Aslam Khan - Academia.edu (original) (raw)

Papers by Aslam Khan

The broad bandgap tin (IV) oxide (SnO 2) is the least investigated semiconductor material for pho... more The broad bandgap tin (IV) oxide (SnO 2) is the least investigated semiconductor material for photo-catalytic water decontamination in sunlight exposure. A detailed study covering the synthesis, characterization and the evaluation of photocatalytic activity of SnO 2 , in the natural sunlight exposure, is presented. The structural characterization by XRD revealed the formation of phase pure tetragonal SnO 2 with the average crystallite size of~41.5 nm whereas minor Sn 2þ states in the material were identified by XPS analysis. As explored by diffuse reflectance (DR) and photoluminescence (PL) spectroscopy, the material exhibited a distinct absorption edge at~3.4 eV. The morphological and microstructure analysis of the synthesized SnO 2 was carried out by FESEM and HRTEM. The electrochemical impedance spec-troscopy (EIS) and chronopotentiometry (CP) predicted the better charge transport and retention ability of the material under illumination whereas the Mott-Schottky extrapolation prophesied the n-type behavior with the flat-band potential of À0.60 V. The photocatalytic activity of SnO 2 was assessed in the exposure of complete spectrum natural sunlight for the removal of 2,4,6-trichlorophenol. The HPLC and TOC analysis monitored the progress of degradation and mineralization whereas the released chloride ions were evaluated by ion chromatography. The effect of the transition metal ions (Fe 3þ , Cu 2þ , Ni 2þ, and Zn 2þ) as electron capture agents and H 2 O 2 as ROS generator was explored during the degradation process. The utility of the material for the simultaneous removal of chlorophenols in the mixture was also investigated. The SnO 2 exhibited sustained activity in the repeated use. Based on experimental evidence congregated, the mechanism of the removal process and the efficacy of SnO 2 for sunlight photocatalytic decontamination of water was established.

Silicon carbide (SiC), owing to its extraordinary chemical stability and refractory properties, i... more Silicon carbide (SiC), owing to its extraordinary chemical stability and refractory properties, is widely used in the manufacturing industry. Despite the semiconducting nature and morphology-tuned band gap, its efficacy as photocatalysts has not been thoroughly investigated. The current study reports the synthesis, characterization and the evaluation of the capability of silicon carbide for hydrogen generation from water splitting. The optical characterization of the as-synthesized powder exposed the formation of multi-wavelength absorbing entities in synthetic process. The structural analysis by XRD and the fine microstructure analysis by HRTEM revealed the cubic 3C-SiC (β-SiC) and hexagonal α-polymorphs (2H-SiC and 6H-SiC) as major and minor phases, respectively. The Mott-Schottky analysis verified the n-type nature of the material with the flat band potential of − 0.7 V. In the electrochemical evaluation, the sharp increase in the peak currents in various potential ranges, under illumination, revealed the plausible potential of the material for the oxidation of water and generation of hydrogen. The generation of hydrogen and oxygen, as a consequence of water splitting in the actual photocatalytic experiments , was observed and measured. A significant increase in the yield of hydrogen was noticed in the presence of methanol as h + scavenger, whereas a retarding effect was offered by the Fe 3+ entities that served as e − scavengers. The combined effect of both methanol and Fe 3+ ions in the photocatalytic process was also investigated. Besides hydrogen gas, the other evolved gasses such as methane and carbon monoxide were also measured to estimate the mechanism of the process.

Concentrations of natural nuclides (226 Ra, 232 Th and 4 K) and some heavy metals (Cu, Fe. Ni, Pb... more Concentrations of natural nuclides (226 Ra, 232 Th and 4 K) and some heavy metals (Cu, Fe. Ni, Pb and As) were measured in groundwater collected from different locations in Makkah region in Saudi Arabia. In the radioactivity measurement, a high purity germanium detector system was used. In addition, chemical analysis was performed by an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The average measured activity concentrations of the nuclides 238 U, 232 Th and 4 K were 0.558, 0.204 and 4.581 BqL −1 , respectively. The total annual effective doses for ingestion of radionuclides in the water samples were 0.472 mSv for children and 0.169 mSv for adults. These results were lower than the recommended value (1.0 mSvy −1), as reported by WHO. The chemical analysis results showed that these water samples contain (Ca, Mg, Cu, Fe. Ni, Pb and As) elements. The concentration values were evaluated and compared with the internationally verified values. This study provides essential information for consumers and authorities; those at exposure risk from mineral water intake.

Natural sunlight 2-Chlorophenol 2-Nitrophenol a b s t r a c t The non-magnetic and magnetic polym... more Natural sunlight 2-Chlorophenol 2-Nitrophenol a b s t r a c t The non-magnetic and magnetic polymorphs of iron oxide (Fe2O3) namely: a-Fe2O3 (hematite) and c-Fe2O3 (maghemite) respectively, were synthesized by a facile surfactant aided hydrogel route. The synthesized polymorphs were characterized by diffuse reflectance, photoluminescence and raman spec-troscopy for optical properties whereas the morphological, structural, chemical and electronic state evaluation were performed by FESEM, HRTEM, XRD, and XPS. The charge transport and the stability of the materials were examined electroche mically. The photocatalytic activity of the synthesized poly-morphs was evaluated for the degradation of 2-chlorophenol and 2-nitrophenol in the exposure of the visible region and complete spectrum natural sunlight. Both the polymorphs exhibited a significantly high activity for the degradation of the phenolic substrate in the exposure of the complete spectrum of sunlight, however, the activity in the visible region of the sunlight was relatively lower. A substantial increase in the activity in the visible region was noticed when the polymorphs were exposed to complete spectrum sunlight prior to the photocatalytic experiments. The comparison of the exposed and unex-posed samples revealed the induction of defects that served as traps for the excited electrons and increased activity of the polymorphs.

The MoO 3 coated ZnO photocatalysts were synthesized for the optimum harvesting of the absorbed u... more The MoO 3 coated ZnO photocatalysts were synthesized for the optimum harvesting of the absorbed ultraviolet sunlight photons by initially permeating Mo 6+ ions at the surface of pre-synthesized ZnO and finally transformed to MoO 3 by thermal treatment in the air. The absorption spectra of the synthesized powders revealed the extension of the absorption edge in the visible region whereas, the photoluminescence spectroscopy established the supporting role of the MoO 3 coating in gradually plummeting the excitons recombination. The growth of additional peaks in Raman as well as X-ray photoelectron spectra and the appearance of the corresponding low-intensity reflection substantiated the surface prevalence of MoO 3. The absence of the individual particles of MoO 3 in FESEM and the verification of coated layer by HRTEM images validated the authenticity of the adopted synthetic route. The electrochemical evaluation of the synthesized powders under illumination revealed the complete elimination of photocorrosion and the synergic role of the MoO 3 layer for improved trap and transfer of charge carriers. The evaluation of the flat-band potentials of the coated powders by Mott-Schottky analysis revealed the suitability of the conduction band edges for the generation of superoxide anion radicals. The photocatalytic activity of the synthesized powders was assessed for the removal of chloro derivatives (mono-, di-, trichloroacetic acids) in comparison to pure acetic acid. A significant effect of the stability, polarity and ste-reochemical structure of the substrate on the photocatalytic removal process was observed and discussed. The experimental evidences from the timescale chemical analysis were interpreted for the identification of the reactive oxygen species (ROS) involved in the degradation/mineralization process. The validation of the http://dx. MARK Langmuir-Hinshelwood kinetic model was also examined. Efforts were made to estimate the plausible route of the degradation/mineralization process.

