Electrocatalytic oxidation of p-nitrophenol from aqueous solutions at Pb/PbO2 anodes

In this work, the elimination of p-nitrophenol (p-NPh) from aqueous solutions by electrochemical oxidation at Pb/PbO₂ anodes was investigated. The process was studied under galvanostatic polarization mode in acidic and alkaline media, as a function of the temperature (20, 40 and 60 °C) and of the anodic current density (J = 10, 20 and 30 mA cm⁻²). In acidic media (0.5 M H₂SO₄), the oxidation process allowed a 94% p-NPh conversion in 7 h, at 20 °C and with J = 20 mA cm⁻², with a wide distribution of degradation products (in particular: 39% p-benzoquinone and 26% hydroquinone, as given by a mass balance at the above electrolysis time). Under these conditions, the current efficiency for the substrate oxidation was 15.4% ([Ah L⁻¹]_exp = 7 versus [Ah L⁻¹]_theo = 1.08 Ah L⁻¹). In alkaline media (0.1 M NaOH, pH 8.5), the most effective p-NPh elimination (97%) was obtained at 60 °C, 20 mA cm⁻² and 420 min of electrolysis time, again with the production of p-benzoquinone and hydroquinone (52.7 and 15.1%, respectively). Under the latter conditions, an almost complete chemical oxygen demand (COD) abatement was attained, with a high level of p-NPh mineralization (>80%), a yield of p-NPh conversion greater than 95% and a scarce formation of aliphatic acids (most probably maleic acid). From the degradation curves ([p-NPh] versus t), in both acidic and alkaline media, the UV analyses and/or COD measurements, a complete oxidation of aliphatic acids to form CO₂ could be predicted for electrolysis time >420 min, according to a suggested oxidation pathway.     

Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

Hydroxyapatite photocatalytic degradation of calmagite (an azo dye) in aqueous suspension

The hydroxyapatite (HAP) is prepared by precipitation method and examined for the photocatalytic degradation of calmagite, a toxic and non-biodegradable azo-dye compound. The physicochemical properties of hydroxyapatite material were characterized using BET surface area, XRD, FT-IR, and SEM analysis. The FT-IR analysis of the hydroxyapatite revealed that the peak intensity due to absorbance of surface PO₄³⁻ group centered at wave number 1030 cm⁻¹ is drastically decreased upon exposure to UV for 1 h. The study includes dark adsorption experiments at different pH conditions, influence of the amount of catalyst, and effect of pH on photocatalytic degradation of dye, chemical oxygen demand (COD) removal, biological oxygen demand (BOD₅) increase and SO₄²⁻ and NO₃⁻ ions evolution during the degradation. At optimum photocatalytic experimental conditions the same is compared with commercial degussa P-25 TiO₂. The photocatalytic treatment significantly reduced the COD (92% removal) and increased the BOD₅/COD ratio to 0.78. Considerable evolution of SO₄²⁻ (8.5 mg L⁻¹) and NO₃⁻ (12.2 mg L⁻¹) ions are achieved during the degradation process, thus reflecting the usefulness of the hydroxyapatite photocatalytic treatment in calmagite removal in wastewater.     

Photoelectrochemical treatment of the dye reactive red 198 using DSA electrodes

The study of the oxidation of the dye reactive red 198 on Ti/Ru_0.3Ti_0.7O₂ electrode is presented. Three different techniques were employed: photocatalytic (interaction of UV radiation and electrode surface), electrochemical (application of a constant current) and photoelectrochemical (simultaneous application of a constant current and UV radiation). The effect of temperature (20–45 °C) and current density (5–89 mA cm⁻²) were investigated. No significant temperature effect was observed for the three techniques used. It was observed that at low current densities (5–30 mA cm⁻²) the photoelectrochemical (PhEC) rate of colour and TOC removal is simply the sum of the photocatalytic (PC) and electrochemical (EC) rates. However, as the current density increases, the rate of PhEC removal is much greater. This phenomenon is interpreted as being due to the increased production of O₂, which goes on to interact with the UV radiation and cause the oxidation of the dye.     

