Reduced formation of undesirable by-products from photocatalytic degradation of trichloroethylene

Photocatalytic degradation of trichloroethylene (TCE) was investigated using a tubular photoreactor packed with TiO₂ powders prepared by sol–gel techniques. Powders of the following metals: Cr, Fe, Ni, Cu and Pt, or Ca(OH)₂ were uniformly mixed with the TiO₂ powders and then their effect on the formation of COCl₂, CHCl₃, and CHCl₂COCl as by-products was examined. Concentrations of COCl₂ and CHCl₃ were determined in a product gas stream by GC/MS while CHCl₂COCl accumulated on the catalyst surface. When the catalysts were immersed in water after TCE photodegradation, the formation of Cl^- and CHCl₂COO⁻ ions was confirmed by ion-chromatography. Of the chemicals tested, only Cu and Ca(OH)₂ inhibited the formation of the chlorinated by-products. With increasing Cu and Ca(OH)₂ content, TCE conversion decreased while the stoichiometric ratio ([CO₂]_formed/[TCE]_degraded) increased. Concentrations of COCl₂, CHCl₃, and CHCl₂COCl decreased with increasing Cu and Ca(OH)₂ content. Especially, the formation of COCl₂ was remarkably suppressed with Ca(OH)₂.     

Phosgene-Free Photocatalytic Degradation of TCE and PCE Vapors with Au/TiO2

Photocatalytic oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) in air had been carried out with TiO₂ film alone and Au/TiO₂ film. On the TiO₂ film TCE and PCE were converted mainly into toxic COCl₂, while COCl₂ free TEC and PCE oxidation could be achieved with Au/TiO₂.     

Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO₂ were developed in a plate shape. The ceramic surface was coated with TiO₂ by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO₂ loading and the layer thickness. Photocatalysts were characterised by N₂ adsorption–desorption, mercury intrusion porosimetry, SEM, UV–vis spectroscopy and XRD. A direct relationship between the TiO₂ content and the photocatalytic activity was observed up to three layers of TiO₂ (0.66 wt.%). Our results indicate that intermediate species generated on the TiO₂ layer can migrate through relatively long distances to react with the OH⁻ surface groups of the support. By increasing the TiO₂ loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl₂ and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO₂ amount, TCE conversion and CO₂, and COCl₂ selectivity.     

Preparation and Characterization of Titanium Dioxide (TiO2) from Sludge produced by TiCl4 Flocculation with FeCl3, Al2(SO4)3 and Ca(OH)2 Coagulant Aids in Wastewater

Abstract

In this study, TiCl₄ coagulant together with coagulant aids such as FeCl₃, Al₂(SO₄)₃, and Ca(OH)₂ were investigated to improve the photoactivity of titanium dioxide (TiO₂) produced from sludge and to increase the resulting low pH value. After TiCl₄ flocculation with three coagulant aids, the settled floc (sludge) was incinerated at 600°C to produce TiO₂ doped with Fe, Al, and Ca elements. Fe-, Al-, and Ca-doped TiO₂ was characterized in terms of structural, chemical, and photo-electronic properties. All the coagulant aids used together with Ti-salt flocculation effectively increased the pH values. The surface area of TiO₂-WO (without any coagulant aids), Fe/TiO₂, Al/TiO₂, and Ca/TiO₂ was 122 m²/g, 77 m²/g, 136 m²/g and 116 m²/g, respectively. The TiO₂-WO, Fe/TiO₂, Al/TiO₂, and Ca/TiO₂ was found to be of anatase phase. The XRD pattern on the Fe/TiO₂ included an additional peak of hematite (α-Fe₂O₃). The majority of gaseous acetaldehyde with TiO₂-WO and Ca/TiO₂ for photocatalytic activity was completely removed within 40 minutes under UV irradiation.     

Gas‐Phase Hydrogenolysis of Glycerol Catalyzed by Cu/MOx Catalysts

The catalytic activities of Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H₂. Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu⁰). Cu/Al₂O₃ catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO₂ and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature.     

