Amino-functionalized Silica Research Articles

Amino-Modified Silica as Effective Support of the Palladium Catalyst for 4-Nitroaniline Hydrogenation

The article describes the synthesis of aminoorgano-functionalized silica as a prospective material for catalysis application. The amino groups have electron donor properties which are valuable for the metal chemical state of palladium. Therefore, the presence of electron donor groups is important for increasing catalysts’ stability. The research is devoted to the investigation of silica amino-modified support influence on the activity and stability of palladium species in 4-nitroaniline hydrogenation process. A series of catalysts with different supports such as SiO2, SiO2-C3H6-NH2 (amino-functionalized silica), γ-Al2O3 and activated carbon were studied. The catalytic activity was studied in the hydrogenation of 4-nitroaniline to 1,4-phenylenediamine. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and chemisorption of hydrogen by the pulse technique. The 5 wt.% Pd/SiO2-C3H6-NH2 catalyst exhibited the highest catalytic activity for 4-nitroaniline hydrogenation with 100% conversion and 99% selectivity with respect to 1,4-phenylenediamine.

Gold-Based Nanoparticles on Amino-Functionalized Mesoporous Silica Supports as Nanozymes for Glucose Oxidation

The transformation of glucose represents a topic of great interest at different levels. In the first place, glucose is currently conceived as a green feedstock for the sustainable production of chemicals. Secondly, the depletion of glucose at the cellular level is currently envisioned as a promising strategy to treat and alter the erratic metabolism of tumoral cells. The use of natural enzymes offers multiple advantages in terms of specificity towards the glucose substrate but may lack sufficient robustness and recyclability beyond the optimal operating conditions of these natural systems. In the present work, we have evaluated the potential use of an inorganic based nanohybrid containing gold nanoparticles supported onto ordered mesoporous supports. We have performed different assays that corroborate the enzyme-mimicking response of these inorganic surrogates towards the selective conversion of glucose into gluconic acid and hydrogen peroxide. Moreover, we conclude that these enzyme-like mimicking surrogates can operate at different pH ranges and under mild reaction conditions, can be recycled multiple times and maintain excellent catalytic response in comparison with other gold-based catalysts.

A Convenient and Versatile Strategy for the Functionalization of Silica Foams Using High Internal Phase Emulsion Templates as Microreactors.

Functional porous materials show extensive applications in the environment, biology, aerospace, and so on. In this work, the generation of silica foams and functionalization of pore surface were simultaneously realized through an interfacial sol-gel reaction within high internal phase emulsion (HIPE) microreactors, where a hyperbranched polyethoxysiloxane (PEOS) was used as the sole stabilizer for the HIPEs. With various functional substances containing amino, epoxy, and carboxyl groups initially dissolved in the aqueous phase of HIPEs, these functional groups could be grafted onto the pore surface in the process of forming silica foams. Amino-functionalized silica foam showed fast adsorption of sunset yellow, and the adsorption capacity could reach as high as 1213.13 mg/g. Sodium polyacrylate-modified silica foam exhibited good adsorption capacity of cationic dyes and metal ions, e.g., 280.11 mg/g to methylene and 226.24 mg/g to Cu(II). Epoxy-functionalized silica foam particles were confirmed with a pronounced activity at the oil/water interface due to their Janus-like surface, which could be used as Pickering stabilizer. This HIPE-based synthesis strategy for silica foams shows promising future in adsorption, emulsion stabilization, and compatibilization.

