Search Results (57)

Tomato waste (TW) was employed as a sustainable source for the synthesis of fluorescent carbon dots (CDs) via a microwave-assisted hydrothermal carbonization (Mw-HTC) method, aiming at its valorization. Several amines were used as nitrogen additives to enhance the fluorescence quantum yield (QY) of CDs, and a set of reaction conditions, including additive/TW mass ratio (0.04–0.32), dwell time (15–60 min), and temperature (200–230 °C) of the HTC process, were scrutinized. The structural analysis of the tomato waste carbon dots (TWCDs) was undertaken by FTIR and ¹H NMR techniques, revealing their most relevant features. In solid state, transmission electron microscopy (TEM) analysis showed the presence of nearly spherical nanoparticles with an average lateral size of 8.1 nm. Likewise, the topographical assessment by atomic force microscopy (AFM) also indicated particles’ heights between 3 and 10 nm. Their photophysical properties, revealed by UV–Vis, steady-state, and time-resolved fluorescence spectroscopies, are fully discussed. Higher photoluminescent quantum yields (up to 0.08) were attained when the biomass residues were mixed with organic aliphatic amines during the Mw-HTC process. Emission tunability is a characteristic feature of these CDs, which display an intensity average fluorescence lifetime of 8 ns. The new TWCDs demonstrated good antioxidant properties by the ABTS radical cation method (75% inhibition at TWCDs’ concentration of 5 mg/mL), which proved to be related to the dwell time used in the CDs synthesis. Moreover, the synthesized TWCDs suppressed the growth of Escherichia coli and Staphylococcus aureus at concentrations higher than 2000 μg/mL, encouraging future antibacterial applications. Full article

With the continuous growth of global energy demand and the increasingly severe environmental issues, the extensive utilization of traditional fossil fuels has led to serious energy crises and environmental pollution problems. In this study, a hydrothermal method was employed, and by adding ethanolamine and controlling different temperatures, pink zinc sulfide with zinc vacancies was synthesized. UV-Vis DRS analysis indicated that the sample exhibited significant visible light absorption characteristics within the wavelength range of 500–550 nm. The presence of zinc vacancies was confirmed through XPS. Due to the existence of zinc vacancies, the sample demonstrated excellent photocatalytic hydrogen evolution activity without the need for co-catalysts, with the optimal sample achieving a hydrogen evolution rate of 7631.70 μmol h⁻¹ g⁻¹. Zinc vacancies can provide additional active sites, enhance catalytic efficiency, and promote the separation of photogenerated electrons and holes. Furthermore, the introduction of vacancies effectively reduces the bandgap of the material, significantly broadening its visible light absorption range. This work provides a new approach for enhancing hydrogen evolution in pure ZnS and offers novel strategies for the further design of ZnS-related photocatalysts. Full article

In this work, room-temperature UV-assisted ozone detection was investigated using ZnO nanoplates synthesized via precipitation, ultrasound-, ultrasonic tip-, and microwave-assisted hydrothermal (MAH) methods. X-ray diffraction confirmed the formation of crystalline phases with an ~3.3 eV band gap, independent of the synthesis used. Raman spectroscopy revealed oxygen-related defects. Plate-like morphologies were observed, with the ultrasonic tip-assisted synthesis yielding ~17 nm-thick plates. Electrical measurements showed 10–170 ppb ozone sensitivity under UV. The sample synthesized via the MAH method (ZM) demonstrated superior conductance, with a baseline resistance of ~1.2% for the ultrasound (ZU) sample and less than 50% for the precipitation (ZA) and ultrasonic tip (ZP) samples. Despite the appreciable response in dark mode, the recovery was slow (>>30 min), except for the UV illumination condition, which reduced the recovery response to ~2 min. With top areas of ~0.0122 µm², ZP and ZU showed high specific surface areas (24.75 and 19.37 m²/g, respectively), in contrast to ZM, which exhibited the lowest value (15.32 m²/g) with a top area of ~0.0332 µm² and a thickness of 26.0 nm. The superior performance of ZM was attributed to the larger nanoplate sizes and the lower baseline resistance. The ultrasound method showed the lowest sensitivity due to the higher resistance and the depletion layer effect. The results indicate that the synthesis methods presented herein for the production of reactive ZnO nanoplates using NaOH as a growth-directing agent are reliable, simple, and cost-effective, in addition to being capable of detecting ozone with high sensitivity and reproducibility at concentrations as low as 10 ppb. Full article

