The purpose of this study was to remove lead and arsenic ions from aqueous solutions using the activated carbon prepared from Citrus limon tree leaves. Characteristics of the prepared adsorbent were studied thoroughly using BET, SEM, EDS and mapping, XRD, and RAMAN analyses. The results of experiments showed that the highest adsorption efficiencies were 97.67% and 95.89% for Pb (II) and As (III), respectively. Additionally, the adsorbent was successfully regenerated four times and therefore it was able to perform the adsorption and desorption processes well. Moreover, the results of adsorption kinetics showed that the pseudo second-order kinetic model was more effective for the description of adsorption mechanism of both metals. Furthermore, the equilibrium studies indicated that Langmuir and Freundlich isotherm models were desirable for lead and arsenic ions, respectively.

This study describes the successful establishment of a cryopreservation protocol for Citrus limon cultivars: ‘Frost Eureka limon’ and ‘Cook Eureka limon’, using a droplet-vitrification method. The shoot tips that were excised from in vitro grown seedlings of the two cultivars were preserved in liquid nitrogen (LN) and successfully regenerated into whole plants. Excised shoot tips were pre-cultured for 1 or 2 days in 0.3 M and 0.5 M sucrose solutions at 25℃ and incubated in a loading solution (LS) composed of 17.5% glycerol + 17.5% sucrose in Murashige and Skoog (MS) medium for 40 min at 25℃. Prior to direct immersion in LN for 1 h, the shoot tips were dehydrated with plant vitrification solution 2 (PVS2) at 0℃ or PVS3 at 25℃. The frozen shoot tips were re-warmed and unloaded with 1.2 M sucrose in ½ MS for 30 min at 25℃. Shoot tips were post-cultured overnight on survival medium and then micrografted onto ‘trifoliate orange’ (Poncirus trifoliate (L.) Raf. seedling rootstocks for recovery and to produce whole plants. The highest regrowth rates were 53.5% and 50.3% for cryopreserved shoot tips of ‘Frost Eureka limon’ and ‘Cook Eureka limon’, respectively, when pre-cultured in 0.3 M and 0.5 M sucrose concentrations in a sequencing manner, with LS and treated with PVS2 for 60 min at 0℃. We also investigated whether the ammonium ion concentration on post-culture medium affected the viability of the cryopreserved Citrus shoot tips. The viability of cooled samples, following culturing on woody plant media (WPM) containing ¼ ammonium nitrate overnight before micrografting, was the highest (70.3%) in ‘Frost Eureka limon’. The study described here is a cost-effective and safe method to conserve Citrus fruit cultivars, for the improvement and large-scale multiplication of fruit plants and for breeding disease resistance.