Recent advancement of multi elements codoped-TiO2 in photocatalytic application demands to unders... more Recent advancement of multi elements codoped-TiO2 in photocatalytic application demands to understand the role of each dopant involved in catalytic mechanism. Here we explore the VN-codoped TiO2 system intended to understand the role played by each dopant in synergistic enhancement in performance of TiO2 semiconductor. The concentrations of V and N were varied and optimized to improve photocatalytic activity. The photocatalytic decomposition of phenol and dye in aqueous solution under visible light was used as a probe reaction to evaluate their performance. With increase in vanadium concentration in VN-codoped TiO2 considerable improvement in visible light absorption is observed as compared to nitrogen doping due to the effective narrowing of the band gap from 3.12 eV to 1.88 eV. At low concentration, the energy levels formed by both V and N act as the trapping centers for photo-generated charges to suppress recombination process as indicated by PL and TRPL results. As V concentration increases, recombination centers are created in form of oxygen vacancies as confirmed by XPS. Addition of N partially fills these oxygen vacancies to reduce the amount of recombination and prolong the lifetime of charge carriers.V improves the visible light absorption to generate large number of electron-hole pair while N reduces the recombination of electron-hole pair creating the synergetic effect to produce three times better performance than pure TiO2.
In this paper we investigate the possibility of formation of AnataseTiO 2 and nitrogen dopedTiO 2... more In this paper we investigate the possibility of formation of AnataseTiO 2 and nitrogen dopedTiO 2 thin films prepared by varying cathodic arc evaporation parameters such as ratio of Ar, O 2 and N 2 gas flow, bias voltage and cathode current. Nanostructured titanium dioxide (TiO 2 ) and nitrogen doped titanium dioxide (N-TiO 2 ) thin films were deposited on soda lime silicate glass samples using Cathodic Arc Physical Vapor Deposition (CA-PVD). X-ray diffraction (XRD), UV-Vis spectrophotometer and scanning electron microscope (SEM) technologies were used to characterize the film. The photocatalytic activities of the samples were tested on the degradation of methylene blue (MB) dye.Crystalline size and phases of the thin films were calculated by using XRD. Morphology and elemental analysis of the thin films were carried by SEM-EDAX. Here, we intensely say that as deposited thin films gives better degradation efficiency without any additional process.
In the present manuscript, we explore the VN-codoped TiO system intended to understand the role p... more In the present manuscript, we explore the VN-codoped TiO system intended to understand the role played by each dopant in synergistic enhancement in performance of TiO photocatalyst. The photocatalytic decomposition of organic pollutants in aqueous solution under visible light was used as a probe reaction to evaluate the performance of VN-codoped TiO samples with different V and N concentrations. An optical measurement of VN-codoped TiO shows considerable improved visible light absorption with increase in V-concentration as compared to increase in N concentration, which was due to the effective narrowing of the band gap by V-doping. The energy levels formed by N-dopants act as the trapping centers for photogenerated holes to suppress recombination process as indicated by PL and TRPL results. It is also observed that at high V-concentrations recombination centers are created in the form of oxygen vacancies as indicated by XPS and PL. In VN-codoped TiO , addition of N partially fills t...
Journal of Photochemistry and Photobiology A: Chemistry, 2021
Abstract The photocatalytic performance of gC3N4 is majorly restricted by insufficient collection... more Abstract The photocatalytic performance of gC3N4 is majorly restricted by insufficient collection of photogenerated charges on the surface during reaction due to highly dense stacking of lamellar structures with lateral size ranging in microns. This deficiency can be overcome by forming thin nanoflakes by systematically breaking the weak bonds that hold the gC3N4 framework without destroying the basic heptazine unit. With this aim, herein, a combination of three different strategies was implemented to design and develop, Ag-loaded and P-doped gC3N4 nanoflakes (Ag3-P1-NF-gC3N4). Using a systematic synthesis method, bulk gC3N4 was first converted into thin nanosheets, followed by fragmentation into nanoflakes, with a planar size up to 100 nm. P doping to replace the corner C atoms in the gC3N4 matrix (forming P-N bonds) and intercalation of plasmonic Ag nanoparticles within the interlayers also assists in the bifurcation of the stacked layers and formation of nanoflakemorphology. These strategies result in a significant increase in BET surface area to ∼196 m2/g from 12 m2/g of bulk gC3N4. Improved inter-planar and intra-planar charge mobility was recorded as a result of the reduced sizes. Doping with P also causes higher absorption of the visible spectrum in gC3N4 while the formation of heterojunction with Ag nanoparticles induces efficient separation of photo-generated charges. All these promoting photo-physical properties lead to an outstanding photocatalytic activity towards degradation of aqueous pollutants with reaction rates ∼20 times higher than bulk gC3N4. Complete mineralization of the pollutant and formation of non-toxic byproducts was also confirmed with suitable chromatography techniques.
