One-step Hydrothermal Process Research Articles

Facile one-step synthesis of in situ WO3@Gr nanorods as an efficient material for antimicrobial and decoloration applications

This work examined the synthesis, antibacterial activity, and decolourisation of WO3@Graphene nanorods (WO3@Gr NR). WO3@Gr NR nanocomposite was in situ produced via a facile one-step hydrothermal process employing sodium tungstate dihydrate and exfoliated graphene as precursors. The resulted NR exhibited an average diameter of 13 nm, a large specific surface area of 53.3 m2 g−1, and a bimodal pore size distribution with an average pore size of 5.5 nm. The optical bandgap is extrapolated to be 2.75 eV. Graphene was shown to be responsible for the sample’s elaborate visible-light absorption, which improved adsorption and the ability to harvest visible light. WO3@Gr NR are more efficient against E. coli than S. aureus, killing up to 52% and 39% of cells, respectively, after two hours of treatment. When used in conjunction with invisible light, the NR killed E. coli and S. aureus by 78 and 62%, respectively. The bactericidal activity of photoinduced WO3@Gr NR was evaluated against P. aerugunosa, E. faecalis, E. coli, and S. aureus. The photocatalytic constant rates of organic dye methylene blue (MB) were determined to be 0.01 min−1. An IC50 (50% cell growth inhibition) value of 97 (μg ml−1) was determined for the nanocomposite against human liver cancer cell lines (HepG2). Our findings suggest that this nanorod may be utilised to degrade bacteria and organic colours in wastewater simultaneously while posing no risk to human health.

Synergistic boost in Fe3O4 anode performance for li-ion batteries via Zn and Cu double doping and multi-walled carbon nanotube composite integration

In this study, a novel nanocomposite material comprising pure Fe3O4 (FO), doped Zn0.5Cu0.5Fe2O4-3 (ZCFO-3), and Zn0.5Cu0.5Fe2O4-3@ Multi-walled carbon nanotube (ZCFO-3@MWCNT) nanocomposite material is carefully prepared using a simple one-step hydrothermal process. Comprehensive surface and morphological analysis are conducted using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and High-resolution transmission electron microscopy (HRTEM), while compositional studies are investigated through Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical performance is fully analyzed through Cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), rate capability tests, discharge/charge capacity, and cyclic stability evaluations. Among these three nanomaterials, ZCFO-3@MWCNT nanocomposite at 100 mA g−1 current density reveals the best performance, with a discharge capacity of 1974 mAh g–1, ZCFO-3 and FO reveal 1340 mAh g–1 and 1317 mAh g–1 respectively. After 800 cycles at 500 mA g−1 current density, ZCFO-3@MWCNT stays strong with a discharge capacity of 646 mAh g–1, while ZCFO-3 manages only 362 mAh g–1 and FO only 111 mAh g–1. After 1200 cycles at 500 mA g−1, the nanocomposite still delivers 518 mAh g–1. This study suggests that ZCFO-3@MWCNT could be a promising anode material for lithium-ion batteries.

Hydrochloric acid induced microstructural reconfiguration from bulk α-NiS microspheres to porous/hollow NiSx microspheres for high-performance hybrid supercapacitor

Nickel sulfide is well known as a promising energy storage/conversion material considering its high redox activity, high theoretical capacity, easy preparation, and rich phase structures. Unfortunately, nickel sulfide prepared by conventional methods usually exhibits a bulk structure, which significantly limited its charge storage. To overcome this obstacle, we developed a facile hydrochloric acid-induced structure reconstruction strategy to fabricate porous and hollow structured nickel sulfide via a one-step hydrothermal process. We found that nickel sulfide undergoes de-nickelization in the presence of 3 M hydrochloric acid, resulting in the transformation from bulk structure to porous/hollow structures, accompanied by a transition from nickel-rich phase (α-NiS) to nickel-deficient phase (Ni3S4 or NiS2). The electrochemical results demonstrated the obviously improved specific capacity of nickel sulfide after structure reconstruction, among which the porous NS-HCl-1 h (α-NiS/Ni3S4) microspheres delivers the highest specific capacity (204.4 mAh g-1 at 1 A g-1) and show a rate performance about 50.0% from 1 to 20 A g-1. The assembled NS-HCl-1 h//rGO supercapacitor delivers a maximum energy density of 47.1 Wh kg-1 at a power density of 803.6 W kg-1, and maintain a capacity retention rate about 88.6% after 10,000 cycles. This work provides a novel method and contributes new insight for the structural reconstruction of transition metal sulfides (TMSs).

