Preparation And Adsorption Performance Of Wheat Straw Cellulous Based Hydrogel

A wheat straw cellulous-g-poly (potassium acrylate)/polyvinyl alcohol (WSC-g-PKA/PVA) semi-interpenetrating polymer networks (semi-IPN) hydrogel was prepared by grafting AA on straw cellulous and then semi-interpenetrating with PVA. Moreover, wheat straw cellulous-g-poly (potassium acrylate)/Poly dimethyl diallyl ammonium chloride (WSC-g-PKA/PDMDAAC) semi-IPNs hydrogel was also prepared using PDMDAAC as a semi-IPNs polymer. The effect of different synthetic processes on the performance of hydrogel was studied and the optimal synthetic method and parameters were determined as a result. The structure of the hydrogels were investigated by varies physical chemistry methods and modern instruments analysis. Based on the water absorbency researching, the adsorption property and mechanism of hydrogels for NH4+, PO43- and two kinds of heavy metals were investigated. Moreover, the catalytic performances of metal nanoparticles using hydrogel as soft template exploringly studied. The main contents and results are following:(1) Two kinds of wheat straw cellulous based semi-IPNs hydrogels were synthesized using PVA and PDMDAAC as the semi-IPNs polymer, respectively. The structure and performance of the hydrogels were characterized by FTIR, SEM and TGA analysis. Different influence factors on water absorbency of semi-IPNs hydrogels including AA, PVA (PDMDAAC), neutralization degree of AA, crosslinker content and initiator were investigated. The results showed the optimum condition for WSC-g-PKA/PVA semi-IPNs hydrogel preparation was m(WSC):m(AA):m(PVA)=1:10:2, m (K2S2O8): m (AA)=2%; m (MBA):m(AA)=0.4%, neutralization degree of AA 65%, reaction tempreture 50℃ and reaction time 4 h. The water absorbency was 266.82 g/g in distilled water and 34.32 g/g in 0.9 wt% NaCl solution, respectively. The results showed the optimum condition for WSC-g-PKA/PDMDAAC) semi-IPNs hydrogel was that m(WSC):m(AA):m(PDMDAAC)=1:8:1.8, m (K2S2O8):m (AA)=1.5%; m (MBA):m(AA)= 0.3%, neutralization degree of AA 75%, reaction tempreture 60℃ and reaction time 3 h. The highest water absorbency was 210.57 g/g in distilled water and 22.13 g/g in 0.9 wt% NaCl solution, respectively.(2) The swelling behavior and water retention of the WSC-g-PKA/PVA semi-IPNs hydrogel in various conditions were investigated and compared with WSC-g-PKA hydrogel, which indicated the better water absorbency due to the PVA semi-IPN. At pH=6, WSC-g-PKA/PVA semi-IPNs hydrogel reached the maximum water absorbency. The influence of different cations and anions on water absorbency of the hydrogel followed by Na+< K+<Mg2+<Ca2+and Cl-< SO42-. The hydrogel possess lager water adsorption capacity and rate under lower ionic strength and smaller particles. Improving temperatures was helpful to accelerated water adsorption rate except too much higher temperature. Moreover, the ability of the hydrogel to improve the water retention ability of soil was verified by the water retention test in nature, under pressures and in soil, respectively.(3) The adsorption performance and mechanism of WSC-g-PKA/PVA semi-IPNs hydrogel for NH4+ and PO43- were investigated. The effects of time, pH, and salt concentration on the adsorption properties were also studied. The results indicated that hydrogel possessed better adsorption capacities under pH 4.0-9.0 and the effects of different salts were NaCl> MgCl2>FeCl3>CaCl2. The compatibility of Freundlic model for the experimental data indicated the adsorption of NH4+ and PO43- is inhomogeneous multilayer adsorption. The kinetics study indicated that the pseudo-second-order equation was more suitable in describing the whole process of hydrogel for NH4+ and PO43- adsorption. In addition, intraparticle diffussion existed in the whole adsorption process but was not rate control stage. The wheat straw based hydrogel loaded with NH4+ and PO43- could not only be used in the regulating the soil water and fertilizer but could also be regenerated by NaOH.(4) The adsorption performance and mechanism of WSC-g-PKA/PVA semi-IPNs hydrogel for Ni(Ⅱ) and Pb(Ⅱ) were investigated. The effects of pH, temperature and concentration on the adsorption properties were also studied. The differences between the nonlinear and linear least squares methods in estimateing the dynamics and isothermal model parameter were contrastivly analyzed. The results indicated that hydrogel possessed better adsorption capacities under pH 4.0-9.0 for both Ni(Ⅱ) and Pb(Ⅱ). Nonlinear regression analysis can better access to the model parameters. The pseudo-second-order equation was more suitable in describing the whole adsorption process and the process included three-stage intraparticle diffusion and mass transfer. Both Langmuir and Dubinin-Radushkevic could better describe the adsorption process compared with Freundlich. The results of adsorption thermodynamics indicated the physical, endothermic and spontaneous adsorption process. The hydrogel can be regenerated by NaOH to realize recycling utilization.(5) In order to eliminate the secondary pollution and realize the recycling of WSC-g-PKA/PVA semi-IPNs hydrogel loaded heavy metal, the catalytic performance of Ni(Ⅱ) nanoparticle in-situ transformed using hydrogel as soft template was investigated and a new semi-IPNs hydrogel-Ni(Ⅱ) nanoparticle catalytic system was established. The results indicated that the using WSC-g-PKA/PVA semi-IPNs hydrogel-Ni(Ⅱ) nanoparticle catalytic system, NaBH4 could be decomposed to produce H2. The catalytic rate increased as the amount of catalyst increased. The concentration of NaBH4 was an important influence on H2 production amount. As the increasing of temperature, the catalytic rate increased. The semi-IPNs hydrogel-Ni(Ⅱ) nanoparticle catalytic system could be used several times with no influence on catalytic conversion and little decreasing in catalytic activity.