| Tannin is polyphenolic compound that produce astringency and is mainly found in certain fruits.The presence of tannin makes the juice produce bitterness and has a certain influence on the storage stability of the product.In addition,tannin can be used directly as a tanning agent or as a retanning agent together with chromium salts,resulting in a large amount of tannin-rich wastewater during the leather tanning process,causing serious pollution to the environment.At present,there are few reports on the removal or recovery of tannins.This topic proposes the use of gelatin/dialdehyde cellulose(DAC)cross-links as adsorbents to study the adsorption characteristics of tannin.Tannin recycling has high theoretical significance and practical value.In this paper,microcrystalline cellulose(MCC)was used as raw material to prepare DAC with certain aldehyde group content by selective oxidation of sodium periodate.Then,the edible gelatin was combined with DAC through a cross-linking reaction to obtain a series of cross-linked products(DACG1-7)with DAC as the skeleton,and their physicochemical properties and adsorption performance were evaluated.Infrared spectroscopic analysis showed that the hydroxyl groups of microcrystalline cellulose were oxidized to aldehyde groups,and the Schiff base reaction occurred between DAC and gelatin.The results of X-ray diffraction showed that the crystal structure of cellulose was changed due to oxidation,and the degree of crystallinity decreased.It showed the successful cross-linking of DAC and gelatin,and the long-range and short-range structures of the polymer were changed after gelatin was cross-linked with DAC.Scanning electron microscopy results showed that DAC reacted with gelatin to form a three-dimensional network structure.Thermogravimetric analysis showed that the thermal stability of DAC and DACG1-7 was lower than that of MCC.The evaluation results of the adsorption performance of tannic acid showed that the adsorption equilibrium time of all cross-linked compounds was 24 h,and the adsorption effect was good in the range of p H 2.5～6.0;When it was 0.45 g,the adsorption effect was better;DACG3 to DACG7 showed better adsorption effect at 40 ℃ and the addition amount was 0.35 g;and DACG7 had the best adsorption effect on tannic acid,and its equilibrium adsorption capacity reached 284.15mg/g.All cross-linked products were reused no less than 3 times.The adsorption kinetics fitting results showed that the adsorption of tannins by DACG1-7 was dominated by chemical adsorption.The adsorption isotherm fitting showed that DACG1 belonged to the Freundlich model adsorption;DACG2 to DACG7 belonged to the Langmuir model adsorption.The adsorption thermodynamic fitting results showed that the adsorption of tannins by DACG1 and DACG2 was a spontaneous exothermic reaction,and the adsorption of tannins by DACG3 to DACG7 was a spontaneous endothermic reaction.These gelatin/dialdehyde cellulose cross-linked products have good adsorption performance to tannins,are non-toxic and recyclable,and can provide a new way for the deastringency of some fruit juice beverages and the recycling of tannins in industrial wastewater. |
