Wei Zhou
Harbin Insititute of Technology, Energy science and engineering, Graduate Student
- Advance oxidation processes (AOPS) for water and wastewater treatment, Advanced Oxidation Processes, Activated Carbon, Activated carbon preparation, Catalysis of Oxygen Reduction Reaction, Capacitive Deionization, and 6 moreHydrogen Peroxide, Hydrogen Peroxide Mediated Oxidation, Hydroxyl Radicals, electro-Fenton, Advanced Oxidation Process, and Chemical Engineeringedit
- (1) Advanced oxidation processes (AOPs);
(2) Oxygen reduction reaction (ORR);
(3) Water electrolysis for H2 evolution (HER);
(4) Electrocatalytic coal oxidation technology.edit
Hydrogen peroxide (H2O2) electrosynthesis from 2-electron O2 reduction reaction (2eORR) is widely regarded as a promising alternative to the current industry-dominant anthraquinone process. Design and fabrication of effective, low-cost... more
Hydrogen peroxide (H2O2) electrosynthesis from 2-electron O2 reduction reaction (2eORR) is widely regarded as a promising alternative to the current industry-dominant anthraquinone process. Design and fabrication of effective, low-cost carbon-based electrodes is one of the priorities. Many previous work well confirmed that hydrophilic carbon-based electrodes are preferable for 2eORR. Here, we proposed a strategy of hydrophilicity-hydrophobicity regulation. By using commercially available graphite felt (GF) as electrodes, we showed that both hydrophilic GF, hydrophobic GF, and Janus GF yielded significantly higher H2O2 production, which is 7.3 times, 7.6 times, and 7.7 times higher than the original GF, respectively. Results showed that currents and stirring rates affect the H2O2 yields. The enhancement of hydrophilic GF is due to the incorporation of oxygen-containing functional groups, while the hydrophobic and Janus GF comes from the locally confined O2 bubbles, which built a gas-liquid-solid interface inside GF and thus enhance the H2O2 formation kinetics. Finally, the effectiveness of the hydrophilicity-hydrophobicity regulation concept was tested in Electro-Fenton process by removing typical dyes and antibiotics. This work supply an effective but facile strategy to enhance the performance of carbon-based electrodes towards 2eORR by regulating the micro-environment of electrodes.
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The chemical-assisted electrochemical hydrogen evolution reaction (CAHER) emerges as a prospective energy-saving method to obtain high-purity hydrogen. Selecting suitable auxiliary reactive chemicals (ARC) for the CAHER system is vital.... more
The chemical-assisted electrochemical hydrogen evolution reaction (CAHER) emerges as a prospective energy-saving method to obtain high-purity hydrogen. Selecting suitable auxiliary reactive chemicals (ARC) for the CAHER system is vital. In this study, we propose that oxalic acid can be used as ARC of the CAHER system. Compared with water electrolysis, lower energy consumption is required for hydrogen production in the presence of oxalic acid. The anode potential needed by oxalic acid assisted water electrolysis (OAWE) is half of that of water electrolysis. For OAWE, more hydrogen is produced with the increase of oxalic acid concentration and temperature.
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The potential energy of SO 2 is wasted in the process of converting Na 2 SO 3 to Na 2 SO 4 via air oxidation during conventional treatment of SO 2-contaminated air. Considering that the oxidation of Na 2 SO 3 is thermodynamically and... more
The potential energy of SO 2 is wasted in the process of converting Na 2 SO 3 to Na 2 SO 4 via air oxidation during conventional treatment of SO 2-contaminated air. Considering that the oxidation of Na 2 SO 3 is thermodynamically and kinetically much easier than the oxygen evolution reaction (OER), this study proposes replacing the OER with Na 2 SO 3 oxidation to recover the potential energy of SO 2 and simultaneously reduce the energy consumption of water electrolysis. First, the influences of the reaction temperature and Na 2 SO 3 concentration on Na 2 SO 3-assisted water electrolysis (SAWE) were studied. Then, the difference between Na 2 SO 3 electrolysis and water electrolysis was compared under optimum conditions. Furthermore, the long-term stability of SAWE was assessed. The results of this study suggest that the onset potential of water electrolysis decreases from 0.73 V vs saturated calomel electrode (SCE) to 0.28 V vs SCE by replacing the OER with Na 2 SO 3 oxidation. The energy consumption of producing hydrogen by water electrolysis is reduced with the use of the potential energy of SO 2. For SAWE, the Na 2 SO 3 oxidation kinetics and hydrogen production rate are improved as the reaction temperature and Na 2 SO 3 concentration increase.
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Electrochemical oxygen reduction has been regarded as a promising choice to enable H 2 O 2 on-site production and utilization wherein the exploration of high-efficiency yet cost-effective catalysts is the key. Here, we demonstrate a... more
Electrochemical oxygen reduction has been regarded as a promising choice to enable H 2 O 2 on-site production and utilization wherein the exploration of high-efficiency yet cost-effective catalysts is the key. Here, we demonstrate a low-cost activated coke (AC) electrocatalyst with size-tailored amorphous carbon clusters doped by oxygen groups, prepared through a facile CO 2 assisted mechanochemistry approach, to deliver among the highest performances reported in a typical alkaline system, including high activity (onset potential of 0.83 V), high H 2 O 2 selectivity (~90 %) and long-term stability. A series of control experiments, structural characterizations before and after electrochemical tests and density functional theory calculations provide a new insight into the coupling role of carbon cluster size and oxygen doping in H 2 O 2 electrochemical production process, that is, size-reduced amorphous carbon lattices with abundant edges contribute to the high activity, while the basal carbon atoms in ether-doped small-size carbon plane are the most active sites towards H 2 O 2 selectivity.
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Understanding the evolution of carbon structure in coal-assisted water electrolysis for hydrogen production (CAWE) is essential for seeking strategies to improve the rate of CAWE and getting more insight into the potential significance of... more
Understanding the evolution of carbon structure in coal-assisted water electrolysis for hydrogen production (CAWE) is essential for seeking strategies to improve the rate of CAWE and getting more insight into the potential significance of CAWE. In this study, 13C nuclear magnetic resonance (NMR) is used to understand the evolution of carbon structure in the CAWE. First, the electrolysis characteristics of three different-rank coals are revealed by using electrochemical methods. After then, before and after electrolysis, the evolution of carbon structure is analyzed. The results show that CAWE is a process of reducing carbon and increasing oxygen, and the accumulation of oxygen-containing groups is mainly owing to the increase of oxygen aliphatic carbons and oxygen aromatic carbons. After the CAWE, the aromatic cluster size decreases and increases for low-rank coals and high-rank coals, respectively.
