Conventional Hydrothermal Synthesis Research Articles

Atom-Economic Synthesis of Zeolites.

Zeolites are typically synthesized in the presence of strong alkaline or fluoride species, which is not atom-economic for zeolite synthesis due to the high solubility of strong alkaline and fluoride species to silica. One of the solutions for this issue is to reduce solubility of silica in the zeolite synthesis, but it is challenging. Herein, we show that nucleation and growth of zeolites can occur under near neutral conditions, giving an atom-economical synthesis of zeolites with almost full silica utilization due to very low silica solubility. Compared to conventional hydrothermal synthesis, this work both enhances the zeolite yield and reduces waste emissions, even water zero emission. Particularly, structural defects (terminal silanols) in zeolites are obviously lowered, thus giving high thermal and hydrothermal stabilities and good performance in the Beckmann rearrangement.

Effect of microwave irradiation on the synthesis of zeolite with ferrierite structure: Study of acid and catalytic properties

Ferrierite zeolite (FER) was synthesized under microwave conditions while varying the microwave exposure time from 6 to 12 h. For comparison, commercial FER and a FER zeolite synthesized by the conventional hydrothermal synthesis (72 h) were studied. The structure, texture, and acidic properties of the samples were investigated by XRD, low-temperature N2 adsorption, ICP-AES, SEM, and DRIFT spectroscopy using adsorption of CO, CD3CN and pyridine as probe molecules. The catalytic characteristics of the obtained zeolites were studied in the cyclocondensation reaction of 1,2-phenylenediamine and acetone to produce 1,5-benzodiazepine. The activity of the zeolites in this reaction was found to increase with increasing microwave exposure time. The FER-MW sample synthesized in 12 h showed the best results.

Conventional Hydrothermal Synthesis of MFI Zeolite in Methanol Solution.

The synthesis of zeolites through more efficient, environmentally friendly, and cost-effective methods was deemed significant in both industrial applications and academic fields. Conventional hydrothermal synthesis strategies have encountered difficulties in producing pure silica MFI zeolite (silicalite-1) under amine-free conditions. This was primarily attributed to the competitive growth of quartz, keatite, or magadiite during the crystallization process. In this work, it was found that the lack of nucleation ability was an important reason for the poor crystallization stability of the methanol solution. Well-crystallized silicalite-1 zeolites with uniform particle sizes were achieved through the cooperative guidance of methanol and seed crystals. Large-scale experiments with silicalite-1 zeolite demonstrated good reproducibility. Combined with the TG-IR and N2 adsorption-desorption results, it was observed that, when an extremely small amount of seed (0.97 wt %) was introduced, methanol could play a role as a crystallization promoter in the hydrothermal synthesis system. Furthermore, a lower alkaline-to-silica ratio and water-to-silica ratio were conducive to the progression of the crystallization process. In summary, this work presented a hydrothermal synthesis strategy for the synthesis of silicalite-1 zeolite in a methanol solution without the need for a large amount of seeds and provided an effective pathway for the low-cost, large-scale production of silicalite-1 zeolite.

Synthesis and Photoreforming Reaction of CdS Prepared from MOF Precursor

AbstractThe photoreforming reaction, which can produce hydrogen simultaneously with the decomposition of organic waste, is a promising method for resolving longstanding global issues such as the depletion of energy resources and climate change. However, ZnS photocatalysts, one of the most optimal catalysts for such reactions, has an inadequate visible‐light response; thus, the extensibility of the reaction is limited. In this study, CdS photocatalysts are prepared from metal–organic framework (MOF) precursors, that is, Cd‐MOFs. The prepared CdS exhibits high hydrogen production activity in the photoreforming of lignocellulosic biomass under quasi‐sunlight conditions. This activity is approximately 13.4 times that of the CdS prepared via the conventional hydrothermal method. Further, CdS can utilize light energy in the visible region of sunlight, providing a high quantum yield and demonstrating the potential for the extensibility of the reaction. The results of this study will facilitate the fabrication of novel materials for sustainable and efficient hydrogen production.

