Ag/TiO2光催化膜降解高浓度对氯苯酚溶液的研究

依据光催化还原原理 ,在活性碳负载的TiO2 纳米粒子膜表面上制备出载银光催化剂 ,采用该催化剂对初始COD≥ 6 0 0mg·L-1的高浓度 4 氯苯酚水溶液进行降解研究 ,分别考察了光催化剂的用量、反应液初始浓度和初始 pH值等对降解性能的影响 ,并与DegussaP2 5微粉光催化剂等进行比较 ,得出负载型Ag/TiO2 光催化膜具有光催化活性高、固液易分离的特点。     

Selective photocatalytic destruction of airborne VOCs

This article describes a photocatalytic method for selective oxidation of the airborne nitroglycerine (NG), in the presence of ethanol and acetone vapors at high concentrations (exceeding 1% by volume). Process selectivities toward NG photooxidation were examined for various photoreactor configurations and UV lamps and techniques used for the photocatalyst preparation. In addition, we have studied the effect of temperature, residence time, various additives (e.g. ozone, water vapor, nitrogen), and initial concentration of the solvents in air. Our data indicate that modifying TiO₂ with silico-tungstic acid (STA) catalyst results in selective NG oxidation without affecting ethanol and acetone significantly. Platinization of TiO₂ showed an adverse effect on NG destruction selectivity. In general, low residence times and initial concentration of oxidants and high temperatures and initial concentration of solvents favor selectivity toward NG destruction. In the case of temperature, our observation can be explained by the temperature dependent gas diffusion and surface processes. In most cases, the yield of ethanol oxidation was generally higher than that of acetone. Results from the bench-scale experiments using artificial UV light sources were used to build and test a solar photocatalytic oxidation reactor for selective NG treatment in the presence of ethanol and acetone.     

Peroxomonosulphate, an efficient oxidant for the photocatalysed degradation of a textile dye, acid red 88

Visible light-assisted degradation of a mono azo textile dye acid red 88 (AR88) was carried out in presence of titanium dioxide photocatalyst. Various operational parameters such as variation of the initial dye concentration, photocatalyst and pH on the photocatalytic degradation rate were studied. Effect of the amount of oxidants such as peroxomonosulphate (PMS) and peroxodisulphate (PDS) and the ratio of concentration of oxidant to the concentration of dye (C_oxidant/C_dye) on the photocatalysed degradation rate were also investigated. Though the rate of photodegradation of the dye decreased with increase in dye concentration, the rate increased with C_oxidant/C_dye ratio. Total organic carbon (TOC) analysis revealed a rapid mineralisation of AR88 in the presence of PMS. A suitable mechanism explaining the observed enhanced decolorisation and mineralisation rate of the dye with PMS is presented.     

A systematic study on the effect of OH− and Ni2+ ions on the electro-catalytic oxidation of methanol at Ni-S-1 electrode

The effect of varying nickel ions as well as OH⁻ ions concentration on the electrochemical oxidation of methanol on nickel impregnated silicalite-1 (Ni-S-1) electrodes was investigated. The study of nickel ions concentration effect was carried out in two different ways: by varying the soaking time in one and the same concentration of NiSO₄ solution, or by fixing the soaking time in different concentrations of NiSO₄ solution. The results showed that for electrodes pre-soaked in 1.0 M NiSO₄ solution for 90 s, increasing the OH⁻ ions concentration results in increasing the oxidation current density of methanol. On the basis of this result, high concentration of KOH is preferable as a medium for methanol oxidation at the Ni-S-1 electrode in presence of nickel ions. On the other hand, at a certain OH⁻ ions concentration, the peak height of methanol oxidation increases with increasing Ni ions concentration up to a certain value after which no effect was observed. A first order reaction kinetics with respect to both nickel ions and OH⁻ ions was estimated for the oxidation of methanol.     

Enhanced photoelectrochemical water oxidation on BiVO4 by addition of ZnCo-MOFs as effective hole transfer co-catalyst

