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Manu Jaiswal
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Manu Jaiswal
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Manu Jaiswal
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Jaiswal, Manu
Jaiswal, M.
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7 results
Now showing 1 - 7 of 7
- PublicationProbing the charge recombination in rGO decorated mixed phase (anatase-rutile) TiO2 multi-leg nanotubes(01-11-2016)
;Rambabu, Y.; Recombination of photo-generated charges is one of the most significant challenges in designing efficient photo-anode for photo electrochemical water oxidation. In the case of TiO2, mixed phase (anatase-rutile) junctions often shown to be more effective in suppressing electron-hole recombination compared to a single (anatase or rutile) phase. Here, we report the study of bulk and surface recombination process in TiO2 multi-leg nanotube (MLNTs) anatase-rutile (A-R) junctions decorated with reduced graphene oxide (rGO) layers, through an analysis of the photo-current and impedance characteristics. To quantify the charge transport/transfer process involved in these junctions, holes arriving at the interface of semiconductor/electrolyte were collected by adding H2O2 to the electrolyte. This enabled us to interpret the bulk and surface recombination process involved in anatase/rutile/rGO junctions for photo-electrochemical water oxidation. We correlated this quantification to the electrochemical impedance spectroscopy (EIS) measurements, and showed that in anatase/rutile junction the increase in PEC performance was due to suppression in electron-hole recombination rate at the surface states that effectively enhances the hole transfer rate to the electrolyte. On the other hand, in rGO wrapped A-R MLNTs junction it was due to both phenomenon i.e decrease in bulk recombination rate as well as increase in hole transfer rate to the electrolyte at the semiconductor/electrolyte interface. - PublicationGraphene oxide modified TiO2 micro whiskers and their photo electrochemical performance(01-05-2016)
;Rambabu, Y.; Harnessing the solar energy and producing clean fuel hydrogen through efficient photoelectrochemical water splitting has remained one of the most challenging endeavors in materials science. The core problem is to develop a suitable photo-catalyst material that absorbs a significant part of the solar spectrum and produces electron-hole pairs that can be easily separated without recombination. In the recent times, the composite of Titanium dioxide with graphene have been investigated to explore the advantages of both class of materials. Here we report on the photo-electrochemical properties of reduced graphene oxide functionalised TiO2 whiskers. The TiO2 whiskers are obtained from potassium titanium oxide (KTi8O16) synthesized through hydrothermal technique followed by ion exchange method and heat treatment. Graphene oxide was deposited on the as repared TiO2 whiskers using hydrothermal method. As formed samples were characterized by Raman pectroscopy to confirm the presence of reduced graphene oxide (RGO) attached to TiO2 whiskers. Comparative photo electrochemical studies were carried out for TiO2 and reduced graphene oxide modified TiO2 whiskers. Among these, RGO modified TiO2 whiskers show significantly higher photo current density possibly due to enhancement in charge separation ability and longer electron life times. - PublicationEffect of annealing temperature on the phase transition, structural stability and photo-electrochemical performance of TiO2 multi-leg nanotubes(01-12-2016)
;Rambabu, Y.; In this report we study the effect of annealing temperature on the structural stability, phase transformation and photo-electrochemical performance of TiO2 multi-leg nanotubes. Multi-leg nanotubes were synthesized using electrochemical anodization method, and as synthesized nanotubes were annealed in air at the temperatures ranging from 500 to 900 °C.We observed that multi-leg morphology is preserved upto 900 °C and a dominant rutile phase is observed at this temperature. X-ray diffraction and Raman spectra measurements were carried out to study the crystallite size, phase transformation and phonon confinement effects. The multi-leg nanotubes annealed at 900 °C shows enhanced photo-electrochemical performance; this is attributed to mixed phase, increase in crystallite size and decrease in defects. - PublicationHigh photoelectrochemical performance of reduced graphene oxide wrapped, CdS functionalized, TiO2 multi-leg nanotubes(17-04-2020)
