Tunable Mesopore Sizes Research Articles

Combined Effect of Oxygen Vacancies and Mesopore Sizes in ZnO/SiO2 Adsorbents on Boosting the H2S Removal Efficiency in Moist Conditions

AbstractWhile both pore sizes and oxygen vacancies benefit desulfurization on ZnO, their specific roles and the combined effect on the efficiency of this process are still unclear. To address this, ZnO‐based adsorbents with tunable mesopore sizes and concentrations of oxygen vacancies are synthesized. These two features are directly regulated through varying the carbon chain length of dihydric alcohol, which is used as a precursor in the synthesis process. They influenced the desulfurization performance through affecting the diffusion and dissociation of H2S. The sizes of mesopores determined the amounts of adsorbed water/ thickness of a water film while the amount of oxygen vacancies controlled the contents of hydroxyl groups. The latter not only are replaced by (bi)sulfide anions but also promote the dissociation of H2S through acid‐base interaction. Adsorbed water contributed to hydroxylation of the surface until the cease of desulfurization. However, too much‐adsorbed water increased the resistance of H2S diffusion through the water film to the surface of ZnO, deteriorating the performance. The optimal amounts of adsorbed water/thickness of water film and a sufficient amount of oxygen vacancies/hydroxyl groups are provided in the adsorbent with a mesopore size of ∼10 nm leading to a maximum H2S removal capacity of 151.9 mg g−1.

Specific Screening of Prostate Cancer Individuals Using an Enzyme-Assisted Substrate Sensing Platform Based on Hierarchical MOFs with Tunable Mesopore Size.

Rapid and specific identification of tumor metabolic markers is of great significance. Herein, a convenient, reliable and specific strategy was proposed to screen prostate cancer (PCa) individuals through indirectly quantifying sarcosine, an early indicator of PCa, in the clinical urine samples. The success roots in the rational design of a cascade response model, which takes integrated sarcosine oxidase (SOX) as a specific recognition unit and oxygen-sensitive molecule as a signal reporter. The newly developed hierarchical mesoporous Zr-based metal-organic frameworks with continuously tunable mesopore size ensure the synergetic work of the SOX and response unit spatially separated in their neighboring mesoporous and microporous domains, respectively. The large mesopore up to 12.1 nm not only greatly enhances the loading capacity of SOX but also spares enough space for the free diffusion of sarcosine. On this basis, the probe is competent to specifically check out the tiny concentration change of sarcosine in the urine sample between PCa patients and healthy humans. Such a concept of enzyme-assisted substrate sensing could be simply extended by altering the type of immobilized enzymes, hopefully setting a guideline for the rational design of multiple probes to quantify specific biomarkers in complex biological samples.

Modulating Ion Diffusivity and Electrode Conductivity of Carbon Nanotube@Mesoporous Carbon Fibers for High Performance Aluminum-Selenium Batteries.

Selenium (Se)-based rechargeable aluminum batteries (RABs), known as aluminum-selenium (Al-Se) batteries, are an appealing new battery design that holds great promise for addressing the low-capacity problem of current RAB technology. However, their applications are hindered by mediocre high-rate capacity (≈100 mAh g-1 at 0.5 A g-1 ) and insufficient cycling life (50 cycles). Herein, the synthesis of mesoporous carbon fibers (MCFs) by coating mesoporous carbon with short-length mesopores and tunable mesopore sizes (2.7 to 8.9 nm) coaxially on carbon nanotubes (CNT) is reported. When compositing MCFs with Se for Al-Se batteries, a positive correlation between mesopore size and electrolyte ion diffusivity is observed, however when pore size is increased to 8.9 nm, large voids are created at the interface of CNT core and mesoporous carbon shell, leading to decreased electrode conductivity. The trade-off between ion diffusivity and interfacial connectivity/conductivity determines MCF with pore size of 7.1 nm as the best host material for Al-Se batteries. The composite cathode delivers high specific capacities (366 and 230 mAh g-1 at 0.5 and 1 A g-1 ), good rate performance, and excellent cycling stability (152 mAh g-1 after 500 cycles at 2 A g-1 ), superior over previously reported Se cathodes and other cathodes for RABs.

