Magnetic Pd@Fe3O4 composite nanostructure as recoverable catalyst for sonoelectrohybrid degradation of Ibuprofen

In the present research, the degradation of an emerging pharmaceutical micro-pollutant, Ibuprofen (IBP) by using Pd@Fe₃O₄ and a hybrid sono-electrolytical (US/EC) treatment system has been demonstrated for the first time. The magnetically separable nanocomposite, Pd@Fe₃O₄ catalyst was synthesized following co-precipitation method to enhance the efficiency of US/EC system. The synthesized catalyst showed a strong reusable property even after applying for five times and in all the five cases, 100% degradation of IBP was maintained. It not only enhanced the IBP degradation rate, but also reduced the energy consumption of the system by ∼35%. Its strong magnetization value of 64.27 emu g⁻¹ made it easily separable. Hence, a comprehensive knowledge on the application of combined energy based US/EC system and magnetically separable multifunctional catalysts for degradation of intractable pollutants like Ibuprofen was achieved, assuring that US/EC can be an effective option for IBP treatment.     

Degradation of imidacloprid containing wastewaters using ultrasound based treatment strategies

The present work deals with application of sonochemical reactors for the treatment of imidacloprid containing wastewaters either individually or in combination with other advanced oxidation processes. Experiments have been performed using two different configurations of sonochemical reactors viz. ultrasonic horn (20 kHz frequency and rated power of 240 W) and ultrasonic bath equipped with radially vibrating horn (25 kHz frequency and 1 kW rated power). The work also investigates the effect of addition of process intensifying agents such as H₂O₂ and CuO, which can enhance the production of free radicals in the system. The combination studies with advanced oxidation process involve the advanced Fenton process and combination of ultrasound with UV based oxidation. The extent of degradation obtained using combination of US and H₂O₂ at optimum loading of H₂O₂ was found to be 92.7% whereas 96.5% degradation of imidacloprid was achieved using the combination of US and advanced Fenton process. The process involving the combination of US, UV and H₂O₂ was found to be the best treatment approach where complete degradation of imidacloprid was obtained with 79% TOC removal. It has been established that the use of cavitation in combination with different oxidation processes can be effectively used for the treatment of imidacloprid containing wastewater.     

Intensification of degradation of methomyl (carbamate group pesticide) by using the combination of ultrasonic cavitation and process intensifying additives

In the present work, the degradation of methomyl has been carried out by using the ultrasound cavitation (US) and its combination with H₂O₂, Fenton and photo-Fenton process. The study of effect of operating pH and ultrasound power density has indicated that maximum extent of degradation of 28.57% could be obtained at the optimal pH of 2.5 and power density of 0.155 W/mL. Application of US in combination with H₂O₂, Fenton and photo-Fenton process has further accelerated the rate of degradation of methomyl with complete degradation of methomyl in 27 min, 18 min and 9 min respectively. Mineralization study has proved that a combination of US and photo-Fenton process is the most effective process with maximum extent of mineralization of 78.8%. Comparison of energy efficiency and cost effectiveness of various processes has indicated that the electrical cost of 79892.34 Rs./m³ for ultrasonic degradation of methomyl has drastically reduced to 2277.00 Rs./m³, 1518.00 Rs./m³ and 807.58 Rs./m³ by using US in combination with H₂O₂, Fenton and photo-Fenton process respectively. The cost analysis has also indicated that the combination of US and photo-Fenton process is the most energy efficient and cost effective process.     

Alternate pulses of ultrasound and electricity enhanced electrochemical process for p-nitrophenol degradation

