P25光催化还原水溶液中CO_2的性能

本实验研究了以P25纳米材料作为光催化剂,在碱性条件下对CO2进行光催化还原。在波长为254 nm的紫外灯下反应20 h后,气相中主要产物是CH4,液相中主要产物为CH3OH,同时,还检测到一定量的H2,HCHO和CO。     

污泥低温热处理过程研究

研究了脱水干燥污泥在管式炉中不同条件下的热处理行为。主要考察了热处理气氛(空气、氮气)、时间、温度、气体流量等对污泥热处理行为的影响。结果表明,在空气气氛(20 mL/min)、440℃、热处理50 min时液体收率最高,为42.5%,固体和气体分别为49.5%和8.0%。     

Kinetic study on the first stage during thermal degradation of polystyrene

The kinetic parameters of the first stage of polystyrene degradation have been investigated to elucidate the reaction mechanisms using the flow reactor system. The decrease in molecular weight of polystyrene was recorded at minute intervals over the temperature range 310°–390°C. Generally, the first and second stages were observed by thermogravimetric analysis (t.g.a.), however in the early stage of the degradation volatile yields of at least 5% occurred. Therefore, using t.g.a. analysis it is difficult to detect this earlier stage. It became evident that the first stage in the earlier part of the reaction could be detected by g.p.c. analysis. We have observed the hidden kinetic parameters of the nature of the first stage of the polystyrene degradation. The results indicate that the main chains were degraded randomly with the small quantitative volatile groups in the first stage and the rates of decrease in molecular weight in the first stage against reaction temperatures were evaluated as log k_s = 12.0 ? 41300/RT.     

Greener photocatalysts: Hydroxyapatite derived from waste mussel shells for the photocatalytic degradation of a model azo dye wastewater

This paper demonstrates for the first time the feasibility of utilising waste mussel shells for the synthesis of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (denoted as HAP) to be used as a greener, renewable photocatalyst for recalcitrant wastewater remediation. HAP was synthesised from Perna canaliculus (green-lipped mussel) shells using a novel pyrolysis–wet slurry precipitation process. The physicochemical properties of the HAP were characterised using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The HAP produced was of comparable quality to commercial (Sulzer Metco) HAP. The synthesised HAP had good photocatalytic activity, whereby methylene blue (a model textile wastewater compound) and its azo dye breakdown products were degraded with an initial rate of 2.5 × 10⁻⁸ mol L⁻¹ min⁻¹. The overall azo dye degradation was nearly 54% within 6 h and 62% within 24 h in an oxygen saturated feed in a batch reactor using a HAP concentration of 2.0 g/L, methylene blue concentration of 5 mg L⁻¹, UV irradiation wavelength of 254 nm and a stirring speed of 300 rpm. The kinetics were well described by three first order reactions in series, reflecting the reaction pathway from methylene blue to azo dye intermediates, then to smaller more highly oxidised intermediates and finally degradation of the recalcitrants. The final two steps of the reaction had significantly slower rates than the initial step (rates constants of 6.2 × 10⁻³ min⁻¹, 1.2 × 10⁻³ min⁻¹ and approximately (due to limited data points) 1.6 × 10⁻⁴ min⁻¹ for the first, second and third step respectively), which tie in with this mechanism, however it could also indicate that the reaction is either product inhibited and/or affected by catalyst deactivation. FTIR analysis of the post-reaction HAP revealed surface PO₄³⁻ group loss. Since there is good photocatalytic activity with oxygen in limited and excess supply during the photoreaction, this indicates the possibility of lattice oxygen participation in the photocatalytic reaction, which needs to be characterised more fully. However, overall, these results indicate that the HAP derived from the mussel shells is a promising greener, renewable photocatalyst for the photocatalytic degradation of wastewater components.     