Preparation and electrochemical properties of pitch-based activated carbon aerogels

The porous structure of pitch-based carbon aerogels (P-CAs) can be modified by KOH activation. It is found that decreasing the carbonization temperature of precursor CAs and increasing the mass ratio of KOH to CAs help to the formation of 0.7 nm-sized micropores and 2.7 nm-sized mesopores, respectively. The origin and the pore size of micropores play an important role in controlling electrochemical properties. The carbonization-forming micropores have stronger energy storage efficiency than activation-forming micropores, and only those with diameter below 1 nm (Microp < 1 nm) are the crucial place to storage energy. Due to the substantive increase of the number of the Microp < 1 nm, the highest specific capacitance of the as-prepared activated samples can reach 187.2 F g⁻¹ at 5 mA cm⁻², 1.8 times as large as that of their precursor CAs. Furthermore, this capacitance is still up to 173.3 F g⁻¹ when increasing the current density to 50 mA cm⁻², indicating that the activated samples have a high-rate charge–discharge performance.     

Enhanced degradation of organic wastewater containing p-nitrophenol by a novel wet electrocatalytic oxidation process: Parameter optimization and degradation mechanism

This paper explored a novel advanced oxidation process (AOP) for wastewater treatment—wet electrocatalytic oxidation (WEO), which introduced a small current into wet air oxidation (WAO) to promote the formation of hydroxyl radical and accelerate the oxidation of organic pollutants. The results showed that this novel process could couple the advantages of both WAO and electrochemical oxidation (EO). The effects of major operational factors of WEO were studied at relatively moderate condition (T = 100–160 °C, C = 1000 mg L⁻¹, P_O2 = 4 TOD, P_N2 = 0.50 MPa, current density = 0–7.08 mA cm⁻² and pH 2.7–10.6) aiming to p-nitrophenol (PNP) degradation, TOC and COD removal. The cost-effective operational parameters were found and the current efficiencies were highly beyond 100% with the maximum value of 386%. The degradation mechanism of WEO was carefully studied based on the formation of free radical. After the detail analysis of Hammett theory and quantitative structure-activity relationships (QSAR), the reaction pathway of hydroxyl radical with PNP was analyzed with the help of Gaussian 03W and the probable degradation pathway of PNP by WEO was deduced.     

Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous catalysis by mixed iron oxides

Heterogeneous catalysts based on magnetic mixed iron oxides (MO·Fe₂O₃; M: Fe, Co, Cu, Mn) were used for the decolorization of several synthetic dyes (Bromophenol Blue, Chicago Sky Blue, Cu Phthalocyanine, Eosin Yellowish, Evans Blue, Naphthol Blue Black, Phenol Red, Poly B-411, and Reactive Orange 16). All the catalysts decomposed H₂O₂ yielding highly reactive hydroxyl radicals, and were able to decolorize the synthetic dyes. The most effective catalyst FeO·Fe₂O₃ (25 mg mL⁻¹ with 100 mmol L⁻¹ H₂O₂) produced more than 90% decolorization of 50 mg L⁻¹ Bromophenol Blue, Chicago Sky Blue, Evans Blue and Naphthol Blue Black within 24 h. The fastest decomposition proceeded during the first hour of the reaction. In addition to dye decolorization, all the catalysts also caused a significant decrease of chemical oxygen demand (COD). Individual catalysts were active in the pH range 2–10 depending on their structure and were able to perform sequential catalytic cycles with low metal leaching.     

Treatability studies on domestic wastewater using UV/H2O2 process

Advanced oxidation processes (AOPs) are emerging and promising technology both as an alternative treatment to conventional wastewater treatment methods and enhancement of current biological treatment methods especially dealing with highly toxic and low biodegradable wastes. In this paper, the results of domestic wastewater treatment using H₂O₂/UV process in both batch and continuous mode are presented. Over 95% reduction in COD was achieved in less than 60 min of reaction time. Optimum conditions for pH and H₂O₂ dosage for this process was found to be 3 and 50 mg L⁻¹, respectively. A pretreatment in the form of removal of turbidity is recommended for the success of the process in the long run. Electric energy required is estimated to be 10 kWh kg⁻¹ COD on the average.     

Mechanistic approach of the combined (iron–TiO2) photocatalytic system for the degradation of pollutants in aqueous solution: an attempt of rationalisation

Kinetics of oxidative photodegradation of Monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in different photocatalytic systems (iron, TiO₂ and combined system iron + TiO₂) were investigated and compared. The influence of iron addition on TiO₂ photocatalyst and of TiO₂ on the photocatalytic cycle Fe(III)/Fe(II) were carefully studied. A very positive effect of iron addition was observed. This phenomenon was more and more pronounced when TiO₂ concentration was lower. In a suspension of TiO₂ (24 mg L⁻¹) with addition of Fe(III) (3 × 10⁻⁴ mol L⁻¹) the measured rate constant was similar to that obtained in a suspension of TiO₂ with a concentration more than 20 times higher (500 mg L⁻¹). The mechanistic approach carried out in this study allows us to identify the main reactions governing the combined system and a photochemical cycle was proposed. The optimisation of the photocatalytic systems was obtained when each photocatalyst plays a specific role: Fe(III) as a main OH radicals source and TiO₂ as an oxidizing agent of Fe(II).     