A novel alternated ultrasonic and electric pulse enhanced electrochemical process was developed and used for investigating its effectiveness on the degradation of p-nitrophenol (PNP) in an aqueous solution. The impacts of pulse mode, pH, cell voltage, supporting electrolyte concentration, ultrasonic power and the initial concentration of PNP on the performance of PNP degradation were evaluated. Possible pathway of PNP degradation in this system was proposed based on the intermediates identified by GC–MS. Experimental results showed that 94.1% of PNP could be removed at 2 h in the dual-pulse ultrasound enhanced electrochemical (dual-pulse US-EC) process at mild operating conditions (i.e., pulse mode of electrochemical pulse time (T_EC) = 50 ms and ultrasonic pulse time (T_US) = 100 ms, initial pH of 3.0, cell voltage of 10 V, Na₂SO₄ concentration of 0.05 M, ultrasonic powder of 48.8 W and initial concentration of PNP of 100 mg/L), compared with 89.0%, 58.9%, 2.4% in simultaneous ultrasound enhanced electrochemical (US-EC) process, pulsed electrochemical (EC) process and pulsed ultrasound (US), respectively. Moreover, energy used in the dual-pulse US-EC process was reduced by 50.4% as compared to the US-EC process. The degradation of PNP in the pulsed EC process, US-EC process and dual-pulse process followed pseudo-first-order kinetics. Therefore, the dual-pulse US-EC process was found to be a more effective technique for the degradation of PNP and would have a promising application in wastewater treatment.     

Sonochemical degradation of ethyl paraben in environmental samples: Statistically important parameters determining kinetics,by-products and pathways

The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250–1250 μg/L, ultrasound (US) density 20–60 W/L, reaction time up to 120 min, initial pH 3–8 and sodium persulfate 0–100 mg/L, either in ultrapure water or secondary treated wastewater.A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration) × (US density), (EP concentration) × (pH_o) and (EP concentration) × (time).Experiments at an increased EP concentration of 3.5 mg/L were also performed to identify degradation by-products. LC–TOF–MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound.     

Sonocatalytic and sonophotocatalytic degradation of rhodamine 6G containing wastewaters

The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO₂) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5–4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO₂ maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH₃OH) and n-butanol (C₄H₉OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO_2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO₂ (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.     

Electrochemical redox supercapacitors using PVdF-HFP based gel electrolytes and polypyrrole as conducting polymer electrode

Electrochemical redox supercapacitors have been fabricated using polymeric gel electrolytes polyvinylidene fluoride co-hexafluoropropylene (PVdF-HFP)–ethylene carbonate (EC)–propylene carbonate (PC)–MClO₄: M = Li, Na, (C₂H₅)₄N and electrochemically deposited polypyrrole as conducting polymer electrode. The performance of the capacitors have been characterized using a.c impedance spectroscopy, cyclic linear sweep voltammetry and galvanostatic charge–discharge techniques. The capacitors shows larger values of overall capacitance of about 14–25 mF cm^− 2 (equivalent to a single electrode specific capacitance of 78–137 F g^− 1 of polypyrrole), which corresponds to the energy density of 11–19 W h kg^− 1 and power density of 0.22–0.44 kW kg^− 1. The values of capacitance have been found to be almost stable up to 5000 cycles and even more. A comparison indicates that the capacitive behaviour and the capacitance values are not much affected with the size of cations of the salts incorporated in gel electrolytes, rather predominant role of anions is possible at the electrode–electrolyte interfaces. Furthermore the coulombic efficiencies of all the cells were found to be nearly 100% that is comparable to the liquid electrolytes based capacitors.     

Optimization of hydrostatic pressure at varied sonication conditions – power density,intensity, very low frequency – for isothermal ultrasonic sludge treatment

This work aims at investigating for the first time the key sonication (US) parameters: power density (D_US), intensity (I_US), and frequency (F_S) – down to audible range, under varied hydrostatic pressure (P_h) and low temperature isothermal conditions (to avoid any thermal effect).The selected application was activated sludge disintegration, a major industrial US process. For a rational approach all comparisons were made at same specific energy input (ES, US energy per solid weight) which is also the relevant economic criterion.The decoupling of power density and intensity was obtained by either changing the sludge volume or most often by changing probe diameter, all other characteristics being unchanged. Comprehensive results were obtained by varying the hydrostatic pressure at given power density and intensity. In all cases marked maxima of sludge disintegration appeared at optimum pressures, which values increased at increasing power intensity and density. Such optimum was expected due to opposite effects of increasing hydrostatic pressure: higher cavitation threshold then smaller and fewer bubbles, but higher temperature and pressure at the end of collapse.In addition the first attempt to lower US frequency down to audible range was very successful: at any operation condition (D_US, I_US, P_h, sludge concentration and type) higher sludge disintegration was obtained at 12 kHz than at 20 kHz. The same values of optimum pressure were observed at 12 and 20 kHz.At same energy consumption the best conditions – obtained at 12 kHz, maximum power density 720 W/L and 3.25 bar – provided about 100% improvement with respect to usual conditions (1 bar, 20 kHz). Important energy savings and equipment size reduction may then be expected.     