C 16 H15ClN 2 O 2 , monoclinic, P21/c (no. 14), a = 33.491(11) Å, b = 7.124(2) Å, c = 6.1977(19) ... more C 16 H15ClN 2 O 2 , monoclinic, P21/c (no. 14), a = 33.491(11) Å, b = 7.124(2) Å, c = 6.1977(19) Å, β = 92.212(6)°, V = 1477.6(8) Å 3 , Z = 4, Rgt(F) = 0.0418, wR ref (F 2) = 0.1193, T = 296(2) K. CCDC no.: 1828200 Tables 1 and 2 contain details on crystal structure and measurement conditions and a list of the atoms including atomic coordinates and displacement parameters.
Study of corrosion properties of CrN and multilayer CrN/Cr coating at different electrolyte tempe... more Study of corrosion properties of CrN and multilayer CrN/Cr coating at different electrolyte temperatures deposited on stainless steel by vacuum arc process
A (q, k, t)-design matrix is an m × n matrix whose pattern of zeros/non-zeros satisfies the follo... more A (q, k, t)-design matrix is an m × n matrix whose pattern of zeros/non-zeros satisfies the following design-like condition: each row has at most q non-zeros, each column has at least k non-zeros and the supports of every two columns intersect in at most t rows. We prove that for m ≥ n, the rank of any (q, k, t)-design matrix over a field of characteristic zero (or sufficiently large finite characteristic) is at least
Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °... more Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °C, and 500 °C for 60 min. The exchanged glasses were either annealed at 500 °C for 60 min or swift heavy ion (SHI) irradiated using 120 MeV Ag 9+ ions at a fluence of 5 x 10 12 ions/cm 2 . Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any postexchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.
Ag–TiO2 nanocomposite systems have been investigated with the aim of understanding the relationsh... more Ag–TiO2 nanocomposite systems have been investigated with the aim of understanding the relationship between the photocatalytic efficiency and the contributions of various structures resulting in charge carrier separation, charge transfer and extension of light absorption to the visible range.
Abstract Lattice location of B in TiO2 is tuned to determine its effect on the photocatalytic act... more Abstract Lattice location of B in TiO2 is tuned to determine its effect on the photocatalytic activity of Co-B codoped TiO2. Sol–gel method was used to synthesize the samples. The concentrations of Co and B were first optimized by maximizing the photocatalytic activity for the monodoped (Co or B)-TiO2. In addition to the DFT calculations for discovering new energetic levels introduced in TiO2 by codoping, various characterization techniques were used to determine the dopant lattice sites in TiO2 and interactions between them; and also determining their consequences on electronic, morphological, structural, and optical properties. At low concentration of B-doping (1 at.%), B occupies the interstitial site (Bint), but as the concentration increases (2 at.% and 3 at.%) B also occupies substitutional O position (Bsub) in addition to Bint to form TiO2 containing Bint+sub. Both these B-doped TiO2 showed improved photocatalytic activity attributed to effective charge separation obtained for TiO2–Bint due to the formation of shallow energy level while higher visible light absorption is achieved with TiO2–Bint+sub owing to the presence of two deep energy levels in the band gap as confirmed by DFT calculations. In the case of Co doping, the band gap of TiO2 is reduced but the recombination rates are always high and are caused by the formation of Co states in the band gap. For Co monodoped TiO2, the photocatalytic activity is low for all the concentrations considered, except for very low concentration of Co (0.1 at.%). Two opposite effects were observed when small amount of Co (0.1 at.%) was codoped with Bint or Bint+sub. In particular, the photocatalytic degradation rate of organic aqueous pollutants (p-nitrophenol and rhodamine B dye) reduces for TiO2–Co–Bint whereas it is enhanced remarkably for TiO2–Co–Bint+sub as compared to (Co or B) monodoped (∼2.1 times) and undoped (∼7.8 times) TiO2. Higher photocatalytic activity observed in Co-doped TiO2–Bint+sub is discussed in terms of the interactions of Co with B at two different lattice positions in TiO2 and the synergistic effect created by higher visible light absorption and the improved charge separation.
