A. Hameed

Surface Phases and Photocatalytic Activity Correlation of Bi2O3/Bi2O4-x Nanocomposite

UV-visible irradiation induces surface alteration of Bi2O3 leading to Bi2O3/Bi2O4-x nanocomposites with excellent photocatalytic activity.

Photocatalytic decolourization of dyes on NiO–ZnO nano-composites

NiO-ZnO nanocomposite photocatalysts were synthesized by co-precipitation/co-gel formation techniques using potassium hydroxide (KOH), sodium carbonate (Na(2)CO(3)) and oxalic acid (H(2)C(2)O(4)) as precipitating agents. X-Ray diffraction (XRD) analysis was employed for the determination of crystallite size and phase purity, while BET surface areas were estimated by nitrogen physisorption analysis. The photocatalytic activities of the NiO-ZnO nanocomposites, evaluated using the photo-decolourization of two structurally different dyes, methyl orange and methylene blue, were correlated with the variation in the crystallite size of the constituents of the composites. All the three synthesized nanocomposites showed appreciable activity for the decolourization of dyes. NiO-ZnO nanocomposite derived by KOH exhibited maximum activity for the decolourization of both the dyes and the decolourization rate of methylene blue was found to be comparable with that of Degussa P-25 TiO(2). Finally, the activity of the most active NiO-ZnO composite with relatively large crystallite sizes was compared with the pure components and their physical mixture, synthesized by the identical synthetic route, in the same molar ratio as that of nanocomposite.

Morphology controlled bulk synthesis of disc-shaped WO3 powder and evaluation of its photocatalytic activity for the degradation of phenols

The surfactant assisted synthesis of disc-shaped WO3 powder and its photocatalytic performance in sunlight exposure is reported. UV-vis DRS, XRD and FESEM characterized the synthesized WO3. The synthesized powder exhibited a bandgap of ∼2.55eV with cubic lattice and high crystallinity. The photocatalytic activity of the synthesized WO3 was examined for the degradation of phenol, resorcinol, 2-chlorophenol and 2-nitrophenol in complete spectrum and visible segment of sunlight. The highly efficient degradation/mineralization of 2-chloro and 2-nitrophenol compared to that of phenol and resorcinol, under identical experimental conditions, suggested the regulatory role of substituents attached to the aromatic ring in degradation/mineralization process. The time-scale HPLC degradation profiles, identification of intermediates by GC-MS and removal of organic carbon during the course of reaction were utilized to approximate the possible route of degradation/mineralization of phenolic substrates. The measurement of the anions released during the photocatalytic process was used to identify the nature of the major oxidants (O2(•-), OH(•)) and the possible interaction sites. A significant decrease in the photocatalytic activity of synthesized WO3, ∼50%, was observed in visible portion of sunlight however, a sustained activity was observed in the repeated exposures.

Photo-catalytic conversion of methane into methanol using visible laser

Abstract The photo-catalytic conversion of methane into methanol was investigated under different experimental parameters such as catalyst concentration, laser power, laser exposure time, effects of free radical generator (H 2 O 2 ) and electron capture agent (Fe 3+ ), using visible laser light. The study was carried out at room temperature with a simple set up using a laser light, water and a semiconductor photo-catalyst WO 3 . The reaction products (methanol, O 2 and CO 2 ) were characterized using gas chromatography. The use of WO 3 as photo-catalyst replaces the UV laser light with visible laser light. This greatly simplifies reactor design and permits flexibility in the selection of a laser source in the visible region. The oxygen to tungsten ratio in WO 3 at different temperatures was studied by XPS.