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H2O2 generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the H2O2... more
H2O2 generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the H2O2 electrogeneration, is regarded as an important environmental application of H2O2 generation by 2eORR. However, its application is hindered by the relatively expensive electrode materials. Proposing cathode materials with low cost and facile synthetic procedures are the priority to advance the EF process. In this work, a composite cathode structure that uses graphitic granular bamboo-based biochar (GB) and stainless steel (SS) mesh (GBSS) is proposed, where SS mesh functions as current distributor and GB supports synergistic H2O2 electrogeneration and activation. The graphitic carbon makes GB conductive and the oxygen-containing groups serve as active sites for H2O2 production. 11.3 mg/L H2O2 was produced from 2.0 g GB at 50 mA after 50 min under neutral pH without external O2/air supply. The O-doped biochar further increased the H2O2 yield to 18.3 mg/L under same conditions. The GBSS electrode is also effective for H2O2 activation to generate ·OH, especially under neutral pH. Ultimately, a neutral Fe-free EF process enabled by GBSS cathode is effective for removal of various model organic pollutants (reactive blue 19, orange II, 4-nitrophenol) within 120 min, and for their partial mineralization (48.4% to 63.5%). Long-term stability of the GBSS electrode for H2O2 electrogeneration, H2O2 activation, and pollutants degradation were also examined and analyzed. This work offers a promising application for biomass waste for removals of organic pollutants in neutral Fe-free EF process.
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Hydrogen peroxide (H2O2) electrosynthesis via the oxygen reduction reaction (ORR) presents an attractive decentralized alternative to the industry-dominant anthraquinone process. Oxidized carbon materials have proven to be promising... more
Hydrogen peroxide (H2O2) electrosynthesis via the oxygen reduction reaction (ORR) presents an attractive decentralized alternative to the industry-dominant anthraquinone process. Oxidized carbon materials have proven to be promising catalysts due to their low cost and facile synthesis procedures. However, the nature of the active sites is still controversial. The objective of this paper is to provide a critical review of the advances of this topic. The fundamentals of the ORR pathway and O-doping effects are described, followed by the experimental preparation methods for O-doped carbon, including chemical oxidation and electrochemical oxidation. To identify the contribution of each oxygen-containing functional group (OG) or combination of OGs towards 2-electron ORR, combined experimental and DFT calculation results were analyzed. This paper also reviews the new advancement in the co-doping of O and transition metals, which could realize high activity and high selectivity toward H2O2 generation. Future directions in this fascinating field are also highlighted.
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Fe3+-mediated coal-assisted water electrolysis (CAWE) for hydrogen production is an effective way to utilize coal resources. Low-rank coal, which has a high abundance, is rich in mineral matter and oxygen-containing functional groups... more
Fe3+-mediated coal-assisted water electrolysis (CAWE) for hydrogen production is an effective way to utilize coal resources. Low-rank coal, which has a high abundance, is rich in mineral matter and oxygen-containing functional groups (OGs). To promote the development of Fe3+-mediated CAWE of low-rank coal, the roles of mineral matter and OGs in Fe3+-mediated CAWE are investigated in this study. Besides, to understand the reaction mechanism of coal electrolysis and provide guidance for the effective use of electrolyzed coal, the microstructural, surface structure, and microcrystalline changes of the coal are analyzed via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. The results show that minerals and OGs have a positive and negative influence on the Fe3+-mediated CAWE, respectively. The hydrogen yields of demineralized coal and oxidized coal are 33.15% and 68.47% lower than that of raw coal owing to the influence of minerals and OGs, respectively. After electrolysis, the degree of aromatic ring condensation increases whereas coal rank decreases; the content of -OH on the coal surface increases and the composition of organic sulfur on the coal surface is altered; and the crystallite diameter of the coal changes.
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The reusability of carbon-based adsorbents determines the techno-economics of the adsorption technology. Various methods, which include conventional thermal and biological regeneration and the subsequently developed new methods are... more
The reusability of carbon-based adsorbents determines the techno-economics of the adsorption technology. Various methods, which include conventional thermal and biological regeneration and the subsequently developed new methods are continuously being investigated and engineered. Among these, electrochemical regeneration is promising due to its energy efficiency, selectivity, cost-effectiveness, and environmental compatibility. Electrochemical regeneration covers various regeneration mechanisms and operational methods, but till now, they have not been properly classified or deeply reviewed. In this review, the basic mechanisms of electrochemical regeneration are summarized, followed by a review of various electrochemical regeneration methods with a detailed comparison in terms of regeneration efficiency. Electrochemical reactors are then given special attention because they are significant for the scaling-up of individual regeneration methods. Additionally, the cycling performances of carbon adsorbents are assessed based on an analysis of the physicochemical property changes of carbon adsorbents. Finally, future trends of electrochemical regeneration methods are discussed.
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The effect of preheating primary air on the co-combustion characteristics of a 50-50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 • C. The co-combustion characteristics were... more
The effect of preheating primary air on the co-combustion characteristics of a 50-50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 • C. The co-combustion characteristics were included the co-combustion behaviors and emissions. In order to reveal the features of the combustion process in the porous bed, a two-dimensional unsteady state model was employed to investigate the combustion process in a fixed bed of blended biomass on the combustion process in a fixed bed reactor. Conservation equations of the bed were implemented to describe the combustion process. The gas phase turbulence was modeled using the k-ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. Results showed that by increasing primary air temperature the residual mass on bed decreased, while the average burning rates and ignition front propagation velocity increased At the primary air temperature of 85 • C the smallest unburned carbon was left in the ash, and the emissions of nitrogen-compounds were relatively small. In contrast, the primary air temperature of 85 • C was found to be well-operating condition, which can be suggested for industrial boiler during blend co-combustion. The simulation results were then compared with experimental data for different temperature, which shows that the combustion process in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data.
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Microwave-induced active coke discharge has been used in many researches in environment and energy due to its kinetics and thermal effect. However, the mechanisms of discharge for submillimeter particles are still not clear. The paper... more
Microwave-induced active coke discharge has been used in many researches in environment and energy due to its kinetics and thermal effect. However, the mechanisms of discharge for submillimeter particles are still not clear. The paper presents that the particle shape and gap distance between particles are the possible mechanisms of the microwave discharge. This paper also gives the scope of application of several mechanisms for different particulate materials. Submillimeter particles with about 40-110° tip angle and micron gap distance have the best effect on microwave electric field enhancement. The gap effect is only applicable to material with large refractive index, in detail, n > 3 or k > 2 for 300 μm particle. When gap distance is too narrow, the electron loss is large enough, leading to the failure of discharge.
