Triethoxysilane Research Articles

Development of Functionalized Polylactide Thin Films Using Poly(methylhydrogenosiloxane) Sol-Gel Process with Improved Antifouling Properties.

Biobased polylactide (PLA) films were modified with low reticulate polysiloxane gel acting as a scalable platform for the hydrophilization of polymeric film surface. The PLA thin film was first coated with poly(methylhydrogenosiloxane) (PMHS) by the sol-gel transition via the condensation of diethoxymethylsilane (DH) and triethoxysilane (TH) using trifluoromethanesulfonic acid as a catalyst. Then, hydrosilylation of Si-H bonds in the presence of Karstedt's catalyst allowed the covalent grafting of hydrophilic alkene-containing molecules, i.e., triethylene glycol monomethyl allyl (TEGMEA) and a new zwitterionic allylcarboxybetaine (ACB) synthesized for the first time by the quaternization of dimethyl allyl amine (DMAA) with β-propiolactone. PMHS coating on the PLA film was evidenced by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The observation by atomic force microscopy (AFM) revealed a homogeneous coating with low roughness (RMS = 0.29 nm). The hydrophilicity of functionalized PLA films was determined by water contact angle (WCA) measurements using the captive bubble method. A large increase in wettability properties was observed for both grafting with TEGMEA (WCA = 38°) and ACB (WCA = 42°) in comparison with the native PLA film (WCA = 80°). Moreover, the biocompatibility and antifouling efficiency of functionalized PLA films were evaluated by protein adsorption, bacterial adhesion, and cytotoxicity tests. The results indicate that the grafting of the two types of hydrophilic compounds does not affect the biocompatibility of PLA while significantly reducing protein adsorption and bacterial adhesion, thus showing the great potential of this surface functionalization strategy for applications in the medical field.

Surface modification of Cu-coated carbon fiber for improved mechanical performance of Acrylonitrile Butadiene Styrene composites using 3-Aminopropyl triethoxy silane

This study investigates the use of 3-Aminopropyl triethoxy silane as a surface modifier for Cu-coated Carbon Fibers. The modified fibers were subsequently incorporated into Acrylonitrile Butadiene Styrene matrix composites through melt blending and high-temperature compression molding. The research evaluates the effect of 3-Aminopropyl triethoxy silane on the interfacial structure and mechanical performance of these composites. Results demonstrate a substantial enhancement in the wettability and surface energy of Cu-coated Carbon Fibers, with the static contact angle reduced from 111.2° to 84.5° and surface energy increased from 44.67 mN·m−1 to 56.66 mN·m−1. These surface modifications contributed to an 82.7 % increase in tensile strength and a 76.4 % improvement in tensile modulus of the resultant composites.

Effects of silane hydrolysis time on the physicochemical properties of bioplastics based on starch and epoxidized soybean oil

This work investigated the effects of 3-aminopropyl triethoxy silane (APTES) hydrolysis time on the physicochemical properties of the resulting starch/epoxidized soybean oil (ESO) bioplastics comprehensively. FTIR analysis confirmed that APTES hydrolyzed for 4 h had the best modification effect on starch. The results of XRD and TGA demonstrated the successful silylation of starch by APTES despite hydrolysis time. Silylation treatment reduced the thermal stability of starch slightly, but enhanced the thermal stability of the resultant bioplastics, revealing better interaction between silylated starch and ESO. The interfacial adhesion of starch and ESO in the bioplastics was obviously enhanced when APTES was hydrolyzed for 2–24 h. The bioplastics with APTES hydrolyzed for 2–4 h showed more desirable tensile properties as the silane hydrolysis was complete and self-condensation of hydrolyzed silanes was avoided. The bioplastics containing silylated starch still showed superior opacity and biodegradability.