Preparation of seven kinds of amino bonded silica gels and their adsorption to heavy metal Pb2

Seven kinds of amino bonded silica gels were prepared. They were aminopropyl bonded silica gel (SiO2-N), ethylenediamine-N-propyl bonded silica gel (SiO2-2N), diethylenetriamine bonded silica gel (SiO2-3N), triethylenetetramine bonded silica gel (SiO2-4N), tetraethylene pentamine bonded silica gel (SiO2-5N), pentaethylene hexamine bonded silica gel (SiO2-6N) and polyvinylimide bonded silica gel (SiO2-nN). The densities of the bonded amino groups in SiO2-N and SiO2-2N prepared by a one-step method were up to 2.07mmol/g and 1.71mmol/g, respectively. The density of the bonded amino groups in SiO2-nN with ethylene imine units prepared by a two-step method, was 0.02mmol/g. The densities of the bonded amino groups in the other silica gels were similar, about 0.50mmol/g. The synthesized silica gels were used to investigate the adsorption of the heavy metal ion Pb2+ which commonly exists in aqueous solutions. About 20 mg of the silica gel was added to 10 mL of 400 mg/L Pb2+, at pH 5 and 30℃. The results indicated that the adsorption capacity reached the maximum value after 10 h. The adsorption process was fit to the Freundlich isothermal equation. The adsorption capacities of SiO2-N, SiO2-2N, SiO2-3N, SiO2-4N, SiO2-5N, SiO2-6N and SiO2-nN to Pb2+were 131.28, 138.98, 85.37, 75.22, 61.87, 79.12 and 114.06 mg/g, respectively, indicating the potential utility of these amino-functionalized silica gels for the adsorption of Pb2+.

Comparison of immune responses in guinea pigs by intranasal delivery with different nanoparticles-loaded FMDV DNA vaccine

To compare different nanoparticle-based nasal vaccines against foot-and-mouth disease (FMD), chitosan (CS)-coated poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) (CS/PLGA-NPs) and amino-functionalized mesoporous silica nanoparticles (Am/MSNs) loaded with FMDV recombinant plasmid (pP12A3C/IFN-CS/PLGA-NPs and pP12A3C/IFN-Am/MS-NPs) were used to induce mucosal and systemic immune responses in guinea pigs via intranasal delivery. Simultaneously, CpG oligodeoxy nucleotides (ODNs) as a vaccine adjuvant were encapsulated in chitosan-coated poly (lactic-co-glycolic acid) nanoparticles (CpG-CS/PLGA-NPs). The pP12A3C/IFN-CS/PLGA-NPs and CpG-CS/PLGA-NPs generated displayed good morphology, high stability, mean diameters of 500 and 400 nm and encapsulation efficiencies of 83.8% and 88.4%, respectively. Data from the in vitro release assay showed that plasmid and CpG were sustainably released from nanoparticles (up to 66.73% and 64%, respectively, of the total amount loaded). Guinea pigs immunized with pP12A3C/IFN-CS/PLGA-NPs + CpG-CS/PLGA-NPs showed markedly higher mucosal, cellular and humoral immune responses than those administered pP12A3C/IFN-CS/PLGA-NPs or naked plasmid vaccine alone. FMDV-specific secretory immunoglobulin A (sIgA) antibodies in nasal washes were initially detected at 3 days post-vaccination with CS/PLGA-NPs loaded with plasmid. Guinea pigs immunized with pP12A3C/IFN-CS/PLGA-NPs also displayed higher cellular and humoral immune responses than pP12A3C-CS/PLGA-NPs and naked plasmid vaccine alone. FMDV-specific immunoglobulin G (IgG) antibodies in serum were initially detected at 5 days post-vaccination (intramuscularly) with the naked plasmid. Finally, challenge experiments 42 days post-vaccine revealed 100% protection in guinea pigs immunized with pP12A3C/IFN-CS/PLGA-NPs + CpG-CS/PLGA-NPs and pP12A3C/IFN-CS/PLGA-NPs. However, plasmid DNA was burst released from pP12A3C/IFN-Am/MS-NPs. Our attempts to use pP12A3C/IFN-Am/MS-NPs to immunize guinea pigs failed to induce immune responses. In conclusion, CpG and IFN-α adjuvant based FMD vaccines elicit protection in guinea pigs. Moreover, CS-coated PLGA NPs present an efficient and safe mucosal immune delivery system for FMDV DNA vaccine. Data from the current study provide a foundation for understanding and further evaluating protective immune responses in pigs.

