Low Temperature Hydrothermal Synthesis Research Articles

Using solid waste to treat wastewater: Preparation of flowerlike calcium silicate hydrate from coal fly ash for cadmium removal

Efficient utilization of Coal fly ash (CFA) and ingenious treatment of cadmium (Cd (II)) in the water environment are interesting topics. In this paper, a mesoporous floral calcium silicate hydrate (MCSH) for removal of Cd (II) was prepared by low temperature hydrothermal synthesis using CFA desilication solution. Different synthesis parameters (molar ratio of Ca to Si (Ca/Si), temperature, time) of MCSH were investigated and optimized. All synthesized MCSH showed good adsorption properties for Cd (II), and MCSH synthesized at Ca/Si molar ratio of 1.0, temperature of 363 K and time of 120 min had the optimum Cd (II) adsorption capacity of 357.43 mg/g. The effects of solution pH, MCSH dosage, coexisting cations and ionic strength on the Cd (II) adsorption performance by MCSH were further considered systematically. The adsorption process was a spontaneous and endothermic process, conformed to the pseudo-second-order kinetic and Langmuir isothermal model. The main mechanism of Cd (II) removal by MCSH was the precipitation between Cd (II) and OH– released by MCSH, accompanied by ion exchange, surface complexation and electrostatic adsorption. The mesoporous flowery MCSH prepared from CFA provides an satisfactory solution for the utilization of solid waste resources and the purification of heavy metal wastewater.

Nanoengineered β-MnO2/rGO nanobead-based bioconjugate interfaces for the electrochemical detection of dopamine for the potential to manage neurological diseases and depression

In this study, we successfully developed a highly effective nanobead (nb) morphology-based β-MnO2/rGO nanocomposite via low-temperature hydrothermal synthesis.

Enhancing Photocatalytic Properties of TiO2 Photocatalyst and Heterojunctions: A Comprehensive Review of the Impact of Biphasic Systems in Aerogels and Xerogels Synthesis, Methods, and Mechanisms for Environmental Applications.

This review provides a detailed exploration of titanium dioxide (TiO2) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). The review delves into the influence of acid-base donors on gelation, dissects crucial drying techniques for TiO2 aerogel or xerogel catalysts, and meticulously examines mechanisms underlying photocatalytic activity. It highlights the role of physicochemical properties in charge diffusion, carrier recombination, and the impact of scavengers in photo-oxidation/reduction. Additionally, TiO2 doping techniques and heterostructures and their potential for enhancing efficiency are briefly discussed, all within the context of environmental applications.

Nanoscale Titanium Surface Engineering via Low-Temperature Hydrothermal Etching for Enhanced Antimicrobial Properties.

Bioinspired nanotopography artificially fabricated on titanium surfaces offers a solution for the rising issue of postoperative infections within orthopedics. On a small scale, hydrothermal etching has proven to deliver an effective antimicrobial nanospike surface. However, translation to an industrial setting is limited by the elevated synthesis temperature (150 °C) and associated equipment requirements. Here, for the first time, we fabricate surface nanostructures using comparatively milder synthesis temperatures (75 °C), which deliver physicochemical properties and antimicrobial capability comparable to the high-temperature surface. Using a KOH etchant, the simultaneous formation of titania and titanate crystals at both temperatures produces a one-dimensional nanostructure array. Analysis indicated that the formation mechanism comprises dissolution and reprecipitation processes, identifying the deposited titanates as hydrated layered tetra-titanates (K2Ti4O9·nH2O). A proposed nanospike formation mechanism was confirmed through the identification of a core and outer shell for individual nanostructures, primarily comprised of titanates and titania, respectively. Etching conditions dictated crystalline formation, favoring a thicker titanate core for nanorods under higher synthesis temperatures and etchant concentrations. A bactericidal investigation showed the efficacy against Gram-negative bacteria for a representative low-temperature nanosurface (34.4 ± 14.4%) was comparable to the higher temperature nanosurface (34.0 ± 17.0%), illustrating the potential of low-temperature hydrothermal synthesis. Our results provide valuable insight into the applicability of low-temperature etching protocols that are more favorable in large-scale manufacturing settings.

