Removal of dinitrotoluenes in wastewater by sono-activated persulfate

Oxidative degradation of dinitrotoluenes (DNTs) in wastewater was performed using persulfate anions combined with ultrasonic irradiation, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on sono-activated persulfate oxidation, including ultrasonic power intensity, persulfate anion concentration, reaction temperature and acidity of wastewater. It is noteworthy that the nitrotoluene contaminants could be almost completely eliminated by virtue of sono-activated persulfate oxidation, wherein sulfate radicals serve as principal oxidants, of which amounts are significantly enhanced via addition of sodium sulfate. Based on the results given by gas chromatograph-mass spectrometer (GC-MS), it is postulated that the methyl group of DNTs preliminarily underwent oxidation pathway into dinitrobenzoic acid, followed by decarboxylation to form 1,3-dinitrobenzene (DNB). In sum, the sono-activated persulfate oxidation is a promising method for treatment of nitrotoluenes in wastewater.     

Remarkably enhanced photocatalytic activity by sulfur-doped titanium dioxide in nanohybrids with carbon nanotubes

TiO₂ doped S nanohybrids with carbon nanotubes (CNTs) were synthesized with CNTs, thiourea and TiO₂ nanoparticles. The result indicated that the TiO₂ nanoparticles with about 8 nm in size are attached on the sidewall of CNTs. The nanohybrids material can absorb at longer wavelength and the absorption even covers the whole range of visible region than that only TiO₂ nanoparticles. Application of the catalysts to photocatalytic degradation of methylene blue (MB) was tested under visible light irradiation. The result suggests that a high MB degradation activity of S-TiO₂/CNTs due to a reduce band gap of TiO₂ when S is doped, and the decrease in the possibility of electron–hole recombination by CNTs. In addition, the density functional-theory (DFT) calculations of the electronic band structures and density of states (DOS) to understand the bonding states between TiO₂ and CNTs, proved that the TiO₂/CNTs system is stable.     

Electromigration with enhanced green emission in the titanium dioxide nanotube/graphene composite

One of the most studied photoluminescence emission peaks of anatase titanium dioxide (TiO₂) is green, located at about 520 nm, which is assigned to the radiative recombination between a mobile electron in the conduction band and oxygen vacancy defect as a trapped hole in the bandgap. Composite materials of TiO₂ with graphene are normally shown by the gradual quenching of photoluminescence intensity as a result of carrier lifetime extension, which is important to enhance photocatalytic activity. Herein we report an observation of the intensity enhancement of the green PL emission in a composite TiO₂ nanotube (TNT) and graphene produced through facile hydrothermal synthesis. The heterojunction formation of graphene and TNT makes the excited photoelectrons easy to diffuse from TNT to graphene. Hence, the recombination rate of mobile electrons in graphene and trapped holes located on the nanotube surface is enhanced due to the high mobility of electrons in graphene.     

Removal of carbon dioxide from gas mixtures by wollastonite

Wollastonite synthesis and decomposition were analyzed from the viewpoint of thermodynamics (using the TERRA software). It is shown that wollastonite synthesis from limestone and silica takes place at a minimum content of nitrogen (10^?5 N₂) with a release of carbon dioxide. The synthesis temperature is T ≥ 560 K. Wollastonite is decomposed in the presence of flue gas (4N₂) with limestone and silica formation and burial of carbon dioxide in the form of CaCO₃(c). Wollastonite decomposition temperature is T ≤ 420 K. The cyclic reciprocating process for complete removal of carbon dioxide by wollastonite is suggested. Four strokes of the reciprocating system with the fixed temperatures of wollastonite decomposition (T=300 K) and wollastonite synthesis (T=560 K) are presented. Total energy consumption (T = 560 K) is ΔI ≈ 130 kJ/mole, 30 % of energy is spent for heating and 70 % of energy is spent for chemical reaction. This is comparable with the heat of CO₂ solution in ethanolamin.     

