Xiuheng Wang

A novel stainless steel mesh/cobalt oxide hybrid electrode for efficient catalysis of oxygen reduction in a microbial fuel cell.

To explore efficient and cost-effective cathode material for microbial fuel cells (MFCs), the present study fabricates a new type of binder-free gas diffusion electrode made of cobalt oxide (Co3O4) micro-particles directly grown on stainless steel mesh (SSM) by using an ammonia-evaporation-induced method. In various electrochemical analyses and evaluations in batch-fed dual-chamber MFCs, the SSM/Co3O4 hybrid electrode demonstrates improved performances in terms of electrocatalytic activity, selectivity, durability and economics toward oxygen reduction reaction (ORR) in pH-neutral solution, in comparison with conventional carbon supported platinum catalyst. This study suggests a new strategy to fabricate a more effective electrode for ORR in MFCs, making it more technically and economically viable to produce electrical energy from organic materials for practical applications.

Forward osmosis with a novel thin-film inorganic membrane.

Forward osmosis (FO) represents a new promising membrane technology for liquid separation driven by the osmotic pressure of aqueous solution. Organic polymeric FO membranes are subject to severe internal concentration polarization due to asymmetric membrane structure, and low stability due to inherent chemical composition. To address these limitations, this study focuses on the development of a new kind of thin-film inorganic (TFI) membrane made of microporous silica xerogels immobilized onto a stainless steel mesh (SSM) substrate. The FO performances of the TFI membrane were evaluated upon a lab-scale cell-type FO reactor using deionized water as feed solution and sodium chloride (NaCl) as draw solution. The results demonstrated that the TFI membrane could achieve transmembrane water flux of 60.3 L m(-2) h(-1) driven by 2.0 mol L(-1) NaCl draw solution at ambient temperature. Meanwhile, its specific solute flux, i.e. the solute flux normalized by the water flux (0.19 g L(-1)), was 58.7% lower than that obained for a commercial cellulose triacetate (CTA) membrane (0.46 g L(-1)). The quasi-symmetry thin-film microporous structure of the silica membrane is responsible for low-level internal concentration polarization, and thus enhanced water flux during FO process. Moreover, the TFI membrne demonstrated a substantially improved stability in terms of mechanical strength, and resistance to thermal and chemical stimulation. This study not only provides a new method for fabricating quasi-symmetry thin-film inorganic silica membrane, but also suggests an effective strategy using this alternative membrane to achieve improved FO performances for scale-up applications.

Fabrication of stainless steel mesh gas diffusion electrode for power generation in microbial fuel cell.

This study reports the fabrication of a new membrane electrode assembly by using stainless steel mesh (SSM) as raw material and its effectiveness as gas diffusion electrode (GDE) for electrochemical oxygen reduction in microbial fuel cell (MFC). Based on feeding glucose (0.5 g L(-1)) substrate to a single-chambered MFC, power generation using SSM-based GDE was increased with the decrease of polytetrafluoroethylene (PTFE) content applied during fabrication, reaching the optimum power density of 951.6 mW m(-2) at 20% PTFE. Repeatable cell voltage of 0.51 V (external resistance of 400 Ω) and maximum power density of 951.6 mW m(-2) produced for the MFC with SSM-based GDE are comparable to that of 0.52 V and 972.6 mW m(-2), respectively obtained for the MFC containing typical carbon cloth (CC)-made GDE. Besides, Coulombic efficiency (CE) is found higher for GDE (SSM or CC) with membrane assembly than without, which results preliminarily from the mitigation of Coulombic loss being associated with oxygen diffusion and substrate crossover. This study demonstrates that with its good electrical conductivity and much lower cost, the SSM-made GDE suggests a promising alternative as efficient and more economically viable material to conventional typical carbon for power production from biomass in MFC.

Sustainable conversion of glucose into hydrogen peroxide in a solid polymer electrolyte microbial fuel cell.

