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This article highlights comparative adsorption behavior and photocatalytic activity of TiO2nanostructures (P25, nanorods and nanotubes) for degradation of eriochrome black-T dye (EBT)depending on their structural morphology and metal ions (Fe3+ and Pt4+) deposition. Enhancement inadsorption capacity (qmax) was observed due to impartment of extra positive charges by Fe3+ and Pt4+impregnation and follow the order, Pt4+–P25–TiO2 (400 mg/mg) > Fe3+–P25–TiO2 (344 mg/mg) > P25–TiO2 (248 mg/mg) > nanotubes (123 mg/mg) > nanorods (69 mg/mg). The Fe3+ and Pt4+ loaded TiO2improved dye adsorption and degradation rate of EBT undergoing complete minerization to CO2 underUV light irradiation.
This paper reports the impact of oxidative etching of Au nanospheres and nanorods by KMnO4 on theirsurface morphology, electro-kinetic properties and catalytic activity. A significant blue-shift of thesurface plasmon bands for Au nanospheres (536 to 527 nm) and Au nanorods (679 to 532 nm) wereobserved, due to their size and shape alterations after oxidative dissolution. TEM analysis also revealedthe formation of various irregular Au nano-morphologies such as spheres ( 4-7 nm), low aspect ratiorods (2.6) and spheroids ( 13 nm) of narrow size distribution after KMnO4 etching. As a result, thehydrodynamic diameter of Au nanospheres ( 41 nm) and Au nanorods ( 109 nm) were reduced to4 nm and 34 nm, respectively. The oxidative dissolution of Au0 by KMnO4 occurred via its oxidation toAu3+ ions as confirmed by the measured electrode potential, E0(Au0/Au3+) = -0.90 V by cyclic voltammetrywith significant increase in the zeta potential and conductance values. The etched Au nanoparticlesbeing smaller in size and of higher surface to volume ratio resulted in 2 fold higher catalytic activitiesfor the reduction of p-nitrophenol and p-nitrobenzoic acid as compared to bare unetched Aunanostructures.
Bimetallic Pd@Ni nanostructure exhibited enhanced co-catalytic activity for the selective hydrogenation of benzaldehyde compare to their monometallic counterparts. Impregnation of these mono/bimetallic nanostructures on mesoporous TiO2 leads to several surface modifications. The bimetallic PNT-3 (Pd3@Ni1/mTiO2) exhibited large surface area (212 m2 g−1), and low recombination rate of the charge carriers (e−-h+). The hydrogenation reaction was analyzed under controlled experiments. It was observed that under UV-light irradiations and saturated hydrogen atmosphere the bimetallic PNT-3 photocatalyst display higher rate constant k = 5.31 × 10−1 h−1 owing to reduction in the barrier height which leads to efficiently transfer of electron at bimetallic/mTiO2 interface.
Bimetallic nanostructures have gained immense importance owing to their enhanced co-catalyticeffect in improving photocatalytic activity of TiO2 for various applications relative to monometallicones. However, the use of bimetallic core@shell catalyst/nanocatalyst for hydrogenation ofimportant industrial organic is not much explored relative to conventional metal catalysts. Inthis respect, the present study demonstrated the synthesis of core@shell (Cu@Zn) nanostructurebased on their galvanic interactions. TEM analysis confirmed the formation of Cu@Zn nanoparticleswith a shell thickness of 195 nm. It was observed that with increasing Cu:Zn weight ratio (1:1, 2:1,and 3:1) the average hydrodynamic size increases from 198 to 267 nm. These Cu@Zn nanostructuresshowed superior co-catalytic activity after impregnation on (001) faceted titanium nanosheets(surface area = 72.8 m2 g 1) for the selective hydrogenation of quinoline under visible lightradiations. The optimized Cu@Zn(3:1)/TiO2 photocatalyst showed enhanced conversion, selectivity,and higher rate constant (k = 2.1 10 1 h 1) compared to Cu and Zn-TiO2 nanocomposites. Thesuperior activity of Cu@Zn-TiO2 photocatalyst was attributed to the synergistic interaction occurringat bimetallic-TiO2 interface which effectively promotes the transfer of electron and hydride (H ) forquinoline hydrogenation. The conventional hydrogenation of quinoline required high temperature,solvents, expensive bases and involved multistep procedure. Therefore, the use of Cu@Zn-TiO2photocatalyst might be a greener approach for the selective hydrogenation of industrial importantunsaturated organic compounds under light radiations.