Self-healing of chemically bonded hybrid silica/epoxy for steel coating

New amino-functionalized smart silica composites and nanoparticles were prepared from hydrolyzing microgel based on N-isopropylacrylamide-co-vinyltrimethoxysilane (NIPAM-VTS) with tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTS). The chemical structure, morphology, particle sizes, and thermal stability were evaluated and proved that the amino group contents were increased on the surfaces of silica composites more than that modified after calcination at 700 °C. The amino-functionalized calcined silica nanoparticles and NIPAM-VTS-polysiloxane were found to show better dispersion capability than silica NPs particles existed in the epoxy hybrid coatings. The amino-functionalized hybrid silica epoxy coatings were found to be much superior in the adhesion, mechanical testing and corrosion protection over those of hybrid materials without amino-functionalization. The amino-functionalized NIPAM-VTS-polysiloxane shows new self-healing performance when blended with epoxy matrix at weight content equals or above 6 Wt. % after exposure to salt spray humidity of seawater. The self-healing performance may have probably resulted from the salt sensitivity of amino-functionalized NIPAM-VTS-polysiloxane composite and enhancement of the adhesion strength due to the formation of Fe O Si and Fe NH Si covalent bonds at the interface of epoxy coating.

O-Phenylenediamine/gold nanocluster-based nanoplatform for ratiometric fluorescence detection of alkaline phosphatase activity

This study demonstrates a novel and convenient ratiometric fluorescent method for the detection of alkaline phosphatase (ALP) activity. Amino-functionalized mesoporous silica nanoparticle-gold nanoclusters (MSN-AuNCs) nanocomposites were integrated with o-phenylenediamine (OPD) to form a ratiometric fluorescence nanoplatform. The presence of ALP induced the generation of quinoxaline (QX) derivative which called 3-(dihydroxyethyl)furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission at 450 nm, while the orange-red fluorescence of MSN-AuNCs at 580 nm was slightly quenched. Meanwhile, an obvious fluorescence color change from orange-red to purple and finally to blue can be observed by naked eyes with the increasing of ALP concentration. Therefore, employing the fluorescence emission of DFQ at 450 nm as the reporter signal and the fluorescence emission of MSN-AuNCs at 580 nm as a reference signal, a sensitive ratiometric detection method for ALP was developed. Quantitative detection of ALP activity in the linear range from 0.2 to 80 U/L with a detection limit of 0.1 U/L can be realized in this way, which endows the assay with high sensitivity enough for practical detection of ALP in human serum samples.

Synthesis of temperature-responsive magnetic mesoporous silica and temperature dependence of its physical properties

In this study, a novel composite (PAMMS) was prepared using poly (N-isopropylacrylamide) (PNIPAM) as a temperature-responsive polymer, magnetite as a magnetic substance, and amino-functionalized mesoporous silica (MS) as an adsorbent. The temperature-dependence of the physical properties such as methyl orange (MO) adsorption, aggregation/sedimentation, and magnetic separation of this composite was investigated. It was found that the composite consisted of 11.3 wt% magnetite, 0.6 mmol/g amino groups, and 4.6 wt% PNIPAM. The MO adsorption behaviour of the PAMMS composite could be well-explained by the Langmuir model and pseudo-second-order rate equation. At 20 °C (below the lower critical solution temperature (LCST) of PNIPAM), the composite showed an MO adsorption amount of 174 μmol/g, which is slightly larger than that (143 μmol/g) at observed 35 °C (above the LCST of PNIPAM). The optical microscopic observations revealed that the size of the PAMMS aggregates at 45 °C (above LCST) was larger than that at room temperature. Hence, the magnetic separation ratio of PAMMS at 45 °C was higher than that at room temperature. The PAMMS composite showed effective MO adsorption below the LCST of PNIPAM and magnetic separation above the LCST of PNIPAM.

