Divalent Metal Ion Depletion from Wastewater by RVC Cathodes: A Critical Review.

In this paper, a critical review of results obtained using a reticulated vitreous carbon (RVC) three-dimensional cathode for the electrochemical depletion of various divalent ions, such as Cu+2, Cd+2, Pb+2, Zn+2, Ni+2, and Co+2, often present in wastewater, has been carried out. By analyzing the kinetics and fluid dynamics of the process found in literature, a general dimensionless equation, Sh = f(Re), has been determined, describing a general trend for all the analyzed systems regardless of the geometry, dimensions, and starting conditions. Thus, a map in the log(Sh) vs. log(Re) plane has been reported by characterizing the whole ion electrochemical depletion process and highlighting the existence of a good correlation among all the results. Moreover, because in recent years, the interest in using this three-dimensional cathode material seems to have slowed, the intent is to revive it as a useful tool for metal recovery, recycling processes, and water treatments.

Electrochemical Characteristics of Shewanella loihica PV-4 on Reticulated Vitreous Carbon (RVC) with Different Potentials Applied.

The current output of an anodic bioelectrochemical system (BES) depends upon the extracellular electron transfer (EET) rate from electricigens to the electrodes. Thus, investigation of EET mechanisms between electricigens and solid electrodes is essential. Here, reticulated vitreous carbon (RVC) electrodes are used to increase the surface available for biofilm formation of the known electricigen Shewanella loihica PV-4, which is limited in conventional flat electrodes. S. loihica PV-4 utilizes flavin-mediated EET at potential lower than the outer membrane cytochromes (OMC), while at higher potential, both direct electron transfer (DET) and mediated electron transfer (MET) contribute to the current output. Results show that high electrode potential favors cell attachment on RVC, which enhances the current output. DET is the prevailing mechanism in early biofilm, while the contribution of MET to current output increased as the biofilm matured. Electrochemical analysis under starvation shows that the mediators could be confined in the biofilm. The morphology of biofilm shows bacteria distributed on the top layer of honeycomb structures, preferentially on the flat areas. This study provides insights into the EET pathways of S. loihica PV-4 on porous RVC electrodes at different biofilm ages and different set potential, which is important for the design of real-world BES.

A green slurry electrolysis to recover valuable metals from waste printed circuit board (WPCB) in recyclable pH-neutral ethylene glycol.

The continuous growth of e-waste necessitates an efficient method to recover their metal contents to improve their recycling rate. The successful recovery of the metallic component from Waste Electrical and Electronic Equipment (WEEE) can generate great economic benefits to incentivize the industrial recycling effort. In this study, we report the use of slurry electrolysis (SE) in pH-neutral ethylene glycol (EG) electrolyte to extract and recover the metallic component from waste printed circuit broad (WPCB) powder. The system operates at room temperature and atmospheric pressure, and the electrolyte can be recycled multiple times with no signs of chemical degradation. The EG electrolyte system can oxidize the metallic component without triggering anodic gas evolution, which allowed us to incorporate a reticulated vitreous carbon (RVC) foam anode to maximize the capture and oxidation of the metal content. The system demonstrated up to 99.1% Faraday efficiency for the cathodic metal deposition and could recover Cu from the WPCB powder in a selective manner of 59.7% in the presence of 12 other metals. The SE reaction system was also scalable and displayed no compromises on the Cu recovery selectivity. With the ability to leach and recover metallic content from WPCB in a mild and chemically benign condition, the SE system displayed much promise to be adapted for industrial-scale metal recovery from WPCB.

Silver deposition optimization process on ultrananocrystalline diamond applied to nitrate reduction.

