High Surface Area Silica Research Articles

High Specific Surface Area Silica Nanorod Supported Bimetallic NiCu Effectively Catalyzes Levulinic Acid Hydrogenation to γ-Valerolactone

High Specific Surface Area Silica Nanorod Supported Bimetallic NiCu Effectively Catalyzes Levulinic Acid Hydrogenation to γ-Valerolactone

Synthesis of porous silica from wasted SiO2‐containing molding compounds

AbstractMaterialsIn this study, we provided a simple method to extract the silicate species from the waste silica‐containing molding compounds from the semiconducting industry.MethodsRecycled sodium silicate solution was obtained from alkaline extraction of the silica fillers in the waste molding compounds and dried and redissolved in appropriate amount of water.ResultsPorous silica of high surface area (>500 m2g−1) and tunable pore size (1.5–5.0 nm) could be feasibly synthesized by using the recycled sodium silicate as silica source and nature‐friendly homopolymer polyethylene glycol (PEG) as an organic template. The pore size of the PEG‐templating silicas was made tunable by hydrothermal treatment at different pH.ConclusionTo reduce the emission of CO2 gas from the removal of the PEG template, porous silica with a large surface area has been prepared at a low PEG/sodium silicate weight ratio of 1/20.

Non-supercritical drying synthesis of hydrophobic, low-density, and high surface area silica aerogel using a sonication technique

Replacing the solvent in silica aerogel production with air is critical in getting the desired physical properties. Even though drying by evaporation under ambient pressure is thought to be the simplest way, it shrinks and collapses the gel network. In this research, uniform sol was prepared by sonication at room temperature. The surface of the developed wet gel was modified with trimethylchlorosilane (TMCS) after solvent exchange. The prepared aerogels underwent various characterization techniques to evaluate their functional, structural, morphological, surface, and thermal properties. The textural and physical characteristics of prepared silica aerogel were examined in relation to the precursor concentration, catalysts that affect the density of silica aerogel, volumetric shrinkage, and gelation time. The silica aerogel was found thermally stable up to 800 °C while hydrophobicity retained up to 350 °C. The contact angle of prepared aerogels confirms their hydrophobic nature. Field emission scanning electron microscopy (FE-SEM) and X-Ray Diffraction (XRD) results demonstrate the porous nature of silica aerogel. The Brunauer-Emmett-Teller (BET) surface area analysis revealed that the surface area and the pore radius were 784 m2/g and 36 Å, respectively.

Tires for Mars Rovers: Reinforcing BR and BR/Vinyl-Methyl Silicone Rubber Compounds with Carbon Black, Nano-CaCO3, or Silica for Good Low-Temperature Dynamic-Mechanical Performance

ABSTRACT Dynamic increment in Mars exploration missions necessitates the development of new materials that can satisfy the ever more stringent requirements. Currently, most of the materials used for manufacturing Mars rovers and landers are based on various metal alloys that provide high reliability in the Martian environment. However, the future planned missions, including the first human crew landing on Mars, require the development of new rubber materials that could be used for sealing Mars suits, for tires/tracks, and for damping systems for heavy Mars rovers. This research aims to investigate the properties of butadiene rubber (BR) and butadiene/vinyl-methyl silicone rubber blends (BR/VMQ) filled with various reinforcing fillers: carbon blacks (CBs), silicas, and nanometric calcium carbonate (nano-CaCO3), in order to evaluate their performance from the point of view of Mars' environmental applications. The study revealed that the designed composites exhibit very good low-temperature elasticity, and the addition of 30 phr of high surface area CB (N220) or silica (Ultrasil 9100) results in good mechanical properties of the compounds. The mechanical properties of the BR/VMQ blends depend on the type of reinforcing filler. The addition of the CBs resulted in better mechanical properties, while the incorporation of silicas worsens the mechanical properties of BR/VMQ blends in comparison to their BR counterparts. The high-cis BR grade exhibits a strong tendency to crystallize in the operating temperature range on Mars (crystallization ∼−60 °C, melting ∼−20 °C), and the addition of the fillers nucleates the crystallization, resulting in a higher amount of the crystalline phase. This might be a serious problem for any sealing application of the rubber compounds. For this reason, a non-crystallizable BR grade is recommended for further studies.

