Sol-gel Protocol Research Articles

Enhanced photodegradation of methylene blue by Zr-doped TiO2:A combined DFT and experimental investigation

The effective mitigation of effluents in water has attracted researchers as a foremost task for addressing environmental concerns. To overcome these concerns, TiO2 (labeled as PCT-1) and Zr-doped TiO2 (labeled as PCT-2) nano catalysts are prepared by an efficient sol–gel protocol and their photocatalytic degradation performance of methylene blue (MB) is investigated. The structural integrity of nanostructures is determined by analytical tools. More than 96 % MB degradation is observed when PCT-2 is subjected to ultraviolet light for 180 min. Nanosized PCT-2 exhibits attractively advanced photocatalytic performance than PCT-1 owing to lower electron–hole pair recombination (3.02 eV) as well as superior photon capture via oxidation by photocatalytic response (confirmed through active species trapping scavenger tests). Furthermore, the results of bandgap are also confirmed by spin-polarized density functional theory (DFT) computations. The findings of this study indicate that band tuning is an attractive photocatalytic system for improving catalytic performance.

Fabrication of chitosan-coated calcium tungstate (CaWO4/Chitosan) and its Antioxidant, antimicrobial and phocatalytic activity

In the present era, the applicability of natural bioactive polymers, such as chitosan, has become a significant concern due to its biologically compatible range, ease of biodegradability, and lower hazardous traits. In our investigation, the production of chitosan-coated calcium tungstate (CaWO4/Chitosan) was carried out using a sol–gel protocol. The resulting chitosan-coated calcium tungstate (CaWO4) was subjected to FTIR spectral analysis to identify the functionally active groups in chitosan interacting with calcium tungstate. X-ray analysis revealed the amorphous nature of chitosan-coated calcium tungstate (CaWO4), with a crystallite size ranging from 14.2 nm to 32.0 nm. The surface morphology and size of the CaWO4/Chitosan was analysed using SEM and TEM studies. The chitosan-coated calcium tungstate (CaWO4) exhibited a profound dose-dependent antioxidant activity, as determined by the DPPH assay. Both E. coli and S. aureus were susceptible to chitosan-coated calcium tungstate (CaWO4), showing inhibition zones of 19 mm and 20 mm, respectively. Additionally, chitosan-coated calcium tungstate (CaWO4) demonstrated antifungal activity against pathogenic fungi (A. flavus and A. niger) with inhibitory zones of 11 mm and 15 mm. UV-DRS analysis yielded a unique peak at 234 nm, corresponding to a band gap of 3.9093 eV. The chitosan-coated calcium tungstate (CaWO4) exhibited outstanding photocatalytic activity on alizarin, influenced by dye catalyst and concentration.

In Vitro Synergistic Photodynamic, Photothermal, Chemodynamic, and Starvation Therapy Performance of Chlorin e6 Immobilized, Polydopamine-Coated Hollow, Porous Ceria-Based, Hypoxia-Tolerant Nanozymes Carrying a Cascade System.

A synergistic therapy agent (STA) with photothermal, photodynamic, chemodynamic, and starvation therapy (PTT, PDT, CDT, and ST) functions was developed. Hollow, mesoporous, and nearly uniform CeO2 nanoparticles (H-CeO2 NPs) were synthesized using a staged shape templating sol-gel protocol. Chlorin e6 (Ce6) was adsorbed onto H-CeO2 NPs, and a thin polydopamine (PDA) layer was formed on Ce6-adsorbed H-CeO2 NPs. Glucose oxidase (GOx) was bound onto PDA-coated Ce6-adsorbed H-CeO2 NPs to obtain the targeted STA (H-CeO2@Ce6@PDA@GOx NPs). A reversible photothermal conversion behavior with the temperature elevations up to 34 °C was observed by NIR laser irradiation at 808 nm. A cascade enzyme system based on immobilized GOx and intrinsic catalase-like activity of H-CeO2 NPs was rendered on STA for enhancing the effectiveness of PDT by elevation of ROS generation and alleviation of hypoxia in a tumor microenvironment. Glucose-mediated generation of highly toxic hydroxyl radicals (·OH) was evaluated for CDT. The effectiveness of PDT on glioblastoma T98G cells was markedly enhanced by O2 generation started by the decomposition of glucose. A similar increase in cell death was also observed when ST and CDT functions were enhanced by photothermal action. The viability of T98G cells decreased to 10.6% by in vitro synergistic action including ST, CDT, PDT, and PTT without using any antitumor agent.

