| Polymer/inorganic nano materials hybrid membranes, recently get more attention because of its tremendous characteristics. It has been confirmed that the two different building blocks could boost its properties due to synergetic affects. Membranes for diffusion dialysis (DD) are no exception. DD is a membrane based separation technology and concentration gradient is the unique driving force of DD. DD process is considered to be very effective and efficient in dealing with industrial alkaline wastewater due to its internal advantages (including environment-friendly, low energy consumption and so on). In comparison to acid recovery, usage of cation exchange membranes for alkali recovery is relatively limited due to the lack of suitable membranes which could sustain chemical and mechanical stabilities. In present research, here we report facile fabrication of cation exchange membranes with high OH" flux, low water permeability, strong salts hindering as well as excellent thermal/chemical stability. The as-prepared membranes were employed successfully for alkali recovery via diffusion dialysis. In view of the synthetical properties between polymers and inorganic nano materials, hybrid membranes for DD separation were prepared from sulphonated poly (2,6-dimethyl-1,4-phenyleneoxide) (SPPO) and nano silica via blending method. The as-prepared membranes were detected by diffusion dialysis (DD) of NaOH/Na2WO4 system for alkali recovery, and the relation between structure and property was investigated in the main body. A conclusion was concluded on the bases of experimental results and were given as follows:1) Hybrid membranes for alkali recovery were prepared by incorporating nano silica particles into sulfonated poly (2,6-dimethyl-1,4-phenyleneoxide) (SPPO). The membranes ion exchange capacities (IECs) were observed in the range of 1.48-1.69 mmol/g, water uptake (WR) from 71 to 74%, swelling degree of 73-78% as well as favorable thermal stability and alkali resistance. Prepared membranes were investigated for a simulated waste solution made up of NaOH/Na2WO4 for alkali recovery via diffusion dialysis (DD) at various temperatures. The obtained results showed that the as-prepared hybrid membranes exhibited better separation capacity plus highest hydroxide flux (UOH) i.e.0.014 m/h at 55℃ and an acceptable separation factor of 34.5. The pristine SPPO (as control) exhibited much lower UOH values at the investigated temperature range. The structure and physico-chemical properties of the hybrid membranes were investigated and co-related with the enhanced DD results. Hydroxyl groups at the surface of nano silica particles were supposed to play an important role in OH- diffusion.2) Hybrid membranes for diffusion dialysis were prepared by incorporating sulfonated nano silica particles into sulfonated poly (2,6-dimethyl-1, 4-phenyleneoxide) (SPPO) matrix. The membranes with ion exchange capacities (IECs) of 1.87-2.00 mmol/g showed enhanced thermal stability and alkali resistance. Membranes were tested in NaOH/Na2WO4 feed solution via diffusion dialysis (DD) process. Results showed that as-prepared hybrid membranes exhibited better separation performance at elevated temperature even higher than 35℃. The highest hydroxide flux (UOH) reached 0.015 m/h at 55℃ with a separation factor around 34. Although, pure SPPO (as control) separation factor was higher, however, it exhibits much lower UOH values at the investigated temperature range. The structure and physico-chemical properties of the hybrid membranes were investigated to better understand the DD results. It could be speculated that the presence of sulfonic groups at the surface of nano silica particles were responsible to enhance the transportation of Na+ and OH- ions.3) Hybrid membranes for diffusion dialysis were prepared by blending sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) in hydrogen type (H-SPPO) and amino-functionalized nano silica (AFNS) following by thermal treatment at 80℃. WR (41%-48%), IECs and stability of as-prepared membranes were tested. The obtained results indicated that hybrid membranes possessed good thermal stability and alkali resistance. Microscopic morphology of the membranes was observed by SEM and TEM and results showed well compatibility between H-SPPO and AFNS. Membranes were tested for NaOH/Na2WO4 system via DD process successfully and the membranes exhibited higher OH- dialysis coefficient (UOH=0.0086m*h-1) and ion selectivity (S was 50.3) at ambient temperature, which was much higher than that of commercial cation exchange membranes. The acid-base pairs between -SO3H in H-SPPO main chains and -NH2 in the surface of AFNS play a significant role during separation process.4) Spherical mesoporous silica (SMS) was successfully synthesized firstly and blended with PVA solution to prepare a series of PVA/SMS hybrid membranes. Loading content of SMS (mass ratio to PVA) was 0,2%,4%,6%,8%, respectively. Water uptake (WR) of as-prepared membranes was in the range of 70.1%-105.7% and results of alkali resistance, mechanical strength, thermal stability and microstructure indicated good stability of as-prepared membranes. Membranes performance was tested for a simulated industrial waste solution i.e. NaOH/Na2WO4 system via diffusion dialysis process. The achieved results showed that dialysis coefficients of OH" (UOH) and S were found 0.0105m/h and 36.4 respectively, which increased by 28% and 35.8% than that of pure PVA membrane. These results indicated that the incorporation of SMS might solve the "tradeoff" effect between flux and selectivity in diffusion dialysis process. |
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