Microscopic Origins of the Nonlinear Behavior of Particle-Filled Rubber Probed with Dynamic Strain XPCS.

The underlying microscopic response of filler networks in reinforced rubber to dynamic strain is not well understood due to the experimental difficulty of directly measuring filler network behavior in samples undergoing dynamic strain. This difficulty can be overcome with in situ X-ray photon correlation spectroscopy (XPCS) measurements. The contrast between the silica filler and the rubber matrix for X-ray scattering allows us to isolate the filler network behavior from the overall response of the rubber. This in situ XPCS technique probes the microscopic breakdown and reforming of the filler network structure, which are responsible for the nonlinear dependence of modulus on strain, known in the rubber science community as the Payne effect. These microscopic changes in the filler network structure have consequences for the macroscopic material performance, especially for the fuel efficiency of tire tread compounds. Here, we elucidate the behavior with in situ dynamic strain XPCS experiments on industrially relevant, vulcanized rubbers filled (13 vol %) with novel air-milled silica of ultrahigh-surface area (UHSA) (250 m2/g). The addition of a silane coupling agent to rubber containing this silica causes an unexpected and counterintuitive increase in the Payne effect and decrease in energy dissipation. For this rubber, we observe a nearly two-fold enhancement of the storage modulus and virtually equivalent loss tangent compared to a rubber containing a coupling agent and conventional silica. Interpretation of our in situ XPCS results simultaneously with interpretation of traditional dynamic mechanical analysis (DMA) strain sweep experiments reveals that the debonding or yielding of bridged bound rubber layers is key to understanding the behavior of rubber formulations containing the silane coupling agent and high-surface area silica. These results demonstrate that the combination of XPCS and DMA is a powerful method for unraveling the microscale filler response to strain which dictates the dynamic mechanical properties of reinforced soft matter composites. With this combination of techniques, we have elucidated the great promise of UHSA silica when used in concert with a silane coupling agent in filled rubber. Such composites simultaneously exhibit large moduli and low hysteresis under dynamic strain.

Propane Dehydrogenation on Co-N-C/SiO2 Catalyst: The Role of Single-Atom Active Sites

Recently, significant attention has been drawn to carbon materials containing cobalt coordinated to nitrogen, as the promising inexpensive catalysts of a wide range of applications. Given that non-oxidative propane dehydrogenation to propylene (PDH) is also becoming increasingly important, we present the results on PDH over Co-N-C/SiO2 composites. The latter were prepared by pyrolysis of silicone gel enriched with Co(II) salt and triethanolamine. According to XRD, HRTEM and XPS characterizations, the resulting materials consist of metallic cobalt nanoparticles of about 5 to 10 nm size and subnano-sized cobalt species (cobalt single atom sites coordinated to nitrogen/carbon), which are uniformly distributed in mesoporous silica of high specific surface area (up to 500 m2 g−1). The composites demonstrated significant catalytic activity in PDH, which was examined under typical reaction conditions (600 °C, 1 atm) using a fixed bed flow reactor. The subnano-sized Co centers proved to be the real active catalytic sites responsible for the target reaction, while carbon deposition induced by Co nanoparticles provided the catalyst deactivation. It is shown that the catalyst can be reactivated by the treatment with oxygen, which, in addition, notably increases selectivity to propylene (up to 98%) and enhances the catalyst stability in the next operation cycle. This remarkable change in catalytic behavior is shown to be due to the dramatic structural modification of the catalyst upon high-temperature oxidation.