Synthesis of intrinsic, Manganese and magnesium doped cobalt ferrite nanoparticles: Physical properties for antibacterial activities

The work emplaced in this research is the synthesis of cobalt ferrite nanoparticles (CFNPs) doped with manganese and magnesium for antibacterial activities by sol-gel protocol. The physicochemical properties of CFNPs, Mg_CFNPs and Mn_CFNPs as described by the characterization techniques shows good results. Cubic spinel structures of CFNPs, Mg_CFNPs and Mn_CFNPs were observed by the X-ray diffraction (XRD) technique. The transmission electron microscope (TEM) established the spherical shape of the samples. The functional groups embedded in the sample were observed using FTIR and complimented by the Raman analysis. The formulated sample was used against four pathogenic strains S. epidermidis; B. subtilis; E. coli and K. pneumoniae. Higher susceptibility against E. coli was observed with Mg_CFNPs compared to the pristine (CFNPs) and Mn_CFNPs. Hence, the formulated Mg_CFNPs are highly significant and propitious for antibacterial activities.

Synthesis in ambient air of LaVxFe1−xO3 compounds by the sol-gel method: Structural and optical studies

In the present study, we successfully synthesized LaVxFe1−xO3 powders following a standard sol-gel protocol under ambient air conditions. This synthesis was made possible thanks to the use of ascorbic acid as a reducing agent. There was no need for a controlled environment or vacuum to prevent vanadium from oxidation. Ascorbic acid has the advantage of helping to adjust the pH of the solution until it turns green, which is an indication of the presence of the V+3 oxidation state. Structural characterization was performed using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy, while optical bandgap energies were determined using UV-Visible spectrophotometry. The vanadium fraction of 25% vanadium showed tiny, agglomerated nanoparticles with an estimated size of about 30 nm, and a globally orthorhombic structure was obtained. Deeper infrared analyzes were able to highlight a deformed structure of LaFeO3 inside which very few FeO6 octahedra are replaced by deformed VO6 octahedra. Due to these, a bandgap reduction occurred from 2.31 eV to 1.86 eV, proving that the combination of lanthanum ferrite and lanthanum vanadate is a successful strategy to tune the bandgap energy while retaining the orthorhombic structure. Such a combination therefore offers a promising way for the fabrication of devices with a high potential for harvesting and conversion for applications based on solar irradiation.

PH regulated rapid photocatalytic degradation of methylene blue dye via niobium-nitrogen co-doped titanium dioxide nanostructures under sunlight

Niobium and nitrogen co-doped titanium dioxide (Nb-N-TiO2) semiconductor nanostructures were synthesized through a facile sol-gel protocol using titanium tetra iso-propoxide (TTIP), urea and niobium pentoxide as precursors followed by calcination at 450 °C for 4 h. The synthesized nanomaterial (Nb-N-TiO2) was characterized via Fourier Transform Infrared (FTIR) and Raman spectroscopy, UV-Visible (UV-Vis) Spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) technique, Dynamic Light Scattering (DLS) technique and ZETA Potential analysis. The band gap of Nb-N-TiO2 was reduced as compared to TiO2 due to reduced space between valance and conduction band which also reduced the electron-hole (e-, h+) recombination and led to better photocatalytic activity of the Nb-N-TiO2 as confirmed by TAUC plot. Photocatalytic activity of Nb-N-TiO2 was investigated for degradation of methylene blue (MB) dye under sunlight as cheaper light source. Factors like dye concentration, dosage of catalyst, volume of solution time and pH were studied and optimized for MB degradation. Under finally optimized conditions, 97% of 25 ppm MB was degraded just in one minute using 45 mg of photocatalyst. The co-doped nanocatalyst, was re-used for MB degradation upto 4th cycle with its efficiency reduced to 75% which shows a better catalytic role by the catalyst. Degradation products of MB were recognized through electrospray ionization coupled mass spectroscopy (ESI-MS) and liquid chromatography coupled mass spectroscopy (LC-MS) techniques. The catalyst was also applied for MB degradation in tap water sample.

