Removal of heavy metals from water using multistage functionalized multiwall carbon nanotubes

Abstract

The multistage synthesis of the multi-wall carbon nanotubes (MWCNT) modified with polyamidoamine dendrimers, A1/ and A2/MWCNT, capable of cation removal, is presented in this work, as well as novel ads­orbents based on these precursor materials and modified with goethite nano-deposit, α-FeOOH, A1/ and A2/MWCNT–α-FeO(OH) adsorbents used for As(V) removal. In a batch test, the influence of pH, contact time, initial ion concentration and tem­perature on adsorption efficiency were studied. Adsorption data modelling by the Langmuir isotherm, revealed good adsorption capacities (in mg g^-1) of 18.8 for As(V) and 60.1 and 44.2 for Pb²⁺ and Cd²⁺ on A2/MWCNT, respectively. Also, 27.6 and 29.8 mg g^-1 of As(V) on A1/ and A2/MWCNT–α-FeO(OH), respectively, were removed. Thermodynamic parameters showed that the ads­orp­tion is spontane­ous and endothermic processes. Results of the study of inf­luences of compet­itive ions: bicarbonate, sulfate, phosphate, silicate, chromate, fluoride and nat­ural organic matter (NOM), i.e., humic acid (HA), showed the highest effect of phosphate on the decrease of arsenate adsorption. Time-dep­endent adsorption was best described by pseudo-second-order kinetic model and Weber–Morris model which predicted intra-particle diffusion as a rate-con­trolling step. Also, activation energy (E_a / kJ mol^-1): 8.85 for Cd²⁺, 9.25 for Pb²⁺ and 7.98 for As(V), were obtained from kinetic data.