;Rambabu, Y. ;Dhua, Swati; Absorption of visible light and separation of photogenerated charges are two primary pathways to improve the photocurrent performance of semiconductor photoelectrodes. Here, we present a unique design of tricomponent photocatalyst comprising of TiO2 multileg nanotubes (MLNTs), reduced graphene oxide (rGO) and CdS nanoparticles. The tricomponent photocatalyst shows a significant red-shift in the optical absorption (∼2.2 eV) compared to that of bare TiO2 MLNTs (∼3.2 eV). The availability of both inner and outer surfaces areas of MLNTs, the visible light absorption of CdS, and charge separating behavior of reduced graphene oxide layers contribute coherently to yield a photocurrent density of ∼11 mA cm-2 @ 1 V vs. Ag/AgCl (100 mW cm-2, AM 1.5 G). Such a high PEC performance from TiO2/rGO/CdS photoelectrode system has been analyzed using diffused reflectance (DRS) and electrochemical impedance (EIS) spectroscopy techniques. The efficient generation of charge carriers under light irradiation and easy separation because of favourable band alignment, are attributed to the high photoelectrochemical current density in these tricomponent photocatalyst systems. - PublicationEnhanced photoelectrochemical performance of multi-leg TiO2 nanotubes through efficient light harvesting(29-07-2015)
;Rambabu, Y.; Multi-leg TiO2 nanotubes have been synthesised by electrochemical anodisation of Ti foils with suitable optimisation of the electrolyte (containing NH4F and HF) composition and concentration. As a result, multi-leg nanotube morphology shows a 4-fold enhancement in photocurrent density compared with that of compact tubes of comparable length under UV-VIS (320-500 nm) light illumination. We attribute this enhancement in photocurrent to efficient light scattering within the multi-leg morphology and the availability of a large contact area with the electrolyte compared to that of compact nanotubes. A model has been presented for light trapping and scattering ability on the basis of the graded refractive index behaviour associated with multi-leg nanotubes. Such graded refractive index behaviour is found to reduce specular reflectance, leading to a greater scattering of light into the nanotube structure. The diffused reflectance spectra confirm higher scattering in the multi-leg nanotube arrays, which indicates greater light harvesting by the multi-leg nanotube arrays. - PublicationPhoto-electrochemical properties of graphene wrapped hierarchically branched nanostructures obtained through hydrothermally transformed TiO2 nanotubes(12-09-2017)
;Rambabu, Y.; Hierarchically structured nanomaterials play an important role in both light absorption and separation of photo-generated charges. In the present study, hierarchically branched TiO2 nanostructures (HB-MLNTs) are obtained through hydrothermal transformation of electrochemically anodized TiO2 multi-leg nanotubes (MLNT) arrays. Photo-anodes based on HB-MLNTs demonstrated 5 fold increase in applied bias to photo-conversion efficiency (%ABPE) over that of TiO2 MLNTs without branches. Further, such nanostructures are wrapped with reduced graphene oxide (rGO) films to enhance the charge separation, which resulted in ∼6.5 times enhancement in %ABPE over that of bare MLNTs. We estimated charge transport (η tr) and charge transfer (η ct) efficiencies by analyzing the photo-current data. The ultra-fine nano branches grown on the MLNTs are effective in increasing light absorption through multiple scattering and improving charge transport/transfer efficiencies by enlarging semiconductor/electrolyte interface area. The charge transfer resistance, interfacial capacitance and electron decay time have been estimated through electrochemical impedance measurements which correlate with the results obtained from photocurrent measurements. - PublicationEnhanced photo-electrochemical performance of reduced graphene-oxide wrapped TiO2 multi-leg nanotubes(01-01-2016)
;Rambabu, Y.; We report the synthesis and photo-electrochemical properties of reduced graphene oxide wrapped multi-leg TiO2 nanotubes (MLNTs). The TiO2 nanotubes fabricated by electrochemical anodization were subsequently wrapped with graphene oxide (GO)/ reduced graphene oxide (rGO) using silanization method. Use of separated (multi-leg/branched) TiO2 nanotubes and suitable optimization of the silanization parameters helped to achieve near-conformal wrapping of the nanotubes by GO/rGO layers. The photo-electrochemical performance of rGO/TiO2 samples with multi-leg morphology were studied in 0.5 M Na2SO4 aqueous solution under the illumination of simulated sunlight (AM 1.5G, 100 mW/cm2) and was compared with rGO modified regular (compact) TiO2 nanotubes under similar conditions. Substantial improvement in "applied bias photon to current conversion efficiency" (% ABPE) was observed for rGO wrapped TiO2 multi-leg nanotubes over that of nanotubes without wrapping. Diffuse reflectance spectroscopy was performed to investigate the light scattering capability of the nanotubes arrays, which revealed higher scattering and hence better light harvesting ability of MLNT's. The electrochemical impedance spectroscopy was used to study the charge transfer characteristics across rGO/TiO2 interface. The results showed a decrease in charge transfer resistance for rGO wrapped TiO2 multi-leg nanotubes which helped in the enhancement of photo-electrochemical performance.