Preparation Of In-situ Magnetized Materials And Their Applications In Removal Of Dye Pollutants

Dye-containing wastewater has complicated components and high chromacity, and is difficult to degradate directly. This effluent poses a serious hazard to the environment if it is not treated carefully before discharge. Therefore, it is the trend to develop methods that are low-energy, easily operated, low-cost, efficient and environmentally acceptable for the purification of dye-containing wastewater. Recently, adsorption has been recognized as the most popular treatment method for the removal of dyes from aqueous solution due to its high efficiency, wide-ranging availability and ease of operation. Magnetic micro/nanomaterial possessed strong magnetic response and large specific surface area is a promising adsorbent, which can be collected facilely by application of an external magnet after adsorption. The magnetic micro/nanomaterial becomes one of the hot topics in the field of wastewater treatment. However, almost all reported methods for the preparation of magnetic adsorbents (e.g., prepare magnetic particles first and then modify their surface; introduce magnetite particles into/on the nonmagnetic adsorbents) are time-consuming and laborious, which further restrict their extensive use to some certain extent. On the basis of co-mixing method for facile and rapid fabrication of magnetic micro/nanomaterial, an "in situ magnetization" strategy was proposed, which merged the preparation of magnetic adsorbent and the dye removal into a single process.In this report, the author tried to develope some new in-situ magnetized materials and, meanwhile, apply them as adsorbents for removing dye pollutants. The main contents in the report are as follows:Chapter1The preparation and modification of magnetic micro/nanomaterial were reviewed and emphasis was laid on their applications in environment.Chapter2Magnetic carbon nanotube (abbreviated as mCNT) was in-situ formed in methyl blue (MB) solution by a simple co-mixing procedure and acted as adsorbent for MB removal. The adsorption performance of mCNT was evaluated systematically. Equilibrium of MB adsorption was attained in30min, maximum adsorption occurred at pH36, and MB adsorption was independent of ionic strength. MB adsorption onto mCNT followed pseudo-second-order kinetic model. According to the Langmuir isotherm, adsorption capacity of mCNT for MB was115.34mg-g-’at303.15K. Thermodynamic analysis suggested MB adsorption onto mCNT was a spontaneous process. Reusability study results showed that97.06,96.26,94.33,92.91and90.14%of MB were removed in five consecutive cycles.Chapter3The chitosan-decorated carbon nanotube (CS/CNT), prepared via a "surface deposition-crosslinking" method, exhibited an aggregation microstructure with plentiful interstitial spaces. By introducing magnetic nanoparticle (MNP) into CS/CNT dispersion solution, MNP was embedded in the CS/CNT aggregates, which leaded to the formation of magnetic CS/CNT (mCS/CNT). mCS/CNT was acted as adsorbent for removal of anionic azo dye (acid red18(AR18)). Effects of pH, ionic strength, contact time, temperature, and initial AR18concentration on adsorption efficiency were investigated. Results showed that AR18adsorption could achieve equilibrium quickly and maximum adsorption capacity could be up to809.9mg·g-1at323.15K. Adsorption processes could be well described by the pseudo-second-order kinetic model, and the rate-limiting step was a combination of external and intraparticle diffusions. Adsorption isotherms indicated that the AR18adsorption obeyed Redlich-Peterson and Freundlich models. Thermodynamic analysis suggested the AR18adsorption was a spontaneous process. Reusability study results showed that the removal of AR18kept relatively constant (99.11%-99.76%) in ten consecutive cycles.Chapter4The chitosan-coated lignocellulose (CS/LCF) was prepared via a "surface deposition-crosslinking" approach for the first time using two low-cost biomasses (i.e. LCF and CS) as raw materials. Magnetically retrievable chitosan/lignocellulose (mCS/LCF) was developed via directly mixing CS/LCF and magnetic nanoparticle (MNP) in an anionic azo dye (acid red18(AR18)) solution, and the resultant was acted as adsorbent for removal of AR18. To fully reveal the adsorption property of mCS/LCF for AR18removal, the study to investigate the effect of various operational parameters including solution pH, ionic strength, contact time, initial AR18concentration, and temperature on the removal efficiency was conducted. Under the optimal conditions (pH3.0;303.15K), the maximum adsorption capacity could achieve1184.0mg-g1, which was even much higher than that obtained by pure nanochitosan (828.1mg-g"1)-Kinetic experiments clearly indicated that adsorption of AR18onto mCS/LCF was controlled by both external diffusion and intraparticle diffusion. Equilibrium data could be well described by Sips isotherm, and the thermodynamic data suggested that AR18adsorption onto mCS/LCF was a spontaneous process. Test of reusability suggested mCS/LCF was a cost-efficient adsorbent (the removal rate of AR18kept relatively constant (99.48%-99.88%) in ten consecutive cycles).Chapter5The carbon-decorated lignocellulose fiber (LCF@C) was successfully synthesized via a hydrothermal carbonization (HTC) process for the first time using lignocellulose fiber (LCF) and glucose as raw materials. Magnetically retrievable carbon-decorated lignocellulose fiber (mLCF@C) was developed by directly mixing LCF@C with magnetic nanoparticle (MNP) in methylene blue (MEB) solution, and the resultant was acted as adsorbent for removal of MEB. Results demonstrated that MEB could be efficiently removed by mLCF@C. Under the optimal conditions (pH10.0;313.15K), the maximum adsorption capacity was up to341.2mg-g-’. Kinetic experiments clearly indicated that adsorption of MEB onto mLCF@C was controlled by both external diffusion and intraparticle diffusion. Equilibrium data could be well described by Sips isotherm, and the thermodynamic data suggested that MEB adsorption onto mLCF@C was a spontaneous process. Moreover, reusability of mC@LCF was evaluated, and the results showed that the removal of MB could exceed90%in seven consecutive cycles.