Constructing hierarchical CuS hollow spheres as efficient anode for aqueous zinc-ion batteries

In recent years, aqueous zinc-ion batteries (ZIBs) have emerged as a prominent research topic due to their inherent safety attributes, relatively low cost, and comparatively higher energy density. However, the challenges associated with the zinc metal anode in the form of dendrite formation, hydrogen evolution, and severe side reactions have proven to be particularly vexing. Thus, it is imperative to investigate novel intercalation-type anode materials for ZIBs that exhibit exceptional structural properties and appropriate redox potentials based on conversion mechanisms. In this work, through adding polyvinylpyrrolidone (PVP) surfactant to precursors and tailoring reaction time, hierarchical CuS hollow spheres are successfully constructed by a facile one-step hydrothermal process. When applied as an anode in ZIBs, the hollow hierarchical CuS with large surface area can effectively reduce the transport distance of electrons and Zn2+ and alleviate volume expansion during the insertion/extraction of Zn2+. The hierarchical CuS hollow spheres prepared over 8 h (CuS-8) exhibit a specific capacity of 126 mAh/g and long-term cycle life (1500 cycles) at a current density of 3 A/g. In addition, CuS-8//MnO2@CNTs full-cell shows a capacity retention of 117 mAh/g after 300 cycles at 1 A/g current density, which proves the advantage of hierarchical CuS hollow spheres in serving as an efficient and durable anode material for ZIBs.

High-efficiency electromagnetic shielding based on multipolar effect in RGO/MXene aerogels decorated with ordered Fe3O4 cluster

With the widespread use of digital systems and electronic communication devices, there is an urgent need to develop lightweight and efficient electromagnetic interference (EMI) shielding materials to address the growing problem of radiation pollution. RGO/MXene/Fe3O4 aerogels were successfully designed and synthesised using a one-step hydrothermal process induced by an external magnetic field in this study. Reduced graphene RGO, MXene nanosheets and Fe3O4 nanoparticles were suitably assembled together to achieve the combined advantages. The aerogels exhibited large specific surface area and hierarchical porosity. The material not only achieves an effective synergy between magnetic loss and dielectric loss, but also exhibits satisfactory EMI shielding performance. Magnetic field induced RGO/MXene/Fe3O4 aerogels (MIRMFE-2) exhibits the best EMI shielding performance with an average SET value of 76.9 dB. The excellent shielding performance of MIRMFE is attributed to both its 3D porous structure and the high dielectric loss due to multiple polarization relaxation, magnetic loss due to eddy current loss and natural resonance. The synthesis of MIRMFE provides an effective method for, designing high-performance and lightweight EMI shielding materials.

The Simultaneous Detection of Dopamine and Uric Acid In Vivo Based on a 3D Reduced Graphene Oxide-MXene Composite Electrode.

