Nanofiltration Filter Paper Based on Ultralong Hydroxyapatite Nanowires and Cellulose Fibers/Nanofibers

A filter paper with a large number of nanopores and channels is vital for highly efficient nanofiltration to significantly increase the water flux without sacrificing the separation efficiency. In this work, we report a new kind of nanofiltration filter paper consisting of a cellulose nanofiber (CNF) barrier layer on the cellulose fiber (CF)/ultralong hydroxyapatite nanowire (HAPNW) substrate. The CF/HAPNW filter paper and CNF/HAPNW filter paper can be prepared by a simple papermaking process including filtration, hot pressing, and drying. The porous network formed by the interweaving of CFs and HAPNWs provides vital channels for rapid water transportation. The experiments indicate that the pure water flux (PWF) of the CF/HAPNW filter paper is as high as 544.4 L m –2 h –1 bar –1, which is about 50 times that of the CNF/HAPNW filter paper. Compared with the nanofiltration filter paper based on the CNF/HAPNW substrate, the PWF of the CNF–CF/HAPNW nanofiltration filter paper can be enhanced by 20% with rejection rates above 95% for four different dyes. Moreover, the CNF–CF/HAPNW nanofiltration filter paper shows a relatively high rejection rate for Na 2 SO 4 (75.7%) and NaCl (65.8%). The high PWF and excellent water filtration performance make the as-prepared CNF–CF/HAPNW nanofiltration filter paper promising for application in water purification.