The issues of low photocatalytic activity and dissolution of ZnO in natural sunlight exposure wer... more The issues of low photocatalytic activity and dissolution of ZnO in natural sunlight exposure were addressed by implanting p-type Mn 3 O 4 on its surface. The optical analysis revealed the composite nature and suppression of exciton excitons recombination whereas the cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and chronopotentiometry substantiated the elimination of photocorro-sion respectively, low charge transfer resistance and better charge retention ability for the as-synthesized composites. The Mott-Schottky analysis by staircase potential impedance spectroscopy (SPIES) verified the p-n nature while the measurement of flat band potential (V fb) predicted the suitability of the band potentials for the enhanced generation of reactive oxygen species (ROS). The structure and morphology of the Mn 3 O 4-ZnO composites were evaluated by x-ray diffraction (XRD) and field emission electron microscopy (FESEM) whereas the fine structure analysis was performed by high-resolution transmission electron microscopy (HRTEM) analysis that revealed the discrete fringe patterns of p-type Mn 3 O 4 and ZnO in composites. The x-ray photoelectron spectroscopy (XPS) verified the simultaneous existence of Mn 2+ and Mn 3+ in Mn 3 O 4 nanoparticles. Compared to pure ZnO, due to the existence of charge transfer synergy between the p-type Mn 3 O 4 and n-type ZnO, the composites with moderate Mn 3 O 4 loadings exhibited marked activity for the removal of stable pollutants like 4-bromo and 4-chlorophenol in natural sunlight exposure. The correlation of the findings from various analytic tools of chemical analysis such as high-performance liquid chromatography (HPLC), ion chromatography (IC), total organic carbon (TOC) measurements and GC-MS analysis revealed the persuasive role of Cl and Br groups in regulating the degradation process. The composite catalyst exhibited excellent stability and reproducible activity in the repeated scans.

The use of inexpensive semiconducting materials and abundant natural sunlight can deliver the sus... more The use of inexpensive semiconducting materials and abundant natural sunlight can deliver the sustainable as well as cost-effective cleaning of contaminated water. In the current effort, the low photocatalytic activity of ZnO in sunlight exposure has been addressed by the slow deposition and after calcination, the deposition pattern of Fe 3+ ions was investigated. The appearance of distinct multiple absorption edges in the optical spectra verified the composite nature of the synthesized materials whereas the absorption edge at $2.5 eV indicated the formation of visible light responsive structures other than Fe 2 O 3. The additional reflections, besides the characteristic reflections of ZnO and Fe 2 O 3 , in the X-ray diffraction patterns and the appearance of discrete assortments in HRTEM analysis exposed the formation of surface ZnFe 2 O 4 in the interfacial region between the ZnO and Fe 2 O 3. The X-ray photoelectron analysis revealed the minor transitions in the oxidation state, more pronounced at higher Fe 3+ loadings, during the synthetic route. The electrochemical characterization revealed the p-type nature of the oxides of Fe 3+ whereas the flat-band potentials of the composites were assessed by Mott-Schottky analysis. As compared to pure ZnO, the composites loaded with lower concentrations (0.5% and 1%) of Fe 3+ showed substantially high activity for the removal of 2,4-dichlorophenoxy acetic acid (2,4-D) in the complete spectrum whereas 3% Fe 3+ loading exhibited optimum activity in the exposure of the visible region of natural sunlight. The higher Fe 3+ loadings revealed the detrimental effect on the photocatalytic removal process. The variations in the photocatalytic activity with the increasing Fe 3+ were discussed in correlation with electrochemical properties. The key intermediates were identified and the plausible mechanisms of the removal of 2,4-D were proposed by correlating the evidence from various experimental tools such as HPLC, IC, and TOC. The probable contribution of the reactive oxygen species (ROS) involved in the degradation process was estimated and discussed. The validity of the Langmuir-Hinshelwood kinetic model was also examined for the degradation as well as mineralization process.

Water, the driver of nature, has always been polluted by the blind hurling of highly toxic contam... more Water, the driver of nature, has always been polluted by the blind hurling of highly toxic contaminants, but human-friendly science has continuously been presenting better avenues to help solve these challenging issues. In this connection, the present study introduces novel nanocompo-sites composed of emulsion-templated hierarchically porous poly(1-vinylimidazole) beads loaded with the silver nano-particles generated via an in situ approach. These nano-composites have been thoroughly characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller, and field emission scanning electron microscopy. The appropriate surface chemistry, good thermal stability, swelling behavior, porosity, and nanodimensions contributed to achieve very good performance in water treatment. Owing to their easier handling and separation, these novel nanocomposites are highly efficient to remove arsenic and eriochrome black T with decent adsorption capacities in addition to the inactivation and killing of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria.

The efficacy of the ZnO-α-Fe 2 O 3 composites as carbon paste electrode (CPE) modifier for sensit... more The efficacy of the ZnO-α-Fe 2 O 3 composites as carbon paste electrode (CPE) modifier for sensitive electrochemical detection of loperamide was explored. The composites were synthesized in 1:1, 2:1, and 3:1 (ZnO:α-Fe 2 O 3) ratios by the gradual amalgamation of pre-synthesized α-Fe 2 O 3 and hydrated gel of Zn 2+ that later transformed to the ZnO by thermal treatment. The lattice parameters of the composite ZnO and the probable variations in the oxidation states of the components during the adopted coating procedure were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The field-emission scanning electron microscopy (FESEM) imaging of the as-synthesized and carbon paste (CP) dispersed composite powders at various resolutions exposed the increased surface coverage of the α-Fe 2 O 3 by the ZnO particles with the increasing loading and the uniform distribution of the composite materials in the matrix of carbon paste. Compared to bare CPE, the composites modified CPEs exhibited significantly decreased charge transfer impedance at the electrode/electrolyte interface evaluated by electrochemical impedance spectroscopy (EIS). The sensing ability of the composites modified electrodes for the detection of loperamide in the aqueous medium was investigated. A higher and affectedly improved cyclic voltammetric (CV) oxidation signal of loperamide was noticed at the prepared ZnO:α-Fe 2 O 3 /CPEs compared to pure components modified CPEs i.e. ZnO/CPE and α-Fe 2 O 3 /CPE. Based on the EIS and CV investigations, a superior electrochemical performance of (2:1) ZnO:α-Fe 2 O 3 /CPE was established. Additionally, under optimized experimental conditions of pH, deposition potential, and accumulation time, loperamide was quantified by square wave stripping voltammetry (SWSV) that resulted in the linear calibration ranges from 0.08-1 and 2-10 μmol L −1 with detection limits (S/N = 3) of 7.9 and 3.6 nmol L −1. The findings of various electrochemical investigations were correlated to establish the mechanism of charge transport and oxidation of loperamide.

