K. Y. Simon Ng

Effect of nutrients on growth and lipid accumulation in the green algae Dunaliella tertiolecta

Production of biofuel from algae is dependent on the microalgal biomass production rate and lipid content. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a key role. In this research, the marine microalgae Dunaliella tertiolecta was used as a model organism and a profile of its nutritional requirements was determined. Inorganic phosphate PO4(3-) and trace elements: cobalt (Co2+), iron (Fe3+), molybdenum (Mo2+) and manganese (Mn2+) were identified as required for algae optimum growth. Inorganic nitrogen in the form of nitrate NO3- instead of ammonium (NH4+) was required for maximal biomass production. Lipids accumulated under nitrogen starvation growth condition and this was time-dependent. Results of this research can be applied to maximize production of microalgal lipids in optimally designed photobioreactors.

Influence of silicone surface roughness and hydrophobicity on adhesion and colonization of Staphylococcus epidermidis

Bacterial adhesion and colonization are complicated processes that depend on many factors, including surface chemistry, hydrophobicity, and surface roughness. The contribution of each of these factors has not been fully elucidated because most previous studies used different polymeric surfaces to achieve differences in properties. The objective of this study was to modify hydrophobicity and roughness on one polymeric surface, eliminating the confounding contribution of surface chemistry. Mechanically assembled monolayer (MAM) preparation methods (both one- and two-dimensional) were used to impart different degrees of hydrophobicity on fluoroalkylsilane (FAS)-coated silicone. Surface roughness was varied by casting the silicone to templates prepared with different abrasives. Surface hydrophobicity was determined by contact angle measurement, whereas surface roughness was determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Bacterial adhesion and colonization were analyzed using a direct colony-counting method and SEM images. Hydrophobicity increased as a function of stretched length or width (Deltax or Deltay); it reached a maximum at Deltax = 60% with one-dimensional MAM and decreased as Deltax further increased to 80 and 100%. The same trend was observed for the two-dimensional MAM. After 12-h incubation, all the FAS/silicone surfaces had significantly reduced adherence of Staphylococcus epidermidis by 42-89%, compared to untreated silicone, and the degree of which is inversely related to surface hydrophobicity. On the other hand, surface roughness had a significant effect on bacterial adhesion and colonization only when the root-mean-square roughness was higher than 200 nm.

Culture of microalgae Chlorella minutissima for biodiesel feedstock production

Microalgae are among the most promising of non‐food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light‐emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two‐phase strategy with an initial nutrient‐sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production. Biotechnol. Bioeng. 2011;108: 2280–2287.

Continuous microalgae cultivation in a photobioreactor

New biomass sources for alternative fuels has become a subject of increasing importance as the nation strives to resolve the economic and strategic impacts of limited fossil fuel resources on our national security, environment, and global climate. Algae are among the most promising non‐food‐crop‐based biomass feedstocks. However, there are currently no commercially viable microalgae‐based production systems for biofuel production that have been developed, as limitations include less‐than optimal oil content, growth rates, and cultivation techniques. While batch studies are critical for determining basic growth phases and characteristics of the algal species, steady‐state studies are necessary to better understand and measure the specific growth parameters. This study evaluated the effects of dilution rate on microalgal biomass productivity, lipid content, and fatty acid profile under steady‐state conditions with continuous illumination and carbon dioxide supplemention for two types of algae. Continuous cultures were conducted for more that 3 months. Our results show that the productivity of Chlorella minutissima varied from 39 to 137 mg/L/day (dry mass) when the dilution rate varied from 0.08 to 0.64 day−1. The biomass productivity of C. minutissima reached a maximum value (137 mg/L/day) at a dilution rate of 0.33 day−1, while the productivity of Dunaliella tertiolecta varied from 46 to 91 mg/L/day at a dilution rate of 0.17 to 0.74 day−1. The biomass productivity of D. tertiolecta reached a maximum value of 91 mg/L/day at a dilution rate of 0.42 day−1. Moreover, the lipid content had no significant change with various dilution rates. Biotechnol. Bioeng. 2012; 109: 2468–2474.

Electrocatalysis of lithium polysulfides: current collectors as electrodes in li/s battery configuration

Lithium Sulfur (Li/S) chemistries are amongst the most promising next-generation battery technologies due to their high theoretical energy density. However, the detrimental effects of their intermediate byproducts, polysulfides (PS), have to be resolved to realize these theoretical performance limits. Confined approaches on using porous carbons to entrap PS have yielded limited success. In this study, we deviate from the prevalent approach by introducing catalysis concept in Li/S battery configuration. Engineered current collectors were found to be catalytically active towards PS, thereby eliminating the need for carbon matrix and their processing obligatory binders, additives and solvents. We reveal substantial enhancement in electrochemical performance and corroborate our findings using a detailed experimental parametric study involving variation of several kinetic parameters such as surface area, temperature, current rate and concentration of PS. The resultant novel battery configuration delivered a discharge capacity of 700 mAh g−1 with the two dimensional (2D) planar Ni current collectors and an enhancement in the capacity up to 900 mAh g−1 has been realized using the engineered three dimensional (3D) current collectors. The battery capacity has been tested for stability over 100 cycles of charge-discharge.

