Preparation And Properties Of Hydrophilic Loofah Based Materials

In recent years, heavy metals pollution is a serious threat to the human’s ecological environment and health. Among the many treatment methods, the adsorbent is one of the most effective methods to removal heavy metal ions in water. In this paper, natural loofah materials with high levels cellulose and porous was studied, using the redox initiator system, successful grafted polymerization in loofah to obtain a hydrophilic loofah. And the reaction conditions on the water absorption and adsorption of heavy metal ions also were researched, selecting the optimized preparation conditions to get excellent absorbent / adsorbent performance material, providing a foundation for a wide range of applications in related fields.First, we used sodium hydroxide solution to remove the lignin and hemicellulose on pristine loofah surface at alkali concentration(0-10 mol / L), temperature(0-100oC) and time(0-24h).And then we picked up the optimized alkaline treatment conditions, CNaOH = 1mol / L, 12 h, 50 oC. This process is the basis for next successful graft polymerization.We studied the influence of the feed ratio of [Ce]/[OH] and [AM]/[OH], reaction temperature and reaction time on grafting percent(GP) and grafting efficiency(GE). The experiment data showed that the GP and GE increased at first and then decreased with the feed ratio of [Ce]/[OH] increased. Generally, the grafting sites would be increased with the feed ratio of [Ce]/[OH] increased. However, the high feed ratio of [Ce]/[OH] without sufficient nitric acid would lead to the hydrolysis of ceric(IV) initiator, thus decreasing active sites. Moreover, the oxidative termination of free radicals became dominant and the competing homopolymer formation was more favored than grafting. The increasing the ratio of [AM]/[OH] would leads to the addition of monomers in contact possibility to a grafting site and promotes the copolymerization reaction. However, at a high feed ratio of [AM]/[OH], the reactivity rate of homopolymer formation became dominant, i.e., AM preferred to polymerize into homopolymers. The viscosity of the system increased as grafting polymerization proceeds, thus hindering the movement of free radicals and decreasing the rate of diffusion of AM molecules from the solution phase to the active sites on the luffa sponge. Moreover, the possibility of chain transformation and termination was increased. Thus the GP and GE showed a decreasing trend with a higher ratio of [AM]/[OH]. The GP and GE also increased at first time with temperature and then deceased at high temperatures. The aforementioned result was related to the fact that the decomposition rate of ceric(IV) ions increased with increasing temperature. More active sites were produced on the luffa sponge to initiate the grafting copolymerization, and the rate of diffusion of monomer from the solution phase to the active sites was also accelerated. However, above 25 °C, the possibility of chain transformation and termination was accelerated and the increased reactivity rate of homopolymer led to the GP and GE decreased. At the beginning of the reaction, the GP and GE increased from 0 h to 24 h,. However, after 24 h, both GP and GE maintain a relatively constant level.The amide groups in AM grafted to luffa sponge(luffa-g-PAM) had been partial hydrolyzed under a NaOH solution and the hydrolysis degree(HD) reached approximately 21%. The pristine, alkalized, grafted, and hydrolyzed luffa sponges exhibited rapid water absorption kinetics, which fit the pseudo second-order rate equation well. The hydrolyzed luffa sponge(luffa-g-(PAM-co-PAANa)) also showed high water absorption capacities of up to 75 g·g-1 because of the electrostatic repulsion between the COO- ions in the hydrolyzed sample.We also studied the adsorption performances of hydrophilic luffa sponges luffa-g-(PAM-co-PAANa) for Cu2+ and Pb2+ in water. The adsorption kinetic curves of hydrophilic luffa sponge fit well with the pseudo-second-order kinetic model. The adsorption capacity(Qe) of hydrophilic luffa sponge increasesd with grafting percentage, and the highest Qes can reached up to 647 mg·g-1 for Cu2+ and 887 mg·g-1 for Pb2+ in a single metal ion system. Langmuir and Freundlich isotherm models were applied to fit the experimental data, indicating a monolayer adsorption of Cu(II) and Pb(II) ions on the surface of the hydrophilic luffa sponge. The hydrophilic sample could be regenerated through a simple route and reused in eight adsorption–desorption cycles without any significant loss in the adsorption capacity.Definitely, this kind of hydrophilic luffa sponges not only had a higher saturation water absorption, but also exhibited an excellent adsorption performance for heavy metal ions. It could be reused by a simple elution, indicating that excellent adsorption–desorption property, showed a potential application in the purification of polluted water system.