Organic Porogen Research Articles

Hierarchical ZSM-5 zeolite supported RuOx catalysts via organic mesoporous porogens for catalytic oxidation of vinyl chloride

Hierarchical ZSM-5 zeolites supported RuOx catalysts were prepared via the addition of various organic mesoporous porogens (namely starch, cellulose and sucrose) for catalytic oxidation of vinyl chloride (VC). The usage of mesoporous porogens during catalysts preparation was favorable for boosting the catalytic activity of the resultant catalysts, and 1%RuOx/HZ5-10%sucrose exhibited the optimum catalytic activity, impressive catalytic stability and long-term durability. The structure-activity dependence from catalysts characterizations revealed that the higher specific surface area, more abundant strong acid sites and surface adsorbed oxygen species were regarded as the critical parameters for the noticeable improvement of catalytic activity. Based on in situ infrared spectroscopy analysis, 1%RuOx/HZ5-10%sucrose exhibited higher adsorption capacity and more efficient conversion of VC molecules with fewer formation of organic intermediates because of its superior catalytic activity in comparison with the single 1%RuOx/HZ5. Additionally, enol and carboxylate species were demonstrated to be the key organic intermediates in catalytic VC oxidation.

New insight into biodegradable macropore filler on tuning mechanical properties and bone tissue ingrowth in sparingly dissolvable bioceramic scaffolds

Structural parameters of the implants such as shape, size, and porosity of the pores have been extensively investigated to promote bone tissue repair, however, it is unknown how the pore interconnectivity affects the bone growth behaviors in the scaffolds. Herein we systematically evaluated the effect of biodegradable bioceramics as a secondary phase filler in the macroporous networks on the mechanical and osteogenic behaviors in sparingly dissolvable bioceramic scaffolds. The pure hardystonite (HT) scaffolds with ∼550 & 800 μm in pore sizes were prepared by digital light processing, and then the Sr-doped calcium silicate (SrCSi) bioceramic slurry without and with 30 % organic porogens were intruded into the HT scaffolds with 800 μm pore size and sintered at 1150 °C. It indicated that the organic porogens could endow spherical micropores in the SrCSi filler, and the invasion of the SrCSi component could not only significantly enhance the compressive strength and modulus of the HT-based scaffolds, but also induce osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). The pure HT scaffolds showed extremely slow bio-dissolution in Tris buffer after immersion for 8 weeks (∼1 % mass decay); in contrast, the SrCSi filler would readily dissolve into the aqueous medium and produced a steady mass decay (>6 % mass loss). In vivo experiments in rabbit femoral bone defect models showed that the pure HT scaffolds showed bone tissue ingrowth but the bone growth was impeded in the SrCSi-intruded scaffolds within 4 weeks; however, the group with higher porosity of SrCSi filler showed appreciable osteogenesis after 8 weeks of implantation and the whole scaffold was uniformly covered by new bone tissues after 16 weeks. These findings provide some new insights that the pore interconnectivity is not inevitable to impede bone ingrowth with the prolongation of implantation time, and such a highly biodegradable and bioactive filler intrusion strategy may be beneficial for optimizing the performances of scaffolds in bone regenerative medicine applications.

Fabrication of deep eutectic solvent-molecularly imprinted polymer in water: A green strategy for adsorption of bisphenol A

Molecularly imprinted polymers (MIPs) have been widely used in the field of environmental engineering, but the traditional MIPs are still not green because large quantities of organic porogen and hazardous functional monomers are required during the preparation process. To overcome these challenges, the green deep eutectic solvent (DES) and water were separately used as functional monomer and porogen to prepare molecularly imprinted polymer (MIP). Herein, the multiple functional groups on DES can form various forces with the target (bisphenol A, BPA) resisting the interference of water molecules. Characterization showed MIP had rough surface and rich functional groups. Results of batch experiments demonstrated that the MIP had a maximum adsorption capacity of 110.15 mg g−1 toward BPA from water and the Freundlich isotherm and pseudo-second-order kinetic models were suitable for analyzing the BPA adsorption process. Results of fixed-bed column illustrated that the breakthrough time prolonged with the adsorbent mass increasing, while forwarded with the BPA inlet concentration and flow rate increasing. Both Thomas and Yoon Nelson models could effectively describe fixed-bed adsorption. Additionally, the MIP was used as a pretreatment column adsorbent in combination with HPLC for the determination of BPA in eight environmental samples with satisfactory recoveries (91.02–108.20%). And the selective recognition mechanism of MIP for BPA was due to the combination of imprinting effect, hydrogen bonding and π-π stacking. In this work, a promising way has been developed to prepare green MIP for the selective adsorption of BPA in the field of environmental chemical engineering.