Novel phase-change material based on stearic-acid@MOFs@SiO2 with perfect impermeability promoted by coordination with unsaturated metal sites

In this study, to achieve excellent impermeability and thermal storage performance of metal-organic framework (MOF) based composite phase change materials (PCM), an encapsulation method was prepared by utilizing unsaturated metal sites of MOF, and the PCM composite SA@MOFs@SiO2 were prepared. Stearic acid is adsorbed into the MOF pores through adsorption before encapsulation. To achieve high impermeability, the unsaturated metal site of MOFs forms a coordination Me-SH bond with 3-mercaptopropyltriethoxysilane (KH590), then dense silica was formed on PCM surface through the hydrolysis condensation reaction of both KH590 and triethoxysilane (TEOS). The heat storage of SA@MIL-101(Cr)-NH2@(Cr)-S-Si@SiO2 composite can reach 113.89 J/g, and the melting permeability was as low as 0.69 %, exceptional chemical stability can be obtained at 70 °C for 10 days. This work provides a general method for designing a variety of MOF-based phase-change composites with superior impermeability, demonstrated by three different MOFs derived PCMs. These will be promising materials in the fields of textiles, architecture, solar energy applications, and etc.

A combined experimental and simulations assessment of CO2 capture and CO2/H2 separation performance of aminosilane-grafted MCM-41 and pore-expanded MCM-41

Amine-functionalized mesoporous silica materials have attracted considerable attention as robust adsorbents for large-scale CO2 capture and direct air capture (DAC). Amine grafting increases selective affinity at low pressures, yet also often reduces the adsorbent's pore volume and surface area, affecting the kinetics and capacity upon CO2 adsorption. MCM-41 and pore-expanded MCM-41 (PE-MCM-41) were developed here, functionalized using 3-aminopropyl triethoxy silane (APTES), and comparably evaluated for their carbon capture performance at different conditions by a combinational experimental, equilibrium and kinetic modelling, and molecular simulations approach. In specific, CO2 adsorption capacity, CO2/N2 selectivity, CO2 adsorption at humid conditions, heat of adsorption, and regeneration/cyclability were assessed, coupled to molecular simulation insights on the physisorption and chemisorption contribution to the overall adsorption uptake. Indicatively, a capacity value of 3.07 and 2.44 mmol/g was obtained for APTES-PE-MCM-41, and 2.27 and 1.89 mmol/g for APTES-MCM-41, under wet and dry conditions, respectively. The CO2 selective adsorption from H2 rich gas streams was also examined over APTES-MCM-41 in order to assess the potential application in H2 stream purification process. The latter is of high significance in order to use hydrogen as fuel e.g. in anion exchange membrane fuel cells for power production since the presence of CO2 in the feed composition is considered a major drawback in their commercialization.

Engineering of ceramic membranes with superhydrophobic pores for different size water droplets removal from water-in-oil emulsions

Superhydrophobic (SHB) ceramic membrane surfaces have proved their superiority in water-in-oil (W/O) emulsion separation. However, the construction of ceramic membranes with SHB pores remains challenging and the interaction between the SHB pores and water droplets is still unclear. Herein, by growing uniform ZnO nanoclusters (NCs) onto the SiC grains of a symmetric SiC ceramic membrane and then grafting with triethoxy(octyl)silane, a series of ZnO NCs@SiC membranes with SHB pores were prepared. Prior to secondary hydrothermal synthesis ZnO NCs, the small-sized ZnO nanoparticles (NPs) were grown onto the SiC grains via a sol–gel process. All the ZnO NCs@SiC membranes with SHB pores showed improved water removal performance from W/O emulsions compared with that of the pristine membrane. The optimal membrane with SHB pores displayed a pore size of 0.19 μm with a water contact angle of 163.96°. The smaller water droplets in W/O emulsions, the membrane pores are easier to be polluted. When separating a 1000 ppm W/O emulsion with a water droplet size of 500 nm at a transmembrane pressure of 0.5 bar, the water rejection reached 98.90 %, and the steady-state oil flux was 92.99 L·m−2·h−1. Based on the separation experiments, the separation mechanism was revealed. This work provides significant perceptions into constructing SHB pores of ceramic membranes, which might be useful for other possible applications.