Dopamine (DA) and uric acid (UA) are essential for many physiological processes in the human body. Abnormal levels of DA and UA can lead to multiple diseases, such as Parkinson's disease and gout. In this work, a three-dimensional reduced graphene oxide-MXene (3D rGO-Ti3C2) composite electrode was prepared using a simple one-step hydrothermal reduction process, which could separate the oxidation potentials of DA and UA, enabling the simultaneous detection of DA and UA. The 3D rGO-Ti3C2 electrode exhibited excellent electrocatalytic activity towards both DA and UA. In 0.01 M PBS solution, the linear range of DA was 0.5-500 µM with a sensitivity of 0.74 µA·µM-1·cm-2 and a detection limit of 0.056 µM (S/N = 3), while the linear range of UA was 0.5-60 µM and 80-450 µM, with sensitivity of 2.96 and 0.81 µA·µM-1·cm-2, respectively, and a detection limit of 0.086 µM (S/N = 3). In 10% fetal bovine serum (FBS) solution, the linear range of DA was 0.5-500 µM with a sensitivity of 0.41 µA·µM-1·cm-2 and a detection limit of 0.091 µM (S/N = 3). The linear range of UA was 2-500 µM with a sensitivity of 0.11 µA·µM-1·cm-2 and a detection limit of 0.6 µM (S/N = 3). The modified electrode exhibited advantages such as high sensitivity, a strong anti-interference capability, and good repeatability. Furthermore, the modified electrode was successfully used for DA measurement in vivo. This could present a simple reliable route for neurotransmitter detection in neuroscience.

ZnO nanoflakes decorated graphene oxide acting as an efficient platform for precise detection of uric acid via rhodamine fluorescence quenching

Herein, we report 2D based nanocomposite of metallic architectures as probe material for the detection of uric acid (UA). In brief, ZnO nanoflakes are grown on the basal surface of graphene oxide (GO/ZnO-NF), which eventually influences the fluorescence intensity of Rhodamine B (Rh) with varying concentrations of UA. This nanocomposite was synthesized at a low cost with optimized one-step hydrothermal process. It was observed that the transfer of electrons between GO/ZnO-NF and Rh resulted in the oxidation of UA, corroborating significant quenching of fluorescence intensity of Rh. This conjecture was later applied for the quantitative analysis of UA, affirming gradual quenching of fluorescence as a factor of UA concentration in the range of (50 µM – 8*103 µM) with a detection limit of 5.4 µM. Our fluorescent-based sensor was effective for the serum sample without losing its sensitivity, selectivity and analytical performance. Based on these findings, we anticipate that this simple, non-enzymatic, robust, inexpensive method can be a useful tool for diagnostics and biomedical applications.

Acid modification on ZnIn2S4 with sulfur vacancy for highly efficient photocatalytic reduction of Cr(VI)

Anion vacancies caused by acid treatment over photocatalysts have significant influences on photocatalytic processes. In this study, the ZnIn2S4 (denoted as ZIS) nanoflower samples were synthesized using a one-step hydrothermal process and then impregnated with different amounts of nitric acid solutions. The gathered samples were characterized using XRD, SEM, XPS, BET, and EPR, and their photocatalytic reduction activity of Cr(VI) was also studied. Owing to defect structures, the removal of Cr(VI) of sulfur-rich vacancies ZIS-NA-3 reached nearly 100% within 90 min under simulated solar light, which was about 3 times greater than that of the original ZIS. In summary, this study confirmed that nitric acid treatment could form a defect state on the surface of catalysts, enhancing the light absorption range and improving the electron-hole pair separation efficiency. Furthermore, the stability and recycling of the ZIS-NA-3 catalysts were evaluated. This work offered a simple surface modification technique for constructing high-activity photocatalysts so as to achieve the purpose of removal from polluted wastewater containing Cr(VI).

Sugarcane bagasse valorization through integrated process for single cell oil, sulfonated carbon-based catalyst and biodiesel co-production

