Conventional Hydrothermal Method Research Articles

Structure, dielectric and magnetic properties of hydrothermally synthesized Sn1−x Fe x O2 nanoparticles

Abstract Sn1−x Fe x O2 (x = 0, 1, 2, 3, and 4 %) of the diamagnetic/ferromagnetic phase were synthesized by the conventional hydrothermal method. X-ray diffraction spectra confirm that all the samples have a tetragonal structure. Electronic distribution over the unit cell of Sn1−x Fe x O2 showed the dependence of electronic density on the x. The crystallite size of the obtained samples was in the range of 42–72 nm. Impedance spectroscopy was employed to investigate the variation of the electrical impedance and some related parameters as frequency functions in the range of 75 k Hz–10 MHz at room temperature. The dielectric behavior was explained using the Maxwell–Wagner model of interfacial polarization. The ac conductivity results were used to evaluate the maximum barrier height, the minimum hopping distance, and the density of the localized states at the Fermi level. The effect of adding the iron ion into the tin dioxide compound was apparent, as the electrical and magnetic properties as well as the morphology were affected, although the crystal structure phase still has the same tetragonal crystal system for the different iron concentration (Fe from x = 0 up to x = 0.04) with slight variation in the lattice constants. The magnetic measurements illustrated that the Fe-doped SnO2 nanoparticles exhibit ferromagnetic ordering at room temperature. Variation of the Fe content affects the ferromagnetic characteristics of the samples.

Electrodeposited graphene@TiO2 nanosheets for enhanced photocathodic protection

In this work, TiO2 was firmly attached on freestanding graphene (Gr, rather than graphene oxide or reduced graphene oxide) nanosheets (Gr@e-TiO2) by a novel electrodeposition method. The morphology, crystal structure, band gap characteristics, optical properties and photoelectric properties were systematically investigated. It is indicated that the absorption of visible light increased and the recombination of photogenerated electron-hole pairs decreased for the as-obtained Gr@e-TiO2. Compared with pure TiO2 as well as GO (graphene oxide)@h-TiO2 prepared by conventional hydrothermal method, Gr@e-TiO2 exhibited a more negative open circuit potential and higher photocurrent density for 304SS protection. The enhanced photocathodic protection performance of Gr@e-TiO2 can be attributed to the large specific surface area and good charge transport efficiency of graphene.

Two Short-Wave UV Antimony(III) Sulfates Exhibiting Large Birefringence.

In the present work, we have successfully obtained two new UV antimony-based sulfates, NH4Sb(SO4)2 and Ca2Sb2O(SO4)4, by a conventional hydrothermal method. Interestingly, both compounds share similar structural building blocks, such as SbO4 seesaws and SO4 tetrahedra, yet they endow discrepant birefringence values measured at 546 nm with values of 0.150 and 0.114, respectively, owing to the different distortions of the SbO4 groups with SCALP electrons. Moreover, both compounds display large band gaps (4.32 and 4.43 eV, respectively), so they can be used as short-wavelength UV birefringent materials. Moreover, NH4Sb(SO4)2 is a noncentrosymmetric compound, showing a frequency doubling effect of 0.2 × KDP. Detailed structural analyses and calculations confirm the source of superior optical performance and the reasons for the different birefringence of the two compounds. This work provides ideas for the following discovery of antimony-based optical materials with excellent properties.

Room temperature synthesized layered CAU-17 MOFs for highly active and selective electrocatalytic CO2 reduction to formate

Modulating the morphology of metal-organic frameworks (MOFs) has been identified as an effective strategy for enhancing the electrocatalytic performance of CO2 reduction reactions (CO2RR). In this study, CAU-17 MOFs ([Bi(BTC)(H2O)]·2 H2O·MeOH) were prepared via a sonication-assisted method at room temperature, which is considered a simpler technique compared to the conventional hydrothermal method. Additionally, the morphology of CAU-17 MOFs was further regulated by incorporating a rare-earth metal (La), resulting in the observation of two distinct structures, i.e. CAU-17 hexagonal prism (CAU-17-HP) and CAU-17 layer (CAU-17-Layer). Compared to CAU-17-HP, CAU-17-Layer exhibits an excellent selectivity towards formate with the maximum Faradaic efficiency of 95.5% at − 1.1 VRHE in an H-cell. Subsequently, the limited catalytic activity of CAU-17-Layer was boosted by anchoring nano CeO2 onto its surfaces (CeO2 @CAU-17-Layer). The as-prepared composite catalyst demonstrated outstanding performance in the conversion of CO2 to formate, with a current density surpassing − 100 mA cm-2 at potentials more negative than − 1.0 VRHE and reaching − 200 mA cm-2 at − 1.5 VRHE in a flow cell. This study demonstrates the significant potential of morphology-engineered and rare-earth metals composited MOFs in facilitating highly efficient reduction of CO2.

