Computer-aided design of magnetic molecularly imprinted polymer nanoparticles for solid-phase extraction and determination of levetiracetam in human plasma

Analytical methods should be accurate and specific to measure plasma drug concentration. Nevertheless, current sample preparation techniques suffer from limitations, including matrix interference and intensive sample preparation. In this study, a novel technique was proposed for the synthesis of a molecularly imprinted polymer (MIP) on magnetic Fe₃O₄ nanoparticles (NPs) with uniform core–shell structure. The Fe₃O₄@MIPs NPs were then applied to separate and enrich an antiepileptic drug, levetiracetam, from human plasma. A computational approach was developed to screen the functional monomers and polymerization solvents to provide a suitable design for the synthesized MIP. Different analysis techniques and re-binding experiments were performed to characterize the Fe₃O₄@MIP NPs, as well as to identify optimal conditions for the extraction process. Adsorption isotherms were best fitted to the Langmuir model and adsorption kinetics were modeled with pseudo-second-order kinetics. The Fe₃O₄@MIP NPs showed reasonable adsorption capacity and improved imprinting efficiency. A validated colorimetric assay was introduced as a comparable method to a validated HPLC assay for the quantitation of levetiracetam in plasma in the range of 10–80 μg mL⁻¹ after extraction. The results from the HPLC and colorimetric assays showed good precision (between 1.08% and 9.87%) and recoveries (between 94% and 106%) using the Fe₃O₄@MIP NPs. The limit of detection and limit of quantification were estimated to be 2.58 μg mL⁻¹ and 7.81 μg mL⁻¹, respectively for HPLC assay and 2.32 μg mL⁻¹ and 7.02 μg mL⁻¹, respectively for colorimetric assay. It is believed that synthesized Fe₃O₄@MIP NPs as a sample clean-up technique combined with the proposed assays can be used for determination of levetiracetam in plasma.

A novel molecularly imprinted polymer on Fe₃O₄ nanoparticles was applied to extract antiepileptic drug; levetiracetam from plasma for TDM purposes.     

Synthesis of magnetic core–shell Fe3O4@PDA@Cu-MOFs composites for enrichment of microcystin-LR by MALDI-TOF MS analysis

Microcystin-LR (MC-LR) is a toxin released from cyanobacteria in eutrophicated water. MC-LR is the most abundant and the most toxic among microcystins. In this work, core–shell structured copper-based magnetic metal–organic framework (Fe₃O₄@PDA@Cu-MOFs) composites were synthesized via a solvothermal reaction and a sol–gel method. The Fe₃O₄@PDA@Cu-MOFs composites showed ultra-high surface area, strong magnetic response and outstanding hydrophilicity. The Fe₃O₄@PDA@Cu-MOFs composites combined with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) were used to analyse the content of MC-LR in real water samples. Under the optimised conditions, our proposed method exhibited good linearity within a concentration range of 0.05–4 μg L⁻¹ and good detection even at low limits (0.015 μg L⁻¹). The method was also successfully applied to analyse traces of MC-LR with quantitative recoveries for the real water samples in the range from 98.67% to 106.15%. Furthermore, it was characterized by high sensitivity, short operation time, being environmental friendly and having the ability to analyse other pollutants in the environment.

The synthetic route of the Fe₃O₄@PDA@Cu-MOFs microspheres and enrichment process of MC-LR.     

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO42−, Cr2O72− and MnO4−

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)₂]_n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn₄(modbc)₄ units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb³⁺ in Zn-CP, the as-obtained fluorescent functionalized Tb³⁺@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻ with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

A composite, Tb³⁺@Zn-CP, for sensing Ru³⁺, Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and MnO₄⁻ with fast response times was reported.     

