Study On Preparation And Properties Of Sericin Modified Polyamide Nanofiltration Membrane

Nanofiltration membrane, as a pressure-driven membrane, has been widely used in thefields of drinking water purification, micro-polluted water treatment, waste-water treatment andresource recovery, separation of industrial fluids and so on for its advantages of high perm-selectivity and low operating pressure. However, the main problem facing with the nanofiltrationmembrane is the membrane fouling, which limits the extended applications of nanofiltrationmembrane. Therefore, it is of great importance to explore new nanofiltration membranes withspecial properties such as antifouling.In this study, interfacial polymerization process was adopted to prepare a novel thin-filmcampsite nanofiltration membrane through the interfacial polymerization of piperazine (PIP), silksericin (SS) and trimesoyl chloride (TMC) on the surface of porous polysulfone (PSF) substrate.The hydrophilic polymer SS was added to the PIP-aqueous phase to modulate the structure andproperty of the formed thin-film composite membrane. The preparation parameters includingconcentrations of PIP, TMC and SS, pH of aqueous phase, reaction time, curing temperature, andcuring time were systematically studied and the optimal membrane preparation conditions wereobtained.The membrane properties in terms of surface chemical structure, morphology,hydrophilicity and charge of obtained composite nanofiltration membrane was characterizedthrough FTIR, EDS, SEM, AFM, surface contact angle measurement and streaming potentialmeasurement. The membrane permeation properties including molecular weight cut-off(MWCO), rejections to different inorganic salts and removals to anionic dyes were evaluatedthrough cross-flow permeation tests. Finally, the anti-fouling properties of the compositemembranes prepared using PIP-aqueous phase containing different content of SS were studiedthrough permeation tests with bovine serum albumin (BSA), sodium dodecyl sulfate (SDS) ortween-80(TW-80) as the model foulant, respectively. The conclusions obtained from theexperimental results were as follows:(1) The results of FTIR and EDS analysis showed that a thin active skin layer had beensuccessfully formed on the surface of the PSF ultrafiltration membrane through the reaction ofPIP, SS with TMC. It was found that the membrane properties including surface hydrophilcity,roughness and charge could be modulated by varing the content of SS incorporated in the PIP-aqueous phase. Compared with the Polypiperazine-amide (PA) thin-film composite membraneprepared thought the reaction of PIP and TMC, the addition of SS in the PIP-aqueous phaseresulted in a smoother, more negatively charged and hydrophilic membrane surface. (2) Parametric study showed that the separation performance of PA membrane modifiedwith SS (SS-PA membrane) was largely affected by reactant concentration, additiveconcentration, and surfactant concentration, pH of aqueous phase, reaction time, curingtemperature, and curing time. With the increase of the PIP concentration, SS concentrationand/or reaction time, the fluxes of SS-PA membrane to electrolytes aqueous solutions increasedfirstly and then declined. With the increase of pH of aqueous phase and/or TMC concentration,the salt rejection of the membrane declined and the permeate flux increased. With increasingcuring temperature and/or prolonging curing time, the rejections of the modified membrane toinorganic salts increased firstly and then declined. The optimal conditions for the preparation ofthe SS-PA thin-film composite membrane were as follows： piperazine=0.15wt%, silksericin=0.06wt%, sodium dodecyl sulfate=0.06wt%, trimesoyl chloride=0.3wt%, pH ofaqueous phase=11.00, reaction time=50s, curing time=15min, curing temperature=50℃.(3) The desired SS-PA thin-film composite membrane had a molecular weight cut off ofaround350g/mol and exhibited a pure water flux of about95.1l/m2.h and a salt rejection of96.1%to500ppm Na2SO4aqueous solution at25℃and0.5MPa. The rejections of the desiredSS-PA membrane to different inorganic salts followed the order of Na2SO4(94.4%)>MgSO4(81.5%)> NaCl(22.4%)> MgCl2(6.3%)> CaCl2(2.3%). An increase of feed saltconcentration resulted in declined flux and salt rejection. As the operating pressure increasedfrom0.3to0.7MPa, the flux increased proportionally, while the salt rejections decreasedslowly-to-rapidly. When tested with50ppm dye aqueous solution under0.5MPa, the dyeremovals of the membrane to Congo red, Methyl blue, Sunset yellow, Alizarin Yellow R,Neutral red were99.3,97.6,96.4,74.8and67.2%, respectively.(4) The addition on SS in the PIP-aqueous phase resulted in an improved anti-foulingproperty of the obtained membrane to BSA and SDS aqueous solution, but has less effect on thefouling behavior of the obtained membrane to TW-80aqueous solution. With the increasingcontent of SS in the PIP-aqueous, the antifouling property of the obtained membrane to BSAaqueous became better. Under the same fouling conditions, the flux decline ratios were47%,37%,25%and13%to the membranes prepared with PIP-aqueous solution containing SScontents of0wt%,0.06wt%,0.08wt%and0.1wt%, respectively.