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.

Synthesis of Nanosized Zeolite Catalyst Particles from Waste Materials for Efficient Removal of Fe(III) from aqueous solution

The objective of this study was to prepare zeolite ZSM-5 nanostructure from aluminum foil drug sachet waste by a simple conventional hydrothermal method using different times (24, 48, 72, and 96 h), and to figure out the adsorption capacity of zeolite ZSM-5 nanostructure for heavy metal of Fe(III) . The best time for synthesizing and testing the adsorption effectiveness of the provided ZSM-5 zeolite is 96 h. The ZSM-5 zeolite is defined by X-ray diffraction (XRD), Brunauer Emmett Teller (BET), Field Emission Scanning Electron Microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) for confirming their structure and properties, such as crystal structure, surface area, and surface morphology. The crystallinity percentage of nanosized ZSM-5 was 100%, and the surface area and micropore volume were 368.70 m2/g and 0.158 cm3/g, respectively. In addition, the ZSM-5's adsorption efficiency the solution for Fe(III) was tested. Many factors, including adsorption properties, contact duration, initial iron solution content, and pH, were investigated. The equilibrium was reached after 25 minutes. pH levels between 3.0 and 4.0 were shown to be optimal for the absorption of iron solution. The iron species` adsorption capacities in solutions at 298 K were 56.49 mg/g, at 308 K, 86.20 mg/g, and at 318 K, 68.02 mg/g. The findings of the Freundlich adsorptions and Langmuir were used to represent the isotherm constants. The Langmuir model can adequately describe the Fe(III) solutions` adsorption isotherm data while testing at 298K and 308K, whereas those of Fe(III) testing at 308K and 318K were more closely connected to the Freundlich model.

A carbon quantum dot based on tetramethyl substituted cucurbit[6]uril and 2,7-dihydroxynaphthalene: Selective detection of Fe3+, ClO−and I−

Carbon quantum dots have attracted much attention as novel nanomaterials. In this study, TMeQ[6]-CQDs were synthesized by a conventional hydrothermal method using symmetric tetramethyl-substituted cucurbit[6]uril (TMeQ[6]) and 2,7-dihydroxynaphthalene (DHN) as carbon precursors, which characterized by 1H NMR, UV–vis, FL, SEM, FTIR, and XPS. Futhermore, the crystal structure was determined using Single crystal X-ray crystallography, demonstrating the formation of TMeQ[6]-based supramolecular assemblies (TMeQ[6]-DHN-[CdCl4]2−). The prepared TMeQ[6]-CQDs have abundant oxygen-containing groups with excellent water-solubility and fluorescence properties. Subsequently, using the obtained TMeQ[6]-CQDs, a universal fluorescent probe was prepared for detecting and recognizing Fe3+, I−, and ClO−. In the presence of Fe3+and I− ions, the fluorescent CQDs are quenched. Interestingly, the fluorescence spectral line undergoes a red-shift when interacting with ClO−. The detection limits were 0.41 μM, 3.71 μM and 0.10 μM.

Self-enhancement of phosphorus recovery from anaerobic fermented sludge with MOF-808 synthesized with an improved green method

