Surfactant-assisted Sol-gel Method Research Articles

Synthesis and Characterisation of Mesoporous TiO2 Nanoparticles by Novel Surfactant Assisted Sol-gel Method for the Degradation of Organic Compounds

A sol-gel method was employed to synthesise pure titanium dioxide (TiO2) and surfactant assisted TiO2 nanoparticles (NPs). The effect of novel surfactant viz., Lauryl lactyl lactate on photocatalytic properties of TiO2 was studied. TiO2 NPs were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis Diffuse Reflectance spectra (DRS), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), Thermo gravimetric analysis (TGA), and Brunauer – Emmet - Teller (BET) surface area. Anatase phase of TiO2 was confirmed by X-Ray diffraction pattern and the crystallite size was between 9–19 nm. Addition of surfactant improved the BET surface area, surface defects, while the agglomeration of particles was reduced. DRS results revealed that the addition of surfactant to TiO2 sol induced a red shift of the absorption edge which resulted in the reduction of band gap from 3.23 to 3.21 eV. These physicochemical properties of TiO2 NPs were correlated with photocatalytic degradation of phenol. About 92% of phenol degradation was observed for surfactant assisted TiO2 NPs (SA-TiO2). Salicylic acid and caffeine were also degraded using SA-TiO2 NPs.

Multifunctional nanoporous magnetic zinc silicate-ZnFe2O4 core-shell composite for bone tissue engineering applications

Multifunctional materials have recently gained substantial attraction in bone tissue engineering because of their capabilities to solve essential problems after implantation including inflammation and osteomyelitis and also bone cancerous tissues through hyperthermia treatment. The aim of this study was to design and develop a new multifunctional composite containing a magnetic zinc ferrite as a core, and nanoporous zinc silicate as a shell via a two-step synthesis strategy to meet all above targets simultaneously. ZnFe2O4 particles are synthesized via solvothermal method and then coated through surfactant-assisted sol-gel method to obtain zinc silicate-ZnFe2O4 composite using cetyltrimethylammoniumbromide (CTAB) as a surfactant. The XRD results show that the composite has a glass-ceramic structure. The FESEM micrographs indicate the increase in the size of ZnFe2O4 particles because of zinc silicate formation around them. The vibrating sample magnetometer (VSM) results reveal that the formation of zinc silicate over ZnFe2O4 particles caused the magnetization saturation (Ms) to be reduced from 43 to 30 emu g−1. The antibacterial activity of the composite is evaluated against S. aureus and E. coli bacteria. Heat generation capability of the composite is assessed in vitro and results show that the composite reached the saturation temperature of 45 °C up to 510 s with 200 Oe magnetic field and constant 200 kHz frequency. Potential application of the composite as a controlled release system is assessed in vitro up to 240 h. The cell compatibility of the composite with different concentrations is assessed using osteoblast-like cells (MG63) up to 48 h.

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain.

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 °C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 °C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications. In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Structural, photocatalytic, biological and catalytic properties of SnO2/TiO2 nanoparticles

TiO2 and SnO2/TiO2 nanoparticles with different SnO2 contents (0–20wt%) were synthesized via surfactant-assisted sol-gel method using a cationic surfactant (cetyltrimethylammonium bromide, CTAB). The effects of SnO2 content on the structural, optical, and catalytic activity of TiO2 have been studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), Scanning electron microscope (SEM), Fourier transformer infrared (FTIR) and UV–vis diffuse reflection spectroscopy (DRS). The total surface acidity of the prepared samples was measured by nonaqueous titration of n-butylamine in acetonitrile and the types of Brönsted and Lewis acid sites were distinguish using FTIR spectra of chemisorbed pyridine. XRD patterns analysis indicates that the crystallite size reduced remarkably and the transformation of anatase-to-rutile phase accelerated greatly with increasing the SnO2 content. TEM images exhibit a spherical shape with an average particle size varying in the range 10–24nm and high-resolution TEM images (HRTEM) show lattice fringes with interplanar spacing 0.35nm and 0.32nm which corresponding to anatase and rutile phases, respectively. SEM images show the amount of SnO2 on the TiO2 surface increases with increasing the SnO2 content and the particles of SnO2 were aggregated on TiO2 surface with increasing SnO2 content to 20% wt. The catalytic activity was tested by various applications: Photodegradation of Methylene Blue (MB) and Rhodamine B (RhB) under UV–vis irradiations and synthesis of xanthene (14-phenyl-14H-dibenzo [a,j] xanthene). Antibacterial and antioxidant activities were also studied. The antibacterial property test was carried out via agar disc diffusion method, and the results indicated that the prepared catalysts showed moderate antibacterial activity.

