John Pellegrino

Selective molecular sieving through porous graphene

Membranes act as selective barriers and play an important role in processes such as cellular compartmentalization and industrial-scale chemical and gas purification. The ideal membrane should be as thin as possible to maximize flux, mechanically robust to prevent fracture, and have well-defined pore sizes to increase selectivity. Graphene is an excellent starting point for developing size-selective membranes because of its atomic thickness, high mechanical strength, relative inertness and impermeability to all standard gases. However, pores that can exclude larger molecules but allow smaller molecules to pass through would have to be introduced into the material. Here, we show that ultraviolet-induced oxidative etching can create pores in micrometre-sized graphene membranes, and the resulting membranes can be used as molecular sieves. A pressurized blister test and mechanical resonance are used to measure the transport of a range of gases (H(2), CO(2), Ar, N(2), CH(4) and SF(6)) through the pores. The experimentally measured leak rate, separation factors and Raman spectrum agree well with models based on effusion through a small number of ångstrom-sized pores.

Membrane filtration of natural organic matter: initial comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes

Two source waters containing natural organic matter (NOM) with different physical and chemical characteristics were crossflow-filtered using four types of membranes having different material and geometric properties. Transport measurements of NOM rejection and flux decline were made. A resistances-in-series model was used to represent and quantitatively compare membrane flux decline and recovery. As anticipated, the resistance due to specific adsorption depended on the concentration at the membrane interface. For the two membranes showing evidence of NOM adsorption, reducing the initial flux (which we infer to also reduce the interfacial NOM concentration) also lowered the measured resistance assigned to adsorption in our protocol. Relative molecular mass (RMM) distribution measurements (by size exclusion chromatography) were used to calculate the average RMM of the NOM and persuasively illustrated that the nominal relative molecular mass cut-off (MWCO) of a membrane is not the unique predictor of rejection characteristics for NOM compounds. Size exclusion, electrostatic repulsion, and NOM aromaticity all influenced the NOM rejection. For a given water composition (including pH and ionic strength), membrane characteristics (such as the surface charge, hydrophobicity and nominal MWCO) can be combined with the NOM properties (such as total dissolved organic carbon, specific UV absorbance at 254 nm and humic content) to provide a consistent qualitative rationale for the transport results.

Characterization of clean and natural organic matter (NOM) fouled NF and UF membranes, and foulants characterization☆

Abstract Contact angles, zeta potentials, and IR spectra of clean and NOM-fouled membranes were compared to demonstrate differences in hydrophobicity, surface charge, and functional groups, respectively. Contact angle increased and decreased for membranes fouled with hydrophobic and hydrophilic NOM, respectively. Zeta potential decreased negatively (less negative) for membranes fouled with both hydrophobic and hydrophilic NOM, suggesting that ionizable functional groups were coated with non-ionizable NOM components (possibly neutrals). The IR spectra reduced in absorbance intensity for NOM-fouled membranes, suggesting that aromatic groups were coated with non-aromatic or less aromatic NOM components. The results of XAD- 8 4 fractionations of foulants (desorbed NOM with NaOH) showed that hydrophilic and hydrophobic NOM components were the major foulants for membranes fouled with hydrophilic and hydrophobic NOM-source waters, respectively.

Membrane filtration of natural organic matter: comparison of flux decline, NOM rejection, and foulants during filtration with three UF membranes

Three ultrafiltration membranes [thin-film composite, polyethersulfone (PES), and sulfonated PES] which have different chemistries and nominal relative molecular mass cut-offs (MWCO), were compared in terms of their characteristics of flux decline, rejection of natural organic matter (NOM), and the adsorbed foulants, with two very different (relatively hydrophilic and hydrophobic) NOM-containing source waters. To facilitate comparison, the ratio (Jok) of the initial pure water flux Jo to the estimated boundary layer mass transfer coefficient k was used to define similar initial hydrodynamic operating conditions for the three different membranes. The membranes showed differences in NOM rejection when filtering hydrophilic NOM-source water, and also exhibited differences in flux decline with the hydrophobic NOM-source water. Flux decline and NOM rejection were quantified using a resistances-in-series model and effective molecular mass cut-off, respectively. Non-charged NOM fractions (hydrophilic and hydrophobic neutrals/bases) were found to be significant foulants for these negatively charged membranes.

Technoeconomic analysis of five microalgae-to-biofuels processes of varying complexity.

The economics surrounding five algae-to-fuels process scenarios were examined. The different processes modeled were as follows: an open pond producing either triacylglycerides (TAG) or free fatty acid methyl ester (FAME), a solar-lit photobioreactor producing either FAME or free fatty acids (FFA), and a light emitting diode irradiated (LED-lighted) photobioreactor producing TAG. These processes were chosen to represent both classical and esoteric approaches presented in the open literature. Viable (or suggested) processing techniques to liberate and purify (and convert) the microalgal triacylglycerides were then modeled to accompany each growth option. The investment and cost per kg of fuel or fuel precursor for each process was determined. The open pond produced TAG at ∼

Incorporating Ionic Liquid Electrolytes into Polymer Gels for Solid-State Ultracapacitors

7.50/kg, while the process using the LED-lit photobioreactor produced TAG at ∼

Bench-scale testing of surfactant-modified reverse osmosis/nanofiltration membranes

33/kg. The scenario containing the solar-lit photobioreactor produced FAME at ∼

Variance of streaming potential measurements

25/kg, while the open pond produced FAME at ∼

The Use of Conducting Polymers in Membrane-Based Separations

4/kg. The scenario containing the solar-lit photobioreactor produced FFA at ∼

Molecular valves for controlling gas phase transport made from discrete ångström-sized pores in graphene

29/kg. The open pond scenarios appear to be closest to the