Novel approaches based on ultrasound for treatment of wastewater containing potassium ferrocyanide

Industrial wastewaters containing biorefractory compounds like cyanide offer significant environmental problems attributed to the fact that the conventional methods have limited effectiveness and hence developing efficient treatment approaches is an important requirement. The present work investigates the use of novel treatment approach of ultrasound (US) combined with advanced oxidation techniques for the degradation of potassium ferrocyanide (KFC) for the first time. An ultrasonic bath equipped with longitudinal horn (1 kW rated power and 25 kHz frequency) has been used. The effect of initial pH (2–9) on the progress of degradation has been investigated initially and subsequently using the optimized pH, effect of addition of hydrogen peroxide (ratio of KFC:H₂O₂ varied over the range of 1:0.5–1:5) and TiO₂ in the presence of H₂O₂ (1:1 ratio by weight of TiO₂) as process intensifying approach has been studied. Combination of ultrasonic irradiation with ozone (O₃) (100–400 mg/h) and ultraviolet irradiation (UV) has also been investigated. Use of combination of US with H₂O_2, H₂O₂ + TiO₂ and ozone resulted in extent of KFC degradation as 54.2%, 74.82% and 82.41% respectively. Combination of US with both UV and ozone was established to be the best approach yielding 92.47% degradation. The study also focused on establishing kinetic rate constants for all the treatment approaches which revealed that all the approaches followed first order kinetic mechanism with higher rate constants for the combination approaches. Overall, it has been conclusively established that ultrasound based combined treatment schemes are very effective for the treatment of KFC containing wastewaters.     

Degradation of phenol using a combination of ultrasonic and UV irradiations at pilot scale operation

In the present work, combination of ultraviolet (UV) irradiations (using 8 W UV tube) with ultrasonic (US) irradiations (rated power 1 kW and frequency of 25 kHz) has been investigated for the degradation of phenol at pilot scale of operation. Different modes of operation viz. UV alone, US alone, UV/US, UV/TiO₂ (photocatalysis), UV/H₂O₂, UV/NaCl, UV/US/TiO₂ (sonophotocatalysis) and H₂O₂ assisted sonophotocatalysis have been investigated with an objective of maximizing the extent of phenol degradation. Effect of presence of hydrogen peroxide and sodium chloride at a concentration of 10 g/l and TiO₂ over a range of 0.5–2.5 g/l has been investigated. It has been observed that 2.0 g/l of TiO₂ is the optimum concentration, beyond which a decrease in the extent of degradation is observed. Maximum extent of degradation of phenol was 37.75% for H₂O₂ assisted photosonocatalysis at pH of 2. The present work is first of its kind to report the use of combined ultrasonic and UV irradiations at pilot scale operation and obtained results should induce some degree of certainty in proposed industrial applications of sonochemical reactors for wastewater treatment.     

Effects and mechanism of diclofenac degradation in aqueous solution by US/Zn0

A system of ultrasound radiation coupled with Zn⁰ was applied to degrade diclofenac. The effects of initial pH, dosage of Zn⁰ and ultrasound density were investigated. To further explore the mechanism of the microcosmic reaction, the fresh and used Zn⁰ powders were characterized by SEM, XRD and XPS. Radical scavengers were used to determine the oxidation performance of strong oxidizing free radicals on diclofenac, including hydroxyl radicals and superoxide radicals. The results showed that the optimum removal of diclofenac reached to over 85% at pH of 2.0 in 15 min, with Zn⁰ dosage of 0.1 g/L and ultrasound density of 0.6 W/cm³. TOC removal of 72.6% in 15 min and dechlorination efficiency of diclofenac reached 70% in 30 min. Characterization results showed that a ZnO membrane was generated on the surface of Zn particles after use. According to the mass spectrometry results, several possible pathways of diclofenac degradation were proposed, and most diclofenac was turned into micro-molecules or CO₂ finally. The synergistic effect of US/Zn⁰ in the reactions led to a proposed degradation mechanism in which zinc could directly attack the target contaminant diclofenac because of its good reducibility with the auxiliary functions of ultrasonic irradiation, mechanical shearing and free radical oxidation.     

A simultaneous,direct microwave/ultrasound-assisted digestion procedure for the determination of total Kjeldahl nitrogen

Simultaneous direct irradiation with microwaves and ultrasound was used to determine total Kjeldahl nitrogen. The method involves chemical digestion in two steps, mineralization with sulfuric acid and oxidation with H₂O₂. The most influential variables for the microwave/ultrasound (MW/US)-assisted digestion were optimized using tryptophan as the model substance. The optimum conditions were: H₂SO₄ volume, 10 mL; H₂O₂ volume, 5 mL; weight of sample, 0.05 g; MW power, 500 W; US power, 50 W; digestion time, 7 min (i.e., 5 min mineralization and 2 min oxidation). A modification of the classical Kjeldahl (Hach) method and an US-assisted digestion method were used for comparison. The latter was also optimized; the optimum conditions were: H₂SO₄ volume, 10 mL; H₂O₂ volume, 5 mL; sonication time with H₂SO₄, 15 min; sonication time with H₂O₂,10 min; US power, 50 W; weight of sample, 0.05 g. Five pure amino acids and two certified reference materials (NIST standard reference materials 1547 (peach leaves), and soil, NCS DC 73322) were analyzed to assess the accuracy of our new MW/US-assisted digestion method, that was successfully applied to five real samples. The significant reduction in digestion time (being 30 min and 25 min for classical Kjeldahl and US-assisted digestion methods, respectively) and consumption of reagents show that simultaneous and direct MW/US irradiation is a powerful and promising tool for low-pressure digestion of solid and liquid samples.     

Sonocatalytic removal of ibuprofen and sulfamethoxazole in the presence of different fly ash sources

We examined the feasibility of using two types of fly ash (an industrial waste from thermal power plants) as a low-cost catalyst to enhance the ultrasonic (US) degradation of ibuprofen (IBP) and sulfamethoxazole (SMX). Two fly ashes, Belews Creek fly ash (BFA), from a power station in North Carolina, and Wateree Station fly ash (WFA), from a power station in South Carolina, were used. The results showed that >99% removal of IBP and SMX was achieved within 30 and 60 min of sonication, respectively, at 580 kHz and pH 3.5. Furthermore, the removal of IBP and SMX achieved, in terms of frequency, was in the order 580 kHz > 1000 kHz > 28 kHz, and in terms of pH, was in the order of pH 3.5 > pH 7 > pH 9.5. WFA showed significant enhancement in the removal of IBP and SMX, which reached >99% removal within 20 and 50 min, respectively, at 580 kHz and pH 3.5. This was presumably because WFA contains more silicon dioxide than BFA, which can enhance the formation of OH radicals during sonication. Additionally, WFA has finer particles than BFA, which can increase the adsorption capacity in removing IBP and SMX. The sonocatalytic degradation of IBP and SMX fitted pseudo first-order rate kinetics and the synergistic indices of all the reactions were determined to compare the efficiency of the fly ashes. Overall, the findings have showed that WFA combined with US has potential for treating organic pollutants, such as IBP and SMX, in water and wastewater.     

