Surfactant-free Hydrothermal Method Research Articles

Temperature-controlled morphology and enhanced functionalities of hydrothermally synthesized SrFe2O4 nanostructures for multifaceted applications

In this study, we investigate the effect of synthesis temperature on the morphology and properties of spinel strontium ferrite (SrFe2O4) nanostructures, synthesized using a surfactant-free hydrothermal method. We demonstrate that by varying the temperature from 85 °C to 160 °C, we can control the morphology of SrFe2O4, transitioning from nanoribbons to dendritic structures, and finally to hexagonal nanoplatelets. These morphological changes correspond to significant enhancements in both magnetic and photocatalytic performance. The saturation magnetization (Ms) notably increases by up to 70 % at higher synthesis temperatures. Additionally, these nanostructures show improved efficiency in photocatalytic degradation of methylene blue dye, indicating their potential for environmental remediation. The dielectric properties of the various morphologies were also characterized, suggesting applications in electronics and energy storage. This study establishes a clear link between synthesis conditions, resulting structures, and functional performance in SrFe2O4 nanostructures, contributing to the development of advanced materials.

Green hydrothermally synthesized ultrathin Mg-doped CuO nanoflakes: a structural, electrical and dielectric study

Pure and Mg-doped CuO nanoflakes were synthesized by a surfactant-free hydrothermal approach. The electric and dielectric properties of CuO can be tuned by optimizing the Mg doping level.

Synthesis of nanostructured Co$$_3$$O$$_4$$ by a surfactant-free hydrothermal method and its application to the hydrogen evolution reaction

Synthesis of nanostructured Co$$_3$$O$$_4$$ by a surfactant-free hydrothermal method and its application to the hydrogen evolution reaction

Improved trifunctional electrocatalytic performance of integrated Co3O4 spinel oxide morphologies with abundant oxygen vacancies for oxygen reduction and water-splitting reactions

A simple and surfactant-free hydrothermal method was used to produce different forms of integrated nanostructures of Co3O4 spinel oxides, which exhibited excellent trifunctional electrocatalytic activity toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The surface morphology and structural features of Co3O4 spinel oxide catalysts were investigated, and 40–70-nm nanocube particles were found decorated over petal-, slab-, and flower-like spinel oxide structures with the dominant (111) crystalline plane. According to physicochemical studies, the Co3O4 spinel oxide catalyst with the slab morphology has a high Co3+/Co2+ ratio and an abundance of oxygen vacancies, resulting in improved trifunctional performance with an early ORR onset potential (0.91 V), low overpotential for OER (460 mV) and HER (363 mV), and extended durability. This study provides insights into the design and structural features of Co3O4 spinel oxides through a simple and template-free synthesis approach to compete as an efficient trifunctional electrocatalyst for water splitting and metal–air battery applications.

ZnO Nanoparticles for Photocatalytic Methyl Orange Degradation: Hydrothermal Synthesis, Characterization, and Optimization

This study investigates the production of zinc oxide nanoparticles (ZnO NPs) utilizing an efficient and surfactant-free hydrothermal method for use as a photocatalytic agent in the purification of organic polluted water. The structural features, optical properties and photocatalytic performance of ZnO NPs have been investigated. XRD, SEM, HR-TEM, FTIR and UV–vis absorption spectroscopy were used as analytical and characterization techniques. The ZnO NPs prepared with hexagonal structure and interesting applied properties was obtained by adjusting the processing time at a low treatment temperature of 75 °C. The crystallite size and energy band gap are reaction time-dependent, which in turn affects the photocatalytic performance. ZnO NPs under UV irradiation show an efficiency of 93% in the photocatalytic decomposition of methyl orange (MO) dye. The value of ZnO NPs bandgap (3.38 eV) is suitable for allowing UV light absorption and rapid generation of charge carriers; creating photooxidation reactions for decomposing the organic dye.

Enhanced synchronous photocatalytic 4-chlorophenol degradation and Cr(VI) reduction by novel magnetic separable visible-light-driven Z-scheme CoFe2O4/P-doped BiOBr heterojunction nanocomposites

