Selective Etching Strategy Research Articles

Vinyl Functionalized Porous Silica Nanospheres Prepared by Poly(1-vinyl-2-pyrrolidone) Grafted Surface-Protected Selective Etching Strategy.

A new effective surface poly(1-vinyl-2-pyrrolidone) (PVP) grafted layer protected selective etching strategy has been used for preparing vinyl functionalized porous silica nanospheres (V-PSNSs). The main reaction mechanism was relied on the vinyl groups distributed on the surface of outer vinyl silica nanospheres (V-SiO2) which can be polymerized with another vinyl monomer, such as 1-vinyl-2-pyrrolidone (VP), in the presence of initiator. It was observed from the research results that only grafting PVP on the surface of outer vinyl silica nanospheres (V-SiO2) can V-PSNSs be obtained, because grafting PVP was able to protect outer V-SiO2 from being etched prior to inner pure silica (sSiO2). In addition, effect of the amounts of sSiO2@V-SiO2 as another monomer substrate on the formation of PVP grafted sSiO2@V-SiO2 (sSiO2@V-SiO2/PVP) was discussed. The results showed that the less of the sSiO2@V-SiO2 amounts, the thinner of the PVP grafted layer on the surface of sSiO2@V-SiO2, the poorer protection ability of the surface. In the present study, V-PSNSs with 29 m2g-1 of BET surface areas and 0.1 cm3g-1 pore volumes were successfully synthesized by grafting 0.3 g of VP on the surface of 0.3 g of sSiO2@V-SiO2 and subsequent etching.

Phase and Composition Tuning of 1D Platinum‐Nickel Nanostructures for Highly Efficient Electrocatalysis

Among various platinum (Pt)‐based nanostructures, porous or hollow ones are of great importance because they exhibit fantastic oxygen reduction reaction (ORR) enhancements and maximize atomic utilization by exposing both exterior and interior surfaces. Here, a new class of porous Pt3Ni nanowires (NWs) with 1D architecture, an ultrathin Pt‐rich shell, high index facets, and a highly open structure is designed via a selective etching strategy by using the phase and composition segregated Pt‐Ni NWs as the starting material. The porous feature of Pt3Ni NWs can be readily fulfilled by changing the Pt/Ni atomic ratio of the starting Pt‐Ni NWs. Such porous Pt3Ni NWs show extraordinary activity and stability enhancements toward methanol oxidation reaction and ORR. The porous Pt3Ni NWs can deliver ORR mass activity of 5.60 A mg−1, which is 37.3‐fold higher than that of the Pt/C. They also show outstanding stability with negligible activity loss after 20 000 cycles. This study offers a unique approach for the design of complex nanostructures as efficient catalysts through precisely tailoring.

Highly dispersed molybdenum incorporated hollow mesoporous silica spheres as an efficient catalyst on epoxidation of olefins

Highly dispersed Molybdenum (VI) incorporated hollow mesoporous silica catalyst was facilely synthesized with a selective etching strategy and then followed with a modified immersion method. Firstly, hollow mesoporous silica spheres were obtained from solid silica spheres with the interaction of cetyltrimethyl ammonium bromide (CTAB) and Na2CO3. Then the catalytic sites were loaded by modified and direct immersion methods as comparison. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption and X-ray photoelectron spectra (XPS). The reactivity of the catalysts was also detected under the same condition in olefin epoxidation. Compared with these two immersion methods, modified method exhibited the best turnover number of 3873 at 6h with a better reactivity and textural properties than direct one. Highly dispersed molybdenum indeed brought excellent activity and high stability. The conversion could reach 100% with a selectivity above 99% after 12h. And the catalyst still had a conversion above 86% and a selectivity above 93% after five runs. More importantly, this modified immersion method could also be widely used in the preparation of catalysts as a simple but efficient way.