Application of NiFe2O4 nanoparticles towards the detection of ovarian cancer marker

In this work, we explored the potential application of NiFe2O4 magnetic nanoparticles in sensing platforms due to their cost-effectiveness and good magnetic properties. The spinel-type metal oxide was prepared using the conventional hydrothermal synthesis method. The structural, morphological, and magnetic properties of the as-synthesized NiFe2O4 nanoparticles were discussed. The nanoparticles were functionalized with cystamine, glutaraldehyde, and PVDF and then modified with the CA 125 antibody to obtain the immunosensor. FTIR and electrochemical analyses reveal immobilization of the antibody on the surface of the NiFe2O4 magnetic nanoparticles. The immunosensor developed in this work was made on a printed circuit board, allowing it to be used as a point-of-care device. The immunosensor showed excellent stability, reproducibility, specificity, and selectivity. Our findings are of great significance for developing novel, high-performance point-of-care electrochemical biosensors to be applied in detecting the CA 125 antigen, a widely used biomarker for the prognosis of ovarian cancer.

Comparison of conventional hydrothermal and microwave‐assisted synthesized g‐C3N4/MoS2 nanocomposite coated steel substrate by tribological measurement

AbstractMolybdenum disulfide is an effective solid lubricant, but it suffers from oxidation and moisture absorption issues, resulting in insufficient wear resistance and a shortened lifespan. This study introduces an innovative approach, integrating graphitic carbon nitride with molybdenum disulfide via advanced microwave‐assisted synthesis, offering precise control over synthesis parameters. The research assesses the tribological performance, comparing it with conventional hydrothermal synthesis. The study extensively investigates the morphology, microstructure, and tribology of a g‐C3N4/MoS2 nanocomposite created through novel microwave (g‐C3N4/MoS2‐MW) and hydrothermal techniques (g‐C3N4/MoS2‐HT). MoS2 exhibits a flower‐like structure, while graphitic carbon nitride has a layered structure, as confirmed by elemental analysis via energy‐dispersive X‐ray spectroscopy. X‐ray diffraction identifies g‐C3N4 peaks at 13.0° (100) and 27.5° (002) and hexagonal MoS2 peaks at 14° (002), 32.7° (100), 35.8° (102), and 58.3° (110). The Fourier‐transform infrared spectrum reveals peaks at 1237.4 and 808 cm−1 (aromatic and triazine ring breathing modes in g‐C3N4), 1407.1 and 1638.9 cm−1 (C=N and C−C heterocyclic structures), and 3432 cm−1 (vibrations due to −NH and −OH). The coefficients of friction for microwave‐assisted and traditional hydrothermal synthesized nanocomposites are 0.22 and 0.34, respectively. The wear depths are 98 microns and 141 microns, with a wear scar diameter of 2.87 mm for g‐C3N4/MoS2‐MW and 3.45 mm for g‐C3N4/MoS2‐HT, indicating superior lubrication with the microwave‐assisted coating.

Nano-ZnS photocatalytically active both under UV and solar radiation: A comparison of conventional and microwave-assisted hydrothermal syntheses with various reaction conditions

Influence of reaction conditions on properties of nano-ZnS was investigated. The nano-ZnS was synthesized from ZnCl2 and Na2S via conventional hydrothermal (H) and microwave-assisted hydrothermal (M) method with reaction times 90, 150, 210 min and 10, 20, 30 min, respectively. For all reaction times, three nZn:nS molar ratios (1:1; 1.5:1; 2:1) were tested. Samples were characterized by XRPD, FTIR, Raman microspectroscopy, UV–VIS and SEM. Photocatalytic activity (PA) was determined on Acid orange 7 under UV radiation (λ = 365 nm), and for selected samples also under the sunlight. After 360 min of UV radiation, PA 96% (H; 210 min; 1:1, 1.5:1 or 2:1) and 92% (M; 30 min; 1.5:1 or 2:1) was reached. Under the sunlight, PA 96% (H; 210 min; 2:1) and 92% (M; 20 min; 2:1) was achieved after 120 and 540 min, respectively. M-synthesized nano-ZnS is promising for outdoor applications not requiring a fast PA effect.

