Two-stage Hydrothermal Process Research Articles

Mechanism of Formation of Chabazite-K by Fusion of Fly Ash with KOH Followed by Hydrothermal Reaction and Its Cs+ Sorption Properties

Chabazite-K was synthesized from coal fly ash by a two-stage hydrothermal process. Fly ash was fused with KOH and colloidal SiO2, and the resulting material was characterized by x-ray diffraction (XRD) analysis and Raman spectroscopy. The role of KOH in the nucleation of chabazite is explained in terms of uniform incorporation of Al and Si tetrahedra in aluminosilicate rings at the fusion stage. Cocrystallization of phillipsite with chabazite led to the formation of phillipsite–chabazite combined phase along with chabazite-K. The Cs+ sorption capacity of the material was found to be 299 ± 8 mg/g with selectivity for Cs+. Under the same experimental conditions, fusion of fly ash in NaOH led to formation of sodalite, which can be explained in terms of preferential incorporation of Al tetrahedra in aluminosilicate rings at the fusion stage of synthesis.

Homogeneous Core/Shell NiMoO4@NiMoO4 and Activated Carbon for High Performance Asymmetric Supercapacitor.

Here, we report the extraordinary electrochemical energy storage capability of NiMoO4@NiMoO4 homogeneous hierarchical nanosheet-on-nanowire arrays (SOWAs), synthesized on nickel substrate by a two-stage hydrothermal process. Comparatively speaking, the SOWAs electrode displays superior electrochemical performances over the pure NiMoO4 nanowire arrays. Such improvements can be ascribed to the characteristic homogeneous hierarchical structure, which not only effectively increases the active surface areas for fast charge transfer, but also reduces the electrode resistance significantly by eliminating the potential barrier at the nanowire/nanosheet junction, an issue usually seen in other reported heterogeneous architectures. We further evaluate the performances of the SOWAs by constructing an asymmetric hybrid supercapacitor (ASC) with the SOWAs and activated carbon (AC). The optimized ASC shows excellent electrochemical performances with 47.2 Wh/kg in energy density of 1.38 kW/kg at 0–1.2 V. Moreover, the specific capacity retention can be as high as 91.4% after 4000 cycles, illustrating the remarkable cycling stability of the NiMoO4@NiMoO4//AC ASC device. Our results show that this unique NiMoO4@NiMoO4 SOWA has great prospects for future energy storage applications.

Influence of reaction conditions on the composition of liquid products from two-stage catalytic hydrothermal processing of lignin

The influence of reaction conditions on the composition of liquid products during two-stage hydrothermal conversion of alkali lignin has been investigated in a batch reactor. Reactions were carried out in the presence of formic acid (FA) and Pt/Al2O3 catalyst. The two different sets of reaction conditions involved alternative reaction times of 1h and 5h at 265°C and 350°C, respectively. These provided different contributions to reaction severity, which affected the compositions of liquid products. Yields of liquid products reached up to 40wt% (on lignin feed basis) in the presence of FA under the less severe reaction condition. With 5h reaction time at 350°C, alkylphenols, alkylguaiacols and hydrocarbons were the dominant liquid products. However, with 5h reaction time at 265°C, phenol and methanol became dominant. The two-stage hydrothermal process led to improved lignin conversion, with the potential to manipulate the liquid product range.

Binder-addition effect in TiO2 nanoparticles on dye-sensitized solar cells evidenced by spectroscopic techniques

This study presents a two-stage hydrothermal process to synthesize anatase TiO2 nanoparticles. The first stage formed sodium titanate (Na2Ti9O19). Octahedral TiO6 in Na2Ti9O19 shares crystal edges similar to those of octahedral TiO6 in anatase TiO2. This study used Na2Ti9O19 as an intermediary to generate pure anatase TiO2. The second stage involves disintegrating the structure of the Na2Ti9O19 crystals through an ion exchange of Na+ in Na2Ti9O19 with H+ in HNO3, resulting in the formation of pure anatase TiO2 nanoparticles (7 to 10nm). The static (acid addition) and space repulsion (binder addition) methods (surface area with BET=81.594m2g−1) were used to hinder the coalescence of TiO2 nanoparticles. The proposed approach produces well-dispersed nanoparticles compared to the method using only static repulsion (surface area with BET=68.071m2g−1). These two TiO2 materials were used to prepare photoelectrodes with a film thickness of approximately 6μm in dye-sensitized solar cells (DSSCs), which achieved device efficiencies of 6.23% and 4.66%, respectively.

Evaluation of a two-stage hydrothermal process for enhancing acetic acid production using municipal biosolids

A two-stage hydrothermal process aimed at improving acetic acid production using municipal biosolids was evaluated against thermal hydrolysis and conventional wet oxidation process in a 600 ml Parr batch reactor. Thermal hydrolysis was conducted at 140 °C, wet oxidation at 220 °C and the two-stage process, which acted as a series combination of thermal hydrolysis and wet oxidation, at 220 °C. Initial pressure of 1 MPa was maintained in all the three processes. The results indicated that the highest acetic acid production of up to 58 mg/g dry solids feed was achieved in the wet oxidation process followed by the two-stage process with 36 mg/g dry solids feed and 1.8 mg/g dry solids feed for thermal hydrolysis. The acetic acid yield obtained by the thermal processes increased from 0.4% in the thermal hydrolysis process to 12% during the single stage wet oxidation, with the two-stage process achieving 8%. The purity of the acetic acid improved from 1% in thermal hydrolysis to 38% in the wet oxidation process. The two-stage process achieved acetic acid purity of 25%. This work demonstrated no enhancement of acetic acid production by the two-stage concept compared with the single stage wet oxidation process. This is in contrast to similar work by other researchers, investigated on carbohydrate biomass and vegetable wastes using hydrogen peroxide as the oxidant. However, the data obtained revealed that substrate specificity, reaction severity or oxidant type is clearly important in promoting reaction mechanisms which support enhanced acetic acid production using municipal biosolids.