Facile formation of metallic bismuth/bismuth oxide heterojunction on porous carbon with enhanced photocatalytic activity

Bismuth/bismuth oxide heterojunction on porous carbon (Bi0/Bi2O3@C) was successfully prepared by a surfactant-assisted sol-gel method. This composite photocatalyst was fabricated by depositing Bi2O3 and metallic bismuth nanoparticles (NPs) on porous carbon sheets. Bi NPs were created by in-situ reduction of Bi2O3 with amorphous carbon. During the synthesis, bismuth and carbon precursors were mixed in different ratios, resulting in distinct amounts of metallic bismuth in the composites. The composites showed large specific surface area and pore volume as well as strong light absorption ability due to the existing carbon. In addition, the plasmonic bismuth NPs were found to behave as a noble metal, which is able to generate hot charge carriers under visible light irradiation. Photocatalytic performance of the Bi0/Bi2O3@C composites was investigated by degradation of methylene blue. It turned out that the composites showed much higher efficiency as compared to bare Bi2O3, which may be attributed to the synergistic effects of porous structures, improved optical absorption, and surface plasmon resonance.

Publisher’s Note: “Origin of thermally stable ferroelectricity in a porous barium titanate thin film synthesized through block copolymer templating” [APL Mater. 5, 076111 (2017)

A porous barium titanate (BaTiO3) thin film was chemically synthesized using a surfactant-assisted sol-gel method in which micelles of amphipathic diblock copolymers served as structure-directing agents. In the Raman spectrum of the porous BaTiO3 thin film, a peak corresponding to the ferroelectric tetragonal phase was observed at around 710 cm(-1), and it remained stable at much higher temperature than the Curie temperature of bulk single-crystal BaTiO3 (similar to 130 degrees C). Measurements revealed that the ferroelectricity of the BaTiO3 thin film has high thermal stability. By analyzing high-resolution transmission electron microscope images of the BaTiO3 thin film by the fast Fourier transform mapping method, the spatial distribution of stress in the BaTiO3 framework was clearly visualized. Careful analysis also indicated that the porosity in the BaTiO3 thin film introduced anisotropic compressive stress, which deformed the crystals. The resulting elongated unit cell caused further displacement of the Ti4+ cation from the center of the lattice. This displacement increased the electric dipole moment of the BaTiO3 thin film, effectively enhancing its ferro(piezo) electricity. (C) 2017 Author(s).

Origin of thermally stable ferroelectricity in a porous barium titanate thin film synthesized through block copolymer templating

A porous barium titanate (BaTiO3) thin film was chemically synthesized using a surfactant-assisted sol-gel method in which micelles of amphipathic diblock copolymers served as structure-directing agents. In the Raman spectrum of the porous BaTiO3 thin film, a peak corresponding to the ferroelectric tetragonal phase was observed at around 710 cm−1, and it remained stable at much higher temperature than the Curie temperature of bulk single-crystal BaTiO3 (∼130 °C). Measurements revealed that the ferroelectricity of the BaTiO3 thin film has high thermal stability. By analyzing high-resolution transmission electron microscope images of the BaTiO3 thin film by the fast Fourier transform mapping method, the spatial distribution of stress in the BaTiO3 framework was clearly visualized. Careful analysis also indicated that the porosity in the BaTiO3 thin film introduced anisotropic compressive stress, which deformed the crystals. The resulting elongated unit cell caused further displacement of the Ti4+ cation from the center of the lattice. This displacement increased the electric dipole moment of the BaTiO3 thin film, effectively enhancing its ferro(piezo)electricity.

Morphological and magnetic properties of sol-gel synthetized meso and macroporous spheres of barium hexaferrite (BaFe12O19)

Porous spherical aggregates of barium hexaferrite (BaFe12O19) with 1.5µm in diameter were synthetized by the surfactant-assisted sol-gel method. The surfactant Tween20 (C58H114O26), which enables mesoporous structures, as well as polystyrene spheres (PS), as the template agent for the formation of macropores, were used. Two synthetic routes (hereafter named A and B), whose difference was the absence or presence of PS, were followed for synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in high resolution mode (HRTEM) were used for characterization. Size and morphology of the spheres were similar in both cases and they resemble a nest or ball-of-yarn type structure. Pore size and BaFe12O19 crystal size produced by the two routes are different. The magnetic properties of the spheres were evaluated using a vibrating sample magnetometer (VSM) as function of the calcination temperature. The spheres present ferromagnetic behavior in both routes.

New insights into the photocatalytic activity of 3-D core–shell P25@silica nanocomposites: impact of mesoporous coating

In this report, a three-dimensional (3-D) network of core-shell TiO2 (P25)-mesoporous SiO2 (P25@mSiO2) nanocomposites was prepared via a controllable surfactant-assisted sol-gel method. The nanocomposites were investigated for photocatalytic reactions of organic dye degradation, water splitting, and CO2 reduction to understand the roles of the mSiO2 shell in these photocatalytic reactions. It was found that the mSiO2 shell accelerates the photodegradation of the organic dye, but dramatically reduces the photocatalytic activity of P25 in water splitting and CO2 reduction. The roles played by the mSiO2 shell in the photocatalytic reactions are summarized as: (1) effective prevention of agglomeration of P25 nanoparticles, (2) facilitating the transfer of uncharged photo-generated ˙OH radicals via the abundant -OH groups on the mesoporous surface, (3) provision of increased reaction sites between ˙OH radicals and dye molecules by its mesoporous nanostructure and large surface area, and (4) prevention of diffusion of the photo-generated charge carriers (photoelectrons and photoholes) because of its insulating nature.

Highly efficient Y and V co-doped ZnO photocatalyst with enhanced dye sensitized visible light photocatalytic activity

A series of Y and V co-doped ZnO (YVZ) nanoparticles have been synthesized by surfactant assisted sol gel method with an aim to enhance the photocatalytic activity under visible light for degradation of organic pollutants. The prepared samples were characterized by standard analytical techniques such as XRD, XPS, SEM-EDX, TEM, UV–vis spectroscopy, FT-IR, BET, TGA and PL spectroscopy. The XRD analysis clarifies the coexistence of Y and V into ZnO as evidenced by the shift of plane towards the lower theta value. The photodegradation performances of the prepared samples were evaluated by studying the degradation of Rhodamine B (RhB), Methylene Blue (MB) and 4-nitrophenol (4-NP) under visible light irradiation. Among the series of synthesized YVZ nanoparticles, 3-YVZ (3%Y/1%V-ZnO) was found to be the most active photocatalyst for the degradation of organic pollutants under investigation. This remarkably improved photocatalytic activity of 3-YVZ could be attributed to the strong absorption of visible light and effective separation of photoinduced e−- h+ pair. The mineralization of RhB was investigated by measuring the COD depletion as a function of time. In addition, the influence of operational parameters such as, catalyst dosage and initial reaction pH was optimized with most active 3-YVZ photocatalyst for degradation of RhB as a function of time. The quenching experiments were conducted to determine the main reactive species formed in the reaction mixture and accordingly a mechanism for enhanced photocatalytic activity has been proposed.

Preparation of alpha‐bisabolol and phenylethyl resorcinol/TiO2 hybrid composites for potential applications in cosmetics

