Surfactant-assisted Sol-gel Process Research Articles

Design of Ag3VO4/ZnO nanocrystals as visible-light-active photocatalyst for efficient and rapid oxidation of ciprofloxacin antibiotic waste

BackgroundOxidative mineralization of antibiotic waste by visible light active semiconductor photocatalysts become an important issue to prevent the possible crisis of antimicrobial resistance to these materials. On the other hand, the engineered design of sustainable and efficient photocatalyst is still under development stage due to some obstacles like large bandgap energy (Eg) and the rapid charge recombination MethodsIn this work, a surfactant-assisted sol-gel process is used to synthesize mesostructured ZnO nanocrystals which are subsequently loaded with minor amounts (1.0–4.0 wt.%) of nanocrystalline Ag3VO4 by coprecipitation to form heterostructured Ag3VO4/ZnO photocatalyst. Significant findingsProduced nanostructures revealed the uniform distribution of ∼5.9 nm of monoclinic Ag3VO4 decorating 58.6 nm wurtzite ZnO nanocrystals as confirmed by XRD, TEM, and XPS characterizations. In addition, the samples displayed a mesoporous texture with 123–150 m2 g‒1 of surface area. The incorporation of Ag3VO4 to ZnO enhanced visible-light harvesting and reduced Eg from 3.34 to ∼2.4 eV. The designed photocatalysts showed a rapid photooxidation of ciprofloxacin (CPF) as an emerging antibiotic pollutant in the water. The 3.0% Ag3VO4/ZnO revealed complete mineralization of 10-ppm CPF within 45 min of visible-light irradiation at workable reusability. This magnificent performance is referred to as the homogenous distribution of Ag3VO4 on the ZnO surface that allows efficient separation and mobility of photoinduced charges and subsequent oxidation of CPF in a short time.

Bi2S3-sensitized TiO2 nanostructures prepared by solution process for highly efficient photoreduction of hexavalent chromium ions in water under visible light

The release of hexavalent chromium ions (Cr (VI)) in water can pose critical intimidations to the ecological environments and highly hazardous impacts on health. This study demonstrates the construction of nanostructured Bi2S3/TiO2 as a visible-light active photocatalyst for the rapid reduction of Cr(VI) to trivalent chromium ions (Cr(III)). Mesostructured TiO2 was grown by surfactant-assisted sol-gel process. The Bi2S3 of 8.3 nm in size were anchored the 19.4 nm TiO2 rhombohedra by coprecipitation at 1.0–4.0 wt%, as proved by TEM, XPS, and XRD explorations. The absorption of visible light was enhanced as a result of bandgap reduction to ∼2.5 eV for the 3.0% Bi2S3/TiO2. This developed Bi2S3-sensitized TiO2 achieved a fast photocatalytic reduction of Cr(VI) at 284.2 μmol min−1 within just 30 min by adjusting dose at 2.0 gL−1. In addition, this developed photocatalyst showed magnificent reproducibility for five runs. This promoted photoactivity is ascribed to the efficient interfacial charge separation by Bi2S3 sensitization as inveterate by photoluminescence and photocurrent measurements. This work opens the door for plenty of metal chalcogenide-based oxide nanostructured photocatalysts for heavy metal remediation under visible light.

Use of Materials Based on Polymeric Silica as Bone-Targeted Drug Delivery Systems for Metronidazole.