Comparative microwave- and conventional oven-assisted hydrothermal syntheses of BaTiO3 nanoparticles for improved electroceramics

Barium titanate (BT) nanoparticles were prepared using both microwave- and conventional oven-assisted hydrothermal syntheses with varying reaction times (1 h, 3 h, and 6 h). In the case of the conventional oven-assisted hydrothermal syntheses, 16 h, 24 h, 48 h and 72 h reaction times were also studied. Structural and morphological evolution of BT particles were investigated. Microwave-assisted hydrothermal synthesis allowed for the rapid formation of nearly pure barium titanate (BT) phase in just 1 h at 200 °C. On the other hand, using a conventional oven as the heat source required at least 6 h of synthesis to achieve a similar material. When the different BT powders were pelletized and sintered at 1300 °C, ceramics with over 95 % density were obtained. The room-temperature (RT) dielectric permittivity exceeded 1750 for BT particles prepared over 6 h using both heating methods. However, a significant distinction emerged when comparing the piezoelectric coefficient (d33) values. The BT pellet obtained through the sintering of BT synthesized in the conventional oven for 6 h exhibited a notably higher d33 value, approximately 171 pC/N, as opposed to the 146 pC/N value observed in BT ceramics resulting from the microwave synthesized powders. Among the ceramic BT variations, the one derived from the best-crystallized tetragonal BT particles (CON_72h) displayed the lowest d33 value at 79 pC/N. These findings underscore the immense potential of microwave- and conventional oven-assisted hydrothermal syntheses in the sustainable production of BT nanomaterials, which can then be sintered to enable the preparation of ceramics with enhanced ferroelectric and piezoelectric properties.

Hierarchical porous AlOOH hollow microspheres for efficient CO2 capture

In order to reverse the trend of increasing carbon dioxide (CO2) emissions, the development of efficient and economical CO2 trapping agents is an urgent necessity for the sustainable development of industry. In this paper, hierarchical porous hydroxyl aluminum oxide (AlOOH) hollow microspheres with controllable structure and morphology were prepared by conventional hydrothermal synthesis using malonic acid as a structure guiding agent. Then, potassium carbonate (K2CO3) based adsorbents were prepared using AlOOH hollow microspheres as supports, and their CO2 trapping performance was assessed by simulating industrial flue gas flow in a fixed bed. The results show that the loading of K2CO3, the pore structure, and the surface basic site of the adsorbent have a significant influence on the trapping performance of CO2. Among the prepared K2CO3/AlOOH adsorbents, 30 wt% K2CO3/AlOOH adsorbent has the best CO2 capture ability, which is about 2.15 times higher than that of K2CO3/C–Al2O3 adsorbent prepared from commercial alumina (C–Al2O3). There may be two explanations for this. Firstly, it may be due to the nanostructured shell and hierarchical porous structure of the adsorbent, which reduces the intra-particle diffusion resistance of CO2, and secondly, it may be due to the suitable surface basic sites of the adsorbent. In addition, the adsorbent was regenerated at 120 °C after trapping CO2, and then CO2 was captured in a cycle. It was found that the CO2 capture capability of the adsorbent did not decrease significantly after 10 cycles. In this work, an excellent technique for preparing porous honeycomb adsorbents with suitable surface basic sites has been devised, which provides a creative strategy for capturing and utilizing CO2.