Nanoparticles (NPs) have generated significant interest in various fields due to the unique properties that materials exhibit at the nanoscale. This study presents a comparative analysis of copper nanoparticles (Cu-NPs) and cobalt nanoparticles (Co-NPs) synthesized via conventional solvothermal and green hydrothermal synthesis using ethylene glycol and Medicago sativa extract, respectively. The conventional solvothermal synthesis showed higher efficiency for both Cu-NPs and Co-NPs with yields of 32.5% and 26.7%, respectively. Characterization through UV–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) revealed that while solvothermal synthesis produced larger particles (76.5 nm for Cu-NPs, 86.8 nm for Co-NPs), the green hydrothermal method yielded smaller particles (53.8 nm for Cu-NPs, 67.7 nm for Co-NPs) with better control over particle size distribution and spherical morphology, showing minimal agglomeration. UV–vis confirmed metal oxide formation, while FTIR showed complex patterns in NPs (green hydrothermal), indicating plant extract compounds. Antifungal evaluation against Pseudocercospora fijiensis showed complete inhibition at 2000 ppm for both NP types, with no mycelial growth after 30 days. When integrated into chitosan, solvothermal NPs produced rougher surfaces, and scanning electron microscope (SEM) confirmed the presence of copper and cobalt in the nanocomposites. This study provides insights into the synthesis of nanoparticles using an environmentally friendly process and their microbiological applications for future use in organic agriculture. Full article

The design and preparation of advanced hybrid nanofibers with controllable microstructures will be interesting because of their potential high-efficiency applications in the environmental and energy domains. In this paper, a simple and efficient strategy was developed for preparing hybrid nanofibers of zinc oxide–molybdenum disulfide (ZnO–MoS₂) grown on polyimide (PI) nanofibers by combining electrospinning, a high-pressure hydrothermal process, and in situ growth. Unlike simple composite nanoparticles, the structure is shown in PI–ZnO to be like the skeleton of a tree for the growth of MoS₂ “leaves” as macro-materials with controlled microstructures. The surface morphology, structure, composition, and photocatalytic properties of these structures were characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV–vis spectroscopy. The ultra high-volume fraction of MoS₂ can be grown on the brush-shaped PI–ZnO. Decorating ZnO with nanosheets of MoS₂ (a transition metal dichalcogenide with a relatively narrow band gap) is a promising way to increase the photocatalytic activity of ZnO. The hybrid nanofibers exhibited high photocatalytic properties, which decomposed about 92% of the methylene blue in 90 min under visible light irradiation. The combination of MoS₂ and ZnO with more abundant surface-active sites significantly increases the spectral absorption range, promotes the separation and migration of carriers, and improves the photocatalytic characteristics. Full article

This study presents a comparative analysis of anodization and hydrothermal techniques for synthesizing TiO₂ nanotubes directly on titanium foil. It emphasizes its advantages as a substrate due to its superior conductivity and efficient charge transfer. Optimized synthesis conditions enable a thorough evaluation of the resulting nanotubes’ morphology, structure, and optical properties, ultimately assessing their photoelectrochemical and photocatalytic performances. Scanning electron microscopy (SEM) reveals differences in tube diameter and organization. An X-ray diffraction (XRD) analysis shows a dominant anatase (101) crystal phase in both methods, with the hydrothermally synthesized nanotubes exhibiting a biphase structure after annealing at 500 °C. UV–Vis and photoluminescence analyses indicate slight variations in band gaps (around 0.02 eV) and recombination rates. The anodized TiO₂ nanotubes, exhibiting superior hydrophilicity and order, demonstrate significantly enhanced photocatalytic degradation of a model pollutant, amido black (80 vs. 78%), and achieve a 0.1% higher photoconversion efficiency compared to the hydrothermally synthesized tubes. This study underscores the potential advantages of the anodization method for photocatalytic applications, particularly by demonstrating the efficacy of direct TiO₂ nanotube growth on titanium foil for efficient photocatalysis. Full article