Mesostructured ordered silica-based materials are the promising candidates for local drug delivery systems in bone disease due to their uniform pore size and distribution, and high surface area which affect their excellent adsorption properties, good biocompatibility and bioactivity, and versatile functionalization so that their properties can be controlled. Ordered mesoporous silica (MCM-41 type) was synthesized by a surfactant-assisted sol-gel process using tetraethoxysilane as a silica precursor and hexadecyltrimethylammonium bromide as the structure-directing agent. Functionalized silica materials containing various types of organic groups (3-aminopropyl, 3-mercaptopropyl, or 3-glycidyloxypropyl groups) were synthesized by the post-grafting method onto pre-made mesoporous silica. Comparative studies of their structural characteristics, the surface mineralization activity and release properties for the model drug Metronidazole (MT) were then conducted. It has been found that porosity parameters, mineralization activity and adsorption/release of metronidazole from mesoporous channels of silica can be regulated using functional groups which are chemically bounded with an outer silica surface. The preferential mineral nucleation was found on negatively charged surfaces—MCM-41, and mercaptopropyl and glycidyloxypropyl functionalized silica (MCM-SH and MCM-epoxy, respectively) in simulated body fluid (SBF solution), as well as a sustained release of MT. In contrast to them, aminopropyl-functionalized samples (MCM-NH2) achieved a high MT release rate. These results confirm the potential of silica-based materials for local therapeutic applications (as drug carriers and bone substitutes) in bone disease.

Conformal Titanyl Phosphate Surface Passivation for Enhancing Photocatalytic Activity

A conformal titanyl phosphate passivation with the thickness of ca. 5 nm on the surface of TiO2 nanoparticles for enhancing the photocatalytic degradation of organic pollutants and hydrogen production is described. The phosphate anion species bound to the surface of TiO2 promote the favorable kinetics of photocatalytic activity and influence the catalytic reaction pathway. By using a facile surfactant-assisted sol-gel process, the surface defects of TiO2 associated with deep traps was reduced and passivated by the phosphate anion species to form the titanyl phosphate. The strong bonds between the titanyl phosphate shell and TiO2 core provided a long-term photochemical stability in aqueous electrolytes with enhanced photocatalytic activities. The titanyl phosphate contributed to the production and stabilization of hydroxyl radicals on the surface of photocatalyst, which facilitated the efficient photooxidation of the organic pollutants. Further, enhancing the photocatalytic hydrogen production was achieved by the titanyl phosphate modified TiO2 (TP-TiO2). Consequently, the conformal titanyl phosphate passivation enhanced photocatalytic activity of TiO2. Comparing to the bare TiO2 nanoparticles, approximately two-fold higher photocatalytic H2 production rate was achieved by the TP-TiO2.

Formulation and In Vitro Characterization of Bioactive Mesoporous Silica with Doxorubicin and Metronidazole Intended for Bone Treatment and Regeneration

ABSTRACTThe purpose of this study was to evaluate the surface mineralization activity and in vitro drug behavior potential of two forms of mesoporous silica: powder and granulate. Ordered mesoporous SiO2 powder was synthesized by surfactant-assisted sol-gel process using tetraethoxysilane as a silica precursor and hexadecyltrimethylammonium bromide as the structure-directing agent. The granulate was prepared using silica powder and ethyl cellulose as a binding agent. Metronidazole (MT)—an anti-inflammatory substance and doxorubicin hydrochloride (ChD)—an anti-cancer drug were chosen as drug models for delivery studies. The results of structural characteristic studies, utilizing transmission electron microscope (TEM) and scanning electron microscope (SEM) images, powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption–desorption (BET) measurements, show that obtained materials have two-dimensional hexagonal p6mm symmetry, high specific surface area, narrow pore size, and a satisfactory mineralization behavior in the simulated body solution (SBF, pH = 7.4). The release rate of drugs depends upon the structural features of the drug molecules and the form of the carrier material. Of both the drugs analyzed, faster release was observed for small MT molecules characterized by weaker interactions with the carrier. In addition, the slower drug release was observed with granulate form due to increased diffusion barrier for drugs. Obtained results prove that the MT/ChD-loaded silica formulations could be attractive materials for filling bone defects and for local delivery systems.

