Electrochemical reduction of oxygen catalyzed by Pseudomonas aeruginosa

Pseudomonas aeruginosa has already been shown to catalyze oxidation processes in the anode compartment of a microbial fuel cell. The present study focuses on the reverse capacity of the bacterium, i.e. reduction catalysis. Here we show that P. aeruginosa is able to catalyze the electrochemicalreduction of oxygen. The use of cyclic voltammetry showed that, for a given range of potential values, the current generated in the presence of bacteria could reach up to four times the current obtained without bacteria. The adhesion of bacteria to the working electrode was necessary for the catalysis to be observed but was not sufficient. The electron transfer between the working electrode and the bacteria did not involve mediator metabolites like phenazines. The transfer was by direct contact. The catalysis required a certain contact duration between electrodes and live bacteria but after this delay, the metabolic activity of cells was no longer necessary. Membrane-bound proteins, like catalase, may be involved. Various strains of P. aeruginosa, including clinical isolates, were tested and all of them, even catalase-defective mutants, presented the same catalytic property. P. aeruginosa offers a new model for the analysis of reduction catalysis and the protocol designed here may provide a basis for developing an interesting tool in the field of bacterial adhesion

Spatially resolved electrochemistry in ionic liquids : surface structure effects on triiodide reduction at platinum electrodes

Understanding the relationship between electrochemical activity and electrode structure is vital for improving the efficiency of dye-sensitized solar cells. Here, the reduction of triiodide to iodide in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) room temperature ionic liquid (RTIL) is investigated on polycrystalline platinum using scanning electrochemical cell microscopy (SECCM) and correlated to the crystallographic orientation from electron backscatter diffraction (EBSD). Although the rate determining step in all grains was the first electron transfer, significant grain-dependent variations in activity were revealed, with grains with a dominant (110) crystallographic character exhibiting higher catalytic activity compared to those with a major (100) orientation. The SECCM technique is demonstrated to resolve heterogeneity in activity, highlighting that methods incorporating polycrystalline electrodes miss vital details for understanding and optimizing electrocatalysts. An additional advantage of the SECCM over single-crystal techniques is its ability to probe high index facets

Highly efficient electrochemical and chemical hydrogenation of 4-nitrophenol using recyclable narrow mesoporous magnetic CoPt nanowires

Toxic nitro-compounds, such as 4-nitrophenol, are one of the most common wastewater industrial pollutants. Thus, efficient ways to neutralize them are actively pursued. Here novel procedures to degrade this type of compounds based on the use of mesoporous magnetic nanowires are demonstrated. Fully-mesoporous magnetic narrow (25 nm) CoPt nanowires with an extraordinary effective area are grown by ionic liquid-in-water microemulsions in alumina templates. These mesoporous nanowires are shown to be efficient catalysts for the hydrogenation of 4-nitrophenol by electro-catalysis. Additionally, these nanowires also present an exceptional conventional catalytic activity when used in conjunction with NaBH4, particularly when magnetic stirring is utilized. In fact, magnetically actuated mesoporous CoPt nanowires drastically outperform all state-of-the-art 4-nitrophenol catalysts. Additionally, given their magnetic character, these nanowires can be easily recycled and reused. Thus, the outstanding catalytic performance of mesoporous CoPt nanowires makes them excellent candidates for wastewater treatment agents

DSA to grow electrochemically active biofilms of Geobacter sulfurreducens

Biofilms of Geobacter sulfurreducens were grown on graphite and on dimensionally stable anodes (DSA) in medium that did not contain any soluble electron acceptor. Several working electrodes were individually addressed and placed in the same reactor to compare their electrochemical behaviour in exactly the same biochemical conditions. Under constant polarization at 0.20Vversus Ag/AgCl, the electrodes were able progressively to oxidize acetate (5 mM), and average current densities around 5Am−2 and 8Am−2 were sustained for days on DSA and graphite, respectively. Removing the biofilm from the electrodes led the current to zero, while changing the medium by fresh one did not disturb the current when contact to air was avoided. This confirmed that the biofilm was fully responsible for the electro-catalysis of acetate oxidation and the current was not due to the accumulation of compounds in the bulk. Cyclic voltammetries performed during chronoamperometry indicated that the oxidation started above 0.05V versus Ag/AgCl. The difference in maximal current values obtained with DSA and graphite was not linked to the biofilm coverage ratios, which were of the same order of magnitude in the range of 62–78%. On the contrary, the difference in maximal current values matched the ratio of the average surface roughness of the materials, 5.6 m and 3.2 m for graphite and DSA, respectively