Electrochemical properties of anatase TiO2 nanotubes as an anode material for lithium-ion batteries

Titanium oxides with a one-dimensional nanostructure are of great significance in electrochemical lithium insertion due to their high specific surface area and pore volume. In this paper, anatase TiO₂ nanotubes with diameters of about 10 nm and lengths of 200–400 nm were synthesized by a hydrothermal process. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, and transmission electron microscopy. The electrochemical properties were investigated by constant current discharge–charge and cyclic voltammetry. There is a potential plateau at 1.73 and 1.88 V in the process of Li insertion and extraction, and the initial Li insertion/extraction capacity is 290 and 238 mAh g⁻¹ at 36 mA g⁻¹, respectively. The Li insertion capacity at the potential plateau of 1.73 V in the first cycle is about 150 mAh g⁻¹. In the 20th cycle, the reversible capacity still remains at about 200 mAh g⁻¹, and the coulombic efficiency is approximately 98%, exhibiting excellent cycling stability. The discharging capacity is about 168 mAh g⁻¹ in the 30th cycle at 210 mA g⁻¹, demonstrating a good high-rate performance. Anatase TiO₂ nanotubes might be a promising negative material for lithium-ion batteries.     

Catalytic wet air oxidation of Kraft bleach plant effluents in a trickle-bed reactor over a Ru/TiO2 catalyst

Catalytic wet air oxidation of two acidic and alkaline Kraft bleach plant effluents (total organic carbon (TOC) content 1138 and 1331 mg l⁻¹, respectively) was investigated in a trickle-bed reactor at T=463 K and oxygen partial pressure of 8 bar. The reactor packed with titania or titania-supported ruthenium catalyst was operated in a low-interaction (LIR) trickle-flow regime either in continuous-flow or batch-recycle mode. In the off-gas, no carbon monoxide was detected in any of the runs. When the catalytic bed was composed of TiO₂ particles, moderate abatement of organic compounds from the bleach plant effluents was observed (TOC conversions up to 46 and 26%, respectively). The removal of parent organic material was further enhanced by deposition of metallic ruthenium (3 wt.%) on the titanium oxide support. In that case, the once-through oxidation produced decolorized outlet streams with TOC conversions as high as 89 and 88%, respectively. These values further increased to 98 and 95%, respectively, by running the trickle-bed reactor in the batch-recycle mode of operation; the residual carbon content in treated effluents was found in the form of acetic acid. No leaching of Ru or Ti was detected by ICP-AES analysis to the detection limits of 0.2 and 0.1 mg l⁻¹, respectively.     

Preparation of carbon-based adsorbents from sewage sludge pyrolysis to remove metals from water

The objective of this study was to evaluate the use of cheap carbon-based adsorbents from sewage sludge pyrolysis to remove Na⁺, K⁺, Ca²⁺ and Mg²⁺ from saline water. Four model solutions of NaCl, KCl, CaCl₂ and MgCl₂ that simulated seawater composition were used. The model solutions were 456.54 mmol_c L⁻¹ NaCl, 9.72 mmol_c L⁻¹ KCl, 19.96 mmol_c L⁻¹ CaCl₂ and 111.09 mmol_c L⁻¹ MgCl₂. Two carbon adsorbents, one with chemical activation, were prepared by a new method and evaluated for ion adsorption. The results indicated that carbon adsorbent without chemical activation was the most effective in removing ions from different solutions and the removal of metals followed the sequence: Na⁺ (76.78−69.66) >K⁺ (66.0−57.80) >Mg²⁺ (44.84−42.85) >Ca²⁺ (35.12−12.38). Results showed that it is to possible prepare carbon-based adsorbents from sewage sludge following inexpensive and environmentally acceptable methods.     