Although sludge anaerobic fermented is rich in phosphate, its complicated composition might be a barrier for adsorption approach due to the competing effects of ions and organics. In this study, an interesting phenomenon was found with MOF-808-(25) which exhibited a higher adsorption capacity in anaerobic fermented sludge than in phosphate-water solution. A green synthesis of MOF-808-(25) was first developed by optimizing the microwave synthesis method to reduce the cost of the adsorbent. Under the optimized conditions, i.e., Zr4+/BTC3− ratio of 4:1, 25 min, and microwave power of 350 W, the space–time yield of MOF-808-(25) reached 236.03 kg·m−3d−1, approximately 100 times higher than those achieved through conventional hydrothermal methods. In phosphate-water solution, the maximum adsorption capacity of MOF-808-(25) for phosphate was 66.61 mg P/g (pH = 7, 25 °C). Molecular dynamics simulation revealed that the adsorption of phosphate by MOF-808 was primarily dominated by coordination effects, while, electrostatic interactions, hydrogen bonding, and steric hindrance were also involved. MOF-808-(25) exhibited good adsorptive selectivity over coexisting anions and organic matters in anaerobic fermentation broth. Experimental results also suggest that a higher temperature or a lower pH value favored the adsorption capacity of MOF-808-(25). With this feature, the phosphate adsorption capacity of MOF-808-(25) was surprisingly ∼ 5 mg P/g higher than that obtained in phosphate-water solution due to the acidogenesis of anaerobic fermentation. Additionally, MOF-808-(25) improved the hydrolysis of proteins through non-biological catalysis. These findings depict a promising vision for phosphorus recovery by MOF-808-(25).

Microwave‐assisted hydrothermal green synthesis of selenium nanoparticles incorporated with hyaluronic acid methacrylate/gelatin methacrylate hydrogels for wound healing applications

AbstractWound healing is a topic of significant interest in current times, owing to the escalating incidence of chronic diseases associated with impaired healing, as well as the growing number of elderly individuals within the population. Amongst the various approaches for fabrication of wound healing dressings, the utilization of selenium‐based nanoparticles has garnered considerable attention due to selenium's numerous advantages, including antioxidant, antiviral, antibacterial, and antifungal activities. With this perspective, we focused on the fabrication and characterization of hydrogels incorporated with selenium nanoparticles (SeNPs). In this work, we have developed a microwave‐assisted hydrothermal synthesis strategy for synthesis of the SeNPs that employ non‐toxic precursors, thereby reducing the risk of environmental toxicity and providing a cost‐effective alternative to conventional chemical and hydrothermal methods. Subsequently, we have successfully incorporated SeNPs into hyaluronic acid methacrylate/gelatin methacrylate‐based hydrogels. Hyaluronic acid and gelatin are selected to support the healing process further, and these polymers are methacrylated in order to further control mechanical properties of the hydrogel and improve the stability of the dressing. The nanoparticles and the nanoparticle‐incorporated hydrogels were characterized by various techniques including Fourier transform infrared spectroscopy, UV–Vis spectroscopy, scanning electron microscopy, and dynamic light scattering instruments. Mechanical behaviors, swelling and degradation properties of the dressings were evaluated. Afterwards, we have conducted cell culture studies with SeNPs‐loaded hydrogels to determine the efficacy of SeNPs in wound healing. According to experimental findings, in vitro scratch assay suggests that a hydrogel dressing containing SeNPs (HG‐SeNp2) support the cell migration more compared to other samples incorporated with nanoparticles and to the control study at 24 h, and the wound closure percentage was found to be statistically significant compared with the control study. This dressing hold promise as effective wound dressings that can facilitate and expedite the process of wound healing.

Preparation of hydroxyapatite (HAP) from waste eggshells for enhancing the granulation and treatment performance of aerobic granular sludge: Enhancement effects and mechanism insights

Hydroxyapatite (HAP), an inorganic mineral that is generated in situ within the core of aerobic granular sludge (AGS), plays a pivotal role in both the granulation process and system stability. Due to the slow precipitation rate of HAP, waste eggshells were utilized as a readily available source for preparing HAP by using the conventional hydrothermal (C-HAP) and microwave hydrothermal (M-HAP) methods. Subsequently, the prepared HAP was employed to promote AGS formation. Results showed that the prepared HAP exhibits superior morphology, crystallinity, functional groups, and specific surface area compared to the commercial grade HAP, whereby M-HAP outperforms C-HAP for functional groups and specific surface area. The addition of 0.5 g/L HAP facilitated the granulation process (within 20 days), leading to the development of structurally compact AGS, which was attributed to the microbial attachment onto HAP particles. Moreover, the presence of HAP greatly improved the nutrient removal efficiency (80.8 % of TN and 82.4 % of PO43−-P), most likely due to the enrichment of denitrifying and phosphorus-accumulating microorganisms (e.g., Candidatus_Competibacter and Flavobacterium). Further analysis revealed that an increase in the relative abundance of denitrification-related genes (e.g., narG and nirK) was responsible for the intrinsic mechanism behind the enhanced nitrogen removal, while phosphorus removal occurred through biomineralization and abiotic precipitation pathways. Overall, the present study highlights the potential of utilizing waste eggshells to enhance AGS systems for wastewater treatment, thus realizing a circular economy approach.

