Hydrophobic Nanoporous Silica Research Articles

A novel additive for enhancing biomass energy production from agro-industrial wastes: synthesis of hydrophobic nanoporous silica aerogel and its effect on methane production

AbstractAnaerobic digestion (AD) is one of the most preferred processes for the treatment of organic waste. However, additional processes such as co-digestion, pretreatment, and additive addition continue to be explored to remove the limits on the applicability of AD. This study investigated the effects of hydrophobic nanoporous silica aerogel (NpSA) synthesized from waste rice husks on the anaerobic co-digestion (AnCD) of the mixture consisting of sewage sludge and fruit processing industry wastes. All bioreactors containing NpSA-free, 0.1 g, 0.2 g, 0.5 g, and 1 g NpSA (0.03–0.3 gNpSA/gVSadded) were operated in a mesophilic-batch process. Biogas and methane yields increased from 346 mL/gVS (NpSA-free) to 387 mL/gVS and from 231 mL/gVS (NpSA-free) to 288 mL/gVS, respectively, with 0.1 g NpSA addition. NpSA additive increased biogas production in all bioreactors compared to the blank. However, biogas production rate and methane content increased faster at lower doses of NpSA. Maximum soluble chemical oxygen demand (sCOD), protein, carbohydrate, and volatile solid (VS) reductions were between 45–71%, 35–54%, 44–65%, and 34–91% for NpSA added mixtures, respectively. The hydrophobic NpSA additive was effective in improving the AnCD performance and biogas/methane production. Experimental results fit the kinetic models frequently preferred in such AD processes. In addition, the possible energy and financial potential of the produced methane were also discussed, and it was determined that the direct sale of methane gas produced by the addition of NpSA in the global market could provide 1.4 $/Lmixture more financial gain than the mixture NpSA-free. Graphical Abstract

Nanopore size effect on critical infiltration depth of liquid nanofoam as a reusable energy absorber

Liquid flow in nano-environment has been utilized as an advanced mechanism of energy absorption. While the process of liquid outflow from nanopores has been shown to have a significant effect on the system’s energy absorption efficiencies, its mechanism remains poorly understood. Here, we have studied the liquid defiltration behavior of liquid nanofoam (LN) systems by controlling the infiltration depth. The LN samples, composed of a different non-wettable liquid phase and hydrophobic nanoporous silica with wide pore size distribution, have been compressed in two different loading modes under the quasi-static condition, i.e., the single-step compression and consecutive-step compression. Considerably different mechanical behaviors have been observed in these two loading modes, suggesting that the liquid outflow from nanopores is determined by the critical infiltration depth D*. The nanopore size effect on D* is further studied by a consecutive-step cyclic test. It has been shown that D* increases as the pore size gets smaller, which is related to gas solubility and diffusion rate in the nano-environment. The electrolyte concentration and temperature dependences of the critical infiltration depth have also been investigated. These findings provide a better understanding of the liquid outflow from nanopores and can be exploited to facilitate the design of next-generation reusable energy absorption systems.

Nanoporous aerogel as a bacteria repelling hygienic material for healthcare environment

Healthcare-associated infections (HAIs) caused by pathogenic bacteria are a worldwide problem and responsible for numerous cases of morbidity and mortality. Exogenous cross-contamination is one of the main mechanisms contributing to such infections. This work investigates the potential of hydrophobically modified nanoporous silica aerogel as an antiadhesive hygienic material that can inhibit exogenous bacterial contamination. Nanoporous silica aerogels were synthesized via sol–gel polymerization of tetraethyl orthosilicate and hydrophobized using trimethylsilyl chloride. Bacterial adhesion characteristics were evaluated via dip-inoculation in suspensions of Gram-negative Escherichia coli O157:H7 and Gram-positive Staphylococcus aureus. The attachment of E. coli O157:H7 and S. aureus to hydrophobic nanoporous silica aerogel (HNSA) was found to be significantly lower than that to hydrophilic and hydrophobic nonporous silica materials: 99.91% (E. coli O157:H7) and 99.93% (S. aureus) reduction in comparison to hydrophilic nonporous silica, and 82.95% (E. coli O157:H7) and 84.90% (S. aureus) reduction in comparison to hydrophobic nonporous silica. These results suggest that the use of HNSA as surfaces that come into contact with bacterial pathogens in the healthcare environment can improve bacterial hygiene, and therefore may reduce the rate of HAIs.

Tissue Phantoms Constructed with Hydrophobic Nanoporous Silica Particles

We describe a protocol to create tissue phantoms with hydrophobic nanoporous particles. The nanopores of the particles are loaded with biological molecules at the desired compositions. Tissue phantoms are prepared by immersing dried particles into aqueous biological matrixes. The hydrophobicity of the pore surface prevents the solution from penetrating into the nanopores, thus preserving the designed molecular composition inside the particles. This protocol provides a unique approach to preparing biological systems in small domains, at micrometer and nanometer dimensions, with well-defined boundaries and tailored biological and optical properties. The nanoporous particle approach is easy when compared to the common preparation methods such as with polymers and vesicles as it involves direct loading of the biological molecules into the pores and does not require complex synthetic steps. The method is adaptable, with tunable pore and particle sizes, and robust, with a rigid boundary to protect the designed biological domain. In addition to tissue phantom preparation, this approach is applicable in systems where a well-defined biological domain is desired.