The effect of thermal annealing on Fe/TiO2 coatings deposited with the help of RF PECVD method. Part II. Optical and photocatalytic properties

In this work, morphology, optical properties, photowetting effect, and bactericidal behavior of titanium dioxide coatings, both plain and iron doped within the range of 0.52 and 4.76 at%, are presented. The coatings were synthesized with the help of radio frequency plasma enhanced chemical vapor deposition technique followed by thermal annealing at 500 °C under normal atmospheric conditions. Atomic force microscopy examination of the film morphology reveal roughness differences depending on the concentration of iron. Measurements of optical properties, carried out with the UV–VIS absorption spectrometry, show high transmittance in the visible range. Optical gap values, determined with the help of the Tauc equation, exhibit a decreasing tendency with an increasing iron content, but only up to the concentration of 2.5 at%, with thermally annealed coatings characterized by higher E_g values than those of the non-annealed materials. Results of variable angle spectroscopic ellipsometry measurements indicate that both iron doping and thermal annealing have the effect of increasing refractive index of the films. An analysis of the coatings surface wettability, performed under conditions of an alternative exposure either to daylight or to the UV-B radiation, show the most important parameter to be the time of water contact angle return to its initial value under darkroom conditions. Finally, bactericidity studies of the UV-B irradiated samples, performed with the Escherichia coli DH5α bacteria, reveal the most extensive bactericidal effect observed for low iron concentrations, equally for both non-annealed and thermally annealed materials.     

Sulfanilic acid-modified P25 TiO2 nanoparticles with improved photocatalytic degradation on Congo red under visible light

Visible-light-induced titania/sulfanilic acid nano-composite photocatalysts were prepared and characterized by FTIR, XPS, UV-vis, XRD, and SEM. The results indicate that the formation of Ti-O-S bonds after the modification of P25 TiO₂ nanoparticles with sulfanilic acid ligands extends the photoresponse of the photocatalyst from the UV to the visible range. The photocatalytic activity of the nano-composite photocatalyst was examined by degrading Congo red under visible light, in which its effecting factors such as irradiation time, catalyst dosage, solution pH and the addition of H₂O₂, were investigated in detail. The possible mechanism of photocatalytic degradation under visible irradiation has been also presented.     

Population balance models for the thermal degradation of PMMA

A widely accepted view of the thermal degradation of polymers such as PMMA is that an initiation reaction produces radical fragments that undergo rapid depropagation and are also converted back to molecules by a termination reaction. This mechanism is applied to a population of linear molecules and radicals and the evolution of the population is modelled by appropriate discrete sets of ordinary differential equations. In particular, end-chain and random initiation reactions with first-order termination are analysed and compared with experimental data. We find on comparison with TG data for PMMA that the initiation reaction is important in dictating the qualitative behaviour of the overall rate of thermal degradation. Furthermore, the behaviour of degradation rate with initial degree of polymerisation is also investigated and interpreted within the framework of the model.     

Photoelectro-peroxone process for the degradation of reactive azo dye in aqueous solution

ABSTRACT

This study evaluated the degradation of reactive yellow F3R (RY F3R) dye by photoelectro-peroxone (PEP) process. The study showed that the PEP gave 97.66% colour and 84.64% TOC removals at 1.176 h^?1 which were 14 and 1.4 times greater than photolysis and electro-peroxone processes, respectively. Quenching experiment showed that hydroxyl radical and singlet oxygen were predominant oxidizing species in RY F3R degradation. In addition, results of the colour and TOC removal by the application of PEP to real field textile wastewater showed that PEP offer an efficient and propitious technology for organic pollutant degradation.     