Since years, H2O2 has been widely accepted as one of the most important and versatile chemicals, being utilized in a broad range of areas such as chemical processes, medical disinfection, and wastewater treatment. Recently, attention to H2O2 from the field of “green chemistry” has been increasing, because it serves as a direct and environmentally benign source for hydrogen and oxygen atoms in organic syntheses. Thus, hydrogenation, oxidation, and carbonylation reactions in which H2O2 participates can have low E factors and high atom efficiencies. For these reasons, H2O2 has also been named “Mr. Clean.” Because the current anthraquinone oxidation (AO) method for the industrial-scale production of H2O2 has inherent problems associated with inefficiency and security, a number of alternatives have been explored. Of all the processes for H2O2 synthesis, electrochemical methods offer several particular advantages in terms of cleanliness, safety, and low costs. An illustrative example of an electrochemical system was provided by Yamanaka et al. , who demonstrated highly selective H2O2 formation (93 %) utilizing pure hydrogen gas as feedstock. Biomass, which stores solar energy in chemical bonds, should be a more effective hydrogen-rich carrier compared to gaseous hydrogen because of its large-scale production, costeffectiveness, and renewable nature. These factors give rise to a remarkable potential for biomass as alternative starting material for H2O2 production in a fuel-cell system. The “Biomass-to-H2O2” ideology proposed here is consistent with the current trend towards the use of biomass-based raw materials for the sustainable production of chemicals. Microbial fuel cells (MFCs) represent a new, promising technology for generating electricity through microbial oxidation of organic substances, using micro-organisms as catalyst. Many studies have shown that MFCs are capable of utilizing a wide range of organic materials for generating electricity, including carbohydrates (glucose, sucrose, cellulose, starch), volatile fatty acids (formate, acetate, butyrate), alcohols (methanol, ethanol), and proteins. Being similar to other chemical fuel cells, oxygen has been acknowledged as the most suitable cathodic electron acceptor in MFCs. The electrochemical reduction of oxygen proceeds at the cathode through four-electron [Equation (1); SHE: standard hydrogen electrode] or two-electron [Equation (2)] pathways in aqueous electrolyte (pH 7.0, 1 mmol L , 1 atm, 298.15 K).

Upgrading to urban water system 3.0 through sponge city construction

Facing the pressure of excessive water consumption, high pollution load and rainstorm waterlogging, linear and centralized urban water system, system 2.0, as well as traditional governance measures gradually exposed characters of water-sensitivity, vulnerability and unsustainability, subsequently resulting in a full-blown crisis of water shortage, water pollution and waterlogging. To systematically relieve such crisis, we established urban water system 3.0, in which decentralized sewerage systems, sponge infrastructures and ecological rivers play critical roles. Through unconventional water resource recycling, whole process control of pollutions and ecological restoration, system 3.0 with integrated management measures, is expected to fit for multiple purposes which involve environmental, ecological, economic and social benefits. With advantages of flexibility, resilience and sustainability, water system 3.0 will show an increasingly powerful vitality in the near future.

Improved interfacial oxygen reduction by ethylenediamine tetraacetic acid in the cathode of microbial fuel cell

In this study, ethylenediamine tetraacetic acid (EDTA) was investigated as a new kind of non-polymeric catalyst binder to improve interfacial oxygen reduction reaction (ORR) for the cathode of microbial fuel cell (MFC). The electrochemical analysis and MFC tests show negative correlation between ORR activity and molar concentration of EDTA applied during electrode preparation. In particular, the 0.02mol/L-EDTA yields higher ORR activity than other binder materials like Nafion, water, 0.1mol/L-EDTA and 0.2mol/L-EDTA, as indicated by the strongest response of ORR current and the smallest charge-transfer resistance. Accordingly, the MFC with cathode of 0.02mol/L-EDTA produced a maximum power density of 722mW/m(2), accounting for a value approximately 42% higher than that of commercial Nafion binder (5wt%, 507mW/m(2)). The improved ORR activity should be attributed to the enhanced proton transfer from phosphate ions to EDTA-involved three-phase boundary as a result of dipole ion bonds on nitrogen atoms having unshared pair of electrons in EDTA molecule.

