pH Value Of Synthesis Solution Research Articles

Applying Surface Charge Attraction to Synthesizing TiO2/Ag Composition for VOCs Photodegradation

This study utilized a unique method to prepare TiO2/Ag composites by operating the pH value of synthesis solution, which causes the opposite charges on the surface between TiO2 and Ag to enhance the combination affinity of TiO2 and Ag due to electron attraction. The results showed that the TiO2/Ag prepared in solution at pH 5.8 was characterized as high TiO2 dispersibility and the optimal combination between TiO2/Ag, due to the opposite surface charges and the greatest difference in zeta potentials between TiO2 and Ag. The prepared TiO2/Ag was utilized to process acetone photodegradation, and the results illustrated that TiO2/Ag prepared in solution at pH 5.8 showed the best performance in photodegrading acetone. With increasing TiO2 coated on Ag in TiO2/Ag, the photodegradation efficiency of acetone was enhanced. In terms of the average efficiency via TiO2 coating amount, 10 wt% was the most optimal efficient proportion of TiO2/Ag for the photodegradation of acetone.

Synthesis of CeVO4 Crystals with Different Sizes and Shapes

Tetragonal CeVO4 was prepared through hydrothermal treatment and sonication method with the same precursor in the absence of any catalysts or templates, and the products were characterized by XRD, TEM and Raman. It is found that microrods, nanoparticles, nanorods and nanoplates have been obtained. The bigger nanorods produced through hydrothermal treatment have average diameters of 15–25 nm and lengths of 20–60 nm. The smaller nanorods prepared through ultrasound treatment have average diameters of 6–12 nm and lengths of 10–18 nm. Uniform nanoplates have been produced. The nanoplates produced through hydrothermal method are composed of CeVO4 and CeO2. The mechanism of shape changing has been discussed. And the existing vanadium which is sensitive to the pH value of synthesis solution may be a key factor for the resulted sizes and shapes of the obtained nanocrystals. The samples prepared through hydrothermal treatment and sonication method were used as the catalysts for the combustion of trichloroethylene to test their catalytic activity.

Fabrication of mesh-like bismuth oxide single crystalline nanoflakes and their visible light photocatalytic activity

Mesh-like bismuth oxide single crystalline nanoflakes were synthesized via a bismuth oxalate precursor way. During the synthesis procedure bismuth oxalate precipitate was hydrothermally treated, and variation of the pH value of synthesis solution as well as the addition of l-lysine could effectively tune the crystal phase and morphology of the bismuth oxalate precursor. Depending on the crystalline phase of the precursors and the calcination temperature, monoclinic α-Bi 2O 3 and tetragonal β-Bi 2O 3 were selectively obtained. Optical properties of the Bi 2O 3 materials were investigated by UV–vis absorption and the results proved that bismuth oxides were visible light responsive. Photodegradation of rhodamine B was used as a model reaction to test the photocatalytic activity of the Bi 2O 3 samples. The photocatalytic activity of bismuth oxides was related to its crystalline phase and morphology.

Nonionic surfactant-assisted hydrothermal synthesis of YVO 4:Eu 3+ powders in a wide pH range and their luminescent properties

YVO 4:Eu 3+ powders with different morphologies were fabricated by a simple hydrothermal method at 180 °C for 24 h in a wide pH range with the assistance of polyvinylpyrrolidone (PVP) as a nonionic surfactant. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The obtained results showed that the pH value of synthesis solution played a key role in the formation of final products with different morphologies, such as, microspheres, irregular microspheres with grain-like nanoparticles, stone-like structures with regular short nanorods, and smooth rhombohedrons. The PL measurements revealed that the emission intensity of the samples was first decreased, and then increased with increasing the pH value due mainly to the increase in crystallinity and decrease in surface defects.

Preparation of binderless honeycomb silicalite-1 monolith by using bundled palm fibers as template

Honeycomb silicalite-1 monolith (HSM) was prepared by first binding 27 palm fibers with two Teflon o-rings to form bundled palm fibers, followed by hydrothermal synthesis in a silicalite-1 synthesis solution and removal of the template by calcination. The effect of pH value of the synthesis solution on dissolution of palm fibers was studied. The results indicated that only the centers of palm fibers were dissolved when the pH value of synthesis solution was less than 11, thus keeping original shape of palm fibers. The influence of synthesis cycles was also examined and it was found that two cycles of syntheses were necessary to maintain concrete structure of the resulting HSM. The prepared HSM, with a diameter of 2.3 mm and a length of 15 mm, contained 27 cells, each with a diameter and wall thickness of 350–400 and 25–35 μm, respectively. The specific surface area of the HSM was about 396 m2 g−1. After ultrasonic treatment in water with an ultrasonic frequency of 40 kHz for 60 min, the HSM had a weight loss of only about 5.5%, indicating the strong mechanic strength.

Mineralogical characteristics of Ettringites synthesized from solutions and suspensions

Due to the wide technical importance of Ettringite (3CaO·Al 2O 3·3CaSO 4·32H 2O) in hydrated cement based systems, four different synthesis methods were applied to get a better overview on how and under what favoring conditions Ettringite can be formed. In the first step different precipitation methods resulting in Ettringite were established. For all methods Al 3+ was supplied by aqueous CO 2-free solution of Al 2(SO 4) 3·18H 2O. As a source of CaO-supply a clear solution and otherwise a Ca(OH) 2-suspension was utilized. Four synthesis routes with and without sucrose were employed. Variation of reaction parameter like temperature, time of reaction, pH-value of synthesis solution and influence of additional Gypsum were investigated. The qualitative phase analysis was performed by X-ray diffraction method (XRD). Morphological aspects of some synthesis products were studied by scanning electron microscopy (SEM). Finally lattice and structural parameter of the Ettringites were determined by refinement of XRD-pattern using the Rietveld-Method.

The structure and electrochemical performance of spherical Al-substituted α-Ni(OH) 2 for alkaline rechargeable batteries

Spherical Al-substituted α-Ni(OH) 2 for alkaline rechargeable batteries was prepared by a complexation-coprecipitation method. The morphology and structure of the samples were characterized by SEM, XRD and Raman spectroscopy. Their electrochemical performance including charge–discharge behavior, diffusion coefficient of proton ( D H + ), stability in strong alkaline solution and cycle life was also investigated. The results showed that the Al-substituted α-Ni(OH) 2 prepared by this method manifests perfect spherical shape and the specific discharge capacity of the sample with 18.3 mol% Al reaches 477 mAh g −1 when the pH value of synthesis solution is 11.75. The interlayer distance, the oxygen evolution potential and the half discharge potential of the sample increase greatly with the increase of Al content. Compared with β-Ni(OH) 2 without Al substitution, there are large amounts of proton defects in Al-substituted α-Ni(OH) 2 which increases the diffusion coefficient of proton ( D H + ) measured by current pulse relaxation (CPR). The Al-substituted α-Ni(OH) 2 sample shows an excellent structural stability during ageing treatment in 6 M KOH solution and the loss of Al can be neglected.