Reactive Surface Area Research Articles

A Solid‐State Carrier Transport‐Prompted Z‐Scheme BiVO4 Quantum Dots‐Based Photocatalyst for Boosted Photocatalytic Degradation of Antibiotics

Monoclinic BiVO4 is extensively exploited in organic oxidation because of its appropriate valence band and remarkable catalytic activity. BiVO4 quantum dots not only have a high specific surface area and active sites for photocatalytic reactions, but can address the short carrier diffusion path problem. Herein, a Z‐scheme BiVO4 quantum dots/reduced graphene oxide/g‐C3N4 photocatalyst is constructed. Benefiting from the distinct BiVO4 quantum dots and layered g‐C3N4 sheets, the photocatalytic compound possesses a considerable light capture capability and surface area. The established Z‐scheme photocatalytic compound with a suitable electronic band structure and redox potential is integrated with a “synthesis and assembly” method. The sodium oleate surfactant plays an important role in the preparation of uniform BiVO4 quantum dots with a diameter of 3–6 nm. The optimized photocatalytic degradation experiments show that the ciprofloxacin and amoxicillin photocatalytic efficiencies are up to 92.2% and 70.7% in 1 h, respectively. It is shown that the improved photocatalytic activities involve in the prolonged lifetime of photogenerated electrons and fast carrier migration in the compound upon simulated sunlight exposure. Herein, a prospective stage for developing more Z‐scheme heterojunctions with excellent photocatalytic properties for antibiotic wastewater treatment and reproducible solar capture in photochemical energy conversion is offered.

Three-dimensional ordered macroporous design of heterogeneous nickel-iron phosphide as bifunctional electrocatalyst for enhanced overall water splitting

Developing high-performance oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) bifunctional electrocatalysts is essential for overall water splitting. Herein, heterogeneous engineering-induced strategy was demonstrated by the synthesis of bimetallic Ni2P/FeP/Fe2P heterostructure with three-dimensional ordered macroporous structure (3DOM-Ni2P/FexP) as bifunctional catalyst. The heterogeneous interfaces formed by the three distinct phases can adjust the electron distribution and create abundant active sites to improve the catalytic performance. The 3DOM structure provides large specific surface area and good mass transfer for electrocatalytic reaction occurring at the solid-gas-electrolyte multiphase interfaces. Accordingly, the 3DOM-Ni2P/FexP showed remarkable OER and HER electrocatalytic activity in 1 M KOH electrolyte. Moreover, it demonstrates that the 3DOM-Ni2P/FexP turns out oxidation and transformation during the OER process. Computational results reveal the synergy of the converted Fe2O3/NiOOH, promoting the OER reaction energetics. In addition, an alkaline electrolyzer with the 3DOM-Ni2P/FexP as both the cathode and anode achieves excellent overall water splitting performance, with only 1.54 V voltage to obtain the current density of 10 mA cm−2. This present study gives a novel concept of heterogeneous engineering-induced bimetallic phosphide with macroporous structure design towards the high-performing OER and HER bifunctional electrocatalysts evolvement.

Magma–Shale Interaction in Large Igneous Provinces: Implications for Climate Warming and Sulfide Genesis

Abstract Large igneous provinces (LIPs) whose magma plumbing systems intersect sedimentary basins are linked to upheavals of Earth’s carbon and sulfur cycles and thus climate and life history. However, the underlying mechanistic links between these phenomena are elusive. We address this knowledge gap through short time-scale petrological experiments (1200°C and 150 MPa) that explore interaction between basaltic melt and carbonaceous shale (mudstone) using starting materials from the Canadian High Arctic LIP and the Sverdrup Basin in which it intrudes. Here we show that entrainment of shale xenoliths in basaltic melt causes shale to shatter due to incipient thermal stress and devolatilization, which accelerates assimilation by increasing reactive surface area. Shale assimilation therefore facilitates transfer of sediment-derived volatile elements to LIP magma plumbing systems, whereupon carbon dominates the vapor phase while sulfur is partitioned into sulfide melt droplets. This study reveals that although carbon and sulfur are efficiently mobilized as a consequence of shale assimilation, sulfides can sequester sulfur—an important climate cooling agent—thus enhancing net emissions of climate warming greenhouse gases by shale-intersecting LIPs.