One-pot Facile Preparation of Amino-functionalized Silica Hybrid Monoliths for Mixed-mode Chromatography

Silica hybrid monolithic columns were prepared using two precursors, in which organo-functionalized trialkoxysilanes are mixed with tetraalkoxysilanes. In this study, several types of amino-functionalized silica hybrid monolithic columns were prepared via single-step “one-pot” approach, and the amount of silica precursors, porogens, as well as the reaction conditions were optimized. The preparation was carried out by mixing the silica precursors, i.e. tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS) with amino precursors such as aminopropyltrimethoxysilane (APTES), aminoethylaminopropyl-trimethoxysilane (AEAPTMS), and phenylaminopropyltrimethoxysilane (PAPTMS) in a porogenic solution. The chromatographic performance of these hybrid monolithic columns was optimized by investigating several parameters through the separation of inorganic anions (IO3-, BrO3-, Br-, NO2-, NO3-, I-, SCN-) and some polar compounds (thymine, thymidine, adenosine, adenine, uridine). Results showed that the silica hybrid monolithic columns could be operated at higher flow-rate that favors rapid separation. The run-to-run repeatability of Si-APTES and Si-PAPTMS hybrid monolithic columns were satisfactory with relative standard deviations (n = 5) of less than 8% for all the analyte anions.

Preparation and characterization of antibacterial poly(lactic acid) nanocomposites with N-halamine modified silica

In this work, silica nanoparticles modified with a new N-halamine precursor (EBDMH-SiO2 NPs) were synthesized through immobilization of 3-(4′-epoxyethyl-benzyl)-5,5-dimethylhydantoin (EBDMH) on the surface of amino-functionalized silica NPs. Then, EBDMH-SiO2 NPs and poly(lactic acid) (PLA) were blended at 185 °C to prepare a novel environmentally friendly PLA based nanocomposite (PLA/EBDMH-SiO2). The addition of EBDMH-SiO2 NPs has great influences on the thermal properties of nanocomposite. DSC results show that the grass transition temperature (Tg), cold crystallization temperature (Tcc) and melting temperature (Tm) of PLA in nanocomposites gradually decrease with the increase of EBDMH-SiO2 NPs contents up to 5%. After that, further rise in EBDMH-SiO2 NPs content actually increases Tg, Tcc, and Tm. The overall crystallization and spherulite growth rate of PLA show the similar trend. Furthermore, the introduction of EBDMH-SiO2 NPs increases the storage modulus and viscosity of the melt of nanocomposite, providing an additional benefit for PLA blowing and injection molding. After chlorination, the N-halamine precursors on the nanocomposite surfaces are transformed into N-halamines, which provide strong antibacterial activities against E. coli (CMCC 44103) and S. aureus (ATCC 6538), pointing to good potentials of the PLA/EBDMH-SiO2 nanocomposites for antibacterial applications including food packaging, filters, and a wide range of hygienic products.

Immobilizing amino-functionalized mesoporous silica into sodium alginate for efficiently removing low concentrations of uranium

Abstract A large volume of wastewater containing low concentrations of uranium is generated owing to the development and utilization of nuclear energy, which poses an environmental hazard. Therefore, an efficient strategy to remove uranium from the wastewater is important. In this study, a novel adsorbent, namely aMSP/SA, was prepared by immobilizing amino-functionalized mesoporous silica (aMSP) with sodium alginate (SA) for removing low concentration hexavalent U(VI), which is mobile and soluble. The effects of pH, initial concentration, time, temperature, coexisting ions, and regeneration on the removal efficiency of uranium by aMSP/SA were investigated. Results show that the saturated adsorption capacity of aMSP/SA for uranium was 210 mg/g at pH 4.0 and 313 K, and the concentration of U(VI) could be reduced from 1.0 mg/L to 1.31 μg/L. The aMSP/SA shows a high efficiency uranium removal of 99.41% in mine water and affinity toward uranium in a mixed metal solution. Additionally, the structure and possible adsorption mechanism of aMSP/SA were characterized by Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and energy-dispersive spectrometry (EDS). The main interaction mechanisms may be explained by ion exchange with Ca2+ on carboxyl and coordination with hydroxyl and amino groups. This study highlights that a high removal efficiency (99.87% for 1.0 mg/L) and easy separation of large particle sizes (3–4 mm) makes aMSP/SA a promising material for eliminating low concentration U(VI) in industrial applications.