Bifunctional alpha-bisabolol and phenylethyl resorcinol/TiO2 hybrids were prepared to apply in cosmetic fields, particularly in anti-ageing and hyperpigmentation treatment. The synergistic effect of combined antioxidant and UV filtering properties was achieved through functionalization of TiO2 particles with skin-lightening materials such as alpha-bisabolol and phenylethyl resorcinol. TiO2 microspheres with a diameter of about 1 μm were synthesized through surfactant-assisted sol-gel method for use as supporting materials in the formation of hybrid composites. Carboxylation treatment was performed for surface modification of the TiO2 surface with carboxyl groups as chemical binders. Esterification reaction between carboxyl groups of carboxylated TiO2 and hydroxyl groups of alpha-bisabolol or phenylethyl resorcinol was performed. The hybrids were characterized using various techniques such as FE-SEM, DLS, EDS, ATR-FTIR, XPS and TGA. For application of prepared TiO2 composites in the field of cosmetics, the anti-radicular antioxidant abilities were evaluated using ABTS and DPPH colorimetric antioxidant assay. Organic/inorganic hybrid composites were successfully formed using esterification reaction between the carboxyl groups at TiO2 surface and the hydroxyl groups of the skin-lightening materials. The results demonstrate that both functionalized microspheres show scavenging ability towards the ABTS(•) and DPPH(•) radicals. Specifically, the phenylethyl resorcinol/TiO2 composites exhibited the highest antioxidant ability among the prepared samples owing to the presence of phenolic groups to scavenge free radicals. Using this strategy, it could be possible to prepare not only inorganic UV filter but also hybrid organic/inorganic materials with multifunctions and advantages which would be in a great demand for cosmetic applications.

Synthesis, characterization and photocatalytic applications of Zn-doped TiO2 nanoparticles by sol–gel method

Mesoporous, nanocrystalline, Zinc-doped TiO2 nanoparticles were synthesized by surfactant-assisted sol–gel method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and UV–VIS spectrometer techniques were used to characterize the synthesized products. XRD results confirm the formation of the anatase phase for the TiO2 nanoparticles, with crystallite sizes in the range of 12.6–18.1 nm. The small crystallite size and doping with Zinc ion inhibit phase transformation and promote the growth of the TiO2 anatase phase. The SEM and TEM micrographs revealed the spherical-like morphology with average diameter of about 12–18 nm which is in agreement with XRD results. The optical study shows that doping ions lead to an increase in the absorption edge wavelength and a decrease in the band gap energy of titania. Photocatalytic activity of the synthesized nanomaterials was successfully tested for photodegradation of methyl red as model pollutant under UV light. The photocatalytic activity results confirm that the doped nanoparticles show higher activity than undoped titania. The small grain size, high crystallinity, high specific surface area and decrease in the band gap energy of doped titania may be responsible for the high photocatalytic activity.

Surfactant-assisted sol–gel synthesis of forsterite nanoparticles as a novel drug delivery system

In the present study, forsterite nanoparticles were synthesized via surfactant-assisted sol–gel method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant. The effects of CTAB contents and heat treatment on the textural properties and drug release from nanoparticles were investigated. The synthesized powders were studied by X-ray diffraction, Fourier transform infrared spectra, Brunauer–Emmett–Teller surface area analysis and transmission electron microscope images. Mg2SiO4 materials demonstrated mesoporous characteristics and large specific surface area ranging from 159 to 30m2/g. The TEM results showed that forsterite nanorods had diameters about 4nm and lengths ranging from 10 to 60nm. It was found that the samples with 6g CTAB show slower drug release rate than the other specimens, which is due to smaller pore size. This study revealed that the drug delivery of forsterite can be tailored by changing the amount of surfactant.

Synthesis of Thin Titania Photoanodes with Large Mesopores for Electricity-generating Windows

Abstract Highly transparent mesoporous titania photoanodes with large mesopores and crystallized framework are synthesized by surfactant-assisted sol–gel method. The conversion efficiency of DSC with rare-metal-free dye (MK-2) reaches 2.6%, though the film thickness of photoanode is of sub-micron order (around 445 nm). The thinness of the photoanodes and the red-light transmission of the dye maintain the high transmittance of the dye-adsorbed photoanodes (around 80% for 700-nm light), demonstrates that obtained photoanodes are promising for electricity-generating windows.