Organic salt-assisted pyrolysis for preparation of porous carbon from cellulose, hemicellulose and lignin: New insight from structure evolution

Developing green, high efficient and precursor-universal pore tailoring approach is a major issue for biomass-derived porous carbon (BPC). In this study, the unique effect of organic salt porogen (potassium acetate) was first elucidated through investigating the component and temperature-dependent structure evolution of BPC during pyrolysis-activation process. Hydrogen bonding with biomass char rather than melting would facilitate the dispersion of porogen. Potassium acetate would catalyze cracking of biopolymers (<400 ℃) into H2, CO2, CO and CH4 etc. and lead to plentiful macropores by gas blowing. And it decomposed into potassium species that etch the char to form micropores. Differently, cellulose and hemicellulose char intermediates with abundant carbonyl incline to retain the porous structure. BPCs from cellulose and hemicellulose possess specific surface area (SSA) ~ 1700 m2/g with nano-passages and three-dimensional layer framework structure. While lignin-derived BPC performs equally high SSA but bulky microporous structure. Besides, carbon layer would form from acetate decomposition and deposited on the char surface thus lead to similar surface structure. This study provides a novel insight of interaction between biomass char intermediate and organic salt porogen, which may demonstrate a precursor-universal and high efficient approach for BPC preparation.

Zinc-Sponge Battery Electrodes that Suppress Dendrites.

We report two methods to create zinc-sponge electrodes that suppress dendrite formation and shape change for rechargeable zinc batteries. Both methods are characterized by creating a paste made of zinc particles, organic porogen, and viscosity-enhancing agent that is heated under an inert gas and then air. During heating under the inert gas, the zinc particles anneal together, and the porogen decomposes; under air, the zinc fuses and residual organic burns out, yielding an open-cell metal foam or sponge. We tune the mechanical and electrochemical properties of the zinc sponges by varying zinc-to-porogen mass ratio, heating time under inert gas and air, and size and shape of the zinc and porogen particles. An advantage of the reported methods is their ability to finely tune zinc-sponge architecture. The selected size and shape of the zinc and porogen particles influence the morphology of the pore structure. A limitation is that resulting sponges have disordered pore structures that result in low mechanical strength at low volume fractions of zinc (<30%). Applications for these zinc-sponge electrodes include batteries for grid-storage, personal electronics, electric vehicles, and electric aviation. Users can expect zinc-sponge electrodes to cycle up to 40% depth of discharge at technologically relevant rates and areal capacities without the formation of separator-piercing dendrites.

Intrinsically microporous oligomers as organic porogens for mixed-matrix membranes

Intrinsically microporous oligomers (or oligomers of intrinsic microporosity, OIM) for use as organic poro-gens were first synthesized and subsequently incorporated into polysulfone (PSU) matrices to produce mixed-matrix membranes (MMMs) for gas separation. Their molecular weight was controlled to be about Mn=2,800 (n~5–6), and their end groups were regulated to be either -OH (OH-OIM) or -F (F-OIM) for improvement in the compatibility between OIM and PSU. The intrinsic pores of OIM greatly increase the gas permeability of PSU with only a small loss of gas selectivity. For instance, 20/80 wt% OH-OIM/PSU MMMs yield up to three- to four-fold higher permeability of CO2 and He compared to neat PSU, mostly associated with the intrinsic pores of OIM and its high compatibility with PSU. Additionally, very little reduction in separation performance was observed over 100 days. This suggests OIM as a promising organic porogen of MMMs for improving gas separation performance.