Assessment on Optimal Level of Reactive Biosilica Affected by Incineration Conditions in Perlis Rice Husk Ash as Supplementary Cementitious Materials in Concrete

Rice husk (RH) is an agricultural waste transformed to produce secondary by-products and is widely accepted as a substitution of cement or concrete mixtures. This paper deals with the optimal level of SiO2 content due to various incineration conditions of rice husk grown in Perlis, Malaysia. RH was burnt in a controlled environment with a targeted temperature of 650, 750 and 850 °C at various incineration period between 1 and 6 h. All the ashes were assessed for visual inspection and physiochemical and mineralogical properties using X-ray fluorescence (XRF) and X-ray diffraction (XRD). From the analysis, a significant amount of SiO2 in the range of 89–93 wt % was successfully obtained with the preferable properties of supplementary cementitious materials: amorphous silica with high reactivity, ultrafine size, and large surface area. Contrary, the burning temperature of 850 °C greater than 4 h incineration period is not advisable to be used as it transformed into a crystalline phase. No obvious color changes were observed for the ashes as the amount oxide compound of K2O causes carbon entrapped in surface melting. To sum up, 650 °C incineration for 1 h shows an optimum result, and the RH is bearable to reduce the negative impact on the environment.

Realizing Efficient Photoelectrochemical Performance for Well-Designed CdS@ZnIn2S4 Heterostructure Photoanode with Directional Interfacial Charge Transfer Dynamics

Designing a heterostructure photoanode with an appropriate band alignment, a beneficial charge migration pathway, and an adequate interfacial coupling is crucial for photoelectrochemical (PEC) energy conversion. Herein, we fabricate a hetero-nanostructure photoanode with CdS nanorods (CdS NRs) and two-dimensional (2D) ZnIn2S4 nanosheets (ZIS NSs) via a two-step in situ growth method on FTO glass to acquire a sufficient interfacial contact between two semiconductors. Based on their electronic band structures, the CdS is designed to be firstly grown on FTO to act as a photoelectron transport layer and 2D ZIS is further fabricated on the CdS as a photohole accumulation layer to directly contact the electrolyte. Benefitting from the Type II band alignment between the CdS and ZIS, such a heterostructure significantly enhances the separation efficiency and prolongs the lifetime of photocarriers. More importantly, it ensures that photoholes accumulate on the 2D ZIS with a highly exposed surface area for an oxidation reaction at the surface-active sites, while the photoelectrons transfer to counter electrode for hydrogen evolution. The optimum CdS@ZIS heterostructure photoanode exhibits a superior PEC performance with a photocurrent of 4.19 mA/cm2 at 1.23 VRHE (two times that of the CdS and eight times that of ZIS) and an applied bias photo-to-current efficiency (ABPE) of 1.93% at 0.49 VRHE. This work can inspire the future design of heterostructure photoanodes for highly efficient solar energy conversion.

Bi2O3 nanosheet-coated NiCo2O4 nanoneedle arrays for high-performance supercapacitor electrodes

Supercapacitors are a promising option for next-generation clean energy storage devices, although their capacitance must still be improved through an appropriate choice of electrode material. Herein, NiCo2O4 nanoneedles coated with Bi2O3 nanosheets are successfully prepared using a two-step hydrothermal process to produce electrodes that may be used for supercapacitors. The proposed electrodes are analyzed using both a range of experimental measurement techniques and density functional theory simulations. The NiCo2O4 nanoneedles provide an ideal skeleton for improving specific surface area and present electrical active sites for the Faraday reaction, while Bi2O3 nanosheets have a great potential for use in supercapacitor applications. The proposed NiCo2O4@Bi2O3 electrode shows a high capacity of 766 F g−1 at 1 A g−1. In addition, an asymmetric supercapacitor based on a NiCo2O4@Bi2O3 positive electrode and activated carbon was produced, which provided a working voltage of 1.6 V, achieved a high energy density of 24 Wh kg−1 at 800 W kg−1, and demonstrated excellent cycling stability (capacitance retention of 82 % after 10,000 cycles at 10 A g−1). These results demonstrate that the proposed NiCo2O4@Bi2O3 heterostructure exhibits potential for application in high-performance supercapacitors.