Selective aptamer conjugation to silver-coated magnetite nanoparticles for magnetic solid-phase extraction of trace amounts of Pb2+ ions

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection. First, silver-coated magnetite core–shell nanoparticles (Fe₃O₄@Ag MNPs) were synthesized by the chemical reduction of silver ions on the surface of magnetite nanoparticles. After that, the selective DNA aptamer against Pb²⁺ was conjugated on the surface of the synthesized nanoparticles to form aptamer-modified magnetic nanoparticles (Fe₃O₄@Ag-APT). The characterization of the prepared adsorbent was performed through SEM imaging, XRD, FT-IR, EDX, and DRS instruments. The influence of the various experimental parameters on the adsorption and desorption steps in MSPE was investigated via Taguchi experimental design to optimize different parameters. Under the optimized conditions, the Pb²⁺ calibration graph was linear in the range of 33–1000 μg L⁻¹. The relative standard deviation (RSD%) of the method for six replicates containing 100 μg L⁻¹ of Pb²⁺ ions was 0.34%. Furthermore, the limit of detection (LOD) and the limit of quantification (LOQ) were 10 μg L⁻¹ and 33.3 μg L⁻¹, respectively. Finally, the applicability of the proposed method was successfully confirmed by preconcentration and determination of trace amounts of Pb²⁺ ions in tap and seawater samples. We showed a proof of concept for Fe₃O₄@Ag-APT as an efficient bio-adsorbent, offering a promising strategy for the specific binding/removal of toxic heavy metal ions.

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection.     

A facile synthesis of nanostructured CoFe2O4 for the electrochemical sensing of bisphenol A

This work reports a novel, highly sensitive and cost-effective electrochemical sensor for the detection of bisphenol A in environmental water samples. Attractive non-noble transition metal oxide CoFe₂O₄ nanoparticles were successfully synthesized using a sol–gel combustion method and further characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Under optimal conditions, the CoFe₂O₄ nanoparticle modified glassy carbon electrode exhibits high electrochemical activity and good catalytic performance for the detection of bisphenol A. The linear calibration curves are obtained within a wide concentration range from 0.05 μmol L⁻¹ to 10 μmol L⁻¹, and the limit of detection is 3.6 nmol L⁻¹ for bisphenol A. Moreover, this sensor also demonstrates excellent reproducibility, stability, and good anti-interference ability. The sensor was successfully applied to determine bisphenol A in practical samples, and the satisfactory recovery rate was between 95.5% and 102.0%. Based on the great electrochemical properties and practical application results, this electrochemical sensor has broad application prospects in the sensing of bisphenol A.

A new electrochemical sensor for bisphenol A is reported. CoFe₂O₄ nanoparticles were synthesized by a sol–gel combustion method. A nanoparticle-modified glassy carbon electrode exhibited outstanding electrochemical performance for the detection of bisphenol A.     

Simultaneous detection of l-aspartic acid and glycine using wet-chemically prepared Fe3O4@ZnO nanoparticles: real sample analysis

An easy and reliable wet-chemical method was used to synthesize iron oxide doped zinc oxide nanoparticles (Fe₃O₄@ZnO NPs) at a low-temperature under alkaline medium. The electrochemical characteristics of Fe₃O₄@ZnO NPs were investigated by using different electrochemical techniques such as UV-vis, FTIR, XRD, FESEM, XEDS, and XPS. A sensor was fabricated by deposition of a thin covering of Fe₃O₄@ZnO NPs onto a flat dried glassy carbon electrode (GCE) with a polymer matrix with conducting characteristics (Nafion, Nf). l-Aspartic acid and glycine were detected simultaneously by using the modified GCE/Fe₃O₄@ZnO NPs/Nf sensor in enzyme free conditions. Calibration curves were found to be linear for l-aspartic acid (R² = 0.9593) and glycine (R² = 0.8617) over a broad range of detected bio-molecule concentration (100.0 pM to 100.0 mM). The analytical sensing parameters, for example sensitivity, linear dynamic range (LDR), limit of detection (LOD), and limit of quantification (LOQ), of the proposed sensor (GCE/Fe₃O₄@ZnO NPs/Nf) were calculated at two potentials (+0.4 V and +0.7 V) from the calibration plot for l-aspartic acid (126.58 pM μM⁻¹ cm², 100.0 pM to 10.0 μM, ≈97.5 pM, and 325.0 mM) and glycine (316.46 pM μM⁻¹ cm², 1.0 μM to 1.0 mM, ≈13.5 pM, and 450.0 mM), respectively, by using a reliable current–voltage (I–V) technique. The synthesis of Fe₃O₄@ZnO NPs by means of a wet-chemical route is a good advancement for the development of doped nanomaterial based sensors from the perspective of enzyme-free detection of biological molecules in health-care areas. This proposed GCE/Fe₃O₄@ZnO NPs/Nf sensor was used for the particular detection of l-aspartic acid and glycine in real samples (human and rabbit serum and urine) and found to achieve reasonable and accepted results.

