Participation Of Holes Research Articles

Enhanced Visible‐light Photocatalytic Dye Degradation Ability of CdS/O‐CNTs Nanocomposites

AbstractThe rapid developpment of industrialization and urbanization has caused extensive environmental pollution, especially water pollution. Here, a bud‐like shaped CdS (cadmium sulfide), with O‐CNTs (oxidized multiwalled carbon nanotubes) homogeneously embedde (BCO), were synthesized by a facile hydrothermal process. The surface properties of the composites and the photocatalytic performances were studied systematically. The photocatalytic degrading anionic dye Methyl orange (MO) and cationic dye Rhodamine B (RhB) under visible light (λ≥420 nm) unveiled that BCO nanocomposites exhibited much better photocatalytic decolorization activity than bud‐like shaped CdS. Due to the delaying time of electron recombination to the hole and the participation of holes (h+) and⋅superoxide radicals (⋅O2−) by loading O‐CNTs, BCO‐3 wt% could decolorize 98.5 % RhB in 30 min and 95.5 % MO in 90 min, implying potential applications prospect.

Photocatalytic performance of titanium and zinc oxides in diuron degradation

Diuron is an herbicide used for weed control in agricultural crops that can cause a range of complications in humans from skin irritation to cancer. In this study, heterogeneous photocatalysis were performed using TiO2 and ZnO as catalysts in a batch reactor for Diuron degradation. Experimental designs were carried out in order to assess the influence of pH, catalyst and substrate concentration, in addition to optimizing the Diuron degradation. After 3 h of reaction, the pH showed to be the most important variable on the Diuron degradation using TiO2 as a catalyst. The use of ZnO led to a conversion rate higher than 98% in all tests performed. ZnO showed higher efficiency than TiO2, was attributed to the adsorption step. The mechanistic study suggested different reaction routes compared to the catalysts employed, with the participation of holes and photo-generated electrons in ZnO, whereas in TiO2 only the conduction band was relevant in the process.

Urea-modified ZnWO4 with enhanced photocatalytic activity

The urea-modified ZnWO4 samples were synthesized by hydrothermal method. Urea was used as a nitrogen source. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). Photocatalytic properties of urea-modified ZnWO4 was studied and compared with its parent ZnWO4. Urea-modified ZnWO4 (10 mol%) has shown higher photocatalytic activity in the degradation of methylene blue under the visible light irradiation. Participation of holes, hydroxyl radicals, and super oxide radicals in the photocatalytic dye degradation was investigated.

Facile synthesis of porous graphene-like carbon nitride nanosheets with high surface area and enhanced photocatalytic activity via one-step catalyst-free solution self-polymerization

Porous graphite carbon nitride nanosheets (g-C3N4) are achieved via one-step catalyst-free solution self-polymerization from a single melamine precursor. The resultant porous g-C3N4 nanosheets with the best photodegradation capacity provided the surface area of 669.15m2/g, which is superior to the surface area of any other porous g-C3N4 reported. Results showed enhanced adsorption and degradation capacity of methyl orange (MO) under UV-visible light irradiation (λ>350nm) compared to bulk g-C3N4. The MO oxidation of the porous g-C3N4 nanosheets is driven mostly by the participation of holes, and secondly by O2− and OH radicals. This approach shed lights on porous g-C3N4 production simply by self-polycondensation of single functional monomer. It also provided a low-cost and eco-friendly method to facilely mass-produce g-C3N4 nanosheets with high surface area for many potential applications.

Synthesis, Characterization and Photocatalytic Activity of Ag+ - and Sn2+ -Doped KTi0.5 Te1.5 O6.

