Table 3.

Summary of studies using MNPs as the DS in the FO process.

Particles and Coating/Functionalization	MNP Synthesis Method	Particle Size (nm)	FO Membrane	Draw Solution	Osmotic Pressure (bars)	Feed Solution	Water Flux (LMH)	Reverse Solute Flux (gMH)	MNP Recovery Method	Saturated Mass Magnetization (emu·g−1)	Recovery	Ref.
MNPs coated/functionalized with organic acids and their derivatives
Citric acid-coated MNPs	Co-precipitation	3–7	AIM™ HFFO membrane (Aquaporin A/S, Kongens Lyngby, Denmark); A = 180.0 cm2	3.70% (w/w)	18.7	Deionized water	9.2	0.08	-	44.0	-	[67]
		40	Polyethersulfone thin film composite FO membranes	600.00 g·L−1	80.0	3.5% (w/w) NaCl	8.5	>0.10	Magnetic field and nanofiltration	60.0	≈100.0% t = 10 min	[68]
Dehydroascorbic acid-coated MNPs		20	Cellulose triacetate/ cellulose acetate FO membrane; A = 40.0 cm2	0.06 g·L−1	-	Deionized water	6.0	-	Magnetic field	77.7	≈100.0%	[69]
Multicoated MNPs with polyacrylic acid as a terminal hydrophilic ligand		12	AIM™ HFFO (Aquaporin A/S, Kongens Lyngby, Denmark); A = 180.0 cm2	0.60%	8.9		4.1	-		-	67.6%	[58]
Polyacrylic acid-coated MNPs	Microwave irradiation and co-precipitation	7	AIM™ HFFO module (Aquaporin A/S, Kongens Lyngby, Denmark); A = 180.0 cm2	0.70%	12.8		8.1	-		19.4	≈100.0%	[56]
	Thermal decomposition	8–30	Cellulose triacetate FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 20.0 cm2	0.08 M	-		13.9	-		-	≈100.0%	[70]
						35 g·L−1 NaCl	6.3
		5	Commercial FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 8.0 cm2	0.08 M	70.9	Deionized water	12.0	-	Ultrafiltration	-	≈100.0%	[71]
						3.5% (w/w) NaCl	3.0
		20–30		0.05 M	-	Deionized water	7.7	-	Magnetic field	-	≈100.0%	[72]
Polyethylene glycol dicarboxylic acid- functionalized SiO2-coated MNPs		-	FO membrane (Aquaporin A/S, Kongens Lyngby, Denmark); A = 31.0 cm2	8.00 g·L−1	-	40 mg·L−1 NaCl	12.2	-		5.0	63.4%	[15]
Poly-sodium acrylate-coated MNPs	Co-precipitation	520	AIMTM membrane (Aquaporin A/S, Kongens Lyngby, Denmark); A = 33.2 cm2	7.00%	9	Deionized water	3.8	0.05	-	25.0	-	[73]
		77–166	Cellulose triacetate FO membrane; A = 98.0 cm2	1.00% (w/w)	1.3		-	-	-	-	-	[74]
Poly-sodium acrylate-coated MNPs	Thermal decomposition	7	Specialized carbon nanotube FO membrane (Porifera Inc., San Leandro, CA, USA); A = 42.0 cm2	0.07% (w/v)	25.3	Deionized water	11.7	-	Magnetic field and heating	-	≈100.0% t = 1–5 min	[75]
		9		0.13% (w/w)	11.4		5.3	-	Magnetic field	-	≈100.0% t = 5 min	[76]
Sodium oleate-coated MNPs	Co-precipitation	32	Cellulose triacetate magnetic composite FO membrane; A = 23.7 cm2	0.1 g·L−1	-	1.0 M NaCl	11.4	-		-	84.4%	[77]
Tri-sodium citrate- functionalized SiO2-coated MNPs		20–40	Cellulose triacetate FO membrane; A = 14.0 cm2	80.00 g·L−1	125.6	Deionized water	17.1	1.50		32.7	≈100.0%	[66]
						0.5 M NaCl	2.7	-
Tri-sodium citrate-coated MNPs		66–69	Cellulose triacetate FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 140.0 cm2	2.00 g·L−1	-	Deionized water	34.7	-	-	-	-	[78]
		3–8	Cellulose triacetate FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 20.0 cm2	0.02 g·L−1	-		17.3	-	-	-	-	[79]
MNPs coated/functionalized with organic polymers
Chitosan-coated MNPs	Co-precipitation	20	Cellulose triacetate/ cellulose acetate FO membrane; A = 40.0 cm2	0.06 g·L−1	-	Deionized water	5.0	-	Magnetic field	70.3	≈100.0%	[69]
Hyperbranched polyglycerol carboxylate-coated MNPs	Thermal decomposition	29	OsMem™ (Hydration Tech. Innovations, Albany, OR, USA); A = 50.0 cm2	500.00 g·L−1	15.8		7.2	-	Ultrafiltration	18.7	≈100.0%	[80]
Hyperbranched polyglycerol-coated MNPs		21		300.00 g·L−1	15.2		6.2	-	-	20.7	-	[81]
Hyperbranched polyglycerol-coated MNPs functionalized with succinic anhydride moieties		24	OsMem™ (Hydration Tech. Innovations, Albany, OR, USA); A = 2.4 cm2	400.00 g·L−1	9.7		3.0	-	Ultrafiltration	19.3	≈100.0%	[82]
Magnetic poly (N-isopropylacrylamide-co-sodium 2-acrylamido-2-methylpropane sulfonate) nanogels	Co-precipitation	271	Cellulose triacetate with an embedded polyester screen mesh FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 23.0 cm2	100.00 g·L−1	3.3		0.6	-	Magnetic field and heating	25.3	≈100.0% t = 20 min	[83]