Journal of Environmental Chemical Engineering, 2020
Abstract In the present research Bi2MoO6(BMO) QDs (0D) and reduce graphene oxide nanosheet (2D) (... more Abstract In the present research Bi2MoO6(BMO) QDs (0D) and reduce graphene oxide nanosheet (2D) (BMO/rGO)(0D/2D) heterojunction with different weight ratio of GO nanosheet were synthesized using facile method. XRD, UV–vis spectroscopy, XPS, FTIR, BET, PL, TRPL, TEM/HRTEM, ESR and photoelectrochemical (PEC) measurements were used for the characterization and understanding the enhancement effect on photoactivity of the synthesis photocatalyst. The BMO (0D) QDs provide more active sites and short diffusion length of photogenerated charges. Whereas, 2D rGO nanosheet presents complementary surface area to allow the formation of distinct heterojunction with majority of the 0D QDs by preventing agglomeration of particles and excellent conductivity. TEM images explicitly showed the uniform distribution of 0D BMO particles of size 8−10 nm over 2D rGO which lead to formation of distinct Schottky junction. These exclusive properties of 0D/2D heterojunction result in effective degradation of organic pollutants such as Rhodamine-B dye, p-nitrophenol a phenol group and acetaminophen a pharmaceuticals compound with 100 %, 94 % and 87 % in 180 min; and degradation rate achieved was 9.35, 8.60 and 7.53 as compared to 0D BMO QDs under simulated solar light irradiation. The scavenging experiments revealed that h+ and O 2 • - radicals are main reactive species involved in the photodegradation along with contribution from photogenerated e−. The increased photocatalytic efficiency is ascribed to enlarge solar light absorption, increased adsorption, increased surface area, conductivity with substantial contribution of photo-induced charge separation and transfer in BMO/rGO (0D/2D) heterojunction.
In the present work, we have used swift heavy ions (SHI) irradiation and post irradiation anneali... more In the present work, we have used swift heavy ions (SHI) irradiation and post irradiation annealing to synthesize Ag nanoparticles in fused silica. Fused silica samples deposited with 15 nm of Ag film were irradiated using SHI beam of 120 MeV Ag 9+ ions at different fluences and post irradiation annealing was done at 500 °C in air for 30 min. The samples were characterized using UV-vis absorption spectroscopy, Rutherford Backscattering Spectrometry (RBS), GAXRD, Transmission Electron Microscopy (TEM), and open aperture z-scan measurements. The signature of Ag nanoparticles was observed in optical absorption spectra and the average size of the Ag nanoparticles was estimated using Mie's theory. The size of the nanoparticles (~3 nm) was also confirmed from the GAXRD and TEM measurements. RBS results for Ag/SiO 2 irradiated with the fluence of 5 x10 13 ions/cm 2 shows the decrease in slope at the interface of the Ag profile, indicating a partial mixing at a fluence of 5 x 10 13 ions/cm 2. Open aperture z-scan measurement of Ag/SiO 2 SHI irradiated sample after annealing shows a saturation behavior, indicating that the sample is optically non-linear. The sample shows saturation behavior but does not show optical limiting behavior, which indicates that the size and number density of nanoparticles are low. The ability to control the particle size using ion beam technique as a function of fluence and observed nonlinearity results provide concrete evidence that Ag nano composite glasses can be used in nonlinear and optical limiting application.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Swift heavy ions are used to study the effects of electronic energy loss on Cu cluster formation ... more Swift heavy ions are used to study the effects of electronic energy loss on Cu cluster formation in fused silica after post-irradiation annealing. Fused silica substrates covered with 10 nm thin Cu-films were irradiated using beams of either 120 MeV Ag9+ ions or 350 MeV Au26+ ions at fluences ranging from 2x1013 to 1x1014 cm-2. After irradiation, the samples were annealed for 30 min in argon, at temperatures of 773–1200 K and characterized by UV–VIS absorption spectroscopy. The swift ion irradiations created E0 and B2 defects in silica, which were partially eliminated during annealing. In addition, Cu cluster formation in silica was observed after annealing. Irradiation fluences exceeding 4x1013 cm-2 and annealing temperatures above 1100 K are more effective in forming larger nanoclusters.