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Electro-Fenton (EF) and alkaline/persulfate systems are two important systems capable of producing ·OH and SO4-· for environmental remediation. However, the major drawbacks of these two processes are the necessity of operating in low pH... more
Electro-Fenton (EF) and alkaline/persulfate systems are two important systems capable of producing ·OH and SO4-· for environmental remediation. However, the major drawbacks of these two processes are the necessity of operating in low pH (2.0~4.0) or high pH environments, where the acidification/alkalization steps and subsequent neutralization processes significantly increase the operation cost and limit their applicability. In this work, we propose a system that can simultaneously electrochemically develop acidic and alkaline environments in two divided compartments to solve this problem. pH values of 2.9~3.2 and 10.9~11.9 in two separated compartments were obtained, and the results show that the electrochemically developed acidic environment (pH of 3 and 4) enhances the EF process by facilitating H2O2 electrogeneration and Fe2+ regeneration. The alkaline environment (11 and 12) that was also developed electrochemically is effective for persulfate activation. Finally, the system was found to be effective for Rhodamine B removal using an acidic pH-enhanced EF process and an alkaline pH-supported persulfate process.
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This study aimed to develop a novel sorbent for solar driven thermochemical heat storage. The core-shell CaCl2@C composites with tunable CaCl2 loading were obtained by a facile one-pot pyrolysis strategy, with the low-cost and abundant... more
This study aimed to develop a novel sorbent for solar driven thermochemical heat storage. The core-shell CaCl2@C composites with tunable CaCl2 loading were obtained by a facile one-pot pyrolysis strategy, with the low-cost and abundant coal tar being used as the carbon precursor. CaCl2 was confined to the mesopores and macropores of the carbon shell, which led to a better structural stability than that of the impregnated sorbent. Moreover, the light-to-heat conversion of carbon shell was followed by the thermal energy storage by calcium chloride. In addition, the surface temperature of Ca/CT200-700 under the simulated sunlight of 1000 W/m2 increased to 75 °C. After irradiation for 230 min, the volumetric energy storage density of Ca/CT200-700 was 254 kWh/m3, with the water loss of 0.81 g-H2O/g-sorbent. This core–shell sorbent will provide new insights into the field of solar thermal conversion and storage.
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Development of an efficient and economic NO oxidation technology is the key step for the simultaneous removal of NOx and SO2 in coal‐fired power plants. In this work, a novel advanced oxidation process of NO was proposed, which directly... more
Development of an efficient and economic NO oxidation technology is the key step for the simultaneous removal of NOx and SO2 in coal‐fired power plants. In this work, a novel advanced oxidation process of NO was proposed, which directly delivered highly oxidative hydroxyl radicals (·OH) generated from the thermal activation of H2O2 vapour into flue gas flow. The experiments were demonstrated in a lab‐scale device, measuring the oxidation of NO as the indicator of radical formation and delivery. The influence of various operational parameters on NO oxidation was evaluated. Increasing the H2O2 dosage, the temperature of the hot‐nitrogen, the flow rate of the hot‐nitrogen, and the total gas residence time greatly enhances the NO oxidation. The NO oxidation was inhibited obviously with the increasing of the H2O2 pH and the NO initial concentration. Increasing the H2O2 pH and the NO initial concentration obviously reduced the NO oxidation. The results indicated that the thermal activation of H2O2 is feasible to oxidize NO and that the H2O2 homogeneous thermal decomposition reaction is essential, therefore, the temperature and the flow rate of the hot‐nitrogen can significantly affect the conversion efficiency. Finally, a potential application was proposed, where NO oxidation by gas‐phase H2O2 can be coupled with the general SCR system to meet stringent regulatory requirements and with a low operating cost.
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Hydrogen peroxide (H2O2) is considered to be an environmentally friendly chemical and the production methods of H2O2 based on the oxygen reduction reaction (ORR) in the electrochemical system can achieve in-situ generation. The yield of... more
Hydrogen peroxide (H2O2) is considered to be an environmentally friendly chemical and the production methods of H2O2 based on the oxygen reduction reaction (ORR) in the electrochemical system can achieve in-situ generation. The yield of H2O2 is highly dependent on cathode materials. However, the commercial graphite felts (GFs) have a low electrocatalytic activity, which greatly limits its wide-spread application. Here, three kinds of methods (H2O2 oxidation, Fenton reagent oxidation and electrochemical oxidation) were used to modify GFs as the cathode for electrochemical H2O2 production. Characterized by SEM, contact angle and XPS, the morphology and surface physicochemical properties after modification were considerably changed. After modification, the surface of GFs was etched, and some oxygen-containing functional groups (OGs) especially COOH appeared on the surface, leading to the improvement of the surface hydrophilic and the electrocatalytic activity for ORR. The H2O2 production of three GFs at 90 min were 18.67 mg/L, 32.13 mg/L and 37.47 mg/L, respectively, compared to only 3.24 mg/L by the original GFs. Additionally, the long-term stability of modified GFs were studied and the mechanism of the decreased stability was proposed. After 10 consecutive cycles, the H2O2 production of three modified GFs decreased by 42.29%, 61.24% and 58.19%, respectively. SEM, contact angle and XPS showed that the surface of the GFs was etched more, and the COOH content of all three materials significant decreased.