Bio-based silsesquioxanes nano hybrids for enhancing the tribological performance of silicone oil: A DFT and experimental study

A novel, eco-friendly nanohybrid solid lubricant additive was synthesized using oleic acid, a readily available green material. By esterifying the 18-carbon chain of ethyl oleate (EO) and subjecting it to hydrosilylation with triethoxysilane (TES), the ethyl 9-(triethoxysilyl)octadecanoate (S2EO) was created. Nanosized Polymethyl silsesquioxanes (PMSQ) particles (P-NPs) were then modified with S2EO to produce the lubricant additive P-NPs-S2EO for enhancing silicone oil’s tribological performance. The synthesis processes were verified by FTIR, H-NMR, SEM, and EDS, while TGA demonstrated the nanohybrid’s superior thermal stability, showing only 1.8% weight loss at 200 °C. Tribological tests using a pin-on-disk tribometer with P-NPs and P-NPs-S2EO in silicone oil revealed a friction reduction of up to 93%, outperforming traditionally used borax and other silicone-based lubricants. The sustainable synthesis of P-NPs-S2EO, confirmed by Density Function Theory (DFT) calculations, underscores its thermal stability and efficiency as a lubricant additive.

Detection of tetanus toxoid with iron magnetic nanobioprobe

Diagnosis of diseases with low facilities, speed, accuracy and sensitivity is an important matter in treatment. Bioprobes based on iron oxide nanoparticles are a good candidate for early detection of deadly and infectious diseases such as tetanus due to their high reactivity, biocompatibility, low production cost and sample separation under a magnetic field. In this study, silane groups were coated on surface of iron oxide nanoparticles using tetraethoxysilane (TEOS) hydrolysis. Also, NH2 groups were generated on the surface of silanized nanoparticles using 3-aminopropyl triethoxy silane (APTES). Antibody was immobilized on the surface of silanized nanoparticles using TCT trichlorothriazine as activator. Silanization and stabilized antibody were investigated by using of FT-IR, EDX, VSM, SRB technique. UV/vis spectroscopy, fluorescence, agglutination test and ELISA were used for biosensor performance and specificity. The results of FT-IR spectroscopy showed that Si–O–Si and Si-O-Fe bonds and TCT chlorine and amine groups of tetanus anti-toxoid antibodies were formed on the surface of iron oxide nanoparticles. The presence of Si, N and C elements in EDX analysis confirms the silanization of iron oxide nanoparticles. VSM results showed that the amount of magnetic nanoparticles after conjugation is sufficient for biological applications. Antibody stabilization on nanoparticles increased the adsorption intensity in the uv/vis spectrometer. The fluorescence intensity of nano bioprobe increased in the presence of 10 ng ml−1. Nanobio probes were observed as agglomerates in the presence of tetanus toxoid antigen. The presence of tetanus antigen caused the formation of antigen-nanobioprobe antigen complex. Identification of this complex by HRP-bound antibody confirmed the specificity of nanobioprobe. Tetanus magnetic nanobioprobe with a diagnostic limit of 10 ng ml−1 of tetanus antigen in a short time can be a good tool in LOC devices and microfluidic chips.

In-vitro bioactivity investigation and surface properties of a PMMA-SiO2 composite coating on SS-316L using the Sol-Gel technique