Composition Design of Block Copolymers for Porous Carbon Fibers

Block copolymer-based porous carbon fibers (PCFs) exhibit hierarchical porous structures, high surface areas, and exceptional electrochemical properties. However, the design of block copolymers for PCFs remains a challenge in advancing this type of fibrous material for energy storage applications. Herein, we have systematically synthesized a series of poly(methyl methacrylate-block-acrylonitrile) (PMMA-b-PAN) with well-controlled molecular weights and compositions to study the physical and electrochemical properties of PCFs. PCFs are synthesized via electrospinning, self-assembly, oxidation, and pyrolysis with no additives or chemical activation. By adjusting the molecular weights of polyacrylonitrile (PAN) and poly(methyl methacrylate) blocks, we have achieved tunable mesopore sizes ranging from 10.9 to 18.6 nm and specific capacitances varied from 144 to 345 F g–1 at 10 mV s–1. Interestingly, regardless of the volume fraction of PAN, all the block copolymers produce hierarchical porous structures because of the self-assembly and cross-linking of PAN. Block copolymers with a PAN volume fraction of near 50% show the highest surface areas and gravimetric capacitances. The PCFs represent a new platform material with tunable specific surface areas, pore sizes, and electrochemical properties. This work has an immediate impact on designing block copolymers to create PCFs for applications in energy conversion and storage.

Fabrication of novel hierarchical ZSM-5 zeolite membranes with tunable mesopores for ultrafiltration

A series of novel hierarchical ZSM-5 zeolite membranes with tunable mesopore sizes have been prepared successfully by using amphiphilic organosilane 3-[(trimethoxysilyl) propyl]octyldimethyl-ammonium chloride (TPOAC) as the mesogenous template and part of the Si source. The effects of several synthesis parameters, such as the TPOAC/SiO2 ratio, synthesis temperature and crystallization time, on the microstructures and rejection performance of the hierarchical ZSM-5 zeolite membranes were systematically investigated. Multiple techniques, such as XRD, SEM, N2 adsorption techniques, TEM, IR, 13C MAS NMR and 29Si MAS NMR were employed for the characterizations. The filtration of dextran in water shows that the membranes have molecular weight cutoff (MWCO) ranging from 9500 to 943,000, corresponding to the molecular size in the range of 4.5–37nm. The sharp increase in the rejection of dextran with the increase of molecular weight indicated narrow pore size distribution of the membrane. These results show that the hierarchical mesoporous ZSM-5 zeolite membranes have a great potential for ultrafiltration with high performance.

Single-Layered Mesoporous Carbon Sandwiched Graphene Nanosheets for High Performance Ionic Liquid Supercapacitors

Ionic liquid based supercapacitors generally using nanoporous carbon as electrode materials hold promise for future energy storage devices with improved energy density, but their power performances are limited by the high viscosity and relatively large size of ionic liquid electrolytes. Understanding the relationship between the pore size of nanoporous carbon, the ionic liquid electrolyte diffusivity, and the energy/power density is critical for the development of ionic liquid based supercapacitors with high performance. Herein, we report the synthesis of single-layered mesoporous carbon sandwiched graphene nanosheets (sMC@G) with mesopore-dominant (82% ∼89%) high surface area and tunable mesopore sizes (4.7, 6.8, 9.4, 10.6, and 13.9 nm). When using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) as the electrolyte with a cation size of 0.76 nm, it is demonstrated that the ion diffusion coefficient increases a little when the mesopore size is not larger than 6.8 nm, and then jumps dramatically in ...

Fabrication of high-pore volume carbon nanosheets with uniform arrangement of mesopores

Carbon nanosheets with a tunable mesopore size, large pore volume, and good electronic conductivity are synthesized via a solution-chemistry approach. In this synthesis, diaminohexane and graphene oxide (GO) are used as the structural directing agents, and a silica colloid is used as a mesopores template. Diaminohexane plays a crucial role in bridging silica colloid particles and GO, as well as initiating the polymerization of benzoxazine on the surfaces of both the GO and silica, resulting in the formation of a hybrid nanosheet polymer. The carbon nanosheets have graphene embedded in them and have several spherical mesopores with a pore volume up to 3.5 cm3·g–1 on their surfaces. These nuerous accessible mesopores in the carbon layers can act as reservoirs to host a high loading of active charge-storage materials with good dispersion and a uniform particle size. Compared with active materials with wide particle-size distributions, the unique proposed configuration with confined and uniform particles exhibits superior electrochemical performance during lithiation and delithiation, especially during long cycles and at high rates.