Vanadium doped ZnO powders were used as precursors to deposit thin films of V 5þ incorporated ZnO... more Vanadium doped ZnO powders were used as precursors to deposit thin films of V 5þ incorporated ZnO nanoparticles on glass substrates by the pulsed laser deposition technique. The observed variations in Raman signals, visible region shift in the diffuse reflectance spectra along with a small shift in the (101) reflections of the X-ray diffraction (XRD) confirmed the insertion of V 5þ ions in ZnO lattice. No other additional reflection in the XRD results other than ZnO further endorsed the occupation of lattice positions by V entities rather than independent oxide formation. The asymmetric XPS peaks of Zn2p and V2p core levels confirmed the existence of both in the vicinity. The existence of minimal proportion of V 3þ along with V 5þ states varied the alteration of the oxidation states V in the synthetic route. The SEM images at various resolutions displayed the uniform distribution identical nanoparticles without the presence of additional phases in the deposited films. The SEM cross-section measurements revealed the uniform thickness of~90 nm of each film, whereas the surface studies of the films were performed by AFM. The as-synthesized films were tested for photocatalytic activity in sunlight illumination for the removal of 2-chlorophenol. The unique feature of the study was the estimation of the photocatalytic activity 20 ppm of 2-chlorophenol by exposing the low exposed area. The degradation of the substrate was measured by liquid phase UVevis spectroscopy, whereas total organic carbon measurement revealed the mineralization of the substrate. The released Cl À ions were also measured by ion chromatography. The estimated flatband potentials and pH zpc values of the V doped materials, by Mott-Schottky analysis and zeta potential measurements respectively, were correlated with the photo-catalytic activity. The kinetics of the photocatalytic degradation/mineralization process was estimated and results were correlated with the plausible mechanism.

In an effort to enhance the photocatalytic activity of cubic WO 3 in sunlight exposure, its surfa... more In an effort to enhance the photocatalytic activity of cubic WO 3 in sunlight exposure, its surface was modified by impregnating the Ce 3+ ions ranging from 1% to 25% with a step of 5% with respect to the weight of WO 3. Compared to pure WO 3 , the optical analysis by diffuse reflectance spectroscopy (DRS) revealed better absorption cross-section and red shift in the band edges for Ce loaded catalysts. The decreased intensity of photoluminescence (PL) emissions and the suppression of the Raman active bands of WO 3 verified the recombination quenching ability of Ce surface states. The XRD analysis revealed the existence of Ce 3+ states in the lower loadings (#5%), whereas the majority of Ce 4+ states were noticed at higher loadings. The FESEM analysis also verified the formation of individual particles of Ce(III,IV) oxides at the surface of WO 3 at higher loadings. The XPS analysis of 10% Ce loaded samples also revealed the presence of mixed oxides of Ce at higher loading. Except for 1% Ce loaded WO 3 , the estimation of charge-discharge capacity, in comparison to pure WO 3 , revealed the enhancement in the charge retention ability with the increasing Ce loading. In comparison to pure WO 3 , the synthesized catalysts exhibited superior activity for the removal of 2-nitrophenol and 2-chlorophenol substrates in natural sunlight exposure. The analysis of the degradation data revealed that in the lower concentration the surface oxygen bonded Ce 3+ states serve as electron trapping and transfer centers, whereas with the increasing surface density the synergic composite mechanism is the dominating mode. The exaggerated estimation in the EDX analysis of the samples loaded with 15% and 20% Ce also revealed the major surface coverage by the oxides. The salient feature of the study was the evaluation of the photocatalytic activity with the minimal catalyst loading of 350 mg L À1 .

Fe 3 O 4 nanoparticles Modified CPE SWV Voltammetric sensor A B S T R A C T The magnetite nanopar... more Fe 3 O 4 nanoparticles Modified CPE SWV Voltammetric sensor A B S T R A C T The magnetite nanoparticles (Fe 3 O 4), synthesized by surfactant aided hydrolysis of the stoichiometric amounts of ferrous (Fe 2+) and ferric (Fe 3+) ions, were dispersed in carbon paste (CP) to fabricate magnetite modified carbon paste electrode (Fe 3 O 4 /CPE). The field emission scanning electron microscopy (FESEM) was used to evaluate the morphology of the synthesized powder in the pure phase and its distribution in the CP that revealed the well-dispersed Fe 3 O 4 nanoparticles in the graphite sheet with a mean size of 10 nm. The microstructure analysis of the synthesized magnetite was performed by high-resolution transmission electron microscopy (HRTEM). The phase purity of the synthesized magnetite was evaluated by x-ray diffraction (XRD) analysis. After initial assessment of charge transport in the fabricated electrode by electrochemical impedance spectroscopy (EIS) that exhibited a substantial decrease of 87% in the charge transfer resistance, the suitability of the Fe 3 O 4 /CPE was assessed for the detection and determination of chlorite ion (ClO 2 À) in the aqueous medium. The modified CPE loaded with the optimized amount of Fe 3 O 4 showed considerably enhanced oxidation current as compared to pure CPE for the oxidation of ClO 2 À and exhibited a near-reversible peak at $ + 0.73 V in 0.1 M pH 7 phosphate buffers, at a scan rate of 50 mV/s. The optimum analytical conditions for the nanomolar detection of ClO 2 À by square wave voltammetry (SWV) were established. Likely interferences influencing the detection of ClO 2 À were also investigated. The excellent performance of the fabricated electrode was also established for the real tap and bottled water samples.

In an effort to develop a facile and rapid electrochemical sensing protocol for the detection of ... more In an effort to develop a facile and rapid electrochemical sensing protocol for the detection of tramadol in wastewater, the glassy carbon electrode (GCE) was modified with the blend of cetyltrimethylammonium bromide (CTAB) protected Au nanoparticles (Au NPs) and Nafion 1. The characteristic surface plasmon band at 525 nm and the fading of the NÀ ÀH bands in the absorption and the FTIR spectra revealed the metallic nature and interaction of Au NPs with CTAB molecules. The dispersion of the protected and unprotected Au NPs at the surface of the GCE was investigated by atomic force microscopy (AFM). The charge transfer behavior of the fabricated Nafion 1 /CTAB-Au/GC electrode was investigated by electrochemical AC impedance spectroscopy (EIS). The significantly enhanced response of the polymer distributed CTAB protected Au NPs for the detection of tramadol revealed the salient role of Nafion 1 matrix in facilitating the charge transfer. The square wave anodic stripping voltammetry (SWASV) analysis was employed to quantify the amount of tramadol. Prior to the application on real wastewater samples, the experimental variables for sensitive detection such as SWASV parameters, deposition potential, deposition time, and pH were optimized. The SWASV response of Nafion 1 /CTAB-Au/GCE was linear over the 0.5-1 mg/mL and 2-12 mg/mL ranges with a detection limit (S/N = 3) of 3 Â 10 À4 mg/mL. The fabricated electrode exhibited sustained performance for the detection of tramadol in the repeated scans over a prolonged period.

Although the photocatalytic activity of TiO 2 polymorphs and hexagonal ZnO is well studied with a... more Although the photocatalytic activity of TiO 2 polymorphs and hexagonal ZnO is well studied with artificial UV light sources, however, their efficacy is not well examined in natural sunlight exposure. In the current study, the photocata-lytic activity of the polymorphs of TiO 2 (rutile and anatase) and hexagonal ZnO was evaluated in sunlight exposure for the removal of resonance stabilized 2-, and 4-derivatives of chloro and nitrophenol isomers and compared with that of P-25. The polymorphs of TiO 2 and hexagonal ZnO, after synthesis by sol-gel and hy-drogel routes, were subjected to optical, structural and morphological characterization. The hexagonal ZnO exhibited significantly higher as compared to anatase and rutile polymorphs but comparable with that of P-25 in sunlight illumination. For the hexagonal ZnO, the ring opening route of degradation mediated by superoxide anion radicals was confirmed by the absence of non-hydroxylated aromatic intermediates whereas the contribution of both superoxide anion radicals and hydroxyl radicals was evidenced for the TiO 2 polymorphs and P-25. The kinetics of the degradation/mineralization of substrates was also compared.

