We have modified a glassy carbon electrode by single-step electrodeposition of graphene (GR), gold nanoparticles (AgNPs), and chitosan (CS) directly from a solution containing graphene oxide, tetrachloroauric acid, and chitosan. The surface and electrochemical properties of the film-modified electrode were investigated by SEM and TEM images. The AuNPs have a diameter of about 20 nm and are uniformly dispersed in the matrix. Combining the advantages of GR (i.e., high surface area and conductivity), of AuNPs (excellent electrical conductivity) and CS (excellent film-forming ability and good water permeability), the hybrid film effectively enhances electron-transfer and promotes the response to lead(II) ion. Under the optimum conditions, a linear relationship exists between electrical current and the concentration of lead (II) ion in the range between 0.5 to 100 μg L-1, with a detection limit of 1 ng L-1 (at an SNR of 3). The electrode was successfully applied to the detection of lead(II) in spiked samples of river water.

We have electrodeposited a composite film consisting of graphene oxide, chitosan and glucose oxidase directly on a glassy carbon electrode (GCE) through electrochemical reduction of a solution of the 3 components under controlled direct electrical potential. The procedure takes only several minutes, and the thickness of the resulting film is uniform and controllable. The GOx has uncompromised bioactivity and exhibits reversible 2-proton and 2-electron transfer in presence of glucose. It therefore can be used amperometric sensing of glucose. The biosensor has a fast response (<3 s), a detection limit of 0.4 μM (which is 50-fold lower compared to the biosensor prepared by drop-casting solutions of the same materials onto an GCE), and a linear response in the 0.4 μM to 2 mM concentration range (which again is much better than that of the biosensor prepared by the drop-casting method). Other features include high reproducibility, long-time storage stability, and satisfactory selectivity. We presume that the direct single-step electrodeposition of this nanocomposite offers a promising approach towards novel types of highly sensitive and stable electrochemical biosensors.

A facile and reliable method has been developed to synthesize single crystalline Pt nanotubes (S-PtNTs) with Pt (111) dominated facets. It is verified that the Pt (111) dominated facets in S-PtNTs play a crucial role in improving the catalytic stability for the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR).

A facile strategy has been developed to realize the controllable synthesis of single crystalline NiO nanoflakes. According to the SEM, TEM and BET analysis, it was found that the m-NiO nanoflakes have a hexagonal structure with an average pore diameter of 4.4 nm, and exhibit a high surface area of 113.4 m2 g−1 and a pore volume around 0.142 cm3 g−1. The m-NiO nanoflakes exhibit a significantly improved electrochemical performance as an anode of lithium-ion batteries (LIBs) compared with bulk NiO based on cyclic voltammograms and galvanostatic measurement. Additionally, the m-NiO nanoflakes showed remarkable advanced activity for catalyzing oxygen reduction reaction (ORR ) relative to the bulk NiO electrode and the bare electrode. Further, rotating disk electrodes demonstrated that the m-NiO nanoflakes, as the support of the Pt nanoparticles, shows significantly improved activity for ORRs.

We report on a novel amperometric glassy carbon biosensing electrode for glucose. It is based on the immobilization of a highly sensitive glucose oxidase (GOx) by affinity interaction on carbon nanotubes (CNTs) functionalized with iminodiacetic acid and metal chelates. The new technique for immobilization is exploiting the affinity of Co(II) ions to the histidine and cysteine moieties on the surface of GOx. The direct electrochemistry of immobilized GOx revealed that the functionalized CNTs greatly improve the direct electron transfer between GOx and the surface of the electrode to give a pair of well-defined and almost reversible redox peaks and undergoes fast heterogeneous electron transfer with a rate constant (ks) of 0.59 s−1. The GOx immobilized in this way fully retained its activity for the oxidation of glucose. The resulting biosensor is capable of detecting glucose at levels as low as 0.01 mM, and has excellent operational stability (with no decrease in the activity of enzyme over a 10 days period). The method of immobilizing GOx is easy and also provides a model technique for potential use with other redox enzymes and proteins.

