Monitoring bisphosphonate surface functionalization and acid stability of hierarchically porous titanium zirconium oxides

To take advantage of the full potential of functionalized transition metal oxides, a well-understood nonsilane based grafting technique is required. The functionalization of mixed titanium zirconium oxides was studied in detail using a bisphosphonic acid, featuring two phosphonic acid groups with high surface affinity. The bisphosphonic acid employed was coupled to a UV active benzamide moiety in order to track the progress of the surface functionalization in situ. Using different material compositions, altering the pH environment, and looking at various annealing conditions, key features of the functionalization process were identified that consequently will allow for intelligent material design. Loading with bisphosphonic acid was highest on supports calcined at 650 °C compared to lower calcination temperatures: A maximum capacity of 0.13 mmol g(-1) was obtained and the adsorption process could be modeled with a pseudo-second-order rate relationship. Heating at 650 °C resulted in a phase transition of the mixed binary oxide to a ternary oxide, titanium zirconium oxide in the srilankite phase. This phase transition was crucial in order to achieve high loading of the bisphosphonic acid and enhanced chemical stability in highly acidic solutions. Due to the inert nature of phosphorus-oxygen-metal bonds, materials functionalized by bisphosphonic acids showed increased chemical stability compared to their nonfunctionalized counterparts in harshly acidic solutions. Leaching studies showed that the acid stability of the functionalized material was improved with a partially crystalline srilankite phase. The materials were characterized using nitrogen sorption, X-ray powder diffraction, and UV-vis spectroscopy; X-ray photoelectron spectroscopy was used to study surface coverage with the bisphosphonic acid molecules.     

Surface‐Functionalized Nanoparticles by Olefin Metathesis: A Chemoselective Approach for In Vivo Characterization of Atherosclerosis Plaque

The use of click chemistry reactions for the functionalization of nanoparticles is particularly useful to modify the surface in a well‐defined manner and to enhance the targeting properties, thus facilitating clinical translation. Here it is demonstrated that olefin metathesis can be used for the chemoselective functionalization of iron oxide nanoparticles with three different examples. This approach enables, in one step, the synthesis and functionalization of different water‐stable magnetite‐based particles from oleic acid‐coated counterparts. The surface of the nanoparticles was completely characterized showing how the metathesis approach introduces a large number of hydrophilic molecules on their coating layer. As an example of the possible applications of these new nanocomposites, a focus was taken on atherosclerosis plaques. It is also demonstrated how the in vitro properties of one of the probes, particularly its Ca²⁺‐binding properties, mediate their final in vivo use; that is, the selective accumulation in atherosclerotic plaques. This opens promising new applications to detect possible microcalcifications associated with plaque vulnerability. The accumulation of the new imaging tracers is demonstrated by in vivo magnetic resonance imaging of carotids and aorta in the ApoE^?/? mouse model and the results were confirmed by histology.     

Preparation of Functionalized Carbon-Coated Cobalt Nanoparticles with Sulfonated Arene Derivatives,a Study on Surface Functionalization and Stability

The functionalization of magnetic nanoparticles has been an important field in the last decade due to the versatile applications in catalysis and biomedicine. Generally, a high degree of functionalities on the surface of the nanoparticles is desired. In this study, covalent functionalization of various aromatic sulfonic acids on carbon-coated cobalt nanoparticles are investigated on surface functionalization yield and stability. The nanoparticles are prepared via covalent linkage of an in situ generated diazonium on the graphene-like surface. Adsorption and wash experiments were performed to confirm a covalent bonding of the naphthalene derivatives on the nanoparticle surface. With an increased number of sulfonic acid groups on the aromatic compound a significantly lower loading is observed on the corresponding functionalized nanoparticles. This can be counteracted by a change of nitrite species. With this method, nanoparticles with a high number of sulfonic acid groups can be produced.     