This study demonstrates the conversion of sugarcane bagasse (SB) into single cell oil (SCO), sulfonated carbon-based catalyst and biodiesel; this process aligns with waste-to-energy and circular bioeconomy concepts. SB was treated with dilute sulfuric acid to achieve SB hydrolysate (SBH) and SB solid residue (SBS). Candida tropicalis KKU-NP1, a newly isolated yeast, accumulated SCO content of 26.5 % from undetoxified SBH medium. A novel sulfonated carbon-based catalyst (SBS@SC) was generated from SBS by a one-step hydrothermal sulfonation process. It showed significant catalytic activity for the conversion of SCO-rich KKU-NP1 wet cell into biodiesel (FAME) under direct transesterification optimal conditions, with a FAME conversion yield of 90.1 %. Based on FAME profile, most of the estimated physicochemical and fuel properties of FAME were within the limits of ASTMD6751 and EN 14214 for biodiesel standards. For integrated process the final production of about 12.0 g SCO, 606.3 g SBS@SC catalyst and 10.8 g biodiesel from 1000 g raw SB were achieved.This study highlights the utilization of SB as a low-cost feedstock for producing multiple value-added products, emphasizing the advantages of waste utilization by integrated biorefinery concept, yielding practically no waste by-products over the whole production process.

Simultaneous synthesis of carbon quantum dots and porous carbon using one step hydrothermal method for supercapacitor applications

The present work reports a one-step hydrothermal carbonization process used to simultaneously produce carbon quantum dots and porous carbon. The synthesized materials were characterized by using a Fourier transform infrared spectrometer (FT-IR) to study the chemical interactions, the optical properties were studied with the help of UV-visible absorption spectroscopy, and the morphology analysis of CQDs and porous carbon was examined using FESEM, in which spherical morphology confirms the formation of CQDs, while XRD confirms the amorphous nature of the porous carbon. The application of CQDs and porous materials is evaluated as a supercapacitor material by using the cyclic voltammetry technique. The specific capacitance of porous carbon was 161.33 Fg−1 at 0.01mVs−1 scan rate. This makes CQDs and porous carbon a promising candidate for applications in energy storage devices such as supercapacitors.

Samarium doped carbon dots for near-infrared photo-therapy

Photo-assisted tumor therapy, encompassing photodynamic therapy (PDT) and photothermal therapy (PTT), has garnered considerable attention as a promising approach for tumor treatment owing to its stimuli-responsive nature and noninvasive characteristics. Carbon dots (CDs) have recently emerged as a novel type of nanomaterial with great potential in the field of anticancer therapy. However, the development of multifunctional CDs nano-platforms that integrate multiple therapeutic performance remains a challenge, especially in near-infrared (NIR) window. In this study, we synthesized samarium-doped carbon dots (Sm/CDs) via a one-step hydrothermal process for fluorescence imaging guided PTT/PDT in NIR-II window. Sm/CDs demonstrated remarkable absorption and emission properties in the NIR region, enabling efficient generation of heat energy, superoxide (•O2–) and hydroxyl radicals (•OH) under NIR irradiation. The photothermal conversion efficiencies of Sm/CDs reached up to 34.12 % and 24.38 % when exposed to 808 nm and 1060 nm wavelengths, respectively. Moreover, long-term toxicity experiments conducted in vivo as well as fluorescence experiments confirmed the potential of such functional CDs for fluorescence imaging and excellent biocompatibility. It is noteworthy that the tumor is nearly eradicated when exposed to either 808 nm or 1060 nm, demonstrating significant efficacy in both scenarios. This study provides a multifunctional CDs nano-platform that offers a promising bimodal phototherapeutic strategy to enhance the synergistic treatment of tumors through PDT and PTT.

Rational construction of bromine doped rose-like Bi2O2CO3 microspheres for enhanced visible-light-driven degradation