Two forms of flower-like ZnO nanostructures were synthesized using hydrothermal methods at various growth times/temperatures and zinc precursors. The morphology, structure, chemical composition, and optical properties of these ZnO nanoflowers were studied using a scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy, and UV–Vis spectroscopy. The SEM images revealed two forms of flower-like nanostructures, namely lotus- and tulip-like flower ZnO nanostructures. The XPS analysis revealed the oxidation state of the Zn and O elements, as well as the presence of OH groups on the surface of the lotus-like flower ZnO nanostructure. The XRD results revealed less crystallinity of the lotus-like ZnO nanoflowers (NFs) compared with the tulip-like ZnO NFs. The XRD results revealed the presence of Zn (OH)₂ in the ZnO NFs. The Raman results confirmed less crystallinity of the lotus-like ZnO NFs. The estimated optical bandgap was 2.92 and 3.0 eV for the tulip- and lotus-like ZnO NFs, respectively. The tulip-like ZnO NFs showed superior photocatalytic degradation of methylene blue dye, verified via UV–Vis radiation, compared with the lotus-like ZnO NFs, which show the impact of the structure defects and OH- impurities on the photocatalytic performance of ZnO nanoflowers. Full article

BiOBr with different preferred growth orientation facets would show a different photocatalytic performance. When decorated in situ with metallic Bi nanoparticles, Bi/BiOBr would commonly display an enhanced photocatalytic performance. In this paper, the BiOBr nanoplates with preferred growth orientation (102) facet and (110) facet were first synthesized using a hydrothermal method. Then, some metallic Bi nanoparticles were modified in situ onto the (110)BiOBr nanoplates, which was expected to show a much more enhanced photocatalytic performance. All samples were characterized using XRD, FE-SEM, TEM, N₂ adsorption–desorption, UV–vis and XPS. FE-SEM and TEM images showed that the grain size of the metallic Bi particles was about 5 nm to 10 nm. UV–vis spectra showed that, after some metallic Bi nanoparticles were modified on (110)BiOBr nanoplates, the light absorbance in the visible light region at 400–700 nm became stronger and their optical band gap became larger. N₂ adsorption–desorption tests showed that the Bi(x)/(110)BiOBr nanosheets possessed larger specific surface areas than that of the (102)BiOBr and (110)BiOBr nanoplates. The XPS results showed that Bi(x)/(110)BiOBr contained more oxygen vacancies and a more negative value of the conduction band minimum. The photocatalytic performance of (102)BiOBr, (110)BiOBr and Bi(x)/(110)BiOBr were tested in the photocatalytic degradation of rhodamine B under visible light irradiation for 2 h; their photocatalytic efficiency was 45%, 75% and 80%, respectively. In comparison to (102)BiOBr, (110)BiOBr exhibited much higher photocatalytic activity, while for Bi(x)/(110)BiOBr, despite the surface Plasmon resonance effect, a larger specific surface area and more oxygen vacancies, the enhancement of the efficiency was limited, which might have resulted from the larger optical band gap. Full article

This study aims to improve the photocatalytic properties of titanium dioxide nanorods (TNRs) and other related nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) by modifying them with silver nanoparticles (AgNPs). This preparation is carried out using a two-step method: sol–gel dip-coating deposition combined with hydrothermal crystal growth. Further modification with AgNPs was achieved through the photoreduction of Ag⁺ ions under UV illumination. The investigation explores the impact of different growth factors on the morphological development of TiO₂ nanostructures by modulating (i) the chemical composition, the water:acid ratio, (ii) the precursor concentration involved in the hydrothermal process, and (iii) the duration of the hydrothermal reaction. Morphological characteristics, including the length, diameter, and nanorod density of the nanostructures, were analyzed using scanning electron microscope (SEM). The chemical states were determined through use of the X-ray photoelectron spectroscopy (XPS) technique, while phase composition and crystalline structure analysis was performed using the Grazing Incidence X-ray Diffraction (GIXRD) method. The results indicate that various nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) can be obtained by modifying these parameters. The photocatalytic efficiency of these nanostructures and Ag-coated nanostructures was assessed by measuring the degradation of the organic dye rhodamine B (RhB) under both ultraviolet (UV) irradiation and visible light. The results clearly show that UV light causes the RhB solution to lose its color, whereas under visible light RhB changes into rhodamine 110, indicating a successful photocatalytic transformation. The nanoball-like structures’ modification with the active metal silver (TNRs 4 Ag) exhibited high photocatalytic efficiency under both ultraviolet (UV) and visible light for different chemical composition parameters. The nanorod structure (TNRs 2 Ag) is more efficient under UV, but under visible-light photocatalyst, the TNRs 6 Ag (dense nanorods) sample is more effective. Full article