New prototype for the treatment of falling film liquid effluents by gliding arc discharge part I: Application to the discoloration and degradation of anthraquinonic Acid Green 25

Gliding arc discharge (GAD) reactors are continuously in progress in order to improve the treatment efficiency of recalcitrant compounds. However, up to now, they remain difficult to transfer to industrial applications because of some technical constraints in their design. In this study, a new efficient prototype is proposed for the treatment of gravity falling film shaped of liquid effluents. The liquid flow rate is now continuous as the tank containing the solution to be treated is replaced by an inclined plate along which flows the liquid. The various working parameters are optimized and the new prototype efficiency is tested on discolouration and degradation of the anthraquinonique Acid Green 25. The optimized values obtained are: the liquid flow rate ω = 1 L h⁻¹, the plate tilt angle α = 45° and the channel width Δ = 3 mm. The rates of discolouration and degradation reach 95% and 90% respectively after 12 cycles (180 min) of plasma exposition. The GAD in the presence of humid air generates highly oxidizing radical species such as ^•OH with a standard potential E°[(^•OH/H₂O) = 2.85 V/SHE] and its reducer agent H₂O₂ [E°(H₂O₂/H₂O) = 1.68 V/SHE.     

Visible light induced photocatalytic activity of MnO2/BiVO4 for the degradation of organic dye and tetracycline

In this work, α-MnO₂/BiVO₄ nanocomposites with varying MnO₂ contents (0–7 wt%) were successfully prepared via the simple chemical method. The structure, morphology, and optical properties of prepared nanocomposites were studied by various analytical techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible absorption spectroscopy, and photoluminescence (PL) spectroscopy. The photocatalytic efficiency of α-MnO₂/BiVO₄ nanocomposites was studied via decomposition of rhodamine B (RhB) and tetracycline (TC) under exposure to visible light (λ ≥ 420 nm). Due to good structure and composite advantages, 5%MnO₂/BiVO₄ (MnBV-5) photocatalyst exhibited superior RhB and TC degradation efficiency to all other samples. In addition, the MnBV-5 photocatalyst showed good stability, and no apparent reduction in photocatalysis efficiency was noted after five testing cycles. Therefore, the MnO₂/BiVO₄ nanocomposite demonstrated a good potential for photocatalytic decomposition of new water contaminants.     

反胶束法原位合成P25-MPTMS-CdS及光化学性能研究

本文将反胶束法制备的CdS晶体键合在经γ 巯丙基三甲氧基硅(MPTMS)修饰的P25粒子的表面.产物P25 MPTMS CdS复合粒子的紫外 可见吸收和粒子形貌分别用漫反射光谱仪和透射电镜进行了表征.同时也进行了光催化降解甲基橙溶液的实验,发现P25 MPTMS CdS在紫外和可见光下区域都具备较高的光催化活性.经过18h的可见光照后(λ>400nm),紫外 可见光谱表明,P25 MPTMS CdS粒子具备较好的光稳定性.     

Rutile-TiO2: Post heat treatment and its influence on the photocatalytic degradation of MB dye

Photocatalytic degradation of hazardous Methylene blue (MB) attracts greater concern as it is the dominant effluent of textile industry that is mixing with the ground water resources. In this regard, we have explored the possibility for an efficient optimization of MB dye degradation using rutile TiO₂. We have studied the post heat treatment of faceted Rutile TiO₂ nano crystallites synthesized by sol-gel method, which was carried out towards understanding the generation of surface states and its role on the dye degradation. The phase purity and its morphological structures were confirmed by XRD, Raman analysis, FESEM and HRTEM. The XPS analysis reveals the passivation of Ti³⁺ defect upon high temperature treatment above 600 ?C and also found generating surface defect states which are evidenced from the photoluminescence study. An EPR investigation clearly reveals the distributed presence of electron and hole trap states in the faceted R–TiO₂ nano crystallites. Corresponding EIS measurement of flat band potential of the electrochemical interface between R–TiO₂/NaCl shows the upward band bending of R–TiO₂ favourable for the improved charge transfer between R–TiO₂ to Methylene blue (MB) dye. The consolidated results indicate that the high temperature treatment passivates the Ti³⁺ defects and promotes the generation of surface defects that favourably enhances the photocatalytic performance of MB dye from 63% to 90%. The details are discussed in this paper.     