Ion beam mixing using low energy (LE) ion beams (100 keV Ar + ) has been used to form Au nanopart... more Ion beam mixing using low energy (LE) ion beams (100 keV Ar + ) has been used to form Au nanoparticles in the near-surface region of fused silica glasses. Effect of swift heavy ion (SHI) irradiation (with 120 MeV Ag 9+ ), on the nanoparticles has been studied. Diffusion length of Au after the beam mixing and the irradiation has been found to be 14nm. SHI irradiation causes the increase in the size of the nanoparticles, reduction in size-distribution and increase in number density.
Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °... more Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °C, and 500 °C for 60 min. The exchanged glasses were either annealed at 500 °C for 60 min or swift heavy ion (SHI) irradiated using 120 MeV Ag 9+ ions at a fluence of 5 x 1012 ions/cm2. Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any post-exchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.
Carbon coated thin films of Cu or Au on fused silica glasses have been irradiated using 100 keV A... more Carbon coated thin films of Cu or Au on fused silica glasses have been irradiated using 100 keV Ar + ions at different fluences ranging from 1 x 10 13 to 1 x 10 16 ion/cm 2 . In this article, we explore a route to form noble metal nanoparticles in amorphous glass matrices without post irradiation annealing using low energy ion beam mixing where nuclear energy loss process is dominant. Optical and structural properties were studied using UV-Vis-NIR absorbance spectroscopy and Glancing angle X-ray Diffraction (GXRD). Results showed that Cu and Au nanoparticles are formed at higher fluence of 1 x 10 16 ion/cm 2 used in this work without annealing. The diameters of metal nanoparticles obtained from UV-Vis NIR and GXRD are in agreement.
In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annea... more In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annealing to form Cu nanoparticles in fused silica glass. The sequence of process being: low energy irradiation of fused silica substrate, Cu thin film coating, SHI irradiation and annealing. Fused silica substrates were irradiated using 30 keV argon ions at fluences of 1 × 10 17 ion/cm 2 .10 nm Cu films were deposited on the low energy irradiated fused silica. These thin films coated fused silica samples were then irradiated using 120 MeV Ag 9+ ions at fluences ranging from 4 × 10 13 to 1 × 10 14 ion/cm 2 . The irradiated samples were subjected to isochronal annealing in argon gas flow from 400 K to 1200 K for 30 min. The average sizes of Cu nanoparticles were estimated from optical absorption spectra using Mie's theory. The sizes of the Cu nanoparticles were also confirmed from GAXRD and TEM measurements. Postirradiation annealing results indicate that the formation of Cu 3 nanocluster is favored at annealing temperature of about 700 K. High temperature annealing at 1200 K causes the formation of Cu 4 clusters as well as Cu nanoparticles (larger clusters). After annealing at 1200 K, for the sample 120 MeV Ag 9+ irradiated with high dose (1× 10 14 ion/cm 2 ) only Cu nanoparticles are formed. The study suggests that irradiation induced defects provide nucleation sites for the formation of nanoparticles, latent tracks provide fast diffusion channels for Cu and, annealing provides required energy for the diffusion.
Recent advancement of multi elements codoped-TiO2 in photocatalytic application demands to unders... more Recent advancement of multi elements codoped-TiO2 in photocatalytic application demands to understand the role of each dopant involved in catalytic mechanism. Here we explore the VN-codoped TiO2 system intended to understand the role played by each dopant in synergistic enhancement in performance of TiO2 semiconductor. The concentrations of V and N were varied and optimized to improve photocatalytic activity. The photocatalytic decomposition of phenol and dye in aqueous solution under visible light was used as a probe reaction to evaluate their performance. With increase in vanadium concentration in VN-codoped TiO2 considerable improvement in visible light absorption is observed as compared to nitrogen doping due to the effective narrowing of the band gap from 3.12 eV to 1.88 eV. At low concentration, the energy levels formed by both V and N act as the trapping centers for photo-generated charges to suppress recombination process as indicated by PL and TRPL results. As V concentration increases, recombination centers are created in form of oxygen vacancies as confirmed by XPS. Addition of N partially fills these oxygen vacancies to reduce the amount of recombination and prolong the lifetime of charge carriers.V improves the visible light absorption to generate large number of electron-hole pair while N reduces the recombination of electron-hole pair creating the synergetic effect to produce three times better performance than pure TiO2.