Target‐Specific Capture of Environmentally Relevant Gaseous Aldehydes and Carboxylic Acids with Functional Nanoparticles

Aldehyde and carboxylic acid volatile organic compounds (VOCs) present significant environmental concern due to their prevalence in the atmosphere. We developed biodegradable functional nanoparticles comprised of poly(d,l ‐lactic acid)‐poly(ethylene glycol)‐poly(ethyleneimine) (PDLLA‐PEG‐PEI) block co‐polymers that capture these VOCs by chemical reaction. Polymeric nanoparticles (NPs) preparation involved nanoprecipitation and surface functionalization with branched PEI. The PDLLA‐PEG‐PEI NPs were characterized by using TGA, IR, ¹H NMR, elemental analysis, and TEM. The materials feature 1°, 2°, and 3° amines on their surface, capable of capturing aldehydes and carboxylic acids from gaseous mixtures. Aldehydes were captured by a condensation reaction forming imines, whereas carboxylic acids were captured by acid/base reaction. These materials reacted selectively with target contaminants obviating off‐target binding when challenged by other VOCs with orthogonal reactivity. The NPs outperformed conventional activated carbon sorbents.     

Evaluation of the stability and selectivity for various adjustable stationary phases using zirconium oxide supports in high-performance liquid chromatography

The selectivity and retention properties of a zirconia stationary phase were reversibly altered using various ligands containing Lewis base functional groups. A simple loading procedure allowed a variety of ligands to be attached to the zirconia surface via Lewis interactions. The resulting stationary phases were shown to be stable and produced different selectivity and retention properties from the native zirconia material. The metal oxide adsorbent was converted to a diol-type stationary phase using glucose-6-phosphate for use under normal-phase conditions. Reversed-phase supports were produced by loading either octyl- or octadecylphosphonic acid onto the native zirconia support. The properties of these new phases were then compared to commercially available bonded silica analogs. Ligands bound to the surface in this manner were effectively removed and the native zirconia was regenerated using a dilute base wash procedure.     

Hexadecyltriethoxysilane-induced Dispersions of Metal Oxide Nanoparticles in Nonpolar Solvents

Nanoparticles of CeO₂, Fe₃O₄, TiO₂ and ZnO get coated by hexadecyltriethoxysilane on refluxing the nanoparticles and the organosilane in a hydrocarbon solvent. The organosilane-coated metal oxide nanoparticles give stable dispersions in hydrocarbon solvents due to their hydrophobic surface. On heating in air, the organosilane-coated metal oxide nanoparticles yield to silica-coated core-shell type nanoparticles. Dedicated to Late Professor F. A. Cotton.     

Zirconia‐based Aerogels via Hydrolysis of Salts and Alkoxides: The Influence of the Synthesis Procedures on the Properties of the Aerogels

This contribution aims at evaluating different synthesis procedures leading to zirconia‐based aerogels. A series of undoped and yttrium‐doped zirconia aerogels have been prepared via hydrolysis and condensation reaction of different alkoxy‐ and different inorganic salt‐based precursors followed by supercritical drying. Well‐established but deleterious zirconium n‐propoxide (TPOZ) or zirconium n‐butoxide (TBOZ) were used as metal precursors in combination with acids like nitric acid and acetic acid as auxiliary agent for the generation of non‐yttrium stabilized zirconia aerogels. Yttrium‐stabilized zirconia aerogels as well as pure zirconia aerogels were obtained by the salt route starting from ZrCl₄ and crosslinking agents like propylene oxide or acetylacetone. The characteristics of the products were analyzed by nitrogen adsorption measurements, electron microscopy, and X‐ray scattering. It turned out that with respect to all relevant properties of the aerogels as well as the practicability of the synthesis procedures, approaches based on inexpensive non‐toxic salt precursors are the methods of choice. The salt‐based approaches allow not only for low‐cost, easy‐to‐handle synthesis procedures with realizable gelation times of less than 60 seconds, but also delivered the products with the highest surface area (449 m² g^?1 for ZrCl₄) within this series of syntheses.     

Investigation of Acid-Base Equilibria for Symmetrically Substituted <Emphasis Type="Italic">P,P</Emphasis>′-Dialkyl Partial Esters of Bisphosphonic Acids

Bisphosphonic acids are powerful metal chelating reagents with a wide spectrum of applications. A series of partial ester derivatives of bisphosphonic acids was synthesized in order to investigate the physico-chemical changes induced by partial protection of the acid groups. The acid dissociation constants K₁ and K₂ for a homologous series of short-chain aqueous-soluble dibasic bisphosphonic acids, i.e., the P,P′-diethyl methylene-, ethylene- and propylene-bisphosphonic acid partial esters, H₂DEt[MBP], H₂DEt[EBP] and H₂DEt[PrBP], respectively, were determined by potentiometric titration and ³¹P NMR spectrometry. All three diethyl esters are rather acidic with pK₁ < 1.2 and pK₂ < 2.2. The influence of the separation between the phosphonate groups on ligand acidity and successive pK_a values is rationalized in terms of solvation, inductive and electrostatic effects.     

