Phase and Shape Dependent Photoactivity of Titania for Nitroaromatics Reduction Under UV Light Irradiation.

This work describes importance of TiO2 nanostructures of different shapes (nanospheres and nanorods) and crystal phases (anatase and rutile) for the photoreduction of nitroaromatics into corresponding aminoaromatics under UV light irradiation. Anatase nanoparticles were most active of all the catalysts due to the superior stability of this phase and comparatively the rutile nanorods (L×W = 28-30 nm×3.5-3.8 nm) showed superior photoactivity (~3 times) as compared to rutile nanospheres of size 122 nm for the photoreduction due to electron transport along longitudinal length, larger surface area (69 m²g-1), quenched PL emission, increased lifetime of charge carriers (1.8 ns) of rutile nanorods as compare to rutile nanospheres having lower surface area (18 m²g-1) and charge carrier lifetime (1.1 ns). The overall rate of reduction/hour for m-NBA and m-NT photoreduction with all of these catalysts has been found to vary in the following order ANP > P25-TiO2 > RNR > ANR > RNP.

Remarkably Improved Dispersion Stability and Thermal Conductivity of WO3-H2O Suspension by SiO2 Coating.

The long term dispersion stability for an improved thermal conductivity is a challenging issue that needs to be solved for heat transfer applications. Hence, this research investigated that a thin layer of SiO2 coating (2-5 nm) over WO3 nanostructures (SiO2@WO3) of different shapes exhibit superior dispersion (0.01%) stability for longer duration (∼3 days) as evident by steady zeta potential (-30 ↔ -60.70 mV), no significant change in particle-size (139 ↔ 147 nm) distribution, density (1.001 ↔ 0.988 g/cm3) and refractive index (1.335 ↔ 1.332) etc., are indicator for colloidal stability relative to bare WO3 nanoparticles and bulk SiO2 aqueous suspension which quickly settles down within 1-2 hours after 30 min sonication at 23 °C. Thin Si-OH layer over WO3 surface imparts superior hydrophilicity, larger surface area for effective solute-solvent (SiO2@WO3-H2O) interaction for improved colloidal stability showing no sedimentation and color change of SiO2@WO3 dispersion (0.01%) even after 3 days due to repulsive interaction between negatively charged Si-O- particles. Thereby, thermal conductivity is found to be quite stable (0.631 ↔ 0.618 W/m K) up to 3 days, whereas aqueous suspension of bare WO3 and SiO2 particles quickly settle down and thermal conductivity rapidly decreased to a value of 0.584 W/m K for de-ionized water further indicates the significance of SiO2 coating. Depending on the thickness of SiO2 layer and volume fraction of SiO2@WO3, a maximum of 8-10% increment of thermal conductivity was achieved where anisotropic WO3 displayed always more (∼5%) thermal conductivity than typical spherical nanoparticles.

Photocatalytic Degradation of Methylene Blue by Plasmonic Metal-TiO2 Nanocatalysts Under Visible Light Irradiation.

This study demonstrates photocatalytic activity of 1 wt% plasmonic metal (Au, Ag and Cu)­TiO2 nanocatalysts prepared via photodeposition method for the photo oxidative decomposition of methylene blue (MB 0.01 mM) under visible light (50 mWcm−2) irradiation. Plasmonic metal loaded-TiO2 photocatalysts absorb with an absorption maximum at localized surface plasmon resonance wavelengths (500­785 nm). It has been observed that pH altered the surface charge (ζ) of TiO2 (ζ = ­4.98, ­4.0 and +9.16 at pH = 10, 7 and 3, respectively). The point of zero charge (PZC) at pH 6.3 has been determined from a correlation plot between pH and ζ. Higher rate of degradation was observed at pH = 10 because of electrostatic interaction of cationic MB with anionic TiO2. Higher photocatalytic activity was shown by Cu­TiO2 followed by Au­TiO2 and Ag­TiO2 photocatalysts in comparison to TiO2-P25. This enhancement in photocatalytic efficiency is attributed to the plasmonic effect and effective charge separation at the interface between nano size metal deposits and TiO2 particles. The overall photocatalytic reaction followed pseudo first order kinetics as per Langmuir Hinshelwood kinetic equation. GC and GC-MS studies suggested the formation of thionin after demethylation and derivatives of benzene sulphonic acid which are subsequently degraded to CO2 after prolonged irradiation time.