Applied Catalysis B: Environmental, 2016

The photocatalytic activity of nanostructured CeO 2 was investigated for the degradation of pheno... more The photocatalytic activity of nanostructured CeO 2 was investigated for the degradation of phenol and its derivatives (2-chlorophenol, 2-bromophenol and 2-nitrophenol) in the exposure of complete spectrum and visible region (420-800 nm) of sunlight. The adopted experimental parameters imparted high crystallinity, phase purity, controlled morphology and uniform particle size of ∼11 nm to the synthesized CeO 2. During the evaluation of the photocatalytic activity, the initial low degradation of the substrates till the 90 min of complete spectrum sunlight exposure followed by a piercing increase predicted the favorable photon induced surface changes in CeO 2. The careful examination of the exposed and unex-posed CeO 2 by spectroscopic techniques (diffuse reflectance (DR), photoluminescence (PL), ATR-FTIR and Raman spectroscopy) and electrochemical tools (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP)) revealed the vital role of photon induced surface phases for the improved spectral response and suppressed charge carries recombination process. Based on the appearance of additional weak reflection at 2Â = 28.15 • in the X-ray diffraction (XRD) pattern and inhalation of O 2 in the thermogravimetric analysis (TGA) of sunlight exposed samples revealed the prevalence of photon induced defects generated by the departure of surface oxygen from CeO 2. The induction of defects composed of CeO 2-x states resulted in the improved activity of the exposed compared to unex-posed CeO 2 in the visible spectrum (420-800 nm) of sunlight. The efficient degradation of 2-CP, 2-BP and 2-NP compared to a mild degradation for phenol, in the complete spectrum sunlight exposure, indicated the facilitating role of substituents attached to the aromatic system in the degradation process. The monitoring of the photocatalytic degradation process by HPLC and identification of intermediates by GC-MS analysis revealed the formation of aromatic intermediates in the degradation of phenol and 2-BP while no aromatic intermediate was identified in the degradation of 2-NP and 2-CP. The rapid disappearance of the total carbon and further oxidation of released anions supported the major role of superoxide anion radicals in the oxidation process. Both pure and sunlight exposed CeO 2 exhibited sustained photocatalytic activity in the repeated exposures.

Journal of Molecular Catalysis A: Chemical , 2016

The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4), with va... more The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4), with varying ratios of Au, were synthesized by a facile route. The diffuse reflectance spectroscopy (DRS) verified the upsurge in the intensity of characteristic surface plasmonic resonance (SPR) absorption bands with the increasing Au contents. The photoluminescence (PL) spectroscopy estimated the role of surface dispersed Au-Ag alloy NPs on the luminescence properties of g-C 3 N 4 and the suppression the probable recombination of photo-generated excitons. The structural characterization by XRD and morphological assessment by SEM revealed the uniform dispersion of Au-Ag alloy nanoparticles on the surface of g-C 3 N 4 whereas XPS analysis endorsed the presence of Au and Ag in metallic form. The HRTEM analysis confirmed the homogeneous distribution of Au and Ag contents in the alloys. The photocatalytic activity of the Au-Ag/g-C 3 N 4 was evaluated in the exposure of natural sunlight and artificial visible light for the degradation of dye substrate and compared with that of g-C 3 N 4 , Ag/g-C 3 N 4 and Au/g-C 3 N 4. The Au-Ag alloy modified g-C 3 N 4 photocatalysts exhibited significantly higher activity for the decolorization of Rhodamine B in the visible light as compared to pure, Ag and Au loaded g-C 3 N 4 that signified the contributing role of SPR in the degradation process. The individual role of SPR in the photocatalytic process was also verified by using monochromatic (532 nm) visible laser light. The mineralization ability of the synthesized alloy catalysts was estimated by TOC removal efficiency. The kinetics of the degradation/mineralization processes under various experimental conditions was also evaluated.

Applied Catalysis B: Environmental , 2014

The synthesis, characterization and sunlight photocatalytic activity of W 6+ impregnated ZnO for ... more The synthesis, characterization and sunlight photocatalytic activity of W 6+ impregnated ZnO for the degradation of nitrophenol isomers (2-nitrophenol, 3-nitrophenol, and 4-nitrophenol) is reported. Compared to pure ZnO, the impregnated catalysts exhibited a relatively improved spectral response in the visible region. The significant decrease in luminescence intensity for W 6+ impregnated catalysts, relative to pure ZnO, established the effective trapping of charge carriers by surface bonded W 6+ states. The characterization of the impregnated catalysts by FESEM, XRD and XPS revealed the presence of impregnated W 6+ entities at the surface without affecting the morphology of ZnO. The synthesized catalysts exhibited superior activity for the mineralization of three nitrophenol isomers under sunlight exposure. Based on HPLC analysis, ∼99% of 2-and 4-nitrophenol was degraded in a short span of 120 min while a degradation of >80% was observed in 3-nitrophenol in the same period. Time scale TOC measurements ratified the mineralization capability of impregnated catalysts. The release of NO 2 − , NO 3 − ions in the solution, pH measurements and non-existence of hydroxylated aromatic intermediates revealed that superoxide anion radicals (O 2 •−) are the major contributors in the degradation process. Besides the traces of coupling products, major intermediates identified by GC-MS analysis were either aliphatic dihydroxy alcohols, car-boxylic acids or other oxygen containing species depicting that the degradation process proceeds through ring opening mechanism. The W 6+ impregnated catalyst also furnished high activity in the visible portion of sunlight. Suitable kinetic models were applied to estimate the rate constants (k) of various processes involved in the degradation process. The stability of the photocatalyst against photocorrosion and the possible decrease in the activity of the catalyst in the successive use was also monitored.

Journal of Hazardous Materials , 2014

The surfactant assisted synthesis of disc-shaped WO3 powder and its photocatalytic performance in... more The surfactant assisted synthesis of disc-shaped WO3 powder and its photocatalytic performance in sunlight exposure is reported. UV–vis DRS, XRD and FESEM characterized the synthesized WO3. The synthesized powder exhibited a bandgap of ∼2.55 eV with cubic lattice and high crystallinity. The photocatalytic activity of the synthesized WO3 was examined for the degradation of phenol, resorcinol, 2-chlorophenol and 2-nitrophenol in complete spectrum and visible segment of sunlight. The highly efficient degradation/mineralization of 2-chloro and 2-nitrophenol compared to that of phenol and resorcinol, under identical experimental conditions, suggested the regulatory role of substituents attached to the aromatic ring in degradation/mineralization process. The time-scale HPLC degradation profiles, identification of intermediates by GC-MS and removal of organic carbon during the course of reaction were utilized to approximate the possible route of degradation/mineralization of phenolic substrates. The measurement of the anions released during the photocatalytic process was used to identify the nature of the major oxidants (O2•−, OH•) and the possible interaction sites. A significant decrease in the photocatalytic activity of synthesized WO3, ∼50%, was observed in visible portion of sunlight however, a sustained activity was observed in the repeated exposures.