Metal barrier induced damage in self-assembly based organosilica low-k dielectrics and its reduction by organic template residues

This study describes the damage caused by physical vapor deposition of TaN/Ta barriers on porous self-assembled organosilica low-k dielectrics for IC applications. It is demonstrated that the ion bombardment associated with TaN layer sputtering strongly influences the metal species in-diffusion and modifies the bulk dielectric and pore sealing characteristics. The modulation of the pore structure via controlled decomposition of the organic template, prior to the barrier deposition step, allows to mitigate this damage. The reduction of open porosity, from nominal 39% down to 26%, is realized by partial retention of the sacrificial organic porogen phase in the pores of the low-k dielectric, resulting in the suppression of deep Ta penetration and in the recovery of pore sealing. This approach is successfully tested in a 45 nm half-pitch damascene vehicle. The compatibility of the organic template residues with the subsequent steps of the interconnects integration process flow, such as hard-mask deposition and patterning, are discussed.

Impact of VUV photons on SiO2 and organosilicate low-k dielectrics: General behavior, practical applications, and atomic models

This paper presents an in-depth overview of the application and impact of UV/VUV light in advanced interconnect technology. UV light application in BEOL historically was mainly motivated by the need to remove organic porogen and generate porosity in organosilicate (OSG) low-k films. Porosity lowered the film's dielectric constant, k, which enables one to reduce the interconnect wiring capacitance contribution to the RC signal delay in integrated circuits. The UV-based low-k film curing (λ &amp;gt; 200 nm) proved superior to thermal annealing and electron beam curing. UV and VUV light also play a significant role in plasma-induced damage to pSiCOH. VUV light with λ &amp;lt; 190–200 nm is able to break Si-CH3 bonds and to make low-k materials hydrophilic. The following moisture adsorption degrades the low-k properties and reliability. This fact motivated research into the mechanisms of UV/VUV photon interactions in pSiCOH films and in other materials used in BEOL nanofabrication. Today, the mechanisms of UV/VUV photon interactions with pSiCOH and other films used in interconnect fabrication are fairly well understood after nearly two decades of research. This understanding has allowed engineers to both control the damaging effects of photons and utilize the UV light for material engineering and nanofabrication processes. Some UV-based technological solutions, such as low-k curing and UV-induced stress engineering, have already been widely adopted for high volume manufacturing. Nevertheless, the challenges in nanoscaling technology may promote more widespread adoption of photon-assisted processing. We hope that fundamental insights and prospected applications described in this article will help the reader to find the optimal way in this wide and rapidly developing technology area.

Comparison of various low dielectric constant materials

To reduce the intrinsic resistance-capacitance delay of back-end-of-line (BEOL) interconnects in integrated circuits, low-dielectric-constant (low-k) materials with a dielectric constant (k) <4.0 have been introduced to be used as an interconnecting insulator from 130 nm technological node. In this paper, the physical and electrical characteristics, as well as the reliability, of various commercial low-k dielectric films with k values from 2.50 to 3.60, deposited by plasma-enhanced chemical vapor deposition were investigated. In addition to fluorinated silicate glass and dense organosilicate glass (OSG) low-k dielectric films, two porous OSG (P-OSG) films deposited using different sacrificial organic porogen precursors (alpha-terpinene (ATRP) and cyclooctane (C8H16)) were compared. The P-OSG films provide a lower k value than other low-k dielectric films, however, their resistance to the integration process is relatively low, resulting in a large increase in the k value and degraded electrical performance and reliability. Accordingly, the pursuit of the highly porous low-k dielectric films with a further low k value for the advanced technology nodes remains arguable. If a highly porous low-k dielectric film must be adopted in BEOL interconnects, the use of a sacrificial porogen precursor must be carefully considered because it would affect the properties of the resulting P-OSG films. In this study, the P-OSG film for the ATRP precursor exhibited better mechanical, electrical, and reliability characteristics than that for the C8H16 precursor.

