Effective Antibacterial/Photocatalytic Activity of ZnO Nanomaterials Synthesized under Low Temperature and Alkaline Conditions.

The purpose of this study was to evaluate the surface properties of ZnO nanomaterials based on their ability to photodegrade methyl blue dye (MB) and to show their antibacterial properties against different types of Gram-positive bacteria (Bacillus manliponensis, Micrococcus luteus, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). In this study, ZnO nanomaterials were synthesized rapidly and easily in the presence of 1-4 M NaOH at a low temperature of 40 °C within 4 h. It was found that the ZnO nanomaterials obtained from the 1.0 M (ZnO-1M) and 2.0 M (ZnO-2M) aqueous solutions of NaOH had spherical and needle-shaped forms, respectively. As the concentration of NaOH increased, needle thickness increased and the particles became rod-like. Although the ZnO nanomaterial shapes were different, the bandgap size remained almost unchanged. However, as the NaOH concentration increased, the energy position of the conduction band shifted upward. Photo current curves and photoluminescence intensities suggested that the recombination between photoexcited electrons and holes was low in the ZnO-4M materials prepared in 4.0 M NaOH solution; however, charge transfer was easy. ∙O2- radicals were generated more than ∙OH radicals in ZnO-4M particles, showing stronger antibacterial activity against both Gram-positive and Gram-negative bacteria and stronger decomposition ability on MB dye. The results of this study suggest that on the ZnO nanomaterial surface, ∙O2- radicals generated are more critical for antibacterial activity than particle shape.

Fast and highly efficient catalytic degradation of dyes using κ-carrageenan stabilized silver nanoparticles nanocatalyst.

Herein, we have reported the synthesis of silver nanoparticles (AgNPs) nanocatalyst by using high-molecular-weight κ-carrageenan. The developed methodology was rapid, facile, ecofriendly and cost effective, which did not require subsequent processing for reduction or stabilization of AgNPs. The physico-chemical characterization was performed by FT-IR, zeta potential (ζ), XRD, TGA, XPS and TEM techniques. The TEM results revealed that the AgNPs were spherical in shape, with average size of 12 nm, and face centered cubic (FCC) structure throughout the polymer matrix and was stable without any protecting or capping reagents over two months. The synthesized nanocatalyst exhibited high catalytic degradation and mineralization of industrially important organic dyes such as Rhodamine B, and methylene blue, with a degradation efficiency of ∼100 % in a very short interval. The fast kinetics of the dye degradation is quite unique compared to the reported literatures based on various catalyst systems where slow kinetics was reported.

Fast and highly efficient removal of dye from aqueous solution using natural locust bean gum based hydrogels as adsorbent.

For the first time, stable LBG-cl-Poly(DMAAm) hydrogel is prepared via free radical in situ polymerization of N, N-dimethyl acrylamide by employing N, N'-methylene bis(acrylamide) as cross-linkers. The hydrogel was characterized by different physicochemical techniques like equilibrium swelling percentage, point of zero charges (pHPZC), FTIR, SEM, and TGA. The LBG-cl-Poly(DMAAm) hydrogel was used in experiments on swelling behavior and adsorption of water-soluble cationic dye-Brilliant green (BG). The influence of pH on the structural change of BG dye was discussed. The swelling of hydrogel was sensitive toward the pH, ionic strength, and temperature stimuli. Adsorption behavior of hydrogel was investigated for the adsorption of BG dye and it was found to highly efficient in removing 97.7% of BG dye in 50 mg L-1 of dye solution. Adsorption data displayed that the adsorption of BG followed the pseudo-second-order kinetic model (R2 = 0.998) and Langmuir isotherm model (R2 = 0.988) with a maximum adsorption capacity of 142.85 mg g-1. The developed LBG-cl-Poly(DMAAm) hydrogel demonstrated efficient separation of BG dye and maintained maximum adsorption capacity after 6th regeneration cycles. The results indicated that LBG-cl-Poly(DMAAm) hydrogel can be used as an alternative and promising adsorbent to be applied in the treatment of effluents containing the BG dye.

Electrochemical Synergies of Heterostructured Fe2O3-MnO Catalyst for Oxygen Evolution Reaction in Alkaline Water Splitting.

For efficient electrode development in an electrolysis system, Fe2O3, MnO, and heterojunction Fe2O3-MnO materials were synthesized via a simple sol-gel method. These particles were coated on a Ni-foam (NF) electrode, and the resulting material was used as an electrode to be used during an oxygen evolution reaction (OER). A 1000-cycle OER test in a KOH alkaline electrolyte indicated that the heterojunction Fe2O3-MnO/NF electrode exhibited the most stable and highest OER activity: it exhibited a low overvoltage (n) of 370 mV and a small Tafel slope of 66 mV/dec. X-ray photoelectron spectroscopy indicated that the excellent redox performance contributed to the synergy of Mn and Fe, which enhanced the OER performance of the Fe2O3-MnO/NF electrode. Furthermore, the effective redox reaction of Mn and Fe indicated that the structure maintained stability even under 1000 repeated OER cycles.

Oxygen Transfer Capacity of Pseudobrookite Particles Derived from Ilmenite Mineral (x wt.%CuO/y wt.%red Mud-z wt.%ilmenite).