High Surface Area Silica Particles Using Anionic Surfactant Template Prepared by One-step Spray Drying System for Dye Removal Application

This study reported the effect of sodium lauryl sulfate (SLS) as a template on silica morphology and its properties. The precursor was prepared by producing silica nanofluid by the sol-gel method and mixed with various SLS concentrations. After that, the precursor was spray-dried to generate silica powder. An increase in SLS concentration up to 2 critical micelle concentration (CMC) indicates an increase in the silica particle size from 2.12 μm in untemplated silica particles to 2.58 μm. On the other hand, when the SLS concentration increases to 3 CMC, the particle size decreases to 2.19 μm. A significant increase in total pore volume and surface area is obtained for silica particles synthesized at least at the SLS concentration of 2 CMC, around eight higher volumes than without SLS addition. In addition, they have a macropore compared to silica particles synthesized without SLS addition that only exhibits mesopore. The surface area was 1,011 m2/g for the SLS concentration at 3 CMC, whereas the silica without SLS has only a surface area of 131 m2/g. The SLS concentration at 2 CMC or higher leads to a significant increase in its physical properties because the micelle formation is enough for sacrificed template formation. Methylene blue solution was used as an adsorbate for evaluating the dye adsorption capacity that followed the Langmuir isothermal adsorption model. The highest theoretical maximum monolayer adsorption capacity was 142.9 mg/g, obtained by silica adsorbent with the SLS concentration at 3 CMC.

Shear-induced fabrication of SiO2 nano-meshes for efficient uranium capture

The extraction of uranium from seawater and the safe treatment of wastewater containing uranium (VI) were important to ensure the sustainable development of nuclear-related energy sources. Two-dimensional silica nanomaterials have been extensively investigated in the field of uranium adsorption due to their high adsorption capacity, short equilibration times, and easily modified surface groups. However, the two-dimensional mesoporous silica nanomaterial preparation has become a challenge due to the lack of natural sheet templating agents. The reason will hinder the development of silica nanomaterials for uranium extraction. Here, the specific surface area silica nanomeshes (HSMSMs) uranium adsorbent was prepared by a high shear method to induce nanobubble formation. HSMSMs showed a high uranium adsorption capacity of 822 mg-U/g-abs in seawater with the uranium adsorption concentration was 50 mg/L, which was approximately 2 times higher than the conventional mesoporous silica nanomaterials. Compared to HSMSMs, the amidoxime-modified high specific surface area silica nanomesh (HSMSMs-AO) demonstrated good selectivity for U(VI), and the uranium ions uptake was 877 mg-U/g-abs in 50 mg/L uranium-spiked simulated seawater. Due to HSMSMs-AO's stable chemical properties and high mechanical strength, HSMSMs-AO also displayed long service life. Benefiting from the simple preparation method and high adsorption capacity of HSMSMs, HSMSMs could be a promising candidate for large-scale extraction of uranium from seawater.

Insights into interactions of chlorine-based cleaning products with indoor relevant surfaces

Environmental context The chemistry that occurs in indoor environments and the role that indoor surfaces play have recently received increased attention in the scientific community. Here we have investigated the chemistry of chlorine-based cleaning products and their interactions with indoor relevant surfaces and find that these surfaces react with these cleaning products to yield surface adsorbed chlorine oxides and other surface-bound species. Rationale Indoor chemistry has recently received increased attention in the scientific community due to the fact that there is relatively little known given its unique environment including point combustion sources (candles, gas stoves, etc.) resulting in high aerosol concentrations, high surface to volume ratios and the impact of humans on indoor air quality. Recently, surface-initiated reactions during chlorine cleaning events have been proposed. Methodology In this study, we probe the interaction of bleach headspace gas with high surface area silica as a proxy for window glass – an ‘inert’ and impervious surface – using attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy photothermal infrared (AFM-PTIR) spectroscopy and transmission electron microscopy (TEM) to observe surface chemical and physical changes. Results The results suggest chemical transformations occur at the silica surface forming surface adsorbed chlorine oxides (ClOx). Conductivity and ion chromatography methods support the presence of adsorbed chloride after surfaces have been exposed to bleach and HOCl. Discussion Interactions between HOCl and indoor surfaces have not been previously studied with molecular based techniques. The possibility of surface-mediated reactions has been relatively unexplored on indoor surfaces and this study shows the chemistry of chlorine-containing cleaning products on indoor relevant surfaces.

