The soliton amplitude increases with increasing temperature ratio of free to trapped electrons for both positive and negative dust grains; but Fig. 1 indicates that amplitude goes higher for increasing the number density of positively charged dust grains whereas the amplitude decreases with increasing the negatively charged dust grain number density.
However, in the case of Tiwari and Mishra [45], the amplitude and width of the soliton were found to increase with the increasing concentration of negatively charged dust grains nd0 and charge number Zd in a collisionless unmagnetized plasma consisting of hot isothermal electrons and cold ions.
Similar to our result, Choi et al. [44] have noticed the reduced soliton amplitude and enhanced width with the increasing concentration of negatively charged dust grains in a magnetized dusty plasma.
Since the reactive sites are expected to account for the gibbsite surface charge over a wide pH range, it is likely that the decrease of the bonding capacity was caused by electrostatic repulsion between the increasing number of negatively charged sites and the gluconate anions.
For this reason, with increasing influent pH, the negatively charged HA molecules increase by increasing deprotonation of the carboxylic groups (Mohd Omar et al. 2014; Lin and Zhan 2012).
And the reduced trend of removal at higher pH might be attributed to an increase of negatively charged arsenite species (H2AsO3 −) and negatively charge surface sites (Giri et al. 2011).
The modified DLVO theory can explain how the attraction increases between negatively charged face surfaces and positively charged or neutral edge surfaces in solutions with higher concentrations of electrolytes (Figure 3) [17].
Additionally, the presence of acidic surface groups on the adsorbent or the use of a basic electrolyte improved the desorption process thanks to the increase in negatively charged functionalities and the promotion of electrostatic repulsions.
Furthermore, it could be suggested that at lower pH value the AC surface is surrounded by hydronium ions thereby preventing the metal ions from approaching the binding sites of the adsorbent; in contrast, as the pH increases, more negatively charged surface becomes available thus facilitating greater copper removal (Wong et al. 2003; Tumin et al. 2008).
Several studies suggest that increase in negatively charged phospholipid concentrations favours Penetratin and other basic peptide sequences binding to membranes by electrostatic adsorption.
