D.P. Das

Physicochemical characterization and adsorption behavior of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution

A Zn/Al hydrotalcite-like compound (HTlc) was prepared by co-precipitation (at constant pH) method and was characterized by XRD, TG/DTA, FTIR, and BET surface area. The ability of Zn/Al oxide to remove F- from aqueous solution was investigated. All the adsorption experiments were carried out as a function of time, pH, concentration of adsorbate, adsorbent dose, temperature etc. It was found that the maximum adsorption takes place within 4 h at pH 6.0. The percentage of adsorption increases with increase in the adsorbent dose, but decreases with increase in the adsorbate concentration. From the temperature variation it was found that the percentage of adsorption decreases with increase in temperature, which shows that the adsorption process is exothermic in nature. The adsorption data fitted well into the linearly transformed Langmuir equation. Sulfate and phosphate were found to have profound effects on fluoride removal. Thermodynamic parameters such as DeltaG0, DeltaH0, and DeltaS0 were calculated. The negative value of DeltaH0 indicates that the adsorption process is exothermic. The apparent equilibrium constants (Ka) are also calculated and found to decrease with increase in temperature. With 0.01 M NaOH the adsorbed F- could be completely desorbed from Zn/Al oxide in 6 h.

Facile synthesis of visible light responsive V2O5/N,S–TiO2 composite photocatalyst: enhanced hydrogen production and phenol degradation

A series of novel V2O5/N,S–TiO2 composite photocatalysts were fabricated by a solid state reaction route. The investigated composite materials were successfully characterised by XRD, DRUV-vis spectra, SEM, TEM, XPS, FTIR, NH3-TPD, BET-surface area and photoresponse studies. The photocatalytic applications of the composite materials were evaluated for hydrogen production under visible light irradiation (λ ≥ 400 nm) and phenol degradation under direct solar light. The V2O5 component played a key role for the visible light activity of the composite system at longer wavelengths. Among all the prepared materials, V2O5/N,S–TiO2 activated at 500 °C showed promising activity towards hydrogen production (296.6 μmol h−1) under visible light and successively degraded 88% of 100 mg L−1 phenol solution under direct solar light irradiation in just 4 h. The present investigation is of great importance in view of energy and environmental applications.

One pot synthesis of water-dispersible dehydroascorbic acid coated Fe3O4 nanoparticles under atmospheric air: Blood cell compatibility and enhanced magnetic resonance imaging

Water dispersible and biologically important molecule dehydroascorbic acid (DHA, capable to cross the blood brain barrier) coated Fe3O4 superparamagnetic nanoparticles having an average size of ∼6 nm were synthesized through one pot aqueous coprecipitation method under atmospheric air. An antioxidant ascorbic acid (AA) used in the synthesis oxidized itself to dehydroascorbic acid (DHA) to consume dissolved or available oxygen in reaction mixture which died away the oxidative impact of atmospheric air and formed DHA encapsulated the Fe3O4 nanoparticles which stabilized the Fe3O4 nanoparticles and significantly enhanced their colloidal solubility in water. Fe3O4 phase, superparamagnetic property, DHA coating and stable colloidal solubility in water were confirmed by means of XPS, VSM, IR and zeta potential analysis respectively. T1, T2 and T2(∗) weighted magnetic resonance imaging (MRI) and corresponding relaxivity (r1=0.416, r2=50.28 and r2(∗)=123.65 mM(-1) and r2/r1=120.86, r2(∗)r1=297.23) of colloidally dispersed DHA-coated nanoparticle water phantom revealed a strong contrast enhancement in T2 and T2(∗) weighted images. The compatibility of DHA-coated Fe3O4 nanoparticles toward human blood cells was examined by means of cell counting and cell morphological analysis with the use of optical microscope and scanning electron microscope imaging.

Facile fabrication of hierarchical N-doped GaZn mixed oxides for water splitting reactions

This report briefly highlights our recent research on a series of nanostructured N-doped GaZn mixed oxides concerning their fabrication, characterization and application for the generation of hydrogen from water. N-doped mixed oxides with hierarchical morphology are poised to be a most promising visible light sensitive semiconducting material for water splitting reactions.

Studies on Mg/Fe hydrotalcite‐like – compound (HTlc): removal of Chromium (VI) from aqueous solution

The affinity of Mg/Fe hydrotalcite‐like‐compound (HTlc) for the removal of Cr (VI) from aqueous medium was studied as a function of pH, contact time, temperature, HTlc dose and Cr (VI) concentration. The fraction of Cr (VI) removal decreases with increase in pH of 3 to 10. The reaction kinetic study was undertaken by considering adsorption of Cr (VI) on the outer surface as well as diffusion within the pores of the adsorbent. The adsorption follows first order kinetics. The adsorption data fit well with the Langmuir isotherm model in the temperature range 30–50°C and the thermodynamic parameters viz. ΔG°, ΔH° and ΔS° were calculated to predict the nature of adsorption. The positive value of ΔH° indicates that the adsorption process is endothermic in nature.