A novel route for catalytic activation of peroxymonosulfate by oxygen vacancies improved bismuth-doped titania for the removal of recalcitrant organic contaminant.

In this work, bismuth-doped titania (BixTiO2) with improved oxygen vacancies was synthesized by sol-gel protocol as a novel peroxymonosulfate (PMS, HSO5-) activator. HSO5- and adsorbed oxygen molecules could efficiently be transformed into their respective radicals through defect ionization to attain charge balance after their trapping on oxygen vacancies of the catalyst. XRD study of BixTiO2 with 5 wt% Bi (5BiT) revealed anatase, crystalline nature, and successful doping of Bi into TiO2 crystal lattice. The particle size obtained from BET data and SEM observations was in good agreement. PL spectra showed the formation rates of •OH by 3BiT, 7BiT, 5BiTC, and 5BiT as 0.720, 1.200, 1.489, and 2.153 μmol/h, respectively. 5BiT catalyst with high surface area (216.87 m2 g-1) and high porosity (29.81%) was observed the excellent HSO5- activator. The catalytic performance of 0BiT, 3BiT, 5BiT, and 7BiT when coupled with 2 mM HSO5- for recalcitrant flumequine (FLU) removal under dark was 10, 27, 55, and 37%, respectively. Only 5.4% decrease in catalytic efficiency was observed at the end of seventh cyclic run. Radical scavenging studies indicate that SO4•- is the dominant species that caused 62.0% degradation. Moreover, strong interaction between Bi and TiO2 through Bi-O-Ti bonds prevents Bi leaching (0.081 mg L-1) as shown by AAS. The kinetics, degradation pathways, ecotoxicity, and catalytic mechanism for recalcitrant FLU were also elucidated. Cost-efficient, environment-friendly, and high mineralization recommends this design strategy; BixTiO2/HSO5- system is a promising advanced oxidation process for the aquatic environment remediation.

Biomimetic Amorphous Titania Nanoparticles as Ultrasound Responding Agents to Improve Cavitation and ROS Production for Sonodynamic Therapy

Conventional therapies to treat cancer often exhibit low specificity, reducing the efficiency of the treatment and promoting strong side effects. To overcome these drawbacks, new ways to fight cancer cells have been developed so far focusing on nanosystems. Different action mechanisms to fight cancer cells have been explored using nanomaterials, being their remote activation one of the most promising. Photo- and sonodynamic therapies are relatively new approaches that emerged following this idea. These therapies are based on the ability of specific agents to generate highly cytotoxic reactive oxygen species (ROS) by external stimulation with light or ultrasounds (US), respectively. Crystalline (TiO2) and amorphous titania (a-TiO2) nanoparticles (NPs) present a set of very interesting characteristics, such as their photo-reactivity, photo stability, and effective bactericidal properties. Their production is inexpensive and easily scalable; they are reusable and demonstrated already to be nontoxic. Therefore, these NPs have been increasingly studied as promising photo- or sonosensitizers to be applied in photodynamic/sonodynamic therapies in the future. However, they suffer from poor colloidal stability in aqueous and biological relevant media. Therefore, various organic and polymer-based coatings have been proposed. In this work, the role of a-TiO2 based NPs synthesized through a novel, room-temperature, base-catalyzed, sol-gel protocol in the generation of ROS and as an enhancer of acoustic inertial cavitation was evaluated under ultrasound irradiation. A novel biomimetic coating based on double lipidic bilayer, self-assembled on the a-TiO2-propylamine NPs, is proposed to better stabilize them in water media. The obtained results show that the biomimetic a-TiO2-propylamine NPs are promising candidates to be US responding agents, since an improvement of the cavitation effect occurs in presence of the developed NPs. Further studies will show their efficacy against cancer cells.