Mineral surface area accessibility and sensitivity constraints on carbon mineralization in basaltic aquifers

Estimating mineral reactive surface areas in geologic media remains one of the key challenges limiting the accuracy of reactive transport modeling (RTM) predictions of subsurface processes, particularly those controlling the fate of carbon dioxide (CO2) during geologic storage. Although there have been numerous attempts to combine imaging and experimental techniques to estimate mineral reactive surface area for use in RTM predictions of geologic CO2 storage, these techniques have yet to be adapted to basaltic reservoirs, which have pore structure, mineralogy, and chemical composition that is unique compared to their more often-studied sedimentary counterparts. Here, we address this issue by quantifying fluid-accessible mineral surface areas through image analysis of scanning electron microscope (SEM) backscatter electron images (high-resolution 500 nm/pixel) and Raman spectroscopic mapping of a basaltic rock sample from the Eastern Snake River Plain, Idaho. To evaluate whether the determined pore fluid-accessible mineral surface area accurately reflects reactive surface area, a micro-continuum scale RTM was developed and compared with a high-temperature, high-pressure flow-through CO2 mineralization experiment conducted on the characterized basalt. Importantly, simulations employing the image-derived pore fluid-accessible mineral surface areas match the experimental effluent chemistry well within uncertainties. These mineral surface areas were then used to parametrize a field-scale model representative of the Cascadia basin, Northeastern Pacific, to evaluate impacts of surface area variations on mineral carbonation. Simulations were carried out using variations in image-derived surface areas that cover one to two orders of magnitude increase and decrease in surface area, analogous to previously reported magnitudes of difference between total and reactive surface areas. Carbonation efficiency in terms of CO2 volume mineralized over the simulated period was tracked and compared. Simulations with surface area increased and decreased by two orders of magnitude show basalt carbonation efficiency that is three times faster and six times slower, respectively, than predictions with image-derived mineral surface area. These sensitivity analyses demonstrate that accurate quantification of mineral surface area is crucial for efforts to predict CO2 mineralization, and that efforts such as those employed here can dramatically reduce the uncertainty of field-scale predictions of basalt carbonation.

Underestimation of biogenic silica sinking flux due to dissolution in sediment traps: A case study in the South China Sea

The dissolved silicate concentrations in the supernatant of sediment trap sampling bottles retrieved from deep water (1000-3000 m) at four stations in the South China Sea (SCS) were measured to calculate the underestimated flux of biogenic silica (bSi) in sinking particles due to bSi dissolution. High dissolved silicate concentrations in the supernatant, ranging from 122.6 to 1365.8 μmol/L, indicated significant dissolution of particulate bSi in the sampling bottles. Underestimation of the bSi flux in the SCS by ~2% to ~34% (average: ~10%) due to bSi dissolution was revealed, and the degree of underestimation increased with decreasing total bSi flux. The amount of bSi dissolved within the sampling series at each station was generally positively correlated with dissolution time and to a certain extent influenced by the bSi amount collected by the sampling bottles under a low bSi sinking flux. Apparently stronger bSi dissolution was found at two of the four stations due to relatively high bSi dissolution rates, which were possibly related to a higher reactive surface area of the bSi or bacterial activity. Overall, our results demonstrated that the considerable bSi dissolution in sediment trap sampling bottles should not be ignored, especially in the low-productivity oligotrophic ocean, and bSi flux calibration via measurement of the dissolved silicate in sampling bottles is necessary. To reduce bSi flux underestimation due to the deployment of time-series sediment traps, larger-volume sampling bottles should be avoided in the oligotrophic open ocean, and sinking particle samples should be analyzed as soon as the sediment traps are recovered.

Construction of CoMo2 S4 Nanorods/Nanosheets Electrodes with Enhanced Electrochemical Properties for Asymmetric Pseudocapacitors.