Targeted fabrication of 1T-MoS2 enriched nanosheets vertically oriented on spiny-shaped nanospheres with sufficient sulfur vacancies and “rim” sites for co-enhancing the hydrodesulfurization activity and hydrogenation selectivity

The 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets over the surface was successfully prepared with the novel solvent induced micelle-limited Mo-CTA+ composites self-assembly (SIMMS) strategy under the dual effects of mixed sulfur sources (thiourea and thioacetamide) and cetyltrimethylammonium bromide (CTAB). In the proposed strategy, the molybdenum source and CTAB are firstly assembled to Mo-CTA+ by strong electrostatic attraction to avoid the molybdenum source from polymerization and forming large polymolybdate anions. Meanwhile, the CTAB moleculars self-assemble to spherical micelles, which can adsorb Mo-CTA+ through van der Waals force and obtain spherical precursors with a controllable number of nucleation sites. Under the sulfurization from mixed sulfur source, appropriate reducibility can control the formation of crystal seeds and crystal growth during the crystallization process of MoS2, whereas CTAB can regulate and control the growth behavior and micro-morphology of MoS2, which is ultimately also retained between the MoS2 nanolayersto expand their interlayer spacing and stabilize the 1T phase. Therefore, the 1T-enriched spiny-shaped nanospheres with vertically oriented MoS2 nanosheets can be controllably prepared. In the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT) over these catalysts, the MoS2-75%/0.25 catalyst with the highest concentration of sulfur vacancies as well as “rim” and “rim-like” sites can reach the highest HDS activity (99.1%) and HYD/DDS ratio (4.76), which are much higher than those of the MoS2-H catalyst prepared by conventional hydrothermal method (HDSDBT%=46.0%, HYD/DDS ratio=0.90).

Towards a new avenue for rapid synthesis of electrocatalytic electrodes via laser-induced hydrothermal reaction for water splitting

Abstract Electrochemical production of hydrogen from water requires the development of electrocatalysts that are active, stable, and low-cost for water splitting. To address these challenges, researchers are increasingly exploring binder-free electrocatalytic integrated electrodes (IEs) as an alternative to conventional powder-based electrode preparation methods, for the former is highly desirable to improve the catalytic activity and long-term stability for large-scale applications of electrocatalysts. Herein, we demonstrate a laser-induced hydrothermal reaction (LIHR) technique to grow NiMoO4 nanosheets on nickel foam, which is then calcined under H2/Ar mixed gases to prepare the IE IE-NiMo-LR. This electrode exhibits superior hydrogen evolution reaction performance, requiring overpotentials of 59, 116 and 143 mV to achieve current densities of 100, 500 and 1000 mA·cm−2. During the 350 h chronopotentiometry test at current densities of 100 and 500 mA·cm−2, the overpotential remains essentially unchanged. In addition, NiFe-layered double hydroxide grown on Ni foam is also fabricated with the same LIHR method and coupled with IE-NiMo-IR to achieve water splitting. This combination exhibits excellent durability under industrial current density. The energy consumption and production efficiency of the LIHR method are systematically compared with the conventional hydrothermal method. The LIHR method significantly improves the production rate by over 19 times, while consuming only 27.78% of the total energy required by conventional hydrothermal methods to achieve the same production.

Influence of A‐Site Doping on the Local Structure and Magnetic Behavior of BiFeO3 Nanoparticles Investigated by X‐Ray Absorption Fine Structure Spectroscopy

Structural transformation and magnetic change of pure and 1% La/Nd‐doped multiferroic BiFeO3 (BFO) nanoparticles are presented to study the influence of introducing rare‐earth elements at the A‐site in BFO. All samples are successfully produced by the conventional hydrothermal method. Scanning electron microscopy picture demonstrates that doping has an impact on the surface and size of particles, and the magnetic properties of BFO also are improved, even significant ferromagnetism is observed in the Nd‐doped sample. Though the room‐temperature X‐ray diffraction patterns reveal the rhombohedral R3c symmetry for all samples, further identified by the Bi L3‐edge and Fe K‐edge X‐ray absorption fine structure (XAFS) spectra, the nanoscale secondary orthorhombic phase is only detected in Bi0.99Nd0.01FeO3 when analyzing the doped elements according to the La and Nd L3‐edge XAFS spectra. The different magnetic behavior is speculated to be in connection with the orthorhombic symmetry around the Nd atom.