Solar-driven water splitting is one of greenways for massive conversion of sustainable and nonpolluting energy applied to meet global energy crisis. Photocatalysts are greatly explored to improve photoelectrochemical (PEC) water oxidation efficiency. Bismuth vanadate (BiVO₄) has been extensively used as photocatalyst for water oxidation, but its passive oxygen evolution kinetics and charge carrier recombination lead to inferior PEC performance under light illumination. Tuning interfacial charge separation and transfer is an eminent way to stimulate water oxidation characteristics of BiVO₄. Herein, a BiVO₄/zinc cobalt metal-organic framework (ZnCoMOF) composite is firstly proposed as photocatalyst for water oxidation. ZnCoMOF nanosheets are loaded on BiVO₄ surface as co-catalyst via solvothermal process. Effects of solvothermal duration and mole ratio of zinc and cobalt are investigated. The optimal BiVO₄/ZnCoMOF electrode shows a photocurrent density of 3.08 mA cm^?2 at 1.23 V vs. reversible hydrogen electrode (RHE), which is 4.21 times greater than that of BiVO₄ electrode. The redox properties of high valence metal ions in ZnCoMOF are used to store photoexcited holes and transfer them to the water oxidation process in the BiVO₄/ZnCoMOF system. This work demonstrates that PEC performance of BiVO₄ can be largely improved via controlling water oxidation kinetics and refining charge recombination and transport properties.     

Fe supported on ceria as effective catalyst for the heterogeneous photo-oxidation of basic orange 2 in aqueous solution with sunlight

Fe^III supported on ceria as an effective catalyst for oxidation was prepared and used for the degradation of basic orange 2 azo textile dye (BO2). BO2 was chosen as a model pollutant and the catalytic oxidation was carried out in a batch reactor using hydrogen peroxide as the oxidant at pH 3. The influent factors on BO2 oxidation, such as catalyst dosage, H₂O₂ concentration, and BO2 concentration were studied by considering the BO2 conversion and chemical oxygen demand (COD) removal. The Fe^III-ceria catalyst showed a high catalytic activity for the oxidation of BO2 in aqueous solution. It was observed that the solution became colorless after 5 h of oxidation and over 90% COD removal was achieved with all the Fe^III-ceria catalysts used under dark conditions in the catalytic oxidation system. The catalytic removal of BO2 during BO2 oxidation was improved under solar radiation, which notably increased the BO2 degradation rate. Consecutive BO2 oxidation cycles carried out with the same Fe^III-ceria catalyst and untreated fresh dyestuff solution showed that the catalyst had good stability and good degradation performance, thus evidencing the possibility of being used in continuous processes. This study showed that the Fe^III-ceria catalytic oxidation process is an efficient method for the treatment of BO2 aqueous solutions.     

Photocatalytic reduction of some alkali carbonates in the presence of methylene blue

The photoreduction of aqueous sodium and potassium carbonates has been carried out in the presence of methylene blue solution (which is a photocatalyst also). The photocatalytic formation of formic acid and formaldehyde were measured spectrophotometrically using Nash reagent. The effect of variation of various parameters like pH, amount of photocatalyst (methylene blue concentration), concentration of Na₂CO₃ and K₂CO₃, light intensity, etc. on the yield of photoproducts was also investigated. A tentative mechanism for this reduction has been proposed. Copyright © 1999 John Wiley & Sons, Ltd.     

Enhanced hydrogen production over incorporated Cu and Ni into titania photocatalyst in glycerol-based photoelectrochemical cell: Effect of total metal loading and calcination temperature

The solar driven hydrogen production was successfully investigated in a glycerol-based photoelectrochemical cell (PEC) over nanostructured TiO₂ supported bimetallic Cu and Ni by adjusting total metal loading (5, 10, and 15 mol%) and calcination temperature (400, 450, 500, and 600 °C). The effects of the mentioned parameters on physicochemical and photoelectrochemical properties of prepared Cu–Ni/TiO₂ photoanodes were explored by using different characterization techniques. The hydrogen evolution was experimentally found to be affected total metal loading and calcination temperature. The calcined photocatalyst with the total metal loading of 5 mol% at 450 °C was identified as the most efficient photocatalyst by producing maximum accumulative hydrogen of 694.84 μmol. A high performance of this photocatalyst is mainly attributed to its proper particle size and great ratio of Ti³⁺:Ti⁴⁺ and Cu⁺:Cu²⁺ in TiO₂ matrix. These better physicochemical properties enhanced charge carrier separation, which retarded the charge recombination and enhanced the transportation of photo-induced electrons at the photoelectrode/electrolyte interface. The intermediates from photooxidation of glycerol were verified using high performance liquid chromatography, indicating a partial oxidation of glycerol with selective pathway in KOH (1 M) solution. This work demonstrates that optimization Cu–Ni/TiO₂ photoanode has the practical potential in PEC cell to generate hydrogen from solar and biomass energy.     

