Table 2.

Ag and Cu content and oxidation state in the modified filters, as determined by X-ray photoelectron spectroscopy (XPS) analysis. Metal content is expressed as an average of three measurements ± standard deviation.

Material/preparation method	Modification method	Ag [mg/kg]	Oxidation state of metal
			Ag(0) [%]	Ag(I) [%]
AgNPs	—	19300	94	6
3D printing	Addition of AgNPs	127 ± 12	25	75
Direct foaming	Addition of AgNPs	117 ± 38	42	58
Granulation	Addition of AgNPs	76 ± 0.6	55	45
3D printing	Dipping in colloidal Ag	123 ± 15	68	32
Direct foaming	Dipping in colloidal Ag	133 ± 21	77	23
Granulation	Dipping in colloidal Ag	225 ± 30	82	18
3D printing	Addition of AgNO3	127 ± 15	0	100
Granulation	Addition of AgNO3	74 ± 0.6	0	100
Direct foaming	Ion exchange	110 ± 10 a 73 ± 6 b	0	100
Granulation	Ion exchange	83 ± 2 a 89 ± 6 b	0	100
		Cu [mg/kg]
			Cu(I) [%]	Cu(II) [%]
3D printing	Addition of Cu(NO3)2	350 ± 0	5	95
Granulation	Addition of Cu(NO3)2	377 ± 75	3	97
3D printing	Ion exchange	13300 ± 1752 a 42000 ± 14171 b	5	95
Granulation	Ion exchange	25967 ± 2919 a 45467 ± 709 b	4	96
Direct foaming	Ion exchange	66500 ± 4959 a 61133 ± 1457 b	4	96

AgNPs = Ag nanoparticles; ^a = ion exchange from Na⁺ to Ag⁺/Cu²⁺, ^b = ion exchange from Na⁺ to NH₄⁺ and then to Ag⁺/Cu²⁺.