Hydrothermal-assisted Sol-gel Method Research Articles

Hydrothermal-assisted sol–gel synthesis of Cd-doped TiO2 nanophotocatalyst for removal of acid orange from wastewater

This research is based on synthesis of titania (TiO2) nanophotocatalyst followed by cadmium (Cd) doping to activate the photocatalyst in visible part of the light spectrum. Therefore, the Cd–TiO2 nanophotocatalyst was synthesized in various Cd/Ti molar ratios of 0, 0.05, 0.1, and 0.15 using hydrothermal-assisted sol–gel method. The characterization analyses of X-ray diffraction, field emission scanning electron microscopy, brunauer-emmett-teller, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric-derivative thermogravimetric, transmission electron microscopy, and energy dispersive X-ray were carried out to evaluate the physical, chemical, and optical properties of the catalysts. The X-ray diffraction analysis resulted a decrease in the crystallinity due to cadmium doping. Field emission scanning electron microscopy images have confirmed the nano-sized structure of the catalysts. The analysis also has demonstrated particle size distribution enhancement with a meaningful low average particle size for Cd/TiO2 (0.15) sample. This sample has represented the highest brunauer-emmett-teller surface area. According to energy dispersive X-ray dot mapping analysis, no aggregation was detected on the catalyst surface. Diffuse reflectance spectroscopy analysis has indicated a moderate decrease in band gap, after Cd loading. The photocatalytic degradation of acid orange 7 dye from the synthetic wastewater was carried out to evaluate the photocatalytic activity. The most effective parameters on the process, such as pH, catalyst loading, and dye concentration, were investigated. According to the characterization analyses and degradation tests, Cd/TiO2 (0.15) was selected as a sample having best structural properties and photocatalytic activity. Finally, the experiments resulted the optimum conditions of pH = 2, catalyst loading of 1 g/L, and dye concentration of 10 mg/L, indicating 95 % of dye degradation after 120 min of experiment. The electron–hole pair generation via transition of electron between the valence and conduction bands (band gap) is the fundamental of any photocatalytic process. After Cd doping, the conduction band position shifts toward the valence band. Then, a valence electron in narrow band gap photocatalyst needs lower energy of light to transfer to conduction band, it means that using light in higher wavelengths (visible light spectra) will be available. In photocatalytic wastewater treatment process, degradation occurs in two ways: the first mechanism is direct oxidation-reduction through electron–hole generation, and the second one would be the oxidation through produced reactive species such as hydroxyl radicals, this route of reaction organizes the major part of wastewater treatment.

Efficient green and red up-conversion emissions in Er/Yb co-doped TiO2 nanopowders prepared by hydrothermal-assisted sol–gel process

In this work, erbium and ytterbium co-doped titanium dioxide (Er–Yb:TiO2) nanopowders have been successfully prepared by hydrothermal-assisted sol–gel method using supercritical drying of ethyl alcohol and annealing at 500°C for 1h. Nanopowders were prepared with fixed 5mol% Erbium concentration and various Ytterbium concentrations of 5 and 10mol%. The powders were characterized by studying their structural, morphology and photo-luminescent properties. The annealing treatment at 500°C was found to enhance the crystallinity of the TiO2 anatase structure and the upconversion (UC) emission of the nanopowders. UC emissions were investigated under 980nm excitation, and the Er–Yb:TiO2 nanopowders exhibited the intense green (520–570nm) and red (640–690nm) upconverted emissions of Er ions originating from an efficient Yb–Er energy transfer process. The absolute upconversion quantum yield (UC-QY) of each nanopowders was measured for the UC emissions centered at 525, 550 and 655nm at varying excitation power densities. UC-QY analysis has revealed that 5mol% Er–5mol% Yb:TiO2 nanopowders possess the highest total quantum yield of 2.8±0.1% with a power density of 16.7W/cm2. These results make these nanopowders promising materials for efficient upconversion in photonic applications.

Monoclinic Li3V2(PO4)3/C nanocrystals co-modified with graphene nanosheets and carbon nanotubes as a three-dimensional-network cathode material for rechargeable lithium-ion batteries

A graphene nanosheet and carbon nanotube co-modified Li3V2(PO4)3/C composite has been first prepared via a hydrothermal-assisted sol–gel method.