In this paper we investigate the possibility of formation of AnataseTiO 2 and nitrogen dopedTiO 2... more In this paper we investigate the possibility of formation of AnataseTiO 2 and nitrogen dopedTiO 2 thin films prepared by varying cathodic arc evaporation parameters such as ratio of Ar, O 2 and N 2 gas flow, bias voltage and cathode current. Nanostructured titanium dioxide (TiO 2 ) and nitrogen doped titanium dioxide (N-TiO 2 ) thin films were deposited on soda lime silicate glass samples using Cathodic Arc Physical Vapor Deposition (CA-PVD). X-ray diffraction (XRD), UV-Vis spectrophotometer and scanning electron microscope (SEM) technologies were used to characterize the film. The photocatalytic activities of the samples were tested on the degradation of methylene blue (MB) dye.Crystalline size and phases of the thin films were calculated by using XRD. Morphology and elemental analysis of the thin films were carried by SEM-EDAX. Here, we intensely say that as deposited thin films gives better degradation efficiency without any additional process.
In the present manuscript, we explore the VN-codoped TiO system intended to understand the role p... more In the present manuscript, we explore the VN-codoped TiO system intended to understand the role played by each dopant in synergistic enhancement in performance of TiO photocatalyst. The photocatalytic decomposition of organic pollutants in aqueous solution under visible light was used as a probe reaction to evaluate the performance of VN-codoped TiO samples with different V and N concentrations. An optical measurement of VN-codoped TiO shows considerable improved visible light absorption with increase in V-concentration as compared to increase in N concentration, which was due to the effective narrowing of the band gap by V-doping. The energy levels formed by N-dopants act as the trapping centers for photogenerated holes to suppress recombination process as indicated by PL and TRPL results. It is also observed that at high V-concentrations recombination centers are created in the form of oxygen vacancies as indicated by XPS and PL. In VN-codoped TiO , addition of N partially fills t...
Journal of Photochemistry and Photobiology A: Chemistry, 2021
Abstract The photocatalytic performance of gC3N4 is majorly restricted by insufficient collection... more Abstract The photocatalytic performance of gC3N4 is majorly restricted by insufficient collection of photogenerated charges on the surface during reaction due to highly dense stacking of lamellar structures with lateral size ranging in microns. This deficiency can be overcome by forming thin nanoflakes by systematically breaking the weak bonds that hold the gC3N4 framework without destroying the basic heptazine unit. With this aim, herein, a combination of three different strategies was implemented to design and develop, Ag-loaded and P-doped gC3N4 nanoflakes (Ag3-P1-NF-gC3N4). Using a systematic synthesis method, bulk gC3N4 was first converted into thin nanosheets, followed by fragmentation into nanoflakes, with a planar size up to 100 nm. P doping to replace the corner C atoms in the gC3N4 matrix (forming P-N bonds) and intercalation of plasmonic Ag nanoparticles within the interlayers also assists in the bifurcation of the stacked layers and formation of nanoflakemorphology. These strategies result in a significant increase in BET surface area to ∼196 m2/g from 12 m2/g of bulk gC3N4. Improved inter-planar and intra-planar charge mobility was recorded as a result of the reduced sizes. Doping with P also causes higher absorption of the visible spectrum in gC3N4 while the formation of heterojunction with Ag nanoparticles induces efficient separation of photo-generated charges. All these promoting photo-physical properties lead to an outstanding photocatalytic activity towards degradation of aqueous pollutants with reaction rates ∼20 times higher than bulk gC3N4. Complete mineralization of the pollutant and formation of non-toxic byproducts was also confirmed with suitable chromatography techniques.