The application of high frequency ultrasound waves to remove ammonia from simulated industrial wastewater

This article aims at applying the ultrasound technique in the field of clean technology to protect environment. The principle of ultrasound was conducted here to remove and recover ammonia from industrial wastewater. Three different concentrations of ammonia namely 5%, 15% and 25% (vol.%) were used to study the efficiency of removing ammonia from water. These concentrations are exactly similar to what may be found in wastewater resulting from strippers at petroleum refinery. High ultrasound frequency device with 2.4 and 1.7 MHz was conducted to study the effect of waves on the removal of ammonia. It was found that the ultrasound has the ability to remove ammonia with 5% concentration to meet the local standard of treated wastewater within less than 2 h for 0.080 L solution. It was also found that as the concentration of the ammonia increases the removing of ammonia within 2 h decreases, still the concentration of the ammonia meets the standard of the treated wastewater. The ability of the ultrasound to remove the ammonia failed to produce any mist when the height of the liquid solution increased, namely when the height reached (0.0337 m). This is equivalent to liquid volume of 0.150 L. It means that the device capacity to remove ammonia has certain limitations based on liquid heights. The best condition for ammonia removal was obtained at 5% concentration and 0.080 L liquid volume (equivalent to 0.0165 m).     

Experimental aspects of ultrasonically enhanced cross-flow membrane filtration of industrial wastewater

Ultrasound based on-line cleaning for membrane filtration of industrial wastewater was studied. An ultrasonic transducer was assembled in the membrane module in order to get an efficient cleaning of membranes in fouling conditions. The focus of the studies was on the effects of the ultrasound propagation direction and frequency as well as the transmembrane pressure. The more open the membrane was the easier the membrane became plugged by wastewater colloids, when the ultrasound propagation direction was from the feed flow side of the membrane. If the membrane was tight enough, the ultrasound irradiated from the feed side of the membrane increased the flux significantly. However, in the circumstances studied, the power intensity needed during filtration was so high that the membranes eroded gradually at some spots of the membrane surface. It was discovered that the ultrasonic field produced by the used transducers was uneven in pressurised conditions. On the other hand, the ultrasound treatment at atmospheric pressure during an intermission pause in filtration turned out to be an efficient and, at the same time, a gentle method in membrane cleaning. The input power of 120 W (power intensity of 1.1 W/cm2) for a few seconds was sufficient for cleaning. The flux improvement was significant when using a frequency of 27 kHz but only minor when using 200 kHz.     

Removal of recalcitrant pollutants from wastewater

Triton X-100 was oxidized in aqueous solutions with the presence of O₂ using photocatalysis and H₂O₂ addition alone or coupled. New supported TiO₂/Al₂O₃ catalysts modified with vanadium and cobalt were used. Catalysts were prepared using the classical impregnation method (CIM) and the double impregnation method (DIM). The effect of the physico-chemical properties of the catalysts on its activity were studied. The research on the interactions between the metal precursor and the titania-alumina surface by means of FT-IR/PAS (Fourier transform infrared photoacoustic spectroscopy) were also conducted.     

Removal of organic matter and ammonia nitrogen from landfill leachate by ultrasound

Experiments on the removal of organic matters and ammonia nitrogen from landfill leachate by ultrasound irradiation were carried out. The effects of COD reduction and ammonia removal of power input, initial concentration, initial pH and aeration were studied. It was found that the sonolysis of organic matters proceeds via reaction with ()OH radicals; a thermal reaction also occurs with a small contribution. The rise of COD at some intervals could be explained by the complexity of organic pollutant sonolysis in landfill leachate. Ultrasonic irradiation was shown to be an effective method for the removal of ammonia nitrogen from landfill leachate. After 180 min ultrasound irradiation, up to 96% ammonia nitrogen removal efficiency can be obtained. It was found that the mechanism of ammonia nitrogen removal by ultrasound irradiation is largely that the free ammonia molecules in leachate enter into the cavitation bubbles and transform into nitrogen molecules and hydrogen molecules via pyrolysis under instant high temperature and high pressure in the cavitation bubbles.     

Removal of pharmaceuticals from wastewater by biological processes,hydrodynamic cavitation and UV treatment