The construction of hierarchical nanostructures and the synergistic effect of bimetal compounds provide effective strategies to address the low energy density of supercapacitors. Herein, CoMo2 S4 (CMS) nanosheets anchored on homogeneous nanorods vertically distributed on nickel foam (NF) were fabricated using a two-step hydrothermal method. The hierarchical homostructure CMS materials heavily depend on the vulcanization parameter of the second step synthesis. As an electrode of supercapacitors, CoMo2 S4 exhibits a large specific capacity of 1992.85 F g-1 at 2 mA cm-2 , and specific capacity retention of 106 % through 8000 cycles when sulfurization condition was at 120 °C for 6 h (CMS/NF-120). Such excellent performances benefit from hierarchical homostructure, which can provide a large reaction surface area, fast ion/electron diffusion channels and rich active sites. Furthermore, the asymmetric pseudocapacitors device constructed with CMS/NF-120 and active carbon exhibits a maximum energy density of 39.8 Wh kg-1 , and good long-term stability (80.1 % capacitance retention after 10,000 cycles).

Improved Volume-Of-Solid Formulations for Micro-Continuum Simulation of Mineral Dissolution at the Pore-Scale

We present two novel Volume-of-Solid (VoS) formulations for micro-continuum simulation of mineral dissolution at the pore-scale. The traditional VoS formulation (VoS-ψ) uses a diffuse interface localization function ψ to ensure stability and limit diffusion of the reactive surface. The main limitation of this formulation is that accuracy is strongly dependent on the choice of the localization function. Our first novel improved formulation (iVoS) uses the divergence of a reactive flux to localize the reaction at the fluid-solid interface, so no localization function is required. Our second novel formulation (VoS-ψ′) uses a localization function with a parameter that is fitted to ensure that the reactive surface area is conserved globally. Both novel methods are validated by comparison with experiments, numerical simulations using an interface tracking method based on the Arbitrary Eulerian Lagrangian (ALE) framework, and numerical simulations using the VoS-ψ. All numerical methods are implemented in GeoChemFoam, our reactive transport toolbox and three benchmark test cases in both synthetic and real pore geometries are considered: 1) dissolution of a calcite post by acid injection in a microchannel and experimental comparison, 2) dissolution in a 2D polydisperse disc micromodel at different dissolution regimes and 3) dissolution in a Ketton carbonate rock sample and comparison to in-situ micro-CT experiments. We find that the iVoS results match accurately experimental results and simulation results obtained with the ALE method, while the VoS-ψ method leads to inaccuracies that are mostly corrected by the VoS-ψ’ formulation. In addition, the VoS methods are significantly faster than the ALE method, with a speed-up factor of between 2 and 12.

Copper ferrite and cobalt oxide two-layer coated macroporous SiC substrate for efficient CO2-splitting and thermochemical energy conversion

CO2-splitting and thermochemical energy conversion effectiveness are still challenged by the selectivity of metal/metal oxide-based redox materials and associated chemical reaction constraints. This study proposed an interface/substrate engineering approach for improving CO2-splitting and thermochemical energy conversion through CuFe2O4 and Co3O4 two-layer coating SiC. The newly prepared material reactive surface area available for gas–solid reactions is characterized by micro-pores CuFe2O4 alloy easing inter-layer oxygen micro mass exchanges across a highly stable SiC-Co3O4 layer. Through a thermogravimetry analysis, oxidation of the thermally activated oxygen carriers exhibited remarkably CO2-splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The further analysis of the material CO2-splitting performance at the reactor scale resulted in 919.04 mL (788.94 µmol/g) of CO yield with an instantaneous CO production rate of 22.52 mL/min and chemical energy density of 223.37 kJ/kg at 1000 °C isothermal redox cycles. The reaction kinetic behavior indicated activation energy of 30.65 kJ/mol, which suggested faster CO2 activation and oxidation kinetic on SiC-Co3O4-CuFe2O4 O-deficit surfaces. The underlying mechanism for the remarkable thermochemical performances was analyzed by combining experiment and density functional theory (DFT) calculations. The significance of exploiting the synergy between CuFe2O4 and Co3O4 layers and stoichiometric reaction characteristics provided fundamental insights useful for the theoretical modeling and practical application of the solar thermochemical process.