Preparation of urchin like structures of SiO2/CuO by low temperature hydrothermal synthesis as adsorbent for dyes and efficient catalyst for 4-nitrophenol

Due to the relevance of SiO2/CuO nanocomposites as catalysts, adsorbents, and magnetic materials, continuing research is being done to find more affordable ways of synthesizing them. In the present study, a short-term hydrothermal approach (90 °C for 4 hrs) has been adapted to prepare a uniform urchin-like SiO2 /CuO composite (USC). The prepared composite has been demonstrated to have adsorption as well as catalytic properties. This material therefore has a great potential for use in environmental remediation. The prepared material was characterized by using XRD, SEM, TEM, FTIR, and UV spectroscopy techniques. Surface area analysis revealed that it possesses a specific surface area of 675.5 m2/g which leads to enhanced adsorption by providing access to more active sites for the adsorption. Various anionic and cationic dyes were evaluated for the adsorption process by prepared adsorbent. We discovered that the adsorbent was incredibly effective in capturing the cationic dye (RhB) with an adsorption capacity of 69.4 mg/g; therefore, adsorption parameters such as time, concentration of dye, pH, etc. were studied for the adsorption of RhB. Whereas, 4-NP was 63% eliminated by the SiO2 /CuO by using NaBH4 as reducing agent. Further studies revealed that SiO2 /CuO was able to reproduce and reused to 5 adsorption cycles and follow monolayer adsorption. Using USC adsorbent for more versatile applications in environmental cleanup could be made possible by this work.

Highly-Controlled Soft-Templating Synthesis of Hollow ZIF-8 Nanospheres for Selective CO2 Separation and Storage.

Global warming is an ever-rising environmental concern, and carbon dioxide (CO2) is among its major causes. Different technologies, including adsorption, cryogenic separation, and sequestration, have been developed for CO2 separation and storage/utilization. Among these, carbon capture using nano-adsorbents has the advantages of excellent CO2 separation and storage performance as well as superior heat- and mass-transfer characteristics due to their large surface area and pore volume. In this work, an environmentally friendly, facile, bottom-up synthesis of ZIF-8 hollow nanospheres (with reduced chemical consumption) was developed for selective CO2 separation and storage. During this soft-templating synthesis, a combined effect of ultra-sonication and low-temperature hydrothermal synthesis showed better control over an oil-in-water microemulsion formation and the subsequent growth of large-surface-area hollow ZIF-8 nanospheres having excellent particle size distribution. Systematic studies on the synthesis parameters were also performed to achieve fine-tuning of the ZIF-8 crystallinity, hollow structures, and sphere size. The optimized hollow ZIF-8 nanosphere sample having uniform size distribution exhibited remarkable CO2 adsorption capability (∼2.24 mmol g-1 at 0 °C and 1.75 bar), a CO2/N2 separation selectivity of 12.15, a good CO2 storage capacity (1.5-1.75 wt %), and an excellent cyclic adsorption/desorption performance (up to four CO2 adsorption/desorption cycles) at 25 °C. In addition, the samples showed exceptional structural stability with only ∼15% of overall weight loss up to 600 °C under a nitrogen environment. Therefore, the hollow ZIF-8 nanospheres as well as their highly controlled soft-templating synthesis method reported in this work are useful in the course of the development of nanomaterials with optimized properties for future CO2 capture technologies.

Nb2 CTx MXene Derived Polymorphic Nb2 O5.

Previously, heat treatmentwasthe only feasible route for tuning the crystal phases of niobium pentoxide (Nb2 O5 ). With the use of Nb2 CTx MXene precursors, the first case of phase tuning of Nb2 O5 in the low-temperature hydrothermal synthesis using sulfuric acid regulating agents is presented. By varying the amount of the agent, four pure-phase Nb2 O5 crystals and mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Overall, MXene-derived B-phase Nb2 O5 is of particular interest due to its exceptionally high capacities as lithium-ion battery anodes, which are three times higher than the routine synthesized one. Oxygen vacancies induced by crystallographic shear would be responsible for the extraordinary performance. The proposed phase tuning strategy encourages the prudent synthesis of difficult-to-obtain crystal phases.