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Combustion of biomass in a boiler releases alkali metals and chlorine which, together with silicon and sulfur, are responsible for slagging, fouling, corrosion, and particulate emissions. This research investigated the effects of the... more
Combustion of biomass in a boiler releases alkali metals and chlorine which, together with silicon and sulfur, are responsible for slagging, fouling, corrosion, and particulate emissions. This research investigated the effects of the primary (under-fire) air flow rate, ṁ air , and its preheating temperature on the ignition and burning rates of pinewood chips in a laboratory fixed bed furnace and on the release of alkali metals and alkali earth metals (potassium (K), sodium (Na), calcium (Ca), magnesium (Mg)) and chlorine. The air flow rate, ṁ air , through the bed was varied in the range of 0.085−0.237 kg/(m 2 s), resulting in an overall excess primary air coefficient λ varying from 0.56 to 1.1. Air was also preheated in the range of 20−135 °C. Results showed that increasing either ṁ air or the air preheat temperature increased the flame propagation rate (ignition rate) and the mass burning rate of the fuel. Moreover, the release of Cl was nearly complete (>99%) in all examined cases, whereas the release of alkalis was only partial. Calcium was the most predominant alkali in the pinewood; however, potassium was the predominant alkali in the released gases. The mass fraction of Na in the pinewood was much lower than that of K but it was released more comprehensively. Increasing the air flow rate enhanced the release of K and Na significantly, whereas it enhanced the release of Ca and Mg only slightly. Preheating the primary air preferentially increased the migration of K to the gas phase, whereas Na, Ca, and Mg were affected only mildly. The preheated air promoted the transfer of chlorine to HCl. Overall, moderately high primary air flow rates generate globally fuel lean conditions and mildly preheated air can enhance the mass burning rate of pinewood and its conversion to fully and partially oxidized gases. However, they result in enhanced gasification of the alkalis in the biomass. In the case of pinewood, this may be a minor concern, as the absolute values of such emissions are low relative to other biomass fuels.
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This research investigated the effects of the specific primary (under-fire) air flowrate on the combustion behavior of a 50–50 wt % blend of raw corn straw (CS) and raw pinewood wastes in a fixed-bed reactor. This parameter was varied in... more
This research investigated the effects of the specific primary (under-fire) air flowrate on the combustion behavior of a 50–50 wt % blend of raw corn straw (CS) and raw pinewood wastes in a fixed-bed reactor. This parameter was varied in the range of 0.079–0.226 kg m−2 s−1, which changed the overall combustion stoichiometry from air-lean (excess air coefficient λ = 0.73) to air-rich (excess air coefficient λ = 1.25) and affected the combustion efficiency and stability as well as the emissions of hazardous pollutants. It was observed that by increasing m˙m˙air, the ignition delay time first increased and then decreased, the average bed temperatures increased, both the average flame propagation rates and the fuel burning rates increased, and the combustion efficiencies also increased. The emissions of CO as well as those of cumulative gas phase nitrogen compounds increased, the latter mostly because of increasing HCN, while those of NO were rather constant. The emissions of HCl decreased but those of other chlorine-containing species increased. The effect of m˙m˙air on the conversion of sulfur to SO2 was minor. By considering all of the aforesaid factors, a mildly overall air-rich (fuel-lean) (λ = 1.04) operating condition can be suggested for corn-straw/pinewood burning fixed-bed grate-fired reactors.
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In the present research, experiments were performed on corn straw in a one-dimensional bench fixed-bed combustion test rig. The effects of different corn straw lengths and primary air (supplied through the grate) on the combustion... more
In the present research, experiments were performed on corn straw in a one-dimensional bench fixed-bed combustion test rig. The effects of different corn straw lengths and primary air (supplied through the grate) on the combustion characteristics of corn straw were investigated. The two parameters will directly relate to the burning rate, which affect combustion efficiency, burnout rate and gas emissions. The bed temperature distribution and gas components such as CO2, CO, O2, CH4, C2H6, NO, HCN, and SO2 were measured in the bed. The results indicate that shorter corn straw combustion resulted the higher CO concentration in later stage of combustion, while a higher temperature and less unburned carbon in bottom ash. As the main pyrolysis production, the concentration of CH4 emission was 2 orders of magnitude for C2H6. NO was the main product of NOx, and shared a similar trend to HCN in the combustion process of all parameters, while the yield was less than HCN. The C conversion to CO2 was much higher than to CO. The emission factors of SO2 and NO had the opposite trend with the length variation. With the flowrate increased, there is an increased tendency of C to CO2 and a reduced CO/CO2 ratio. This study improves the understanding of the operational characteristics of small-scale corn straw burning to help with the design and optimization of large-scale fixed-beds for power plants.
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In this paper, mathematical modelling is conducted on the combustion of corn straw in a one-dimensional bench combustion test rig, and the effects of the primary air flow rate are assessed over a wide range. Due to complex solid... more
In this paper, mathematical modelling is conducted on the combustion of corn straw in a one-dimensional bench combustion test rig, and the effects of the primary air flow rate are assessed over a wide range. Due to complex solid combustion mechanisms and inadequate knowledge of the process, the development of such combustion system is limited. Numerical modelling of this combustion system has some advantages over experimental analysis, although the development of a complete model for this type of combustion system remains a challenge. Due to its characteristic properties, modelling of biomass combustion has to overcome many difficulties. One such problem is displaying the process of initiating the combustion in numerical modelling. This study finds that the volatile release and combustion of char increases, thus increasing the amount of primary air up to a critical point, where the starting time of ignition becomes shorter as the primary air flow rate increases. The peak concentration of NO decreases with the increase of primary air, whereas with the increase in the amount of air, there is a reduction in the release of SO2 as well as a reduction in CO emissions in the bed.
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In this paper, both a numerical model and an experimental study were developed to determine the important parameters of corn length for combustion behavior in a fixed-bed reactor. As an important factor impacting thermal conversion,... more
In this paper, both a numerical model and an experimental study were developed to determine the important parameters of corn length for combustion behavior in a fixed-bed reactor. As an important factor impacting thermal conversion, changes in the burning rate follow variations in corn length, which then affect gas emissions. As a result of insufficient knowledge concerning the mechanisms of complex combustion, the development of a combustion system has been restricted. Modeling of this combustion system will complement experimental data; however, improving such a model is challenging as a result of the unique characteristics of corn, such as its moisture content and porosity. The results show that corn straw with a shorter length has a shorter ignition time, increased bed temperature, and reduced amounts of unburned carbon in the ash residues. Furthermore, the burning of shorter corn straw causes high emission concentrations from pyrolysis products, such as CH4 , CO, and most prevalently NO, near the grate, which indicates the beginning of the char oxidation stage. Corn straw with longer lengths increases the difficulty of accurately modeling the irregular shape of corn straw particles for theoretical calculations. In addition, in an actual bed, local bed structures that have not been uniformly mixed result in uncertainties in the flame propagation as well as the time at which the fuel is ignited. The application of numerical modeling allows for a more detailed description of the corn combustion process and can be used as a reference to develop biomass combustion in a large system.
