Anhuai Lu

Naturally Occurring Sphalerite As a Novel Cost-Effective Photocatalyst for Bacterial Disinfection under Visible Light

The photocatalytic disinfection capability of the natural semiconducting mineral sphalerite is studied here for the first time. Natural sphalerite can completely inactivate 1.5 × 10(7) cfu/mL E. coli K-12 within 6 h under visible light irradiation. The photocatalytic disinfection mechanism of natural sphalerite is investigated using multiple scavengers. The critical role that electrons play in bactericidal actions is experimentally demonstrated. The involvement of H(2)O(2) in photocatalytic disinfection is also confirmed using a partition system combined with different scavengers. Moreover, the photocatalytic destruction of bacterial cells is observed through transmission electron microscopic analysis. A catalase activity study reveals that antioxidative enzyme activity is high in the initial stage of photocatalytic disinfection but decreases with time due to damage to enzymatic functioning. Natural sphalerite is abundant and easy to obtain and possesses excellent visible-light photocatalytic activity. These superior properties make it a promising solar-driven photocatalyst for large-scale cost-effective wastewater treatment.

Photocatalytically improved azo dye reduction in a microbial fuel cell with rutile-cathode.

Reductive decolorization of azo dye in wastewater was investigated in a dual-chamber microbial fuel cell (MFC) equipped with cathodes made of graphite or rutile-coated graphite. Rapid reduction of methyl orange (MO) with concomitant electricity production was achieved when the rutile-coated cathode was irradiated by visible light. The electrochemical impedance spectra (EIS) indicate that the polarization resistance (R(p)) of the rutile-cathode MFC decreased from 1378 Omega in dark to 443.4 Omega in light, demonstrating that photocatalysis of rutile can enhance the cathodic electron transfer process. The combination of the biologically active anode and photocatalysis-supported cathodic reduction of MO obeyed the pseudo-first-order kinetics. The analysis of decolorization products indicates that the azo bond of MO was probably cleaved by photoelectrons at the irradiated rutile-cathode, resulting in the products of colorless hydrazine derivatives. In addition, concurrently enhanced electricity generation in the MFCs involving photocatalyzed cathodic reduction of MO was observed throughout this study.

A Recyclable Mineral Catalyst for Visible-Light-Driven Photocatalytic Inactivation of Bacteria: Natural Magnetic Sphalerite

Motivated by recent studies that well-documented mineral photocatalyst for bacterial inactivation, a novel natural magnetic sphalerite (NMS) in lead-zinc deposit was first discovered and evaluated for its visible-light-driven (VLD) photocatalytic bactericidal properties. Superior to the reference natural sphalerite (NS), vibrating sampling magnetometeric (VSM) analysis revealed the ferromagnetic property of NMS, indicating its potential for easy separation after use. Under the irradiation of fluorescence tubes, NMS could inactivate 7 log10 Gram-negative Escherichia coli K-12 without any regrowth and metal ions leached out from NMS show no toxicity to cells. The cell destruction process starting from cell wall to intracellular components was verified by TEM. Some products from damaged cells such as aldehydes, ketones and carboxylic acids were identified by FTIR with a decrease of cell wall functional groups. The relative amounts of potassium ion leakage from damaged cells gradually increased from initial 0 to approximately constant concentration of 1000 ppb with increasing reaction time. Superoxide radical (•O2(-)) rather than hydroxyl radical (•OH) was proposed to be the primary reactive oxidative species (ROSs) responsible for E. coli inactivation by use of probes and electron spin resonance (ESR). H2O2 determined by fluorescence method is greatly involved in bacterial inactivation in both nonpartition and partition system. Multiple cycle runs revealed excellent stability of recycled NMS without any significant loss of activity. This study provides a promising natural magnetic photocatalyst for large-scale bacterial inactivation, as NMS is abundant, easily recycled and possessed an excellent VLD bacterial inactivation ability.

Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis

Phototrophy and chemotrophy are two dominant modes of microbial metabolism. To date, non-phototrophic microorganisms have been excluded from the solar light-centered phototrophic metabolism. Here we report a pathway that demonstrates a role of light in non-phototrophic microbial activity. In lab simulations, visible light-excited photoelectrons from metal oxide, metal sulfide, and iron oxide stimulated the growth of chemoautotrophic and heterotrophic bacteria. The measured bacterial growth was dependent on light wavelength and intensity, and the growth pattern matched the light absorption spectra of the minerals. The photon-to-biomass conversion efficiency was in the range of 0.13-1.90‰. Similar observations were obtained in a natural soil sample containing both bacteria and semiconducting minerals. Results from this study provide evidence for a newly identified, but possibly long-existing pathway, in which the metabolisms and growth of non-phototrophic bacteria can be stimulated by solar light through photocatalysis of semiconducting minerals.

Photo-reductive decolorization of an azo dye by natural sphalerite: Case study of a new type of visible light-sensitized photocatalyst

Natural sphalerite, which represents a new class of mineral-based catalyst, was characterized and investigated for photo-reduction of an azo dye methyl orange (MO) under visible light. After 2h of visible light irradiation, a complete decolorization of the MO solution was achieved. The degradation rate was related to the pH conditions. Spectra from FT-IR analysis indicate an initial adsorption of MO to sphalerite via its sulfonate group. Further reduction of the adsorbed MO by sphalerite under light irradiation led to the destruction of the azo structure, as indicated by the results from UV-vis, FT-IR and ESI-MS analyses. The visible light-induced photocatalytic reductive activity of natural sphalerite was mainly attributed to the distribution of foreign metal atoms in its crystal lattice, which reduces the intrinsic bandgap of sphalerite and also broadens its spectra responding range. In addition, the high conduction band potential of natural sphalerite may also enhance the photo-reduction of MO.

Synthesis, characterization, and catalytic activity of cryptomelane nanomaterials produced with industrial manganese sulfate.

Industrial manganese sulfate from manganese mines has been utilized to synthesize cryptomelane in a simple and feasible route. K-birnessite precursor was prepared by air oxidation of the mixture of MnSO4 and KOH solutions under alkaline conditions, and then transformed to cryptomelane under a heating process. The effects of OH- concentration, airflow rate, liquid reaction temperature, stirring rate, liquid reaction time, washing condition, calcination time, and temperature were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) revealed that cryptomelane prepared under optimal conditions had a tetragonal symmetry and the particles were mostly in short lathy form with sizes of 20-30 nm. The average pore size and BET surface area of cryptomelane examined by N2 adsorption methods were 24.15 nm and 32.21 m2/g, respectively. X-ray photoelectron spectroscopy (XPS) studies demonstrated that the average oxidation state of manganese in cryptomelane was about 3.9 in comparison with prephase K-birnessite of 3.4. The synthesized cryptomelane sample showed improved catalytic activity for decomposition of hydrogen peroxide as compared with natural cryptomelane, but lower than those synthesized with hydrothermal and sol-gel methods. The results of this investigation will provide fundamental information for developing a large-scale production process for transforming manganese sulfate to cryptomelane.

Graphene oxide and H2 production from bioelectrochemical graphite oxidation.

Graphene oxide (GO) is an emerging material for energy and environmental applications, but it has been primarily produced using chemical processes involving high energy consumption and hazardous chemicals. In this study, we reported a new bioelectrochemical method to produce GO from graphite under ambient conditions without chemical amendments, value-added organic compounds and high rate H2 were also produced. Compared with abiotic electrochemical electrolysis control, the microbial assisted graphite oxidation produced high rate of graphite oxide and graphene oxide (BEGO) sheets, CO2, and current at lower applied voltage. The resultant electrons are transferred to a biocathode, where H2 and organic compounds are produced by microbial reduction of protons and CO2, respectively, a process known as microbial electrosynthesis (MES). Pseudomonas is the dominant population on the anode, while abundant anaerobic solvent-producing bacteria Clostridium carboxidivorans is likely responsible for electrosynthesis on the cathode. Oxygen production through water electrolysis was not detected on the anode due to the presence of facultative and aerobic bacteria as O2 sinkers. This new method provides a sustainable route for producing graphene materials and renewable H2 at low cost, and it may stimulate a new area of research in MES.

