Stage Of Hydrothermal Treatment Research Articles

Transformation of polyvinyl chloride (PVC) into a versatile and efficient adsorbent of Cu(II) cations and Cr(VI) anions through hydrothermal treatment and sulfonation

The reuse of waste polyvinyl chloride (PVC) has drawn much attention as it can reduce plastic waste and associated pollution, and provide valuable raw materials and products. In this study, sulfonated PVC-derived hydrochar (HS-PVC) was synthesized by two-stage hydrothermal treatment (HT) and sulfonation, and shown to be a versatile adsorbent. The removal of Cu(II) cations and Cr(VI) anions using HS-PVC reached 81.2 ± 1.6% and 60.3 ± 3.8%, respectively. The first stage of HT was crucial for the dichlorination of PVC and the formation of an aromatic structure. This stage guaranteed the introduction of -SO3H onto PVC-derived hydrochar through subsequent sulfonation. HT intensities (i.e., temperature and time) and sulfonation intensity strongly determined the adsorption capacity of HS-PVC. Competitive adsorption between Cu(II) and Cr(VI) onto HS-PVC was demonstrated by binary and preloading adsorption. The proposed Cu(II) cations adsorption mechanism was electrostatic adsorption, while Cr(VI) were possibly complexed by the phenolic -OH and reduced to Cr(III) cations by CC groups in HS-PVC. In addition, HS-PVC derived from PVC waste pipes performed better than PVC powder for Cu(II) and Cr(VI) removal (＞90%). This study provides an efficient method for recycling waste PVC and production of efficient adsorbents.

Hydrothermal Growth of Nano-Hydroxyapatite Coating Formed on Fluorinated Magnesium Alloy and Its Corrosion Behaviour

In order to explore the hydrothermal growth mechanism of hydroxyapatite (HA) coating on fluorinated magnesium alloy, the changes of morphology, composition and crystal phase of the calcium phosphate coating during the hydrothermal treatment were studied. And the change of electrochemical impedance spectroscopy (EIS) of the coating specimen of different hydrothermal treatment time was discussed to further understanding the change of the coating structure. The results demonstrated that calcium phosphate could rapidly nucleate on fluorinated AZ31 magnesium alloy. The crystal phase of calcium phosphate coating was mainly octacalcium phosphate (OCP) at the early stage of hydrothermal treatment. Then the content of OCP decreased and the content of HA increased with hydrothermal time. The coating consisted of only HA after hydrothermal treatment for about 4h. The HA coating composed of rod-like crystals exhibited an obvious double layer structure. The rod-like crystals of inner layer arranged into dense bundles and the rod-like crystals of outer layer arranged into loose chrysanthemum-like clusters. Fluoride conversion layer acted as an intermediate transition layer to connect magnesium alloy and HA coating into a whole. The results of immersion test in simulated body fluid demonstrated that HA crystals dissolved slowly. No peeling occurred of HA coating during the 12 days' immersion. Pitting corrosion was still the mainly corrosion mode of magnesium alloy substrate due to the electrolyte infiltration during the immersion.

Silicon doping effect on the properties of the hydrotreating catalysts of FCC feedstock pretreatment

Influence of Si addition at the stage of boehmite preparation on properties of NiMo/Al2O3 catalysts for FCC feedstock pretreatment have been studied. The series of boehmites doped by PDMS at the stage of hydrothermal treatment was prepared. Si/Al molar ratio was 0, 0.01, 0.015 and 0.02. Boehmites were used for supports and catalysts preparation. Boehmites, supports and catalysts have been characterized by XRD, TGA, nitrogen adsorption-desorption, IR spectroscopy, UV–Vis, 29Si MAS NMR, HRTEM, EDX, XPS. Catalysts were tested in hydrotreating of FCC feedstock. It is shown that there are changes in morphology of boehmite particles and textural characteristics of aluminas. Introduction of Si to alumina induces formation of wider mesopores and blocks part of the Lewis acid sites of alumina. Testing of catalysts in hydrotreating of FCC feedstock shows that the catalyst with Si/Al ratio of 0.01 in boehmite has the best combination of hydrodesulfurization and hydrodenitrogenation activities.