A case study of aggregation behaviors of titanium dioxide nanoparticles in the presence of dodecylbenzene sulfonate in natural water

The present work aims to ascertain the mechanisms of surfactant (dodecylbenzene sulfonate; DBS) effects on the aggregation behaviors of TiO2 nanoparticles (TiO2-NPs) in natural water samples. Aggregation experiments were conducted at a TiO2-NPs concentration of 10mg/L in deionized water and in natural water samples via dynamic light scattering and Zeta potential determination. Average attachment efficiency was calculated to compare the aggregation behaviors of nanoparticles in the two aqueous media. Results showed that the effects of DBS on aggregation could be interpreted by both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO mechanisms. In natural water samples, aggregation did not occur rapidly and was able to develop slowly under all conditions, and the roles of DBS were obvious at high DBS concentration owing to the impacts of inherent components of natural water samples, such as colloids and natural organic compounds. Future aggregation studies should concentrate on multi-factor, multi-colloidal and dynamic aspects under similar environmental conditions.

Pilot-scale bioelectrochemical system for efficient conversion of 4-chloronitrobenzene

4-Chloronitrobenzene (4-CNB) is one of the highly toxic contaminants that may lead to acute, chronic or persistent physiological toxicity to ecology and environment. Conventional methods for removing 4-CNB from aquatic environment may be problematic due to inefficiency, high cost and low sustainability. This study develops a pilot-scale bioelectrochemical system (BES, effective volume of 18 L) and examines its performance of bioelectrochemical transformation of 4-CNB to 4-chloroaniline (4-CAN) under continuous operation. The results demonstrate that the initial 4-CNB concentration in the influent and hydraulic retention time (HRT) has a significant impact on 4-CNB reduction and 4-CAN formation. Compared with the conventional anaerobic process in the absence of external power supplied, the 4-CNB conversion efficiency can be enhanced with power supplied due to microbial-mediated electron transfer at the negative cathode potential. At a voltage of 0.4 V and HRT of 48 h, the 4-CNB reduction and 4-CAN formation efficiency reached 99% and 94.1%, respectively. Based on a small external voltage applied, the pilot-scale BES is effective in the conversion of 4-CNB to 4-CAN, an intermediate that is of less toxicity and higher bioavailability for subsequent treatment. This study provides a new strategy and methods for eliminating 4-CNB, making wastewater treatment more economical and more sustainable.

Numerical anodic mass transfer of redox mediators in microbial fuel cell

In order to address the role of redox mediator mass transfer in microbial fuel cell (MFC), numerical simulation models are developed on the basis of Monod equation, Ficks second law, Ohms law and Butler-Volmer equation in this study. In the models, microbial metabolizing kinetics, substrate diffusion, electrochemical reaction kinetics and circuit behavior are taken into consideration. Electricity generation and mass transfer process is simulated as function of reaction time under various external resistance conditions (100Ω, 1000Ω, 10000Ω). Besides, spatial mass transfer process of acetate and mediator is also displayed. To further investigate the impact of redox mediator mass transfer on MFC performance, polarization and power-current behavior are obtained at initial acetate concentration of 1000mg/l. The simulation shows that the mass transfer resistance is mainly caused by the diffusion of redox mediator rather than acetate inside the anophilic biofilm. In particular, the mass transfer resistance tends to become the rate-limiting step when the reduced mediator concentration is descended to a low magnitude of 10-2mmol/l.

Treatment of wastewater containing acid rose red dye by biologically aerated filter after chemical oxidation.

Combined processes of pre-chemical oxidation and biological aerated filter (BAF) were used to treat wastewater containing non-biodegradable acid rose red dye. Advance oxidation processes (AOPs) of ozone and Fenton reagent were applied for pre-chemical oxidation, which reduced the degree of color and organic matter simultaneously increasing the biodegradability of the wastewater. The majority of the organic matter was removed by BAF. When using ozone as prechemical oxidation, the operation is simpler. The combined processes of AOPs, including ozone and Fenton reagent, followed by BAF reduced the color and chemical oxygen demand (COD) to less than 20 degrees and 40 mg l-1, respectively from the influent concentration of about 4000 degree color and 300 mg l-1 COD. The effluent water quality could meet the required standard for grey water reuses.