STUDY OF THE INTERACTION BETWEEN BENTONITE AND A STRAIN OF BACILLUS MUCILAGINOSUS

Mineral-microbe interactions are widespread in a number of environmental processes such as mineral weathering, decomposition, and transformation. Both clay minerals and silicate-weathering bacteria are widely distributed in nature, and the latter contribute to weathering, diagenesis, and mineralization of major rock-forming minerals. The purpose of this study was to observe changes in the chemical composition and structure, especially the phase transformation, of smectite after processing by a silicate-weathering bacterium. The interaction between Bacillus mucilaginosus and bentonite was studied using custom culture media. Results from Inductively Coupled Plasma-Atomic Emission Spectrometry revealed that the bacterium promoted release of Si and Al from solid bentonite to solution. Concomitantly, the Ka nd Fe contents of the mineral increased as shown by X-ray photoelectron spectroscopy results. After interaction with the bacterium, the montmorillonite underwent a possible structure transformation to smectite, as indicated by the emergence of a new weak peak (d = 9.08 Å) shown by X-ray diffraction patterns. The mineralogical changes were also demonstrated by the decrease in the specific surface area of the mineral from 33.0 to 24.0 m2/g (these lower values for SSA of bentonite are related to the particle size of the smectite examined (120-160 mesh) and the weakened absorption bands in Al-O-H and Si-O-Si vibrations by Micro Fourier-transform infrared spectroscopy. The morphology changes in the bacteria observed by environmental scanning electron microscopy and atomic force microscopy revealed an obvious growth of the flagella in the presence of bentonite.

Enhanced Alcaligenes faecalis Denitrification Rate with Electrodes as the Electron Donor.

ABSTRACT The utilization by Alcaligenes faecalis of electrodes as the electron donor for denitrification was investigated in this study. The denitrification rate of A. faecalis with a poised potential was greatly enhanced compared with that of the controls without poised potentials. For nitrate reduction, although A. faecalis could not reduce nitrate, at three poised potentials of +0.06, −0.06, and −0.15 V (versus normal hydrogen electrode [NHE]), the nitrate was partially reduced with −0.15- and −0.06-V potentials at rates of 17.3 and 28.5 mg/liter/day, respectively. The percentages of reduction for −0.15 and −0.06 V were 52.4 and 30.4%, respectively. Meanwhile, for nitrite reduction, the poised potentials greatly enhanced the nitrite reduction. The nitrite reduction rates for three poised potentials (−0.06, −0.15, and −0.30 V) were 1.98, 4.37, and 3.91 mg/liter/h, respectively. When the potentials were cut off, the nitrite reduction rate was maintained for 1.5 h (from 2.3 to 2.25 mg/liter/h) and then greatly decreased, and the reduction rate (0.38 mg/liter/h) was about 1/6 compared with the rate (2.3 mg/liter/h) when potential was on. Then the potentials resumed, but the reduction rate did not resume and was only 2 times higher than the rate when the potential was off.

Synergistic Interaction between Electricigens and Natural Pyrrhotite to Produce Active Oxygen Radicals

In this work we demonstrated that the active oxygen radicals could be produced by the synergistic interaction between electricigens and natural pyrrhotite. The identification of such an interactive pathway was conducted by using a fuel cell-type design, in which the electricigen-attached carbon felt electrode was used as the anode and the pyrrhotite-coated graphite electrode was used as the corresponding cathode. Current density, polarization and power density curves obtained at different treatments demonstrated the synergistic effects of electricigens and pyrrhotite improved the electrons transfer rate between them. Cyclic voltammetry (CV) analysis showed the reductive peaks of O2/H2O2 at 0.88 V (vs. SCE, saturated calomel electrode) and ionic and structural Fe(III)/Fe(II) at 0.31 V (vs. SCE) and 0 V (vs. SCE), respectively. The electrochemical results indicated the electricigen-assisted pyrrhotite photoelectrochemical reactions gave rise to Fentons reagents: Fe2+ and H2O2, which underwent a further reaction to generate active oxygen radical ·OH. By using N, N-dimethyl-p-nitrosoaniline discoloration as a model reaction, the ·OH production rate at the pyrrhotite-cathode was found to follow the first-order kinetics. Practical application of the synergistic interaction between the electricigen and natural pyrrhotite to a real old-aged landfill leachate degradation resulted in 78% chemical oxygen demand (COD) removal and 77% decolourization efficiency. The current generation lasted more than 45 days verified the validity of such system in long-term operation. The proposed interactive pathway would be expected as an alternative cost-effective technology for future wastewater treatment.