Inorganic species formation in a discharged water generating system

Inorganic species formation in a discharged water generating (DWG) system consisting of a plane-to-plane electrode arrangement with a 20 kV, 20 mA and 1 kHz power source has been investigated. The DWG system is able to produce the various oxidants HNO₂, HNO₃ and O₃, as well as OH radicals and many other unconfirmed radicals. These products can play an important role in the advanced oxidation of organic compounds and in rot protection. The pH of water discharged from the system for 20 min during inflow of natural air was about 3, nitrogen concentrations of nitrite and nitrate were 4.6 mg/L and 7.9 mg/L, respectively, residual dissolved ozone concentration was 0.7 mg/L and the oxidation power as measured by KI titration methods was approximately equivalent to 46 mg-O₃/L.     

Efficient sonochemical degradation of perfluorooctanoic acid using periodate

A rapid and efficient treatment method, using periodate (PI) for sonochemical oxidation of persistent and bioaccumulative perfluorooctanoic acid (PFOA) was developed. With an addition of 45 mM PI, 96.5% of PFOA was decomposed with a defluorination efficiency of 95.7% after 120 min of ultrasound (US). The removals of PFOA were augmented with an increase in PI doses. In all the PI + US experimental runs, decomposition efficiencies were essentially similar to those of defluorination, indicating that PFOA was decomposed and mineralized into fluoride ions. Lower solution pHs resulted in an increase in decomposition and defluorination efficiencies of PFOA due to acid-catalyzation. Dissolved oxygen increased the amount of IO₄ radicals produced, which consumed the more effective IO₃ radicals. Consequently, presence of oxygen inhibited the destruction of PFOA. The PFOA degradation rates with different gases sparging are in the following order: nitrogen > air > oxygen. Effects of anions follow the Hofmeister effects on PFOA degradation (i.e., Br⁻ > none ⩾ Cl⁻ > SO₄²⁻). Br⁻ could react with OH to yield radical anion Br₂⁻ that enhances the PFOA degradation. A reaction pathway was also proposed to describe the PI oxidation of PFOA under US irradiation.     

Thermal stabilities of metal bottom electrodes for Ta2O5 metal-oxide-metal capacitor structure

Thermal stabilities of various metal bottom electrodes were examined by using a Ta₂O₅ metal-oxide-metal (MOM) capacitor structure. After depositing 10-nm thick Ta₂O₅ on metal-electrode/poly-Si, we performed rapid thermal oxidation (RTO) at 850 °C for 60 s in an O₂ ambient. A chemical-vapor-deposition (CVD) WSi₂ electrode showed satisfactory thermal stability after the RTO, while other examined electrode materials exhibited thermal degradation caused by oxidation failure or interfacial reaction between the substrate poly-Si and the Ta₂O₅. After post-annealing at 650 °C for 30 min (in N₂ condition) with CVD TiN top electrode, an effective oxide thickness (T_ox) of ∼32 Å and a leakage current density of ∼10⁷ A/cm² at 1.25 V were obtained from the MOM capacitor with the WSi₂ bottom electrode. Other electrode materials, such as TiN, TiSi_x, WN_x, W, and Ta, were severely oxidized during the RTO in the MOM structures, and very poor capacitor properties were obtained in terms of T_ox and leakage current.     

Sonoelectrocatalytic decomposition of methylene blue using Ti/Ta2O5–SnO2 electrodes

Sonoelectrochemical decomposition of organic compounds is a developing technique among advanced oxidation processes (AOPs). It has the advantage over sonication alone that it increases the efficiency of the process in terms of a more rapid decrease in chemical oxygen demand (COD) and in total organic carbon (TOC) and accelerates electrochemical oxidation which normally requires a lengthy period of time to achieve significant mineralisation. Moreover the use of an electrocatalytic electrode in the process further accelerates the oxidation reaction rates. The aim of this study was to improve the decomposition efficiency of methylene blue (MB) dye by sonoelectrochemical decomposition using environmentally friendly and cost-effective Ti/Ta₂O₅–SnO₂ electrodes. Decolourisation was used to assess the initial stages of decomposition and COD together with TOC was used as a measure of total degradation. The effect of a range of sonication frequencies 20, 40, 380, 850, 1000 and 1176 kHz at different powers on the decolourisation efficiency of MB is reported. Frequencies of 850 and 380 kHz and the use of higher powers were found more effective towards dye decolourisation. The time for complete MB degradation was reduced from 180 min using electrolysis and from 90 min while carrying out sonolysis to 45 min when conducting a combined sonoelectrocatalytic experiments. The COD reduction of 85.4% was achieved after 2 h of combined sonication and electrolysis which is a slightly higher than after a single electrolysis (78.9%) and twice that of sonolysis (40.4%). A dramatic improvement of mineralisation values were observed within 2 h of sonoelectrocatalytic MB degradation. The TOC removal efficiency increased by a factor of 10.7 comparing to sonication alone and by a factor of 1.5 comparing to the electrolytic process. The energy consumption (kWh/m³) required for the complete degradation of MB was evaluated.     