Optimizing the charge distribution of photocatalysts through halide ion doping has been recognized as an effective approach to enhance photocatalytic activity. Herein, the bromine doped rose-like Bi2O2CO3 microspheres were prepared through a one-step hydrothermal process. The visible diffuse reflectance spectroscopy (DRS) revealed that the bromine doping led to a narrowed band gap of Bi2O2CO3 and optimized band structure. In addition, bromine doping can achieve efficient separation of photogenerated electron-hole pairs. Thus, the photodegradation efficiency of the antibiotic oxytetracycline (OTC) and the dye rhodamine B (RhB) were significantly improved over bromine doped rose-like Bi2O2CO3 microspheres, which is 63.5% for OTC and 97.5% for RhB under visible light irradiation. The kinetic constants of the Br-Bi2O2CO3-2 material are 27.3 times for OTC and 156.2 times for RhB compared with those of pristine Bi2O2CO3. The enhanced photocatalytic performance can be attributed to the optimized carrier separation ability and broadened range of light response. The possible intermediates were identified by mass spectrometry (MS), and the degradation pathways were determined. A gradual decrease in toxicity during degradation was found by the Toxicity Estimation Software Tool (T.E.S.T). This work provides a new idea to construct high-performance photocatalysts for organic pollutants degradation.

Investigating the synergistic effects of NbCo-oxide composite electrodes in supercapacitor and water splitting applications via hydrothermal synthesis

A self-supported, binderless NbCo-oxide composite electrode was synthesized directly on a nickel foam (NF) substrate through a simple one-step hydrothermal process and utilized for energy storage and conversion applications. The optimized NbCo-oxide electrode displayed impressive energy storage capabilities, boasting an areal capacitance of 10.1 F/cm2 (equivalent to 9.10C/cm2), an energy density of 0.57 mWh/cm2, and a power density of 6.75 mW/cm2 at a 15 mA/cm2 current density. Furthermore, this electrode exhibited notable bifunctional activity, with low overpotentials of 217 mV for the hydrogen evolution reaction (HER) and 250 mV for the oxygen evolution reaction (OER) at a 10 mA/cm2 current density. The distinctive morphology, featuring rectangular blocks and plate-like microstructures, provided numerous exposed electro-active sites, facilitating efficient charge transfer, and enhancing overall electrochemical performance. The sturdy self-supporting structure on the NF substrate ensures remarkable stability, highlighting NbCo-composite materials' potential for energy storage and conversion.

Rational construction of defect-enriched α-Fe2O3/Bi2S3 composites for high-effective photocatalytic degradation of p-nitrophenol

Herein, the high-activity α-Fe2O3 (PSNF) was obtained first, and defect-enriched PSNF/Bi2S3 composites were prepared via a one-step hydrothermal process. The obtained PSNF had abundant oxygen vacancies (OV) and low bandgap energy, showing enhanced visible-light catalytic activity. Compared with PSNF and Bi2S3, the PSNF/Bi2S3 composites presented superior adsorption capacity and photocatalytic degradation activity for p-nitrophenol (p-NP). The p-NP degradation process followed the BMG model. The PSNF/Bi2S3-2 exhibited the highest photocatalytic activity, as 90.5% of the p-NP was degraded within 30 min. A tight heterojunction was formed between PSNF and Bi2S3 by the S–O bond, which effectively inhibited the recombination of photoproduced carriers and promoted the generation of OV defects. Under the synergistic effect of OV detects, photo-Fenton, and heterojunction, the generation of active species was promoted in the composite degradation system, thereby resulting in the rapid degradation of p-NP.

Engineering nanoscale nickel sulfide by a “reduction-restriction” strategy for high performance hybrid supercapacitor

Nanostructured materials usually exhibit superior electrical properties than bulk-structured materials, but conventional preparation methods are prone to produce bulk-structured nickel sulfide, leading to unsatisfactory electrochemical properties. In this work, we proposed a novel “reduction-restriction” strategy to synthesize nanoscale β-NiS via a one-step hydrothermal process. We found the introduction of strong reductants accelerates the crystal nucleation and growth of nickel sulfide, and limits further crystal growth, thus generating nanoparticles. Benefiting from the advantages brought by nanoscale effect, both of NS-15mLNaBH4 (β-NiS nanoparticles) and NS-100µLN2H4 (β-NiS nanoparticles) electrodes deliver an outstanding specific capacity of 254.1 mAh g−1 and 256.9 mAh g−1 at 1 A g−1, respectively, obviously higher than bulk-structured NS-0 (β-NiS/Ni3S4) electrode (171.0 mAh g−1 at 1 A g−1). The assembled NS-100µLN2H4//rGO hybrid supercapacitor shows a high energy density of 69.3 Wh kg−1 at a power density of 399.8 W kg−1. This work offers a novel mechanism and approach for fabrication of nanoscale metal sulfides from the perspective of controlling crystal nucleation and growth.