The co-existence of organic contaminants and heavy metals including 4-chlorophenol (4-CP) and Cr(VI) in aquatic system have become a challenging task in the wastewater treatment. Herein, the synchronous photocatalytic decomposition of 4-CP and Cr(VI) over new Z-scheme CoFe2O4/P–BiOBr heterojunction nanocomposites were revealed. In this work, the nanocomposites were successfully developed via a surfactant-free hydrothermal method. The heterojunction interface was created by decorating magnetic CoFe2O4 nanoparticles onto P–BiOBr nanosheets. The as-fabricated CoFe2O4/P–BiOBr nanocomposites substantially improved the synchronous decomposition of 4-CP and Cr(VI) compared to the single-phase component samples under visible light irradiation. Particularly, the 30-CoFe2O4/P–BiOBr nanocomposite displayed the best photocatalytic performance, which decomposed 95.6% 4-CP and 100% Cr(VI) within 75 min. The photocatalytic improvement was assigned to the Z-scheme heterojunction assisted charge migration between CoFe2O4 and P–BiOBr, and the acceleration of charge carrier separation was validated by the findings of charge dynamics measurements. The harmful 4-CP was photodegraded into smaller organics whereas the Cr(VI) was photoreduced into Cr(III) after 30-CoFe2O4/P–BiOBr photocatalysis, and the good recyclability of fabricated nanocomposite in photocatalytic reaction also showed promising potential for practical applications in environmental remediation. Finally, the radical quenching tests confirmed that there existed the Z-scheme path of charge migration in CoFe2O4/P–BiOBr nanocomposite, which was the mechanism responsible for its high photoactivity.

Magnetic and magnetocaloric properties of rare-earth substituted Gd2O3 nanorods

Nanorods of Gd2O3 with 5 at.% Nd3+ and 5 at.% Er3+ ion substitution at Gd-site have been synthesized using a template-free and surfactant-free hydrothermal method. The samples have MnFeO3-type cubic crystal structure (space group Ia-3, N 206, cI80) at 300 K. Using the powder X-ray diffraction data and Scherrer formula, a crystallite size of ∼25 nm and ∼20 nm is estimated for the Nd-substituted and Er-substituted Gd2O3 nanorod samples. Raman spectrum also confirms the cubic structure of the samples at 300 K. Both samples show paramagnetic behaviour in the temperature range of 300 K to 5 K. From the magnetization vs field data measured in the temperature range of 5 K to 31 K, the isothermal magnetic entropy change (ΔSm) is calculated. The maximum ΔSm value at 6 K for 70 kOe field change is about −19.8 Jkg−1K−1 and −23.5 Jkg−1K−1 respectively for 5 at.% Nd- and Er- substituted Gd2O3 nanorods. The magnetocaloric effect is large and is of the same order as in the pure and other rare-earth-substituted Gd2O3 nanostructures. Thus the mixed rare-earth oxide nanostructures are found to be potential candidates for low temperature magnetic cooling applications.

Carnation-like Morphology of BiVO4-7 Enables Sensitive Photoelectrochemical Determination of Cr(VI) in the Food and Environment

Hexavalent chromium, namely, Cr(VI), is a significant threat to ecological and food safety. Current detection methods are not sensitive to Cr(VI). A photoelectrochemical (PEC) sensor based on bismuth vanadate (BiVO4) was developed for sensitive detection of Cr(VI). First, BiVO4-X (X: the pH of the reaction precursor solution) was synthesized using a facile surfactant-free hydrothermal method. The BiVO4-X morphology was well controlled according to pH values, showing rock-like (X = 1), wrinkled bark-like (X = 4), carnation-like (X = 7), and the collapsed sheet-like morphologies (X = 9, 12). BiVO4-7 exhibited excellent photoelectric performance due to a proper band structure under visible light and a large specific surface area. Then, BiVO4-7 was used to construct a PEC sensor to detect Cr(VI), which was demonstrated to have a low detection limit (10 nM) and wide detection range (2–210 μM). The BiVO4-7 PEC sensor had a stable output signal, as well as excellent reproducibility, repeatability, and selectivity. We used the BiVO4-7 PEC sensor to detect Cr(VI) in real environmental and food samples, resulting in a satisfactory recovery of 90.3–103.0%, as determined by comparison with results obtained using a spectrophotometric method. The BiVO4-7 PEC sensor is promising for practical application to heavy metal detection in the food and environment.

A Hierarchical Structure of Flower-Like Zinc Oxide and Poly(Vinyl Alcohol-co-Ethylene) Nanofiber Hybrid Membranes for High-Performance Air Filters.