Shape Dependent Thermal Conductivity of TiO2-Deionized Water and Ethylene Glycol Dispersion.

This paper presents the importance of different shapes and crystal phases of TiO2 nanostructures such as TiO2 P-25 (70:30 anatase and rutile), as-prepared nanorods (pure anatase) and sodium titanate nanotubes (orthorhombic Na2Ti2O5 x H2O crystal) on the thermal conductivity of de-ionized water and ethylene glycol. It revealed that TiO2 nanorods (L x W = 81-134 nm x 8-13 nm and surface area = 79 m2 g(-1)) showed always higher thermal conductivity than porous nanotubes (L x W = 85-115 nm x 9-12 nm and surface area = 176 m2 g(-1)) and commercial TiO2 P-25 (30-55 nm surface area = 56 m2 g(-1)), which was explained by their differences in crystallinity, crystal phases, compactness, surface exposed atoms, surface area and much greater mean free path of longitudinal phonon vibrations along its lateral dimensions. The subsequent effect of sonication time from 5-10 h results into the breakdown of TiO2 nanorods cluster (42 to 28 nm) with the instantaneous increase in negative zeta potential values from -31 to -45 mV, respectively, seems to be an additional cause for enhancement in its thermal conductivity.

Enhanced Photocatalytic Activity of as-Prepared Sodium Titanates for m-Dinitrobenzene Reduction and Sulfosulfuron Oxidation.

This paper demonstrates the preparation and photocatalytic activity of sodium titanate nanorods and nanotubes prepared by hydrothermal method using P25-TiO2 as the precursor. XRD results confirmed the monoclinic structure of sodium titanate nanorods obtained after calcinations of orthorhombic sodium titanate nanotubes at 800 °C for 2 h. The BET surface area of sodium titanate nanotubes (176 m2 g-1) was significantly reduced for sodium titanate nanorods (21 m2 g-1) formation because of the collapsing of the hollow interior of the former during its high temperature sintering. The selective formation of m-diaminobenzene by the photoreduction of the m-dinitrobenzene was found to be comparable by sodium titanate nanorods (89.5 ± 0.5%) and P25-TiO2 (98.2 ± 0.8%), whereas Au-deposition (0.5 and 2 wt%) onto sodium titanate nanorods notably altered the products (m-nitroaniline and m-diaminobenzene) distribution after 8 h of UV-light irradiation and which was confirmed later by GC-MS analysis. This high photoactivity of as-prepared nanorods could be credited to better delocalization and longer relaxation lifetime (68 µs) of photoexcited e-/h+ pairs along the length of crystalline sodium titanate nanorods than P25-TiO2 (45 µs) as measured from Time-resolved spectroscopy. The photooxidation of sulfosulfuron herbicide (1000 ppm) and corresponding CO2 formation was found to be highest with sodium titanate nanotubes due to the presence of more hydroxyl groups over the largest surface area that dominates over its least relaxation lifetime (41 µs).

Selective photo-reduction of p-nitrophenol to p-aminophenol by Au deposited CdS nanostructures of different shapes having large surface area.

