A Study On The Adsorption Of Typical Contaminants By Modified Pomelo Peel

Pomelo peel(PP)is an example of a biomass material,in recent times have been applied as a substrate for the development of novel adsorbents owing to its possession of polar functional groups such as hydroxyl and carboxyl groups which serve as active sites and nodes for further modification processes.In this thesis,novel adsorbents based on PP named as β-CD-PP,CTAB-PP and MIL-101(Fe)-PP were developed using βcyclodextrin,cetyltrimethylammonium bromide(CTAB)and MIL-101(Fe),respectively as modification agents.The suitability and efficiency of these materials as adsorbents for wastewater treatment were assessed using copper ions(Cu2+),bisphenol S(BPS),sulfamethoxazole(SMX),bisphenol A(BPA)and tetracycline hydrochloride(TCH)as pollutants.Furthermore,the adsorption mechanism underlying these adsorption processes were investigated using the following analytical techniques:pH point of zero charge(pHpzc),Scanning electron microscopy(SEM),Fourier-transform Infrared(FTIR),Brunauer-Emmet-Teller(BET)method,X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).In the first study,β-CD-PP was prepared using β-CD and PP as precursors and critic acid as the crosslinker and its adsorption behavior for Cu2+ and BPS were studied.The results showed that the adsorption capacity for Cu2+ reached a maximum of 49.4 mg·g-1 at pH=5,whereas the adsorption capacity for BPS was 26.2 mg·g-1 at pH=7.The presence of coexisting ions did not affect the removal of BPS,whereas the adsorption of Cu2+was significantly reduced with increasing salt concentration.The adsorption processes of Cu2+ and BPS were both well described by the Elovich and Pseudo-second-order kinetic models.,The Freundlich isotherm model was suitable for the adsorption of Cu2+,whereas the Langmuir isotherm model best fitted the experimental data obtained for the adsorption of BPS.The maximum adsorption capacities of β-CD-PP for Cu2+and BPS were 45.8 mg·g-1and 11.3 mg·g-1 at 303 K,respectively.Thermodynamic studies showed that the adsorption of Cu2+ was a spontaneous endothermic reaction with increasing entropy.The adsorption of BPS on the other hand was a spontaneous exothermic reaction with decreasing entropy.In addition,0.1 mol·L-1 HNO3 and 75%ethanol were observed to be the best eluent for the desorption and regeneration of β-CD-PP for Cu2+ and BPS,respectively.β-CD-PP also had weak antibacterial property against E.coli,but strong antibacterial property against S.aureus.The results of the adsorption study of SMX and BPA on CTAB-PP showed that the adsorption performance of the pomelo peel after modification with CTAB was significantly improved exhibiting a maximum adsorption of 123 and 177 mg·g-1 for SMX and BPA,respectively at 303 K.The adsorption quantity of CTAB-PP towards SMX reached a maximum at pH=6 and decreased with increasing coexisting ion concentration,whereas these factors had no obvious effect on its adsorption capacity for BPA.The adsorption processes for both SMX and BPA fitted the Pseudo-secondorder kinetic model and Langmuir isotherm model,indicating that the CTAB-PP adsorption was a homogeneous monolayer adsorption process dominated by chemisorption.The adsorption of SMX was a spontaneous entropy-decrease exothermic reaction,whereas the BPA adsorption was a spontaneous entropy-increase exothermic reaction.Both Thomas model and Clark model could well depict the dynamic adsorption process for SMX and BPA on CTAB-PP.MIL-101(Fe)-PP,was synthesized by loading MIL-101(Fe)onto PP via the hydrothermal method,and its adsorption mechanism for TCH explored.The existing form of TCH in the aqueous phase changed with pH,and the adsorption quantity reached 172 mg·g-1 at pH=10.Compared with PP,the adsorption performance of MIL101(Fe)-PP was obviously improved.In addition,the presence of coexisting ions was not conducive for TCH adsorption.Elovich,Pseudo-second-order kinetic model and Freundlich isotherm model were consistent with the adsorption process,indicating that the adsorption of TCH was mainly a process of heterogeneous multilayer adsorption accompanied by electrostatic interaction and chemical adsorption.Thermodynamic study indicated that the adsorption was a spontaneous endothermic reaction.Desorption and regeneration studies indicated that 0.01 mol·L-1 NaOH was the best eluent for achieving a high reusability efficiency.In this study,novel adsorbents were prepared using pomelo peel as raw material.The synthesis method was simple,green and environmentally benign,and it had excellent adsorption capacity and regeneration performance for specific pollutants.The experimental results provide a theoretical basis for the application of modified biomass materials in wastewater treatment.