The minerals have a somewhat slower than other transition metals at critical reduction rates in their ability to deliver oxygen. Thus, single minerals alone do not exhibit a higher oxygen transfer capacity than metal oxide oxygen carriers. In this study, we try to solve the problem of single mineral ilmenite (FeTiO3) by combining it with Fe-based red mud and Cu oxide. When the ilmenite was used without calcination, the CH4-CO/air redox cycle showed rapid decayed. However, when ilmenite was calcined, the CH4-CO/air redox cycle became stable, and the oxygen transfer rate increased to 4.2%. This is because the FeTiO3 structure was converted to the pseudobrookite (Fe2TiO5) structure through the calcination process. That is, the Fe2+ ion in the ilmenite structure was converted into an Fe3+ ion. When 30 wt.% of red mud was added to the Fe ion, it reacted with the rutile-type titania mixed with pseudobrookite-typed Fe2TiO5, producing an almost perfect pseudobrookite crystal. This resulted in a slight increase in the capacity of oxygen transfer to 4.9%. When 15 wt.% of Cu oxide was added, the oxygen transfer capacity increased to 6.0%. This performance was indicated by the cyclic voltammetry curve that remained constant even after 200 cycles. Here, we argue that if low-cost minerals as a base material are used in appropriate amounts, the production of a lowest-cost oxygen carrier can be achieved.

Effect of Cu Insertion into SnO2 Framework on Surface Properties and Carbonyl Sulfide Adsorption Performances.

The objective of this study is to introduce Cu into SnO2 sorbent for improving its COS adsorption capacity. Cu-doped SnO2 adsorbents were synthesized using a conventional sol-gel method with citric acid. X-ray diffraction studies revealed that up to 0.4 mol of Cu ions were well-inserted within the SnO2 framework. Scanning electron microscopy images confirmed that the addition of Cu ions reduced the particle size of the SnO2 sorbents. Additionally, it led to an increase in the Brunauer-Emmett-Teller surface area of the sorbents. The COS adsorption tests were carried out in the temperature range of 300-400 °C with a gas hourly space velocity of 8,500 h-1. It was found that Cu0.6SnO2 displayed higher COS adsorption capacity than the sorbents of other compositions, and the breakthrough time and COS adsorption capacity on it at 400 °;C were 170 min and 4.87 mg/g, respectively. X-ray photoelectron spectroscopy results indicated that the Cu2+ ions in the CuxSnO2 adsorbent converted into CuS by binding to the S2- ions in COS gas, while the remaining CO segments combined with the Sn atoms in SnO2 and then are adsorbed as SnCO. Overall, this study showed that the hard-soft acid-base rule is better followed in the Cu0.6SnO2 adsorbent than in the SnO2 adsorbent and that the adsorption is more stable.

Photoreduction of Carbon Dioxide to Methane Over Sb1.5Sn8.5-x TixO19.0 with High Conductivity.

In order to enhance the photoreduction of CO2 to CH4, a new type of photocatalyst, Sb1.5Sn8.5-xTixO19.0, with high conductivity and low bandgap was developed by partially incorporating Ti into the framework of Sb1.5Sn8.5O19.0 (antimony-doped tin oxide, ATO) using a controlled hydrothermal method. XRD and TEM analyses indicated that the Sb1.5Sn8.5-xTixO19.0 particles exhibited a tetragonal crystal structure and were approximately 20 nm in size. Furthermore, the bandgap and conductivity of these materials increased with increasing Ti content. A study of the photoreduction of CO2 with H2O revealed a remarkable increase in the generation of CH4 over the Sb1.5Sn8.5-xTixO19.0 catalysts. In particular, CH4 generation was the highest when Sb1.5Sn8.5Ti1.0O19.0 was used as the photocatalyst, and was three-fold higher than that achieved by using anatase TiO2. Photoluminescence studies showed that the enhanced photocatalytic activity of the Sb1.5Sn8.5-xTixO19.0 materials could be attributed to the interfacial transfer of photogenerated charges, which led to an effective charge separation and inhibition of the recombination of photogenerated electron-hole (e-/h+) pairs.

Surface modification of layered perovskite Sr2TiO4 for improved CO2 photoreduction with H2O to CH4.

Layered perovskite Sr2TiO4 photocatalyst was synthesized by using sol-gel method with citric acid. In order to increase the surface area of layered perovskite Sr2TiO4, and thus to improve its photocatalytic activity for CO2 reduction, its surface was modified via hydrogen treatment or exfoliation. The physical and chemical properties of the prepared catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, elemental mapping analysis, energy-dispersive X-ray spectroscopy, N2 adsorption-desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and electrophoretic light scattering. CO2 photoreduction was performed in a closed reactor under 6 W/cm2 UV irradiation. The gaseous products were analyzed using a gas chromatograph equipped with flame ionization and thermal conductivity detectors. The exfoliated Sr2TiO4 catalyst (E-Sr2TiO4) exhibited a narrow band gap, a large surface area, and high dispersion. Owing to these advantageous properties, E-Sr2TiO4 photocatalyst showed an excellent catalytic performance for CO2 photoreduction reaction. The rate of CH4 production from the photoreduction of CO2 with H2O using E-Sr2TiO4 was about 3431.77 µmol/gcat after 8 h.