Transesterification of waste cooking oil using Clay/CaO as a solid base catalyst

This study was conducted to investigate the use of clay/CaO heterogeneous catalyst for the production of biodiesel from waste cooking oil. The catalyst was synthesized from clay and calcined using calcium oxide under controlled conditions. Clay is a natural soil material containing a large amount of amorphous silica. After processing calcium oxide and heating under controlled conditions at 800 °C, high surface area silica with amorphous structure was produced. The amorphous structure of the synthesized catalyst was confirmed by XRD analysis. The results of SEM analysis indicated that the particles had a spherical structure, distributed evenly and uniformly. The effect of five parameters of reaction temperature, catalyst concentration, oil to methanol volume ratio, toluene concentration, and reaction time on the purity of the biodiesel was evaluated through utilizing the response surface methodology (RSM). Under optimal conditions i.e. temperature of 54.97 °C, catalyst concentration of 9.6 wt%, oil to methanol volume ratio of 1.94 vol:vol, toluene concentration of 16.13 wt%, and reaction time of 74.32 min, the conversion rate was 97.16%. The results of catalyst recovery test showed that the prepared catalyst could be reused up to 5 times; thus, it can be used as a stable and cost-effective catalyst for the production of biodiesel.

Phase speciation and surface analysis of copper phosphate on high surface area silica support by in situ XAS/XRD and DFT: Assessment for guaiacol hydrodeoxygenation

In situ characterization has become indispensable technique in the heterogeneous catalyst development because it provides insights into the composition and fundamental nature of materials in a dynamic process. In this work, in situ analysis including X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) could disclose phase transition via several intermediates during the reduction of copper phosphate precursor (CuHPO4·H2O) to copper phosphide on high surface silica support (Cu3P/SiO2). The synthesized Cu3P/SiO2 was further used as a catalyst for hydrodeoxygenation (HDO) reaction of guaiacol, a well-known representative model compound in lignin-derivatives upgrading. Many major products, such as cyclic hydrocarbons, demethylated, deoxygenated, and methylated compounds, were detected in the reaction mixture. The highest selectivity of catechol (72 mol%) was obtained at reaction condition of 300 °C and 50 bar H2 after 150 min. The density-functional theory (DFT) calculations revealed the local electronic charge nature and the different roles of Cu and P active sites towards the interaction between reactants/intermediates and the Cu3P surfaces. The findings of the phase transition during the Cu3P synthesis and its catalytic activity to the guaiacol HDO reaction, the first to be reported, is beneficial for improving the efficiency metal phosphide-based catalyst for lignin-derived bio-oil into biofuels in the future.

Reordering of Depolymerized Silicates as Adsorbents for Large Nitrogen Compounds

The adsorption capacities of two synthesized zeolites (crystalline ZSM-5 and semi-crystalline faujasite Y) for a mixture of indole, quinoline and carbazole were studied. The different samples obtained show different crystalline degree, mesoporosity and Si/Al ratios. The synthesis procedure is based on the simultaneous depolymerization of a mixture of high surface area silica, such as rice hull ashes (RHA), and a crystalline zeolite, such as clinoptilolite or faujasite. The depolymerization step is followed by a partial reorganization induced by a structure-directing agent. A model mixture of nitrogenous compounds was prepared, then it was mixed with the zeolite samples and the amount adsorbed of nitrogenous compounds was determined by gas chromatography. Analysis of the adsorbed molecules reveals selectivity in favor of quinoline, followed by indole and then carbazole. The best adsorbent properties correspond to the solid with highest porous volume. The samples obtained were characterized by X-ray diffraction, 29Si and 27Al magic-angle spinning nuclear magnetic resonance, X-ray fluorescence and Fourier transform infrared spectroscopy. The Barrett-Joyner-Halenda (BJH) pore size distribution and the Brunauer-Emmet-Teller (BET) surface area values were obtained from N2 adsorption/desorption isotherms.