Dependence of sonochemical parameters on the platinization of rutile titania – An observation of a pronounced increase in photocatalytic efficiencies

Using a standing wave sonochemical reactor (SWSR), the influences of parameters of ultrasonic power input, sonication time, sonication temperature and the amount of propanol (which generates the reducing radicals) were systemically investigated to ascertain and optimize the best conditions for the sonochemical reduction of Pt from its precursor hexachloroplatinic acid and then its deposition on rutile TiO₂ (platinization of rutile titania) catalysts. Catalytic activity of the prepared platinized catalysts was tested in the reaction of methyl orange degradation. The results of photocatalytic activity study in the degradation of methyl orange further demonstrate that sonochemically as-prepared Pt/TiO₂ catalysts show a pronounced increase (～2 times) in photodegradation, even with a deposition of small amounts of platinum (1.4 wt.%), as compared to the unsupported or naked rutile titania. Although there are various parameters that influence the sonochemical platinization of rutile titania, the present optimization results clearly indicate that the best photocatalytic degradation of methyl orange can be obtained when the experimental conditions of the preparation were with an input power of 50 W, an initial hexachloroplatinic acid volume of 70 ml (which results into 1.4 wt.% Pt on TiO₂), sonication time of 90 min, 0.18 g of propanol and a temperature of 10 °C were adopted. The method of ultrasound application to prepare metal supported semiconductors has many advantages such as convenience, safety and high efficiency. Furthermore, it is hopeful that this optimization study can also be extended to the generation of similar metal supported semiconductors.     

Efficient H2O2/CH3COOH oxidative desulfurization/denitrification of liquid fuels in sonochemical flow-reactors

The oxidative desulfurization/denitrification of liquid fuels has been widely investigated as an alternative or complement to common catalytic hydrorefining. In this process, all oxidation reactions occur in the heterogeneous phase (the oil and the polar phase containing the oxidant) and therefore the optimization of mass and heat transfer is of crucial importance to enhancing the oxidation rate. This goal can be achieved by performing the reaction in suitable ultrasound (US) reactors. In fact, flow and loop US reactors stand out above classic batch US reactors thanks to their greater efficiency and flexibility as well as lower energy consumption. This paper describes an efficient sonochemical oxidation with H₂O₂/CH₃COOH at flow rates ranging from 60 to 800 ml/min of both a model compound, dibenzotiophene (DBT), and of a mild hydro-treated diesel feedstock. Four different commercially available US loop reactors (single and multi-probe) were tested, two of which were developed in the authors’ laboratory. Full DBT oxidation and efficient diesel feedstock desulfurization/denitrification were observed after the separation of the polar oxidized S/N-containing compounds (S ⩽ 5 ppmw, N ⩽ 1 ppmw). Our studies confirm that high-throughput US applications benefit greatly from flow-reactors.     

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)₆³⁻) and hexacyanoferrate(II) (i.e., Fe(CN)₆⁴⁻) redox couple and 1 M Na₂SO₄ at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current–voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil<the Ir-coated titanium (Ti) mesh<the Pt-coated Ti plate<the graphite foil. Moreover, the Vulcan-coated graphite foil showed 5–10% higher power density than the metal mesh electrodes. From the polarization curve of the Vulcan-coated graphite foil electrode, it was found that total resistance decreased as thickness and geometric surface area of the electrode increased.