Nitrogen-enriched carbon with extremely high mesoporosity and tunable mesopore size for high-performance supercapacitors

As one of the most potential electrode materials for supercapacitors, nitrogen-enriched nanocarbons are still facing challenge of constructing developed mesoporosity for rapid mass transportation and tailoring their pore size for performance optimization and expanding their application scopes. Herein we develop a series of nitrogen-enriched mesoporous carbon (NMC) with extremely high mesoporosity and tunable mesopore size by a two-step method using silica gel as template. In our approach, mesopore size can be easily tailored from 4.7 to 35 nm by increasing the HF/TEOS volume ratio from 1/100 to 1/4. The NMC with mesopores of 6.2 nm presents the largest mesopore volume, surface area and mesopore ratio of 2.56 cm3 g−1, 1003 m2 g−1 and 97.7%, respectively. As a result, the highest specific capacitance of 325 F g−1 can be obtained at the current density of 0.1 A g−1, which can stay over 88% (286 F g−1) as the current density increases by 100 times (10 A g−1). This approach may open the doors for preparation of nitrogen-enriched nanocarbons with desired nanostructure for numerous applications.

Self-arrangement of nanoparticles toward crystalline metal oxides with high surface areas and tunable 3D mesopores.

We demonstrate a new design concept where the interaction between silica nanoparticles (about 1.5 nm in diameter) with titania nanoparticles (anatase, about 4 nm or 6 nm in diameter) guides a successful formation of mesoporous titania with crystalline walls and controllable porosity. At an appropriate solution pH (~1.5, depending on the deprotonation tendencies of two types of nanoparticles), the smaller silica nanoparticles, which attach to the surface of the larger titania nanoparticles and provide a portion of inactive surface and reactive surface of titania nanoparticles, dictate the direction and the degree of condensation of the titania nanoparticles, resulting in a porous 3D framework. Further crystallization by a hydrothermal treatment and subsequent removal of silica nanoparticles result in a mesoporous titania with highly crystalline walls and tunable mesopore sizes. A simple control of the Si/Ti ratio verified the versatility of the present method through the successful control of mean pore diameter in the range of 2–35 nm and specific surface area in the ranges of 180–250 m2 g−1. The present synthesis method is successfully extended to other metal oxides, their mixed oxides and analogues with different particle sizes, regarding as a general method for mesoporous metal (or mixed metal) oxides.

Systematically Controlled Pore System of Ordered Mesoporous Carbons Using Phosphoric Acid as the In situ Generated Catalysts for Carbonization and Activation

We report on a facile synthesis of the ordered mesoporous carbon (OMC) materials with systematically controlled microporosity and mesoporosity simultaneously through the nano‐replication route using phosphoric acid as the acid catalyst and activation agent. The use of phosphoric acid affects the pore structures of OMC materials, such as the formation of numerous micropores by activation of the carbon framework and the enlargement of mesopores by spontaneous phase separation during the carbonization. The mesopore sizes, surface areas, total pore volumes, and micropore volumes of the OMC materials are highly dependent on the phosphoric acid content and can be systematically controlled in the range 3.7–7.5 nm, 1027–2782 m2 g–1, 1.12–3.53 cm3 g–1 and 0.34–0.95 cm3 g–1, respectively. OMC materials with systematically controlled pore structures were successfully synthesized using phosphoric acid as the carbonization catalyst and mesoporous silica materials with cubic Ia3d and 2‐D hexagonal mesostructures as the templates. The phosphoric acid in the synthesis of ordered mesoporous carbon materials acts as the chemical activating agent for micropore generation of the carbon framework and pore‐expanding agent for controlling of mesopore size, in addition to functioning as the acid catalyst. The present synthesis pathway is very useful for preparing OMC materials with tunable mesopore sizes and well‐developed microporosities at the same time.

ChemInform Abstract: Mesostructured Zeolites: Bridging the Gap Between Zeolites and MCM‐41

AbstractReview: 94 refs.

Temperature-induced modulation of mesopore size in hierarchically porous amorphous TiO2/ZrO2 beads for improved dye adsorption capacity

Temperature-based processes combined with a sol–gel templating technique were used to prepare hierarchically porous amorphous TiO2/ZrO2 beads with tunable mesopore sizes for improved dye sorption capacities.