Biocompatible tailored zirconia mesoporous nanoparticles with high surface area for theranostic applications

Nanocarriers as theranostic agents are under the spotlight in modern nanomedicine, and mesoporous nanomaterials represent a class of devices of major interest. Zirconia is biocompatible, inert with good mechanical and thermal properties for in vivo biomedical applications. Although a few examples of zirconia nanoparticles have been described, a major limitation was the low surface area, which is fundamental for payload transport. Here, a simple and highly efficient method is described for the synthesis of spherical mesoporous zirconia nanoparticles (MZNs) with a high surface area through a neutral surfactant-assisted sol-gel method. The combination of alkali halides and vacuum extraction allowed stabilization of the shape and size of MZNs and to avoid porous network failure, respectively. In comparison to published synthesis procedures, a high surface area has been obtained. Biological experiments demonstrated that MZNs were biocompatible, cell permeable and degradable providing a proof of concept for theranostic applications. A comparison with the properties of mesoporous silica nanoparticles has also been performed.

Structure and Electronic States of Zinc-Doped Iron Oxide Nanotubes Prepared by a Surfactant-Assisted Sol–Gel Method

We report the doping of iron oxide nanotubes with zinc, and the characterization of the resulting zinc ferrite nanotubes. Gels were prepared by polycondensing iron nitrate nonahydrate and zinc nitrate hexahydrate on the surface of a self-assembled non-ionic surfactant in 1-propanol at 45 °C. Evaporation of the solvent within the gels at 120 °C led to the formation of tubular structures, as evidenced by transmission electron microscopy. The nanotubes had internal and external diameters of ~2–6 and 4–10 nm, respectively, and were ~50 nm long. X-ray diffraction and X-ray photoelectron spectroscopy indicated that the nanotubes possessed a spinel structure, and had a composition of ZnxFe3−xO4, with x ranging from 0 to 0.66. Direct band gaps were evaluated from optical absorption spectra, using the Tauc plot method. The band gaps ranged from 2.4 (x = 0) to 2.0 eV (x = 0.27), thus narrowing upon doping with Zn. This was tentatively attributed to a widening of the band width, and the formation of sub-levels at octahedral B sites of the spinel structure.

Chemical preparation of ferroelectric mesoporous barium titanate thin films: drastic enhancement of Curie temperature induced by mesopore-derived strain.

Mesoporous barium titanate (BT) thin films are synthesized by a surfactant-assisted sol-gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (T(c)) of the mesoporous BT reaches approximately 470 °C.

Enhanced hydrogen generation using ZrO2-modified coupled ZnO/TiO2 nanocomposites in the absence of noble metal co-catalyst

Mesoporous ZrO2-modified coupled ZnO/TiO2 nanocomposites were prepared by a surfactant assisted sol–gel method. The photocatalytic performance of these materials was investigated for H2 evolution without noble metal co-catalyst using aqueous methanol media under AM1.5 simulated light. The H2 evolution was compared with coupled ZnO/TiO2, TiO2, ZnO and Degussa P25. The ZrO2-modified nanocomposites exhibited higher H2 generation, specifically 0.5 wt.% ZrO2 loading produced 30.78 mmol H2 g−1 compared to 3.55 mmol H2 g−1 obtained with coupled ZnO/TiO2. A multiple absorbance thresholds at 435 nm and 417 nm were observed with 0.5 wt.% ZrO2 loading, corresponding to 2.85 eV and 2.97 eV band gap energies. The high surface area, large pore volume, uniform crystallite sizes and enhanced light harvesting observed in ZrO2-modified nanocomposites were contributing factors for effective charge separation and higher H2 production. The possible mechanism of H2 generation from aqueous methanol solution over ZrO2-modified nanocomposite is presented.

Photocatalytic oxidation of nitrogen oxides on N-F-doped titania thin films

Visible light activated nanostructured TiO2 with nitrogen and fluorine co-dopants were prepared by the surfactant assisted sol–gel method and immobilized on glass substrates by dip coating. The films were inserted inside a continuous flow photoreactor and examined for the photocatalytic oxidation of NO air pollutant with initial concentration of 200–800ppbv. The modified catalysts exhibited significant photocatalytic activity under daylight illumination, with maximum percentage of NO removal equal to 24.2% and photooxidation rate up to 0.66μgm−2s−1. The reaction rates increased proportionally to the incident light intensity whereas for the strongly absorbed UV light a deviation from linearity was observed. Mass balance during photooxidation was confirmed by determining the amount of NO3− product residues onto the photocatalyst surface.