Reduced Graphene Oxide–Ag3PO4 Heterostructure: A Direct Z-Scheme Photocatalyst for Augmented Photoreactivity and Stability

A visible light driven, direct Z-scheme reduced graphene oxide-Ag3PO4 (RGO-Ag3 PO4 ) heterostructure was synthesized by means of a simple one-pot photoreduction route by varying the amount of RGO under visible light illumination. The reduction of graphene oxide (GO) and growth of Ag3PO4 took place simultaneously. The effect of the amount of RGO on the textural properties and photocatalytic activity of the heterostructure was investigated under visible light illumination. Furthermore, total organic carbon (TOC) analysis confirmed 97.1 % mineralization of organic dyes over RGO-Ag3PO4 in just five minutes under visible-light illumination. The use of different quenchers in the photomineralization suggested the presence of hydroxyl radicals ((.)OH), superoxide radicals ((.)O2 (-)), and holes (h(+)), which play a significant role in the mineralization of organic dyes. In addition to that, clean hydrogen fuel generation was also observed with excellent reusability. The 4 RGO-Ag3PO4 heterostructure has a high H2 evolution rate of 3690 μmol h(-1)  g(-1), which is 6.15 times higher than that of RGO.

Visible light induced photo-hydroxylation of phenol to catechol over RGO–Ag3VO4 nanocomposites without the use of H2O2

RGO–Ag3VO4 nanocomposites prepared by a novel one-pot photochemical synthesis route show unusual selectivity towards catechol in the photo-hydroxylation of phenol with complete conversion.

3 D Co3(PO4)2–Reduced Graphene Oxide Flowers for Photocatalytic Water Splitting: A Type II Staggered Heterojunction System

The design, synthesis, and photoelectrochemical characterization of Co3 (PO4 )2 , a hydrogen evolving catalyst modified with reduced graphene oxide (RGO), is reported. The 3 D flowerlike Co3 (PO4 )2 heterojunction system, consisting of 3 D flowerlike Co3 (PO4 )2 and RGO sheets, was synthesized by a one-pot in situ photoassisted method under visible-light irradiation, which was achieved without the addition of surfactant or a structure-directing reagent. For the first time, Co3 (PO4 )2 is demonstrated to act as a hydrogen evolving catalyst rather than being used as an oxygen evolving photoanode. In particular, 3 D flowerlike Co3 (PO4 )2 anchored to RGO nanosheets is shown to possess dramatically improved photocatalytic activity. This enhanced photoactivity is mainly due to the staggered type II heterojunction system, in which photoinduced electrons from 3 D flowerlike Co3 (PO4 )2 transfer to the RGO sheets and result in decreased charge recombination, as evidenced by photoluminescence spectroscopy. The band gap of Co3 (PO4 )2 was calculated to be 2.35 eV by the Kubelka-Munk method. Again, the Co3 (PO4 )2 semiconductor displays n-type behavior, as observed from Mott-Schottky measurements. These RGO-Co3 (PO4 )2 conjugates are active in the visible range of solar light for water splitting and textile dye degradation, and can be used towards the development of greener and cheaper photocatalysts by exploiting solar light.

One-Pot Fabrication of RGO–Ag3VO4 Nanocomposites by in situ Photoreduction using Different Sacrificial Agents: High Selectivity Toward Catechol Synthesis and Photodegradation Ability

Weak photon absorption and fast carrier kinetics in graphene restrict its applications in photosensitive reactions. Such restrictions/limitations can be overcome by covalent coupling of another photosensitive nanostructure to graphene, forming graphene‐semiconductor nanocomposites. Herein, we report one‐pot synthesis of RGO–Ag3VO4 nanocomposites using various sacrificial agents like ethanol, methanol, propanol and ethylene glycol (EG) under visible light illumination. The Raman spectral analysis and 13C MAS NMR suggest ethanol to be the best sacrificial agent among those studied. Thermal analysis studies, further, confirm the stability of the synthesized nanocomposite with ethanol as sacrificial agent. In view of this, the activity toward dye degradation was focused over the composites prepared via ethanol as sacrificial agent. It was observed and proved that cationic dyes could be degraded quantitatively and swiftly compared to anionic dyes (37.79%) in 1.5 h. This suggests that the surface of the nanocomposites is anionic as partial reduction takes place during synthesis process. In case of mixed dye degradation process, it was noticed that the presence of cationic dye doubles the degradation of anionic dye. The activity of these synthesized nanocomposites is more than five‐fold toward the phototransformation of phenol and photodegradation of textile dyes under visible light illumination.

Thermal transformation of trinuclear Fe(III) acetato complex intercalated montmorillonite

FeIII. pillared montmorillonite was prepared using trinuclear acetato complex of FeIII. as the pillaring agent and the resulted material was characterised by different analytical techniques. Basal spacing of the material is found to be 18 A° even after calcination at 5008C indicating the formation of stable pillars. Thermal analysis indicate that the complex decomposes slowly from the silicate layer at higher temperature to form metal oxyhydroxide pillars. Sample calcined at 5008C shows the highest surface area of 284 m2rg. Mo¨ssbauer analysis was carried to identify the exact phase of FeIII. formed during thermal treatment. From the Mo¨ssbauer spectra recorded at 298 and 77 K, it is observed that the species formed from the decomposition of the acetyl group of the complex is g-FeOOH even at 5008C; whereas, the pure complex decomposed directly to a-Fe2O3 at 3008C. This confirmed the role played by the silicate layer in directing the phase formation of FeIII. during the heat treatment.