Enhanced photocatalytic activity of orientationally grown CQD/TiO2 thin film on FTO substrate

We have studied the enhanced light harvesting capacity and reduced recombination rate of TiO2 thin film by composite with Carbon Quantum Dots (CQDs). The CQD/TiO2 film was synthesized using facile, and low-temperature hydrothermal synthesis approach using CQD derived from sugarcane juice and ethanol. The prepared TiO2 and CQD/TiO2 composite thin films were characterized for structural, functional, optical, morphological and elemental compositions analysis using, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Raman Spectroscopy, UV–Vis Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM) and X-ray Photoelectron Spectroscopy (XPS). The optical band gap of CQD/TiO2 was calculated to be 2.87 eV fall under the visible region favorable for photocatalytic activity under sunlight. The Methylene Blue (MB) dye degradation studies of TiO2 and CQD/TiO2 thin films were carried out under the noon sunlight radiation which showed 78% and 82.6% degradation with good reusability. Therefore, this CQD/TiO2 composite thin film can be a promising candidate for industrial dye effluent treatment.

In-depth knowledge of the low-temperature hydrothermal synthesis of nanocrystalline hydroxyapatite from waste green mussel shell (Perna Viridis)

ABSTRACT This study presents the use of a low-temperature hydrothermal method for extracting calcium sources from green mussel shell (P. Viridis) wastes and converting them into synthetic nanosized hydroxyapatite (HA). In this study, raw mussel shells were washed, pulverised, and sieved to start producing a fine calcium carbonate-rich powder. XRD quantitative analysis confirmed that the powder contains 97.6 wt. % aragonite. This powder was then calcined for 5 h at 900 °C to remove water, salt, and mud, yielding a calcium-rich feedstock with major minerals of calcite (68.7 wt.%), portlandite (24.7 wt.%), and minor aragonite (6.5 wt.%). The calcined powders were dissolved in aqueous stock solutions of HNO3 and NH4OH before hydrothermally reacting with phosphoric acid [(NH4)2HPO4], yielding pure, nanoscale (16-18 nm) carbonated HA crystals, according to XRD, FT-IR, and SEM analyses. The use of a low-temperature hydrothermal method for a feedstock powder produced by the calcination of low-cost mussel shell wastes would be a valuable processing approach for the industry's development of large-scale hydroxyapatite nanoparticle production.

One of Nature's Puzzles Is Assembled: Analog of the Earth's Most Complex Mineral, Ewingite, Synthesized in a Laboratory.

Through the combination of low-temperature hydrothermal synthesis and room-temperature evaporation, a synthetic phase similar in composition and crystal structure to the Earth’s most complex mineral, ewingite, was obtained. The crystal structures of both natural and synthetic compounds are based on supertetrahedral uranyl-carbonate nanoclusters that are arranged according to the cubic body-centered lattice principle. The structure and composition of the uranyl carbonate nanocluster were refined using the data on synthetic material. Although the stability of natural ewingite is higher (according to visual observation and experimental studies), the synthetic phase can be regarded as a primary and/or metastable reaction product which further re-crystallizes into a more stable form under environmental conditions.

Low-Temperature Hydrothermal Synthesis of Chromian Spinel from Fe-Cr Hydroxides Using a Flow-Through Reactor

Recent studies have suggested that a chromian spinel can be formed under natural hydrothermal conditions; however, the required conditions, process, and associated redistribution of Cr are still poorly understood. Here, chromian spinel formation was performed by Fe-Cr hydroxides alteration with an Fe2+(aq) supply at 150, 170, and 200 °C and 5 MPa simulating the diagenetic process. The flow-through system enabled the Fe2+(aq) supply to be leached from the magnetite by an acidic solution to synthesize Fe-Cr hydroxides as the starting material with two reaction cells, flow lines, heaters, and a high-performance liquid chromatography (HPLC) pump. The accuracy of the temperature measurement was confirmed based on the amorphous silica solubility. Mineralogical analysis of solid samples recovered from the reaction cell indicated that the chromian spinel was formed between 150 and 170 °C from Fe-Cr hydroxides through goethite with a simultaneous hematite formation, while Mössbauer spectra showed that a large quantity of Fe-Cr ferrihydrites still remained after the experiments probably because of the Cr addition to the stability of ferrihydrites. The Cr/Fe ratio of the chromian spinel was smaller than that of the bulk of the Fe-Cr ferrihydrites and equivalent to Cr-rich magnetite, suggesting a redistribution of Cr during the transformation from goethite to synthesized spinel under the hydrothermal conditions.

