Table 6.

Adsorption capacity toward Cu(II) and Zn(II) ions for various carbonaceous materials.

Material	Metal Ion	Maximum Capacity [mg/g]	Article
N-doped activated carbon prepared from brown coal	Cu(II)	47.4	(this study)
aminated commercial activated carbon		~100	[28]
tannic acid immobilized activated carbon		2.23	[36]
sodium diethyl dithiocarbamate (SDDC) immobilised activated carbon		38.0	[37]
non-thermal plasma modified activated carbons		37.6	[38]
pre-oxidised and ammoxidised commercial activated carbon		~250	[39]
carbonaceous nanofibers		204.1	[40]
crosslinked chitosan		200.0	[41]
granular commercial activated carbon		24.5	[42]
amino –factionalized nano-adsorbent		12.4	[45]
activated carbon from walnut shells		28.4	[46]
spirogyra (green alga)		133.0	[47]
N-doped activated carbon prepared from brown coal	Zn(II)	31.5	(this study)
tannic acid immobilized activated carbon		1.23	[36]
sodium diethyl dithiocarbamate (SDDC) immobilised activated carbon		9.9	[37]
granular commercial activated carbon		8.8	[42]
activated carbon from almond husks		35.3	[43]
dairy manure-derived biochar		31.6	[44]
activated carbon from birch sawdust		20.8	[48]
activated carbon from Typha latifolia L		28.6	[49]
activated carbon from date stones		12.2	[50]