Nitrate is a serious contaminant of ground and surface water, which cause high concern in the field of health and environmental protection. In this work, a ternary composite of silver/boron-doped ultrananocrystalline diamond/reticulated vitreous carbon (Ag/B-UNCD/RVC) was prepared and its electrocatalytic activity for nitrate reduction was examined. B-UNCD films were grown by hot filament chemical vapour deposition technique on RVC after a substrate seeding process improvement using 4 nm diamond powder. Compared to conventional 0.25 µm diamond seeding, this new procedure allowed uniform RVC coverage avoiding its etching process during diamond growth, in addition to obtaining more reproductive electrodes. In order to improve the catalytic effect of B-UNCD/RVC electrodes for nitrate reduction, silver deposition was performed on B-UNCD surface after oxidation for 10, 20 and 30 min in 0.5 mol L-1 H2SO4 solution using a potential of 2 V vs. Ag/AgCl. The most oxidized diamond film (30 min of oxidation) presented the highest silver deposit and particle adhesion. Thus the electrochemical response to nitrate of B-UNCD/RVC oxidized for 30 min was compared to that of RVC and B-UNCD/RVC electrodes showing the important Ag influence in the catalytic process.

Liquid crystal display electrode-assisted bio-electroperoxone treatment train for the abatement of organic contaminants in a pharmaceutical wastewater.

Pharmaceutical contaminants present in wastewaters cause severe health hazards among chronically exposed population. Emerging pharmaceutically active contaminants pose a serious challenge to conventional treatment technologies. Employing advanced treatment technologies for the abatement of such contaminants is usually energy-intensive. In this study, a complex pharmaceutical wastewater from a pharmaceutical industry in California, USA, was treated by employing a novel bio-electrochemical treatment train system. Labeled "Bio-electroperoxone," our proposed system comprises (i) an electrically bound biofilm reactor (EBBR) that accelerates bacterial adhesion for the removal of biodegradable and persistent organics and (ii) an electroperoxone reactor that removes recalcitrant organics with minimal energy uptake. The EBBR comprises a platinum-coated titanium cathode and a conductive nematic liquid crystal display electrode (NLCE) obtained from electronic waste that serves as the anode. Characterization of functional groups, morphology, and elemental mapping of NLCE were carried out to explain mechanisms for rapid biofilm attachment. The concomitant electroperoxone reactor comprises a platinum-coated titanium (Pt-Ti) anode and a reticulated vitreous carbon (RVC) cathode that catalyzes the two-electron reduction of oxygen to form in situ H2O2. The bio-electroperoxone system (i) inactivated 99.99% of the micro-organisms, removed (ii) 92.20% of the color, (iii) 84.72% of the total suspended solids, and (iv) 89% of the total organic carbon (TOC). Possible mechanisms for the degradation of organic contaminants are elucidated. Bio-electroperoxone thus paves the way for an efficient and sustainable approach for the efficient removal of both biodegradable and recalcitrant, persistent organic contaminants from pharmaceutical and possibly other complex wastewaters.

Electrochemical disinfection using a modified reticulated vitreous carbon cathode for drinking water treatment.

A reticulated vitreous carbon (RVC) cathode modified by anodic polarization in 20 wt% H2SO4 solution was used for drinking water disinfection under a neutral low electrolyte concentration (0.25 g/L Na2SO4) condition. The contribution of the modified RVC anode and the Ti/RuO2 cathode to disinfection was investigated. The influences of current, initial Escherichia coli load, temperature and water volume were studied. The results show that H2O2 generation increased to approximately three times using the modification of the RVC. E. coli was mainly deactivated by the H2O2 generated at the cathode. For water with about 106 CFU/mL E. coli, the detection limit (<4 CFU/mL) was reached under different conditions. Increasing current could simultaneously shorten the treatment time and increase the energy consumption (EC) simultaneously. Although decreasing the initial load reduced the treatment time, the EC for per log E. coli removal increased. The time required for disinfection shortened from 3.5 to 2.5 h and the EC for per log removal decreased from 218.5 to 123.2 Wh/m3 when the temperature increased from 20 to 40 °C. Although more time was required for disinfection, the EC decreased from 218.5 to 141.4 Wh/m3 when the volume was doubled.

Kinetics of Acid Orange 7 oxidation by using carbon fiber and reticulated vitreous carbon in an electro-Fenton process.

