Sodium acetate trihydrate (SAT) phase change material (PCM) has been well known for thermal energy storage due to its high latent heat and resource abundance. However, SAT suffers from severe latent heat reduction after heating and cooling cycles. Although a few of previous researches showed the reduction could be effectively inhibited by using thickeners, the mechanisms of the reduction process and thickeners’ inhibition have not been deeply explored till now. In this work, SAT modified by 5 wt.% nucleating agent of disodium hydrogen phosphate dodecahydrate (SAT/5 wt.% DSP) was prepared and 200 thermal cycles were carried out. The differential scanning calorimeter, Rheometer, X-ray diffractometry, and scanning electron microscope were used to investigate the extent of latent heat reduction, viscosity, phase composition and microstructure, respectively, and the infrared thermal imaging method was used to evaluate heat storage capacity. It was found that the latent heat of SAT/5 wt.% DSP dropped dramatically and the relative decrease in latent heat was measured to be 22.44%. The lower layer of SAT/5 wt.% DSP contained 24.1 wt.% CH₃COONa, which was quantitatively consistent with the reduction extent. Furthermore, the phase change endothermic time of the lower layer was only 44.1% of that of the upper. SAT/5 wt.% DSP was further modified by 3 wt.% thickener of carboxymethyl cellulose (SAT/5 wt.% DSP/3 wt.% CMC) and endured 200 thermal cycles. The extent of the latent heat reduction of SAT/5 wt.% DSP/3 wt.% CMC was only 9.29%, and phase compositions were more homogeneous. The 3 wt.% CMC increased viscosity by 14 times, which effectively prevented the Stokes sedimentation velocity of CH₃COONa in melts and inhibited the final macroscopic phase separation.

Graphene (RGO), N-doped graphene (NRG) and N/S co-doped graphene (NSRG) were prepared using an improved Hummers’ method and a hydrothermal method. Then, they were used to modify a glassy carbon electrode (GCE) for simultaneous determination of Cd(II), Pb(II), Cu(II) and Hg(II) via the method of square wave anodic stripping voltammetry (SWASV). The comparative study indicates that NSRG/GCE shows the best electrochemical performance among the three graphene modified electrodes. The doping amounts of N and S, deposition potential, stripping frequency and deposition time have significant influence on the detection performance of NSRG/GCE. Under the optimal experimental conditions, NSRG/GCE exhibits good linearity over a wide concentration range from 0.005 to 2.5 μM for Cd(II) and Hg(II), and from 0.005 to 3.0 μM for Pb(II) and Cu(II). During simultaneous determination of Cd(II), Pb(II), Cu(II) and Hg(II), the limits of detection are 6.5 nM, 1.3 nM, 6.0 nM and 16.1 nM (S/N = 3), and the sensitivities are 25.0, 120.7, 102.4 and 36.0 μA μM⁻¹, respectively. Meanwhile, NSRG/GCE has the advantages of high selectivity, great reproducibility and excellent stability. Moreover, successful detection of metal ions in actual seawater samples manifests that NSRG/GCE can be employed in practical applications.