Amine-free synthesis of high-silica MFI zeolite by the conventional hydrothermal route

High-silica MFI zeolite can hardly be prepared by the conventional hydrothermal synthesis route in the absence of amines, which is ascribed to the competitive growth of quartz, magadiite, or kenyaite phase. In this work, these impurity phases were excluded from the synthetic gel through a low-temperature crystallization method, while the growth of zeolite phase was promoted by seed-directed and C2H5OH filling. Consequently, well-crystallized ZSM-5 samples with controllable Si/Al ratios (46–205) and uniform particle sizes were successfully prepared, and the crystallization process was tracked by multiple characterization techniques, pointing toward a nonclassical particle attachment crystallization process. Interestingly, we found that the optimal C2H5OH/SiO2 ratio can be proportionally reduced by decreasing the H2O/SiO2 ratio in the synthetic gel. More importantly, the obtained high-silica MFI zeolite exhibited a much higher catalytic stability than the conventional sample synthesized using tetrapropylammonium as the template during the methanol-to-propylene and n-butene cracking reactions, which may be attributed to its fewer defect sites determined by 1H magic angle spinning nuclear magnetic resonance techniques. Overall, this work provides an efficient route for the large-scale production of high-silica ZSM-5 samples.

CO2, CH4, and H2 Adsorption Performance of the Metal–Organic Framework HKUST-1 by Modified Synthesis Strategies

High-pressure adsorption of CO2, H2, and CH4 has several applications, including CO2 capture, methane, and hydrogen storage. The performance ultimately depends on the adsorbent design. Herein, we report a comparative assessment of a Cu-metal–organic framework (MOF) (HKUST-1) by conventional hydrothermal synthesis and its modified analogues, HKUST-N with NH4OH and HKUST-Ca with Ca(NO3)2, for CO2, CH4, and H2 adsorption. The materials showed high CO2 (12 mol/Kg), CH4 (2.5–4 mol/Kg), and H2 (0.4–0.8 mol/Kg) capacities at 50 bar. Owing to different synthesis strategies, the differences in surface area, pore size distribution, morphology, and the presence of calcium species in HKUST-Ca considerably impacted CH4 and H2 adsorption, leading to considerable differences in selectivities for various gas mixtures. This work establishes a clear correlation of subtle modifications in synthesis strategies of the MOF HKUST-1 on its morphological characteristics and CO2, CH4, and H2 adsorption performance.

Synthesis and thermal stability of SOD-type SAPO-20 via interzeolite conversion of FAU-type SAPO-37 using tetramethylammonium hydroxide and piperidine

Interzeolite conversion (IZC) of zeolites has attracted significant attention; however, research on silicoaluminophosphate zeolite system is still in its early stages. Herein, an IZC of an FAU-type silicoaluminophosphate zeolite (SAPO-37) is performed using tetramethylammonium hydroxide (TMAOH) and piperidine as organic additives. For comparison, conventional hydrothermal synthesis using an amorphous precursor instead of SAPO-37 is also performed. Using TMAOH, SOD-type silicoaluminophosphate zeolites (SAPO-20) are obtained from both parent SAPO-37 and the amorphous precursor. However, in the case of piperidine, SAPO zeolites with different topologies are obtained from parent SAPO-37 and the amorphous precursor; that is, SOD-type SAPO-20 is obtained from parent SAPO-37, and CHA-type silicoaluminophosphate (SAPO-34) is obtained from the amorphous precursor. Piperidine molecules, as organic additives, are observed to be occluded in the cages of the obtained SAPO-20. The characteristics and thermal stability of the as-synthesized SAPO-20 are analyzed in detail.

Application of microwave hydrothermal synthesis for the solidification of copper: Effect of heavy metal content and microwave time