Addition of Surfactant Tween 80 in Coating Solutions for Making Mesoporous Pure Silica Zeolite MFI Low-k Films

A mesoporous pure-silica-zeolite (PSZ) MFI low dielectric (k) film with smooth surface morphology was successfully synthesized using a centrifuged coating solution composed of a solution with PSZ MFI nanoparticles and surfactant Tween 80. The zeolite nanoparticles were prepared using TEOS as the silica source through a two-stage hydrothermal process. Both the k value and the mechanical strength of the film were strongly affected by the weight ratio of Tween 80 to TEOS and by the hydrothermal period of the second stage. When a higher weight ratio of Tween 80 to TEOS was employed, a lower k value and mechanical strength were obtained. A film coated from a solution prepared under optimal experimental conditions possessed an ultra low k value of 1.83, a hardness of 1.39 GPa, an elastic module of 12.3 GPa, and a leakage current of 1.35 × 10−7 A/cm2, all of which met the needs of the integrated circuits (IC) industry. Moreover, the occurrence of electrical degradation of electronic devices could be minimized because only few pores in the film exceeded 5 nm.

D-Glucose-Derived Polymer Intermediates as Templates for the Synthesis of Ultrastable and Redispersible Gold Colloids

A two-stage hydrothermal process was developed for the synthesis of highly dispersed Au colloids. In the first stage, a novel glucose-derived polymer template was prepared by the hydrothermal treatment of glucose at 160 degrees C. This template was then further used in the next step to synthesize highly dispersed gold (Au) colloids by hydrothermal treatment with HAuCl(4.) The templates treated at 160 degrees C with changing reaction times had different templating effects toward Au species. The 3-h treated template was able tightly adhere to the Au colloids. As a result, an unusual stability was observed for the prepared Au particles that could be repeatedly precipitated and redispersed with the template in H(2)O and were also stable against heating (below 160 degrees C) and aging. Meanwhile, the 5-h and 7-h treated templates had much poorer templating effects to Au species, leading to severe aggregation of the Au colloids immobilized on them. The various templating effects were correlated to the different structural features of the templates. Compared to the 5- or 7-h treated templates that were deeply carbonized, the 3-h treated template was only slightly carbonized, thus possessing a lot of functional and hydrophilic O-containing groups that could bind to Au species. These differences in templating ability were also observed in the Au samples prepared by the sonication-assisted method. The highly dispersed Au colloids immobilized on the 3-h treated template were tested for CO oxidation, and a good catalytic activity and stability for CO oxidation was observed.

Rare earth element and yttrium analyses of sulfides from the Dachang Sn-polymetallic ore field, Guangxi Province, China: Implication for ore genesis

The Dachang Sn-polymetallic ore field (Guangxi, China) is one of the largest tin deposits in the world with a tin reserve of above 106 tons. Several types of orebody occur in this giant ore field, including mainly the Lamo Cu-Zn skarns at the contact of Devonian limestone and the Cretaceous Longxianggai granite, the Changpo-Tongkeng stratiform Sn-Pb-Zn ores in Devonian siliceous rocks, and the Gaofeng massive sulfide ore in Devonian reef limestone. Rare-earth element (REE) and yttrium concentrations in sulfides from different orebody types have been determined by ICP-MS. Sulfides from the Lamo skarn-type Cu-Zn mines display significant LREE-enriched pattern with large negative Eu anomalies. This is in agreement with the mineralizing fluid being of magmatic hydrothermal origin. However, sulfides from massive and stratiform orebodies show significantly different REE distributions. The Gaofeng massive sulfides have very low total REE concentrations and REE patterns range from (1) being strongly enriched in light REE with positive Eu anomalies, to (2) relatively flat patterns with strongly negative Ce and positive Eu anomalies. Pattern 1 resembles REE distributions in modern submarine hydrothermal fluids. Pattern 2 exhibits both seawater and hydrothermal vent-fluid characteristics. Sulfides from stratiform orebodies at Changpo-Tongkeng are LREE-enriched with small or no negative Eu anomalies. REE patterns of sulfides from different stratiform orebodies are slightly different, but they are similar to those of each host rock. It indicates that the sulfides and host rocks are synsedimentary and that their REE patterns are controlled by the local physical-chemical environments. Y/Ho atomic weight ratios of granite, skarn and sulfides at Lamo vary from 26.3 to 33.7, close to the chondritic Y/Ho ratio. But sulfides from massive and stratiform ores have more variable Y/Ho ratios (28.4-134) that are similar to those of many modern hydrothermal fluids. Hence, the ore-forming fluids responsible for mineralization of the stratiform and massive ores at Dachang were likely to be of exhalative hydrothermal origin. It is suggested that the Dachang deposits are formed through a two-stage hydrothermal process, i.e., the Devonian submarine hydrothermal ore-forming stage and the Yanshanian magmatic-hydrothermal ore-forming stage.