Synthesis, Characterization, and Sunlight Mediated Photocatalytic Activity of CuO Coated ZnO for the Removal of Nitrophenols

CuO@ZnO core-shell catalysts, coated by varying the CuO layer density ranging from 0.5% to 10%, were synthesized with the aim to enhance the photocatalytic activity of ZnO in sunlight and control its photocorrosion. Initially, the Cu(2+) ions were impregnated on presynthesized ZnO by wet impregnation and finally converted to CuO layers by calcination. The optical and structural characterization of the synthesized powders was performed by DRS, PL, Raman spectroscopy, and XRD analysis, respectively. The homogeneity of the coated layers was explored by FESEM. The photocatalytic activity of CuO coated ZnO was investigated for the degradation of mononitrophenols (2-, 3-, and 4-nitrophenol) and dinitrophenols (2,4-, 2,5-, and 2,6-dinitrophenol) in the exposure of the complete spectrum and visible region (420-800 nm) of sunlight. The effect of the increasing density coated layers of CuO on photocatalytic activity was evaluated for the degradation of 4-NP. Compared to pristine ZnO, a substantial increase in the degradation/mineralization ability was observable for the catalysts coated with 0.5% and 1% CuO, whereas a detrimental effect was noticed for higher coating density. Prior to photocatalytic studies, as evaluated by cyclic voltammetry (CV), compared to pure ZnO, a significant suppression of photocorrosion was noticed, under illumination, for catalysts coated with lower CuO coating. The progress of the photocatalytic degradation process was monitored by HPLC while the mineralization ability of the synthesized catalysts was estimated by TOC. The estimation of the released ions and their further interaction with the excited states and the reactive oxygen was monitored by ion chromatography (IC).

Enhanced photocatalytic activity of V2O5–ZnO composites for the mineralization of nitrophenols

In an effort to enhance the photocatalytic activity of ZnO in natural sunlight, V2O5-ZnO nanocomposites were synthesized by co-precipitation technique. The characterization of the synthesized powders by FESEM, XRD and UV-visible diffuse reflectance spectroscopy (DRS) revealed that the both V2O5 and ZnO retain their individual identity in the composites but the increasing concentration of V2O5 affect the particle size of ZnO. As estimated by photoluminescence spectroscopy, in comparison to pure ZnO, the presence of V2O5 significantly suppressed the charge carriers recombination process. The photocatalytic activity of the synthesized powders was evaluated for the degradation/mineralization of three potential nitrophenol pollutants (2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol). The synthesized composites showed significantly higher activity for both degradation and mineralization of nitrophenols compared to pure ZnO. The progress of the degradation process was evaluated by HPLC while mineralization was monitored by TOC analysis. The degradation/mineralization route was estimated by identifying the intermediates using GC-MS. The correlation of the experimental data revealed that the position of NO2 group in 2- and 4-nitrophenol significantly affect the rate of degradation. The identification of hydroxyl group containing intermediates in the degradation of 4-NP confirmed the formation and vital role of hydroxyl radicals in degradation process. The rapid mineralization of nitrophenol substrates pointed out superoxide anions as major contributors in degradation and mineralization process. The assessment of the release of relevant ions (NO2(-), NO3(-), ONOO(-) and NH4(+)) during the degradation process assisted in identifying the plausible interaction sites.

Evaluation of sunlight induced structural changes and their effect on the photocatalytic activity of V2O5 for the degradation of phenols

Despite knowing the fact that vanadium pentoxide is slightly soluble in aqueous medium, its photocatalytic activity was evaluated for the degradation of phenol and its derivatives (2-hydroxyphenol, 2-chlorophenol, 2-aminophenol and 2-nitrophenol) in natural sunlight exposure. The prime objective of the study was to differentiate between the homogeneous and heterogeneous photocatalysis incurred by dissolved and undissolved V2O5 in natural sunlight exposure. V2O5 was synthesized by chemical precipitation procedure using Triton X-100 as morphology mediator and characterized by DRS, PLS, Raman, FESEM and XRD. A lower solubility of ∼ 5% per 100ml of water at 23 °C was observed after calcination at 600 °C. The study revealed no contribution of the dissolved V2O5 in the photocatalytic process. In sunlight exposure, V2O5 powder exhibited substantial activity for the degradation, however, a low mineralization of phenolic substrates was observed. The initial low activity of V2O5 followed by a sharp increase both in degradation and mineralization in complete spectrum sunlight exposure, was further investigated that revealed the decrease in the bandgap and the reduction in the particle size with the interaction of UV photons (<420 nm) as this effect was not observable in the exposure of visible region of sunlight. The role of the chemically different substituents attached to an aromatic ring at 2-positions and the secondary interaction of released ions during the degradation process with the reactive oxygen species (ROS) was also explored.