Characterization of ThO2 and (Th,U)O2 pellets consolidated from NSD-sol gel derived nanoparticles

Sinterable ThO2 and mixed 70%ThO2-30%UO2 nanopowders were synthesized and calcined at a low temperature by surfactant assisted sol-gel process using three different nonionic structure directing (NSD) agents: TritonX100, Polysorbate 80 and Polysorbate 20. The produced powder samples, with high surface area and micro and meso pores, were pressed and sintered to form high density ThO2 and (Th,U)O2 pellets. The calculated green and sintered densities of the fabricated pellets, and the results of their microstructural characteristics studies, utilizing SEM images, show that developed synthesizing method yields a satisfactory sinterability of the synthesized ThO2 and ThO2-UO2 nanopowders at low temperature. Also, the final grain size of the pellets reached less than a micrometer in size. The ThO2 and (Th,U)O2 pellets fabricated by synthesized powder using Triton X100 had a higher density and better grain growth. The uranium presence in the mixed oxide pellets led to better sinterability and more normal grain growth.

Sol–gel derived nanoscale ThO2 using nonionic surfactant agents

In this research, two different types of sinterable ThO2 nanopowders were synthesized by surfactant assisted sol–gel process using thorium nitrate as a starting material, and Triton X100 and Polysorbate 80, as two different structure directing agents. Both of the prepared gels were dried and characterized by thermogravimetry–differential scanning calorimetry (TGA–DSC) and X-ray diffraction (XRD). The dried gels were finally calcined and, the produced powders were subjected to XRD, Brunauer–Emett–Teller (BET), Barret–Joyner–Halenda (BJH) analyses and SEM studies. Detailed analyses show that thorium dioxide powders of different crystallite sizes, surface areas, pore volumes and sizes and sinterabilities were prepared using two different surfactants. This synthesizing route yielded the well crystallite nano-sized ThO2 powders with relatively high surface area and good sinterability at low temperature of 1400°C. The powder synthesized using Triton X100 surfactant exhibited higher surface area, pore volume, pore size and crystallite size. It contained some aggregated particles along with the smaller seeds. Furthermore, the pellet which is fabricated by powder synthesized using Triton X100 had a higher density and better grain growth, to some extent.

Electrochromic properties of nanostructured tungsten oxide films prepared by surfactant-assisted sol–gel process

Pristine and surfactant F-127 added tungsten oxide films have been prepared successfully by sol–gel method using PTA as the precursor sol. After annealing at 300°C, amorphous WO3 films with or without F-127 additions were prepared. The F-127-added tungsten oxide films exhibit porous microstructure, which are affected by the amount of F-127 addition. Nanosized microstructure with pore size less than 10nm can be observed with small amount of F-127 addition (less than 0.06g/ml) , where as larger spherical or tubular pores are found with superfluous F-127 addition (higher than 0.08g/ml). Not only the transmittance modulation but also the coloration efficiency can be improved by adding surfactant F-127. Tungsten oxide film with 0.10g/mlF-127 addition exhibits the best electrochromic performance with a transmittance modulation of 67.6% and a coloration efficiency of 38.3cm2C−1.

Preparation of Porous Hollow SiO2 Spheres by a Modified Stöber Process Using MF Microspheres as Templates

Using the surface charged and acid dissolvable melamine formaldehyde (MF) microspheres as sacrificial hard templates, silica coated MF core–shell composite microspheres, denoted as MF@SiO2, were synthesized via a surfactant-assisted sol–gel process by using tetraethyl orthosilicate (TEOS) as silica source. Hollow SiO2 spheres with mesoporous shells were then obtained after selective removal of the MF cores and the pore directing surfactant by hydrochloric acid etching or calcinations in air. Interesting shrinkage phenomena were observed in both the hollow products derived from hydrochloric acid etching and calcinations. The influence of the ratio of MF sphere to TEOS and the removal method of the MF core on the size of the hollow spheres, the shell thickness and the shell surface roughness have been studied. The composition, the thermal stability, the morphology, the surface area and pore size distribution, the wall thickness and adsorption properties of the hollow spheres derived from hydrochloric acid etching and calcinations were also investigated and compared based on the FTIR, SEM, TEM, TGA, Nitrogen adsorption–desorption and spectrophotometer techniques or measurements.

