Efficient adsorption of benzoic acid from aqueous solution by nitrogen-containing activated carbon

Role of Basic Surface Groups of Activated Carbon in Chlordecone and β-Hexachlorocyclohexane Adsorption: A Molecular Modelling Study

The influence of nitrogen-containing surface groups (SGs) onto activated carbon (AC) over the adsorption of chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH) was characterized by a molecular modelling study, considering pH (single protonated SGs) and hydration effect (up to three water molecules). The interactions of both pollutants with amines and pyridine as basic SGs of AC were studied, applying the multiple minima hypersurface (MMH) methodology and using PM7 semiempirical Hamiltonian. Representative structures from MMH were reoptimized using the M06-2X density functional theory. The quantum theory of atoms in molecules (QTAIM) was used to characterize the interaction types in order understanding the adsorption process. A favorable association of both pesticides with the amines and pyridine SGs onto AC was observed at all pH ranges, both in the absence and presence of water molecules. However, a greater association of both pollutants with the primary amine was found under an acidic pH condition. QTAIM results show that the interactions of CLD and β-HCH with the SGs onto AC are governed by Cl···C interactions of chlorine atoms of both pesticides with the graphitic surface. Electrostatic interactions (H-bonds) were observed when water molecules were added to the systems. A physisorption mechanism is suggested for CLD and β-HCH adsorption on nitrogen-containing SGs of AC.

Enhanced adsorption performance of methylene blue from aqueous solutions onto modified adsorbents prepared from sewage sludge

In the present work, an attractive and creative adsorbent derived from sewage sludge was freshly fabricated via pyrolysis technology, followed by modification for improving the absorptive ability. First, the (NH₄)₂S₂O₈ modified pyrolytic sludge (MS_AP) was selected from 19 modified pyrolytic sludges for the highest removal efficiency and adsorption capacity for methylene blue (MB). Then, the adsorption performance for MB of MS_AP was compared systematically with the pristine adsorbent (MS_DW) by batch adsorption experiments. The main conclusions were that the adsorption process was better fitted with the Langmuir model, and the maximum adsorption capacity (q_max) of MS_AP was observed to be 149.05 mg g^-1. Moreover, the adsorption kinetics data showed a good fit with the pseudo second order model; when the addition of MS_AP was 1.0 g·L^-1, the rate constant was 0.05 g·mg^-1·min^-1, which was far greater than that of the other modified adsorbents.