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Mesoporous silica is a highly ordered material which possesses a regular two-dimensional hexagonal array of channels. Mesoporous silica is efficient for cadmium removal because of its high surface area and 2–10 nm pore size (Bhattacharyya et al. 2006). Mesoporous silica may be chemically modified via the attachment of groups including carboxylic acid, sulfonic acid and amino-carbonyl. Javadian et al. (2014) prepared polyaniline/polypyrrole/hexagonal type mesoporous silica for cadmium removal and reported a removal of 99.2% cadmium at an optimum pH of 8. Hajiaghababaei et al. (2011) modified SBA-15 nanoporous silica by functionalising it with ethylenediamine. SBA-15 is a highly ordered material with a regular two-dimensional hexagonal array of channels with a pore diameter of the order of 7–10 nm. The reported removal was 98% at pH > 4.5. Similarly, Burke et al. (2009) also used aminopropyl and mercaptopropyl, functionalised and bi-functionalised, large pore mesoporous silica spheres for the removal of chromium from wastewater. These researchers reported a maximum sorption capacity of 43.16 mg/g for Cr. Pérez-Quintanilla et al. (2007) modified silica and amorphous silica using 2-mercaptopyridine and reported maximum adsorption capacities of 205 mg/g and 97 mg/g, respectively. Table 12 documents the available data for mesoporous silica for cadmium removal from wastewater.

Table 12

Cadmium removal using mesoporous silica as an adsorbent

Adsorbent functionalised withMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorbent capacity (mg/g)Removal per cent (%)References
Silica functionalised with mono amino and mercapto groups 25 <8 Langmuir 1,440–2,880 20 12.36, 14.61, 28.10 80% Machida et al. (2012)  
Amino functionalised silica 50 Langmuir 120 18.25 90% Heidari et al. (2009)  
Amino functionalised mesoporous silica 5–300 – Langmuir 1,440 1.11 93.30 100% Aguado et al. (2009)  
Iminodiacetic acid-modified mesoporous SBA-15 50–1,000 5.6 Langmuir 1,440 4.0 – 99.8% Gao et al. (2007)  
Polyamine-functionalised 100 5.5–7 – 2,880 – – 70% Alothman & Apblett (2010)  
Adsorbent functionalised withMetal concentration (mg/L)Optimum pHBest model fitContact time (min)Adsorbent dose (g/L)Adsorbent capacity (mg/g)Removal per cent (%)References
Silica functionalised with mono amino and mercapto groups 25 <8 Langmuir 1,440–2,880 20 12.36, 14.61, 28.10 80% Machida et al. (2012)  
Amino functionalised silica 50 Langmuir 120 18.25 90% Heidari et al. (2009)  
Amino functionalised mesoporous silica 5–300 – Langmuir 1,440 1.11 93.30 100% Aguado et al. (2009)  
Iminodiacetic acid-modified mesoporous SBA-15 50–1,000 5.6 Langmuir 1,440 4.0 – 99.8% Gao et al. (2007)  
Polyamine-functionalised 100 5.5–7 – 2,880 – – 70% Alothman & Apblett (2010)  

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