The preparation and photocatalytic reductive ability of a new spongy flower or cotton bud like amorphous CdS microstructures (size = 200-300 nm) having intermediate crystal phase between cubic and hexagonal structure and possesses much larger surface area ca. 119 m2 g(-1) is demonstrated here. Structural analysis has been done by TEM, XRD, BET surface area, UV-Vis absorption, luminescence analysis, and photocatalytic study. The photoreactivity of as-prepared CdS for p-nitrophenol reduction to p-aminophenol conversion under visible light (150 W halogen lamp) irradiation has been found to be greatly enhanced from 62% to 94% (yield) and 81% to 100% (selectivity) after 1 wt% Au deposition. The obtained p-aminophenol yield is always better than 32% for CdS nanosphere (size 10-12 nm) and 40% for CdS nanorod (length/width in nm = 126/6). Surface passivation with a thin layer of SiO2 coating over this flower like spongy CdS appreciably increased the BET surface area to 158 m2 g(-1) and displayed stable photocatalytic activity for p-nitrophenol reduction up to 30 h of light exposure as compared to bare CdS of low activity because of its easy photodissolution. A good co-relation between the BET surface area and surface photoactivity of as-prepared CdS with the conventional cubic and hexagonal CdS nanoparticles of different dimensions is established here.

Superior photoluminescence and photocatalytic activity of CdS (core)-SiO2 (shell) nanostructures obtained by CdS photoetching and Au deposition.

Core-shell morphology of silica (SiO2) coated CdS nanocomposites (SiO2@CdS) of different shapes have been made for better stability, luminescence and photochemical activity of CdS nanoparticles. A thin layer (thickness 1-1.4 nm) of SiO2 shell is deposited over CdS nanorods (CdS-NR) of aspect ratio = 21 and CdS nanospheres (CdS-NS) of size 6-8 nm by alkyl silane agents. Synthesized nanostructures were characterized by diffuse reflectance spectra, HR-TEM, BET surface measurement, LB surface film, and absorption and photoluminescence analysis. Photoetching (PE) of CdS core led to blue shift of the absorbance onset of SiO2@CdS-NR along with the appearance of an exciton band at 485 nm due to the quantum confinement effect. Photodissolution of CdS core shifts the band gap energy from initial 2.4 to 2.6 eV for CdS-NR and 2.5 to 2.67 eV for CdS-NS. TEM images reveal the increase in aspect ratio of NR from 21 to 31 and decrease in the spherical core to 2.5 nm from 6-8 nm after PE. Photoetched SiO2@CdS-NC displayed highly intense fluorescence emission (SiO2@CdS-NS > SiO2@CdS-NR) than unetched SiO2@CdS-NC at 488 nm corresponding to band edge position. The Au (0.5 wt.%) deposition onto photoetched SiO2@CdS-NR(PE) composites highly enhanced the fluorescence intensity in comparison to 1 wt.% of Au and Ag loading. SiO2@CdS-NC(PE) displayed improved photocatalytic activity during benzaldehyde photooxidation under UV (125 W, Hg-arc, 10.4 mW/cm2) irradiation. Silica coating onto CdS particles improves the photostability and photoactivity of CdS upon long UV irradiation.

Priority PAHs in orthodox black tea during manufacturing process.

Orthodox black tea is obtained from fresh leaves followed by withering, rolling, fermentation and drying. The presence of 16 priority polycyclic aromatic hydrocarbons (PAHs) was studied in fresh leaves and at various stages of manufacturing. Benzo(a)pyrene (2A: probable human carcinogen) was found in dried tea leaves only whereas, naphthalene (2B: probable human carcinogen) was present during all the stages of manufacturing. Dry tea leaves showed higher content of total 16 PAHs (∑PAHs) about 3 and 211 times than present in withered and dried leaves, respectively. Chrysene, benzo[g,h,i]perylene, indendo[1,2,3-c,d]pyrene, dibenzo[a,h]pyrene and benzo[a]antracene were not found during manufacturing stages of tea.

Polycyclic aromatic hydrocarbons in some grounded coffee brands.

