A novel cellulose/chitosan composite nanofiltration membrane prepared with piperazine and trimesoyl chloride by interfacial polymerization

Abstract

Bamboo cellulose (BC) is one of the most abundant renewable, hydrophilic, inexpensive, and biodegradable organic materials. The cellulose membrane is one of the best materials for replacing petroleum-based polymer films used for water purification. In this study, N-methylmorpholine-N-oxide (NMMO) was used as a solvent to dissolve cellulose and chitosan, and a regenerated cellulose/chitosan membrane (BC/CSM) was prepared by phase inversion. A new kind of cellulose/chitosan nanofiltration membrane (IP-BC/CS-NFM) was obtained by the interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC). The IP-BC/CS-NFM was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), the retention rate, and water flux. FT-IR analysis showed that polypiperazine amide was formed. Additionally, FE-SEM and AFM showed that a uniform roughness and dense functional layer was formed on the surface of the IP-BC/CS-NFM. Furthermore, TGA analysis showed that the thermal stability of IP-BC/CS-NFM is better than that of BC/CSM. The inorganic salt retention of IP-BC/CS-NFM was measured using a membrane performance evaluation instrument, following the order R(Na₂SO₄) > R(MgSO₄) > R(MgCl₂) > R(NaCl). At a pressure of 0.5 MPa, the retention rates for NaCl, Na₂SO₄, MgSO₄, MgCl₂, Methyl Orange, and Methyl Blue were 40.26%, 71.34%, 62.55%, 53.28%, 93.65%, and 98.86%, and the water flux values were 15.64, 13.56, 14.03, 14.88, 13.28, and 12.35 L m^-2 h^-1, respectively. The IP-BC/CS-NFM showed better water flux and a higher rejection rate in aqueous dye-salt solutions, and had a good separation performance under different operating pressure conditions.

Fig. 1. Schematic diagram of interfacial polymerization.

Fig. 2. Membrane performance evaluation instrument: (1) feed tank; (2) pump; (3) pressure gauge; (4) membrane cell; (5) permeate end; (6) valve.

Fig. 3. The influence of the PIP concentration on the performance of the membrane: (a) NaCl and (b) Na₂SO₄. The testing conditions employed were 500 mg L⁻¹ NaCl or Na₂SO₄ solution as feed, an operating pressure of 0.5 MPa, and room temperature solution.

Fig. 4. The influence of the time in the aqueous phase on the performance of the membrane: (a) NaCl and (b) Na₂SO₄. The testing conditions employed were 500 mg L⁻¹ NaCl or Na₂SO₄ solution as feed, an operating pressure of 0.5 MPa, and room temperature solution.

Fig. 5. The influence of the TMC concentration on the performance of the membrane: (a) NaCl and (b) Na₂SO₄. The testing conditions employed were 500 mg L⁻¹ NaCl or Na₂SO₄ solution as feed, an operating pressure of 0.5 MPa, and room temperature solution.

Fig. 6. The influence of time in the organic phase on the performance of the membrane: (a) NaCl and (b) Na₂SO₄. The testing conditions employed were 500 mg L⁻¹ NaCl or Na₂SO₄ solution as feed, an operating pressure of 0.5 MPa, and room temperature solution.

Fig. 7. The influence of operating pressure on the performance of IP-BC/CS-NFM: (a) NaCl and (b) Na₂SO₄. The testing conditions employed were 500 mg L⁻¹ NaCl or Na₂SO₄ solution as feed and room temperature solution.

Fig. 8. FT-IR spectra of IP-BC/CS-NFM (a), BC/CSM (b), CS (c), and BC (d).

Fig. 9. (a) SEM of the BC/CSM surface, (b) SEM of the BC/CSM cross-section, (c) SEM of the IP-BC/CS-NFM surface, (d) SEM of the IP-BC/CS-NFM cross-section.

Fig. 10. AFM images of BC/CSM (a) and IP-BC/CS-NFM (b).

Fig. 11. TG and DTG patterns for BC, CS, BC/CSM, and IP-BC/CS-NFM.

Fig. 12. PEG retention curves of IP-BC/CS-NFM. The testing conditions employed were 100 mg L⁻¹ PEG solutions as feed, an operating pressure of 0.5 MPa, and room temperature solution.

Fig. 13. Contact angle images of BC/CSM and IP-BC/CS-NFM.