Effects of calcination temperature on organic functional groups of TiO2 and the adsorption performance of the TiO2 for methylene blue

PDMS/TiO2 and PDMS/SiO2 Nanocomposites: Mechanical Properties' Evaluation for Improved Insulating Coatings

The use of nanoparticles (NPs) as reinforcements in polymeric coatings allows for direct interaction with the polymeric chains of the matrix, resulting in a synergistic process through physical (electrostatic forces) and chemical interactions (bond formation) for the improvement of the mechanical properties with relatively low weight concentrations of the NPs. In this investigation, different nanocomposite polymers were synthesized from the crosslinking reaction of the hydroxy-terminated polydimethylsiloxane elastomer. Different concentrations (0, 2, 4, 8, and 10 wt%) of TiO₂ and SiO₂ nanoparticles synthesized by the sol-gel method were added as reinforcing structures. The crystalline and morphological properties of the nanoparticles were determined through X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The molecular structure of coatings was through infrared spectroscopy (IR). The crosslinking, efficiency, hydrophobicity, and adhesion degree of the study groups were evaluated with gravimetric crosslinking tests, contact angle, and adhesion tests. It was observed that the crosslinking efficiency and surface adhesion properties of the different nanocomposites obtained were maintained. A slight increase in the contact angle was observed for the nanocomposites with 8 wt% compared to the polymer without reinforcements. The mechanical tests of indentation hardness and tensile strength following the ASTM E-384 and ISO 527 standards, respectively, were performed. As the nanoparticle concentration increased, a maximum increase of 157% in Vickers hardness, 71.4% in elastic modulus, and 80% in tensile strength was observed. However, the maximum elongation remained between 60 and 75%, ensuring that the composites did not become brittle.

Nanolayer-Constructed TiO(OH)2 Microstructures for the Efficiently Selective Removal of Cationic Dyes via an Electrostatic Interaction and Adsorption Mechanism

Efficient removal of organic dyes from contaminated water has become a great challenge and urgent work due to increasingly serious environmental problems. Here, we have for the first time prepared nanolayer-constructed TiO(OH)₂ microstructures which can present negative charge by deprotonation of the hydroxyl group to efficiently and selectively remove cationic dyes from aqueous solution through electrostatic interaction and an attraction mechanism. The nanolayer-constructed TiO(OH)₂ microstructures achieve a high adsorption capacity of 257 mg g^-1 for methylene blue (MB). The adsorption kinetics, thermodynamics, and isotherms of MB over the TiO(OH)₂ microstructures have been studied systemically. The experimental measurements and corresponding analyses demonstrate that the adsorption process of MB on TiO(OH)₂ microstructures follows a kinetic model of pseudo-second-order adsorption, agrees well with the Langmuir isotherm mode, and is a spontaneous and exothermic physisorption. Fourier transform infrared (FT-IR) spectra confirm that the prepared TiO(OH)₂ microstructures possess hydroxyl group which can deprotonate to present negative charge in solution. Further experimental studies evidently demonstrate that the TiO(OH)₂ microstructures also can remove other cationic dyes with positive charge such as basic yellow 1, basic green 4, and crystal violet but cannot adsorb anionic dye of methyl orange (MO) with negative charge in aqueous solution. The measurements for FT-IR spectra and the adsorption of cationic and anionic dyes evidently reveal that the adsorption of cationic dyes over the TiO(OH)₂ microstructures is achieved by the electrostatic interaction and attraction between TiO(OH)₂ and the dye. This work opens a strategy for the design of new absorbents to efficiently remove organic dyes from aqueous solution through an electrostatic attraction-driven adsorption process.

Annealing temperature variation and its influence on the self-cleaning properties of TiO2 thin films

Titanium dioxide (TiO2) is an important material in science and engineering because of its basic and synthetic properties. Nevertheless, there is a dearth of reports in the open literature focusing on its ability to self-clean under temperature changes. In this study, we used the spin coating technique to produce TiO2 thin films to evaluate its self-cleaning ability after annealing at different temperatures. The TiO2 sol was obtained through an endothermal sol-gel process, and the gel was coated on a glass substrate using a spin coater. The deposited films were then annealed at 400 °C, 600 °C, and 800 °C for 1 h. The influence of annealing temperature variation on the self-cleaning properties of the thin film was characterized using X-ray diffraction, scanning electron microscope; Fourier transformed infrared spectrometric analysis and UV-vis spectrophotometer. A test to ascertain self-cleaning was conducted using the degradation of methylene blue, and the different films were tested for durability. The durability test confirmed the connection between solid coating and substrate at all annealing temperatures. Thin films annealed at 600 °C revealed the best self-cleaning properties. The morphological analysis revealed snowflake shapes uniformly distributed over the substrate at 400 °C, and agglomeration improved as the annealing temperature increased. Structural analysis showed an increase in crystallinity with an increase in annealing temperature for both rutile and anatase phases. At three different temperatures, the chemical bond and the absorption band pattern followed the same path, although the peak intensity declined with temperature rise. Finally, the optical bandgap of the thin coated TiO2 declined from 3.39 eV to 3.20 eV as the binding temperature increased from 400 to 800 °C.

Immobilization of Ochrobactrum sp. on Biochar/Clay Composite Particle: Optimization of Preparation and Performance for Nitrogen Removal

The objective of this study was to prepare biochar/clay composite particle (BCCP) as carrier to immobilize Ochrobactrum sp. to degrade ammonia nitrogen (NH4 +-N), and the effects of calcined program and immobilizing material were investigated. Results reflected that the parameters were as follows: calcined temperature 400°C, heating rate 20°C min-1, and holding time 2 h, and the adsorption capacity could reach 0.492 mg g-1. Sodium alginate/polyvinyl alcohol, as embedding material, jointed with NH4 +-N adsorption process and then degraded by Ochrobactrum sp. with 79.39% degradation efficiency at 168 h. Immobilizing Ochrobactrum sp. could protect strain from high salt concentration to achieve the exceeding degradation efficiency than free bacteria, but could not block the impact of low temperature.

Insight into the ion exchange in the adsorptive removal of fluoride by doped polypyrrole from water

In this study, the polypyrrole (PPy) samples doped with Cl^- (PPy-Cl), SO₄^2- (PPy-SO4) and SO₄^2-+Cl^- (PPy-SO4+Cl) were synthesized by chemical polymerization for the adsorptive removal of fluoride ion from water. The structure and morphology of the as-prepared PPy samples were characterized by FT-IR, BET, SEM, XPS, and zeta potential. The adsorption experiments revealed that the PPy-Cl exhibited faster kinetics and higher adsorption capacity (13.98 mg/g), more than 4 times that of PPy-SO4 (3.08 mg/g) and PPy-SO4+Cl (3.17 mg/g). The kinetics of the adsorption followed the pseudo-second-order model and the adsorption isotherm data fitted well to the Langmuir model. FT-IR, EDX, and XPS tests for PPy samples before and after fluoride adsorption demonstrated that anion exchange between F^- and Cl^- or SO4^2- was the prior mechanism for fluoride ion removal from water. Cl^- was more favorable than SO₄^2- in the ion exchange with F^-. Meanwhile, the Cl^- or SO₄^2- exchanged with F^- was mainly bound to the active nitrogen that accounts for 6% of the total nitrogen in PPy molecular matrix. Further study of zeta potential and pH influence experiment demonstrated the electrostatic interaction is auxiliary interaction for the fluoride removal by doped PPy samples.