Catalytic performance of a copper–promoted CeO2 catalyst in the CO oxidation: Influence of the operating variables and kinetic study

A study of the CO oxidation reaction was conducted on a CuO–CeO₂ catalyst, with a copper content of 20 at%. The stability, activity and selectivity of this sample were evaluated in the absence of H₂ and also under PROX conditions (i.e. in great H₂ excess). The influence of the reaction temperature and the feed composition was also analyzed. It was found that water and CO₂ have a negative effect on the catalytic activity. Except for the undesired oxidation of hydrogen, the occurrence of other lateral reactions that could be present in the PROX reactor can be discarded. A kinetic study was carried out in order to fit a classical power-law expression for CO oxidation rate. Although this mathematical expression gave a good fit in limited concentration ranges, it was found that the partial reaction orders depend on the reactant molar fractions.     

Catalytic partial oxidation of coke oven gas to syngas in an oxygen permeation membrane reactor combined with NiO/MgO catalyst

A high oxygen permeability and sufficient chemical and mechanical stability mixed ion and electron conductivity membrane to withstand the hash strong oxidation and reduction working conditions is significant for the membrane reactor to commercial-scale plant. In this paper, a disk-shaped Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3−δ membrane was applied to a membrane reactor for the partial oxidation of methane in coke oven gas (COG) to syngas. The reaction was carried out using NiO/MgO solid solution catalyst by feeding COG. The reforming process was performed successfully; 95% CH₄ conversion, 80% H₂ selectivity, 106% CO selectivity and 16.3 ml cm⁻² min⁻¹ oxygen permeation flux were achieved at 1148 K. The reaction has been steadily carried out for more than 100 h. The NiO/MgO catalyst used in the membrane reactor exhibited good catalytic activity and resistance to coking in the COG atmosphere. Characterization of the membrane surface by SEM and XRD after long life test showed that both the surface exposed to the air side and reaction side still preserved the Perovskite structure which is implied that the practical application of this membrane as membrane reactor for partial oxidation of COG is promising.     

A sorption rate hypothesis for the increase in H2 permeability of palladium-silver (Pd-Ag) membranes caused by air oxidation

Hydrogen permeation measurements were performed at 300 °C for 25-μm cold-rolled Pd-Ag 25 wt% membranes before and after air oxidation at the same temperature as permeation. The air oxidation resulted in enhanced H₂ permeation through the membrane, as well as a roughening of the surface with the formation of surface grains and defects. The protruding grains can be leveled off by exposure to H₂ but the surface defects cannot. These microstructure changes are only on the membrane surfaces and do not create transmembrane defects that would allow permeation for gas species other than H₂. The H₂ permeability of the oxidized membrane increased by 25-90% compared to that of the as-received film at the same permeation condition, and the membranes retained perfect H₂ selectivity over N₂. The percent improvement of H₂ permeability decreases with increasing H₂ feed pressure. A new sorption kinetics hypothesis is proposed to elucidate the increase in H₂ permeability of Pd-Ag membranes caused by oxidation. H₂ solubility and sorption rate results were presented to test the new hypothesis. It is found that air oxidation does not change the H₂ solubility in Pd-Ag membranes, but enhances the H₂ sorption kinetics significantly. The extent of kinetics enhancement also decreases with increasing H₂ pressures. The much faster sorption equilibrium implies higher effective H₂ diffusivity at the Pd-Ag membrane surface for the oxidized sample and a higher transfer rate of atomic hydrogen from surface/sub-surface to the membrane bulk that contributes to the increase of H₂ permeability observed in experiments.     

Hydrogen and synthesis gas co-production on oxygen membranes of mixed conductor: Scale-sensitive features of the process

The tubular ceramic membrane of La_0.5Sr_0.5FeO_3–δ was tested in a condition of simultaneous partial oxidation of methane (POM), occurring in space adjacent to the outer surface of the membrane, and water splitting (WS) accompanied by hydrogen generation taking place in the internal membrane space. It was shown that a membrane with a surface area of more than 10 cm² could successfully operate without carrier gases. A detected effect of CO selectivity in POM on the thermal condition of the process was another result using a membrane of notable size. The heat power released/absorbed on the membrane, associated with partial oxidation of methane and water splitting, was calculated using experimental data. The absorbed heat power of the overall process was found to be sensitive to CO selectivity, especially if selectivity exceeded 80%. The combined POM and WS process with the hydrogen production rate of ∼2 mL min⁻¹cm⁻² during 300 h with stable methane conversion of about 99% and CO selectivity around 96% was successfully carried out.     