Surface modification of SS-316L using an organic and inorganic hybrid coating of polymethyl methacrylate (PMMA) and silicon dioxide (SiO2) is being conducted in the current investigation with crosslinking agent 3-aminopropyl tri-ethoxy silane (APTES). The solvent-gel method and dip coating with varying amount of SiO2 (i.e. 0.5, 1, and 1.5 wt.%) is used for surface modification. On the coated surface, Fourier transform infrared spectroscopy (FTIR) at 1000–1250 cm−1 reveals the crosslinking of silicon and PMMA. The coatings formed on SS-316L are homogenous, transparent, and free of defects and voids when seen macroscopically. A good crystallinity and presence of coated material can be seen from the X-ray diffraction and microstructure analysis of coated surface. The PMMA coating with 1.5 wt.% SiO2 has the most apatite crystals deposited on surface as observed with 7 days of immersion on simulated body fluid (SBF). These findings provide a solid link that coating SS-316L with SiO2 promotes bone bioactivity, and the PMMA+1.5 wt.% SiO2 coating can be employed on implants. The results of this study suggest a sustainable coating solution for improved bioactivity in medical applications and surgical instruments.

High performance double layer hydrophobic antireflective coatings on glass prepared by sol–gel method

A double layer coating was designed and fabricated on glass surfaces by sol-gel method using a silica-titania (SiO2–TiO2) thin film as the bottom layer and an inorganic-organic (triethoxy(octyl)silane (OTES) modified SiO2) upper layer. SiO2 and TiO2 sols were prepared using tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) as precursors and nitric acid (HNO3) as catalyst. The refractive index of the SiO2–TiO2 and OTES modified SiO2 layers were 1.79 and 1.45, and their thicknesses were approximately 76.8 nm and 94.2 nm, respectively. The results show an increase of 7% in transmittance respect to the uncoated glass substrate. At the same time, OTES-modified SiO2 top layer significantly improved the hydrophobicity of the system; the water contact angle of film increased from 56° for system without the OTES modified SiO2 layer to 102° for the system with OTES-modified SiO2 top layer.

Facile and Rapid Synthesis of Gold Nanoparticles on Unconventional Imine‐ Decorated Silica

AbstractWe demonstrate the reduction of gold (Au) on silica monoliths by surface decoration of amine and imine (formed by reaction of amine present in 3‐amino propyl triethoxy silane (APTES) and acetone) functionalities on the surface of silica. The reduction of Au3+ to Au0 was confirmed by X‐ray diffraction (XRD), UV‐Diffuse reflectance and X‐ray Photo electron spectroscopic techniques. Without employing the conventional strategies with reducing agents like sodium borohydride and sodium citrate, here, the surface functionalized amine and imine was found to reduce the metal ions, additionally, the surface silanols was found to anchor and serve as the adsorption sites to hold the metal ions prior to reduction. The control experiment was performed with silica monoliths without the surface functionalities displayed no evident reduction of Au3+ to their respective metallic form. Interestingly, the reduction of Au was found to be more facile on imine modified silica, due to the strong electrostatic interaction of highly polarized imine with Au3+ ions.

Starch microsphere silicon-boron crosslinker for low concentration hydroxypropyl guar gum based fracturing fluid

Hydroxypropyl guar gum (HPG) is a critical thickener to increase viscosity and lubrication to improve the water-based hydraulic fracturing efficiency. However, current crosslinkers require a large amount of HPG (>0.3 wt%) to form gel with sufficient viscosity, and high concentrations of HPG may cause adverse effects to the production and the environment. In this study, a novel starch microsphere silica‑boron crosslinker (SMSB) was developed using starch microspheres as a carrier and γ-aminopropyl triethoxy silane (KH550) as a modifier with an in-house method. Both the rheology and surface reactions of the SMSB-HPG crosslinking system were studied using multiple laboratory experiments and molecular dynamics simulation. The results showed that SMSB crosslinker caused multi-site cross-linking with low concentration (only 0.2 wt%) of HPG molecules, reducing the twisting of single molecular chain in the crosslinking system, enhancing the cross-linking strength between molecular chains, and making HPG molecular chains stretcher in the aqueous solution. The apparent viscosity and viscoelasticity of the HPG system were substantially higher than the organoboron crosslinker, and the temperature resistance of the SMSB-HPG crosslinking system was up to 140 °C. This study provides an alternative green crosslinker for more sustainable industrial applications and provides theoretical basis for the modification of biomaterials.