The broad bandgap tin (IV) oxide (SnO 2) is the least investigated semiconductor material for pho... more The broad bandgap tin (IV) oxide (SnO 2) is the least investigated semiconductor material for photo-catalytic water decontamination in sunlight exposure. A detailed study covering the synthesis, characterization and the evaluation of photocatalytic activity of SnO 2 , in the natural sunlight exposure, is presented. The structural characterization by XRD revealed the formation of phase pure tetragonal SnO 2 with the average crystallite size of~41.5 nm whereas minor Sn 2þ states in the material were identified by XPS analysis. As explored by diffuse reflectance (DR) and photoluminescence (PL) spectroscopy, the material exhibited a distinct absorption edge at~3.4 eV. The morphological and microstructure analysis of the synthesized SnO 2 was carried out by FESEM and HRTEM. The electrochemical impedance spec-troscopy (EIS) and chronopotentiometry (CP) predicted the better charge transport and retention ability of the material under illumination whereas the Mott-Schottky extrapolation prophesied the n-type behavior with the flat-band potential of À0.60 V. The photocatalytic activity of SnO 2 was assessed in the exposure of complete spectrum natural sunlight for the removal of 2,4,6-trichlorophenol. The HPLC and TOC analysis monitored the progress of degradation and mineralization whereas the released chloride ions were evaluated by ion chromatography. The effect of the transition metal ions (Fe 3þ , Cu 2þ , Ni 2þ, and Zn 2þ) as electron capture agents and H 2 O 2 as ROS generator was explored during the degradation process. The utility of the material for the simultaneous removal of chlorophenols in the mixture was also investigated. The SnO 2 exhibited sustained activity in the repeated use. Based on experimental evidence congregated, the mechanism of the removal process and the efficacy of SnO 2 for sunlight photocatalytic decontamination of water was established.

Silicon carbide (SiC), owing to its extraordinary chemical stability and refractory properties, i... more Silicon carbide (SiC), owing to its extraordinary chemical stability and refractory properties, is widely used in the manufacturing industry. Despite the semiconducting nature and morphology-tuned band gap, its efficacy as photocatalysts has not been thoroughly investigated. The current study reports the synthesis, characterization and the evaluation of the capability of silicon carbide for hydrogen generation from water splitting. The optical characterization of the as-synthesized powder exposed the formation of multi-wavelength absorbing entities in synthetic process. The structural analysis by XRD and the fine microstructure analysis by HRTEM revealed the cubic 3C-SiC (β-SiC) and hexagonal α-polymorphs (2H-SiC and 6H-SiC) as major and minor phases, respectively. The Mott-Schottky analysis verified the n-type nature of the material with the flat band potential of − 0.7 V. In the electrochemical evaluation, the sharp increase in the peak currents in various potential ranges, under illumination, revealed the plausible potential of the material for the oxidation of water and generation of hydrogen. The generation of hydrogen and oxygen, as a consequence of water splitting in the actual photocatalytic experiments , was observed and measured. A significant increase in the yield of hydrogen was noticed in the presence of methanol as h + scavenger, whereas a retarding effect was offered by the Fe 3+ entities that served as e − scavengers. The combined effect of both methanol and Fe 3+ ions in the photocatalytic process was also investigated. Besides hydrogen gas, the other evolved gasses such as methane and carbon monoxide were also measured to estimate the mechanism of the process.

Concentrations of natural nuclides (226 Ra, 232 Th and 4 K) and some heavy metals (Cu, Fe. Ni, Pb... more Concentrations of natural nuclides (226 Ra, 232 Th and 4 K) and some heavy metals (Cu, Fe. Ni, Pb and As) were measured in groundwater collected from different locations in Makkah region in Saudi Arabia. In the radioactivity measurement, a high purity germanium detector system was used. In addition, chemical analysis was performed by an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The average measured activity concentrations of the nuclides 238 U, 232 Th and 4 K were 0.558, 0.204 and 4.581 BqL −1 , respectively. The total annual effective doses for ingestion of radionuclides in the water samples were 0.472 mSv for children and 0.169 mSv for adults. These results were lower than the recommended value (1.0 mSvy −1), as reported by WHO. The chemical analysis results showed that these water samples contain (Ca, Mg, Cu, Fe. Ni, Pb and As) elements. The concentration values were evaluated and compared with the internationally verified values. This study provides essential information for consumers and authorities; those at exposure risk from mineral water intake.

Natural sunlight 2-Chlorophenol 2-Nitrophenol a b s t r a c t The non-magnetic and magnetic polym... more Natural sunlight 2-Chlorophenol 2-Nitrophenol a b s t r a c t The non-magnetic and magnetic polymorphs of iron oxide (Fe2O3) namely: a-Fe2O3 (hematite) and c-Fe2O3 (maghemite) respectively, were synthesized by a facile surfactant aided hydrogel route. The synthesized polymorphs were characterized by diffuse reflectance, photoluminescence and raman spec-troscopy for optical properties whereas the morphological, structural, chemical and electronic state evaluation were performed by FESEM, HRTEM, XRD, and XPS. The charge transport and the stability of the materials were examined electroche mically. The photocatalytic activity of the synthesized poly-morphs was evaluated for the degradation of 2-chlorophenol and 2-nitrophenol in the exposure of the visible region and complete spectrum natural sunlight. Both the polymorphs exhibited a significantly high activity for the degradation of the phenolic substrate in the exposure of the complete spectrum of sunlight, however, the activity in the visible region of the sunlight was relatively lower. A substantial increase in the activity in the visible region was noticed when the polymorphs were exposed to complete spectrum sunlight prior to the photocatalytic experiments. The comparison of the exposed and unex-posed samples revealed the induction of defects that served as traps for the excited electrons and increased activity of the polymorphs.

The MoO 3 coated ZnO photocatalysts were synthesized for the optimum harvesting of the absorbed u... more The MoO 3 coated ZnO photocatalysts were synthesized for the optimum harvesting of the absorbed ultraviolet sunlight photons by initially permeating Mo 6+ ions at the surface of pre-synthesized ZnO and finally transformed to MoO 3 by thermal treatment in the air. The absorption spectra of the synthesized powders revealed the extension of the absorption edge in the visible region whereas, the photoluminescence spectroscopy established the supporting role of the MoO 3 coating in gradually plummeting the excitons recombination. The growth of additional peaks in Raman as well as X-ray photoelectron spectra and the appearance of the corresponding low-intensity reflection substantiated the surface prevalence of MoO 3. The absence of the individual particles of MoO 3 in FESEM and the verification of coated layer by HRTEM images validated the authenticity of the adopted synthetic route. The electrochemical evaluation of the synthesized powders under illumination revealed the complete elimination of photocorrosion and the synergic role of the MoO 3 layer for improved trap and transfer of charge carriers. The evaluation of the flat-band potentials of the coated powders by Mott-Schottky analysis revealed the suitability of the conduction band edges for the generation of superoxide anion radicals. The photocatalytic activity of the synthesized powders was assessed for the removal of chloro derivatives (mono-, di-, trichloroacetic acids) in comparison to pure acetic acid. A significant effect of the stability, polarity and ste-reochemical structure of the substrate on the photocatalytic removal process was observed and discussed. The experimental evidences from the timescale chemical analysis were interpreted for the identification of the reactive oxygen species (ROS) involved in the degradation/mineralization process. The validation of the http://dx. MARK Langmuir-Hinshelwood kinetic model was also examined. Efforts were made to estimate the plausible route of the degradation/mineralization process.