Investigation of the thermal degradation of polyurea: The effect of ammonium polyphosphate and expandable graphite

Polyurea was compounded with ammonium polyphosphate and expandable graphite and the morphology was studied by atomic force microscopy. The thermal degradation of polyurea and polyurea compounded with the additives has been investigated using thermogravimetry coupled with Fourier Transform infrared spectroscopy and mass spectrometry. The study of the thermal degradation and the parameters affecting the thermal stability of PU is essential in order to effectively design flame retarded polyurea. In general, thermal decomposition of polyurea occurs in two steps assigned to the degradation of the hard segment and soft segment, respectively. Adding these additives accelerates the decomposition reaction of polyurea. However, it is clear that more char is formed. This char is thermally more stable than the carbonaceous structure obtained from neat PU. The intumescent shield traps the polymer fragments and limits the evolution of small flammable molecules that are able to feed the flame.     

High-temperature corrosion during the thermal treatment of footwear leather wastes

The footwear leather waste (FLW) has shown some distinct features of a conventional biomass, among which high concentrations of sulfur and chromium. The paper presents the obtained experimental results from gasification and combustion of FLW performed in a semi-pilot plant (350 kW_th). The corrosion tests were carried out with one low carbon steel and three stainless steels at temperature around 500 °C. The obtained corrosion rates for all the tested alloys were significantly lower than those observed on other types of biomass. The presence of chromium oxide and sulfur dioxide in the flue gas was associated with reduction in the corrosion rate.     

A new kinetic model for titanium dioxide mediated heterogeneous photocatalytic degradation of trichloroethylene in gas-phase

This paper focuses on the kinetics of photocatalytic removal and carbon mineralization of gaseous trichloroethylene (TCE) on near-UV irradiated TiO₂ Degussa P25. Experiments were carried out in a flat-plate photoreactor at TCE inlet concentrations of 100–500 ppmv, relative humidities (RH) of 0–62% and gas residence times of 2.5–60.3 s. Gas residence time distribution (RTD) curves revealed an axial dispersed plug flow in the photoreactor with Peclet numbers above 59.4. For all experimental conditions, the carbon mineralization efficiency (5.1–73.0%) was lower than the removal efficiency (8.6–99.9%) and dichloroacetylchloride (DCAC) was detected as a gas-phase degradation product. TCE removal efficiencies increased with lower TCE inlet concentrations, lower RH and higher gas residence times. Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir–Hinshelwood (LH) model could not give an adequate fitting to the experimental results. A new kinetic model, explicitly taking into account electron–hole pair reactions, was developed based on linear TCE adsorption–desorption equilibrium and first order reaction kinetics. The new kinetic model described the experimental results in a more accurate way, as exemplified by a more randomly distributed set of residuals and by a reduction of the sum of squares (SSQ) by a factor 1.7–8.5. The effect of TCE gas-phase concentration, RH and light intensity on adsorption–desorption kinetics, electron–hole concentrations and chemical conversion rates is discussed.     

Effect of thermal treatment and applied potential on the electrochemical behaviour of CoCrMo biomedical alloy

CoCrMo alloy are one of the most important biomaterials for orthopaedic applications, widely used in total joint replacements. The thermal treatments applied to CoCrMo alloys modifies the microstructure of the alloy and change the electrochemical and mechanical properties of the biomaterial. Thus, the aim of this research is to characterize the electrochemical behaviour of CoCrMo alloy depending on the thermal treatment at different applied potentials (according to the cathodic, anodic and transpassive electrochemical domains of the alloy).Metallographic study and electrochemical techniques such as potentiodynamic curves, potentiostatic tests at different potentials (selected according to the electrochemical regions of the potentiodynamic curves) and electrochemical impedance spectroscopy (EIS) are employed to characterize the CoCrMo alloy after three different thermal treatments in simulated body fluid (bovine serum solution).The same corrosion mechanisms were observed for the CoCrMo alloy under the three thermal treatments at different applied potentials, however, the rate of the corrosion reactions which take place on the metallic surfaces depends on those thermal treatments and it is related to the amount of carbide inclusions. At passive potentials the study reveals that the properties of the passive layer depend on the microstructure of the alloy. EIS results show that the resistance of the passive layer in bovine serum solution increased with the carbides solubilisation.     

