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1,5 Diphenylcarbazide (DPC) functionalized sol–gel silicas (DPCSG) were prepared and investigated for the solid phase extraction of Hg(II) from aqueous solution by a batch equilibrium technique. The metal sorption properties of DPCSG were examined to evaluate their performance toward metal extraction under different controlling factors, such as pH of solutions, equilibration shaking times, effect of foreign ions and complexing agents. The equilibration was fast and was achieved within 30 min. Maximum extraction capacity of Hg(II) ions onto the DPCSG from non-competitive solutions was 5.6 mg/g (0.028 mmol/g) at 28 ± 2 °C and the enhancement factor was found to be 560 at optimized pH 6 when compared with control and commercial silica gel. The adsorption data obtained as a function of mercury concentration were fitted to a Langmuir adsorption model. The stripping and regeneration of the sorbent were reported and it was further observed that extraction and regeneration were indicated by the dark violet colouration and decoloration of the extractant, respectively. It is concluded from the extraction data that DPCSG is a promising material for the extraction of mercury.

Summary A TAN (1-(2-Thiazolylazo)-2-naphthol)) doped sol gel silica sorbent (reddish colour, porous, stable, hard, non- swelling) were prepared and investigated for the removal of Zn (II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and pH effect on the removal were studied from non competitive aqueous solution to optimize the conditions to be utilized on a large scale. Fast equilibration was observed and adsorption equilibria were reached within 30minutes. Adsorption of zinc ions on the blank (un-doped) sol gel was found negligible. The maximum adsorption of Zn (II) ions onto the TAN doped sol-gel from single solutions were 2.33mg/g (0.035mmol/g). TAN doped sol gel can be regenerated through washing with a solution of 0.1M HCl solution. The maximum regeneration value was as high as 99.0. The TAN-doped sol gel silica is suitable at least for four adsorption-desorption cycles without experiencing considerable loss of adsorption capacity. The uptake route and the nature of the Zn-TAN complex have been discussed.

1-(2-Pyridylazo)-2-Naphthol (PAN) doped sol-gel silica has been investigated for removal of metal ions from aqueous media. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was applied for removal of Cd(II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and pH effect on the removal were studied to optimize the conditions to be utilized on a large scale. It was observed that a sol gel loaded with 0.09 mmol PAN/g, had a capacity of 0.044 mmol Cd/g. The desorption of metal ions was carried by 1 M HCl and the sol-gel silica sorbent could be regenerated and reused repeatedly.

1-Naphthylthiocarbamide (ANTU) doped xerogel was prepared and investigated for removal of mercury ions from aqueous media. Physicochemical parameters such as effect of pH, equilibration time, and adsorption isotherm on the removal of mercury were evaluated to optimize the conditions to utilize the data on a large scale. It was observed that uptake and retention of mercury ions inside the pores take place by the formation of a complex with the entrapped reagent molecules. The data show that a xerogel doped with 0.2 mmol ANTU/g of sorbent can remove 0.096 mmol Hg. The probable composition of the mercury complex has been deduced and a removal mechanism is suggested. The regeneration and reuse of doped gel for the removal of targeted metal has been discussed.