In this article, we reported a hierarchical structure of flower-like zinc oxide (ZnO) and poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofiber (ZnO@NF) hybrid membranes for high-performance air filters. Monodispersed flower-like ZnO superstructures were fabricated using a template-free and surfactant-free hydrothermal method, and PVA-co-PE nanofiber yarns were prepared using a melt extrusion phase separation approach. The PVA-co-PE nanofiber yarns were subjected to high-speed shearing in a mixed aqueous solution of isopropanol and water to obtain a stably dispersed nanofiber suspension. The ZnO@NF hybrid air filter was obtained by coating the mixture of flower-like ZnO superstructures and the PVA-co-PE nanofiber suspension on the surface of the polypropylene (PP) meltblown nonwoven with the electret charge eliminated. The filtration efficiency of the ZnO@NF hybrid air filter increases with increasing loading amount of the flower-like ZnO superstructures, while the pressure drop decreases. The flower-like ZnO superstructures were incorporated into the nanofiber-interconnected networks, which significantly reduces the pressure drop of the pure PVA-co-PE nanofiber air filter. The filtration efficiency of the ZnO@NF hybrid air filter is much higher than that of PP meltblown nonwoven with eliminated electret charge, solving the hidden problem of electret charge dissipation during the protection process. It is demonstrated that these nanofiber hybrid air filters have great application potential in some special areas such as high-temperature and high-humidity environments.

Synthesis and characterization of novel coral spherical bismuth oxide

Bismuth oxide, a widely studied semiconductor material, has been discovered in a variety of forms. Novel coral spherical α-Bi2O3 with a diameter of 2–4 μm was successfully prepared by a simple template-free and surfactant-free hydrothermal method. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission electron scanning microscopy (FESEM), energy dispersive spectroscopy (EDX) and transmission electron microscopy (TEM). The experimental results revealed that the reaction time and the urea concentration could regulate the morphology of Bi2O3, and a possible formation mechanism was proposed based on the results. This study provides a new idea for the morphological synthesis of bismuth oxide.

Fabrication of sea urchin-like Au@SiO2 nanoparticles SERS substrate for the determination of malachite green in tilapia

The quantitative determination of malachite green (MG) is of great importance in aquatic product safety. Although it has been testifying that sea urchin-like gold nanoparticles (SGNPs) have good enhancement effect, the practical application remains challenging for surface-enhanced Raman spectroscopy (SERS) due to poor stability. Here, sea urchin-like Au@SiO2 nanoparticles (SG@SiO2 NPs) is designed and synthesized through a controllable and surfactant-free hydrothermal method to improve its stability. The morphology of SG@SiO2 NPs and the SiO2 shell thickness were adjusted to obtain good SERS performance. The SERS signal intensity was linear for MG, crystal violet (CV) and methylene blue (MB) at 1619 cm−1, 1623 cm−1 and 1627 cm−1 over the concentration range of 10−5-10−9 M, 10−5-10−9 M and 10−5-10−8 M, respectively. The substrate was easily used for MG detection with limit of detection (LOD) as low as 1.5 × 10−9 M. The recovery of MG added to several tilapia fillets samples at different concentrations ranged from 90 % to 110 %. Results indicated that SERS substrate can be used for the determination of trace amounts of MG in tilapia and demonstrated the potential of SG@SiO2 NPs SERS substrate in food analysis fields.

Evaluation of Antimicrobial, Antioxidant, and Cytotoxicity Activities of CuO Nanopellets Synthesized by Surfactant-Free Hydrothermal Method

Abstract Copper oxide nanopellets (CONPs) were produced by hydrothermal strategy. The particles were characterized by distinctive techniques. The synthesized particles were found to have pellet morphology with nonuniform thickness and varying sizes extending between 200 and 550 nm. Studies revealed their microbial nature against both Gram-positive and Gram-negative microscopic organisms, specifically Staphylococcus aureus, Bacillus subtilis, Pseudomonas fluorescens, and Escherichia coli and a plant parasitic pathogen Fusarium oxysporum. Studies demonstrated the antioxidant ability of CONPs at higher concentrations. In this paper, cytotoxicity was measured by blood hemolysis. Anticancer activity of CONPs tested against PC-3, HCT116, A549 and MDA-MB-231 cell lines after 24 hours exhibited IC50 values of 72.27, 144.2, 173.9, and 13.07 μg/mL, respectively. Although these phenomena have been determined in other reports, this report is indeed of significance for CONPs within the particle length of 200–550 nm.