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This experiment was conducted on fixed bed combustion in a one-dimensional bench. The effects of ash and moisture content on the combustion characteristics of corn straw were determined. The two parameters directly relate to the burning... more
This experiment was conducted on fixed bed combustion in a one-dimensional bench. The effects of ash and moisture content on the combustion characteristics of corn straw were determined. The two parameters directly relate to the burning rate and affect combustion efficiency and the release of gas. The bed temperature distribution, mass loss rate and gas composition were measured in the bed. The results show that the optimum char combustion efficiency was achieved at 10% moisture content of corn combustion. A slight increasing the moisture content to 10% can obtain a higher bed temperature and accelerate the ignition rate in the char oxidation stage, while there is also a slight decrease in the conversion ratio of C to CO. The conversion rate of S to SO 2 for 10% moisture content was higher with the temperature zone above 1000 C. With the increased ash content, there was a slight increase in the average ignition rate; the bottom bed temperature increased with a serious ash slagging. C was converted to CO and presented a slightly increasing trend for higher ash content and the conversion of N to HCN. This work provides an overall understanding of corn combustion for large boiler system.
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In this study, the effect of corn ratio on pine chip and corn straw (high alkali metals and chlorine) co-combustion in a fixed bed were investigated. The combustion efficiency, gas emissions, and problems of corrosion and deposits were... more
In this study, the effect of corn ratio on pine chip and corn straw (high alkali metals and chlorine) co-combustion in a fixed bed were investigated. The combustion efficiency, gas emissions, and problems of corrosion and deposits were analyzed by detecting bed temperatures, gas compositions (CO2, CO, O2, CH4, C2H6, NOx, HCN, NH3, SO2, and HCl), and alkali metal emissions. The appropriate increase in the corn ratio improved flame propagation speed and shortened ignition time. Pure pine combustion caused some amount of thermal NO emissions, and the high content of N resulted to a relatively high emission of NH3 and HCN, whereas its relationship with the release of NO in the main burning stage was slight. A 30% corn ratio aided in the reduction of NO emission, and the amount of alkali metals in the corn fixed the effect of SO2. The release of KCl and HCl can be considered as the prevalent emission formation of Cl in the blended biomass co-combustion process; the additional corn straw increased the release ratio of metal chloride. The optimum corn ratio (30–50%) provide a certain reference value for the selection of fuel mixture ratio in the operation of real large-scale systems.
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This study conducted a comparison of the CaO2-based Fenton (CaO2/Fe(II)) and Fenton-like (CaO2/Fe(III)) systems on their benzene degradation performance. The H2O2, Fe(II), Fe(III), and HO variations were investigated during the benzene... more
This study conducted a comparison of the CaO2-based Fenton (CaO2/Fe(II)) and Fenton-like (CaO2/Fe(III)) systems on their benzene degradation performance. The H2O2, Fe(II), Fe(III), and HO variations were investigated during the benzene degradation. Although benzene has been totally removed in the two systems, the variation patterns of the investigated parameters were different, leading to different benzene degradation patterns. In terms of the Fe(II)/Fe(III) conversion, the CaO2/Fe(II) and CaO2/Fe(III) systems were actually inseparable and had the inherent mechanism relationships. For the CaO2/Fe(III) system, the initial Fe(III) must be converted to Fe(II), and then the consequent Fenton reaction could be later developed with the regenerated Fe(II). Moreover, some benzene degradation intermediates could have the ability to facilitate the transformation of the Fe(III) to Fe(II) without the classic H2O2-associated propagation reactions. By varying the Fe(II) dosing method, an effective degradation strategy has been developed to take advantage of the two CaO2-based oxidation systems. The proposed strategy was further successfully tested in TCE degradation, therefore extending the potential for the application of this technique.
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Electro-Fenton (EF) and ultrasound radiation (US) have been of interest for the removal of chlorinated compounds from water. This study evaluates the effects of different parameters on sono-electro-Fenton (SEF) for degradation of... more
Electro-Fenton (EF) and ultrasound radiation (US) have been of interest for the removal of chlorinated compounds from water. This study evaluates the effects of different parameters on sono-electro-Fenton (SEF) for degradation of 4-chlorophenol (4-CP) in an aqueous solution. This study uses pulsing US waves along with Pd-catalyzed EF to degrade contaminants in water while maintaining temperature. The usage of pulsing US waves along with Pd catalyzed EF to remove contaminants while maintaining temperature has not been reported previously. SEF ability to degrade 4-CP was compared with the performance of each process (EF and sonolysis) alone. Initial pH, current density, background electrolyte, Fe 2+ concentration, Pd/Al2O3 catalyst concentration, US waves, and sonifier amplitude were optimized in a two electrode (Ti/mixed metal oxide or Ti/MMO) batch system. The degradation of 4-CP increased from 1.85% by US to 83% by EF to nearly >99.9% by coupled SEF. With US radiation under 70% amplitude and 1:10 ON/OFF ratio, the removal rate of 4-CP increased to 98% compared to 62% under EF alone within the first 120 min in the presence of 80 mg L-1 Fe 2+ , 16.94 mA cm ─2 of current density, 1 g L-1 Pd/Al2O3 catalyst (10 mg Pd), and initial pH of 3. However, the degradation rate decreased after 120 min of treatment, and complete 4-CP removal was observed after 300 minutes. The sonolysis impacted the 4-CP removal under coupled SEF, mostly due to the contribution of mass transfer (micromixing), while radical formation was found to be absent under the conditions tested (20kHz). The pulsed US was found to increase the temperature by only 8.7 o C, which was found not to impact the 4-CP volatilization or degradation. These results imply that low-level US frequency through pulses is a practical and efficient approach to support electro-Fenton reaction, improving reaction rates without the need for electrolyte cooling.
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This study investigates the effect of palladium (Pd) form on the electrochemical degradation of chlorobenzene in groundwater by palladium-catalyzed electro-Fenton (EF) reaction. In batch and flow-through column reactors, EF was initiated... more
This study investigates the effect of palladium (Pd) form on the electrochemical degradation of chlorobenzene in groundwater by palladium-catalyzed electro-Fenton (EF) reaction. In batch and flow-through column reactors, EF was initiated via in-situ electrochemical formation of hydrogen peroxide (H2O2) supported by Pd on alumina powder or by palladized polyacrylic acid (PAA) in a polyvinylidene fluoride (PVDF) membrane (Pd-PVDF/PAA). In a mixed batch reactor containing 10 mg L−1 Fe2+, 2 g L−1 of catalyst in powder form (1% Pd, 20 mg L−1 of Pd) and an initial pH of 3, chlorobenzene was degraded under 120 mA current following a first-order decay rate showing 96% removal within 60 min. Under the same conditions, a rotating Pd-PVDF/PAA disk produced 88% of chlorobenzene degradation. In the column experiment with automatic pH adjustment, 71% of chlorobenzene was removed within 120 min with 10 mg L−1 Fe2+, and 2 g L−1 catalyst in pellet form (0.5% Pd, 10 mg L−1 of Pd) under 60 mA. The EF reaction can be achieved under flow, without external pH adjustment and H2O2 addition, and can be applied for in-situ groundwater treatment. Furthermore, the rotating PVDF-PAA membrane with immobilized Pd-catalyst showed an effective and low maintenance option for employing Pd catalyst for water treatment.