C 16 H15ClN 2 O 2 , monoclinic, P21/c (no. 14), a = 33.491(11) Å, b = 7.124(2) Å, c = 6.1977(19) ... more C 16 H15ClN 2 O 2 , monoclinic, P21/c (no. 14), a = 33.491(11) Å, b = 7.124(2) Å, c = 6.1977(19) Å, β = 92.212(6)°, V = 1477.6(8) Å 3 , Z = 4, Rgt(F) = 0.0418, wR ref (F 2) = 0.1193, T = 296(2) K. CCDC no.: 1828200 Tables 1 and 2 contain details on crystal structure and measurement conditions and a list of the atoms including atomic coordinates and displacement parameters.
Study of corrosion properties of CrN and multilayer CrN/Cr coating at different electrolyte tempe... more Study of corrosion properties of CrN and multilayer CrN/Cr coating at different electrolyte temperatures deposited on stainless steel by vacuum arc process
A (q, k, t)-design matrix is an m × n matrix whose pattern of zeros/non-zeros satisfies the follo... more A (q, k, t)-design matrix is an m × n matrix whose pattern of zeros/non-zeros satisfies the following design-like condition: each row has at most q non-zeros, each column has at least k non-zeros and the supports of every two columns intersect in at most t rows. We prove that for m ≥ n, the rank of any (q, k, t)-design matrix over a field of characteristic zero (or sufficiently large finite characteristic) is at least
Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °... more Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °C, and 500 °C for 60 min. The exchanged glasses were either annealed at 500 °C for 60 min or swift heavy ion (SHI) irradiated using 120 MeV Ag 9+ ions at a fluence of 5 x 10 12 ions/cm 2 . Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any postexchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.
Ag–TiO2 nanocomposite systems have been investigated with the aim of understanding the relationsh... more Ag–TiO2 nanocomposite systems have been investigated with the aim of understanding the relationship between the photocatalytic efficiency and the contributions of various structures resulting in charge carrier separation, charge transfer and extension of light absorption to the visible range.
Abstract Lattice location of B in TiO2 is tuned to determine its effect on the photocatalytic act... more Abstract Lattice location of B in TiO2 is tuned to determine its effect on the photocatalytic activity of Co-B codoped TiO2. Sol–gel method was used to synthesize the samples. The concentrations of Co and B were first optimized by maximizing the photocatalytic activity for the monodoped (Co or B)-TiO2. In addition to the DFT calculations for discovering new energetic levels introduced in TiO2 by codoping, various characterization techniques were used to determine the dopant lattice sites in TiO2 and interactions between them; and also determining their consequences on electronic, morphological, structural, and optical properties. At low concentration of B-doping (1 at.%), B occupies the interstitial site (Bint), but as the concentration increases (2 at.% and 3 at.%) B also occupies substitutional O position (Bsub) in addition to Bint to form TiO2 containing Bint+sub. Both these B-doped TiO2 showed improved photocatalytic activity attributed to effective charge separation obtained for TiO2–Bint due to the formation of shallow energy level while higher visible light absorption is achieved with TiO2–Bint+sub owing to the presence of two deep energy levels in the band gap as confirmed by DFT calculations. In the case of Co doping, the band gap of TiO2 is reduced but the recombination rates are always high and are caused by the formation of Co states in the band gap. For Co monodoped TiO2, the photocatalytic activity is low for all the concentrations considered, except for very low concentration of Co (0.1 at.%). Two opposite effects were observed when small amount of Co (0.1 at.%) was codoped with Bint or Bint+sub. In particular, the photocatalytic degradation rate of organic aqueous pollutants (p-nitrophenol and rhodamine B dye) reduces for TiO2–Co–Bint whereas it is enhanced remarkably for TiO2–Co–Bint+sub as compared to (Co or B) monodoped (∼2.1 times) and undoped (∼7.8 times) TiO2. Higher photocatalytic activity observed in Co-doped TiO2–Bint+sub is discussed in terms of the interactions of Co with B at two different lattice positions in TiO2 and the synergistic effect created by higher visible light absorption and the improved charge separation.
