Adsorptive Removal Of PPCPs By Biomorphic Nano-HAP Templated From Cotton

PPCPs is short for pharmaceutical and personal care products, which is closely related to human life. As an emerging class of environmental pollutants, PPCPs have been frequently detected in different environment mediums such as surface water, groundwater, drinking water and soil. Most of PPCPs are polar and low volatility, thus contamination of PPCPs in water is quite serious. PPCPs are repoeted as "pseudo persistent" substance and may pose potential risks to human and the ecosystems. The removal of PPCPs is therefore of great importance and urgency.Nano-hydroxyapatite (HAP) in cotton morphology was prepared and employed in adsorptive removal study. Triclosan (TCS) and Ofloxacin (OFL), two typical and representative PPCPs have been chosen to be adsorbate by virtue of quite different physico-chemical property. The surface area and porosity, crystal phase, functional group, morphology and micro-structure of the synthesized HAP were characterized by BET, XRD, FTIR, SEM and TEM. The effects of initial pH, adsorbent dose, initial concentration, contact time, temperature, pH and ionic strength on triclosan and ofloxacin adsorption using HAP in cotton morphology were investigated. Adsorption kinetics, isotherms and thermodynamic parameters were also evaluated and reported. The adsorption mechanism of triclosan and ofloxacin were discussed. Nano-HAP after triclosan and ofloxacin adsorption was also characterized by FTIR, SEM and TEM-EDX.(1) BET results indicated that as-obtained HAP were mesoporous material and has large specific surface area and pore volume. The most probable aperture appeared at3nm and5nm. The formation of slitlike pore was caused by aggregates of HAP nanoparticles. The XRD and FTIR results indicated that the prepared HAP was well crystallized and pure. SEM images showed that the original fibrous morphology of cotton was replicated by HAP. The biomorphic HAP fibers were long, curly, hollow and uniform, which retain the cotton morphology. Further microstructural information of the nano-HAP was provided by TEM. Single HAP was cylindrical rod like, which length was50-100nm and diameter was10-30nm. The crystal lattice of HAP can be seen in the high resolution TEM images. EDX analysis revealed that besides the Cu peaks which came from the copper grids, only Ca, P and O peaks appeared in the spectrum of HAP.(2) Initial pH had crucial effect on adsorption of triclosan and ofloxacin on nano-HAP. The aqueous chemistry and surface charge of the adsorbent are both affected by solution pH. The maximum adsorption of TCS and OFL was observed at pH2.5and4.5respectively. The removal efficiency of TCS and OFL increased with the increased HAP addition, and decreased with the icreased initial TCS and OFL concentration. The adsorption percentage of TCS significantly increased as a function of the ionic strength. Both the charge screening effect and the salting out effect contribute to the increase in TCS adsorption by HAP when ionic strength increases. Ionic strength has little influence on the adsorption of OFL by HAP, the removal rate increased slightly while ionic strength increased.(3) TCS and OFL adsorption on HAP are rapid and almost accomplished within40min and50min respectively. The pseudo-second-order model fits the TCS adsorption experimental data quite well. This implied that chemisorption was the main rate controlling step of the TCS adsorption process. Adsorption of OFL followed the pseudo-first-order model. It was therefore suggested the adsorption of OFL onto HAP was not controlled by a chemisorption process but rather a physical process. Intraparticle diffusion was not the only rate controlling step. Langmuir isotherm can provide a satisfactory fit to the TCS adsorption data, suggesting that TCS adsoption on HAP was mainly a chemisorption process. OFL adsorption on HAP could be well fitted by Freundlich isotherm. The maximum adsorption capacity of the prepared HAP for TCS and OFL were133.33mg/g and29.15mg/g and respectively. The adsorption capacity of the biomorphic HAP for TCS and OFL is comparable as to other various sorbents, especially for TCS.(4) FTIR and TEM-EDX results indicated that TCS and OFL had been adsorbed to HAP respectively. Lewis acid-base reaction may be the dominating mechanism of TCS adsorption. While hydrogen bond between OFL and POH of HAP surface may be the dominating mechanism of OFL adsorption.