Surfactant-assisted selective etching strategy for generation of rattle-like mesoporous silica nanoparticles

Nowadays, rattle-like or so-called yolk-shell nanostructures have set off a new wave of research in view of their prominent features including large surface area, tunable void and flexible functional core, etc. Herein, rattle-like mesoporous silica nanoparticles (RMSNs) with a pure silica core, a hollow cavity and a mesoporous shell have been successfully fabricated via a surfactant-assisted selective etching strategy. The synthetic approach involves the preparation of solid silica spheres with three-layer different structural silica containing the inner core of pure silica, middle layer of hybrid silica and outer shell of surfactant/SiO2 composite, followed by a hydrothermal treatment in hot water. The resulting products show a distinct rattle-like structure and spherical morphology. The average diameter, the shell thickness, and the solid core size of RMSNs are about 290, 35 and 90nm, respectively. During the etching process, the surfactant with different length of alkyl chain (CnTAB, e.g. cetyltrimethylammonium bromide) in outer shell plays a decisive role for the formation of rattle-like structure. Benefiting from the residual amino groups in RMSNs, Au@RMSNs composites can be further constructed by in-situ generating Au nanoparticles into their hollow cavity, demonstrating an excellent catalytic performance for reduction of 4-nitrophenol. Additionally, RMSNs also show a strong ability for adsorption of rhodamine B.

Porous AgPt@Pt Nanooctahedra as an Efficient Catalyst toward Formic Acid Oxidation with Predominant Dehydrogenation Pathway.

For direct formic acid fuel cells (DFAFCs), the dehydrogenation pathway is a desired reaction pathway, to boost the overall cell efficiency. Elaborate composition tuning and nanostructure engineering provide two promising strategies to design efficient electrocatalysts for DFAFCs. Herein, we present a facile synthesis of porous AgPt bimetallic nanooctahedra with enriched Pt surface (denoted as AgPt@Pt nanooctahedra) by a selective etching strategy. The smart integration of geometric and electronic effect confers a substantial enhancement of desired dehydrogenation pathway as well as electro-oxidation activity for the formic acid oxidation reaction (FAOR). We anticipate that the obtained nanocatalyst may hold great promises in fuel cell devices, and furthermore, the facile synthetic strategy demonstrated here can be extendable for the fabrication of other multicomponent nanoalloys with desirable morphologies and enhanced electrocatalytic performances.

Synchronous synthesis/modification of multifunctional hollow silica nanospheres through selective etching and application in catalysis

An effective selective etching strategy has been developed to simultaneously synthesize and modify multifunctional hollow SiO2 nanospheres (HSNs). The key point of this strategy lies in the utilization of (3-aminopropyl)triethoxysilane (APTES) or H2SO4 to etch core-shell composite particles, which contribute to the grafting or transformation of organic functional groups in multifunctional HSNs during the etching process. In our study, cyano-SiO2@cyano-thiol-SiO2 (CN-SiO2@SH-CN-SiO2) composite particles were firstly synthesized by two-step sol-gel reaction of 2-cyanoethyltriethoxysliane (CTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), and then the obtained composite particles could be transformed to be different type of multifunctional HSNs (SH-CN-NH2-HSNs and SH-COOH-HSNs) after respectively etched by APTES or H2SO4. The selective etching strategy greatly simplifies the procedures of preparing multifunctional HSNs. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have demonstrated the hollow structure, and it’s found that the morphology of SH-CN-NH2-HSNs can be regularly changed by manipulating the amount of APTES. Fourier transform infrared (FT-IR) and elemental analyzer have also confirmed that the corresponding organic groups certainly exist in the obtained multifunctional HSNs. In addition, when the as-prepared multifunctional hollow SiO2 spheres were loaded with Au nanoparticles, the composite nanoreactor presented high activity for the catalytic reduction of p-nitrophenol.

A novel functional group difference-based selective etching strategy for the synthesis of hollow organic silica nanospheres

CTES@TCPTES were synthesized by CTES and TCPTES, and then TC-HSNSs could be fabricated with the basic etching agent based on stability difference between core and shell.