Amino-functionalized mesostructured cellular foam silica: a highly efficient andrecyclable catalyst in the Knoevenagel condensation reaction

Amino-functionalized mesostructured cellular foam silica: a highly efficient andrecyclable catalyst in the Knoevenagel condensation reaction

Ultrasonic assisted adsorptive removal of toxic heavy metals from environmental samples using functionalized silica-coated magnetic multiwall carbon nanotubes (MagMWCNTs@SiO2)

In this approach, an amino-functionalized silica coated multiwall carbon nanotube (AminMagMWCNTs@SiO2), for the first time, was rationally designed, prepared, and then investigated as an adsorbent for the adsorption and removal of Pb (II) and Cd (II) from environmental samples. The properties of synthesized magnetic nanoadsorbents were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The diameter of magnetic nanoadsorbents was in the range of 60–80 nm. The effects of various parameters on the adsorption efficiency were simultaneously studied using a chemometric design. The variables of interest were the amount of nanoadsorbent, pH and ultrasonication time. The experimental parameters were optimized using a Box–Behnken design and the response surface equations were derived. The removal of magnetic nanoadsorbents from the aqueous solution was simply achieved by applying an external magnetic field following the adsorption process. The adsorption efficiencies of AminMagMWCNTs@SiO2 nanoadsorbent for Pb (II) and Cd (II) ions were in the range of 98–104% under the optimum condition. The results demonstrated that the amino-functionalized MagMWCNTs@SiO2 nanoadsorbent could be used as a simple, efficient, regenerable and cost-consuming material for the removal of desired heavy metal ions from environmental water and soil samples.

Preparation of amino-functionalized mesoporous silica (MCM-41) for Nitrate anion adsorption from aqueous solution

In this study, mesoporous silica MCM-41 material was synthesized using simple method at room temperature, and then loaded it with amine group by grafting method. MCM-41 was characterized by means of atomic force microscopy (AFM), X-ray diffraction (XRD), BET surface area; Thermal Gravimetric Analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. Then the ability of MCM-41 as adsorbents to treat NO3 anion as inorganic pollutant from synthetic wastewater was investigated. Batch adsorption was employed to determine the effects of initial concentration (25-150 mg/L), pH (2-11), temperature (297,313,333 K), adsorbent dose (0.1-2g), and contact time (0–140 min). The results indicated that the kinetic data for nitrate anion adsorption with MCM-41 was fitted well with the pseudo-second-order kinetic model (R2=1). It was found that the Freundlich adsorption isotherm model for nitrate anion had the best fit with the experimental data. Various adsorbents (activated carbon, SBA-15, MCM-48) have been utilized to investigate their ability to remove nitrate anion and the results show that MCM-48 could be used to remove NO3 better than other adsorbents.

Green iron nanoparticles supported on amino-functionalized silica for removal of the dye methyl orange

This work describes the synthesis of green iron nanoparticles (FeNPs) supported on amino-functionalized silica, carried out in presence of the extract of the plants Yerba Mate (Ilex paraguariensis) or black tea (Camellia sinensis), or in presence of the biodiesel co-product glycerol, as green reducing and stabilizing agents. The materials were characterized by AAS, SEM, TEM, FTIR, XRD, ASAP, Mössbauer spectroscopy and thermogravimetric analysis, which revealed the formation of amorphous FeNPs of iron oxyhydroxides, such as akaganeite and ferrihydrite. FeNPs in the order of 5 to 20 nm were obtained from tea. Besides, the plant extracts were able to reduce the Fe3+ precursor ion to Fe2+ species bound to the plant polyphenols. The FeNPs were applied in the removal of the azo dye methyl orange by adsorption and heterogeneous Fenton degradation, at different reaction conditions, such as catalyst dosage, pH, hydrogen peroxide concentration, and temperature. All iron compounds prepared removed the dye completely after three hours of reaction, and could be successfully recycled. In particular the FeNPs prepared with glycerol were active up to the fifth cycle in the Fenton degradation tests, due to the lower iron and organic compounds leaching. Kinetics showed that the adsorption is a key step in the dye removal, and that the adsorption sites are composed by the FeNPs bound to polyphenols/glycerol. The superior activity of the supported FeNPs in relation to the free analogues showed the benefits of the functionalization of the silica by the amino groups to stabilize the green iron nanoparticles.