The issues of low photocatalytic activity and dissolution of ZnO in natural sunlight exposure wer... more The issues of low photocatalytic activity and dissolution of ZnO in natural sunlight exposure were addressed by implanting p-type Mn 3 O 4 on its surface. The optical analysis revealed the composite nature and suppression of exciton excitons recombination whereas the cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and chronopotentiometry substantiated the elimination of photocorro-sion respectively, low charge transfer resistance and better charge retention ability for the as-synthesized composites. The Mott-Schottky analysis by staircase potential impedance spectroscopy (SPIES) verified the p-n nature while the measurement of flat band potential (V fb) predicted the suitability of the band potentials for the enhanced generation of reactive oxygen species (ROS). The structure and morphology of the Mn 3 O 4-ZnO composites were evaluated by x-ray diffraction (XRD) and field emission electron microscopy (FESEM) whereas the fine structure analysis was performed by high-resolution transmission electron microscopy (HRTEM) analysis that revealed the discrete fringe patterns of p-type Mn 3 O 4 and ZnO in composites. The x-ray photoelectron spectroscopy (XPS) verified the simultaneous existence of Mn 2+ and Mn 3+ in Mn 3 O 4 nanoparticles. Compared to pure ZnO, due to the existence of charge transfer synergy between the p-type Mn 3 O 4 and n-type ZnO, the composites with moderate Mn 3 O 4 loadings exhibited marked activity for the removal of stable pollutants like 4-bromo and 4-chlorophenol in natural sunlight exposure. The correlation of the findings from various analytic tools of chemical analysis such as high-performance liquid chromatography (HPLC), ion chromatography (IC), total organic carbon (TOC) measurements and GC-MS analysis revealed the persuasive role of Cl and Br groups in regulating the degradation process. The composite catalyst exhibited excellent stability and reproducible activity in the repeated scans.

The use of inexpensive semiconducting materials and abundant natural sunlight can deliver the sus... more The use of inexpensive semiconducting materials and abundant natural sunlight can deliver the sustainable as well as cost-effective cleaning of contaminated water. In the current effort, the low photocatalytic activity of ZnO in sunlight exposure has been addressed by the slow deposition and after calcination, the deposition pattern of Fe 3+ ions was investigated. The appearance of distinct multiple absorption edges in the optical spectra verified the composite nature of the synthesized materials whereas the absorption edge at $2.5 eV indicated the formation of visible light responsive structures other than Fe 2 O 3. The additional reflections, besides the characteristic reflections of ZnO and Fe 2 O 3 , in the X-ray diffraction patterns and the appearance of discrete assortments in HRTEM analysis exposed the formation of surface ZnFe 2 O 4 in the interfacial region between the ZnO and Fe 2 O 3. The X-ray photoelectron analysis revealed the minor transitions in the oxidation state, more pronounced at higher Fe 3+ loadings, during the synthetic route. The electrochemical characterization revealed the p-type nature of the oxides of Fe 3+ whereas the flat-band potentials of the composites were assessed by Mott-Schottky analysis. As compared to pure ZnO, the composites loaded with lower concentrations (0.5% and 1%) of Fe 3+ showed substantially high activity for the removal of 2,4-dichlorophenoxy acetic acid (2,4-D) in the complete spectrum whereas 3% Fe 3+ loading exhibited optimum activity in the exposure of the visible region of natural sunlight. The higher Fe 3+ loadings revealed the detrimental effect on the photocatalytic removal process. The variations in the photocatalytic activity with the increasing Fe 3+ were discussed in correlation with electrochemical properties. The key intermediates were identified and the plausible mechanisms of the removal of 2,4-D were proposed by correlating the evidence from various experimental tools such as HPLC, IC, and TOC. The probable contribution of the reactive oxygen species (ROS) involved in the degradation process was estimated and discussed. The validity of the Langmuir-Hinshelwood kinetic model was also examined for the degradation as well as mineralization process.

Water, the driver of nature, has always been polluted by the blind hurling of highly toxic contam... more Water, the driver of nature, has always been polluted by the blind hurling of highly toxic contaminants, but human-friendly science has continuously been presenting better avenues to help solve these challenging issues. In this connection, the present study introduces novel nanocompo-sites composed of emulsion-templated hierarchically porous poly(1-vinylimidazole) beads loaded with the silver nano-particles generated via an in situ approach. These nano-composites have been thoroughly characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller, and field emission scanning electron microscopy. The appropriate surface chemistry, good thermal stability, swelling behavior, porosity, and nanodimensions contributed to achieve very good performance in water treatment. Owing to their easier handling and separation, these novel nanocomposites are highly efficient to remove arsenic and eriochrome black T with decent adsorption capacities in addition to the inactivation and killing of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria.

The efficacy of the ZnO-α-Fe 2 O 3 composites as carbon paste electrode (CPE) modifier for sensit... more The efficacy of the ZnO-α-Fe 2 O 3 composites as carbon paste electrode (CPE) modifier for sensitive electrochemical detection of loperamide was explored. The composites were synthesized in 1:1, 2:1, and 3:1 (ZnO:α-Fe 2 O 3) ratios by the gradual amalgamation of pre-synthesized α-Fe 2 O 3 and hydrated gel of Zn 2+ that later transformed to the ZnO by thermal treatment. The lattice parameters of the composite ZnO and the probable variations in the oxidation states of the components during the adopted coating procedure were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The field-emission scanning electron microscopy (FESEM) imaging of the as-synthesized and carbon paste (CP) dispersed composite powders at various resolutions exposed the increased surface coverage of the α-Fe 2 O 3 by the ZnO particles with the increasing loading and the uniform distribution of the composite materials in the matrix of carbon paste. Compared to bare CPE, the composites modified CPEs exhibited significantly decreased charge transfer impedance at the electrode/electrolyte interface evaluated by electrochemical impedance spectroscopy (EIS). The sensing ability of the composites modified electrodes for the detection of loperamide in the aqueous medium was investigated. A higher and affectedly improved cyclic voltammetric (CV) oxidation signal of loperamide was noticed at the prepared ZnO:α-Fe 2 O 3 /CPEs compared to pure components modified CPEs i.e. ZnO/CPE and α-Fe 2 O 3 /CPE. Based on the EIS and CV investigations, a superior electrochemical performance of (2:1) ZnO:α-Fe 2 O 3 /CPE was established. Additionally, under optimized experimental conditions of pH, deposition potential, and accumulation time, loperamide was quantified by square wave stripping voltammetry (SWSV) that resulted in the linear calibration ranges from 0.08-1 and 2-10 μmol L −1 with detection limits (S/N = 3) of 7.9 and 3.6 nmol L −1. The findings of various electrochemical investigations were correlated to establish the mechanism of charge transport and oxidation of loperamide.