Effect of polystyrene characteristic on photocatalytic hydrogen production by porous polystyrene photocatalyst film under simulated solar light irradiation

In this study, we developed a polystyrene-platinum/nitrogen-doped titanium dioxide/strontium titanate composite-polyvinylpyrrolidone (PS-PNS-PVP) photocatalyst film, which is applied in the process of photocatalytic hydrolysis under simulated sunlight to produce hydrogen, is developed. PS, which is cheap, non-toxic, with high UV resistance, and chemical inertness, is used as a carrier, and a highly effective hydrogen production of Pt/N–TiO₂/SrTiO₃ as a photocatalyst. The influence of the PS concentration on the stability, optical, and electrical properties of the photocatalyst film is discussed. In addition, the influence of the photocatalyst dispersion in the film on the activity under various photocatalyst concentrations was investigated. A polyvinylpyrrolidone pore-forming agent was then used to examine the effect on the photocatalyst film structure and optical properties, and the subsequent influence on photocatalytic hydrogen energy activity. Adjusting the PS concentration to 20 wt% produced good film-forming stability, and the photocatalyst dispersibility in the film under different photocatalyst concentrations. A photocatalyst concentration of 2.5 wt% resulted in good film dispersibility and the realization of added pore-forming agent. The modified photocatalyst film changed the film from a blind pore structure to a connecting void structure, increasing the film's porosity and hydrophilicity. This increased the number of photocatalytic sites, and the optimal hydrogen production of the photocatalyst film reached 21,333 μmol h^?1 g^?1.     

Design of efficient photocatalytic processes for the production of hydrogen from biomass derived substrates

The photoreforming of glucose has been studied over TiO₂ photocatalyst with different photoreactors, focusing on the effect of the reaction conditions: temperature, pressure, catalyst and substrate concentration. The effect of pressure was particularly significant, decreasing hydrogen evolution rate, but improving the conversion of the substrate. Furthermore, pressure moderately higher than ambient allowed to operate at high temperature (80 °C), boosting hydrogen productivity. Most experiments were carried out on glucose photoreforming, but, for the first time, the photoconversion of levulinic acid was investigated, as an interesting product of biomass hydrolysis under harsh conditions. Levulinic acid led to the production of ethane and ethylene in gas phase, interpreted according to a preliminary hypothesis of the photoconversion mechanism. High hydrogen productivity was achieved, in most cases higher than the literature benchmark.     

Catalytic conversion of CO2 to biofuel (methanol) and downstream separation in membrane-integrated photoreactor system under suitable conditions

A heterogeneous photocatalyst has been developed using sono-chemical assisted sol-gel method by maintaining aweight ratio of 1:2:3 for hydrogen exfoliation graphene, titanium oxide andcopper sulphateand exhaustively characterized. Rigorous experimentations have been done using newly developed heterogeneous photocatalyst for efficient capturing and maximum conversion of carbon di oxide to methanol by mutual effects of governing conditions, like as catalyst dose, pH, CO₂ flow rate and temperature. Optimization study has been carried out employing a statistical approach of response surface methodology which reveals the maximum methanol productivity and yield. Approximately, 134 g/Lh of productivity and 40 mg/g_catof yield were found after 3 h of illumination under UV in an annular type Pyrex reactor at an optimum catalyst dosage of 10 g/L, CO₂ flow rate of 3 L/m, pH of 3, and process temperature of 50 °C. By the judicial integration of flat-sheet cross flow microfiltration membrane module for catalyst separation and recycle, a steady state permeate flux 145 L/m²h was achieved at an applied pressure of 3 bar and cross-flow feed rate of 700 L/h.     

Fabrication of noble-metal-free Cd0.5Zn0.5S/NiS hybrid photocatalyst for efficient solar hydrogen evolution

Up to now, most of the semiconductor photocatalysts can only achieve their high photocatalytic activity for hydrogen production with the loading of noble metals, such as Pt or Ru, as cocatalysts, which drastically increases the total cost of the designed photocatalyst. Herein, we report the design and fabrication of a highly efficient Cd_0.5Zn_0.5S photocatalyst decorated with nanosized NiS surface heterojunctions. The hydrogen evolution rate over this photocatalyst reached 1.4 mmol/h, with a remarkable quantum yield of 33.9%. This efficiency is even much higher than many noble metal loaded photocatalysts. In this hybrid photocatalyst, the nanosized NiS on the surface can serve as electron trapping sites, by which, photogenerated electrons were extracted from Cd_0.5Zn_0.5S substrate, leading to spatially separated photoreduction and oxidation reactions. More interestingly, it was found that NiS played a similar role as noble metal, providing active sites for proton reduction, and hence efficiently enhancing the overall hydrogen production rate. Our work demonstrates the possibility of substitution of noble metal cocatalyst by a properly engineered surface hetero-junction to achieve efficient and low cost photocatalytic hydrogen production.     

