Study On The Adsorption Properties Of Cr(?) And Cu(?) By Bacterial Cellulose-based Composites

At present,human activities cause a large amount of heavy metal pollutants to enter the environment.Among them,Cr???and Cu???are two typical heavy metal ions,which pose a huge threat to human health and plant growth.Adsorption method is an effective method for the treatment of heavy metal ions in water and has been widely used.The structure and performance of the adsorbent are the key factors affecting the adsorption effect.It is of great significance to study economical and efficient adsorption materials.Biopolymers have been widely used in the field of adsorption due to their advantages of low cost,availability,regeneration and degradation.Among them,bacterial cellulose?BC?with high specific surface and nanofiber structure is a good matrix material.Functionalized bacterial cellulose composites are obtained by compounding with different adsorption materials.In this paper,BC was compounded with polypyrrole?PPy?and chitosan?CS?,respectively.Polypyrrole/bacterial cellulose composite?PPy/BC?was prepared by in-situ oxidative polymerization for the removal of Cr???,and chitosan/bacterial cellulose composite?m CS/BC?prepared with malic acid?MA?as a cross-linking agent for Cu???removal.The adsorption characteristics of the two adsorbents were studied,the structure characteristics and adsorption mechanism of the adsorbents were analyzed by characterization such as SEM,FTIR and XPS.The main conclusions are as follows:?1?Using FeCl₃ as oxidant,PPy/BC composite was prepared by in-situ oxidation polymerization method.The obtained composite can still maintain the fiber structure,and its diameter increased with the increase of the amount of pyrrole.It was used to remove Cr???in water.When the amount of pyrrole was 0.6 ml?PPy/BC-6?,the specific surface area was as high as 95.9 m²/g,and the adsorption effect of Cr???was the best.The adsorption process of PPy/BC-6 was analyzed,and the results showed that the adsorption effect was the best at p H 2.When the dosage was 0.25 g/L,the removal rate of Cr???solution with a concentration of 100mg/L can reach 97.5%.The adsorption process was spontaneous and endothermic,and conformed to the pseudo-second-order kinetic model.PPy/BC-6 can efficiently remove Cr???and possess the maximum adsorption capacity of 555.6 mg g^-1 at 298 K,significantly higher than BC and PPy.In addition,PPy/BC-6 can maintain high Cr???removal efficiency after five adsorption and desorption cycles.The Cr???adsorption on PPy/BC was involved in ion exchange and electrostatic attraction.Meanwhile,partial Cr???was reduced to trivalent chromium?Cr??I??by pyrrolic nitrogen.?2?The mCS/BC composite was prepared by physical crosslinking with MA as crosslinking agent,which was used to remove Cu???from water.SEM,FTIR and XPS were used to characterize the morphology and structure of the composite,and the adsorption characteristics of the composite were studied.The results showed that when the amount of CS was 0.5 g and the molar ratio of carboxyl group in MA to amino group in CS was 5:1,the composite?m CS/BC-3?had the best adsorption effect on Cu???.In addition,m CS/BC-3 was a macro ball with a diameter of 2?3 mm.Microscopically,CS and BC formed an interpenetrating network structure with a specific surface area of 75.8 m²/g.m CS/BC-3 had the best removal effect on Cu???at p H 4.The maximum adsorption capacity calculated by Langmuir isotherm model was 204.5 mg/g.The removal mechanism was mainly the complexation of amino groups and oxygen-containing groups on the adsorbent with Cu???.