Oxidized cellulose as bio‐adhesive for hydrophobic lignocellulosic bioplastic

AbstractThis study presents a novel hydrophobic lignocellulosic bioplastic from corn stover reinforced by oxidized cellulose and in situ regenerated lignin. Cellulose‐lignin mixture as a matrix was obtained by acid‐recyclable deep eutectic solvent (DES) pretreatment of corn stover in mild conditions. Triethoxy(octyl)silane (C14H32O3Si) was employed to improve the water stability of the bioplastic by vapor deposition. The results show that the hydrophobic bioplastic has a high tensile strength, measuring 62.36 MPa. The water contact angle of the bioplastic was increased from 8.50° to 121.9° after hydrophobic modification. We prepared oxidized cellulose‐reinforced cellulose paper by different particle size distributions of oxidized cellulose to investigate the reinforcement of oxidized cellulose. The tensile strength of oxidized cellulose cellulose paper increased from 14.41 to 21.18 MPa with the addition of oxidized cellulose. The zeta potential of oxidized cellulose is −47.99 mV, which shows a more negative charge due to carbonyl groups. The repulsive force of oxidized cellulose contributes to the formation of a brick‐and‐mortar microstructure with cellulose‐lignin mixture. It demonstrates that oxidized cellulose can act as bio‐adhesives and has a good toughening effect on the mechanical properties of bioplastic.Highlights Lignocellulosic bioplastic was prepared by DES pretreatment of corn stover. Oxidized cellulose was used to reinforce the lignocellulosic bioplastic. The tensile strength of the bioplastic was 62.36 MPa after the reinforcement process. Trieth‐oxy(octyl)silane was employed to improve water stability. The water contact angle of the bioplastic was increased from 8.50° to 121.9°.

Surface modified single-step nanofluid for improved CO2 absorption and storage Prospects at pore-scale in micromodels: CO2 utilization for saline porous media

The utilization (absorption and areal sweep) of injected carbon dioxide (CO2) can be enhanced if a viscous and agglomeration free nanofluid is used as most of the nanoparticles (NPs) prefer to stay in bulk phase rather than adsorbing on CO2 surface. NP adsorption can be improved if non-participating NPs are surface modified with a suitable surface modifying agent e.g., triethoxy (vinyl)silane (TVS). Thus, in this study, single-step approach was used to synthesize agglomeration free TiO2 nanofluid whose surface modification was carried out in varying proportion of TVS (1–5% v/v) followed by the discussion on comparative CO2 absorption and storage performance by different tools such as DLS, IFT, Rheology, Contact-angle, and Micromodel flow. The basic nanofluid (To) showed greater CO2 absorption after surface modification as demonstrated by molality results. However, surface modification also decreased dispersion stability of surface modified nanofluids (T1, T2, and T3) and T2 was regarded as the most stable nanofluid with −64.4 mV (ζ-potential) and 153 nm (NP size). After surface modification, increase in NP size and settlement was higher for surface modified nanofluids than To, which exhibited dispersion stability of 84 d with −53.4 mV and 15 nm. Contact angle results also showed that surface modified nanofluids possess greater affinity for CO2 absorption than basic nanofluid (To). Rheological analysis was also consistent with other tests where viscosity was found dependent on both storage period and temperature, and NP settlement was found to be the most influential parameter on flow properties of nanofluid. Finally, pore scale analysis was performed to understand areal sweep of injected CO2 in micromodel with and without nanofluid, where nanofluid imparted greater CO2 storage by diverting it in un-swept pore networks of micromodel which were untapped by CO2 without nanofluid.

