Nanoporous Xerogel for Adsorption of Pb2+ and Cd2+

Classical  xerogels  are  robust,  inexpensive  and  nontoxic  materials with  low-ordered  nanoporous  structures.  in water  streams where  the ph  is  higher  than  the  point  of zero charge,  the  surface  of  classical xerogels  such as  tetraethoxy orthosilan  (teos) xerogel  is negatively charged.  it  was  assumed  that  a  xerogel  can  work  as  a  strong adsorbent  for metal  ions without  further modification. therefore,  the capability of teos xerogel  for  adsorption of  two heavy metal  ions, pb2+  and  cd2+,  from  aqueous  solution  was  studied.  the  batch experiments  revealed  that  the  adsorbent  has  higher  adsorption capacity  for  pb2+  (58.82 mg/g)  and cd2+  (35.71 mg/g)  as  compared with  the  reported  low-cost  adsorbents.  kinetics  and  thermodynamic studies were  employed  to  explain  the  adsorption mechanism.  it was concluded  that  the  adsorption  of  both  ions  on  teos  xerogel  obey chemisorption  mechanism.  however,  the  reaction  of  pb2+  with  the adsorbent  is  thermodynamic controlled  and  the one of cd2+  is kinetic controlled.