To augment the removal of pharmaceuticals different conventional and alternative wastewater treatment processes and their combinations were investigated. We tested the efficiency of (1) two distinct laboratory scale biological processes: suspended activated sludge and attached-growth biomass, (2) a combined hydrodynamic cavitation–hydrogen peroxide process and (3) UV treatment. Five pharmaceuticals were chosen including ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac, and an active metabolite of the lipid regulating agent clofibric acid.Biological treatment efficiency was evaluated using lab-scale suspended activated sludge and moving bed biofilm flow-through reactors, which were operated under identical conditions in respect to hydraulic retention time, working volume, concentration of added pharmaceuticals and synthetic wastewater composition. The suspended activated sludge process showed poor and inconsistent removal of clofibric acid, carbamazepine and diclofenac, while ibuprofen, naproxen and ketoprofen yielded over 74% removal. Moving bed biofilm reactors were filled with two different types of carriers i.e. Kaldnes K1 and Mutag BioChip? and resulted in higher removal efficiencies for ibuprofen and diclofenac. Augmentation and consistency in the removal of diclofenac were observed in reactors using Mutag BioChip? carriers (85% ± 10%) compared to reactors using Kaldnes carriers and suspended activated sludge (74% ± 22% and 48% ± 19%, respectively). To enhance the removal of pharmaceuticals hydrodynamic cavitation with hydrogen peroxide process was evaluated and optimal conditions for removal were established regarding the duration of cavitation, amount of added hydrogen peroxide and initial pressure, all of which influence the efficiency of the process. Optimal parameters resulted in removal efficiencies between 3–70%. Coupling the attached-growth biomass biological treatment, hydrodynamic cavitation/hydrogen peroxide process and UV treatment resulted in removal efficiencies of >90% for clofibric acid and >98% for carbamazepine and diclofenac, while the remaining compounds were reduced to levels below the LOD. For ibuprofen, naproxen, ketoprofen and diclofenac the highest contribution to overall removal was attributed to biological treatment, for clofibric acid UV treatment was the most efficient, while for carbamazepine hydrodynamic cavitation/hydrogen peroxide process and UV treatment were equally efficient.     

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

Micro-, submicron-, and nano-scale titanium dioxide particles were reduced by reduction with a metallic calcium reductant in calcium chloride molten salt at 1173 K, and the reduction mechanism of the oxides by the calcium reductant was explored. These oxide particles, metallic calcium as a reducing agent, and calcium chloride as a molten salt were placed in a titanium crucible and heated under an argon atmosphere. Titanium dioxide was reduced to metallic titanium through a calcium titanate and lower titanium oxide, and the materials were sintered together to form a micro-porous titanium structure in molten salt at high temperature. The reduction rate of titanium dioxide was observed to increase with decreasing particle size; accordingly, the residual oxygen content in the reduced titanium decreases. The obtained micro-porous titanium appeared dark gray in color because of its low surface reflection. Micro-porous metallic titanium with a low oxygen content (0.42 wt%) and a large surface area (1.794 m² g⁻¹) can be successfully obtained by reduction under optimal conditions.     

Electrochemical capacitance from carbon nanotubes decorated with titanium dioxide nanoparticles in acid electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with TiO₂ nanoparticles was investigated. A chemical-wet impregnation was used to deposit different TiO₂ particle densities onto the CNT surface, which was chemically oxidized by nitric acid. Transmission electron microscopy showed that each TiO₂ nanoparticle has an average size of 30-50 nm. Nitrogen physisorption measurement indicated that the porosity of CNTs is partially hindered by some titania aggregations at high surface coverage. Cyclic voltammetry measurements in 1 M H₂SO₄ showed that (i) an obvious redox peak can be found after the introduction of TiO₂ and (ii) the specific peak current is proportional to the TiO₂ loading. This enhancement of electrochemical activity was attributed to the fact that TiO₂ particles act as a redox site for the improvement of energy storage. According to our calculation, the electrochemical capacitance of TiO₂ nanocatalysts in acid electrolyte was estimated to be 180 F/g. Charge-discharge cycling demonstrated that the TiO₂-CNT composite electrode maintains stable cycleability of over 200 cycles.     

RHEED study of titanium dioxide with pulsed laser deposition

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the growth of thin films of titanium dioxide (TiO₂) on (1 0 0) magnesium oxide (MgO) substrates by pulsed laser deposition (PLD). The deposition is performed with a synthetic rutile TiO₂ target at low fluence. The topography and structure of the deposited layers are characterized using in situ high pressure RHEED and atomic force microscope (AFM). Based on these observations the growth mode of the films is discussed. The results will be compared to earlier results obtained for the growth of TiN films on (1 0 0) MgO.     

Atomic layer deposition of titanium dioxide thin films from tetraethoxytitanium and water

The structure and chemical composition of the titanium dioxide thin films formed by atomiclayer deposition (ALD) from tetraethoxytitanium and water precursors were studied by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. The deposited films were demonstrated to have good stoichiometry and anatase type polycrystalline structure. The growth per cycle of titanium dioxide was calculated by an ALD model taking into account the sizes and number of ligands in reactant molecules.     