Cyclometalated platinum(II) complexes bearing eugenol as effective catalyst for hydrosilylation of phenylacetylene by triethoxysilane

The catalytic activities of the platinacyclic complexes bearing eugenol (EugH) including [Pt(μ-Cl)(Eug)]2 (1) and [PtCl(Eug)(amine)] (2–4) [amine: pyridine/2, 4-methylpyridine/3, quinoline/4] for hydrosilylation of phenylacetylene by triethoxysilane have been studied for the first time. The results showed that the complexes 1–4 exhibited good catalytic abilities. With loading 0.5 mol% each of the catalysts 1–4 at 70 oC without solvents and any other additives in the air for 2 hours, the triethoxysilane was completely converted to (E)-triethoxy(styryl)silane) (β(E) – the major product) and (triethoxy(1-phenylvinyl)silane) (α – the minor product) with the α/β(E) molar ratio ranging from 1 : 2.6 to 1 : 2.8. At the same reaction conditions with loading 0.1 mol% each of the catalysts 2–4, the conversion of triethoxysilane slightly reduced with an efficiency of 97–99% and the α/β(E) molar ratio of 1 : 2.6 indicating the important role of the Pt-(C=Calkene) in 1–4 for their catalytic activity. Furthermore, the verification of structures of complexes 2–4 by 13C NMR spectroscopy indicated that in chloroform-d1, complex 3 formed two distinct structural forms due to strong intermolecular interactions between the chloroform solvent and the complex, including a Cl3C-H...ClPt(II) hydrogen bond and a Cl2HC-Cl...Pt(II) halogen bond.

Synthesis, drug loading and release study of spherical bioactive glass regulated by two templates

In this paper, the particle size and morphology of spherical biogalsses(BGs) were regulated by changing the amount of catalyst and templating agent using the dual template method. The prepared BGs had good morphology, dispersibility, and rapid induction of hydroxyapatite generation. The cell activity was above 75 % after co-culture of BG extracts with mBMSCs cells. The surface modification of BG was carried out by γ-aminopropyl triethoxy silane (KH-550) to obtain amino functionalized BG (BG-NH2), which was then loaded doxorubicin hydrochloride (DOX) to obtain BG-DOX. The maximum loading of BG was 19.2 % and the encapsulation rate was 91.8 %. The drug release rate of BG-DOX was proportional to specific surface area, and it was capable to release DOX at high concentration for up to 10 days, which can be a good drug carrier.

A superhydrophilic/air superoleophobic sponge based on low-temperature vacuum evaporation deposition modification for saving marine crude oil pollution and leakage

Oil pollution and crude oil leakage in the ocean have severely impacted marine ecology. The emergence of super-wetting materials provides a new approach to addressing the issue of oil leakage. Chemical vapor deposition, which can be applied to prepare super-wetting materials, is a method that can modify uniformly and enhance the stability of the material, while mostly needing to be performed at high temperatures. In this study, melamine sponge (MS) was preliminarily modified by low-temperature vacuum evaporation deposition (LTVED) of hydrolyzed γ-mercaptopropyl triethoxy silane (KH580). The nano-silica and FS-50 were stepwise coated on the MS skeleton by a simple immersion-drying process. A superhydrophilic/air superoleophobic sponge (MS-KCSiF) as obtained with water contact angle of nearly 0° and crude oil contact angle of approximately 154° in the air, which can retain the wetting properties after immersion in different chemical solutions, ultraviolet irradiation aging, and mechanical destruction like cutting, twisting, bending, and pressing. Its efficiency for high-viscosity crude oil-seawater mixtures was maintained at over 96 % after 20 cycles. Empowered with the shape of mortise and tenon joint structure, MS-KCSiF can scoop up spilled crude oil from the sea surface. This strategy provides a new idea for the construction of super-wetting materials and oil spill collection.