Surfactant-free synthesis of carbon-supported silver (Ag/C) nanobars as an efficient electrocatalyst for alcohol tolerance and oxidation of sodium borohydride in alkaline medium

We have synthesized carbon-supported silver (Ag/C) nanobars by a simple surfactant-free hydrothermal method using glucose as the reducing reagent as well as the source of carbon in Ag/C nanobars. Physicochemical characterization of the materials was performed by X-ray Diffraction (XRD), field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The XRD pattern confirmed the presence of a pure metallic silver phase. No carbon phase was detected, which indicates that the carbon exists mainly in the amorphous form. The electrocatalytic activity of Ag/C in different electrolyte solutions such as 0.5 M NaOH, 0.5 M NaOH + 1 M ethanol (EtOH), 0.5 M NaOH + 1 M ethylene glycol (EG), and 0.5 M NaOH + 0.01 M NaBH4 (sodium borohydride) was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) study. Alcohol tolerance of the catalysts was also established in the presence of ethanol and ethylene glycol. The forward-to-backward current ratio from cyclic voltammetry (CV) study of Ag/C-20 (20 h) in 0.5 M NaOH + 1 M ethanol solution at 100 mV s−1 scan rate is 4.13 times higher compared to that of Ag/C-5 (5 h). Hence, Ag/C-20 is a better candidate for the tolerance of ethanol. In the presence of ethylene glycol (1 M) in 0.5 M NaOH solution, it is obtained that the forward-to-backward current ratio at the same scan rate for Ag/C-20 is lower than that in the presence of ethanol. The durability of the catalyst was studied by chronoamperometry measurement. We studied the electrochemical kinetics of Ag/C catalysts for borohydride oxidation in an alkaline medium. The basic electrochemical results for borohydride oxidation show that Ag/C has very well strength and activity for direct borohydride oxidation in an alkaline medium. The reaction of borohydride oxidation with the contemporaneous BH4−. hydrolysis was noticed at the oxidized silver surface. Among all the synthesized Ag/C catalysts, Ag/C-20 exhibited the best electrocatalytic performance for borohydride oxidation in an alkaline medium. The activation energy and the number of exchange electrons at Ag/C-20 electrode surface for borohydride electro-oxidation were estimated as 57.2 kJ mol−1 and 2.27, respectively.

Synthesis and characterization of Photochromic inkless coating based on WO3-Titania nanocomposite under sun light and solar simulation condition

A highly efficient and surfactant free hydrothermal method is adopted to synthesis tungsten trioxide (WO3) modified Titania (TiO2) composite for direct visible light photochromic applications. The physico chemical characterization of anatase phase formation confirmed by X-Ray diffraction (XRD) and Raman Spectroscopy. The different weight percent amount of tungsten trioxide incorporated into TiO2 nanocomposite have been studied for coloration and bleaching property under in the presence and absence of visible light irradiation. The as prepared composite form of WO3-Titania shows efficient and stable cycle performance up to 15 cycles at various time intervals. The Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) reveals the largely consisting of square and small circular like particles formation and each square and spherical shapes. The photochromic response of the materials increases in the order of WO3/TiO2(0.5:1)> WO3/TiO2 (1:1)> >WO3/TiO2-2(1:2) and in the case of WO3/TiO2-3(1:3) and WO3/TiO2-(1:4) are consumed little more time for coloration and bleaching process. The cycle stability and color transformation have also been studied for efficient WO3/TiO2 (WT-2) sample under direct sun light and in controlled solar simulator reaction condition.

Integrating lithiation and metal dopants in Sb2S3 nanoneedles for energy storage applications

Abstract We present an approach to improve the electrochemical performance by simultaneously integrating metal dopants, lithiation process and controlled morphology by surfactant free hydrothermal method on antimony sulphide Sb2S3 (SS) nano-structures. The powder X-ray diffraction (XRD) study confirmed the formation of SS and metal doped SS with orthorhombic crystalline phase and few secondary phases due to metal dopant impurity. The inclusion of metal dopant manipulates the self-assembly of SS nanorods, leading to a dense packed structure as affirmed from the scanning electron microscopic (SEM) images. Among the added dopants, the lithiated graphene doped Sb2S3 (LGSS) revealed the improved capacitive controlled charge storage mechanism due to the absence of secondary phase impurity, high electrical conductivity σ, good surface adherence and modification thus, forming a closed cocoon-like morphology, and improved electrode-electrolyte contact. The above features raised the specific capacitance CS of LGSS (704 Fg-1) by six times greater than the pure SS (111 Fg-1) anode material at scan rate 10 mVs−1. The significance of lithiation improved the CS value to 323 Fg-1 while integrating with the graphene dopant, the CS value gets doubled.

Constructing magnetic separable BiOBr/MnFe2O4 as efficient Z-scheme nanocomposite for visible light-driven degradation of palm oil mill effluent and inactivation of bacteria

Z-scheme BiOBr/MnFe2O4 nanocomposite was successfully prepared by a surfactant-free hydrothermal method. A series of characterizations revealed that the MnFe2O4 nanoparticles were intimately decorated on the BiOBr nanosheets. The as-prepared BiOBr/MnFe2O4 displayed lower charge recombination and higher hydroxyl radical formation rates compared to BiOBr and MnFe2O4. Visible light photocatalytic experimental results showed that the BiOBr/MnFe2O4 possessed excellent performances towards the palm oil mill effluent degradation and Escherichia coli inactivation. The high photoactivity of BiOBr/MnFe2O4 was attributed to the successful establishment of Z-scheme heterojunction between BiOBr and MnFe2O4. Moreover, the BiOBr/MnFe2O4 can easily be recovered using an external magnet and exhibited good repeatability of photoactivity.

