Efficient Solar-Thermal Distillation Desalination Device by Light Absorptive Carbon Composite Porous Foam.

Solar-thermal driven desalination based on porous carbon materials has promise for fresh water production. Exploration of high-efficiency solar desalination devices has not solved issues for practical application, namely complicated fabrication, cost-effectiveness, and scalability. Here, direct solar-thermal carbon distillation (DS-CD) tubular devices are introduced that have a facile fabrication process, are scalable, and use an inexpensive but efficient microporous graphite foam coated with carbon nanoparticle and superhydrophobic materials. The "black" composite foam serving as a solar light absorber heats up salt water effectively to produce fresh water vapor, and the superhydrophobic surface of the foam traps the liquid feed in the device. Two proof-of-principle distillation systems are adopted, i.e., solar still and membrane distillation and the fabricated devices are evaluated for direct solar desalination efficiency. For the solar still, nanoparticle and fluorosilane coatings on the porous surface increase the solar energy absorbance, resulting in a solar-steam generation efficiency of 64% from simulated seawater at 1 sun. The membrane distillation demonstrates excellent vapor production (≈6.6 kg m-2 h-1) with >99.5% salt rejection under simulated 3 sun solar-thermal irradiation. Unlike traditional solar desalination, the adaptable DS-CD can easily be scaled up to larger systems such as high-temperature tubular modules, presenting a promising solution for solar-energy-driven desalination.

Surface-Engineered Inorganic Nanoporous Membranes for Vapor and Pervaporative Separations of Water⁻Ethanol Mixtures.

Surface wettability-tailored porous ceramic/metallic membranes (in the tubular and planar disc form) were prepared and studied for both vapor-phase separation and liquid pervaporative separations of water-ethanol mixtures. Superhydrophobic nanoceramic membranes demonstrated more selective permeation of ethanol (relative to water) by cross-flow pervaporation of liquid ethanol⁻water mixture (10 wt % ethanol feed at 80 °C). In addition, both superhydrophilic and superhydrophobic membranes were tested for the vapor-phase separations of water⁻ethanol mixtures. Porous inorganic membranes having relatively large nanopores (up to 8-nm) demonstrated good separation selectivity with higher permeation flux through a non-molecular-sieving mechanism. Due to surface-enhanced separation selectivity, larger nanopore-sized membranes (~5⁻100 nm) can be employed for both pervaporation and vapor phase separations to obtain higher selectivity (e.g., permselectivity for ethanol of 13.9 during pervaporation and a vapor phase separation factor of 1.6), with higher flux due to larger nanopores than the traditional size-exclusion membranes (e.g., inorganic zeolite-based membranes having sub-nanometer pores). The prepared superhydrophobic porous inorganic membranes in this work showed good thermal stability (i.e., the large contact angle remains the same after 300 °C for 4 h) and chemical stability to ethanol, while the silica-textured superhydrophilic surfaced membranes can tolerate even higher temperatures. These surface-engineered metallic/ceramic nanoporous membranes should have better high-temperature tolerance for hot vapor processing than those reported for polymeric membranes.

Electric-Field-Oriented Growth of Long Hair-Like Silica Microfibrils and Derived Functional Monolithic Solids.

BACKGROUND: Controlled self-assembly using molecules/nanoparticles as building block materials represents an important approach for nanofabrication. METHOD: We present a "bottom-up" fabrication approach to first grow a new class of inorganic (silica) long hair-like microfibrils or microwires and then to form monolithic solid pellet that contains parallel arrays of bundled microfibrils with a controlled orientation. During the sol-gel solution processing, reactive precursor species are utilized as molecular "building blocks" for the field-directed assembly growth of microfibrils driven by an electric field of pulsed direct current (dc) with controlled frequency. RESULTS: We have demonstrated a novel reactive electrofibrilation process that combines an external field with a solid-phase nucleation and growth process which in principle has no limitation on the type of reactions (such as the one here that involves sol-gel reaction chemistry) and on materials compositions (such as the example silica oxide), thus will enable bulk production of long microfibrils of wide variety of inorganic materials (other oxides or metals). Furthermore, we have fabricated uniquely architectured monolithic solid materials containing aligned microfibrils by "wet press" of the in-situ grown microfibril structure in the electric field. The consolidated monolithic slabs (1 cm × 1 cm × 3 mm) have shown anisotropic properties and desirable retention of DNA molecule fragments, thus, could serve as a platform stationary-phase materials for future development of capillary electrochromatography for biomolecule separations. CONCLUSION: Electrical field-guided self-assembly is an effective approach in producing long (hair-like) ceramic microfibrils, which can be further used in consolidation fabrication of oriented structured ceramic monoliths with potential for capillary electrophoretic chromatography and other separations applications. This original work was recorded through a patent application to understand the fibril formation mechanism and its process.

