K.M. Parida

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 highly active g-C3N4 for efficient hydrogen production under visible light

A highly active graphitic C3N4 photocatalyst prepared from a mixture of urea and melamine with advanced structural, optical and electronic properties and enhanced photocatalytic activity for the production of hydrogen gas is explored. The prepared photocatalyst is able to generate a high rate of hydrogen gas production (135 μmol h−1) by loading with 1 wt% Pt as a co-catalyst. The good separation of C3N4 sheets, lower recombination rate of excitons and the high amount of generated photocurrent have significantly contributed towards the photocatalytic activity of graphitic carbon nitride prepared from a mixture of urea and melamine.

Facile Synthesis of Au/g-C3N4 Nanocomposites: An Inorganic/Organic Hybrid Plasmonic Photocatalyst with Enhanced Hydrogen Gas Evolution Under Visible-Light Irradiation

Noble‐metal Au nanoparticles deposited on graphitic carbon nitride polymer (g‐C3N4) photocatalyst by a facile deposition–precipitation method exhibited high photocatalytic activity for hydrogen gas production under visible‐light irradiation. The Au/g‐C3N4 nanocomposite plasmonic photocatalysts were characterized by X‐ray diffraction spectroscopy, diffuse reflectance UV/Vis spectroscopy, FTIR spectroscopy, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, selected‐area electron diffraction, X‐ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical measurements. We studied the effect of Au deposition on the photocatalytic activity of g‐C3N4 by investigation of optical, electronic, and electrical properties. Enhanced photocatalytic activity of Au/g‐C3N4 naocomposite for hydrogen production was attributed to the synergic mechanism operating between the conduction band minimum of g‐C3N4 and the plasmonic band of Au nanoparticles including high optical absorption, uniform distribution, and nanoscale particle size of gold. The mechanism of te photocatalytic activity of the nanocomposite photocatalyst is discussed in detail. Deposition of Au nanoparticles on g‐C3N4 was optimized and it was found that 1 wt % Au‐loaded g‐C3N4 composite plasmonic photocatalyst generated a photocurrent density of 49 mA cm−2 and produced a hydrogen gas amount of 532 μmol under visible light, which were more than 3000 times higher and 23 times higher, respectively, than the values of neat g‐C3N4.

Fabrication of Novel p-BiOI/n-ZnTiO3 Heterojunction for Degradation of Rhodamine 6G under Visible Light Irradiation

With the purpose of efficient electron-hole separation and enhancement of photocatalytic performance in the visible region, we have fabricated a novel p-BiOI/n-ZnTiO3 heterojunction by a precipitation-deposition method and studied its activity toward dye degradation. The physicochemical characteristics of the fabricated BiOI/ZnTiO3 heterojunctions were surveyed by powder X-ray diffraction pattern (PXRD), BET-surface area, diffuse reflectance UV-vis (DRUV-vis), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL spectra), X-ray photoelectron spectroscopy (XPS), and photoelectrochemical measurement. The photosensitization effect of BiOI enhanced the spectral response of ZnTiO3 from UV to visible region, making all the BiOI/ZnTiO3 heterojunctions active under visible light. The PEC measurement confirmed the p-type character of BiOI and n-type character of ZnTiO3. The optimal amount of BiOI in BiOI/ZnTiO3 heterojunctions was found to be 50% which degraded 82% of 50 ppm Rh 6G under visible light irradiation. The degradation rate of 50% BiOI/ZnTiO3 heterojunction was found to be 9.8 and 11.1 times higher than that of bare BiOI and ZnTiO3, respectively. The photosensitization effect of BiOI and the formed heterojunction between p-type BiOI and n-type ZnTiO3 contribute to improved electron-hole separation and enhancement in photocatalytic activity.

Fabrication of α-Fe2O3 Nanorod/RGO Composite: A Novel Hybrid Photocatalyst for Phenol Degradation

We report herein the fabrication of a hematite nanorod-graphene composite (α-Fe2O3 nanorod/RGO) via a facile template-free hydrothermal route with an aim to improve the photocatalytic efficiency of the α-Fe2O3 nanorod. The structural and morphological characterizations of the as-prepared composites were carried out using X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, etc. The α-Fe2O3 nanorods were well-decorated on the surface of the graphene sheets, which helps in electron transfer from α-Fe2O3 to graphene and hence can delay the recombination process, leading to the improvement in photocatalytic activity. The composite containing 5 wt % RGO and α-Fe2O3 nanorods shows a 4-fold enhancement in the photocatalytic activity. The performance of photocatalytic activity was discussed in light of surface area, interaction between nanorods and graphene nanosheets, synergism between α-Fe2O3 nanorods and RGO sheets, light-harvesting properties of the composites, photoluminescence spectra, photocurrent measurement, and hydroxyl radical formation.

Fabrication, Growth Mechanism, and Characterization of α-Fe2O3 Nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.