Graphene film was formed on the surface of titanium dioxide nanotube (TiO2 NT) arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp3-hybridized carbons in the electrodeposited graphene were further removed by photo-assisted reduction of the underlying TiO2 NTs, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photoelectrochemical techniques were used to characterize the graphene films, and the use of the resulting graphene–TiO2 NT material in photocatalysis was investigated. The results showed that the graphene–TiO2 NT material exhibited a greatly improved photocatalytic activity compared with unmodified TiO2 NTs.

Novel water-compatible molecularly imprinted polymers were synthesized in methanol–water systems with Tratarzine as template and 1-(α-methyl acrylate)-3-methylimidazolium bromide (1-MA-3MI-Br) as functional monomer, which has π–π hydrophobic, hydrogen-bonding and electrostatic interactions with template molecule. 1-MA-3MI-Br molecularly imprinted polymers (1-MA-3MI-Br-MIPs) were used as selective sorbents for the solid-phase extraction (SPE) of water-soluble acid dyes from wastewater and soft drink. The good linearity of the method was obtained in a range of 5.0–2000 μg/L with the correlation coefficient of >0.999. The detection limits were in a range of 0.13–0.51 μg/L for the water-soluble acid dyes in wastewater and 0.095–0.84 μg/L for those in soft drink. The mean recoveries for the acid dyes are from 89.1% to 101.0% in spiked wastewater and 91.0–101.3% in spiked soft drink. Compared with strongly anion exchange solid phase extraction (SAX-SPE), mixture anion exchange solid phase extraction (MAX-SPE), and 1-MA-3MI-Br non-imprinted solid phase extraction (1-MA-3MI-Br-NISPE), almost all of the matrix interferences were removed by 1-MA-3MI-Br-MISPE, exhibiting higher selectivity, recovery and enrichment ability for the acid dyes and better baselines in the results of HPLC analysis.

A novel Cu(II) magnetic ion-imprinted polymer (MIIP) was prepared via the sol−gel method. The Cu(II)-MIIP exhibited good magnetic property and thermal stability. The binding characteristics of Cu(II)-MIIP were studied by adopting both static and dynamic adsorption experiments. The maximum adsorptions calculated from the Langmuir isotherm are 58.20 and 23.10 mg/g for Cu(II)-MIIP and magnetic nonimprinted polymer (MNIP), respectively. The kinetics studies showed that the adsorption process obeyed a pseudo-second-order kinetic model. The selectivity coefficients of the Cu(II)-MIIP for Cu(II) in the presence of Zn(II) and Ni(II) are 49.44 and 50.38, respectively. The relative selectivity coefficients of Cu(II)-MIIP for Cu(II)/Zn(II) and Cu(II)/Ni(II) are 12.36 and 8.73, respectively. Moreover, Cu(II)-MIIP could be used five times without obvious deterioration in their adsorption capacities.

Gold nanotubes consisting of compact and tiny Au particles were embedded in the pores of anodic TiO2 nanotube arrays by a simple pulse electrodeposition technique, constructing a novel metal-semiconductor heterojunction with a tube-in-tube structure. Under illumination, the electric potential difference generated on the interface of Au/TiO2 heterojunction facilitated the separation of the photogenerated hole–electron pairs, accelerating the transferring rate of the electrons and resulting in an enhanced photocatalytic activity. In comparison with the single system, simultaneously enhanced photocatalytic degradation rate of acid orange 7 (AO7) and reduction rate of Cr(VI) were observed due to the synergetic effect of Cr(VI)-AO7. Investigation results show that acidic solution is favorable for both the photocatalytic reduction of Cr(VI) and the degradation of AO7. The possible roles of the additives on the reactions are also discussed.Graphical abstractGold nanotubes consisting of compact and tiny Au particles were embedded in the pores of anodic TiO2 nanotube arrays by a simple pulse electrodeposition technique, constructing a novel metal-semiconductor heterojunction with a tube-in-tube structure. The resulting Au/TiO2 composite NTs were applied in the simultaneous detoxification of hexavalent chromium and acid orange 7. High photocatalytic efficiencies were obtained due to the large specific surface area, high porosity as well as the novel construction.Highlights► We prepared a novel Au/TiO2 composite NTs with a tube-in-tube structure. ► The composite was employed in the simultaneous detoxification of Cr(VI) and acid orange 7. ► High photocatalytic efficiencies were obtained. ► The unique construction and high activity make the composite has potential utility.