Mesoporous metal-organic frameworks with size-, shape-, and space-distribution-controlled pore structure.

Mesoporous Metal–organic frameworks (meso-MOFs) with size-, shape-, and space-distribution-controlled mesopores are obtained by a facile encapsulation and selective etching strategy of metal nanoparticles. Hierarchical or functionalized meso-MOFs are achieved by the above strategy. Interestingly, the functional meso-MOFs display higher catalytic activity originating from the mesopores existing in the MOFs, as well as good selectivity due to protection of the micro­porous frameworks.

Hollow organosilica nanospheres prepared through surface hydrophobic layer protected selective etching

In this study, a facile and effective surface hydrophobic layer protected selective etching strategy has been adopted to fabricate organic functionalized hollow silica nanospheres (OHSNSs). Our experiments demonstrated that the morphology and structure of OHSNSs were greatly affected by the types of organosilanes and concentrations of cetyltrimethylammonium bromide (CTAB) as pore-making agent. At low concentration of CTAB (1.9mg/mL−1), it was found that the protective effect of the hydrophobic layer of 3-thiocyanatopropyltriethoxysilane (TCPTES) was so strong that can be endured long time etching (8h), leading to the formation of hollow core and organic porous shell structure. And yet, the protective effect of the hydrophobic layer of vinyltriethoxysilane (VTES) was too weak to withstand alkali etching, resulting in preferentially etched of the outer vinyl protection shell. Whereas, at a higher concentration of CTAB (2.5mg/mL−1), for TCPTES, the irregular and capsules-like spheres were obtained. In contrast, for VTES, porous core/solid shell structures with shell thickness of 16nm were generated. In addition, no particles were observed when the CTAB concentration was above 2.5mg/mL−1.

Single peptide ligand-functionalized uniform hollow mesoporous silica nanoparticles achieving dual-targeting drug delivery to tumor cells and angiogenic blood vessel cells.

BackgroundThe purpose of this study was to construct hollow mesoporous silica nanoparticles (HMSN) decorated with tLyp-1 peptide (tHMSN) for dual-targeting drug delivery to tumor cells and angiogenic blood vessel cells.MethodsHMSN were synthesized de novo using a novel cationic surfactant-assisted selective etching strategy and were then modified with tLyp-1. Multiple methods, including transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, bicinchoninic acid assay, and nitrogen adsorption and desorption isotherms, were used to characterize the tHMSN. Doxorubicin were chosen as the model cargo, and the uptake of doxorubicin-loaded tHMSN into MDA-MB-231 cells and human umbilical vein endothelial cells (HUVECs), as models of tumor cells and tumor neovascular endothelial cells, respectively, were observed and detected by confocal laser scanning microscopy and flow cytometry. An in vitro pharmacodynamic study and a study of the mechanism via which the nanoparticles were endocytosed were also performed.ResultsHMSN with a highly uniform size and well oriented mesopores were synthesized. After tHMSN were characterized, enhanced uptake of the cargo carried by tHMSN into MDA-MB-231 cells and HUVECs compared with that of their unmodified counterparts was validated by confocal laser scanning microscopy and flow cytometry at the qualitative and quantitative levels, respectively. Further, the pharmacodynamic study suggested that, compared with their unmodified counterparts, doxorubicin-loaded tHMSN had an enhanced inhibitory effect on MDA-MB-231 cells and HUVECs in vitro. Finally, a preliminary study on the mechanism by which the nanoparticles were endocytosed indicated that the clathrin-mediated endocytosis pathway has a primary role in the transport of tHMSN into the cytoplasm.ConclusiontHMSN might serve as an effective active targeting nanocarrier strategy for anti-mammary cancer drug delivery.

