Introduction and Literature Review
1.2 Prior art
1.2.5 Pd(II) adsorption and desorption characteristics of chitosan and its derivatives
Few research groups targeted the effectiveness of chitosan and chitosan coated activated charcoal adsorbents for the removal and recovery of Pd(II) and Pt(IV) from aqueous solutions. Among these, while both adsorbents exhibited promising affinity towards Pd(II) than Pt(IV), and chitosan provided good adsorption capacities than activated charcoal coated with chitosan (Sharififard et al. 2013). For L-lysine modified cross-linked resin (LMCCCR), other researchers indicated that among Au(III), Pt(IV) and Pd(II), Pt(IV) and Pd(II) uptake was significant for aqueous adsorbate systems (Fujiwara et al. 2007). Another investigation reported upon the superior performance of glycine modified cross-linked resin (GMCCR) for Pt(IV) and Pd(II) removal but not Au(III) from aqueous solutions (Ramesh, Hasegawa et al. 2008). Zhou et al., (2009) investigated adsorption characteristics of Pt(IV) and Pd(II) onto thiourea modified chitosan microspheres (TCS) (Zhou et al. 2009). Ethylenediamine-adjusted magnetic chitosan nanoparticles (EMCN) were used for the removal of Pt(IV) and Pd(II) from aqueous solutions.
EMCN was synthesized through NaOH assisted precipitation in water-in-oil micro-emulsion system. For the EMCN, among Pd(II) and Pt(IV), Pt(IV) uptake efficiency was higher. The total sorption capacity was comparable to that of each metal individually. This indicates that the metals compete to get adsorbed onto the same sorption sites (Zhou et al. 2010).
The removal of Pd(II) using glutaraldehyde cross-linked chitosan derivatives was carried out by Ruiz et al., (2000). The authors targeted the role of acid deployed to control solution pH in the
presence of other competitor anions. The authors observed that compared to HCl, H2SO4 was unfavourable (Ruiz et al. 2000). Other researchers targeted sulfur groups (in thiourea and rubeanic acid compounds) grafted chitosan derivatives for Pd(II) removal and inferred that the rubeanic acid derivative of chitosan was efficient for Pd(II) uptake from dilute solutions (Guibal et al. 2002). Ding et al., (2006) investigated the adsorption properties of two types of diaza- crown ether cross-linked chitosan resins for Pd(II) and Ag(I) recovery. The authors produced diaza-crown ether chitosan (CTSDC) through grafting of N, N’-diallyldibenzo 18-crown-6 crown ether with chitosan. On the other hand, the alternative diaza-crown ether cross-linked chitosan (CCTSDC) was prepared through crosslinking of CTSDC and epichlorohydrine. For both Pd(II) and Ag(I) cases, CCTSDC outperformed CTSDC in terms of Pd(II) uptake (Ding et al. 2006).
Alternatively, persimmon tannin chitosan derivative (PTCS) was targeted for the Pd(II) adsorption and was inferred to possess a maximum adsorption capacity of 330 mg g-1(Zhou et al.
2015). The Pd(II) adsorption capacity of ion-imprinted chitosan and extremely acidic solution system was investigated by Lin et al., (2015). The authors concluded that the highest metal uptake was about 324.6-326.4 mg g-1 (Lin et al. 2015).
Adopting ion-imprinting technique, Monier et al., (2016) prepared 2-aminobenzaldehyde modified chitosan Schiff’s base (Pd-CAZ) resin for selective chelation of Pd(II). The authors evaluated thermodynamic, kinetic and isotherm parameters associated to Pd(II) adsorption onto Pd-CAZ and non-imprinted CAZ (NI-CAZ) resins. The authors reported maximum Pd(II) adsorption capacities of 275 and 114 mg g-1 for Pd-CAZ and NI-CAZ, respectively. Further, the resin regeneration and recovery experiments affirmed that 96% of the resin could be restored even after fifth adsorption-desorption cycle and hence highly promising performance.
Table 1.2 presents a summary of pertinent functional groups, adsorption and desorption capacities along with optimized experimental conditions for various chitosan based synthesized adsorbents.
The adsorption characteristics of competent chitosan based derivatives investigated for heavy metal adsorption would be worth consideration in the near future, given the fact that Pd(II) adsorption characteristics of such resins have not been studied on these till date. Hence, few resins have been identified and the available prior art has been presented in the following paragraphs:
Liao et al., investigated the triethylenetetramine derivative of chitosan for its ability to recovery Ni(II) from aqueous solutions. The authors reported performance efficiency of the resin under acidic conditions and indicated optimal adsorption capacity at about 4.5 pH. The maximum Ni(II) adsorption capacity of chitosan and chitosan derivatives have been evaluated to be 58.09 and 91.44 mg g-1, respectively (Liao et al. 2016).
Wu et al., synthesized magnetic chitosan modified with melamine and evaluated its adsorption capacity for Cu(II) in aqueous solutions. The authors summarized a maximum Cu(II) adsorption capacity of 2.58 mmol g−1 for an optimal process parameter set of 5.5 pH, 25 min adsorption time and 5.0 mmol L−1 initial Pd(II) concentration (Wu et al. 2015).
Li et al., synthesized thiosemicarbazide modified chitosan (TCS) to recover Pb(II) and Cd(II) from aqueous solutions. The authors reported their adsorption capacities to be 325.2 and 257.2 mg g-1 for Pb(II) and Cd(II) respectively (Li et al. 2016).
Elwakeel et al., prepared 3-amino-1,2,4 triazole,5-thiol and melamine grafted chitosan derivatives for the removal of Reactive Black 5 from aqueous solutions. At an optimal pH of 3 and at 25 oC, the maximum adsorption capacities of the resins have been reported as 0.492 and
0.330 mmol g-1 for 3-amino-1,2,4 triazole,5-thiol and melamine grafted chitosan derivatives, respectively (Elwakeel et al. 2016).
Recently, our research group carried out experimental investigations that targeted Pd(II) removal and recovery from synthetic ELP solutions using glutaraldehyde cross-linked chitosan derivative (Nagireddi et al. 2017) and commercial Lewatit TP214 ion-exchange resin (Nagireddi et al.
2018). Optimal batch adsorption process parameters were 8 pH, 300 min contact time for both resins and 0.6 and 2 g L−1adsorbent dosage for glutaraldehyde cross-linked chitosan and Lewatit TP214 ion-exchange resin respectively. Corresponding maximum adsorption capacity and desorption efficiency of the resins has been evaluated as 166.67 and 172.41 mg g-1 and 42.35 and 66.95 %, respectively. Based on these studies, Lewatit TP 214 anion exchange resin can be inferred to provide excellent Pd(II) removal and reuse characteristics from synthetic electroless plating solutions.