Genipin crosslinked bioactive collagen/chitosan/hyaluronic acid injectable hydrogels structurally amended via covalent attachment of surface-modified silica particles

Collagen, chitosan and hyaluronic acid based multicomponent injectable and in situ gellating biomimetic hybrid materials for bone tissue engineering applications were prepared in one-step procedure. The bioactive phase in the form of surface-modified silica particles was introduced to the solutions of biopolymers and simultaneously crosslinked with genipin both the biopolymer matrix and dispersed particles at 37 °C. The novel approach presented here involved the use of silica particles which surfaces were priory functionalized with amino groups. That modification makes possible the covalent attachment of silica particles to the polymeric hydrogel network on crosslinking with genipin. That methodology is especially important as it makes possible to obtain the hybrid materials (biopolymer-silica particles) in which the problems related to the potential phase separation of mineral particles, hindering their in vivo application can be eliminated. The hybrids of various compositions were obtained and their physicochemical and biological properties were determined. The in vitro experiments performed under simulated body fluid conditions revealed that the amino-functionalized silica particles covalently attached to the biopolymeric network are still bioactive. Finally, the in vitro cell culture studies shown that the materials developed are biocompatible as they supported MG-63 cells adhesion, proliferation as well as Alkaline phosphatase (ALP) expression.

Synthesis of imprinted amino-functionalized mesoporous silica and their selective adsorption performance of Pb2+, Cu2+, and Zn2+

The synthesis of imprinted amino-functionalized mesoporous silica (IAFMS) are using lead, copper, and zinc ions as imprinting species, anhydrous ethanol as a solvent, PEG-2000 as a template agent, tetramethylammonium hydroxide (TMAOH) as an auxiliary template agent, and tetraethoxysilane (TEOS) as a source of silica. The amino group was provided via the most common agent (3-aminopropyl)triethoxysilane (APTES). Based on the uniform design and response surface analysis, the optimum molar ratios of synthetic species such as APTES:heavy metal ions:TMAOH:PEG-2000:TEOS:anhydrous ethanol were determined as 0.270:0.065:0.25:0.073:1:50. Subsequently, Pb-IAFMS, Cu-IAFMS, and Zn-IAFMS were prepared with the same ratios as the above. Then, isothermal adsorption and selective adsorption of Pb(II), Cu(II), and Zn(II) were carried out. The results showed that the adsorption of heavy metal ions was mainly a chemical adsorption, the adsorbent surface was not a completely uniform adsorption, and a higher temperature was beneficial to the adsorption of heavy metal ions. Compared with q(m) values in the Langmuir model, the adsorption capacities of target ions onto imprinted materials can be 32.6-71.2% higher than those on the non-imprinted material. Values of relatively selective coefficients of IAFMS ranged from 4.35 to 18.45, which reveals the remarkable affinities of imprinted samples to the corresponding ions.[GRAPHICS].

Synthesis of anionic gemini surfactant-templated mesoporous silica nanoparticles and its adsorption application for Pb2+

Amino-functionalized mesoporous silica nanoparticles (AFMSN) were prepared based on the self-assembly process of the pre-fabricated template of anionic gemini surfactant. The perfect mass ration of the reactants for the synthesis of the AFMSN with high surface area and amino loading was optimized by orthogonal experiments. Adsorption capability of the optimized product for lead ion (Pb2+) was investigated in detail. Specially, the effects of the amino content, solution pH, adsorbent dosage, temperature, and interference of other metal ions on the removal efficiency of Pb2+ were studied. It is found that these factors can greatly affect the removal efficiency of Pb2+ and the prepared adsorbent exhibits the high adsorption selectivity for Pb2+. At an optimal condition, the AFMSN adsorbent presents an excellent adsorption capacity for Pb2+ up to 211.42 mg/g. The adsorption kinetics study revealed that the pseudo-second-order model could well describe the Pb2+ adsorption process, and the adsorption isotherm was fitted well with the Langmuir model. More importantly, the AFMSN adsorbent could be recycled 8 times and a high adsorption efficiency of Pb2+ could still be maintained. Therefore, the prepared AFMSN adsorbent may find practical application in removing Pb2+ from the polluted water.

