Tanujjal Bora | Sultan Qaboos University (original) (raw)

Papers by Tanujjal Bora

We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods t... more We report the synthesis of silver (Ag) nano-spheres (NS) supported on zinc oxide (ZnO) nanorods through two step mechanism, using open vessel microwave reactor. Direct reduction of ZnO from zinc nitrates was followed by deposition precipitation of the silver on the ZnO nanorods. The supported Ag/ZnO nanoparticles were then characterized by electron microscopy, X-ray diffraction, FTIR, photoluminescence and UV–vis spectroscopy. The visible light photocatalytic activity of Ag/ZnO system was investigated using a test contaminant, methylene blue (MB). Almost complete removal of MB in about 60 min for doses higher than 0.5 g/L of the Ag/ZnO photocatalyst was achieved. This significant improvement in the photocatalytic efficiency of Ag/ZnO photocatalyst under visible light irradiation can be attributed to the presence of Ag nanoparticles on the ZnO nanoparticles which greatly enhances absorption in the visible range of solar spectrum enabled by surface plasmon resonance effect from Ag nanoparticles.

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Controlled light coupling from surrounding to the cladding mode of zinc oxide (ZnO) nanorod coate... more Controlled light coupling from surrounding to the cladding mode of zinc oxide (ZnO) nanorod coated multimode optical fiber induced by the light scattering properties of the nanorod coating and their applications of sensing are reported here. A dense and highly ordered array of ZnO nanorods is grown on the cladding of silica fibers by using low temperature hydrothermal process and the effect of the hydrothermal growth conditions of the nanorods on the light scattering and coupling to the optical fibers is experimentally investigated. The nanorod length and its number per unit area are found to be most crucial parameters for the optimum side coupling of light into the fibers. Maximum excitation of the cladding mode by side coupling of light is obtained with ZnO nanorods of length ∼2.2 μm, demonstrating average coupling efficiency of ∼2.65%. Upon exposure to different concentrations of various chemical vapors, the nanorod coated fibers demonstrated significant enhancement in the side coupled light intensity, indicating the potential use of these ZnO nanorod coated fibers as simple, low cost and efficient optical sensors. The sensor responses to methanol, ethanol, toluene and benzene vapor were investigated and compared, while the effect of humidity in the sensing environment on the sensor performance was explored as well.

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Nanocomposites of vertically aligned zinc oxide (ZnO) nanorod arrays incorporated with gold (Au) ... more Nanocomposites of vertically aligned zinc oxide (ZnO) nanorod arrays incorporated with gold (Au) nanoparticles have been used as photoelectrodes to fabricate dye sensitized solar cells (DSSCs). Due to the surface plasmon resonance of the Au nanoparticles, the nanocomposite photoelectrodes demonstrate enhancement in the visible light absorption resulting in ~8% higher photocurrent compared to ZnO photoelectrode based DSSCs fabricated without any Au nanoparticles. In addition to the higher optical absorption due to the gold nanoparticles, a Schottky barrier forms at the ZnO/Au interface preventing the back electron transfer from the conduction band of the semiconductor nanorods to the redox electrolyte providing improvement in the charge separation at the nanocomposite photoelectrode. Upon incorporation of Au nanoparticles, the overall efficiency of the DSSC increased from 2.41% to 3.27%. The role of Au nanoparticles on the performance of the DSSCs for varying concentration of the Au nanoparticles as well as the post-growth annealing treatment of the nanocomposite photoelectrode is reported.

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Water on Earth is a precious and finite resource, which is endlessly recycled in the water cycle.... more Water on Earth is a precious and finite resource, which is endlessly recycled in the water cycle. Water, whose physical, chemical, or biological properties have been altered due to the addition of contaminants such as organic/inorganic materials, pathogens, heavy metals or other toxins making it unsafe for the ecosystem, can be termed as wastewater. Various schemes have been adopted by industries across the world to treat wastewater prior to its release to the ecosystem, and several new concepts and technologies are fast replacing the traditional methods. This article briefly reviews the recent advances and application of nanotechnology for wastewater treatment. Nanomaterials typically have high reactivity and a high degree of functionalization, large specific surface area, size-dependent properties etc., which makes them suitable for applications in wastewater treatment and for water purification. In this article, the application of various nanomaterials such as metal nanoparticles, metal oxides, carbon compounds, zeolite, filtration membranes, etc., in the field of wastewater treatment is discussed.