Synthesis of SrTiO3-TiO2-CaTiO3/Cu2O composite for stable and efficient H2 generation in deionized water and river water

Herein, the SrTiO3-TiO2-CaTiO3/Cu2O quaternary composite has been designed and prepared via one-step hydrothermal process followed by a NaBH4 reduction treatment. By comparing the H2 production rate (HPR) of Sr-Ti-Ca/Cu samples prepared by different Cu sources, it is found that Sr-Ti-Ca/Cu has the best H2 production performance when CuCl2 is as Cu source. As expected, the highest HPR of Sr-Ti-Ca/Cu sample is up to 5.088 mmol g−1 h−1, which is 195.7 times as higher as that of the Sr-Ti-Ca sample (0.026 mmol g−1 h−1) under the same conditions. Moreover, the HPR reached 0.692, 0.530 and 0.647 mmol g−1 h−1 in tap water, lake water and river water, indicating that the photocatalyst has high practicability in natural water sources. In addition, the experiment of the tap water composition effect on H2 production performance shows that NO3− and SO42− ions have great negative influence on the HPR. Compared with Sr-Ti-Ca, the light absorption of Sr-Ti-Ca/Cu extends over the entire visible region, the interface resistance decreases, and the photocurrent density increases. These results suggest that the well-designed dual p-n heterojunctions and dual type-II heterojunctions in Sr-Ti-Ca/Cu sample can enhance the light absorption in the ultraviolet region and realize the rapid separation and migration of photogenerated charge, thereby accelerating the production of H2. This work shows the strong advantage and potential of non-precious metal efficient photocatalyst system for producing H2 from deionized water and natural fresh water.

Electrical and structural engineering of nanoflower-like NiMn-layered double hydroxide by V modulation for high-performance hybrid supercapacitors

This work produced V-doped NiMn-layered double hydroxide(V-NiMnLDH) composite positive electrode material directly on nickel foam using a simple one-step hydrothermal synthesis process. The composite's 3D nanoflower-like design increased spatial utilization, surface area, and active sites for Faradaic redox reactions. The composite material has a specific capacitance of 1551 F g−1 at 1 A g−1 and 85.6 % capacitance retention at 10 A g−1, demonstrating exceptional cycle stability. In addition, we combined V-NiMnLDH with commercial activated carbon to create an asymmetric supercapacitor (ASC) with 63.5 Wh kg−1 energy density and 975 W kg−1 power density. After 5000 charge-discharge cycles, the gadget preserved 89.7 % of its specific capacitance. This material outperforms similar electrode materials in certain performance evaluations. We also used density functional theory (DFT) computations to analyze each element in the V-NiMnLDH composite and explain their electronic density of states contributions. This theoretical framework explains how V doping improves capacitance. Band structure simulations also showed V-NiMnLDH's higher charge transfer and conductivity compared to intermediate products, explaining its extraordinary capacitance performance. Our work combines theoretical and experimental data to advance catalyst design and high-performance energy storage materials.

