ABSTRACT
BACKGROUND: The aim of this study was to investigate the removal of Cr (VI) using Green-Graphene Nanosheets (GGN) synthesized from rice straw. METHODS: Synthesis of the GGN was optimized using response surface methodology and central composite design (CCD). The effect of two independent variables including KOH-to-raw rice ash (KOH/RRA) ratio and temperature on the specific surface area of the GGN was determined. To have better removal of Cr (VI), GGN was modified using the grafting amine group method. In the Cr (VI) removal process, the effects of four independent variables including initial Cr (VI) concentration, adsorbent dosage, contact time, and initial solution pH were studied. RESULTS: The results of this study showed that the optimum values of the KOH/RRA ratio and temperature for the preparation of GGN were 10.85 and 749.61 °C, respectively. The maximum amount of SSA obtained at optimum conditions for GGN was 551.14 ± 3.83 m 2 /g. The optimum conditions for Cr (VI) removal were 48.35 mg/L, 1.46 g/L, 44.30 min, and 6.87 for Cr (VI) concentration, adsorbent dosage, contact time, and pH, respectively. Based on variance analysis, the adsorbent dose was the most sensitive factor for Cr (VI) removal. Langmuir isotherm (R2 = 0.991) and Pseudo-second-order kinetic models (R2 = 0.999) were the best fit for the study results and the Q max was 138.89 mg/g. CONCLUSIONS: It can be concluded that the predicted conditions from the GGN synthesis model and the optimum conditions from the Cr (VI) removal model both agreed with the experimental findings.
ABSTRACT
The performance of a photo-reactor packed with titanium dioxide (TiO2) immobilized on glass beads, initiated by irradiation with natural and artificial ultraviolet (UV) sources, was evaluated in terms of the degradation efficiency of petroleum aromatic hydrocarbons. The effects of parameters such as pH, reaction time, hydrogen peroxide (H2O2) concentration and some ions were investigated. Additionally, the degradation of total organic carbon (TOC) and the formation of byproducts were studied. Photodegradation rates ofbenzene, toluene, ethylbenzene and xylenes (BTEX) by processes of UV/TiO2 and UV/TiO2/H2O2 were found to obey pseudo first-order kinetic models. Results indicated that the effect of pH value was negligible at the pH range of 5.5 to 8.5. TOC removal improved with addition of H2O2 demonstrating that a lack of hydrogen peroxide leads to incomplete mineralization. The effect of cations and anions on the photodegradation efficiencies of BTEX revealed that Mg2+ and Ca2+ caused the most deterioration in BTEX degradation efficiency. However S4O(2-) and CO3(2-) had the most salient inhibitory effects compared with other tested anions. The degradation efficiencies of both systems were investigated for the treatment of real polluted groundwater collected from the city of Tehran. Results showed that the degradation efficiencies of BTEX declined in the presence of inorganic and organic competitor species.