Effect of different high surface area silicas on the rheology of cement paste

This work studies the effect of nanosilica (NS) on the rheology of cement paste by comparing it with two high specific surface area silicas: silica fume (SF) and pyrogenic silica (PS). Portland cement pastes were produced with different water-to-cementing material ratios and different solid substitutions of cement by silica. Water demand, setting time, and rheology tests were performed. Results showed that NS and SF decreased plastic viscosity, while PS increased it. Only PS was found to have an effect on yield stress. NS showed the most decreasing effect on viscosity, regardless of its higher water demand. It was concluded that the behavior of pastes containing NS and SF is governed by the “ball-bearing” effect from silica particles, by their agglomeration degree, and their impact on the solid volume fraction. The behavior of pastes containing PS is governed by its ability to absorb a portion of the mixing water.

The nonlinear stress relaxation behavior after a step shear of star‐shaped styrene‐butadiene rubber filled with precipitated silica: Experiment and simulation

AbstractThe nonlinear stress relaxation behavior after a step shear strain of star‐shaped SSBR/silica compounds containing 21 vol% filler of various surface areas was measured and simulated using constitutive equations. A styrene‐butadiene rubber (SBR) gum and SBR filled with silica having BET surface areas of 55, 135, 160, and 195 m2/g were used. Relaxation modulus behavior of the filled compounds was found to be dependent on surface area. Specifically, stress relaxation tests indicated that an increase in surface area led to increase in values of relaxation moduli in both the linear and nonlinear regimes. The time‐dependent relaxation modulus exhibited a plateau at long times of relaxation in compounds containing silica of high surface area. Additionally, good time‐strain superpositions were achieved for all samples at intermediate times of relaxation, and the strain‐dependent damping function decreased with filler surface area. The constitutive equations proposed by Leonov and Simhambhatla and Leonov, modified to include multimodal relaxation of the particle network, were used to predict the time evolution of the relaxation modulus in the nonlinear regime for all samples. The simulations provided good results for the SBR gum for all tested strain levels. Also, in the compounds filled with silica, both models satisfactorily described the experimental observation in the nonlinear regime at low strain levels. However, at higher strain levels, due to a possible slip effect, the simulations overpredicted measured values of the relaxation moduli, thus leading to only qualitative predictions of the observed behavior. It is also possible that neither model accurately captured the floc rupture kinetics of these complex rubber compounds.

Experimental and Computational Studies of Carbon–Carbon Bond Formation via Ketonization and Aldol Condensation over Site-Isolated Zirconium Catalysts

We report here the preparation and investigation of isolated Zr centers supported on a high surface area silica for the conversion of carboxylic acids to internal ketones by ketonic decarboxylation...

Effective SERS substrate obtained by Au deposition at silica surfaces through a top down method