Semiconductor Nanocrystal Quantum Dot Synthesis Approaches Towards Large-Scale Industrial Production for Energy Applications.

This paper reviews the experimental synthesis and engineering developments that focused on various green approaches and large-scale process production routes for quantum dots. Fundamental process engineering principles were illustrated. In relation to the small-scale hot injection method, our discussions focus on the non-injection route that could be scaled up with engineering stir-tank reactors. In addition, applications that demand to utilize quantum dots as "commodity" chemicals are discussed, including solar cells and solid-state lightings.

Scalable economic extracellular synthesis of CdS nanostructured particles by a non-pathogenic thermophile.

We report microbially facilitated synthesis of cadmium sulfide (CdS) nanostructured particles (NP) using anaerobic, metal-reducing Thermoanaerobacter sp. The extracellular CdS crystallites were <10 nm in size with yields of ~3 g/L of growth medium/month with demonstrated reproducibility and scalability up to 24 L. During synthesis, Thermoanaerobacter cultures reduced thiosulfate and sulfite salts to H2S, which reacted with Cd²âº cations to produce thermodynamically favored NP in a single step at 65 °C with catalytic nucleation on the cell surfaces. Photoluminescence (PL) analysis of dry CdS NP revealed an exciton-dominated PL peak at 440 nm, having a narrow full width at half maximum of 10 nm. A PL spectrum of CdS NP produced by dissimilatory sulfur reducing bacteria was dominated by features associated with radiative exciton relaxation at the surface. High reproducibility of CdS NP PL features important for scale-up conditions was confirmed from test tubes to 24 L batches at a small fraction of the manufacturing cost associated with conventional inorganic NP production processes.

Semiconductor-nanocrystals-based white light-emitting diodes.

In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white light-emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.

Size-dependent temperature effects on PbSe nanocrystals.

An investigation show that the temperature-induced band gap (E(g)) variation of PbSe nanocrystals is strongly size-dependent. The temperature coefficients (dE(g)/dT) evolve from negative to zero and then to positive values, with the increase of PbSe nanocrystal sizes. Such phenomena imply that PbSe nanocrystals may be the potential candidate as sensitive temperature markers. Additional analyses disclose that the molar extinction coefficients of PbSe nanocrystals remain unchanged in the investigated temperature range (25-120 degrees C).

STEM characterization on silica nanowires with new mesopore structures by space-confined self-assembly within nano-scale channels.

"Critical" channel diameters were found (below which space confinement takes effect, leading to more uniform and ordered mesopore structures) in the study of evaporation-induced co-assembly of triblock-copolymer (P123) and silica molecular precursors (TEOS, tetraethyl orthosilicate) by employing channels in anodized aluminum oxide (AAO, 13-200 nm channel diameter) and in track-etched polycarbonate (EPC, 10-80 nm channel diameter) and for the first time we have observed a new mesopore structure (i.e., packed hollow spheres) in silica nanowires formed in AAO channels with diameters from 30 to 80 nm.

Grain growth in nanocrystalline yttrium-stabilized zirconia thin films synthesized by spin coating of polymeric precursors.

This article reports results of experimental studies on the microstructural evolution of nanocrystalline yttrium-stabilized zirconia thin films synthesized on a Si substrate via a polymeric precursor spin-coating approach. Grain growth behavior has been investigated at different annealing temperatures (700-1200 degrees C) for periods of up to 240 h. A similar film thickness (approximately 120 nm) was maintained for all of the samples used in this study, to avoid variation in film thickness-dependent grain growth. The effects of the thermal history of the film and the annealing atmosphere on the grain growth were also studied. A simple semiempirical grain growth model has been developed to describe isothermal annealing data and to predict dynamic grain growth behavior during the sintering of polymeric precursor layers to form cubic-phase nanocrystalline yttrium-stabilized zirconia films.

Transport properties of nanosystems: viscosity of nanofluids confined in slit nanopores.

A fundamental nonequilibrium statistical mechanical approach due to Pozhar and Gubbins (PG) is used to study the Poiseuille flow and momentum transport in 20 model nanofluids confined in slit pores several molecular diameters in width. A simplified version of a general expression for the PG theoretical viscosity is applied to calculate the localized viscosity of the nanofluids in terms of the equilibrium structure factors (density and correlation functions) of nanosystems. These structure factors are calculated by means of the equilibrium molecular dynamics simulations. The localized theoretical viscosity so obtained is used further to calculate the theoretical pore-average viscosity of the nanosystems, and the latter is successfully compared with that extracted from nonequilibrium molecular dynamics simulation data. A simple correlation between the pore-average velocity, viscosity, nanofluid density, and the pore width for nanosystems of moderate density has been developed and recommended for applications in engineering.