Aminopropyl triethoxy silane capped ZnO quantum dots for highly selective dopamine

Quantum dots (QDs) can be used as labels with fluorescent nanoprobes and ZnO QDs have band gap over 4 eV with a large 60 meV exciton binding energy. Capped ZnO presents high quantum efficiency and surface enhancement in biochemical analysis and ultrasensitive detection of biomaterials and proteins. This work reported the synthesis of ZnO QDs capped with different agents of 3-aminopropyl triethoxy silane (APTES), tetraethyl orthosilicate (TEOS) and dimethyl sulfoxide (DMSO) from nonaqueous medium. ZnO QDs were characterized by different techniques of UV-vis absorption spectra, fluorescent emission spectra, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Zeta potential and high-resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) emissions illustrated that APTES capped ZnO QDs have the highest PL intensity and applied as an optical sensor for dopamine (DA) determination in an aqueous solution and real serum samples. The visible luminescence of ZnO may result from either the recombination of a delocalized electron with a deeply trapped hole or the recombination of a delocalized hole with a deeply trapped electron. Zeta potential values showed that the surface potentials of - 4.23, -7.70, -14, -1.94 mV for uncapped ZnO, DMSO, APTES capped, TEOS capped ZnO QDs, respectively. The fluorescence quenching observed in ZnO QDs primarily stemmed from electron transfer between the ZnO QDs and two variants of dopamine: reduced dopamine acting as electron donors and oxidized dopamine-quinone serving as electron acceptors. APTES capped ZnO QDs probe exhibited a linear dynamic range from 6.2 – 0. 195 nM of DA with correlation coefficient (R2) of 0.99, limit of detection (LOD) of 0.2 nM and a sensitivity of 406.6 µM-1.

A DFT study to unravel the fluorescence mechanisms of APTES-modified carbon dots

Surface passivation is a well-established method for modifying carbon dots (CDs), intended to improve their properties. We present a theoretical study employing density functional theory (DFT) and time-dependent-DFT (TD-DFT) to explain the photoluminescence (PL) mechanism of amine-modified carbon dots (CD-NH2) [CDs modified with (3-Aminopropyl) triethoxy silane (APTES)] considering their local geometry at the terminal ends; the zig-zag (CDZZ-NH2) and armchair (CDAC-NH2) structural orientations. The experimental evidence from our previous report suggests that the amine groups were tethered on the surface of CDs through a Si-O bond realized by the silane coupling reaction between the ethoxy group of APTES and the hydroxyl group of the CDs. The effect of pH in tweaking the PL of these systems is scrutinized in the present study. The influence of pH and structure on the bandgap of CD-NH2 is demonstrated by analyzing the difference in HOMO-LUMO energies, the density of states (DoS) spectra, and electrostatic potentials (ESP).

Study of protective hard coatings of SiO<sub>2</sub>-TiO<sub>2</sub> on aluminum substrates

<abstract> <p>Aluminum alloys are frequently employed in the aeronautics industry due to the remarkable mechanical properties and lightweight nature of these materials. Moreover, thin film coatings are commonly applied in order to improve the corrosion resistance under harsh environments. In this work, Al 7075-T6 substrates were coated with nanostructured SiO<sub>2</sub>-TiO<sub>2</sub> films using a sol-gel method. The experimental approach initially consisted in the preparation of a precursor agent using tetraethyl orthosilicate (TEOS) and triethoxy(octyl)silane (ETOS). Subsequently, nanoparticles of SiO<sub>2</sub>-TiO<sub>2</sub> were mixed in order to develop thin films using a one-step dip coating method. The roughness, nanoindentation and corrosion properties were evaluated for the coated substrates. A finite element model was created for the nanoindentation test, which determined the mechanical response between the film-contact interface during loading conditions. The average hardness, elastic modulus and critical loads leading to fracture were verified. The nanoindentation test presented a significant increase in hardness for the coated Al 7075-T6 alloy, reaching a value of 4.6 GPa. The SiO<sub>2</sub>-TiO<sub>2</sub> thin films presented uniform and compact surface coatings with high mechanical properties. Furthermore, the performed corrosion tests indicated moderate protection by the SiO<sub>2</sub>-TiO<sub>2</sub> thin films. The SiO<sub>2</sub>-TiO<sub>2</sub> thin films displayed a generalized corrosion throughout the surface, presenting oxides and fractured crystals in localized regions.</p> </abstract>