Multi-walled carbon nanotubes as adsorbents for the removal of parts per billion levels of hexavalent chromium from aqueous solution

Removal of heavy metals and pollutants by membrane adsorption techniques

“…The Pb in the form of PbO, Pb(OH) 2 , and PbCO 3 adsorbed on the surface of the acidified MWCNTs is only 3.4% of the total Pb 2+ adsorption capacity. Pillay et al (2009) studied the adsorption capabilities for the removal of parts per billion levels (ppb) of hexavalent chromium by three adsorbents namely activated carbon, functionalized multi-walled carbon nanotubes (MWCNTs) and unfunctionalized multi-walled carbon nanotubes. Highest adsorption capability with up to 98% Tijani et al (2013) of a 100 ppb Cr(VI) solution was shown by unfunctionalized MWCNTs.…”

Carbon Nanomaterials – A New Form of Ion Exchangers

“…This is supported conclusively by experimental evidence where Rao et al [4] have reported that oxidized SWCNTs showed a better uptake for Ni(II) and Zn(II) ions than unmodified MWCNTs. Further, Pillay et al [13] have also shown conclusively that unmodified MWCNTs were more effective for removal of Cr(VI) than oxidized MWCNTs due to a higher (pHPZC).…”

“…Conversely, it has also been shown that unoxidised MWCNTs are more effective for uptake of anions such as dichromate than oxidized MWCNTs [13]. In such observations it has been argued that oxidation has an impact on the point of zero charge (pHPZC) of these materials which ultimately governs the overall surface charge [4,13,14].…”

“…However, complete selectivity was not achieved. Pillay et al [13] also showed that unfunctionalised MWCNTs were not selective to the uptake of Cr(VI) in the presence of competing anions such as chloride and sulphate ions. This also applied to industrial effluents where sulphites are present [14].…”

Removal of Hg2+ and methylmercury in waters by functionalized multi-walled carbon nanotubes: adsorption behavior and the impacts of some environmentally relevant factors

“…It should be noted that a slight increase of removal efficiency of Hg 2+ and MeHg were observed for pH > 8.0. This might be attributed to the fact that when the solution pH is larger than the critial value pH pzc , mostly in the range of 4-6 [9,42], the negative charge surface, which can provide electrostatic interactions, enhances the absorption of Hg 2+ and MeHg [40].…”