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This work presents a scheme for in situ monitoring of thin-film growth. A fiber-optic sensor base... more This work presents a scheme for in situ monitoring of thin-film growth. A fiber-optic sensor based on Fabry–Perot interferometric technique has been established for the first time to monitor in situ growth of thin films. This was applied for determining thickness of cadmium sulfide (CdS) thin films during growth. The fabrication process of CdS film was carried out in 30 mM cadmium acetate and thioacetamide solution at 60°C temperature. The estimated thickness determined during the growth was verified by scanning electron microscopy. This study shows that in situ measurement of the thickness of thin films is feasible by this new technique, and a close match of the estimated thickness was achieved.

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In recent years, nanotechnology has gained significant interest for applications in the medical f... more In recent years, nanotechnology has gained significant interest for applications in the medical field. In this regard, a utilization of the ZnO nanoparticles for the efficient degradation of bilirubin (BR) through photocatalysis was explored. BR is a water insoluble byproduct of the heme catabolism that can cause jaundice when its excretion is impaired. The photocatalytic degradation of BR activated by ZnO nanoparticles through a non-radiative energy transfer pathway can be influenced by the surface defect-states (mainly the oxygen vacancies) of the catalyst nanoparticles. These were modulated by applying a simple annealing in an oxygen-rich atmosphere. The mechanism of the energy transfer process between the ZnO nanoparticles and the BR molecules adsorbed at the surface was studied by using steady-state and picosecond-resolved fluorescence spectroscopy. A correlation of photocatalytic degradation and time-correlated single photon counting studies revealed that the defect-engineered ZnO nanoparticles that were obtained through post-annealing treatments led to an efficient decomposition of BR molecules that was enabled by Förster resonance energy transfer.

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A novel concept is introduced that utilizes the scattering properties of zinc oxide nanorods to c... more A novel concept is introduced that utilizes the scattering properties of zinc oxide nanorods to control light guidance
and leakage inside optical fibers coated with nanorods. The effect of the hydrothermal growth conditions of the
nanorods on light scattering and coupling to optical fiber are experimentally investigated. At optimum conditions,
5% of the incident light is side coupled to the cladding modes. This coupling scheme could be used in different
applications such as distributed sensors and light combing. Implementation of the nanorods on fiber provides low
cost and controllable nonlithography-based solutions for free space to fiber coupling. Higher coupling efficiencies
can be achieved with further optimization.

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Photocatalytic activities of hydrothermally synthesised ZnO nanorod films in synergism with visib... more Photocatalytic activities of hydrothermally synthesised ZnO nanorod films in synergism with visible light have been studied. Influence of each of the synthesis parameters, like concentration of precursor solution, relative concentration of hexamine and zinc nitrate, growth time, growth temperature, pre-growth seeding, post-growth annealing, concentration and pH of the contaminant suspension, and light source have been investigated. Appraisal of photocatalytic efficiencies of all the synthesised samples have been done on degradation of aqueous Methylene Blue (MB) solution under artificial/ambient light. Maximum photocatalytic activities were obtained when ZnO nanorods were synthesised with equimolar concentration of 10 mM hexamine and zinc nitrate grown for 15 hr at 90°C with post-synthesis annealing at 250°C in air. Solar irradiation was found more effective than artificial white light while the activity increased exponentially with pH value of the contaminant suspension

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Light-harvesting nanohybrids (LHNs) are systems composed of an inorganic nanostructure associated... more Light-harvesting nanohybrids (LHNs) are systems composed of an inorganic nanostructure associated with an organic pigment that have been exploited to improve the light-harvesting performance over individual components. The present study is focused on developing a potential LHN, attained by the functionalization of dense arrays of ZnO nanorods (NRs) with a biologically important organic pigment hematoporphyrin (HP), which is an integral part of red blood cells (hemoglobin). Application of spectroscopic techniques, namely, Fourier transform infrared spectroscopy (FTIR) and Raman scattering, confirm successful monodentate binding of HP carboxylic groups to Zn2+ located at the surface of ZnO NRs. Picosecond-resolved fluorescence studies on the resulting HP–ZnO nanohybrid show efficient electron migration from photoexcited HP to the host ZnO NRs. This essential photoinduced event activates the LHN under sunlight, which ultimately leads to the realization of visible-light photocatalysis (VLP) of a model contaminant Methylene Blue (MB) in aqueous solution. A control experiment in an inert gas atmosphere clearly reveals that the photocatalytic activity is influenced by the formation of reactive oxygen species (ROS) in the media. Furthermore, the stable LHNs prepared by optimized dye loading have also been used as an active layer in dye-sensitized solar cells (DSSCs). We believe these promising LHNs to find their dual applications in organic electronics and for the treatment of contaminant wastewater