An easy and reliable wet-chemical method was used to synthesize iron oxide doped zinc oxide nanoparticles (Fe₃O₄@ZnO NPs) at a low-temperature under alkaline medium.     

Synthesis of Fe3O4@PVBC–TMT nanoparticles for the efficient removal of heavy metals ions

Core–shell magnetic Fe₃O₄@PVBC–TMT (Fe₃O₄@polyvinylbenzyl chloride–trithiocyanuric acid) nanoparticles containing trithiocyanuric acid groups were fabricated and employed for the fast removal of heavy metals from an aquatic environment. The morphology, structure and properties of Fe₃O₄@PVBC–TMT nanoparticles were characterized by a series of modern analytical tools. The adsorption behavior of the Fe₃O₄@PVBC–TMT nanoparticles for heavy metals ions in aqueous solutions was investigated by batch experiments. The maximum removal capacities of the Fe₃O₄@PVBC–TMT nanoparticles toward Mn²⁺, Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺ ions were 127.4, 146.6, 180.5, 311.5, and 528.8 mg g⁻¹, respectively. Importantly, it is found that Pb²⁺ ions can be completely and quickly removed by the Fe₃O₄@PVBC–TMT nanoparticles. The equilibrium was established within 6 min, and the removal efficiencies were found to be 99.9%, 99.8% and 99.5% for Pb²⁺ ions at the initial concentrations of 100 mg L⁻¹, 200 mg L⁻¹ and 300 mg L⁻¹, respectively. It is hoped that the core–shell magnetic Fe₃O₄@PVBC–TMT nanoparticles may find application in wastewater treatment.

Core–shell Fe₃O₄@PVBC–TMT nanoparticles were fabricated and served as a valid magnetic adsorbent for the removal of heavy metals ions.     

The construction of a simple sensor for the simultaneous detection of nitrite and thiosulfate by heme catalysis

Several simple sensors were fabricated through a one-step method. By depositing electro-active compounds, such as β-cyclodextrins (β-CD), heme, dopamine (DA), or Fc-ECG, onto a screen-printed electrode (SPE), the successful simultaneous detection of nitrite (NO₂⁻) and thiosulfate (S₂O₃²⁻) ions was observed. Under optimal operating conditions, the notable electrocatalytic abilities of a Heme/SPE sensor were detected for the oxidation of NO₂⁻ and S₂O₃²⁻, with remarkable peak potential differences, after characterization via SEM, CV, and DPV. Linear relationships were obtained in the ranges of 5.0–200.0 μmol L⁻¹ and 1.0–100.0 μmol L⁻¹ for the current response versus concentration of NO₂⁻ and S₂O₃²⁻, respectively. The limits of detection were determined to be 1.67 and 0.33 μmol L⁻¹ while the sensitivities of detection were noted to be 0.43 and 1.43 μA μM⁻¹ cm⁻², respectively. During the detection of NO₂⁻ and S₂O₃²⁻, no interfering common ions were observed. Furthermore, average recoveries from 96.0 to 104.3% and a total R.S.D. of less than 3.1% were found for the detection of NO₂⁻ and S₂O₃²⁻ in pickled juice and tap water using the simple sensor. These results showed that rapid and precise measurements for actual application in NO₂⁻ and S₂O₃²⁻ detection could be conducted in food samples, indicating a potential use in food safety.

Several simple sensors were fabricated through a one-step method.     