The synthesis type and heavy metal content significantly affect the performance of microwave hydrothermal synthesis. This synthesis approach has lower energy consumption and shorter reaction time for consolidating the heavy metals in the tobermorite lattice. The goal of this study was to investigate the influence of microwave reaction time and copper (Cu) content on the preparation of Cu-substituted tobermorite (Cu-tobermorite). Fumed silica, calcium hydroxide and copper chloride dihydrate were used to prepare the Cu-tobermorite under a liquid-solid ratio of 30 mL/g, reaction temperature of 220 ℃, and (Ca+Cu)/Si ratio of 0.83. The effect of reaction time (2 h and 4 h) and Cu content (Cu/Ca ratios are 0, 0.05, 0.1, 0.15 and 0.2) on the microstructure and morphology of the Cu-tobermorite were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry (TG), and Fourier-transform infrared (FTIR) spectroscopy. Moreover, the solidification efficiency was assessed by inductively coupled plasma-optical emission spectrometry (ICP-OES). The results showed that the main products of microwave synthesis were Cu-tobermorite and tobermorite, while the conventional hydrothermal synthesis products were Cu-tobermorite and gyrolite. Prolonging the elongation of the reaction time did not change the type of hydration product. Both microwave and traditional hydrothermal synthesis of tobermorite solidified Cu with a solidification rate of almost 100%. However, the microwave method provided a 1/7th shorter reaction time and less than 10% of the energy composition (< 10%

Nanocrystalline HZSM‐5prepared by supercritical hydrothermal synthesis and its catalytic esterification performances

AbstractThe nanocrystalline HZSM‐5 was synthesized by supercritical hydrothermal synthesis for the first time and investigated in catalytic esterification of pyromellitic dianhydride(PMD)and n‐butanol to tetrabutyl pyromellitate(TBPM). The HZSM‐5 prepared by conventional hydrothermal synthesis was also examined for comparison. The catalysts were studied using XRD, N2 adsorption, NH3‐TPD, Pyridine‐adsorption FT‐IR, SEM,[27] Al MAS NMRandCHNS analysis. According to the results of characterization, the supercritical hydrothermal condition was helpful to reduce the size of crystal particles and improve the crystallinity of HZSM‐5, and shorten the crystallization time. The surface area, especially external surface area, and pore volume were increased, and the total acidity was increased. The strong acid sites were transformed into the weak acid sites, and the strength of weak and strong acid was weakened. The amount of framework tetrahedral Al species and Brönsted acid sites were increased. Therefore, the formation of coke was retarded, and thePMD conversion, the TBPM selectivity and the catalytic stability were obviously improved.

Synthesis of titanosilicate nanoparticles with high titanium content from a silsesquioxane-based precursor for a model epoxidation reaction.

In conventional hydrothermal synthesis of porous titanosilicate materials, undesired aggregation of TiO2 species during the synthesis limits the content of active four-coordinated Ti to an Si/Ti ratio of about 40. Aiming to increase the content of active four-coordinated Ti species, we report a bottom-up synthesis of titanosilicate nanoparticles using a Ti-incorporated cubic silsesquioxane cage as a precursor, which allowed incorporating a larger number of four-coordinated Ti species in the silica matrix to reach an Si/Ti ratio of 19. Even at this relatively high Ti concentration, the catalytic activity in the epoxidation of cyclohexene over the titanosilicate nanoparticles was comparable to that of a conventional reference Ti catalyst, Ti-MCM-41, with an Si/Ti ratio of 60. The activity per Ti site was not affected by the Ti content in the nanoparticles, suggesting that well dispersed and stabilized Ti species were the active sites.

Ultra-fast microwave-assisted synthesis of photoluminescent carbon dots with an ultra-high quantum yield for H2O2 detection

The conventional hydrothermal bottom-up synthesis for preparing carbon dots (CDs) usually requires stringent conditions and high energy consumption, whereas the quantum yield (QY) of CDs remains at a relatively low level. Herein, CDs exhibiting strong blue photoluminescence (PL) with an ultra-high QY (up to 94.4%) were prepared via a simple one-step microwave-assisted route using citric acid (CA) and o-phenylenediamine (o-PD) as precursors. The operating conditions, including reaction time, solvent species, amount of solvent, and precursor molar ratio, were optimized. The CDs synthesized within 3.5 min of microwave heating in ethylene glycol (EG) at a CA-to-PD molar ratio of 5:1 exhibited the highest QY (94.4%). A synergistic PL mechanism of the molecule state and carbon core state emissive centers was proposed according to the characterization results of CDs. Moreover, the proof-to-concept H2O2 fluorescent detection performances of the prepared CDs confirmed their great application potential as probe materials. Through directly mixing the CD products and H2O2, a strong PL response could be rapidly detected after merely 1 min, and the detection limit was calculated to be as low as 8.6 nM. Besides, the CDs exhibited high biocompatibility, making them suitable for in-vivo detection of H2O2. Therefore, this work provides a novel and efficient approach for synthesis of ultra-high QY CDs that can be directly applied in biological detection.