Effect of melamine polyphosphate on thermal degradation of polyamides: a combined X-ray diffraction and solid-state NMR study

The effect of melamine polyphosphate (MpolyP) on the thermal degradation of both polyamide 66 (PA66) and polyamide 6 (PA6) was studied using a combination of solid-state techniques. The mixtures of MpolyP with polyamides were heated for different times at 350 and 450 °C. The residues were then analyzed by X-ray diffraction and both solid-state ¹³C NMR and ³¹P NMR. The chemical structures formed in these oven experiments were used to study the chemical changes that take place during a standard flammability test. The mixtures of MpolyP with polyamides were also characterized by frequency-dependent rheological experiments. It was shown that MpolyP could induce significant cross-linking in PA66 and leads to dramatic depolymerization of PA6. These results were used to explain the performance of MpolyP as a flame retardant in these polyamides.     

The effect of thermal treatment on the properties of expanded polystyrene

Expanded polystyrene (EPS) is a commonly used polymer in the packaging industry and for the thermal insulation of buildings. It has poor mechanical properties, which limit its application in some areas. A heat treatment was carried out on a sample of EPS, in order to improve its mechanical properties. The treatment consists of operations that combine the heating and cooling of the material. It is executed to improve the characteristics of the treated polymer and make it more favorable for use in new applications. In the case of EPS, this process changes the behavior of the polymer in a beneficial manner and maximizes its density and hardness. Indeed, the treated version shows interesting mechanical, tribological, and hygroscopic properties. This improvement was obtained mainly due to the morphological modification of the structure of EPS. Indeed, heat treatment leads to the creation of a polystyrene crust, which covers every EPS bead. This crust protects the cell structure of each bead against stretching and supports most of the load applied to the treated version of EPS. Thus, the treated EPS can be used not only for packaging and thermal insulation but also for more structural applications.     

Synergy effect on a suspended mixture of ceria and activated carbon for the photocatalytic degradation of phenol

Ceria, prepared by a precipitation method, was used as a new photocatalyst under UV light irradiation. The as-prepared sample was characterized by XRD and SEM. Results showed that the ceria was cubic fluorite structure and sized in nanometer range. The photocatalytic degradation of phenol was investigated in the presence of a suspended mixture of ceria and activated carbon. A synergy effect was observed with an enhancement of the apparent rate constant by a factor of 5.6 times. The apparent quantum yield of the ceria-AC system was also increased 2.9 times. The activated carbon with strong adsorption activity provided sites for the adsorption of phenol. Then, the adsorbed phenol would migrate continuously to the surface of ceria particles. Some phenol still remained adsorbing on the catalyst when no traces of phenol were detected in the solution. This adsorbed phenol could be degraded by maintaining UV-irradiation.     

Analysis and modeling of the pore size effect on the thermal conductivity of alumina foams for high temperature applications

Analytical and finite element analyses were carried out to investigate the influence of the pore sizes on the effective thermal conductivity, which is the main physical property related to the ceramic microstructure insulating capacity at high temperatures. Thermal conductivity was estimated by analytical models using Litovsky's and Rosseland's approaches for a monodisperse pore distribution, whereas via finite element analysis a high porosity microstructure with three different pore sizes was investigated. Based on this, an ideal pore size range (0.5–3.0 µm) was found that optimizes the reduction of thermal energy transmission in the 1000–1700 °C range. Furthermore, the ideal pore size range seems to be independent of the ceramic foam material. When considering a pore size distribution, the ideal range is narrowed due to less effective thermal radiation scattering by sub-micron and large pores. The results obtained showed that nanopores (< 0.1 µm) are not the best option to reduce thermal conductivity at high temperatures. This statement is supported by experimental data on nanopore aerogels, which show a significant thermal conductivity increase at the high temperature range.