Facile construction of magnetic core–shell covalent organic frameworks as efficient solid-phase extraction adsorbents for highly sensitive determination of sulfonamide residues against complex food sample matrices

Integration of advanced sample pretreatment techniques, with the involvement of functional nano/micro-materials as adsorbents, is of great importance and value for food-safety precise inspection. For now, the major demands for functional adsorbents are ease of fabrication, fast adsorption and separation performance, low toxicity, robustness, and reusability. In the present work, core–shell structured magnetic covalent organic frameworks (COFs) that employed Fe₃O₄ microspheres as the magnetic core and TpBD COFs as the adsorption shell have been successfully constructed as efficient solid phase extraction (SPE) adsorbents for complex food sample analysis. In favor of the combination of magnetic separation and effective preconcentration, the proposed magnetic COF-SPE method gave a rapid detection performance of the simultaneous detection of ten sulfonamide residues as well as high sensitivity, with detection limits in the range of 0.28–1.45 μg L⁻¹ under the optimized experimental conditions. The Fe₃O₄@TpBD core–shell adsorbents also demonstrated good stability, robust SPE preconcentration ability, excellent determination recovery, and good reusability. The applicability of the developed SPE method was well demonstrated by real sample analysis, with the recoveries ranging from 82–94%. Through this example, it was believed that the new emerging porous nano/micro-materials, like COFs, metal–organic networks, or hybrid structures, would play more and more important roles as functional materials in food-safety inspection, especially for highly efficient determination of targets against complicated food sample matrices.

Robust and efficient solid-phase extraction adsorbents based on magnetic core–shell covalent organic frameworks gave excellent analytical performance for determination of sulfonamide residues in food samples.     

Magnetic surface molecularly imprinted poly(3-aminophenylboronic acid) for selective capture and determination of diethylstilbestrol

Diethylstilbestrol (DES) is considered a representative example of an exogenous endocrine disrupting compound (EDC). It can retard development in infants, lead to serious metabolic regulation disorders, and even result in distortion and cancer in the reproductive system. Therefore, achieving rapid and accurate analysis of trace amounts of DES in complex environments is of great importance to human health and for environmental protection. Novel magnetic molecularly imprinted polymers (MIPs) with excellent molecular recognition ability and super water-compatibility were developed for the selective capture of DES in water samples. Fe₃O₄@SiO₂ magnetic nanoparticles (NPs) were synthesized and used as support cores. Molecularly imprinted poly(3-aminophenylboronic acid) (poly(APBA)), synthesized on magnetic cores based on a surface-imprinting strategy, can preferentially bind DES molecules in water samples. The magnetic core–shell MIPs (denoted as Fe₃O₄@SiO₂@APBA/MIPs) exhibited high binding capacity and favorable recognition specificity for DES in water. The adsorption kinetics and experimental isotherm data of DES on magnetic MIPs can be well described by the pseudo-second-order kinetic model and the Langmuir isotherm, respectively. The imprinted nanoparticles were subjected to magnetic solid-phase extraction (MSPE) of DES from water samples. The DES content in the samples was determined by high-performance liquid chromatography (HPLC). The peak area increased linearly with increasing DES concentration over the range 0.08–150 μg L⁻¹, with a detection limit of 0.03 μg L⁻¹. The recoveries for spiked lake water samples were in the range 97.1–103.2%, with relative standard deviation (RSD) of 2.8–4.3% (n = 6).

Imprinted poly(APBA) nanoshell on Fe₃O₄@SiO₂ surface was first synthesized and used for MSPE of diethylstilbestrol followed by HPLC determination.     

Enhancing the chloramphenicol sensing performance of Cu–MoS2 nanocomposite-based electrochemical nanosensors: roles of phase composition and copper loading amount

