activity of CdS nanorods was observed after the incorporation of RGO in the composite. Here, RGO plays a key role towards efficient photo induced charge separation which subsequently decreases the electron-hole recombination possibility and improves the photocatalytic activity of the RGO-CdS composite. Chapter 4 describes the one pot single step solvothermal synthesis of reduced graphene oxide - cadmium zinc sulfide (RGO-CdZnS) composite. The reduction of graphene oxide (GO), synthesis of Cd 0.5 Zn 0.5 S nanorod and decoration of nanorods onto RGO sheet was done simultaneously. The structural, morphological and optical properties were studied thoroughly by different techniques, such as XRD, TEM, UV-Vis and PL. The PL intensity of CdZnS nanorods quench significantly after the attachment of RGO, confirms photo induced charge transformation from CdZnS nanorods to RGO sheet through the interface of RGO-CdZnS. An excellent photo current generation in RGO-CdZnS thin film device has been observed under simulated solar light irradiation. The photo current as well as photo sensitivity increases linearly with the solar light intensity. Our study establishes that, the synergistic effect of RGO and CdZnS in the composite is capable of getting promising applications in the field of optoelectronic devising. The photocatalytic activity of the RGO-CdZnS composite was investigated towards the degradation of 4-Nitrophenol. A notable increase of photocatalytic efficiency of RGO-CdZnS compare to controlled CdZnS was observed. Here RGO plays a crucial role to efficient photo induced charge separation from the CdZnS, and decreases the electron-hole recombination probability and subsequently enhanced the photocatalytic activity of the RGO-CdZnS composite material under simulated solar light irradiation. This work highlights the potential application of RGO-based materials in the field of photocatalytic degradation of organic water pollutant. In chapter 5, the synthesis of a molybdenum disulfide–zinc phthalocyanine (MoS synthesis of MoS2 2 -ZnTTBPc) composite is reported, where the scalable was done by a simple solvothermal route followed by the sono-chemical attachment of ZnTTBPc. The as-synthesized material acquires a monolayer with an average thickness of 2 nm. Raman studies give sufficient evidence of the existence of monolayer MoS2 in the MoS composite. The highly exfoliated abundant active sites available on the 2D surface of MoS2 efficiently act as photocatalytic reaction centres. Moreover, the high energy transfer efficiency, authenticated by steady-state photoluminescence and time-correlated single photon counting studies, makes the MoS2 -ZnTTBPc (3:1) composite a promising optoelectronic and photocatalytic material. The photo-generated electrons from the conduction 2-ZnTTBPc band of ZnTTBPc transfer to the conduction band of MoS2 leaving holes at the valence band of ZnTTBPc and simultaneously the photo-generated holes from the valence band of MoS2 transfer to the valence band of ZnTTBPc. These well-separated charges reduce the electron–hole recombination probability in the composite, subsequently offering a positive synergetic effect among ZnTTBPc and single-layered MoS2 sheets. It could thus have promise as a new photo-catalyst towards removing different organic pollutants and for other optoelectronic devices.

2021-04-19T00:00:00Z Pradhan, Ashok Kr. https://ir.vidyasagar.ac.in/jspui/handle/123456789/6012 2021-05-06T08:29:40Z 2021-04-04T00:00:00Z

Title: Effect of Mo substitution on structural, dielectric, electrical and magnetic properties of Cobalt-Zinc spinel ferrites Authors: Pradhan, Ashok Kr. Abstract: Magnetic materials are widely used in different technological applications like, power generation, communication, data storage and retrieval, sensors etc. Continuous efforts by many researchers during the past many decades have led to the discovery of many novel magnetic materials and properties like high-T C oxide superconductors, giant and colossal magnetoresistive materials, high magneto-dielectric material, giant magnetostrictive materials, etc. Here we report the synthesis of Molybdenum substituted Cobalt-Zinc inverse spinel ferrites and their characterization with structural, dielectric, complex impedance, electric modulus, electrical conductivity and magnetic properties. All the polycrystalline Mo doped Co-Zn ferrite samples was prepared with the help of conventional ceramic technique. The XRD pattern affirms the formation of exact cubic inverse spinel structure with having Fd3m space group. The calculated lattice constant and grain size was observed to be increased with Mo concentration. The temperature variation of dielectric constant recommend that the origin of dielectric constant in ferrite is four types of polarization. Also the temperature reliance of dielectric constant can be clarified based on thermally assisted relaxation mechanism. The dielectric dispersion of all the sample can be best illuminated in light of Maxwell- Wagner type of interfacial polarization in agreement with Koop’s phenomenological theory. The variation of dielectric loss tangent with temperature and frequency reveals very low value of tanδ at room temperature and high frequency. Both the real and imaginary part of impedance decreased with frequency due to decrease in space charge polarization. The Zʺ vs. f curves have some broad Debye peaks at a hopping frequency and peaks are shifted to higher temperature at high frequency due to increase in rate of electron hopping at higher temperature. The Cole-Cole plot suggest that there is a contribution of only grain boundary in the conduction process and also existance of non-Debye type relaxation in the materials was verified. All the curves of electric modulus were well fitted according to modified Kohlrausch- Williums-Watts (KWW) function proposed by Bergman. The scaling behavior gives the concrete evidence for existence of non-Debye type relaxation in the present samples. The activation energy of all the samples was calculated from both the impedance and modulus spectra. The variation of ac conductivity with frequency predict that the conduction is because of the correlated barrier hopping mechanism. Also all the curves were well fitted according to Jonscher’s single power law. The temperature dependence of ac conductivity displayed the semiconducting nature of the sample. The activation energy of all the samples in both paramagnetic and ferrimagnetic region was estimated using the Arrhenius relation. It has been seen that the value of activation energy in ferrimagnetic state is lower than that in paramagnetic state due to the fact that ferrimagnetic state is ordered than the paramagnetic state. The variation of magnetic moment with temperature showed the increase of both maturation magnetization and Curie temperature due to Mo substitution. The low value of Tc might be because of the disordered cation distribution in the material under study. Also the variation of real permeability with temperature have the similar trend as M-T plot.

2021-04-04T00:00:00Z