Synthesis of nickel nanoparticles supported on metal oxides using electroless plating: Controlling the dispersion and size of nickel nanoparticles

Nickel nanoparticles supported on metal oxides were prepared by a modified electroless nickel-plating method. The process and mechanism of electroless plating were studied by changing the active metal (Ag) loading, acidity, and surface area of metal oxides and were characterized by UV–vis spectroscopy, transmission electron microscopy, scanning electron microscopy, and H₂ chemisorption. The results showed that the dispersion of nickel nanoparticles was dependent on the interface reaction between the metal oxide and the plating solution or the active metal and the plating solution. The Ag loading and acidity of the metal oxide mainly affected the interface reaction to change the dispersion of nickel nanoparticles. The use of ultrasonic waves and microwaves and the change of solvents from water to ethylene glycol in the electroless plating could affect the dispersion and size of nickel nanoparticles.     

Simple Preparation and Application of TEMPO‐Coated Fe3O4 Superparamagnetic Nanoparticles for Selective Oxidation of Alcohols

The organic oxidant TEMPO (2,2,4,4‐tetramethylpiperdine‐1‐oxyl) was immobilized on iron oxide (Fe₃O₄) superparamagnetic nanoparticles by employing strong metal‐oxide chelating phosphonates and azide/alkyne “click” chemistry. This simple preparation yields recyclable TEMPO‐coated nanoparticles with good TEMPO loadings. They have excellent magnetic response and efficiently catalyze the oxidation of a wide range of primary and secondary alcohols to aldehydes, ketones, and lactones under either aerobic acidic Mn^II/Cu^II oxidizing Minisci conditions, or basic NaOCl Anelli conditions. The nanoparticles could be recycled more than 20 times under the Minisci conditions and up to eight times under the Anelli conditions with good to excellent substrate conversions and product selectivities. Immobilization of the catalyst through a phosphonate linkage allows the particles to withstand acidic oxidizing environments with minimal catalyst leaching. Clicking TEMPO to the phosphonate prior to phosphonate immobilization, rather than after, ensures the clicked catalyst is the only species on the particle surface. This facilitates quantification of the catalyst loading. The stability of the phosphonate linker and simplicity of this catalyst immobilization method make this an attractive approach for tethering catalysts to oxide supports, creating magnetically separable catalysts that can be used under neutral or acidic conditions.     

Bacitracin‐Conjugated Superparamagnetic Iron Oxide Nanoparticles: Synthesis,Characterization and Antibacterial Activity

Bacitracin‐conjugated superparamagnetic iron oxide (Fe₃O₄) nanoparticles were prepared by click chemistry and their antibacterial activity was investigated. After functionalization with hydrophilic and biocompatible poly(acrylic acid), water‐soluble Fe₃O₄ nanoparticles were obtained. Propargylated Fe₃O₄ nanoparticles were then synthesized by carbodiimide reaction of propargylamine with the carboxyl groups on the surface of the iron oxide nanoparticles. By further reaction with N₃‐bacitracin in a Cu^I‐catalyzed azide–alkyne cycloaddition, the magnetic Fe₃O₄ nanoparticles were modified with the peptide bacitracin. The functionalized magnetic nanoparticles were characterized by powder X‐ray diffraction, X‐ray photoelectron spectroscopy, TEM, zeta‐potential analysis, FTIR spectroscopy and vibrating‐sample magnetometry. Cell cytotoxicity tests indicate that bacitracin‐conjugated Fe₃O₄ nanoparticles show very low cytotoxicity to human fibroblast cells, even at relatively high concentrations. In view of the antibacterial activity of bacitracin, the biofunctionalized Fe₃O₄ nanoparticles exhibit an antibacterial effect against both Gram‐positive and Gram‐negative organisms, which is even higher than that of bacitracin itself. The enhanced antibacterial activity of the magnetic nanocomposites allows the dosage and the side effects of the antibiotic to be reduced. Due to the antibacterial effect and magnetism, the bacitracin‐functionalized magnetic nanoparticles have potential application in magnetic‐targeting biomedical applications.     

