| Nowadays, the face of increasing scarcity of fossil energy and the environment caused by pollution has become the two major crises of the current threat to human survival and sustainable social development. To develop environmentally friendly-, renewable-new energy and to seek development on the positive application of new processes and new materials has attracted so much attention as a promising solution for sustainable development. Carbon is one of the most abundant chemical elements in the universe. The element carbon is capable of forming long chains of carbon-carbon bonds which are strong and stable in nature. This property is known as catenation. Due to this property, compounds of carbon are found in infinite numbers. It is a fact that the numbers of compounds of carbon are much higher than the compounds of any other element, except hydrogen. Thus, expanded graphite (EG) is an excellent inorganic carbon material, which has many advantages such as low density, non-toxicity, non-pollution and easy disposal. Recently, EG was reported to exhibit excellent adsorption for spilled oil floating on water and gas adsorbent due to the worm-like pore structure, weak polarity, hydrophobic and lipophilic nature. So, from the late1980s, much research work of EG has been done as a new type of eco-friendly absorbent. Meanwhile, many scientists focus on the preparation of eco-friendly expanded graphite-based composite materials from modification or composite modification, and then their environmental applications. Based on the report of EG with good adsorption properties of the non-polar organic molecules (such as oils, etc.) and certain adsorption characteristics of the polar molecules under certain conditions, in this paper, new EG-based composite adsorbents was prepared from composite modified loose stated EG and their use in treatment of specified pollutants from aqueous solution.The present study dealt with the preparation of loose stated EG as matrix materials from the expandable graphite by microwave irradiation. Preparation conditions of EG/AC (EG/AC-1and EG/AC-2) were optimized using response surface methodology (RSM). Two quadratic models were developed for yield of EG/AC and adsorption of specified pollutants using Design-Expert software. Then, Co3O4/EG/AC (Co3O4/EG/AC-1and Co3O4/EG/AC-2) were fabricated in situ as heterogeneous catalysts by the decomposition of cobalt nitrate through heat and crystal growth of Co3O4on the surface of EG/AC in1-hexanol solvent. The characteristics of the as-prepared materials were analyzed. Adsorption capacities and mechanism of Cr(Ⅵ) by EG and EG/AC-1were investigated. Adsorption capacities and mechanism of dye MB by EG and EG/AC-2was investigated, too. The as-prepared Co3O4/EG/AC were used to activate peroxymonosulfate (PMS) for azo dye AO7removal from aqueous solution using advanced oxidation processes (AOPs) based on sulfate radicals. The main research results are as follows:(1) EG was prepared in our laboratory by microwave irradiation treatment of the expandable graphite in an EM-3011EB1microwave oven (Sanyo Inc., China). The characteristics of the as-prepared graphite materials were analyzed by SEM-EDX, FT-IR and XRD. The results show that microwave irradiation gives EG with the properties comparable with that prepared by rapid heating.(2) RSM was successfully applied to investigate the effects of preparation conditions, on the adsorption capacity of specified pollutants and yield of the developed EG/AC. The models were used to calculate the optimum operating conditions of preparation of adsorbent providing a compromise between yield and adsorption of the process.①After optimization studies, to preparation of EG/AC-1, the best production methodology involved a0.93of Xp, a40.53%of impregnation concentration and a heating rate of10℃·min-1to413.8℃of activation temperature, which resulted in83.66%of Cr(Ⅵ) removal and35.74%of EG/AC-1yield.②Thus, to preparation of EG/AC-2after optimization studies, the best production methodology involved a22.63%of impregnation concentration, a282.62%of chemical ratio and a heating rate of10℃·min-1to639.53℃of activation temperature, which resulted in99.40%of MB removal and36.11%of novel adsorbent yield. Based on the present work, the prepared EG/AC prove to be economical and cost effective adsorbents to remove specified pollutants from aqueous solution.(3) The adsorption of Cr(Ⅵ) from aqueous solution onto EG and EG/AC-1were investigated in the respective of initial pH value, adsorbent dosage, concentration of initial metal ions and contact time, etc. EG and EG/AC-1adsorbed with Cr(Ⅵ) were characterized by SEM, EDX and FT-1R analysis. The results indicated that EG/AC-1was an effective adsorbent for Cr(Ⅵ). The maximum adsorption amount of Cr(Ⅵ) reach to75.7576mg-g-1. The adsorption capacity of Cr(Ⅵ) onto EG/AC-1was higher than EG at the same pH value. Adsorption of Cr(Ⅵ) is highly pH dependent and the maximum uptake of Cr(Ⅵ) by EG/AC-1was obtained at pH2. Thus, the maximum uptake of Cr(Ⅵ) by EG was obtained at pH3. The adsorption isotherm was determined and fit to three models. But the adsorption of Cr(Ⅵ) by EG and EG/AC-1fit the Langmuir equilibrium isotherm best. The kinetic of the Cr(Ⅵ) ions adsorption onto EG and EG/AC-1were also found to follow pseudo-second-order model. The thermodynamic studies showed that the Cr(Ⅵ) ions adsorption onto EG/AC-1is a spontaneous, endothermic and physical reaction. Thus, the Cr(Ⅵ) ions adsorption onto EG is a non-spontaneous, exothermic reaction.(4) This study investigated the potential use of the as-prepared EG and EG/AC-2as effective adsorbent for the removal of cationic dyes, namely methylene blue (MB), from aqueous solution. The effect of dye concentration, contact time, temperature, adsorbent dosage and pH were experimentally studied to evaluate the adsorption capacity, kinetics and isotherm. Results showed that both EG and EG/AC-2could be employed to remove cationic dyes from aqueous solutions. The adsorbed amount of cationic dye on EG and EG/AC-2increased sharply with an increase of adsorbent dose up to2.0g·L-1and1.0g·L-1, respectively. The initial pH value in the range of10-12does not have any noticeable effect on dye removal by both EG and EG/AC-2. The kinetics of the cationic dye adsorption on the EG and EG/AC-2obey the pseudo-second-order model. Adsorptions of MB on the two adsorbents follow the Langmuir equilibrium isotherm perfectly.-The thermodynamic studies showed that the dye adsorption onto the two adsorbents were all a spontaneous, endothermic and physical reaction.(5) Co3O4/EG/AC (Co3O4/EG/AC-1and Co3O4/EG/AC-2) were synthesized in situ as heterogeneous catalysts by the decomposition of cobalt nitrate through heat and crystal growth of Co3O4on the surface of EG/AC in1-hexanol solvent. The Co3O4/EG/AC catalysts were characterized by SEM, XRD and FT-IR. Results show that Co3O4/EG/AC catalysts are large EG/AC decorated homogenously with dispersed Co3O4nanoparticles. The Co3O4/EG/AC catalysts exhibits an unexpectedly high catalytic activity in the degradation of AO7in aqueous solutions by AOPs based on sulfate radicals, and almost100%decomposition can be achieved in10min with0.2mM Orange Ⅱ,0.05g·L-1catalysts dosage, and2mM PMS dose at room temperature. Though, the degradation rate of AO7in Co3O4/EG/AC-1-PMS system is a little faster than Co3O4/EG/AC-2-PMS system. Meanwhile, in both the two systems the leach of cobalt ions was low. The catalysts exhibited stable performance after three rounds of regeneration. |
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