HTDMA-modified bentonite clay for effective removal of Pb(II) from aqueous solution

Area of Science:

• Environmental Chemistry
• Materials Science
• Adsorption Science

Background:

• Lead (Pb(II)) contamination poses significant environmental and health risks.
• Bentonite clay is a low-cost adsorbent, but its efficiency for heavy metal removal can be limited.
• Surface modification of adsorbents is crucial for enhancing their performance.

Purpose of the Study:

• To synthesize and characterize hexadecyl trimethyl ammonium bromide (HDTMA) modified bentonite clay.
• To investigate the adsorption capacity and mechanism of Pb(II) removal by the modified bentonite.
• To explore novel characterization techniques for understanding adsorption mechanisms.

Main Methods:

• Bentonite modification using HDTMA.
• Material characterization via XRD, SEM, TG-DSC, FT-IR, and BET.
• Adsorption experiments varying pH, ion strength, time, dosage, and concentration.
• Isotherm and kinetic modeling (Sips, pseudo-second-order, Langmuir).
• Advanced characterization using Positron Annihilation Lifetime (PAL) and Electron Momentum Density (EMD) measurements.

Main Results:

• HDTMA modification increased bentonite surface area by ~70%.
• Optimal Pb(II) adsorption achieved at pH 5.0 within 120 minutes.
• Adsorption followed Sips isotherm and pseudo-second-order kinetics.
• Maximum monolayer adsorption capacity was 25.8 mg/g (Langmuir model), significantly higher than unmodified bentonite (18.9 mg/g).
• PAL and EMD revealed Al and Si mono-vacancies contributing to adsorption within interlayer spaces.

Conclusions:

• HDTMA-modified bentonite is a highly effective adsorbent for Pb(II) removal.
• Inner-sphere complex formation and adsorption within interlayer spaces are key mechanisms.
• Novel techniques like PAL and EMD provide valuable insights into adsorption mechanisms at the atomic level.