钴掺杂的磁性氧化铁纳米粒子的可控合成

通过油酸盐前驱体高温热解法制备出大小均匀的钴掺杂四氧化三铁球形纳米粒子, 其钴/铁摩尔比可以通过调节油酸钴与油酸铁的比例进行调变. 当产物中钴/铁摩尔比从0.024增加到0.156, 所制备的氧化铁纳米粒子的饱和磁矩从39 emu·g^-1逐渐减小到30 emu·g^-1, 而矫顽力从0 Oe升至190 Oe. 在305℃下, 随着反应体系的热解时间由0.5 h 增加到3 h, 所制备出的氧化铁纳米粒子尺寸逐渐由7 nm增加到14 nm. 热解时间较短时, 以高价态的四氧化三铁的晶型为主, 辅之以少量的氧化亚铁; 热解时间增加至2 h, 产物的晶型为四氧化三铁和氧化亚铁的复合物; 而继续增加热解时间至3 h, 除四氧化三铁和氧化亚铁之外, 还出现少量的零价态的CoFe合金, 说明铁(钴)元素经历了由三价到二价, 最后被还原为零价的过程. 随着反应温度的升高, 产物的尺寸逐渐增大, 同时产物中氧化亚铁的含量增多.     

The Structure of Multicomponent (Titania/Zirconia) Nanoparticles

The local structure of titania/zirconia nanoparticles has been investigated using small-angle neutron scattering (SANS). The colloids were prepared either by hydrolyzing a mixture of titanium and zirconium alkoxides, and peptizing the resulting hydrolysate with nitric acid (homogeneous) or hydrolyzing a titanium alkoxide, and peptizing the hydrolysate with zirconium(IV) nitrate (heterogeneous). The final titania/zirconia and metal oxide/nitrate mole ratios were 16.0 and 10.0, respectively. The nanoparticles were crystalline anatase (crystallite size ca.8 nm) and amorphous zirconia.The results of SANS contrast-variation experiments are described. The minimum-contrast points for the homogeneous and heterogeneous colloids, determined using either the known analytic form of the scattering at q = 0 or the scattering invariant, gave similar results. Significant differences from the expected value were attributed to the sorption of nitrate counter-ions and hydroxyl species on the surface of the colloids. In both cases, the scattering at minimum contrast was consistent with a fractal network of uni-dimensional zirconia, with a typical diameter of 1.5 nm. The results indicate that in the homogeneous colloids, the zirconia is segregated within the matrix of the titania crystallites (on 1 nm scale), whereas in the heterogeneous colloids, the zirconia is segregated on the surface of the titania crystallites (on 10 nm scale).     

Reversible Diels–Alder Reactions with a Fluorescent Dye on the Surface of Magnetite Nanoparticles

Diels–Alder reactions on the surface of nanoparticles allow a thermoreversible functionalization of the nanosized building blocks. We report the synthesis of well-defined magnetite nanoparticles by thermal decomposition reaction and their functionalization with maleimide groups. Attachment of these dienophiles was realized by the synthesis of organophosphonate coupling agents and a partial ligand exchange of the original carboxylic acid groups. The functionalized iron oxide particles allow a covalent surface attachment of a furfuryl-functionalized rhodamine B dye by a Diels–Alder reaction at 60 °C. The resulting particles showed the typical fluorescence of rhodamine B. The dye can be cleaved off the particle surface by a retro-Diels–Alder reaction. The study showed that organic functions can be thermoreversibly attached onto inorganic nanoparticles.     

A citric acid-derived ligand for modular functionalization of metal oxide surfaces via "click" chemistry

Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.     