Micro-/Mesoporous Polymer-Derived Ceramic Structures Using Molecular Porogens

Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO2/TiO2 supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

Comparison of Various Low Dielectric Constant Materials

In order to reduce resistance-capacitance (RC) delay of back-end-of-line (BEOL), a low-dielectric constant (low-k) material with the dielectric constant (k) below 4.0 has been introduced to be used as an insulator of Cu integration from 130 nm technological node. In this study, the electrical and reliability characteristics of various commercial low-k dielectric films with k value ranging from 3.6~2.5 deposited using plasma-enhanced chemical vapor deposition (PECVD) were investigated. In addition to FSG and dense OSG low-k dielectric films, porous OSG (P-OSG) films with two different sacrificial organic porogen precursors (alpha terpinene (ATRP) and cyclooctane (C8H16) were also compared. Although P-OSG films have a low k value, their resistance to the process integration is relatively low, resulting in a higher increase of k value and a degraded reliability performance as compared to OSG film. Hence, it is doubtable to use porous OSG films with a higher porosity in the following advanced technology nodes. Furthermore, the sacrificial porogen precursor used for porous OSG film deposition influences the film’s property. The P-OSG film for ATRP precursor has a better mechanical, electrical, and reliability characteristics as compared to that for C8H16 precursor in this study.

Preparation of Chamottes as a Raw Material for Low‐Cost Ceramic Membranes

Low‐cost ceramic membranes are usually prepared from a mixture of natural raw materials and some organic porogen agent such as starch. The fact that porogen must be completely eliminated during firing, leaving an interconnected porous structure, impose large firing times, increasing the final price. A study about the synthesis of porous chamottes as an alternative to organic pore formers was conducted to reduce firing costs. Chamottes were obtained from mixtures of clay and starch. Different starches were used and the influence of the composition and processing variables were studied. The viability of the porous chamottes was demonstrated.

Simple emulsion technique as an innovative template for preparation of porous, spongelike poly(lactide-co-glycolide) microspheres with pore-closing capability

The objective of this study was to develop a new oil-in-water emulsion template for the preparation of highly porous poly(lactide-co-glycolide) (PLGA) microspheres having a spongelike skeleton and a pore-closing functionality. A dispersed phase consisting of isopropyl formate and PLGA was emulsified in an aqueous phase. Ammonia was added toward this emulsion, in order to induce ammonolysis in the dispersed phase. Subsequently, isopropyl formate was broken into water-soluble isopropanol and formamide. As they functioned as anti-solvents against PLGA, microsphere hardening occurred. Also, their leaching into the aqueous phase led to the formation of highly porous, spongelike microspheres. The microsphere porosity was found to be controlled by adjusting isopropyl formate volume, PLGA type and concentration, ammonia volume, and ammonia–isopropyl formate molar ratio. When these dried microspheres were dispersed into an aqueous phase, the pores closed themselves autonomously. Herein, the self-closing capability of the microspheres was greatly influenced by microsphere Tg and the aqueous phase temperature. FITC-dextran and lysozyme were successfully encapsulated into the microspheres by simply equilibrating their aqueous solutions with the self-closing microspheres. In conclusion, the new emulsion template did not use either a halogenated organic solvent or conventional porogens. It did not require high-shear or high-energy mixing devices that must be used in the practice of most contemporary microencapsulation techniques. Despite these facts, this new technique was able to fabricate spongelike microspheres with an extremely high porosity and an outstanding pore-closing functionality.

