Amino-functionalization Of Nanocrystalline Cellulose And Its Absorption Behavior

In recent years, the waste water released by various chemical industries such as textile, plastic, papermaking, printing and food contains an increasing amount of dyes and heavy metal ions, which not only causes environmental pollution, but also brings great harm to human health. Therefore, exploiting an effective and cheap dyes and heavy metal ions removal method has become an urgent problem. Adsorption is the most commonly method used to remove dyes and heavy metal ions due to the fact that it possesses many advantages such as low cost, simple and flexible procedure, and not sensitive to toxic pollutants. Recently, nano-adsorbents, which have large specific surface area and numerous adsorption sites, have attracted more and more attention.In this paper, nanocrystalline cellulose (NCC) was firstly oxidized by periodate to yield the corresponding C2/C3 dialdehyde nanocellulose (DANC). DANC was then grafted with ethylenediamine to obtain ANCC with free amino groups through a reductive amination treatment. Finally, the adsorption capacity and mechanism were evaluated of ANCC as an adsorbent to remove anionic dyes and Cr(VI) in aqueous solutions.Firstly, NCC was extracted from fully bleached hardwood kraft pulp (BHKP) by sulfuric acid hydrolysis. NCC was then oxidized by sodium periodate to yield DANC. The effects of NaIO4 dosage, reaction time and temperature on the aldehyde content, Zeta potential, crystallization index and crystal size of DANC were investigated. The results showed that aldehyde content of DANC increased gradually with the increasing of NaIO4 dosage. Prolonging reaction time could improve the aldehyde content. When the temperature was less than 40℃, raising the temperature could promote the oxidation reaction; whereas when the temperature was higher than 40℃, raising the temperature would inhibit the reaction. When the NaIO4 dosage was 6 mmol/g, with a reaction temperature of 40℃ and time of 48 h, DANC with the aldehyde content of 105.1%, Zeta potential of-19.5 mV was obtained. The DANC samples were characterized by FT-IR, XRD and TGA. The FT-IR analysis showed that aldehyde group was introduced into DANC successfully by periodate oxidation. XRD analysis indicated that DANC remianed crystal structure of cellulose-I, while, the crystallization index of DANC decreased to some extent compared with that of NCC. With the increasing of NaIO4 dosage, crystallization index of DANC decreased gradually.Subsequently, DANC was grafted with ethylenediamine to obtain ANCC with free amino groups through a reductive amination treatment. The effects of DANC dosage on yield, the amino content and Zeta potential of ANCC were investigated. With the increasing of ethylenediamine dosage, the amino content and Zeta potential of ANCC gradually increased. ANCC was characterized by FT-IR, XRD, TGA, AFM and element analysis. The successful grafting was further evidenced by Kaiser test and FT-IR analysis. Zeta potential measurements showed that ANCCs were amphoteric, and their isoelectric points were between pH of 7-8. XRD analysis indicated that ANCC still kept crystal structure of cellulose-I. The cross-sectional dimension of nanowhiskers was slightly decreased from about 5-10 nm to 3-8 nm after the oxidation, and a better dispersibility was observed.Finally, ANCC sample was then applied as an adsorbent to remove anionic dyes and Cr(VI) in aqueous solutions. The effects of ANCC dosage, adsorption time and the pH value of reaction system on the adsorption capacity were investigated. For anionic dyes, it demonstrated the maximum removal efficiency at acidic conditions. When the adsorbent dosage increased from 0.5 g/L to 1.0 g/L, the removal rose from 62% to 100%. The acid red GR adsorption on ANCC fitted well with the Langmuir model, with a maximum theoretical adsorption capacity of 555.6 mg/g. The adsorption of congo red 4BS, acid red GR and reactive light yellow K-4G followed pseudo second order kinetics, indicating a chemisorption nature. ANCC showed higher removal efficiency of Cr(VI) at pH 2. The adsorption of Cr(VI) on ANCC followed pseudo second order kinetics and BET isotherm.