Effects of the Addition of Electrolyte on Liquid Infiltration in a Hydrophobic Nanoporous Silica Gel

In this letter, we report the experimental results of pressure induced infiltration in the hydrophobic nanopores of a silica gel. The infiltration pressure increases with the prolonged surface treatment time, whereas the infiltration volume is not dependent on the surface coverage. When temperature increases, if the liquid phase is pure water, the infiltration pressure would decrease, which is in agreement with the classic contact angle measurement results at large solid surfaces. As an electrolyte is added, however, the variation in infiltration pressure is negligible over a broad temperature range.

A selectively-energy-absorbing nanoporous system

By forcing an aqueous solution of N-lauroylsarcosine sodium salt and 8-anilino-1-naphthalenesulfonic acid ammonium salt in a hydrophobic nanoporous silica gel, the external work can be largely dissipated due to the amplified capillary effect. The sorption isotherm curve is two-staged, and the height and the width of stage-I infiltration plateau can be adjusted separately by controlling the liquid composition. It provides a scientific basis for developing selective protection and damping liquids.

Suppression effect of liquid composition on defiltration of nanofluids in lyophobic environment

Understanding nanofluidic behaviours in energetically unfavourable confining environments is essential for the development of high-performance nanoporous energy absorption systems. In the current study, the effect of liquid composition on defiltration in a hydrophobic nanoporous silica gel is investigated experimentally using two types of admixtures: carbamide of a relatively small molecular size and sodium bis(2-ethylhexyl) sulfosuccinate of a relatively large molecular size. By adding carbamide in the liquid phase, while the change in the solid–liquid interfacial tension is secondary, the defiltration volume can be lowered significantly, which can be related to the difficulties in gas phase formation and growth in nanopores. The factor of sodium bis(2-ethylhexyl) sulfosuccinate comes in mostly by affecting the liquid motions in relatively small nanopores.

Energy absorption performance of steel tubes enhanced by a nanoporous material functionalized liquid

The compressive behaviors of steel cells enhanced by a nanoporous silica functionalized liquid are investigated. As the empty space in the ductile cell is filled by an aqueous suspension of hydrophobic nanoporous silica gel, the work done by the compressive load along the axial direction can be dissipated not only through the ordinary cell-wall buckling but also via the extended yielding and the pressure-induced infiltration. As a result, the energy absorption efficiency, either on mass or on volumetric basis, is considerably improved.

Energy absorption of nanoporous silica particles in aqueous solutions of sodium chloride

An experimental study is carried out on the effect of chemical admixtures, particularly sodium chloride, on the energy absorption behaviour of a hydrophobic nanoporous silica. As the pressure increases, once the capillary effect is overcome, the liquid is forced into the nanopores; and when the pressure is reduced, outflow is difficult, resulting in a pronounced hysteresis. The inflow pressure and the specific absorbed energy are strongly dependent on the sodium chloride concentration, providing a promising way to adjust the system performance.

Pressure-Induced Infiltration of Aqueous Solutions of Multiple Promoters in a Nanoporous Silica

By applying an external pressure, an aqueous solution of promoters can be forced into a hydrophobic nanoporous silica gel. The promoter molecule demands a free volume several times larger than itself to enter the nanoenvironment. The free volume size is a function of the promoter concentration. If more than one promoter is used, the system behavior does not follow the principle of superposition. These results have important relevance to intelligent absorption and adsorption, programmable catalysis, and so on.

Pressure induced liquid infiltration in nanopores

In this article, we report the results of an infiltration∕defiltration experiment of a hydrophobic nanoporous silica gel. As the pressure is increased to the critical value, water can be forced into the nanopores. When the pressure is reduced, however, the “outflow” is difficult, leading to a significant hysteresis of sorption isotherm. A first-order thermodynamics analysis is performed to capture the confinement effect of nanopore walls and the mass and energy exchanges between liquid and gas phases in nanopores.

Pressure-induced infiltration of an epsomite–silica system

The pressure-induced infiltration of hydrophobic nanoporous silica gel immersed in epsomite solutions or mixed with epsomite crystals is investigated. Owing to the hysteresis of sorption isotherm curves, these systems are energy absorbing. In the liquid system, as the epsomite concentration increases, both the first-cycle infiltration pressure and the system recoverability increase. The energy-absorption properties of the saturated-solution- and the solid-crystal-based systems are quite similar. The experimental data suggests that, while the solid–liquid interfacial energy dominates the infiltration behaviour, the defiltration process is somewhat independent of it.

An energy-absorbing polyelectrolyte gel matrix composite material

A novel polyacrylic acid gel matrix composite material functionalized by hydrophobic nanoporous silica particulates is developed. When subjected to a high pressure, water molecules can be released from the polyacrylic acid network and forced into the nanopores. Due to the exposure of the large pore surface to the nonwetting liquid, the system free energy increases significantly. As the pressure is removed, the water remains in the confining nanoenvironment, and thus the material is energy absorbing. The energy absorption efficiency is much higher than that of many conventional protective materials.