Abstract

Few researches focused on the combination of ultrasound and multi-walled carbon nanotubes (MWCNT) in wastewater treatment. In this study, it was found that the combination of ultrasound and MWCNT was more effective in the removal of Acid orange 74 (AO 74) in comparison to single method. And there was a remarkable synergistic effect in the ultrasound/MWCNT combined system. The adsorption behaviour of AO 74 by the combination of ultrasound and multi-walled carbon nanotubes (MWCNT) was investigated under various experimental conditions. The adsorption performance was slightly inhibited with increasing temperature. This fact showed that the adsorption process was exothermic. The removal ratio was improved with increase in MWCNT dosage, which could be attributed to the increased adsorption sites and increased surface area. The dye removal decreasedfrom 96.0 to 41.5% with an increase in the initial concentration of dye from 15 to 100 mg/L. Lower removal ratios at higher dye concentrations were due to the saturation of adsorption, though the adsorption capacity increased from 14 to 41.5 mg/g. It may be due to the high concentration of dye which can provide a high driving force of concentration gradient to overcome all mass transfer resistance. With the increase in pH, removal ratios of AO 74 decreased gradually from pH 3 to 11. At low pH values, the surface of the adsorbent solids was positively charged and easily adsorbed the AO 74 ions having negative charges. But at high pH values, the surface charge of MWCNT got negatively charged, which did not favour the adsorption of negatively charged dye anions. Experimental isotherm data were represented with Langmuir and Freundlich adsorption models. Langmuir isotherm equation fitted better than Freundlich isotherm equation for this system, which meant adsorption of dye onto MWCNT was monolayer adsorption with a finite number of identical sites. The adsorption of AO 74 followed pseudo second-order kinetics. Kinetics analysis suggested lower temperature was favourable for AO 74 adsorption on MWCNT under ultrasound and justified the exothermic adsorption process.

中文翻译：

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超声辐照下多壁碳纳米管对酸性橙74水溶液的脱色

摘要

很少有研究将超声波和多壁碳纳米管（MWCNT）结合用于废水处理。在这项研究中，发现与单方法相比，超声和MWCNT的组合在去除酸性橙74（AO 74）方面更有效。超声/ MWCNT组合系统具有显着的协同作用。在各种实验条件下研究了超声与多壁碳纳米管（MWCNT）结合对AO 74的吸附行为。随着温度的升高，吸附性能受到轻微抑制。该事实表明吸附过程是放热的。随着MWCNT剂量的增加，去除率得以提高，这可以归因于增加的吸附位点和增加的表面积。随着染料初始浓度从15 mg / L增加到100 mg / L，染料去除率从96.0降低到41.5％。尽管吸附容量从14增加到41.5 mg / g，但在较高的染料浓度下，较低的去除率是由于吸附饱和所致。可能是由于染料的高浓度可以提供高浓度梯度驱动力来克服所有传质阻力。随着pH的增加，AO 74的去除率从pH 3逐渐降低到11。在低pH值下，吸附固体表面带正电，并易于吸附带负电的AO 74离子。但是，在高pH值下，MWCNT的表面电荷带负电，这不利于负电荷染料阴离子的吸附。等温线实验数据用Langmuir和Freundlich吸附模型表示。对于该系统，Langmuir等温线方程比Freundlich等温线方程拟合得更好，这意味着染料在MWCNT上的吸附是单层吸附，具有有限数目的相同位点。AO 74的吸附遵循伪二级动力学。动力学分析表明，较低的温度有利于超声下AO 74在MWCNT上的吸附，并证明了放热吸附过程的合理性。