Niobia-based magnetic nanocomposites: Design and application in direct glucose dehydration to HMF

Niobia-based magnetic nanocomposites were prepared by covering magnetite nanoparticle cores (Fe3O4, MNP) with either Nb2O5 or Nb2O5-SiO2 shells using a two-step procedure. In the first step magnetite nanoparticles were prepared by the coprecipitation method. The second step involved their coverage with either Nb2O5 shells, through a precipitation method, or with Nb2O5-SiO2 shells, through a sol-gel protocol followed by precipitation in the presence of the CTAB surfactant. The obtained materials were exhaustively characterised by X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, ICP-OES, DRIFT and Raman spectroscopy, and CO2 - and NH3-TPD measurements, and investigated for glucose dehydration to HMF. The catalytic performances were directly correlated to the nature of the supported niobia phases, which, in turn, has been dictated by the niobia content and the preparation route. The high selectivity to HMF was correlated with to the large pseudohexagonal niobium oxide (TT-Nb2O5) phase while the catalytic activity was directly correlated to the small nanoparticles size. A proper combination of these features led to an optimum catalytic system for the selective production of HMF through glucose dehydration. A third important feature making the developed catalyst promising is its magnetic property, ensured by the magnetite nanoparticles core. This allowed its easy separation from the reaction products.

Performance of oil sorbents based on reduced graphene oxide–silica composite aerogels

Clean-up of crude-oil spills ranks among the major environmental remediation issues and demands for sorbents with high and stable oleophilic and hydrophobic features. Here, aerogels with durable hydrophobicity are produced by incorporating reduced graphene oxide (rGO) in highly porous silica matrices. By a sol-gel protocol, high rGO loadings are achieved by exploiting highly dispersible hydrophilic graphene oxide as rGO precursor. Homogeneous rGO-silica composite monoliths are obtained with tunable loading up to 10 wt%, enabling a detailed analysis of the sorption behaviour towards oil spills. Composite aerogels demonstrate an excellent performance towards oil sorption with oil uptake from ∼7 to ∼10 times the aerogel mass. Although the sorption ability is lower than for plain hydrophobic silica, composites with a minimum loading of 5 wt% exhibit very high oil selectivity and show a durable and reliable behaviour over time, providing longer shelf-life than plain SiO2 aerogels. The synergetic effect of rGO towards long-term hydrophobicity and oil selectivity on silica composite aerogels allows for the implementation of such composite materials in real water remediation processes.

Photodynamic therapy, facile synthesis, and effect of sintering temperature on the structure, morphology, optical properties, and anticancer activity of Co3O4 nanocrystalline materials in the HepG2 cell line

This research project focused on the assessment of the anticancer activity of Co3O4 nanocrystalline materials (NCMs), annealed at various temperatures in the HepG2 (liver hepatocellular carcinoma) cell line. Co3O4 NCMs were synthesized using a sol-gel protocol and then calcined at various temperatures. The structure, morphology, and purity of synthesized nanocrystalline materials and their optical properties were studied via various material analysis techniques, including XRD, SEM, EDX, UV/Vis, and Raman spectroscopy. The anticancer activity of cobalt oxide nanocrystalline materials (Co3O4 NCMs) were explored in human liver carcinoma by performing and optimizing photodynamic therapy (PDT) through a variety of specific steps. This included the labeling of liver cancer cells with various concentrations at several different incubation times. Additionally, light-induced PDT was employed to assess the phototoxic effects of synthesized nanocrystalline materials in HepG2 cells. Here, we established optimized conditions for this novel therapeutic approach by highlighting the temperature-dependent toxicity of Co3O4 NCMs as a means to improve current PDT standards and precision. Our experimental findings were verified by developing and analyzing a mathematical model to describe annealed Co3O4 NCMs at various temperatures, and the results of this modeling agreed strongly with our experimental data.