Removal of colloidal precipitation plugging with high-power ultrasound

Petroleum is a continuous and dynamically stable colloidal system. In the process of oil extraction, transportation, and post-treatment, the stability of the petroleum sol system is easily destroyed, resulting in asphaltenes precipitation that can make pore throat, oil wells, and pipelines blocked, thereby damaging the reservoir and reducing oil recovery. In this paper, removing near-well plugging caused by asphaltene deposition with high-power ultrasound is investigated. Six PZT transducers with different parameters were used to carry out the experimental study. Results show that ultrasonic frequency is one important factor for removing colloidal precipitation plugging in cores, it could not be too high nor too low. The optimum ultrasonic frequency is 25 kHz; Selecting transducers with a higher power is an effective way to improve the removal efficiency. The optimum ultrasonic power is 1000 W. With the increase of ultrasonic treatment time, the recovery rate reaches the maximum and tends to be stable. ultrasonic processing time should be controlled within 120 min. Besides, three methods — ultrasonic treatment alone, chemical injection alone, and ultrasound-chemical method — for removing colloidal precipitation plugging are compared. Results indicate that the ultrasound-assisted chemical method is better than chemical injection alone or ultrasonic treatment alone to remove colloidal sediment in the core. Finally, the mechanism of the ultrasonic deplugging technique is analyzed from three aspects: cavitation effect, the thermal effect, and mechanical vibration.     

Efficient removal of crystal violet and methylene blue from wastewater by ultrasound nanoparticles Cu-MOF in comparison with mechanosynthesis method

The present investigation reports the synthesis of CuBTC (BTC = 1,3,5-benzenetricarboxylate) metal–organic frameworks (MOFs) under solid-state conditions and ultrasound irradiation. Herein, we study uptake and release properties of crystal violet (CV) and methylene blue (MB) from ultrasound nano-CuBTC MOF in comparison with mechanosynthesis method (bulk structure). The ultrasound-assisted methods give a decrease in the surface area as calculated from the reduced nitrogen adsorption capability. In comparison, the uptake of guest molecules on ultrasound nano-CuBTC is remarkable and clearly exceeds that of bulk structure in the aqueous solution of guests. In bulk compound the channel length is increased so that the amount of adsorption is decreased a little. The small guest enters and leaves the cavity rapidly, whereas larger guests enter slowly due to their size relative to the size of the gaps in the capsule. As a result, the uptake and release of MB from CuBTC is faster than that of CV.     

Study of the sonophotocatalytic degradation of basic blue 9 industrial textile dye over slurry titanium dioxide and influencing factors

The sonophotocatalytic degradation of basic blue 9 industrial textile dye has been studied in the presence of ultrasound (20 kHz) over a TiO(2) slurry employing an UV lamp (15 W, 352 nm). It was observed that the color removal efficiency was influenced by the pH of the solution, initial dye concentration and TiO(2) amount. It was found that the dye degradation followed apparent first order kinetics. The rate constant increased by decreasing dye concentration and was affected by the pH of the solution with the highest degradation obtained at pH 7. The first order rate constants obtained with sonophotocatalysis were twofold and tenfold than those obtained under photocatalysis and sonolysis, respectively. The chemical oxygen demand was abated over 80%.     

Removal of disperse blue 2BLN from aqueous solution by combination of ultrasound and exfoliated graphite

This paper reports an efficient and convenient removal of disperse blue 2BLN from aqueous solution by the combination of ultrasound and exfoliated graphite. The various affecting factors were studied. The removal ratio of disperse blue 2BLN is 96.9% for the initial concentration of 200 mg/L using 600 mg/L exfoliated graphite (exfoliation volume of 300 mL/g) at 45 degrees C within 120 min under ultrasound. The combination method was more effective than sonolysis or exfoliated graphite treatment individually.     

Compositional and structural evolution of the titanium dioxide formation by thermal oxidation

Titanium oxide films were prepared by annealing DC magnetron sputtered titanium films in an oxygen ambient. X-ray diffraction （XRD）, Auger electron spectroscopy （AES） sputter profiling, MCs^＋-mode secondary ion mass spectrometry （MCs^＋-SIMS） and atomic force microscopy （AFM） were employed, respectively, for the structural, com- positional and morphological characterization of the obtained films. For temperatures below 875 K, titanium films could not be fully oxidized within one hour. Above that temperature, the completely oxidized films were found to be rutile in structure. Detailed studies on the oxidation process at 925K were carried out for the understanding of the underlying mechanism of titanium dioxide （TiO2） formation by thermal oxidation. It was demonstrated that the formation of crystalline TiO2 could be divided into a short oxidation stage, followed by crystal forming stage. Relevance of this recognition was further discussed.