Graphene oxide-TiO2 composite as a novel adsorbent for the preconcentration of heavy metals and rare earth elements in environmental samples followed by on-line inductively coupled plasma optical emission spectrometry detection

A graphene oxide (GO)-titanium dioxide (TiO2) composite was prepared by hydrolysis of Ti(BuO)(4) to TiO2 on GO nanosheets. The mass ratio of GO-TiO2 in the composite was optimized and the GO-TiO2 (1 : 1) composite was selected as the adsorbent for the preconcentration of heavy metals and rare earth elements (REEs). The prepared GO-TiO2 (1 : 1) composite was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis and differential thermal gravimetry measurements (TGA/DTG), powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicated that the anchored TiO2 was in the nanometer-sized anatase form and the GO-TiO2 (1 : 1) composite inherited both features of GO and TiO2. It exhibited good stability, strong anti-interference capability, and high adsorption capacities for target ions. By using GO-TiO2 (1 : 1) composite as the micro-column packing material, a method for on-line solid phase extraction (SPE) coupling with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed for the quantification of heavy metals and REEs in environmental water and sediment samples. The parameters influencing the on-line SPE of target elements including pH, elution conditions, sample flow rate and sample volume were optimized. Under the optimized conditions, a wide linear range over 0.5-1000 ng mL(-1) was obtained for target elements. The detection limits (LODs) and the relative standard deviations (RSDs) of Cu, Pb, La, Ce, Eu, Dy and Yb were 0.48, 2.64, 0.41, 0.24, 0.13, 0.26 and 0.21 ng mL(-1) and 6.4, 9.8, 8.6, 3.2, 5.6, 4.5 and 6.2% (C = 10 ng mL(-1), n = 7), respectively. For all the analytes, the overall adsorption process was controlled by diffusion and chemical reaction, and chemical reaction played a dominant role. The established method of on-line SPE-ICP-OES was validated by analyzing Certified Reference Material GBW07301a (Stream sediment), and the determined values are in good agreement with the certified values. The method was also applied for the determination of the target heavy metals and REEs in environmental water (even sea water) and sediment samples, and the recoveries were 82.4-115.5% and 83.8-114.8% for the spiked water and sediment samples, respectively.