Sustainable synthesis of AEI/CHA intergrowth zeolites for methanol-to-olefins conversion

The conventional hydrothermal synthesis of zeolites is inevitably accompanied by the production of mother liquors containing plentiful unreacted raw materials and organic templates. The direct emission or improper use of these mother liquors will cause not only the environmental contamination but also the waste of resources. Here we report a promising synthetic strategy for the effective recycle of mother liquors produced from the industrial production of SAPO-34 zeolites. Mother liquors with the addition of extra Si, P and Al were spray-dried and subsequently converted to the crystal seeds by vapor-phase-transport (VPT) method. Zeolite products with improved porosity and altered acidity were eventually acquired by VPT-Seeds-assisted hydrothermal crystallization, in which the topologic structures (e.g., CHA, AEI or AEI/CHA intergrowth) of zeolites depended significantly on the crystalline phase of VPT-Seeds. We demonstrated further via FT-IR and kinetics study that VPT-Seeds accelerated the crystallization of zeolites dramatically without the severe dissolution during the whole stage of synthesis. The as-synthesized AEI/CHA intergrowth zeolites showed the enhanced catalytic lifetime (increased at least by 27.6%) and higher selectivity in (C2H4+C3H6) (increased by 2.5%) during methanol-to-olefins (MTO) reactions than the pure CHA zeolites synthesized by the conventional hydrothermal method. Zeolites synthesized using the secondary recycled mother liquors in the same way also showed the comparable catalytic performances in MTO process, again verifying the feasibility of our methods to recycle mother liquors. The sustainable synthesis route developed in this work should be applicable to the industrial production of a wide variety of zeolites.

Electronic structures and thermoelectric properties of (Ag, Te), (Sn, Te) and (Sb, Te) dually doped PbSe on cationic and anionic sites

PbSe has attracted considerable attentions because it is a promising alternative of PbTe. In the present work, dual substitution, both cation and anion by (Ag, Te), (Sn, Te), and (Sb, Te) three different dopants, has been attempted to enhance figure of merit (ZT) of PbSe. The results indicate that (Ag,Te) and (Sb,Te) dual doping introduces additional bands near the Fermi levels, anticipated to improve the thermoelectric properties. The dual-doped PbSe samples have been fabricated by a simple conventional hydrothermal synthesis method combined with a hot-pressing sintering. (Ag, Te) co-doping PbSe shows the best thermoelectric performance, and its ZT value reaches 0.78 at 550 K, which is 63% higher than that of PbSe matrix.

Synthesis of thin ZSM-5 zeolite membranes in a self-terminating mother liquor

Low-cost synthesis of thin zeolite membranes is extremely desirable, yet challenging. In this study, we realized template-free synthesis of ultrathin ZSM-5 membranes by conventional hydrothermal synthesis on regular ceramic support. The key is to choose a self-terminating mother liquor with high Si/Al ratio. The crystallization process (formation of ZSM-5 zeolite crystals and membrane) in this Al-deficient mother liquor is an Al-driven process. The crystallization led to fast depletion of Al in the mother liquor which triggered the termination of crystallization process in this template-free mother liquor. Therefore, the thickness of ZSM-5 membrane can be controlled easily by adjusting the ratio of mother liquor/membrane area, which is much simpler than membrane synthesis in conventional mother liquor. The obtained ultrathin MFI membranes exhibited outstanding separation performance for butane isomers. This strategy can also be applied to the synthesis of other types high-silica zeolite membranes.

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.