黏胶纤维用落叶松溶解浆的清洁漂白

引言近年来,随着棉花价格的总体上涨和消费者对纺织材料舒适度的要求,给黏胶纤维带来了需求增长空间。作为黏胶纤维的原材料,国内目前的溶解浆产能难以满足客户需求。据统计,国内溶解浆存     

Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells

In this communication we discuss the properties of tungsten carbide, WC, as anodic electrocatalyst for microbial fuel cell application. The electrocatalytic activity of tungsten carbide is evaluated in the light of its preparation procedure, its structural properties as well as the pH and the composition of the anolyte solution and the catalyst load. The activity of the noble-metal-free electrocatalyst towards the oxidation of several common microbial fermentation products (hydrogen, formate, lactate, ethanol) is studied for microbial fuel cell conditions (e.g., pH 5, room temperature and ambient pressure). Current densities of up to 8.8 mA cm⁻² are achieved for hydrogen (hydrogen saturated electrolyte solution), and up to 2 mA cm⁻² for formate and lactate, respectively. No activity was observed for ethanol electrooxidation.

The electrocatalytic activity and chemical stability of tungsten carbide is excellent in acidic to pH neutral potassium chloride electrolyte solutions, whereas higher phosphate concentrations at neutral pH support an oxidative degradation.     

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm⁻¹ were identified in the region of the CH overtones (5200–6200 cm⁻¹). Among them, two bands at 5810 (aliphatic) and 6010 cm⁻¹ (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm⁻¹), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm⁻¹ (free-end) can be observed.     

Analysis of Fe species in zeolites by UV–VIS–NIR, IR spectra and voltammetry. Effect of preparation, Fe loading and zeolite type

Three procedures were employed for the preparation of Fe-zeolites with ZSM-5 (MFI), ferrierite (FER) and beta (BEA) structures: ion exchange from FeCl₃ solution in acetyl acetonate and solid-state ion exchange from FeCl₂ using an oxygen or nitrogen stream. A combination of UV–VIS–NIR spectra, IR spectra of skeletal vibrations and of adsorbed NO, as well as voltammetry provided information on the type of Fe species introduced. Single Fe(III) ion complexes (Fe(H₂O)_6−xOH_x) in hydrated zeolites were reflected in the charge-transfer bands at 33 100, 37 300 and 45 600 cm⁻¹. The single Fe(II) ions at cationic sites in evacuated zeolites yielded (through perturbation of framework T–O bonds) characteristic bands (910–950 cm⁻¹) in the region of the skeletal window. These Fe(II) ions with adsorbed NO were also reflected in vibrations at 1880 cm⁻¹. Dinuclear Fe–oxo complexes yielded the Vis band at 28 200 cm⁻¹. Voltammetry indicated the presence of Fe oxides (hematite) through the reduction peak at −0.7 V. Such oxide-like species were also reflected in the absorption edge at 19 800 cm⁻¹, and a doublet at 11 000 and 11 800 cm⁻¹ in the Vis spectra. Fe(II)–NO vibrations at 1840, 1810 and 1760 cm⁻¹ belonged to the undefined exposed Fe cations, probably originating from supported oxides. Using an ion exchange procedure, employing FeCl₃ in acetyl acetonate, exclusively Fe ions at cationic sites could be introduced at low concentrations (Fe/Al < 0.1). At higher Fe loadings, dinuclear Fe–oxo complexes were formed preferably in Fe-ZSM-5, but were absent in Fe-beta. Exclusively single Fe species could not be prepared at Fe concentrations above Fe/Al > 0.2; all three types of Fe species, single Fe ions, dinuclear Fe–oxo complexes and Fe oxides were formed.     

Preparation of ultra-active alumina of designed porous structure by successive hydrothermal and thermal treatments of porous anodic Al2O3 films

A porous anodic alumina film was prepared by the anodic oxidation of Al metal sheet in a thermostated and vigorously stirred bath of H₂SO₄ 15% (w/v) at a temperature of 25°C and a current density of 15 mA cm⁻². It had a geometric surface area of 33 cm², a surface density of pores 1.269×10¹¹ cm⁻² and the maximum limiting thickness and porosity achieved at these conditions which are 50.3 μm and 0.42, respectively. This oxide was tried in the catalytic test reaction of the decomposition of HCOOH at temperatures 270–390°C. Then, the oxide was treated hydrothermally in H₂O at 100°C for 5 h and tried in the same test reaction. The procedure of hydrothermal treatment and catalysis experiment was repeated 40 times. In all cases the oxide showed an almost exclusively dehydrative catalytic effect, 98–100%. Both the total activity of the alumina film with the aforementioned constant geometric surface area and its specific activity referred to the unit of oxide mass gave a maximum in the first and a minimum about the fourth hydrothermal treatment; then, they increased strongly with the order of hydrothermal treatment. Despite the decrease of the oxide mass during hydrothermal treatment, the final promotion of the total catalytic activity of oxide was 13.7–10.6 times that of non-treated oxide for temperatures 330–390°C. The corresponding promotion of specific activity was 31.5–24.5 times that of the non-treated oxide. The results of the present study showed that the successive hydrothermal and thermal treatments of porous anodic Al₂O₃ films produce more and more active alumina catalysts. In this way ultra-active alumina catalysts or supports can be prepared.     