In this study, the photocatalytic dye degradation efficiency of KTi0.5 Te1.5 O6 synthesized through solid-state method was enhanced by cation (Ag+ /Sn+2 ) doping at potassium site via ion exchange method. As prepared materials were characterized by XRD, SEM-EDS, IR, TGA and UV-Vis Diffuse reflectance spectroscopic (DRS) techniques. All the compounds were crystallized in cubic lattice with Fd3¯m space group. The bandgap energies of parent, Ag+ - and Sn+2 -doped KTi0.5 Te1.5 O6 materials obtained from DRS profiles were found to be 2.96, 2.55 and 2.40eV, respectively. Photocatalytic efficiency of parent, Ag+ - and Sn+2 -doped materials was evaluated against the degradation of methylene blue (MB) and methyl violet (MV) dyes under visible light irradiation. The Sn+2 -doped KTi0.5 Te1.5 O6 showed higher activity toward the degradation of both MB and MV dyes and its higher activity is ascribed to the lower bandgap energy compared to the parent and Ag+ -doped KTi0.5 Te1.5 O6 . The mechanistic degradation pathway of methylene blue (MB) was studied in the presence of Sn2+ -doped KTi0.5 Te1.5 O6 . Quenching experiments were performed to know the participation of holes, super oxide and hydroxyl radicals in the dye degradation process. The stability and reusability of the catalysts were studied.

Novel magnetic NiFe2O4/multi-walled carbon nanotubes hybrids: Facile synthesis, characterization, and application to the treatment of dyeing wastewater

Novel magnetically recyclable spinel nickel ferrite/multi-walled carbon nanotubes hybrids (NiFe2O4/MWCNTs hybrids) with different MWCNTs content were prepared by a facile one-step hydrothermal method. The as-prepared NiFe2O4/MWCNTs hybrids were characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). Photocatalytic activity of NiFe2O4/MWCNTs hybrids was investigated by photocatalytic decolorization of Congo Red (CR) in aqueous solution under simulated solar light irradiation. NiFe2O4/MWCNTs yielded efficient decolorization of CR solution with an apparent rate constant of 0.01433min−1, which was 2.18 times that of NiFe2O4. Significantly enhanced activity of NiFe2O4/MWCNTs hybrids resulted from the synergistic contribution of both high adsorption capacity towards CR and the participation of holes (h+), •OH radicals and O2•− radicals. In addition, the NiFe2O4/MWCNTs hybrids can be recovered conveniently using an external magnet. As a result, the novel NiFe2O4/MWCNTs could gain a promising application in treatment of various dyestuff wastewaters on a large scale.

Photocatalytic degradation of imazalil in an aqueous suspension of TiO2 and influence of alcohols on the degradation

The photocatalytic degradation of imazalil, a probably carcinogen fungicide, was carried out in an aqueous suspension of titanium dioxide under UV irradiation. The influence of alcohols as hydroxyl scavengers (isopropanol, methanol) on the degradation was studied and different concentrations were used. We conclude that the degradation of imazalil occurs mainly by OH attack, since 80% of the degradation was inhibited in the presence of isopropanol [isopropanol]=1000[imazalil]. Using HPLC/DAD and LC–MS/MS analysis, nine intermediates were identified giving monohydroxylated, dihydroxylated and mostly a hole attack for other products. Their kinetic evolution profiles were plotted and compared to those with isopropanol. The quantity of photoproducts formed by OH radicals was decreased in the presence of isopropanol. After that a tentative pathway mechanism was proposed including mainly hydroxyl radical attack with the participation of holes in the degradation. Ion chromatography showed that nitrogen groups in imidazole were converted to both NH4+ and NO3−. In addition, TOC was examined in details and total mineralization was reached.

The growth of thin oxide layers on GaAs in methanol

Oxide layer growth on GaAs, kept in methanol and without applying an external voltage, up to a thickness of about 20 nm is reported. A growth law is found indicating that diffusion (with a diffusion constant approximately=10-22 m2 s-1), probably of a water or a water related species, is the dominating growth mechanism. The observed light-dependence of the growth on n-type material can be explained by the participation of holes in the first reaction step. Auger depth profiles show that the As-content of the layers grown in methanol is higher than that of layers grown in water, explaining the observed difference in the layers conductivity.