The rational design of nanomaterials for electrochemical nanosensors from the perspective of structure–property–performance relationships is a key factor in improving the analytical performance toward residual antibiotics in food. We have investigated the effects of the crystalline phase and copper loading amount on the detection performance of Cu–MoS₂ nanocomposite-based electrochemical sensors for the antibiotic chloramphenicol (CAP). The phase composition and copper loading amount on the MoS₂ nanosheets can be controlled using a facile electrochemical method. Cu and Cu₂O nanoparticle-based electrochemical sensors showed a higher CAP electrochemical sensing performance as compared to CuO nanoparticles due to their higher electrocatalytic activity and conductivity. Moreover, the design of Cu–MoS₂ nanocomposites with appropriate copper loading amounts could significantly improve their electrochemical responses for CAP. Under optimized conditions, Cu–MoS₂ nanocomposite-based electrochemical nanosensor showed a remarkable sensing performance for CAP with an electrochemical sensitivity of 1.74 μA μM⁻¹ cm⁻² and a detection limit of 0.19 μM in the detection range from 0.5–50 μM. These findings provide deeper insight into the effects of nanoelectrode designs on the analytical performance of electrochemical nanosensors.

In this work, we clarify the roles of phase composition and copper loading amount on the CAP sensing performance of Cu–MoS₂ nanocomposite-based electrochemical nanosensors.     

Novel easily separable core–shell Fe3O4/PVP/ZIF-8 nanostructure adsorbent: optimization of phosphorus removal from Fosfomycin pharmaceutical wastewater

A new easily separable core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent was synthesized and then examined for removal of Fosfomycin antibiotic from synthetic pharmaceutical wastewater. The removal process of Fosfomycin was expressed through testing the total phosphorus (TP). A response surface model (RSM) for Fosfomycin adsorption (as mg-P L⁻¹) was used by carrying out the experiments using a central composite design. The adsorption model showed that Fosfomycin adsorption is directly proportional to core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent dosage and time, and indirectly to initial Fosfomycin concentration. The removal increased by decreasing the pH to 2. The Fosfomycin removal was done at room temperature under an orbital agitation speed of 250 rpm. The adsorption capacity of core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent reached around 1200 mg-P g⁻¹, which is significantly higher than other MOF adsorbents reported in the literature. The maximum Langmuir adsorption capacity of the adsorbent for Fosfomycin was 126.58 mg g⁻¹ and Fosfomycin adsorption behavior followed the Freundlich isotherm (R² = 0.9505) in the present study. The kinetics was best fitted by the pseudo-second-order model (R² = 0.9764). The RSM model was used for the adsorption process in different target modes.

The synthesis of an easily separable novel core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent and its usage for Fosfomycin pharmaceutical wastewater treatment.     

Upconversion luminescence and temperature sensing properties of NaGd(WO4)2:Yb3+/Er3+@SiO2 core–shell nanoparticles

Optical thermometry based on the fluorescence intensity ratio (FIR) of two thermally coupled levels in lanthanide ions has potential application in non-contact optical temperature sensing techniques. In this work, a shell of SiO₂ with tunable thickness was uniformly coated on NaGd(WO₄)₂:Yb³⁺/Er³⁺ core upconversion nanoparticles (UCNPs). The effects of the silica shell on UC luminescence and thermal sensing properties of core–shell NaGd(WO₄)₂:Yb³⁺/Er³⁺@SiO₂ UCNPs were investigated. Under 980 nm laser excitation, the temperature-dependent UC emission spectra of obtained samples were measured. The FIR was analyzed based on the thermally coupled ²H_11/2 and ⁴S_3/2 levels of Er³⁺ in the biological temperature range of 300–350 K, in which the Boltzmann distribution is applied. The emission from the upper ²H_11/2 state within Er³⁺ was enhanced as temperature increased due to the thermal effect. Absolute sensitivities (S_A) and relative sensitivities (S_R) of the core and core–shell UCNPs were calculated. It was found that after SiO₂ coating, the maximum S_A was enhanced by ∼2-fold (1.03% K⁻¹ at 350 K). Especially, S_A was as high as 2.14% K⁻¹ at 350 K by analyzing the FIR of the non-thermally coupled ²H_11/2 and ⁴F_9/2 levels.

A shell of SiO₂ with tunable thickness was uniformly coated on NaGd(WO₄)₂:Yb³⁺/Er³⁺ core upconversion nanoparticles (UCNPs). The effects of the silica shell on UC luminescence and thermal sensing properties of the core–shell UCNPs were investigated.     

