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Modified hydroxypropyl methylcellulose was synthesized by hydroxypropyl methylcellulose (HPMC), epichlorohydrin, dimethylformamide (DMF) and diethylenetriamine. The chemical functional groups and morphology of the modified hydroxypropyl methylcellulose (MHPMC) were characterized by the Fourier transform infrared spectroscopy, and scanning electronic microscopy, and the crystal structure of MHPMC was studied by X-ray diffraction analyzer. Additionally, the element composition of the adsorbent was analyzed by the energy dispersive spectrometer, and the factors affecting the adsorption performance, such as time (15−240 min), the amount of adsorbent (0.1−0.8 g), initial concentration of ions (30−350 mg•L −1 ) and pH (4−7.5) were estimated. Results from the experimental data showed, under the optimum experimental parameters condition like adsorption time (110 min), adsorption quantity (0.4 g), initial ion concentration (100 mg•L −1 ), and pH (5.5), the adsorption removal rate reached 99.78%. In addition, the adsorption process is well consistent with the quasi-two-stage kinetic model and the Langmuir model, and the negative value of ΔG and the positive value of ΔH denote that the adsorption process of hexavalent chromium loaded on the MHPMC is endothermic and spontaneous.

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Water hyacinth was modified by citric acid to prepare a carboxyl-functionalized water hyacinth (CWH) adsorption material. The effects of pH, contact time, amount of the adsorbent, initial concentration, and temperature on the adsorption of heavy metal ions were investigated. In the experimental study, the optimal pH values of Ni2+, Cu2+, and Cr6+ in the CWH adsorption solution were 7.5, 6.0, and 5.0; the optimum contact times were 300, 180, and 120 min; and the optimum adsorbent dosages were 0.65, 0.50, and 0.40 g, respectively. The adsorption processes of Ni2+, Cu2+, and Cr6+ by CWH are in accordance with the quasi-second-order kinetic model and Langmuir model, with the maximum adsorption capacity being 59.64, 77.98, and 96.89 mg/g, respectively. The thermodynamic model shows that it is an endothermic spontaneous process. Even after five adsorption–desorption cycles, the removal ratios of Ni2+, Cu2+, and Cr6+ by CWH remained about 55.23, 65.63, and 71.46%, respectively. The structure of the water hyacinth before and after modification was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy. The results indicate that the surface of CWH was rough and the number of microporous increased and water hyacinth has been successfully carboxylated. The abovementioned results indicate that CWH can be used as an environmentally friendly and economical adsorbent.

A novel poly-geminal dicationic ionic liquid (PGDIL)-TiO2/Au composite film electrode was successfully prepared by electrochemical polymerization of 1,4-bis(3-(m-aminobenzyl)imidazol-1-yl)butane bis(hexafluorinephosphate) containing polymerizable anilino groups in the electrolyte containing nano-TiO2. The basic properties of PGDIL–TiO2/Au composite films were studied by SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry. The SEM results revealed that the PGDIL–TiO2 powder has a more uniform and smaller particle size than the PGDIL. The cyclic voltammetry results showed that the catalytic effect on electrochemical oxidation of hydroquinone and catechol of the PGDIL–TiO2 electrode is the best, yet the Rct of PGDIL–TiO2 electrode is higher than that of PGDIL and TiO2 electrode, which is caused by the synergistic effect between TiO2 and PGDIL. The PGDIL–TiO2/Au composite electrode presents a good enhancement effect on the reversible electrochemical oxidation of hydroquinone and catechol, and differential pulse voltammetry tests of the hydroquinone and catechol in a certain concentration range revealed that the PGDIL–TiO2/Au electrode enables a high sensitivity to the differentiation and detection of hydroquinone and catechol. Furthermore, the electrochemical catalytic mechanism of the PGDIL–TiO2/Au electrode was studied. It was found that the recombination of TiO2 improved the reversibility and activity of the PGDIL–TiO2/Au electrode for the electrocatalytic reaction of HQ and CC. The PGDIL–TiO2/Au electrode is also expected to be used for catalytic oxidation and detection of other organic pollutants containing –OH groups.