In this report, we presented a new method to fabricate TiO2 nanotube (TiO2 NT) arrays modified with cupric oxide (CuO) nanofibers, getting a novel TiO2 NT arrays composition electrode for sensitive nonenzymatic glucose detection. For the preparation of CuO nanofibers, Cu nanoparticles were firstly electrodeposited onto the TiO2 NT arrays, and then oxidized to CuO nanofibers followed by annealing in air. The CuO nanofibers modified TiO2 NT (CuO/TiO2 NT) arrays electrode for electrocatalytic detection of glucose was investigated by cyclic voltammetry and chronoamperometry in 0.10 M NaOH solution. The linear range of detection of glucose extended up to 2.0 mM (R = 0.997, n = 10) at a potential of 0.50 V (vs. SCE). The sensitivity was 79.79 μA cm−2 mM−1, and the detection limit was 1 μM (S/N = 3). Significantly, the poisoning by chloride ion and the interferences from ascorbic acid, uric acid, lactose, sucrose, fructose and dopamine were negligible. Particularly, the CuO/TiO2 NT arrays electrode showed excellent stability and repeatability over 1 month. The sensor was also investigated detecting glucose in human blood serum samples.Highlights► A novel CuO/TiO2 nanotube arrays electrode was fabricated by a new method. ► The sensor was used to detect glucose. ► The CuO/TiO2 electrode showed excellent stability and repeatability. ► The sensor was investigated detecting glucose in human blood serum samples.

The paper reports a novel amperometric biosensor for catechol based on immobilization of a highly sensitive horseradish peroxidase by affinity interactions on metal chelate-functionalized agarose/carbon nanotubes composites. Metal chelate affinity takes advantage of the affinity of Ni2+ ions to bind strongly and reversibly to histidine or cysteine tails found on the surface of the horseradish peroxidase. Thus, enzymes with such residues in their molecules can be easily attached to functionalized agarose/carbon nanotubes composites support containing a nickel chelate. Linear sweep voltammograms and amperometry are used to study the proposed electrochemical biosensor. Catechol is determined by direct reduction of biocatalytically liberated quinone species at −0.05 V (vs. SCE). The effect of pH, applied electrode potential and the concentration of H2O2 on the sensitivity of the biosensor has been investigated. The performance of the proposed biosensor is tested using four different phenolic compounds, showing very high sensitivity, in particular, the linearity of catechol is observed from 2.0 × 10−8 to 1.05 × 10−5 M with a detection limit of 5.0 × 10−9 M.

Highly ordered TiO2 nanotube arrays are with unique photoelectrical properties due to their highly ordered nanostructure and the resulted short charge transportation path. We report, for the first time, on the application of Ag nanoparticle-modified TiO2 nanotubes (Ag/TiO2 NTs) in the electrochemiluminescence detection of polycyclic aromatic hydrocarbons (PAHs) using the Ag/TiO2 NT film as working electrode and S2O82− as coreactant, with benzo(a)pyrene (BaP) as the model compound. The hydrophobic BaP absorbs onto the TiO2 NTs surface, and oxidized with consumption of the excited TiO2 (TiO2*+) resulting in a decrease in ECL. Under the optimal conditions, a detection limit of 1.0 × 10−12 M is achieved with a linear range of 3.0 × 10−12 ∼1.0 × 10−9 M. Compounds which can not be oxidized by the excited TiO2 (TiO2*+), such as benzene, naphthalene (NAP), anthracene (ANT), and tris-2,3-dibrominepropyl isocyanurate (TBC) show little interference on the detection, whereas PAHs with more than four rings can be detected by the proposed method.

Driven by the urgent demand of detecting trace amounts of pentachlorophenol (PCP) in contaminative water, a label-free immunosensor with ultra sensitivity and high selectivity was constructed based on a hybrid CdSexTe1−x (0 ≤ x ≤ 1) nanocrystal (NCs)-modified TiO2 nanotube (NT) arrays for the first time. The CdSexTe1−x NCs were photoelectrodeposited on inner and outer space of the TiO2 NTs, leading to high photoelectrical conversion efficiency in the visible region. PCP antibodies are covalently conjugated on the TiO2 NTs due to the large surface area and good biocompatibility. Since the photocurrent is highly dependent on the TiO2 surface properties, the specific interaction between PCP and the antibodies results in a sensitive change in the photocurrent, with a limit of detection (LOD) of 1 pM. High sensor-to-sensor reproducibility is achieved. The sensor was applied for the direct analysis of river water samples.

