Dev Chidambaram

Concomitant microbial generation of palladium nanoparticles and hydrogen to immobilize chromate

The catalytic properties of various metal nanoparticles have led to their use in environmental remediation. Our aim is to develop and apply an efficient bioremediation method based on in situ biosynthesis of bio-Pd nanoparticles and hydrogen. C. pasteurianum BC1 was used to reduce Pd(II) ions to form Pd nanoparticles (bio-Pd) that primarily precipitated on the cell wall and in the cytoplasm. C. pasteurianum BC1 cells, loaded with bio-Pd nanoparticle in the presence of glucose, were subsequently used to fermentatively produce hydrogen and to effectively catalyze the removal of soluble Cr(VI) via reductive transformation to insoluble Cr(III) species. Batch and aquifer microcosm experiments using C. pasteurianum BC1 cells loaded with bio-Pd showed efficient reductive Cr(VI) removal, while in control experiments with killed or viable but Pd-free bacterial cultures no reductive Cr(VI) removal was observed. Our results suggest a novel process where the in situ microbial production of hydrogen is directly coupled to the catalytic bio-Pd mediated reduction of chromate. This process offers significant advantages over the current groundwater treatment technologies that rely on introducing preformed catalytic nanoparticles into groundwater treatment zones and the costly addition of molecular hydrogen to above ground pump and treat systems.

Virus Removal by Biogenic Cerium

The rare earth element cerium has been known to exert antifungal and antibacterial properties in the oxidation states +III and +IV. This study reports on an innovative strategy for virus removal in drinking water by the combination of Ce(III) on a bacterial carrier matrix. The biogenic cerium (bio-Ce) was produced by addition of aqueous Ce(III) to actively growing cultures of either freshwater manganese-oxidizing bacteria (MOB) Leptothrix discophora or Pseudomonas putida MnB29. X-ray absorption spectroscopy results indicated that Ce remained in its trivalent state on the bacterial surface. The spectra were consistent with Ce(III) ions associated with the phosphoryl groups of the bacterial cell wall. In disinfection assays using a bacteriophage as model, it was demonstrated that bio-Ce exhibited antiviral properties. A 4.4 log decrease of the phage was observed after 2 h of contact with 50 mg L(-1) bio-Ce. Given the fact that virus removal with 50 mg L(-1) Ce(III) as CeNO(3) was lower, the presence of the bacterial carrier matrix in bio-Ce significantly enhanced virus removal.

Application of ZnxCd1−xSe-sensitized TiO2 nanotube arrays as photoanodes for solar cells

This study reports the synthesis of ZnxCd1−xSe quantum dot-sensitized titania nanotube array photoelectrodes using a successive ionic layer adsorption and reaction technique and evaluates the photoelectrochemical performance as anodes. The effect of altering the number of sensitization cycles and annealing temperature on optical and photoelectrochemical properties of prepared photoanodes was studied. Surface morphology of the sensitized tubes was analyzed by scanning electron microscopy, while the phase composition was determined using X-ray diffraction and X-ray photoelectron spectroscopy techniques. Spectral response measurements indicated that TiO2 nanotube arrays coupled with ZnxCd1−xSe quantum dots synthesized in 7 cycles of deposition and annealed at 300 °C for 1 h under N2 exhibited excellent photoelectrochemical properties. The notably high photovoltaic characteristics demonstrate the potential of the ZnxCd1−xSe/TiO2 heterostructure as an efficient photoanode.

Ni-Ci oxygen evolution catalyst integrated BiVO4 photoanodes for solar induced water oxidation

A nickel-based oxygen evolution catalyst, nickel-bicarbonate (Ni-Ci), was electrochemically deposited for varying intervals on the surface of W-doped BiVO4 in a 0.1 M bicarbonate electrolyte at neutral pH conditions. Optimally deposited Ni-Ci successfully catalyzed the photoelectrochemical water oxidation of W-doped BiVO4 photoelectrodes under benign pH conditions as evidenced by an enhanced photocurrent during photocurrent–potential characterizations. Efficient charge-transfer at the electrode–electrolyte interface in the presence of the Ni-Ci catalyst improved the kinetics of the W-doped BiVO4 photoanodes. The W-doped BiVO4 photoanodes integrated with a Ni-Ci oxygen evolution catalyst exhibited a large cathodic shift (∼371 mV) in the onset potential for water oxidation and maintained a stable photocurrent.

Presence of Li Clusters in Molten LiCl-Li

Molten mixtures of lithium chloride and metallic lithium are of significant interest in various metal oxide reduction processes. These solutions have been reported to exhibit seemingly anomalous physical characteristics that lack a comprehensive explanation. In the current work, the physical chemistry of molten solutions of lithium chloride and metallic lithium, with and without lithium oxide, was investigated using in situ Raman spectroscopy. The Raman spectra obtained from these solutions were in agreement with the previously reported spectrum of the lithium cluster, Li8. This observation is indicative of a nanofluid type colloidal suspension of Li8 in a molten salt matrix. It is suggested that the formation and suspension of lithium clusters in lithium chloride is the cause of various phenomena exhibited by these solutions that were previously unexplainable.