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The reason for the prominent error in the hydroxyl radical detection method by UV-vis spectrophotometry with fast blue BB salt (FBBs) as the chromogenic agent was detected, and a modified method was proposed. The simultaneous extraction... more
The reason for the prominent error in the hydroxyl radical detection method by UV-vis spectrophotometry with fast blue BB salt (FBBs) as the chromogenic agent was detected, and a modified method was proposed. The simultaneous extraction of FBBs in the diazosulfone extraction process was proven to have a distinct influence on the test results. In the modified method, FeSO4 was adopted to limit the extraction of FBBs by a toluene/butanol extraction agent, which sharply decreased the influence of FBBs on diazosulfone detection. The FBBs amount and extraction time played an important role in its extraction. The appropriate FBBs/MSIA ratio was 50, and the reasonable extraction time was 300 s for the modified method. ·OH concentration in the directional decomposition of the Fenton system was detected. The test error was about 7%. This method is quite significant to test ·OH quantificationally to better understand Fenton reaction mechanisms and promote the generation of ·OH.
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The electrochemical production of hydrogen peroxide (H2O2) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a... more
The electrochemical production of hydrogen peroxide (H2O2) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a state-of-the-arts review of the most important aspects of this process. First, recent advances in H2O2 production are reviewed and the advantages of H2O2 electrogeneration via 2-electron ORR are highlighted. Second, the selectivity of the ORR pathway towards H2O2 formation as well as the development process of H2O2 production are presented. The cathode characteristics are the decisive factors of H2O2 production. Thus the focus is shifted to the introduction of commonly used carbon cathodes and their modification methods, including the introduction of other active carbon materials, hetero-atoms doping (i.e., O, N, F, B, and P) and decoration with metal oxides. Cathode stability is evaluated due to its significance for long-term application. Effects of various operational parameters, such as electrode potential/current density, supporting electrolyte, electrolyte pH, temperature, dissolved oxygen, and current mode on H2O2 production are then discussed. Additionally, the environmental application of electrogenerated H2O2 on aqueous and gaseous contaminants removal, including dyes, pesticides, herbicides, phenolic compounds, drugs, VOCs, SO2, NO, and Hg0, are described. Finally, a brief conclusion about the recent progress achieved in H2O2 electrogeneration via 2-electron ORR and an outlook on future research challenges are proposed.
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A low maintenance, “self-cleaning” electrochemical approach is evaluated for regeneration of dye-loaded granular activated carbon (GAC). To do so, batch experiments were conducted using a low-cost granular activated carbon/stainless steel... more
A low maintenance, “self-cleaning” electrochemical approach is evaluated for regeneration of dye-loaded granular activated carbon (GAC). To do so, batch experiments were conducted using a low-cost granular activated carbon/stainless steel mesh (GACSS) composite cathode and a stable Ti/mixed metal oxides (Ti/MMO) anode without the addition of oxidants or iron catalysts. The GACSS cathode supports simultaneous H2O2 electrogeneration via the in situ supplied O2 from Ti/MMO anode and the subsequent H2O2 activation for OH generation, thus enabling the cracking of dye molecules adsorbed on GAC and regenerating the GAC's sorption capacity. Results show that a prolonged electrochemical processing for 12 h will achieve up to 88.7% regeneration efficiency (RE). While RE decreases with multi-cycle application, up to 52.3% could still be achieved after 10 adsorption-regeneration cycles. To identify the mechanism, experiments were conducted to measure H2O2 electrogeneration, H2O2 activation, and OH generation by various GAC samples. The dye-loaded GAC and GAC treated after 10 adsorption-regeneration cycles were still capable of OH generation, which contributes to effective “self-cleaning” and regeneration over multi-cycles.
Research Interests: Environmental Engineering, Advanced Oxidation Processes, Regeneration, Electrochemical Engineering, Activated carbon adsorption, and 8 moreActivated Carbon, AOP, Hydrogen Peroxide, Advance oxidation processes (AOPS) for water and wastewater treatment, Oxygen Reduction Reaction, electro-Fenton, Activated carbons, and Hydroxyl Radicals
Electrochemical synthesis of H2O2 offers a great potential for water treatment. However, a significant challenge is the development of efficient cathode materials for the process. Herein, we implement a practical electrochemical cathode... more
Electrochemical synthesis of H2O2 offers a great potential for water treatment. However, a significant challenge is the development of efficient cathode materials for the process. Herein, we implement a practical electrochemical cathode modification to support efficient H2O2 electrogeneration via the reduction of dissolved anodic O2. Graphite felt (GF) is in situ anodically modified by electrode polarity reversal technique in an acid-free, low-conductivity electrolyte. The modified GF exhibits a significantly higher activity towards O2 reduction. Up to 183.3% higher H2O2 yield is obtained by the anodized GF due to the increased concentrations of oxygen-containing groups and the hydrophilicity of the surface, which facilitates electron and mass transfer between GF and the electrolyte. Another significant finding is the ability to produce H2O2 at a high yield under neutral pH and low current intensity by the modified GF (35% of the charge need to produce the same amount by unmodified GF). Long-term stability testing of the modified GF showed a decay in the electrode’s activity for H2O2 production after 30 consecutive applications. However, the electrode regained its optimal activity for H2O2 production after a secondary modification by electrode polarity reversal. Finally, in situ electrochemically modified GF is more effective for removal of reactive blue 19 (RB19, 20 mg/L) and ibuprofen (IBP, 10 mg/L) by the electro-Fenton process. The modified GF removed 62.7% of RB19 compared to only 28.1% by the unmodified GF in batch reactors after 50 min. Similarly, 75.3% IBP is removed by the modified GF compared to 57.6% by the unmodified GF in a flow-through reactor after 100 min.