Mono-dispersed and smaller sized TiO2 nanospheres (~8 nm and ~20 nm) exhibited superior photo-reductive efficiency for few aromatic aldehydes under UV light. It has been found that pnitrobenzaldehydeand benzaldehyde are efficiently reduced to p-aminobenzyl alcohol (80% and 61%)and benzyl alcohol (59% and 38%) by 8 nm and 20 nm particles respectively, relative to negligiblereduction by TiO2 (P25) under same experimental conditions. However, the successful photo-reductionof p-nitrotoluene (97%) was observed with P25 whose reduction potential ( 0.5 eV) lies below theconduction band (CB,0.85 eV vs NHE) of the catalyst. Thesefindings can be explained on the basis ofunsuitable and mismatched CB of P25 with respect to the lowest unoccupied molecular orbital ofCHOgroup to access its photo-activity. However, this hydrogenation occurred by synthesized smaller sizedTiO2 particles (~8 nm and~20 nm) due to their favorable band gap (3.85 eV and 3.62 eV) and conductionband edge ( 0.61 eV and0.50 eV). Moreover, the other physio-chemical characteristics of 8 nm and20 nm sized particles such as surface area (323 m2 g 1 and 297 m2 g 1), higher charge carrier relaxationtime (61 ms and 40 ms) are also co-related for ease of photo-activity relative to TiO2 (P25).
Layered double hydroxides are traditional positively charged inorganic materials generally considered as efficient and low-cost adsorbents for the removal of anionic organic molecules. In this study, we prepared a series of g- C3N4@NiCo LDH composites by loading 10-30 wt% of g-C3N4 onto the LDH through the electrostatic self-assembly method. The bare LDH and g-C3N4 loaded LDH composites were characterized by XRD, SEM-EDS, Zeta, DLS, and FTIR techniques. Results revealed that extra peak corresponds to g-C3N4 originating in the XRD patterns, distorted morphology of LDH, reduction in positive surface zeta potential, and enhancement in hydrodynamic size after loading of g-C3N4 affirmed the successful formation of the composite. The adsorption performance of as-modified LDH was evaluated by removing the most commonly used salicylic acid and methylene blue as anionic and cationic model pollutant, respectively, from aqueous solution. The adsorption mechanism for both the pollutants by as-synthesized samples follows Langmuir isotherm. The results demonstrated that the bare LDH exhibited maximum adsorption efficiency of 75.16mg/g and only 3.66mg/g for salicylic acid and methylene blue, respectively. With 30 wt% loading of g- C3N4, the adsorption capacity for methylene blue increased to 25.16mg/g almost 6-7 times higher than that of bare LDH. On the other hand, the opposite effect on adsorptive removal of salicylic acid was observed with increase in the wt% loading of g-C3N4. With 30 wt% loading of g-C3N4, the adsorption capacity for salicylic acid decreased to 38.37mg/g, almost half that of bare LDH. A possible mechanism has been proposed. The kinetics for adsorption of salicylic acid onto bare LDH obeys the second-order model aside from the methylene blue adsorption which follows first-order kinetics. On the other han
This study demonstrates the thermal conductivity (TC) and viscosity of as prepared crystalline a-Al2O3 and amorphous g-Al2O3 particles, having size in the range of 30–50 nm. The a and g-Al2O3 aqueous suspension exhibited 10% and 6% enhancement in TC than de-ionized water, but a-Al2O3 showed (4–6%) higher TC than g-Al2O3 aqueous suspension due to more crystallinity of a phase than g phase. Ultrasonication helps in the breakdown of large clusters which further improves the dispersion stability and TC as verified by dynamic light scattering and zeta potential measurements. The Al2O3 aqueous suspension showed Newtonian characteristics at lower concentration.
The core–shell morphology of graphene oxide (GO) coated Au-TiO2 (Au-TiO2@GO) nanocatalysts hasdisplayed enhanced photocatalytic activity for hydrogen production from water. The structuralmorphology of Au-TiO2@GO revealed a thin layer ( 2.5 nm) of GO shell over Au-TiO2 core, possessinghigher specific surface area ( 100 m2 g 1). Raman spectroscopy revealed bands at 1593 cm 1 and1317 cm 1 corresponding to G and D lines. GO facilitates decreases in the rate of e /h+ recombinationdue to its reduction potential and Au loading increase sensitization of TiO2 in the visible light resulting inthe increased activity for H2 production ( 114 mmol) from the water.