Fabrication of mesoporous Fe3O4@SiO2@CTAB–SiO2 magnetic microspheres with a core/shell structure and their efficient adsorption performance for the removal of trace PFOS from water

• A novel adsorbent for trace PFOS removal from water was prepared by a simple method. • Morphology, porosity, composition, and structure of adsorbent were well characterized. • The adsorbent was successfully applied to remove trace PFOS from water at pH = 3. • The impact factors on the trace PFOS removal from water were systematically studied. • Stable adsorption ability is attributed to strong interaction between CTAB and SiO 2 . Novel mesoporous CTAB-functionalized magnetic microspheres with a core/shell structure (mesoporous Fe 3 O 4 @SiO 2 @CTAB–SiO 2 ) was fabricated via a simple sol–gel method combined with selective etching strategy. The morphology, porosity, magnetic property, composition, and structure of mesoporous Fe 3 O 4 @SiO 2 @CTAB–SiO 2 were characterized. Subsequently, the as-prepared composites were successfully applied to remove trace PFOS (500 ng L −1 ) from water at acidic conditions (pH = 3). The fabrication mechanism of mesoporous Fe 3 O 4 @SiO 2 @CTAB–SiO 2 and the impact of various factors on the removal of trace PFOS from water were systematically studied. The recyclability of the as-prepared composites was tested for, five times, at the same conditions.

Synthesis of porous ZnO nanospheres for gas sensor and photocatalysis

Monodispersed porous ZnO nanospheres with diameters about 400–600 nm were successfully fabricated by a facile and effective cationic surfactant assisted selective etching strategy. The as-synthesized ZnO materials were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N2 adsorption–desorption. These samples were used as the gas sensor, showing the high, stable and fast response to acetone, revealing the potential application as gas sensor to detect acetone. In addition, the photocatalytic degradation property of the porous ZnO nanospheres for methyl orange (MO) under UV irradiation was investigated. The degradation efficiency of MO reaches 96 % of the porous ZnO samples after 50 min of UV-light irradiation.

A chemical bottom-up and successive top-down approach for nanoporous SnO2 hollows from Ni3Sn2 nanoalloys: high surface area photocatalysts and anode materials for lithium ion batteries

This work shows that a chemical bottom-up and successive top-down approach is a good synthetic strategy for nanoporous hollow materials. The heating of 3 eq. nickel chloride and 2 eq. tin chloride at 280 °C in the presence of oleylamine resulted in the formation of intermetallic Ni3Sn2 alloy materials. According to mechanistic studies, zerovalent nickel formed by the reduction of precursor induced the reduction of the tin precursor to form Ni3Sn2 alloys. The Ni3Sn2 nanoparticles were characterized by SEM, TEM, PXRD and EDS. When the Ni3Sn2 nanoparticles were treated with 1% nitric acid for 48 hours, the nickel component was completely etched. The resultant materials were nanoporous SnO2 hollow materials, which were characterized by TEM, PXRD and XPS. Due to the nanoparticulate characteristics of shells, BET analysis on the SnO2 hollows showed nanoporosity and a high surface area of 101 m2 g−1. The hollow SnO2 materials with nanoparticulate shells showed excellent photocatalytic activities in the decomposition of Rhodamine B. Moreover, they showed promising electrochemical performances with a discharge capacity of 560 mA h g−1 after 30 cycles and stabilities as anode materials in lithium ion batteries. The preparation of a multi-component alloy and the selective etching strategy can be further expanded to other intermetallic alloy systems for the development of functional materials.

Formation of CdSe/CdS/ZnS-Au/SiO2 dual-yolk/shell nanostructures through a Trojan-type inside-out etching strategy

In this work we report the development of a rapid and selective etching strategy to synthesize a dual-yolk/shell nanostructure consisting of semiconductor-metal hybrid nanocrystals and hollow SiO2 for the first time. By utilizing CdSe/CdS/ZnS quantum dot (CSSQD)/SiO2 core/shell nanoparticles as the template and aurate hydroxyl complexes (Au(OH)4 - ) as the Trojan-type inside-out etching agent, rapid formation of CSSQD-Au hybrid nanocrystal dual-yolk and SiO2 hollow shell occur during the reduction of Au(OH)4 - on CSSQD cores