Vanadium doped ZnO powders were used as precursors to deposit thin films of V 5þ incorporated ZnO... more Vanadium doped ZnO powders were used as precursors to deposit thin films of V 5þ incorporated ZnO nanoparticles on glass substrates by the pulsed laser deposition technique. The observed variations in Raman signals, visible region shift in the diffuse reflectance spectra along with a small shift in the (101) reflections of the X-ray diffraction (XRD) confirmed the insertion of V 5þ ions in ZnO lattice. No other additional reflection in the XRD results other than ZnO further endorsed the occupation of lattice positions by V entities rather than independent oxide formation. The asymmetric XPS peaks of Zn2p and V2p core levels confirmed the existence of both in the vicinity. The existence of minimal proportion of V 3þ along with V 5þ states varied the alteration of the oxidation states V in the synthetic route. The SEM images at various resolutions displayed the uniform distribution identical nanoparticles without the presence of additional phases in the deposited films. The SEM cross-section measurements revealed the uniform thickness of~90 nm of each film, whereas the surface studies of the films were performed by AFM. The as-synthesized films were tested for photocatalytic activity in sunlight illumination for the removal of 2-chlorophenol. The unique feature of the study was the estimation of the photocatalytic activity 20 ppm of 2-chlorophenol by exposing the low exposed area. The degradation of the substrate was measured by liquid phase UVevis spectroscopy, whereas total organic carbon measurement revealed the mineralization of the substrate. The released Cl À ions were also measured by ion chromatography. The estimated flatband potentials and pH zpc values of the V doped materials, by Mott-Schottky analysis and zeta potential measurements respectively, were correlated with the photo-catalytic activity. The kinetics of the photocatalytic degradation/mineralization process was estimated and results were correlated with the plausible mechanism.

In an effort to enhance the photocatalytic activity of cubic WO 3 in sunlight exposure, its surfa... more In an effort to enhance the photocatalytic activity of cubic WO 3 in sunlight exposure, its surface was modified by impregnating the Ce 3+ ions ranging from 1% to 25% with a step of 5% with respect to the weight of WO 3. Compared to pure WO 3 , the optical analysis by diffuse reflectance spectroscopy (DRS) revealed better absorption cross-section and red shift in the band edges for Ce loaded catalysts. The decreased intensity of photoluminescence (PL) emissions and the suppression of the Raman active bands of WO 3 verified the recombination quenching ability of Ce surface states. The XRD analysis revealed the existence of Ce 3+ states in the lower loadings (#5%), whereas the majority of Ce 4+ states were noticed at higher loadings. The FESEM analysis also verified the formation of individual particles of Ce(III,IV) oxides at the surface of WO 3 at higher loadings. The XPS analysis of 10% Ce loaded samples also revealed the presence of mixed oxides of Ce at higher loading. Except for 1% Ce loaded WO 3 , the estimation of charge-discharge capacity, in comparison to pure WO 3 , revealed the enhancement in the charge retention ability with the increasing Ce loading. In comparison to pure WO 3 , the synthesized catalysts exhibited superior activity for the removal of 2-nitrophenol and 2-chlorophenol substrates in natural sunlight exposure. The analysis of the degradation data revealed that in the lower concentration the surface oxygen bonded Ce 3+ states serve as electron trapping and transfer centers, whereas with the increasing surface density the synergic composite mechanism is the dominating mode. The exaggerated estimation in the EDX analysis of the samples loaded with 15% and 20% Ce also revealed the major surface coverage by the oxides. The salient feature of the study was the evaluation of the photocatalytic activity with the minimal catalyst loading of 350 mg L À1 .

Fe 3 O 4 nanoparticles Modified CPE SWV Voltammetric sensor A B S T R A C T The magnetite nanopar... more Fe 3 O 4 nanoparticles Modified CPE SWV Voltammetric sensor A B S T R A C T The magnetite nanoparticles (Fe 3 O 4), synthesized by surfactant aided hydrolysis of the stoichiometric amounts of ferrous (Fe 2+) and ferric (Fe 3+) ions, were dispersed in carbon paste (CP) to fabricate magnetite modified carbon paste electrode (Fe 3 O 4 /CPE). The field emission scanning electron microscopy (FESEM) was used to evaluate the morphology of the synthesized powder in the pure phase and its distribution in the CP that revealed the well-dispersed Fe 3 O 4 nanoparticles in the graphite sheet with a mean size of 10 nm. The microstructure analysis of the synthesized magnetite was performed by high-resolution transmission electron microscopy (HRTEM). The phase purity of the synthesized magnetite was evaluated by x-ray diffraction (XRD) analysis. After initial assessment of charge transport in the fabricated electrode by electrochemical impedance spectroscopy (EIS) that exhibited a substantial decrease of 87% in the charge transfer resistance, the suitability of the Fe 3 O 4 /CPE was assessed for the detection and determination of chlorite ion (ClO 2 À) in the aqueous medium. The modified CPE loaded with the optimized amount of Fe 3 O 4 showed considerably enhanced oxidation current as compared to pure CPE for the oxidation of ClO 2 À and exhibited a near-reversible peak at $ + 0.73 V in 0.1 M pH 7 phosphate buffers, at a scan rate of 50 mV/s. The optimum analytical conditions for the nanomolar detection of ClO 2 À by square wave voltammetry (SWV) were established. Likely interferences influencing the detection of ClO 2 À were also investigated. The excellent performance of the fabricated electrode was also established for the real tap and bottled water samples.

In an effort to develop a facile and rapid electrochemical sensing protocol for the detection of ... more In an effort to develop a facile and rapid electrochemical sensing protocol for the detection of tramadol in wastewater, the glassy carbon electrode (GCE) was modified with the blend of cetyltrimethylammonium bromide (CTAB) protected Au nanoparticles (Au NPs) and Nafion 1. The characteristic surface plasmon band at 525 nm and the fading of the NÀ ÀH bands in the absorption and the FTIR spectra revealed the metallic nature and interaction of Au NPs with CTAB molecules. The dispersion of the protected and unprotected Au NPs at the surface of the GCE was investigated by atomic force microscopy (AFM). The charge transfer behavior of the fabricated Nafion 1 /CTAB-Au/GC electrode was investigated by electrochemical AC impedance spectroscopy (EIS). The significantly enhanced response of the polymer distributed CTAB protected Au NPs for the detection of tramadol revealed the salient role of Nafion 1 matrix in facilitating the charge transfer. The square wave anodic stripping voltammetry (SWASV) analysis was employed to quantify the amount of tramadol. Prior to the application on real wastewater samples, the experimental variables for sensitive detection such as SWASV parameters, deposition potential, deposition time, and pH were optimized. The SWASV response of Nafion 1 /CTAB-Au/GCE was linear over the 0.5-1 mg/mL and 2-12 mg/mL ranges with a detection limit (S/N = 3) of 3 Â 10 À4 mg/mL. The fabricated electrode exhibited sustained performance for the detection of tramadol in the repeated scans over a prolonged period.

Although the photocatalytic activity of TiO 2 polymorphs and hexagonal ZnO is well studied with a... more Although the photocatalytic activity of TiO 2 polymorphs and hexagonal ZnO is well studied with artificial UV light sources, however, their efficacy is not well examined in natural sunlight exposure. In the current study, the photocata-lytic activity of the polymorphs of TiO 2 (rutile and anatase) and hexagonal ZnO was evaluated in sunlight exposure for the removal of resonance stabilized 2-, and 4-derivatives of chloro and nitrophenol isomers and compared with that of P-25. The polymorphs of TiO 2 and hexagonal ZnO, after synthesis by sol-gel and hy-drogel routes, were subjected to optical, structural and morphological characterization. The hexagonal ZnO exhibited significantly higher as compared to anatase and rutile polymorphs but comparable with that of P-25 in sunlight illumination. For the hexagonal ZnO, the ring opening route of degradation mediated by superoxide anion radicals was confirmed by the absence of non-hydroxylated aromatic intermediates whereas the contribution of both superoxide anion radicals and hydroxyl radicals was evidenced for the TiO 2 polymorphs and P-25. The kinetics of the degradation/mineralization of substrates was also compared.