Formation mechanism of Cu2O particles using layered CaSi2 as a reduction/oxidation mediator

We demonstrate that Cu₂O particles can be produced along with siloxene formation by simply dispersing layered CaSi₂ into an aqueous solution of CuCl₂ and HCl at room temperature. The Cl⁻ ions induce oxidative extraction of Ca from CaSi₂ to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu₂O particles under optimized conditions as follows. A trace amount of residual CaSi₂ is dissolved in the solution, which provides OH⁻ ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)₄]²⁻ ions. Accordingly, Cu₂O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)₄]²⁻ ions in the solution. However, under conditions with an excess amount of Cl⁻ ions results in further oxidation of Cu to also form Cu₂Cl(OH)₃. Thus, CaSi₂ acts as an effective reduction and/or oxidation mediator to tune the number of Cl⁻ and OH⁻ ions and control the oxidation state of Cu.     

Preparation of novel Cu/TiO2 mischcrystal composites and antibacterial activities for Escherichia coli under visible light

In this paper, novel copper/titanium dioxide (Cu/TiO₂) composites were facilely prepared by simple sol-gel hydrothermal method. The crystalline phases, surface morphology and antibacterial activity of Cu/TiO₂ were investigated systematically. Interestingly, the as-prepared Cu/TiO₂ materials were made up with three different crystalline phases, including cuprite Cu₂Cl(OH)₃, Cu₂₊₁O, and anatase TiO₂. Next, the ‘zone of inhibition’ experiment was performed against E. coli using Cu/TiO₂ catalysts with different Cu doping concentration as the antibacterial agents. Our results show that the Cu/TiO₂-3.00 catalyst possesses optimal antibacterial ability against E. coli, which may be connected with the strong oxidizing reactive oxygen species (ROS) destroying the bacteria and photogenerated charge separation and recombination.     

Partially Fluorinated Metal Oxide Catalysts for a Friedel–Crafts-type Reaction of Dichlorofluoromethane with Tetrafluoroethylene

Partially fluorinated metal oxides were studied for manufacturing dichloropentafluoropropanes (CF₃CF₂CHCl₂ and CCl₂FCF₂CHClF) and controlling the selectivity of their isomers. When activated by elemental fluorine or dichlorodifluoromethane, metal oxides such as TiO₂, HfO₂, Al₂O₃, and ZrO₂, exhibited catalytic activity in the reaction of dichlorofluoromethane with tetrafluoroethylene. In the case of the TiO₂ catalyst, the more fluorine incorporated, the higher the selectivity was for the CCl₂FCF₂CHClF formation. The fluorine-activated TiO₂ catalyst was identified by XRD and XPS as a mixture of TiO₂ and partially fluorinated TiO₂ including TiOF₂.     

Parallel Reactor Activity Studies of the Preferential Oxidation of CO on Transition Metals Supported on TiO2 and TiO2 Nanotubes

The preferential oxidation of carbon monoxide in the presence of hydrogen (PROX reaction) was studied on Cu catalysts promoted with Fe, Nb, Ce, and Ni supported on TiO₂ and on TiO₂ nanotubes. The surface area of the untreated TiO₂ anatase (150 m²/g) support was increase to 350 m²/g when transformed into TiO₂ nanotubes (NT). XRD and SEM results confirm the formation of nanotubular structures responsible of the increase in BET surface area. The activity results indicate that a 10% Cu/5% Nb/TiO₂-NT catalyst is highly active for this reaction compared to other transition metals and with a catalyst with the same composition supported on untreated TiO₂. We found close to 80% CO conversion and 40% selectivity to CO₂ formation at 170 °C. The higher activity is ascribed to a higher dispersion of Cu on the TiO₂ NT structures.     

Effect of metal oxides on electrochemical performances of La–Mg–Ni-based alloys

Metal oxides (TiO₂, Er₂O₃ and ZnO) were added to La–Mg–Ni-based hydrogen storage alloy electrodes and their effects on the structural and electrochemical properties were studied. The charge efficiency, especially at high charge current density was greatly ameliorated, and the high rate charge capability at 1440 mA g⁻¹ increased from 85.1% (blank) to 94.1% (TiO₂), 93.3% (Er₂O₃) and 90.5% (ZnO). The high temperature dischargeability was also improved in case of TiO₂, Er₂O₃ and ZnO additives. These additives suppressed formation of Mg(OH)₂ and La(OH)₃ during charge/discharge process and therefore the cycling stability was improved. The discharge capacity retention at the 200th cycle increased from 72.9% (blank) to 79.6% (TiO₂), 87.5% (Er₂O₃) and 77.9% (ZnO).     