One-step synthesis of CoxS/Ni3S2@NF on 3D nickel foam with different sulfur sources as a novel heterogeneous catalyst efficient activation of peroxymonosulfate in lomefloxacin degradation

In this study, we have successfully synthesized Co9S8/CoS/Ni3S2 and Co3S4/Ni3S2 materials in situ on three-dimensional (3D) nickel foam (NF) substrates using a one-step hydrothermal process with different sulfur sources. Under the experimental conditions of catalyst dosage of 0.50 cm × 0.50 cm and peroxymonosulfate (PMS) dosage of 0.30 g/L, the Co3S4/Ni3S2@NF catalyst exhibited superior catalytic performance in activating PMS and degrading 91.0 % of lomefloxacin (LOM) as compared to 76 % of Co9S8/CoS/Ni3S2@NF. Both Co9S8/CoS/Ni3S2@NF and Co3S4/Ni3S2@NF showed excellent stability and performed effectively over a wide pH range. The Co9S8/CoS/Ni3S2@NF and Co3S4/Ni3S2@NF demonstrated significant differences in morphology, crystal plane properties, surface functional groups, chemical composition, elemental valence states, and coordination environment as revealed by XRD, TEM, SEM, FTIR, and XPS analyses, contributing to their distinct mechanisms and performance in LOM degradation. Additionally, the NF acted as a support carrier, exposing multiple active sites to enhance electron transport and providing a nickel source for the catalytic reaction. The degradation of LOM in the CoxS/Ni3S2@NF&PMS system was thoroughly investigated, revealing the involvement of SO4−, OH, 1O2, and electron transfer in the process. Additionally, the mechanism of PMS activation and the pathway of LOM decomposition in the reaction system were elucidated by theoretical analysis. Furthermore, the ecotoxicity of the by-products generated during LOM degradation was assessed using the ECOSAR software. In summary, the CoxS/Ni3S2@NF catalysts proved to be efficient, stable, easily prepared, environmentally friendly, and recyclable heterogeneous nanocomposites. It is a promising candidate for heterogeneous PMS process.

Strategy for establishing sensitive fluorescent sensor toward p-nitrophenol integrating magnetic molecularly imprinted materials and carbon dots

In this work, a sensitive fluorescent sensor toward p-nitrophenol (4-NP) integrating magnetic molecularly imprinted materials and carbon dots (CDs) was proposed. Magnetic material and CDs derived from K3 [Fe(CN)6] and glucose were simultaneously obtained through simple one-step hydrothermal process. Introducing of molecularly imprinted materials based magnetic solid phase extraction (MSPE) endowed the constructed fluorescent sensor with higher sensitivity and selectivity. The significant factors affecting the sensitivity of the sensor toward 4-NP were optimized. Good linearity was obtained between fluorescent intensity of CDs and different concentration of 4-NP from 0.08 to 62.5 μg L−1. The sensitivity of constructed sensor was very low with detection limit of 0.02 μg L−1. Reliable applicability was also proved by the well-pleasing recoveries of 94.2–97.8% with different spiked concentrations of 4-NP in real environmental waters.

Ratiometric electrochemical determination of hydroxyl radical based on graphite paper modified with metal-organic frameworks and impregnated with salicylic acid.

Hydroxyl radical (•OH) detection is pivotal in medicine, biochemistry and environmental chemistry. Yet, electrochemical method-specific detection is challenging because of hydroxyl radicals'high reactivity and short half-life. In this study, we aimed to modify the electrode surface with a specific recognition probe for •OH. To achieve this, we conducted a one-step hydrothermal process to fabricate a CoZnMOF bimetallic organic framework directly onto conductive graphite paper (Gp). Subsequently, we introduced salicylic acid (SA) and methylene blue (MB), which easily penetrated the pores of CoZnMOF. By selectively capturing •OH by SA and leveragingtheelectrochemical signal generated by the reaction product, we successfully developed an electrochemical sensor Gp/CoZnMOF/SA + MB. The prepared sensor exhibited a good linear relationship with •OH concentrations ranging from 1.25 to 1200 nM, with a detection limit of 0.2 nM. Additionally, the sensor demonstrated excellent reproducibility and accuracy due to the incorporation of an internal reference. It exhibited remarkable selectivity for •OH detection, unaffected by otherelectrochemically active substances. The establishment of this sensor provides a way to construct MOF-modified sensors for the selective detection of other reactive oxygen species (ROS), offering a valuable experimental basis for ROS-related disease research and environmental safety investigations.