Pore-scale study of effects of relative humidity on reactive transport processes in catalyst layers in PEMFC

High surface area carbon (HSC) particles can be adopted to increase the specific surface area of catalyst layer (CL) in proton exchange membrane fuel cells. Relative humidity (RH) has a significant effect on the Pt activity inside HSC particles, and the underlying mechanisms need to be further investigated. In this study, a pore-scale model considering the effects of RH on the reactive transport processes inside the CLs is developed. Two kinds of liquid water distributions affected by the RH, including capillary condensation in pores and ultra-thin liquid film on Pt surface, are considered. The liquid water distribution, Pt activity and local oxygen transport resistance (Rlocal) under different RH are studied in detail. It is found that as RH increases from 0.3 to 1.0, the condensed water in micropores of HSC particles increases, resulting in an increase in reactive surface area by about 43 %. Combined effect of the RH, Pt loading, I/C ratio and different kinds of carbon particles is investigated. It is found that due to the lack of sufficient reaction sites, compared with that under a high Pt loading, Rlocal under a low Pt loading is more sensitive to the RH. Besides, since the Pt activity inside HSC particles depends on the condensed water, the Rlocal of HSC particles is more sensitive to the RH than solid carbon particles. Finally, the Rlocal at low ionomer content is more sensitive to RH due to low ionomer coverage on Pt particles. The present study provides a pore-scale model for investigating the coupled effects of RH and CL porous structures on local transport processes, and can facilitate the optimization of CL nanoscale structures for better cell performance.

Exsolution of phase-separated nanoparticles via trigger effect toward reversible solid oxide cell

The electrocatalytic characteristics of heterostructure nanoparticles have attracted attention for use in devices addressing energy and environmental issues. Among the various features, exsolved alloy or core–shell nanoparticles display high reactive surface area and strong interaction between the metal and substrate oxide. Herein, we report multifunctional heterostructure nanoparticles, namely Fe/Cu Janus nanoparticles (JN) and verify an exsolution trigger effect using Cu as a seed in the La0.43Sr0.37Fe0.09Cu0.03Ti0.88O3-δ (Fe75) perovskite substrate. During the exsolution process, the exsolved Cu particles played a key role in triggering the Fe exsolution by contributing additional surface energy. These Fe/Cu JNs exhibited outstanding catalytic activity in a reversible solid oxide cell fed with H2O/H2 and CO/CO2 fuels. A single cell with Fe75 showed an impressive current density of − 1.11 A cm−2 at 1.3 V and 900 °C. Our study experimentally elucidated the mechanism of the triggering of co-exsolution and demonstrated a multifunctional catalyst using Fe/Cu JNs.

(Invited, Digital Presentation) Infiltrated Electrodes for High Temperature Energy Conversion, Electrolysis, and Chemical Synthesis

Solid oxide cell (SOC) infiltrated electrodes typically consist of a ceramic or cermet porous scaffold with the pore walls coated with catalyst particles. The pore size of the scaffold is 1 to 50 mm, whereas the catalyst particles are 10 to 300 nm. This scaffold provides a stable and durable mechanical structure, and the fine catalyst particles provide high surface area for electrochemical and heterogeneous reactions. The scaffold is sintered and bonded to the other layers of the complete cell. After this high temperature processing is finished, catalyst precursor solution is flooded into the scaffold and fired at moderate temperature to form the desired catalyst composition and phase. Because the scaffold is sintered in the absence of catalysts, re-optimization of the fabrication process, ink formulation, deposition process, and sintering protocol is not needed when a new catalyst is introduced to the cell design. Instead, a new precursor solution can be prepared from a stoichiometric mixture of metal salts, with minimal change in processing. This approach makes it straightforward to screen many catalyst compositions in a short period of time, and adapt an existing cell structure for a wide variety of applications.The Lawrence Berkeley National Laboratory metal-supported solid oxide cell (MS-SOC) design has a thin electrode scaffold of zirconia ceramic co-sintered on a thick porous stainless steel support layer. Both layers are coated with infiltrated catalysts. The catalyst precursor solution is an aqueous mixture of metal nitrate salts. After the solution is flooded into the pores of the scaffold, it is dried and heated in air to convert the nitrate salts to mixed metal oxides. The oxides can then be reduced to metals by firing in reducing atmosphere, if desired. The drying rate, heating rate, conversion temperature, and other processing parameters can have a dramatic impact on the catalyst particle morphology and ultimately on the performance and durability of the electrochemical device.Depending on the choice of catalyst composition, the MS-SOCs can be configured as fuel cells, electrolysis cells, or chemical conversion reactors. Several examples will be highlighted, including: fuel cell operation with hydrogen, ethanol, and natural gas; steam electrolysis for hydrogen production; and oxidative coupling of methane for valuable chemical synthesis. In each case, technical progress will be presented with a focus on catalyst development and device performance. Figure 1

