In this work, the adsorbent based on tannin (TN) and polyethylenimine (PEI) was prepared via a simple and green method (TNP). The characteristics of the TNP were determined using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, and the results revealed that TNP was synthesized by TN and PEI, and Cu(II) was combined with the -NH or -OH groups of TNP. The effects of the n((TN)):n((PEI)), adsorbent dosage, pH, time, initial metal concentration, and temperature on the adsorption of Cu(II) were investigated in detail. The adsorption of Cu(II) by TNP was greatly affected by pH, and n((TN)):n((PEI)), = 1.5:3 was the optimum mole ratio of raw material to obtain TNP. TNP possessed excellent adsorption properties, and the maximum adsorption capacity of TNP for Cu(II) was 94.5 mg/g at 338.15 K. The adsorption process was in agreement with the Langmuir model and the pseudo-second-order model. Regeneration and reusability of TNP did not decrease significantly after four times of regeneration experiments. The order of competitive ability for the three metal ions was as follows: Pb(II) > Cu(II) > Zn(II). These experimental results suggested that TNP could effectively remove metal ions from aqueous solution. This study is of great significance for environmental protection.

Nitrogen-doped graphene oxide (NGO) was synthesized via pyrolysis of graphene oxide and urea and was characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). An electrochemically reduced nitrogen-doped graphene oxide-modified glassy carbon electrode (ERNGO/GCE) was developed for the determination of carbendazim (CBZ) in food samples. The surface morphology of the modified electrode was characterized by scanning electron microscopy (SEM). Cyclic voltammetry and electrochemical impedance spectroscopy were employed to demonstrate the large electrode surface and fast electron transfer of the ERNGO/GCE. Electrochemical behaviors of CBZ at different electrodes were studied by voltammetry. Experimental results showed that the ERNGO/GCE achieved better performance for the electrochemical oxidation of CBZ than either the bare glassy carbon electrode (GCE) or the nitrogen-doped graphene oxide-modified GCE (NGO/GCE). Under optimized conditions, the ERNGO/GCE exhibited a wide linearity of 5.0~850 μg/L with a detection limit of 1.0 μg/L (signal-to-noise ratio = 3). Application of our proposed method in food products was shown to be practical and reliable.