Constructing Rh–Rh3+ modified Ta2O5@TaON@Ta3N5 with special double n–n mutant heterojunctions for enhanced photocatalytic H2-evolution

A multiple core–shell heterostructure Rh–Rh³⁺ modified Ta₂O₅@TaON@Ta₃N₅ nanophotocatalyst was successfully constructed through nitriding Rh³⁺-doped Ta₂O₅ nanoparticles, which exhibited a much higher carrier separation efficiency about one order of magnitude higher than the Ta₂O₅@Ta₃N₅ precursor, and thus an excellent visible light photocatalytic H₂-evolution activity (83.64 μmol g⁻¹ h⁻¹), much superior to that of Rh anchored Ta₂O₅@TaON (39.41 μmol g⁻¹ h⁻¹), and improved stability due to the residual Rh–O/N in the Ta₃N₅ shell layer. Rh-modifying significantly extended light absorption to the overall visible region. Localized built-in electric fields with hierarchical potential gradients at the multiple interfaces including a Rh/Ta₃N₅ Schottky junction and double n–n Ta₃N₅/TaON/Ta₂O₅ mutant heterojunctions, drove charge carriers to directionally transfer from inside to outside, and efficiently separate. Enhanced photoactivity was ascribed to a synergetic effect of improved light absorption ability, increased carrier separation efficiency, and accelerated surface reaction. A promising strategy of developing excellent Ta₃N₅-based photocatalysts for solar energy conversion is provided by constructing double n–n mutant heterojunctions.

Localized built-in electric fields at multiple hierarchical interfaces facilitate the efficient separation and fast inside-out directional transfer of photogenerated carriers.     

Nanostructured RuO2–Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.     

Pt-grown carbon nanofibers for detection of hydrogen peroxide

Removal of left-over catalyst particles from carbon nanomaterials is a significant scientific and technological problem. Here, we present the physical and electrochemical study of application-specific carbon nanofibers grown from Pt-catalyst layers. The use of Pt catalyst removes the requirement for any cleaning procedure as the remaining catalyst particles have a specific role in the end-application. Despite the relatively small amount of Pt in the samples (7.0 ± 0.2%), they show electrochemical features closely resembling those of polycrystalline Pt. In O₂-containing environment, the material shows two separate linear ranges for hydrogen peroxide reduction: 1–100 μM and 100–1000 μM with sensitivities of 0.432 μA μM⁻¹ cm⁻² and 0.257 μA μM⁻¹ cm⁻², respectively, with a 0.21 μM limit of detection. In deaerated solution, there is only one linear range with sensitivity 0.244 μA μM⁻¹ cm⁻² and 0.22 μM limit of detection. We suggest that the high sensitivity between 1 μM and 100 μM in solutions where O₂ is present is due to oxygen reduction reaction occurring on the CNFs producing a small additional cathodic contribution to the measured current. This has important implications when Pt-containing sensors are utilized to detect hydrogen peroxide reduction in biological, O₂-containing environment.

Application specific Pt-grown carbon nanofibers for H₂O₂ detection were characterized and the roles of dissolved oxygen and chloride ions on the electrochemical performance were assessed in detail.     

Surface plasmon-driven photocatalytic activity of Ni@NiO/NiCO3 core–shell nanostructures

Ni@NiO/NiCO₃ core–shell nanostructures have been investigated for surface plasmon driven photocatalytic solar H₂ generation without any co-catalyst. Huge variation in the photocatalytic activity has been observed in the pristine vs. post-vacuum annealed samples with the maximum H₂ yield (∼110 μmol g⁻¹ h⁻¹) for the vacuum annealed sample (N70-100/2 h) compared to ∼92 μmol g⁻¹ h⁻¹ for the pristine (N70) photocatalyst. Thorough structural (X-ray diffraction) and spectroscopic (X-ray photoelectron spectroscopy and transmission electron microscopy coupled electron energy loss spectroscopy) investigations reveal the core Ni nanoparticle decorated with the shell, a composite of crystalline NiO and amorphous NiCO₃. Significant visible light absorption at ∼475 nm in the UV-vis region along with the absence of a peak/edge corresponding to NiO suggest the role of surface plasmons in the observed catalytic activity. As per the proposed mechanism, amorphous NiCO₃ in the shell has been suggested to serve as the dielectric medium/interface, which enhances the surface plasmon resonance and boosts the HER activity.