Characterization of Cu Nanoparticles on TiO2 Photocatalysts Fabricated by Electroless Plating Method

Cu-modified TiO₂ photocatalysts (Cu/TiO₂) were fabricated by electroless plating and wet impregnation methods. Photocatalytic activity for H₂ production over Cu/TiO₂ by electroless plating method was higher than that over Cu/TiO₂ by impregnation method. Characterization of Cu nanoparticles by HRTEM, STEM-EDX, XRD and XAFS was studied. As compared to the wet impregnation method, the electroless plating method resulted in the formation of Cu nanoparticles with small size and uniform distribution on the TiO₂ surface, which caused the enhancement of H₂ production. XAFS measurement provided the evidences for the chemical state change of Cu species during the photocatalytic reaction. The process that Cu species varied from Cu²⁺ into Cu⁰ via Cu¹⁺ as the intermediate under photoirradiation is very important for the H₂ production, which indicates that the metallic Cu nanoparticles acted as the active sites and restrained the photogenerated charges recombination.     

On the photooxidative behavior of TiO2 and PW12O403−: OH radicals versus holes

Parallel experiments under similar conditions, using various substrates (atrazine, fenitrothion, 4-chlorophenol and 2,4-D) and OH radical scavengers (Br⁻, isopropyl alcohol, tertiary butyl alcohol and acetone), have shown that the photooxidizing mode of PW₁₂O₄₀³⁻ and TiO₂, i.e., OH radicals and/or holes (h⁺), depends on the nature of substrate and the mode of investigation. This provides an explanation for the controversial results reported in the literature. Atrazine shows that both PW₁₂O₄₀³⁻ and TiO₂ operate, mainly, via OH radicals and to a lesser extent with holes (h⁺), whereas, fenitrothion suggests that both systems operate almost exclusively, via OH radicals. Differences in the action of the catalysts are encountered in the photodegradation of 4-chlorophenol (4-ClPh) and 2,4-dichlorophenoxyacetic acid (2,4-D). PW₁₂O₄₀³⁻ appears to operate essentially via OH radicals, whereas, h⁺ appear to be the major oxidant with TiO₂. Overall, though, the action of OH radicals relative to h⁺ appears to be more pronounced with PW₁₂O₄₀³⁻ than TiO₂.     

In situ DRIFTS study of photocatalytic CO2 reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

Development of iron-based sorbents for Hg0 removal from coal derived fuel gas: Effect of hydrogen chloride

Laboratory studies were conducted to develop an elemental mercury (Hg⁰) removal process based on the reaction of H₂S and Hg⁰ using iron-based sorbents for coal derived fuel gas. It is well known that hydrogen chloride (HCl) is present in fuel gases derived from some types of coal, but the effect of HCl on the Hg⁰ removal performance of iron-based sorbents in coal derived fuel gas is not yet well understood. In this study, the effects of HCl on the removal of Hg⁰ from coal derived fuel gases over iron-based sorbents such as iron oxide (Fe₂O₃), supported iron oxides on TiO₂, iron oxide–Ca(OH)₂, and iron sulfides were investigated. The Hg⁰ removal experiments were carried out in a laboratory-scale fixed-bed reactor at 80 °C using simulated fuel gas. In the case of iron oxide (Fe₂O₃), the presence of HCl suppressed the Hg⁰ removal rate. In the case of Fe₂O₃ (2 or 5 wt%)/TiO₂, the presence of HCl did not suppress the Hg⁰ removal rate and the activity was stable. The Hg⁰ removal performance of reagent FeS₂ was higher than that of the iron oxide, and not affected by the presence of HCl. The Hg⁰ removal rate of iron oxide–Ca(OH)₂ was not effected by the presence of HCl, because HCl was captured by Ca(OH)₂. The reagent FeS₂ showed higher Hg⁰ removal activity than that of FeS₂ ore. However, the Hg⁰ removal performance of ground and kneaded FeS₂ ore was comparable to that of reagent FeS₂ probably due to the increase in porosity of the FeS₂ ore by grinding and kneading.     