Luminescence investigations of hydrothermally synthesized terbium doped zirconium tungstate nanorods

Rare-earth based phosphors play a key role in enhancing the quality of the phosphor converted LEDs (pc-LEDs). But the creation of phosphors with high thermal stability is still a task. This work aims to investigate the luminescence properties of ZrW2O8, which is known to have a negative or almost zero coefficient of thermal expansion. ZrW2O8 doped with Tb3+ is optimized by the conventional hydrothermal method in acidic medium. The PXRD analysis confirms the crystallization of the material into high purity cubic phase to the P213 space group. The tungstate group's distinctive vibrational modes were identified by FTIR analysis. TGA analysis demonstrates the remarkable thermal stability of the material over a wide temperature range. The preferential growth along one direction to form distinct nanorods was investigated using TEM. The optical band gap is found to increase after doping. The high and broad charge transfer band at 284 nm in the excitation spectra is an indication of the efficient energy transfer from the host to Tb3+ ions and the possibility of NUV excitation. The characteristic green emission peak of the Tb3+ at 543 nm and the values of the CCT and CP obtained using the colorimetry study suggest that the obtained material can be used as a green component to produce cold white LEDs.

Characterization and magnetic properties of two mixed-valence compounds A2MnⅡMn2III(SeO3)6 (A = Sr and Ba)

A2MnⅡMn2III(SeO3)6 (A = Sr and Ba) are found to have a monoclinic space group P21/c, where Mn3+ ions form a distorted honeycomb lattice centred by the Mn2+ ions. The samples of two isostructural compounds were synthesized using a conventional hydrothermal method and characterized by many methods including EDS, XRD, FT-IR, UV–vis diffuse reflectance spectra and thermal analysis. Magnetic measurements confirm that two compounds display a similar magnetic behavior with a short-range and a long-range antiferromagnetic order at low temperature, while the metamagnetic transition can be observed under applied magnetic field. In addition, the spin-frustration effects of two compounds are also investigated.

Microwave-Processable Cu Nanostructures -the Morphology and Chemical Properties

The work presented a facile method using a domestic microwave-assisted technique in synthesising the Cu nanostructures solution. By controlling the microwave reaction time, the morphological structures and the ultra-fast growth of the as-synthesised Cu nanostructures are varied. The method is much preferable as compared to the conventional hydrothermal method due to the ultrafast supersaturation of Cu nuclei and high-quality structures. Those different morphologies with different average size distributions show a direct influence on their intrinsic physical behaviour. The study focuses on the morphology, particle size distribution and element bonding effect of the growth reaction and solution’s concentration. The combination of the CuSO4·5H2O, PEG (polyethylene glycol) and PVP (polyvinyl pyrrolidone) without any extra reagents shows the capabilities of mixture to yield the Cu nanostructures with the average particle size distribution below 100 nm. The produced Cu nanostructures via microwave-assisted demonstrated that the allocated time of reaction (∼7 mins) shows a good supersaturated homogeneous nucleated suspension yield. Simultaneously, they undergo a size-dependent multi-stage aggregation mechanism to yield different morphologies of Cu nanostructures.

Fluoride removal from coal mining water using novel polymeric aluminum modified activated carbon prepared through mechanochemical process

Defluoridation of coal mining water is of great significance for sustainable development of coal industry in western China. A novel one-step mechanochemical method was developed to prepare polymeric aluminum modified powder activated carbon (PAC) for effective fluoride removal from coal mining water. Aluminum was stably loaded on the PAC through facile solid-phase reaction between polymeric aluminum (polyaluminum chloride (PACl) or polyaluminum ferric chloride (PAFC)) and PAC (1:15 W/W). Fluoride adsorption on PACl and PAFC modified PAC (C-PACl and C-PAFC) all reached equilibrium within 5 min, at rate of 2.56 g mg-1 sec-1 and 1.31 g mg-1 sec-1 respectively. Larger increase of binding energy of Al on C-PACl (AlF bond: 76.64 eV and AlFOH bond: 77.70 eV) relative to that of Al on C-PAFC (AlF bond: 76.52 eV) explained higher fluoride uptake capacity of C-PACl. Less chloride was released from C-PACl than that from C-PAFC due to its higher proportion of covalent chlorine and lower proportion of ionic chlorine. The elements mapping and atomic composition proved the stability of Al loaded on the PAC as well as the enrichment of fluoride on both C-PACl and C-PAFC. The Bader charge, formation energy and bond length obtained from DFT computational results explained the fluoride adsorption mechanism further. The carbon emission was 7.73 kg CO2-eq/kg adsorbent prepared through mechanochemical process, which was as low as 1:82.3 to 1:8.07 × 104 compared with the ones prepared by conventional hydrothermal methods.