Corrosion of INCONEL Alloy 625 in Molten LiCl-Li2O-Li

Abstract INCONEL alloy 625® (I625) was exposed to molten LiCl-Li2O-Li to evaluate the material reliability for applications involving the electrolytic reduction of uranium oxide. Samples of I625 were exposed to solutions of LiCl with 1 and 2 wt% Li2O, containing either 0, 0.5, or 1 wt% metallic lithium for 20 h at 650°C. Additional experiments exposed samples to LiCl saturated with Li2O to investigate the mechanism of interaction between materials and the melt. Postexposure sample surface morphology and chemistry were studied using scanning electron microscopy and X-ray photoelectron spectroscopy. Additionally, inductively coupled plasma–optical emission spectroscopy was used to analyze the melt to determine the alloy constituents that leached out of the coupon during the exposure. The inclusion of 0.5 wt% metallic lithium in the molten solution was found to increase the stability of chromium-rich surface films and suppress the dissolution rate of alloying elements, compared to melts of LiCl-Li2O containing no metallic Li. Alternatively, samples exposed to solutions containing 1 wt% metallic lithium did not form surface films and demonstrated evidence of chromium depletion. The degradation of materials exposed to solutions containing 1 wt% metallic lithium was observed to be different from samples exposed to solutions saturated with lithium oxide, demonstrating a chemical effect other than, or in addition to, salt basicity.

Production of renewable aviation fuel range alkanes from algae oil

Jet fuels produced from sources other than petroleum are receiving considerable attention since they offer the potential to diversify energy supplies while mitigating the net environmental impact of aviation. Here we report a novel single-step catalytic process for the production of jet fuel range alkanes from a renewable oil source, algae oil. The catalyst materials were characterized using scanning electron microscopy, X-ray diffraction, surface area and pore size measurements. The feedstock and the product hydrocarbons were characterized using gas chromatography. We discuss the effect of temperature, pressure, time, catalyst type and quantity on feedstock cracking quality and selectivity. The results show that Ce exchanged zeolite β shows higher selectivity towards C10–C14 hydrocarbons at elevated temperatures and pressures. A high liquid product mass conversion of 98% was obtained at a temperature and reaction pressure of 400 °C and 400 psi, respectively. Selectivity was 85% for cracking algae oil on 4% Ce exchanged zeolite β and thus the catalyst shows promise for the synthesis of aviation range hydrocarbons for future large scale bio-jet fuel production.

Sensitization of TiO2 nanotube array photoelectrodes with MnxCdySe

The photoanode obtained by the deposition of MnxCdySe nanocrystals onto TiO2 nanotube arrays using a successive ionic layer adsorption and reaction technique realized a significant improvement in the charge transport and current generation compared with a pristine TiO2 nanotube based anode. The concentration of manganese was determined to be 10% of the concentration of cadmium, and thus x = 0.1y. The widening of absorption spectra and the magnitude of photocurrent density were found to be significantly affected with a variation in the number of SILAR cycles and the annealing temperature. A stable photocurrent density of ∼8 mA cm−2 under AM 1.5 illumination (1 sun) was achieved for MnxCdySe nanocrystals-embedded TiO2 nanotube arrays heterostructure based photoelectrodes prepared through 9 cycles of SILAR deposition, followed by annealing at 400 °C under a nitrogen atmosphere. The results obtained suggest the versatility of the MnxCdySe-sensitized TiO2 nanotube matrix as an efficient electrode for photovoltaic applications.

Nanotechnology and Microbial Electrochemistry for Environmental Remediation

Introduction: Metal nanoparticles, by virtue of their catalytic properties, have the potential to be exploited for applications in environmental remediation [1]. For instance, numerous studies have explored the use of Fe(0) nanoparticles to remove organic and inorganic contaminants [2]. In the presence of suitable electron donor, these nanomaterials can catalyze the reduction of pollutants. A variety of pollutants such carcinogenic hexavalent chromium, and hexavalent uranium are soluble in their highly oxidized form and become sparingly soluble on reduction (to trivalent chromium and tetravalent uranium in the above case, respectively). Further, several organic compounds such as organic dyes, fertilizers and pharmaceutical compounds and intermediates undergo degradation on reduction. In all these cases, the contamination levels in the subsurface environment and their downstream flow can be significantly controlled and managed. However, these remediation strategies are limited by their ability to deliver catalytic nanoparticles plus a suitable electron donor to large treatment zones.

Photoelectrochemical characterization of dual-layered anodic TiO2 nanotubes with honeycomb morphology

Titanium dioxide (TiO2) nanotubes having a novel honeycomb like morphology were synthesized by a two-step anodization process and characterized for photoelectrochemical behavior. The titania nanotubes with honeycomb morphology showed at least 32% higher photocurrent density than the regular vertically oriented titania nanotubes at any given bias potential. The enhanced photoactivity of the honeycomb morphology was attributed to the better charge transport properties and the presence of a hemispherical surface morphology that enhanced the light harvesting behavior.