Engineering Inorganic Nanoemulsions/Nanoliposomes by Fluoride‐Silica Chemistry for Efficient Delivery/Co‐Delivery of Hydrophobic Agents

AbstractA novel drug‐formulation protocol is developed to solve the delivery problem of hydrophobic drug molecules by using inorganic mesoporous silica nanocapsules (IMNCs) as an alternative to traditional organic emulsions and liposomes while preserving the advantages of inorganic materials. The unique structures of IMNCs are engineered by a novel fluoride‐silica chemistry based on a structural difference‐based selective etching strategy. The prepared IMNCs combine the functions of organic nanoemulsions or nanoliposomes with the properties of inorganic materials. Various spherical nanostructures can be fabricated simply by varying the synthetic parameters. The drug loading amount of a typical highly hydrophobic anticancer drug‐camptothecin (CPT) in IMNCs reaches as high as 35.1 wt%. The intracellular release of CPT from carriers is demonstrated in situ. In addition, IMNCs can play the role of organic nanoliposome (multivesicular liposome) in co‐encapsulating and co‐delivering hydrophobic (CPT) and hydrophilic (doxorubicin, DOX) anticancer drugs simultaneously. The co‐delivery of multi‐drugs in the same carrier and the intracellular release of the drug combinations enables a drug delivery system with efficient enhanced chemotherapeutic effect for DOX‐resistant MCF‐7/ADR cancer cells. The special IMNCs‐based “inorganic nanoemulsion”, as a proof‐of‐concept, can also be employed successfully to encapsulate and deliver biocompatible hydrophobic perfluorohexane (PFH) molecules for high intensity focused ultrasound (HIFU) synergistic therapy ex vivo and in vivo. Based on this novel design strategy, a wide range of inorganic material systems with similar “inorganic nanoemulsion or nanoliposome” functions will be developed to satisfy varied clinical requirements.

A facile in situ hydrophobic layer protected selective etching strategy for the synchronous synthesis/modification of hollow or rattle-type silica nanoconstructs

A novel and general in situ hydrophobic shell-protected selective etching strategy has been developed to synchronously synthesize and modify hollow mesoporous silica nanoparticles (HMSNs) and rattle-type mesoporous silica nanoparticles (RMSNs) with well-defined morphology, effectively avoiding the drawbacks of post-modification. The key point of the strategy lies in the hydrophilicity differences between the pure silica inner core and the organic hybrid silica shell, which results in the preferential etching of the pure silica inner core. Except that amino group functionalized HMSNs (amino-HMSNs) can be synthesized via this strategy, it can be readily applied for the synthesis of HMSNs and RMSNs synchronously grafted with different kinds of functional groups by employing other silane coupling agents, directly indicating the generality of this strategy. Furthermore, adding no additional reduction agents, the amino-HMSNs can be regarded as nanoreactors, and a distinctively heterogeneous rattle-type structure, Au@HMSN/Au, with an entrapped size-tunable Au nanoparticle and some small Au nanocrystals embedded in the hollow cavity and shell of each nanoparticle, respectively, is obtained. As hybrid ultrasound contrast agents (UCAs), unlike micro-sized organic UCAs merely confined to blood pool imaging, the as-synthesized nano-sized amino-HMSNs can achieve excellent in vitro ultrasound imaging, and potentially be applied in cell-level imaging. More importantly, relying on the process merits of our strategy, such as the doping of silane coupling agents and no calcination treatment, amino-HMSNs exhibit enhanced ultrasound imaging to some certain extent compared to the calcined ones.

