Modification Of Natural Cellulose And Hydrotalcite Materials And Their Adsorption Of Heavy Metal And Phosphate

Adsorption is a method that utilizes the interaction between adsorbates and adsorbents to remove pollutants from wastewater. One of the most urgent problems to be solved in water pollution control process is how to explore and develop efficient and low-cost adsorbent. It is an environmental friendly and economical way of treating wastewater using natural substances after modifying them with functional groups. In this essay, the natural-acquirable material, cellulose and Mg-Al Layered Double Hydroxide (Mg-Al LDH), were used as substance to be modified. The chemical and physical properties of the adsorbents before and after modification were carefully characterized and the modified adsorbents were applied in Cu(II) and phosphate adsorption removal, respectively. The adsorption kinetics and thermodynamics were studied and the adsorption mechanism was also interpreted. The main contents are as follow:1. A two-step modification method, first 2,2,6,6-tetramethyl piperidine-1-oxygen (TEMPO) oxidation and then (polyethyleneimine) PEI grafting, was used on cellulose raw material. The modified adsorbent, TEMPO oxidized cellulose nanofibril-PEI (TOCN-PEI), has a cellulose nanofibril structure with quantities of carboxyl and amino groups on its surface and characterization of adsorbents proved the successful introduction of functional groups. Adsorption experiments showed that the Cu(II) adsorption capacity of TOCN-PEI was improved from 0.97 mg g-1 to 52.32 mg g-1 compared with raw cellulose and it was further proved that carboxyl and amino groups were responsible for Cu(II) binding. The adsorption process suited pseudo-second order and Langmuir model. The adsorption was an exothermic reaction driven by enthalpy change. The initial Cu(II) concentration and pH have influence on Cu(II) adsorption. Recycling experiment showed that the adsorbent can retain about 33 mg g-1 Cu(Ⅱ) adsorption capacity after regeneration. The study provides a highly efficient and recyclable adsorbent for Cu(Ⅱ) removal.2. The Mg-Al LDH was used as substance and it was further modified with Hydrated Ferric Oxide (HFO) to obtain a composite material LDH-HFO. The LDH-HFO adsorbent was applied in phosphate removal and adsorption experiments show the phosphate removal capacity of LDH-HFO was improved from 8.82 mg g-1 to 42.60 mg g-1 compared with raw LDH. The adsorption of phosphate on LDH-HFO was due to two parts:first is the anion exchange capacity of LDH and second is the complexity effect of LDH-HFO adsorbent. The adsorption suited pseudo-second order and Langmuir model. Increase of pH would first increase the phosphate adsorption capacity and then decrease it. High concentration of different competing anions in solution have different impact on phosphate uptake. Common ions in water like chloride ions and nitrate have little impact on phosphate uptake capacity. The study provides a potential adsorbent for effective and selective removal of phosphate.