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Major challenges for effective implementation of the Electro-Fenton (EF) water treatment process are that conventional efficient cathodes are relatively expensive, and H2O2 activation by Fe2+ may cause secondary pollution. Herein, we... more
Major challenges for effective implementation of the Electro-Fenton (EF) water treatment process are that conventional efficient cathodes are relatively expensive, and H2O2 activation by Fe2+ may cause secondary pollution. Herein, we propose a low-cost activated carbon/stainless steel mesh (ACSS) composite cathode, where the SS mesh distributes the current and the AC simultaneously supports H2O2 electrogeneration, H2O2 activation, and organic compounds (OCs) adsorption. The oxygen-containing groups on the AC function as oxygen reduction reaction (ORR) sites for H2O2 electrogeneration; while the porous configuration supply sufficient reactive surface area for ORR. 8.9 mg/L H2O2 was obtained with 1.5 g AC at 100 mA under neutral pH without external O2 supply. The ACSS electrode is also effective for H2O2 activation to generate OH, especially under neutral pH. Adsorption shows limited influence on both H2O2 electrogeneration and activation. The iron-free EF process enabled by the ACSS cathode is effective for reactive blue 19 (RB19) degradation. 61.5% RB19 was removed after 90 min and 74.3% TOC was removed after 720 min. Moreover, long-term stability test proved its relatively stable performance. Thus, the ACSS electrode configuration is promising for practical and cost-effective EF process for transformation of OCs in water.
Research Interests: Environmental Engineering, Advanced Oxidation Processes, Wastewater Treatment, Activated Carbon, AOP, and 10 moreAdsorption and wastewater treatment, Hydrogen Peroxide, Advance oxidation processes (AOPS) for water and wastewater treatment, Oxygen Reduction Reaction, Civil and Environmental Engineering, electro-Fenton, Activated carbons, Hydroxyl Radicals, Fenton's Reagent, and All About Environmental and Civil Engineering
The performance of the Electro-Fenton (EF) process for contaminant degradation depends on the rate of H2O2 production at the cathode via 2-electron dissolved O2 reduction. However, the low solubility of O2 (≈1 × 10−3 mol dm−3) limits H2O2... more
The performance of the Electro-Fenton (EF) process for contaminant degradation depends on the rate of H2O2 production at the cathode via 2-electron dissolved O2 reduction. However, the low solubility of O2 (≈1 × 10−3 mol dm−3) limits H2O2 production. Herein, a novel and practical strategy that enables the synergistic utilization of O2 from the bulk electrolyte and ambient air for efficient H2O2 production is proposed. Compared with a conventional “submerged” cathode, the H2O2 concentration obtained using the “floating” cathode is 4.3 and 1.5 times higher using porous graphite felt (GF) and reticulated vitreous carbon (RVC) foam electrodes, respectively. This surprising enhancement results from the formation of a three-phase interface inside the porous cathode, where the O2 from ambient air is also utilized for H2O2 production. The contribution of O2 from ambient air varies depending on the cathode material and is calculated to be 76.7% for the GF cathode and 35.6% for the RVC foam cathode. The effects of pH, current, and mixing on H2O2 production are evaluated. Finally, the EF process enhanced by the “floating” cathode degraded 78.3% of the anti-inflammatory drug ibuprofen after 120 min compared to only 25.4% using a conventional “submerged” electrode, without any increase in the cost.
Research Interests: Environmental Engineering, Advanced Oxidation Processes, Wastewater Treatment, Gas Diffusion Layers, Emerging Contaminants, Fate and Transport, Organic Contaminants, and 10 moreHydrogen Peroxide, Fenton, Gas-Diffusion Layer, Advance oxidation processes (AOPS) for water and wastewater treatment, Civil and Environmental Engineering, electro-Fenton, Hydroxyl Radicals, Fenton's Reagent, Gas Diffusion electrode, and Organic Contaminants
The Fenton system (Fe2+/H2O2) generates ·OH with a high oxidation potential. However, as reactants themselves, H2O2 and Fe2+ can act as ·OH initiators as well as ·OH scavengers, leading to the need for a high dosage of reactants and... more
The Fenton system (Fe2+/H2O2) generates ·OH with a high oxidation potential. However, as reactants themselves, H2O2 and Fe2+ can act as ·OH initiators as well as ·OH scavengers, leading to the need for a high dosage of reactants and increased costs. As a mixing-sensitive reaction, the ·OH-related reaction kinetics (·OH with Fe2+, H2O2, and RhB) was determined from the reaction rates (which were a constant in this work) and stoichiometry, in which the latter could be regulated by an addition strategy of Fenton reagents. This suggests that ·OH competitive reactions could be controlled by applying a macrolevel addition strategy. Herein, the effects of different addition approaches of Fe2+ and H2O2 on ·OH competitive reactions were quantitatively and systematically studied by analyzing the removal of the model pollutant RhB. We found that without stirring, and compared with a one-time addition, once H2O2 or Fe2+ was added in a step-wise pattern (e.g., one drop by one drop, 2 times, or 4 times), a high concentration of H2O2 or Fe2+ existed in a localized place for a longer period, resulting in a lower proportion of ·OH reacting with RhB, which we ascribed to an enhanced reaction between Fe2+, H2O2, and ·OH. However, when H2O2 and Fe2+ were added from two close points without stirring, a larger proportion of ·OH was scavenged by H2O2 and Fe2+; while under stirring, even a one-time addition of H2O2 or Fe2+ could cause severe scavenging of ·OH. The results also revealed a linear relationship between the RhB removal percentage and wavelength blue-shifts. This study showed that microlevel ·OH competitive reactions could be controlled by applying a macrolevel addition strategy of Fenton reagents without the addition of external chemicals. The results suggest this methodology can also offer an approach to lower ·OH invalid consumption by regulating the addition strategy in bigger reactors.
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The reaction between Fe2+ and H2O2 generates highly reactive ·OH. However, the weak conversion from Fe3+ to Fe2+ limits its continuous reaction. Here, the difference between the Fenton system and modified Fenton system for the... more
The reaction between Fe2+ and H2O2 generates highly reactive ·OH. However, the weak conversion from Fe3+ to Fe2+ limits its continuous reaction. Here, the difference between the Fenton system and modified Fenton system for the regeneration of Fe2+ was analyzed. A UV-vis spectrometer and redox potential measurements were used to detect Fe2+ concentration. Results indicated that Fe2+ could be better regenerated in the modified Fenton system. The regeneration of Fe2+ was facilitated by the consumption of NH2OH, while in hydroquinone (HQ)- and 1,4-bezoquinone (1,4-BQ)-modified Fenton systems, the quinone cycle could be built up and Fe3+ could be converted to Fe2+ continuously. However, results showed that HQ and 1,4-BQ reacted with ·OH, which caused a gradual decline in the enhancement effect. In order to keep Fe2+ concentration stable for a longer time, the influence of [HQ/1,4-BQ]0/[Fe2+]0 on Fe2+ concentration was carefully studied. When the mole ratio was 5:1, Fe2+ concentration remained nearly 90% of total iron at 40 min. But when the mole ratios were 0.5:1 and 0.1:1, Fe2+ concentration decreased to a very low level at 20 min. Oxidation–reduction potential (ORP) results further confirmed the role of quinone cycle.