CdTe quantum dots (QDs) are prepared on TiO2 nanotubes (TiO2 NTs), for the first time, with pulse electrodeposition. A novel single-drop optical sensor is prepared with the CdTe QDs-modified TiO2 NTs, and applied for the detection of polycyclic aromatic hydrocarbons (PAHs) based on fluorescence resonance energy transfer (FRET). Excited at 270 nm, the sensor shows fluorescence emission at around 370 nm. As PAHs are with absorption/fluorescence emission at around 364/410 nm, FRET happens between the CdTe QDs and PAHs with the CdTe QDs as donors and PAHs as receptors. The sensitivity is dependent on the number of rings of the PAHs, with the highest sensitivity observed in the response to benzo(a)pyrene (BaP). Using FRET, the sensitivity to BaP is enhanced by about 2 orders with respect to the direct fluorescent spectrometry. The proposed sensor shows a linear response to the logarithm of BaP concentration in the range of 400 nM to 40 pM, with a detection limit of 15 pM, which is much close to the quality criteria (15.1 pM) in drinking water set by U.S. Environment Protection, suggesting that the proposed sensor can be used for quick scanning of PAHs. The achieved sensitivity is much higher than that of the published sensor-based methods. As PAHs are quantified based on the relative fluorescence intensity at 410−370 nm, the sensor need no calibration with a standard sensor, avoiding the influence from the sensor-to-sensor difference. The practicability of the sensor is tested by analyzing PAHs in Xiangjiang River water, the PAHs contents ranges from 0.045 to 2.847 ng/L based on the sampling spots.

p-Nitrophenol (PNP) is a difficultly decomposed organic pollutant under solar light in the absence of strong oxidants. This study shows that under artificial solar light PNP can be effectively degraded by a Cu2O/TiO2 p-n junction network which is fabricated by anodizing Cu0 particles-loaded TiO2 nanotubes (NTs). The network is composed of p-type Cu2O nanowires on the top surface and Cu2O nanoparticles on the inner walls of the n-type TiO2 NT arrays. The Cu2O/TiO2 network shows much higher degradation rate (1.97 μg/min cm2) than the unmodified TiO2 NTs (0.85 μg/min cm2). The enhanced photocatalytic acitivity can be attributed to the extended absorption in the visible resulting from the Cu2O nanowire networks and the effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Cu2O/TiO2 p-n junction interface.

We report a novel method for biological thiols detection using ssDNA/sliver nanoparticles system. The adsorbing ssDNA supplies silver nanoparticles high density charge to rescue nanoparticles from aggregation induced by salt. However, homocysteine (cysteine or glutathione) is conjugated more powerfully than ssDNA to AgNPs via Ag–S bond, which holds back ssDNA binding to AgNPs surface. When salt is added, AgNPs aggregation occurs and the corresponding color changes from yellow to brown after these biological thiols is introduced. A high sensitivity can be achieved using salt as an amplifier to assay thiols. In our study, a favorable linear correlation between the A0/Ax ratio and homocysteine concentration was obtained in the range of 10 to 500 nM with a low detection limit of 10 nM, indicating that homocysteine could be analyzed at low concentration. A concentration as low as 300 nM homocysteine caused a visible color change. As well as, cysteine and glutathione can be detected at a detection limit of 50 nM and 100 nM, respectively. In addition, study on the selectivity of this method shows that only homocysteine, cysteine and glutathione can generate signal response.

Hydroxyl ionic liquid grafted onto cross-linked divinylbenzene polymer (PDVB-HEIMBr) was fabricated and evaluated as a catalyst for the synthesis of cyclic carbonates from CO2 and epoxides without the use of any co-catalyst and organic solvent. The catalyst shows good performance across a wide range of epoxides, giving almost quantitative yield of carbonates (140 °C, 2.0 MPa of initial CO2, and ≤4 h). The effects of reaction temperature, time and initial CO2 pressure on product yield were investigated. It is suggested that the synergetic effect between the bromide ions and the hydroxyl groups facilitates the coupling reaction. Furthermore, the PDVB-HEIMBr catalyst shows excellent stability and reusability. From the viewpoint of industrial application, the catalyst is very attractive because of its simplicity, activity, stability, and reusability.