Surface plasmonic resonance enabled Ni@NiO/NiCO₃ core–shell nanostructures as promising photocatalysts for hydrogen evolution under visible light.     

Adsorption mechanism of polyethyleneimine modified magnetic core–shell Fe3O4@SiO2 nanoparticles for anionic dye removal

In this paper, polyethyleneimine modified magnetic core–shell Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS. The adsorption performance based on the removal of the anionic dyes Methyl orange and Congo red from aqueous solution was studied systematically. The results showed that the adsorption rate of anionic dyes MO and CR increased rapidly then decreased gradually as the pH increased, the adsorption capacity of Fe₃O₄@SiO₂/PEI for MO was better than that for CR, and the maximum adsorption capacity for MO and CR was 231.0 mg g⁻¹ at pH 4 and 134.6 mg g⁻¹ at pH 6, respectively. The equilibrium adsorption capacities for MO and CR increased rapidly in the initial 40 min, and reached equilibrium in approximately 180 min, while the adsorption capacity for MB was relative low even negligible, demonstrating the strong adsorptive affinity of Fe₃O₄@SiO₂/PEI toward anionic compounds. Both of the adsorption processes followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The mechanism of adsorption was mainly related to electrostatic attraction and the number of active sites occupied by anionic dyes. This study provides valuable guidance and is an effective method for the removal of anionic dyes from aquatic environments.

In this paper, polyethyleneimine modified magnetic core–shell Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS.     

A novel MnO–CrN nanocomposite based non-enzymatic hydrogen peroxide sensor

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method. The specific surface area of the synthesized powder was measured via BET analysis and it was found to be 262 m² g⁻¹. Regarding its application, the electrochemical sensing performance toward hydrogen peroxide (H₂O₂) was studied via applying cyclic voltammetry (CV) and amperometry (i–t) analysis. The linear response range was 0.33–15 000 μM with a correlation coefficient (R²) value of 0.995. Excellent performance toward H₂O₂ was observed with a limit of detection of 0.059 μM, a limit of quantification of 0.199 μM, and sensitivity of 2156.25 μA mM⁻¹ cm⁻². A short response time of within 2 s was achieved. Hence, we develop and offer an efficient approach for synthesizing a new cost-efficient material for H₂O₂ sensing.

A MnO–CrN composite was obtained via the ammonolysis of the low-cost nitride precursors Cr(NO₃)₃·9H₂O and Mn(NO₃)₂·4H₂O at 800 °C for 8 h using a sol–gel method.     

Constructing a TiO2/PDA core/shell nanorod array electrode as a highly sensitive and stable photoelectrochemical glucose biosensor

Developing stable PEC glucose biosensors with high sensitivity and low detection limit is highly desirable in the biosensor field. Herein, a highly stable and sensitive enzymatic glucose photoelectrochemical biosensor is rationally designed and fabricated by constructing TiO₂/PDA core/shell nanorod arrays. The TiO₂ nanorod as the core has the advantages of increasing charge transportation towards interfaces and enhancing the absorption of incident sunlight due to its single-crystal nature and one dimensional array structure. The PDA shell not only induces a rapid charge transfer across the interfaces but also stabilizes the biosensor performance by avoiding the decomposition of enzymes induced by the strong oxidizing holes from the TiO₂ core. A remarkable performance with an ultrahigh sensitivity of 57.72 μA mM⁻¹ cm⁻², a linear range of 0.2–1.0 mM, a glucose detection limit of 0.0285 mM (S/N = 3) and a high sensitivity of 8.75 μA mM⁻¹ cm⁻² in a dynamic range of 1.0–6.0 mM were obtained for the glucose detection. This study might provide a strategy for constructing inorganic/organic core/shell structures with a satisfactory PEC performance.

Developing stable PEC glucose biosensors with high sensitivity and low detection limit is highly desirable in the biosensor field.