A Low-Temperature Hydrothermal Synthesis of Prussian Blue Nanocrystal and Its Application in H2O2 Detection

Uniform Prussian blue Fe3[Fe(CN)6]2 nanocrystals were synthesized by a direct dissociation and reduction of the single-Fe(III)-source precursor K3Fe(CN)6 under low-temperature hydrothermal conditions. UV-visible absorption spectrum, Fourier transform infrared spectrum, X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectra, high-resolution transmission electron microscopy, and electrochemical testing were used to characterize and verify the synthesized Prussian blue nanocrystal product. The size of the synthesized product had a strong dependence on the acidity condition and the concentration of K3Fe(CN)6 solution. This result may facilitate not only the exploration of preparing Fe3[Fe(CN)6]2 nanocrystals for particular applications but also an in-depth explanation of the nature of the hydrothermal reaction. The Prussian blue nanocrystals were deposited onto an electrode support through lyotropic liquid crystalline templates to detect hydrogen peroxide (H2O2) by reduction reaction. Cyclic voltammograms showed that the Prussian blue modified electrode was of excellent electrocatalytic activity for H2O2. This electrode demonstrated a detection limit (1 × 10−7 M) and a linear range starting from the detection limit and extending over 6 orders of magnitude of H2O2 concentrations (1 × 10−7 to 1 × 10−1 M), which was of excellent performance in detecting H2O2.

Tailoring the morphology of orthorhombic Li2MnSiO4 by carbon additive and its impact on transport and Li-storage properties

Carbon additive is an exciting approach for tailoring the surface morphology and improving the material's structural stability, electrical conductivity, and interface chemistry for achieving high capacity and long cycling stability simultaneously. Herein, we successfully introduce sucrose as a carbon additive to tailor the morphology of Li2MnSiO4 (LMS). The low-temperature hydrothermal synthesis route is adopted for preparing pure phase LMS/Cx (x = 0, 2, 5, 7, and 10 wt % refereed as PLMS, LMSC2, LMSC5, LMSC7 and LMSC10). FE-SEM and HR-TEM analyses are used to monitor the changes in the morphology of LMS/Cx composites. The one-dimensional nanorods (formed by the addition of carbon additives) embedded in the as-synthesized best composite sample (LMSC7) are found responsible for the fast lithium-ion diffusion, reactivity, and enhancing the electronic conduction from 26% to 67%, almost three times higher than PLMS. The electronic conductivity of LMSC7 is calculated to be 3.93 × 10−8 (±0.001) Scm−1. It also exhibits an initial charge capacity of 240 (±5) mAhg−1, which is found to be ∼66% higher than PLMS (90 ± 5) at 10 mAg−1 current density at ambient temperature. Furthermore, after a few early cycles, the cyclability profile of LMSC7 demonstrates excellent 100% coulombic efficiency.

Low-temperature large-scale hydrothermal synthesis of optically active PEG-200 capped single domain MnFe2O4 nanoparticles