In this study, a micro-scale parallel plate reactor was built to electrochemically generate hydrogen peroxide (H2O2) and to develop the Fenton reaction in situ, for the treatment of toxic organic pollutants. Two types of carbon materials were compared and used as cathodes: unidirectional carbon fiber (CF) and reticulated vitreous carbon (RVC). As anode, a stainless steel mesh was used. The results of H2O2 were experimentally compared by means of electrogeneration process. RVC cathode with dimensions of 2.5 × 1 × 5 cm (170 mA and variable voltage V = 2.0-2.7) and 180 min produced 5.3 mM H2O2, with an H2O2 production efficiency of 54%. Unidirectional carbon fiber cathode produced 7.5 mM of H2O2 (96% of H2O2 production efficiency) when a voltage of 1.8 V was applied during 180 min to a total area of 480 cm2 of this material. Acid Orange 7 (AO7) was degraded to a concentration of 0.16 mM during the first 40 min of the process, which represented 95% of the initial concentration. Electrolysis process removed nearly 100% of the AO7 using both cathodes at the end of these experiments (180 min).

Electrophoretic deposition of carbon nanotube on reticulated vitreous carbon for hexavalent chromium removal in a biocathode microbial fuel cell.

For Cr(VI)-removal microbial fuel cell (MFC), a more efficient biocathode in MFCs is required to improve the Cr(VI) removal and electricity generation. RVC-CNT electrode was prepared through the electrophoretic deposition of carbon nanotube (CNT) on reticulated vitreous carbon (RVC). The power density of MFC with an RVC-CNT electrode increased to 132.1 ± 2.8 mW m-2, and 80.9% removal of Cr(VI) was achieved within 48 h; compared to only 44.5% removal of Cr(VI) in unmodified RVC. Cyclic voltammetry, energy-dispersive spectrometry and X-ray photoelectron spectrometry showed that the RVC-CNT electrode enhanced the electrical conductivity and the electron transfer rate; and provided more reaction sites for Cr(VI) reduction. This approach provides process simplicity and a thickness control method for fabricating three-dimensional biocathodes to improve the performance of MFCs for Cr(VI) removal.

Growth, structure and stability of sputter-deposited MoS2 thin films.

Molybdenum disulphide (MoS2) thin films have received increasing interest as device-active layers in low-dimensional electronics and also as novel catalysts in electrochemical processes such as the hydrogen evolution reaction (HER) in electrochemical water splitting. For both types of applications, industrially scalable fabrication methods with good control over the MoS2 film properties are crucial. Here, we investigate scalable physical vapour deposition (PVD) of MoS2 films by magnetron sputtering. MoS2 films with thicknesses from ≈10 to ≈1000 nm were deposited on SiO2/Si and reticulated vitreous carbon (RVC) substrates. Samples deposited at room temperature (RT) and at 400 °C were compared. The deposited MoS2 was characterized by macro- and microscopic X-ray, electron beam and light scattering, scanning and spectroscopic methods as well as electrical device characterization. We find that room-temperature-deposited MoS2 films are amorphous, of smooth surface morphology and easily degraded upon moderate laser-induced annealing in ambient conditions. In contrast, films deposited at 400 °C are nano-crystalline, show a nano-grained surface morphology and are comparatively stable against laser-induced degradation. Interestingly, results from electrical transport measurements indicate an unexpected metallic-like conduction character of the studied PVD MoS2 films, independent of deposition temperature. Possible reasons for these unusual electrical properties of our PVD MoS2 thin films are discussed. A potential application for such conductive nanostructured MoS2 films could be as catalytically active electrodes in (photo-)electrocatalysis and initial electrochemical measurements suggest directions for future work on our PVD MoS2 films.

Reticulated vitreous carbon as a scaffold for enzymatic fuel cell designing.