Applied Catalysis B: Environmental, 2016

The photocatalytic activity of nanostructured CeO 2 was investigated for the degradation of pheno... more The photocatalytic activity of nanostructured CeO 2 was investigated for the degradation of phenol and its derivatives (2-chlorophenol, 2-bromophenol and 2-nitrophenol) in the exposure of complete spectrum and visible region (420-800 nm) of sunlight. The adopted experimental parameters imparted high crystallinity, phase purity, controlled morphology and uniform particle size of ∼11 nm to the synthesized CeO 2. During the evaluation of the photocatalytic activity, the initial low degradation of the substrates till the 90 min of complete spectrum sunlight exposure followed by a piercing increase predicted the favorable photon induced surface changes in CeO 2. The careful examination of the exposed and unex-posed CeO 2 by spectroscopic techniques (diffuse reflectance (DR), photoluminescence (PL), ATR-FTIR and Raman spectroscopy) and electrochemical tools (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP)) revealed the vital role of photon induced surface phases for the improved spectral response and suppressed charge carries recombination process. Based on the appearance of additional weak reflection at 2Â = 28.15 • in the X-ray diffraction (XRD) pattern and inhalation of O 2 in the thermogravimetric analysis (TGA) of sunlight exposed samples revealed the prevalence of photon induced defects generated by the departure of surface oxygen from CeO 2. The induction of defects composed of CeO 2-x states resulted in the improved activity of the exposed compared to unex-posed CeO 2 in the visible spectrum (420-800 nm) of sunlight. The efficient degradation of 2-CP, 2-BP and 2-NP compared to a mild degradation for phenol, in the complete spectrum sunlight exposure, indicated the facilitating role of substituents attached to the aromatic system in the degradation process. The monitoring of the photocatalytic degradation process by HPLC and identification of intermediates by GC-MS analysis revealed the formation of aromatic intermediates in the degradation of phenol and 2-BP while no aromatic intermediate was identified in the degradation of 2-NP and 2-CP. The rapid disappearance of the total carbon and further oxidation of released anions supported the major role of superoxide anion radicals in the oxidation process. Both pure and sunlight exposed CeO 2 exhibited sustained photocatalytic activity in the repeated exposures.

Journal of Molecular Catalysis A: Chemical , 2016

The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4), with va... more The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4), with varying ratios of Au, were synthesized by a facile route. The diffuse reflectance spectroscopy (DRS) verified the upsurge in the intensity of characteristic surface plasmonic resonance (SPR) absorption bands with the increasing Au contents. The photoluminescence (PL) spectroscopy estimated the role of surface dispersed Au-Ag alloy NPs on the luminescence properties of g-C 3 N 4 and the suppression the probable recombination of photo-generated excitons. The structural characterization by XRD and morphological assessment by SEM revealed the uniform dispersion of Au-Ag alloy nanoparticles on the surface of g-C 3 N 4 whereas XPS analysis endorsed the presence of Au and Ag in metallic form. The HRTEM analysis confirmed the homogeneous distribution of Au and Ag contents in the alloys. The photocatalytic activity of the Au-Ag/g-C 3 N 4 was evaluated in the exposure of natural sunlight and artificial visible light for the degradation of dye substrate and compared with that of g-C 3 N 4 , Ag/g-C 3 N 4 and Au/g-C 3 N 4. The Au-Ag alloy modified g-C 3 N 4 photocatalysts exhibited significantly higher activity for the decolorization of Rhodamine B in the visible light as compared to pure, Ag and Au loaded g-C 3 N 4 that signified the contributing role of SPR in the degradation process. The individual role of SPR in the photocatalytic process was also verified by using monochromatic (532 nm) visible laser light. The mineralization ability of the synthesized alloy catalysts was estimated by TOC removal efficiency. The kinetics of the degradation/mineralization processes under various experimental conditions was also evaluated.

Applied Catalysis B: Environmental , 2014

The synthesis, characterization and sunlight photocatalytic activity of W 6+ impregnated ZnO for ... more The synthesis, characterization and sunlight photocatalytic activity of W 6+ impregnated ZnO for the degradation of nitrophenol isomers (2-nitrophenol, 3-nitrophenol, and 4-nitrophenol) is reported. Compared to pure ZnO, the impregnated catalysts exhibited a relatively improved spectral response in the visible region. The significant decrease in luminescence intensity for W 6+ impregnated catalysts, relative to pure ZnO, established the effective trapping of charge carriers by surface bonded W 6+ states. The characterization of the impregnated catalysts by FESEM, XRD and XPS revealed the presence of impregnated W 6+ entities at the surface without affecting the morphology of ZnO. The synthesized catalysts exhibited superior activity for the mineralization of three nitrophenol isomers under sunlight exposure. Based on HPLC analysis, ∼99% of 2-and 4-nitrophenol was degraded in a short span of 120 min while a degradation of >80% was observed in 3-nitrophenol in the same period. Time scale TOC measurements ratified the mineralization capability of impregnated catalysts. The release of NO 2 − , NO 3 − ions in the solution, pH measurements and non-existence of hydroxylated aromatic intermediates revealed that superoxide anion radicals (O 2 •−) are the major contributors in the degradation process. Besides the traces of coupling products, major intermediates identified by GC-MS analysis were either aliphatic dihydroxy alcohols, car-boxylic acids or other oxygen containing species depicting that the degradation process proceeds through ring opening mechanism. The W 6+ impregnated catalyst also furnished high activity in the visible portion of sunlight. Suitable kinetic models were applied to estimate the rate constants (k) of various processes involved in the degradation process. The stability of the photocatalyst against photocorrosion and the possible decrease in the activity of the catalyst in the successive use was also monitored.

Journal of Hazardous Materials , 2014

The surfactant assisted synthesis of disc-shaped WO3 powder and its photocatalytic performance in... more The surfactant assisted synthesis of disc-shaped WO3 powder and its photocatalytic performance in sunlight exposure is reported. UV–vis DRS, XRD and FESEM characterized the synthesized WO3. The synthesized powder exhibited a bandgap of ∼2.55 eV with cubic lattice and high crystallinity. The photocatalytic activity of the synthesized WO3 was examined for the degradation of phenol, resorcinol, 2-chlorophenol and 2-nitrophenol in complete spectrum and visible segment of sunlight. The highly efficient degradation/mineralization of 2-chloro and 2-nitrophenol compared to that of phenol and resorcinol, under identical experimental conditions, suggested the regulatory role of substituents attached to the aromatic ring in degradation/mineralization process. The time-scale HPLC degradation profiles, identification of intermediates by GC-MS and removal of organic carbon during the course of reaction were utilized to approximate the possible route of degradation/mineralization of phenolic substrates. The measurement of the anions released during the photocatalytic process was used to identify the nature of the major oxidants (O2•−, OH•) and the possible interaction sites. A significant decrease in the photocatalytic activity of synthesized WO3, ∼50%, was observed in visible portion of sunlight however, a sustained activity was observed in the repeated exposures.