Ultralong hydroxyapatite-based forward osmosis membrane for freshwater generation

Increasing global water shortages are accelerating the pace of membrane manufacturing, which generates many environmentally harmful solvents. Such challenges need a radical rethink of developing innovative membranes that can address freshwater production without generating environmentally harmful solvents. This work utilized the synthesized ultra-long hydroxyapatite (UHA) by the solvothermal method using the green solvent oleic acid in preparing UHA-based forward osmosis membranes. The membranes were developed using different loading ratios of graphene oxide (GO) by vacuum-assisted filtration technique. The prepared GO/UHA membranes were identified using X-ray diffraction, scanning electron microscope, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Water contact angle and pore size distribution were determined for the obtained GO/UHA membranes. The obtained hierarchical porous structure in the prepared membranes with interconnected channels results in a stable water flux with reverse salt flux. The best water flux rate of 42 ± 2 L·m⁻²·h⁻¹ was achieved using the 50 mg GO/UHA membrane, which is 3.3 times higher than the pristine membrane, and a reverse salt flux of 67 g·m⁻²·h⁻¹. The obtained results showed a promising capability of a new generation of sustainable inorganic-based membranes that can be utilized in freshwater generation by energy-efficient techniques such as forward osmosis.