One-pot hydrothermal synthesis of nitrogen-doped hierarchically porous carbon monoliths for supercapacitors

The nitrogen-doped hierarchically porous carbon monoliths (N-HPCMs) were successfully synthesized by using dicyandiamide (DCDA) as nitrogen source, phenolic resol as carbon precursor and mixed triblock copolymers as templates via a one-pot hydrothermal approach. The obtained carbon monoliths possess tunable mesopore size (4.3–11.4 nm), large surface area (552–660 m2/g), and high nitrogen content (up to 12.1 wt%). Ascribed to the nitrogen-doped frameworks and hierarchical porosity, N-HPCMs exhibit good electrochemical performance as the supercapacitor electrode with specific capacitance of 268.9 F/g (in 6 M KOH) at a current density of 1 A/g, and a 4.1 % loss of the specific capacitance after 5,000 charge–discharge cycles, indicating a long-term cycling stability. Such unique features make N-HPCMs promising electrode materials for high performance supercapacitors.

“Brick‐and‐Mortar” Self‐Assembly Approach to Graphitic Mesoporous Carbon Nanocomposites

AbstractMesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially‐graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 °C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium‐ion batteries. In this work, we successfully implemented a “brick‐and‐mortar” approach to obtain ordered graphitic mesoporous carbon nanocomposites with tunable mesopore sizes below 850 °C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin‐based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitance and resistivity of final materials can be tailored by changing the mortar to brick ratios.

Synthesis of colloidal silica nanoparticles of a tunable mesopore size and their application to the adsorption of biomolecules

A synthetic method for the fabrication of colloidal mesoporous silica nanoparticles of a tunable mesopore size is presented. These nanoparticles form stable colloidal suspensions, have narrow particle size distributions in the 50–300 nm range and exhibit a framework-confined porosity made up of large mesopores with a diameter of up to 9 nm. The size of the mesopores was enlarged by means of two different swelling agents (SA), i.e. 1,3,5-trimethylbenzene (TMB) and N, N-dimethylhexadecylamine (DMHA). Colloidal mesoporous silica nanoparticles exhibit a strong affinity for the adsorption of hemoglobin (Hb) and the immobilization of lysozyme (Lz). These nanoparticles can adsorb up to 2080 mg Hb g −1 support and 690 mg Lz g −1 support. Moreover, the adsorption of these biomolecules on silica nanoparticles occurs very quickly and most of what is adsorbed is accommodated on the external surface area of the silica nanoparticles.

Synthesis of ordered nanoporous carbons of tunable mesopore size by templating SBA-15 silica materials

Ordered mesoporous carbons with controllable pore size distributions were synthesised by using mesostructured SBA-15 silica samples as templates. By varying the synthesis temperature of SBA-15 between 90 and 150 °C, it is possible to tune the size of silica mesopores between 7.2 and 11.3 nm. As the synthesis temperature of SBA-15 silica increases over this range, the size of the mesopores of templated carbons can be modified between 3.0 and 5.2 nm. Modification of the synthesis temperature of silica does not affect its structural order, which is that characteristic of SBA-15. Independent of the type of SBA-15 used as template, the prepared carbons are highly ordered. The porosity of the carbons synthesised from SBA-15 silica in one impregnation–carbonisation (N 2) cycle is made up of two types of mesopores, i.e. structural mesopores (derived from the silica skeleton) and mesopores confined within the carbon rods. The structure of a carbon with these characteristics is described by the CMK-3/5 model, which is presented here for the first time. When the impregnation–carbonisation cycle is repeated twice, the carbon rod confined mesopores disappear and the structure of the resulting carbon is well described by the CMK-3 model.

Low-Cost Synthetic Route to Mesoporous Carbons with Narrow Pore Size Distributions and Tunable Porosity through Silica Xerogel Templates

Silica xerogels synthesized by the sol−gel process were used as templates to fabricate mesoporous carbons. The silica was prepared in a two-step process, under acid pH conditions, at a high H2O/Si molar ratio of 194 and at different HCl/Si molar ratios. Two sources were used as silica precursors: tetraethoxysilane (TEOS) and sodium silicate. The resulting silica xerogels have surface areas of >500 m2·g-1, pore volumes of >0.4 cm3·g-1, and a tunable mesopore size of between 2 and 10 nm, depending on the HCl/Si molar ratio. The mesoporous carbons obtained as inverse replicas of silica xerogel templates have large pore volumes (in the 1.5−2.1 cm3·g-1 range), large BET surface areas of up to 2200 m2·g-1, and narrow pore size distributions (PSD) in the mesopore range. The mesopore size of the carbons can be tuned between 3 and 4.5 nm depending on the type of silica xerogel selected as template. Carbons prepared in this way have structural characteristics comparable to those of mesoporous carbons made by templ...