A Facile One-Pot Stepwise Hydrothermal Method for the Synthesis of 3D MoS2/RGO Composites with Improved Lithium Storage Properties

Three-dimensional reduced graphene oxide (RGO) matrix decorated with nanoflowers of layered MoS2 (denoted as 3D MoS2/RGO) have been synthesized via a facile one-pot stepwise hydrothermal method. Graphene oxide (GO) is used as precursor of RGO and a 3D GO network is formed in the first-step of hydrothermal treatment. At the second stage of hydrothermal treatment, nanoflowers of layered MoS2 form and anchor on the surface of previously formed 3D RGO network. In this preparation, thiourea not only induces the formation of the 3D architecture at a relatively low temperature, but also works as sulfur precursor of MoS2. The synthesized composites have been investigated with XRD, SEM, TEM, Raman spectra, TGA, N2 sorption technique and electrochemical measurements. In comparison with normal MoS2/RGO composites, the 3D MoS2/RGO composite shows improved electrochemical performance as anode material for lithium-ion batteries. A high reversible capacity of 930[Formula: see text]mAh[Formula: see text][Formula: see text][Formula: see text]g[Formula: see text] after 130 cycles under a current density of 200[Formula: see text]mA[Formula: see text][Formula: see text][Formula: see text]g[Formula: see text] as well as good rate capability and superior cyclic stability have been observed. The superior electrochemical performance of the 3D MoS2/RGO composite as anode active material for lithium-ion battery is ascribed to its robust 3D structures, enhanced surface area and the synergistic effect between graphene matrix and the MoS2 nanoflowers subunit.

In vitro ageing and wear behaviour of ceria stabilized zirconia toughened alumina (CSZ-TA) bio-ceramic

15–25 wt% zirconia (stabilized with 14 mol% ceria) toughened alumina was synthesized by co-precipitation technique. The synthesized powders were calcined at different temperatures, compacted and conventionally sintered following two steps sintering process. Uniformly distributed submicron sized grains with Vickers' hardness value up to 1730±6HV20 were achieved after conventional sintering. In order to assess the ageing behaviour, samples were hydrothermally treated (in vitro) at 134 °C under 0.2 MPa in presence of simulated body fluid. Rietveld refinement of the X-ray diffraction patterns was carried out to estimate the phase content after calcination, sintering and after different stages of hydrothermal treatment. No significant phase change (only ∼3%) was observed even after 100 h of hydrothermal treatment. Very few bulged grains (resulted from the tetragonal to monoclinic phase transformation) on the surface and slight decrease in hardness value were observed after hydrothermal treatment. Fretting wear in dry condition was carried out taking ball on flat geometry for 105 cycles at different loads before and after hydrothermal treatment. Wear volumes were directly estimated from the surface scanning of the wear scar using profilometer. Transition of wear and its related mechanisms at different loads along with the effect of ageing on wear were discussed.

Facile synthesis of hollow zeolite microspheres through dissolution–recrystallization procedure in the presence of organosilanes

Abstract Hollow zeolite microspheres have been hydrothermally synthesized in the presence of organosilanes via a dissolution–recrystallization procedure. In the presence of organosilanes, zeolite particles with a core/shell structure formed at the first stage of hydrothermal treatment, then the core was consumed and recrystallized into zeolite framework to form the hollow structure during the second hydrothermal process. The influence of organosilanes was discussed, and a related dissolution–recrystallization mechanism was proposed. In addition, the hollow zeolite microspheres exhibited an obvious advantage in catalytic reactions compared to conventional ZSM-5 catalysts, such as in the alkylation of toluene with benzyl chloride.

The effect of iridium(III) ions on the formation of iron oxides in a highly alkaline medium

The effect of the presence of Ir 3+ ions on the formation of iron oxides in a highly alkaline precipitation system was investigated using X-ray powder diffraction (XRD), 57Fe Mössbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Monodispersed lath-like α-FeOOH (goethite) particles precipitated by hydrothermal treatment in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as reference material. The presence of Ir 3+ ions in the precipitation system strongly influenced the phase composition, magnetic, structural and morphological properties of obtained samples. The formation of α-Fe 2O 3 (hematite) along with α-FeOOH in the first stage of hydrothermal treatment and the transformation of α-FeOOH and α-Fe 2O 3 to Fe 3O 4 (magnetite) by a longer hydrothermal treatment was caused by the presence of Ir 3+ ions. Ir 3+ for Fe 3+ substitution in the structure of α-FeOOH brought about changes in unit-cell dimensions, crystallinity, particle size and shape, hyperfine magnetic field and infrared bands positions. Ir 3+ for Fe 3+ substitution in the structure of α-Fe 2O 3 led to an increase in the temperature of the Morin transition; Mössbauer spectroscopy showed the presence of α-Fe 2O 3 in the antiferromagnetically ordered state at 293 K.