Laser Induced Photocatalytic Splitting of Water Over WO3 Catalyst

The photocatalytic activity of WO 3 semiconductor powder for water splitting into H 2 and O 2 was studied. Instead of conventional broad spectrum light sources like lamps, monochromatic laser radiations in the UV region (γ = 355 nm) were used as the light source for the study of photocatalytic water splitting over WO 3 . An alternate route based upon the photo-chromic properties of WO 3 for the production of hydrogen was suggested. The effect of dissolved metal ions on H 2 and O 2 yield in the presence of various metal ions was also investigated. The effect of the hole-capture agent on H 2 and O 2 yield was also studied by using methanol as a hole-capture agent. The data on pH measurements during the course of reaction was found very useful in explaining the reaction mechanism in general, and metal ions action in particular.

The suitability of Ce3+-modified ZnO photocatalyst for the mineralization of monochlorophenol isomers in sunlight exposure

The photocatalytic activity of Ce3+-modified hexagonal ZnO for the degradation/mineralization of monochlorophenol isomers (2-chlorophenol, 3-chlorophenol and 4-chlorophenol), in natural sunlight exposure, is reported. Compared to bare ZnO, the modified catalysts showed superior activity for the mineralization of MCP isomers. The identification of the intermediates disclosed that the mode of degradation of chlorophenol substrates also varies with increased Ce3+ loading. Increased mineralization was discovered with increasing concentration of Ce3+ at the surface of ZnO. The correlation of the results obtained by various analytical tools revealed that the photocatalytic removal of MCP isomers initially proceeds with the cleavage of the aromatic ring, the release of chloride ions and the formation of oxygenated intermediates. Finally, the intermediates are oxidized further by the oxidizing species to mineralization. The efficacy of the synthesized catalysts was tested for the mixture of chlorophenol isomers. Based on the intermediates formed, the major contribution of superoxide anion radicals was evidenced in the removal process. The Ce3+ impregnation protected the surface of ZnO against photocorrosion.

The suitability of ZnO film-coated glassy carbon electrode for the sensitive detection of 4-nitrophenol in aqueous medium

The performance of a ZnO nanoparticle-based electrochemical sensor, fabricated by different treatments of ZnO on glassy carbon electrode, was evaluated for the determination of 4-nitrophenol (4-NP) in aqueous medium. The sensing performance of ZnO film-coated GCE (ZnO/F/GCE) was compared with a variety of electrodes, which included GCEs modified with ZnO powder, RGO (reduced graphene oxide), and RGO-Nafion® composite. Among the fabricated electrodes, the ZnO film-coated electrode, prepared by dispersing the well-sonicated chloroform suspension of ZnO on the GCE, showed excellent response toward the sensitive detection of 4-NP in aqueous medium, and a significant enhancement in the reduction peak current predicted the suitability of the developed sensor. Square wave voltammetry (SWV) detection mode was applied for the determination of 4-NP. The reproducibility and accuracy of ZnO/F/GCE were evaluated in the linear concentration ranges of 0.035 μM to 1.4 μM and 2.1 μM to 6.3 μM. Appreciably low SWV detection limits of 0.008 μM and 0.02 μM were estimated. Minimal influence was observed from the interfering species, added into the sample solution, on the determination of 4-NP. The performance of the developed electrode was initially optimized for 4-NP samples prepared in-house and finally tested against two real samples collected from municipality wastewater. The recovery of the ZnO/F/GCE varied from 96.8% to 105.7%.