Autodecomposition Approach for the Low-Temperature Mesostructuring of Nanocrystal Semiconductor Electrodes

Templating nanocrystals into mesoporous electrodes using an organic porogen typically requires thermal oxidation at >400 °C to completely remove the organic material and afford good electronic properties. These oxidation conditions are incompatible with many NC materials. Here, we demonstrate that nitrocellulose can afford mesoporous CdS and CZTS nanocrystal thin film electrodes at only 250–300 °C in air or under argon. Remarkable control over the surface area and the average pore size (20–100 nm) in thin films are demonstrated by varying the ratio of preformed nanocrystals and nitrocellulose. Moreover the mesoporous electrodes exhibit excellent optoelectronic properties. Photoelectrochemical performance is enhanced due to the increased active surface area, showing an 8-fold photocurrent increase over compact nanocrystal films, and an IPCE over 70%.

Preparation of porous ultra low k films using different sacrificial porogen precursors for 28 nM technological node

In order to reduce resistance capacitance (RC) delay and crosstalk between adjacent interconnect lines, the porous ultra low k (PULK) film with dielectric constant value ranging from 2.4 to 2.6 was introduced to be used as an insulator of the Cu integration in back end of the line (BEOL) for 28nm technological node. In this paper, the PULK films were deposited by plasma enhanced chemical vapor deposition (PECVD) using two different sacrificial organic porogen precursors of bicycloheptadiene (BCHD) and alpha-terpinene (ATRP), and then the above co-deposited films were expose to UV radialization for removing sacrificial organic porogens to create pores. The effects of the different sacrificial organic porogen on the PULK film properties such as the dielectric constant, pore and porosity, k shift, mechanic strength, and RC were studied in detail. Results indicated that the hardness and modulus of the PULK film for the BCHD and ATRP precursors were 0.7 and 5.1GPa and 1.0 and 7.1Gpa, and their pore radiuses and porosities were 1.18nm and 25% and 0.95nm and 23%. The dielectric constant value of the PULK film for the BCHD and ATRP precursors were measured as 2.48 and 2.59 with Hg probe. The adhesion test indicated that the interfacial strength of the PULK film for the ATRP precursor was higher than that of the PULK film for the BCHD precursor. By the RC examination, it was seen that RC curve of the PULK film for the ATRP precursor was located below the curve of the PULK film for the BCHD precursor.

Fabrication of three-dimensional interconnected hierarchically macroporous SiC by a modified freeze-gelcasting method

In this work, three-dimensional interconnected hierarchically macroporous SiC (HMS) materials with trimodal macropores were fabricated by a modified freeze-gelcasting method. In the HMS, the large and uniform 1st modal macropores up to 1mm in size form the primary porosity, while the SiC walls contain the 2nd and 3rd modal macropores on different scales. The formation mechanism of the 1st, 2nd and 3rd modal macropores is proposed to be due to the H2O2 foaming process, unidirectional freezing and presence of organic porogens (polyacrylamide (PAM) and polyvinyl alcohol (PVA)), respectively. Both polymerized PAM and PVA cryogel upon freezing together help consolidate the foamed macroporous structures before sintering. The contents of PVA, H2O2 and surfactant all have the influence on the structures of HMS.

Effect of vacuum-ultraviolet irradiation on the dielectric constant of low-k organosilicate dielectrics

Vacuum ultraviolet (VUV) irradiation is generated during plasma processing in semiconductor fabrications, while the effect of VUV irradiation on the dielectric constant (k value) of low-k materials is still an open question. To clarify this problem, VUV photons with a range of energies were exposed on low-k organosilicate dielectrics (SiCOH) samples at room temperature. Photon energies equal to or larger than 6.0 eV were found to decrease the k value of SiCOH films. VUV photons with lower energies do not have this effect. This shows the need for thermal heating in traditional ultraviolet (UV) curing since UV light sources do not have sufficient energy to change the dielectric constant of SiCOH and additional energy is required from thermal heating. In addition, 6.2 eV photon irradiation was found to be the most effective in decreasing the dielectric constant of low-k organosilicate films. Fourier Transform Infra-red Spectroscopy shows that these 6.2 eV VUV exposures removed organic porogens. This contributes to the decrease of the dielectric constant. This information provides the range of VUV photon energies that could decrease the dielectric constant of low-k materials most effectively.