The manipulation of trap states plays a crucial role in the development of efficient photocatalysts. An ultrathin-shelled Zn-AgIn₅S₈/ZnS quantum dots (QDs) photocatalyst was synthesized via in situ growth using a low-temperature hydrothermal method. The optical properties of the samples coated with ZnS shell were studied vis UV-vis absorption and fluorescence spectra. The ultrathin ZnS shell plays an important role in the Zn-AgIn₅S₈/ZnS core–shell heterostructure photocatalytic water splitting system, which could reduce surface defects, prolong the carrier lifetime and improve the photo-generated electron–hole pair separation effectively, resulting in the improved photocatalytic efficiency and enhanced stability of the catalyst. The results provide an effective guideline for shell thickness design in future constructions of the core–shell heterostructure photocatalyst. Full article

A composite material composed of anodized aluminum oxide (AAO), carbon (C), and magnesium oxide (MgO) was developed for CO₂ capture applications. Inspired by the bryophyte organism, the AAO/C/MgO composite mirrors two primary features of these species—(1) morphological characteristics and (2) elemental composition—specifically carbon, oxygen, and magnesium. The synthesis process involved two sequential steps: electroanodization of aluminum foil followed by a hydrothermal method using a mixture of glucose and magnesium chloride (MgCl₂). The concentration of MgCl₂ was systematically varied as the sole experimental variable across five levels—1 mM, 2 mM, 3 mM, 4 mM, and 5 mM—to investigate the impact of MgO formation on the samples’ chemical and physical properties, and consequently, their CO₂ capture efficiency. Thus, scanning electron microscopy analysis revealed the AAO substrate’s porous structure, with pore diameters measuring 250 ± 30 nm. The growth of MgO on the AAO substrate resulted in spherical structures, whose diameter expanded from 15 nm ± 3 nm to 1000 nm ± 250 nm with increasing MgCl₂ concentration from the minor to major concentrations explored, respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that carbon serves as a linking agent between AAO and MgO within the composite. Notably, the composite synthesized with a 4 mM MgCl₂ concentration exhibited the highest CO₂ capture efficiency, as determined by UV-Vis absorbance studies using a sodium carbonate solution as the CO₂ source. This efficiency was quantified with a ‘k’ constant of 0.10531, significantly higher than those of other studied samples. The superior performance of the 4 mM MgCl₂ sample in CO₂ capture is likely due to the optimal density of MgO structures formed on the sample’s surface, enhancing its adsorptive capabilities as suggested by the XPS results. Full article

Metal–organic frameworks (MOFs) are hybrid materials that are being explored as active electrode materials in energy storage devices, such as rechargeable batteries and supercapacitors (SCs), due to their high surface area, controllable chemical composition, and periodic ordering. However, the facile and controlled synthesis of a pure MOF phase without impurities or without going through a complicated purification process (that also reduces the yield) are challenges that must be resolved for their potential industrial applications. Moreover, various oxide formations of the Ni during Ni-MOF synthesis also represent an issue that affects the purity and performance. To resolve these issues, we report the controlled synthesis of nickel-based metal–organic frameworks (NiMOFs) by optimizing different growth parameters during hydrothermal synthesis and by utilizing nickel chloride as metal salt and H₂bdt as the organic ligand, in a ratio of 1:1 at 150 °C. Furthermore, the synthesis was optimized by introducing a magnetic stirring stage, and the reaction temperature varied across 100, 150, and 200 °C to achieve the optimized growth of the NiMOFs crystal. The rarely used H₂bdt ligand for Ni-MOF synthesis and the introduction of the ultrasonication stage before putting it in the furnace led to the formation of a pure phase without impurities and oxide formation. The synthesized materials were further characterized by powder X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), and UV–vis spectroscopy. The SEM images exhibited the formation of nano NiMOFs having a rectangular prism shape. The average size was 126.25 nm, 176.0 nm, and 268.4 nm for the samples (1:1)s synthesized at 100 °C, 150 °C, and 200 °C, respectively. The electrochemical performances were examined in a three-electrode configuration, in a wide potential window from −0.4 V to 0.55 V, and an electrolyte concentration of 2M KOH was maintained for each measurement. The charge–discharge galvanostatic measurement results in specific capacitances of 606.62 F/g, 307.33 F/g, and 287.42 F/g at a current density of 1 A/g for the synthesized materials at 100 °C, 150 °C, and 200 °C, respectively. Full article