Kinetics of Thermal Dissociation–Restoration Processes of J-Aggregate

We investigated the kinetics of thermally induced dissociation–restoration processes of the J-band in merocyanine (MS)–Cd arachidate mixed Langmuir–Blodgett (LB) films. The UV–visible absorbance spectrum A of the as-deposited film is associated with a prominent J-band (Band III) with its peak located at ∼590 nm besides Bands I and II centered at 500–515 and 545–555 nm, respectively. In the case of dry-heat treatments (DHTs), the Band III fraction decreases and the Band I fraction increases as the process proceeds, while the Band II fraction remains almost constant. The remaining fraction of Band III is found to obey an exponential decay law, f(tH,TH) = exp [- k(TH)tH], governed by an activation-type rate, k(TH) = k(∞)exp [- E/(RTH)] with k(∞) = 4.50 ×108 s-1 and E = 79.7 kJ/mol, where tH and TH are the heating time and temperature, respectively. The above E is 12–16 kJ/mol higher than that for the J-band dissociation process in the first stage of the hydrothermal treatment (HTT) under 100% humidity. This difference is explained as a barrier-lowering effect due to the water present in the HTT case. In the DHT-treated LB films, further application of HTT restores the J-band in a similar manner to that observed in the second stage of HTT when HTT is directly applied to the as-deposited films. The J-band restoration is described in both cases as a first-order process where [Band I] → [Band III] predominates over the reverse reaction. The k(∞) and E for the forward reaction of 5.13 ×107 s-1 and 68.5 kJ/mol, respectively, for the DHT-subjected films, are comparable to those of 4.31 ×107 s-1 and 64.8 kJ/mol in the case of second-stage HTT reported previously.

Transformation of ZrO2 crystal structure under hydrothermal conditions

The preparation of ZrO2 powders under hydrothermal conditions has been extensively studied, but the details of the transformation in crystal structure associated with hydrothermal treatment, which will be discussed in the present paper, are unclear. The present results indicate that the t-ZrO2 phase formed from the precursor in the early stages of hydrothermal treatment is converted to m-ZrO2 as hydrothermal treatment proceeds. The pure m-ZrO2 phase was formed after 18 h at 180°C. These results differ from those reported by Stefanic et al., which probably refer to an intermediate stage in the transformation during hydrothermal treatment at 95°C, reflecting the kinetics of the crystallisation process. The present results indicate that the kinetics of crystallisation is significantly delayed at this relatively low temperature when compared with the transformation at the relatively high temperature of 180°C.

水熱処理による風化花こう岩微粒物の精製

The fine particles in weathered granite were refined by hydrothermal method in order to utilize them as pottery clay.Feldspar and vermiculite included in weathered granite were altered into kaolin mineral using 0.14mol/l hydrochloric acid adding aluminum chloride under the hydrothermal condition at 200°C. However, the values of pyrometric cone number and the whiteness of the refined samples were lower than that of the common pottery clay.The concentration by HGMS (high gradient magnetic separator) using the fine particles are hydrothermally altered. The whiteness of the treated samples were improved, however, total yield of the refined products from the fine particles in weathered granite were low in the range of 27.8 to 48.7 wt%. Then two stages of hydrothermal treatment were performed. The first stage is to extract ferrous ions from the fine particles using 6 mol/l hydrochloric acid, and the second stage is that the treated fine particles is altered into kaolin mineral under the previous hydrothermal conditions. In addition to increasing the total yield of the refined products more than 60 wt%, the values of pyrometric cone number and the whiteness of the treated samples were improved similar to those of the common pottery clay.