Graphene oxide wrapped Na3V2(PO4)3/C nanocomposite as superior cathode material for sodium-ion batteries

Na3V2(PO4)3 is one of the most promising cathode materials for rechargeable sodium-ion batteries, which can deliver two Na+ ions extraction/insertion from/into the crystal structure. To further improve the electrochemical performance of the carbon-coated Na3V2(PO4)3 electrode, the conducting graphene has been adopted. In this paper, graphene-wrapped Na3V2(PO4)3/C nanocomposite has been successfully synthesized through a hydrothermal-assisted sol–gel method. X-ray diffraction (XRD) results demonstrate that the obtained nanocomposite is well crystallized with NASICON-type structure. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that the modification of Na3V2(PO4)3/C with graphene could construct an effective conducting network, which significantly enhances the electronic conductivity of Na3V2(PO4)3/C based sample. Thus, the graphene-wrapped Na3V2(PO4)3/C exhibits superior high-rate capacity and excellent cycling stability. It shows an initial charge capacity of 113mAhg−1 and a discharge capacity of 106.5mAhg−1 at 0.1C, and retains stable discharge capacities of 104.3, 101.1, 96.4 and 93mAhg−1 at current rates of 0.2C, 0.5C, 1C and 2C, respectively. Even at higher rate of 5C, it can still deliver a discharge capacity of 88.7mAhg−1 with remarkable capacity retention of 92.5% after 200 cycles. This synthetic strategy should be helpful for the design of other conducting network structured electrodes with high-performances.

Synthesis of Li2FeSiO4/C nanocomposite via a hydrothermal-assisted sol–gel process

A porous Li2FeSiO4/C composite is synthesized via a hydrothermal-assisted sol–gel method. The porous Li2FeSiO4/C composite consisted of nanoparticles with only 20–30nm size, surrounded by a nitrogen-doped carbon coating layer. Hydrothermal treatment plays a key role to control the crystallite size of the Li2FeSiO4 particles and to form the porous structure. The Li2FeSiO4/C composite obtained via a hydrothermal treatment exhibited a large surface area (50.2m2·g−1), which not only effectively prevents the agglomeration of Li2FeSiO4 particles, but also facilitates fast electron and Li+ transport.More than 1mol Li+ can be extracted from the Li2FeSiO4/C electrode, which exhibits excellent electrochemical performance with a high discharge capacity of 195.5mAh·g−1 at 0.1C and 127.1mAh·g−1 at 5C (1C=166mA·g−1). These results illustrate that the porous Li2FeSiO4/C composite is a promising cathode material for lithium ion batteries.

Colloidal stability of dextran and dextran/poly ethylene glycol coated TiO2 nanoparticles by hydrothermal assisted sol–gel method

Abstract Colloidal stability of dextran (Dex) and Dex/poly ethylene glycol (PEG) coated TiO2 nanoparticles (NPs) were investigated. The particles were successfully synthesized by a hydrothermal assisted sol–gel technique. The results of Ultraviolet–visible (UV–vis) spectrophotometry showed that Dex and PEG additions during hydrothermal process (HTP) led to the formation of long-term (more than 60 days) stable colloids, while the addition of dispersants after HTP did not have a significant impact on the colloidal stability of NPs. X-ray diffraction (XRD) and selected area electron diffraction (SAED) analyses proved that PEG and/or Dex coated NPs had less crystallinity than the plain TiO2. Fourier transform infrared (FTIR) spectroscopy demonstrated the formation of primary bonds between NPs and polymeric dispersants. High-resolution transmission electron microscopy (HRTEM) displayed stable particles with a core-shell structure resulting from coating of NPs by polymeric materials. Thermo gravimetric analysis (TGA) was also utilized to calculate the proportion of NPs to polymeric dispersant.

Li3V2(PO4)3@C core–shell nanocomposite as a superior cathode material for lithium-ion batteries

Li3V2(PO4)3@C core-shell nanoparticles with typical sizes of 20-40 nm were synthesized using a hydrothermal-assisted sol-gel method. Ascorbic acid and PEG-400 were adopted as carbon sources and reductants. The uniform Li3V2(PO4)3@C nanocomposite obtained was composed of a Li3V2(PO4)3 core with high-phase purity and a graphitized carbon shell, which was characterized using XRD, SEM, TEM, and Raman analysis. The nanocomposite exhibited a remarkably high rate capability and long cyclability, delivering a discharge capacity of 138 mA h g(-1) at 5 C within a voltage range of 3-4.8 V and the capacity retention was 86% after 1000 cycles. The superior electrochemical performance of Li3V2(PO4)3@C indicates that it has potential for application as a cathode material in advanced rechargeable lithium-ion batteries.