Visible light-driven novel g-C3N4/NiFe-LDH composite photocatalyst with enhanced photocatalytic activity towards water oxidation and reduction reaction

Exploiting the advantage of a layered architecture, layered graphitic carbon nitride (CN) and NiFe-layered double hydroxide (LDH) have been coupled in the present investigation to design a series of highly efficient novel CNLDH composites for visible light-induced photocatalytic H2 and O2 evolution. The syntheses of these composites were carried out using a facile weight impregnation method while varying the wt% of CN on LDH. The structural, optical, and morphological properties of these composites were characterized by various physicochemical techniques. The results indicate a tuned-in band gap energy within the range of pure LDH to pure CN. In addition, the remarkable quenching of the PL signal and prolonged photogenerated charge lifetime confirmed by TRPL spectra demonstrates the excellent photocatalytic activity of these composites. The activity could be ascribed to the dispersion of exfoliated CN over the brucite layer of LDH, in which strong energy transfer takes place in terms of charge carriers. The visible light-induced photocatalytic H2 and O2 evolution study resulted in an enhancement in the activity of the CNLDH10 composite with a H2 evolution rate of 1488 μmol 2 h−1 and O2 evolution rate of 886 μmol 2 h−1. The high photocatalytic activities of these composites may be due to good dispersion of exfoliated CN over the brucite layer of edge-shared MO6 octahedra, higher life time of charge carriers, low PL intensity, appropriate band gap energy and enhancement in photocurrent density.

Synthesis of mesoporous TiO2-xNx spheres by template free homogeneous co-precipitation method and their photo-catalytic activity under visible light illumination

The article presents preparation, characterization and catalytic activity evaluation of an efficient nitrogen doped mesoporous titania sphere photo-catalyst for degradation of methylene blue (MB) and methyl orange (MO) under visible light illumination. Nitrogen doped titania was prepared by soft chemical route i.e. template free, slow and controlled homogeneous co-precipitation from titanium oxysulfate sulfuric acid complex hydrate, urea, ethanol and water. The molar composition of TiOSO(4) to urea was varied to prepare different atomic % nitrogen doped titania. Mesoporous anatase TiO(2-x)N(x) spheres with average crystallite size of 10 nm and formation of titanium oxynitride center were confirmed from HRTEM, XRD and XPS study. UV-vis DRS showed a strong absorption in the range of 400-500 nm which supports its use in visible spectrum of light. Nitrogen adsorption-desorption study supports the porous nature of the doped material. All the TiO(2-x)N(x) samples showed higher photo-catalytic activity than Degussa P(25) and undoped mesoporous titania. Sample containing around one atomic % nitrogen showed highest activity among the TiO(2-x)N(x) samples.

A review on the recent progress, challenges and perspective of layered double hydroxides as promising photocatalysts

Considering the previous work on layered double hydroxides (LDHs) as novel photocatalysts, research on this group of materials has become one of the most exciting subjects of today. LDH has become an important class of layered materials having prospects in photocatalysis, wherein great attention has been paid to the exhaustive aerobic degradation of pollutants, photocatalytic water splitting, and CO2 photo-reduction. The unique structure, uniform distribution of different metal cations in the brucite layer, surface hydroxyl groups, flexible tunability, intercalated anions with interlayer spaces, swelling properties, oxo-bridged linkage, and high chemical stability are some of the important advantages of this group of materials. This article provides an up-to-date review on significant progress in the fabrication of LDH photocatalytic systems aiming at environmental clean-up and energy production, such as degradation of pollutants, photocatalytic H2 generation and photocatalytic CO2-reduction. This article, after discussing the recent significant progress in the synthesis of different photoactive LDH materials and photocatalytic applications through their structural and electronic properties, considers many typical examples. In particular, recent progress on the emerging strategies of LDH to improve their photocatalytic activity is also presented. Eventually, the future challenges and outlooks for this group of materials are also discussed.

Incorporation of Fe3+ into Mg/Al layered double hydroxide framework: effects on textural properties and photocatalytic activity for H2 generation

This present work highlights the successful preparation of the ternary series of (Mg/Al + Fe)-CO3 layered double hydroxides with a constant ratio of Mg/(Al + Fe) = 2 : 1 and their application for photocatalytic hydrogen generation from water. At Mg/(Al + Fe) = 2 : 1, the Al : Fe ratio was varied from 1 : 4 to lower the concentration of iron in the synthetic gel, in order to get samples with different amounts of iron in the brucite layers, and to find out the role of iron in photocatalytic activity. The presence of a hydrotalcite structure in the catalysts was clearly demonstrated from the powder X-ray diffraction (PXRD) pattern. The shifting of the diffraction plane d110 towards lower angles clearly indicated the amount of Fe3+ substitution in the brucite layer increases with increasing addendum (Fe3+) concentration up to a certain limit and thereafter shows a decreasing trend. Further characterizations like Fourier transform infrared (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA) described the formation of amorphous Fe2O3 upon addition of a higher amount of Fe3+ than the optimum amount that can be accommodated in the brucite layer. Other characterizations like UV–Vis DRS, BET surface area, transmission electron microscopy (TEM), photoluminescence spectra (PL) and X-ray photoelectron spectral studies (XPS) were performed to detect the efficiency of the catalysts towards H2 evolution. Among all the prepared photocatalysts, LDH1(Mg/Al + Fe = 10 : 4 + 1), containing the highest amount of iron in the brucite layer, was found to be the most promising towards hydrogen evolution (301 μmol g−1 h−1) under visible light irradiation, which was attributed to the favourable surface structure and higher crystalline nature of hydrotalcites.