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The performance of cathode on H2O2 electrogeneration is a critical factor that limits the practical application of electro-Fenton (EF) process. Herein, we report a simple but effective electrochemical modification of reticulated vitreous... more
The performance of cathode on H2O2 electrogeneration is a critical factor that limits the practical application of electro-Fenton (EF) process. Herein, we report a simple but effective electrochemical modification of reticulated vitreous carbon foam (RVC foam) electrode for enhanced H2O2 electrogeneration. Cyclic voltammetry, chronoamperometry, and X-ray photoelectron spectrum were used to characterize the modified electrode. Oxygen-containing groups (72.5–184.0 μmol/g) were introduced to RVC foam surface, thus resulting in a 59.8–258.2% higher H2O2 yield. The modified electrodes showed much higher electrocatalytic activity toward O2 reduction and good stability. Moreover, aimed at weakening the extent of electroreduction of H2O2 in porous RVC foam, the strategy of pulsed current was proposed. H2O2 concentration was 582.3 and 114.0% higher than the unmodified and modified electrodes, respectively. To test the feasibility of modification, as well as pulsed current, EF process was operated for removal of Reactive Blue 19 (RB19). The fluorescence intensity of hydroxybenzoic acid in EF with modified electrode is 3.2 times higher than EF with unmodified electrode, illustrating more hydroxyl radicals were generated. The removal efficiency of RB 19 in EF with unmodified electrode, modified electrode, and unmodified electrode assisted by pulsed current was 53.9, 68.9, and 81.1%, respectively, demonstrating that the green modification approach, as well as pulsed current, is applicable in EF system for pollutant removal.
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Efficient H2O2 electrogeneration from 2-electron oxygen reduction reaction (ORR) represents an important challenge for environmental remediation application. H2O2 production is determined by 2-electron ORR as well as H2O2 decomposition.... more
Efficient H2O2 electrogeneration from 2-electron oxygen reduction reaction (ORR) represents an important challenge for environmental remediation application. H2O2 production is determined by 2-electron ORR as well as H2O2 decomposition. In this work, a novel strategy based on the systematical investigation on H2O2 decomposition pathways was reported, presenting a drastically improved bulk H2O2 concentration. Results showed that bulk phase disproportion, cathodic reduction, and anodic oxidation all contributed to H2O2 depletion. To decrease the extent of H2O2 cathodic reduction, the pulsed current was applied and proved to be highly effective to lower the extent of H2O2 electroreduction. A systematic study of various pulsed current parameters showed that H2O2 concentration was significantly enhanced by 61.6% under pulsed current of “2 s ON + 2 s OFF” than constant current. A mechanism was proposed that under pulsed current, less H2O2 molecules were electroreduced when they diffused from the porous cathode to the bulk electrolyte. Further results demonstrated that a proper pulse frequency was necessary to achieve a higher H2O2 production. Finally, this strategy was applied to Electro-Fenton (EF) process with ibuprofen as model pollutant. 75.0% and 34.1% ibuprofen were removed under pulsed and constant current at 10 min, respectively. The result was in consistent with the higher H2O2 and ·OH production in EF under pulsed current. This work poses a potential approach to drastically enhance H2O2 production for improved EF performance on organic pollutants degradation without making any changes to the system except for power mode.
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H2O2 production is the decisive factor of Electro-Fenton performance on contaminants degradation. Herein, a novel but simple strategy was proposed for drastically enhanced H2O2 production from anodic O2 electroreduction. H2O2... more
H2O2 production is the decisive factor of Electro-Fenton performance on contaminants degradation. Herein, a novel but simple strategy was proposed for drastically enhanced H2O2 production from anodic O2 electroreduction. H2O2 concentration at steady-state is 99.5% higher under pulsed current of “2sON + 2sOFF” than under constant current when using reticulated vitreous carbon foam (RVC foam) cathode. This was caused by the facilitated H2O2 diffusion from the porous cathode to bulk as H2O2 electroreduction pathway was weakened. Additionally, the enhancement effect is more significant for RVC foam with low PPI. This strategy is also applicable to graphite felt (GF) cathode, in which a 56.0% higher H2O2 concentration was observed at steady-state under pulsed current of “2sON + 2sOFF”. Investigation on pulse frequency shows there exists an optimal frequency that achieves both effective H2O2 electrogeneration and decreased H2O2 electroreduction.
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The Electro-Fenton process for in-situ H2O2 electrogeneration is impacted by low O2 utilization efficiency (<0.1%) and the need of acid for pH adjustment. An electrochemical flow-through cell can develop localized acidic conditions,... more
The Electro-Fenton process for in-situ H2O2 electrogeneration is impacted by low O2 utilization efficiency (<0.1%) and the need of acid for pH adjustment. An electrochemical flow-through cell can develop localized acidic conditions, coupled with simultaneous formation and utilization of O2 to enhance H2O2 formation. Multiple electrode configurations using reticulated vitreous carbon (RVC) foam and Ti/mixed metal oxides (MMO) are proposed to identify the optimum conditions for H2O2 formation in batch and flow-through cells. A pH of 2.75 ± 0.25 is developed locally in the flow-through cell that supports effective O2 reduction. Up to 9.66 mg/L H2O2 is generated in a 180 mL batch cell under 100 mA, at pH 2, and mixing at 350 rpm. In flow-through conditions, both flow rate and current significantly influence H2O2 production. A current of 120 mA produced 2.27 mg/L H2O2 under a flow rate of 3 mL/min in a 3-electrode cell with one RVC foam cathode at 60 min. The low current of 60 mA does not enable effective H2O2 production, while the high current of 250 mA produced less H2O2 due to parasitic reactions competing with O2 reduction. Higher flow rates decrease the retention time, but also increase the O2 mass transfer. Furthermore, 3-electrode flow-through cell with two RVC foam cathodes was not effective for H2O2 production due to the limited O2 supply for the secondary cathode. Finally, a coupled process that uses both O2 and H2 from water electrolysis is proposed to improve the H2O2 yield further.