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Different-sized, 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs) have been prep... more Different-sized, 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs) have been prepared in aqueous solution, and potential cosensitization of such QDs in ZnO nanorod (NR)-based dye-sensitized solar cells (DSSCs) has been established. The results presented in this study highlight two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs to ZnO semiconductor via photoinduced electron transfer (PET) and (2) an indirect excitation of the sensitizing dye (SD) N719 molecules by funneling harvested light via Förster resonance energy transfer (FRET). The steady-state and picosecond-resolved luminescence measurements were combined to clarify the process of PET and FRET from the excited QDs to ZnO NR and SD N719, respectively. On the basis of these advantages, the short-circuit current density and the photoconductivity of the QD-assembled DSSCs with distinct architectures are found to be much higher than DSSCs fabricated with N719 sensitizer only.

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Electrical characteristics of 1-D zinc oxide (ZnO) nanorod-based dye-sensitized solar cells (DSSC... more Electrical characteristics of 1-D zinc oxide (ZnO) nanorod-based dye-sensitized solar cells (DSSCs) were experimentally measured and followed by theoretical analysis using simple one-diode model. Defect sites (mostly oxygen vacancies) in ZnO are typically responsible for lower DSSC performance, which are removed by annealing the ZnO nanorods at high temperatures up to 450 °C. The DSSC performances with respect to the different annealing temperatures (250 °C, 350 °C, and 450°C) were determined by measuring their I-V characteristics at 1-sun irradiation (AM 1.5G). The variations in series and shunt resistances of DSSC were estimated by fitting the experimental I-V characteristics with the ideal I-V curve obtained from the one-diode equivalent model of the DSSC. By increasing annealing temperature, reduction in the series resistance Rs of the DSSCs with a subsequent increase in the shunt resistance Rsh was obtained. Annealing temperature of 350 °C was found to be optimum at which maximum DSSC performances with 1-cm2 cell active area showing minimum Rs (0.02 kΩ) with high Rsh (1.08 kΩ) values were observed. Reduction in the active area of the DSSCs from 1 to 0.25 cm2 and further to 0.1 cm2 demonstrated improved device performance with ~56% and ~24% enhancement in the fill factor and open-circuit voltage Voc, respectively, due to the reduced sheet resistance and lower recombination rate resulting low series resistance and high shunt resistance, respectively. At the optimum annealing temperature, maximum DSSC efficiency of 4.60% was obtained for the 0.1-cm2 cell active area.

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Nanorod arrays of zinc oxide–zinc stannate core–shell photoelectrodes were prepared by a simple h... more Nanorod arrays of zinc oxide–zinc stannate core–shell photoelectrodes were prepared by a simple hydrothermal process and cadmium sulfide (CdS) quantum dot sensitized solar cells were fabricated. The photocurrent density of the core–shell photoelectrode was found to improve by ∼2.4 times compared to ZnO nanorod photoelectrodes, due to improved surface area and charge transport in the core–shell photoelectrodes. With a thin layer of ZnS on the CdS quantum dot surface, the core–shell quantum dot sensitized solar cell demonstrated maximum power conversion efficiency of 1.24% under 1 sun illumination (AM1.5).

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Zinc oxide (ZnO) nanorods decorated with gold (Au) nanoparticles have been synthesized and used t... more Zinc oxide (ZnO) nanorods decorated with gold (Au) nanoparticles have been synthesized and used to fabricate dye-sensitized solar cells (DSSC). The picosecond-resolved, time-correlated single-photon-count (TCSPC) spectroscopy technique was used to explore the charge-transfer mechanism in the ZnO/Au-nanocomposite DSSC. Due to the formation of the Schottky barrier at the ZnO/Au interface and the higher optical absorptions of the ZnO/Au photoelectrodes arising from the surface plasmon absorption of the Au nanoparticles, enhanced power-conversion efficiency (PCE) of 6.49% for small-area (0.1 cm2) ZnO/Au-nanocomposite DSSC was achieved compared to the 5.34% efficiency of the bare ZnO nanorod DSSC. The TCSPC studies revealed similar dynamics for the charge transfer from dye molecules to ZnO both in the presence and absence of Au nanoparticles. A slower fluorescence decay associated with the electron recombination process, observed in the presence of Au nanoparticles, confirmed the blocking of the electron transfer from ZnO back to the dye or electrolyte by the Schottky barrier formed at the ZnO/Au interface. For large area DSSC (1 cm2), ~130% enhancement in PCE (from 0.50% to 1.16%) was achieved after incorporation of the Au nanoparticles into the ZnO nanorods.

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