Potentially toxic 16 priority polycyclic aromatic hydrocarbons (PAHs) were determined in four brands of grounded coffee. Four to 13 PAHs were detected. Concentrations of total PAHs in different brands of coffee samples were in the range of 831.7-1,589.7 µg/kg. Benzo[a]pyrene (2A: probable human carcinogen) was found in Nescafe Premium whereas naphthalene (2B: possible human carcinogen) was found in all the samples of coffee.

Starch modified NiFe layered double hydroxide composites for better adsorption and photocatalytic removal of reactive dye and piroxicam-20 drug.

One of the most omnipresent problems to the environment is the efficient removal of textile dyes and non-steroidal drugs from wastewater. For this purpose, renewable, sustainable, and biodegradable biopolymers are used. In this study, starch (S) modified NiFe-layered double hydroxide (LDH) composites were successfully synthesized by the co-precipitation method and have been examined as a catalyst for the effective adsorption of reactive blue 19 dye, reactive orange 16 dye, and piroxicam-20 NSAID from wastewater and photocatalytic degradation of reactive red 120 dye. The physicochemical properties of the prepared catalyst were assessed by XRD, FTIR, HRTEM, FE-SEM, DLS, ZETA, and BET. The coarser and more porous micrographs are shown in FESEM, indicating the homogeneous dispersion of layered double hydroxide on starch polymer chains. The S/NiFe-LDH composites have a slightly greater SBET (6.736 m2/g) than NiFe LDH (4.78 m2/g). The S/NiFe-LDH composite shows remarkable ability in the removal of reactive dyes. The band gap value of NiFe LDH, S/NiFe LDH (0.5:1), and S/NiFe LDH (1:1) composites was calculated as 2.28 eV, 1.80 eV, and 1.74 eV, respectively. The qmax assessed from Langmuir isotherm for removal of piroxicam-20 drug, reactive blue 19 dye, and reactive orange 16 was 2840 mg/g, 149.47 mg/g, and 182.4 mg/g, respectively. The activated chemical adsorption without product desorption is predicted by the Elovich kinetic model. With reactive red 120 dye, S/NiFe-LDH shows photocatalytic degradation within 3 h of irradiation of visible light with 90% removal efficiency and follows a pseudo-first-order kinetic model. The scavenging experiment confirms the involvement of electrons and holes in photocatalytic degradation. With a little decline in adsorption capacity up to five cycles, starch/NiFe LDH was easily regenerated. So, the suitable adsorbent required for wastewater treatment is nanocomposites of LDHs and starch as they enhance the chemical and physical attributes of the composite structure with greater absorption capabilities.

Graphene oxide-coated Ag-TiO2 hybrid nanocomposites for superior photocatalytic activity.

Graphene oxide (GO) has now emerged as one of the most promising materials in different areas such as photocatalysis, adsorption, and energy storage due to its high surface area, unique layered structure, etc. Among various types of precursors, anthracite coal has attracted a lot of attention nowadays as it affords GO a high concentration of sp2 carbons resulting in high conductivity and superior absorbance in the visible region. In this report, we have prepared GO-TiO2 nanocomposites as it is supposed to possess high photocatalytic activity owing to facile electron transmission from the conduction band of TiO2 to the GO surface resulting in a much lower degree of electron-hole pair recombination. To boost the photocatalytic activity further, TiO2 was coated with Ag nanoparticles as well. These hybrid structures were characterized by different analytical techniques, for example, XRD, HR-TEM, SEM, and Raman spectroscopy. The XRD pattern of these composites consists of characteristic peaks corresponding to GO, TiO2, and Ag. The HR-TEM studies confirm the presence of GO layers, cube-shaped TiO2, and spherical Ag nanoparticles. Phenol and 4-nitrophenol have been used as model pollutants to evaluate the photooxidation efficiencies under both UV and visible light irradiation. Under UV irradiation, the GO/Ag-TiO2 ternary nanocomposite shows better photooxidation efficiency (62%) compared to Ag-TiO2 (38%), GO-TiO2 (9%), GO (17%), and TiO2 (8%) toward phenol degradation. The GO/Ag-TiO2 is also having the highest photocatalytic activity toward the removal of phenol under visible light irradiation (34%). The ternary heterostructure (85%) also possesses superior photooxidation activity compared to Ag-TiO2 (44%) and GO-TiO2 (71%) toward the degradation of p-nitrophenol under UV light radiation for 60 min. The above observation reveals that the cooperative effect of Ag, TiO2, and GO is playing a crucial role to result in the high photooxidation activity of the GO/Ag-TiO2 hetero-nanocomposites.

