Evaluation of Carbon Nanotubes and Quartz Sand for the Removal of Formaldehyde–(2,4-Dinitrophenylhydrazine) from Aqueous Solutions

The assessment of the potential impact of engineered carbon nanotubes on the removal of synthetic chemical contaminants (e.g., pesticides, pharmaceuticals, and chemical reaction products) from aqueous solutions has become an increasingly important aspect of environmental research. This study has focused on the interaction of the reaction product of formaldehyde (FA) with 2,4-dinitrophe-nylhydrazine (2,4-DNPH) with multiwalled carbon nanotubes (MWCNTs) and quartz sand under static and dynamic conditions. Several batch adsorption experiments were conducted in test tubes, under controlled conditions and at laboratory room temperature (23 degrees C). The experimental results suggested that FA (2,4-DNPH) has a low affinity for quartz sand but an enhanced potential for adsorption onto small quantities of MWCNTs. FA (2,4-DNPH) adsorption onto quartz sand and MWCNTs was more pronounced under dynamic than static conditions, probably due to agitation improved mixing of the absorbent within the solution. The collected adsorption data were adequately described by a pseudo-second-order kinetic model and intraparticle diffusion model. On the basis of root-mean-square error (RMSE) values, better fitting of experimental data was achieved with the Weber-Morris intraparticle diffusion model. Our findings suggested that a rapid surface chemisorption of FA-(2,4-DNPH) onto available adsorption sites of sand and MWCNTs, followed by a slower intra-aggregate diffusion of FA-(2,4-DNPH) onto interstitial spaces of entangled MWCNTs, occurred. The observed FA-(2,4-DNPH) removal by combined MWCNTs and quartz sand was 78.1%. Thus, MWCNTs could be promising adsorbent materials for removal of complicated organic compounds from aqueous solutions and for groundwater remediation.