Delivery of Highly Active Noble‐Metal Nanoparticles into Microspherical Supports by an Aerosol‐Spray Method

Noble metal nanoparticles (NPs) with 1–5 nm diameter obtained from NaHB₄ reduction possess high catalytic activity. However, they are rarely used directly. This work presents a facile, versatile, and efficient aerosol‐spray approach to deliver noble‐metal NPs into metal oxide supports, while maintaining the size of the NPs and the ability to easily adjust the loading amount. In comparison with the conventional spray approach, the size of the loaded noble‐metal nanoparticles can be significantly decreased. An investigation of the 4‐nitrophenol hydrogenation reaction catalyzed by these materials suggests that the NPs/oxides catalysts have high activity and good endurance. For 1 % Au/CeO₂ and Pd/Al₂O₃ catalysts, the rate constants reach 2.03 and 1.46 min^?1, which is much higher than many other reports with the same noble‐metal loading scale. Besides, the thermal stability of catalysts can be significantly enhanced by modifying the supports. Therefore, this work contributes an efficient method as well as some guidance on how to produce highly active and stable supported noble‐metal catalysts.     

Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil

Improved synthetic approaches for preparing small‐sized Ni nanoparticles (d=3 nm) supported on HBEA zeolite have been explored and compared with the traditional impregnation method. The formation of surface nickel silicate/aluminate involved in the two precipitation processes are inferred to lead to the stronger interaction between the metal and the support. The lower Brønsted acid concentrations of these two Ni/HBEA catalysts compared with the parent zeolite caused by the partial exchange of Brønsted acid sites by Ni²⁺ cations do not influence the hydrodeoxygenation rates, but alter the product selectivity. Higher initial rates and higher stability have been achieved with these optimized catalysts for the hydrodeoxygenation of stearic acid and microalgae oil. Small metal particles facilitate high initial catalytic activity in the fresh sample and size uniformity ensures high catalyst stability.     

ATO纳米粉体的燃烧合成研究

锑掺杂氧化锡(Antimony鄄dopedtinoxideATO)是一种新型多功能材料,具有耐高温、耐腐蚀、机械稳定性好的特点而被广泛应用。作为新型导电填料,可用于材料的抗静电,其效果优于传统的碳黑、金属粉体,表面活性剂等,性价比高于最近提出的碳纳米管导电材料。用于电致变色材料可以替代     

Oxide‐Nanotrap‐Anchored Platinum Nanoparticles with High Activity and Sintering Resistance by Area‐Selective Atomic Layer Deposition

An area‐selective atomic layer deposition (AS‐ALD) method is described to construct oxide nanotraps to anchor Pt nanoparticles (NPs) on Al₂O₃ supports. The as‐synthesized catalysts have exhibited outstanding room‐temperature CO oxidation activity, with a significantly lowered apparent activation energy (ca. 22.17 kJ mol⁻¹) that is half that of pure Pt catalyst with the same loading. Furthermore, the structure shows excellent sintering resistance with the high catalytic activity retention up to 600 °C calcination. The key feature of the oxide nanotraps lies in its ability to anchor Pt NPs via strong metal–oxide interactions while still leaving active metal facets exposed. Our reported method for forming such oxide structure with nanotraps shows great potential for the simultaneous enhancement of thermal stability and activity of precious metal NPs.     

Selectivity in the Ligand Functionalization of Photocatalytic Metal Oxide Nanoparticles for Phase Transfer and Self-Assembly Applications

The functionalization of photocatalytic metal oxide nanoparticles of TiO₂, ZnO, WO₃ and CuO with amine-terminated (oleylamine) and thiol-terminated (dodecane-1-thiol) alkyl-chain ligands was studied under ambient conditions. A high selectivity was observed in the binding specificity of a ligand towards nanoparticles of these different oxides. It was observed that oleylamine binds stably to only TiO₂ and WO₃, whereas dodecane-1-thiol binds stably only to ZnO and CuO. Similarly, polar-to-nonpolar solvent phase transfer of TiO₂ and WO₃ nanoparticles could be achieved by using oleylamine, but not dodecane-1-thiol, whereas the opposite holds for ZnO and CuO. The surface chemistry of ligand-functionalized nanoparticles was probed by attenuated total reflectance (ATR)-FTIR spectroscopy, which enabled the occupation of the ligands at the active sites to be elucidated. The photostability of the ligands on the nanoparticle surface was determined by the photocatalytic self-cleaning properties of the material. Although TiO₂ and WO₃ degrade the ligands within 24 h under both UV and visible light, ligands on ZnO and CuO remain unaffected. The gathered insights are also highly relevant from an application point of view. As an example, because the ligand-functionalized nanoparticles are hydrophobic in nature, they can be self-assembled at the air-water interface to give nanoparticle films with demonstrated photocatalytic as well as anti-fogging properties.