Background: In the last years some of us developed methods for preparing, through simple synthesis protocols, gold nanoparticles supported on silica surfaces: in that cases, bottom-up approaches has been adopted (i.e. starting from HAuCl4 precursor) and high surface area silica (Aerosil 300) was chosen as support (together with controlled pH conditions), to facilitate Au dispersion. The obtained substrates showed the ability to enhance Raman signals of dosed molecules pyridine and bi-pyridine and/or of silanols species populating the silica surface. Following this idea, in this paper we will present results concerning surface-enhanced Raman spectroscopy (SERS) activity of substrates obtained by a top-down technique (i.e. gold sputtering) which allowed depositing gold nanoparticles at surfaces of silica nanoparticles. Pyridine molecule has been then used as a probe molecule to estimate the SERS activity of the obtained substrates. Objectives: The purpose of the work was to study the SERS activity of the prepared substrates through the estimation of limit of detection (LoD) of pyridine molecule dosed from solutions (benzene was used as solvent) with decreasing pyridine concentration. Materials and methods: For the preparation of the samples AOX50 silica (Evonik Industries, surface area of 50 m2/g) in form of pressed disk, a gold target and a K575X Turbo Sputter Coater (Quorum Technologies) were used. Methods applied: UV-Vis-NIR spectroscopy; HR-TEM microscopy; Raman spectroscopy. Results: Prepared Au/AOX50 substrates with nominal Au thickness 10 nm were characterized by the UV-Vis spectroscopy and HR-TEM microscopy. They showed a relatively complex absorption profile extending to the NIR region. The substrates contained gold nanoparticles with diameter in the range of 2.0–3.5 nm. By using the 785 nm exciting laser line (suggested by the results coming from UV-Vis spectroscopy) for recording Raman spectra, it was possible to observe characteristic pyridine Raman signals by contacting Au/AOX50 substrates with vapour phase of benzene solutions with pyridine concentration as low as 10-7 M comprising LoD. This allowed us to estimate roughly an enhancement factor of 108, as compared with 12.4 M pyridine dosed at naked AOX50 silica surface. Conclusion: Through a top-down technique it was possible to prepare effective SERS substrates composed by Au nanoparticles dispersed at AOX50 silica surfaces. LoD for pyridine dosed from the vapour of its benzene solution appeared to be 10-7 M and the SERS enhancement factor, using as a reference Raman spectra of 12.4 M pyridine interacting with naked AOX50 silica, has been estimated to be approximately 108.

Partial oxidation of methane over SiO2 supported Ni and NiCe catalysts

Abstract Nickel and nickel-ceria catalysts supported on high surface area silica, with 6 wt% Ni and 20 wt% CeO2 were prepared by microwave assisted (co) precipitation method. The catalysts were investigated by XRD, TPR and XPS analyses and they were tested in partial oxidation of methane (CPO). The catalytic reaction was carried out at atmospheric pressure in a temperature range of 400–800 °C with a feed gas mixture containing methane and oxygen in a molecular ratio CH4/O2 = 2. The Ni catalyst exhibited 60% methane conversion with 60% selectivity to CO already at 500 °C. On the contrary, the Ni–Ce catalyst was inert to CPO up to 700 °C. Moreover, the former catalyst reproduced its activity at the descending temperatures maintaining a good stability at 600 °C, over a reaction time of 80 h, whereas the latter one completely deactivated. Test of CH4 temperature programmed surface reaction (CH4-TPSR) revealed a higher methane activation temperature (> 100 °C) for the Ni–Ce catalyst as compared to the Ni one. Noticeable improvement of the ceria containing catalyst occurred when the reaction test started at a temperature higher than the methane decomposition temperature. In this case, the sample achieved the same catalytic behavior of the Ni catalyst. As confirmed by XPS analyses, the distinct electronic state of the supported nickel was responsible for the differences in catalytic behavior.

Asymmetrical Double Flame Spray Pyrolysis-Designed SiO2/Ce0.7Zr0.3O2 for the Dry Reforming of Methane.

