where: [C.sub.0] and [C.sub.eq] = represent, respectively, the initial and at balance concentrations (mg.[L.sup.-1]); V = the
adsorbate volume (L); and m = the adsorbent mass (g).
At higher temperature
adsorbate are known to be less viscous and more mobile thus their molecules diffuses faster across the external boundary layer and in the internal pores of the adsorbent particle.
The Langmuir pertains to monolayer adsorption of
adsorbates onto homogeneous adsorption sites, while the Freundlich advocates the multilayer adsorption mechanism on heterogeneous sites.
It can be seen from Table 1 that the adsorption processes of N[H.sub.2]-SH-GO/o-MWCNTs at different temperatures for [Pb.sup.2+] and phenol conformed to the pseudo-second-order kinetic model ([R.sup.2] = 0.999): this indicated that the adsorption rate was positively correlated with the concentrations of the two
adsorbates. As the temperature increased, the equilibrium adsorption capacities of N[H.sub.2]-SH-GO/o-MWCNTs for [Pb.sup.2+] and phenol gradually increased, implying that the increasing temperature promoted the adsorptions of the adsorbent.
The removal efficiency is influenced by various factors, such as solution concentration, solution pH, ionic strength, and nature of
adsorbate, adsorbent modification procedure, physical properties (surface area, porosity) and the chemical nature of activated carbon [4].
Where Ce is the equilibrium concentration of the
adsorbate (mg/L), qe the amount of
adsorbate adsorbed per unit mass of
adsorbate (mg/g), Qo and KL are Langmuir constants related to adsorption capacity and rate of adsorption, respectively.
(2) The Langmuir isotherm model is applicable to homogeneous adsorption where the adsorption of each
adsorbate molecule on to the surface has equal sorption activation energy.
The aim of the adsorption isotherms is to relate the
adsorbate concentration in the bulk to the adsorbed amount at the interface.
After a certain period of time, the rate of adsorption decreases due to accumulation of
adsorbate in the vacant sites.
After adsorption, organic
adsorbates were desorbed from silica aerogel at ambient temperature.
The SERS activity of the hollow silver spheres was evaluated by using 4-MBA as the probing
adsorbate with excitation at 632.8 nm.
A double-beam Shimadzu UV-Visible spectrophotometer was used to measure the concentration of the
adsorbates. According to Beer's law, the linear relationship between absorbance and absorbing species concentration can be written as follows:
