J. 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.

Mg/Al hydrotalcites : preparation, characterisation and ketonisation of acetic acid

Mg/Al hydrotalcites with different Mg:Al ratios were prepared and characterized by PXRD, FTIR, TG/DTA, basic sites and nitrogen adsorption–desorption methods. It is confirmed from PXRD that the materials have hydrotalcite structure. The basic sites of the samples were determined spectrophotometrically by irreversible adsorption of acids having different pKa values which showed that the basic sites increases with increase in Mg:Al ratio. The specific surface area of all samples lies in the range 170–231 m2/g. All the samples were predominantly mesoporous in nature and pore diameters lie in the range 40–70 A. The sample with Mg:Al ratio of 4:1 showed highest specific surface area and conversion (>86.5%) of acetic acid to acetone with high selectivity at 350°C.

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.

Catalytic Ketonization of Acetic Acid on Zn/Al Layered Double Hydroxides

Zn/Al Layered double hydroxides (LDHs) with various Zn:Al ratios were prepared, characterized by chemical analysis, PXRD, IR, thermal analysis, nitrogen adsorption-desorption and basic sites. The catalytic activity of samples calcined at 450°C for the ketonization of acetic acid was studied in a fixed bed catalytic reactor (10 mm id) with an on-line gas chromatograph. Amongst all, the sample with Zn:Al ratio 3:1 showed the highest surface area (103.5 m2/g) and yield of acetone (>89%) with high selectivity.

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.