Improving photoelectrochemical activity of dye sensitized solar cell by a bilayered electrode with an overlayer of mesoporous anatase TiO 2

For better performance of dye sensitized solar cells (DSSCs), a bilayer structured electrode was constructed by employing a mesoporous anatase TiO 2 overlayer above a commercial P25 TiO 2 nanoparticles underlayer. The mesoporous anatase TiO 2, prepared through a facile surfactant-assisted sol–gel process, possessed large pore size and well inter-connected network structure, both beneficial for dye adsorption and electron transfer. The dye adsorption capability of the mesoporous TiO 2 was nearly twice that of the P25 counterpart. In the electrode, the mesoporous TiO 2 film enhanced both dye adsorption and light-harvest, to increase photocurrent ( J sc) from 12.32 to 14.78 mA/cm 2. Compared to the single P25 TiO 2 film, the synergy of the mesoporous TiO 2 and the P25 TiO 2 nanoparticle films in the electrode resulted in a 24% improvement in light-to-electricity conversion efficiency ( η). This bilayered electrode provides an alternative approach for further developing a photovoltaic device with better cell performance.

Surfactant-Assisted Sol-Gel Synthesis of TiO2 with Uniform Particle Size Distribution

TiO2 materials were prepared from a titanium isopropoxide precursor by sol-gel processing in water media with or without various templates (polyethylenimine or Pluronic P-123). The photocatalytic efficiency of the samples was found to depend strongly on the use of and type of template added. Titania/Pluronic sols resulted in homogeneous anatase TiO2—rutile with uniform particle size distribution after calcination (400°C). Optical properties of the samples were characterized by UV-Vis spectroscopy and crystalline structures by X-ray diffraction. A surfactant-assisted sol-gel process retarded crystallization of the anatase and rutile titania, which resulted in smaller grain sizes and presumably a larger active surface area. The morphology of the surfaces was obtained by AFM techniques. The highest photobleaching rate was found for samples deposited from the sol with the addition of the Pluronic P-123 surfactant, and it was almost twice as high as that for films deposited from sols with polyethylenimine.

Microstructure and photocatalytic activity of mesoporous TiO 2 film coated on an aluminum foam

A TiO 2 film was synthesized via a surfactant assisted sol–gel process and dip-coated on the surface of an open-celled aluminum foam. The film shows a typical mesoporous structure composed of anatase crystalline grains with the average size of 10 nm, and has the thickness of about 3.5 μm as well as the BET surface area of 78.1 m 2/g. It exhibits high photocatalytic efficiency toward the decomposition of formaldehyde at continuous flow mode. The relatively small grain size of TiO 2 and relatively thick mesoporous structure, which is favorable for high photochemical activity and the mass transfer of the reactants, should be responsible for the properties.

Photocatalytically active TiO 2 thin films produced by surfactant-assisted sol–gel processing

Thin TiO 2 films were prepared from a titanium isopropoxide precursor by sol–gel processing with or without various nonionic surfactant molecules (Brij 56, Triton X-100 or Pluronic F-127). The photocatalytic efficiency of the transparent films obtained by a dip-coating technique was found to depend strongly on the use of and type of surfactant added. Titania/Pluronic sols resulted in homogeneous and crack-free TiO 2 anatase films with a thickness as much as 300 nm after one dipping and heat-treatment (500 °C) cycle. Optical properties of the films were characterized by UV-Vis spectroscopy and crystalline structures by X-ray diffraction. A surfactant-assisted sol–gel process retarded crystallization of the anatase titania films, which resulted in smaller grain sizes (down to 10 nm) and presumably a larger active surface area. The morphology of the film surfaces as obtained by SEM techniques could be also correlated with the results of our photodegradation studies. The photocatalytic activity of the films was enhanced by first coating the glass substrate with a SiO 2 protective layer prior to the deposition of the titania film. For our in situ studies of photodegradation we chose the monoazo dye Plasmocorinth B as a model compound as it is stable under environmental conditions and its degradation products are not coloured. The highest photobleaching rate was found for films deposited from the sol with addition of the Pluronic surfactant and it was almost twice as high as that for films deposited from sols without the surfactant.