An eco-friendly composite hydrogel based on covalently crosslinked cellulose/poly (glycerol citrate) for thallium (Ι) removal from aqueous solutions.

Cellulose/poly (glycerol citrate) reinforced with thiol-rich polyhedral oligomeric silsesquioxane and apple peel (POSS-SH@CAG-CEL/AP) was synthesized using gelation method in the presence of glutaraldehyde as a crosslinker agent and used as an efficient composite hydrogel for elimination of Tl(Ι) from aqueous solutions. This composite hydrogel and synthesized thiol-rich polyhedral oligomeric silsesquioxane were characterized by elemental analysis, FT-IR, NMR, TGA, and FE-SEM techniques. The effects of synthetic and environmental parameters on the adsorption capacity of the composite hydrogel were investigated and it was found that thiol-rich polyhedral oligomeric silsesquioxane has improved the hydrogel properties including the Tl(Ι) uptake and the thermal stability. The maximum adsorption capacity of 352.3 mg g-1 was obtained within 30 min under optimum reaction conditions. A typical Langmuir adsorption isotherm with was observed for adsorption of Tl(I) onto POSS-SH@CAG-CEL/AP and pseudo-second-order kinetic model provided the best correlation between experimental data. Thermodynamic studies showed that the Tl(I) adsorption was spontaneous process and exothermic. Also, the reusability tests confirmed that the POSS-SH@CAG-CEL/AP can be reused for four times without any remarkable change in its adsorption capacity. Thus, this reusable biobased composite hydrogel can be an ideal candidate for elimination of Tl(I) from aqueous solutions.

Bio-based nanocomposite hydrogels derived from poly (glycerol tartrate) and cellulose: Thermally stable and green adsorbents for efficient adsorption of heavy metals.

The eco-friendly polymeric nanocomposite hydrogels were prepared by incorporating dendritic fibrous nanosilica (DFNS) and apple peel (AP) as reinforcements into the crosslinked polymer produced by cellulose (CL) and poly (glycerol tartrate) (TAGL) via gelation method and used for efficient adsorption of Pb2+, Co2+, Ni2+, and Cu2+ metal ions. DFNS and DFNS/TAGL-CL/AP samples were characterized by FESEM, FTIR, TEM, TGA, and nitrogen adsorption/desorption methods. The results of TGA analysis showed that the thermal stability of the prepared hydrogels improved significantly in the presence of DFNS. Both synthetic and environmental parameters were investigated and the adsorption capacity reached 560.2 (pH = 4) and 473.12 (pH = 5) mg/g for Pb2+ and Cu2+ respectively, using initial ion concentration of 200 mg/L. Also, the maximum adsorption capacity was 340.9, and 350.3 mg/g for Co2+ and Ni2+, respectively under optimum conditions (pH = 6, initial ion concentration of 100 mg/L). These experiments indicated that the DFNS/TAGL-CL/AP nanocomposite hydrogel has an excellent performance in removal of Pb2+ and can adsorb this toxic metal in only 30 min while the optimum contact time for other metals was 60 min. Pseudo-second-order and Langmuir models were used to define the kinetic and adsorption isotherms, respectively and thermodynamic studies demonstrated that the adsorption was endothermic for Co2+, Ni2+ and Cu2+, exothermic for Pb2+, and spontaneous in nature for all metal ions. Furthermore, the reusability tests indicated that the hydrogels could maintain up to 93% of their initial adsorption capacity for all metal ions after four cycles. Therefore, the prepared nanocomposite hydrogels can be suggested as efficient adsorbents to remove the toxic metals from wastewater.

Efficient hydrolysis of starch by α-amylase immobilized on cloisite 30B and modified forms of cloisite 30B by adsorption and covalent methods.

In this paper, α-amylase from Bacillus subtilis was successfully immobilized on three supports. First, α-amylase was immobilized on cloisite 30B via the adsorption method. Then cloisite 30B was activated with tosyl chloride and epichlorohydrin. These activated supports were used for covalent immobilization of α-amylase, and their enzymatic activities were effectively tested in the starch hydrolysis. The results demonstrated that the specific activity of α-amylase immobilized on cloisite 30B was 2.39 ± 0.03, for α-amylase immobilized on activated cloisite 30B with epichlorohydrin was 1.96 ± 0.05 and for α-amylase immobilized on activated cloisite 30B with tosyl chloride was 2.17 ± 0.05 U mg-1. The optimum pH for the activity of free α-amylase was 7, but for α-amylase immobilized on cloisite 30B was 8, and for α-amylase immobilized on activated supports was 7.5. The immobilized enzymes had better thermal resistance and storage stability than free α-amylase, and they also showed excellent reusability.

Synthesis of a novel superabsorbent with slow-release urea fertilizer using modified cellulose as a grafting agent and flexible copolymer.

In this work, a number of glucose unites in polymeric structure of cellulose was converted to 2,4-dihydroxy-3-(1-hydroxy-2-oxoethoxy)butanal (cellulose containing di aldehyde units (CCDAUs)) by oxidation with sodium periodate, followed by condensation with acetone to produce 5,7-dihydroxy-6-((1-hydroxy-4-oxopent-2-en-1-yl)oxy)hept-3-en-2-one unites (cellulose containing di ene units (CCDEUs)). This modified cellulose was characterized by different methods and applied as a copolymer and grafting agent to synthesize an eco-friendly (CCDEUs-g-poly(AA)/urea) superabsorbent with slow-release urea fertilizer. The created double bonds in C2 and C3 positions of ß-d-glucose units increased the linkage between cellulose and acrylic acid, leading to the formation of a strong network for slow-release urea fertilizer. Also, this modification created an expanded network for storage a high amount of water by increasing the cellulose flexibility. The reaction conditions for modification and synthesis of the superabsorbent, the oxidation degree value of glucose units, kinetics models, the effect of different saline solutions, various pH and reswelling time on the water absorbency, water retention capacity, reusability, biodegradability, and slow-release property were investigated. Also, the effect of synthesized CCDEUs-g-poly(AA)/urea on plant growth was tested and excellent results were obtained.

4-(6-Aminohexyl) amino-4-oxo-2-butenoic acid as a novel hydrophilic monomer for synthesis of cellulose-based superabsorbents with high water absorption capacity.

An efficient cellulosic superabsorbent based on a novel functional monomer 4-(6-aminohexyl) amino-4-oxo-2-butenoic acid (AHOB) and acrylic acid was successfully synthesized by free-radical solution polymerization and the effect of the AHOB monomer on the structure, morphology, thermal behavior and viscoelastic features of this superabsorbent was investigated by FTIR, SEM, TGA and rheology methods. Also, the influence of this monomer on the water absorption capacity in various pH and different saline solutions, kinetic behavior, water retention capacity and reusability of the superabsorbent was perused. The results of these experiments confirmed the significant role of the AHOB monomer in improving the properties of the superabsorbent. The excellent absorbency (800.37 g/g in distilled water and 78.02 g/g in 1 wt.% NaCl solution) and high water retention capacity of the prepared superabsorbent showed that it can be used as an efficient water-saving material for agricultural applications.