Journal of Environmental Chemical Engineering, 2020
Abstract In the present research Bi2MoO6(BMO) QDs (0D) and reduce graphene oxide nanosheet (2D) (... more Abstract In the present research Bi2MoO6(BMO) QDs (0D) and reduce graphene oxide nanosheet (2D) (BMO/rGO)(0D/2D) heterojunction with different weight ratio of GO nanosheet were synthesized using facile method. XRD, UV–vis spectroscopy, XPS, FTIR, BET, PL, TRPL, TEM/HRTEM, ESR and photoelectrochemical (PEC) measurements were used for the characterization and understanding the enhancement effect on photoactivity of the synthesis photocatalyst. The BMO (0D) QDs provide more active sites and short diffusion length of photogenerated charges. Whereas, 2D rGO nanosheet presents complementary surface area to allow the formation of distinct heterojunction with majority of the 0D QDs by preventing agglomeration of particles and excellent conductivity. TEM images explicitly showed the uniform distribution of 0D BMO particles of size 8−10 nm over 2D rGO which lead to formation of distinct Schottky junction. These exclusive properties of 0D/2D heterojunction result in effective degradation of organic pollutants such as Rhodamine-B dye, p-nitrophenol a phenol group and acetaminophen a pharmaceuticals compound with 100 %, 94 % and 87 % in 180 min; and degradation rate achieved was 9.35, 8.60 and 7.53 as compared to 0D BMO QDs under simulated solar light irradiation. The scavenging experiments revealed that h+ and O 2 • - radicals are main reactive species involved in the photodegradation along with contribution from photogenerated e−. The increased photocatalytic efficiency is ascribed to enlarge solar light absorption, increased adsorption, increased surface area, conductivity with substantial contribution of photo-induced charge separation and transfer in BMO/rGO (0D/2D) heterojunction.
In the present work, we have used swift heavy ions (SHI) irradiation and post irradiation anneali... more In the present work, we have used swift heavy ions (SHI) irradiation and post irradiation annealing to synthesize Ag nanoparticles in fused silica. Fused silica samples deposited with 15 nm of Ag film were irradiated using SHI beam of 120 MeV Ag 9+ ions at different fluences and post irradiation annealing was done at 500 °C in air for 30 min. The samples were characterized using UV-vis absorption spectroscopy, Rutherford Backscattering Spectrometry (RBS), GAXRD, Transmission Electron Microscopy (TEM), and open aperture z-scan measurements. The signature of Ag nanoparticles was observed in optical absorption spectra and the average size of the Ag nanoparticles was estimated using Mie's theory. The size of the nanoparticles (~3 nm) was also confirmed from the GAXRD and TEM measurements. RBS results for Ag/SiO 2 irradiated with the fluence of 5 x10 13 ions/cm 2 shows the decrease in slope at the interface of the Ag profile, indicating a partial mixing at a fluence of 5 x 10 13 ions/cm 2. Open aperture z-scan measurement of Ag/SiO 2 SHI irradiated sample after annealing shows a saturation behavior, indicating that the sample is optically non-linear. The sample shows saturation behavior but does not show optical limiting behavior, which indicates that the size and number density of nanoparticles are low. The ability to control the particle size using ion beam technique as a function of fluence and observed nonlinearity results provide concrete evidence that Ag nano composite glasses can be used in nonlinear and optical limiting application.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Swift heavy ions are used to study the effects of electronic energy loss on Cu cluster formation ... more Swift heavy ions are used to study the effects of electronic energy loss on Cu cluster formation in fused silica after post-irradiation annealing. Fused silica substrates covered with 10 nm thin Cu-films were irradiated using beams of either 120 MeV Ag9+ ions or 350 MeV Au26+ ions at fluences ranging from 2x1013 to 1x1014 cm-2. After irradiation, the samples were annealed for 30 min in argon, at temperatures of 773–1200 K and characterized by UV–VIS absorption spectroscopy. The swift ion irradiations created E0 and B2 defects in silica, which were partially eliminated during annealing. In addition, Cu cluster formation in silica was observed after annealing. Irradiation fluences exceeding 4x1013 cm-2 and annealing temperatures above 1100 K are more effective in forming larger nanoclusters.
Ion beam mixing using low energy (LE) ion beams (100 keV Ar + ) has been used to form Au nanopart... more Ion beam mixing using low energy (LE) ion beams (100 keV Ar + ) has been used to form Au nanoparticles in the near-surface region of fused silica glasses. Effect of swift heavy ion (SHI) irradiation (with 120 MeV Ag 9+ ), on the nanoparticles has been studied. Diffusion length of Au after the beam mixing and the irradiation has been found to be 14nm. SHI irradiation causes the increase in the size of the nanoparticles, reduction in size-distribution and increase in number density.
Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °... more Silver ion exchanges on silicate glasses were carried out at different temperatures 320 °C, 400 °C, and 500 °C for 60 min. The exchanged glasses were either annealed at 500 °C for 60 min or swift heavy ion (SHI) irradiated using 120 MeV Ag 9+ ions at a fluence of 5 x 1012 ions/cm2. Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any post-exchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.
Carbon coated thin films of Cu or Au on fused silica glasses have been irradiated using 100 keV A... more Carbon coated thin films of Cu or Au on fused silica glasses have been irradiated using 100 keV Ar + ions at different fluences ranging from 1 x 10 13 to 1 x 10 16 ion/cm 2 . In this article, we explore a route to form noble metal nanoparticles in amorphous glass matrices without post irradiation annealing using low energy ion beam mixing where nuclear energy loss process is dominant. Optical and structural properties were studied using UV-Vis-NIR absorbance spectroscopy and Glancing angle X-ray Diffraction (GXRD). Results showed that Cu and Au nanoparticles are formed at higher fluence of 1 x 10 16 ion/cm 2 used in this work without annealing. The diameters of metal nanoparticles obtained from UV-Vis NIR and GXRD are in agreement.
In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annea... more In this paper, we present the use of keV and MeV ion beam irradiations and post-irradiation annealing to form Cu nanoparticles in fused silica glass. The sequence of process being: low energy irradiation of fused silica substrate, Cu thin film coating, SHI irradiation and annealing. Fused silica substrates were irradiated using 30 keV argon ions at fluences of 1 × 10 17 ion/cm 2 .10 nm Cu films were deposited on the low energy irradiated fused silica. These thin films coated fused silica samples were then irradiated using 120 MeV Ag 9+ ions at fluences ranging from 4 × 10 13 to 1 × 10 14 ion/cm 2 . The irradiated samples were subjected to isochronal annealing in argon gas flow from 400 K to 1200 K for 30 min. The average sizes of Cu nanoparticles were estimated from optical absorption spectra using Mie's theory. The sizes of the Cu nanoparticles were also confirmed from GAXRD and TEM measurements. Postirradiation annealing results indicate that the formation of Cu 3 nanocluster is favored at annealing temperature of about 700 K. High temperature annealing at 1200 K causes the formation of Cu 4 clusters as well as Cu nanoparticles (larger clusters). After annealing at 1200 K, for the sample 120 MeV Ag 9+ irradiated with high dose (1× 10 14 ion/cm 2 ) only Cu nanoparticles are formed. The study suggests that irradiation induced defects provide nucleation sites for the formation of nanoparticles, latent tracks provide fast diffusion channels for Cu and, annealing provides required energy for the diffusion.
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Papers by Ranjana Varma
ions at a fluence of 5 x 1012 ions/cm2. Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any post-exchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at
temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission
Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows
optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.
ions at a fluence of 5 x 1012 ions/cm2. Silver nanoparticles were formed in the samples ion exchanged at 500 °C without any post-exchange treatments. Post-exchange annealing treatment resulted in silver nanoparticle formation for samples ion exchanged at
temperature of 320 °C and 400 °C. Whereas post irradiation treatment for ion exchanged sample at 320 °C resulted in Ag 4 nanocluster formation. After post-irradiation, the density of Ag nanoparticles increases for the sample ion exchanged at temperature of 500 °C. RBS was used to obtain silver depth profiles in the ion exchanged samples. Near surface accumulation of Ag atoms is observed in the RBS spectra for the samples prepared at high ion exchange temperature of 500 °C or SHI irradiated samples, in which Ag nanoparticle formation was also observed. UV-vis absorption spectroscopy and Transmission
Electron Microscopy (TEM) were used to obtain signatures of nano-particles and to estimate their size. The ion exchanged glasses without nanoparticles were characterized for their possible use in multimode planar waveguides. The post-exchange treated glasses lost their waveguide property, but exhibited nonlinear optical property indicating their potential use for optical switching. Open aperture z-scan measurements for the sample prepared at high ion exchange temperature of 500 °C shows
optical limiting behavior, whereas the samples prepared at low ion exchange temperature followed by annealing or irradiation show saturation behavior.