Single-pot green synthesis of novel thiol-engineered iron thiomalate (Fe-TA) metal organic framework for selective adsorption of mercury in water

A novel thiol-functionalized iron thiomalate metal organic framework (Fe-TA) was synthesized using a facile, single step and green coprecipitation route. The synthesis procedure was optimized and it was proven to be an exclusive way over conventional hydrothermal method. This newly reported MOF was characterized in detail using XRD, FTIR, FESEM, EDX, BET, and Zetasizer to determine the morphological and compositional properties that indicated to the amorphous nature of Fe-TA. The MOF demonstrated high adsorption of aqueous inorganic mercury that was thoroughly explored in varying range of experimental conditions, namely, adsorbent dose, solution pH, feed Hg concentration, temperature, and time to analyze the adsorption isotherms along with the kinetic and thermodynamic parameters. The maximum capacity was evaluated as 1223 mg/g at 298 K using the Langmuir isotherm model and the adsorption followed pseudo-second order kinetics. XPS analysis was used to confirm chemisorption as the governing mechanism by strong lone pair interactions between S and Hg forming a Hg-S complex. The high negative zeta potential of Fe-TA (-18 mV) aided in strong electrostatic interactions with Hg2+ favoring the adsorption process. The selective affinity (Kd: 5.35 × 105 mL/g) and substantial regenerative quality (>93%) of the adsorbent was also reported.

Highly porous silica synthesized by a microwave-assisted hydrothermal method derived from recycled silicon sludge for thermal insulation applications

In this study, we synthesize a porous silica nanoparticles (SiO2) derived from recycled semi-conducting silica sludge via a conventional hydrothermal and microwave-assisted hydrothermal methods for flame-resistant applications. The corresponding thermal properties of as-synthesized SiO2 nanoparticles are investigated. The effects of reaction temperature and urea concentration are investigated in terms of surface morphology and thermal conductivity. The results of thermal conductivity tests indicate that 180 °C reaction temperature for both conventional hydrothermal reaction and microwave-assisted hydrothermal reaction demonstrated the best thermal insulator performance. The thermal conductivities are determined to be 0.0193 W/m·K and 0.0192 W/m·K, respectively. For flame penetration and combustion tests, microwave-assisted one exhibits much better performance, maintaining a temperature of 34 °C after 600 s of combustion under a butane torch at nearly 800 °C. Furthermore, there is no deformation occurred when direct contact with the flame at a high temperature, proving that microwave-assisted hydrothermal reaction-synthesized silica is a potential candidate for thermal barrier applications.

High-performance chrysanthemum flower-like structure of Ni doped ZnO nanoflowers for pseudo-supercapacitors

In this study, the chrysanthemum-flower-like structure of Ni-doped ZnO nanoflowers pseudo-capacitance behaviour was synthesized by a conventional hydrothermal method. The X-ray diffraction (XRD) results showed that the prepared materials had formed ZnO and Ni-doped ZnO nanopowder in their hexagonal wurtzite structure. The morphologies of the Ni-doped ZnO have a chrysanthemum-flower-like structure, which was confirmed by SEM and HR-TEM. Galvanostatic charge-discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques were used to investigate the pseudo-capacitance behaviour of Ni-doped ZnO. The Ni-doped ZnO nanoflower-modified electrode achieved a maximum specific capacitance value of 1090 F/g at 0.25 A/g, and 3 M KOH was used as the electrolyte. Eight thousand cycles of testing revealed that the Ni-doped ZnO nanoflowers electrode was very stable, far outperforming the stability of undoped ZnO nanoflowers modified electrodes. The fabricated Ni-doped ZnO nanoflower electrode has high capacitance retention and high columbic efficiencies of 101 % and 89 %, respectively. The prepared Ni-doped ZnO nanoflowers are a very effective electrode material and are considerably better suited for supercapacitor applications.