Table 3. Kinetics of Adsorption of Cu²⁺ on PPy and PPy/GO Composite Electrodes^a.

adsorption equation	material	fitting straight line	R2
Lagergren first-order equation ln(qe – qt) = ln qe – k1t	PPy	y = 2.883 – 0.0992x	0.9599
	PPy/GO	y = 4.518 – 0.1193x	0.9545
Lagergren second-order equation t/qt = 1/(k2 × qe2) + t/qe	PPy	y = 0.7410 + 0.3640t	0.9932
	PPy/GO	y = 0.4365 + 0.0106t	0.9961

^aq_e is the amount of adsorbed ions at equilibrium, mg/g; q_t is the amount of adsorbed ions at time t, mg/g; k₁ is the first adsorption rate constant, min^–1; and k₂ is the secondary adsorption rate constant, g/(mg·min).