Three - dimensional (3D) electrodes are successfully used to overcome the limitations of the low space - time yield and low normalized space velocity obtained in electrochemical processes with two - dimensional electrodes. In this study, we developed a three - dimensional reticulated vitreous carbon - gold (RVC-Au) sponge as a scaffold for enzymatic fuel cells (EFC). The structure of gold and the real electrode surface area can be controlled by the parameters of metal electrodeposition. In particular, a 3D RVC-Au sponge provides a large accessible surface area for immobilization of enzyme and electron mediators, moreover, effective mass diffusion can also take place through the uniform macro - porous scaffold. To efficiently bind the enzyme to the electrode and enhance electron transfer parameters the gold surface was modified with ultrasmall gold nanoparticles stabilized with glutathione. These quantum sized nanoparticles exhibit specific electronic properties and also expand the working surface of the electrode. Significantly, at the steady state of power generation, the EFC device with RVC-Au electrodes provided high volumetric power density of 1.18±0.14mWcm-3 (41.3±3.8µWcm-2) calculated based on the volume of electrode material with OCV 0.741±0.021V. These new 3D RVC-Au electrodes showed great promise for improving the power generation of EFC devices.

Treatment of industrial effluents by electrochemical generation of H2O2 using an RVC cathode in a parallel plate reactor.

Electrochemical techniques have been used for the discolouration of synthetic textile industrial wastewater by Fenton's process using a parallel plate reactor with a reticulated vitreous carbon (RVC) cathode. It has been shown that RVC is capable of electro-generating and activating H2O2 in the presence of Fe(2+) added as catalyst and using a stainless steel mesh as anode material. A catholyte comprising 0.05 M Na2SO4, 0.001 M FeSO4.7H2O, 0.01 M H2SO4 and fed with oxygen was used to activate H2O2.The anolyte contained only 0.8 M H2SO4. The operating experimental conditions were 170 mA (2.0 V < ΔECell < 3.0 V) to generate 5.3 mM H2O2. Synthetic effluents containing various concentrations (millimolar - mM) of three different dyes, Blue Basic 9 (BB9), Reactive Black 5 (RB5) and Acid Orange 7 (AO7), were evaluated for discolouration using the electro-assisted Fenton reaction. Water discolouration was measured by UV-VIS absorbance reduction. Dye removal by electrolysis was a function of time: 90% discolouration of 0.08, 0.04 and 0.02 mM BB9 was obtained at 14, 10 and 6 min, respectively. In the same way, 90% discolouration of 0.063, 0.031 and 0.016 mM RB5 was achieved at 90, 60 and 30 min, respectively. Finally, 90% discolouration of 0.14, 0.07 and 0.035 mM AO7 was achieved at 70, 40 and 20 min, respectively. The experimental results confirmed the effectiveness of electro-assisted Fenton reaction as a strong oxidizing process in water discolouration and the ability of RVC cathode to electro-generate and activate H2O2 in situ.

Study on cytocompatibility and animal implantation test of domestic reticulated vitreous carbon / 中华显微外科杂志

Objective To investigate the possibility of the domestic reticulated vitreous carbon as a kind of scaffold material for bone tissue engineering,the biocompatibility of domestic reticulated vitreous carbon was first successfully tested with bone marrow stromal cells (BMSCs) in vitro and for bone tissue repair in vivo.Methods From June,2013 to August,2014,the morphology and proliferation of BMSCs co-cultured with scaffold material in vitro was measured.Differences of measurement were compared with single factor analysis of variance to detect the cytotoxicity of reticulated vitreous carbon.In vivo reticulated vitreous carbon were implanted into the bone defect site and the groin.After 12 weeks,the biocompatibility of reticulated vitreous carbon was observed.Results MTT results showed that after 7d co-culture,the survival and proliferation of BMSCs had not been significantly inhibited (P ＞ 0.05).Inverted fluorescence microscope and scanning electron microscope found that newly developed three-dimensional domestic reticulated vitreous carbon could promote adhesion,aggregation and proliferation of BMSCs in vitro.Studies in vivo demonstrate that implanted reticulated vitreous carbon with a high porosity and host bone may produce a stable connection and integration.Conclusion Non-cytotoxic domestic reticulated vitreous carbon can promote the adhesion and proliferation of bone marrow mesenchymal stem cells in vitro and has good bone induction properties in vivo.