The utilization of lithium slag (LS), a solid waste generated during the production of lithium carbonate, poses challenges due to its high sulfur content. This study presents a novel approach to enhancing the value of LS by employing alkali fusion and hydrothermal synthesis techniques to produce zeolite A at low temperatures. The synthesis of high-purity and crystalline lithium-slag-based zeolite A (LSZ) at 60 °C is reported for the first time in this research. The phase, morphology, particle size, and structure of LSZ were characterized by XRD, SEM, TEM, N₂ adsorption, and UV Raman spectroscopy, respectively. High-purity and crystalline zeolite A was successfully obtained under hydrothermal conditions of 60 °C, an NaOH concentration of 2.0 mol/L, and a hydrothermal time of 8 h. The samples synthesized at 60 °C exhibited better controllability and almost no byproduct of sodalite occurred compared to zeolite A synthesized at room temperature or conventional temperature (approximately 90 °C). Additionally, the growth mechanism of LSZ was elucidated, challenging the traditional understanding of utilization of lithium and enabling the synthesis of various zeolites at lower temperatures. Full article

A multi-step procedure was effectively employed to synthesize innovative three-dimensional (3D) heterostructures encompassing sodium titanate (Na₂Ti₃O₇) nanowire cores, an intermediate resorcinol–formaldehyde (RF) layer, and outer silver (Ag) nanoparticle sheaths, referred to as Na₂Ti₃O₇@RF@Ag heterostructures. Initially, a one-step hydrothermal technique facilitated the direct growth of single-crystal Na₂Ti₃O₇ nanowires onto a flexible Ti foil. Subsequently, a two-step wet chemical process facilitated the sequential deposition of an RF layer and Ag nanoparticles onto the Na₂Ti₃O₇ nanowires at a low reaction temperature. Optimal concentrations of silver nitrate and L-ascorbic acid can lead to the cultivation of Na₂Ti₃O₇@RF@Ag heterostructures exhibiting heightened surface-enhanced Raman scattering (SERS), which is particularly beneficial for the detection of rhodamine B (RhB) molecules. This phenomenon can be ascribed to the distinctive geometry of the Na₂Ti₃O₇@RF@Ag heterostructures, which offer an increased number of hot spots and surface-active sites, thereby showcasing notable SERS enhancement, commendable reproducibility, and enduring stability over the long term. Furthermore, the Na₂Ti₃O₇@RF@Ag heterostructures demonstrate remarkable follow-up as first-order chemical kinetic and recyclable photocatalysts for the photodecomposition of an RhB solution under UV light irradiation. This result can be attributed to the enhanced inhibition of electron–hole pair recombination and increased surface-active sites. Full article

Given the growing concern over antibiotic resistance, there is an urgent need to explore alternative antibacterial strategies. Metal oxide nanostructures have emerged as a promising option, and in particular, zinc oxide (ZnO) nanostructures have demonstrated strong antifungal and antibacterial properties. This study focuses on ZnO nanowires (ZnO NWs) and their potential as antibacterial agents against Pseudomonas putida, a Gram-negative bacterium. The objective is to investigate the antibacterial mechanisms and assess their efficiency. The unique shape of ZnO NWs, obtained through hydrothermal growth, may rupture bacterial cells and inhibit bacterial growth. In addition to their morphology, the release of Zn²⁺ ions from ZnO NWs may contribute to their antibacterial properties. These ions have the potential to disrupt the bacterial cell membrane, further impeding bacterial growth. Moreover, ZnO nanostructures exhibit excellent photocatalytic properties under UV light, enhancing their antibacterial effects. Overall, this study highlights the potential of hydrothermally synthesized ZnO NWs in inhibiting P. putida growth and provides valuable insights into their antibacterial mechanisms. The findings suggest that ZnO nanostructures have the potential to be effective antibacterial agents and could be utilized in various settings to fight microbial infections and maintain hygiene. Full article