NH2-MCM-41 supported on nitrogen-doped graphene as bifunctional composites for removing phenol compounds: Synergistic effect between catalytic degradation and adsorption

Nitrogen-doped graphene (NG) has received increasing attention as a metal-free catalyst in advanced oxidation processes (AOPs). In the present study, amino-functionalized mesoporous silica (NH2-MCM-41) was anchored onto NG surface and stacked NG sheets were unfolded with porous channels, thereby constructing unique catalytic and adsorption cells for removing p-cresol (p-CR) and bisphenol A (BPA). Compared with pristine NG, the nitrogen content of NG/NH2-MCM-41 composites increased from 3.61% to 4.83%, and the surface area enlarged from 98.03 m2/g to 193.93 m2/g. Meanwhile, the water contact angle reduced from 70.7° to 36.3°, indicating improved dispersibility of NG/NH2-MCM-41 composites in aqueous solution. Furthermore, modified NG in NG/NH2-MCM-41 composites exhibited 4.5-fold and 3.4-fold removal amount for p-CR and BPA, respectively, compared to that on pristine NG. Quenching experiments and characterization of reactive oxygen species (ROS) revealed that radical and nonradical mechanisms were involved in the catalytic process. Based on an investigation of interactions between NG/NH2-MCM-41, ROS and pollutants, a synergistic effect between catalytic degradation and adsorption was found and clarified by contrastive experiments. This work provided a strategy for modifying NG-based bifunctional composites and promoted the environmental remediation of aromatic pollutants by AOPs.

New Insights into the Effects of Surface Functionalization on the Peroxidase Activity of Cytochrome c Adsorbed on Silica Nanoparticles.

The immobilization of proteins on inorganic supports is attracting increasing interest since the realization of active surfaces finds application in enzyme-assisted catalysis, environmental sciences, and medical fields. In the present study, cytochrome c (cyt c) is adsorbed on silica nanoparticles (SNPs) and amino-functionalized silica nanoparticles (SNPs-APTES), which are prepared for this purpose and having a diameter of about 50 nm. The peroxidase activity of the protein is investigated under different experimental conditions, to evaluate the impact of differently charged surfaces on the catalytic activity of the biomolecule. The peroxidase activity of cyt c increases upon adsorption on SNPs, and it shows a linear behavior with nanoparticles concentration; on the other hand, the contact with increasing amounts of SNPs-APTES does not affect the catalytic activity of the protein. The kinetic profile of the oxidation reaction is altered for cyt c-SNPs sample, suggesting that upon adsorption, changes in the catalytic process take place. Moreover, we observe that the enhancement of peroxidase activity of cyt c-SNPs is almost completely inhibited in high-ionic-strength buffer: this indicates that the protein establishes electrostatic interactions with SNP. The spectroscopic properties of the adsorbed protein on the two different matrices are investigated by using fluorescence and Raman spectroscopies to account for the enzymatic activity of the hybrid materials. The fluorescence spectra of cyt c-silica bio-composites reveal that the adsorption on silica modifies the microenvironments of the emitting amino acid residues of the protein. Indeed, their fluorescence gains intensity and appears blue-shifted compared to that of the native protein; these modifications are more evident when cyt c is adsorbed on SNPs. Raman spectra suggest that both oxidation and spin state of heme iron change when cyt c is adsorbed on SNPs but not on SNPs-APTES. The spectroscopic data of biocomposite materials are discussed in terms of structural changes to account for the increment of peroxidase activity upon adsorption on the negatively charged surface of SNPs.