Adsorption capacities of metal oxide nanomaterials for various dyes and heavy metal ions removal.

Metal oxide	Preparation method	Tested dye/heavy metal	Capacities (mg g−1)/removal efficiency (%)	Size range/crystallite size (nm)/surface area (m2 g−1)	Ref.
MgO	Green synthesis using Tecoma stans (L.) extract	Congo red (CR) and crystal violet (CV)	142.17–150.49	SR: from 20 to 50	195
	Microwave-assisted combustion method	CR and trypan blue	136–132	Average particle size 18	4
	Precipitation method	Reactive blue 19 (RB19), reactive red 195 (RR 195), CR, MB, and rhodamine B	549.45 to RB19, 348.43 to CR, and 442.48 to RR195	CS: 37/SA: 154.85	196
	Green synthesis using Aspergillus niger	Textile wastewater containing Cr, Co, Pb, Cd, and Ni, heavy metals	94.2% ± 1.2%, 63.4% ± 1.7%, 72.7% ± 1.3%, 74.1% ± 1.8%, and 70.8% ± 1.5%	SR: nano-rectangular (18.6–27.6) and nano-rods (30–85)	197
TiO2	Sol–gel/green synthesis using Tridax procumbens leaf extract	MO	273.37 at 303 K	—	198
CdS/TiO2 decorated carbon nanofibers	Electrospinning method	MB reactive black 5, and reactive orange 16	95% removal after 5 min	—	199
MgFe2O4–TiO2@GO	Ultrasonication method	MB	99% removal at 50 ppm/0.05 g conc. and adsorbent dose	SR: from 20 to 30 – SA: 58.48	200
AC/TiO2/chitosan	Impregnation method	Safranin O	357.14	SR: 29.83–50 – SA: 834.477	201
Al2O3/GO-based cellulose	Green synthesis	Fluoride	5.34 in pH 5 after 120 min	CS of Al2O3: 5.52	202
ZnO	Green synthesis	CR – malachite green	92.30% after 120 min to 90.7% after 90 min	MD: 44 – CS: 37.86 – SA: 63.09	203