Cation removal using cellulose chemically modified by a Schiff base procedure applying green principles

Abstract

Pentane-2,4-dione (acetylacetone) molecules were covalently incorporated under several different conditions to ethylene-1,2-diamine (en)-modified cellulose, using polar solvents or without solvents. The quantitative amount of en incorporated was given from 0.37+/-0.01 to 3.03+/-0.01 mmol of nitrogen per gram of cellulose, depending on the synthetic routes and after Schiff base formation this percentage was reduced by 1.38-6.12%. The synthetic routes indicated that lower solvent volumes produced higher amounts of en incorporation. However, the highest degree of pendant groups on the polymeric cellulose structure was obtained from a solvent-free reaction route. This procedure was applied for synthesizing all Schiff bases, causing a decrease in the amount of nitrogen. The available basic centers on the best covalently bonded biopolymer were investigated for adsorption of divalent copper, cobalt, nickel, and zinc from aqueous solution, with a capacity order of Cu2+ > Co2+ > Ni2+ > Zn2+.

Surface cellulose modification with 2-aminomethylpyridine for copper, cobalt, nickel and zinc removal from aqueous solution

“…The sorption isotherms for divalent copper, cobalt, nickel and zinc for cellulose chemically modified with 2-aminopyridine are shown in Figure 6. As observed, the sorption order was the same as for cellulose containing ethylenediamine plus acetylacetone 8 , for this biopolymer chemically modified with butyldiamine 7 and for other anchored materials 50,55,56 , having maximum sorption values of: 0.100 ± 0.012, 0.093 ± 0.021, 0.074 ± 0.011 and 0.071 ± 0.019 mmol. , respectively.…”

“…The next step of the chemical modification occurs by nucleophilic attack, which is provided by organic molecules embracing basic centers to act as chelating agents in the corresponding structure, such as nitrogen, sulfur, oxygen and/or phosphorous atoms. As mentioned before, these Lewis bases present great efficiency for aqueous metal ion removal [6][7][8] . However, functional basic groups attached to the pendant chains have also been employed for other important applications 9,[14][15][16][17][18] .…”

“…A lot of these supports are derived from inorganic compounds, such as silica and other oxides, however, some important reports describe excellent results in which are related to biopolymers [3][4][5] . In this sense, the most abundant biopolymer is cellulose, but, the effectiveness of its applications is associated with new synthesized polymers after chemical surface modifications, by incorporating desired molecules that possess functional groups, which are, in general, Lewis basic sites, with the investigations normally focused on sorption processes [6][7][8] . One of the most known synthetic methods is based on preparing, in the first step, a halogen derivative 9 , by including it on the original polymeric structure at carbon 6, as shown in Figure 1.…”

“…Thus, some investigations have already demonstrated solvent-free syntheses are desirable and the amount of organic groups immobilized under these conditions has increased 6,7,[21][22][23][24][25] . Regarding the application of natural or synthetic materials, many pristine or chemically modified polymeric compounds have been extensively applied for cation removal from aqueous solutions and these processes can provide large amounts of metal ion retention or ion exchange processes.…”

“…Regarding the application of natural or synthetic materials, many pristine or chemically modified polymeric compounds have been extensively applied for cation removal from aqueous solutions and these processes can provide large amounts of metal ion retention or ion exchange processes. In this context, a lot of investigated materials with excellent sorption properties are those on synthetic mesoporous silicas and silica gel supports [26][27][28] , chemically modified phyllosilicates [29][30][31] , chitosan, as obtained and after modification with a series of pendant chains 24,32,33 , synthetic phosphates 34,35 , chemically modified celluloses [6][7][8][21][22][23] and others [36][37][38] . These inorganic or biopolymer materials research fields are continuously expanding, however, the biopolymers, and specially cellulose, have a huge advantage, since they are quite abundant in nature, renewable, biodegradable and easily obtained at low cost.…”