Electrochemical and morphological properties of Ti/Ru0.3Pb(0.7−x)TixO2-coated electrodes

In this work, a ternary coating with the nominal composition Ti/Ru_0.3Pb_(0.7−x)Ti_xO₂ (0≤x≤0.7) deposited on Ti has been prepared through thermal decomposition of ruthenium, titanium and lead inorganic salts dissolved in isopropanol. To find out coatings with reasonable service life for application in electrolysis devices, changes in the firing temperature, heating time and supporting electrolyte have been investigated. Surface morphology and microstructure have been investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). SEM data show that the mud-crack structure is progressively lost with the substitution of titanium by lead oxides. EDS results suggest that lead segregates, forming islands with a high content of Pb. Changes in crystallinity have been obtained with an increase in the lead content. Electrochemical analyses have been carried out in acid medium (HClO₄ 1.0 mol dm⁻³ and H₂SO₄ 0.5 mol dm⁻³). Cyclic voltammetric data and quasi-steady-state polarization curves have been recorded and accelerated life tests have been performed with an anodic current of 400 mA cm⁻². High coating stability has been obtained with the electrode fired at 550 °C. Replacing Ti with Pb extends the service life and improves the catalytic activity for oxygen evolution reaction (OER).     

Rapid discharge performance of composite electrode of hydrated sodium manganese oxide and acetylene black

Hydrated sodium manganese oxide was synthesized by reducing permanganate ion using ethanol by a sol–gel method. By including acetylene black in the synthetic reaction, we obtained composite materials in which sodium manganese oxide hydrate particles were small and mixed well with the acetylene black. We evaluated those composites as a lithium battery cathode and found that they showed 170 mA h g⁻¹ under 5 mA g⁻¹ and 117 mA h g⁻¹ under 5 A g⁻¹ on the basis of composite weight. This rapid discharge performance was probably caused by the favorable contact condition of the composite constituents.     

Kaolinite, montmorillonite, and their modified derivatives as adsorbents for removal of Cu(II) from aqueous solution

Adsorption of metals by clay minerals is a complex process controlled by a number of environmental variables. The present work investigates the removal of Cu(II) ions from an aqueous solution by kaolinite, montmorillonite, and their poly(oxo zirconium) and tetrabutylammonium derivatives. The entry of ZrO and TBA into the layers of both kaolinite and montmorillonite was confirmed by XRD measurement. The specific surface areas of kaolinite, ZrO-kaolinite, TBA-kaolinite, montmorillonite, ZrO-montmorillonite, TBA-montmorillonite were 3.8, 13.4, 14.0, 19.8, 35.8 and 42.2 m²/g, respectively. The cation exchange capacity (CEC) was measured as 11.3, 10.2, 3.9, 153.0, 73.2 and 47.6 meq/100 g for kaolinite, ZrO-kaolinite, TBA-kaolinite, montmorillonite, ZrO-montmorillonite, TBA-montmorillonite, respectively. Adsorption increased with pH till Cu(II) ions became insoluble in alkaline medium. The kinetics of the interactions suggests that the interactions could be best represented by a mechanism based on second order kinetics (k₂ = 7.7 × 10⁻² to 15.4 × 10⁻² g mg⁻¹ min⁻¹). The adsorption followed Langmuir isotherm model with monolayer adsorption capacity of 3.0–28.8 mg g⁻¹. The process was endothermic with ΔH in the range 29.2–50.7 kJ mol⁻¹ accompanied by increase in entropy and decrease in Gibbs energy. The results have shown that kaolinite, montmorillonite and their poly(oxo zirconium) and tetrabutyl-ammonium derivatives could be used as adsorbents for separation of Cu(II) from aqueous solution.