Improved photocatalytic degradation of rhodamine B by g-C3N4 loaded BiVO4 nanocomposites.

Photocatalytic degradation has emerged as one of the most efficient methods to eliminate toxic dyes from wastewater. In this context, graphitic nitride (g-C3N4) loaded BiVO4 nanocomposites (5 wt% g-CN@BiVO4 and 10 wt% g-CN@BiVO4) have been fabricated by the wet impregnation method, and their efficiency towards photocatalytic removal of rhodamine B have been investigated under visible light irradiation. These hybrid composites have been characterized by XRD, FESEM, HRTEM, EDS-mapping, UV-Vis DRS, DLS, XPS and BET, etc. The HRTEM images revealed that BiVO4 has a decagonal shape covered by a layered nanosheet-like structure of g-C3N4. BET measurements suggest increasing the proportion of g-C3N4 results enhancement of the specific surface area. Among different photocatalysts, the 10 wt% g-C3N4@BiVO4 hybrid possesses the best catalytic activity with 86% degradation efficiency after 60 min of reaction time. The LC-MS studies suggest that the degradation reactions follow the de-ethylation pathway. Even after five cycles, the heterostructure shows only a 14% decrease in photocatalytic activity, confirming its stability. As a result, the binary composite can be regarded as a promising catalyst for the degradation of pollutants due to its ease of preparation, high stability and superior catalytic activity.

Morphology Dependent Photocatalytic Activity of CuO/CuO-TiO2 Nanocatalyst for Degradation of Methyl Orange Under Sunlight.

CuO nanoparticles have been extensively used as a photocatalyst because of their superior activity, selectivity and stability properties. The catalytic efficiency of these oxide nanoparticles can be improved by varying the size and shape of nanoparticles. Here, we report the synthesis of different shaped CuO nanoparticles and their impregnation on TiO2. Optical analysis revealed that a considerable red shift (420 nm to 550 nm) in absorption spectra of CuO-TiO2 nanocomposites was observed compared to bare CuO nanoparticles. DLS measurements showed that the average hydrodynamic size of CuO nanostars was increased from 160 nm to 584 nm after deposition on TiO2. These nanocomposites were examined for photocatalytic degradation of methyl orange under sunlight radiation. It was observed that CuO-TiO2 nanostars exhibited superior photocatalytic efficiency compared to CuO-nanoneedles, nanocrumbles and bare CuO nanoparticles. The CuO nanoparticles act as co-catalyst on the surface of TiO2 and alter the physicochemical properties of TiO2. The higher activity arises due to the fact that the doping of CuO reduces the recombination of charge carries (e--h+) and creates the intra-gap states which result in higher absorption of light radiations. Therefore, CuO nanoparticles impregnated on TiO2 found to be an effective and ideal catalyst for the photodegradation of methyl orange dye.

Photocatalytic syntheses of azoxybenzene by visible light irradiation of silica-coated cadmium sulfide nanocomposites.

Photoirradiation (lambda= 436 nm) of a deaerated 2-propanol aqueous solution containing nitrobenzene and rhodium-loaded silica-coated cadmium sulfide nanoparticles produced azoxybenzene with relatively high selectivity (68%), the photocatalytic activity being enhanced with a decrease in the size of the semiconductor particle core.

Selective detection of Mg2+ ions via enhanced fluorescence emission using Au-DNA nanocomposites.