Synthesis of core–shell structured TS-1@mesocarbon materials and their applications as a tandem catalyst

Core–shell structured TS-1@mesocarbon (TS-1@MC) materials with mesoporous carbon as the shell and microporous TS-1 titanosilicate as the core were synthesized through a nanocasting and selective silica etching strategy. The faithful replica structure was constructed from the composite of TS-1@mesosilica and carbon when tetrapropylammonium hydroxide (TPAOH) was employed to selectively remove the amorphous mesosilica shell while the core zeolite crystal structure was not destroyed. In contrast, the protective effect was not seen when sodium hydroxide or hydrogen fluoride was employed as a silica-leaching agent. The obtained TS-1@MC had a bimodal pore structure consisting of 2.9 nm mesopores in the carbon shell and 0.51 nm micropores in the TS-1 core. Its specific surface area and total pore volume reached 883 m2 g−1 and 0.63 cm3 g−1, respectively. TS-1@MC was used as the support to load palladium nanoparticles (Pd NPs) in the carbon shell. Having an average particle size of approximately 2 nm, the Pd NPs were highly dispersed and confined in the mesopores of the carbon shell. Pd/TS-1@MC thus obtained served as an efficient tandem catalyst in the direct epoxidation of propylene with hydrogen and oxygen.

Magnetic Hollow Mesoporous Silica Nanospheres: Facile Fabrication and Ultrafast Immobilization of Enzymes

Hollow mesoporous silica nanospheres with large pore size of around 11 nm have been synthesized by a structural difference based selective etching strategy, and the highly dispersed hydrophobic Fe3O4 nanoparticles with a particle size of 5 nm were then impregnated into hollow cores of nanospheres through these large pores by a vacuum impregnation technique. The structural characteristics of obtained magnetic composites were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Selected Area Electron Diffraction (SAED), Ultraviolet-visible (UV-Vis) and Vibrating Sample Magnetometer (VSM). The results show that the obtained Fe3O4-hollow mesoporous silica composites exhibit superparamagnetic property with saturation magnetization value of 4.17 emu/g. Furthermore, the obtained supports show ultrafast immobilization of hemoglobin and the immobilized enzymes are not denatured, indicating that the superparamagnetic hollow mesoporous silica spheres are excellent support for immobilization of enzymes with magnetic recycling property.

A cationic surfactant assisted selective etching strategy to hollow mesoporous silica spheres

Hollow mesoporous silica spheres have recently attracted increasing attention. However, effective synthesis of uniform hollow mesoporous spheres with controllable well-defined pore structures for fundamental research and practical applications has remained a significant challenge. In this work, a straightforward and effective "cationic surfactant assisted selective etching" synthetic strategy was developed for the preparation of high-quality hollow mesoporous silica spheres with either wormhole-like or oriented mesoporous shell. The as-prepared hollow mesoporous silica spheres have large surface area, high pore volume, and controllable structure parameters. Our experiments demonstrated that cationic surfactant plays critical roles in forming the hollow mesoporous structure. A formation mechanism involving the etching of solid SiO(2) accelerated by cationic surfactant followed by the redeposition of dissolved silica species directed by cationic surfactant is proposed. Furthermore, the strategy can be extended as a general strategy to transform silica-coated composite materials into yolk-shell structures with either wormhole-like or oriented mesoporous shell.

Silica@Carbon mesoporous nanorattle structures synthesised by means of a selective etching strategy

A facile route for the fabrication of nanorattles composed of tunable silica spherical nanoparticles confined inside mesoporous carbon shells is presented. The synthetic strategy involves several steps: i) the synthesis of solid core/mesoporous shell silica microspheres, ii) the infiltration of the mesoporous shell with a carbon precursor and its conversion to carbon through a carbonization process and iii) the controlled dissolution of the silica by means of a soft etching agent (NaOH 1.5 M). Following this procedure, a variety of Silica@Carbon nanorattles of diameter ∼ 430 nm is produced. The diameter of the silica core can be uniformly tuned between 330 nm and 160 nm by varying the etching time in a range of 2 h–44 h. The rate constant for the dissolution process of the silica core was estimated to be k ≈ 1.2 × 10 − 10 g cm − 2 s − 1 . These nanorattles have a high BET surface area and a large pore volume, depending on the amount of silica in the composite.