Herein, we report an intrinsic fluorescence in polyethylene glycol (PEG) coated manganese ferrite (MnFe2O4) magnetic nano particles (MNPs). Generally, nano ferrites (NFs) do not show fluorescence characteristics, however, imparting fluorescence in these materials can be valuable for many applications as the stipulation of external control over the properties by external field provides an opportunity to develop active-controlled devices. In the present work, PEG-200 coated MnFe2O4 MNPs have been synthesized by a large-scale, facile one-pot hydrothermal method. The optical properties of MnFe2O4 MNPs have been by photoluminescence (PL) spectroscopy suggest that the prepared sample is showing sharp emission spectra at 422 nm, corresponding to the violet band, and second at 458 nm corresponding to the blue band. The presence of oxygen vacancy created at both tetrahedral and octahedral sites and shallow hole defects are responsible for the PL behavior in the PEG-coated MnFe2O4. The time-resolved PL (TRPL) results suggest that the MnFe2O4 MNPs have two decay times τ1=1.29ns and τ2=6.85ns which are non-correlated and correspond to different defect states. The electronic bandgap of the MNPs is 3 eV obtained from the Tauc plot using UV absorption spectra. Moreover, the structural analysis has been carried out using X-ray diffraction and various optical and magnetic properties have been correlated to structural parameters and cation distribution. The ferromagnetic resonance (FMR) spectra of the MnFe2O4 MNPs sample show a broad single peak which confirms the ferromagnetic characteristics of the sample and the g-value obtained for the sample is 1.98 which suggests that the super exchange interactions (SEI) dominates over the dipolar interaction. The M-H loop confirms the single domain nature of the sample and the saturation magnetization (SM) is 68 emu/g. The obtained value of SM is higher than the previously reported literature due to an increase in the occupancy of Fe3+ and Mn2+ ions at octahedral sites (Neel’s model). Further, the FTIR spectra confirm the spinel phase formation, and the size distribution and average size are obtained using electron microscopy analysis. The intrinsic fluorescent PEG-coated MnFe2O4 are highly suitable for a diverse range of biomedical (bio-imaging, sensing, magnetic resonance imaging (MRI) contrast agent), optoelectronics, and optical applications.

Eco-valorification of marine shells by hydrothermal conversion in alkaline media

Marine shells are a natural, cheap, abundant and renewable resource, which can be used to produce useful materials, such as for the construction industry. The present study focuses on the transformation of Mya arenaria exoskeletons from the Black Sea into calcium hydroxide by using low-temperature hydrothermal synthesis. In contrast with other methods, this energy-saving process does not involve calcination of shells prior to the hydrothermal treatment. XRD results show the formation of calcium hydroxide with preferential orientation and interesting atypical morphology, which is strongly influenced by the composition of the reaction medium.

Low-Temperature Synthesis of Amorphous FePO4@rGO Composites for Cost-Effective Sodium-Ion Batteries

The dramatic growth of the sodium-ion battery market evokes a high demand for high-performance cathodes. In this work, a nanosized amorphous FePO4@rGO composite is developed using coprecipitation combined with low-temperature hydrothermal synthesis, which registered a surface area of 179.43 m2 g-1. The composites maintain three-dimensional mesoporous morphology with a pore size in the range of 3-4 nm. Uniform distribution of amorphous FePO4 allows a reversible capacity of 175.4 mA h g-1 at 50 mA g-1 while maintaining a stable cycle life of 500 cycles at 200 mA g-1. The amorphous FePO4@rGO, obtained by energy-efficient synthesis, significantly improved the rate performance compared to the crystalline material prepared at high temperatures. Cyclic voltammetry tests reveal that the fast reaction kinetics can be attributed to the pseudocapacitive behavior of the electrode. In addition, we demonstrated the promise of FePO4@rGO cathodes for low-temperature sodium-ion batteries.

Photocatalytic GO/M88A “interceptor plate” assembled nanofibrous membrane with photo-Fenton self-cleaning performance for oil/water emulsion separation

Developing the high-efficient and robust antifouling membranes for oily emulsions to achieve the purpose of prolonging the service life of the membrane shows great demand because of the restriction of hydration anti-fouling mechanism strategy to against pollution. Herein, a hydrophilic photo-Fenton-like catalyst – GO/Fe-MOF assembled stabilized polyacrylonitrile (SPAN) nanofibrous membrane with underwater superoleophobicity, robust mechanical strength and photo-Fenton self-cleaning performance was firstly designed and fabricated via ultrasonic assistance, mussel-inspired fixation and low temperature hydrothermal synthesis methods. In this work, benefiting by the regulable amounts of GO nanosheets on the SPAN@GO/M88A membrane surface, the obtained membrane possessed sub-micrometer skin layer, which guarantees the balance of fast permeation flux (920–7083 ± 47 L m−2 h−1) and separation efficiency (>99.2%) for diesel/water emulsion with small emulsified oils. Moreover, introduced hydrophilic Metal-organic frame nanoparticles (MIL-88A (Fe)) into modified membrane endowed underwater anti-oil-fouling and photo-Fenton catalytic degradation performance for organic contaminants. Meanwhile, the charged GO/M88A heterostructure can assist to achieve demulsification for separation of surfactant-stabilized emulsions by strong electrostatic force. More importantly, attached and irremovable contaminants on the membrane can be quickly removed by photo-Fenton self-cleaning method, and achieved over 96% of recovery flux recovery ratio, which effectively prolonged the service life of the membrane. We believe the newly designed SPAN@GO/M88A membrane with hydration antifouling and photo-Fenton self-cleaning properties can stimulate more studies on revivable separation membranes for multifunctional applications.