The biophysical properties of DNA-modified Au nanoparticles (AuNPs) have attracted a great deal of research interest for various applications in biosensing. AuNPs have strong binding capability to the phosphate and sugar groups in DNA, rendering unique physicochemical properties for detection of metal ions. The formation of Au-DNA nanocomposites is evident from the observed changes in the optical absorption, plasmon band, zeta potential, DLS particle size distribution, as well as TEM and AFM surface morphology analysis. Circular dichroism studies also revealed that DNA-functionalized AuNP binding caused a conformational change in the DNA structure. Due to the size and shape dependent plasmonic interactions of AuNPs (33-78 nm) with DNA, the resultant Au-DNA nanocomposites (NCs) exhibit superior fluorescence emission due to chemical binding with Ca2+, Fe2+ and Mg2+ ions. A significant increase in fluorescence emission (λex = 260 nm) of Au-DNA NCs was observed after selectively binding with Mg2+ ions (20-800 ppm) in an aqueous solution where a minimum of 100 ppm Mg2+ ions was detected based on the linearity of concentration versus fluorescence intensity curve (λem = 400 nm). The effectiveness of Au-DNA nanocomposites was further verified by comparing the known concentration (50-120 ppm) of Mg2+ ions in synthetic tap water and a real life sample of Gelusil (300-360 ppm Mg2+), a widely used antacid medicine. Therefore, this method could be a sensitive tool for the estimation of water hardness after careful preparation of a suitably designed Au-DNA nanostructure.

Fine CuO anisotropic nanoparticles supported on mesoporous SBA-15 for selective hydrogenation of nitroaromatics.

SBA-15 modified with APTMS (3-aminopropyl trimethoxysilane) having pore diameter (∼8 nm) has been synthesized and impregnated with 1-10 wt.% Cu using Cu(NO3)2 as a metal source followed by calcination at 350 °C. As-prepared CuO/ap-SBA-15 powder showed changes in the color from white for bare SBA-15 to light green due to formation of anisotropic CuO nanoparticles that exhibited a characteristic plasmon absorption band at 359 and 747 nm. TEM studies showed a change in the morphology of CuO NPs as a function of increased Cu loading. Moreover, well dispersed CuO nanospheres (∼5-6 nm) and nanorods (aspect ratio ∼11-20 nm) having monoclinic crystal phase were observed within the mesoporous channels of SBA-15. Elemental mapping studies confirmed uniform distribution of CuO nanoparticles on the surface of SBA-15. An increase in surface area was also observed from 694 m(2) g(-1) for SBA-15 to 762 m(2) g(-1) for 10 wt.% Cu loading probably due to the deposition of excess of CuO nanoparticles on the outer siliceous surface. The catalytic activity also increased with Cu loading and 10 wt.% CuO/ap-SBA-15 catalyst displayed the highest catalytic activity for the reduction of m-chloronitrobenzene and m-nitrotoluene with 83% and 100% selectivity for m-chloroaniline and m-aminotoluene respectively.

Preparation, Surface and Crystal Structure, Band Energetics, Optoelectronic, and Photocatalytic Properties of Aux Cd1-x S Nanorods.

A series of novel Aux Cd1-x S materials (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) were prepared and their optical properties, structural-surface morphology, and photocatalytic activity for oxidation and reduction reactions under visible-light irradiation were studied. X-ray diffraction confirmed the shrinkage of the hexagonal crystal structure of CdS; the lattice parameters decreased as a=4.190→4.072 Šand b=c=6.790→6.635 Šwith increased loading (1-10 mol %) of the Au3+ dopant. Optical spectra of Aux Cd1-x S revealed a significant red-shift (485→538 nm) of the absorption onset and band edge emission (506→530 nm) with notable quenching in photoluminescence. The bandgap energy decreases (2.71→2.41 eV) with increasing Au3+ doping of the CdS nanorods along with considerable shifting of valence band (+1.13→+1.04 eV) and conduction band positions (-1.58→-1.36 eV) versus NHE. The surface area of bare CdS (90.56 m2 g-1 ) is gradually reduced to 12.32 m2 g-1 with increasing Au3+ doping content. The photocatalytic activity considerably improves with doping, where the Au0.1 Cd0.9 S composite displays the highest levels of photooxidation (95 %) of 0.5 mM salicyldehyde and reduction of 5 mM m-dinitrobenzene to m-nitroaniline (44 %) and m-phenylenediamine (52 %) relative to bare CdS (50 %) probably due to the homogeneous dispersion of Au3+ ions throughout CdS crystal, their superior band-energetics for facile charge-separation and better photostability.