Synthesis and Photocatalytic Studies of Fe3O4 Nanoparticles

Advances in nanoscience and nanotechnology are centered in the control of size and shape of nanoparticles, as well as attainment of the extended arrangement of nanoparticles in different structures. One dimensional nanostructured magnetic materials are interesting because of their enhanced magnetic properties and potential applications such as information storage and gas sensor. The advanced electronic applications of Fe3O4 magnetic nanomaterials are considered to require improvement in the powder processing, particularly, meticulous particle control in the nanometer range and phase purity. Structural properties of Fe3O4 nanoparticles were synthesized via sol-gel protocol, the morphology and particles size were determined by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray, UV- diffuse reflectance spectrophotometer and particle size analyzer. The structure of as prepared Fe3O4 nanoparticles was used for photocatalytic applications.

Modifications in structural, morphological, optical and photocatalytic properties of ZnO:Mn nanoparticles by sol-gel protocol

ZnO:Mn nanoparticles with different Mn concentrations (0, 1 and 3 at%) have been produced by sol-gel wet chemical route. The effect of manganese doping on the structural, micro-structural, optical and photocatalytic properties of zinc oxide nanoparticles (ZnO NPs) has been investigated. X-ray diffraction and Raman investigations confirmed high quality monophase wurtzite hexagonal structure of pure and Mn-doped ZnO NPs; and no separate phase of dopant has been found. The chemical composition of Mn-doped ZnO NPs has been confirmed by X-ray photoelectron spectroscopic measurements. Additionally, the presence of Mn 2p3/2 peak at 640 eV in XPS spectra confirmed the addition of Mn in ZnO host matrix. TEM micrograph showed spherical shaped NPs with an average size in the range of 21–35 nm. The high resolution TEM images exhibit the highly crystalline nature and the inter-planar distances of hexagonal wurtzite ZnO:Mn nanoparticles. Raman study also confirmed the hexagonal wurtzite structure of ZnO:Mn (0, 1 and 3 at%) NPs. Optical absorption spectra showed a red shift in the absorbance band edge with increasing Mn doping in ZnO. The increasing doping level of Mn in ZnO resulted in the narrowing of bandgap and the increasing of visible light absorption. For photocatalytic behavior, the methylene blue (MB) decolorization efficiency in the very presence of synthesized pure and Mn-doped ZnO NPs has been studied under visible light irradiation. Photoluminescence measurements showed that the band edges of ultraviolet and green emissions are slightly red shifted; and PL intensity decreases with the increasing concentration of Mn in ZnO NPs. The significantly enhanced photocatalytic activity of Mn doped ZnO NPs is because of the increase in light absorption and the effective separation between photogenerated electron-hole pairs.

Tetragonal zirconia quantum dots in silica matrix prepared by a modified sol–gel protocol