High efficiency polyethylene glycol diacrylate monoliths for reversed-phase capillary liquid chromatography of small molecules

Highly cross-linked monolithic networks (i.e., polyethylene glycol diacrylate, PEGDA) synthesized from monomers containing varying ethylene oxide chain lengths were fabricated inside fused silica capillary columns for use in liquid chromatography (LC) of small molecules. Tergitol was used as a surfactant porogen in combination with other typical organic liquid porogens. Column performance was correlated with quantitative descriptors of the physical/chemical properties of the monomers and porogens using a statistical model. Solubility and viscosity values of the components were identified as important predictors of monolith morphology and efficiency. The chromatographic retention mechanism was determined to be principally reversed-phase (RP) with additional hydrogen bonding between the polar groups of the analytes and the ethylene oxide groups embedded in the monolith structure. The fabricated monolithic columns were evaluated under RPLC conditions using phenols, hydroxy benzoic acids, and alkyl parabens as test compounds. Isocratic elution of hydroxy benzoic acids at a linear velocity of 0.04cm/s using a PEGDA-700 monolith gave chromatographic peaks with little tailing (i.e., tailing factor<1.28). The chromatographic efficiency measured for a non-retained compound (uracil) using this column was 186,000plates/m when corrected for injector dead volume. High resolution gradient separations of selected pharmaceutical compounds and phenylurea herbicides were achieved in less than 18min. Optimized monoliths synthesized from all four crosslinking monomers exhibited high permeability and demonstrated little swelling or shrinking in different polarity solvents. Column preparation was highly reproducible, with relative standard deviation (RSD) values less than 2.1%, based on retention times of the phenol standards (3 different columns).

Preparation and characterization of poly (vinylidene fluoride) ultrafiltration membrane with organic and inorganic porogens

In this paper, the effects of high molecular weight additive (PEO-PPO-PEO), low molecular weight additive (oxalic acid) and inorganic additive (nano-TiO2) on PVDF membranes were studied by phase inversion method. The experimental results showed that the contact angle decreased as PEO-PPO-PEO was added in the casting solution. With the increasing concentration of PEO-PPO-PEO from 0.5 to 3.0 wt.%, the water flux increased from 0 to 1136L/m2h and the rejection decreased from 99.0% to 64.0%, meanwhile, the static contact angle stabilized basically around 66°. When the oxalic acid concentration increased from 0 to 3.0 wt.% and the concentration of PEO-PPO-PEO maintained at 0.5 wt.%, the water flux increased from 0 to 192L/m2h, while the rejection firstly decreased and then stabilized around 88.0%. Compared with PEO-PPO-PEO, PEO-PPO-PEO/nano-TiO2 and PEO-PPO-PEO/oxalic acid/nano-TiO2, the PVDF membrane with PEO-PPO-PEO/oxalic acid combined addition showed the best properties. As the concentrations of PEO-PPO-PEO and oxalic acid were 2.0 and 3.0 wt.% respectively, the water flux of PVDF membrane reached 2271L/m2h.

Solvent Free Generation of Open and Skinless Foam in Poly(l-lactic acid)/Poly(d,l-lactic acid) Blends Using Carbon Dioxide

Foams generated via carbon dioxide (CO2) processing typically exhibit a solid skin layer on the exterior surface and a closed-pore structure with limited interconnectivity in the core section thus limiting its application for biomedical intent. By controlling the properties of poly(l-lactic acid)/poly(d,l-lactic acid) (PLLA/PDLLA) blends and using CO2 with specific processing parameters, skinless foams with interconnected porous structure were prepared in this work using only CO2 as a physical foaming agent, which overcome the necessity to use organic solvents and solid porogens. The crystallization behaviors and sorption kinetics of PLLA and its blends were studied. Addition of PDLLA reduces the crystallinity of PLLA/PDLLA blends while treated with CO2 as compared to neat PLLA. The solubility and diffusion coefficients of CO2 in PLLA and its blends were found to be similar. Furthermore, the effect of PLLA/PDLLA blend ratio and CO2 treatment conditions on the foam morphologies was investigated. Through fi...