Silica has the potential to enhance the performance of ceria-zirconia as a support for the dry reforming of methane; however, controlling the integration of silica with the ceria-zirconia using flame spray pyrolysis (FSP) is a significant challenge. To address this challenge, an asymmetrically variable double-FSP (DFSP) system was established to control the SiO2 interaction with Ce0.7Zr0.3O2. The engineered materials were then utilized as supports for Ni for the dry reforming of methane. Initially, silica formation during FSP synthesis was examined where it was revealed that, at a low precursor concentration (<1.5 M tetraethyl orthosilicate in xylenes), the physical characteristics of the silica varied differently in relation to what is typically encountered during FSP synthesis. Explicitly, on using a 0.5 M tetraethyl orthosilicate precursor, increasing the FSP feed rate provided an increase in the specific surface area from 217 m2/g at 3 mL/min to 363 m2/g at 7 mL/min. Adopting this knowledge on silica formation under these conditions, the asymmetrical DFSP system was then exploited to regulate the integration of ceria-zirconia with the silica. To restrict the silica from coating the particles during DFSP, the intersection distance along the silica flame was tuned from 18.5 to 28.5 cm, whereas the distance along the ceria-zirconia flame was fixed at 5 cm. It was found that at short intersection distances the ceria-zirconia provided sites for silica nucleation and growth, resulting in high surface-area silica encapsulating the ceria-zirconia. At large intersection distances, encapsulation of the ceria-zirconia by silica was suppressed. An enhanced oxygen storage capacity and basicity along with the small Ni sizes facilitated by the longer intersection distances produced the most selective catalyst for the dry reforming of methane.

Silica-chitosan nanocomposite mediated pH-sensitive drug delivery

Stimuli-based drug release is extremely important for therapeutics and organ-specific drug delivery. Chitosan (CS), a deacetylated form of chitin, natural biopolymer, having wide range of properties including antimicrobial and antifungal. High surface area silica nanoparticles (Si NPs) are good drug-vehicular candidates. Curcumin (Cu), a well-known anti-microbial, anti-cancer, anti-fungal, anti-inflammatory drug has been loaded (in-situ) onto the CS-Si NPs nanocomposite, synthesized using sol gel method to yield CS-Si-Cur NPs. The bare (Si-Cur NPs)and drug-loaded (CS-Si-Cur NPs) show particle size of ∼30 nm and ∼130 nm respectively. UV-visible spectroscopy shows the Cur peak at 430 nm; especially of the active enolic group, and the drug loading efficiency ∼60%. Conjugation studies reveal that a weak hydrogen bonding hold the Cur drug molecules in conjugated system. The pH dependent release of Cur drug at pH 4, pH 7.4 and pH 9.2 reveal that 100%, 60% and 35% drug release in 48 h, respectively, at 37 °C (∼body temperature). CS-Si-Cur NPs showing good antimicrobial activity against B. subtilis, Salmonella. thyphimurium, Serritia mercescens, Proteus vulgarism and S. aureus. A pH-sensitive, antimicrobial formulation is hence suggested, whose release profile can be tuned using the pH of the release media.

Towards viable CO2 sequestration: Production of high specific surface area silica by olivine dissolution in concentrated acidic solutions

CO2 sequestration by reaction with ultramafic minerals such as olivine has been considered for decades. However, the moderate leaching yield of olivine by CO2 even at high temperature and pressure, led to consider an alternative. For this purpose, indirect sequestration process has been investigated with acidic dissolution of olivine for the formation of valuable silica. The remaining concentrated solutions of magnesium, iron and nickel salts could be used for production of the separate carbonates. Numerous dissolution tests of industry-grade 120 μm olivine were carried out in a 250 mL stirred reactor under non-oxidant atmosphere with concentrated acidic solutions. Two solid fractions (“Upper” and “Bottom”) and a metal-rich liquor were recovered, then thoroughly characterized. Results are discussed in terms of quality of the silica nanoparticles produced (BET specific area, pore size distribution, purity) as well as of dissolution yields, depending on operating conditions. BET surface area of the silica over 500 m2/g and nearly complete dissolution could be obtained for 3 h at 80 °C, however with appreciable excess of acid. A final test was conducted with an acid excess fixed at 12%, a solid/liquid ratio at 180 g/L, for 2 h at 95 °C: olivine was converted at 72% to silica. The “Upper” solid fraction recovered consisted of regular 15–20 nm particles in agglomerates with an overall BET area near 400 m2/g.