In situ DRIFTS study of photocatalytic CO<Subscript>2</Subscript> reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

线-筒式脉冲电晕反应器降解三氯乙烯废气研究

采用线-筒式电晕反应器对三氯乙烯在氮气中和有氧气存在情况下的降解效果进行了实验研究. 研究结果表明三氯乙烯在氮气中的降解效果要好于在氮气和氧气混合中的降解效果. 三氯乙烯在氮气中的主要气相降解产物是HCl和Cl2;在氮气和氧气的混合气中的主要降解产物是COCl2、CO2和C2HCl3O (DCAC). 为了去除三氯乙烯分解过程中生成的有害产物,在反应器内壁上涂覆一层Ca(OH)2吸收剂. 实验发现采用电晕结合现场化学吸收能有效地去除COCl2等有害产物的产生,同时三氯乙烯的去除率大大高于反应器内没有固体吸收剂的情况.当反应器的输入能量为20 W时,对浓度为1090 mg·m-3的三氯乙烯在10% O2和90% N2的混合气中的分解率从62%提高到了99.5%. 可以认为反应器内的Ca(OH)2吸收剂通过气-固吸收反应参加了三氯乙烯的分解过程,从而提高了三氯乙烯的降解率.     

Removal of Cu(II) from Aqueous Solution by Oil-Water Interfacial Emulsion Technique with Adsorbing Colloids

Abstract

Experimental investigations on the removal of Cu(II) from an aqueous solution were carried out by an interfacial emulsion technique with an adsorbing colloid (Al(OH)₃, FE(OH)₃), Cu(II) from the aqueous solution was segregated into a compact emulsion between water and a water-immiscible oil phase by an interfacial emulsion technique that uses the adsorptive power of the oil-water interface. Trimethylamine was effective as a surfactant for the removal of Cu(II), and the optimum pH for the removal of Cu(II) was found at 9.0 when using Fe(OH)₃ and at 10.0 when using Al(OH)₃ as an adsorbing colloid, respectively. The effects of pH, mixing time, initial surfactant concentration, initial Fe(III) concentration, and foreign ions (Na⁺, Ca²⁺, CI^?, NO₃ ^?, HPO₄ ^2?) on the removal efficiency were investigated. The adsorption and separation mechanisms for the removal of Cu(II) by the interfacial emulsion technique of adsorbing colloids were observed.     

Zirconium Incorporation into CaTiO3 Perovskite Prepared from Xerogels and Implication for the Fate of (Ca,Sr)TiO3 Nuclear Waste Ceramics

CaTiO₃ perovskite has been proposed as a ceramic waste form for immobilization of ⁹⁰Sr. Nonradioactive coprecipitated xerogel powders with nominal atomic ratios of Ca:Zr:Ti = 0.75:0.25:1.00 were synthesized to mimic the fate of (Ca_0.75⁹⁰Sr_0.25)TiO₃ solid solution after complete decay of the Sr and its intermediate product Y to stable Zr when an excess B⁴⁺ (Ti and ⁹⁰Zr) cations will present. Ca:Ti = 1.00:1.00 samples were used as a reference. The powders were heated to various conditions to explore the thermodynamic stability of its oxides. The heated Ca:Zr:Ti = 0.75:0.25:1.00 samples formed a major orthorhombic Ca(Zr_1?xTi_x)O₃ perovskite phase. The Ti/(Ti + Zr) ratio of the perovskite preserves its nominal ratio at 600°C. The Zr rejects from the Ca(Zr_1?xTi_x)O₃ with further increasing the temperature, following the formation of Ca–Ti–Zr–O secondary phases. This study indicates a tendency of the Zr to segregate from an original (Ca,Sr)TiO₃ waste form when the stoichiometry is controlled by the conversion of Sr to Zr (in normal oxidation states).     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Selectivity of Hydrophilic and Hydrophobic TiO2 for Organic‐Based Dispersants

The effects of the surface chemistry of TiO₂ powders on the dispersion performance of various dispersants are studied. Four common dispersants (oleic acid, oleylamine, oleyl phosphate, and tris‐(2‐butoxyethyl) phosphate) with different functional groups (carboxyl (–COOH), amino (–NH₂), phosphate (–P(=O)(OH)₂), and –P(=O)) are investigated for their potential to disperse hydrophilic and hydrophobic titania (TiO₂) powders. The outcomes, based on adsorption kinetics, adsorption isotherms, rheologies, and theoretical calculations, indicate that the hydrophilic TiO₂ is more sensitive to the chemistry of dispersants as compared to the hydrophobic TiO₂. However, the relative dispersion efficiencies of the dispersants are not found relevant to the adsorption kinetics, which is dominated by the adsorption amount. In addition, hydrogen bonding between –OH groups of the phosphate‐based dispersants dominates their dispersion ability for TiO₂.