pembangunan rumah susun sebagai strategi hunian layak huni baru di kota solo

ABSTRAK Radin Suryo Pranoto, D0313057, 2013, PEMBANGUNAN RUMAH SUSUN SEBAGAI STRATEGI HUNIAN LAYAK HUNI BARU BAGI WARGA DI KOTA SOLO, Skripsi. Pembimbing : Akhmad Ramdhon, S.Sos,. M.A. Program Studi Sosiologi, Fakultas Ilmu Sosial dan Ilmu Politik, Universitas Sebelas Maret Surakarta. Pemukiman merupakan lingkungan hunian dengan fungsi utama sebagai tempat tinggal yang dilengkapi dengan prasarana dan sarana lingkungan dan tempat kerja yang mendukung peri kehidupan dan penghidupan sehingga fungsi-fungsi perumahan dapat berdayaguna dan berhasil guna. Karena habisnya lahan yang ada maka pemerintah mencanangkan program pembangunan rusunawa yang bisa menampung banyak keluarga dengan lahan yang sedikit. Perubahan dari kampung ke rumah susun ini mengalami perubahan fisik lingkungan, ekonomi dan juga sosial. Tujuan dari penelitian ini adalah untuk mengetahui bentuk dari strategi adaptasi yang dilakukan masyarakat terhadap lingkungan baru mereka serta selanjutnya untuk mengetahui perubahan apa saja yang terjadi pada para penghuni rusunawa. Penelitian ini menggunakan jenis penelitian kualitatif dengan metode studi kasus. Teknik pengambilan yang digunakan adalah Purposive Sampling. Teknik pengumpulan data dilakukan dengan observasi lapangan, wawancara dan dokumentasi. Teknik analisis data dimulai dari tahap pengumpulan data, reduksi data, penyajian data hingga penarikan kesimpulan, serta untuk validitas data menggunakan triangulasi data. Hasil penelitian menunjukan bahwa masyarakat penghuni melakukan berbagai cara untuk beradaptasi dengan hunian baru mereka dan bentuknya antar rusunawa ada yang berbeda ada pula yang sama. Tinggal di rusunawa sangat efektif dan membawa dampak dari segi lingkungan, ekonomi, dan sosial. Kecenderungan ke arah perubahan kualitas hidup yang lebih baik dari pada tinggal pada hunian sebelumnya. Penerapan kriteria kenyamanan tinggal memberian manfaat peningkatan kualitas hidup pada tingkat sejahtera. Perubahan yang paling banyak menimpa adalah perubahan fisik yang sangat berbeda dengan hunian mereka yang dulu berada di kampung horisontal. Untuk perubahan sosial masih terasa sama walaupun ada perbedaan tempat dan ekonomi hanya untuk sebagian orang saja. Akan tetapi tinggal di rusunawa bukan tanpa masalah, masalah – masalah tetap saja ada karena pembangunannya yang kurang melibatkan masyarakat. Bisa dikatakan rusunawa Kota Solo masih jauh dari kata sempurna yang sudah membantu masyarakat miskin. Sehingga dari sana dapat di gambarkan bagaimana efektifitas rumah susun sebagai strategi hunian baru di perkotaan yang bisa menjadi solusi hunian yang murah dan merakyat di Kota Solo. Kata Kunci: Perubahan Sosial, Rusunawa, Hunian bar