Tetragonal zirconia quantum dots (t-ZrO2 QDs) in silica matrix with different compositions (x)ZrO2–(100 − x)SiO2 were fabricated by a modified sol–gel protocol. Acetylacetone was added as a chelating agent to zirconium propoxide to avoid precipitation. The powders as well as thin films were given thermal treatment at 650, 875 and 1100 °C for 4 h. The silica matrix remained amorphous after thermal treatment and acted as an inert support for zirconia quantum dots. The tetragonal zirconia embedded in silica matrix transformed into monoclinic form due to thermal treatment ≥ 1100 °C. The stability of tetragonal phase of zirconia is found to enhance with increase in silica content. A homogenous dispersion of t-ZrO2 QDs in silica matrix was indicated by the mapping of Zr, Si and O elements obtained from scanning electron microscope with energy dispersive X-ray analyser. The transmission electron images confirmed the formation of tetragonal zirconia quantum dots embedded in silica. The optical band gap of zirconia QDs (3.65–5.58 eV) was found to increase with increase in zirconia content in silica. The red shift of PL emission has been exhibited with increase in zirconia content in silica.

Constructing hierarchical porous carbon via tin punching for efficient electrochemical energy storage

To achieve large-scale preparation of high-performance carbon materials for electrochemical energy storage with a simple and cost-effective method remains a challenge. Here, we report a novel approach to synthesize hierarchical porous carbon with a low melting point metal tin (Sn) as pore forming agent. An aqueous processed tin chloride-polyethylene glycol (SnCl2-PEG) gel is used as precursor to form Sn/Carbon (Sn/C) composites with homogeneously distributed ultrafine Sn particles (<2 nm) by pyrolysis. After etching Sn nanoparticles, hierarchical porous carbon with high specific surface area (SSA: 846 m2 g−1) and abundant pore structure (coexistence of mesopore and micropore) was obtained. The SSA, pore size distribution and pore volume were successfully tuned by controlling the size of the Sn nanoparticle. The capacitive performance of the as-prepared hierarchical porous carbon was evaluated in 1 M H2SO4, which exhibits excellent specific capacitance of 240 F g−1. In order to further increase the electrochemical performance, N-doped porous carbon was fabricated by thermal nitridation in ammonia, which shows favorable features for electrochemical energy storage such as high specific surface area (1175 m2 g−1), uniform micropore volume (0.46 cm3 g−1) and rich nitrogen-doping (4.45 wt%). This N-doped sample exhibits outstanding specific capacitances of 360 F g−1 and excellent cycling stability in aqueous electrolytes. The above achievements indicate that combining low melting point metal as pore forming agent with a sol-gel protocol can be a unique and reliable method for preparation of high performance supercapacitor electrode materials.

Studies on gas sensing behavior of ZnNb2O6 nano composite towards hydrogen

In the present study, semiconductor gas sensor based on nanoporous Zinc Niobate (ZnNb2O6) synthesized via Sol-Gel protocol followed by impregnation and calcined at different temperatures i.e., from 400 °C to 800 °C (coded as ZNb4 to ZNb8) and its formation is demonstrated. We systematically monitored the formation of ZnNb2O6 through diverse characterization techniques such as Energy Dispersive X-Ray Analysis (EDX), X-Ray Diffraction (XRD), Particle Size Analyzer (PSA) and Transmission Electron Microscope (TEM). The XRD studies confirmed the formation of single phase ZnNb2O6 for the samples ZNb7 & ZNb8. The TEM images revealed the particles morphology of single phase ZnNb2O6 samples which exhibited considerably high sensing response of S = 0.7 & selectivity towards H2 gas compared to LPG and NH3 gas. The gas sensing characteristics towards the H2 gas was carried out and it’s resistance was measured in air (Ra) & in presence of gas (Rg) and the sensitivity was calculated as S = Ra − Rg/Ra. Plausible gas sensing mechanism is proposed based on the gas sensing studies carried out with our materials. The achieved features make the sample ZNb7 a potential candidate for development of H2 gas sensor.