Surface engineering of phosphorus low-doping palladium nanoalloys anchored on the three-dimensional nitrogen-doped graphene for enhancing ethanol electroxidation

The development of superior supporting materials supported surface-engineered metallic nanocrystals is desired and necessary for promoting the electrocatalytic performance of ethanol electroxidation. Additionally, the facile and mild synthetic strategy for advanced electrocatalyst is also urgently needed. Herein, a new catalyst comprising of phosphorus low-doping palladium nanoalloys uniformly anchored on the three-dimensional nitrogen-doped graphene (denoted as Pd-P/3DNGS) is synthesized by a facile one-pot surfactant-free hydrothermal method. Notably, the optimized Pd-P/3DNGS-2 displays an inspiring enhanced electrochemical behavior to ethanol oxidation in terms of catalytic activity, accelerated kinetics, improved long-term stability and boosted anti-poisoning capability, which may be derived from the unique architecture of 3DNGS and the providential electron effect between Pd and P. This work provides a new access for rational design of nano-electrocatalysts.

WO3 nanocrystals decorated Ag3PO4 tetrapods as an efficient visible-light responsive Z-scheme photocatalyst for the enhanced degradation of tetracycline in aqueous medium

A series of WO3/Ag3PO4 composites with varying amounts of WO3 were successfully synthesized by a surfactant-free hydrothermal method and utilized for the photocatalytic degradation of tetracycline (TC) under visible-light irradiation. The formation of a composite structure with the decoration of WO3 nanocrystals on the surface of tetrapod-like Ag3PO4 was clearly seen in the materials characterization. The surface of Ag3PO4 tetrapods was found to be homogenously decorated with WO3 nanocrystals depending on their incremental amount, and an adjacent contact between the coupling materials was resulted that instigated the formation of heterointerfaces in the composites. The visible light absorption of WO3 was significantly improved by its coupling with Ag3PO4 tetrapods. The photoluminescence, electrochemical impedance and photocurrent density analyses indicated the increased life time of the charge carriers with reduced electron-hole pair recombination rate. The photocatalytic activity results had shown that within 24 min of visible light irradiation, the 50 % WO3/Ag3PO4 composite achieved ∼96 % TC degradation with a TC mineralization efficiency of 15.4 %. The enhanced photocatalytic activity of the composites could be attributed to the facile separation of the photoinduced charge carriers through a Z-scheme type charge transfer mechanism at the heterointerface. The scavenger studies specified the primary role of holes and hydroxyl radicals in the oxidative degradation of TC. Additionally, the 50 % WO3/Ag3PO4 composite was effectively reused for four cycles of TC degradation with a gradual loss in its activity, whereas the Ag3PO4 tetrapods suffered a rapid photocorrosion. It validates the superior role of charge transfer process in the photocorrosion inhibition of Ag3PO4 tetrapods.

Enhanced cathode performance of Fe2O3, boron nitride-doped rGO nanosheets for microbial fuel cell applications

Iron(iii) oxide (Fe2O3) and boron nitride (BN)-doped reduced graphene oxide (rGO) nanosheets were prepared successfully using a surfactant-free hydrothermal method.

Facile hydrothermal synthesis of egg-like BiVO4 nanostructures for photocatalytic desulfurization of thiophene under visible light irradiation

Herein, egg-shape bismuth vanadate (BiVO4) nanostructures were prepared by a one-pot and surfactant-free hydrothermal method using ethylenediamine and hydrazine hydrate as novel reactants. The obtained products were identified by FTIR, XRD, SEM, EDS, and DRS analyzes. Finally, the photocatalytic oxidation activity of as-prepared nanostructures on desulfurization of thiophene dissolved in n-hexane as a model light oil was studied. According to the results, the desulfurization rate was 81% after 180 min, which is higher than the other reported morphologies for pure BiVO4. Also, the trapping experiments of radical active species showed that superoxide (⋅O2−) and holes (h+) are the most active species in the process of desulfurization oxidation from thiophene. In addition, the photocatalytic recyclability test indicated that after five times the reuse of the as-synthesized nanostructures does not occur a significant change in the oxidation efficiency.