Poly (N-isopropylacrylamide)-coated MNPs	Thermal decomposition	7	Specialized carbon nanotube FO membrane (Porifera Inc., San Leandro, CA, USA); A = 42.0 cm2	0.07% (w/v)	25.3		11.7	-		-	≈100.0% t = 1–5 min	[75]
Polyethylene glycol 4000- coated MNPs	Co-precipitation	-	Cellulose triacetate FO membrane (Fluid Tech. Solutions, Inc., San José, CA, USA); A = 49.0 cm2	10.00 g·L−1	-	Deionized water	14.9	-	Magnetic field	-	≈100.0% t = 2 min	[65]
Polyethylene glycol-coated MNPs	Polyol process	9–32	Cellulose triacetate FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 20.0 cm2	0.08 M	-		11.3	-		-	≈100.0%	[70]
						35 g·L−1 NaCl	5.2
Polyethylene glycol dicarboxylic -coated MNPs	Thermal decomposition	13	Flat sheet FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 12.0 cm2	0.07 M	73.9	Deionized water	9.1	-		35.5	≈100.0%	[84]
Poly(amidoamine) dendrimer-coated MNPs	Co-precipitation	17	Thin film composite FO membrane (Porifera Inc., San Leandro, CA, USA); A = 42.0 cm2	30.00 g·L−1	-		12.9	-		48.0	100.0% t = 2 min	[14]
Poly(sodium styrene-4-sulfonate)-co-poly (N-isopropylacrylamide)-coated MNPs	Thermal decomposition	5	Thin film composite FO membrane (Hydration Tech. Innovations, Albany, OR, USA)	33.00% (w/w)	55.7	Deionized water	14.9	-	Magnetic field, ultrafiltration, and heating	11.1	≈100.0%	[85]
						3.5% (w/w) NaCl	2.7
Sodium alginate sulfate-functionalized SiO2-coated MNPs	Co-precipitation	63–76	Cellulose triacetate A = 14.0 cm2	60.00 g·L−1	118.8	Deionized water	8.5	0.23	Magnetic field	50.6	100.0%	[86]
Triethylene glycol-coated MNPS	Thermal decomposition	20	Commercially FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 8.0 cm2	0.20 M	-		6.0	-	-	20.0	-	[71]
MNPs coated/functionalized with polysaccharides
Dextran-coated MNPs	Co-precipitation	10	Commercially FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 48.0 cm2	0.50 M	-	Deionized water	4.0	-	Magnetic field	32.4	≈100.0% t = 10–15 min	[87]
						2 g·L−1 MgSO4	3.0
D-Xylose-coated MNPs	Hydrothermal method	-	Commercial FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 1.8 cm2	6.50% (w/v)	1.5	Deionized water	2.9	-		30.0	≈100.0%	[88]
						0.01 M NaCl	1.3
Pectin-coated MNPs	Co-precipitation	390	Polyamide FO membrane (Porifera Inc., San Leandro, CA, USA); A = 12.6 cm2	0.50%	-	Deionized water	26.6	-		18.6	≈100.0% t = 12–16 min	[89]
						1% (w/w) NaCl	6.6
MNPs coated/functionalized with other organic compounds
3-(Trimethoxysilyl) propyl methacrylate-functionalized SiO2-coated MNPs	Co-precipitation and sol-gel method	80	Thin film composite FO membrane; A = 4.9 cm2	-	-	Deionized water	10.2	-	Magnetic field	44.2	≈100.0%	[90]
Poly (deep eutectic solvent)-coated MNPs	Solvothermal procedure	15–25	Cellulose triacetate FO membrane (Hydration Tech. Innovations, Albany, OR, USA); A = 15.0 cm2	3.50 g·L−1	68.9		17.9	0.12		60.4	≈100.0%	[91]
Bare MNPs and MNPs coated/functionalized with inorganic compounds
Bare MNPs	Co-precipitation	10–20	FTSH2O (Porifera Inc., San Leandro, CA, USA); A = 42.0 cm2	-	-	-	1.9	-	-	-	-	[16]
		127	Polyamide FO membrane (Porifera Inc., San Leandro, CA, USA); A = 12.6 cm2	5.00% (w/w)	-	Deionized water	35.7	-	Magnetic field	3.8	≈100.0% t = 7 min	[92]
						20 g·L−1 NaCl	2.5
EDTA-functionalized SiO2-coated MNPs	Hydrothermal method	280	Polyamide thin film composite FO membrane (Porifera Inc., San Leandro, CA, USA); A = 20.0 cm2	60.00 g·L−1	-	0.5 g·L−1 octanoic acid	9.6	-		18.7	>90.0%	[59]
Potassium-functionalized iron oxide-doped carbon nanofiber MNPs	Co-precipitation	4500	FTSH2O™ (Sterlitech Corporation, Auburn, WA, USA); A = 42.0 cm2	0.10% (w/v)	86.1	Deionized water	3.4	0.10	-	22.3	-	[20]
						1.0 M NaCl	2.1
SiO2-coated MNPs	Thermal decomposition	-	FO membrane (Aquaporin A/S, Kongens Lyngby, Denmark); A = 31.0 cm2	8.00 g·L−1	-	40 mg·L−1 NaCl	11.0	-	Magnetic field	5.0	83.9%	[15]