Low-Temperature Hydrothermal Synthesis of Novel 3D Hybrid Nanostructures on Titanium Surface with Mechano-bactericidal Performance.

Titanium is extensively employed in modern medicines as orthopedic and dental implants, but implant failures frequently occur because of bacterial infections. Herein, three types of 3D nanostructured titanium surfaces with nanowire clusters (NWC), nanowire/sheet clusters (NW/SC) and nanosheet clusters (NSC), were fabricated using the low-temperature hydrothermal synthesis under normal pressure, and assessed for the sterilization against two common human pathogens. The results show that the NWC and NSC surfaces merely display good bactericidal activity against Escherichia coli, whereas the NW/SC surface represents optimal bactericidal efficiency against both Escherichia coli (98.6 ± 1.23%) and Staphylococcus aureus (69.82 ± 2.79%). That is attributed to the hybrid geometric nanostructure of NW/SC, i.e., the pyramidal structures of ∼23 nm in tip diameter formed with tall clustered wires, and the sharper sheets of ∼8 nm in thickness in-between these nanopyramids. This nanostructure displays a unique mechano-bactericidal performance via the synergistic effect of capturing the bacteria cells and penetrating the cell membrane. This study proves that the low-temperature hydrothermal synthesized hybrid mechano-bactericidal titanium surfaces provide a promising solution for the construction of bactericidal biomedical implants.

Enhancement of the performance of ZnO based natural dye sensitized solar cells via PVA morphology controlled nanorods

ZnO nanoparticles were synthesized via low temperature hydrothermal synthesis procedures at 90 °C using zinc nitrate hexahydrate as the zinc oxide precursors and hexamethyleneamine as the precipitating agent. The structural, surface morphology and optical studies of the hydrothermally synthesized ZnO nanoparticles revealed that the synthesized products were nano-rods, grown in very high-density with well-crystalline wurtzite hexagonal phase and good optical properties. Ployvinyl alcohol (PVA) was used as surfactant to modify the surface features of the ZnO nanorods. The ZnO nano-rods were employed as photo-anode for dye sensitized solar cell (DSSC) and were sensitized by natural dye extracted from Baphia nitida plant. The photovoltaic characteristics of the cell such as the short circuit current, open circuit voltage as well as the shunt and series resistances of the cell were studied. The incident photon to current conversion efficiency was also studied. The study revealed that the PVA improved the overall photo-conversion efficiency of the DSSC.

Hydrothermal Synthesis: Low−Temperature Subcritical Water for Ceria−Zirconia Mixed Oxides Preparation

A low-temperature hydrothermal synthesis technique was employed as a medium to produce ceria−zirconia mixed oxides particles at temperatures of 200–300 °C and pressure of 10 MPa in a batch process. At these conditions, the average crystallite sizes of ceria−zirconia mixed oxides increased slightly with increasing reaction temperature when the feed solution containing ceria and zirconia with a ratio of 1:1 was fed. SEM images illustrated that the morphologies of the ceria−zirconia mixed oxides particles were spherical and spherical−like with a diameter of around 100 nm. The EDX spectrum indicated that the signal corresponding to the ceria and the zirconia elements at 5 and 2 keV, respectively, were strongly detected in the products. The XRD pattern revealed that the mixed metal oxides particle products that comprised of cerium and zirconium oxides particles with cubic and monoclinic structures, respectively, were affected by their molar content in the feed solution.