Selective formation of benzo[c]cinnoline by photocatalytic reduction of 2,2'-dinitrobiphenyl using TiO2 and under UV light irradiation.

Photocatalytic reduction of 25 µmol 2,2'-dinitrobiphenyl in 50% aqueous iso-propanol and 50 mg P25-TiO2 under an argon atmosphere and 20 h UV light irradiation selectively produced 23.8 µmol of benzo[c]cinnoline (95%), and 2,2'-biphenyldiamine (5%) whose amount gradually increased with the irradiation time beyond 20-24 h due to further reduction of benzo[c]cinnoline.

Influence of Different Reducing Agents on the Ag Nanostructures and Their Electrokinetic and Catalytic Properties.

This paper shows the impact of various reducing agents; sodium borohydride, trisodium citrate and polyvinyl pyrollidone (PVP) on the surface morphology of Ag nanoparticles (AgNPs). The AgNPs prepared by PVP are found to be much larger in size ca. ≈ 40-70 nm having red shifted surface plasmon band (SPR band) at 475 nm as compared to relatively smaller size ≈ 10-14 nm (SPR band ≈ 392 nm) prepared by reduction with sodium borohydride as confirmed by both TEM and DLS analysis. PVP act as a shape-control agent and results in well defined bipyramid shaped particles while sodium borohydride and trisodium citrate yields spherical, oval and polygonal morphologies. The measured zeta potential of AgNPs prepared by sodium citrate (-28.9 mV), sodium borohydride (-20.0 mV) and PVP (-6.0 mV) is notably decreased with geometric faces. Both co-catalytic and catalytic properties of various Ag nanostructures were evaluated for the photo oxidation of benzoic acid by AgNPs-TiO2 mixture, and for the reduction of p-nitrophenol to p-aminophenol, respectively. A significant increase in the catalytic (17 to 55%) and co-catalytic activity (20 to 50%) was found with decreasing size (50 to 12 nm) and increasing the surface to volume ratio (0.096 to 0.48 nm(-1)) of obtained AgNPs of different surface structure.

Photodegradation of imidacloprid insecticide by Ag-deposited titanate nanotubes: a study of intermediates and their reaction pathways.

The present work demonstrates the influence of Ag-loading (0.2-1.0 wt %) onto sodium titanate nanotubes (TNT) for complete photomineralization of the neurotoxic imidacloprid (IMI) insecticide under UV light illumination. It has been observed that degradation of IMI follows pseudo-first-order kinetics, where 0.5 wt % Ag-loaded TNT exhibited highest apparent rate constant (2.2 × 10(-2) min(-1)) and corresponding least half-life (t1/2) of 31 min for IMI relative to bare P25-TiO2 (3.4 × 10(-3) min(-1), t1/2 = 230 min). The mineralization of IMI intermediates to CO2 during its photooxidation has been described by time course GC-MS and GC analysis and has been correlated with the kinetic analysis. The investigation for the role and quantitative estimation of the fate of heteroatoms (N, O, and Cl) present in IMI revealed an increase in the amount of nitrate, nitrite, and chloride ions with time during its photooxidation. On the basis of these results a mechanistic pathway for photomineralization of IMI is proposed.