Studies of the oxygen release reaction in the platinum-ceria-zirconia system

Abstract The relative rates of the CO+oxygen storage material (OSM)⇒CO2 reaction (RCO2) and the amounts of rate enhancement obtained upon Pt promotion were examined for ceria and ceria–zirconia OSM. The effect of Pt surface area on RCO2 was de-coupled from metal–oxide surface area by pre-sintering the oxides prior to Pt deposition. We find that RCO2 is linearly dependent on Pt area over Pt/CeO2, but over Pt/Ce0.75Zr0.25O2, the rate is independent of Pt surface area above a threshold surface area. Although Pt sinters more readily on the Ce0.75Zr0.25O2 support, the dispersion effect is more than compensated by the enhanced availability of “bulk” O2− within the Ce0.75Zr0.25O2 particles. Furthermore, this study demonstrates that, on a unit surface area basis, the ceria–zirconia support is at least two times more active for the oxygen release reaction than the pure ceria support when the materials are slightly reduced. It is also shown that O2− diffusion is not rate-limiting for the ceria reduction reaction when the reaction is carried out in the kinetically limited regime at 500°C with CO as the reductant.

Active sites of H-ZSM5 catalysts for the oxidation of nitric oxide by oxygen

The catalytic activities of H-ZSM5-18, H-ZSM5-150, Li-ZSM5-18, and H-Mag (numerical suffixes mark the Si/Al ratios of zeolites, H-Mag is the proton exchanged form of the layered sodium silicate, magadiite) were compared for the oxidation of NO by O2 at different ratios of reactants at reaction temperatures from 25 to 600°C. H-ZSM5-18 typically has activity maxima near 25 and 400°C at most O2/NO reactant ratios. Regardless of the partial pressures of reactants, NO±1/2O2 ⇋ NO2 equilibria are attained at 400°C and above. The H-ZSM5-150 and Li-ZSM5-18 zeolites are only active at temperatures near 25°C. H-Mag is practically inactive at the reaction conditions used. Results indicate that Lewis acidic lattice aluminium ions and silanol hydroxyls are not active in the oxidation of NO to NO2 over H-ZSM5 zeolites. Brønsted acidic bridging hydroxyls are probably active sites for this reaction at temperatures above 200°C.

Electro-synthesis of 3D porous hierarchical Ni–Fe phosphate film/Ni foam as a high-efficiency bifunctional electrocatalyst for overall water splitting

A highly efficient bifunctional electrocatalyst of nickel–iron phosphates for hydrogen and oxygen evolution reactions (HER and OER) was designed and prepared via a simple electrodeposition method. The as-obtained catalyst presents remarkable catalytic activities for both the HER and OER, which requires overpotentials of 87 mV to reach −10 mA cm−2 for the HER and 204 mV to generate 20 mA cm−2 for the OER in 1 M KOH. Employed as both the anode and cathode for full water splitting, the electrodeposited catalyst also exhibits excellent activity, which requires an overpotential of only 326 mV to attain 10 mA cm−2 and yields a faradic efficiency close to 100%.

Performance of heterogeneous ZrO2 supported metaloxide catalysts for brown grease esterification and sulfur removal

In order to achieve a viable biodiesel industry, new catalyst technology is needed which can process a variety of less expensive waste oils, such as yellow grease and brown grease. However, for these catalysts to be effective for biodiesel production using these feedstocks, they must be able to tolerate higher concentrations of free fatty acids (FFA), water, and sulfur. We have developed a class of zirconia supported metaloxide catalysts that achieve high FAME yields through esterification of FFAs while simultaneously performing desulfurization and de-metallization functions. In fact, methanolysis, with the zirconia supported catalysts, was more effective for desulfurization than an acid washing process. In addition, using zirconia supported catalysts to convert waste grease, high in sulfur content, resulted in a FAME product that could meet the in-use ASTM diesel fuel sulfur specification (<500 ppm). Possible mechanisms of desulfurization and de-metallization by methanolysis were proposed to explain this activity.

Hollow Cocoon-Like Hematite Mesoparticles of Nanoparticle Aggregates: Structural Evolution and Superior Performances in Lithium Ion Batteries

We report the facile, fast, and template-free preparation of hollow α-Fe2O3 with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe2O3 nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge-discharge cycles. The unusual structural stability of the hollow α-Fe2O3 nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage.