A new cellulose nanocrystal–reduced graphene oxide (CNC–rGO) nanocomposite was successfully used for mediatorless electrochemical sensing of methyl paraben (MP). Fourier-transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM) studies confirmed the formation of the CNC–rGO nanocomposite. Cyclic voltammetry (CV) studies of the nanocomposite showed quasi-reversible redox behavior. Differential pulse voltammetry (DPV) was employed for the sensor optimization. Under optimized conditions, the sensor demonstrated a linear calibration curve in the range of 2 × 10−4–9 × 10−4 M with a limit of detection (LOD) of 1 × 10−4 M. The MP sensor showed good reproducibility with a relative standard deviation (RSD) of about 8.20%. The sensor also exhibited good stability and repeatability toward MP determinations. Analysis of MP in cream samples showed recovery percentages between 83% and 106%. Advantages of this sensor are the possibility for the determination of higher concentrations of MP when compared with most other reported sensors for MP. The CNC–rGO nanocomposite-based sensor also depicted good reproducibility and reusability compared to the rGO-based sensor. Furthermore, the CNC–rGO nanocomposite sensor showed good selectivity toward MP with little interference from easily oxidizable species such as ascorbic acid.
Cellulose nanomaterial with rod-like structure and highly crystalline order, usually formed by elimination of the amorphous region from cellulose during acid hydrolysis. Cellulose nanomaterial with the property of biocompatibility and nontoxicity can be used for enzyme immobilization. In this work, urease enzyme was used as a model enzyme to study the surface modification of cellulose nanomaterial and its potential for biosensor application. The cellulose nanocrystal (CNC) surface was modified using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation to introduce the carboxyl group at C6 primary alcohol. The success of enzyme immobilization and surface modification was confirmed using chemical tests and measured using UV-Visible spectrophotometer. The immobilization strategy was then applied for biosensor application for urea detection. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques were used for electroanalytical characterization of the urea biosensor.
Bi3Ni2Ta3O14 pyrochlores and related materials were prepared by solid state reaction at sintering temperatures ranging from 900°C to 1150°C. The BNT cubic pyrochlores could be represented by a general formula Bi3Ni2-xTa3O14-x and phase pure sample was obtained at temperature 1050°C with x = 0.6. This was confirmed by X-ray diffraction analysis and detailed lattice refinement. The single phase material crystallized in a cubic system, space group Fd3m with a = b = c = 10.5134 Å, α = β = γ = 90o, respectively. The sample was further characterized using a combination of techniques including Fourier-Transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), thermogravimetric analysis (TGA) and inductively coupled plasma – atomic emission spectrometry (ICP-AES). The material was thermally stable without any thermal events being observed. Electrical properties of the single phase material were studied by ac impedance spectroscopy starting from room temperature to 800 oC over a frequency range of 5 Hz to 13 MHz. The phase formation and solid solutions of cubic pyrochlores in the Bi2O3-NiO-Ta2O5 (BNT) ternary system were studied thoroughly via combination of characterization techniques.
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