Tailoring Chemical Absorption-Precipitation to Lower the Regeneration Energy of a CO2 Capture Solvent

Solvent-based CO2 capture consumes significant amounts of energy for solvent regeneration. To improve energy efficiency, this study investigates CO2 fixation in a solid form through solvation, followed by ionic self-assembly-aided precipitation. Based on the hypothesis that CO3 2- ions may bind with monovalent metal ions, we introduced Na+ into an aqueous hexane-1,6-diamine solution where CO2 forms carbamate and bicarbonate. Then, Na+ ions in the solvent act as a seed for ionic self-assembly with diamine carbamate to form an intermediate ionic complex. The recurring chemical reactions lead to the formation of an ionic solid from a mixture of organic carbamate/carbonate and inorganic sodium bicarbonate (NaHCO3 ), which can be easily removed from the aqueous solvent through sedimentation or centrifugation and heated to release the captured CO2 . Mild-temperature heating of the solids at 80-150 °C causes decomposition of the solid CO2 -diamine-Na molecular aggregates and discharge of CO2 . This sorbent regeneration process requires 6.5-8.6 GJ/t CO2 . It was also found that the organic carbamate/carbonate solid, without NaHCO3 , contains a significant amount of CO2 , up to 6.2 mmol CO2 /g-sorbent, requiring as low as 2.9-5.8 GJ/t CO2 . Molecular dynamic simulations support the hypothesis of using Na+ to form relatively less stable, yet sufficiently solid, complexes for the least energy-intensive recovery of diamine solvents compared to bivalent carbonate-forming ions.

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.

Transparent superhydrophilic and superhydrophobic nanoparticle textured coatings: comparative study of anti-soiling performance

The anti-soiling (AS) performance of highly reflective, superhydrophilic (SPH, 0° water contact angle) coated mirrors was characterized and compared with that of superhydrophobic (SP, >165° water contact angle) coated mirrors. A simple one-step nanotextured silica nanoparticle coating on a mirror exhibited SPH properties associated with hydrophilic rough surfaces. Another mirror surface post-functionalized with low-surface-energy ligand molecules displayed SP behavior. Both coated mirrors, with no solar reflectance loss, demonstrated excellent AS performance because the engineered surface roughness reduced the adhesive force of dust particles. The daily degradation in solar reflectance induced by dust accumulation under outdoor field testing demonstrated that the SPH- and SP-coated mirrors, compared with an uncoated mirror, maintained higher solar reflectance, which was associated with the designed self-cleaning behavior and natural cleaning. However, over the long term, dust-moisture cementation-evidenced by organic hard water stains on the mirror-initiated unrecoverable reflectance loss on the SP-coated mirror after 3 months, whereas the SPH-coated mirror maintained higher reflectance for 7.5 months. Considering fabrication costs and maintenance, SPH-coated nanotextured mirrors offer potential benefits for application in solar energy harvesting.

Improved ZnS nanoparticle properties through sequential NanoFermentation

Sequential NanoFermentation (SNF) is a novel process which entails sparging microbially produced gas containing H₂S from a primary reactor through a concentrated metal-acetate solution contained in a secondary reactor, thereby precipitating metallic sulfide nanoparticles (e.g., ZnS, CuS, or SnS). SNF holds an advantage over single reactor nanoparticle synthesis strategies, because it avoids exposing the microorganisms to high concentrations of toxic metal and sulfide ions. Also, by segregating the nanoparticle products from biological materials, SNF avoids coating nanoparticles with bioproducts that alter their desired properties. Herein, we report the properties of ZnS nanoparticles formed from SNF as compared with ones produced directly in a primary reactor (i.e., conventional NanoFermentation, or "CNF"), commercially available ZnS, and ZnS chemically synthesized by bubbling H₂S gas through a Zn-acetate solution. The ZnS nanoparticles produced by SNF provided improved optical properties due to their smaller crystallite size, smaller overall particle sizes, reduced biotic surface coatings, and reduced structural defects. SNF still maintained the advantages of NanoFermentation technology over chemical synthesis including scalability, reproducibility, and lower hazardous waste burden.

The anti-soiling performance of highly reflective superhydrophobic nanoparticle-textured mirrors

The anti-soiling (AS) performance of solar mirrors coated with a highly transparent, superhydrophobic nanoparticle-textured coating has been characterized. The AS coatings were created on the mirror surface by depositing nano-textured silica nanoparticle layers of ∼250 nm thickness using a draw-down coating process, followed by fluorination of the nanoparticles in a molecular vapor deposition process. Highly uniform surface features of the AS-coated mirrors (20 × 30 cm2, no measurable loss in specular reflectance, and water contact angle >165°) provided an outstanding AS performance. A 4× reduction in the rate of dust accumulation as determined by gravimetric measurement of the accumulated dust on coated versus uncoated mirrors was observed. Additional evidence of a significant reduction in soiling rate was determined during measurements of specular reflectance in an outdoor environment test. The adhesion force between a model sand particle and nano-textured coatings in the hydrophobic to superhydrophobic range was also studied. A dramatic decrease in adhesive force acting on the particle was observed with increasing surface hydrophobicity. The results align well with the observed dust accumulation on the AS-coated mirrors. The AS-coated mirror maintains a high reflectivity by shedding dust and resisting dust accumulation, providing a potential benefit when applied to mirrors in the solar field of a concentrated solar power generation plant.

Scalable production of microbially mediated zinc sulfide nanoparticles and application to functional thin films

A series of semiconducting zinc sulfide (ZnS) nanoparticles were scalably, reproducibly, controllably and economically synthesized with anaerobic metal-reducing Thermoanaerobacter species. These bacteria reduced partially oxidized sulfur sources to sulfides that extracellularly and thermodynamically incorporated with zinc ions to produce sparingly soluble ZnS nanoparticles with ∼5nm crystallites at yields of ∼5gl(-1)month(-1). A predominant sphalerite formation was facilitated by rapid precipitation kinetics, a low cation/anion ratio and a higher zinc concentration compared to background to produce a naturally occurring hexagonal form at the low temperature, and/or water adsorption in aqueous conditions. The sphalerite ZnS nanoparticles exhibited narrow size distribution, high emission intensity and few native defects. Scale-up and emission tunability using copper doping were confirmed spectroscopically. Surface characterization was determined using Fourier transform infrared and X-ray photoelectron spectroscopies, which confirmed amino acid as proteins and bacterial fermentation end products not only maintaining a nano-dimensional average crystallite size, but also increasing aggregation. The application of ZnS nanoparticle ink to a functional thin film was successfully tested for potential future applications.

Rate-limited electroless gold thin film growth: a real-time study

Time-resolved, in situ spectroscopy of electroless (EL) gold (Au) films combined with electron microscopy showed that the deposition rate increased up to two-fold on surfaces swept by the bulk flow of adjacent fluid at Reynolds numbers less than 1.0, compared to batch immersion. Deposition rates from 5.0 to 9.0 nm/min and thicknesses of the EL Au film from 20 to 100 nm, respectively, increased predictably with flow rate at conditions when the deposition was limited primarily by Fickian diffusion. Time-frames were identified for metal island nucleation, growth, and subsequent film development during EL Au deposition by real-time UV-visible spectroscopy of photoluminescence (PL) and surface plasmon features of nanoscale metal deposits. Film thicknesses measured by scanning electron microscopy and X-ray photoelectron spectroscopy paired with real-time optical spectroscopy of kinetic aspects of plasmon and PL optical features indicated that Au film deposition on surfaces swept by a steady flow of adjacent fluid can be primarily diffusion limited.