Rational construction of reduced NiCo2S4@CuCo2S4 composites with sulfur vacancies as high-performance supercapacitor electrode for enhancing electrochemical energy storage

Rational design of NiCo2S4-based nanostructures supercapacitor electrodes was considered as an important route for increasing specific capacitance in the field of electrochemical energy storage. Here we reported that a novel reduced NiCo2S4@CuCo2S4 (R–NiCo2S4@CuCo2S4) core-shell heterostructure with sulfur vacancies improved electrochemical performance of supercapacitor electrode material. These composites were designed and synthesized by a combination of solvothermal, electrochemical deposition and reduction of sodium borohydride (NaBH4). Among them, NiCo2S4 nanosheets were grown on nickel foam as a core and act scaffold for the reaction by a solvothermal method, while CuCo2S4 as a shell to aggrandizement specific surface area of reaction by electrochemical deposition method and to further raise active sites and conductivity of reaction, sulfur vacancies were further constructed in NiCo2S4@CuCo2S4. The construction of sulfur vacancies shortens the reaction distance and accelerated electrons and ions transmission. Therefore, R–NiCo2S4@CuCo2S4 exhibited an excellent capacity (2922.9 F g−1 at 0.5 A g−1), superior rate capability (68% retention from 0.5 A g−1 to 10 A g−1) and extraordinary cycling stability (99.92% capacitance after 10000 cycles at 30 A g−1). This strategy successfully fabricated the R–NiCo2S4@CuCo2S4 core-shell heterostructure with excellent electrochemical performance, making it a potential candidate as supercapacitor electrode materials for enhanced electrochemical energy storage.

Evaporation of As and Sn from Liquid Iron: Experiments and a Kinetic Model during Top-Blown Oxygen Steelmaking Process.

Evaporation kinetics of tramp elements (M = As and Sn) in liquid iron were investigated by high-temperature gas–liquid reaction experiments and a phenomenological kinetic model. Residual content of As or Sn in the liquid iron ([pct M]) during the evaporation was measured in the temperature range of 1680 C to 1760 C. [pct As] and [pct Sn] decreased faster as the reaction temperature and [pct C] increased. Assuming first-order reaction kinetics, the apparent rate constants () were obtained at each reaction temperature and [pct C]. [pct M] in a liquid iron during the top-blown oxygen steelmaking process was simulated, with an emphasis on enlarging the reaction surface area by forming a large number of liquid iron droplets. The surface area and the droplet generation rate were obtained based on the oxygen-blowing condition. The whole surface area increased up to ∼163 times the initial liquid iron (bath) surface area, due to the generation of the droplets. Using the obtained in the present study, the evaporation of M during the top-blown oxygen steelmaking process for 200 tonnes of liquid iron was simulated. For a condition of [pct M] = 0.005 (M = As and Sn), As and Sn could be removed from the liquid iron, which was seen to be much improved by the consideration of the droplet generation. However, additional actions are required to improve the evaporation rate, as the evaporation rate in the BOF process was not fast enough to be practically considered.

Adopting co-metabolism strategy for optimized biotreatment of ortho-hydroxytoluene and bioelectricity generation in microbial fuel cell: Transformation products and pathways

This study investigated the effects of carbon source availability and concentrations, external loads (Rload), and cathode conditions on the overall removal rate of ortho-hydroxytoluene and bioelectricity generation characteristics in anti-gravity flow microbial fuel cell (AGF-MFC) through co-metabolism approach. Sodium acetate outperformed sucrose, glucose and carbamide, and the optimum influent acetate concentration (1000 mg L−1) significantly enhanced the o-hydroxytoluene degradation by 13.41 % (98.71 %), output voltage by 15.14 % (609.25 mV) and power generation by 30.96 % (159.44 mW m−2). The results demonstrated that there were prominent differences in MFC performances under different Rload (p < 0.05). Different external load conditions resulted in varying electron transfer reactions, and thus affecting the removal efficiency and power responses of MFC system. A complete removal of o-hydroxytoluene and highest power density of 173.10 mW m−2, with a Chemical Oxygen Demand (COD) removal of 93.56 % were obtained with the Rload of 230 Ω, where the Rload approaches the cell design point. Hysteresis phenomenon was detected in the dynamic polarization during Rload variations. Moreover, it was observed that the removal efficiency of o-hydroxytoluene was significantly enhanced with aeration rate of 50 mL min−1, and dissolved oxygen concentration of 5.4 mg L−1. Conversely, higher aeration rate (400 mL min−1) had caused a decline of 26 % in power generation, ascribed to the limited active surface area for oxygen reduction reaction. Additionally, the degradation pathway of o-hydroxytoluene was proposed based on the identified intermediates.

One-dimensional hierarchical porous carbon nanofibers with cobalt oxide in a hollow channel for electrochemical applications

One-dimensional hierarchical porous carbon nanofibers (CNFs) embedded with Co3O4 nanoparticles in a hollow channel (PPMCo) are fabricated by coaxial electrospinning followed by thermal treatment. The degree to which the CNF surface is exposed to Co3O4 nanoparticles was controlled by the cobalt(II) acetate concentration. The well-controlled structure of PPMCo with porous structure, heteroatoms, and amorphous Co3O4 nanoparticles provided fast ion transport and large reaction surface area, resulting in effective ion migration to the active site and a high rate capacity of the electrode. Benefitting from the unique structure, the PPMCo supercapacitor electrodes displays a high specific capacitance of 188 Fg−1 at 1 mAcm−2, rate capability of 82% when the current density is increased from 1 to 20 mAcm−2, and cycling stability of 93% for 10,000 cycles. The good capacitive performance of the PPMCo electrode is attributed to the synergistic effect of the hierarchical porosity, electroactive material of Co3O4, high effective surface area, and polar effects by heteroatoms.

Production and Optimization of Biodiesel in a Membrane Reactor, Using a Solid Base Catalyst.

The commercial Calcium oxide was successfully embedded on activated carbon surfaces to increase the reactive surface area of a composite catalyst material CaO/AC. The composite catalyst material was also successfully packed in the tubular titanium dioxide/Aluminum dioxide ceramic membrane reactor used to separate the biodiesel produced. Virgin soybean oil was used as precursor feedstock for the reaction. Using a central composite approach, response surface methodology (RSM) was employed to obtain the optimum conditions for producing biodiesel from soybean oil. A total of four process factors were examined (24 experimental designs). 30 experiments were derived and run to investigate the effects of temperature, reaction time, methanol to oil molar ratio, and catalyst concentration (calcium oxide attached on activated carbon). 96.9 percent of soybean oil methyl ester (SOME/biodiesel) was produced at 65 °C temperature, 90 min of reaction time, 4.2:1 molar ratio of methanol to oil, and 3.0 wt.% catalyst concentration. The measured yield and expected biodiesel production values were correlated in a linear sequence. The fuel qualities of SOME/biodiesel were tested, including kinematic viscosity, density, flash point, copper corrosion, calorific value, cloud point, pour point, ash content, and carbon residue.

The reduction in porosity of permeable reactive barriers due to bio-geochemical clogging caused by acidic groundwater flow

This study demonstrates the change in porosity of permeable reactive barrier (PRB) material when it reacts with acidic flow. The laboratory column test data obtained over 9 months prove that the porosity of a granular limestone assembly decreases significantly due to bio-geochemical clogging caused by a continuous flow of acidic groundwater. The variations in pH, the pressure measurements, ion concentrations, and the results from X-ray diffraction suggest that clogging at the outlet of the column is much less than at the inlet. About 57% of the total reduction in porosity of the column is attributed to chemical clogging, while the remainder is mainly due to biological clogging. In this paper, a mathematical approach is proposed to estimate the reduction of reactive surface area based on changes in the pore volume. These proposed equations suggest that at the end of experimentation, the dissolution of calcite and bio-geochemical clogging can reduce the total surface area of limestone aggregates by more than 70%. The rigorous approach presented in this paper to determine the dominant clogging component within a granular filter at a given time is vital in estimating the longevity of a PRB and for planning its maintenance.