Thermodynamic vs kinetic control of particle assembly and pattern replication

This research aims to investigate how particles assemble together through thermodynamic and kinetic control. Particle assembly with thermodynamic control is achieved in part due to electrostatic attraction between particles. Electrostatic attraction between particles can be achieved by functionalizing polystyrene or SiO2 particles with different charges. Particles with different charges will come together in solution slowly and self-assemble to form ordered crystals with different patterns based on size and charge ratios of two oppositely charged particles. Kinetic control of particle assembly is achieved by pattern aided exponential amplification of nanoscale structures. Some of these nanoscale structures are difficult to build with other conventional synthetic methods. On the other hand, as for kinetically controlled particle replication, the patterns can be synthesized by one of two ways i) crystal products which are produced by thermodynamically controlled particle assembly or ii) single particle deposition. Specifically, kinetically controlled particle assembly focuses on constructing SiO2 particles. Exponential replication of SiO2 particles is achieved by growing a bridge layer , between templates of SiO2 particles and next generation SiO2 replicas. By dissolving the bridge layer, two times the amount of the SiO2 particles with the shape of the original templates can be formed. In the next generation, all the particles serve as template particles. Thus, after n cycles of replication, 2n amount of products can be formed. If successful, particle assembly can be thermodynamic controlled and particle exponential replication can be kinetical controlled, which will enable new ways to build particles with well-defined shapes from readily available building blocks

DNA sensing by electrocatalysis with hemoglobin

Electrocatalysis offers a means of electrochemical signal amplification, yet in DNA-based sensors, electrocatalysis has required high-density DNA films and strict assembly and passivation conditions. Here, we describe the use of hemoglobin as a robust and effective electron sink for electrocatalysis in DNA sensing on low-density DNA films. Protein shielding of the heme redox center minimizes direct reduction at the electrode surface and permits assays on low-density DNA films. Electrocatalysis with methylene blue that is covalently tethered to the DNA by a flexible alkyl chain linkage allows for efficient interactions with both the base stack and hemoglobin. Consistent suppression of the redox signal upon incorporation of a single cytosine-adenine (CA) mismatch in the DNA oligomer demonstrates that both the unamplified and the electrocatalytically amplified redox signals are generated through DNA-mediated charge transport. Electrocatalysis with hemoglobin is robust: It is stable to pH and temperature variations. The utility and applicability of electrocatalysis with hemoglobin is demonstrated through restriction enzyme detection, and an enhancement in sensitivity permits femtomole DNA sampling

Microbial electrocatalysis with Geobacter sulfurreducens biofilm on stainless steel cathodes

Stainless steel and graphite electrodes were individually addressed and polarized at−0.60V vs. Ag/AgCl in reactors filled with a growth medium that contained 25mM fumarate as the electron acceptor and no electron donor, in order to force the microbial cells to use the electrode as electron source. When the reactor was inoculated with Geobacter sulfurreducens, the current increased and stabilized at average values around 0.75Am−2 for graphite and 20.5Am−2 for stainless steel. Cyclic voltammetry performed at the end of the experiment indicated that the reduction started at around −0.30V vs. Ag/AgCl on stainless steel. Removing the biofilm formed on the electrode surface made the current totally disappear, confirming that the G.sulfurreducens biofilm was fully responsible for the electrocatalysis of fumarate reduction. Similar current densities were recorded when the electrodes were polarized after being kept in open circuit for several days. The reasons for the bacteria presence and survival on non-connected stainless steel coupons were discussed. Chronoamperometry experiments performed at different potential values suggested that the biofilm-driven catalysis was controlled by electrochemical kinetics. The high current density obtained, quite close to the redox potential of the fumarate/succinate couple, presents stainless steel as a remarkable material to support biocathodes

Treatment of dairy wastes with a microbial anode formed from garden compost

Garden compost has already been identified as a source of efficient electro-active (EA) biofilms. The work described here consisted of lixiviating the compost and then using the leachate as a microbial source. This procedure gave promising results for the treatment of yogurt waste (YW) in a microbial fuel cell (MFC). Experiments performed in MFC set-ups were compared with electrochemical cells under polarization at +0.1 V versus SCE. Different parameters were tested to optimize the microbial anode. Preliminary acclimation of the compost microbial flora to YW was revealed to be unnecessary. Forming biofilms firstly in pure leachate before exposing them to YW showed that high concentrations of this type of substrate were detrimental to current generation. Pre-treatment of the electrode by pre-adsorbing YW led to a 10-fold increase in the current density. The highest current densities were obtained at 40 and 60 °C, revealing the diversity of electro-active microorganisms coming from soils. Values up to 1,450 mA m−2 were reached at 40 °C