Plasmonic-excitonic multi-hybrid glass-based nanocomposites incorporating Ag plus core-shell CdSe/CdS and alloyed CdSxSe1−x nanoparticles

Successful fabrication of glass-based hybrid nanocomposites (GHNCs) incorporating Ag, core-shell CdSe/CdS and CdSxSe1−x nanoparticles (NPs) is herein reported. Both metallic (Ag) and semiconductor (CdSe/CdS) NPs were pre-synthesized, suspended in colloids and added into the sol-gel reaction medium which was used to fabricate the GHNCs. During fabrication of the nanocomposites a fraction (20–60%) of core-shell CdSe/CdS NPs was alloyed into CdSxSe1−x (0.20 < x < 0.35) NPs without changing morphology. Modulation of in situ alloying is possible via the relative content of organics added into the sol-gel protocol. Within colloids Ag (core-shell CdSe/CdS) NPs presented average diameter and polydispersity index of 49.5nm (4.2nm) and 0.41 (0.21), respectively. On the other hand, the Ag (core-shell CdSe/CdS) NPs’ average diameter and polydispersity index assessed from the GHNCs were respectively 51.5nm (4.1nm) and 0.43 (0.25), revealing negligible aggregation of the nanophases within the glass template. The new GHNCs herein introduced presented two independent excitonic transitions associated to homogenously dispersed semiconductor NPs, peaking around 420nm (core-shell CdSe/CdS) and 650nm (CdSxSe1−x) and matching the plasmonic resonance (Ag NPs) in the 400–500nm range. We envisage that the new GHNCs represent very promising candidates for superior light manipulation while illuminated with multiple laser beams in quantum interference-based devices.

Sol-Gel Derived ZnO: Nb2O5 Nanocomposite as Selective Hydrogen (H2) Gas Sensor

The present study investigates the incentive studies on phase transformations of ZnO: Nb2O5 nano composite, synthesized by sol gel protocol followed by impregnation process for sensing hydrogen gas. Detailed analyses of the synthesized nanomaterials were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Particle size analysis. The material was subjected to different annealing temperatures ranging from 400°C to 800°C. The XRD result revealed the formation of single phase ZnNb2O6 at 700°C and above with average particle size of ∼ 67nm. ZnO: Nb2O5 based sensor has shown enhanced gas sensing properties towards 1000ppm H2 gas.

Effect of pH on Synthesis of Single-Phase Titania (TiO2) Nanoparticles and its Characterization

In the present study, we investigated the effect of pH on phase transition of TiO2 nanoparticles synthesized by sol-gel protocol and identification by various techniques as x-ray diffraction, energy dispersive x-ray spectroscopy (EDX), Raman spectroscopy, scanning electron microscopy, etc. Corresponding TiO2 phase change from rutile to anatase and mixture of both anatase and rutile phases by tuning the pH of the reaction mixture is clear from x-ray diffraction studies. The presence of (101) and (110) planes corresponded to anatase and rutile phases of TiO2, respectively.

Silica Sol-Gel Entrapment of the Enzyme Chloroperoxidase

The enzyme chloroperoxidase (CPO) was immobilized in silica sol-gel beads prepared from tetramethoxysilane. The average pore diameter of the silica host structure (~3 nm) was smaller than the globular CPO diameter (~6 nm) and the enzyme remained entrapped after sol-gel maturation. The catalytic performance of the entrapped enzyme was assessed via the pyrogallol peroxidation reaction. Sol-gel beads loaded with 4 μg CPO per mL sol solution reached 9–12% relative activity compared to free CPO in solution. Enzyme kinetic analysis revealed a decrease inkcatbut no changes inKMorKI. Product release or enzyme damage might thus limit catalytic performance. Yet circular dichroism and visible absorption spectra of transparent CPO sol-gel sheets did not indicate enzyme damage. Activity decline due to methanol exposure was shown to be reversible in solution. To improve catalytic performance the sol-gel protocol was modified. The incorporation of 5, 20, or 40% methyltrimethoxysilane resulted in more brittle sol-gel beads but the catalytic performance increased to 14% relative to free CPO in solution. The use of more acidic casting buffers (pH 4.5 or 5.5 instead of 6.5) resulted in a more porous silica host reaching up to 18% relative activity.