A carbon-modified TiO2 nanotube (C−TiO2 NT) array is fabricated by depositing carbon in TiO2 NTs, which are prepared by anodization of the Ti sheet. Well-dispersed Pt nanoparticles (NPs) are electrochemically deposited on the C−TiO2 NTs. The performances of the as-prepared NT array electrode in the methanol oxidation reaction (MOR) as an anode are investigated. The results present in this study highlight such a finding: depositing partly graphitized carbon on the inside of TiO2 NTs can significantly enhance the catalytic efficiency. An optimum forward oxidation peak current density (Ipf) of 71.6 mA cm−2 is obtained from the Pt/C−TiO2 NT anode at a low Pt loading of 23 μg cm−2. The achieved Ipf is almost 27 times that achieved on Pt-modified TiO2 NTs without carbon modification. The enhanced catalytic efficiency is mainly attributed to the superior electrical conductivity of the deposited carbon, which facilitates the well dispersion of Pt NPs, charge transfer during the MOR, and removal of the byproduct CO-like species.

A sensor for methanol was fabricated by incorporating the antibiotic cefixime (CEF) along with Ni(II) ion into a chitosan membrane matrix. Sensing is based on the electrocatalytic effect that the complex membrane exerts on the electro-oxidation of methanol. The resulting CEF-Ni(II)/chitosan glassy carbon (GC) electrode had a good electrocatalytic activity to the electro-oxidation of methanol in alkaline medium. The modified electrode had an immense electrocatalytic activity on the second process of methanol oxidation (methanol oxidation intermediate(s) to the final product). The modified electrode had a wide linear range from 20 μM to 12 mM for the determination of methanol in alkaline medium, and a detection limit of 5.24 μM based on a signal-to-noise ratio of 3. In addition, the sensor exhibited good stability.

Large-scale synthesis of semiconductor nanocrystals or quantum dots (QDs) with high concentration and high yield through simultaneously increasing the precursor concentration was introduced. This synthetic route conducted in diesel has produced gram-scale CdSe semiconductor quantum dots (In optimal scale-up synthetic condition, the one-pot yield of QDs is up to 9.6g). The reaction has been conducted in open air and at relatively low temperature at 190−230 °C in the absence of expensive organic phosphine ligands, aliphatic amine and octadecene, which is really green chemistry without high energy cost for high temperature reaction and unessential toxic chemicals except for Cd, which is the essential building block for QDs.

Gold nanotubes consisting of compact and tiny Au particles were embedded in the pores of anodic TiO2 nanotube arrays by a simple pulse electrodeposition technique, constructing a novel metal-semiconductor heterojunction with a tube-in-tube structure. Under illumination, the electric potential difference generated on the interface of Au/TiO2 heterojunction facilitated the separation of the photogenerated hole–electron pairs, accelerating the transferring rate of the electrons and resulting in an enhanced photocatalytic activity. In comparison with the single system, simultaneously enhanced photocatalytic degradation rate of acid orange 7 (AO7) and reduction rate of Cr(VI) were observed due to the synergetic effect of Cr(VI)-AO7. Investigation results show that acidic solution is favorable for both the photocatalytic reduction of Cr(VI) and the degradation of AO7. The possible roles of the additives on the reactions are also discussed.Graphical abstractGold nanotubes consisting of compact and tiny Au particles were embedded in the pores of anodic TiO2 nanotube arrays by a simple pulse electrodeposition technique, constructing a novel metal-semiconductor heterojunction with a tube-in-tube structure. The resulting Au/TiO2 composite NTs were applied in the simultaneous detoxification of hexavalent chromium and acid orange 7. High photocatalytic efficiencies were obtained due to the large specific surface area, high porosity as well as the novel construction.Download full-size imageHighlights► We prepared a novel Au/TiO2 composite NTs with a tube-in-tube structure. ► The composite was employed in the simultaneous detoxification of Cr(VI) and acid orange 7. ► High photocatalytic efficiencies were obtained. ► The unique construction and high activity make the composite has potential utility.