Studies on hydriding kinetics of some La-based metal hydride alloys

In this paper, the hydriding kinetics of LaNi₅, LaNi_4.7Al_0.3 and LmNi_4.91Sn_0.15 is presented. Experiments were carried out by maintaining the pressure ratio (supply pressure to equilibrium pressure at the mid-point of the pressure–concentration–isotherm) equal to 2 and by maintaining nearly isothermal reaction conditions. Two widely used reaction kinetics models, namely Johnson–Mehl–Avrami (JMA) model and Jander diffusion model (JDM) are considered for the analysis. Two JMA models are considered; in the first model, the order of the reaction is assumed as unit and in the second model, the rate constant is calculated by estimating the order by fitting the reaction kinetics data with a reaction kinetics equation. The activation energy and pre-exponential constants of the above-mentioned alloys are estimated by constructing the Arrhenius plot. Activation energies estimated from the different models are compared and the accurate values of activation energy for the different alloys are determined by comparing the reaction kinetics data obtained from the models with the experimental data. The rate-controlling step of the hydriding reaction is obtained for all the alloys investigated.     

Solar photocatalytic degradation of a reactive azo dye in TiO2-suspension

The photocatalytic decolourisation and degradation of an azo dye reactive orange 4 (RO4) in aqueous solution with TiO₂-P25 (Degussa) as photocatalyst in slurry form have been investigated using solarlight. There is a significant difference in adsorption of dye on TiO₂ surface with the change in solution pH. The effect of various photocatalysts such as TiO₂-P25, TiO₂ (anatase), ZnO, CdS, Fe₂O₃, SnO₂ on the decolourisation and degradation has been studied. The order of reactivity of photocatalysts is TiO₂-P25>ZnO>TiO₂ (anatase). CdS, Fe₂O₃ and SnO₂ have negligible activity on RO4 decolourisation and degradation. The effects of various parameters such as catalyst loading, pH and initial concentration of the dye on decolourisation and degradation have been determined. The degradation was strongly enhanced in the presence of electron acceptors such as H₂O₂, (NH₄)₂S₂O₈ and KBrO₃. The effects of dye-assisting chemicals such as Na₂CO₃, NaCl have been carried out. Addition of these chemicals inhibits the removal rate. The photodecolourisation and degradation kinetics are discussed in terms of Langmuir–Hinshelwood kinetic model.     

Kinetic study and modeling of the high temperature CO2 capture by Na2ZrO3 solid absorbent

Hydrogen production through sorption enhanced reforming (SER) use a solid CO₂ absorbent to increase hydrogen purity (98%) and to perform reforming and WGS reactions in one single step, thus producing high methane conversions and important energy savings. Na₂ZrO₃ is as an alternate synthetic CO₂ solid absorbent for SER applications. The present research is aimed to establish CO₂ sorption kinetics parameters; reaction order, rate constant, apparent, intrinsic and diffusional activation energies. Na₂ZrO₃ sorption kinetics was studied through TGA as a function of CO₂ concentration and temperature. A global reaction rate of first order in CO₂ and a strong dependence in temperature was found. The approximate solution to the shrinking core model was used to fit the data. Modeling results indicated the surface reaction as the main resistance to the reaction rate, controlling reaction kinetics with only a minor contribution of the product layer diffusion resistance toward the end of the reaction.     

Kinetic Monte Carlo simulation of hydrogen production from photocatalytic water splitting in the presence of methanol by 1 wt% Au/TiO2

In this research, using the kinetic Monte Carlo simulation (KMC), the hydrogen production from a water-methanol mixture using Au/TiO₂ photocatalyst is investigated. A mechanism is proposed, and the rate constants of the reaction steps are specified. The reaction rate constants of different steps and the concentration of the active sites on the photocatalyst surface were determined. An excellent match between simulated and experimental data confirms the results. The electron-hole pair production, methanol adsorption on the photocatalyst surface, and electron-hole recombination steps are considered the most critical steps. To study the effects of independent variables (initial concentration of methanol, photocatalyst dosage, pH, and time of reaction) on the produced hydrogen, a combination of KMC simulation and design of experiment was employed. The concentration of photocatalysis has the highest and pH has the lowest effect on the hydrogen production. The optimal conditions for photocatalytic hydrogen production are presented.