Despite
growing demands for high-temperature wastewater treatment,
most available polymeric membranes are limited to mild operating temperatures
(<50 °C) and become less efficient at high temperatures. Herein
we show how to make thermally stable reverse osmosis thin-film nanocomposite
(TFN) membranes by embedding nanodiamond (ND) particles. Polyamide
composite layers containing different loadings of surface-modified
ND particles were synthesized through interfacial polymerization.
The reactive functional groups and the hydrophilic surface of the
NDs
intensified the interactions of the nanoparticles with the polymer
matrix and increased the surface wettability of the TFN membranes.
Contact angle measurement showed a maximum decrease from 88.4°
for the pristine membrane to 58.3° for the TFN membrane fabricated
with 400 ppm ND particles. The addition of ND particles and ethyl
acetate created larger surface features on the polyamide surface of
TFN membranes. The average roughness of the membranes increased from
108.4 nm for the pristine membrane to 177.5 nm for the TFN membrane
prepared with highest ND concentration. The ND-modified TFN membranes
showed a higher pure water flux (up to 76.5 LMH) than the pristine
membrane (17 LMH) at ambient temperature at 220 psi and room temperature.
The TFN membrane with the highest loading of ND particles overcame
the trade-off relation between the water flux and NaCl rejection with
76.5 LMH and 97.3% when 2000 ppm of NaCl solution was filtered at
220 psi. Furthermore, with increasing ND concentration, the TFN membrane
showed a lower flux decline at high temperatures over time. The TFN400
prepared with 400 ppm of m-phenylene diamine functionalized
ND particles had a 13% flux decline over a 9 h filtration test at
75 °C. This research provides a promising path to the development
of high-performance TFN membranes with enhanced thermal stability
for the treatment of wastewaters at high temperatures.
Lignin, the second
most plentiful biopolymer, is produced on a
large scale as the waste of the pulp and paper industries. Conventionally,
lignin is incinerated for energy generation, while less than 2% of
the produced mass is converted to value-added products. Herein, we
employed hydrophilic sulfonated kraft lignin (SKL) to modify the selective
layer of thin-film composite (TFC) forward osmosis (FO) membranes.
Different concentrations of SKL (1, 3, and 6 wt %) were dispersed
in m-phenylenediamine solution prior to the polymerization
reaction with trimesoyl chloride-heptane solution. The modified membrane
with a maximum amount of SKL (M3) provided 33.5 LMH water flux, a
twofold improvement compared to the pristine membrane, when tested
in the FO configuration with 2 M NaCl and deionized water as draw
and feed solutions, respectively. Moreover, M3 showed a significantly
lower flux decline than the unmodified membrane in the fouling experiments
against sodium alginate solution as a synthetic wastewater and boiler
feed water as an industrial process-affected water of the oil sands
industry. The water contact angle decreased from 88.7° for the
pristine membrane to 70.6° for M3, indicating the enhanced wettability
of the modified membranes by the incorporation of SKL particles. Our
work presents a novel application for SKL to be used as a hydrophilic
modifier in the synthesis of TFC polyamide membranes with enhanced
permeation and antifouling performance.
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